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The determination of the rates of attack of the hydroxides of first group metals on 790 vycor glass Colclough, John Reed 1947

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• t i f f ft%  THE DETERMINATION OF THE RATES OF ATTACK OF THE HYDROXIDES OF FIRST GROUP METALS ON 790 VYOOR GLASS by John R. Colclough  Submitted i n partial fulfillment of the requirements for the degree of Master of Arts.  Department of Chemistry , University of British Columbia. April 1947.  T A B L E OF CONTENTS Pag© Acknowledgment  .  .  Abstract  .  .  i  . . . . .  i i  P r e v i o u s Work  . . . . . . . . .  1  Apparatus and M a t e r i a l s  . . . .  5  Temperature Bath Reaction lubes 790  Vycor G l a s s Samples  fydroxide  solutions  Observations  5 . . . . .  5 4 5 7  Treatment o f R e s u l t s  22  S u g g e s t i o n s f o r F u t u r e Work  24  Bibliography  27  ACKNOWLEDGEMENT  Only through the kind and helpful suggestions offered by Dr. J . Q. Hpoley was this thesis completed. I wish to express my sincere thanks for his generous assistance.  ABSTRACT  1.  The effect of concentration of a l k a l i on the i n i t i a l rate  of attack of vitreous s i l i c a was measured at 80 C for LiOH, NaOH, KOH, RbOH and CsOH.  Maximum rates of attaokwere observed at  concentrations of 5 N for NaOH and ION for KOH. 2.  The effect of temperature on rate of attack was measured  in the range 5.  60°0 to 90°0 for NaOH and from 70°0 to 90°0 for KOH.  Por a given concentration, the order of a decreasing  attack is NaOH, KOH, LiOH, RbOH and CsOH. 4.  With 9?% ethanol and 100$ methanol as solvent for NaOH  and KOH, the rate is n i l . 5.  With crystalline s i l i c a i n aqueous a l k a l i , the rate of  attack is about 1/8 of vitreous s i l i c a .  ooOQOoo  t*  1  PREVIOUS WORK Comparatively l i t t l e researching has been done in regard to the determination of rates of attack of hydroxides of f i r s t group metals on silica.  Whenever a vit%Jous s i l i c a sample was immersed i n the hot  hydroxide solution, crazing of the sample made results anomalous. Weighings after the immersion could not be regarded as the true loss of s i l i c a resulting from chemical action, since this chipping and cracking phenomena allowed small particles of the s i l i d a to drop out. Also, two samples whose surfaces had apparently been prepared i n the same aay would craze to a greater or lesser extent, for no apparent reason. These phenomena were investigated by Hooley and. Wainwright ® with the following results:  Their attempts to eliminate the crazing  of the vitSfejous s i l i c a surface failed* but suggestions as to the reason why the glass crazed led to a satisfactory solution, of this problem.  They noted that a freshly formed surface resulting from a  fracture, did not craze .  They also noted that a blown surface did not  craze as much as a ground and polished sample.  From this they  postulated that the crazing was due to minute cracks or other weak areas i n the surface, which cted as centres from which crazing spread a  SurFace  over the CSBBOES of the glass. Containers of different materials ere used to hold the hydroxide w  Into which the glass samples were immersed.  Crazing varied consistently  with the container used, which led them to further postulate that an electrical phenomena also played an important role i n crazing, i t being felt that a cell was set up between the glass sample and the container. Measurements on the rate of attack with time indicated that i t was :. t lineafc for periods up to fifteen hours.  2  GENERAL PROCEDURE. The problem of crazing had to be solved i n order that reproducible data could be obtained.  In view of the work done by G„ Hooley and J .  Wainwright i t was decided to study the effect of insulation of the glass sample from the container and also . . to try by some means to eliminate surface scratches on the s i l i c a . The satisfying solution to this problem led to the determination of the effect of concentratation and temperature on the rate of attack.  790 Vycor glass was used for the experiments and was ground  as flat squares of approximately 40 mm. square and 6 mm. thick. It was decided to standardize the procedure with Sodium hydroxide* then to include Potassium, Lithium, Cesium and Rubidium hydroxide measurements. The effect of different solvents for the Sodium and Potassium hydroxides was investigated as well as the influence of products resulting from the reaction between the hydroxide and the s i l i c a .  5 APPARATUS AND MATERIALS.  A constant temperature bath was made from an enamelled iron tube. It was  insulated with three inches of gyprotf wool and set on a sheet  of transite which rested on insulating bricks.  The top was covered with  a sheet of lead with eight holes of 2 " diameter to allow reaction tubes to f i t i n , and with six smaller holes through which a: stirrer, a ther^mometer, a thermostat and three heating elements passed.  The  level i n the bath was maintained by means of an overflow lake which was connected to the bath by a siphon.  The f i r s t thermoswitch was a b i -  metallic strip but since this controlled to only — 1°C and a mercury switch with a relay was used instead. temperatures with a  t  i t was set aside  This gave constant  0 , 1 ° 0 aocuracy and proved to be very  satisfactory.  The current controlled was"constant" and was fed to one element.  The  other two elements had;- a "variable" current by means, of a sliding resistance c o i l , which allowed temperatures ranging from 60° C to  95°  c  to be obtained. Reaction tubes were made from pyrex tubing, pulled apart and blown, copper tubing with silver soldered base, sheet silver rolled and silver soldered, and iron boiler tubes with welded bases. stood about 1 2 " high and had a diameter of i f - 2 ° .  They each  They were supported  by means of lugs attached to the base of the tubes approximately 2" from the bottom of the bath.  The f u l l capacity of the tubes was 5 0 0 r . mis.  which allowed the JOO mis. of solution used to be completely under the level of the water i n the bath.  The solution was maintained at 5 0 0 mis.  by means of air condensers set into corks. with the air condensers were used.  Eventually rubber stoppers  Evaporation^ was negligible and could  not be detected by means of the 5 0 0 mis. graduate used to measure the solutions. /  4  The glass samples used were cut from a large 790 Vycor plate, obtained from Corning Glass works. square and 6 mm. thick.  They measured approximately 40 mm.  The urfaeeof the sample was standardized by 8  grinding i n a fine emery powder i n a solution of glycerol and water. disc  A round flat,cast-iron was spun and the grinding compound applied. The A  glass sample was held against the wheel until the surface became uniform •b and ny chips on the edges were removed. a  To facil^ate  of chips on the edges they were slightly bevelled.  the elimination  For the f i r s t couple  of runs this completed the sample, but later i t was found necessary to immerse the sample i n a heated lead bath (50°C) of $0% H.F. (60%) and $0% HgSO^. (cone. ).  A copper wire holder was made to support sixteen  samples, so that this number could be etched at one time.  This turned the  surface from a seHlmVtransparent white sheen to a more transparent o i l y - l i k e surface.  Only about 15 minutes i n the. bath was required, to do this.  Thirty-two samples were ground and i t was possible to etch sixteen samples gt the same time.  The small numbers scratched on were done so  before the acid treatment. The samples after treatment were dried at room temperature- . and placed i n a des|icjptor f i l l e d with Calcium chloride.  They were left  in the des^ic^ator for at least 2k hours before they were weighed. Heating test samples i n an. oven pat a temperature of 150°C for 2-5 hours did not make any significant change i n the weight of the sample, hence this procedure was neglected.  The glass samples were suspended, by means of holders which were fashioned from the same material as the tube.  The samples were allowed  to hang freely i n the tubes midway i n the solution.  They were placed i n  the solution after the solution had a chance to come to equilibrium and the time noted on the immersion of the f i r s t sample. noted on the removal of the f i r s t sample.  The final time was  They were usually allowed to  remain i n the tubes for 15 hours. The samples were, washed free of the a l k a l i and weighed. were next treated with the acid bath reedy for the new run.  They  The area was  calculated from time to time to allow for the s i l i c a removed by the acid treatment. The Sodium hydroxide and Potassium hydroxide, solutions were made up i n volumes of 5000 mis. and stored at room temperature in 5000 mis. Florence flasks.  They were, stoppered with corks.  Eaoh solution was  standardized against HC1 using phenolpthalein as indicator.  A fresh  solution was used on each run except where It i s specified differently. Water used was d i s t i l l e d and no attempt was made to remove any carbonates or other impurities that were introduced by the NAOH and KOH pellets. The very concentrated solutions used were standardized by pouring when hot into graduate, then allowing to cool and noting volume, diluting with known volumes and thus dissolving the crystallized NaOH. The accuracy of these was checked by treating a known solution by same procedure.  6 The Cesium hydroxide was made from CsCl^I.  It was heated until  white, then concentrated HgSO^ added and again heated until fuming ' stopped.  When dissolved i t gave a test for Cl hence i t was necessary  to evaporate the Cs^SO^to dryness along with HNOj and to heat until no more brown fumes came off.  Then concentrated H^SO^ was again added and  the solution evaporated to dryness. This CsgSO^ was dissolved and diluted.  Solid BaCOH^SH^O was  added until no further precipitation [and the solution filtered.  £  j^U  It was  evaporated in a silver tube, the solution dripping into the tube at about the rate of evaporation.  Air, passed through soda lime, and bubbled  through three normal NaOH and saturated Ba(OH^solutio$ in order to remove the COgwas kept over the evaporating solution.  The final con-  centration was &.8Q6 N and the volume approximately 100 mis.  This CsOH  solution was filtered through a Pt. Munro crucible using suction. normality was determined by pippetting 1 ml. solution and standardized with HOI,  The  from the hot (80°0)  After a run a new normality was  obtained by adding a known volume of water to the solution. small known volume was removed and titrated,  However a  as a check on the normalities.  No attempt was made to remove the products of reaction from the previous run. The Rubidium hydroxide was made from a RbNO^, RbCl mixture. It WSB heated to a white salt with concentrated H^SQ^, This was dissolved i n nper and filtered.  The clear solution was evaporated to dryness.  Its solution gave no test for the halides Cl, Br, or I. dissolved, diluted and heated.  The Rb^SO^was  To i t was added hot Ba(OH)Z — solution  until no more precipitation was noted.  '  through a Pt. Munro crucible using suction.  _ JiJLt  The solution was decanted The RbOH solution was  ^ •  evaporated i n like manner as the CsOH. Normalities were also calculated similarly.  :  of  tubing  Solution  (<I,/Pr*)  6  A  Silver tithe flppdnxfus usee/ /or  RbQH and (sOH sol'ns.  tick  cr  It  OBSERVATIONS. Since preparation and procedure for each run varied, these topics shall be discussed under each run heading.  The conclusions  conclusions arising from the experiment shall also be included. Run No.l  (NaOH) T=  PURPOSEt  To discover a means by which the irregular weight losses due  79.5°C  Time-  15  hours  N=  1.202  to chipping of the glass sample, experienced in previous experiments could be overcome by use of insulation of the glass sample from the container. The glass samples were ground  with fine emery powder.  Rubber insulators were made for 2 silver, 2 iron and 2 glass tubes, so fashioned that the glass sample did not touch the container.  One  silver and one iron tube was used as a contfol, that i s , contact made with the glass sample through the holder to the container. A l l the samples were cracked and jwere chipped.  There was  no significant differences i n weight losses between the insulated and non-insulated glass samples.  Inspection with a high-powered microscope  failed to bring forth any means of distinguishing the samples . Intention of the insulation was to eliminate any possible electri&al potential which might arise due to the c e l l - l i k e nature of the glass sample and tube.  This supposed potential might be responsible for  the crackingand chipping which occured at confined areas;  the remaining  glass surface remaintRg. semi-transparent as i t had been ground.  However  the insulation failed to produce the desired results and whereas i t did not by any means prove conclusively that no potential existed , this line of attack was abandoned i n the light of the next run.  8  Run  No. 2,  PURPOSE:  (NaOH) T = 80°C  Time = 15 hours  N = 0.6084  To discover the effect of etching the glass samples with  Hydrofluoric acid before they atfe immersed. The samples were ground and etched i n a ml ture of 50% RF(60%) x  and 50% H2S04 (cone) by weight. temperature for five hours.  Insulation was similar to t r i a l No. 1  with 2 tubes u ed as controls. 8  The reaction took place at room  The samples were not weighed.  There was no cracking or any change by which a sample could be identified as having been treated with sodium hydroxide.  As before,  the sample afterward had an o i l y - l i k e semi-transparent surface.  Samples  are apparently left with a uniform surface which resists chipping and cracking.  Any strains i n the glass surface put there through grinding  would be eliminated by the action of the  H 4 F 4  acid and since chipping  ceased i t would appear that an area of strain^as responsible for the cracking,, <A a. Jfc^ Run No. 5 PURPOSE:  (Na6H)  T t 79?8 0  Time s 15 hours  N • .8808  To check the results of previous run.  Samples the same as run No. 2 w  e r e  placed i n the acid bath for  one hour at room temperature • Insulation was contained as above.  Glass  samples were weighed• There was neither any change i n appearance of samples, nor in the weight loss between insulated and non-insulated samples. weight losses for tubes of same construction was good. highest weight losses, (av.  Agreement i n Iron gave the  .0^4 mgs./ hr/ cm* ) with silver container  next ( .045 mgs /hr/ cm ) and glass the lowest ( .Q29 mgs. / h r / cm ). 2  1  9 It i s interesting to note that previously, glass samples gave the highest values, when the samples were not treated with HF and the clipping observed.  Differences i n weight losses between the tube  containers was felt to be due to interference of products arising from reaction between the alkali and the tubes themselves*  However, neither  the solutions from silver nor ifcon gave tests for those metals.  Reason  for low results i n pyrex tubes was attributed to the amount of Silicates coming from the tube i t s e l f , and hence interfering with the silicates from the glass, sample* experiments  The effect of temperature as shown by later  gave rise to the fact that  radiation losses from the tubes,  (about 2/5 of tube above surfac© line of bath)  may have effectually re-  duced temperature within tube and thus affected loss^of s i l i c a . Run No. 4 , PURPOSEt  (NaOH)  T • 82°0  Time « 15 hours  N a .8870  To determine rate of attack on crystalline quartz and to note effect of container on reaction rate.  The glass samples were treated with acid for tfc hours at room temperature.  They ware not ground since previous run.  A clear  crystalline quartz sample was. ground and was not treated with HF. The f  insulation was discontinued and the glass tubes substituted with coper tubes. For Iron an average loss of . 0 5 6 gms /hr/ cm?" was noted, for silver a loss of ,052mgs / hr/ cm*" and for copper a loss of . 0 5 8 5 mgs/ hr/ cm ". 2  The quartz sample gave a loss of . 0 0 7 mgs/ hr / cm . 1  The copper tube gave a blue coloration to the alkali solution.  \  10 It appears that copper is unsatisfactory as a container*  Loss  i s quite low but this is greater than would be expected even from the bluish coloration.  ome other factor must have been responsible for this  s  low weight. Purecrystalline quartz has a very high resistance to a l k a l i and i s not effected at points of strain., since no chipping was observed. This however may take place Run No. 5 FURgPOSE:  i f a longer time than 15 hours had been chosen.  Temp 79.5  (NaOH)  Time 15 hours  N a .9568  ibihty  To check reproduc*4*4*y.  Samples were reground and placed i n acid treatment for 4 hours. Two samples of thin Vycor ware were cut from the side of a Vycor dish and treated as above. Loss i n weight i n milligrams per hour per square centimeter for iron was . 042; for Ag was .057, and for copper was .0581.  The blue  coloration was s t i l l , present and no explanation.for the rise i n copper values can be given.  The Vycor dish losses compared well with the  Vycor glass samples. This run shows that reproducibility is not as yet certain as far as different tubes is concerned. Run No. 6 PURPOSEi  (NaOH)  T • 80°0  Time 15 hours  N»  1.001  To determine the resistance of acid treated samples to  crazing. The samples were not given any acid treatment but used directly after Run No. 5*  The same tubes as before were used. There was no  chipping or checking. highest values.  Very good agreement with the silver tubes which gave  The copper tubes dropped slightly below the iron tubes.  11  Run No. 7* PURPOSE:  (NaOH)  F = 80.0*0  Time 15 hours  N = 1.025  To determine the resistance of acid treated samples to crazing.  Same samples as Run No. 6 with no acid treatment.  Same time,  temperature and approximately the same normality of NaOH as Run No. 6. The results within experimental error were the same as Run No. 6. Run No. 8# PURPOSE;  (NaOH)  T •• 80°0  Time 42.5 hours  N*  1.025  Same as No. 7 .  Same conditions as Run No. 7 except time extended to 4 2 . 5 hours. The Sodium hydroxide solution w s not changed from Run No. 7 but left a  i n the reaction tubes.  Samples were badly chipped and cracked except  the three which were i n the iron tubes.  On weighing,these samples  gave weight losses inagreement with weight losses for only 15 hours. The significance of this i s somewhat lost i n the light of later work done in regard to temperature control'-., hence i t is well not to con ider this g  result toe closely.  It does indicate however that interference of  product during the 15 hour runs does not appreciably slow the r t e of a  attack. The samples in handling were evidently scratched so that chipping i  occured.  It i s interesting however to note that only the iron tubes  did not chip the. glass samples.  No explanation i s apparent.  case results indicate that the samples should be treated every second exposure to the of a l l tubes used.  NaOH.  In any  at least after  Iron tubes appear to be the best  12 Run No.9>  (NaOH)  T * 80 C  Time -  16  N»  1.427  PURPOSE:  To determine the effect o^uaing glass containers with acid treated sample.  New pieces of Vycor were ground and polished with the fine white powder.  They were treated with HF and H^SO^ , being left i n the bath  over-night. Some had  The samples after, this treatment were not uniform.  a roughness and a cloudiness, whereas others had the character-  i s t i c §mooth oil-like, >  increased.  semi-transparent surface.  The normality was  The copper tubes were replaced with the former pyrex glass  tubes. Iron again gave the highest values. of the loss as shown by the iron tubes. -the  Glass gave approximately half  Agreement was poor.  It appears  that glass surface may have an effect on the rate of attack.  However no  ft  agreement could be made between apparent roughness of sample and the loss in weight that i t experienced. Run No. 10,  (NaOH)  T » 80.0°C  Time  »  15.5  *  N =  1.582  PURPOSE: To determine the effect of f i r e polishing the glass samples and to note the. effect of allowing a stream of Sodium hydroxide to pass Over samples. The rough samples from Run No. 9 were reground and giv$n acid treatment.  Four of the eight samples were then fire-polished with a  oxy-coal gas flame.  A reservoir of NaOH was set up i n order that a  continuous flow (7.5  oc/min.) of solution would pass the glass sample.  This was 'done to one iron and one glass tube, the solution coming from v  reservoir into iron tube, then passing into glass tube and so into the waste reservoir.  15  The sample loss ln glass tube was slightly greater than sample loss i n iron tube.  No cracking or chipping took place with the f i r e -  polished samples, and no difference could be detected i n their apparent weight losses.  The weight loss was smaller i n the iron tube through  which the NaOH flowed than i n the oontrol. polished and one acid sample)  The silver tubes, ( 2 f i r e -  agreed quite well.  Apparently the glass tube interferes with the sample loss because of i t being attacked by the NaOH.  This would introduce by-products which  would interfere, and also reduce normality of the solution , thus reducing the activity.  As above experiment indicates, when solution  i s renewed continuously, the above factors cannot influence the rate of attack of the glass sample. H.j30^ and HF  Fire-polishing is effective as well as the  •'. treatment i n the prevention of chipping and cracking. v  Similar weight losses would indicate the roughness of the surface has l i t t l e effect.  This would be explained by the fact that a layer of  saturated film exists about the sample, i n w h i c h the effective area ;  i s not that of the glass but i s that of the bounory of the saturated film.  The temperature drop caused by the continuous addition of cold  NaOH solution would explain the drop i n the weight loss of the sample in the iron tube(flowing) from that of the control. Runs No. 11 and 1 2 .  These runs were similar to run No. 10 and served  only to check results. PURPOSE; To find the interference of added Sodium silicate to rate of attack. Runs No. 1 5 , 14, 1 5 . Samples were prepared as befpre. A solution of Sodium silicate was made up to a known concentration. Amounts of the ttluhor* were addecL'So that the tubes contained 5  lOmg and 5 0 mg of  14 Results showed a slight deorease l n the loss weight per sample, but agreement was poor. a constant factor. correct.  Temperature control was difficult and was not  The manner of adding the Sodium silicate was not  The assumption had been made that the product arising from the  reaction of NaOH on the Vycor glass would be satisfactorily duplicated by the straight addition of Sodium s i l i c a t e .  This i s not necessarily  correct. Runs 16, 1?, 18, 19 and 20. PURPOSEt  To determine the effect of concentration on rate of attack at constant temperature.  New samples were cut from a Vycor flat dish, thirty-two In a l l . They were prepared as described under apparatus and materials.  The  runs were.standardized on iron tubes and the concentrations on the NaOH varied from 0.1 N to 10 N. e  Runs No. 16 and 17 were made at a temperature of 80 C. However, o  the temperature dropped to a value approximately equal to 75 °» during the 15 hour run. Run No. 18 was continued for 45 hours and Run No. 19 at 15 hours i n order to check effect of product on the rate. However, the b i ai metallic thermo-switch f i l e d to mintain a/steady current. Hence results a  were treated qualitatively only. An important outcome of these experiments was the increasing of the current through both the constant and the variable heaters, which ensured the maintainence of temperature.  Also  a  mercury thermo-switch with  i. relay was installed, which gave a constant current to  1 o  _ T0~~  0.  15  In the past fair agreement was obtained i n the individual runs. However, agreement was poor from one run to another.  Factors which may  influence this arei Size of Samples,  Size was not standard, a small sample in same  amount of solution as a large sample would have less weight loss.  That  i s , there would be less product to interfere with further reaction and also a relative higher activity.  However, this could not have been  appreciable as borne out by experiments run at long time intervals. Surface Treatment of Glass. bevelled. occur.  The glass samples were ground and  Corners were hard to bevel and sometimes chipping would This would facilitate further chipping which may take place  during handling.  Since cracking does not occur on a chipped surface  this would pass unnoticed and account for anomalous, weight losses. The surface as a whole was treated with HF and HjSO^, but this procedure was not standardized.  Some samples became cloudy and rough to the touch  while others retained their translucent surface. Temperature. better than t  The bi-metallic thermoswitch would not control,  1°0 .  Considerable trouble was experienced i n main-  taining the same temperature for each run. s  This would introduce a  erious error and would satisfactorily account for previous differences. As previously mentioned the temperature for future rtims was  controlled to  - 0.1°C.  The size of samples very closely equals one  another and the surface treatment has been standardized.  16 With the procedure standardized the following runs were made. Weight losseB are expressed i n milligrams per square centimeter per hour. Normality _ " Hun NaOH _2I_  22  _25_  24  _25_  26  _2Z_  0.0901  .0165  .0217  .0084  .0074  •0059  .0042  .0002  0.1767  .0265  .0564  .0156  .0159  .0097  .0070  .005  0.477  .0444  .0654  .0256  .0265  .0170  .0119  .005  0.975  .0585  .0902  .0526  .0558  .0220  .0146  .QD62  1.415  .0706  .0104  .0595  .0597  .0254  .0185  .0075  1.949  .0714  .110  .0457  .0415  .0280  .0204  .0082  4.695  .0942  .162  .0598  .0574  .0407  .0271  .0115  9.280  .0897  0.157  .0557  .0517  .0568  .0255  .0085  90.8  79.7  79.7  75.1  70.1  60.0  15  15  42  15  15  15.  Temp(!c)  85.5  Time (hr) 15  Note:  <*8  9  Run 24 was left for 42 hours using the same  solution asprevious runs and the same samples,(i.e, no acid treatment between run 25 and 24.)  17 Normality KOH  _2Z_  .4864  .0140  -5SL .0524  .0072  1.286  .0502  .0625  .0116  5.018  .0525  .0727  .0145  4.265  .0457  .0877  .0175  5.7174  .0445  .102  .0195  7.055  .0505  .1185  .0226  9.055  .0450  .1160  .0256  10.05  .0570  .1590  .0242  Temp (0)  80.2  90.4  70.1  Time(hr)  15  15  15  {mg*l<* /br.) %  Normality NaOH  40  41  42  10.4  .0277  .0614  .1465  15.41  .0217  .0492  .1215  20.6  .0166  .0411  .1082  25.4  .0075  .0182  .052  9.25  .0259  .0548  .1260  15.15  .0707  .0414  .0940  17.45  .0127  0,0275  .0656  18.20  .0119  .0258  .0626  Temp fe)  70.7  79.8  90.5  Time (hr)  15  15  15.  KOH  (mg*/un7  h<:)  18 Runs No. 45, 44 and 45, were made using Methanol and Ethanol the solvent, for the NaOH and KOH. However weight losses were n i l . Normality LiOH  Temp.  Loss.  Vol.  Run  5.096  80.2  .0516  500  46  2.o5o  80.5  .0276  500  48  2.050  80.0  .0258  500  49  1.015  80.0  .0182  500  50  0.555  80.0  .0145  500  51  Time five hours. Normality• NaOH  Temp  Loss  Vol.  Run  15.45  80.2  .0585  100  46  7.15  80.5  .0774  150  48  4.86  80.0  .069  185  49  5.009  80.0  .0510  500  50  0.900  80.0  .029  500  51  Time five hours RbOH  Temp.  Loss  Vol.  Run  6.079  80.2  .0204  100  46  5.21  80.5  .0210  122  48  5.089  80.0  .0175  212  49  2.048  80.0  .0147  500  50  0.976  80.0  .0087  500  51  Time five hours  19 Normality CsOH  Temp,  Loss.  Vol.  Run.  9.806  80.2  .0068  100  46  7.930  80.5  .0075  i4o  48  80.0  .0069  222  49  5.157  80.0  .00616  500  50  1.179  80.0  .OO65  500  51  Time five hours Viscosities i n gentistokes were  for NaOH and KOH. The  correct viscometer was not available at time of these measurements and i n i t s place a viscometer of larger capillary tubing was used.  This  allowed.a shorter time for the liquid to pass through the capillary tubing*, hence a larger experimnntal error. Normality NaOH  Temp (0)  16.10  10,42  5.29  5.65  1  Time (sec)  Vigoosity  69.2  67.7  5.790  80.0  51.8  2.905  91.8  40.2  2.255  70.1  57.7  2.112  80.7  30.5  1.709  91.8  25.5  1.417  68.7  19.1  1.070  79.9  16.9  0.949  92.2  15.1  0.848  70.4  15.8  O.887  80.6 91.4  14.5 15.1  O.805 0.755  20  Normality KOH  Temp.( C)  14.8  69.8  58.2  2.155  80.0  51.8  1.780  91.5  27.45  1.557  70.5  26.5  1.485  80.7  22.6  1.521  89.0  21.4  1.199  69.5  18.76  1.052  80.0  16.9  0.948  89.0  15.8  0.886  69.5  14.8  O.851  80.7  15.4  0.752  90.5  12.6  0.707  12.5  8.55  5.14  Time (sec)  Viscosity  (centistokes)  The following data was taken from Chemioal Society of JapanJournal.  52  Molality 27.06 24.105 20.75 18.95 16.95  14.56  11.14 8.099  5.996 4.08  2.05 1.025 0.552 0.252  1951  p.646.  -6 50.96 27.15  19.21 18.02 15.66 8.87 4.57 2.07 1.51 0.917 0.727  0.680  KOH Molality 20.02  18.94 16.25 12.996  10.04  7.056 4.057 2.05 1.022 0.502 0.099  —  J_ 67.5  48.8 28.7 14.1 6.7 5.0 1.57 0.875 0.76 0.757 0.792  0.681 0.726  Temperature of concentration celllfrcm which activity coefficient was calculated was 25 C  21  GRAPH 1  Data from Runs,  21, 22,  2?,  and  42.  41  25,  GRAPH 2  "  d  GRAPH  n  n  n  25,  57,  46,  Graph 4  "  n  n  25  and  24.  GRAPH 5  n  n  n  From graphs 1 and 2 .  GRAPH 6  •  "  From Rune 2 5 and 5 7 .  5  n  (i  ^  5 9 <  4  26,  0 >  48,  4  L  49,  27, 40,  a n d  50  42. and  51.  Normality has  been changed to molality and multiplied by the activity-coefficient  as obtained  from page 2 0 . GRAPH 7  Data from visco ity measurements page 19 and 2 0 . B  o  22  Treatment of Results. When the I n i t i a l rate of attack is plotted against the concentrateion of the hydroxide, the general form of the curve rises rapidly to a maximum, then f a l l s off slower i n the case of Sodium hydroxide and much faster i n the case of Potassium hydroxide.  These maxima occur at about  5 and 10 normal respectively. The mechanism of a heterogeneous reaction of this typejis the diffusion of the reacting agent to the surface of the reactant, then the subsequent diffusion of the product or products away from the surface. It w i l l be chemically controlled i f this, i s the slower process and diffusion controlled i f this i n turn happens to be the slower prooess. Another important aspect of this heterogeneous reaction i s the fact that surrounding the s i l i c a sample there w i l l exist a layer or film of solution, which i s saturated with the products of reaction. It i s this film that controls the reaction since the solution must diffuse through i t to the surface of the glass and the products diffuse back out into the solution.  That i s , the effective  of the hydroxide w i l l be i t s activity in this layer,  activity  ^actors which will  influence the activity of the hydroxide i n this layer are, (l) Temperature, (2) Viscosity of solution, (?) product or products, (5) solution, (7)  Viscosity of layer, (4) Solubility of the  Thickness of film,  (6) Concentration of  Amount of product i n solution.  The samples were immersed for 15 hours which would eliminate the need to consider the amount of product i n solution, since runs No. 25 and 24 indicate l i t t l e influence on the rate i n this regard. Viscosity measurements on Sodium and Potassium hydroxide give a  ft* curve with an increasing slope.  Since j = nr  k the effect of the  viscosity of the solution on the rate vs. cone, would be to give a curve  25  with a decreasing slope, assuming that rate is directly proportional to concentration.  Thus the maximum due to a falling off of rate with higher  concentration i s not explained by the viscosity of the solution. an unknown factor is the viscosity of the saturated layer.  As yet,  The viscosity  of this layer w i l l change with the viscosity of the solution, depending on the concentration of the hydroxide as well as the concentration of the product.  However, this film will have a thickness which w i l l also vary  with the viscosity of the solution and the viscosity of the layer, becoming greater with increasing viscosity of solution and layer.  The  time taken for an OH ion w i l l thus depend on its diffusion through the solution into the saturated layer and its travelling the thickness of the film to the surface of the sample.  It w i l l also be controlled by the  speed with which the resulting product can escape. An equation which would correctly interpret the values of concentration vs rate of attack must take the above facts into consideration. Since a l l the required information is not available at present i t is felt that any derived equation would be s t i f f with assumptions and limited i n i t s application. The negative results obtained by the use of alcohol a a solvent a  indicate two possibilities.  One i s that the hydroxyl ion is prevented  from reacting with s i l i c a because of the alcohol and (two) is that the product formed i s insoluble in alcohol, thereby putting a thin protective film around the Vycor which prevents further reaction. The effect of the positive ion i s indicated by the set of curves obtained by plotting rate of attack vs concentration of a l l five metals. The hydroxides are stronger for the heavier metals but this does not seem to influence the order of the curves.  24 Sodium i s highest with potassium next, then comes lithium which appears out of place.  The rubidium and eeslum f a l l in line, with cesium  giving a very flat and non-characteristic curve.  No viscosities were  taken on lithium, ubidium or cesium, but indications point to an exr  ceptionally high viscosity for cesium.  Since the s i z  e  of the positive ion  increases with, the heavier metal this would make i t s diffusion to f a l l and thus would correspondingly slow up the reaction.  „ The lithium  may f a l l into i t s place because of a hydrated positive ion , thereby i n creasing its size and decreasing its ability to diffuse.  It may also be  notedtt that lithium i n many respects i s similar to a group II metal. This may have some heaping onlts displaced position .  SUGGESTIONS FOR FUTURE WORK. Whereas the phenomena of crazing was overcome, the reason for i t was not determined.  Indications point to a catalytic effect which  may be caused by the distortion of surface molecules due to strain.  (3) Many catalysts are believed taact as such because of their abnormal and misplaced structure lattice, the secondary forces thus created acting to speed up or hinder the reaction of the material i t is catalysing. The effect of the container cannot be neglected. glass samples, the pyrex container speeded up crazing.  For untreated This would i n -  dicate that the products of reaction speed up the effect of crazing. i n what way this i s done remains to be solved. treated glass,  Just  Also for long runs on  (several handlings had likely inflicted areas of strlee)  the iron tube did not cause crazing as did the other tubes used.  As a  check however asid treated glass should be left i n the various containers  25  for a long time i n order to positively establish the fact that acid treatment w i l l permanently prevent crazing. In order to check the existence of a saturated layer or film surrounding the glass sample, samples should be so ground that varying degrees of roughness are obtained before final treatment with acid. The rate of attack should be effectively gize of the sample mask any roughness.  the same since the. r e l a t i v e  is that created by the film.  This would probably  Another method would be to rotate sample ( a round  cylindric sample would be required)  at varying speeds -  s i l i c a depending upon the speed of rotation.  the loss i n  This same effect may be ob-  tained by allowing solution to stream past sample fit a f a i r l y rapid rate. If i t could be put under pressure this would help to remove products of reaction and prevent their forming a saturated layer about the sample. The last two suggestions<are given on the assumption that the rate of a attack is controlled by the  saturated Ljrer and i t s thickness.  A method  for the sweeping of the sample with a brush or rubber wiper should be considered since i t would be more efficient i n removing any products of reaction which may cling to the sample. Further work on the effect of product on the samples should be done.  I£ was assumed that the product did not appreciably hinder the re-  action for a period of 15 hours. Sodium silicate does interfere.  Runs have shown that the addition of However these results could not be counted  too seriously because of temperature controlling difficulties and also because the simple addition of sodium silicate does not necessarily give like products as are formed by sodium hydroxide on the s i l i c a . volume of standard NaOH should be made up and half of this  A large  allowed to  stand with the glass samples at the desired temperature necessary to react with a desired weight of s i l i c a .  26  The samples weighed before and after would give the exact amount of St Ojthat had gone into solution.  With these solutions and original  solutions a series of runs could be made which would determine the interference of product.  This procedure would ensure identical temperature  conditions which i n the past have been largely responsible for anomalous values.  Gentle  stirring of the solutions should be done since this  would keep normality of solution immediately surrounding sample more constant. The diffusion of product through the solution should fee investigated.  This may be done by allowing sample to rest on bottom of tube and  to draw off small amounts of solution from the top and determine the amount of s i l i c a that has diffused up to the top surface of the glass. A more exact method than this may be thought necessary however. Determination of the value of the solubility of product in sodium hydroxide solution should be done.  This may be accomplished by powdering  Vycor and allowing i t to react with hydroxide solutions, of varying for a time longenough to ensure a saturated condition.  C o n e ,  Then an analysis  on the amount of s i l i c a could be made on the filtered solutions.Viscosities of these solutions could then be made which would aid i n the derivations of a satisfactory equation. Some experiments may be done using a mixture of methanol and water, or ethanol and water.  The influence of the alcohol may give some  indication as to the medbanlsm of the reaction.  Also a qualitative test  in alcohol, voul^ indicate "the to find the solubility of sodium silicate failure of alcoholic solutions A  of sodium and potassium hydroxide to react. The effect of group two metal hydroxides on s i l i c a may help to explain the misplaced lithium curve.  BIBLIOGRAPHY  (1)  The determination of the rates of attack of Sodium and w  Potassium hydroxides on 790 Vycor glass and Vitreous s i l i c a .  J . fr. Hooley and J . W. Wainwright, University of British Columbia. M*>j  (2)  A Treatise on Physical Chemistry,  B.fl. tU«U..  (vol. 2, page  H.S.Taylor. (5)  Text-book of Physical Chemistry.  (page 1121)  S. Glasstone.  


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