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Radiochemical studies on graphite ferric chloride Lazo, Robert Martin 1950

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L (5 5ft7  RADIOCHEMICAL STUDIES' on GRAPHITE FERRIC CHLORIDE  BY  ROBERT MARTIN LAZO  A T h e s i s Submitted i n P a r t i a l Fulfilment  o f the Requirements  for  the Degree o f  MASTER o f  ARTS  i n the DEPARTMENT  of  CHEMISTRY  The U n i v e r s i t y o f B r i t i s h Columbia. A p r i l 1950.  ABSTRACT Graphite f e r r i c c h l o r i d e , C j ^ F e C ^ , by h e a t i n g The  anhydrous f e r r i c  prepared  s  53$ f e r r i c c h l o r i d e was  o  not  X-ray d i f f r a c t i o n measurements gave a powder p a t -  t e r n which was  d i s t i n c t l y d i f f e r e n t from t h a t o f e i t h e r g r a -  p h i t e o r f e r r i c c h l o r i d e and  from w h i c h i t was  no f r e e f e r r i c c h l o r i d e e x i s t e d i n the t i o n of the g r a p h i t e  layer-planes  was  apparent t h a t  compound. ,The  by the i n t e r c a l a t i o n of the f e r r i c  i n no  measurable exchange observed.  compound was  neutron i r r a d i a t i o n and the  t e d o f Fe$9  t  identified.  l e s s than 1% of the t o t a l  P^  2  and  p o s i t i o n products.  S^, The  instance  Fe was  ion  + + +  any  subjected  to  S z i l a r d - C h a l m e r s y i e l d of sepa-  r a b l e a c t i v i t y c a l c u l a t e d and t i o n contained  to  c h l o r i d e molecules.  were made u s i n g r a d i o a c t i v e F e 5 9 . The  separa-  increased from 3.36  T e s t s f o r exchange between C i 2 F e C l 3 and  ether  at 3 0 5 ° C  by hot 6N h y d r o c h l o r i c a c i d or 6N sodium hydroxide  solutions.  9.4A  a  chloride with graphite  p u r i f i e d compound c o n t a i n i n g  attacked  w  The  separated por-  a c t i v i t y and  f r e e of d e t e c t a b l e a c t i v e Fe p o r t i o n was  consis-  r a d i a t i o n decomseparated  by  extraction. The  l a c k of exchange and  the low  Szilard-Chalmers  y i e l d are both a t t r i b u t e d t o the f o r m i d a b l e s t e r i c hindrance e f f e c t s which r e s u l t from the c o n f i g u r a t i o n of the layers" structure f o r graphite  ferric  chloride.  "stacked  ACKNOWLEDGEMENTS  I wish t o express my g r a t i t u d e t o D r . J.G. Hooley who so ably d i r e c t e d t h i s r e s e a r c h p r o j e c t . A p p r e c i a t i o n i s a l s o expressed t o the National! Research C o u n c i l o f Canada f o r the summer r e s e a r c h s c h o l a r s h i p awarded the author d u r i n g t h e course of t h i s study, and t o the B r i t i s h Columbia Research C o u n c i l who so k i n d l y p e r m i t t e d X-ray spectrometer.  the use o f t h e i r  TABLE o f CONTENTS Introduction 1.  2*  Graphite and Graphite Compounds  1  A. ) Graphite F e r r i c , C h l o r i d e  9  Radiochemical A*)  Theory  16  I s o t o p i c Exchange Reactions  ....18  B. ) The S z i l a r d - C h a l m e r s R e a c t i o n i n the Chain R e a c t i n g P i l e 3»  26 33  Radiochemical Techniques  Experimental Results 1»  P r e p a r a t i o n o f Graphite F e r r i c C h l o r i d e 36  [c FeCl ] . 1 2  2.  3  n  T e s t s f o r Exchange between Graphite C h l o r i d e and F e r r i c en Radioactive F e ^  3«  Ferric  Ion, u s i n g  7  45  The S z i l a r d Chalmers R e a c t i o n w i t h Graphite F e r r i c Chloride  56  Discussion of Results  63  Suggestions f o r Future Research.  66  Bibliography  67  Radiochemical  S t u d i e s on Graphite F e r r i c C h l o r i d e .  INTRODUCTION Carbon I t s e l f I s a r e f r a c t o r y , n o n - v o l a t i l e , i n s o l u b l e s o l i d , and g i v e s r i s e t o l a m e l l a r compounds which are  insol-  u b l e , n o n - v o l a t i l e and o f t e n u n s t a b l e s o l i d s about which c l a s s i c a l chemical methods g i v e very l i t t l e  i n f o r m a t i o n . X-  r a y s t u d i e s have proved p a r t i c u l a r l y f r u i t f u l , and most of the i n f o r m a t i o n concerning the s t r u c t u r e of s o l i d and i t s l a m e l l a r compounds has been determined  carbon,  from X-ray  d i f f r a c t i o n measurements• Carbon, i n the form of diamond, b e l o n g i n g to the cubic system, was  one of the e a r l i e s t c r y s t a l s to be i n v e s t i g a t e d  by X - r a y s ( 2 ) .  The  e s s e n t i a l p o i n t of the space  lattice  s t r u c t u r e f o r diamond, i s t h a t every atom of carbon  i s surr-  ounded by f o u r other atoms s i t u a t e d at the corners of a regular tetrahedron. two  The d i s t a n c e between the c e n t e r s of  a d j o i n i n g atoms i s 1.54&  , which corresponds  l y t o the d i s t a n c e between two  very close-  carbon atoms a t t a c h e d to each  other by a s i n g l e c o v a l e n t bond i n a l i p h a t i c o r g a n i c compounds.  T h i s agreement, t o g e t h e r w i t h the f a c t t h a t each  carbon atom i n diamond has f o u r others s i t u a t e d round i t at the c o r n e r s of a r e g u l a r t e t r a h e d r o n , suggests  t h a t every  atom i s j o i n e d t o f o u r others by c o v a l e n t l i n k a g e s . diamond c r y s t a l may carbon.  A  then, be regarded as a macromolecule of  I t s hardness can be a s c r i b e d to the s t r e n g t h of  the chemical bonding of the atoms and d i r e c t i o n s throughout  the (1)  crystal.  i t s uniformity i n a l l  The p h y s i c a l p r o p e r t i e s of the other a l l o t r o p i c  form  of carbon v i z . , g r a p h i t e , o f the hexagonal system, are q u i t e d i f f e r e n t from those of diamond.  These  differences  are found t o correspond t o important changes i n the i n t e r n a l s t r u c t u r e o f the c r y s t a l * Although g r a p h i t e i s so o b v i o u s l y c r y s t a l l i n e , i t s opaque cha r a c t e r and the r a r i t y o f w e l l developed c r y s t a l s r e s t r i c t c o n s i d e r a b l y the c r y s t a l l o g r a p h l c i n f o r m a t i o n which can be o b t a i n e d by o p t i c a 1 methods.  The l a t t i c e  s t r u c t u r e which f i r s t r e c e i v e d wide acceptance was  deduced  i n 1924 by J.D. B e r n a l (1) and confirmed by C. Mauguin (1926). (12) and by H. O t t (1928) (16). The carbon atoms are arranged i n f l a t having aa hexagonal honeycomb-like  layers  structure.  each  These are  s t a c k e d p a r a l l e l t o each other i n such a way t h a t h a l f the atoms In one l a y e r H e i n the l a y e r beneath. mormally  normally above h a l f the a toms  A l t e r n a t e l a y e r s H e , atom f o r atom  above each o t h e r *  The carbon atoms i n the l a y e r s  are spaced c e n t e r t o c e n t e r s t a d i s t a n c e o f 1.415 A compared w i t h a s p a c i n g o f 1.54 A In the diamond  lattice.  The s p a c i n g between adjacent l a y e r - p l a n e s o f g r a p h i t e i s 3«36 A' •  The carbon atoms w i t h i n the l a y e r - p l a n e s t h e r e f o r e  are bonded t o g e t h e r by powerful c o v a l e n t v a l e n c y f o r c e s , more powerful t h a n those In the diamond.  The f o u r v a l e n c e s  of each carbon atom are used t o form bonds w i t h i t s t h r e e neighbors, aand the g i a n t l a y s e r molecule resonates among many v a lence-bond s t r u c t u r e s i n such a; way t h a t carbon-carbon bond a c h i e v e s o n e - t h i r d double-bond  each character.  T h i s arrangement corresponds very  c l o s e l y t o the s i x - memb-  ered r i n g s formed i n benaene, naphthalene and hydrocarbons*  other  aromatic  Indeed, i n h i s review of recent work on  the  s i m l l i a r i t y of the g r a p h i t e e l e c t r o n s t r u c t u r e w i t h t h a t aromatic compounds ( 6 ) , Hofmann has ary i s found. c o a l amd  The  intermediary  s t a t e d , "No  of  sharp bound-  stages of g r a p h i t e  nuclei in  i n v a r i o u s charcoa Is c o n s t i t u t e ar. gradual  cha  nge  from aromatic compound t o c r y s t a l l i n e g r a p h i t e " .  However  the resonance system i n the g r a p h i t e  i s so deg-  layer-planes  enerate t h a t odd e l e c t r o n s behave more l i k e m e t a l l i c e l e c t r o n s and  account f o r the e l e c t r o n i c c o n d u c t i v i t y of  which w i t h c e r t a The  graphite,  i n pure specimens i s twice that of mercury.  e l e c t r i c a l c o n d u c t i v i t y i n a d i r e c t i o n p a r a l l e l to  layer-planes  the  i s much g r e a t e r t h a n i n a d i r e c t i o n at r i g h t  angles to i t . The by a  hexagona 1 l a y e r s of carbon molecules are  distance- so l a r g e  (3.36  bonds between them, and held together  A ) that there can be no  l a y e r - l a t t i c e set up f o r g r a p h i t e which occurs so e a s i l y between the the use  on t h i s a b i l i t y of one another.  covalent  the superimposed l a y e r molecules  only by weak van der Waals f o r c e s  the c r y s t a l , and  separated  (17).  accounts f o r the  The  cleavage  separate l a y e r - p l a n e s  of g r a p h i t e  as a  are  in  l u b r i c a n t depends  plane of atoms t o s l i d e e a s i l y  over  14;  Figure  1.  The arrangement, of c a r b o n at i n the g r a p h i t e  crystal*  (5) The  s t r u c t u r e o f the g r a p h i t e c r y s t a l  to be d e f i n i t e l y Taylpr  lattice  e s t a b l i s h e d u n t i l D.S. L a i d l e r  (10) i n 194-0 p o i n t e d out t h a t t h i s  not account f o r some f a i n t  appeared and A.  s t r u c t u r e does  l i n e s w h i c h occur  i n the X-ray  powder photographs o f many specimens o f g r a p h i t e . form o f g r a p h i t e present  to about 10% i s s u g g e s t e d .  o f the a l t e r n a t e planes being normally  Instead  above one another,  at t h i r d plane  i s I n s e r t e d w h i c h Is symmetrically  t o the planes  above and below.  F i g u r e 2.  Another  related  The two ways of s t a c k i n g the hexagon l a y e r - p l a n e s i n the g r a p h i t e l a t t i c e .  The  g r a p h i t e l a t t i c e s t r u c t u r e w i t h i t s powerful  covalent  bonds w i t h i n the l a y e r - p l a n e s and the r e l a t i v e l y weak bonding f o r c e s between the l a y e r - p l a n e s o f f e r s  an e x p l a n a t i o n of  the i n t e r e s t i n g a n i s o t r o p i c p r o p e r t i e s both p h y s i c a l and chemical,  associated with graphite c r y s t a l s .  Observations  on the s w e l l i n g o f g r a p h i t e e l e c t r o d e s and the intumescence of g r a p h i t e , l e d t o the d i s c o v e r y that c e r t a i n molecules and/or ions c o u l d penetrate  between the l a y e r - p l a n e s o f  the g r a p h i t e l a t t i c e t o form more or l e s s s t a b l e s t r u c t u r e s . T h i s s w e l l i n g , as p o i n t e d out by H. T h i e l e (33), occurs w i t h h i g h l y c r y s t a l l i n e forms o f g r a p h i t e and occurs  excl-  u s i v e l y along the C a x i s o f the hexagonal f l a k e . Graphite S a l t s : The a c t i o n o f c o n c e n t r a t e d  a c i d s i n the  presence o f a s u i t a b l e o x i d i z i n g agent, has been shown t o b r i n g about the f o r m a t i o n (6f> blue g r a p h i t e s a l t s E a c h hexagon l a y e r - p l a n e becomes a  (7) (23) •  macro p o s i t i v e i o n w i t h  m charge equal and opposite t o the number o f negative bonded t o I t .  When g r a p h i t e  i s treated with b o i l i n g  ions sul-  f u r i c a c i d i n the presence o f a few drops o f n i t r i c a c i d , the  i r i d e s c e n t blue g r a p h i t e b i s u l f a t e Graphite + nH SO g  The  +  + n/20  -»  results.  Graphite™" (HSO^"") n £ H 0 +  a  compound c o n t a i n i n g the maximum amount of i n t e r c a l a t e d  b i s u l f a t e i o n and s u l f u r i c a c i d corresponds t o the i d e a l i z e d s t i o c h i o m e t r i c composition Cg HS0 '2 H SO^ . 4  The  4  g  a d d i t i o n o f a s m a l l q u a n t i t y of water t o the  s u l f u r i c a c i d , even from exposure o f the a c i d t o the atmosphere b r i n g s about the decomposition o f the blue i n t o the o r i g i n a l g r a p h i t e .  graphite  X-ray examination o f a specimen  of g r a p h i t e b i s u l f a t e suspended i n pyrophosphoric  acid  showed t h a t the I n t e r c a l a t i o n of the s u l f u r i c a c i d had i n c r e a s e d the i n t e r l a y e r - p l a n e spacing of the g r a p h i t e from 3.36  A t o 7.98  A  (19).  Besides the b i s u l f a t e , g r a p h i t e forms o t h e r s i m i l a r compounds. of carbon"  H.L. (19)  R i l e y , i n h i s review of "Lamellar compounds d e s c r i b e s the g r a p h i t e s a l t s n i t r a t e ,  c h l o r a t e , b i s e l e n a t e , phosphate, pyrophospha te and  per-  arsenate,  a l l p r e p a r e d and c h a r a c t e r i z e d by Rttdorff and Hofmann ( 2 3 ) . Graphite M o n o f l u o r i d e t  (27) G r a p h i t e combines w i t h f l u o r i n e  at one atmosphere p r e s s u r e and a temperature form a grey hydrophobic (CP)n  •  The  of 4 2 0 ° C . t o  s o l i d the composition of which i s  constant composition, the grey c o l o r and the  low  e l e c t r i c a l c o n d u c t i v i t y , which i s o n l y one-hundred-thousandth t h a t of g r a p h i t e , a l l suggest i s a chemical campound.  The  that g r a p h i t e mono- f l u o r i d e f l u o r i n e atoms are  arranged  i n s i x p a r a l l e l planes between each p a i r of carbon  layer-  p l a nes which a re spaced at 8.17  recently  A .  announced the p r e p a r a t i o n of a new pound (24)  t e t r a c a r b o n monofluoride  Rttdorff has  g r a p h i t e - f l u o r i n e com(C^F)^  •  The  compound  i s not a t t a c k e d by d i l u t e a c i d s or a l k a l i even on h e a t i n g although c o n c e n t r a t e d s u l f u r i c  a c i d above 100°C s l o w l y dec-  omposes i t . Brom-graphite:  A p e c u l a r bromine a d s o r p t i o n complex of  g r a p h i t e has been produced  (21)  by shaking a suspension  of g r a p h i t e i n c o l d c o n c e n t r a t e d s u l f u r i c a c i d w i t h bromine. The  g r a p h i t e samples w i l l take up roughly one  atom of  bromine t o each e i g h t atoms of carbon and g i v e i t up a g a i n completely on s t a n d i n g i n the a i r . The X-ray a n a l y s i s of brom-graphite  showed a. carbon l a y e r - p l a n e s p a c i n g of 7.05  Alkali-graphite;  A •  When g r a p h i t e i s heated w i t h potassium,  rubidium or cesium i n an evacuated tube, a b l u e - b l a c k a l k a l i - g r a p h i t e compound i s produced* i n mercury c o n v e r t s i t t o g r a p h i t e , the  Shaking the compound i t was  a l s o found t h a t  a d s o r p t i o n o f potassium vapor occured In a  stepwise  manner, i n d i c a t i n g the f o r m a t i o n of more than one Schleede and Wellmann (28) determined from X-ray that f o r the C K 8  compound. studies  compound, each potassium atom l a y normally  over the c e n t e r of every second carbon atom hexagon of the basal planes.  C/«K has a l a y e r of potassium atoms i n every  second I n t e r - l a y e r - p l a n e space i n the g r a p h i t e l a t t i c e . These substances were shown to be q u i t e d i f f e r e n t o r d i n a r y a l k a l i metal c a r b i d e s because no t r a c e of hydrocarbon was water.  only hydrogen  and  e v o l v e d when they r e a c t e d w i t h  The heat of f o r m a t i o n of CgK  or C, K u s i n g excess  potassium, was determined t o be about 1500 of carbon  from  6  cal./gm. atom  (4)»  Graphitic oxide:  Samples o f g r a p h i t i c oxide have been p r -  epared by t r e a t i n g g r a p h i t e that had been p r e v i o u s l y washed with hydrochloric acid, with concentrated s u l f u r i c  acid  and n i t r i c a c i d i n the presence of potassium c h l o r a t e  (26).  A f t e r the product has been d r i e d under vacuum over potassium pentoxide the a c i d groups  can be determined by m e t h y l a t i o n (81  and  acetylation.  However,  i n no case has a f i x e d  c h i o m e t r i c a l r e l a t i o n s h i p been found, as analyses v a r i e s between 6 j l and 6:2.5*  Further  stiofor C:0  s t u d i e s o f the c r y s t a l  s t r u c t u r e have i n d i c a t e d that the carbon l a y e r s d i s p l a y a hydroaromatlc  character.  I t i s i n t e r e s t i n g t o note the c l o s e p a r a l l e l i s m between the chemistry  of the g r a p h i t e compounds t h a t have been men-  t i o n e d and t h a t of the t r i a r y l m e t h y l s ( 1 8 ) . T h i s i s i n d i c a t e d by: t h e e x i s t e n c e o f the g r a p h i t e s a l t s , g r a p h i t e monofluoride, the a l k a l i g r a p h i t e s and g r a p h i t e to: be d e f i n i t e compounds. alkali  oxide, a l l of which appear  The t r i a r y l m e t h y l s a l s o form  s a l t s , h a l i d e s and peroxides  and i n g e n e r a l show the  same amphoteric p r o p e r t i e s as do the hexagon l a y e r - p l a n e s o f the g r a p h i t e c r y s t a l l a t t i c e . for  T h i s Is not s u r p r i s i n g ,  c o n s i d e r i n g one carbon atom i n a l a y e r - p l a n e , I t w i l l  be seen t h a t i t s three v a l e n c y bonds are connected each t o an aromatic grouping of carbon atoms and t h a t these bonds are c o - p l a n a r , stability  like  those i n t r i p h e n y l m e t h y l .  of the t r i p h e n y l m e t h y l  three The  f r e e r a d i c a l has been e x p l -  a i n e d by assuming t h a t the odd e l e c t r o n on the c e n t r a l carbon a torn resonates atoms i n the m o l e c u l e .  among many o f the aromatic carbon T h i s i s a v e r y s i m i l a r type o f  resonance t o t h a t o c c u r i n g i n g r a p h i t e .  A* Graphite  ferric chloride:  Perhaps the most i n t e r e s t i n g o f the g r a p h i t e compounds r e p o r t e d t o date, graphite f e r r i c  i s the s u r p r i s i n g l y s t a b l e  c h l o r i d e , which a p p i f ^ s t o f a l l  into a  (10) d i f f e r e n t category,  as no s i m i l a r compound i s formed by the  triarylmethyls• Graphite f e r r i c chloride was prepared and characterized by W. RUdorff and H. Schulz  (25) i n 1940 and i s reviewed i n the  U. S. publication F.I.A.T. (1946*)  (22).  When graphite i s heated t o 200°C. and above with two or three times i t s own weight of anhydrous f e r r i c chloride i n a sealed tube, the amount of free f e r r i c chloride decreases.  The  f e r r i c chloride which does not react can be sublimed o f f or extracted i n d i l u t e acid solutions, leaving an apparently homogeneous green to matt black reaction product which has increased i n weight up t o 2 0 0 $ of the weight of the o r i g i n a l graphite. Specimens prepared between 180° and 300°C. contain between 7 2 $ and 60$ of f e r r i c chloride, which i s equivalent t o 1 FeCl : 5.5-9 C atoms.  Using reaction temperatures between  325° and 400°C, the f e r r i c chloride content f a l l s t o between 37$ and 31$ i . e . 1 FeCl : 23-29 C atoms, and between 400° and 500°C  o  the product contains only 5$ f e r r i c c h l o r i d e .  completely  This i s  expelled only at a temperature above 500°C.  At 309°C. the graphite f e r r i c chloride complex showed a pronounced intumescence accompanied by the evolution of F e C l vapour.  This phenomenon was repeated  5  again at 409°C. and there  then remained a grey pulverulent substance which s t i l l contained about 5$ f e r r i c chloride. RUdorff and Schulz found that part of the f e r r i c chloride could be extracted from the complex with water or d i l u t e acids or with alcohol, ether, benzene, e t c .  When extracted i n  (11) t h i s way the g r a p h i t e f e r r i c  c h l o r i d e prepared below 309°C.  l e f t a product c o n t a i n i n g about 56% f e r r i c c h l o r i d e no matter what solvent was employed and independently of the g r a p h i t e c r y s t a l form.  T h i s value of 5 6 % f e r r i c  original  c h l o r i d e cor-  responds t o about one molecule o f FeCl-j t o t e n G atoms. i n the same way  a specimen prepared between 310 and 400  Treated degrees  c e n t i g r a d e gave a product c o n t a i n i n g 31% f e r r i c c h l o r i d e or one FeCl3 molecule t o t h i r t y C atoms'.  The f e r r i c c h l o r i d e remaining  i n the complex a f t e r the e x t r a c t i o n was found to be e x t r a o r d i n a r i l y u n r e a c t i v e and specimens of the compound were s c a r c e l y attacked by hot d i l u t e a c i d or a l k a l i .  Reducing agents such as  hydrazine and s u l f u r o u s a c i d were found to be without a p p r e c i able a c t i o n .  O x i d i z i n g agents such as c o n c e n t r a t e d n i t r i c  acid  or not concentrated s u l f u r i c a c i d however, decomposed the complex. The p r o p e r t i e s of g r a p h i t e f e r r i c stepwise decrease i n f e r r i c  c h l o r i d e content, suggested the  e x i s t e n c e o f two compounds and t h i s was d i f f r a c t i o n measurements. c o n t a i n i n g 56-72% f e r r i c  c h l o r i d e and the  confirmed by X-ray  The powder photographs of c h l o r i d e showed pronounced  specimens differ-  ences from those of specimens c o n t a i n i n g 30-37$ o f the metallic salt.  The d i f f r a c t i o n p a t t e r n s were a l l d i s t i n c t l y  d i f f e r e n t from those of e i t h e r g r a p h i t e o r f e r r i c  chloride.  RUdorff confirmed from X-ray d i f f r a c t i o n measurements, t h a t the  s p a c i n g between the l a y e r - p l a n e s i n the g r a p h i t e had  been i n c r e a s e d from 3.36 ferric  t o 9.4  chloride molecules.  A  by the p e n e t r a t i o n of  T h i s agreed w i t h the i n c r e a s e  i n volume of a s i n g l e c r y s t a l t o about 2.5  times observed  m i c r o s c o p i c a l l y and from d e n s i t y measurements.  It  i s known t h a t anhydrous f e r r i c  in a layer l a t t i c e .  The  cHriLoride c r y s t a l l i z e s  i r o n ions form a r e g u l a r  hexagonal  network above and below which there i s a p a r a l l e l net plane of c h l o r i d e of The  ions.  The d i m e n s i o n a l  triangular  requirements  these l a y e r - p l a n e s along the C a x i s i s about 5.8?A . q u e s t i o n a r i s e s as t o how  f a r the l i m i t s of the  ferric  c h l o r i d e content found by chemical a n a l y s i s v i z . 1 PeCl3: 5»5G to 1 PeCl3: 9C can be c o r r e l a t e d w i t h the c r y s t a l structure f o r graphite f e r r i c  chloride.  s t a t e s t h a t t h i s r e q u i r e s an upper l i m i t FeCl^C  of  RUdorff  of 1:6.02 f o r tBoe  r a t i o , and t h a t somewhat h i g h e r value i s due  i b l y t o c a p i l l a r y condensation. est  suggested  ferric  The  poss-  compound w i t h the h i g h -  c h l o r i d e content p r o b a b l y has a hexagonal  the f e r r i c  Ions, and when the excess  i s removed by washing the f e r r i c packing I.e. one  of f e r r i c  chloride  ions take up a t r i a n g u l a r  i n which a l t e r n a t e f e r r i c  e l i m i n a t e d from the ' hexagonal  packing  ions have been  arrangement..  case w i t h the removal - of h a l f the f e r r i c  In the  limiting  ions to form  the  t r i a n g u l a r arrangement, the r a t i o of F e C l ^ t C would become 1:12.04.  In the work done by RUdorff  the r a t i o of 1:10.4 was graphite f e r r i c  and Schulz i n  1940,  r e p o r t e d f o r washed specimens of  chloride.  One  w i t h 10$ H S0^ f o r twenty-four 2  sample a f t e r b e i n g b o i l e d hours gave the r a t i o  11.9.  Vapour pressure measurements i n d i c a t e d t h a t the ferric  c h l o r i d e taken up by the g r a p h i t e i n excess  about 56$ was  of  l o o s e l y bound and probably only s e r v e d to  holes In the l a r g e mesh network of the' more f i r m l y bound ferric  chloride  molecules.  fill  (13)  10  10  ZOO  500  4-00  SOO  TEMPERATURE °C Figure  3-  The e f f e c t o f temperature on G r a p h i t e  ferric chloride.  F i g u r e 3 * shows t h e change i n t h e amount of i n t e r c a l a t e d f e r r i c c h l o r i d e w i t h t e m p e r a t u r e , as i l l u s t r a t e d by R t t d o r f f .  I n t h e compound prepared  below .309° 0. t h e  f e r r i c c h l o r i d e has p e n e t r a t e d between a l l t h e l a y e r - p l a n e s of t h e g r a p h i t e l a t t i c e .  When t h i s compound i s h e a t e d t o  309°Oe and above t h e r e i s a sudden e v o l u t i o n o f f e r r i c c h l o r i d e as these m o l e c u l e s a r e f o r c e d from between every alternate pair of layer-planes of graphite. represent  The d o t t e d  the p u r i f i e d compounds, l ) w i t h f e r r i c c h l o r i d e  between a 11 t h e g r a p h i t e l a y e r - p l a n e s , and 2 ) w i t h t h e intercala  t i o n o f f e r r i c c h l o r i d e o n l y between  every  lines  second p a i r .of l a y e r - p l a n e s . 200 and 3 0 9 ° C  I t w i l l be noted t h a t between  temperature has no e f f e c t on the percentage  of f e r r i c c h l o r i d e h e l d by the g r a p h i t e f u l l y I n t e r c a l a t e d compound.  i n the p u r i f i e d  The same i s t r u e f o r the  second compound between the temperature of 3 0 9 and Above 409  the percentage o f f e r r i c c h l o r i d e drops a g a i n  l e a v i n g o n l y about % « sequence  F i g u r e 4» shows the l a y e r - p l a n e  o f the two compounds.  C Cl  c • a  Fe -  Feci  409*0.  a c«-  -..  c —  Fe <U • c ct  c ct  if n  Fe a  fe a c  c C Figure  5 0  feQ  3  C.2 Fe Cl  5  4°  The l a y e r - p l a n e sequence o f G r a p h i t e f e r r i c c h l o r i d e .  The p a r t i c u l a r s t a b i l i t y of the g r a p h i t e  ferric  c h l o r i d e compounds has n e c e s s i t a t e d some e x p l a n a t i o n of the t y p e of bonding they e x h i b i t .  As has been mentioned  p r e v i o u s l y , the s t r o n g l y bonded c a r b o n atom l a y e r - p l a n e s  o f the g r a p h i t e  l a t t i c e are h e l d t o g e t h e r o n l y by weak  van d e r Waals f o r c e s .  The extreme i n a c t i v i t y  exhibited  by g r a p h i t e f e r r i c c h l o r i d e , i n w h i c h t h e g r a p h i t e p l a n e s have been s e p a r a t e d from 3.36 t o 9 . 4 A  layer-  , makes  i t seem q u i t e u n l i k e l y t h a t t h e b o n d i n g o f the f e r r i c  chloride  i n t h e compound Is o f t h e same t y p e . Rttdorff has found t h a t the magnetic moment o f the *e  i o n s i n t h e compound i s  +++•  the same as t h a t o f pe  i n F e C l ^ and c o n c l u d e s t h a t co-  v a l e n t bonding o f t h e Fe-C type i s out o f the q u e s t i o n ( 2 2 ) . He s u g g e s t s i n s t e a d , t h a t t h e r e i s a p o l a r i z a t i o n o f the c o n d u c t i v i t y e l e c t r o n s o f the carbon l a y e r - p l a n e s  toward  the c e n t r a l l a y e r o f i r o n atoms but t h a t these remain essentially ionic.  One c a n t h e n imagine some degree of  e l e c t r o v a l e n t b o n d i n g of the c h l o r i n e i o n s t o the macro positive ion layer-planes. I n view o f t h e nature o f t h e bonding o f t h e f e r r i c i o n s and the c o n f i g u r a t i o n o f atoms about them, i n the graphite  f e r r i c c h l o r i d e s t r u c t u r e , i t seemed t h a t an i n -  v e s t i g a t i o n of the p o s s i b i l i t y  o f exchanging t h e s e i o n s  or o f e j e c t i n g them from the l a t t i c e by S z i l a r d Chalmers r e a c t i o n , would be o f i n t e r e s t and perhaps f u r t h e r e l u c i d a t e t h e s t r u c t u r e of the compound.  2.  RADIOCHEMICAL THEORY Nuclear  chemistry  as n u c l e a r p h y s i c s .  is a field  of a c t i v i t y as o l d  The workers In the l a t e n i n e t i e s  made s t u d i e s of the p o s s i b l e i n f l u e n c e of chemical on r a d i o a c t i v e decay and searched  among the elements f o r  those d i s p l a y i n g r a d i o a c t i v e p r o p e r t i e s , w i t h the that a number of new  elements were d i s c o v e r e d ,  only i n r a d i o a c t i v e forms.  binding  Nuclear  result  existing  s c i e n c e remained pre-  dominantly i n the hands of p h y s i c i s t s , however, i n s p i t e of  the v a s t chemical  n u c l e a r transmutation  i m p l i c a t i o n s of developments i n and  a r t i f i c i a l r a d i o a c t i v i t y that  had made a v a i l a b l e r a d i o a c t i v e forms of a l l of the  chemical  elements.W i t h the developments i n "modern alchemy", born w i t h the emergence of the uranium c h a i n - r e a c t i n g p i l e , chemists  of the world began t o p l a y a more prominent r o l e  i n nuclear research.  Today n u c l e a r chemistry has  g r e a t e r importance as a p a r t of chemical  achieved  science, rather  than as an o p e r a t i o n a l appendage of nuclear p h y s i c s . The b a s i c p r i n c i p l e s of r a d i o c h e m i s t r y have been well, worked out  on the na t u r a l l y o c c u r i n g r a d i o a c t i v e  elements by such pioneers as Heresy, Paneth, Fajans, Hahn and  others  niques  (5).  With the e x t e n s i o n of r a d i o c h e m i c a l  to a l l the elements, the f i e l d  expanded tremendously as chemists t h i s powerful  new  of r a d i o c h e m i s t r y  hastened t o make use  tool f o r research.  e r a t u r e that has been compiled  tech-  The  voluminous  on r a d i o c h e m i c a l work  of lit-  n e c e s s i t a t e s t h a t t h i s d i s c u s s i o n be  confined  to only  p a r t i c u l a r l y r e l e v a n t t o p i c s of exchange r e a c t i o n s and Szilard-Chalmers r e a c t i o n .  the the  (lb) A. I s o t o p i o Exchange  Reactions*  Since a r t i f i c i a l l y  produced r a d i o a c t i v e  isotopes  have become r e a d i l y a v a i l a b l e t o s c i e n t i f i c w o r k e r s , a, g r e a t d e a l o f i n f o r m a t i o n c o n c e r n i n g the nature o f c h e m i c a l l i n k a g e s and the mechanism o f r e a c t i o n s has been f r o m a study o f the exchange o f i s o t o p i c atoms.  obtained The  lit-  e r a t u r e o f such r e s e a r c h e s has become q u i t e voluminous and  i t i s not w i t h i n t h e r e a l m o f t h i s paper t o more than  m e n t i o n some g e n e r a l The  considerations.  k i n e t i c mechanisms o p e r a t i n g  i n systems a t  e q u i l i b r i u m o r i n the s t e a d y s t a t e can be s t u d i e d d i r e c t l y by t h e use o f i s o t o p i c l a b e l i n g t e c h n i q u e s .  In typical  e x p e r i m e n t s on i s o t o p i c exchange a l l p a r t i c i p a t i n g molecu l a r species are i n elementic  e q u i l i b r i u m and the o v e r a l l  c h e m i c a l c o m p o s i t i o n o f the system i s m a i n t a i n e d i n v a r i a n t throughout the e x p e r i m e n t a l  period.  One or more of the  r e a c t i n g m o l e c u l e s i s l a b e l l e d by i n c o r p o r a t i o n o f a r a d i o a c t i v e i s o t o p e o f a. c o n s t i t u e n t atom and o b s e r v a t i o n s are made on the r a t e a t w h i c h i s o t o p i c e q u i l i b r a t i o n i s a t t a i n e d . The  r a t e law f o r i s o t o p i c exchange r e a c t i o n s i s  f i r s t - o r d e r i n the c o n c e n t r a t i o n ecules  (15)*  o f l s o t o p i c - l a b e l l e d mol-  T h i s g e n e r a l i s a t i o n i s a consequence o f the  r e q u i r e m e n t t h a t the o v e r a l l c h e m i c a l c o m p o s i t i o n o f t h e r e a c t i n g system, be m a i n t a i n e d i n v a r i a n t .  Thus, suppose  the exchange r e a c t i o n t o be w r i t t e n i n t h e form AX + BX' *=* AX* + BX ^ where the prime symbol r e f e r s t o the i s o t o p i c a l l y l a b e l l e d  (19) atom.  I n such a r e a c t i o n , there must e x i s t some r e v e r s i b l e  mechanism whereby t h e atomic p a r t n e r s  are enabled t o exch-  ange p o s i t i o n s i n t h e m o l e c u l e s AX and BX.  Suppose t h i s  mechanism d i c t a t e s a r a t e o f exchange R w h i c h i s any f u n c t i o n of t h e thermodynamic c o n c e n t r a t i o n s s u c h as t e m p e r a t u r e .  and a system v a r i a b l e  Then, the f i r s t - o r d e r law f o r t h e  exchange o f i s o t o p e i s dx  =  d  /  dt where  (2)  a- /  i n moles per l i t r e o f molec-  , b the c o n c e n t r a t i o n  the c o n c e n t r a t i o n concentration  *_]  l b  a i s the concentration  \\lea(AX)+(AX')  y  o f m o l e c u l e s (6x)+(s\'J , x  o f i s o t o p i c m o l e c u l e s (AX') and y, t h e  o f i s o t o p i c m o l e c u l e s (BX')»  The g e n e r a l i z e d  e q u a t i o n I n v o l v i n g p o l y a t o m i c t y p e s AXn w i l l be amenable t o t h e same treatment i f the c o n c e n t r a t i o n species  o f the r e a c t i n g  a r e e x p r e s s e d i n gram atoms per l i t r e .  This  expr-  e s s i o n i m p l i e s t h a t , no matter what the o v e r a l l r a t e o f exchange r e a c t i o n may be, t h e r a t e o f appearance o f l a b e l l e d Isotopes i n the molecules i n i t i a l l y u n l a b e l l e d f o l l o w s a f i r s t - o r d e r law. Prom e q u a t i o n (2) i t i s easy t o show t h a t Rt = -  ( a )  ( b )  JU (\ - x / x J  where t I s t h e time and Xoo i s t h e c o n c e n t r a t i o n  of isotope  i n AX a t e q u i l i b r i u m . The r e q u i r e m e n t s f o r an I s o t o p i c exchange t h e n a r e , (l)the existence  o f some r e v e r s i b l e e q u i l i b r i u m whereby  the r e a c t i n g m o l e c u l a r s p e c i e s may consummate t h e exchange,  (20) and (2) t h a t no I s o t o p i c d i f f e r e n t i a t i o n can o c c u r .  It is  i m p o r t a n t a l s o t o note t h a t s i d e r e a c t i o n s due t o r a d i a t i o n e f f e c t s s h o u l d he t a k e n c a r e of i n c o n t r o l experiments a t different radiation levels. A g r e a t number o f e x p e r i m e n t s have been c a r r i e d out by v a r i o u s workers s e e k i n g correspondences between t y p e s o f c h e m i c a l b o n d i n g and the k i n e t i c s of i s o t o p i c  exchange.  I t i s of i n t e r e s t t o mention some of these experiments h e r e . The g r e a t mass of i n f o r m a t i o n g a t h e r e d about the s t r u c t u r e of m o l e c u l e s u s i n g methods based on X-ray d i f f r a c t i o n e l e c t r o n - d i f f r a c t i o n , magnetic a n a l y s i s , measurement of e l e c t r i c moments, band spectrum a n a l y s i s , e t c . , has been r e m a r k a b l y w e l l c o r r e l a t e d and s y s t e m a t i z e d i n terms o f the c l a s s i f i c a t i o n of chemica v a l e n t and m e t a l l i c t y p e s .  1 bonds i n t o c o v a l e n t , e l e c t r o -  P a u l i n g has extended t h i s  class-  i f i c a t i o n of c h e m i c a l bond type (17) u s i n g a quantum mecha n i c a l approach based on the a d d i t i v i t y of bond e n e r g i e s c a l c u l a t e d from atomic o r b i t a l t h e o r y . To e v a l u a t e c o r r e l a t i o n s between I s o t o p i c exchange data  and bond t y p e , one s h o u l d n e g l e c t systems i n w h i c h  t h e r e e x i s t o b v i o u s r o u t e s f o r exchange t h r o u g h i o n i c mechanisms.  Systems i n v o l v i n g c o u p l e s s u c h as Br2 / Br" , E g * /  HgjT*', P e ( C N ) g " / Pe(CN)g " e t c . , have been o b s e r v e d t o e x h i b i t 3  r a p i d exchange t h r o u g h e l e c t r o n t r a n s f e r , e i t h e r t h r o u g h an i o n i z a t i o n mechanism or through an i n t e r m e d i a t e complex. However, u s e f u l i n f o r m a t i o n about such bonds i s i n f r e q u e n t l y o b t a i n e d from o b s e r v a t i o n s o f exchange r a t e s .  (21) Other i n v e s t i g a t i o n s i n v o l v e systems f o r w h i c h r e a c t i o n mechanisms i n v o l v i n g bond s p l i t t i n g and d i s s o c i a t i o n e q u i l i b r i a o t h e r t h a n those o f i o n i z a t i o n a r e r e q u i s i t e i n p r o d u c i n g exchange.  Bonds between atoms i n m o l e c u l e s p a r t i c -  i p a t i n g i n s u c h exchanges were c l a s s i f i e d , as "pure"  covalent  or e l e c t r o v a l e n t or as a m i x t u r e o f these two extreme t y p e s , on t h e b a s i s o f n o n - i s o t o p i c  techniques.  Then t h e . c r i t e r i o n  b a s e d on r a p i d i t y o f exchange was a p p l i e d t o a s c e r t a i n whethe r any correspondence e x i s t e d between degree o f c o v a l e n c y and r a t e o f exchange. I n c r y s t a l l i n e d i p h e n y l i o d o n i u m i o d i d e i t has been shown b y X - r a y a n l y s i s (13) t h a t two i o d i n e bonds a r e c o v a l e n t and one i o n i c . The X-ray d a t a a r e c o n s t i t u e n t  with  a scheme i n v o l v i n g the two c o v a l e n t bonds i n the iodonium i o n w i t h the i o n i c bond between t h e iodonium i o n and t h e i o d i d e v i z . (CgH^gl*".- I ~ • When t h i s substance i s brought i n t o aqueous s o l u t i o n i n the presence o f l a b e l l e d i " and t h e n r e c r y s t a l l i z e d from s o l u t i o n , l a b e l l e d i o d i n e i s found i n the s o l i d .  T h i s l a b e l l e d i o d i n e can be removed w i t h  s i l v e r i o n (as the h y d r o x i d e ) , c o n t a i n i n g no l a b e l l e d i o d i n e .  the r e s u l t i n g  (CgH^^IOH  Furthermore no exchange  can be d e t e c t e d between the two i o d i n e atoms o f the d i p h e n y l iodonium i o d i d e i t s e l f (9)« I t has been showm by J.F. F l a g g , t h a t i n c o b a l t o u s c o b a l t i c y a n i d e , t h e r e i s no exchange between t h e c o b a l t atoms (3)« Here t h e c o b a l t o u s  atoms a r e o b v i o u s l y i  ionic  whereas the c o b a l t i c atoms a r e assumed t o be h e l d m a i n l y by c o v a l e n t bonds by a n a l o g y w i t h o t h e r c o b a l t i c complexes  (22)  f o r w h i c h magnetic s u s c e p t i b i l i t y d a t a are a v a i l a b l e . Another experiment i l l u s t r a t i n g  good c o r r e l a t i o n  between c o v a l e n a y and no exchange and between i o n i c and r a p i d exchange was c a r r i e d out by P.A.Long  i n 1941. ( 1 1 ) •  The r e s e a r c h r e p o r t e d on the exchange between f r e e i o n s and complex o x a l a t e s of i r o n and c o b a l t .  binding  oxalate  Prom measure-  ments o f ma g n e t i c s u s c e p t i b i l i t y i t appears t h a t the bonds between the c e n t r a l atom and the o x a l a t e i o n s i n the c o b a l t complex are c o v a l e n t whereas i n the i r o n complex they a r e mainly e l e c t r o v a l e n t .  When these complexes are b r o u g h t  i n t o aqueous s o l u t i o n as the a l k a I I s a l t s i n the p r e s e n c e of f r e e o x a l a t e i o n s l a b e l l e d w i t h C" i t i s f o u n d t h a t  ferric  t r i o x a l a t e exchanges r a p i d l y whereas the c o b a l t complex shows no exchange. S. Ruben s t a t e s t h a t , "many examples may be c i t e d t o s u p p o r t the n o t i o n t h a t e l e c t r o v a l e n t l i n k a g e s l e n d s e l v e s t o r a p i d exchange and c o v a l e n t  them-  l i n k a g e s do n o t .  However the cogeny of examples s u c h as those c i t e d i s weakened by the f a c t t h a t i n p r a c t i c a l l y a l l cases the exchange i s observed i n a  p o l a r solvent i n which d i s s o c i a t i o n e q u i l -  i b r i a operate and what i s u s u a l l y b e i n g measured i s m e r e l y the tendency o f i o n i c l i n k a g e s t o I o n i z e .  I t i s not d i f f -  i c u l t t o f i n d systems i n w h i c h the r e a d i n e s s  o f atoms t o  exchange b e a r s l i t t l e r e l a t i o n t o the a s s i g n e d bond  type".  (20).  There i s no exchange between magnesium  i o n s and the acetone A  magnesium p o r p h y r i n , c h l o r o p h y l l , d i s s o l v e d i n an ution.  One may assume the c e n t r a l magnesium  &0% solA  atom t o be h e l d  (23)  p r i m a r i l y by e l e c t r o v a l e n t l i n k a g e because of the  high  degree of e l e c t r o p o s i t i v e c h a r a c t e r of magnesium compared t o the c o o r d i n a t i n g n i t r o g e n atoms of the p y r r o l e c o n s t i t uents of c h l o r p h y l l . and f e r r i h e m e ,  Nor does exchange occur between p e  f e r r i h e m o g l o b i n , f e r r i c p h e o p h y t i n and  tetraphenylporphin,  + + +  ferric  or between C u a n d c u p r i c p h e o p h y t i n + +  u s i n g v a r i o u s mixed s o v e n t s t o e f f e c t a homogeneous system (20).  In ferriheme  the other p o r p h i n s  ~  or f e r r i h e m o g l o b i n , and presumably i n c i t e d , the magnetic d a t a  e l e c t r o v a l e n t bonding.  Yet no exchange  i n d i c a t e mainly  occurs.  A n o t h e r i n t e r e s t i n g experiment was  c a r r i e d out  u s i n g the compound ferrous<*,ct.' - d i p y r i d y l s u l f a t e ( C i Q H g ^ ) ^ FeSO^.  The  complex s a l t i s known t o be d i a m a g n e t i c  P a u l i n g has c o n c l u d e d t h a t Jbfee Fe-N mainly  covalent.  w i t h Fe  Nevertheless  bonds are  therefore  an exchange of about  i n aqueous s o l u t i o n was  and  25$  noted a f t e r two hours  (20).  From a c o n s i d e r a t i o n of the d a t a a v a i l a b l e at p r e s ent i t appears t h a t t h e r e need be no s y s t e m a t i c c o r r e l a t i o n between c o v a l e n c y exchange.  The  or e l e c t r o v a l e n c y and r a t e of i s o t o p i c  f a c t o r s w h i c h i n f l u e n c e s u c h exchange, i . e .  s t r e n g t h of bond, s t e r i c h i n d r a n c e ,  solvent i n t e r a c t i o n s ,  e q u i v a l e n t s t a t e s a v a i l a b l e , e t c . , are not y e t c l e a r l y i n e d or s e p a r a b l e  def-  f o r e i t h e r extreme type of b o n d i n g , l e t  a l o n e f o r mixed t y p e s .  Therefore  t o make the r a t h e r a t t e n u a t e d  i t i s permissible  only  statement t h a t any atom bound  i n a molecule whether by a c o v a l e n t  or e l e c t r o v a l e n t bond,  w i l l not exchange w i t h s i m i l i a r atoms i n a n o t h e r  molecular  s p e c i e s u n l e s s a. mechanism e x i s t s f o r b r i n g i n g such atoms  (24)  r e v e r s i b l y Into equivalent  states.  I t i s becoming more apparent t o i n v e s t i g a t o r s i n these researches,  t h a t s t r u c t u r a l r e l a t i o n s are v e r y  important  and perhaps predominate over bond type I n d e t e r m i n i n g  exchange  rate.  I n the p o r p h i n  type s t r u c t u r e s a l r e a d y mentioned  i t i s n e c e s s a r y t o break a " f u s e d " r i n g , i . e . f o u r bonds must be b r o k e n s i m u l t a n e o u s l y .  Hence one may  expect  little  or no exchange because the " f u s e d " r i n g s t r u c t u r e does not p e r m i t the escape of the c e n t r a l atom and  the e q u i l i b r i u m  i n v o l v e d i s p r a c t i c a l l y i r r e v e r s i b l e i n f a v o r of the bound atom.  I n exchangeable compounds w i t h a r i n g c o n s i s t i n g  of s e p a r a t e d m o l e c u l e s i n s t e a d of a " f u s e d " r i n g t y p e , e x i s t s the p o s s i b i l i t y of s t e p w i s e d i s s o c i a t i o n w i t h i b r i a i n v o l v i n g molecular species i s h e l d by two  there  equil-  i n w h i c h the m e t a l i o n  or l e s s bonds..  I t has seemed of i n t e r e s t t o e x t e n d these I n v e s t i g a t i o n s t o a n o t h e r "bound atom" type s t r u c t u r e , namely, graphite f e r r i c chloride (C^FeCl^) . " x  shown t h a t the F e  + + +  r a  y s t u d i e s have  i o n s between the l a r g e  layer-planes  o f t i g h t l y bonded c a r b o n atoms of the g r a p h i t e l a t t i c e , form a t r i a n g u l a r p l a n a r network above and below w h i c h t h e r e i s a p a r a l l e l net plane of CI  ions.  t h a t the magnetic moment of the Pe i s unchanged w i t h t h a t of Pe  Rttdorff (22) has  found  i o n s i n the compound  i o n s i n P e C l ^ and  suggests  t h a t the bonding of the f e r r i c c h l o r i d e I n the l a t t i c e i s the r e s u l t o f a p o l a r i z a t i o n of the c o n d u c t i v i t y e l e c t r o n s o f t h e c a r b o n l a y e r - p l a n e s toward the c e n t r a l i r o n i o n s .  (25) This explanation  seems v a l i d , f o r i t would be  difficult  to account f o r the extreme  i n a c t i v i t y e x h i b i t e d by  f e r r i c c h l o r i d e i f one was  to assume t h a t the m e t a l l i c  c h l o r i d e was  graphite  h e l d by no more than the van der Waals f o r c e s  between the l a t t i c e  layer-planes.  From a c o n s i d e r a t i o n of the c o n f i g u r a t i o n of atoms around the Fe ~^" ions i n t h i s "sandwich" s t r u c t u r e f o r +4  (Ci^FeCl^)  , i t seemed u n l i k e l y that the i r o n ions i n the  compound would e x h i b i t any r a p i d exchange w i t h F e i n a queous s o l u t i o n . described  h e r e i n was  + + +  ions  The s e r i e s of experiments to be  done to determine whether such exch-  ange took p l a ce under any of a v a r i e t y of c o n d i t i o n s .  (26)  B. The S z i l a r d - C h a l m e r s R e a c t i o n i n the C h a i n R e a c t i n g P i l e * A w e l l known f i e l d of n u c l e a r c h e m i s t r y based on the s p e c i a l p r o p e r t i e s o f r e c o i l atoms i s t h a t o f the  Szilard-  Chalmers r e a c t i o n , wherein the r a d i o a c t i v e atoms from  neutron  a c t i v a t i o n s e p a r a t e themselves i r r a d i a t e d (36)  (30).  The  from the b u l k of m a t e r i a l b e i n g  r a d i a t i v e c a p t u r e of a  neutron  by a s t a b l e nucleus i s an important n u c l e a r r e a c t i o n , w h i c h f r e q u e n t l y g i v e s r i s e t o a u s e f u l r a d i o i s o t o p e . However, the c h e m i c a l i d e n t i t y o f the a c t i v e i s o t o p e w i t h the unchanged t a r g e t element p l a c e s s e r i o u s l i m i t a t i o n s on the a c t i v i t i e s o b t a i n e d by t h i s r e a c t i o n .  The  specific  Szilard-Chalmers  r e a c t i o n , w h i c h e f f e c t s s e p a r a t i o n of the a c t i v a t e d atoms from the t a r g e t m a t e r i a l by v i r t u e of the gamma-ray r e c o i l , can be used t o enhance the s p e c i f i c a c t i v i t y of the a c t i v e m a t e r i a l under f a v o r a b l e c i r c u m s t a n c e s . Three c o n d i t i o n s have t o be f u l f i l l e d t o make a Szilard-Chalmers chemical separation p o s s i b l e , ( l ) T h e r a d i o a c t i v e atom I n the p r o c e s s of i t s f o r m a t i o n must be broken l o o s e from i t s m o l e c u l e  and i t must not recombine w i t h the  m o l e c u l a r fragment from w h i c h i t s e p a r a t e d .  (2) The  element  must be capable of e x i s t e n c e i n at l e a s t two m u t u a l l y s t a b l e and s e p a r a b l e forms.  (3) At l e a s t two of these forms must  show l a c k o f r a p i d i s o t o p i c exchange. Most c h e m i c a l bond e n e r g i e s are i n the range of 1  t o 5 ev. ( 2 0 - 1 0 0 k . c a l . per m o l e ) . I n any n u c l e a r r e a c t i o n  i n v o l v i n g heavy p a r t i c l e s e i t h e r e n t e r i n g or l e a v i n g the nucl e u s w i t h e n e r g i e s i n excess of 10 or 100 kev. the k i n e t i c  (27)  energy i m p a r t e d t o the r e s i d u a l n u c l e u s f a r exceeds t h e magn i t u d e o f bond e n e r g i e s .  I n the case o f t h e r m a l - n e u t r o n  c a p t u r e , where t h e S z i l a r d - C h a l m e r s method has i t s most impo r t a n t a p p l i c a t i o n s , the i n c i d e n t n e u t r o n does not impart n e a r l y enough energy t o t h e nucleus t o cause any bond r u p t u r e . But n e u t r o n c a p t u r e by a nucleus i s accompanied by the  rel-  ease o f 8 o r 9 m.e.v. o f evergy i n the form o f s e v e r a l energ e t i c gamma quanta.  The r e c o i l energy thus i m p a r t e d t o t h e  c a p t u r i n g atom may be as much as one hundred times as g r e a t as t h e e n e r g i e s o f the c h e m i c a l bonds I n w h i c h i t p a r t i c i p a t e s . Thus i n most n, y p r o c e s s e s the p r o b a b i l i t y o f bond r u p t u r e i s very high. The t h i r d c o n d i t i o n f o r t h e o p e r a t i o n o f the S z i l a r d Chalmers method r e q u i r e s a t l e a s t t h a t t h e r m a l exchange be slow between the r a d i o a c t i v e atoms i n t h e i r new c h e m i c a l state? and the i n a c t i v e atoms i n the t a r g e t compound.  However,  the e n e r g e t i c r e c o i l atoms may undergo exchange more r e a d i l y t h a n atoms w i t h o r d i n a r y thermal e n e r g i e s .  I t i s these ex-  change r e a c t i o n s and o t h e r r e a c t i o n s o f t h e high-energy  recoil  atoms ("hot atoms") t h a t determine t o a* l a r g e e x t e n t t h e sepa r a t i o n e f f i c i e n c i e s obtainable i n Szilard-Chalmers processes (36).  Recent attempts t o e n r i c h a c t i v i t i e s produced  i n the  h i g h f l u x o f t h e c h a i n - r e a c t i n g p i l e have shown t h e h i g h gamma and n e u t r o n r a d i a t i o n f i e l d s cause marked c h e m i c a l changes i n the bombarded^compounds a s i d e from t h e e f f e c t s of accompanying a c t i v a t i o n .  That such r e a c t i o n s may y i e l d  p r o d u c t s s i m i l i a r t o those o b t a i n e d i n a c t i v a t i o n r e a c t i o n s i s t o be e x p e c t e d , s i n c e b o t h types a r e e s s e n t i a l l y a. decomp—  (28)  o s i t i o n by e x c i t a t i o n .  But r a d i a t i o n d e c o m p o s i t i o n can  y i e l d s m a l l amounts of the c h e m i c a l form i n w h i c h the a c t i v i t y i s f o u n d , thus d i l u t i n g the a c t i v e i s o t o p e .  I t i s also  p o s s i b l e t h a t the r a d i a t i o n f i e l d w i l l cause f u r t h e r c h e m i c a l r e a c t i o n s of the s e p a r a b l e a c t i v e i s o t o p e w h i c h may  change i t ,  ;  to a form which i s no l o n g e r s e p a r a b l e , or cause some o f the i n i t i a l l y s e p a r a t e d a c t i v i t y t o be l o s t by a r a d i a t i o n - i n d u c e d back r e a c t i o n .  As suggested by R.R.  W i l l i a m s , the r a t e o f  d e c o m p o s i t i o n i s undoubtedly r e l a t e d t o d i f f e r e n t f l u x components from those r e s p o n s i b l e f o r a c t i v a t i o n (36).  Variations  among these components must be e l i m i n a t e d or measured b e f o r e a q u a n t i t a t i v e t e s t o f the proposed r a t e e q u a t i o n s w i l l possible.  be  Many workers are engaged i n a s t u d y of these p r o c -  esses and i t i s l i k e l y t h a t much more than the p r e s e n t q u a l i t a t i v e d a t a w i l l soon be  available.  The r e a c t i o n s w h i c h the " h o t " atom or fragment  will"  undergo depend t o some e x t e n t on t h e n a t u r e o f I t s environment and i n t h i s c o n n e c t i o n the p r e s e n t r e s e a r c h on the e f f e c t of p i l e I r r a d i a t i o n on g r a p h i t e f e r r i c c h l o r i d e  (CijjFeCl-^)  was c a r r i e d o u t . The l a r g e s t amount o f work i n the f i e l d o f S z i l a r d Chalmers sepa r a t i o n s has been done on halogen compounds (32).  Many d i f f e r e n t o r g a n i c h a l i d e s ( i n c l u d i n g C H ^ I , 2  CCl^,  (29) CH^I,  C2H/C1 , C H B r , C H B r , CgELBr) have been i r r a d i a t e d * 128 38 and the p r o d u c t s o f n e u t r o n c a p t u r e r e a c t i o n s ( I ,01 , 80 82  Br  2  , Br  2  5  2  2  2  ) removed by v a r i o u s t e c h n i q u e s .  S e p a r a t i o n s of  ha logens w i t h 70 t o 100 per cent y i e l d s have a l s o been  (29)  obtained  i n n e u t r o n i r r a d i a t i o n s o f s o l i d or d i s s o l v e d c h l o r -  a t e s , bromates, i o d a t e s , p e r c h l o r a t e s and p e r i o d a t e s . The bombardment o f m e t a l - o r g a n i c  compounds and  complex s a l t s i s o f t e n u s e f u l f o r Szilard'-Chalmers  separat-  i o n s i f t h e f r e e m e t a l i o n does not exchange w i t h the compound and  i f t h e two a r e s e p a r a b l e .  Some o f t h e compounds w h i c h  have been used s u c c e s s f u l l y a r e : c a c o d y l i c a c i d (CH^J^AsOOH, 76 ^ f r o m w h i c h As c a n be s e p a r a t e d as s i l v e r a r s e n i t e i n 95% y i e l d j copper s a l i c y l a l d e h y d e o-phenylene d i a m i n e , from w h i c h as much as 97% o f t h e Cu ion;  a c t i v i t y c a n be removed as Cu  uranyl benzoylacetonate*  VO2(0qE^GOGEGOGE^) , 2  from which  TJ^29 a c t i v i t y has been e x t r a c t e d i n about 10% y i e l d .  I t has  been s u g g e s t e d t h a t m e t a l i o n complexes w h i c h e x i s t i n opti c a l l y a c t i v e forms and do not racemize r a p i d l y may be genera l l y s u i t a b l e f o r Szilard-Chalmers ion  p r o c e s s e s because the m e t a l  i n s u c h a>. complex i s not e x p e c t e d t o exchange r a p i d l y  w i t h free metal i o n i n s o l u t i o n .  Some complexes o f t h i s type  have been used s u c c e s s f u l l y , e.g. the t r i e t h y l e n e d i a m i n e n i t r a t e s of i r i d i u m , platinum,  rhodium, and c o b a l t .  Recent s t u d i e s o f the i r r a d i a t i o n o f these c o b a l t complexes have shown t h e dependence o f a s u c c e s s f u l Szilard-Chalmers'  r e a c t i o n on-the c o n f i g u r a t i o n o f the compl-  exing molecules surrounding  t h e c e n t r a l m e t a l l i c atom.  P.  Stte and G-. Kayas i n 1948, I r r a d i a t e d i n a n e u t r o n f l u x , t h e three cobalticomplexes Co(lTH^) Co(en)3  6  (N03)^, (NO3).,  , hexamine c o b a l t I I I n i t r a t e  triethylenediamine cobalt I I I nitrate and d i e t h y l e n e t r i a m i n e c o b a l t I I I n i t r a t e  (30) Co(tri)  (N0^)^  2  ( 3 1 ) . They found f o r a l l t h r e e compounds,  t h a t i s o t o p i c exchange, w i t h i n e x p e r i m e n t a l e r r o r s , was  nil.  The p e r c e n t y i e l d s o f s e p a r a t e d a c t i v i t y , however, v a r i e d g r e a t l y f o r the t h r e e compounds.  Prom s a l t no. I , hexamine  c o b a l t I I I n i t r a t e , t h e y were a b l e t o e x t r a c t 86$ of the a c t i v i t y as the h y d r o x i d e .  total  Prom s a l t n o . I I , where the e t h y -  l e n e d i a m i n e m o l e c u l e s each t a k e up two p o s i t i o n s i n the o c t a h e d r a l c o n f i g u r a t i o n o f the c a t i o n , t h e amount o f the a c t i v i t y s e p a r a t e d dropped t o 75$ of the t o t a l I n the case o f s a l t n o . I l l , d i e t h y l e n e t r i a m l n e c o b a l t I I I n i t r a t e , the e t h y l e n e t r i a m i n e m o l e c u l e s each cover t h r e e p o s i t i o n s of the o c t a h e d r a l arrangement around the c e n t r a l c o b a l t atom. the S z i l a r d - C h a l m e r s s e p a r a t i o n was  Here  s u c c e s s f u l t o the e x t e n t  o f o n l y 10$.  \ \  Co(NH ) (N0 ) 5  6  Figure 5 -  3  3  Co(en) (N0 ) 3  3  3  Co(tri) (N0 ) 2  3  3  S t e r i c hindrance i n cobalt-complexes.  These somewhat c o n c l u s i v e r e s u l t s are e x p l a i n e d by the a u t h o r s who  s t a t e t h a t when an a c t i v a t e d r e c o i l i n g atom of t h i s  type  i s surrounded by a number of l a r g e i n t e r f e r i n g m o l e c u l e s ,  (31)  t h a t i t i s more or l e s s improbable  that there w i l l f o l l o w  any bond r u p t u r e a l l o w i n g the e j e c t i o n of the "hot" atom from the compound.  I t i s assumed t h a t , under the e f f e c t  the shock, the c o o r d i n a t i n g c h a i n e n t e r s i n t o v i b r a t i o n absorbs s u f f i c i e n t energy t o p r e v e n t l e a v i n g the m o l e c u l e .  of and  the r e c o i l atom f r o m  T h i s s t e r i c e f f e c t r e s u l t s i n the  p r o d u c t i o n of an a c t i v e compound w i t h most o f the A+1 o p i c atoms s t i l l bonded i n the same p o s i t i o n as the  isotneutron  c a p t u r i n g atom they r e p l a c e d . I t i s suggested  t h a t , i n the case of a c o p l a n a r mol-  e c u l e , t h i s s t e r i c e f f e c t would not be as pronounced, l e a d i n g t o a f a i r l y h i g h y i e l d of s e p a r a t e d a c t i v i t y .  I t may  be  of  i n t e r e s t t o m e n t i o n t h a t S z i l a r d - C h a l m e r s r e a c t i o n on uranium by means of u r a n y l s & l i c y l a l d e h y d e o-phenylenediimine y i e l d of about 80%  (14).  The  c e n t r a l atom of t h i s compound  i s e n c l o s e d i n a l a r g e and coherent  o r g a n i c molecule  h i g h y i e l d i s l i k e l y due t o the p r o b a b l e molecule  w h i c h enables  C o n s i d e r now  gives a  and  the  c o p l a n a r i t y of the  the uranium atom t o escape.  the case o f the v e r y s t a b l e g r a p h i t e  ic chloride ( C ^ F e C l ^ )  n  ferr-  w i t h the f e r r i c c h l o r i d e m o l e c u l e s  bound between the l a y e r - p l a n e s o f c a r b o n atoms i n the g r a p h i t e lattice.  As has been suggested,  the p r o b a b i l i t y o f any r a p i d  i s o t o p i c exchange between f e r r i c i o n s i n s o l u t i o n and  the  i r o n e x i s t i n g as f e r r i c c h l o r i d e bound i n the g r a p h i t e seems somewhat remote.  lattice,  I t i s t h e r e f o r e l i k e l y t h a t any  a c t i v i t y s e p a r a t e d by a S z i l a r d - C h a l m e r s p r o c e s s compound c o u l d be o b t a i n e d i n h i g h s p e c i f i c  on t h i s  activity.  iron  (32)  However t h e c o n f i g u r a t i o n o f atoms s u r r o u n d i n g e a c h i r o n atom i n t h i s "sandwich" s t r u c t u r e , would v e r y defi-nliaLy be e x p e c t e d t o c o n t r i b u t e t o a l a r g e r e t e n t i o n o f t h e a c t i v i t y by r e c o m b i n a t i o n r e a c t i o n s , and r e s u l t i n a low y i e l d of separated a c t i v i t y f o l l o w i n g neutron  irradiation.  The s u c c e s s o f a S z i l a r d - C h a l m e r s s e p a r a t i o n on ^12^ ^^3^n e  W  a  S  c  3- " e  t e r m  ^  n e <  ^ f o l l o w i n g i r r a d i a t i o n of a dry  p u r i f i e d sample o f t h e compound C o u n c i l atomic p i l e .  i n Canada's N a t i o n a l  Research  The r e s u l t s and d i s c u s s i o n o f these  experiments f o l l o w i n t h e e x p e r i m e n t a l s e c t i o n o f t h i s  paper.  (33)  3* RADIOCHEMICAL TECHNIQUES. In r a d i o a c t i v e t r a c e r experiments, a r a d i o a c t i v e isotope  i s used as an i n d i c a t o r t o t r a c e or f o l l o w the  t a k e n by the i n a c t i v e i s o t o p e *  The  w i t h the e m i s s i o n of a l p h a , b e t a , p o s i t r o n s and  path  r a d i o a c t i v e isotope  decays  or gamma r a y s , or p o s s i b l y  t h e s e r a d i a t i o n s can be measured w i t h a s u i t a b l e  i n s t r u m e n t s u c h as an i o n i z a t i o n chamber or a G e l g e r c o u n t e r . By t a k i n g s u i t a b l e p r e c a u t i o n s ,  the measurements can be made  quantitative. The exponential  decay of a r a d i o a c t i v e substance f o l l o w s  the  -Kt  law N  «  N.e  where N i s the number o f unchanged atoms at time t , No  is  the number p r e s e n t at t = 0, and A. i s the decay c o n s t a n t . h a l f - l i f e t-|- of a r a d i o a c t i v e s p e c i e s  i s given  The  by  I n p r a c t i c a l work the number of atoms N i s not d i r e c t l y evaluated,  a nd even the r a t e of change d^/d.t ±  u s u a l l y not measured a b s o l u t e l y .  The  u s u a l procedure i s t o  determine the a c t i v i t y A, w i t h A-CA.N . The i c i e n t C, depends upon the n a t u r e and recording  i n s t r u m e n t and  and d e t e c t o r . species  detection  e f f i c i e n c y of  the g e o m e t r i c a l  coeff-  the  arrangement of sample  I n cases where the decay of the  i s appreciable  s  d u r i n g the course of the  radioactive experiment  i t i s n e c e s s a r y t o c o r r e c t f o r the r e s u l t i n g decrease i n a c t i v i t y b e f o r e comparative d e t e r m i n a t i o n s can be The  obtained*  l i m i t o f s e n s i t i v i t y of a G e i g e r - M t t l l e r c o u n t e r  i s s e t by the background c o u n t i n g  r a t e w h i c h must be  subtrac-  (34)  t e d t o f i n d t h e a c t i v i t y o f the sample.  By s h e a t h i n g the  e n c l o s e d c o u n t e r w i t h a few c e n t i m e t e r s t h i c k n e s s o f l e a d most o f t h e i o n i z a t i o n from s m a l l amounts o f a c t i v i t y  present  as i m p u r i t i e s i n c o n s t r u c t i o n m a t e r i a l s , and from the appreci a b l e and v a r i a b l e amount of radon, t h o r o n , and t h e i r decay products contained  i n t h e a i r , can be e l i m i n a t e d .  However  the c o s m i c - r a y e f f e c t w i l l s t i l l be s i g n i f i c a n t and r e s u l t s i n a. background c o u n t i n g r a t e o f from 20-25 counts p e r minute. Because r a d i o a c t i v e decay i s a random p r o c e s s , u l t i m a t e a c c u r a c y i n assay o f r a d i o a c t i v i t y i s l i m i t e d by s t a t i s t i c a l f l u c t u a t i o n s inherent i n counting data.  T h i s random phenom-  enon i s s u b j e c t t o e s t a b l i s h e d methods o f s t a t i s t i c a l a n a l y s i s w h i c h have been v e r i f i e d abundantly by experiment.  The  term  " s t a n d a r d d e v i a t i o n " as used i n t h e e x p e r i m e n t a l s e c t i o n of t h i s t h e s i s i s e q u a l t o t h e square r o o t o f the number o f counts o b s e r v e d .  The p r o b a b l e e r r o r , d e f i n e d as the e r r o r  w h i c h i s as l i k e l y t o be exceeded as n o t , i s 0.6745 the s t a n d a r d d e v i a t i o n .  times  I n g e n e r a l , the c o u n t i n g i s s u f f -  i c i e n t i n d u r a t i o n t o make t h e s t a n d a r d d e v i a t i o n l e s s e r r o r s from n o n - s t a t i s t i c a l sources such as sampling  than  uncert-  a i n t i e s and u n c o n t r o l l a b l e c h e m i c a l l o s s e s . I n t h e r e s e a r c h t o be d e s c r i b e d , o n l y r e l a t i v e  counts  from a c t i v i t i e s were r e q u i r e d and many o f t h e c o r r e c t i o n s n e c e s s a r y t o o b t a i n an a b s o l u t e c o u n t , such as e x t e r n a l abs o r p t i o n l o s s , b a c k s c a t t e r i n g and sample geometry, were e l i m i n a t e d by s t a n d a r d i z a t i o n of c o u n t i n g t e c h n i q u e s .  A com-  p l e t e d e s c r i p t i o n o f t h e e x p e r i m e n t a l methods f o l l o w e d i n  (35)  t h i s r e s e a r c h has been i n c l u d e d i n the e x p e r i m e n t a l s e c t i o n o f t h e t h e s i s . I t has seemed more c o n v e n i e n t  t o l e a v e any  d i s c u s s i o n concerning the v a l i d i t y of counting rate r e s u l t s and t h e j u s t i f i c a t i o n o f t h e manner o f h a n d l i n g the r e q u i r e d c o r r e c t i o n problems u n t i l t h a t more a p p r o p r i a t e t i m e .  EXPERIMENTAL• 1«  P r e p a r a t i o n of Graphite F e r r i c C h l o r i d e ,  [c^FeCl^j  •  n  In view o f - t h e nature o f the experiments t o be c a r r ied  out, i t was decided t h a t the f u l l y i n t e r c a l a t e d g r a p h i t e  ferric  chloride  [c^FeCl^j  n  would be b e t t e r s u i t e d t o our  purpose than the second compound c o n t a i n i n g l e s s f e r r i c  A c c o r d i n g l y , I t was the compound c o n t a i n i n g about 5 6 $  ide. ferric the  chlor-  c h l o r i d e which was prepared i n a l l cases by keeping  r e a c t i o n temperature below 3 0 9 * C .  a. ) Anhydrous F e r r i c C h l o r i d e : Dry C I 2 was passed over C.P. i r o n powder c o n t a i n e d i n an e l e c t r i c a l l y heated Pyrex tube at 350°C. B e a u t i f u l hexagonal p l a t e l e t s o f a deep r e d wine c o l o r formed  throughout the c o o l p o r t i o n of the tube.  Dry  a i r was admitted d u r i n g the c o o l i n g and the c r y s t a l s were removed and handled o n l y i n a d r y box.  To prepare the  a c t i v e c h l o r i d e , r a d i o a c t i v e i r o n wire was used together w i t h the powder. b . ) C 1 2 F 9 C I 3 : A c i d p u r i f i e d , 2 0 0 mesh g r a p h i t e , ( G - 6 6 Graphite p o w d e r - F i s h e r S c i e n t i f i c Co.) was mixed w i t h t h r e e times i t s weight  of anhydrous  ferric  c h l o r i d e , sealed i n a  C a r i u s bomb tube, and heated f o r twelve hours a t 3 0 5 * 0 . The approximately ^7% o f the r e a c t i o n product which i s excess ferric  c h l o r i d e was removed by s u c c e s s i v e r e f l u x i n g s w i t h  hot 6 N H C 1 .  A f t e r a t o t a l washing  time of 3 6 hours a f u r t h e r  r e f l u x l n g at. 1 0 0 ° C w i t h a one gram sample gave no t e s t f o r Fe  + + +  w i t h NHyCNS or l e s s than 4 . 3 u g m .  radiometrically.  Fe as determined  6 k NaOH at 80°C showed no a c t i o n on t h e  (56)  (37)  graphite-ferric chloride after purification.  The compound  was s t a b l e i n a i r and decomposed at temperatures o n l y above 309°C  ( w i t h e v o l u t i o n of F e C l ^ v a p o u r ) . From the i n i t i a l weight o f g r a p h i t e and f i n a l weight  o f compound, t h e p e r c e n t a g e c o m p o s i t i o n was d e t e r m i n e d and found always t o c o r r e s p o n d t o C ^ F e C l ^ * a compound c o n t a i n i n g 53$ f e r r i c c h l o r i d e *  A c c o r d i n g t o R U d o r f f ( 2 2 ) t h i s same  c o m p o s i t i o n r e s u l t s throughout the p r e p a r a t i o n range 2 0 0 t o 309°G. and i n d e p e n d e n t l y of the o r i g i n a l g r a p h i t e form  crystal  (8). X-ray d i f f r a c t i o n measurements on the G - ^ F s C l ^ powder,  made w i t h a P h i l l i p s - G e i g e r Counter X - r a y S p e c t r o m e t e r and u s i n g the 1 . 5 3 9 4 . 6 6 and 3 . 1 3  Cu l i n e , showed t h r e e peaks a t d = 9 » 4 0 ,  A  A  .  The f i r s t of t h e s e has been I n t e r p r e t e d  by Rttdorff as the s e p a r a t i o n of the p l a n e s o f c a r b o n atoms. ©  H i s v a l u e was 9 4  A .  I n the t h r e e t a b l e s w h i c h f o l l o w , are s e t down the n u m e r i c a l r e s u l t s from X - r a y d i f f r a c t i o n measurements on g r a p h i t e , anhydrous f e r r i c c h l o r i d e and C-^pFeCl^*  In "the  column headed "degrees" i s l i s t e d the g l a n c i n g a n g l e , e q u a l t o t w i c e the & i n the Bragg e q u a t i o n  n A  = 2,^  s i n  e  .  The  second column c o n t a i n s the v a l u e s o f d, the d i s t a n c e s between r e f l e c t i n g atomic p l a n e s .  The v a l u e s I/Io l i s t e d i n the t h i r d  column, are the r a t i o s of the i n t e n s i t y of the r e f l e c t e d beam o f X - r a y s t o the g r e a t e s t i n t e n s i t y o b s e r v e d .  The v a l u e s  l i s t e d f o r anhydrous f e r r i c c h l o r i d e I n Table I I . have been o b t a i n e d from the l i t e r a t u r e .  T a b l e s I and I I I c o n t a i n the  (38)  v a l u e s o b t a i n e d f o r g r a p h i t e and C F e C l 3 from d i f f r a c t i o n 1 2  measurements made i n the l a b o r a t o r i e s o f the B r i t i s h Columb i a R e s e a r c h C o u n c i l , who so k i n d l y p e r m i t t e d the use o f t h e i r X-ray S p e c t r o m e t e r .  (39)  TABLE I X - r a y D i f f r a c t i o n Measurements on G r a p h i t e Graphite  Degrees ( 2 0 )  3-36  1.68  0  dA  2.02  i/lo  24.0  3.701  0.13  26.5  3.36  1.0  41.2  2.187  0.1  42.2  2.137  0.13  43.0  2.100  0.16  44.8  2.02  0.3  46.0  1.969  0.12  50.2  1.82  0.1  54.5  1.68  0.7  56.2  I.63  0.09  60.0  1.539  0.1  61.6  1.503  0.06  77.0  1.236  0.21  83.7  1.154  0.19  85.0  1.139  0.06  86.4  1.122  0.13  (40)  TABLE I I X-ray D i f f r a c t i o n Measurements on Anhydrous x  Ferric Chloride*  FeClo  Decrees ( 2 a )  x  2.68  2*08  5.9  dA  15.0  5.90  0.32  17*4  5.10  0.05  18.5  4-79  0.06  19.8  4.50  0.03  29.4  3.03  0.03  33.4  2.68  1.00  37*4  2.40  0.02  43.5  2^.08  0.40  46.2  1.96  0.03  52.1  1.75  0*30  55.0  1.67  0.06  56.5  1.63  0.16  63.5  I.46  0.06  70.1  1.34  0.05  80.5  1.19  0.03  87.2  1.12  0.05  *  *  '  A . S . T . M . P h i l a d e l p h i a , P a . , X - r a y d i f f r a c t i o n powder p a t t e r n s J.D.Hanawalt and c o - w o r k e r s , c a r d i n d e x .  (41)  TABLE I I I  X - r a y D i f f r a c t i o n Measurements on G r a p h i t e F e r r i c Chloride  C  12  P e C l  3  Degrees (2a)  9.4  4*66  dA  C  FeCl . -L/C 3 1 : )  3.13  i/lo  8..1  10.90  0.30  9.4  9.40  O.64  11.8  7.49  0.25  19.0  4.66  1.00  26.8  3.32  0.21  28.5  3.126  0.81  35.5  2.524  0.09  45.9  1.973  0.07  52.2  1.42  0.11  55.1  1.663  0.09  58.8  1.567  0.10  63.6  1.464  0.08  68.1  1.374  0.12  80.2  1.195  0.05  80.. 8  1.187  0.05  81,8  1.175  0.09  *  10  io  i°  *o  ,ro  GLANCING ANGLE  •  —  Plate I X - R a y  co  7o  ao  yo  (m;uui.s)  . _ :  d i f f r a c t i o n patterns of  I - Graphite I I - Anhydrous F e r r i c I I I - Graphite F e r r i c  Chloride Chloride.  ;  .  (42)  P l a t e I shows t h e comparison between t h e t h r e e X-ray;'*? d i f f r a c t i o n diagrams.  I - graphite,  c h l o r i d e and I I I - g r a p h i t e  I I - anhydrous f e r r i c  f e r r i c chloride  (C^FeCl^).  I t w i l l be seen t h a t t h e p a t t e r n f o r g r a p h i t e  ferric  i d e i s d i s t i n c t l y d i f f e r e n t from t h a t o f e i t h e r  chlor-  graphite  or f e r r i c c h l o r i d e a nd i t i s apparent t h a t no f r e e  ferric  c h l o r i d e e x i s t s i n t h e compound. The  value obtained f o r the percentage f e r r i c  chloride  i n the compound compares v e r y w e l l w i t h t h e l i m i t i n g v a l u e o f F e C l ^ t C e q u a l t o 1 : 1 2 . 0 4 r e q u i r e d by t h e c r y s t a l s t r u c t u r e as d e t e r m i n e d by R U d o r f f . imens gave t h e c o n s i s t e n t  Rigorously  p u r i f i e d spec-  f i g u r e 53% f e r r i c c h l o r i d e , w h i c h  c o r r e s p o n d s t o a F e C ^ t C r a t i o o f 1:12.02.  This f i g u r e  w h i c h i s somewhat b e t t e r t h a n t h e v a l u e 1:11.9 by R U d o r f f (22)  i s p r o b a b l y due t o t h e l o n g e r  reported period of  a c i d - l e a c h p u r i f i c a t i o n employed i n t h i s work. I n view o f t h e e x p e r i m e n t s t o f o l l o w , i t was n e c e s s a r y t o determine t o what degree o f c e r t a i n t y t h e l a s t  traces  o f f r e e f e r r i c c h l o r i d e had been removed from the p u r i f i e d c  12  F e C l  3'  1 ) . 5 gms. o f C ^ F e C l c j were p u r i f i e d by r e f l u x i n g s I n 6N. HC1 f o r t h i r t y - s i x h o u r s . was  successive T h i s specimen  then t r e a t e d t o a f u r t h e r r e f l u x i n g i n lOOmls. o f 6N.  HCl f o r s i x hours, and t h e a c i d e x t r a c t t e s t e d f o r  Fe*  w i t h 1% NH^CNS s o l u t i o n .  Fe  The NH^CNS r e a c t i o n w i t h  ++  +++  w h i c h i s w e l l adapted t o spot t e s t s has a s e n s i t i v i t y o f 0.25  u.g.m. F e ^ a n d a c o n c e n t r a t i o n + +  l i m i t o f 1 i n 200,000.  (43)  The a c i d e x t r a c t  s o l u t i o n was e v a p o r a t e d t o 10 m i s .  before t e s t i n g .  1 ml. portions  the r e a g e n t and were t h e r e f o r e t h a n 5 u. gnu F e  + + +  gave no c o l o r a t i o n assumed t o c o n t a i n  less  . T h e r e f o r e t h e 100 m l . a c i d .extract  from t h e 5 gm. sample o f C P e C l 3  could  l 2  more t h a n 50 u. gm. F e gram o f g r a p h i t e  with  + + +  ,  not have c o n t a i n e d  o r l e s s t h a n 10 u.gm. F e  f e r r i c chloride  + + +  per  tested.  2 ) . A second t e s t f o r completeness o f removal o f f r e e F e ^ ^ w a s made u s i n g r a d i o a c t i v e <  -'12  Fe  *  ^ 3  w  a  3  measured a t 229*10  s  C-^FeCl-^. The a c t i v e  c o u n t s p e r minute p e r 3  gm. w h i c h was e q u i v a l e n t t o 229 10 x  gm. Pe •  c.p.m. from 0.1820  The sample was t r e a t e d by the 36 hour washing  procedure and t h e n examined as f o l l o w s : 5 gms. C F e * C l 1 2  3  r e f l u x e d w i t h lOOmls. 6N HC1 f o r  4 hours. The 100ml. a c i d s o l u t i o n was e v a p o r a t e d t o 10ml. and t e s t e d f o r a c t i v i t y . l m l . a c i d e x t r a c t s o l n . gave 4 4 0 * 2 1 counts/10 m i n . =44*2 c.p.m.  Background count = 44*2 c.p.m. P r o b a b l e e r r o r 0.6745* 2= ± 1 . 3 5 c.p.m. Maximum a c t i v i t y due t o F e i n extract= 2x1.35 c.p.m./ml.= 2.7*10 c.p.m. i n t o t a l volume o f e x t r a c t . + + +  3  229*10  c.p.m. a r e r e c o r d e d from 0.1820 gm. Pe.  /.Max, Pe i n a c i d e x t r a c t s 27 3 x 0.1820 =21.5 u.gm. from 229*1& 5 gm.  .-.less t h a n 4 . 3 u.gm. P© e x t r a c t a b l e / g m . C P e G l o l p  (C  1 2  F e C 1  3)  (U)  From a c o n s i d e r a t i o n of the above r e s u l t s i t appeared r e a s o n a b l y c e r t a i n t h a t we werB d e a l i n g w i t h  C]^ ^!^* 9  and of s u f f i c i e n t p u r i t y t o be s u i t a b l e f o r use i n the f o l l o w i n g experiments on exchange and the S z i l a r d - C h a l m ers r e a c t i o n .  (45)  2. Te3ts f o r Exchange between G r a p h i t e F e r r i c C h l o r i d e 59 12 3 F e r r i c i o n , u s i n g R a d i o a c t i v e Fe . G  F e C l  a n d  The exchange experiments were performed by s h a k i n g p o r t i o n s o f f i n e l y powdered r a d i o - a c t i v e g r a p h i t e I r o n I I I c h l o r i d e i n s o l u t i o n s of i n a c t i v e f e r r i c P.H.'s, t e m p e r a t u r e s , and s o l v e n t s .  i o n of v a r i o u s  The r e v e r s e p r o c e d u r e ,  u s i n g r a d i o a c t i v e i r o n (59)111 c h l o r i d e s o l u t i o n s , was c a r r i e d out i n some c a s e s .  (59)  also  These m i x t u r e s were m e c h a n i c a l l y  shaken f o r v a r i o u s l e n g t h s o f t i m e , t h e n s e p a r a t e d by c e n t r i f u g i n g . A l i q u o t s were withdrawn and t h e s p e c i f i c  activity  of the a c t i v e components d e t e r m i n e d from the c o u n t i n g r a t e , c o r r e c t e d f o r decay. The c o n d i t i o n s o f the experiments were v a r i e d c o n s i d e r a b l y but the same g e n e r a l procedure was f o l l o w e d i n e v e r y case.  T e s t s f o r exchange were c a r r i e d out i n a c i d  media.  As w e l l as f e r r i c c h l o r i d e , aqueous s o l u t i o n s of f e r r i c n i t r a t e and f e r r i c s u l f a t e were mixed w i t h the a c t i v e compound.  To t e s t the e f f e c t of temperature on the r a t e of exchange  a l l the m i x t u r e s i n aqueous media were shaken at temperatures of b o t h 20 and 80*C.  The i n f l u e n c e of s o l v e n t  interaction  on the exchange was observed by c a r r y i n g out e x p e r i m e n t s u s i n g f e r r i c c h l o r i d e dissolved i n e t h a n o l , d i e t h y l e t h e r , i s o - p r o p y l e t h e r , acetone and b e n z y l a l c o h o l .  I n one exper-  iment u s i n g b e n z y l a l c o h o l as the media, t e s t s f o r exchange between g r a p h i t e f e r r i c  c h l o r i d e and f e r r i c 0  at  a temperature o f 190  C.  Ions were made  (46)  R a d i o a c t i v i t y Measurements:  Pure i r o n w i r e was a c t i v a t e d  i n t h e n e u t r o n f l u x o f the Canadian N.R.C. p i l e a t C h a l k 59  R i v e r , O n t a r i o . A m i x t u r e o f the 47 day Fe e m i t t i n g 0.26 and O . 4 6 Mev. b e t a ' s and 1 . 1 0 and 1 . 3 0 Mev. gamma's and t h e 4 y e a r Fe  55  w h i c h decays by K c a p t u r e e m i t t i n g 0.07 Mev X59  r a y s , was r e c e i v e d w i t h an a c t i v i t y o f 0 . 0 5 9 mc. Fe  /gm.  55 ,  p l u s about 0.29 mc. Fe  /gm.  T h i s was mixed w i t h Fe powder  and c o n v e r t e d t o f e r r i c c h l o r i d e as a l r e a d y d e s c r i b e d . The decay curve ( F i g . V I ) , over a f i v e month p e r i o d i s l i n e a r w i t h a Tir o f 4 7 days, i n d i c a t i n g no need f o r a 55  c o r r e c t i o n f o r t h e weak Fe  radiation.  Measurements were made w i t h an "end on" G.M. quenching c o u n t e r made by the U.B.C. P h y s i c s I t had a 3mg./cm  self  Department.  window 2 . 0 c m . i n d i a m e t e r , and a 1 5 0 v o l t  p l a t e a u w h i c h was f l a t w i t h i n 1% s t a t i s t i c a l e r r o r and over w h i c h the count i n c r e a s e d 8$. ( F i g . V I I ) The c o u n t e r was mounted on a l u c i t e base and s h i e l d e d t o a background o f 4 2 * 2 counts p e r m i n u t e .  The p u l s e s were counted by a  N u c l e a r Instrument Co. Model 163 s c a l i n g u n i t . was  count  Response  l i n e a r t o 2% up t o 3 3 0 0 c o u n t s / m i n u t e . Samples were c o u n t e d on l " d i a m e t e r watch g l a s s e s ,  p l a c e d i n an e a s i l y r e p r o d u c i b l e p o s i t i o n about 3 c m . t h e c o u n t e r window.  The samples o f g r a p h i t e f e r r i c 2  compared were always l e s s than 0 . 2 mg. p e r cm.  below chloride  and hence  no s e l f a b s o r p t i o n c o r r e c t i o n was made i n c a l c u l a t i n g specific activity.  The I n i t i a l a c t i v i t y was 0 . 1 u c . p e r gm.  of compound, c o r r e c t e d o n l y f o r background.  The e v a p o r a t e d  f e r r i c c h l o r i d e s o l u t i o n samples however, wer© o f t e n t h i c k  T I M E  Figure VI -  IN  PAYS  Rate of decay of radioactive Fe  COUNTS  PER MINUTE  (47)  enough t o r e q u i r e  a s e l f absorption correction..  h a n d l e d i n the u s u a l f a s h i o n . and  0.8  Aliquots  m l , of s o l u t i o n were p i p e t t e d  This  of 0.2,  0.4,  0.6  onto the watch  e v a p o r a t e d t o d r y n e s s u s i n g an i n f r a r e d lamp, and  was  glasses,  counted.  The  measured a c t i v i t y per u n i t volume of sample i n each case  was  calculated  (apparent s p e c i f i c a c t i v i t y ) , and  a g a i n s t the a c t u a l volume of the sample u s e d . curve, extrapolated sample) was  a r e d from a  true s p e c i f i c a c t i v i t y .  i r o n (59)  s t a n d a r d 0.4M  580  s o l u t i o n of P.H.  l.Q.  as above and  counts per minute per mg.  ments of b o t h s o l i d and  The  of solut-  I I I c h l o r i d e used were p r e p -  i t y of t h i s s o l u t i o n corrected was  Prom t h i s  t o z e r o volume ( i . e . z e r o t h i c k n e s s  o b t a i n e d the  ions of r a d i o a c t i v e  plotted  of i r o n .  The  activ-  f o r background Later  s o l u t i o n were c o r r e c t e d  measure-  f o r decay  back t o t h i s t i m e . Exchange Measurements! A 0.01 was  t o 0.15  m e c h a n i c a l l y shaken w i t h 5ml.  f e r r i c i o n and  centrifuged.  washed s o l i d and  of the  e c t e d f o r background and  The  gm.  sample of C]2FeCl3  of a s o l u t i o n  containing  s p e c i f i c a c t i v i t y of  s o l u t i o n were d e t e r m i n e d ( and decay, and  i n the case of the  the correvap-  o r a t e d s o l u t i o n a l i q u o t , f o r s e l f a b s o r p t i o n ) as d e s c r i b e d above.  , The  1) P.H.  v a r i a t i o n s made i n the c o n d i t i o n s : 0.2  to  3.0  2.) Temperature : 20 benzyl  were:  t o 80°C. f o r water and  t o 190°for  alcohol.  3£) S o l v e n t f o r P e G l ^ : w a t e r , e t h a n o l , ether, isopropyl ether, benzyl  acetone, d i e t h y l  alcohol.  (48)  4.) A n i o n : c h l o r i d e ,  nitrate, sulfate.  5) A c t i v e i r o n i n the compound o n l y or i n the s o l u t i o n only. 6) Time o f s h a k i n g . 7) C o n c e n t r a t i o n o f f e r r i c i o n and weight o f compound.  (-49)  RESULTS AND The  DISCUSSION.  d a t a o b t a i n e d on the exchange o f g r a p h i t e  ferric  c h l o r i d e and f e r r i c i o n s i n a c i d s o l u t i o n , are p r e s e n t e d Table  I.  expressed  The  q u a n t i t y r e p r e s e n t s the s p e c i f i c  in  activity  i n a r b i t r a r y u n i t s . I i s the c o u n t i n g r a t e i n  counts per minute c o r r e c t e d f o r decay, and C i s the number of m i l l i g r a m s of i r o n . p r e s e n t i n the sample o f the g r a p h i t e f e r r i c c h l o r i d e being counted,  i n column 7 i s r e c o r d e d  the  s p e c i f i c a c t i v i t y o f the o r i g i n a l g r a p h i t e i r o n (59)111 c h l o r i d e , i n column 8 i t s s p e c i f i c a c t i v i t y a f t e r  remaining  f o r the r e c o r d e d l e n g t h of time i n the s o l u t i o n d e s c r i b e d , and i n the l a s t column the s p e c i f i c a c t i v i t y c a l c u l a t e d f o r complete exchange. • The  r e s u l t s of the experiments r e p o r t e d i n T a b l e  I  show t h a t no a p p r e c i a b l e exchange takes p l a c e between C-^Fe C l ^ and F e  i n a c i d s o l u t i o n w i t h i n p e r i o d s of time up t o  + ++  twelve hours.  s i x h o u r s , and a g a i n a f t e r s t a n d i n g i n the l a b o r a t o r y f o r a p e r i o d of f o u r months.  I n a l l cases the exchange  was  (Table I I ) .  R e a c t i o n t e m p e r a t u r e s above room temperature were o b t a i n e d by c o n n e c t i n g a hot water c i r c u l a t o r y system t o the m e c h a n i c a l  shaker.  Where t e s t s f o r exchange were  made u s i n g an aqueous medium a maximum temperature o f was  used.  ./  F u r t h e r o b s e r v a t i o n s on some o f these r e a c t i o n  m i x t u r e s were made a f t e r they had been shaken f o r n i n e t y -  negligible.  ~  Table  80  I I I shows the r e s u l t s o b t a i n e d from comp-  a r i s o n s at d i f f e r e n t temperatures,  of t e s t s f o r exchange  No.  c  12 * 3 gms •, F e  c l  FeClo s o l n . mis.  Cone, o f F e C l ^ M.  and F e ^ i n Aqueous A c i d S o l u t i o n at 2 0 ^ 2 C, P.H. Time o f i/c I/O 1 /o Shaking ( o r i g i n a l ) (obs. at time t ) (*>ealc  1.  0.025  5  0.01  1.1  4 min.  2.  0.025  5  0.01  1.1.  2 hrs.  3.  0.010  5  0.05  3.0  4.  0.010  5  0.05  3.0  5.  0.025  5  0.10  1.2  6. •  0.025  5  0.10  7.  0.030  8.  1259*9  1257*8  780  1259±9  1251+10  780  1260±10  1249+14  145  1260*10  1249±12  145  4 min.  1260*10  1253 + H  176  1.2  2 hrs. .  1260±10  1262*10  176  5  0.167  1.0  4 min.  1257*11  1254±10  131  0.030  5  0.167  1.0  6 hrs.  1257*11  1251+11  131  9.  0.025  5  0.25  1.0  4 min.  1255±8  1261±10  78  10.  .0.025  5  0.25  1.0  12 h r s .  1255±8  1260±9  78  0.025  5  0.10  2.5  8 hrs.  1257*11  1259±10  176  12.  0.050  5  0.5  0.5  1 hr.  1250*10  1254*10  78  13.  0.050  5  0.5  0.5  4 hrs.  1250±10  1246±10  78  14.  0.100  5  0.78  0.2  4 min.  1258±8.  1252*10  100  15.  0.100  5  0.78  0.2  4 hr.  1258+8  1254+10  100  16.  0.100  5  0.78  0.2  10 h r s .  1258*8  1246±12  100  17.  0.150  5  1.0  0.5  4 min.  1252±10  1260*10  123  18.  0.150  5  1.0  0.5  8 hrs.  1252*10  1248*10  123  11.  .  1 nr.  8 hrs •  '  >  >J1 o  1  H  No.  Composition  P.H.  I/C (original)  I /0 ( a f t e r 4min. shaking)  I /C ( a f t e r 96hrs. shaking)  • I /C ( a f t e r 4mo. contact)  I/O («ecalc.)  1.  O.Olgm. C F e C l o , 3»0 5ml. 0.051 P e C l | .  1260±10  1262*10  1248±10  1252*10  145  2.  0.025gm. C P e C l q 1.2 5ml. 0.1M P5Cl3.^  1260±9  1253±H  1255±10  1259±10  176  1.0  1255±8  1261±10  1260±10  1248±10  78  0.5  1250±10  1259±10  1251±10  1242±10  78  1 2  1 ?  3.  0.025gm. C P e C l 5ml. 0.25M F e C l ^ .  4.  0.05ga. C F e C l 5ml. 0.5M F e C ^ .  5.  O.lOgm. C F e * C l 0.2 5ml. 0.780M F e c L . 3  1258*8  1252±10  1239±10  1247±10  100  0.15gm. C-ipFeCl, 0.! 5ml. 1.0M PeCl|.  1252*10  1260±10  1247^10  1245±10  123  1 2  1 2  3  3  12  b  6.  T e s t s f o r Exchange between C F e * C l ^ and F e * i n A c i d 1 2  S o l u t i o n at 20 ± 2 ° C A f t e r 4 minutes, 96 hours and 4 months. TABLE I I  (52)  TABLE I I I E f f e c t o f Temperature on Tests f o r Exchange C  12 ® F  o * H  r-i <S O  CD  C 1  3  r-i  r-i  r-i  o  O  O  H  V f\ cv rH  o  rH 44  o a  o CO cv H  O  CD B  Ji CO o  So En —  o  EH  CV  <M CD O bO G as a3  F  IA  H  -H  -<t  ct!  d  IA  o B a)  n  in  H•H  -P  a  CM  rH  o  rH  o cv r-i  r-i •H O CV  H  cv  rH+l  O cv rH  CO  to o  O  O  CO  CV  e  ^  +  oc v w  o  03  O O ITv O • ^— O rH T> CV  r-i  O O  125  fc?  Various  Acid  Solutions.  lf\  O  O  O  O  lf\ CV  -H ir\ ir\ (V  •H O  I T\ CV  r-i •H O  rH  rH  rH  rH  iH  rH  -H CO ir\ cv r-i  cv  o  o  o  ir\ ir\ CV  CO  to  o  CV  CV  rH+i H  £ CO  O  co  rH •H  <o cv H  Jl co o  o  cv  rH +t  rH  £  rH rH  O  rH  -H  CO CV  rH  cv  cv  rH •H  r-i M CV  to cv rH  CO  to o  -*  to o  o  o  O  o  CO  cv  O  c-«* v  -H ir> ir\ cv  •H O ir\ CV  rH  r-i a t> m cv r-i  o  o  o  CV  -4" CV  •H CV ir\ cv  cv  o  o  O  o  c\ ir\  O cv r-i  o cv  fr-  ies  rH •M rH ITS  H  r-i  CO  a to o  CO  CO  O  o cv  o  o  -*  rH  rH  H  lf\ CM r-i  r-i a  CV r-i  rH rH rH•h  U Xi  to o>  O  cv  O  •H O -<t CV  rH  rH  O  o  cv  rH H  rH•H  o  O  CV  e  c  c  E  o O O  rH  •  H  O rH O O  •  CV  e  »— cv CD  o O O  o H O O  o CV o o  •  •  •  *— ' CD  fe  o cv o o  o H o o  . '.  to  o  fe  o r-i o o  .  CO  o o o H  .  o  •P CD O  ^  <J  c*\  o  r-i O <D  fe  •  e  f—  o  ^— CD  rH  1  fe  OA —•  o  r-i O CD Em  a o  w o -p  -4rH  *  rH  CO  r-i  cv to cv  rH  O  •H  H  r-i  O  ITv  ICVT\  r-i  O  rH  -H CV  lf\  r-i  O  O  rH  Ift  •sf  H  r-i  ^—*  « ° *CD  n  <D  •H  •  i  between  O  00 e  o rH O O O  rH  ' CD  fe  O CV O O H  rH  c  O CV O O CV  H  rH •H rH rH  r-i -h  cv  rH  rH  lf\  rH  rH-H  rH  H  o  O  rH  +t  C-  IT\  r-i  CV r-i  CV r-i  h  i!  i*  cv  o  cv  o  o  CV  Vf\  CO  CV CV  rH  cv  rH -h  CO ir\ CV  rH D3  h  3  O  rH O rH CD O. CD O >?-d O J 3 H o Si -P PH 43 >»rH •P CD p4 CD ta odi O C CD 10 CD H  CQ  r-i O ' CD  fe  O O O  O rH O O  O rH O O  O rH O O  rH  r-i  ir\ r-i  to  rH  rH  O H O O  O rH O O  O  CO  rH  H  (53)  between g r a p h i t e f e r r i c c h l o r i d e and f e r r i c iron i n s o l u t i o n s of water, e t h y l a l c o h o l , acetone, d i e t h y l ether, i s o p r o p y l e t h e r and b e n z y l a l c o h o l .  The  i n f l u e n c e of both solvent  I n t e r a c t i o n and temperature appear t o be n i l .  Even•at*temp-  o  e r a t u r e of about 190 C w i t h b o i l i n g b e n z y l a l c o h o l no exchange was observed a f t e r f o u r hours r e f l u x i n g . To complete the r a t h e r s t r o n g e v i d e n c e t h a t no exchange t a k e s p l a c e between C P e C l 3 1 2  s e t of experiments was performed.  and F e  + + +  ,  one f u r t h e r  I n the e x p e r i m e n t s s e t  f o r t h i n t a b l e s I , I I and I I I , r a d i o a c t i v e g r a p h i t e  iron  (59)111 c h l o r i d e was brought I n t o c o n t a c t w i t h i n a c t i v e f e r r i c i r o n I n s o l u t i o n and a f t e r s u i t a b l e p e r i o d s of time the components were s e p a r a t e d and t h e i r s p e c i f i c  activity  ascertained.  activity  I n no i n s t a n c e was any a p p r e c i a b l e  d e t e c t e d i n the i n a c t i v e i r o n c o n t a i n i n g s p e c i e s nor  was  t h e r e any t r a n s f e r of a c t i v i t y from the s o l i d compound. I n the above experiments however, no account  was  t a k e n of the p o s s i b i l i t y of p r e f e r e n t i a l a d s o r p t i o n of the m i g r a t i n g a c t i v e i o n s by the a c t i v e compound.  I f exchanging  a c t i v e i o n s , t r a p p e d i n the complex by c a p i l l a r y condensati o n were not removed by washing the compound b e f o r e  counting,  t h e r e would of course be no d e c r e a s e i n t h e s p e c i f i c of the s o l i d .  activity  L i k e w i s e no i n c r e a s e i n the a c t i v i t y of the  f e r r i c i o n s o l u t i o n would be o b s e r v e d . T h e r e f o r e t e s t s f o r exchange between r a d i o a c t i v e i r o n (59)111 c h l o r i d e and i n a c t i v e g r a p h i t e f e r r i c c h l o r i d e were c a r r i e d o u t . r e s u l t s of t h e s e experiments are shown i n t a b l e IV.  The  No.  * PeClo 5 mis.  PH  (M,)  C]_2PeGl3 (j»"s)  r/c (original)  r/c (after 4 h r s . )  i/c (after 96hrs.)  .  i/c (after 4mo.)  i/c (~calc.)  ,  1.  0.4  1.0  0.150  582*6  584*6  580 6  570±6  468  2.  0.25  1.0  0.150  580*5  581*5  584*5  578±5  417  3.  0.10  1.0  0.150  581*6  580±6  587±6  585*6  292  4»  0.08  1.0  0.150  584*6  575*6  578*6  570*6  262  5.  0.06  1.0  0.150  582*6  580±6  582*6  576±6  220  6.  0.04  1.0  0.150  580±6  572*5  572*5  569*6  170  7.  0.01  1.0  0.150  579*6  575*6  579*6  574*6  54  8.  0.005  1.0  0.150  580*6  581*6  580*6  578±6  28  t  T e s t s f o r Exchange Between F e * a n d C ^ g F e C l ^ i n Aqueous A c i d +  +  S o l u t i o n a t 20 ±2°C. TABLE IV.  (55)  As b e f o r e , no  raeasureable  ved even a f t e r l o n g p e r i o d s o f t i m e . ive  exchange was  obser-  The samples o f i n a c t -  g r a p h i t e f e r r i c c h l o r i d e were e a s i l y washed c l e a r o f  any a c t i v i t y  f o l l o w i n g s e p a r a t i o n from the r a d i o a c t i v e  f e r r i c chloride solution.  (56)  3» The S z i l a r d Chalmers R e a c t i o n  w i t h Graphite  Ferric  Chloride. I t has been shown t h a t t h e r e exchange between C solution.  i s no measurable  C l i ^ and f e r r i c i o n i n s u r r o u n d i n g  F 9 1 2  I t i s t h e r e f o r e l i k e l y t h a t any i r o n a c t i v i t y  s e p a r a t e d by a S z i l a r d - C h a l m e r s c o u l d be o b t a i n e d  p r o c e s s on t h e compound  i n high s p e c i f i c a c t i v i t y .  I t i s of i n t -  e r e s t t o note t h e s u c c e s s o f a S z i l a r d - C h a l m e r s w i t h regard  separation,  t o t h e s t r u c t u r e o f t h i s compound.  Pure C 2 1  P e C l  3  w  a  s  i r r a d i a t e d i n the neutron f l u x  of t h e C a n a d i a n N.R.C. p i l e a t C h a l k R i v e r , O n t a r i o .  . The  a c t i v i t y o f t h e compound was measured, t h e s e p a r a t e d p o r t i o n of a c t i v i t y removed i n hot h y d r o c h l o r i c a c i d s o l u t i o n , and the y i e l d c a l c u l a t e d . 1 . 5 0 g m s . o f C^gFe. C l ^ powder ( c o n t a i n i n g 0.27gm. Fe) were a c t i v a t e d b y 4 8 hours i r r a d i a t i o n a t about 3 » 9 12 2 59 10 n./cm. / s e c . A m i x t u r e o f t h e 4 7 day Fe and 4 y e a r 55  Fe was o b t a i n e d , b u t as w e l l , t h e r e a c t i o n s o c c u r i n g on neutron i r r a d i a t i o n of c h l o r i n e r e s u l t e d i n the production 35  of f o u r o t h e r a c t i v e i s o t o p e s . r e a c t i o n t o produce t h e 1 0  6  Cl  36  year C l  undergoes an (n,)r) e m i t t i n g 0 . 6 6 Mev. 35  b e t a ' s , an (n,p) r e a c t i o n p r o d u c i n g 8 7 day S which e m i t s 0.17 Mev. b e t a ' s , and a l s o an (n,«t) r e a c t i o n t o 1 4 . 7 32 37 day P e m i t t i n g 1.7 Mev. b e t a ' s . Cl a l s o undergoes an 38  (n,fc) r e a c t i o n t o C l  w h i c h has a 37 minute h a l f l i f e and  decays w i t h the e m i s s i o n o f 1.1, 218 and 5 . 0 Mev. b e t a ' s and 1 . 6 5 and 2 . 1 5 Mev. gamma's.  (57)  Because of i t s long h a l f l i f e , developed  Contamination  Short-lived C l 32  by P  radioactivity irradiation  decays i n a day or so.  i s of the order of 1% of the  , i n terms of b e t a p a r t i c l e s emitted  (35)•  a c t i v i t y of the i r r a d i a t e d compound was mc.  3^  is. n e g l i g i b l e when r e l a t i v e l y short  p e r i o d s are used.  S  the C l  Fe^/gra», 0.027 mc.  Fe^Vs » m  a  n  d  total  The  initial  estimated at 0.008  1*27  mc.  S^Vs «  The  m  separated p o r t i o n of the a c t i v i t y from the S z i l a r d - C h a l m e r s r e a c t i o n would then be expected  t o be composed mainly  these three r a d i o a c t i v e i s o t o p e s .  The  iron activitiescan  be separated by a very e f f i c i e n t and simple procedure (34) •  based  used as s o l v e n t . of f e r r i c  r e p o r t e d here, d i e t h y l ether  c h l o r i d e by d i e t h y l ether from aqueous 6N  0.100  gm.  of p i l e  i r r a d i a t e d graphite f e r r i c  A few drops  hydr-  of 30$  chloride  (~6>N) h y d r o c h l o r i c acid,  f o r s i x hours and the aqueous s o l u t i o n separated by  t o ensure  was  100.  r e f l u x e d w i t h constant b o i l i n g  uging«  chloride  The p a r t i t i o n c o e f f i c i e n t f o r e x t r a c t i o n  c h l o r i c a c i d i s about  was  extraction  on the s o l v e n t e x t r a c t i o n of f e r r i c  In the experiments  of  centrif-  hydrogen peroxide were added,  that a l l the i r o n was  c o l o r l e s s aqueous s o l u t i o n was  present as f e r r i c  ion.  shaken w i t h s u c c e s s i v e  The 1/4  volumes of d i e t h y l ether s a t u r a t e d w i t h h y d r o c h l o r i c a c i d , and f i n a l l y washed w i t h an e q u a l l volume of s o l v e n t .  The  e t h e r e x t r a c t s were then c o l l e c t i v e l y s t r i p p e d w i t h d i s t i l l e d water.  The r a d i o a c t i v i t y of the r e s u l t a n t s o l u t i o n s was mea-  sured and the components d i f f e r e n t i a t e d by a d s o r p t i o n meas-  (58)  urements. . F i g u r e s V I I I , IX and X give the a b s o r p t i o n curves f o r the aqueous,residue s o l u t i o n , the s t r i p p e d e t h e r , and the water e x t r a c t r e s p e c t i v e l y .  I t i s evident t h a t no d e t e c t -  able amount of r a d i o a c t i v e i r o n r e m a i n s ' i n the aqueous 35 r e s i d u e , nor can the a c t i v i t y of S be d e t e c t e d i n the 32 . e x t r a c t . Apparently the P i s present i n a form which has a s m a l l but measurable p a r t i t i o n c o e f f i c i e n t , as I t i s e x t r a c t a b l e t o some e x t e n t .  The small amount of S^- taken up 5  by the s o l v e n t ( p o s s i b l y as s u l f u r c h l o r i d e ) i s not r e - e x t r acted 'by d i s t i l l l e d water.  The chemical form o f the  the aqueous r e s i d u e Is presumably as F e (S-^o^) ^.  in In a  2  s i m i l l a r type of s o l v e n t e x t r a c t i o n of i r r a d i a t e d F e C l ^ , 35 M.B. W i l « (35) has r e p o r t e d 99.5$ of the o r i g i n a l S  and  32 83$ o f the P  t o be c o n t a i n e d i n the aqueous r e s i d u e s o l 59 u t i o n which i s f r e e of d e t e c t a b l e Fe • The s t r i p p e d e t h e r .  35  p o r t i o n c o n t a i n e d only the remaining 0.5% o f the S and 32 59 0.01% o f the P • A l l the o r i g i n a l Fe and the s m a l l amount of remaining  P^  2  was found  i n the water e x t r a c t which was  • 35 free of detectable S activity. The  t o t a l a c t i v i t y o f the h y d r o c h l o r i c a c i d  solution,  which had been r e f l u x e d f o r s i x hours with the 0.100 gm. sample o f i r r a d i a t e d ^2.2^ ^3' e  the a c t i v i t y of the untreated i v i t y was obtained  w  a  s  m e a s i ; i r e c  compound.  i n a f u r t h e r treatment  * * 0.682$ of a  No d e t e c t a b l e a c t with hot HCl  solution. The v e r y low energy of the beta p a r t i c l e s from S  35  1000  F i g u r e IX - A c t i v i t y i n s t r i p p e d e t h e r .  10 ooo  too  500  zoo ABSORBER  THICKNESS  400 M  ^  /  ^  soo  (59) poses s p e c i a l problems as regards t h e i r q u a n t i t a t i v e d e t e c t ion.  The low energy o f the r a d i a t i o n makes the  i n g e f f e c t a major one.  self-weaken-  Experiments have shown t h a t samples  o f t h i c k n e s s 3 mgm./cm w i l l be weakened t o the extent o f 2  1+0% of the t o t a l a c t i v i t y  (35).  I n a c t i v i t y measurements  o f the v a r i o u s s o l u t i o n s i n v o l v e d , the s e l f c o r r e c t i o n s were obtained  absorption  i n the same manner as a l r e a d y  d i s c u s s e d under exchange experiments.  The g r a p h i t e  ferric  c h l o r i d e samples compared were always l e s s than 0.2 mgm./cm . 2  The  a c t i v i t y of the i r r a d i a t e d Ci2FeCl3 was compared  with the a c t i v i t y o f h y d r o c h l o r i c a c i d s o l u t i o n c o n t a i n i n g the separated two.  i s o t o p e s , by a b s o r p t i o n measurements on the  Both samples measured were l e s s than 0.2 mgm./cm . 2  F i g u r e XI g i v e s the a b s o r p t i o n curves comparing I - i r r a d i a t e d C-L2F l3 snd I I - evaporated a c i d e x t r a c t s o l u t i o n . eC  I t w i l l be seen t h a t the two a b s o r p t i o n curves are i d e n t ical.^  From t h i s i t seems apparent t h a t the component r a d i o -  a c t i v e i s o t o p e s e x i s t i n the a c t i v i t y separated  by the  S z i l a r d Chalmers r e a c t i o n i n the same r a t i o as they present  i n the i r r a d i a t e d compound,  are  A third series of  a b s o r p t i o n measurments on the i r r a d i a t e d compound from which the separated curve  p o r t i o n o f a c t i v i t y had  i d e n t i c a l w i t h the other  been removed gave a  two.  I t i s apparent t h a t some of the r e c o i l i n g atoms o f both c h l o r i n e and i r o n have achieved  bond rupture and  e j e c t i o n from the C ^ F e C ^ l a t t i c e .  However, the very low  f r a c t i o n o f the t o t a l a c t i v i t y separated  i n hot h y d r o c h l o r i c  ABSORB&K  THICKNESS  M&n./cw flL z  (60)  a c i d , i n d i c a t e s that almost a l l the neutron c a p t u r i n g atoms are s t i l l f i r m l y bound i n the g r a p h i t e compound.  A  series  o f experiments, designed to see whether or not changing the method of r e c o v e r i n g the separated a c t i v i t y would r e s u l t i n a l a r g e r S z i l a r d - C h a l m e r s y i e l d , was  c a r r i e d out.  Samples  of the i r r a d i a t e d compound that were r e f l u x e d w i t h  HCl  f o r f o u r , e i g h t and s i x t e e n hours, r e l i n q u i s h e d no more of t h e i r t o t a l a c t i v i t y than d i d a sample which was 15 minutes  i n a s o l u t i o n of 4N HCl at 80 C. The  washed f o r valuetffor  the percentage of t o t a l a c t i v i t y separated, which were o b t a i n e d from these experiments, were a l l w i t h i n the range 0.681  to 0.688$,  I t was  iated graphite f e r r i c  noted, however, that i f the  c h l o r i d e was  irrad-  subjected to a f i n e  grin-  d i n g p r e v i o u s t o the a c i d - l e a c h treatment, the f r a c t i o n of a c t i v i t y separated i n c r e a s e d s l i g h t l y . was  The  raised, from about 0 . 6 8 4 $ t o an average  percentage  value of 0 . 7 2 7 $  by g r i n d i n g the samples by hand i n a mortar .ground-glass p l a t e s .  yield  or between  The use of a f i n e aluminum oxide  g r i n d i n g powder r a i s e d t h i s value t o 0 . 7 3 7 $ . from these above experiments  are l i s t e d  The  results  i n Table V.  In a l l cases the aqueous a c i d s o l u t i o n s c o n t a i n i n g the separated a c t i v i t y , were c o l o r l e s s and gave no t e s t f o r Pe '*' +4  with NH4CNS.  I t i s t h e r e f o r e apparent that l i t t l e  or no  r a d i a t i o n decomposition takes p l a c e as a r e s u l t of the i r r a d i a t i o n of the compound.  It i s unfortunate that  the  s m a l l amount o f i r o n separated i s not d e t e c t a b l e by o t h e r than r a d i o c h e m i c a l methods, as f a c i l i t i e s f o r h a n d l i n g the l a r g e  (61)  TABLE V. The E f f e c t o f D i f f e r e n t E x t r a c t i o n  Methods on  the jo S z i l a r d Chalmers S e p a r a t i o n . Exp. No.  Conditions f o r acid e x t r a c t i o n of separable a c t i v i t y from Cl2 Cl3» FQ  Initial Separated activity activity in o f C i 2 0 l 3 HCl s o l n . (c.p.m.) (c.p.m.) P e  5  3  1.  0.0827gm. i n 4-N HCl at 80°C. Stirred in b l e n d e r f o r 15 min.  58.11*10  2.  0.200gm. i n ~ 6 N H C l at 100*C. R e f l u x e d f o r 4 hours.  134.32*I0 92.4*10  3.  0.200gm. i n ~ 6 N HCl at 100 °C. Refluxed f o r 8 hours.  4'i.  0.1523gm. i n ^6N HCl at 1100° C. R e f l u x e d f o r 16 hours.  5»  6.  7.  $Szilard Chalmers separation.  39.6*10  5  5 120x1.0)  0.681  0.688  3  ? 82*KT 5  0.0530gm. i n -6N HCl 13.187-10 at 100"C. Sample ground as 1A #6, hut w i t h f i n e AI2O3 g r i n d i n g powder.  0.683 3  87.06*10  5 0.1094gm. i n ~6N HCl 38.56*10^ at 25°C. Ground i n a mortar(approx. 1 hr.) 5 0i0482gm. i n ~ 6 N H C l 11.99*10^ at 100 C. Sample ground between two ground-glass plates before acid extraction.  •  59.4-10  0.682: 3  28.08*10  0.728  3 8.7>KT  0.7255  5  3 9.72A10  0.737  (62)  , a c t i v i t i e s t h a t would be  necessary to make a  d e t e r m i n a t i o n of the s p e c i f i c a c t i v i t i e s s u l f u r , were not  available.  quantitative  of i r o n  and  (63)  DISCUSSION o f RESULTS. It has been shown that the Szilard-Chalmers a t i o n on C-^FeCl^  i s s u c c e s s f u l t o l e s s than 1$.  separ-  As has  been  a l r e a d y suggested, t h i s r e s u l t does not appear too s u r p r i s i n g when one sion.  c o n s i d e r s the s t r u c t u r e of the compound under d i s c u s -  Above and  below the planar f e r r i c  i o n network there i s  a p a r a l l e l t r i a n g u l a r net plane of c h l o r i d e i o n s , and and below these planes  of c h l o r i d e ions there  bonded hexagonal plane of carbon atoms. repeated  through the l a t t i c e , serves  above  is a tightly  T h i s arrangement  to produce  formidable  s t e r i c hindrance e f f e c t s f o r an atom of e i t h e r i r o n or c h l o r ine which might leave the l a t t i c e . t s f o r exchange between the F e l a t t i c e and Fe"^ exchange was The  T h i s has been shown i n t e s -  ions bound i n the. g r a p h i t e  +++  ions i n surrounding  solution.  No  measurable  observed even a f t e r a f o u r month p e r i o d . r e t e n t i o n by the C - ^ F e C ^ , of over 99$  a c t i v i t y developed by neutron i r r a d i a t i o n may  of  the  possibly also  be e x p l a i n e d by the pronounced s t e r i c e f f e c t .  Recombination  of "hot" fragments ( i n a s o - c a l l e d r e a c t i o n cage) would appear to be  q u i t e probable i n a s o l i d m a t e r i a l of t h i s type.  s e p a r a t i o n of a c t i v i t y which does r e s u l t from the Chalmers r e a c t i o n (approx. 0.68$),. cannot the b a s i s of i m p u r i t i e s i n the C 2  PeCll  1  that the p u r i f i e d compound contained as f r e e f e r r i c c h l o r i d e . 0.3$  3 > ,  be J t  h  Szilard-  explained a  3  The  on  heen shown  l e s s than 4 u.gm.  Fe/gm.  T h i s amount c o u l d only account f o r  of the f r a c t i o n of a c t i v i t y t h a t was  i t were a l l e x t r a c t a b l e f o l l o w i n g  separated,  irradiation.  emen i f  (64)  One  theory which might e x p l a i n the s m a l l s e p a r a t i o n  of a c t i v i t y , i s t h a t i t i s only the edge atoms i n t h i s  "stacked  l a y e r s " s t r u c t u r e which are able to break away f o l l o w i n g neutron capture*  T h i s i d e a f i n d s some support  i n the experiments.which  showed.that g r i n d i n g the powdered compound to a f i n e r s i z e  inc-  reased to some; extent the f r a c t i o n of a c t i v i t y s e p a r a t e d .  Thus  the percentage due  y i e l d was  r a i s e d from 0 . 6 8 4 to 0 . 7 3 7 $  presumably  to the b r e a k i n g of the c r y s t a l s and exposure of new  edges  from which i r r a d i a t i o n f r e e d a c t i v e atoms were removed by hydrochloric acid  the  solution* G^^sO-j  I t would be of i n t e r e s t to s u b j e c t samples of of d i f f e r e n t p a r t i c l e s i z e to neutron the S z i l a r d - C h a l m e r s y i e l d .  i r r a d i a t i o n and  compare  A l s o there i s the p o s s i b i l i t y t h a t  the i r r a d i a t i o n of the compound f o r a s h o r t e r p e r i o d or i n a lower neutron f l u x might l e a d to a more s u c c e s s f u l s e p a r a t i o n of.activity.  R a d i a t i o n experiments have shown t h a t the  estab-  lishment of a s u c c e s s f u l S z i l a r d - C h a l m e r s enrichment r e a c t i o n , i n experiments of low f l u x or short bombardment, does not. ensure i t s success when l o n g e r or more intense bombardments are employed.  I t may  the i n i t i a l l y  be t h a t i n the case of C ^ P s C l ^ *  some of  separated a c t i v i t y i s l o s t by a r a d i a t i o n -  induced back r e a c t i o n .  T h i s s i t u a t i o n does not seem too  l i k e l y , s i n c e the separable form r e p r e s e n t s a l e s s breakdown product  of the s t a r t i n g m a t e r i a l .  The  complicated  Szilard-  Chalmers enrichment experiments w i t h antimony p e n t a f l u o r i d e (R.R.  Williams  (36)  ) however, show t h i s l o s s of a c t i v i t y :  :  (65)  w i t h o u t apparent d e c o m p o s i t i o n .  The a c t i v i t y i n the separ-  a b l e form dropped from 60 t o 5% o f the t o t a l a f t e r s e v e r a l hours bdmbardment a t c o n s t a n t p i l e power.  N e v e r t h e l e s s , . i t seems  apparent t h a t even under more s u i t a b l e c o n d i t i o n s , a compound of the g r a p h i t e f e r r i c c h l o r i d e type c o u l d not be expected g i v e any a p p r e c i a b l e s e p a r a t i o n of a c t i v i t y by a S z i l a r d Chalmers r e a c t i o n .  to  (66)  SUGGESTIONS f o r FURTHER RESEARCH. 1.  I t i s probable  t h a t g r a p h i t e f e r r i c . c h l o r i d e and  other g r a p h i t e compounds d e s c r i b e d represent  the  only a few  of  the"stacked  l a y e r " s t r u c t u r e s which are capable  Rttdorff has  attempted the p r e p a r a t i o n of g r a p h i t e compounds  of A s l j , SDI3, B H 3 , C r C l ^ , without  result.  of e x i s t a n c e .  A s C l ^ , S b C l ^ , BiCl-j, AICI3, C 0 C I 3 (22)  and  There i s l i t t l e doubt however,  that f u r t h e r r e s e a r c h w i l l b r i n g to l i g h t a d d i t i o n a l examples o f molecules p e n e t r a t i n g between the l a y e r planes  of  the  g r a p h i t e l a t t i c e ' t o form more or l e s s s t a b l e s t r u c t u r e s . 2.  The  i d e a t h a t i t i s only a few  exposed edge atoms that  are able t o achieve bond rupture  and  subsequent e j e c t i o n from  the c r y s t a l l a t t i c e of C-^FeCl^*  could be  investigated.  neutron i r r a d i a t i o n of samples of d i f f e r e n t p a r t i c l e  The  size  ( d i f f e r e n t r a t i o of edge atoms to t o t a l atoms) might p o s s i b l y l e a d to g r e a t e r percentage y i e l d s of separated 3>»  A f u r t h e r r e s e a r c h concerning  a study  activity.  of r a d i a t i o n e f f e c t s  on g r a p h i t e f e r r i c c h l o r i d e would be of i n t e r e s t .  The  a t i o n between f l u x i n t e n s i t y and p e r i o d of bombardment f r a c t i o n o f a c t i v i t y separable,  c o u l d be  ascertained.  correland  (67)  BIBLIOGRAPHY. (1)  B e r n a l , J*D.»  P r o c . Roy. Soc.  Acvi  749  (1924)  (2)  Bragg, W.L.,  P r o c . Roy. Soc.  A89  277  (1913)  (3)  F l a g g , J.P.,  J . Aim-Chem. Soc.  63  577  (194D  (4)  Fredenhagen, Cadenbach, and Suck, Z. anorg. a l l g . Chem. • 158 178"  249  353  (1926) (1929)  (5)'  Heyesy, G.> and Paneth, P., Manual of R a d i o a c t i v i t y , Oxford U n i v e r s i t y Press, (1938) Hahn, 0., A p p l i e d Radiocbemistry, C o r n e l l U n i v e r s i t y Press, (1936) Hofman, U.,  (7)  Hofman, U«, and p r e n z e l , A.,  (8)  H u l l , A.W.,- Phy. Rev.,  (9)  J u l i u s b e r g e r , P., Topley, B., and Weiss , J • > J . Chem. S o c , p.1295 (1935)  (10)  L a i d l e r , D.S., and T a y l o r , A.,  (11) Long, P.Ao,  Naturwissenshaften,  32  260  (6)  Z. Elektrochem. 4^0 511 '(1934) 661  X  130  (1940)  63  1353  (194D  32  (1926)  1026  (1935)  (12) Manguin, C.» B u l l . S o c Franc. Min.,  XLIX (13) M e d l i n , W.V.,  J . Am. Chem. S o c , 57  (14) .Melander, L.,  Acta Chem. Scand.,  (16) O t t . H..  Nature,  Ann. Physik.,  (1917)  Nature, 146  J.Am. Chem. S o c ,  (15) McKay, H.A.C.,  (1944)  1  169 (1947)  142  997 (1938)  LXXXV(IV) 81 (1928)  (17) P a u l i n g , L.,  The Nature of the Chemical Bond C o r n e l l U n i v e r s i t y Press,-2nd E d i t i o n , . (1948)  (18) R i l e y , H.L.,  Journ. I n s t . F u e l ,  X  1 4 9 (1937)  (68)  (19)  R i l e y , H.L.,  (20)  Ruben, S ., Kamen, M.D., A l l e n , M.B., and Nahinsky, P. J . Am. Chem. S o c , 6£ 2297 (1942)  (21)  RUdorff, W.,  Z. anorg. Chem.  (22)  RUdorff, W.,  F i e l d I n f o r m a t i o n Agency, T e c h n i c a l ( F . I . A . Review of German Science 1939-4 Inorganic chemistry, P a r t I 239 (1948)  (23)  RUdorff, W. and Eofmann, H., Z. anorg. 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