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A radiochemical study of the mechanism of polishing glass Smith, John Graham 1951-12-31

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£ p. I 0  A RADIOCHEMICAL STUDY OF THE MECHANISM OF POLISHING GLASS  by JOHN GORDON SMITH  A THESIS SUBMITTED I N PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF ARTS i n t h e Department of Chemistry  We a c c e p t t h i s t h e s i s as conforming t o t h e standard required fr^m candidates f o r the degree of MASTER OF ARTS/ . -  Members of t h e Department o f Chemistry THE UNIVERSITY OF BRITISH COLUMBIA  September, 1951  Ill ABSTRACT I n an e f f o r t t o d e t e r m i n e whether g l a s s flows when p o l i s h e d u r a n i u m g l a s s e s were fused t o non u r a n i u m g l a s s e s and p o l i s h i n g s c a r r i e d out i n a d i r e c t i o n from t h e a c t i v e t o t h e i n a c t i v e s i d e . S o d a - l e a d - s i l i c a t e and phosphate g l a s s e s were p o l i s h e d w i t h rouge and c e r i c o x i d e .  To l o c a t e any of t h e u r a n i u m g l a s s w h i c h may  have been t r a n s f e r r e d d u r i n g t h e p o l i s h i n g , n u c l e a r t r a c k were u s e d .  Thus by a u t o r a d i o g r a p h s t a k e n b e f o r e and  p o l i s h i n g , any a l p h a p a r t i c l e s from t h e u r a n i u m g l a s s  plates  after transferred  t o t h e s i d e of t h e non u r a n i u m g l a s s would have r e g i s t e r e d on t h e developed p l a t e s . 4 . 5 A° flowed  This method was oapable of d e t e c t i n g a  l a y e r or c h i p s of u r a n i u m g l a s s 0.019 mms i n d i a m e t e r .  No e v i d e n c e of any f l o w , was found by t h e  g r e a t e r t h a n over a d i s t a n c e o f 0.2 mms,  authors.  Experiments were a l s o c a r r i e d out u s i n g r a d i o a c t i v e c e r i c oxide.  Thus i f t h e c o n t a c t temperatures  reached d u r i n g p o l i s h i n g  approached t h e s o f t e n i n g p o i n t of t h e g l a s s i t was reasoned t h e agent might, have become fused w i t h t h e p o l i s h e d s u r f a c e .  that By -7  u s i n g t h i s method i t would have been p o s s i b l e t o d e t e c t 2 . 3 X 10 grams of Ce02 spread over 6 crn^ on t h e s u r f a c e of t h e g l a s s . assuming t h a t t h e C e 0  2  By  would f u s e w i t h and become p a r t of t h e g l a s s  i t was p o s s i b l e t o d e t e c t a 15 A° l a y e r of t h i s changed g l a s s , i f 10% of t h i s changed g l a s s was CeOg. of any f u s i o n of t h e C e 0 p o l i s h i n g used i n t h i s  2  The a u t h o r s found no e v i d e n c e  w i t h the g l a s s under t h e c o n d i t i o n s of  project.  TABLE OF CONTENTS  Page INTRODUCTION  1  GENERAL METHOD OF ATTACK  5  EXPERIMENTAL  7  (a) PREPARATION OF GLASSES ( l ) S i l i c a t e Glasses F i g . I Sohematic Diagram of E l e c t r i c Resistance Furnace (2) Phosphate Glasses (b) GRINDING AND POLISHING EQUIPMENT Photograph I Polishing Apparatus Photograph I I Apparatus f o r Polishing with Radioactive Cerio Oxide (o) AUTORADIOGRAPHIC MEASUREMENTS (1) Emulsions (2) Development of Plates (3) S e n s i t i v i t y of the Photographic Method (4) Determination of Polishing Compound Transferred to Glass RESULTS  21  Autoradiographs of Glasses Polished with Radioactive Cerio Oxide DISCUSSION  35  FUTURE WORK  39  BIBLIOGRAPHY  40  II  ACKNOWLEDGMENT  Grateful thanks are extended t o Dr. J.G. Hooley, under whose d i r e c t i o n this investigation was carried out. Through his knowledge and experience i n the f i e l d s of r a d i o a c t i v i t y and glass, Dr. Hooley imparted invaluable advice i n the development of the techniques used i n this  project.  INTRODUCTION Before polishing glass, the surface i s ground to the desired contour with an abrasive such as emery, alumina, or carborundum s l u r r i e d with water on a revolving iron form. recognized  This process i s  to be.one of chipping p a r t i c l e s of glass away from the  surface and  leaves the l a t t e r rough and  translucent.  In the ensuing polishing, a f i n e r powder i s used, s l u r r i e d with water on moving f e l t or wax.  The powder p a r t i c l e s must be  hard and insoluble and have a melting point higher than the softening point of the glass being polished.  They must also  not be too f i n e as shown by S i r H. Jackson's f a i l u r e to p o l i s h 1 glass with the very f i n e powder obtained  from an i r o n arc.  Rouge and ceric oxide are both i n common use today and were used i n our work. There are three schools of the polishing operation.  of thought about the mechanism The f i r s t claims that i t i s simply  a continuation of the grinding operation, a chipping off process, continued  to such a degree of fineness that the r e f l e c t e d l i g h t  waves cannot show any measurable amount of straying.  The second  believes that the f r i o t i o n a l heat of polishing raises the surface temperature to the softening point of the glass and thereby smooths the surface by an actual flow of glass. claims a combination of these two mechanisms.  The t h i r d  - 2 -  The evidence for these alternatives w i l l now be considered. POLISHING IS A CONTINUATION OF THE GRINDING PROCESS 2  Sir George Beilby reported that the flawed layer on orystals, such as caloite, was vastly tougher than the crystalline material below.  He interpreted this toughening as being due to a non-  crystalline flowed layer.  This layer was considered to be tougher  for i t was able to resist the cutting action of the agent by which 3 the original surface had been satisfactorily ground.  Preston,  however, found nothing of this sort with glass for he was unable to detect any progressive toughening of the glass with prolonged polishing.  He found that material came off steadily at the same  rate whether the glass was quite "grey" or had been polished for many hours.  From this he concluded that the flowed film, i f i t  existed at a l l , had no direct influence on the process and that mechanical abrasion, i.e., the complete removal of glass was the conspicuous feature. Further evidence supporting this mechanism may be obtained 4 from the method Strong recommends for the polishing of precision lenses and prisms.  He uses wax instead of f e l t as the base,  and recommends that the contour of the wax base be altered i n order to remove any high spots which may have been left on the surface after the i n i t i a l polishing.  This prooedure of altering  the wax base i s continued until the surfaoe becomes planar.  This method of e l i m i n a t i n g h i g h s p o t s suggests t h a t t h e f e a t u r e of t h e p o l i s h i n g o p e r a t i o n  important  i s t h a t of a removal of  glass.  THE SURFACE IS SMOOTHED BY AM ACTUAL FLOW OF GLASS 5  D r e y e r and E r t e l used a t e c h n i q u e w h i c h a f f o r d e d differentiating  a means of  between a s u r f a c e w h i o h had been p o l i s h e d and a  s u r f a c e w h i c h had been ground.  They a p p l i e d a l i g h t  polarizing  s o l u t i o n c a l l e d " p o l a c o a t " t o the s u r f a c e b e i n g s t u d i e d . s o l u t i o n on d r y i n g t a k e s on the which i t is i n contact.  orientation  of t h e s u r f a c e w i t h  When t h i s s o l u t i o n was a p p l i e d onto a  polished surface a uniform polarized f i l m resulted v i s i b l e record  This  and l e f t  of t h e s u r f a c e , w h i l e w i t h a rough s u r f a c e  p o l a r i z a t i o n was n o n - u n i f o r m .  They removed a p o l i s h e d  on p l a t e g l a s s by r u b b i n g w i t h w h i t i n g , an a b r a s i v e  a the  layer  material.  Then, when " p o l a c o a t " was a p p l i e d t o t h i s s u r f a c e , the marks made i n t h e  o r i g i n a l g r i n d i n g of the g l a s s r e a p p e a r e d .  e x p l a i n e d t h i s by a f l o w , f l o w e d over d u r i n g  i.e.,  They  t h e o r i g i n a l g r i n d i n g marks were  polishing.  A n o t h e r argument i n f a v o u r of the flowed l a y e r i s t h e  so-  c a l l e d b u r n w h i c h i s u s u a l l y made when the t a b l e i s a l l o w e d 1 r u n too d r y . surface. solvents,  Burns may be i n c r u s t a t i o n s of rouge on the  glass  C h e m i c a l t e s t s show t h e s e t o ' b e i n s o l u b l e i n a l l and i n a g r e a t many cases may be removed by  to  organi  hydrofluoric  - 4 -  acid only.  However, burns are not necessarily incrustations  of rouge and i n some cases rouge may be absent.  A burn is  readily recognizable for i t is always raised above the surface of the glass.  In view of this i t would appear that they may be  particles of glass which have been removed during the polishing and re-attached later due to high contact temperatures.  Hence  i t may be reasoned that i f such high contact temperatures are reached during polishing i t may be possible that there is a smoothing action at work. POLISHING IS A COMBINATION OF FLOW AMD REMOVAL 6 Bayer, i n 1938, pointed out that when an attempt was made to improve a poor polish by further polishing, the effort proved fruitless.  He interpreted this as a different process at work  during polishing than during grinding.  He also stated,  " With proper fine grinding, after twenty minutes of polishing there w i l l be no unevenness, but only scattered depressions of grinding holes.  The surface has  already assumed an incipient shine and appears to the layman as 'finished'. At closer observation, however, there is s t i l l a general blueishness on the glass, which disappears with further working.  This i s occasioned by the flowing process, which takes place with dry polishing material, when the temperature of the glass surface i s so high that s h e l l edges of extraordinary small height extenuate into the s h e l l oups ".  Those who claim the operation i s a combination of the two processes maintain that glass i s removed during the i n i t i a l of polishing.  stages  They consider the wet polishing to be a continua-  t i o n of the grinding, the difference being one of rate.  From  such considerations i t i s evident that further polishing w i l l not improve the r e s u l t i n g surface.  For i f the areas which require  polishing l i e i n surface depressions they would remain untouched during subsequent p o l i s h i n g .  They believe that these areas are,  however, flowed over during the dry polishing.  GENERAL METHOD OF ATTACK To determine whether glass flows during polishing a piece of radioactive glass was fused t o a non radioactive sample and polishing carried out i n a d i r e c t i o n from the radioaotive side to the non radioactive side.  Autoradiographs taken before and  a f t e r polishing were used to show whether active glass flowed over to the inactive side.  Uranium was used as the source of  r a d i o a c t i v i t y because i t i s an alpha emittor.  One reason for  - 6 -  using an alpha emittor was because of the very short range of these particles.  Hence alphas originating below the surface  would not activate the emulsion for they would be effectively absorbed i n the glass.  This would result i n a sharp boundary  between the two glasses on the ensuing autoradiograph.  If a  beta emittor had been used a distinct boundary would not have resulted because beta particles originating below the surface would have caused a darkening on the side of the inactive glass in the resulting autoradiograph.  The other reason that an  alpha emittor was chosen is due to the fact that alpha particles register as distinct individual tracks i n nuclear traok plates. This affords a very sensitive method to detect minute amounts of such radioactive materials.  Soda-lead-silicate and phosphate  glasses were the types polished and were chosen because of their relatively low softening points. Another phase of this project was that of using a radioactive polishing oompound.  Thus i f sufficiently high contact tempera-  tures were reached during the polishing i t was reasoned that the agent might become fused with the glass, indicating that a flow would be possible.  Polishings were carried out using radio141  active ceric oxide.  After neutron irradiation Ce  particles and gamma rays.  emits beta  A Geiger counter was used for detect-  ing beta particles emitted from the radioactive agent incorporated  - 7 with the polished glass.  In cases where there was a s u f f i c i e n t  amount of a c t i v i t y transferred to the surface autoradiographs of the sample were taken to determine the d i s t r i b u t i o n of this a c t i v i t y .  EXPERIMENTAL  PREPARATION OF GLASSES (a) S i l i c a t e Glasses F i g . 1 i l l u s t r a t e s the e l e c t r i c resistance furnace used to prepare the soda-iead-silicate glasses.  The resistance wire was  50 m i l Platinum 10% Rhodium imbedded i n high grade alumdum cement. Some of the advantages this a l l o y possesses over pure platinum are: the t e n s i l e strength (at the operating temperature of the furnace) of the a l l o y i s considerably higher than that of 100$ platinums the rate of vaporization i s less than platinum;  and the melting  point of this a l l o y i s I860 °C whereas that of 100$ platinum i s 1773 °C.  The temperature of the furnace was controlled by a  Wheeloo Potentiotrol to  ±  20 °C.  Glasses of the following compositions were prepared: TYPE "A" Non Uranium Glass SiOg  56.5 per cent  SCHEMATIC DIAGRAM OF ELECTRIC RESISTANCE FURNACE  (To follow page 7)  KEY TO DIAGRAM  Pot eati omet er. Chromel - Alumel Thermocouple leading to inside of oven. Oven - clay core consisting of sixteen turns of the a l l o y , diameter - 9 cms height - 17 cms Insulation - Finely divided clay. Size of c i r c u l a r furnace diameter - 60 cms height - 43 oms Chromel - Alumel Thermocouple leading to outside of oven. Ammeter. Fuse. Cut-off  Control.  Variac. Source - 110 v o l t s . To P o t e n t i o t r o l . To P o t e n t i o t r o l .  - 8 TYPE "B" Uranium Glass This i s composition "A" plus 5% of i t s weight of U-jOg. Si0  53.7 per cent  2  Na 0 2  13.3  "  "  PbO  28.2  "  "  4.8  "  "  U 0 3  8  Batch materials used for the above compositions were: Si0  2  PbO, Na C0 , and U0 (N0 ) .6H 0. 2  3  2  3  2  2  The S i 0 was i n the form 2  of a very fine powder and was obtained from Linde.  The batch  was melted i n a cylindrical platinum crucible, 5 centimeters i n diameter and 4.5 centimeters i n height, at a temperature of 1160 °C for a period of 12 hours after the batoh had become molten. Immediately prior to being poured i t was heated to 1260 °C, then poured onto a previously heated graphite tray and placed in an annealing oven.  I t was kept at a temperature of 532 °C for 30  minutes, then allowed to cool to room temperature at a rate of 5 °C per minute. (b)  Phosphate Glasses  Glasses of the following compositions were prepared:  v.  - 9 TYPE "C Non Uranium Glass PgOj.  67.0  A1 0  4.0  "  »  BaO  19.0  "  "  CaO  10.0  2  3  per cent  11  n  TYPE "D" Uranium Glass This i s Type C" n  plus 5% of i t s weight of  P 0,-  63.7  o  U^Og. per cent  3.9  "  "  BaO  18.0  "  "  CaO  9.5  "  "  4.9  "  "  A1 0 2  U 0 5  3  8  TYPE "E" Non Uranium Glass This i s composition "D  tt  PgOpj A1,0„ I 3 BaO  but contains ••  PbO  U~0 .  instead of 63.8 3.8 18.1  o  per cent 11  "  u  "  CaO  9.5  "  "  PbO  4.8  "  n  - 10 -  Batch materials used f o r the phosphate glasses were: H P0 , A1 0 .3H 0, BaHP0 , C a ( H P 0 ) . H 0 , PbO, and UOg (NO^g.eHgO. 3  4  2  3  2  4  2  4  2  2  In the preparation of these glasses the batch was thoroughlymixed i n a beaker then added to a clay crucible and placed i n an ordinary laboratory blast furnace. A f t e r the batch had become molten the glass was allowed to remain i n the furnace f o r a period of 1 hour and 30 minutes.  I t was then  poured onto a previously heated graphite tray and placed i n an annealing oven, kept at a temperature of 500 °C f o r a period of 30 minutes, then allowed to cool to room temperature at the rate of 5 °C per minute.  When an attempt was made to j o i n the uranium glass  phosphate  (Type "D") to non uranium phosphate glass (Type "C")  i t was found that upon annealing and cooling a fracture developed at the j o i n .  To surmount this d i f f i c u l t y i t was  decided to use Type "E" instead of Type "C".  I t was hoped  that by adding the same percentage of PbO as of U 0  the co-  3 8 e f f i c i e n t s of expansion of these two glasses would be s i m i l a r . However, this also proved f r u i t l e s s with fractures occurring i n the same place.  In an e f f o r t to make such a j o i n two pieces  were placed end to end i n a graphite holder, a f t e r the ends had previously been polished.  Then the holder and glass were  placed i n a furnace and the temperature raised to 670 °C.  - 11 The glass flowed, hence a j o i n was made and the ensuing sample annealed by allowing the furnace to cool to room temperature i n a period of 15 hours.  This did not completely remove a l l the  s t r a i n , f o r a l l the samples developed a fracture near this j o i n i n the subsequent grinding and polishing procedure.  However,  only those samples whioh did not fracture a l l the way across the j o i n were used.  In some cases these fractures resulted i n  a complete break between the two glasses, the breaks occurring upon the removal of the samples from the discs after polishing, the samples having been adhered to the disos with wax,  GRINDING AND  POLISHING EQUIPMENT  The machine used i n this experiment was a standard commercial model, the rotating i r o n disc being 12 centimeters in.diameter. The i n i t i a l f i n e grinding was  performed on this diso, using a f i n e  grade of emery, s l u r r i e d with water.  Polishings were then  carried out by using a f e l t pad 10 centimeters i n diameter glued onto the diso. (5.5  In most of the polishings the standard weight  kilograms) supplied with the machine was used.  the flow of s l u r r y a gravity fed arrangement was shown i n the attaohed photograph I . rate of flow. averaged.  To regulate  constructed as  A pinoh cock controlled the  This was measured before and a f t e r polishing and  During polishing the sample was held by hand i n such  a manner as to ensure that the d i r e c t i o n of polish was always i n a d i r e c t i o n from the active to inactive side.  PHOTOGRAPH I (To follow page l l )  - 12 -  I n the polishings made with radioactive c e r i c oxide the s l u r r y was not applied by this arrangement but poured onto the disc from a beaker.  I n this case pressure was applied by hand  and not by the standard weight.  For these experiments the  polishing disc was completely covered by a l u c i t e dome with a pair of heavy duty rubber gloves f i t t e d into two conveniently placed holes cut i n t o i t s w a l l .  In addition to this dome a  small c i r c u l a r cellophane holder was b u i l t around the rotating disc.  These precautions were taken t o prevent radioactive  contamination to workers and surroundings.  Photograph II.  demonstrates this arrangement.  AUTORADIOGRAPHIC MEASUREMENTS (a) Emulsions For alpha measurement NTB - 3 plates were used.  An alpha  p a r t i c l e entering this emulsion i s registered as an i n d i v i d u a l track upon subsequent development of the plate, thus enabling a minute amount of an alpha emittor to be detected.  The alpha  tracks registered on the plates were counted on a B & L microscope with magnification of 560 X, with an occular disc i n the eye piece. (b) Development of Plates The procedure used f o r the development of the nuclear track plates i s given i n d e t a i l below.  PHOTOGRAPH  II (To follow page 12)  - 13 (1)  The plates were developed i n D - 19, diluted with an equal volume of water at a temperature of 4 °C f o r a period of 30 minutes.  Then two  volumes of water at a temperature of 22 °C were added and the r e s u l t i n g solution kept at room temperature f o r a further period of 30 minutes.  (2)  The plates were then placed i n a 2% acetic acid bath at 4 °C f o r a period of 30 minutes.  Strong  nitrogen a g i t a t i o n was applied while the plates were i n this stop bath.  (3)  Upon removal from the stop bath the plates were placed i n the f i x i n g solution, (30$ hypo) maintained at a temperature of 4 °C f o r a period of 1 hour.  A f t e r this time the f i x i n g bath was  allowed t o come to room temperature and strong nitrogen a g i t a t i o n was again applied.  The plates began t o clear approximately 5 hours a f t e r the commencement of the f i x i n g . of 15 hours.  The f i x i n g was continued f o r a period  Following this the plates were washed i n running tap  water f o r 3 or 4 hours. (o)  S e n s i t i v i t y of the Photographic Method  7 Cook and Hudswell were able to prepare t h i n films of U_0  Q  -  14  -  on platinum f o i l or stainless s t e e l by, (1)  Defining the area to be covered by the U^Og with a solution of n i t r o - c e l l u l o s e i n ether-alcohol.  (2)  Applying uranyl n i t r a t e i n pyridine to this area.  (3)  Heating gently to drive o f f the pyridine and to destroy the boundary, then they ignited t o convert the uranyl s a l t to U^Og.  They were able t o determine the amount of U^Og by weighing, finding i t necessary to follow this procedure since losses of uranyl s a l t or oxide may have occurred during i g n i t i o n . For the purpose of this experiment  i t was not p r a c t i c a l to  weigh out very small amounts of uranium, therefore i t was..decided to use the same method as Cook and Hudswell, but to omit the i g n i t i o n , hence eliminating the necessity of weighing.  A minute amount of uranyl n i t r a t e i n pyridine was prepared, -5  6.132 X 10  grams per ml of solution.  Of this solution 0 . 5 ml  was pipetted onto a previously cleaned pieoe of platinum f o i l . 2 An area of 9 cms  was defined on the platinum by painting a border  with collodion.  The pyridine was allowed to evaporate at room  - 15 temperature.  F i n a l l y , to expel any excess pyridine, the sample  was very gently warmed. taken of this area.  At this point an autoradiograph was  The track plate was placed d i r e c t l y over  this area and clamped.  A c a l c u l a t i o n giving the t h e o r e t i c a l  number of alpha tracks that this activated area w i l l give per cin^ i s given below.  Concentration of uranyl n i t r a t e  =  6.132 X 10"°  gms/ml  Quantity of uranyl n i t r a t e used  =  3.066 X 1 0 "  gms  Area covered  =  8.85 cm  Concentration of uranyl n i t r a t e  =  3.47  Time of exposure of autoradiograph  -  2 hours  t i of uranium  =  4.5 X 10  Molecular weight of uranyl n i t r a t e  =  502 gms  5  2  X 10"  9  6  gms/cm  2  years  The rate of decay of uranyl n i t r a t e f o r 3.47 X 10 ° gms per hour is given by,  .693-1  6.02  X  10  J  X  3.47  X  10  4.5 X 10 X 365 X 24 X 502 9  = But U  2 3 4  74 disintegrations per hour  i s i n equilibrium with U  alpha emittors.  2 3 8  therefore there are two  - 16 Therefore rate of decay, i f this amount i s spread evenly over one square cm. 148 disintegrations/hour/cm  2  However, only one half of the alpha particles w i l l activate the film.  For a 2 hour exposure this w i l l represent 148 alpha tracks/cm  Experimental  (Theory)  2  results:  Three different areas of this plate were counted.  When this  plate was observed under the microscope the d i s t r i b u t i o n of alpha tracks appeared to be random and no clumps were noticed.  To de-  termine the background two blank plates were also counted. Below are the results of these counts.  Area Counted  Ho. of alpha tracks  o  Blanks with no uranium  0.4228 cm 0.3881 "  59 53  Total area  0.8109 cm  Total number of alpha tracks  112 ± 10.6  2  o  Therefore number of alpha tracks/cm  138 ± 13  Sample  0.4101 cm  114  2  0.4536  "  128  0.4040  "  111  Total area  1.2677 cm  Total number of alpha tracks  353 t 18.8  Therefore number of alpha tracks/cm  2  2  280 £'14.7  Therefore the number of alpha traoks/om  from the  uranyl n i t r a t e i s  \j(l3) -h 2  138 ±  280  (H.7)'  = 142 ± 17 tracks cm I f the exposure were increased to a period of 200 hours, —8 3.47 X 10"  grams of uranyl n i t r a t e would give this same number  of tracks.  Thus, the reasonable l i m i t of the s e n s i t i v i t y of  this method i s reached, f o r i n order t o decrease the amount of the n i t r a t e by a factor of 10 this would necessitate  prolonging  the exposure to 2,000 hours which i s impractical. ••8 A similar c a l c u l a t i o n shows that 1.98 X 10 grams of U_0 3 8 o  w i l l give 148 tracks/cm with a 200 hour exposure. 2  the polishing operation 1.98 X 10  8  I f during  grams of U^Og were trans-  ported from the active side to the inactive side and assuming the glass transported was spread evenly over a square cm of the surface, the depth of t h i s flowed layer would be, Density of glass  2.5 gms/cm  Composition of glass  4.8% U^O^  3  —8 Therefore number of grams of glass which contain 3.47 X l o " grams of U 0 3  8  — 4.8  X 1.98 X 10"  8  -7 = Volume of this layer  4.1 X 10 4.1 X l o "  — 2.5  gms of uranium glass 7  , ^ -7 — 1,54 X 10 cos.  - 18 -  This would represent a layer of 16.4 A . 0  However, i t xvould be possible to detect an increase i n track count of 40 tracks/cm^ over the background instead of 148 tracks/cm . 2  This would represent a layer of 4.5 A . 0  This then i s the minimum thickness of a layer which could be detected by this photographic method.  (d)  Determination of Polishing Compound Transferred to Glass  To detect any of the activated polishing agent that may have fused with the glass during•polishing, i t was decided to f i r s t use the Geiger counter, then when positive results were obtained autoradiographs of the surface were taken.  From the following c a l -  culation i t may r e a d i l y be seen that the method of detection of betas by the Geiger counter i s more s e n s i t i v e than the method of autoradiography.  20 mcs of activated CeOg were available f o r this project. 7  1.0 mcs 20 mcs  =  3.7 X 10  =  8 ' 7.4 X 10 disintegrations/sec.  disintegrations/sec.  The 20 mcs were contained i n 5 grams of the activated Ce02» Therefore 5 grams of activated Ce02= 4.4 X lO"^ disintegrations/min. I f the sample i s placed 1.25 cms from the window of the tube i n the counter approximately ijr of the t o t a l count w i l l r e g i s t e r .  Hence  f o r the purpose of counting 1.1 X 1 0 ^ counts per minute were  - 19 available.  I t was  planned to use. activated CeCv) i n the r a t i o  of 1:20 with ordinary Ce02. Therefore 10 grams of the mixture would equal I.I X 109 cts/min. I t i s possible to detect with ease a count of 25 cts/min over the background. Therefore  25  X 10  1.1 X i o  =  2.3 X l O  grams of  - 7  9  the mixture are needed to give this count of 25 cts/min over the background. One of the best films f o r detecting beta particles screen X-ray f i l m . beta particles  10  7  i s No-  To darken this f i l m s u f f i c i e n t l y to detect / 2 8 disintegrations/cm are needed.  The  sensitivity  of the photographic method w i l l now be considered and compared with the s e n s i t i v i t y obtainable with the Geiger counter. 141 t i . of Ce  -~  21 days 3 X 10  4  mins  Nov/ 25 cts/min on the counter i s equivalent to approximately 100 disintegrations/min. dx dt Therefore  N I00 =  X  3  =  X  - "V N 10*  ^  4 # 3  x  1Q  6  a  t  o  m  s  o f  ^141.  .693 From this i t may readily be seen that i t i s impossible f o r the f i l m to be darkened by 10^ beta particles spread uniformly over one square cm.  i f the a c t i v i t y i s  However, i f the t o t a l  - 20 count were 1000 ots/min i t i s obvious from the above that 4 . 3 X 10^ atoms of C e " ^ would be present.  Since one half 7  of the beta particles activate the f i l m approximately 2 X 10' atoms would be a v a i l a b l e .  Therefore i t would require approxim-  ately 21 days to activate the f i l m .  From previous calculations  —6 i t may be seen that 2 . 3 X 10~  grams of the mixture would be  necessary to give a t o t a l disintegration rate of 1000 dis/min. Thus the counter method i s more sensitive than this photographic method by a factor of approximately  10.  The following calculation i l l u s t r a t e s the depth a disturbed layer must be i n order that i t may be detected by the counter method.  I t i s necessary, f o r the purpose of this calculation,  to assume that the glass into which the ceric oxide i s incorporated contains 10% of this activated agent.  As previously calculated —7  the minimum amount of Ce0  2  detectable i s approximately 2 . 3 X 10  grams. -6 2 . 3 X 10  Number of grams of glass detectable = Density  =  2.5 grams/cc  Volume of glass =  9.2 X 10"  7  ccs  o Area of the sample polished = Therefore depth of the layer  6.2 cm 9.2 6.2 X 10""  7  - 21 -  The following equation gives the r e l a t i o n between the depth of this layer and percentage of-incorporated Ce0 . 2  d  X  % =  C  Where d —  depth of layer i n Angstrom u n i t s .  c —  constant, i n this case equal to 150.  RESULTS  A series of blank autoradiography were taken at random whenever a new batch of photographic plates were opened and used. Listed below are the results of these blanks from which i t was possible to determine the background  count.  In addition to these  blanks autoradiographs of glass, ground from the inactive to the active side, were also taken.  In these cases i t was most unreason-  able to suppose that there would be any probability of glass being flowed onto the inactive side.  This series also acted as a check  i n determining whether there happened to be any r a d i o a c t i v i t y i n the material used to prepare the glass, excluding uranium, of course.  - 22 -  BLANKS Sample No*  Area Counted  No. of Alpha Tracks  1  0.377 cm  52  2  0.325  42  3  0.390  4  0.372  "  51  5  0.342  "  44  2  "  54  n  Total area  1.806 cm  Total number of alpha tracks  243 — 15.6  Therefore number of alpha tracks/om  2  2  135 - 8.6  GROUND GLASS AUTORADIOGRAPHS Sample No.  Area Counted  1  0.403 om  58  0.390  "  53  3  0.387  "  52  4  0.396  5  0.345  2  No. of Alpha Tracks  2  '  53  ,f  "  46  Total area  1.921 cm  Total number of alpha tracks  262 ± 16.2  Therefore number of alpha traoks/cm  2  2  137 — 8.5  In the results tabulated below, the method used to record the number of alpha tracks per square centimeter was to mark o f f  - 23 a small square (approximately 0.5 radiograph, about 0.2  cms  cm )  on the resulting auto-  2  from the boundary between the  and  inactive side.  was  then counted, use being made of a microscope with magnifi-  cation of 560 X.  The number of alpha tracks  active  For any positive results  i t i s implied that uranium glass was  i n this area  (by positive results  flowed over to the  non  uranium glass) one half of the t o t a l of the alpha particles from the uranium would register as d i s t i n c t tracks i n the photographic emulsion.  I t was  possible to a r r i v e at t h i s factor of one  because the glass surface was  clamped t i g h t l y to the  half  plate.  There would have been no correction necessary for absorption of alpha tracks by the glass.  Any  amount flowed would have been  so small that the absorption of alpha particles by t h i s flowed glass would have proved n e g l i g i b l e .  The following series of polishings standard conditions  had the undermentioned  :SERIES A  (1)  Type of glass  lead glass  (2)  F i n e l y ground with f i n e emery  (3)  Composition of s l u r r y  25 gms  (4)  Rate of flow of s l u r r y  40 mls/min  (5)  Standard weight of 5.5  (6)  Time of exposure of autoradiograph  (Type A & Type B)  of Ce0 /l000 mis 2  kilograms 100 hours  of water  - 24 Sample Ho.  Time of Polish  IA 2A 3A 4A  5 sees 10 » 20 it  5A  1 min 2 mins 4 t: 8 it 10 tt  30  6A 7A 8A 9A  No. of Tracks  n  130 132 128 134 132 131 136 132 132  In the above series the time of polishing was increased continually from f i v e seconds to ten minutes, thus, i f a flow did take place, i t would have been possible to determine at which time during the polishing operation this flow was most pronounced, and i f i t varied with the degree of p o l i s h . p  By comparing the number of tracks recorded per cur on the p  above autoradiographs with the number of tracks per cm blanks, i t i s at once obvious that there was  on the  no flow during  this set of polishings. I t was  then decided to increase the amount of polishing  agent i n an e f f o r t to determine whether this variable had any effect on flow. next set was  Hence, the amount of polishing agent i n the  increased from 25 grams to 50 grams of CeOg/lOOO mis  of water.  Other than this change i n composition of the s l u r r y ,  this series B" had the same standard conditions as the previous W  s eri es.  - 25 SERIES B Sample No,  Time of P o l i s h 5 sees 10 " 20 " 30 " 1 min 2 mins 4 " 8 " 20 "  IB 2B 3B 4B 5B 6B 7B 8B 9B There was  No. of Tracks per cm' 140 138 134 135 131 136 130 132 143  no indication of flow, even with twice the rate of  addition of ceric oxide. I f the manner of recording results i s considered, i t i s possible to reason that there may have been flow i n the previous polishings, but this flow was i t was  over such a minute distance that  impossible to detect i t because no glass would have flowed  a l l the way from the boundary to the area counted, i . e . , a d i s tance of 0.2 cms.  In an e f f o r t to answer t h i s question counts  were made as close as possible to the boundary f o r a l l plates i n the "A" and "B" series.  This was  done by making a single sweep  of the autoradiograph, the edge of the f i e l d being 0.218  nuns from  the outermost position of the boundary between the inactive and active sides.  This dividing l i n e could readily be seen on the  plate, i t was very d i s t i n c t both v i s u a l l y and under the microsoope.  - 26 Sample No. IA  2A  Area Counted  Uo. of Tracks  0.015 cm '  1  2  0.033  3  n  3A 4A  0.028 0.040  5A  0.034  6A 7A 8A 9A  0.042 0.041 0.043 0.031  " " " "  6 7 6 4  13 2B 3B • 4B 5B 6B 7B 8B 9B  0.011  " *.* " " " "  2 3 4 2 2 3 4 3 3  0.026 0.012 0.020 0.019 0.026 0.020 0.021 0.014  " "  4 5  2  tt  n  " "  Total area counted  0.476  Total number of alpha tracks  64  Therefore number of alpha tracks/cm  ±  2  cm  8  138± 17  Again no evidence of any increase i n track count i s apparent, thus indicating that i f flow does take place i t i s over a distance of less than 0*22 mms. After negative results were obtained using ceric oxide as the polishing compound i t was decided to use rouge i n order to determine whether this type of agent had any effect on a flow process. Because i n the previous series the amount of agent appeared to have no effect i n a flow i t was deemed unnecessary to vary the amount of the polishing compound.  The following set of polishings  had the undermentioned standard conditions.  - 27 SERIES '0 (1)  Type of glass  (2)  F i n e l y ground using f i n e emery  (3)  Composition of s l u r r y  (4)  Rate of flow of s l u r r y  (5)  Standard weight of 5.5 kilograms  (6)  Time of exposure of autoradiograph  Sample No. 1C 2C 3C 4C 5C  lead glass (Type A & Type B)  Time of Polish  50 gms of Fe20y^l000 mis of water 40 mls/min  100 hours  No. of Tracks per cm'  5 sees 20 " 50 " 100 " 200 "  129 136 135 133 136  Again there was no evidence of any flow. A phosphate glass was then polished with the thought that i t s lower softening point would be more conducive to flow.  Again i t  was deemed unnecessary to vary the amount of the agent supplied f o r reasons already given.  The following series had the under-  mentioned standard conditions :SERIES D (1)  Type of glass  phosphate glass (Type D & Type E)  (2)  Finely ground using f i n e emery  (3)  Composition of s l u r r y  50 gms  of Fe„0.,/1000 mis of water  - 28 -  (4)  Rate of flow of s l u r r y  (5)  Standard weight of 5.5 kilograms  (6)  Time of exposure of autoradiograph  Sample No. ID 2D 3D 4D 5D  Time of P o l i s h 5 sees 15 " 50 " 120 " 240 "  40 mls/min  100 hours  No. of Tracks per cm' 137 130 141 136 129  Again i t i s r e a d i l y seen that there was no increase i n the background count i n d i c a t i n g no flow.  Hence this l e f t the alterna-  t i v e of using c e r i c oxide instead of rouge as the polishing agent, therefore, i n the following series the only change i n the standard conditions of polishing was that ceric oxide was used i n place of rouge.  The composition of the s l u r r y being 50 grams of ceric  oxide per 1000 mis of water.  Sample No. IE 2E 3E 4E 5E  Time of P o l i s h 5 sees 15 " 50 " 120 " 240 "  No. of tracks per cm' 133 138 135 150 129  Again there was no evidence of any flow taking place. In the f i n a l set of polishings both types of glass were polished with ceric oxide and rouge.  The procedure of polishing  was altered i n that force was applied by hand and not by means of  - 29 the standard weight.  The method employed was that of polishing  for a period of twenty minutes using a s l u r r y composed of 50 grams of the agent i n 1000 mis of water, the rate of flow of s l u r r y during this wet p o l i s h being 40 mis per minute.  At the end of  20 minutes the table was allowed to run dry and there were no further additions of the polishing compound.  This operation  of the dry p o l i s h was continued f o r a period of 10 minutes, following this an autoradiograph with a 100 hour exposure was taken of the r e s u l t i n g polished surface.  SERIES F Lead Glass Sample Ho.  Type of Agent  Ho. of alpha tracks/cm  IF  Ceric oxide  133  2F  Rouge  131  Phosphate Glass 3F  Ceric oxide  129  4F  Rouge  129  There was no indication of flow even when the table was allowed to run dry.  Dry polishing was continued f o r a period  of 10 minutes a f t e r 20 minutes of wet polishing.  Counts were again made as close as possible to the boundary i n a similar manner t o that done i n series "A" and B". The !,  outermost point of the boundary being 0.218 mms from the edge of  - 30 -  the f i e l d and again a single sweep taken of the autoradiograph. Sample No.  Area Counted  No. of alpha tracks  IF  0.033 cm  5  2F  0.021  "  2  3F  0.045  "  7  2  Total area counted  0.099  Total number of alpha tracks  14 ±  Therefore number of alpha tracks/cm  141  2  cm  2  3.7 ^37.4  Again there appears to be no evidence of a flow, however, the- probable error i s great because of the limited number of plates.  Therefore these results are not conclusive i n themselves  and serve only as an indication. The following procedure was  carried out when the glasses  were polished with radioactive ceric oxide. (1)  2 mcs  of i r r a d i a t e d ceric oxide were mixed  with non-irradiated ceric oxide to give 10 grams of the mixture.  This was  then  s l u r r i e d i n 200 mis of water. (2)  Approximately 5 mis of this s l u r r y was rubbed into the f e l t and polishing carried on f o r 15 seconds. this time the table was  At the end of  stopped and a  further 5 mis of the s l u r r y added, this  - 31 procedure being repeated every 15 seconds. Pressure was applied by hand. Picture (2) represents this technique. s l u r r y i n the beaker was  However, the  poured through a funnel i n the l u c i t e  dome. When polished, the samples were thoroughly washed and scrubbed with a nylon brush i n running water, alcohol, a soap solution and f i n a l l y more water. Below i s an example of the procedure followed i n recording the counting rate of a l l samples.  A standard sample was  first  counted to determine whether the plateau of the tube had changed. Following this the background was  taken and f i n a l l y the sample  counted. Example In one determination of the background, 294 counts were recorded i n 5 minutes and the sample recorded 406 i n the same period of time. Therefore background rate i s  5  ' 294 ± 5  17.0  59 i 3.4  cts/min  Total rate of sample i s 406 ± 5  20.1  5 81 ± 4.02  cts/min  - 32 -  Therefore net rate i s 81 - 59 ±  Sample No. I  = 22 ±  5.2  — 22±  5  2  cts/min  Phosphate Glass Type "C"  This sample was  \K3.4) + (4.02)  6.2  om  polished 2jg minutes then washed as i n  the above procedure.  92 ±  Net rate  7 cts/min  After t h i s treatment the polished glass was to re-washing  and re-scrubbing as before and i n addition was  allowed to stand overnight i n alcohol. 48 hours later  subjected  The oount taken  was  80±  Net rate  The decrease i n a c t i v i t y was the decay of the active cerium.  6 cts/min  completely accounted f o r by Hence this treatment of re-  washing and re-scrubbing did not remove any activated CeO>,.  An autoradiograph (l) of the sample was taken with a 72 hour exposure.  From a study of the radiograph i t was  seen that the a c t i v i t y accumulated not i n a uniform manner.  on the surface i n spots and  The spots on the f i l m corresponded  exactly with minute pits i n the polished surface of the glass.  AUTORADIOGRAPHY  (to follow page 32)  Autoradiograph III 4  The sample was then placed i n a solution of 6 N HC1 and KI f o r twenty seconds at 70 °C. solves Ce0 . 2  This solution r e a d i l y d i s -  The count taken of the sample before and a f t e r  being immersed i n this solution i s given below.  Count before being placed i n the acid solution "  after  "  "  "  "  "  59 — 6 cts/min  "  13 -± 5  "  "  An autoradiograph with an exposure of 72- hours f a i l e d to show any a c t i v i t y on the polished surface.  Only a f a i n t blacken-  ing of the f i l m was observed from a c t i v i t y lodged i n the roughly ground sides of the sample. Sample Mo. 2  Phosphate Glass Type "C"  6.4 cm  2  This sample was polished and treated, i n the usual manner, t o t a l polishing time being 8 minutes.  Net rate  22 ± 5 cts/min  An autoradiograph taken of this surface gave only a few scattered spots similar to radiograph No.l, but they were less dense.  This lack of density made i t impossible f o r a print to  be made of this ..film.  Again the spots corresponded  exactly with  minute pits i n the polished surface of the glass.  Sample No. 3  Soda-lead-silioate Glass  3.0 cm  2  This sample was polished 6 minutes and treated i n the  - 34 -  usual manner. Net rate  384 ± 9 cts/min  The r e s u l t i n g autoradiograph (2) taken with an  exposure  of 24 hours again showed the a c t i v i t y to be accumulated i n spots on the surface which corresponded with minute pits i n the polished surface of the glass.  This sample was  polished  for a further 15 minutes, giving a t o t a l polishing time of 21 minutes.  Net rate  242 + 9 cts/min  Autoradiograph (3) had an exposure of 44 hours. i t i s seen that the a c t i v i t y was accumulated  Again  i n spots.  Scratches v i s i b l e to the naked eye appeared i n this sample when the polishing f e l t was end of the polishing. the new f e l t . appeared  changed f i v e minutes before the  They were attributed to particles on  In the r e s u l t i n g autoradiograph (3) darkening  on the f i l m d i r e c t l y above these scratches, indicating  the presence of CeOg. polishing was  Net rate  To improve the p o l i s h of the sample,  carried on f o r an additional 21 minutes.  12 ± 2 cts/min  The autoradiograph of this sample showed no darkening whatsoever.  - 35 -  DISCUSSION The method used to investigate the problem of whether glass flows during polishing was  determining  primarily one of being  able to detect any radioactive glass flowed over to a non radioactive g l a s s .  As previously shown the  photographic  method used enabled the detection of a layer 4.5 A  0  i n thickness.  However, i f during the polishing operation particles of glass are removed and  later re-attached these particles would leave  clumps of alpha tracks on the resulting autoradiograph.  For  example, i f 6 alpha tracks were l e f t i n a clump this would represent  :-8  1.98 X 10  / o grams of U^Og  give 148 alpha tracks/cmr  on an auto-  radiograph with a 200 hour exposure. Therefore  6 - .X 148 -8.04  R  1.98 X  X lO  - 1 0  10"°  grams of U^Og  are required to  give such a clump. Composition  4.8%  U,0 j o o  _io  100 Therefore  X 8.04 X  10  4.8 —8 - 1.67 X 10 give such a clump. Density  2,5 gms/co  grams of uranium glass w i l l  - 36 -  Therefore volume occupied by this weight of glass i s  1.67 X  10"  8  2.5 6.7 X 10~  9  ccs  Hence a clump of 6 alpha tracks observed i n the resulting -9 autoradiograph would have represented a chip of 6.7 X 10  ccs  of uranium glass, had t h i s chip been removed from the active side and l a t e r incorporated on the i n a c t i v e side.  Assuming  such a chip to be spherical the diameter would be 0.019 Such clumps were noticed i n a few radiographs.  mms. However,  upon re-washing and re-scrubbing these particular samples the clumps were not reproduced i n the ensuing autoradiographs. Because the particles were so e a s i l y removed i t was  concluded  that they were merely trapped i n the surface and not due to any flow. I f during polishing a flow did take place i t was  reasoned  that the sharp boundary would have disappeared leaving instead a gradient.  In a l l the autoradiographs taken there was  no  evidence whatsoever of t h i s phenomenon, the boundary remained sharp and d i s t i n c t .  - 37 - • From the results of the experiments conducted using radioactive glass, i t was concluded that the most conspicuous feature during polishing was that of removal of glass, rather than that of a smoothing or flowing action resulting from the softening point of the glass being reached.  This statement  i s modified to include the type of glass polished and the conditions of polishing.  I t may also be pointed out that even  when the table was allowed to run dry there was s t i l l no evidence of any flow taking place.  Thus i f flow occurs, i t i s over a  distance of less than 0.22 mms even when the polishing i s done with a dry f e l t under .3 kg/cm f o r 10 minutes. 2  The results of the experiments conducted with activated CeOg indicate that some of this polishing agent remains on the polished surface i n spots a f t e r polishing i s ceased.  I f ceric oxide i s entrapped i n the crevices of the surface this would account f o r the spottiness of the resulting autoradiographs.  I t would also account f o r the decrease i n a c t i v i t y with  longer polishing times f o r with prolonged polishing a f i n e r p o l i s h i s naturally attained, thus fewer crevices are available to entrap the ceric oxide.  The pits and lines i n the surface  corresponded exactly with the dark areas on the autoradiographs, as could be seen with the naked eye.  Further evidence whioh  suggests that the CeOg i s merely entrapped i n the surface was  - 38 gained from the experiments i n which the ceric oxide was so readily dissolved by the acid solution.  I f the C e 0 were 2  fused with the glass i t would be expected that the rate of attack would have been much slower.  The acid solution w i l l  attack the glass, therefore this evidence i s not at a l l conclusive and i s presented as a suggestion.  I f fusion of the CeCv, with the surface glass took place i t was reasoned that there would probably have been an increase i n the amount of the agent incorporated with the glass as the polishing time was prolonged.  However, there was no increase  i n the amount of ceric oxide on the surface with prolonged polishing times but rather a decrease.  This mechanism, there-  fore, does not appear to be the one involved.  To account f o r the i m p o s s i b i l i t y of removing CeO^ from the surface by washing i t was possible to reason that during polishing crevices were flowed over, thus securely entrapping this polishing agent.  I f this were the case i t was expected  that a considerable amount of a c t i v i t y would have been present on the surface a f t e r prolonged polishing.  Such was not the  case, hence i t was again reasoned that the most conspicuous feature of the polishing operation was that of glass removal.  - 39 -  FUTURE WORK (1)  Use radioactive rouge to determine whether this agent fuses  with the glass during the polishing operation. (2)  Further work might be carried out on the study of the flowing  over of scratches.  A possible method of attacking this problem  would be that of scratching a well polished surface then rubbing radioactive ceric oxide or rouge into the scratches.  After this  treatment the glass could be polished i n an attempt to flow over these scratches.  A f a i l u r e to remove any of the radioactive  material by washing would indicate that the scratches had been flowed over.  By using a glass that i s not r e a d i l y attacked  by a solution which would dissolve the radioactive agent i t would be possible to determine the depth of the glass flowed over.  The rate of attack of this solution on the glass would  have to be determined. (3)  The work done on phosphate glasses might be checked to de-  termine whether the fractures interfered with a flow.  A study  of the c o e f f i c i e n t s of expansion of this glass would f i r s t be necessary i n order that a good j o i n be made.  Y/hen a j o i n i s  made i n a flame the boundary is more d i s t i n c t than i f it-' i s made i n a furnace.  

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