- I.- I. 50.9' than 1‘- A“ ,_.4 PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. MAY BE RECALLED with earlier due date if requested. DATE DUE DATE DUE DATE DUE 6/01 cJCIRC/DateDuepss-p. 15 vii—v 2’5). 1, rtfri- it it pill! Current Efficiency of Electrolytic Chromium Processes A Thesis Submitted to the Faculty of the Michigan State College By To Haia Kao Candidate for the Degree of M.S. June, 1927. In Appreciation I wish to express my sincere appreciation to Dr. Dwight Tarbell Ewing, Professor of Chemistry, for the kind assistance, supervision, and ready suggestions which have made possible the successful completion of this investigation. T.H.K. '. Geuther (Leibig's Ann. 22, 314, (1856)) electrolysed solu- tions of chromic acid and noted that the formation of electrolytic ohranium is accompanied by the evolution of hydrogen at the cathode and of oxygen at the anode. _Geuther stated that, ”the amount of metal deposited stands in direct relation to the hydrogen deficiency”. Buff (Leib. Ann. 1, 101, (1867)) repeated Geuther's work and reports that the results of Geuther are unreliable. The electrolysis of chronic acid solutions containing various addition agents offers several problems for further investi- gation. There is produced during electrolysis of‘such solutions various substances and changes. For example, there is formed chromium, hydrogen, and trivalent chromium (probably some di-valent chrmium) at the cathode. Oxygen is evolved and chromiumiin the lower states of valence is oxidized at the anode. Heat effects are also produced upon the pssage of the current. It is the object of this‘work to study quantitatively sole of these effects. An attempt has been made to account for the total reduction taking place at the cathode and to determine'with the aid cf‘Faraday's laws of electrolysis if all such changes are accounted for. Three changes are assumed to take place, namely, the electrolytic deposition of metallic chromium, the evolution of hydrogen, and the reduction of chronium in the chranate-ion to trivalent chrmium. The work of the Bureau of Standards indicates that the current effi- ciency of the bath employed for the formation of electrolytic chromium is about twelve per cent.. Obviously this is very low for practical purposes. Other solutions do not offer much greater yields of chromium. Two lines of approach are offered for improving this -1- ,. efficiency. One is to alter the composition of the bath; for example, by changing the concentration of the solution or by the addition of various other substances which would effect the decomposition poten- tial of chronic acid, or the over-voltage of chranium and hydrogen. The second line of approach is the study of such physical factors as changes in current density, temperature, etc. This investigation was undertaken from the second viewpoint. The main points of investigation are as follows: 1. The percentage of the current used for the reduction of six valent chraniun to the lower valent chronium, if any reduction takes place. 2. The percentage of the current used in depositing chromium on the cathode. 3. The percentage of the current used for liberating the hydrogen gas at the cathode. 4. The effect of the temperature changes upon the current efficiency of the chromium deposit, and the color of deposit. 5. The effect of current density upon the nature of the deposit of chromium. In general the chromic acid solution contained about 250 grams of chromic acid per liter of solution. Various addition agents were added, but in general the same type of bath was used thruughout the investigation. The record of the composition of the bath was care- fully made and referred to as used. A steel anode was used. The vessel containing the electrolyte had a capacity of about one liter. A small porous cup was used for the anelyte. The hydrogen was collect- ed under an inverted short stem funnel and led into a 600 cc. flask as described later. -2- I r, I '.‘ ‘ .7." 'a s , . , i . . , . . I ,_ ‘ _ I' I "‘ A t ! ‘ '\ s v I u‘. ' }' v ‘ - .. . - 0 Ir ' { V r " l I. i 't ~, v The Analytical Method The analytical work involved the determination of three valent chrasium in the presence of six valent chromium. Several methods were tried. The most successful one was the iodine titration method which is described here. The three valent chromium is oxidized to six valent chronium by sodium peroxide, and then reduced by potassium iodide, whereupon the free iodine is titrated with a standard solution of sodium thiosulphate. Procedure: Transfer with a 5 cc. pipett a sample of chromic acid into a 500 cc. graduated flask and dilute it up to the 500 cc. mark. Draw out three portions of 25 cc. each. This contains one-fourth of a cc. of original solution. Acidify each with five cc. concentrated hydro- chloric acid and dilute it up to about 100 cc. Add 10 cc. of 20% potas- sium iodide. Shake and titrate with 0.lN sodium thiosulphate until the color changes from yellow to sea green. Add 5 cc. of 10% fresh starch solution and cautiously titrate again with sodium thiosulphate until the sharp light green and point appears. Formulas: 2 H Cr 04 e 6 KI e 12 320 -———-r 6K01 1- 201‘013 a 81120 e 312 2 - lazszoa e 12 -——> Nazs406 1- 2NaI Calculations: Since 1 cc. 0.1N'sodium thiosulphate is equivalent to 0.001733 grams of chromium, then 0.001733 x cc. of sodium thiosulphate used .x 4 equals to grams of chromium per cc. of original solution. Divide the amber of grams of chromic acid by 52% to get the metallic chromium in terms of chromic acid in grams per cc. -3- Analysis of Trivalent Chromium. Dilute 6 cc. original solution to 500 cc. Analyze for six valence chraniun by previous method. Pipett out three portions of the diluted solution previously analyzed for six valent chromium into an erlenmeyer flask. To these three portions of diluted sample add two grams of sodium peroxide and gently heat for a few minutes until the excess sodium peroxide is deconposed. The trivalence chromium present in the solution is oxidized into the six valence state. Acidify the solution with concentrated hydrochloric acid and add 5 co. in excess. Analyze again for. the total chromium present in the six valence state by the method of the preceding paragrah. Treat the result as in the preceding paragraph. Total chromium minus the six valent chranium equals the three valent chromium present in the solution. There were quite a number of trivalence chromium salts analysed. The only one which contained a definite amount of water of hydration was chromium sulphate. Analysis of chromium sulphate: Crz (SO4)S.5H20 ‘ Weight tabn Weight found 1. 1 0e1195 so 0.1042 so. 2 0.1018 ” 0.1012 “ The determination of trivalence chromium in the presence of s ix valent chronium. Sample 1. Weight taken Weight found KZCrO4 0.2125 g. 0.2121 g. 0r2(304)3.5 n20 0.1025 ' 0.1024 ' . Q . =1: ' l I . ' ‘l . , I ,_ . L I J . ‘ C O D Sample 2. Weight taken Tdeight found 0:2(304)3 51120 0.1692 " 0.1609 " E5 ' ’ E] A u". «3i; fir‘HHH’HHrMHL‘ . 1r [EM The Electrolysis of the Solutions. A steel anode was used. A porous cup separated the anolyte from the catholyte. The cathode was made of a sheet copper held by a copper wire sealed into a glass tube as shown in Fig. I. It was bent in such a shape as to readily go under the funnel. When the current is passing, the chrmium is deposited on the copper electrode and the hydrogen gas liberated 1. lead by the funnel into. the flask, as shown in Fig. 1. Procedure Before each run the cathode electrode is cleaned, dried, and weighed after it is cooled to room temperature. It is then inserted under the short funnel. Fill the flask A with the chromium solution, close the stop cock B, and use the finger to stop the outlet 0. Quickly invert the flask over the tip of the inverted funnel in the vessel D. Fill up the vessel D with chromic acid solution until the funnel is immersed in the solution. Examine the circuit before closing the switch. Be sure to close the stop cock B and let it remain closed until the current is on. Close the circuit and let the current flow a minute or so until the gas liberated forces the level of the solution down to 20-30 cm. Then gently open the stop cock B and adjust to an appropriate point so that the solution can not flow back into the flask A from the gas delivery tube. Open the circuit when the solution in the flask A is displaced by hydro- gen gas to the oalberated points x and Y on the tube. Note the time required for liberation of the hydrogen gas. Find the amount of the hydrogen gas liberated and the weight of chromium deposited on the -5- copper electrode. Calculated by’Faraday's Law, the amount of the current used. The temperature of the vessel D can be controlled by surrounding it with a large vessel filled with water and ice. For higher tempera- tures a.microaburner was used. The study of the change taking place in the solution when current passed. Data for‘bath No. 03: All results are in grams per liter. Data Or. as Cr03 0:203 Orzo3 in terms of metallic 0. Aug. 6, 1926 243.23 g. 5.439 g. 2.828 g. Aug. 17, 1926 236.34 g. 13.467 g. 7.003 g. Aug. 18, 1926 256.27 g. 9.799 g. 5.091 g. Sept. 6, 1926 288.87 g. 14.69 g. 7.6395 g. Oct. 9, 1926 254.6 g. 42.6 g. 22.18 g. Oct. 18, 1926 265.28 g. 15.337 g. 7.994 g. Nov. ?, 1926 277.06 g. 38.2 g. 19.8 g. The analysis of trivalent chromium of same solution when the current is passed at an average of 110 ampere minutes on each run. 20 L. Tank Or as Grog Orzo Change 0:203 to Cr. 3 1 221.4 g. 4.252 g. 2.211 g. 2 ' 5.115 g. 2.659 g. 3 . . . 4 " 6.82 g. 3.546 g. 5 " 5.115 g. 2.659 g. 6 " 6.82 g. 3.546 g. 7 ' 6.82 g. 3.546 g. -7- 17 L. Tank (Solution prepared by Professor D. T. Ewing, Dec. 20, 1926.) In this table below are recorded the results of ten consec- utive runs without changing the solution 500 cc. of solution from 17 L. tank was taken. No. of Run Date CrO3 1 12/22, 1926 226.75 g. 2. ' ' 3 ' 248.489 g. 4 12/23, 1926 245.29 g. 5 ' 247.22 g. 6 12/27,1926 278.2 g. 7 ' 319.942 g. 8 ' 317.935 g. 9 12/30,1926 341.87 g. 10 ” 319.942 g. Cr203 Orzo3 in terms of Cr. 5.115 g. 2.659 g. I II a n n n a n n n 6.82 g. 3.456 g. n n I. I n n The following data shows the effect of changing various fac- tors on current efficiency, etc. Data of 20 liter tank: (Solution prepared by Dr. D. T. hMing) C. D. Amp. Time Ampere Volt Grams coil. 1 7% on I 7% on Temp. min. Min't. Depst. Gas Cr. H.0as 0°. 16.66 2.5 51.5 128.75 5 .205 553 29.56 58.47 20-21 ' ' 51.0 127.5 5.5 .1971 ' 28.71 59.3 ' ' ' 51.5 128.75 5.3 .1993 ' 28.73 58.47 " 20.00 3.0 40.0 120.0 5.7 .1868 " 28.91 62.75 21. ' ' 39.7 119.0 ' .1878 ' 29.6 63.5 " ' ' 39.4 118.0 ' .1810 ' 29.07 63.8 21-22 26.33 3.5 33.5 117.0 6.5 .1805 ' 28.66 64.2 20-2 ' ' 33.3 116.5 “ .1814 ' 28.89 64.6 ' ' ' 33.0 115.5 7.0 .1763 ' 28.35 65.1 ' 33.33 4.0 28.0 112.0 7.7 .1783 ' 29.56 67.24 20. ' ' 28.5 114.0 7.0 .1821 ' 29.66 66.06 " ' ' 28.0 112.0 7.5 .1775 ' 29.43 67.24 ' 16.66 2.5 39.17 97.85 5.0 .0879 553 16.67 76.92 29. ' ' 39.0 97.5 5.2 .0873 ' 16.17 77.04 “ 20.0 3.0 31.3 93.9 6.5 .0891 " 17.41 80.1 29-30 ' ' ' ' 6.0 .0834 " 16.93 82.7 ' 26.33 3.5 26.5 92.75 6.8 .0854 ' 17.09 81.2 29 ' ' 26.0 92.0 6.6 .0836 " 16.9 82.75 30 33.33 4.0 21.00 84.0 7.5 .0548 ” 12.19 88.86 31-32 ' ' 21.17 84.68 7.2 .0557 ' 12.21 89.01 ' See graphs on next page. -9- .1 ... . I w.\ i 3‘: n 1 .-\i . 1 , . . i '1 ' I O o. I ‘ '1 4 vs at x . O 1 U1 0 I. ' . v 4 , . . . 1, . 6 , I D I I c O C O O . . a r 1 . . . 1‘ . w a - 1 I O o C O l D o v a x i. l‘ e s I o 0 e O s e a I . e a 0 w 6 . f- . . . .\ .. 4 (hi . . 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Gas Co Min. 13.33 2.0 118.0 5.0 .1624 533 26.1 63.82 ‘20.21 59.0 ' " ' " .1666 ' 26.27 63.82 20-22 ' 20.00 3.00 123.0 7.0 .1850 " , 27.95 62.24 ' 41.0 ' ' 123.75 6.5 .1809 ' 27.99 62.31 29-21 41.2 23.33 3.5 122.5 7.7 .1953 ' 29.61. 61.49 20-225 35.0 ' " 126.0 7.6 .2017 " 29.45 59.76 20-21 36.0 26.66 4.0 136.0 7.5 .2309 " 31.53 55.36 “ 34.0 " ‘ 126.0 7.3 .2110 " 31.23 59.77 20-22 31.5 33.33 *5.0 132.5 9.0 .2345 ' 32.53 56.83 20.21 26.5 ' " 127.5 9.2 .2228 ' 32.45 59.04 20.21,5 25.5 13.33 2.5 114.34 4.7 .1282 553 20.8 65.83 27-29 57.17 " ' 115.0 ” .1279 ' 20.62 65.48 ' 57.5 20.00 3.0 105.0 5.3 .1216 ' 21.7 71.72 26 35.0 ' " 104.0 5.2 .1204 " 21.5 72.42 30.0 34.66 23.33 3.5 113.75 6.5 .1304 ' 21.2 66.24 “ 32.5 ' " 112.0 " .1261 ' 20.97 67.24 ' 32.0 26.66 4.0 112.0 7.5 .1261 " 20.92 67.24 30-32 28.0 ' " 108.0 7.2 .1257 ' 21.07 69.73 ' 27.0 33.33 5.0 100.85 8.2 .1233 ' 22.70 74.7 30. 20.17 ' ' 100.00 7.5 .1191 " 22.13 75.3 _ 30-31 20. . s I 0 . e ..n e .r e . . _ v . . e I l e i O 1 O I . . . 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