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Topochemical reactions of boron nitride Korinek, George Jiri 1954

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TOPGCHEMICAL REACTIONS OF BORON NITRIDE  by  GEORGE JIRI KORINEK  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE In the Department of Chemistry  We accept t h i s th.-e-si.s as conforming t o t h e standard required from candidates f o r the degree of MASTER OF SGtBWCE.  Mfembers of the Department of •Chemistry.  THE UNIVERSITY OF BRITISH. COLUMBIA APRIL, 1954.  ABSTRACT An absorption complex or compound between boron n i t r i d e and chromyl chloride was discovered and studied i n some d e t a i l . The method used to prepare the boron n i t r i d e had some e f f e c t on the composition of the complex but f o r a given sample of boron n i t r i d e the equilibrium composition f o r temperatures from 0°C. to l60°C. was  constant.  The k i n e t i c s of formation were studied at 2 4 . 1 ° C , 67.1°C., and 117.0°C.  The reaction was  interpreted as d i f f u s i o n con-  t r o l l e d with two d i f f u s i o n coefficisnts--each f o r a c e r t a i n concentration range.  The corresponding two energies of  a c t i v a t i o n were 5.0 and 6.1  kcal.  These are of the same order  • of magnitude as f o r s i m i l a r processes. X-ray studies of the complex showed a strong r e f l e c t i o n l i n e at the same place as f o r the main layer separation i n boron n i t r i d e i t s e l f .  There could have been a small amount of  r e f l e c t i o n due to a greater layer spacing, but i t was not detected. Water hydrolyses the chromyl chloride i n the complex, leaving the o r i g i n a l boron, n i t r i d e and a solution of dichromate and HCl.  Carbon tetrachloride would not dissolve out the  chromyl chloride from the complex. Similar complexes of chromyl chloride with d i s u l f i d e s of molybdenum, tungsten and uranium and of cupric and aluminum chlorides with boron n i t r i d e were discovered but the k i n e t i c s of t h e i r formation were riot studied. The theory of formation of lamellar compounds i s discussed.  ACKNOWLEDGEMENT I wish t o express my indebtedness p r i m a r i l y t o Dr. J . G. Hooley f o r his able d i r e c t i o n and kind assistance i n t h i s project. I would also l i k e t o acknowledge the f i n a n c i a l a i d received from the University of B r i t i s h Columbia  President's  Research fund during the summer of 1953, without which t h i s project could not have been undertaken. Appreciation i s also expressed to the B r i t i s h Columbia Research Council who so k i n d l y permitted the use- of t h e i r X-ray spectrometer.  TABLE OF CONTENTS Page I.  II.  INTRODUCTION 1. The Topochemical Reactions.... 2. Graphite Compounds 3. The S t r u c t u r a l Relationship of Graphite, Boron N i t r i d e and the Disulphides of Molybdenum and Tungsten. 4. Theory of Diffusion i n Solids EXPERIMENTAL 1. Preparation and Analysis of Compounds.... A) Boron N i t r i d e B> Analysis of the Boron N i t r i d e C) Preparation of the Substances t o be Intercalated D) Preparation of I n t e r s t i t i a l Compounds E) The Analysis of the Complex of Boron N i t r i d e - Chromyl Chloride. 2. X-ray Study 3.  4.  1 1 2 7 15 22 22 22 25 23 30 34 36  The Experimental Results of the Kinetic Study of the System Boron N i t r i d e Chromyl Chloride  42  Other Lamellar Compounds Prepared  4#  III.  DISCUSSION OF RESULTS  50  IV.  SUGGESTION FOR FURTHER RESEARCH....  53  V.  BIBLIOGRAPHY  54  VI.  APPENDIX.  TABLE OF CONTENTS FOR TABLES Page Table I.  Magnetic S u s c e p t i b i l i t y and E l e c t r i c a l Conductance of Graphitic Compounds  4  Table I I .  Results of the Analysis of Boron N i t r i d e . . . .  27  Table I I I . Table IV. V. VI.  D i f f r a c t i o n Pattern of Boron N i t r i d e Theoretical & Experimental Results of the Diffusion Study at Three Temperatures..  40  Table  Composition of Molybdenum, Tungsten and' Uranium Disulfide Complexes............  VII.  Table VIII. Influence of Source on Composition of Boron N i t r i d e plus Chromyl Chloride Complex..  Ap.  1+& Ap.  I. 1.  Topochemical  INTRODUCTION  Reactions.  Under t h i s heading come the reactions of s o l i d  substances  i n which the structure of the s o l i d i s not completely l o s t , but i s found i n a more or less modified form i n the reaction products.  The study of such reactions was f i r s t c a l l e d topo-  chemistry by V. Kohlschutter i n 1926.  Some other workers i n  t h i s f i e l d mainly Kautsky, Cadenbach, Fredenhagen (12) Rudorff (36*)  and  developed the ideas of Kohlschutter and applied  them to many new reactions.  The f i e l d of topochemistry has  no sharp l i m i t s and i s not the only term used to describe these reactions. The name permutoid:/ i s used often with the same meaning.  This word was l a t e r reserved by Kautsky f o r  more or less ordered structures which are so openly constructed from one dimensional frameworks or two dimensional nets, that vapors or l i q u i d s are able to pass through them.  In permutoid  reactions the c o l l e c t i v e groups of chains or networks from which the permutoids are constructed are able to i n t e r a c t , be i t i n absorptive processes or i n chemical reactions. The attack of reagents on s o l i d substances can be represented most c l e a r l y f o r layer l a t t i c e s .  The d i r e c t i o n of  attack i s .usually indicated by the weak cohesion of the atoms between the individual layers.  It i s consequently possible  that reactions take place with the atoms which l o o s e l y bind the layers, thus leaving the binding of the atoms within the l a y e r s e s s e n t i a l l y untouched.  Examples of reactions of t h i s  2  type are the swelling processes of clay minerals such as montmorilonite where the i n s e r t i o n of water molecules between the layers changes the distance separating the l a t t e r considerably.  The other substance which has been studied i n t h i s  respect i s graphite.  Because of the s t r u c t u r a l s i m i l a r i t y of  graphite t o boron n i t r i d e and the d i s u l f i d e s of tungsten and molybdenum we decided to t r y to prepare the same kind of compounds with these substances.  Before t e l l i n g about these  experiments, however, i t w i l l be h e l p f u l to describe graphite compounds, the s t r u c t u r a l s i m i l a r i t i e s mentioned above and the theory of d i f f u s i o n i n s o l i d s . 2.  Graphite Compounds. The s p e c i f i c i t y shown .by graphite i n compound formation  i s remarkable and w i l l be of extreme importance f o r a t h e o r e t i c a l explanation of these reactions.  It has been found that e i t h e r  a substantial quantity (15-83% by weight i n a compound), or none at  a l l of a test substance could be intercalated (£). The graphitic compounds can be divided b a s i c a l l y into  three groups dependent on the state of the substances i n t e r c a l a t e d : 1. 2.. 3.  Ionic. Atomic. Molecular.  The compounds of the f i r s t two groups were the f i r s t and known.  prepared  They contain substances such as graphitic acid (1$),  s a l t s of graphite with s u l f u r i c , n i t r i c and perchloric acids (19^ compounds with the halogens f l u o r i n e and bromine (41)» a l l o y s of graphite with potassium, rubidium and cesium and others (12).  The molecular compounds of graphite started with the preparation of the g r a p h i t e - f e r r i c chloride complex by W. Rudorff i n 193# ( 4 0 ) . I t i s t h i s group which has evoked considerable interest l a t e l y .  Most of the newly intercalated.;  substances of t h i s group have been m e t a l l i c chlorides.  With  the exception of iodine and boron, chlorides of the non-metals were not occluded.  Of the metal chlorides tested, only those  in which the cation exhibits multivalence and which were i n t h e i r higher valence states were intercalated. P t G l ^ and GuCl  2  Thus SbGl^,  r e a d i l y formed compounds with graphite, but the  lower chlorides SbCl^, PtClg and C u C l 2  2  did not react with  graphite over a wide range o f conditions ( 8 ) . Since multivalence i s associated with an electronic conf i g u r a t i o n generally involving unsaturated penultimate electron s h e l l s , i t i s very l i k e l y that these molecular compounds of graphite owe t h e i r existence to the transference of electrons of the incompletely f i l l e d bands of graphite to the intercalated m e t a l l i c cations.  It i s a reasonable assumption that t h i s t r a n s f e r  should occur when the cations possess their maximum electron a f f i n i t i e s , as i n t h e i r highest valence states.  Paramagnetism  should also be a good c r i t e r i o n of the p o s s i b i l i t y of i n t e r calation.  I t was found that there i s good agreement of these  two t h e o r e t i c a l predictions with the experimental evidence-. These postulates are i n agreement with Weiss' and Brackmann's explanations of the formation of molecular complexes ( 2 8 ) . Weiss proposed that a l l molecular complexes have an e s s e n t i a l l y i o n i c structure A" B  +  where A i s electron acceptor or Lewis a c i d and  B an electron donor or Lewis base.  He pointed out that a low  i o n i z a t i o n p o t e n t i a l f o r the base B and high electron a f f i n i t y f o r the acid A should then favour a stable complex., Brackmann also emphasized that reversible formation of a resonance complex, by reducing the a c t i v a t i o n b a r r i e r , may often be a preliminary step i n an i r r e v e r s i b l e chemical reaction.  In the case of  s o l i d s , the s i t u a t i o n i s further substantially complicated by the f a c t that s t r u c t u r a l and geometrical f a c t o r s are of extreme importance,  and w i l l not allow the formation of complexes i n .  some cases, where, i f l i q u i d s , substances would couple. Measurements of magnetic s u s c e p t i b i l i t i e s . a n d  electrical  conductance of the compounds of graphite with bromine and graphite with potassium made by MacDonell,  Pink and Ubelohde  (23), show that the electrons of graphite are very markedly affected by the intercalated atoms.  The behaviour of both  CgK  and CgBr i s a c t u a l l y c l o s e r to that of good metals than to that of the o r i g i n a l graphite as shown in Table. I. TABLE I Magnetic S u s c e p t i b i l i t y (23). ( e g .s. 10"•6)  Substance 90° K Xs  288°K  195°K Xm  Xs  Xm  Xs  Xm  +0.538  +21.0  +0.539 +21.1  Potassium  +o;.54o +21.1  Graphite  -7.909  -94.81  -6.757  -81.0  -6.04  -72.4  8.47  +1.01  +16.78  +1.07  +16.78  +1.00  +16.61  8.79  +0.95  +16.23  +0.95  +16.17  +0.95  +16.23  -0.411  -8.23  -0.399  -7.99  -0.403  -8.07  KC  Ke  BrC9.9  Electrical  Conductances. (ohm"  Graphite KGg BrC  9 # 9  cm" )  1  1  90°K  288°K  26.5  35.2  1302.0  960.0  197.0  384.0 150,000.0  K (compact)  850.0  Cu (powdered)  5^0,000.0  Cu (compact)  The data i n Table I show that the metallic character of graphite a c t u a l l y increases on forming compounds.  The marked diamagnetism  associated with the large o r b i t a l s i s destoryed, and the elect r i c a l conductance  i s increased.  The experimental observations  can be explained on the basis of a model i n which the layers of graphite behave amphoterically and take, up electrons from the potassium, or give up electrons to the bromine. The nature of the bonds formed between the potassium or bromine atoms and the graphite layers i s probably m e t a l l i c .  As  i n other intermetallic compounds, a range of composition around the stochiometric value has approximately the same s t a b i l i t y . The reaction mechanism can be explained e n e r g e t i c a l l y as follows: K(gas)-> K  +  A H - J " 101.1  (gas) + e  e + C(lam.) —» G" (lam.) K (gas)  +  +  G" (lam.)  d GgK  0  kcals./mole  kcals./mole  A  and so the o v e r a l l process i s K (gas)  +  C (lam.)  The order of magnitude of  CgK  A H=  A  H  3  . +  101.1  can be determined from a  similar reaction K ( l i q . ) + C (lam.) — f o r which  ^ H = 6.0  ^ h\j = 126.0  C^K  (12)  k c a l s . and so we d e r i v e the value f o r  kcals./mole.  T h i s h i g h v a l u e seems t o compensate f o r the energy o f the potassium.  The 126.0  ionisation  kcals./mole i s i n s u f f i c i e n t  t o overcome the i o n i s a t i o n energy o f sodium (&H = 119.5  kcals./  mole), and t h e r e f o r e no f o r m a t i o n of l a m e l l a r compounds w i t h sodium was  observed.  Rubidium and cesium, which have lower  i o n i s a t i o n e n e r g i e s than potassium, both form l a m e l l a r compounds. The marked i n c r e a s e i n conductance  on forming l a m e l l a r  compounds of g r a p h i t e can be more r e a d i l y e x p l a i n e d i n t h e terms o f p a r t - f i l l i n g o f the empty e l e c t r o n band i n the case of  CgK  and part-emptying of t h e f u l l e l e c t r o n band by CgBr. Figure I.  I.  E l e c t r o n energy l e v e l s i n g r a p h i t e a c c o r d i n g to Coulson.  II.  Suggested e l e c t r o n bands i n C-jK by McDonnell, Ubbelohde (23). -  III.  Suggested e l e c t r o n bands i n CgBr by McDonnell, Ubbelohde (23). I f we  Pink and Pink and  summarize t h e t h e o r e t i c a l e x p l a n a t i o n f o r the  f o r m a t i o n of lammellar compounds from the evidence a v a i l a b l e at t h i s time, we  can say t h a t the i n t e r c a l a t i o n i s dependent  7 on two main f a c t o r s :  3.  1.  Structural and geometrical- the s i z e of the intercalated molecules.  2.  Charge Transfer- to lower the energy of the' complex with respect to single substances, thereby s t a b i l i z i n g the structure.  The Structural Relationship of Graphite. Boron N i t r i d e and the D i s u l f i d e s of Molybdenum and Tungsten. Because the s t r u c t u r a l s i m i l a r i t y of boron n i t r i d e and  graphite was  one of the main reasons f o r our investigation of  the formation of possible i n t e r s t i t i a l compounds of boron n i t r i d e , at least a short comparison of graphite and boron n i t r i d e w i l l be of use. Graphite i s the hexagonal modification of carbon.  Struc-  t u r a l l y i t consists of layers of regular hexagons ( 4 ) , where the distance between two neighbouring atoms i n the l a y e r i s 1.42 and the i n t e r l a y e r distance i s 3.4 A ( 3 ) .  A  The l a s t dimension  changes s l i g h t l y between d i f f e r e n t samples, the change depending mainly on the p a r t i c l e size ( 1 ) .  The bonds among the atoms i n  the l a y e r are very strong, not too d i f f e r e n t from those of diamonds.  But the electron density which i s a c t u a l l y the  measure of the firmness of the bond, i s very small between the two l a y e r s , and i t i s believed that the layers are attached to each other only by means of weak van der Waal*s forces (31)• The dispersion energy between the graphite layers has the value of 1-2 k c a l s .  It i s therefore possible to separate the d i f -  ferent l a y e r s very e a s i l y .  This easy separation i s the base f o r  the use of graphite as a s o l i d l u b r i c a n t . Each carbon atom forms three <T bonds with i t s neighbours  and one of &  IT  bond, which i s i n the plane perpendicular to that  bonds and i s a c t u a l l y c l o s e l y r e l a t e d i n i t s nature t o .  those of benzene.  Because we have only two bonds i n one  graphite hexagon, the aromaticity which i s connected with them i s l e s s pronounced i n graphite than i n benzene. The electrons which are i n the i n t e r l a y e r space can move far  more f r e e l y than those i n the planes and resemble i n be-  haviour the electrons i n metals.  These m e t a l l i c electrons are  responsible f o r some metallic properties of graphite, e l e c t r i c a l conductivity and metallic l u s t e r .  The  possibility  of those electrons moving f r e e l y i s related to t h e i r localised  e.g.  non-  character.  Boron n i t r i d e was prepared f o r the f i r s t time by B alma i n i n 1042  (2).  He f i r s t believed that the products of the  reaction of KGN  and molten boric a c i d were compounds s i m i l a r  to the cyanides and he named them aethonides.  Later he r e a l i z e d  that h i s aethonides were compounds of boron and nitrogen.  One  form was unalterable by white heat but i t was decomposed by hot water.  Later Wohler and Sainte-Claire D e v i l l e (49)  formed BN  by heating amorphous boron or a mixture of boric acid and carbon i n a stream of nitrogen or dry ammonia.  Since that time boron  n i t r i d e has been investigated by many research workers, but only recently has i t become an a r t i c l e of commerce. Many methods of preparation have been described i n the erature and i n patents.  lit-  The boron n i t r i d e available on the  market, however, has frequently been impure and very expensive. The more p r a c t i c a l ways t o make boron n i t r i d e are summarized  i n the equations l i s t e d below.  These reactions are a l l carried  out at elevated temperatures, ranging from 600-2000°C.  In most  cases these equations are approximations and there i s no proof that the reactions proceed exactly as shown.  No account has  been taken of possible intermediate steps. B +'N  -  2  2.  B 0 2  3  +  3.  B 0 2  3  + 2NH4CI = 2BN + 2HG1  4.  B 0  3  + 2NaCN = 2BN + Na 0 + 2C0  5.  4H H:BF  6.  4NH t BC1  2  2  3  3  2  BN  1.  2NH3  —* 3  (35)  - 2BN + 3H 0 2  + 3H 0 (17) 2  2  (46)  BN + 3NH4BF  (21)  —> BN + 3NH4CI  (11)  In a l l these methods the most d i f f i c u l t step i s the separation of boron n i t r i d e from the by-products.  Since the  desired product;:is very f i n e l y divided, bulky, and i s rather e a s i l y hydrolysed, before i t has been f i r e d at high temperatures, t h i s process always presents d i f f i c u l t i e s . The chemical s t a b i l i t y of boron n i t r i d e depends on the temperature at which i t i s produced or to which i t i s l a t e r heated.  In general the products of lower temperatures are l e s s  stable and decompose much easier than those prepared at the high temperatures  (45). -The stable-high temperature-products are  decomposed only by molten potassium hydroxide, hydrolysed by acids to ammonia and boric a c i d only upon extensive b o i l i n g and oxidized at red heat with oxygen or carbon dioxide to boric acid and nitrogen (13, 26).  However with the proper atmosphere boron  n i t f i d e i s an excellent refractory (34). The following, table shows some of the most important p h y s i c a l properties of boron n i t r i d e .  10 Color:  White ( 1 5 ) , transparent .to l i g h t J m a t e r i a l containing carbon as impurity i s gray (13).  Feel:  Greasy, s i m i l a r t o t a l c ( 1 5 ) .  Hardness:  1-2 on Mohs* scale (15 ) i  System and Habit:  Hexagonal, g e n e r a l l y t h i n , flexible plates. Unit c e l l dimensions: a - 2,50399 0.005. A c - 6.6612 i 0.005 A c/a = 2.66 A l l dimensions a r e a t 35°C, assuming CuK = 1.54051 A. Cleavage: Good basal (15). 1  Calculated d e n s i t y :  (32)  2.270 as determined from X-ray data (32).  Observed d e n s i t y :  2.3 (13,32).  R e f r a c t i v e index:  Above 1.74 (15).  Electrical resistivity: Sublimation temperature:  High a t a l l temperatures (35). 3000°C. at 760 mm. (27).  Melting point:  Above 3000°C. under pressure of nitrogen (34). Thermal c o n d u c t i v i t y : Very low f o r the powder ( l l ) . Diamagnetic s u s c e p t i b i l i t y : For the powder kx 10"^ = - 0 i n e.g. s. ( 2 5 ) . :  Boron n i t r i d e , from the s t r u c t u r a l point of view, i s very s i m i l a r t o graphite', being composed o f s i x member ed r i n g s cont a i n i n g a l t e r n a t e boron and nitrogen atoms.  These hexagonal  r i n g s are s i m i l a r t o those i n graphite l a y e r s , w i t h most o f t h e e l e c t r o n d e n s i t y i n t h e sheets and only 16% between t h e l a y e r planes.  This corresponds t o two e l e c t r o n s per p a i r of B + N  atoms, s i m i l a r t o graphite w i t h i t s two e l e c t r o n s per p a i r o f carbon atoms. represented  The a c t u a l s t r u c t u r e of boron n i t r i d e can be  as the covalent s t r u c t u r e I . w i t h some c o n t r i b u t i o n  11 of ionic structure I I . FIGURE I I  The p a i r of boron and nitrogen atoms have an electronic conf i g u r a t i o n and certain physical properties l i k e carbon atoms i n graphite.  The:ionic structure and the absence of non  l o c a l i s e d electrons i n greater extent explains the lack of m e t a l l i c properties.  The structure of boron n i t r i d e which  was determined by Hassel i n 1926 and l a t e r confirmed by Brager (5) was accepted u n t i l 1951 when R. S. Pease (32) proposed a new arrangement  of the atoms.  Of necessity the X-ray exam-  i n a t i o n was confined to powder specimens; CuK^ and MnKoc radiations were used.  The non r e c r y s t a l l i s e d sample gave a  picture on which i t was very d i f f i c u l t to determine the i n t e n s i t i e s and exact positions of the l i n e s , because of t h e i r unsharpness.  The r e c r y s t a l l i s a t i o n of boron n i t r i d e which.is  done by heating the sample f o r at l e a s t 2 hours at 2050°C. i n a nitrogen atmosphere gave a product whose X-ray photograph cons i s t e d of. very sharp l i n e s , so that they could be used f o r precise, determination of the unit c e l l dimensions.  A l l the  r e f l e c t i o n s can be indexed on the basis of a hexagonal unit cell.  The dimensions of the unit c e l l have been determined  from the observed interplanar spacing using the Bragg equation  n • 2 d sin $  and the r e l a t i o n of d to c e l l parameters a and  c f o r hexagonal systems  ?  3  .  — 1 2  ^  The dimensions at 3 5 ° C , assuming Gu Koc = 1 . 5 4 0 5 1 A, were given by ft. S. Pease ( 3 2 ) as: a = 2.50399 :c = 6 . 6 6 1 2  +  0.0005 A  + 0.0005 A  The absence of large systematic errors was confirmed using the same equipment and technique to determine the a dimension of well c r y s t a l l i z e d graphite. 1 odd are absent.  Reflexions with h +• 2k = 3n and  From these f a c t s , and from the values f o r  i n t e n s i t i e s f o r 0 0 1 planes, i t was found that the structure i s hexagonal, layer type with interplanar spacing of 1/2 c. There are four possible ways i n which the layers may be packed. Three are simply d i f f e r e n t arrangements of nitrogen and boron atoms at the s i t e s occupied by carbon atoms i n graphite and the fourth possible structure, accepted by Pease, i s shown i n Figure  III.  Structure I  Structure I I  Atomic p o s i t i o n s :  Atomic p o s i t i o n s :  N: (000 , 001/2)  N: (000  B: (1/3 2/3 0, 2/3 1/3 0)  B: (001/2, 1/2  The thermal expansion  ,1/3 2/3  1/3)  2/3 0 )  c o e f f i c i e n t f o r boron n i t r i d e i s of the  same order of magnitude and consistent with that of graphite. On the basis of the data a v a i l a b l e (X-ray, physical prop., chemical behaviour) i t i s shown that graphite i s the closest analogue of boron n i t r i d e .  The s t r u c t u r a l difference between  them, i f we accept the structure proposed by H. S. Pease (32), l i e s i n the nature of the l a y e r packing.  In boron n i t r i d e the  hexagonal rings are packed d i r e e t l y on top of each other, whereas i n graphite a form of close packing exists, i n which h a l f the atoms l i e between the centres of the hexagonal rings of the adjacent l a y e r s .  Unlike the C-G bond i n graphite, the  B-N has an e l e c t r i c a l dipole moment; the difference i n packing may be due to the i n t e r l a y e r interaction of thosedipoles, which favours the observed type of packing above a l l others. s i m i l a r i t y of the two substances  indicates that the  The  packing  d i f f e r e n c e i s of secondary importance, and that the deciding f a c t o r i s the magnitude of the interatomic forces i n the substances which i s very s i m i l a r . one strong bond, the B-N  two  The structrue contains only  joining each atom to i t s three nearest  neighbours i n the same plane.  The sum of the single covalent  r a d i i of boron and nitrogen as given by Pauling i s 1.56  A.  As f a r as the nature of the B-N bond i n boron n i t r i d e i s concerned, there are two d i f f e r e n t views.  They are  expressed  14 mainly by Levy, ( 2 2 ) , who  supposed that the short bond length  indicates a part-double bond, and by W. Huckel, who  on the base  of extremely low e l e c t r i c conductivity and whitness of the material, r e j e c t s the presence of resonating electrons and assumes therefore that the bond must be single.  Since boron  n i t r i d e i s the on.'l y ~:;;klnown boron compound with an accurate value f o r the bond length B-N,  we have no p o s s i b i l i t y of using  a comparison with a reference substance. The  s i m i l a r i t y of th e interatomic forces i n graphite and  boron n i t r i d e seems to indicate the part-double  band.  But the  d i f f e r e n c e i n colour, conductivity and magnetic s u s c e p t i b i l i t y indicate the single bond. interstitial  Therefore, the formation of the  compounds could be a f a c t o r which could bring  new  l i g h t into the problem of the nature of bonding i n boron n i t r i d e . . The other substances which we b r i e f l y examined f o r formation of i n t e r s t i t i a l  compounds were molybdenum and tungsten  disulfides.  Both these substances are hexagonal, have l a ^ e r l a t t i c e s and resemble very much graphite i n t h e i r colour and m e t a l l i c luster.  The hexagonal unit c e l l of molybdenum d i s u l f i d e i s  i l l u s t r a t e d i n Figure IV. FIGURE IV  The structure i s formed by superposition sheets.  of a s e r i e s of  Each sheet i s i t s e l f b u i l t up of a layer of molybdenum  atoms enclosed between two layers of sulphur atoms.  The sep-  arate sheets of the structure may therefore be regarded as d i s c r e t e macromolecules.  The binding between the sheets i s  predominantly m e t a l l i c .  The molybdenum s u l f i d e structure i s  also exhibited  by:  Mb S , Mo Se , Mo Te , 2  W.S , 2  2  W Se , W T e 2  2  2  Both Mo £3 and W £> are soft, dark-grey powders, insoluble 2  2  i n water, and burn i n a i r into the t r i o x i d e .  **oth have metallic  conductivity and decompose to sulphur and the metal when heated i n vacuo to 1200°C. and above. If we should summarize the structural relationship of boron n i t r i d e , molybdenum and tungsten d i s u l f i d e s with graphite, could  we  say that the unit c e l l of a l l these substances i s close  packed hexagonal, they, a l l posses l a y e r - l i k e structure, have good basal cleavage and the s u l f i d e s have metallic and l u s t e r .  conductivity  Therefore the formation of lamellar compounds  s i m i l a r to those known i n graphite should be-more probable i n these substances than i n any others. 4.  Theory of Diffusion i n Solids. One of the main parts of our investigation was the k i n e t i c  study of the formation of the complex between boron n i t r i d e and chromyl chloride.  The speed of t h i s reaction i s controlled by  the rate of d i f f u s i o n of chromyl chloride molecules into boron  n i t r i d e , and therefore the basic p r i n c i p l e s of d i f f u s i o n i n s o l i d s w i l l be  presented.  Diffusion i s a process which leads to an equalisation of concentrations within a single phase.  The f i r s t cases of  d i f f u s i o n i n s o l i d s were studied i n metals. investigated was gold-lead.  fioberts-Austen  The  f i r s t system  (37), clamped  d i s c s of gold to the bases of lead cylinders, the bases of cont a c t being accurately smoothed and the golden d i s c s s p e c i a l l y cleaned.  A f t e r standing f o r four years at temperature l£°C.  i t was found that the gold penetrated # mm.,  into the lead as deep as  the concentration being highest nearer the gold p l a t e .  In general there i s interest i n two d i s t i n c t phases of the d i f f u s i o n , namely i n the displacement  of chemically i d e n t i c a l  u n i t s r e l a t i v e to one another and i n the displacement chemically d i f f e r e n t u n i t s .  of  The f i r s t , which i s termed s e l f -  d i f f u s i o n , can be exemplified by the migration of the atoms i n a pure monoatomic s o l i d and the second by migration of one constituent of an a l l o y r e l a t i v e to the other i n the two component systems.  Because of the nature of the problem, we  will  be concerned with the second case, d i f f u s i o n of one substance into the other. The laws of d i f f u s i o n connect the rate of flow of the diffusing,usubstance with the concentration gradient responsible for  t h i s flow.  In the case of two components we should, i n  general, consider two d i f f u s i o n equations expressing the f a c t that the rate of flow of the second component i s of opposite  .  d i r e c t i o n , but of equal magnitude as: that of the f i r s t .  1 u  7  s u a l l y we  take the l a t t i c e of one system as a frame of reference, and the d i f f u s i o n equation r e f e r s to the flow of the other substance into the l a t t i c e of the f i r s t  one.  The d i f f u s i o n flow of the substance, otherwise  c a l l e d current  J, i n a mixture, i s defined as the amount of t h i s substance passing perpendicularly through a reference surface of unit area during u n i t time.  The dimensions of J i n c.g*s. u n i t s are the quantity  ' of the substance per cm^..per second.  The u n i t s f o r quantity are  free to choose. The r e l a t i o n of the concentration and current J i s given by the f i r s t Fick's law J  ~ -D  2 c/d  x  1.  where J i s the d i f f u s i o n flow D i s the c o e f f i c i e n t of d i f f u s i o n f o r the substance under consideration. c i s concentration x i s the coordinate chosen perpendicular to the reference sphere. If we wish to determine the d i f f u s i o n c o e f f i c i e n t by means of equation 1, we must f i n d an arrangement i n which both J and #c/<?x are accessible t o measurements.  Generally i t i s not  possible to investigate d i f f u s i o n under conditions of constant concentration gradient, which implies the establishment steady state.  of a  One therefore has to determine the change of  concentration with time. When there i s d i f f u s i o n i n one d i r e c t i o n only, and when we observe the increase of the amount of substance within a volume  i  element bounded by two p a r a l l e l p l a n e s o f u n i t a r e a s i t u a t e d at x and x + dx, t h i s i n c r e a s e i s J  x= x d x f ^ / ^ ^ = D(3 c/ax ) dx J  =  B  c  +  2  x  +  2  d  x- O c / M 2.  •  By d i v i d i n g e q u a t i o n 2 by t h e volume element d x . l cm we o b t a i n 2  for  the increase of t h e c o n c e n t r a t i o n w i t h time, i n t h e l i m i t  dx -» 0  2c/£t  3.  = V3 c/dx 2  2  E q u a t i o n 3 i s c a l l e d P i c k ' s second l a w o f d i f f u s i o n , and i s d e r i v e d on t h e assumption t h a t D i s c o n s t a n t .  I f we extend  t h i s e x p r e s s i o n i n r e s p e c t t o y and z we g e t Ic/dt  where V  = D(£ c/2x 2  2  +  2 c/dy 2  + 2 c/dz )  2  2  2  = UVc  i s L a p l a c e ' s o p e r a t o r 3 / # x - d /9y 2  2  2  2  4.  - d /3z . 2  2  E q u a t i o n 4 can be t r a n s f o r m e d i n t o o t h e r systems o f c o o r d i n ates.  S'or p r a c t i c a l purposes most i m p o r t a n t a r e the cases o f c y -  lindrical  o r s p h e r i c a l symmetry, where c depends on t h e r a d i u s  r o n l y and i s independent  o f t h e o t h e r two c o o r d i n a t e s z and *f i n  t h e case o f c y l i n d r i c a l and a n g l e s d s p h e r i c a l ones.  and  i n t h e case o f  *'or..our c a s e , a s w i l l be seen f u r t h e r , t h e  c y l i n d r i c a l c o o r d i n a t e s a r e important and by c o n v e r t i n g t h e e q u a t i o n 4 we g e t  0c#t =  D  O  c/dr  2  2  + 1 / r do/dr)  5.  The n a t u r e of our problem, t h e e x p e r i m e n t a l r e s u l t s and t h e s i m i l a r i t y t o t h e case o f d i f f u s i o n of f e r r i c  chloride  i n t o g r a p h i t e , suggest t h a t t h e r a t e of t h e d i f f u s i o n o f c h r o myl c h l n r i d e i n t o boron n i t r i d e w i l l be t h e d e t e r m i n i n g s t e p  19 of the reaction. well j u s t i f i e d .  Two assumptions are made, which are f a i r l y The boron n i t r i d e p a r t i c l e s are considered as  roughly disk shaped, and secondly the d i f f u s i o n i s assumed t o take place only between the boron n i t r i d e l a y e r planes.  The  f i r s t assumption i s j u s t i f i e d on the base of the c r y s t a l l o g r a p h i c studies which were done on boron n i t r i d e mainly by 'W. Goldsmith (15), who describes the habit of boron n i t r i d e crystals as hexagonal, generally t h i n , f l e x i b l e p l a t e s .  The second assumption  i s generally accepted f o r the formation of the i n t e r s t i t i a l compounds of graphite where we assume very loose bonds between the.planes and very strong ones i n the same plane and therefore the d i f f u s i o n takes place only i n the d i r e c t i o n shown i n Figure V. Figure V  * layers of EN 3.33A »  4  directions of. difussion The s i m i l a r i t y of the interatomic forces i n graphite and boron n i t r i d e was established before.  We can conclude from t h i s  that i n boron n i t r i d e d i f f u s i o n takes place only i n the d i r e c t i o n i d e n t i c a l with that i n graphite. The problem i s therefore geometrically equivalent t o one of d i f f u s i o n into an i n f i n i t e c y l i n d e r .  This consideration gives  us the boundary values f o r the problem. dc/dt  = D( d c / a r 2  a> r > 0  c - G c = c  0  r = a  2  + 1/r dc/9 r )  t - 0 t> 0  where t = time a " particle  size—diameter  r = a x i a l coordinate c = average concentration i n the'cylinder CQ- f i n a l concentration The s o l u t i o n of t h i s equation i s  c/c - 1 - 2Ze^(-&\ d)Jo(r/3„/a)/ 3nJ ('3k 0  /  i  = F(r/a,# ) where 4 * and J*  0  0  m  6.  l  (/3) » 0  are the roots of J  a  Dt/a . 2  (/3 ) i s the Bessel function of zero order.  For the amount Q  adsorbed at time t t h i s gives  Q/Qoo " g ^) " 1  g( 0 ) where 4£exp  Q)/^  Figure V4E shows the plot of the function g (6) versus Q ,  Figure VI  By establishing the values f o r D/a  2  at d i f f e r e n t tem-  peratures we are able to f i n d the a c t i v a t i o n energy of the process because the r e l a t i o n between *» and D i s similar to that of K to E.  We can write T D - A e / E  R  where A i s the p r o b a b i l i t y f a c t o r  corresponding to P i n the theory of reaction rates. expression f o r D we can write log D = l o g A - E/RT  From t h e  and by p l o t t i n g l o g D vs. 1/T the slope of the l i n e w i l l be r e l a t e d to activation energy i n the following r e l a t i o n : Slope =  (9)  - E/2.303H  The intercept will.be equal to l o g A. The t h e o r e t i c a l explanation of the f a c t o r A and r e l a t i o n to other quantities i s outside of the scope of t h i s work.  II. 1.  EXPERIMENTAL  Preparation and Analysis of Compounds. A) Boron N i t r i d e . During the work we were dealing with four com-  mercial samples of boron n i t r i d e from these companies: 1.  Elmer and Amend - New ^ork.  2.  A. D. McKay - New *ork.  3.  Fairmont'Chemical Co. - Newark,'N. J .  4.  Fisher S c i e n t i f i c Co. - New York.  5.  Our own sample.  Sample No. 3 was not used f o r the preparation of compounds, because i t was announced by the company that i t contained over 1% combined CaO-MgO, some moisture and excess nitrogen i n the form BN^ (10). The colour of the .substance was greyish which indicated the presence of carbon as impurity,  '-"-'he material l o s t  up to 25% of i t s weight when heated to higher temperatures. It t  was a very f i n e powder and therefore probably l e s s c r y s t a l l i n e ' than the other samples.  Because we t r i e d to work with material  with as pronounced c r y s t a l l i n e properties as possible, we concentrated on the other three samples,  A H three of them were  declared by the companies which produced them as very pure. These samples of boron n i t r i d e didn't dissolve i n cold water; decomposed only s l i g h t l y i n b o i l i n g water; and were decomposed by the a c t i o n o f molten potassium hydroxide by which reaction NH^ was given o f f . The f i r s t step was to f i n d out a possible way i n which the material could be r e c r y s t a l l i z e d because the r e c r y s t a l l i z e d form would be more suitable to our investigation than the o r i g i n a l one.  23 We t r i e d to achieve the r e c r y s t a l l i z a t i o n by heating the sample of boron n i t r i d e to higher temperatures.  The highest  working temperature was limited by the temperature range of our furnace.  The furnace used was a high temperature resistance  furnace from the "Hevi Duty" E l e c t r i c Co.  The highest safe  working temperature was 2550°F. which corresponds to 1400°C. By heating the boron n i t r i d e t o t h i s temperature' i n a stream of nitrogen i t reacted with the quartz crucible, BeO crucible and Pt sheet.  By heating BN on a graphite block i t did not change  in physical appearance and was impurified with carbon. Therefore i t was not possible to prepare the r e c r y s t a l l i z e d from of boron n i t r i d e and we used the o r i g i n a l sample of BN a f t e r private communication with Mr. R. our r e s u l t s ( 3 3 ) .  Pease of Harwell, England, confirmed  He achieved r e c r y s t a l l i z a t i o n of boron n i t r i d e  only by heating i t up to 2000°C . i n a z i r c o n i a c r u c i b l e , and r  found that graphite and BeO crucibles reacted at t h i s temperature with boron n i t r i d e .  Nevertheless, the X-ray studies have shown  that our samples have the same c r y s t a l structure as the r e c r y s t a l l i z e d form, only the orientation was not so pronounced and the p a r t i c l e s were smaller.  N  Because the r e c r y s t a l l i z a t i o n of the commercial samples was not achieved, we t r i e d to prepare our own boron n i t r i d e by the use of the reaction: B Cl  3  +  4NH3  - 'BN  +  3NH^C1  This method gives very pure boron n i t r i d e according to F i n l e y (11).  For t h i s preparation we used the apparatus of F. Meyer  (25) with only minor changes.  The t h e o r e t i c a l basis of t h i s  procedure i s the reaction between NH3 and BCI3 which gives a  24 white voluminous addition compound NH^  : BCl^., On heating to  800° - 1000°C. i t decomposes to BN and NH^Cl. used i s shown i n 'Graph I 1.  The apparatus  and the procedure w a s : r ?  Dry the whole apparatus at 300°(3. i n a slight stream  of hydrogen f o r two hours. 2.  Raise the temperature.to 500°C. at the heating c o i l I.  and switch on one of the t;hree c o i l s of heating I I . A powerful stream of ammonia i s used and the BCl^ d i l u t e d with hydrogen, i s d i s t i l l e d slowly iito the apparatus.  When a l l the boron t r i -  chloride i s i n , weswitch the c o i l s 1., 2.,  3." of the heating I I .  every hour during a 5-6 hour period, and a f t e r we slowly bring the temperature to 1000°C. and l e t go a slight stream of ammonia over the product.  The back sublimation of the product i s  hindered by heating c o i l no. 2. to 800°C.  We use the heating  no. I I I . f o r regular s e t t l i n g of the ammonium s a l t .  After the  temperature has been at 1000°C. f o r one hour and a s l i g h t stream of nitrogen has gone over the product, the whole apparatus i s cooled down slowly.  The product on both ends of the quartz tube  i s disregarded and i n the middle part of the quartz tube, there i s a l i g h t , white powder—BN. On the f i r s t run, white clouds escaped through leaks at the top of the apparatus.  The back pressure at the end of the  tubing was too great and the excess of ammonia was not s u f f i c i e n t . The f i n a l temperature of the tube was 800°G. the  middle part of the tube was c o l l e c t e d .  and the product smelled of ammonia.  The product from The y i e l d was poor  On the second run" these  troubles were eliminated and the y i e l d was better.  In general  the work of the apparatus can be described as not s a t i s f a c t o r y because the amount of boron n i t r i d e obtained' was quite small and the product gave odor of NH^ a long time which shows that i t i s not a; pure boron n i t r i d e . was irregular..  ...  The s e t t l i n g of the ammonium s a l t  . ."  The hydrogen used was p u r i f i e d by streaming i t over r e d hot Pt  gauze, and then through potassium hydroxide and calcium  chloride tubes.  The nitrogen used was p u r i f i e d by bubbling  i t through an alkaline solution of pyrogallic acid and then over drierite.  The ammonia was dried over CaO. B) Analysis of the Bpron N i t r i d e .  ;  Boron n i t r i d e was f i r s t analysed f o r nitrogen using the method recommended by G. Schaffran ( 4 2 ) . A small amount o f boron n i t r i d e ( 0 . 2 gms.) was weighed t o four decimal places and quantitatively transferred into a glass tube which was sealed at one end and the walls of which were covered with a layer of fused sodium hydroxide.  This was achieved by melting  several p e l l e t s of sodium hydroxide i n the tube and l e t t i n g i t s o l i d i f y regularly at the walls.  To the boron n i t r i d e approxi-  mately 0 . 5 gms. o f sodium hydroxide was added and the tube inserted i n a test tube.  The test tube was provided with a  stopper with a tube f o r escaping ammonia.  The other end of t h i s  tube was inserted i n an Erlenmeyer f l a s k which was f i l l e d with 50  cc. 0 . 1 9 8 0 N s u l f u r i c acid.  The acid was t i t r a t e d with  normalized sodium hydroxide solution.  From the amount of the  acid neutralized by ammonia, the nitrogen content of boron n i t r i d e was calculated by the usual means.  The percentage of  nitrogen given was very low, 23% by repeated t r i a l s and therefore  26 the method was The  considered  second method used was  selenium catalyst (29) type.  as riot s a t i s f a c t o r y . the Kjeldahl procedure with a  and the apparatus of the conventional •-  An accurately weighed amount of boron n i t r i d e was  f e r r e d into a clean, dry Kjeldahl digestion f l a s k .  trans-  0.3  gm.  selenium catalyst was added to the sample, and then 2 mis. concentrated s u l f u r i c acid were introduced.  The  of .: of  digestion  f l a s k was placed on the digestion oven and at f i r s t slowly then vigourosly b o i l e d .  Because even a f t e r 1 hour digestion  incomplete, 4 drops of H 0 2  continued f o r 1 more hour. contained  2  (30%)  was  were added and digestion  was  Even a f t e r that time the solution  some undigested material.  This i s i n agreement with  information given by G. Firiley (11) who  even a f t e r & hours of  digestion and adding extra s u l f u r i c acid could not secure comp l e t e solution of the sample.  He achieved the complete solution  by carrying out the digestion i n a sealed glass tube i n a Carius bomb.  enclosed  For p r a c t i c a l purposes, the material not d i s -  solved can be ignored,  since l i t t l e extra nitrogen was  recovered  even with greatly increasing digestion time. The next step was  the d i s t i l l a t i o n of the mixture.  t e l y measured 20 cc. of 0.0101N H S0^ was 2  Accura-  run from a pipet into  an Erlenmeyer f l a s k and 3 drops of methyl red i n d i c a t o r were added. With the water i n the steam generator b o i l i n g , the contents of the digestion f l a s k were quantitatively transferred to the d i s t i l l i n g chamber of the apparatus by pouring the digestion material and 2 mis. of water, used f o r washing, into the  small  funnel on top of the d i s t i l l i n g f l a s k .  Then the Erlenmeyer  f l a s k containing the 0.0101N acid was placed under the quartz tube of the condenser and raised u n t i l the t i p of the tube dips w e l l below the l i q u i d .  Eight mis. of 30% sodium hydroxide were  poured through the introduction funnel into the d i s t i l l i n g f l a s k , which amount i s s u f f i c i e n t to make the reaction material decidedly basic.  To begin the d i s t i l l a t i o n i t s e l f , the pinch  clamp on the funnel and then, the pinch clamp at the bottom of the steam trap were closed, f o r c i n g the steam to pass to the d i s t i l l i n g flask. three minutes.  The duration of the d i s t i l l a t i o n was exactly  After t h i s time the Erlenmeyer f l a s k was lowered  u n t i l the t i p of the quartz tube condenser was about 1 cm. above the l i q u i d .  The d i s t i l l a t i o n was continued f o r another minute  and the top of the quartz tube was rinsed with d i s t i l l e d water. The solution was then boiled f o r about 20 seconds t o expel carbon dioxide absorbed from the a i r and t i t r a t e d to a canary yellow end point with Q.01N  sodium hydroxide solution.  From  the amount of s u l f u r i c acid neutralized by ammonia the percentage of nitrogen i n the sample was found. TABLE I I . ) Results of the Analysis of Boron N i t r i d e Sample  Weight  O r i g i n a l BN  u  BN treated with CC1 4  cc. of acid • . neutralized with NH^  % Nitrogen content  1.  .0051  17.2  47.3  2.  .0049  16.4  46.9  1. .  .0046 .0055  15.3 16.5  46.5 47.2  2  1 cc. of 0 . 0 1 0 1 N acid corresponds to 0.00014-  gms. of nitrogen.  23  The analysis of the sample treated with carbon t e t r a chloride was done to be sure that carbon tetrachloride d i d not a f f e c t , during the washing, the composition of boron n i t r i d e . A 1 gram sample o f boron n i t r i d e was treated twice with 200 cc. of carbon tetrachloride f o r two hours at room temperature and dried at 115° C  The t h e o r e t i c a l amount of nitrogen i n boron  n i t r i d e i s 56.5%.  The difference i s due to ibhe f a c t that the  digestion of the sample was not complete and the observed values were low.  F i n l e y (11) gives the values f o r nitrogen content  f o r d i f f e r e n t commercially produced boron n i t r i d e s available on the market on t h i s continent and i n England from 3S%-48%. C) Preparation of the Substances to be Intercalated. 1.  Chromyl Chloride (43). A solution of 150 gms. of CrOj i n 100 mis.  of water was placed i n a 2000 ml. three-necked f l a s k , provided with a mechanical s t i r r e r , a thermometer, a dropping funnel and a tube to carry away the vapours of chromyl chloride and hydroc h l o r i c acid.  Three hundred t h i r t y ml. of cone, hydrochloric  a c i d (c.p.) was added and the solution cooled to 0°C. with an i c e - s a l t mixture.  M  h i l e the solution was s t i r r e d , 450 mis. of  cone, s u l f u r i c acid (c.p.) was added i n small portions from the dropping;funnel.  The rate of addition was regulated so that the  temperature of the mixture did not r i s e above 15-20°C.  When a l l  the s u l f u r i c acid had been added, the reaction mixture was transf e r r e d to a separatory funnel.  After the two liquid;- layers  separated, the lower layer of chromyl chloride was drawn o f f  29 i n t o a glass-stoppered container.  The product was then d i s t i l l e d  through.an 18 inch Vigreux column and 60% came over between 115-116°C.  This portion was stored i n a dark container i n a  cool place and used i n the preparation of compounds. 2.  Tungsten Oxvchloride (44). The t h e o r e t i c a l base f o r the preparation i s  the reaction between WO^ and HGl.  WO3  +  2HC1 =  W0  2  Cl  +  2  H0 2  W0^ (c.p., anhydrous) was reacted with dry HCl gas i n a glass tube i n the furnace heated to 400°C. f o r 8 hours. WO3 changed a f t e r t h i s time to the products. W0 C1 2  98% of the 2  formed  yellow c r y s t a l s melting at 265°G. and v o l a t i l e on further heating.  Because i n the formation of W0 C1 2  2  some WOCl^ i s also  formed, we heated the product f o r four hours i n the oven to 250°C.  Because the b o i l i n g point of WOCl^ i s 233°C. i t v o l a t i l i z e d  at t h i s temperature and ¥ 0 C 1 2  3.  2  stayed behind.  Cupric Chloride. Cupric chloride was prepared by careful  heating of the dihydrate CuCl .2H 0 2  at room temperature, t o 200°C.  2  which i s a stable product  While drying, i t changed colour  from green t o dark brown which i s the colour of the anhydrous chloride (43). 4.  Aluminum Chloride. Aluminum chloride used as. supplied by  B.D.H.  Grade: C e r t i f i e d chemical, anhydrous. 5«  Boron T r i c h l o r i d e . The commercial sample supplied by  Matheson Company was used.  30 D) Preparation of I n t e r s t i t i a l Compounds. Of the halides intercalated i n graphite byCroft (8).the following were studied with boron n i t r i d e ; chromyl chloride, aluminum chloride, cupric chloride and boron trichloride. The two reactants were mixed either i n g l a s s or a -stainless s t e e l bomb arid heated either i n a water bath f o r temperatures below 100°C. or i n a controlled e l e c t r i c furnace above 100°C. to  -  The bath was constant to - 01°C. and the furnace  5°C. The general procedure f o r the i n t e r c a l a t i o n was i n a l l *  cases the same.  The amount of boron n i t r i d e , weighed to f o u r  decimal places, was mixed with an excess of the other reactent^ (4 times the weight of boron n i t r i d e ) , placed i n the bomb and heated to the selected temperature.  After the reaction,. the bcmb  was";, allowed., to .cool down, opened, and the excess of the reactants was dissolved i n a solvent which does not react with boron n i t r i d e or i t was  sublimed o f f . From the increase i n  weight, the percentage of the i n t e r c a l a t i o n and the composition was  determined. 1.  Boron N i t r i d e - Chromyl Chloride. This complex was the main object of study.  The washing cfofl..; excess chromyl chloride with carbon t e t r a chloride was continued as long as the carbon tetrachloride, was coloured by Cr02Cl2.  After that the complex was heated for  two hours at 115°C. and weighed.  As f a r as composition i s con-  cerned, we mainly studied the influence of two f a c t o r s :  31  a) The source of the boron n i t r i d e . b) The temperature. In a l l cases the same time of r e f l u x i n g was used - 48 hours. At t h i s time the composition of the complexes has an equilibrium value as w i l l be seen i n the k i n e t i c study.  For the study of the  influence of the source of the o r i g i n , the same temperature, 117°C., and approximately the same weight of the boron n i t r i d e were used.  The r e s u l t s of t h i s study are seen i n Table VIII The  v a r i a t i o n i n amounts of chromyl chloride absorbed are caused by v a r i a t i o n s i n the p a r t i c l e size, i n the temperature of preparation and possibly i n the amounts of impurities. Because the composition of many i n t e r s t i t i a l compounds depends on the temperature at which the components are heated, i t was of interest to make a temperature study. boron nitride, sample from MacKay Company. reaction was set f i r s t at 48 hours. of did at  We used the  The tine f o r the  By prolonging the time  reaction f o r the sample at higher temperature the composition not change.  Because there was a suspicion that the values  low temperatures are not those of equilibrium, the reaction  time was prolonged to 92 hours at 0° and  9°C. and i t was found  that the composition corresponds to that of higher temperatures at  48 hours.  As the r e s u l t of the temperature study which  covered the range from 0°-4Q0°C. we can say (graph 2):  There  are  The  two d e f i n i t e r a t i o s of composition of the complex.  first  contains 56-57% of C r 0 C l , the temperature range i s from 2  2  0°C. t o 150°C.(I.) and the other round 84% C r 0 C L from 1 6 0 ° 2  2  400°C. (II.) These two products d i f f e r c l e a r l y i n physical.  state.  The colour of I. i s reddish-brown, of I I . very dark  brown-black.  From the low temperature f r a c t i o n , the washings  with carbon t e t r a c h l o r i d e had a red colour at the beginning of the washing from the dissolved CrOgGlg but sample I I . gave colourless washings from the beginning.  The two products are  probably due to d i f f e r e n t reaction mechanism.  This i s proved by  the difference i n X-ray pattern as discussed l a t e r . By heating the lower temperature complex to 2 0 0 - 3 0 0 ° C . i n a t e s t tube connected with a U-tube, which was cooled i n the i c e s a l t mixture, red l i q u i d was condensed i n the U-tube.  The l i q u i d  was fuming i n the a i r and was hydrolyzed i n water and gave a yellow solution of chromate.  Therefore i t was assumed that the  l i q u i d was chromyl chloride.  By increasing the temperature the  weight of the sample decreased.  By heating the complex f o r 16  hours at 700°C. the loss i n weight was 8l.f>% of the o r i g i n a l CrC^C^ content.  At t h i s temperature the colour of t h e complex  changed to green which must have been due to the formation of C^Oj.  The same change i n colour was observed by heating the  chromyl chloride-graphite complex i n our previous i n v e s t i g a t i o n . The complex was hydrolyzed by water and gave a yellow, solution.  Both thromate and chloride ions were found i n the  solution.  The colour of the complex changed to white.  The  amount of chromate i n the complex was determined q u a n t i t a t i v e l y as w i l l be seen further.  The X-ray d i f f r a c t i o n pattern of the  complex heated t o 900°C. d i d not show the peaks corresponding to e i t h e r B2O3 or CrgO^. The study of composition as a function of time i s treated i n the chapter on k i n e t i c study of t h i s r e a c t i o n .  332.  Boron N i t r i d e - Aluminum Chloride.  0.471S gms.  of boron n i t r i d e was heated  with excess of aluminum chloride (approx. 4 times the weight of C r 0 C L ) f o r 25 hours at 250°C (subl. p. of 2  2  AICI3  i s 177.8°C.).  A f t e r opening the bomb and heating the opened bomb i n dry a i r atmosphere to 2 5 0 ° C , f r e e aluminum chloride sublimed o f f .  After  4 hours there was no more sublimation of aluminum chloride and the  gain i n weight corresponded.to 75% aluminum chloride i n the  complex.  By heating the complex f o r additional two hours at  400°C., the amount of aluminum chloride decreased to 64% and stayed constant on further heating at t h i s temperature. f i n a l stage corresponds to the formula: (BN) 3.  2  The  (AlCi^).  Boron N i t r i d e - Cupric Chloride. The procedure was the same as with aluminum  chloride, only the temperature used was 350°C. and the time 23 hours.  .( V. pressure of C C l u  2  at 350°C. i s rj 15 mm;)  After  that the complex was washed with d i s t i l l e d water and dried f o r two hours at 1 1 5 ° C .  The gain i n weight corresponded to 5 1 . 6 % cupric  chloride i n the complex.  By further washing f o r several hours  and drying, the percent of cupric chloride decreased tS which corresponds to the formula (BN)g(CuCl ). 2  continued to the moment when the washing, did not blue colour with ammonium hydroxide. i s r e a d i l y soluble i n water  (75•5  47.5%  The washing  give  was  any more  Because cupric chloride  gms. per 1 0 0 cc.) we see that  a l l the amount of cupric chloride i n the complex l e f t does not dissolve i n water and must be bound somehow t o the boron n i t r i d e .  34 '  4.  Boron N i t r i d e - Tungsten Oxvchloride. By reacting these two substances together at  200°C. i n a Stainless Steel bomb and after heating the mixture i n a i r to 4 0 0 ° C . , there was no gain i n weight, and we can assume that there i s no formation of compounds s i m i l a r to the other cases, at least not under the same conditions. 5.  Boron N i t r i d e - Boron T r i c h l o r i d e . The weighed amount of boron n i t r i d e was  treated with excess of boron t r i c h l o r i d e , which i s a l i q u i d under 1 2 . $ ° C , at 0°C. (ice bath) f o r 2 4 hours. the mixture l a t e r at room temperature  By leaving  the excess of boron  tri-  chloride boiled o f f , the complex was washed with d i s t i l l e d water and dried f o r two hours at 115°C.  A decrease i n weight  was observed, corresponding to the loss of 30% of the o r i g i n a l weight of boron n i t r i d e . E) The Analysis of the Complex of Boron N i t r i d e - * Chromyl Chloride. ' The complex was analysed f o r the amount of chromium present.  It was destroyed by hydrolyzing with d i l u t e d  hydrochloric acid.  Chromyl chloride hydrolyses as shown by the  reaction: 2Cr0 Cl 2  +  2  3H 0 — * 4HC1 2  +  Cr 0 2  +  = 7  2H  +  In acid medium dichromate reacts with iodide according to the equation: Cr 0 2  = 7  +  14H  +  +  61"  =  3I  + 2  and iodine subsequently with t h i o s u l f a t e 2S 0f 2  +  I  2  =  S 0 2  = 6  +  21"  '2Cr " ' +  M  +  7H 0 2  35 The l a s t reaction does not take place instantaneously, but the speed increases with the. concentration of hydrogen ions. To the solution containing the G^Oy iodide was added.  an excess o f potassium  The formed iodine coloured the solution brown.  The formed iodine was t i t r a t e d with standardized solution of IyJa  2 ^ 2 ^ 3 u n t i l the colour changed to yellow.  Then several, cc. of  f r e s h l y prepared starch solution was added as i n d i c a t o r and the t i t r a t i o n continued u n t i l the colour changed sharply from blue to l i g h t green.  The normality of ^ 2 ^ 0 3 used was 0.16 N.  If we designate the difference between the weight of the complex and the o r i g i n a l weight of boron n i t r i d e as 1 0 0 % C r 0 2 G l 2 , 9 5 . 5 % of chromyl chloride was proved present by a n a l y t i c a l means. Result's o f Analysis weight of the BN  0 . 5 4 3 6 gms.  0.5378  weight of the complex  1 . 2 3 1 5 gms.  1.2233 gms.  weight of the C r 0 2 C l 2  0 . 6 8 7 9 gms.  0.6855  % of Cr02Cl2 intercalated  55.8%  gms.  gms.  56.0%  1 cc. of 0.16 N Na2S203 corresponds t o 0.00815 gms. of C r 0 C l . 2  weight of the complex used f o r analysis  .1206 gms.  volume of , l 6 N a 2 S 2 0 3 used 7.03 cc. corresponding weight of Gr02Gl2 weight of Gr02Cl2 proved a n a l y t i c a l / weight of Cr02Cl2 intercalated  . 1 2 2 0 gms. 8.80 cc.  . 0 6 5 7 gms.  . 0 6 6 0 gms.  -.95.5%  96.5%  Mean value • 96%  2  The difference of 4.0% i s due probably to the f a c t that some chromyl chloride i s s t i l l absorbed i n boron n i t r i d e and to a possible presence of impurities i n chromyl chloride. 2.  X-ray Study. From the nature of the problem i t i s obvious that  f o r the topochemical reactions the X-ray study of the products and the s t r u c t u r a l r e l a t i o n s h i p to the reactants i s very important.  Therefore we decided to make an X-ray study of our  complex of boron n i t r i d e with chromyl chloride and molybdenum s u l f i d e with chromyl chloride. powdered material,  Because we had to deal with the- v  (single c r y s t a l s of s u f f i c i e n t dimensions of  boron n i t r i d e have not yet been prepared) the powder method of Debye-Sherrer was used.  Some of the basic p r i n c i p l e s of t h i s  method w i l l be mentioned. A c r y s t a l consists of a three dimensional array of atoms. X-rays are scattered from these atoms i n a manner s i m i l a r to that i n which l i g h t waves are scattered from the l i n e s of a d i f f r a c t i o n grating.  >.  The conditions f o r additive interference  between the X-rays can be seen from Figure VI,?./1. which i s the well known proof of the Bragg law.  \  \  /  <  /  1/ .f  Figure VI  37 In order that the waves scattered by two  consecutive  planes, and therefore, by a l l l a t t i c e planes, s h a l l be i n phase, i t i s necessary that 2dsin 0  -  n A  n being an integer  This means, that i f an incident ray, of wave length \ l a t t i c e planes of spacing d, at an angle 0  , encounters  , i t gives r i s e to a  maximum d i f f r a c t e d ray i n the d i r e c t i o n of the ray r e f l e c t e d by the planes considered, on the condition mentioned before that n X  -  2dsin 0  where &  i s h a l f the angle of d i f f r a c t i o n .  Therefore the c r y s t a l spacing can be determined  by measuring the  angles of d i f f r a c t i o n , ii' the wavelength of the 2-rays i s known. Because the p o s i t i o n of the d i f f r a c t e d beams i s e n t i r e l y dependent on the c r y s t a l l a t t i c e , the measurements of the angles of d i f f r a c t i o n of X-rays allow us to determine the point l a t t i c e , of the c r y s t a l .  To acquire infermation about the arrangement of  atoms within the unit celL, measurements of the i n t e n s i t i e s of d i f f r a c t e d beams are necessary. The Debye-tJcherrer method i s based on the f a c t that i f we have a specimen composed of a very great number of small crystals whose size i s of the order of 0.01-0.001 of a millimeter, these c r y s t a l s have a completely random d i s t r i b u t i o n so that even a small volume of matter always contains a c e r t a i n number of c r y s t a l s having a given a r b i t r a r y orientation. If we allow a narrow p e n c i l of' monochromatic radiation to be incident on a very small specimen^, there w i l l be a number of c r y s t a l s whose (h k l ) planes make the angle &  with the incident  ray; they give r i s e to a ray d i f f r a c t e d through an angle 2 0  .  The rays d i f f r a c t e d by the plane of one family cover the surface of the cone of revolution having the incident ray as axis and a v e r t i c a l angle of 2 6  .  A cone of d i f f r a c t e d rays corresponds  to each l a t t i c e plane of the c r y s t a l , provided t h * i t s spacing i s greater than  A / 2 , so that the Bragg r e l a t i o n s h a l l give a  value of s i n 9 l e s s than unity.  To record these refracted rays  conveniently, a photographic f i l m i s f o l d e d into a cylinder whose a x i s , normal to the incident ray passes through the  specimen.  The cones of d i f f r a c t e d rays appear as a series of curves along the c y l i n d r i c a l f i l m .  For small Q  angles the curves surround  the trace of the d i r e c t beam, f o r large @ point where the 2 - r a y s enter the cylinder. meter of a ring i s equal to 4 (9 &,R camera; from i t s measurements $  they surround the The dia*.':.u'..'.'.•..•'-  being the radius of the  i s deduced, and thence, using  the Bragg equation, we obtain the d i f f e r e n t planes of the c r y s t a l . The specimen was ground in'an agate mortar.and only p a r t i c l e s smaller than 0.08 mm. mination.  by screening  were used f o r X-ray deter-  A very f i n e f i b r e of the Lindemann glass was coated  with adhesive (special grease) and covered with the powder. f i b r e was centred i n the camera.  The r a d i a t i o n used was that of  copper target with a n i c k e l f i l t e r to remove the /3 The exposure time was 10 hours. washed and d r i e d .  The  radiation.  The f i l m was developed, f i x e d ,  The r e s u l t s were not s a t i s f a c t o r y .  The  lines  were too feeble and because of the long exposure time the f i l m was heavily blackened.  Some l i n e s were missing completely and  i n place of some were diffuse bands.  When the procedure  was  39 repeated the same kind of r e s u l t s were obtained,  'i'his was  caused mainly by two f a c t o r s : 1.  small size of c r y s t a l l i t e s present.  2. because of the low atomic scattering c o e f f i c i e n t f o r boron and nitrogen, long exposure time was needed and therefore the f i l m blackened badly. These d i f f i c u l t i e s could be removed by: 1. r e c r y s t a l l i z a t i o n of the sample. 2. using pure monochromatic radiation (using prism). Because we could not carry out either of these, the only chance was t o use, riot the f i l m f o r taking the picture of the pattern, but the Geiger-Muller counter charts.  The basis of the  Geiger-Muller counter f o r the detection.of the X-rays i s the property of X-rays t o ionise atoms i n a ^convenient  atmosphere.  The experimental set up i s b a s i c a l l y l i k e t h i s ; along the axis of a metal chamber f i l l e d with a convenient atmosphere is- stretched a f i n e wire.  A continuous p o t e n t i a l d i f f e r e n c e i s established  between the wire and the walls, which i s just not s u f f i c i e n t l y high f o r a discharge.  I f , however, an ionising p a r t i c l e traverses  the counter the discharge i s t r i g g e r e d . Electronic relays can be used to count the discharges and hence the p a r t i c l e s received by the counter.  The mean current produced by the sum of the  discharges i s measured. • As a result we get a graph which gives us the i n t e n s i t y of the refracted beams as a function of the angle  .  From the  graph we can determine the p o s i t i o n of the peaks and therefore d i f f e r e n t angles and by using the expression: Slh 9 - £ f t \^J^„  ll  l  if. Li  a>  u  £  i  j  40 we can determine the dimensions of the unit c e l l i n the same way as from the f i l m . The positions of the peaks can not be determined as exactly as f o r the f i l m , but f o r our determination t h i s method should give s a t i s f a c t o r y r e s u l t s . During our study we made 1 7 of those charts.  .Naturally our  main attention was directed towards boron n i t r i d e and the boron nitride-chromyl chloride  complex.  F i r s t we made an X-ray pattern of our samples of boron nitride.  The three main l i n e s representing the r e f l e c t i o n from  the planes 0 0 2 ,  1 0 1 , and 1 0 0 were found on a l l the samples.  The  d i f f r a c t i o n pattern corresponding to these planes were found i n the Eimer-Amend sample: TABLE I I I . D i f f r a c t i o n Pattern of BN. Index of the l i n e  d(experimental from & )  d(calc. from -I)  Relat: inten-  3.347  100  20°10'  2.236  50  2.170  20°40'  .2.184  20  101  2.120  21°25  2.116  .70  102  1'.805  25°25'  1.796  15  004  1.660  27°25'  1.674  20  103  1.502  29°38»  1.510  20  104.  1.420  32°35'  1.433  10  110  1.251  39°10  1.240  20  112  1.173  40°55  1.177  10  002  3.3306  13°19  003  2.2204  100  !  T  !  !  41 Our main i n t e r e s t was t o estimate i f the of  boron n i t r i d e which e q u a l s 1/2  inter l a y e r spacing  c = 3.33A as given by R.  Pease (32) does change a f t e r i n t e r c a l a t i o n w i t h chromyl As a r e s u l t  o f our study we  can say:  S.  chloride.  On a l l the c h a r t s the peak  c o r r e s p o n d i n g t o 002 planes w i t h d =» 3.347A i s present even a f t e r i n t e r c a l a t i o n of chromyl c h l o r i d e and i t i s of the h i g h e s t relative intensity.  The p o s i t i o n of the peak i s p r a c t i c a l l y  unchanged so that we have t o assume t h a t i n t e r l a y e r s s p a c i n g d = 1/2  c = 3.33A i s p r e s e r v e d .  i n t e r c a l a t i o n o f chromyl  A l l t h i s i s v a l i d f o r the  c h l o r i d e at temperatures  to 150°C.  The  d i f f r a c t i o n p a t t e r n of the complex prepared a t h i g h e r tempera t u r e s i s d i f f e r e n t from t h a t o f boron n i t r i d e . peak w i t h the index d  There i s a  new  8.25A ( i n t e n s i t y 100) which i s i n a N  l o c a t i o n s i m i l a r to t h a t o f i n t e r s t i t i a l The main peak of boron n i t r i d e a t 3.4A peaks w i t h the indexes 3.49  compound by g r a p h i t e .  broke down i n t o two  small  and 3.3#A (graph 3 ) .  The p a t t e r n of molybdenum d i s u l f i d e and the complex o f molybdenum d i s u l f i d e w i t h chromyl c h l o r i d e were i d e n t i c a l As a r e s u l t  of our X-ray  study we  (graph 4).  can s a y t h a t t h e r e i s no  s u b s t a n t i a l change i n the i n t e r l a y e r s p a c i n g o f boron  nitride.  But d u r i n g our p r e v i o u s i n v e s t i g a t i o n on t h e complex o f g r a p h i t e w i t h chromyl we  c h l o r i d e , which was  announced by C r o f t i n 1951  (7),  got the same composition as he d i d 39% of c h r o m y l . c h l o r i d e  but we  c o u l d not index an i n t e n s i v e new  peak a t a l a r g e r d i s t a n c e  and the peak f o r g r a p h i t e corresponding t o d = 3.34A was f o u n d at the d i f f r a c t i o n p a t t e r n of the complex with t h e i n t e n s i t y  100.  No peaks corresponding to t h e b o r i c oxide or a c i d were found on the p a t t e r n of boron n i t r i d e - c h r o m y l c h l o r i d e complex, which  42 i s a further proof that the oxidation of boron n i t r i d e to boric oxide does not occur. Because from the indexing of. the peaks of boron n i t r i d e we found that corresponding angles and distances d are i n f a i r agreement with the data of other workers, i t i s highly improbable that the displacement of the peaks would not be observed i f i t r e a l l y d i d happen. In the case that chromyl chloride does not enter a l l the i n t e r l a y e r spacings but only.some of them, e.g. i n the case of the compound (BN)^ CrC^C^ every s i x t h layer, the value of d =  3.33A  of boron n i t r i d e would be predominant at the d i f f r a c t i o n pattern of the complex.  The large d corresponding to every s i x t h spacing  would be not easy to detect, because of low i n t e n s i t y and the small angle problem. 3.  The Experimental Results of the Kinetic Study of the System Boron N i t r i d e - Chromyl Chloride. The reaction of boron n i t r i d e with chromyl chloride  was studied at 24.1°, 67.1° and 117.0°C.  These three temperatures  were selected because of the easy control of temperatures i n t h i s range.  At 24.1 and 67.1°C. the weight amount of boron n i t r i d e  were reacted with excess of chromyl chloride i n a thermostat. The control of temperatue was checked by using a Taylor temperature recorder.  The range i n temperature d i d not exceed 0.1°C.  The study at 117°C. was made by means of refluxing boron n i t r i d e with chromyl chloride at the b o i l i n g point of chromyl chloride. Because the chromyl chloride was prepared by the same method a l l the time and the product was p u r i f i e d by r e d i s t i l l a t i o n , the  amount of boron n i t r i d e i n a l l t r i a l s was approximately the same (usually 0.5 gms.)  and therefore the refluxing temperature  should be s u f f i c i e n t l y constant. In a l l the t r i a l s a p r e c i s e l y weighed amount of boron n i t r i d e was reacted  i n a 100 ml. round bottom f l a s k with an  excess of chromyl chloride. was used.  U g l i l y 2-3 ml. of chromyl chloride  A short time at the beginning of the reaction  3-4  minutes was allowed f o r the heating of the mixture to the preselected temperature.  After the chosen reaction time the mix-  ture was treated with carbon tetrachloride which dissolves chromyl chloride.  The content of the f l a s k was quantitatively  transferred to a f i l t e r by making use of large amounts of carbon t e t r a c h l o r i d e . "When the carbon t e t r a c h l o r i d e used f o r washing l o s t a l l the colour which was due to dissolved chromyl chloride, the residue was dried at 1 1 5 ° C hours.  i n an e l e c t r i c heated oven for two  After t h i s treatment there should not be any free  chromyl chloride present.  The difference i n weight of the  product and the i n i t i a l weight of the boron n i t r i d e was taken as the amount of chromyl chloride i n the compound.  From the  difference the percentage of chromyl chloride and the stochiometric ratio, was determined.  The r e l a t i o n of chromyl chloride  bonded to boron n i t r i d e as a function of time i s to be seen on the graph V. We see from the graphs that the equilibrium composition i s attained at the highest temperature (117.0°C.) a f t e r 12 hours. At the lower temperatures the composition i s not constant and i s s t i l l r i s i n g even a f t e r reaction time of over 40 hours.  The  44 type of curves f o r a l l three temperatures i s very s i m i l a r i n shape.  The f i r s t part i s very steep and therefore the actual  determination of points f o r reaction times lower than 30 minutes i s not r e l i a b l e . the  The general type of the curves and e s p e c i a l l y  f a s t reaction at the beginning i s i n a very good agreement  with r e s u l t s which Croft obtained f o r d i f f u s i o n of f e r r i c chloride i n the graphite l a t t i c e ( 9 ) . For  better understanding of the f i r s t f a s t stage of the  reaction, we lowered the concentration of chromyl chloride by using i n the place of pure chromyl chloride i t s d i l u t e d solution in carbon t e t r a c h l o r i d e .  We used two concentrations:  1.  25% solution of C r 0 C l  2  i n CCl^.  2.  5%> solution of C r 0 C l  2  i n CCl^.  2  2  The general type of the plot of composition versus time did not change, only the amount of chromyl chloride which was bound t o boron n i t r i d e was lower f o r the same temperature and time.  It  i s remarkable that the formation of the boron n i t r i d e - chromyl chloride complex takes place even from the solution. If we plot the log of the chromyl chloride absorbed vs. time, the f i r s t part of the reaction corresponds t o a straight line.  This represents the f i r s t order reaction.  applicable only i n a short range. changes.  But i t i s  After the rate of the r e a c t i o n  This feature i s c h a r a c t e r i s t i c of heterogeneous reactions.  The next step i n our k i n e t i c study was t o determine the d i f f u s i o n c o e f f i c i e n t f o r the reaction.  When we assumed that the  d i f f u s i o n c o e f f i c i e n t does not change with concentration we got  large disagreement reaction times.  with experimental values, mainly at shorter  Therefore we had to assume the existence of  two c o e f f i c i e n t s , one which has a constant value D = D-^ to a certain concentration c-j_ and then drops to a lower constant value D = D  2  for c  2  greater than c^.  The same kind of r e s u l t  was derived by Croft f o r d i f f u s i o n of f e r r i c chloride into graphite (9).  .The constant D]_/a was determined to give exact 2  agreement at 60 minutes and Dj^/a at 3, 4 and 6 hours f o r the 2  three temperatures.  The r e s u l t s are given i n Tables IV, V and  VI i n the Appendix. The constant D^/a  2  was determined  so as. to give agreement 2  f o r a l l three temperatures  at 60 minutes.  The constant D;?/a  i s "chosen so as t o give agreement at 1#0 min. f o r 117.0°C, at 240 min. f o r 67.1°C. and 360 f o r 24.1°C. By using the two d i f f u s i o n c o e f f i c i e n t s f o r each temperature we got f a i r l y good agreement between the experimental and calculated values. obvious.  The evaluating of the 0/Qoo (obs.) i s  It i s the r a t i o of the amount of chromyl chloride i n  the compound at d i f f e r e n t reaction times t and the amount of the same substance i n the compound when equilibrium composition was attained. The calculated values were obtained i n the following  g (6> )  Q/Q = o0  g (8 ) For evaluating g ( 6* ) from v  way:  =  1-4 f  exp(-/& S)//3«J  we can use the arithmetical t r e a t -  ment (we have to f i n d the Bessel function of tye type J (G> ) - 0 0  where (h are the roots of t h i s function and S evaluate the g (Q )  •  Dt/a  2  and so  Q/QpoUalc.) f o r the sets of fh  and $ .  46 The other way g (0  ) vs. &  i s the graphical.  Because we had the plot of Plot of the g (c9 ) vs. &  we used t h i s method.  i s to be seen i n the Figure* VII.',  «  1  0.2  1  0  0.4  ——t  1  0.6  >  0.8  As mentioned before we assumed the agreement between the t h e o r e t i c a l and experimental values at a certain time. g (# )  -  Q/Q*>  (obs.)  We get the value f o r g ( $ ): from the plot we determine the 6 corresponding to t h i s value of g (& ).  From the 0  by d i v i d i n g  i t by the time, we got the value of the constant D/a . 2  0  constant was used f o r c a l c u l a t i n g  This  's and from the plot  determining g's ( $ ) f o r a l l the other time i n t e r v a l s . The evaluating of the D/a i t a f t e r f o r calculating the  2  from experimental data and using (calc.) f o r the other times  Q/Qoo  was the only f e a s i b l e way to solve the problem.  The other picture  where the d i f f u s i o n constant f a l l s o f f l i n e a r l y with concentration was not solved even approximately  ( 3 ) and therefore t h i s t r e a t -  ment w i l l be no more rigorous than ours and the treatment w i l l be more complicated.  mathematical  47 Having derived the d i f f u s i o n c o e f f i c i e n t s at three d i f ferent temperatures we were able to determine the a c t i v a t i o n energy of the process by p l o t t i n g the l o g of the d i f f u s i o n coe f f i c i e n t vs. l / T . We got two plots and subsequently two a c t i v a t i o n energies, one f o r the f i r s t fast stage of the reaction and one f o r the second slower one (Graph V I ) . The a c t i v a t i o n energies were determined from the plot I and I I . from the r e l a t i o n :  the slope  = -E/2.303R • -E/4.5#  For the f i r s t stage of the reaction the a c t i v a t i o n energy equals 5.0 k c a l . and f o r the second part 6.1 keal.  The higher a c t i v a t i o n  energy f o r the second stage can be related t o the f a c t that the chromyl chloride molecules- i n the l a t e r stage have to overcome a higher energy b a r r i e r to d i f f u s e more into the centre of the p a r t i c l e s than at the beginning.  Because the change, i s quite  small, the more substantial difference  i n the d i f f u s i o n co-  e f f i c i e n t w i l l be apparently due t o the changing value of the p r o b a b i l i t y factor, than only to a change.in a c t i v a t i o n energy. In general we can say that the values of the activation energies are of the order of magnitude which we could expect in regard to similar processes.  Croft  (9) found the activation  energy f o r the d i f f u s i o n of f e r r i c chloride into graphite 3.1 k c a l . The evaluation  of the d i f f u s i o n c o e f f i c i e n t s and the  a c t i v a t i o n energies was the goal of our k i n e t i c  investigation.  46  4.  Other Lamellar Compounds Prepared. Because of the s i m i l a r i t y to graphite as mentioned  before, we t r i e d to prepare i n t e r s t i t i a l compounds of the d i s u l f i d e s of molybdenum, tungsten and uranium.  A l l these substances  have layer structures and the s i m i l a r i t y to graphite i s immediately apparent.  They are black powders, where one plane  can e a s i l y s l i p over the other, which gives them the l u b r i c a t i n g properties of graphite. Because of the substantial gain i n weight of boron n i t r i d e with the chromyl chloride we t r i e d the same reaction with the three mentioned s u l f i d e s . The procedure was e s s e n t i a l l y the same as i n the case of boron n i t r i d e .  The temperature used was 1 1 7 . 0 ° C . and the r e -  f l u x i n g time 4 6 hours. out  Carbon tetrachloride was used f o r washing  the excess of chromyl chloride.  The following table shows the  r e s u l t s obtained. TABLE 711 Composition of Molybdenum, Tungsten and Uranium D i s u l f i d e Complexes % CrOoClo  Substance Mo S  2  - Cr0 Cl2 2  2  - Cr0 Cl 2  2  2  - Cr0 Cl 2  2  17.35  (MbS ) Cr0 Cl  33.0  (W S ) C r 0 C l  2  34.25  (U S ) C r 0 C l  2  33.5 32.5  U S  Formulas  16.6 17.5  ¥ S  Mean  34.5 34.0  2  2  2  6  5  1  2  2  2  2  49 As a result of the d i f f r a c t i o n pattern of M0S2 - CrC^C^ i t can be said that there i s no change i n the i n t e r l a y e r spacing of M0S2 a f t e r reaction with chromyl chloride. The  case of t h e sulfides i s s i m i l a r t o that of boron n i t r i d e .  There i s a substantial weight increase  a f t e r the reaction with  chromyl chloride, which can be "boiled o f f " by heating the complex to 500°G.  'i'he d i f f r a c t i o n pattern shows that the distance  -between two layers i s the same as i t was before.  The same State-  ment as f o r the complex of BN with chromyl chloride i s v a l i d . I f the i n t e r c a l a t i o n of chromyl chloride into M0S2 l a t t i c e occurs only i n every sixth layer, the change i n d w i l l not be easy to detect.  III.  DISCUSSION OF RESULTS  The results which were obtained can be treated under four headings: 1.  Composition and s t a b i l i t y of complex of boron n i t r i d e with chromyl chloride.  2.  Results of the X-ray study of the complex.  3.  The k i n e t i c r e s u l t s .  4.  The q u a l i t a t i v e evidence of p o s s i b i l i t y of the formation of the complexes of a) of other substances which boron n i t r i d e , b) of chromyl chloride with the d i s u l f i d e s of molybdenum, tungsten and uranium.  The accuracy of the r e s u l t s i s f a i r l y good f o r a problem of t h i s kind.  The errors correspond i n the order of magnitude t o  other similar studies of s o l i d substances.  The investigation  was complicated by the fact that boron n i t r i d e i s a c t u a l l y s t i l l a substance, where the physical , chemical properties and bonding are explained f a r l e s s s a t i s f a c t o r i l y than with graphite. Many references i n the l i t e r a t u r e are i n disagreement,  which i s  probably because many workers were not dealing with the pure material.  The influence of the temperature  of preparation on  the properties of boron n i t r i d e i s remarkable. The loss of chromyl chloride on heating of the complex, the p o s i t i v e results of the q u a l i t a t i v e tests f o r Cl~and C^Oy ions by hydrolysing the complex and the r e s u l t s of titration of C^O^  -  indicate strongly that chromyl chloride i s present i n boron n i t r i d e i n the o r i g i n a l form.  This i s f u r t h e r supported by the  absence of the peaks c h a r a c t e r i s t i c of boric oxide, the possible oxidation product and of C r O o the possible reduction product ?  51 used i n the d i f f r a c t i o n pattern of the complex.  The value of  the activation energy f o r the process 5 k&al.' i s i n agreement with the previous f a c t s .  I f there should be an ..ordinary  chemical reaction, the a c t i v a t i o n energy would have to be much higher, usually over 20 k c a l .  The same value of the a c t i v a t i o n  energy i s required f o r chemisorption.  The van der Waals'  adsorption would have the activation energy of the order of magnitude of 5 k c a l . but the following fact speaks strongly against t h i s . With increasing temperature  the equilibrium amount of  Cr02Cl2 bounded to boron n i t r i d e i s unchanged t o 150°C. For van der Waals' adsorption the amount adsorbed at lower temperature would be higher.  This i s i n disagreement  with our  results. . On the other hand, i f we assume the formation of the i n t e r s t i t i a l compound of chromyl chloride with boron n i t r i d e s i m i l a r to those of graphite, a l l the experimental evidence agrees very well with the f a c t s observed i n graphitic compounds and the t h e o r e t i c a l predictions, there being only one important ference.  dif-  We did not f i n d the increase i n the i n t e r l a y e r spacing  which i s connected with the formation of s i m i l a r compounds of graphite.  I t i s quite d i f f i c u l t t o imagine the i n t e r c a l a t i o n of  chromyl chloride into the i n t e r l a y e r spacing without changing the distance.  The p o s i t i v e results of the reaction of boron n i t r i d e  with aluminum chloride (64% intercalated) and cupric chloride (47.$intercalated) support the lamellar compounds formation theory.  52 If we summarize a l l the deductions, we can say that there i s a compound formation between chromyl chloride and boron n i t r i d e connected with a l l the f a c t s c h a r a c t e r i s t i c f o r i n t e r lamellar compounds known but the absence of the increase of the i n t e r l a y e r distance.  In the case that chromyl chloride does  not enter a l l the i n t e r l a y e r spacings but only some of them, e.g. i n the case of the compound (BN)^Cr0 Cl 2  2  every sixth layer,  the value of d = 3.33A of boron n i t r i d e would be predominant i n the d i f f r a c t i o n pattern of the complex.  The large d corresponding  to every sixth spacing would not be easy t o detect, because of the low i n t e n s i t y and the small angle problem.  The reactions of  aluminum chloride and cupric chloride with boron n i t r i d e and chromyl chloride with the s u l f i d e s of molybdenum, tungsten and uranium show that formation of the i n t e r s t i t i a l compounds by substances s t r u c t u r a l l y s i m i l a r to graphite i s to be expected.  IV.  SUGGESTION FOR FURTHER RESEARCH  Further research on the subject of lamellar compounds can be i n two d i r e c t i o n s : 1.  Intercalation of new substances into graphite,  boron n i t r i d e and s u l f i d e s of molybdenum, tungsten and uranium. 2.  Try t o intercalate chromyl chloride, aluminum  chloride and other substances which were intercalated graphite or boron n i t r i d e into new substances. most successful  into  Very probably  i n t h i s d i r e c t i o n should be the substances .  with layers or some other kind of loose  structure.  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Chem. Ber. 34 *• 3039. 1901.  74. I85O.  A P P E N D I X  TABLE IV T h e o r e t i c a l & E x p e r i m e n t a l R e s u l t s o f the D i f f u s i o n Study a t Three Temperatures Temperature: 1 1 7 ° C . Dj/a . 2  0.0030  Time, minutes  30  60  Q/Qoo(exp.)  .628  .746  Q/Qco (calc.)  .615  .740  D /a 2  90  120  180  240  .780  .800  .835  .775  .810  .835  300  2  -  0.00125  360  .420  480  600  .872  . 8 9 2 .907  .926  .943  .980  .875  . 8 9 0 .900  .930  .950  Q i s the amount o f chromyl c h l o r i d e i n t h e compound a t time t Q 0 0 i s the e q u i l i b r i u m o f chromyl c h l o r i d e i n t h e compound = . 5 6 gm. of CrOgGlg i n 1 gm. o f t h e complex.  .975  TABLE V Temperature Dj/a  -  2  30  Time, minutes  67.1°C.  0.0011  60  D /a  =  2  2  90  120  180  240  300  360  0.00035  420  480  600  Q/Qoo (exp.)  .455  .490  .515 .545 .5^0 .600 .620 .268 .635 .654 .665  (calc.) Q/Qoo  .425  .490  .520  .560 .570 .600 .620 .635 .650 .670 .690  TABLE ¥1 Termperature 2 4 . 1 ° C . Hi/a Time, minutes Q/Qco(exp.) Q/Qerf?(calc.)  2  30  0.00044, 60  *' 9 0  .091 .136  .183 —  D  120  180  240  .200 .237 .272  2/  300  a  2  =  360  0.00011 420  480 600  .308 .327 .348 .363  .400  .200 .240 .280 .300 .327 .340 .370.410  TABLE V I I I Influence  of Source on Composition o f BN + C r 0 C l 2  Source of BN Eimer and Amend Co.  Composition % BN 64.6 Cr0 Cl 35.4 2  Fairmont Co. ,  M  10.5  ( C r  °2  G 1  2)  2  BN 43.3 Cr0 Cl  56.7  BN  4 # 7  (Cr0 Cl )  BN 45.5 Cr0 Cl  54.5  BN  5 < 2  (Cr0 Cl )  BN  5 # 7  (Cr0 Cl )  2  Our own sample  Formula  BN6.5(Cr0 Cl )  2  F i s h e r Co.  Complex  BN 51.0 Cr0 Cl 49.0 2  MacKay Co.  2  2  2  BN 48.0 Cr0 Cl 52.0 2  A l l Temperatures  2  2  2  2  - 117°C.  Time of R e f l u x i n g =  48 hours.  2  2  2  2  2  2  Figure S i f e i IA BN  generator. Heating No. 3  asbestos insulation  Tube t o t h e t r a p and out • Heating No. 2, i three c o i l s  Heating No.  dry +  H  1  2  BC1,"  Pt-Rh thermocouple  GRAPH I I . . Temperature i n f l u e n c e on cproposition o f BN + C r Q p C l  ?  complex  Time o f r e a c t i o n : 4$ hours  ioo r  SO  60  40  Reaction t i m e : 92  hours  <2>  not  51  equilibrium  values  20(  100  T#uipera£u.r« ir 1  » w  J5C  300  '•50  400  GRAPH I I I . X-ray d i f f r a c t i o n  patterns.  The nuraturs a t the top of trie p e a k s give d, separation i n A, The r e l a t i v e heights of the peaks a t a l l three p i c t u r e s are preserved. 1*  BN .+ I*  ^  ^  J  2  \*  tf*  1  BN  "  Cr0 Gl  +  C r 0  2  — 250°C., 85% C r p C l  2  A'  S  C 1  2  2 "~  1 1 7  ° -» c  57% C r 0 C l 2  2  2  Content.  Content  —  BN. - o r i g i n a l sample.  . 1<  36  ,1*  V  .  ^  Glacing angle  63  71  •<7o  GRAPH IV. X-ray d i f f r a c t i o n MoS  + 2  Cr0 Cl  Cr02Cl2  The  relative  2  2  patterns of: - 117°C.,  content,  17%.  h e i g h t s of thepeaks a t b o t h p i c t u r e s are  preserved.  GRAPH  Time of r e f l u x i n g v s .  0«  :  1 — —  .  10  20 Time  V.  composition o f C r 0 C l 2 • BN 2  :  ,_  30 Hours  GRAPH V I . A c t i v a t i o n energy g r a p h . Plot  of^Sj/a  2  and D / a 2  vs. 1 f Slope  3.0  -1-  .00200  -i 1• 1-0250'  -.00300 t—e 1/T  -  ,S  OS  2  

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