THE EFFECTS OF TRACE AMOUNTS OF ZINC UPON SOME PHYSICAL PROPERTIES OI? ELECTRODEPOSII’ED NICKEL Thesis for the chrcc of M. S. MICHIGAN STATE COLLEGE DonaId DeGmII Clark I949 'rhh m N)cenflg Hmtthe lhoflscnfidpd "The Effects of Trace Amounts of Zinc on some Physical Properties of Electra-depositéd Nickel. [II‘C‘SHllt-II In] Dona 1d D. C larlc hm bran {It‘l‘fillh't‘ Immrds fulfillment ”I ”In requimmmls fur M.S. .Lflpvpi“ Physical Chemistry AIM __ Majnr [.rnItéssng ham December 6L 19149 I u _ —-——— . n - ~—-.—__ -— _— - -_--.‘—"_n i ' .I-filu --—‘-_\ u“.- -4- il- ' ‘5“— 'ME _:I 25": '1‘ ""1 u' .- m-‘_ h "3 . Inflrun-“a w- 9. -—'-—- ‘ -- —i-.— ‘-— *u- r— - THE EFFECTS OF TRACE AMOUNTS 0F ZINC UPON SOME PHYSICAL PROPERTIES OF ELECTRODEPOSITED NICKEL By Donald DeGroff Clark A THESIS Sabmitted 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 MASTER OF SCIENCE Department of Chemistry 1949 ACKNOWLEDGMENT The author‘wishes to exPress his sincere appreciation to Dr. D. T. Ewing, Professor of Physical Chemistry, for his guidance and assistance throughout the course of this investigation. The author is also indebted to the American Electroplaters Society for a grant of a fellowship through which this work was made possible, and to the project committee; Mr. B. C. Case, Chairman, Hanson—VanWinkleéMunning Company, later succeeded as Chairman'by Hr. G. H. Cole, Fisher Bodbeernstedt Division, General Motors Corporation and Mr. L. B. Sperry, Doehler- Jarvis Corporation for their contributions and to Robert J. Rominski and Arthur A. Brouwer for their assistance. ******#*** ******** **#*** **** ** $ 00*.“ 1"4 Fir-".1 {gvsfi'g TABLE OF CONTENTS I Introduction............................................... 1 II Procedure Plating Solutions Formulae......................................... 3 Purification..................................... h Preparation Of TEST; Panels...........................o LL Salt Spray............................................ 5 Analytical Method........................................... 5 Concentrations................................... 8 ”Working curve Depletion rate of zinc at ho a.s.f.................... 8 Depletion rate curves III Results Appearance............................................ 9 Adherence.............................................12 Ductility.............................................12 Throwing power and Efficiency.........................12 Salt Spray Corrosion Resistance Results..........................................lh Curves for Removal of Zinc Electrolytic......................................16 Curves for pH precipitation of...............................l7 Curves for IV Conclusions.................................................18 V References.................................................920 -1- INTRODUCTION The purpose of this investigation is to determine the effects of trace amounts of zinc Upon some physical properties of electrodeposited nickel. The nickel solutions were chosen to best show the effects of zinc on different types of nickel deposits. These solutions were a Watts type at a pH of 2.2 and 5.2, an organic type and a cobalt nickel type. The watts type solution was chosen because significant changes in the character of the deposit are Obtained with a change in pH. The organic type solutions, which contain nickel benzene disulfonate, produce de- posits which are bright and reflective. This deposit is sensitive to metallic impurities and it was desired to determine this sensitivity relative to zinc. In the cobalt nickel binary type deposit, nickel and cobalt deposit together, with the aid of an organic compound in the form of formaldehyde, to produce a mirrorebright deposit. It was of interest to determine how this deposit would.be effected by the addition of zinc in trace amounts. The technique and methods for this investigation follow that set forth in a publication by Ewing, Rominski and King (5). Thompson and Thomas (12) observed that the appearance of the nickel deposit was bright but pitted when formed from a nickel solution, pH 5.1 to 6.h,'with 280 mgs. of zinc per liter added as an impurity. Anderson (1) reported that more than 300 mgs. of zinc per liter brightened the deposit. According to Diggin (h), zinc causes a dark plate to result from.bright nickel solutions at low current density regions. Gardam (6) found pitting to occur at concentrations of zinc less than 10 mgs. per liter. Brittle deposits were found by.Meyer (9) to result from a nickel solution containing 225 mgs. of zinc per liter. Wesley and Roehl (1h) have found that the throwing power is decreased more in a Watts pH 2.0 solution than in a Watts pH 5.5 solution. Haring (7) states that the effect of zinc upon the character of the I deposit is more significant than that upon throwing power. 'Wiesner (15) found that zinc was not removed from a nickel solution using ammonium hydroxide until a pH of 6.6 was reached. Mattacotte (8) found that zinc could be removed electrolytically at a current density of 5 a.s.f.. B. C. Case (3) has stated that zinc can best be removed electrolytically at 6 to 7 a.s.f. PROCEDURE Plating Solutions (formulae) Formulae for the nickel plating solutions used in this investigation follow: 'Watts type Ni so4 7 mac 2140 g/l Ni 03.2 6 3120 L5 g/l H3B 30 g/l pH electrometric) 2.2 and 5.2 Temperature 50°C Cobalt nickel alloy" Ni so4 7 0 21m g/l Ni 01, 6 E0 h5 g/i H3B03 30 g/l Formic acid h5 g/l Co so4 7 H20 15 g/l (N114) 504 0.75 1 FormaIdehyde 2.5 1 pH (electrometric) 3.75 Temperature 55.0 Organic type‘I Ni so4 7 ago 262.2 g/l Ni 012 6 H20 60 g/l H3BO3 314 g/l Sodium benzene disulfonate 7.5 8/1 Triaminodiphenylamine O.1h.ml/l pH (electrometric) 3.2 Temperature 55’C I Hanson VanWinkle MMnning Company *+ Schlotter, U. S. Patent 1,972,695 All plating solutions were operated at current densities of to a.s.f. and agitation past the cathode of four feet per minute. 4;- Purification of Plating Solutions The purification of all plating solutions used in this investigation followed that established by Ewing, Rominski and King (5), which consists of precipitating the iron impurities by raising the pH, using nickelous carbonate, to 5.5 to 5.6. Air agitation was used to oxidize ferrous iron. The solution was filtered and remaining metallic impurities were removed.by electrolysis for 80 hours using a corrugated cathode, current density of 5 a.s.f., air agitation and temperature of 70°C. Preparation of Test Panels The test panels used in this study were composed of S. A. E.-1008 sheet steel, furnished.by Dr. Wick of the Bethlehem Steel Company, having a R. M. S. value of 0.006 microinches surface reading obtained on a Brush Surface Analyzer. The dimensions of the panel were: 2 x 3-1/2 inches long having a horizontal lip section 2 x Isl/h inches. Excess grease or oil was removed with carbon tetrachloride. The panel was then subjected to hot alkaline anodic cleaning for two minutes. This was followed by'a two minute 20°/. hydrochloric acid dip. After rinsing with zinc-free water (redistilled), the panel was placed in the plating solution. Alkaline Cleaner Sodium Hydroxide 21 g/l Sodium.Metasilicate 15 g/l Trisodium phosphate 18 g/l Sodium Carbonate 6 g/l Sodium Acetate 7 g/l Sodium lauryl alcohol sulfate 0.05 g/l Temperature 90°C Current Density‘ 120 a.s.f. Salt Spray;Procedure This procedure follows that as set forth by ASTM standards, 19h6 (2). Analytical Method The method for the analysis of zinc in nickel plating solutions follows that by E. J. Serfass et. a1., (11). Solutions Required: 1. Sodium Tartrate - 10°/. Dissolve 10 g. of sodium tartrate in 100 ml. of zinc-free distilled water. Purify by shaking with three portions of dithizone. 2. Sodium diethanoldithiocarbamate - 20'/. Dissolve 200 g. of sodium diethanoldithiocarbamate in zinc-free dis- tilled water to form a liter of solution and adjust the pH to 8.8 with 1-1 hydrochloric acid. .3. Dithizone reagent (100 mg./l) Dissolve 100 mg. of pure dithizone in 50 ml. of zinc free carbon tetrachloride and filter to remove any solids. Run the filtrate into a separatory funnel and shake with 50 ml. of 1°/. annuonimn hydroxide. Run the carbon tetrachloride layer into another separatory funnel and shake with 50 ml. more of 1'/. annnonimn hydroxide. Then discard the carbon tetrachloride layer and combine the aqueous extracts. 'Wash the aqueous solution with 10 ml. portions of carbon tetrachloride three times and then acidify with 2 ml. of concentrated hydrochloric acid precipitating the dithizone. Finally, extract the dithizone with 10 ml. portions of carbon tetrachloride until the aqueous layer becomes colorless and dilute the combined extracts to a liter with carbon tetrachloride. Cover the green dithizone solution with one half inch layer of 5'/, aqueous hydroxylamine hydrochloride to retard oxidation. The solution should be kept in a pyrex flask, and stored in a cool dark place. h. Distilled water (zinc-free) 'Water should.be tested for zinc by adding 5 ml. of dithizone to 25 ml. of water made alkaline with a drop of ammonium hydroxide. On shaking, the carbon tetrachloride layer should be colorless or very weakly pink, showing little or no zinc present. 'Water obtained from a pyrex glass still was found to be pure. 5. Carbon tetrachloride (zinc-free) All carbon tetrachloride should first be distilled in a pyrex still at least once and preferably twice, to insure freedom from zinc. 6. 'Wash solution (0.02°/} ammonium hydroxide) Add 0.5 m1. of concentrated ammonium hydroxide to one liter of zinc- free distilled water. Add 10 ml. of 10‘/. sodium tartrate. Apparatus: A Klett-Summerson Photoelectric Colorimeter was used for this ‘work employing a No. 5h green filter. Procedure A 1 ml. sample of the plating solution is diluted with 9 m1. of zinc- free distilled water. A 1 ml. sample of this is added to 25 ml. of zinc- free distilled water in a 125 m1. separatory funnel. To this is added 2 ml. of 10’/. sodium tartrate and 10 ml. of sodium diethanoldithiocar— bamate reagent. Shake for two minutes. The color of the sclution changes from dark brown to yellow and a green precipitate forms at this point. This is the nickel complex. Formation of the colored system. From a burette, 5 ml. of dithizone reagent is added. Shake vigor- ously for one minute. Allow all the carbon tetrachloride to drain out even though some of the green precipitate goes with it. Add an additional 5 ml. of dithizone reagent and shake again for one minute followed by draining the carbon tetrachloride layer into the funnel containing the first extraction. Repeat this extraction until the carbon tetrachloride layer comes through with a greenish or colorless tint indicating that all the zinc has been extracted from the solution which is then discarded. The carbon tetrachloride solution may now be freed of any entrained precipitate by washing with 25 ml. of zinc-free distilled water. After shaking and allowing the organic layer to settle, run it into another clean separatory funnel. Now add 15 ml. of zinc-free distilled water and 5 ml. of the sodium diethanoldithiocarbamate reagent. Shake thirty seconds. The greenish color of the excess dithizone should disappear leaving a pure red or pink color. If all the excess dithizone is not removed, the carbon tetrachloride layer is run into another separatory funnel and washed again with 15 ml. of 0.02°/o ammonium hydroxide wash solution. Carefully .8— run the red solution into a 50 ml. volumetric flask and dilute to the mark with zinc-free carbon tetrachloride. Filter through a'Whatman No. to filter paper to remove any water present and collect the filtrate in a clean dry beaker. Run a blank following exactly the same procedure except that no sample is taken. Zinc Concentration Range The concentrations of zinc over which this investigation was con- ducted were: 2.5, 10, 25, 75, 150 and 500 mgs. per liter of plating solution. The zinc ion was added in the form of ZnSQ4 7Héo. A standard calibration curve was established over the range of 0 to 500 mgs. of zinc per liter and is shown in Fig. 1. Depletion Rate It was necessary, in order that a given zinc concentration level might be maintained for the preparation of subsequent test panels, to determine the rate of depletion of zinc from the four nickel plating solutions at a current density othO a.s.f. These depletion rate curves are shown in.Figs. 2, 5, h.and 5. A lO‘/. depletion of zinc was allowed by deposition before the concentration was reestablished to the original value. (“a O 0 70 lb 0 1...: (D O a Milligrams zinc per liter 1...: N) <3 03 O O 50 100 150 200 250 200 sec 4cm Colorimetric units Figure l.~ Calibration curve for the determination of zinc in nickel plating solutions. (0.1 m1. sample.) £5 320 to a: C) r’II ‘0 A) 0 lb 0 O R \ Milligrams zinc per liter 160 120 I so V v i 40 \\ ' I s O N 0 2 4 6 8 10 nickel solution. Time in hours Figure 2.- The electrolytic removal of zinc from a Vatts type Current density of 40 a.s.f., pH 5.2, 50 C, 19 (O G) O 0:) .b ’3 O O F r Milligrams zinc per liter 160 120 80 4C <‘l0~“‘ c \fiL— 4L 4 0 2 4 6 8 10 12 Time in hours Figure 3.- The electrolytic removal of zinc from a Yatts type Current density of 40 a.s.f., pH 2.2, nickel solution. 505C. Milligrams zinc per liter Milligrams zinc per liter m .p. 0 PO 8 /'v / /’ I \< ‘——1 80 \ «— ewe—4 4O \ 0 Ni 0 2 4 6 8 10 1? Time in hours Figure 4.- The electrolytic removal of zinc from an organic type bright nickel solution. Current density of 40 a.s.f., p? of 3.2 and at 55°C. 5205 28 (’0 as \ A) O O H O) O k//4 H N O O) A 4 ~s\ G O 2 4 6 8 10 12 Time in hours Figure 5.- The electrolytic removal of zinc from a cobalt- nickel alloy type nickel solution. Current density of 4C a.s.f. pH 3.75 and at 55°C. RESULTS Appearancg For the evaluation of appearance, bent steel panels having vertical sections of 2 x 3-1/2 inches and horizontal sections of 2 x l—l/h inches lwere plated, for the grading of the surface, in the four type bathS'with various concentrations of zinc as an impurity. The vertical sections had an overall current density range of to a.s.f. The horizontal sections possessed low, medium, and high current density areas, these being approx~ imately 10, to and 50 a.s.f. respectively. In addition to reporting the appearance of the vertical section of the nickel deposited panel, an attempt was made to correlate the appearance of the vertical section of the nickel deposited panel with the corresponding current density area of the horizontal section. Also, effort was made to observe the backs of the vertical panels for blackening in very low current density areas (2 - b a.s.f.). The usual difficulty of grading the greyness and brightness was encountered. For the grey deposits from the Watts type baths, the method formerly reported was used (5). The grey deposits were compared with the Eastman grey scale. This scale began with (one) as the lightest shade of grey followed‘by (two) as the next successively darker tone. For this work a value of (three) was the darkest value found. For the bright nickel deposits, an arbitrary scale was chosen by the investigator. This consisted of appearance values ranging from dullébright to mirror- bright. Table 1. summarizes the effects of zinc on the appearance of the ~10— vertical deposits from the four nickel plating solutions with regard to the general brightness of the overall panel. Table 1. Effect of Zinc as an Impurity on the Appearance of Nickel Deposits Zn Conc. watts 'Watts Co-Ni Organic mg./liter pH 2.2 pH 5.2 pH 3.75 pH 3.2 O 2 2 mirror bright bright 2.5 2 2 bright dull bright lO 2 2-3 semi bright dull bright 25 2 2-5 semi bright bright 75 2 2 semi bright bright 150 2 2-5 semi bright semi bright 300 spotted.bright 2-3 bright mirror bright It was noted, in the case of the deposits from the'Watts pH 2.2 solution, that no change in appearance occurred to 150 mgs. of zinc per liter. ‘With the addition of 300 mgs. of zinc, areas would show a tendency to brighten. This was further substantiated by brightening of the medium current density area on the horizontal section at 2.5 mgs. per liter of zinc, very low current density areas on the pane1.back show blackening. In the case of the high pH latte bath (5.2), the trend.was to darken slightly with increasing concentrations of zinc. Observance of the hori- zontal section showed a darkening which further supports the conclusions made in correSponding areas of the vertical panel. The very low current density areas on the panel back show a blackening at 2.5 mgs. of zinc per liter. The cobalt nickel deposits showed a decrease in brightness with increasing zinc. 'With 300 mgs. of zinc there was noted an increase in the brightness value but this is less bright than the panel from the standard solution. Medium current density areas on horizontal sections follow the same trend as do the vertical sections. Blackening is also noted at a concentration of 25 mgs. of zinc in the low and very low current density areas. The organic type deposits increased in brightness with increasing concentrations of zinc. 'With the addition of 300 mgs. of zinc per liter of plating solution, the deposit exhibits an improved brightness over that of the standard panel. Blackening is found to occur in the very low current density areas beginning with a concentration of 2.5 mgs. of zinc. In addition to the above effects upon the appearance with increasing amounts of zinc, it was seen that gassing at the cathode, which resulted in pitted deposits, occurred with the addition of 2.5 mgs. of zinc in all baths except the high pH Watts (pH 5.2). Each of the baths, Watts pH 2.2, cobalt nickel and organic type continued to produce gassing resulting in pitting from 2.5 to 300 mgs. zinc per liter. It was found that by the addition of a wetting agent in the form of sodium lauryl alcohol sulfate (85./.), this pitting could be remedied. It can be generally stated that the nickel deposit is brightened at high concentrations of zinc (150 - 300.mgs. per liter) and at high current densities (to to 50 a.s.f.). Also, that the deposit is darkened with low concentrations of zinc (2.5 to 25 mgs. per liter) and low current density ranges (2 to h.a.s.f.). Adherence No appreciable change in the adherence of the nickel deposit to the steel base was noted over the range of O to 500 mgs. of zinc per liter and current densities of 6 to 50 a.s.f. for the four nickel solutions studied in this investigation. Ductilitv Deposits were made from the four baths over the concentration range of O to 300 mgs. of zinc on an oxidized nickel surface. These deposits were stripped from the oxidized surface and subjected to the bend test (5). This test consisted of repeatedly bending and creasing the deposit across a predesignated area with the fingers, until a break was noted. By this mmthod, comparative ductilities were evaluated as being the number of bends a deposit would withstand before fracture was noted. While the deposit from zinc-free Watts pH 2.2 solution was more ductile than that from the'Watts pH 5.2 bath, deposits from both solutions de- creased in ductility as the concentration of zinc increased. Little change was noted in the ductility of the deposits from the cobalt nickel solution until a concentration of 500 mgs. per liter was reached. Deposits from the organic type solution did not change appreciably in ductility in the range of O to 500 mgs. of zinc per liter of solution. ThrowingpPower and Efficiency Throwing power and efficiency was evaluated by the procedure previously followed in this project (5). Assuming that the cathode efficiency was lOO‘/. , any change in the -13.. thickness of the deposit from solutions containing zinc as an impurity, as compared with deposits from a standard solutions, is a measure of throwing power. Table 2. summarizes the percent change in the thickness of the deposit from each of the four baths due to variation of the con- centration of zinc. A wetting agent was found to be necessary to prevent pitting in each of the solutions except the watts pH 5.2 Table 2. Effect of Zinc as an Impurity on the Throwing Power and Efficiency of Nickel Plating Solutions. Cone. Zn watts ‘Watts Co—Ni Organic mg./l pH 2.2 pH 5.2 2.5 1.0 ~5.5 -2.0 6.5 10 —2.5 -5.0 5.0 5.0 25 -l.0 10.0 7.0 -5.0 75 -1o.o 1.0 1.0 h.o 150 -9.0 10.0 5.0 2.5 300 2.0 10.0 2.0 14.5 The deposits from the'Watts pH 2.2 bath show a general decrease in throwing power with increasing concentrations of zinc down to -lO’/., up to and including the 150 mgs. of zinc per liter. A slight increase is noted at a concentration of 300 mgs. of zinc per liter. 'With an increase of pH from 2.2 to 5.2, in the'Watts type bath, a decided increase in throwing power is noted with zinc concentrations of 25 to 300 mgs. per liter. -1... Deposits from the cobalt nickel solution s1owed an increased throwing power with zinc as an impurity above a concentration of 2.5 mgs. per liter. 'With the exception of the concentration of 25 mgs. of zinc per liter, deposits from the organic type solution showed an increase in throwing power as a result of zinc impurities in the plating solution. Salt Spray Corrosion Resistance Three thicknesses of deposits, 0.0005, 0.001 and 0.0015 inches were made to determine if any change resulted in corrosion resistance due to this variable. Test panels were made with varying concentrations of zinc and their breakdown time compared.with that of the deposit free of zinc impurities. The final results were reported in percent deviation from the pure deposit. Generally with the addition of 2.5 mgs. of zinc per liter of solution, an increase in corrosion resistance is noted for the deposits from the different type of solutions. The greatest increase in corrosion resistance due to zinc impurities, appears in deposits from the watts pH 2.2 and 5.2 solutions. The thickest deposits show the greatest in- crease in corrosion resistance with increasing concentrations of zinc. The thinner deposits from these solutions are progressively less resistant. Deposits from the organic type nickel solution show the same general trend as do the deposits from the watts solutions but do not show as great an improvement in salt spray corrosion resistance. 'With increasing concentrations of zinc impurities, in the cobalt nickel solution, the corrosion resistance of the resulting deposits are adversely effected. .15. Figs. 6, 7, 8, and 9 show the percent change in corrosion resistance with increasing concentrations of zinc in each of the four nickel solutions. Percent chemo in corrosion res O 50 100 150 200 950 300 Milligrams zinc per liter Figure 6.- Salt spray corrosion resistance of the nickel deposit as affected by thickness; (1) 0.0003, (2) 0.001, (7) 0.0015 inche" and by zinc as an impurity in the watts pH 5.2 solution. Percent change in corrosion resistance 50 100 150 200 250 300 Milligrams zinc per liter Figure '7.- Salt spray corrosion resistance of the nickel deposit as effected by thickness; (1) 0.0003 (2) 0.001, (3) 0.0015 inches and by zinc as an impurity in the Watts pH 2.2 solution. -16... The Removal of Zinc from Nickel Plating Solutions The study of methods of removal of zinc impurities was limited to two in this investigation. These consisted of the removal of zinc electrolytically and.by pH precipitation. 1. The Electrolytic Removal of Zinc The method follows that of a pUblication previously mentioned (5), ‘with the exception that l, 2, h.and 6 a.s.f. were selected to determine the optimum rate of removal. It was found that in the four baths investigated, zinc was removed most rapidly, on the basis of ampere hours per gallon, by a current density of.h,a.s.f. for solutions containing greater amounts than 50 mgs. of zinc per liter. For lower concentrations of zinc, 2 a.s.f. was the optimum for removing the remaining zinc. 0n the basis of nickel economy, 2 a.s.f. would be the optimum current density to employ. If time is the criterion, h to 6 a.s.f. would be most advantageous. Figs. 10 - 17 show the optimum rate in terms of ampere hours per gallon and in time in hours for the removal of zinc from nickel plating solutions. 3 I , . I 1 \i it ~ W ; i % ‘\\:$;é;;::l;;;33§igggg::::::::_fi A a .‘O O O H O O Milligrams zinc per liter H 0‘ O 0‘ O 0 i .5 z 0 50 100 150 200 250 300 ?50 4‘“ Ampere hours per gallon Figure 10.- Rate of removal of zinc from a watts type riclol solution of pH 5.2 at current densities of (1) A, (2) 2, (7‘ 1 and (4) 6 a.s.f., at 50°C and agitation past the catht”e v? frur feet per minute. 3O I‘ :3 U! M O 5.. 0| \ m \ w 1 0 10 20 30 40 50 60 70 80 Time in hours Figure ll.- Rate or removal of zinc from a watts type nickel solution of pH 5.2 at current densities of (1) l, (2) 2, (3) 6 and (4) 4 a.s.f., at 5060 and agitation past the cathode of four feet per minute. H Milligrams zinc per lite U‘ Q I 3 3250 .p :1 \ £200 \ .3 Vs \ g1 \ \\ S \1\",\ 4 '2? 5 \ \ . 0 50 100 150 200 250 300 350 400 Ampere hours per gallon Figure 12.— Rate of removal of zinc from a Watts type nickel solution of pH 2.2 at current densities of (1) 4, (2) 2, (7) l and (4) 6 a.s.f., at 50cc and agitation past the cathode of four feet per minute. 300 2SOI§§ 4 N O O § Milligrams zinc per liter 2: (3 0| 0 "\T\ O 10 20 30 40 50 60 70 80 Time in hours Figure 13.- Rate of removal of zinc from a Watts type nick solution of pH 2.2 at current densities of (l) l, (2) 2, K and (4) 4 a.s.f. at SOCC and agitation past the cathode of feet per minute. 0 4'4 e our *5 O Milligrams zinc per liter 3 250 15- ‘\\\\ 1 VN§ l 2 3 \l 4 \ O 50 100 150 200 250 300 350 400 Ampere hours per gallon Figure 14.- Rate of removal of zinc from an organic tvre nickel solution of pH 3.2 at current densities of (1) 4, (2)'2, (3) l and (4) 6 a.s.f., at 55°C and agitation past the cathode of four feet per minute. 300 l0 0‘ O ”a \\\ a \ \\\ 4 3 2 \%%>‘ ‘\\:::::=iir 0 0 lo 20 50 4O 50 60 70 80 Time in hours F e 15.- Rate of removal of zinc from an organic type nickel so ution of pH 3.2 at current densities of (1) 1, (2) 2, (3) 6 and (4) 4 a.s.f., at 5500 and agitation past the cathode of four feet per minute. 5.. 0| 0 H 8 4/ Milligrams sine per liter S 800 .8250 .p v: st "200‘ 8. \ 0 £150 Q. \ In \ 2 ~‘() N“;. 4 100 <\\\ a 3 \ 5'3 50 \ \ 1\ u \ \W H c. 0 50 100 150 200 250 300 350 40‘ Ampere hours per gallon Figure 16. - Rate of removal of zinc from a cobalt-nickel alloy e nickel solution of pH 5. 75 at current densities of (1) P, (y)% (3) 1 and (4) 6 a. s. f. 'é at 55°C and agitation past the e. cathg eof four feet per minu 50 :;250 .p H H g 200 o. O 3.150 ‘ B a 100 i \ \< 5‘ 4&3 Y 1\ O O 10 20 50 40 50 60 70 80 Time in hours Figure117. - Rate of removal of zinc from a cobalt-nickel alloy e solution of pH 5. 75 at current densities of (l) 1, (2) 2, (g) 4 and (4) 6 a. s .f., at 55°C and agitation past the cathode of f’nnr feet m1- mimi‘ a -17- 2. The pH Removal of Zinc. USing solutions of nickel containing 300 mgs. of zinc per liter, small amounts of nickelous carbonate were added to give pH values over a range from 2.2 to 6.1. Samples were taken at pH intervals at room temperature and filtered. These were allowed to stand for a period of time to attain equilibrium. The sample was again filtered, pH measured (electrometric) and the concentration of the remaining zinc determined. These results are graphed in Fig. 18 for the three solutions. It is noted that this method is of no value for the removal of zinc from the three nickel plating solutions to below 2h0 mgs. of zinc per liter. At this high pH, where 2h0 mgs. of zinc still remain, nickel begins to precipitate appreciably. Thus the complete removal of zinc by this method is impractical. pH (electrometric) 5.0 P ‘3\ 4.0 < (> 1 2 3 3.0 200 250 300 200 250 300 200 250 390 Figure 18.- The pH precipitation of zinc from nickel solut- ions. Milligrams zinc per liter (1) cobalt-nickel (2) watts ( 7 L ) organic type. .18— CONCLUSIONS Appearance Zinc impurities have little effect in dull nickel solutions at either high or low pH except at a concentration of 500 mgs. per liter when a current density of to a.s.f. is used. With lower current densities, 2 to h a.s.f., blackening is noted with a concentration of 2.5 mgs. per liter. Zinc aids the appearance of the organic type de- posit and is detrimental to the appearance of the cobalt nickel alloy type deposit in concentrations of 300 mgs. per liter and at a current density of MO a.s.f. At low current densities, the organic deposit is more sensitive to zinc as an impurity than is the cobalt nickel deposit. Adherence No change in adherence due to zinc impurities in the nickel plating ' solution is noted. Duct-i121 'With increasing concentrations of zinc there is a slight loss of ductility in the deposits from the four nickel solutions. Throwing Power and Efficiency There is a general loss of throwing power in the Watts pH 2.2 bath. A general slight gain is noted in the Watts 5.2 organic and cobalt nickel type deposits. -19... Salt Spray Corrosion Resistance A general increase in salt spray corrosion resistance with in- creasing concentrations of zinc is noted with the exception of the CObalt nickel alloy type deposit. Here there is a decrease in corrosion resistance noted for higher concentrations of zinc. Removal of Zing l. Electrolytic: 2 to h.a.s.f. is the optimum current density range for the removal of zinc from the four nickel solutions investigated on the basis of ampere hours per gallon. For the most rapid removal on the basis of time,.h to 6 a.s.f. was found to be optimum. 2. pH Precipitation: - This method left 80’/} of the Zinc in solution at the maximum.pH level. Thus pH precipitation could not be used to completely remove zinc impurities from nickel solutions. (1) (2) (3) (u) (5) (6) (7) (8) (9) (10) (11) (12) (13) (11.1) -20- RIFERENCES Anderson, E. 11., Monthly Rev. Am. Electroplaters Soc., _2_2_, 211-32 (1935). ASTM Standards, No. l-B, 773 (19%). Case, B. 0., Products Finishing, _]_._2_, 60-68 (l9h7). Diggin, M. B., Paper presented before Detroit Branch Am. Electro- platers Soc., November 2, 19145. Ewing, D. T., Rominski, R. J. and King, W. M., Plating, fié, 1137-115 (19119). Gardam, G. E., J. Electrodepositors Soc., g, 8-1} (19117). Haring, H. 13., Monthly Rev. Am. Electroplaters Soc., ll, h-lS (192A). Mattacotti, v., Ibid., g5, 51342.0 (1938). Meyer, W. R., Proc. Am. ElectrOplaters Soc., 22, 65-68 (l9L11). Proctor, C. H., Metal Ind., 11, 57 (1915). Serfass, E. J., Levine, W. 5., Prang, P.J., and Perry, H. M., Plating, 18, 818-23 (1916). Thompson, M. R., and Thomas, C. T., Trans. Am. Electrochem. Soc., 53, 79-9h (1922). Weisner, H. J., Michigan State College,Ph. D. Thesis (1915). Wesley, W. A. and Roehl, E. J., Trans. Am. Electrochem. Soc., 88, 1119-99 (19%). _._’ // samurai! LlBRARY ,T541.3 227953 .' C592 Clark i