This thesis contains the results of experiments of the effects of electrolysis of the viscosity and time of set of silicic acid gels

Rhoades, John W.

English

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Union CollegeUnion | Digital WorksHonors Theses Student Work6-1942The effect of electrolytes on the viscosity and timeof set of silicic acid gelsJohn W. RhoadesUnion College - Schenectady, NYFollow this and additional works at: https://digitalworks.union.edu/thesesPart of the Chemistry CommonsThis Open Access is brought to you for free and open access by the Student Work at Union | Digital Works. It has been accepted for inclusion in HonorsTheses by an authorized administrator of Union | Digital Works. For more information, please contact digitalworks@union.edu.Recommended CitationRhoades, John W., "The effect of electrolytes on the viscosity and time of set of silicic acid gels" (1942). Honors Theses. 2109.https://digitalworks.union.edu/theses/2109THE EPFEC1l1 OF' iiLECT'ROl.JYTES ON 'fHB VIBCOSI'l1Y AND r11IME OE' SE'r OF SILICIC ACID GELS THE EF1~"'ECT OF SLECTROLYTES ON THE VISCOSI1'Y AND 'l'IHE O~, SET OF SILICIC ACID GELS 1\ thesis presented to ·the Depar tment of Chemistry at Union College in partial fulfillment of the requirements for the degree of Bachelor of Science in Chemistry, by Approved by __ ~--~- __ (;3_._~--......:-·--- April, 1942 INTRODUCTION The phenomenon of gelation of silicic acid gels has been round to be infl uenoed by seven variables. 11he factors determining the time of set have been sum- marized by Flemning (1), Hurd and Carver (2), and Hall- strom (3). These factors are: 1. The silica concentration 2. The acid concentration 3. pH 4. 'I' empez-a ture 5. Agitation 6. Added 80luble material 7. TYPe of silicate Of the above factors all we:re held constant with the exceput on of (6), which was being. studied. The time of set was determined by the tilted. rocl method, but before the gel set the time: of flow uas observed at frequent intervals, using an Ostwald viscometer. rrhe Ostwald vis- come't er- has been used ui th success by Pr-aaad, Mehta, and Desai ( 5), Santora ( 4), and (lormley ( 6). By using this v Lacoue t er' a study of the complete period of gelr ... tion can be ~~de from the tiue of mixing until the gel becomes too viscous to flow tnr-ough the cs .. pillary. 'fhif.i thesis contains the results of experiments · on the effect of electrolytes on the viscoaity and time of set of silicic acid gels. HISTOH.ICAL l?re.kash and Da.hr (7) have shown that viscosity measurements of ao.Lu t.Lon of· sodium siLicate and an acid ar-e an Lnd Lca t Lcn of what they believe happens as a gel sets. As mentioned by Santora, Dahr and Chakravarty (8) have noted the effects of salts on the viscosity of silicic acid solutions, and found that with increasing quantities of electrolytes the vlscosity first falls and then rises. Dahr carae to the conclusion that the rise in viscosi t;y was a measure of the degree of hydration of a particle. The viscosity curveo in this thesis are similar to those obtained by Santora and Prasad, Mehta, and Desai. Fraser (9) conducted vi,cosity ex-oeriments uith both the Ostwald and the Stormer type visco:-:1eter and found that although the Stormer type had great possibili- ties, the Ostwald viscometer ua.s better to use because of its sir::plicity. A. Einstein and E. Hatschek, as mentioned by 0-ormley, devised an equation to.calculate the viscosity of a dispersed system, provided. that: (1) the particles are spherical and not deformable; (2) the dimensions of the particles are large in comparison to the molecular dinenaions of the dispersion rnedlum; (3) the particles must be small in comparison to the measuring instrument; and {4) the mave~ent of the dispersion medium 1n the direct vicinity of the particles may not be influenced by the or-es enc e of other particles. 'l'he hydration has been calculated, although these conditions are not fuJ..- filled in the case of silica gels. PROCEDURE Pre~aration of Solutions A quantity of E brnnd sodium silicate, a product of the Philadelphia Quartz Company, was diluted with r-ecen t Ly boiled distilled water. 'l'he resulting solution uas titrated with standard sulfuric acid and its equiva- lent as NaOH determined as 1.295 N, using methyl orange as an indicator. The acetic acid uas prepared by diluting 99.5% glacial acetic acid with recently boiled distilled water. 'l1he norma.11 ty of the acetic acid. as determined. by the standard sodium hydroxide, and using phenolphthalein as an indicator, was 1.908 N. 'J:'he electrolytic solutions ver e pr-epar-ed by dis- solving pre-determined amounts of the salts in distilled water anc1 mixing the gel solution with the proper amount o r sul t solution to give a f'Lna.l, solution of all.rays 155 c.c. and.3M with respect to the salt. T.em,perature Co,ntroJ, The temperature was controlled by a thyritron cir- cuit and a mercury-B.lcohol thermo-regulator. As all experiments uer-e per-ro rmed at ?.5° C., once the t enrcer-a- t ur-e was set the thermo-regulator· needed no more ad juat;- rnent. 'I'he temperature of the bath was only slightly above room temperature and the ther.r.:J.o-reguln.tor worl{ed very well, not varying more than !.1° C. Prenaration o:t' Gels In order that the viscosity measurements are to have any meaning, it is necessary that the gel-forming solutions are accurately controlled and recorded. In the procedure, the silicate solution was measured into a clry, clean 250 c . c . beaker ui th a p i.pe t t e . 1I111e acid solution and the thir·d ocns t i tuent were measur-ed into another 250 c;c , beaker \~rith pipette • 1i1he t'tJO solu- tions uer-e placed in the water and allowed to remain there until they reached the temperature of the water bath. The silicate solution uas then poured into the acid solution and the two ver-e well mixed by rapidly pouring back and forth. The viscosity measurements were then ready to be made. The tirae after mixlng was measux-ed by an ordinary wrist watch with a :sueep second hand, and was measured from the time the silicate solution was first poured into the acid solution. The time of flow in the viscometer was measured by means of a stopwatch. :Q~l .JjeasuJ;:,ements It has been shorm by Hurd and Griffeth (10) that the quinhydrone potentiometer gives reliable results in an ao td gel mlxtu!'t'. It was used in th2.s case as all measurements were in the anid rag:ton. A calomel cell with saturated KC.l solution. and a platlnum wire electrode were prepared and used in the noz-aal, way. The pH measurements ver-e taken in beakers and , s tnce the quinhydrone was added, this solution was not used in the viscosity measure- ments. The Ostuflld Viscometer Since only- relative Lna t ead, of absof.ute viscosi- ties were required, tine Ostwa.ld Viscometer was used. This type has previously been used by many workers with success. '.rhe Ostwald Viscometer is essentially a U tube with a capillary in one arm. Near the top of the capil- lary there is a. small bulb of about 2 or 3 c.o. Above and below the bulb are marks on the capillary tube to serve a s reference maz-ks . A definite volume of gel solutlon is pipetted .into the large a.rm arid sucked up a short Nay above the top reference mark. As the liquid goes back dovrn , the time from which the meniscus passes the top reference uark. until it passes the lower reference mark is measured by the stopwatch. '11he instrument ie cal fbr-a- ted by determining the tine of flow of a liquid whose viocosity is known at that, tempe:ratu.l"e at which the run is made. Distilled wate;r and 11ropyl alcohol uere used in this case. The viscometer used. on these experiments had a large capillary and for that reason the time of flow vas short. If a sms.11 capillary ls used in the case of silicic acid gel, the r-e sul. ts are not very sa tis- factory, as the size ¢lf the cap111ury is too near the size of\ the coagulated particles. Determt_nation of Time of .Sfi2.t. by 1til:.ted Rod The t Lme of set 't:lll.8 determined by the tilted rod method, as described by Hurd and Le t t er-cn (11). The glass rocl should. be 3 m .rn , in d Lane t er- and 10 om. long, one encl of which is drawn to a point. Ths- glass rod is placed in the gel at an angle o r about 20° to the verti- .l. ea.1 and the gel is said to be set when it is etii'.f enough to hold the rod in the ti1 tea. po s I t Lon , The time of set as determined by this method is longer than the time of set determined by the viscometer. That is, when the gel has ceased to flow in the viscometer, it is not yet stiff enough to hold the rod in the tilted. position. In the following exper-tnent s , the time of set was determined by the tilted rod method. .EXJ?EHLIENTAL The process of gel-forming 1'11as studied by the indirect method of noting 'the effects of adding electro- lytes in add.i tion to the Nao2n3o2 f·:i1~med naturally from the combination of sodium siliea·te and acetic ac Ld . By adding predetermined. amounts of salt solution, the final concentrations were- made .3 molar with respect to the salts, with the exception of K2S04 and Na2so4, uhioh uere not soluble enough. The solutions were prepared as mentioned before and 10 c.c. pipetted into the thermo- stated viscometer. The time of flow and the tl~e after mixing was noted. as i-rnll as the pH and the time of set as determined by the tilted rod method. The data obt;ained is recorded at the end of the paper in Tablss I through XXIII. Visco::1ity runs were made, using as tne tb.ird constituent: H20, Na.Cl, KCl, i.rci , NH4Cl, NaBr, KBr, LiBr, NH4Br, Na.I, KI, and NH4I. All the viscosity curves (Plates I-IV) have the same general shape and therefore the viscosity runs wer-e discontinued and mer·ely the tir.1e of set noted on the rest of the salts. 'l'.he viscosity curves came out as one would expect. That ia, the viscosity lnoreasec slowly at first but, as tine goes on 1 it Lncr-ease s rap1<1ly. '1'he sal te were so chosen that the effect of both the anion and cation could be observed and studied, In addition to the before-mentioned s al, ts, the time o.r set was meaaur-ed )Jhen the following .salts were used: NaN03, NH4N03, KN03, Na.CNS, KCNS, ~m4cms, (Nlti)2so4, K2so4, and Na2so4. RESULTS AND PISCUB.§ION When the S.:.d.t solutions we:re used in place of!- pure ;ir:;i.tr:r, the t Lme of set 1'.ra.s very markedly decreased and the viscosity our-ves s~1eep up much sooner, as is shotm b 1"1 .;.. ,_ -v y Jf H\•CS l.-.,1. • the order of the coagulating :pouer of the For the anions_ the order is: ~ ;r.-- / cNs /Br >No: 7.c'i / so=4 0 · Thes.e results compare very wall with the ·work done by Santora and others on sil iclo acid. gels and also w1 th the ·work done by Klobusitzky {12) on the speed of bLood coagul.a- t1on. Ths proeess of gel fornat1on i.s not fully under- stood and, for th.a.t reason, it Ls difficult to say how the salts affect the gel. One theory is th~t a latt1ce ls set up and trai;rn the water molecules so that the solution soli- clifies. Another is that the 11articles coagulate and grow larger and larg~r· unt:ll the sol becomes imruab11a. The clE:crease in the tiz:.10 of set when ti salt is present is said to be clue to either the fact th&t the sn.lt;s act as a cat a- l~st or that the salts neutrcllize the charged particles so that they do not repel ea.ch other and therefore coagulate more rapidly and become hydrated. As the pe.rti;;:.les be- cone more and more hydrated they become la:r:•ger and, a Lso , the dispersion liquid decreases 60 that both raots tend to make the; :solution become mor-e solid. It seems reason- able that v Lacos t ty curves have there shape because of the increaning size of the .r.·'a.rtloles. When ths particles az·e small (as when the gel i.s first mixed), a compara- tively la.rge increase in size would not affeo·t the vis- cosity greatly unlen£ ·the particle size 11.ras approaching the .size of the capillary tube in >;rhich case a small Lncr-eas e in size would greatly increase the tlm.e of flow. This would account for the sudden up-sweep in the vis- co sf ty curves and also for the fact that thd •riscosity depends on the size of the capillary used. ilthough the formation of the gel may be due to the lattice structure or- the coac;v.latiot1 and hydration, it is very lik.ely that it: is a comb.i.nation of the two effects (per.haps others) ~;rhich actually cause the gel to 80l1-11fy. Hofmeister experimented on the lowering of the tsmperature of gelP.t.ton and arrived at the following order: SCN > I > Br - > No; > 0103 >Cl- > C2H302 > so4- 1tJi th the first having the greatest influence and the la.st the least lnfluenoe (13). This aeries le knovn as a Ifofmeister or Lyotropic series and agrees l·.rell with the uor1t reported in this thesis. l. J1he Ostwald viscometer- has been used to .study the viscosity during the p~ocees of gelation. 2. The time of eet of the gels has been shown to decre~tse in a typlcal lyotropio series when oat.t s are added. 3. Some ideas of hm.r a gel sets and how the salts aff'ect the time or set have been state(l .. 4. The order of the salto has bet'n shown to agree with the work of others. I TABLE I Galibra.tion of Viscomf!Jter Time of Flow (Sec.) Pure distilled HzO - 25° C. 9~0 9~0 9.o 9.0 Av·e, 9.C Propyl Alooho1. - 25° C. 2.2. o 22.0 22.0 21 •. 9 1\ve. 22 .0 !11 the following tables, the total volume ls always 155 c . c , In each ca ae 10 c , e • :..rae pipetted into U1e viscometer and the t eraper-a.tur-e held constant at 25° C. Mixture as follotrn: Time aft1r M1x (min.~ ~ 10 l\;, 26 34 42 46 50 54 58 62 66 68 70 72 74 '(6 78 80 82 100 .Time of l:i.,.low (sec. ~ 11.·6 12.0 12.5 13.2 1·4.4 15.8 16.8 18.3 19.8 21.8 25.0 28,6 31.4 34.6 38.6 43.6 50.0 59.1 ''/2. 7 96.4 Set Mixture as follows: t'.! 10 18 26 34 11.6 12.0 12.5 13.4 14.1 16.0 16.6 42 46 50 54 18.0 19~? 21.? ;24.8 28.7 31.2 ~3·1.6 38.4 43.0 50 .. 4 58.9 72.6 96.5 Bet 58 62 f56 6a 70 72 '(4 ?'6 78 80 B2 100 TABLE IV hixture as follows: 55 c.c. 50 c.c. 50 c.c. HAc NazSiO H 0 3 2 pH - 4.7 Tirae after Hix (min.) Time of Flow (sec.l 2 11.8 10 12.2 18 12.6 26 13.4 35 14.7 42 15.9 50 18.2 54 19.7 58 21.9 62 24.6 66 28.6 70 34.0 72 38.3 74 43.0 76 49.5 78 58.0 80 72.2 82 '91.2 100 Set Potentiometer -168 -174 -174 -174 Mixture as follows: 5 5 c • e • HAc e pH - 4 • 8 50 c.c. Na2Si03 40 c.c. H20 10 c.c. 4.65 M NaCl ir:l.me after Hix (min· l Tim.a of JPlow (sec.2 2 11.B 10 12.4 18 13.4 26 14.8 32 16.0 36 17.6 40 19.6 {2 20.8 •14 22.4 4'6 24.4 48 26.4 50 29.4 52 ;53. 7 54 38.4 56 46.4 58 57.6 60 75.7 74 Set Potentiometer -168 -170 -1?0 -170 Mixture as follows: 55 o.c. HAc pH - 4.8 50 c .c . ~rans103 30 c.c. H26 20 o.c. 2.326 M KCl Time after h1x (min.) 2 10 18 26 30 34 38 40 42 44 46 58 Time of Flow (sec.) 11.6 . 12.4 13.8 16.6 19.1 22.8 29 .. 6 35.1 44.0 5?.7 94.6 Set Potentioneter -170 -184 -177 -172 TABLE VII Mixture as follows: 55 c.c. HAc pH - 4.8 50 c.c. Na2Sl03 30 c.c. HzO 20 c.c. 2.325 M LiCl Tioe after Hix (min. ) TiF1e of' Flow (sec.) 2 12.0 10 12.4 18 13.4 26 14.6 30 15.5 34 16.6 38 18.0 42 19.6 46 22.0 50 26.l 52 28.5 54 ~1.8 56 36.0 58 41.3 60 48.4 62 59.4 64 76.2 66 128.4 85 Set Potentiometer -170 -170 -172 -172 lilxture as f'ollowe: 56 c i c . Hi c pH - 4.8 50 o.c. Na2Si03 30 c.c. H20 20 c.c. 2:325 M NH4Cl '.r'lme e.fte:r Hix (min.) Time of Flow (sec.) 2 10 18 26 ;y!, 38 40 42 44 46 48 50 52 66 11 • .S 12.·4 13.8 15.8 19.S 23.2 25.6 29.l 33.4 39.0 51.7 61.5 104.0 Set Pot en tior.1ete:r -166 -169 -170 TABLE IX Mixture as follows: 55 c.c. HAc pH - 4.8 50 c.o • ~ta a iO • ~ .•".}0. ·3 30 C. • G • H2b 20 o , c , 2.325 M Na.Br Time after Mix {min.) 2 10 18 26 30 34 3£1 42 tj.L_l 46 48 50 52 51:1.; 56 70 Time of Flow (sec.) 11.8 12. ~1 13.2 15.0 16~0 18.0 20.5 24.2 26.6 ~0.2 34.S 'U.4 51.8 6.6.2 106,0 Set Potentiometer -148 -158 -169 -168 Hixture as i'ollous: B5 c , c . HA.c pH - 4.9 no c.c. Ha?SiO 30 c , c , Ho 3 2 - 2.325 M KBr J - . c. 2 10 18 26 30 46 55 'l'lf..lLOf l''low { ~ec .l .11.6 12.4 J .. 3.5 16.2 18.6 20.2 22.2 (')- .... , '--0. (.; 28.8 34.l 42.8 55.8 89.2 Set -158 -164 -163 !itixtur·e as follows: 55 o.o. HAc 50 0 •I.} • ~e.25103 30 c • c . .tf,.,Q 20 c.c. 2~325 M L1Br \)rt - 4. 9 .. 2 10 18 26 ,34 38 4f~ -~6 48 50 62 54 56 58 60 62 77 11.8 12.6 1.3.1 11.9 16.8 18. f.) 21.0 2-1.2 26. ·1: r?.9. 7 3.:). ~1 ,38 .4 45.6 55.? 71.2 117.6 Set -166 -166 Hixture as follows: 55 c . c , HAc pH - 4.8 50 c.c . 111.-·o'JtO ... 1 .. 1,·;. .. '3 ,30 c. c , l-• .... 0 ,. ..... c,, ~ 20 c.c. 2 •• 325 l-1 NH4Br 10 18 34 38 40 48 60 11.6 12.4 114:. 5 l5.2 19.8 2-'1.3 :~7. 4 ;51 .6 .38 .5 "~8. 5 Go.2 f}e1; -168 -170 -1?0 11ABLS XIII --··""·~-,. ... ~ Mixture as foll01.rn: pB - 4..7 r,1• r t '1" J! iJL..l ~ioe a er ~ix m n . .. ....-~.... . _.....,_..__ ...._. 2 10 18 26 Z50 34 ·:'.)8 42 .cj,4 46 .... rn bO 32 66 ll.6 1'8.2 13.2 1.4.8 J. ·). ~ ra.s 21.3 26.4 so .o ~)4. 9 42.4 50.6 ?.:j;,8 f~st Potentiometer .....__,,.,,., __ ._ .. _ -1'?8 -176 -174 Kixture as fallows: 55 c . c , L10 c . c , ::10 (; • !.,.~ • GU (; • (J • (.:! :tO J.8 22 ~6 ::10 pH - 4.6 :i :i .·1 :er .. r; 13.H i s.a :L 'i' • ::s 20.4. 23.1 ??.O ;)}.. .• O ~l.l b6.l Set 'rABLE XV llixture as follows: 55 c.c. 50 c.c. 30 c.c. 20 c.c. Time after Mix (rain,) 2 10 18 26 34 38 40 42 jt4 55 pH - 4.6 NH I 4 Ti~e of Flov (sec.) 11.4 12.0 13.5 16.0 22.0 29.0 35.2 43.5 60.2 Set -17·4 -174 -J.'73 -173 Potentior.1eter -192 -180 -180 Mixture as follows: 55 c.c. HAc pH - 4.7 50 c.c. NazSi03 30 c.c. H20 20 c.c. 2 .325 !{ NaN03 Tine after Mix (rain,) Potent.\op1eter 10 30 60 72 Bet -184 -178 -179 -178 TABLE XVII Hixture as follows: 55 c.c. P.l!..C pH - 4.6 50 c.c. Na2Si03 30 c.c, H20 20 c.c. 2,325 F ?H4tl03 Time after Hix \1:..1JL..l Potentiometer 6 -180 19 -180 39 -180 60 Set -180 Mixture as follows: 50 30 20 55 c.c, HAc c.c. Ha2S103 c , c , HzO c • c . 2 • 32£.; M pE - 4,7 Tine after Mix (min.) Pot en tic-i:v:: ter __,.......,..........,..:::;......,.... ... 10 30 54 58 Set -176 -176 -176 -1?6 TaBLE XIX Mixture as follows: 55 c.c. 50 c.c:. 30 c.c. 20 c.c. HAc Na8Si03 ~:325 H NaCNS pH - 4.8 ~ime after Mix (min,) Potentiometer 11 45 63 Set -167 -168 -170 Mixture as follows: 55 c.c. HAc pH - 4.8 50 c , c , Ne.2Si03 30 c.c. H20 20 c.c. 2.325 H K0HS Tiue after Hix (0.-:iW PotentioIJ:eter 10 32 48 52 Set -156 -159 -166 -168 !!!BLE XXI Mixture as foll en-rs: 55 c .. ,"";. !iflC pH - I L ... 1 - ' ._, 50 c.c. ., s· o ~'Hi2 .L 3 30 c , c . H20 20 c.c. 2.325 H NTlACNS . ... T irne aft er Ml 'X'. { :.nin • ) 13 21 32 47 56 Set ·-152 -158 -169 -169 -169 Mixture as follows: 55 c.c. pH - 5 .~~ f.() G. C. ;3() ?O :Potent1t1ueter -~·------ 20 40 55 67 Set -132 -142 -144 -144 '11ABLE XXIII Mixture as follows: 55 c.c. HAc pH - 5.0 50 c , o , N'a2Sl~3 _ , 50 c . c , 1398 .tYI K2S04 'l'ime ,a.ft er Mix (min,, l Potent1omete1~ 12 50 70 74 Set ... 141 -145 -160 -160 TABJ.,,g XXIV Nixture as follows: 55 c.c. HAc pH - 5.2 50 c.c. Na2Si03 50 c.c •• 400 M Na2S64 10 40 65 89 Set -139 -1•!4 -160 -148 31 BIBLIC{}H.APHY 1. Flemming - Z. Physilt.,Chem. 411427 (1902). 2. Hurd and Carver - J. Phys. Chem. 37,321 (1933). 3. HD.llstrom - Senior rl1hesis, Union College. 4. Santora - Senior Thesis, Union College. 5. Pr-asad , Mehta, and Desei - J. Phys. Jhem. 36,1384 (1932). 6. Gormley - Senior Thesis, Union College. 7. PrakaBh and lJahr - J. Indian Chem. Society, 6,391 {1929). 8. Dahr and Chn.1rravnrty - l{ollolcl Z.J 44,2?5 (1928). 9. lt"'raser, clenior 'I'he s Ls , Union College. 10. Hurd and Griffeth - J. :Phys. Chern. 39,1159 (1935). 11. Letteron - Senior Thesis, Union Collerye. 12. Klobusitzky - Biochem. 2,157,273,354 (1925). 13. Getman and Daniels - Outlines of 'Theoretical Chem. 230. 

The effect of electrolytes on the viscosity and time of set of silicic acid gels

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The effect of electrolytes on the viscosity and time of set of silicic acid gels

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