“"- II‘II III IIII'I IIII IIIII IIII I“II II: 'VI .II‘ I I II'I IIIIIII I I I II I II‘ I III II II IIII 'I II I I II II I II I II\I I I III II I I II I I‘. I II I III :——-—-—:: ‘III III II I II I IIII III I III THE ELECTROLYTIC SEPARATION OF IRON FROM CC‘NCENTRATED SOLUTIONS OF NICKEL ANS COBALT FOR THE ELECTROLYTIC DEPOSITION 0F NICKEL mm In» flue Dagm or! M. S. MICHIGAN STATE COLLEGE Walmr OrviIIo Dew, Jr. 1949 M-795 This is to certify that the thesis entitled $04M CM‘l\a,fo¢’ SfpifiAm 67 /{/’/‘«¢ Mk Creed 7114/ sue-neg“; JDJIWQLM J1 AJAL’M ' presented by WW 0, 0W, \Tw. has been accepted towards fulfillment of the requirements for Major professd' WM7'Q9 Date m ._...-. “*‘WM ,_ THE ELECTROLYTIC SEPARATION OF IRON FROM CONCEETRATED SOLUTICFS $F NICKEL AND COBALT FOR THE ELECTROLYTIC DEPOSITION OF VICVEL By WALTER ORVILLE DOW JR. A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of 1&st (OF SCIENCE Department of Chemistny 1949 WMBTRY (El-J“. T542; D7 4—4 ACKNOWLEDGMENT I hereby gratefully acknowledge the help and guidance of Dr. D. T. Ewing in the completion of this work. I wish to thank the HansonAVanWinkle-Munning Company whose grant of a fellowship made this research possi- ble. I also wish to thank Donald D. Clark for his valuable assistance in analysis. *#***¥***# *tttt *** ##ttI‘t itti it * . . o. 0.:v-evu . o c -co‘g.0t 0'... II~OOOO§O IIIIo-eo... O CCIOQOQIQoOIC’UIIIQOC. ..n-a¢-..I'OoO.-Oolo INTRODUCTION It has been known for some time that small amounts of iron will markedly affect an alloy deposit from.a nickel cobalt solution for the electrodeposition of nickel. Not only the appearance but the ductility of the deposit are adversely affected. Since no literature directly applicable to electrolytic removal of metallic ions from concentrated nickel solutions has been so far advanced, only such information as chemical precipitation of iron in some salts was obtained from that source.1 In determining the course of study of the electrolytic separation of the iron from the nickel cobalt plating solution, such factors as the range of current density, type of cathode, temperature, and agita- tion were derived from commercial experience and applications of funda- mental theory. It was decided that an arbitrary set of standard conditions would be adapted and that each of the conditions would be varied in the suc- ceeding experiments. As each condition was varied and evaluated, the optimum.condition was used in all subsequent experiments. These standard conditions were as follows: Agitation 20 feet per minute past the cathode; Current Density 10 ampere per square foot; Temperature 80.00 C. (175°F.); Cathode indentation 1/2 inch and a pH of 3.75 electrometric. Fernic sulphate ’7 HOH was used for contamina- tion to give a ferric ion concentration of 100 milligrams per liter. Figure A. shows the combination of conditions for each experiment. For the 2.1 pH series of rate of removal experiments the best tem- perature and best cathode derived from the 3.75 pH series were accepted as optimum conditions and research was confined to variations of agita— tion, current density, and type of ion. (Ferrous rather than Ferric). One experiment was performed with a flat cathode. Experiments dupli- cating the conditions of the 50 feet per minute and optimum conditions experiments were also performed as checks. -2- FIGURE.A. 3.75 pH Series Standard Conditions: Cathode indentation 1/2 inch; Temper- ature 80°C. (175°F.); Current density 10 amperes per square foot; Agitation 20 feet per minute; pH 3.75 electrometric. 80°C 65°C Cathode inden ation Current Density 5 8.81,. 7e5 38f. 10 38f. Solution ' Agitation 4 ft./min; 20 ft./min. 5 ft./min. 2.1 pH Series Standard conditions: Cathode indentation 1/2 inch; Temper- ature 80°C. (175°F.); Current density 10 amperes per square foot; Agitation 20 feet per minute; pH 2.1 electrometric. 5 asf. 7.5 asf. 10 asf. 15 asf. Solution Agit tion 10 ft. min. so ft./min. 50 ft./min (repeat) Flat CIthode Ferrou1 Ion Optimum conditions for analysis of the plate. Procedure- Solution preparation and purification. 3.75 pH Plating Solution Niso4 32 oz./ga1. 240 g./1. NiCl 6 " 45 " Boric acid 4 " 30 " Ni Formate 6 " 45 " COSC 0.33 " 2.5 " Ammofiium.$u1phate 0.33 “ 2.5 " Formaldehyde 0.33 " 2.5 " 2.1 pH Plating Solution NiSO4 32 oz./gal. 24o g./1. NiCl 4 " 3O " Boric acid 4.5 " 34 " Ni Formats 4.5 " 34 " COSO4 0.2-0.35 " 2.6 " The plating solution was prepared with the amount of single nickel salts; nickel chloride and boric acid, omitting out cobalt sulphate and formaldehyde. After the salts had dissolved the pH was adjusted to 3.5-3.7 electrometric and the nickel formats then added. A slurry was prepared using one pound of filter aid with ten gallons of water per 100 gallons of plating solution and was spread over a filter paper on a suction filter flask. The bath was then filtered hot through activated charcoal slurry. (1 lb. char- coal to 100 gallons plating solution). The anodes were placed in the tank and cathodes of corrugated crimped sheet steel were hung from the cathode rod. The solution was electrolyzed at a current density of 5 amperes per square foot until 2-5 ampere hours per gallon had passed through the plating solution. The remaining salts were then added and the bath was ready for use. -4- Procedure- Rate of Removal Experiments on 1% NiCo Plating Bath. A 15 liter glass jar with 11.36 liters (3 gals.) of plating solution was set up on asbestos board insulation inside a water bath. Two stirring motors were placed so that the two shafts were at 1/4 and 3/4 of the tank diameter. Two stirrers were constructed with blades 1 cm. by 2 cm. tilted 45 degrees from the horizontal. For agitation greater than 20 feet per minute, stirrers were constructed udth blades 1-3/4 cm. by 2-1/2 cm. 1201* t «mom The blades were placed 5-1/2 inches below the surface of the bath, and lifted solution.up from the bottom toward the top of the jar. The agitation, while reproducible, varies over the surface of the cathode. .All agitation.measurements were made at the edge of the oathadaiutpre the flow was most steady. “‘*“ . 4 ft./min. 400-450 rpms. ‘4’ . 5 rt./min. 600-650 rpms. ' - 10 ft./min. 870-900 rpms. Agitation 20 ft./min. 1500 rpms. ”ensurements 50 ft./min. 1200 rpms. (with made here. larger propellors) I and accuracy. Chuck diameter was 11/l6 inches. Knurled Chuck -5- The two corrugated cathodes were constructed from copper sheet to the following specifications: 8“ x 11-5/8" with bends 1-1/8" apart for the 1/2" indentation 8" x 13-3/4" with bands 1-1/4" apart for the 3/4" indentation A” \/ ‘\/ 4" Ni/ \x" \[X £iQ-—¢- £2” The cathode was plated with a thin coat of nickel to prevent contam- ination of the bath by the exposed copper. A foot of heavy nickel wire was soldered to the cathode to lead completely away from the plating solution before other connections were made. Both anode hooks were plated heavily with nickel and 1% Nickel Cobalt anodes were placed against the sides of the jar behind the two stirrers. All connections leading from the bath were soldered to insure good connections. The bath was heated to temperature with stirrers go- ing and 100 milligrams per liter of iron.as ferric sulphate (Fez(SO4)3-7 HCH) (8.57 g. per 3 gallons) were added. The cathode was cleaned electrolytically in boiling alkaline cleaner, rinsed, dipped in 20% HCl for 30 seconds, rinsed with distilled water, then placed between the stirrers at right angles to the line between the anodes. 1.23 square feet were submerged. The time was checked and a 5 ml. sample taken, numbered and saved for analysis. Samples were taken at intervals which were short (every 100 ampere minutes per gallon) at the beginning of the run and much longer at the end of the run. -5- (Every 1000 ampere minutes per gallon.) The pH was checked at each sample and if necessary, lowered with sulphuric acid or raised with nickel carbonate. The samples were analyzed for iron and plotted with iron content against ampere minutes per gallon. -7- Fig. B. Apparatus for Rate of Removal Runs on a 1% (9H) NiCo Plating Solution. Fig. C. Large stirring propellor used in 50 ft. per min. agitation. Analysis of Iron- Separation of the Iron. (1) (2) (3) (4) (5) (6) (7) Isolation Add enough chopped distilled water ice to fill a 100 m1. separatory funnel one third. Add 2 m1. nickel plating solution. Add 4 m1. ice cold cupferron. (1% solution.) (Make up fresh every day) Shake 1 minute and let stand for 10 minutes. Do not shorten this standing period. Add 5 m1. amyl acetate from a burette. Shake 1 minute, allow liquid layers to separate and draw off aqueous layer into another separatory funnel. Repeat twice with 5 ml. portions of amyl acetate. If an amber color persists in this last extraction.use a smaller amount of nickel plating solution for a sample. Combine amyl acetate extracts and wash with 10 ml. of water. Shake 1 minute and discard the aqueous layer. or the F90 (8) (9)' Add 4 ml. nitric acid (1:1). Shake 2 minutes or until the yellow color disappears. (This has taken as long as 10 minutes.) Run aqueous layer into a 100 ml. volumetric flask. Shake amyl acetate layer with 10 ml. water. Run aqueous layer into volumetric flasks. The amyl acetate should be light green in color. -10- (10) NOW'add in succession with mixing in between additions, 6 ml. hydroxylamine hydrochloride, 2 ml. o-phenanthroline and 20 m1. of 40% sodium acetate. (11) Dilute to the mark with redistilled water and mix well. (12) Using a test tube partially full of water as the reference liquid, adjust the colorimeter so that the galvanometer pointer is set at zero when the dial reading is at zero. Use the green #54 filter. (13) Rinse the test tube with small amount of colored solution and fill to the mark with sample. (14) Put the tube in the calorimeter (Klett-Somerson) and flip side switch on. Adjust dial to make galvanometer needle hit zero, then read dial. (15) Run a blank following the above procedure exactly 33222: for adding the o-phenanthroline. (16) Subtract the blank from the scale reading and read milli- grams per liter of iron from the calibration curve. Notes This procedure was worked out from results obtained using the method proposed by Serfass and Levine, Leheigh University. Recogniz- ing the fact that coloration of amyl acetate portions in excess of the extractions used by Serfass and Levine indicated more iron to be gotten out and that the curve at higher concentrations of iron was not showing high enough colorimetric readings to make it a straight line function, more extractions of amyl acetate were added, color changes stressed as end points in shaking and extraction, and double quantities of sample and most reagents were used to insure greater accuracy. Result: straight line calibration curve and highly re- producible results. -11- E‘KPERI? TENT NIH-T”? ER X l Sample Amp.Min. Mg./l. Conditions of the Run Number For Gal. Iron 1 41 132 Agitation 20 rt./min. 2 Current density 10 asf. 3 250 128 Cathode indentation 1/2 in. 4 500 128 Temperature 80°C. (175° F.) 5 1125 100 Contamination 100 mg./l. Fe*** 8 1500 80 (8.57 grms. Fe (so )3 per 3 gal.) 7 1700 76 pH 2.1 2 4 8 2500 85 9 3500 52 10 4250 39 11 5000 30 At 6875 amp. min./ga1. a nickel 12 5375 30 plated copper cathode was in- 13 6227 30 sorted in place 0f the nickel 14 6875 28 plated steel cathode used in the 15 7195 26% 15a 7195 24 18 7695 23 17 8887 22 18 9302 23 EXPE} 1211:5117 NUl-IB ER x2 Sample Amp.Min. Mg./l. Conditions of the Run Number For Gal. Iron 1 0 120 Agitation 20 ft./min. 2 368 113 Current Density 7.5 asf. 3 1008 103 Cathode Indentation 1/2 in. 4 2200 90 Temperature 80°C. (175° F.) 5 2997 78 Contamination 100 mg./l Fe*** 8 4808 63 pH 2.1 7 5711 58 8 6631 47 At 5000 amp.min./gal. the plate 9 7750 43 was stripped of all peeling Ni, 10 9053 36 cleaned electrolytically, ethched 11 9636 36 and the run was begun again. -12- EXPERIMENT NUMBER X3 Sample Amdein. I-.‘Eg./1. Conditions of the Experiment. Number For Gal. Iron 1 0 Agitation 20 ft./min. 2 246 Current Density 5 asf. 3 492 Cathode Indentation 1/2 in. 4 984 123 Temperature 80°C. (175° F.) 5 1968 112 Contamination 100 mg./l. Fe“ 8 2952 107 pH 2.1 7 3938 90 8 4920 79 9 8930 80 10 8582 88 11 10918 85 EXPERIMENT NUMBER x4 Sample Amp.Min. Mg./1. Conditions of the Experiment. Number For Gal. Iron 1 0 . 133 Agitation 10 it./nin. 2 246 Current Density 10 asf. 3 492 127 Cathode Indentation 1/2 in. 4 984 Temperature 80°C. (175° F.) 5 1820 Contamination 100 mg./l. Fe"’ 8 2870 87 pH 2.1 7 3936 81 8 5904 78 -13... EXPFRIT'IENT NUMBER X5 Sample Amp.Min. Mg./1. Conditions of the Experiment. Number For Gel. Iron 1 0 135 Agitation 20 ft./min. 2 185 122 Current Density 15 asf. 3 389 108 Cathode Indentation 1/2 in. 4 955 95 Temperature 80°C. (175° F.) 5 1107 Contamination 100 mg./1. Fe*** 8 1478 89 pH 2.1 7 1845 70 8 2583 52 9 3750 47 10 4797 48 EXPERIMENT NUMBER X6 Sample Ampdviin. Mg./1.‘ Conditions of the Experiment. Number Per Gal. Iron 1 O 144 Agitation 5O ft./min. 2 348 127 Current Density 10 asf. 3 492 Cathode Indentation 1/2 in. 4 738 103 Temperature 80°C. (175° F.) 5 984 85 Contamination 100 mg./1. Fe‘** 8 1478 89 pH 2.1 7 1988 89 B 2952 58 9 3808 82 10 5100 45 -14.. EXPERIHENT NUMBER.X7 Sample .Amp.Min. Mg./l. Conditions of the Experiment. Number For Gal. Iron 1 0 99 Agitation 50 ft./min. 2 246 84 Current Density lO asf. 3 492 -- Cathode Indentation 1/2 in. 4 738 59 Temperature 80°C. (175° F.) 5 984 50 Contamination 100 mg./1. Ee**+ 8 1478 85 pH 2.1 7 1570 61 8 2062 58 9 2800 50 Values plotted were the average 10 3784 57 of two analysis. 11 4522 55 EXPERIMENT NUMBER X8 Sample Amp.Nin. Mg./1. Conditions of the Experiment. Number For Gal. Iron 1 O 107 Agitation 20 ft./min. 2 246 98 Current Density 10 asf. 3 492 82 Cathoded Indentation Flat 4 738 72 Temperature 80°C. (175° F.) 5 984 70 Contamination 100 mg./l. F6117 6 1189 61 pH 2.1 7 1189 65 8 1435 47 9 1927 54 10 3054 43 11 3054 48 12 4038 42 13 4653 41 Sample Amp.Min. Hg./d. Conditions of the Experiment. Number Per Gal. Iron 1 0 75 Agitation 20 Tt./min. 2 246 69 Current Density lO asf. 3 492 50 Cathode Indentation 1/2 in. 4 815 89 Temperature 80°C. (175° F.) 5 738 47 Contamination 100 mg./fi. Fe"+ 6 738 47 pH 2.1 7 984 52 8 1230 62 Averages of two or more 9 1415 52 analysis were used in plotting. 10 1907 54 There were 8-10 mg./l of ferric 11 2599 50 iron left in the bath when the ferrous iron was added. ECPERI’iET‘TT 111048311 X10 Sample Amp.Min. Mg./1. Conditions of the Experiment. Number For Gal. Iron 1 0 98 Agitation 20 rt./min. 2 246 75 Current Density 10 asf. 3 492 70 Cathode Indentation 1/2 in. 4 738 74 Temperature 80°C. (175° F.) 5 984 45 Contamination 100 mg./L Fe*** 7 1476 38 8 1722 36 Copper Cathode was plated udth 9 1968 -- nickel, then oxidized in alkaline 10 2460 32 cleaner for 15-30 secs. Rinsed in 11 2952 35 distilled water and replaced in 12 3444 33 plating bath. 3 3936 -- -16- EXPERIWENT NUMBER X11 Sample Hours Mg./d. Conditions of the Experiment. Number Iron 1 0 127.5 Agitation 20 ft./min. 2 1 127.5 Temperature 80°C. (175° F.) 3 3 128 pH 2.1 4 4 125 Contamination 100 mg./l. Felll 5 20 130 Sample number 5 was taken the next day after the solution had cooled. Agitation only was used. EXPERIMENT NUMBER XXl Sample Amp.Min. Mg./l. Conditions of the Experiment. Number For Gal. Iron - l 0 115 Agitation 20 ft./min. 2 246 -- Current Density 10 asf. 3 492 56 Cathode Indentation 1/2 in. 4 738 -- Temperature 65°C. (150° F.) 5 984 38 Contamination 100 mg./l. Fe’** 6 1476 -- pH 3.75 7 1968 35 8 2766 29 Solution was filtered hot at the 9 3444 -- end of the experiment. 10 4774 -- 11 5166 26 -17- EXPERIMEK I-TUNB 31 DOCZ Sample Amp.Hin. Mg./l. Conditions of the Experiment. Number For Gal. Iron 1 66 90 This experiment is a combination 2 150 89; of two; One from 90 mg./1. to 12 3 344 55 mg./1. and the other from 12mg./l. 4 552 52 to 9 mg./l. 5 676 25 8 1352 12 Agitation 20 Tt./min. 7 1800 10 Current Density 10 asf. 8 2280 9 Cathode Indentation 1/2 in. Temperature 80°C. (175° F.) Contamination 100 mg./l. Fe*‘* pH 3.75 This experiment was performed in a. 1% gal. battery jar. EXPERIMENT NUMBER XXS Sample .Amp.Min. Mg./d. Conditions of the Experiment. Number Per Gal. Iron 1 0 83 Agitation 20 Tt./min. 2 246 49 Current Density 10 asf. 3 492 27 Cathode Indentation 3/4 in. 4 738 34 Temperature 80° C. (175° F.) 5 984 -- Contamination 100 mg./l. Fe+’* 8 1353 17 pH 3.75 . 7 2275 -- 8 3198 10 9 4182 6 -18.. EKPERINSNT NUMBER XX4 Sample Amp.Min. Mg./d. Conditions of the Experiment. Number Per Gal. Iron 1 0 100 Agitation 20 ft./min. 2 244 53 Current Density 5 asf. 3 488 30 Cathode Indentation 1/2 in. 4 732 28 Temperature 80° C. (175° F.) 5 976 23 Contamination lOO mg./l. Fe’** 8 1952 18 pH 3.75 7 2928 17 EXPERIMENT NUMBER XX5 Sample Amp.min. Mg./l. Conditions of the Experiment. Number Per Gal. Iron 1 0 119 Agitation 20 rt./min. 2 184 74 Current Density 7.5 asf. 3 797 32 Cathode Indentation 1/2 in. 4 1288 22 Temperature 80° C. (175° F.) 5 2085 14 Contamination 100 mg./l. Fe II pH 3.75 -19- EXP ER. IVENT NINE E R 10(6 Sample Amp.min. ng./l. Conditions of the Experiment. Number Per Gal. Iron 1 0 102 Agitation 10 Tt./min. 2 246 70 Current Density 10 asf. 3 492 53 Cathode Indentation 1/2 in. 4 738 48 Temperature 80°C. (175° F.) 5 984 37 Contamination 100 mg./l. Fe*** 8 1476 27 pH 3.75 7 1878 27 8 2496 16 This table is a combination of 2 9 3558 9 experiments, one from 102 to 27 10 4478 4 mg./1. and the other from 27 to 11 5478 2 2 mg./1. EXPERIMENT NVHBER XX7 —v Sample Amp.Nin. Mg./l. Conditions of the Experiment. Number Per Gal. Iron 1 0 92 Agitation 5 ft./min. 2 200 56 Current Density 10 asf. 3 1020 40 Cathode Indentation 1/2 in. 4 2082 12% Temperature 800 0. (175° F. 5 3033 8 Contamination 100 mg./l. Fe ** 8 4000 4 pH 3.75 Formic Acid was used to lower pH. -20- EXPE1ITA’YENT NUMRER XXB Sample Hours Mg./l. Conditions of the biperiment Number Iron 1 0 102 Agitation 80 ft./min. 2 1 82 Temperature 80°C. (175° F.) 3 3%.- 27 Contamination 100 mg./l. Fe*“ 4 4%: 35 pH 3.75 5 6% 20 6 773‘ -- -21- MILLIGRAMS PER LITER 9O 80 7O 60 50 40 30 20 10 (2) l l l 1000 l 1 l l 1 l 2000 3000 4000 5000 6000 7000 8000 9000 AMP. MIN. PER GAL. Fig. 1. Effect of Temperature on the Electrolytic Removal of Iron from a 3.75 pH NiCo (9H) Plating Solution. Curve 1 - 150°F; Curve 2 - 175°F. -22- MI LLIGRAMS PER LITER l A J l j l n J - vi 1000 2000 3000 4000 5000 6000 7000 8000 9000 AMP. MT N. PER GAL. Fig. 2. Effect of Depth of Cathode Indentation on the Electrolytic Removal of Iron from a 3.75 pH NiCo (98) Plating Solution. Curve 1 - 3/4 in. Indentation; Curve 2 - 1/2 in. Indentation. -23.. RLTER ‘ 5 MILLIGRAVS P' I L A 1 l 1 l J I 1000 2000 3000 4000 5000 6000 7000 8000 9000 AMP. MIN. PER GAL. Fig. 3. Effect of Current Density on the Electrolytic Removal of Iron from a 3.75 pH NiCo (9H) Plating Solu- tion. Curve 1 - 5 amps per ft.2 Curve 3 - 10 amps per ft. . Curve 2 - 7-1/2 amps per ft.2; -24- MILLIGRAMS PER LI TER ‘40 7 80. 70 601 50 301 20 . 10 . ° 2 o 3) . e e 1) 1000 2000 3000 4000 5000 6000 7000 8000 9000 AMP. MIN. PER GAL. Fig. 4. Effect of Agitation on the Electrolytic Removal of Iron from a 3.75 pH NiCo (9H) Plating Solution. Curve 1 - 4 ft. per min. past the Cathode; Curve 2 - 5 ft. per min. past the Cathode; Curve 3 - 20 ft. per min. past the Cathode. ~25- MILLIGRAMS PER LI .111 lO A l l L P L J_ l I 1000 2 000 3000 4000 5000 6000 7000 8 000 9000 A‘EP. ”IN. PER GAL. Pig. 5. Effect of Current Density on the Electrolytic Removal of Iron from.a 2 1 pH NiCo (9H) Plating Solution. Curve 1 - 5 amps per ft. ° Curve 2 - 7-1/2 amps per ft.2; Curve 3 - 10 amps per ft.2; Curve 4 - 15 amps per ft. . -25- PER LI 3R q k Ml LLI G RA-‘l 90 80 70 60 30 20 10 (3) (2) g 1 A L l L 1 l_ l L 1000 2000 3000 4000 5000 6000 7000 8000 9000 AMP. MIN. PER GAL. Fig. 6. Effect of Solution Agitation on the Electrolytic Removal of Iron from a 2.1 pH NiCo (9H) Plating Solution. Curve 1 - 10 ft. per min. past the Cathode; Curve 2 - 20 ft. per min. past the Cathode; Curve 3 - 50 ft. per min. past the Cathode. liiIILIGRAliS PER LI ER I I l I I I I l I 1000 2 000 3000 4000 5 000 6000 7000 8000 9000 AMP. MIN. PER GAL. Fig. 7. Effect of pH on the Electrolytic Removal of Iron from a NiCo (9H) Plating Solution. Curve 1 - 2.1 pH; Curve 2 - 3.75 pH. -28- 20 10 r l 1 I J 1 J 1 l A 2000 4000 6000 8000 AMP. MIN. PER GAL. Fig. 8. The Effect of a Flat Cathode and a re- peat experiment of Optimim Conditions Using a Copper Base Cathode. C11”. 1. Flat CIthOdeo Curve 2. Optimm con- ditions (steel base cathode). Curve 3. Optimum Conditions (copper base cathode). -29- 90 20 10 - l .-..1 A.-- L -11 . 4 11.... _l—__A l l 2000 4000 6000 8000 AMP. MIN. PER GAIu Fig. 9. The Rate of Removal of Ferrous iron from a 2.1 pH 1% Nickel Cobalt Solution. Curve 1. Ferric iron (steel base cathode) Curve 2. Ferrous iron (copper base cathode) Curve 3. Ferric iron (copper base cathode) Note: Only the points for Curve 2 are plotted. -30- 120 110 100 80 60 50 4O 30 20 10 l \i \< \, <4) (2) 3) \ \ b h p- F p l L J I 12 16 20 24 28 32 35 TIME IN HOURS .5 a) Fig. 10. Effect of Precipitation of the Hydroxide on the Electrolytic Removal of Iron from a 1% Nickel Cobalt Plating Solution. Curve 1. Precipitation Effect on a 2.1 pH bath. Curve 2. Optimum condi- tions of electrolytic removal from a 2.1 pH bath. Curve 3. Precipitation effect on 3.75 pH bath. Curve 4. Optimum conditions of electrolytic removal in a 3.75 pH bath. -31- 90 80 70 6O 5O 4O 30 - 20 10 TIME IN HOURS Fig. 11. Some of the Effects of Combined Precipita- tion and electrolysis in the Rate of Removal of Iron from a 3.75 pH T% Nickel Cobalt Bath. Solution Current Temp. Cathode A itati on Densi? °C. Indgntati on Curve 1. 20 ft.7min. as . 55 éfiinch Curve 2. 10 " " lO ” 80 " " CHI'VO 3. 20 N n 5 N n n 9! Curve 4. n n n 7%: n n n Curve 5. " " " 10 " " 3/4 09 Curve 6. " ” " 10 ” % " Curve 7. Precipitation effect only. -32- ‘T‘7"_’fi— r W I I ’_ T """ o . 4 11) g 12> .4 ___o d a \(_ 2, 20- N 1 104 - O ----____.1_1_-___ L 1 1 1 1 i 1 1 5 10 15 20 25 30 35 40 45 TIME IN HOURS Fig. 12. Time Efficiency Against Amperes Per Square Foot Current Density in a 2.1 pH Nickel Cobalt Plat- ing Solution. Curve 1. 5 amps per ft.2 Curve 2. % amps per ft.2 Curve 3. 10 amps per ft.2 (steel base cathode) Curve 4. 10 amps per ft.2 (copper base cathode) Curve 5. 15 amps per ft. -33- Discussion of Results- This discussion will present each of the variable conditions, temperature, cathode indentation, current density, and agitation, which were used in the electrolytic removal of iron from a 1% Nickel Cobalt plating bath and treat them in turn in two series, a 3.75 pH series, and a 2.1 pH series. The effect of chemical precipitation as it affects the electrolytic rate of removal of iron will then be discussed. 3.75 pH Series StandardPCondItions- 80°C. (1750 F.), 1/2 inch cathode indentation, 10 amperes per square foot current density, 20 feet per minute solu- tion agitation past the cathode, and ferric ion contamination at a pH of 3.75 (electrometric). The temperature was varied from the standard 80°C. (1750 F.) to 85° C. (1500 F.) (Fig. l) and very little difference in the effective rate of removal of the iron was noticed until a concentration of 40 to 50 milligrams per liter was reached. At this point the higher tempera- ture (800 C.) continued to deplete the iron content to 8 milligrams per liter while the 650 C. temperature experiment began to level off near 30 milligrams per liter. This deviation was probably due to a com- bination of effects, namely, the increased precipitation of the hydroxide on increase in temperature and the enhanced electrolytic rate of re- moval. 800 C. (1750 F.) was used subsequentLy as the best temperature. The change in cathode indentation had no effect until the lower concentrations of iron were reached as shown in Fig. 2. The rate of removal of the iron was identical down to 25 milligrams per liter, at -34.. which point the 1/2 inch indentation cathode lowered the iron content to 10 milligrams per liter at 2000 ampere minutes per gallon while the 3/4 inch cathode needed 3400 ampere minutes per gallon to accomp- lish the same measure of purification. The 1/2 inch indentation was used for all subsequent cathodes. The effect of a change in current density on the rate of removal of the iron was not as easily interpreted as the preceding variations. Five amperes per square foot current density removed the iron faster than 7.5 or 10 amperes per square foot until an iron concentration of 30 milligrams per liter was reached. (Fig. 3.) At this point 5 am- peres per square foot rapidly leveled off. Seven and a half amperes per square foot current density removed the iron equally as fast as 5 amperes per square foot down to a concentration of 74 milligrams per liter. At this point it began to taper gently until at 30 milligrams per liter it began to level off but to a lesser extent than the 5 am- peres per square foot curve. Ten amperes per square foot removed iron a little more slowly at the higher concentrations but continued to remove it down to 8 milligranm Eur liter at 2250 ampere minutes per gallon while 5 and 7.5 amperes per square foot were at 17.5 milli- grams per liter and 14 milligrams per liter respectively. It would seem from these curves that the range of 25-35 milligrams per liter of iron is near a critical concentration above which iron is removed easily and below which more care in conditions of rate of removal must be exercised. This critical range is apparently a function of the chemical precipitation effect. -35.. The effect of agitation on the rate of removal of iron was more regular than current density. Although the planned agitation varia- tion called for series of 5, 10, 20, and 50 feet per mimite solution flow past the cathode, later check measurements showed a 4, 5, 20, and 50 feet per minute series were actually accomplished. The 4 feet per minute of solution past the cathode removed the iron slowly at the higher concentrations (Fig. 4). However, it continued to remove iron in the concentrations below 15 milligrams per liter when higher agita- tion was much less effective. Five feet per minute removed the iron faster at higher concentrations than even 20 feet per minute but it began to lose effect at 55 milligrams per liter and followed the same rate as 4 feet per minute except that it had more tendency to level off under 10 milligrams per liter concentration of iron. Twenty feet per minute dropped the iron content fast and evenly to 25 milligrams per liter at which point it made a steeper leveling curve and is prob- ably less effective in removing the remaining iron than the lower rates of agitation. Precipitation affect In order to insure that all removal was due to electrolysis, two runs were made, one on each pH bath, with heat and agitation, but no anodes, cathodes, or current used. Fig. 10, shows that there is no precipitation effect in the 2.1 pH series and that all of the removal is due to electrolysis. On the other hand, almost all of the removal of iron from the 3.75 pH bath is due to precipitation of the hydroxide and it is only after a concentration of 25 milligrams per liter has been reached that the electrolytic effect is noticed slightly. Pre- cipitation will take place in the cold over a long period of time to the extent of about 38% of the original content in solutions with a pH range of 2.2 to 2.5 electrometric. This was determined by test- ing the original solutions used in making up the calibration curve for the iron analysis after a standing period of about 6 months. 2.1 pH Series 0 0 Standard Conditions- 80 c. (175 F.), 1/2 inch cathode indentation, 20 feet per minute agitation past the cathode, ferric ion, and a pH of 2.1. After inspection of the results with the 3.75 pH series it was decided to accept the 800 C. (1750 F.) temperature and the 1/2 inch cathode indentation as optimum conditions and not to vary these fac- tors in the 2.1 pH 1% nickel cobalt solution experiments. .Figure 0, shows the effect of a circular steel cathode which had been previously plated with nickel but had cracked due to strains set up by plating only on the inside of the circle. This cathode was abandoned after determining by six more experiments that increased thickness of nickel deposited would not protect the steel and that it dissolved into the 2.1 pH solution as quickly as it was removed electrolytically. Ten and 7.5 amperes per square foot gave similar curves and 5 amperes per square foot actually increased the iron content. Even the straight corrugated cathode gave some iron into solution as shown in curves 2 and 3 of Figure 8. At 50 milligrams per liter on curve 2, the curve was level. However when a copper cathode was then introduced it lower- ed the iron content an additional 8 milligrams per liter. Therefore, when a check experiment was made (a cathode to be stripped and analy- zed) a copper base cathode was used with the result that the rate of re- moval of iron (Fig. 8, curve 3) was increased in the higher concentra- tion and leveled out at 35 milligrams per liter to a slope which indi- cated that it might reach 26.5 milligrams per liter in the same number of ampere minutes per gallon as the steel and copper cathodes of curve 2, Fig. 8 required. -38- 440 420 400 d J 580 l .1 43> 360 ,’/ _1 I 340 J 320 a Soon a 280L 4 2000 4000 6000 8000 AMP. MIN. PER GAL. Fig. D. The Effect of a Circular Cathode on the Electrolytic rate of Removal of Iron from a 2.1 pH 1% Nickel Cobalt bath. Curve 1. 5 amps per ft.2. Curve 3. 10 amps per ft.2. Curve 2. Curve 4. 10 amps per ft.2 7% amps per ft. 2. The effect of current density on the rate of removal of iron from a 2.1 pH 1% nickel cobalt plating solution is demonstrated in.Fig. 5. Five amperes per square foot was very ineffective in removing iron since the curve leveled off at 65 ndlligrams per liter. Seven and a half amperes per square foot had about the same rate of removal of iron as 5 amperes per square foot but continued to remove iron down to a concentration of 35 milligrams per liter before leveling off. Ten amperes per square foot removed iron at a faster rate in the high concentrations; at about the same rate as 7.5 amperes per square foot for the portion of the curve from 80 milligrams per liter to 30 milli- grams per liter; and than leveled until the copper cathode was intro- duced. Fifteen amperes per square foot had a faster rate of removal along the straight portion of the curve but leveled off at 45 milli- grams per liter, well above the 10 amperes per square foot curve. The effect of solution agitation on the rate of removal of iron from a 2.1 pH 1% nickel cobalt plating solution is shown in Fig. 6. Ten feet per minute past the cathode was very ineffective, leveling off at 80 milligrams per liter concentration of iron. Twenty feet per minute agitation was most effective, leveling off at 30 milligrams per liter. Fifty feet per minute caused a faster rate of removal in the higher concentrations, but below a concentration of 70 milligrams per liter it showed a slower rate of removal than 20 feet per minute solution agitation. A check experiment was made to verify this curve since theoretically more agitation should improve the rate of removal. -40.. However, the check curve was identical except for the small portion of the curve from 400 ampere minutes per gallon to 1000 ampere minutes per gallon. This would seem to indicate a solution agitation optimum below 50 feet per minute and above 10 feet per minute. The effect of a change in pH on the rate of removal of iron from a 1% nickel cobalt plating solution is evidenced in Fig. 7. The opti- mum rate of removal curves were used from each pH series. The 5.75 pH value is much more effective than a 2.1 pH since it removes the same amount of iron in about one sixth the number of ampere minutes per gallon down to a concentration of 50 milligrams per liter and levels off below 8 milligrams per liter as compared to 25-30 milli- grams per liter leveling point of the 2.1 pH series. This is, of course, due to the large amount of chemical precipitation at the high- er pH. The effect of a flat cathode on the rate of removal of iron from a 2.1 pH solution is shown in Fig. 8. The flat cathode curve had no flat portions as had the corrugated cathodes version of rate of re- moval. It matched the optimum conditions until a concentration of about 70 milligrams of iron per liter was reached and gradually level- ed out at 40 milligrams per liter at 6000 ampere minutes per gallon. ' This is a singular demonstration of the advantage of the corrugated cathode. Still it is a question whether the difference is entirely due to increased variation in current density or due partly to increas- ed area of the cathode. The flat cathode had the least total area in -41- solution and removed iron.most slowly. The 1/2 inch cathode indenta- tion had 5 square inches more area and removed iron most rapidly in spite of the fact that the 3/4 inch cathode indentation had 22 square inches more area than the flat cathode. This would seem to indicate that it is not just increased area but also the corrugation effect which gives better conditions for removal of iron from a 1% nickel cobalt plating solution. In addition it might be stated that the 1/2 inch indentation seems to be near an optimum.for cathode corruga- tion. The ferrous ion was used (Fig. 9) to determine its effect on the rate of removal of iron from a 1% nickel cobalt plating solution. However, the analysis was vety poor in this case in spite of checks and rechecks. It seems possible to assume however, that removal does not proceed much below 50 milligrams per liter and that the course of removal from 100 to 50 milligrams per liter is generally the same as for the ferric ion. A rather peculiar effect was observed in the electrolysis of the 3.75 pH 1% nickel cobalt plating solution. (Fig. 11) The precipita- tion effect alone removed iron faster than some conditions of electroly- glg. Curves #l,=#2,:#3, and #4 represent a lower temperature, slower agitation, and lower current density respectively than the optimum conditions. The lower temperature probably did not coagulate the pre- cipitate as fast, and the failure of the lower current density to remove more iron may be explained by the equilibrium which will exist at the -42 ... electrodes giving some ferrous ion at the cathode which cannot be precipitated. The decreased agitation (curve #2) should have had no effect on the precipitation behavior. However, it was not until after eight hours that this lower agitation exceeded the rate of removal of precipitation effect alone. Either the 3/4 inch or 1/2 inch cathode indentation at high temperature, agitation, and current density, removed iron faster than precipitation alone. After three hours, electrolytic removal by either of these cathodes had removed as much as the precipitation effect alone did in six hours. All of the previous discussion has dealt with the differences in power efficiency of different sets of conditions. In order to show how time efficiency is affected with change in current density. The 2.1 pH series of current density curves are plotted with iron content against time in hours. (Fig. 12). This shows that in point of time, 10 amperes per square foot is again an optimum and that 7.5 and 5 amperes per square feet are not even feasable. Conclusion- Certain conditions of electrolysis, namely, current density, agitation, and depth of cathode indentation, have an opti- mum, above and below which the rate of removal of iron from the 1% Nickel Cobalt solution will not be as rapid or effective. These opti- mum conditions (among those tested) are the following: current dens- ity lO amperes per square foot; agitation 20 feet of solution past the cathode per minute; cathode indentation 1/2 inch. A temperature of 800 Centigrade was found superior to 650 Centigrade in the 3.75 pH bath. Since the faster rate of removal obtained with higher tempera- ture in the 3.75 pH bath was probably due to the increase of pre- cipitation with temperature it is suggested that a lower tenperature be tried in the 2.1 pH bath where there is no precipitation effect. In dropping the concentration from 100 milligrams per liter to 35 milligrams per liter, a copper cathode will save 1500 ampere min- utes per gallon over a steel base cathode when both have been operat- ed at optimum conditions. Future studies should include weighing of the cathode before and after each experiment to determine the nickel loss at different condi- tions. Optimum conditions have been established from 100 milligrams per liter down to 10 to 20 milligrams per liter. Further study on the lower limits of the 2.1 pH curves (20 mg./l. to O mg./l.) may be necessary if detrimental effects are still encountered at that concentration. -44- BIBLIOGRAPHY ‘Wiesner, H. J., "Colloidal State and Precipitation of Certain Metallic Hydroxides in Concentrated Solutions of Nickel Sulphate" Thesis for Ph. D., 1943, Michigan State College. Serfass, E. J., Levine, W} S., Smith, G. F., Duke, F., "Determ- ination of Impurities in Electroplating Solutions” (IV) Iron in Nickel Plating Solutions. Chem. Abstracts, Vol. 41, p. 661i, 1947. ‘"' -45- AUG 1 3 e. . . 216965 T543 i 9744 D0“ T542 216965 D744 Dow The electrolytic separ- ation of iron from conc- \ entrated solutions of nickel and cobalt for the electrolytic depos- ition of nickel. llHlllHllHllllIllHHllIllllllllllllllllllillll'lllili‘lll 31293 02446 8468