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INDUSTRIAL AND ENGINEERING CHEMISTRY
perforations. This mill is not intended actually to grind the product but simply to disperse the particles fed to it from the mixer so that no clusters of particles will enter the air stream. The zein passing the mill is sucked into a stream of air heated to 330" F., and passes through a drying chamber 32 feet high a t a velocity of 3500 to 6000 feet per minute. The air containing the zein is discharged directly into a cyclone. The temperature of the drying air is reduced to about 120" F. and the zein leaving the cyclone has a moisture content of 15 per cent. The zein leaving the cyclone enters an air stream having a velocity of 3500 feet per minute and is cooled to 40" F. It is not found advisable to use any type of mechanical seal between these air systems, and excessive interchange of air is prevented simply by proper balancing of the air pressure a t the point of transfer. The amount of air in this cooling system is sufficient to reduce the temperature of the zein to a
Vol. 33, No. 12
point below 60" F., after which it is collected in a cyclone. The cooled product is divided into two portions; one returns to the mixer as previously described, the other passes into a secondary drying system where it is in contact with air heated t o 225' F. and where the moisture content is reduced to approximately 6 per cent. The product from the secondary drying system is screened through a 60-mesh screen and passes to the storage bin. Since the tailings from this system have been subjected to somewhat unfavorable temperature conditions in the moist state, they are not particularly suitable for returning to the system and must find use where their particle size does not interfere.
Literature Cited (1) Horesi, A. C.,Flint, A. H., and Swallen, L. C., U. 5. Patent 2,238,591(1941). (2) Swallen, L. C., IND.ENQ.CHEN.,33, 394 (1941).
Effect of Wetting Agents on Electrodeposition of Nickel I
NFORMATION regarding the effects of wetting agents on nickel electrodeposits has been of comparatively recent origin. Patents (4) involving the use of such wetting agents as gluconates or sulfonated alcohols having more than three carbon atoms t o eliminate pitting in nickel deposits have been issued. Schlotter (7) used aromatic sulfonic acids or their salts to obtain bright nickel deposits. Schlotter (8) also obtained deposits having a grain size of less than 0.0001 mm. from a nickel sulfate bath containing nickel naphthalenetrisulfonate. Blount (2) used sodium alkyl aromatic sulfonates in hot nickel electrolytes to eliminate pitting in the deposits. The Newark Branch of the American Electroplater's Society ( I ) reported the use of sodium alkyl sulfates, alkyl naphthalene sulfonates, and fatty acid amides in nickel baths to prevent pitted deposits. It is believed (6) that pitting in nickel deposits is caused by bubbles of hydrogen, oxygen, or air collecting on the cathode surface and preventing the further deposition of nickel a t that point. Boiling the plating solution eliminates air pitting, and the use of nonpassive anodes eliminates oxygen pitting. Although hydrogen pitting continues to be a serious problem in nickel plating, the use of wetting agents holds considerable promise of offering a satisfactory solution. Briefly stated, the action of wetting agents ( 2 ) on electrodeposits is believed to be as follows: Wetting agents have the property of reducing the surface tension of aqueous systems. This, in turn, lowers the interfacial tension between the cathode and the electrolyte; thus any bubbles of hydrogen collecting on the cathode fail t o adhere and are forced to the surface of the bath by the hydrostatic pressure of the electrolyte. The result is a smooth, fine-grained, and pit-free deposit.
Experiments with Plating Baths
Six strongly and three mildly surface-active agents were added to the bath in different concentrations. Members of the former group were Igepon-T (represented by the formula
ROGERS F. DAVIS, KATHRYN &I. WOLFE, AND WESLEY G. FRANCE The Ohio State
University, Columbus, Ohio
CI.~H~S-CO-NH-CH~--CH~-SO~N~), Lyofix D. E. and Sapamine K. W. C. (belonging to the quaternary ammonium type of wetting compounds), Nekal B. X., 1,4-isopropyl naphthalene sulfonic acid, cetyl pyridinium bromide, and citronellal. The three mildly surface-active agents were o-nitrotoluene, m-tolualdehyde, and pyrrole. Liquid agents such as m-tolualdehyde, pyrrole, o-nitrotoluene, and citronellal were added t o 200-cc. volumes of bath in quantities of 0.01 to 0.5 cc. The other wetting agents-e. g., solids-were added in quantities up to 500 mg. A recent list of a variety of surface-active agents was given by Van Antwerpen (9). A plating bath (8) composed of 105 grams of nickel sulfate, 15 grams of nickel chloride, 15 grams of boric acid, 15 grams of ammonium chloride, and 1000 cc. of distilled water was employed. Sheet copper cathodes and rolled sheet nickel anodes were used in the plating cell. A copper coulometer served to measure the quantity of electricity passed through the solution. The current density maintained throughout the investigation was 1 ampere per sq. dm. The temperature varied from 25" to 28" C. The pH measurements were made with a Coleman glass electrode, before and after each electrolysis. Surface tensions were determined by means of a du Nouy tensiometer. The solution used for the measurement of the surface tension was prepared as follows: 200 cc. of the original plating bath were measured into a bottle with a buret. An accurately weighed quantity of a wetting agent was dissolved in distilled water in a volumetric flask. A pipet which could be read t o 0.01 cc. was used to transfer an accurate volume of the wetting agent solution to the 200-cc. bath, which was then shaken until the wetting agent was completely dissolved. An 11-cm.
December, 1941
INDUSTRIAL AND ENGINEERINQ CHEMISTRY
A study of the effects of six strongly and three mildly surface-active agents on the electrodeposition of nickel upon copper cathodes has been made. The strongly surface-active agents were Igepon-T, Nekal B. X., Sapamine K. W. C., Lyofix D. E., cetyl pyridinium bromide, and citronellal 8 the mildly surface-active agents were o-nitrotoluene, m-tolualdehyde, and pyrrole. The wetting agents were present in the baths in small concentrations. Igepon-T produced the most satisfactory deposits. The wetting agents tended to produce smooth, fine-grained, and pit-free deposits. They rapidly lowered the surface tension of the electrolyte to a relatively constant value. The smoothest deposits were obtained when the surface tension of the plating baths attained values between, 30 and 35 dynes per cm. The cathode current efficiencies tended to decrease with increasing concentration of wetting agent. The pH of the bath gradually became higher as more electricity passed through the solution.
watch glass was filled within 1mm. of the edge, &d sufficient time was allowed after pouring for equilibrium to result before the tensiometer reading was taken. The solution in the watch glass was then returned to the original bath, more of the wetting agent solution was added, followed by another measurement, and this procedure was repeated until the desired maximum concentration was attained. Figure 1 shows graphically the effect of increasing concentrations of Sapamine K. W. C., Lyofix D. E., Nekal B. X., and Igepon-T in lowering the surface tension of the bath.
1547
tion. The relative order of effectivenessof the wetting agents in producing the same surface tension lowering was as follows: cetyl pyridinium bromide > Lyofix D. E. > Igepon-T > Sapamine K. W. C. > Nekal B. X. The general effect of the wetting agents, with the exception of citronellal, was to decrease the crystal size of the electrodeposited nickel. This decrease was greater, the higher the concentration of wetting agent; and the smallest crystals were produced when the minimum surface tension was attained. The most satisfactory deposits were obtained with Igepon-T. They were dull, smooth, fine-grained, compact, pit-free, and strongly adherent. The smoothest deposits were obtained in all cases after the surface tension of the bath had been reduced to 38 dynes or less. Citronellal and Sapamine were the least satisfactory of the strongly surface-active agents in that they gave peeled and loosely adherent deposits. With these exceptions the strongly surface-active substances were more satisfactory than the mildly surface-active ones. Figure 2 illustrates the character of the deposits obtained without the use of surface-active'agents and with Igepon-T, cetyl pyridinium bromide, and Nekal B. X. A is a photograph of the nickel deposit in the absence of the surface-active agent, and B is a photomicrograph ( X 90) taken from within the circled area of A . C is a photograph of the deposit obtained with cetyl pyridinium bromide, and D with Nekal B. X. E is a photograph of the nickel deposit obtained with Igepon-T, and F is a photomicrograph ( X 90) taken within the circled area of E. The pH of the bath in all cases gradually increased as more electricity passed through the solution (Table I). Since pH is readily determined with considerably more accuracy than anode or cathode efficiency, i t is evident that the cathode efficiency for nickel deposition was a t least slightly less than the anode efficiency for nickel solution in all these runs, and that any inconsistency in the data af Table I may be charged to errors in determining anode and cathode efficiencies.
Effects of Wetting Agents In comparing the concentrations of different wetting agents necessary to produce the same surface-tension lowering in the nickel plating solution, the actual molecular structure, the solubility of the wetting agent, and the concentration of other materials in the solution are important factors (6). Of the nine capillary active substances used, less cetyl pyridinium bromide was needed to produce a given surface tension lowering than any other substance, while pyrrole had the least effect on the surface tension of the nickel plating bath. The minimum reached in the surface tension of the bath by addition of m-tolualdehyde was much greater than with any other of the wetting agents used. No minimum was reached by using citronellal in the nickel plating solu-
DE --+-
Lyofix
70 lgepon T --o-BX
Nekal
3 5
IO
b
1 30
0 0
15
20
25
5
IO
15
20
25
30
35
'k
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 33, No. 12
sibility is that the Igepon-T may have been specifically adsorbed by the nickel crystals during their
proposed t o i n vestigate this postion studies. A
B
. .
D
E
FIGURE 2. .TYPICAL DEPOSITS WITH
AND WITHOUT
IN PRESESCE OF IGEPON-T TABLE I. A-ICKELDEPOSITION
Run NO. 13D 14D l5D 16D 17D 18D 19D 20D 2lD 22D 23D 24D 25D 26D 27D 28D 29D 30D
uantity of lertrioity, %Coulombs
Cathode Efficiency,
Anode Efficiency,
648 626 650 664 672
100.3 97.9 99.0 99.5 98.1 98.1 98.3 99.3 99.0 99.6 98.6 97.7 97.5 98.3 97.9 97.9 98.6 98.0
95.4 96.3 99.0 97.9 99.0 99.6 97.6 97.9 99.4 98.6 99.8 100.1 98.8 97.6 99.0 98.3 97.7 100.4
655
616 685 651 654 671 661 654 655 647 639 652 638
%
%
pH of Bath after Electrolysis 3.98 4.18 4.48 4.70 4.85 4.96 4.98 5.00 5.06 5.10 5.12 5.19 5.20 5.20 5.22 5.26 6.22 5.26
C
Summary
1. Of the surface-active agents used, I g e p o n - T produced the most s a t i s f a c t o r y deposits. In general, the strongly active agents were more effective than the mildly active ones. 2. These wetting agents rapidly lowered the surface tension of the nickel plating bath to a relatively conF stant value. The SURFACE-ACTIVE AGENTS most satisfactory deposits were obtained a t thelowest surface tensions-e. g., 30-35 dynes per cm. 3. The size of the nickel crystals was decreased with increased concentrations of wetting agent and reached a limiting value a t the minimum surfape tension. 4. The pH of the bath increased with increase in the quantity of electricity passed. 5. Relatively high (97-99 per cent) anode and cathode efficiencieswere attained in the presence of the wetting agents, with the exception of cetyl pyridinium bromide. 6. Apparently other factors than a sufficiently lowered surface tension determine the effect of the wetting agent on the character of the deposit. It is suggested that one factor may be the specific adsorption of the wetting agent by the growing nickel crystal with an accompanying modification of its crystal habit.
Literature Cited The cathode current efficiencies decreased slightly when more wetting agent was present in the bath. However, relatively constant (97-99 per cent) cathode efficiencies were attained in the Igepon-T, Sapamine K. W. C., Sekal B. X., and citronellal series of electrolyses a t the more effective concentrations. A consideration of the results obtained in this study shows that, whereas each of the surface-active agents used appreciably lowered the surface tension of the bath, only one, Igepon-T, produced completely satisfactory deposits. I n view of this fact, it is clear that some factor or factors other than a sufficiently lowered surface tension are effective in determining the character of the deposit. Otherwise each of the surface-active agents should have proved beneficial. One pos-
(1) Am. Electroplaters’ Soc., Newark Branch, Mcmthly Rev. Am. EZectropZaters’ SOC.,25, No. 1, 124-5; No. 6, 458; No. 7, 643; No. 11, 845 (1938). (2) Blount, E. A,, Products Finishing, 2, No. 8, 37-9, 42 (1939). (3) Blum, W., and Hogaboom, G., “Principles of Electroplating and Electroforming”, pp. 259-60, New York, MoGraw-Hill Book Co., 1930. (4) Harshaw Chemical Co., Brit. Patents 438,412 and 472,514 (1935). (5) Hartshorn, D.S.,Jr., Metal Finishing, 39, No.3,123-30 (1941). (6) Maonaughton, D. J., and Hothersall, A. W., Trans. Faraday SOO., 24,497-509 (1928). (7) Schlatter, M., Brit. Patent 459,887 (1935). (8) Schlatter, M.,U.S. Patent 1,972,693(1932). (9) Van Antwerpen, F.J., IND. ENQ.CHEM.,33, 16-22 (1941). P I ~ P ~ B ~ Nbefore T H I Dthe Division of Colloid Chemistry a t the l O l s t Meeting of the American Chemical Society, St. Louis, Mo.
