HI 1 1 ”—— __'_— ——_— _’—’ _———— ’g ____— ’—d ——_— __—_d —_———— ____’ ____— __.___.__— _——_—— _———— —__—— _____— ____’4 _—‘_— ___—— _—_——— _—_—— ’4 ,__———— ’I— ’— \H ELECTROLYTIC FREPARATEON CF LEAD CHROMATE TEESES FOB TEE DEGREE OF M. 3. Vincent E. Shulnburg ' i934 2r mwmdcft ‘6';th ELECTROLYTIC PREPARATION OF LEAD ChRDEATE A.TEESIS SUBLITTED TD TEE FACULTY OF M I C H I G A N S T A T E C O L L E G E AS PARTIAL FYLFILLKENT OF TEE REQ"IREIEETS FER TEE DEGREE OF EASTER CF SCIENCE BY VINCENT E. SEULNBURG TABLE OF CONTENTS Introduction 1 Description of Apparatus 3 Preparation of Electrolyte 5 Procedure and Results 6 Discussion 22 Summary 24 '1 @1153- U ELECTRLLITIC PREPARATION CF LEAD CZRCXATE _— INTRODYCTIGN Lost of the work in this investigation was devoted to a study of the various factors which effect the electrolytic preparation of lead chronate. These factors include current density, composition of electrolyte, temperature and cell design. The first electrolytic process for the electrolytic preparation of insoluble compounds was developed by Luckow. For such preparations he recomwended a solution of 1.5% of a mixture of 9 parts of NaClOB and 1 part of Na CrOh. This was electrolysed between a pure lead anode and a hard lead cathode. The anofiic current density was about .EA amo/dmg and bath voltage being 1.4 volts. These processes were later studied by LeBlanc and Bindschedler, Killer, and Gillett. They worked with different secondary salts at different concentrations and mixtures. The effect of temper— ature was also studied. It would be expected that the precipitated particles by the electrolytic process would be finer the higher the concentration and the greater the cur— V rent density. do ever, the above investigators found that if very low concentrations of the precipitating sclt enfl low current densities were not used, adherent deposits on the anode would be formed instead of fine precipitates. In the attem2t to prepare electrolytic lead chromate the cell would yield Pb Greg for a short time 'and then a mixture of Pb CrOh and PhD would form. This would give an undesirable color. The two Opposing sets of conditions have rendered it im ossible to produce particles beyond a certain degree of fineness and color. The percent solution and mixture recommended by the above investigators was first used and then a cell was devised and electrolyte made up as described later in this thesis. The purpose of this investigation was to devise a cell and to formulate an electrolyte which would yield Pb CrOh continuously and maintain a uniform color. DESCRIPTION OF APPARATUS A rectangular aouarium jar holding 25 liters of electrolyte was used for the preliminary trials. This did not prove satisfactory because the lead chromate could not be removed immediately upon formation and only short runs could be effected. A large cell was made from a flat bottomed carboy which had a capacity of 40 liters. The bottom was cut off and when inverted formed a cell with a conical bottom. A rubber stOpper, to which a rubber and glass tubing had been fastened, vas placed in the mouth of the carboy. This formed an outlet for the product without interrupting the Operation of the cell. The carbov was placed in the original container after it had been inverted and supported with four legs about 60 on. long. The part of the box through which the neck of the carboy protruded was re—enforced to hold the weight of the electrolyte and product made. A platform, connected to the container, was built over the cell to hold the storage tank of electrolyte and the solution of chromic acid. A half-inch lead coil (50 feet long) was placed in the cell to cool or heat the electrolyte as desired. Two half-inch COpper rods were used to conduct the current and to support the electrodes. The electrodes were made of sheet lead and were connected by battery clips to insure a good contact. Each electrode was placed 1 cm. apart and separated from each other by two glass rods. If they are not separated by the glass rods, they will short and cause cell to cease Operating. The switch board was built in with the buss bars and was capable of giving 1200 amperes. 15 volts were used across the bars. / A ’IIIIIIlI/I[I’ll/I’llIll/III/IIIIIIIIIIII/ -+-+-+- 00000000 IIIIIIIIIIIIIIIIIII'l’lll’IJ I‘lglllll/ll’lli/’I”’//’////l 7/////////’//////’//A’//I’////////’//”’.’””’/I/””’.’I Wood 802: c... A- Lead coil D - Lead flan-ode: 8' Glass C:// E ~ Cfiromic aazd PLATE 1 PREPARATION OF THE ELECTROLYTE In the beginning a 1.5% solution was made, con— sisting of 20% sodium chromate and 80% sodium chlorate. This gave an electrolyte with a pH of 8. xperiment showed that the pH should be below 7. In order to have a common ion and also to lower the cost of he chemicals, the equiv— alent of sodium acetate was substituted for the sodium chlorate. LeBlanc and Bindschedler showed that equally good results would be obtained with the acetate. Glacial acetic acid was used to correct the PH to 6.5 or 6.$. To include the acetic acid in the percent solution and to have the percentage of the acetates direct, a correction was made in the percent solution. It is now 1.3% consisting of 23% sodium chromate, 69% sodium acetate and 8% acetic acid. This mixture of salts and acid was nade up to the calculated volume with ordinary tap water. Distilled water gave the same results. When a PH lower tha 6.5 was desired, more acetic acid was added; but this addition was not taken in— to account in the percent solution. During the Operation of the cell the pH is kept con— stant by replacing the chromates used and the hydrogen evolved by use of a two molar solution of chromic acid. The chromic oxide was a high grade commercial product. The re- mainder of the chemicals were of the C.P. quality. PRQCEDURE The anode electrodes were cleaned mechanically until the metal was bright. This is necessary before each run. The electrodes were suspended on the cooper rods in the cell. The electrodes were then connected with battery clips to the cooper rod to insure better contact. After the electrolyte was slaced in the cell the pH was cheched with the Helige comparator and then corrected to the de— sired pH. If the run is to be other than room temperature, the electrolyte is heated by means of the coil through which steam is passed. The chromic acid solution is placed above the cell which is then ready for operation. As the current is passed through the cell, the chromic acid is allowed to dron at a rate to just keep the pg constant. The pH is check d at frequent intervals. Lhen the Pb Crou settles to the bottom of the cell, it is drawn off and nlaced in a storage tank to be washed. Washing is done by decantation. When free of acetates, the chromate is filtered with a suction filter and air— dryed in the room. Weighing was done on a large scales. U Boaaow comaw eoaao» momma aoaacw soaamw BOsHmw aoaats pasaum SCHHew BOHHQW pas Hoaoo ow capoom m.H mm.m sm.H m.m PPQB uoaau \mUQTOnw \ 9 \ monoflo Iflmym zmnosm 2m .mpmpmoa hocoao Iamwm puma Iago asaeom amm m.m m.l~ .QH damfiw .H qu49 mofiphnpcmomoo mpmaoapomfim OMH O O O ‘0 cm H C) O N 00H mm om paob mOHm Imsm Hapoe N U\ 0 LO 0 N N OJ 0 N H.H m. mm. apamnmm, pmmahso cow 00m com com com 0mm 00m 00m 0. 0C .mEmB m m .opaaosgo Edatom fimm I moapflmocsoo mm.a m.x m.m opmadaoosH m m m.m m.m m.m m.m .cflos capoos am soaats o.m aoaao» m.m FPOHHQW phaflq m.H aoafio» haaq m.H hoaam» pzaflq :m.: #03 PPGEOHHM Hoaoo \mmssom .GPNPOOu Edwwom fimw .mpsEOHgo fisfloow x \‘ 3...). d “mu.” A.» moflpflmomSoo coflpsnpcmosoo mpzaoapooam fim.m am.s ha.¢m mm.m m.m ma amw.¢ aces mm.¢ m.m oo am.fl a .am m.mH OH emu smms.fi amm ma.a s oma $4.: dam 3 am ow .ahm .umm .QH sacs .caa amnmcm paoauso oawflw Hapoe i.H 0mm :.H com w omm m 0mm s.H 0mm ,Npamcoo .oo psoHHso .mhma m.m m.m : w.m m m.w m m.m m m.m as M. ofios oapmow $m mphpmow Esfiaom opwanzo EdafiOm o... \ . aow . wmm u soapamooaoo coflpwnusmosoo mpaaoapomao fim Boflam» vfiow anoago opmma EOHM ovum nmmsw Hana so.m amw.a anoa : a ooa m.m oom ms.a m.m .mH sm.a, aH:.H am.mm m.m m.m mam NH 0mm m w.m .sH mm.a a~.m ham m m ow m.H oom m m.m .mH sesams phauq mpmaasoo poz amm m.m 01H a com m m.m .mH pma ppaaoaua ,qaam «has xlwna .pHos .asa spumaon .oo .Hg .u: .02 HOHOO \mocsom mmnocm pconnso wamflw Hmpoe pnmanso .QEoB mafia mg cam lO ”:m.mm.mmnam mash mo :oHpHmooEoo Beast» macaw a aoaats phaasm Boaaow phaunm Boast» phausm soaats pamahm no; Hoaoo Uflow capoom fiw opwpoos Edacom am mmeoaho Egaeom flma m4 . m. “mm H . m mo.w a~:.m ~.H amm.a ppsa .mmm Ioawu amaosm \mCQsom w v uHow oapmow opsmea EsfiaOm opmsosho EsflwOm "cm a ma mass mo coHpHmocaoo aoflpsapsoocoo opmaoapooao flea am.om mm m.m 0mm w om wa m.w .am haw H.m m.a 0s :.a om m m.m .mm am.am mm.a m.m 0mm m om m w.m .mm aooa m.a m.~ oma ma om m w.m .Hm owoapooflo 0p xospm poswoam t opoadficosa mum .om meospomam 0p mNOflpm poscosm amm mo.m m a oma ma om H m.m .mH .amm .nH pao> .osa mph Moo .Hh m .om puma Gama» aspoe Imamo .Qfoe made a mum Iago paws Iago 11 Boaamw 'oumur‘ra ”lb paauu Boaamw Immcwam paths Soaamw :mmssan pgaflq “EH9 Hoaoo ©ao¢ owpood Boaamw amonm soaao» compo aoaaw» pox Hoaoo mm.m P Pat. Ioafim \mtmsom as.a aom m.m m oma m m.a m m fimo.m fimm m.: m oma m m.m m w a¢H.m how a m oom m.m m.m m m . .mmm .aam .QH .pao> .mra mph >mamsm pawn UHoH» th09 :mch ma .Hg .02 name psma mafia Gum Iago .ooom ! waspmnmmEme flm .opmpooa Esflwom flaw .opmsoago Edfiaom wmm I mpaaoapooam ac nofipflmoaaoo m.H u godpsfiom a ma mafia soflpmfiam> .HH Hamde 12 The temperature varied a little during the Opera- tion of the cell before the cooling coil was installed. As the pH was lowered, the color at the time of forma- tion changed from a light yellow to a green yellow. The green color was very pronounced in the electrolyte of 9.5 pH. However, after being washed and dried, the color of all the trials was very nearly of the same shade. The green color may be due to the formation of chromous acetate which is soluble and easily washes out. The drop in the percent yield in the last run seems to indicate that such a reaction may have taken place. It is better to Operate the cell at a pH of 6.5 to 6.8 since the final color is the same regardless of what the color was when formed. The change in the concentration of the electro- lyte, when the acetic acid is added to change the pH, was not taken into account. This is only a small amount, and the voltage shows that the conductivity was not raised a1 appreciable amount. 13 BbHHmw IGUGGHO EOHHQV Soaaow Immense pawns aoaat» Roads» Boaacw pnmflq Ham pea Hoaoo Hoaoo Ufiom ofipmom fin xxx .mpmpmo¢ m.m amw.s sooa mm.s ow m.m o.m aw.: as.sa mm.m ms m.m $3 $3.: ammo ad. ow fim ppaaoaam .nmm .mwm .QH .oaa pao> \mucoom mwnmcm pawn UHmH» Hmpoa Iago 00m i .MH 0mm m.m .ja 0mm m .oa Orko GHQ OOH/H .Qsme made Gym mEU\.m§w :.H I mpfimsma pmossso Edafiom &mm .mpssoago Edflvom Rmm I mpsaospOc m.m m.m whopwymmflme SPHE .HHH aqmae sofipwfihm> Hm mo noHpHmOQEoo Gowpoaom & opsacapomam we mg In this series of runs (TABLE III) the tenpera- ture was varied from room temperature up to 5000. The results show a snall increase in current efficiency but a darkenino of the color. The increase in temper- ature increases the conductivity and thus shows better results. The change in color is more noticeable when the lead chromate is dry. This gain in energy efficiency is not sufficient to Warrant heatin: the electrolyte to 5000 and the darker color is not as desirable. However, when high current densities are used, the temperature will rise unless cooled. If the color difference did not matter, then it would be better to allot the temperature to rise. 15 mm.m :w.: sm.m spas Ioawm \mucsow a3. a La a5: asm.m .mmm mmscam ah ER 360 O\ 0 $1 0\ O\ fil 3‘ GI .mwm pawn Iago ow s.H m.H com m m mm NH OH . a om m.H m com m w mm mm m .mH om s.H ~.m 0mm m w mm mm m.m .OH OCH H.H m.m 0mm m w mm mm m.H .m .msa .msmm.pao> .00 .He cam 0« as .Nmmmmmm .Hom .oz Hmpoe wmmm .QEmB mafia ccfiufimoosoo & fi gum w.m I mpmaonpooam “0 mg soapsaom psoonmm npfis coflpmanm> .>H mamde a 6/6: fro {7 212 0f % com: ell Tra 17072 \ 1.: ~ ~ I § U ”Q I Q ‘8 0‘ I (v Q (o 1 l l ‘0? §L 5/ 3 6 7 9 76 energy eff/Clancy Curl/e is for cérrenf' de/‘Isiry 0f 1.7 amf/Jn‘ Grafih I c... 16 The percent couoosition of the electrolyte is the same in all cases except that of the 10% solution. The 10% solution if made like the others as to percentage composition would give the sane product and color but would adhere to the electrodes. The amount of chromate must be lessened and so a different comoosition was made. This gave smoother runs and a product of the same color. Using 8% of acetic acid makes the 93 too low for the 10% solution, so 6% acetic acid was used. The color or current efficiency does not vary with the change in concentration. The energy efficiency and the pounds per kilowatt are the variables. These more than doubled over the range of the difference in percent of solution. Trials Bo. 3 and 16 have values slightly higher than have the others at the same current density. The curve (see Graph 1) indicates that over the range from 0% solution to 10% solution, the energy effi- ciency increases considerable; but that above the 10% solution there will only be a slight rise in the energy efficiency. he runs were made with solutions of more than 10%. However, tests were nude to see what the voltage would be for solutions above the 10%. The cur- rent density was kept constant and for each concentration . ,. . . n .c ‘h the voltage was the same. This would indicate tn.t the solutions above 10% are not more conductive than the 13% solution. The curve is straightening cu and bears out this fact. For the above reason it would not pay to use concentrations above 10%. 17 18 m~.H am.a aooa m.u m.~ oma :m.H aH:.H am.wm m.m m.w mam m.a am.a am.nm m.mH OH owH m.H am.a how m m oma apes .aum .amm .QH pHo> .mem ICHHM mwsmwm puma camfiw Hepom \mcswom IHoo aoflpwapmmosoo gone now .> was com m m mm NH ma 0mm m w mm mm m 0mm m w mm mm m.m CON m w mm mm ummm. oo .Hg 04 m oddznauno an Icon .osoe mane ecupumoasoo a puma iHfiO zpfimsme pcmanso Essflmem aqmda .Hm .NH .mH .m 03 de I5- H” .‘L ”31 imam Curran?“ Jefisiz; [6 /cJfiZ v on ~o : = t I r I fit 8 r ‘t 0: N ' 1 4 4 4L o I i T q 5 5 7 % 6077097753710” of (9/96 Gra/b/I II #— 1‘ fio/yre All attempts to raise the current density above these points for the different percent solutions re- sulted only in an increase of the voltage. The readings taken are for the lowest voltage at the highest current density. Graph II shows that the current density goes up as th percent of solution is increased. The graph indicates that solutions with a percentage of concen- tration above 10% will not be appreciably more conduct— ive tha the 13% solution. This means that the results shown in the previous Fraph are arrived at from another point of experiment. The highest percentage solutions are more economical to operate them at the maximum capacity of the cell. 19 A CCKTIHUZUS RUN % electrolyte ed % composition 12% Sodium Chromate, 82p Sodium Acetate, {‘2 . . , . Op ACthC ACld. Time 12 hr. m rs m - Coo -ewoerattre so 0. 9L 6.5 - 6.5 A. .4 Voltage 3.5 volts ‘ Current density 5 enp./dm Total emperes 250 Yiels 36 1b. Current efficiency 93.6% Energy efficiency 3.16% Pounds/kilowatt hr. 3.42 This run was nade to determine if the cell mould work continuously for a long period of time and if a product of the same quality could be obtained. Conner- cial chromic acid was used for the first 10 hours, and then the acid from a rejected plating bath. The product r mained the same for the ten hours; but after the elat— ing acid was used,the particles of Po.Cr04 did not seem to settle out. It acted like colloidal suspension. The color of the chromate from the used chromic acid was of a green yellow; but after being washed free of all acetates, it vas nearly the same shade as hat obtained 21 in the first part of the run. This very clearly showed that the cell would work for an indefinite period of time. The last part of the run showed that the effect of some addition agent would be to cause a finer forma— tion of particles and perhaps a slightly different color. A run vas made using the same chronic acid, but the sul- fates had been removed. The cell worked in the same way, showing that it was not sulfates which caused the emuls- ified action. 22 DISCUSdION During Operation of the cell, the pH should not be allowed to vary over 0.5 pH, at low concentration of chromates they are removed if pg rises and this con— dition is followed by a formation of ejongy lead. If the DH drops too much, the chromate will adhere to the anodes and cause the cell to cease operating. All work in this thesis was done with'the pH below 7. This does not mean that the cell will not work at a higher pH. If a pH above 7 is used, pure lead chromate will not be formed but rill yield a mixture of lead chromate and lead oxide. It is not necessary to use a diaphram in the making of lead chromate. Reduction will not take place at the cathode after the cell has Operated for a short time. A coating of chromium chromate forms over the cathode and thus stops all reduction which would tend to take place. Any coarse particles present in the lead chromate can be removed by passinr the solution of chromate and electrolyte as it comes from the cell through a cloth of fine weave. The lead chromate made with the various percent solutions of electrolyte was in a comparatively pure state. The chemical analysis gave a product of over 93 98% lead chromate. The color was not definitely deter- mined, but it app are that the higher concentrations 5nd the higher current densities give a lighter color and also with more luster. The product becomes finer as the current density and concentration increases. This was determined by mixing a weighed amount of ground Eb Crfh with a definite amount of raw linseed oil. The product which took the most oil was said to be the finest. This may be in error as the fine particles of powder might be agglomerates and thus use less oil. The product when formed at the anodes did not ad- here to the anodes but rolled off in a fine amorphous state. xhile being washed, and filtered, the product was so fine that it would go through the filter paper until the pores of the paper had become filled. After drying, the lead chromate is in chunks, and must be ground. The state here may be crystalline and thus ac- count for the change in color when drying. The differences in current efficiency may be ac— counted for in the product lost in the washing and fil- tering Operations. Because of the large quantity, it was imoossible to keep from a constant loss in each pro- cedure. Also, the percentage of moisture present varies. All drying operations were carried out in the air at room temperature. 24 S U K H A R Y Lead chromate can be made electrolytically in a pure state by controlling the pH of the electrdudfi with acetic acid. The higher current densities and concentrations yield a finer product. A change in color takes place when the lead chromate is dried. An increase in temperature will cause the product to be darker and will also increase the efficiency of the cell. The best results will'be had with a 10% solution and a airly low current density. Cell will work continuously for a long period of time. BIBLIOGRAPHY C. F. Carrier - Transactions of American Electro—Chemical Society 5 - 229 (1904-) LeBlanc & Binsschedler - Z. Elektrochemie 8 - 255 (1902) E. E. Free - Journal of Physical Chemistry 13 114 (1909) D. Miller — Journal of Physical Chemistry 13 - 256 (909) I- { tr( . W. Gillett — Journal of Physical Chemistry 13 - 332 (1909) Applied Electro-Chemistry — allmand & Ellingham 465 K. Jableznski — Chemical Industries 31 - 7?1 (1908) 'TI. .ITJEI. III! i. 1’. I DEC 6 “'9 2 8 ’51 “303% 8"E’f': 3 rm V ‘, q "31 Name 9 “0 NQ‘.’ :2 '51 W 1549 act 31'“ Decl'O Iov 1 a '7“ 0ct23‘45 genzvsa 01.1.“: "f: “‘3 .. M72063 . w M2953 NOVZ 9 ’54 OCT 1 6 ’57 00110149 can 1m 9m???” 103510 T541 5562 Shnlnburg Electrolytic preparation of lead chromate. ' I )3“. 1'"?! 103510 Shulnburg 1293 0244