# Electroplating with Cobalt. - Industrial & Engineering Chemistry (ACS

Ind. Eng. Chem. , 1915, 7 (5), pp 379â399. DOI: 10.1021/ie50077a004. Publication Date: May 1915. ACS Legacy Archive. Cite this:Ind. Eng. Chem. 1915,...

May, I g I j

T H E J O l ' K S A L O F I S D C S T R I A L A;VD E S G I S E E K I S G C H E J I I S T K Y

t o be i t will have served its purpose if i t has brought freshly home t o some of you who live in this supremely favored section of our country t h e responsibility for in di vi d u a1 initiative imposed u p on you . 0p p or t u n it y

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implies responsibility. Gentlemen, you are heirs t o a n imperial inheritance a n d its responsibilities are yours. 93 BROADS T , B O S T O N

ORIGINAL PAPERS ELECTROPLATING WITH COBALT' B y HERBERT T. KALMUS,C. H. HARPERA K D W. L. S A V E L L Received February 13, 1935

I n 1842, Professor Boetger pointed out t h a t dense a n d lustrous deposits of nickel could be obtained. I\-hich, on account of their resistance t o oxidation. great hardness a n d elegant appearance, !!-ere capnl>lc of m a n y applications. T h e outcome of this h a s been t h a t during t h e last 20 years commercial platins n-it11 nickel has developed t o a n industry of very great magnitude. On t h e other h a n d , no plates of cobalt or of i t s alloys have ever been in extended commercial use. N o d o u b t p a r t of the reason is because of t h e difficulty of obtaining a supply of cobalt metal a t a n attractive price. On t h e other h a n d . for commercial plating. where labor. overhead charges, t h e preparation of t h e surface t o be plated, t h e difficulty of maintaining t h e bath: t h e a m o u n t of buffing, t h e current efficiency, a n d particularly t h e speed with which t h e work m a y be r u n through t h e baths, are so considerable a fraction of t h e cost of t h e finished work, t h e price of t h e metal t o make u p t h e anodes a n d t h e salts is b y n o means alone t h e determining factor in t h e choice of t h a t metal. Aloreover, t h e speed of plating largely determines t h e hardness a n d other physical properties of t h e plate, which in t u r n determine t h e weight of metal required for satisfactory commercial tests. iZ great m a n y technical points in connection with t h e plating of cobalt have n o t been investigated; the corresponding in\-estigations for nickel h a r e been comparatively thorough. Before platers can a d o p t cobalt for m a n y purposes, on a considerable scale, a n u m b e r of questions must be definitely answered b y experiments, such a s : ]-Can cobalt be plated on iron, steel, brass, tin, German silver, lead, etc., t o yield as uniform, as adhesive, and as satisfactory a finished surface as nickel? 2-1s cobalt plate harder than nickel plate? 3-1s cobalt plate less corrosive than nickel plate under ordinary atmospheric action? 4-IThat bath is most suitable for the deposition of cobalt where a heavy protective coating, which may be buffed t o a superior finish, is required to be deposited in a minimum of time? j--Can a satisfactory cobalt bath be maintained a t such an Authors' abstract of report under t h e above title t o t h e Canadian D e p a r t m e n t of Mines, published b y permission of t h e Director of Mines, O t t a \ \ a , Canada. T h i s publication is one of a series on t h e genelal investigations of t h e metal cobalt a n d its alloys, particularly with reference t o finding increased commercial usage for them, now being conducted a t t h e School of Mining, Queen's University, Kingston, Ontario, for the Mines Blanch, Canadian Department of Mines. See also THISJOURXAL, 6 (1914). 107 a n d 115, 7 (1915), 6. T h i s paper is concerned with t h e presentation of a large a m o u n t of experimental d a t a on cobalt plating. It a t t e m p t s t o record data, t o summarize, a n d t o dram conclusions Kith reference t o practical cobalt plating a n d its application in t h e industries. Theoretical considerations concerning the explanation of t h e r e d t s are reserved f o r a separate publication.

increased coilcentration as compared with the nickel bath, that plating from it may proceed with greater speed? 6-1s the cobalt bath more or less troublesome than the nickel bath as regards crystallization, etc.? :--Should alkali, acid, or neutral l-laths be used for cobalt Ihting?

8-1s

the nature of the deposit improved by hardeners such

as ?mric acid, citric acid, magnesium salts, etc.?

g-How does the maximum current density at which cobalt mal- lie deposited commercially compare with the maximum current densities used in the commercial deposition of nickel? Io-IVhat electromotive force had best be used for cobalt plating, using the bath found most suitable for a given class of

work? 11--HOT\- do cobalt anodes compare with nickel anodes as regards solubility, under the conditions of the plating bath? rz-IThat are the relativc current efficiencies of cobalt and nickel plating under the best conditions? 13-How do the electrical conductivities of satisfactory cobalt and nickel plating solutions compare? 14-Can cobalt be deposited t o considerable thicknesses from any solution in accordance with commercial practice? Ig-IThat is the relative cost of cobalt and nickel plating? Xlthough numerous s t a t e m e n t s have been published in t h e past with regard t o cobalt plating, t h e conclusions t o be drawn from a survey of t h e existing literature a n d p a t e n t s would lead one t o be very skeptical as t o t h e advantages of cobalt plating over nickel plating. It is noticeable, however, t h a t t h e conditions for t h e production of good cobalt plates, as given b y different authors, v a r y tremendously among themselves. Not only are t h e conclusions o f t e n diametrically opposite, as shown belowv, h u t liken-ise t h e d a t a from which these conclusions are drawn. Consider alone t h e question of t h e relative maximum current densities with n-hich cobalt a n d nickel m a y be successfully plated. There is little or nothing in t h e literature relating t o t h e solutions of cobalt nhich we have found in this laboratory t o be most suitable for fast plating. If it can be shown t o be practically feasible t o plate cobalt from a b a t h a t speed possible for nickel, other things being equal or in favor of t h e cobalt, this greater speed of turning o u t t h e v-ork, with a t t e n d a n t economics, mighi. ofiset a very considerable difierence in t h e initial cost of the anodes a n d salts of t h e t w o metals. I t must c'ertainly appeal t o anyone t h a t if cobalt-ammonium sulfate. because of its T-ery much higher solubility tlian nickel-ammonium sulfate, or for other rcasons, niay be used as a plating b a t h a t very much higher c u r r r n t densities, t h a t with such a b a t h t h e plater might t u r n o u t cobalt plates more economically t h a n nickci plates. Moreover: plating a t greater speed mcans ;L harder a n d denser plate with consequent less \\-eight of metal required.

T H E J O U R N A L OF I N D U S T R I A L d Y D E-VGINEERING C H E M I S T R Y

A large number of plating experiments were undert a k e n a t t h i s laboratory in t h e s t u d y of t h e questions outlined above. Xumerous t y p e s of . cobalt b a t h s were used a n d various concentrations of each solution. T h e object of t h i s paper is t o set forth t h e d a t a of these experiments a n d t h e conclusions t o be d r a w n therefrom. L I T E R A T U R E O N E L E C T R O D E P O S I T I O h - O F COBALT

Langbein, i n his well-known work, ‘ I Electro-Deposition of Metals,”l devotes nearly I 7 j pages t o t h e deposition of nickel, a n d a scant 2 pages t o t h e deposition of cobalt. W i t h regard t o cobalt, Langbein remarks:l “ F o r plating with cobalt, t h e b a t h s given under ‘Nickeling’ m a y be used b y substituting for t h e nickel salt a corresponding q u a n t i t y of cobalt salt. B y observing t h e rules given for nickeling, t h e operation proceeds with ease. Anodes of metallic cobalt a r e t o be used i n place of nickel anodes. “ Nickel being cheaper a n d i t s color somewhat whiter, electroplating with cobalt is b u t little practiced. On account of t h e greater solubility of cobalt i n dilute sulfuric acid, i t is, however, under all circumstances, t o be preferred for facing valuable copper plates for printing. “According t o t h e more or less careful a d j u s t m e n t of such plates i n t h e press, t h e facing i n some places is more or less a t t a c k e d , a n d i t m a y be desired t o remove t h e coating a n d m a k e a fresh deposit. For t h i s purpose Gaiffe has proposed t h e use of cobalt i n place of nickel, because t h e former dissolves slowly b u t completely i n dilute sulfuric acid. H e recommends a solution of one p a r t of chloride of cobalt i n t e n of water. T h e solution is t o be neutralized with a q u a a m m o n i a , a n d t h e plates are t o be electroplated with t h e use of a moderate current.” F r o m o u r experiments we find i n general t h a t t h e substitution of cobalt for nickel in Langbein’s baths, as recommended b y him, does not d o justice t o t h e metal cobalt. These b a t h s h a v e been primarily worked o u t for nickel, whereas cobalt, being i n m a n y instances of f a r greater solubility, requires a much more concentrated b a t h t h a n t h a t recommended for t h e fastest a n d best plating. Some of our best cobalt solutions are not included a t all i n Langbein’s list. hlachlil!an,2 W a t t , 3 a n d others report t h a t cobalt deposits a r e harder t h a n t h e corresponding nickel deposits. Brochet4 s a y s : “Cobalting has been proposed in place of nickeling when a deposit of greatest hardness is desired.” On t h e other h a n d Langbein,5 Wah16 a n d others s a y t h a t cobalt plates are softer t h a n t h e corresponding nickel ones. S. P. Thompson’ finds t h a t articles plated with cobalt are less corroded i n t h e atmosphere of London t h a n . 1 Dr. Geo. Langbein, “Electro-Deposition of Metals,” 6th Edition Revised, Henry Carey Baird and Co., Philadelphia, p. 318. 1 MacMillan, “ Electro-Metallurgy,” 1901, p. 2 2 7 . 8 Watt-Phillips, “Electro-Plating a n d Electro-Refining of hIetals,” 1902, p. 360. 4 “Manuel Pratique de Galvanoplastie,” 1908, p. 313. 5 “Electro-plating of Metals,” 6th Edition, p. 319. e Watt-Phillips, “Electro-Plating and Electro-Refining of Metals.” 1902, p. 360. 7 Jouvnal of Instilute of Electrical Engineers, 1892, p. 561.

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either silver or nickel plate, while Stolba’ reports t h a t cobalt salts treated like nickel salts yield metallic deposits of a steel-gray color. less lustrous t h a n nickel a n d more liable t o tarnish. While some authorities report t h a t i t is practically impossible t o obtain a deposit of cobalt more t h a n a few h u n d r e d t h s of a millimeter in thickness, Bouant2 says: Electrolytic deposits of cobalt are easily obtained even of a very great thickness, so t h a t electrodeposition of cobalt is a s easy a s t h a t of copper.” A review of much of t h e literature on t h e electrodeposition of cobalt was presented a t t h e meeting of t h e American Electrochemical Society, a t Atlantic C i t y . i n April, 1913, b y 0. P. m a t t s . A consideration of Watts’ paper emphasizes t h e diversity of opinion with regard t o cobalt plating above mentioned. W a t t s mentions a b o u t fifty solutions of cobalt which have been used with greater or lesser success. Some of these are similar t o ones used b y us i n our experiments, b u t several of our best solutions a r e not included i n t h e list. RIany of these b a t h s are recommended only for very weak currents, others are more or less indefinite, a n d t h e r e is much contradiction among t h e m . For example, t h e first solution in It7atts’ list is-“ Becquerel’s solution, 3 7 . j grams of cobalt chloride neutralized b y ammonia or potassium hydroxide, gives a brilliant, white, h a r d a n d brittle deposit; a very weak current must be used.” L a t e r , quoting from W a t t s , Isaac Adams says in a p a t e n t application: “ I have found t h a t a solution m a d e a n d used i n t h e manner described i n t h e books will n o t produce such a continuous a n d uniform deposit of cobalt a s is necessary for t h e successful a n d practical electroplating of metals with cobalt. * * * I have found further t h a t t h e simple salts of cobalt, such as are recommended b y Becquerel a n d others, are n o t such salts as could be used in practical electroplating with cobalt. * * * * * ” E v e n i n a m a t t e r so immediate a n d i m p o r t a n t t o t h e practical plater a s t h e acidity or basicity of his plating b a t h , t h e r e is n o general agreement among t h e authorities even for nickel solutions, much less for cobalt. Dr. Langbein3 writes: “All nickel b a t h s work best when t h e y possess a neutral or slightly acid reaction * * a n alkaline reaction of nickel b a t h s is absolutely detrimental ; such b a t h s deposit a metal dull a n d with yellowish color a n d d o n o t yield thick deposits.” Bennett, K e n n y a n d Dugliss, in a paper read before t h e American Electrochemical Society a t S e w York C i t y , April, 1914,s t a t e a s t%%-o of their seven general conclusions t h e following: “ 4 good deposit of nickel m a y be obtained from t h e double sulf a t e if t h e solution a t t h e surface of t h e cathode is kept alkaline. * * * Since alkalinity is necessary for good efficiency, i t is very probable t h a t in acid solutions nickel is deposited only when impoverishment of t h e hydrogen ions has caused t h e solution t o become alkaline a n d given t h e conditions under which nickel m a y deposit.” 1 2

p

Electrrcol Reuiew, Piov. 18, 1887, p 503. Bouant, “La Galvanoplastie,” 1894, p. 294.

2 Langbein. 251

”Electro-Deposition of Metals.” 6th

Edition Rcvired,

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T H E J O l - R S A L O F I S D C S T R I d L A ;L'D ENGIL\'EERISG

These are but a few of many contradictory statements t o be found in the literature. SUBDIYISIOiK A S D A R R A S G E Y E S T O F E X P E R I J I E S T S

A very large number of plating experiments were conducted b y us a t this laboratory for the purposes outlined above. in connection with which some sisteen different types of solution or baths n-ere employed and studied, as noted belon-: :s SOLUTIOKS SERIE I Cobalt-ammonium sulfate. I 1 Cobalt-ammonium sulfate, with an excess of ammonium sulfate. I11 Cobalt-ammonium sulfate, ammonium sulfate and citric acid. I V Cobalt-ammonium sulfate and ammonium chloride. V Cobalt chloride with ammonium chloride. V i Cobalt-ammdnium sulfate and boric acid. V I 1 Cobalt-ammonium sulfate, cobalt carbonate and boric acid. VI11 Cobalt sulfate, potassium citrate and ammonium chloride. I X Cobalt phosphate and sodium pyrophosphate. X Cobalt-ammonium sulfate and magnesium sulfate. XI Cobalt sulfate neutral ammonium tartrate, and tannic acid. X I 1 Cobalt sulfate: potassium t a r t r a t e and tartaric acid. X I 1 1 Cobalt sulfate, sodium chloride and boric acid. X I V Cobalt sulfate, ammonium sulfate, magnesium sulfate and boric acid. X V Cobalt-ethyl sulfate sodium sulfate and ammonium chloride. X V I Cobalt sulfate, ammonium sulfate, ammonium chloride and boric acid.

Each set of plating experiments with a definite group of principal components in t h e b a t h has been given a series number. Variations in concentration or changes in the relative proportions of t h e components or additions t o a b a t h , have been designated b y t h e use of letters, A, B, C, etc. Also, where a nickel b a t h has been used, analogous t o a given cobalt b a t h , t h e d a t a for t h e experiments on i t are noted under t h e corresponding cobalt series. There were two distinct series of plating experiments, one set conducted a t this laboratory a n d one in t h e plating department of the Russell Motor Car Co., Toronto. M E T H 0 D AX D A R R .A X G E M E S T F 0 R L A B 0 R A T 0 R T P L A T I S G EXPERIMEXTS cIRcrIT-Power was t a k e n from three storage batteries connected in series, yielding approximately 6 volts. T h e various baths were connected independently across the 6 volt terminals of this storage-battery set, with appropriate resistance in series with each. I n this way the potential across t h e electrodes of each was cut down t o the desired value. B j \*olt range Weston voltmeter, reading t o o 0 1 volt, was connected directly across t h e electrodes of each b a t h . X Weston milliammeter, 600 milliampere scale. was connected in series Rith each bath.

A R R A N G E M E K T OF ELECTRICAL

PLATISG

AXD

C03IPL~TATIOS OF

EFFECTIVE

SuRFAcE-The plating t a n k s used were of glass. rectangular in shape. a n d of approximately t h e following internal dimensions: 1 2 in. X 6 in. X 6 in., though some were deeper. In general. if the b a t h is not large in cross-section in comparison with t h e area of the electrodes, the results obtained will not he reproducible. K e tried experiments using a t a n k not much larger in crosssection t h a n the electrodes. I n t h a t case the voltage required for a given current density, with electrodes I O cm. a p a r t . is very much greater t h a n with a t a n k of considerably larger cross-section, other conditions being the same. This is largely due t o the fact t h a t with the smaller cross-section of t a n k the available solution between the electrodes is diminished ELECTRODE

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For the most part. our electrodes v e r e approximately 3 in. x 2 in. in surface. placed from I O t o 20 cm. a p a r t , in t h e center of t h e rectangular plating t a n k above mentioned. If the electrodes were kept in place, t h e t a n k lowered away from t h e m and substit u t e d b y a very large t a n k of the same solution, we found t h a t t h e electromotive force across t h e electrodes for a given current density diminished by nearly 20 per cent. The leads of the electrodes were coated with a layer of insulating asphaltum, as described in t h e paragraph on electrodes. I n t h e case of these experiments, therefore, t h e effective electrode area is something like 2 0 per cent less than t h e exposed surface. Again, instead of submerging electrodes of the above size in t h e middle of the t a n k , in some of our experiments t h e electrodes were lowered into a t a n k t o such a depth a s t o be just covered b y t h e solution. It is obvious, in this case, a s we found b y test, t h a t the electromotive force across t h e electrodes would diminish if t h e height of t h e b a t h around t h e m were raised. This is t r u e even though no greater area of electrode is thereby covered with solution, and although t h e leads are insulated with asphaltum. T h e reason is t h a t , with t h e level of solution just covering the t o p of t h e electrodes, t h e electrical field between t h e upper portion of t h e electrodes was limited b y t h e surface of electrolyte, as compared with w h a t i t was with the electrodes immersed in the center of a large body of electrolyte. Consequently h a d our experiments been performed in a n ideally large t a n k , t h e electromotive forces would have been smaller for t h e same current densities. We preferred t o use a b a t h approximating t o the conditions of plating practice, a n d have in all cases noted, in the tables t o follow, the values of current density, electromotive force, etc., just as observed. without correction. Good practice for commercial nickel plating with many solutions, is t o have about eight gallons of solution for each sq. f t . of anode surface. In our experiments we have not departed widely from this value. although we find different solutions require a somewhat different magnitude of this ratio for t h e best results. T H E P LA T I N G E X P E R I 31E X T S- T h e plating e I( pe ri ment itself consisted in noting changes in appearance of t h e solution and electrodes as the deposition progressed, as well as making a record of milliammeter, voltmeter and time readings a t frequent intervals. T h e concentration of the b a t h was measured from time t o time, and t h e physical properties of the resulting plate were studied. TTherel-er current efficiencies were desired, milliammeter readings were made a t intervals a t not more t h a n two minutes. These readings were very constant in all cases, so t h a t more frequent readings were not necessary. Also the cathode was carefully dried and weighed before and after t h e deposition. Precautions were taken so t h a t conditions of weighing of the electrode before plating and after plating were identical. Advantage was taken of t h e well-known fact, for

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T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E R I N G CHE-${ISTRY t h e deposition of nickel a n d other metals, t h a t t h e deposit is more adhesive when struck o n initially a t a higher potential t h a n is t o be used throughout t h e greater p a r t of t h e plating run. Our practice was t o diminish t h e resistance in series with the b a t h , so t h a t a n initial electromotive force of about 6 volts was used, sending very considerable currents through t h e b a t h during approximately t h e first t h i r t y seconds of t h e run. T h e effect of this was uniformly satisfactory in causing t h e plates t o adhere firmly. After a sufficient plate had been deposited on t h e cathode i t was removed from t h e bath, immediately washed in cold water, and t h e n rinsed in boiling water until i t came t o a uniform temperature, after TJ-hich i t was dried in hot sawdust. This procedure was practiced throughout t h e plating experiments. BUFFIKG ASD FINISHIKG COBALT PLATES-The cathode after being removed from t h e plating b a t h a n d dried, is, in general, white and metallic, a n d requires b u t little buffing t o produce a satisfactory mirror surface. Our practice has been t o employ a large buffing wheel rotating a t high speed which will b‘color” t h e work in one operation. Cobalt plates color more readily t h a n nickel, and for commercial purposes should not require cutting with Tripoli, etc. PREPARATION AND USE OF ELECTRODES ANODES-Both cast and rolled anodes were used for these experiments, t h e cobalt employed analyzing as follows: LAB ANODESMADE PERCENTAGE ANALYSES OF ANODES No. No. Size-Inches Co Ni Fe As C S P Si H 218 2, cast 31/z X 2 X l/4 95.70 0.80 2.10 . 0.040 0.043 0.004 0.050 0.060 0.042 0.007 0.067 H 2 1 9 4,cast 31/2 X 2 X 1/4 98.00 0.75 1.35 . . H 221 4, rolled 31/1 X 2 X 1/4 95.63 0.75 3.72 0 . 0 4 8 0.052 0.029 0.005 . ... . .. . . . .. T h e cast anodes were poured in sand and smoothed down with a n emery wheel t o a finished surface. T h e rolled anodes were made from ingots about 8 in. long a n d I sq. in. in cross-section, which were rolled down t o plates of l/4 in. thickness, from which t h e anodes were finished. I M P U R I T I E S I S ANODES-Kickel anodes, a s sold in t h e market, frequently contain in t h e neighborhood of 9 2 per cent nickel a n d 7 l / 2 t o 8 per cent iron. T h e iron is cast in t h e anode because pure nickel is not corroded rapidly enough under most conditions t o furnish t h e necessary metal t o t h e b a t h . Iron is a cheap material and has a solution tension enough greater t h a n nickel t o make i t effective for t h e end in view. T h e greater solution tension of cobalt in t h e plating baths, as compared with nickel, renders practicable t h e use of a lesser amount of iron, or of no iron at all. T e r y pure cobalt anodes were readily dissolved in t h e solution under t h e conditions of many or’ our best plating tests. T h e freedom of the cobalt anode from iron no doubt has much t o do n-ith t h e diminished corrosion of t h e cobalt plate as compared with t h e nickel plates. R O L L E D ‘3s. C.4ST ASoDEs-cast anodes of both nickel a n d cobalt go into solution much more readily t h a n t h e rolled anodes. With a number of each in a nickel or cobalt b a t h , the proportion between t h e t w o may be so chosen t h a t t h e composition of t h e Vol. 7 , No. 5 electrolyte remains constant as t h e anodes go into solution. If too large a proportion of cast anodes is used, t h e anodes dissolve with too great readiness a n d t h e b a t h may become alkaline. Conversely, if too large a proportion of rolled anodes is used, t h e solution of the anodes may not t a k e place with sufficient readiness, and t h e b a t h may become acid and depleted in metal. T h e greater solubility of cobalt anodes in a number of t h e plating baths described in this paper, as compared with nickel anodes in t h e corresponding nickel bath, renders t h e use of a larger proportion of rolled anodes possible in t h e case of cobalt t h a n is customary a t present with nickel in t h e nickel plating trade. The greater solubilty of t h e cobalt anode is distinctly in its favor for practical plating purposes. CATIIODES-The cathodes for these experiments were of brass, iron or steel, and were usually 3l,’* in. X z in. X ‘ / e in. in size. One side was given a high polish with emery and buffing wheels, and t h e other was covered with a thin coat of asphaltum varnish. I t is of t h e utmost importance in all plating work t h a t t h e cathode be absolutely smooth and thoroughly cleansed from particles of dust, grease, etc. This was accomplished b y t h e following procedure : Brass, steel or other stock, as required, was first machined down t o t h e required size, after which i t was smoothed down with an emery wheel and finished with a n appropriate buffing wheel t o a mirror surface. This left t h e surface with a certain amount of grease and adherent buffing material, which was removed b y scrubbing with Kalye” caustic solution. After thorough rinsing with water t h e elecltrode was immersed in dilute hydrochloric acid, or in dilute potassium cyanide solution and again thoroughly rinsed with water. It was t h e n ready for use in the bath. I n addition t o smooth plane cathodes, a number of t h e m were prepared b y cutting patterns and depressions on one side. These were used in t h e same manner as t h e smooth ones after cleansing and buffing as described. P R E P A R A T I O N OF S A L T S T h e ammonium sulfate, ammonium chloride, boric acid, citric acid, potassium citrate, tannic acid, sodium sulfite, sodium phosphate, ammonium t a r t r a t e , and magnesium sulfate used for these experiments iyere Merck’s chemically pure, purchased from a supply house, as were t h e reagents used in t h e preparation of t h e cobalt salts. All cobalt compounds used for these experiments were prepared a t this laboratory, and t h e method of preparation of each is given as follows: COBALT SULFATE was prepared by dissolving CoaOl in HC1 and adding a n equivalent of H2SOa. The solution was then evaporated t o drive off HC1 and crystallize CoSOI.7H20. The crystals were collected in the usual manner and heated in the presence of H2S04until SO3 fumes disappeared and the salt became dehydrated. Or the collected crystals were recrystallized in the usual manner where dehydrated salt was not desired. COBALT-AMMONIUM SCLFATE was prepared by mixing hot solutions of cobalt sulfate and ammonium sulfate containing molecular proportions of each of the salts. As the cobalt ammonium sulfate is less soluble than either of the single salts, May. 1 9 1 j T H E J O C R N A L O F I S D C S T R I . 1 L A.YD E S G I A - E E R I S G C H E I I I S ’ T R I - most of the crystallization was effected in the hot mixed solution. The crystals were collected and washed n i t h alcohol. COBALT CHLORIDE was prepared by dissolving CoaO, in HCl, arid after filtering off the excess co304, crystallizing t h e salt and collecting and washing the crystals in the usual manner. COBALT ETHYLSULFATE-Ethyl alcohol and concentrated sulfuric acid were heated together to form eth5-I sulfuric acid. This was theii neutralized with calcium carbonate and the calcium ethyl sulfate crystallized by evaporation of the solution after filtering ofi precipitated calcium sulfate. The crystals were re-dissolved and the calcium precipitated as calcium sulfate by adding sulfuric acid in molecular proportion, reforming ethyl sulfuric acid. Freshly precipitated cobalt hydroxide was added t o this acid until it failed t o dissolve any more. The cohalt-ethyl sullate was crystallized by evaporation. The crystals were collected and washed in the usual manner. SOLL-BILITIES OF COBALT ASD S I C K E L SALTS The relative solubilities of cobalt sulfate a n d nickel sulfate, ant1 of cobalt-ammonium sulfate a n d nickelammoniuin sulfate are i m p o r t a n t in considering t h e greater conductivities of t h e cobalt solutions a s compared with t h e corresponding ones of nickel. Thesc solubilities are considered later when discussing the greater speed of cobalt plating, a n d a s well in considering t h e saturation concentration of some of t h e b a t h s employed, so t h a t a brief table of solubilities a t room temperature is given herewith. This Grams of salts dissolved b y one liter of water O C. Comey(a) K r a u t @ ) Lab. C o S O c . , , , , , , , , , , . . . . anhydrous 23 362 380 362.2 23 405 379 363 NiSOa, . . . . . , , . anhydrous 23 171 171 164 C O ( N H I ) Z ( S O I ) Z, ., ,, . , , , . anhydrous 66 72.8 23 66 Ni(NHd)z([email protected])?., , . . . . . . . anhydrous ( a ) A . hf. C o n e y , “A Dictionary of Chemical Solubilities,” MacMillan and Co., 1896. ( b ) Gmelin, Kraut’s “ H a n d b u c h der anorganischen Chemie,” 1909, Vol. V, Sect. 1. T h e salts actually used in making up t h e solutions were CoSO4.7 H?O, NiS04. 7 H 2 0 , CoSO4. (NHI)?SOd.6 H 2 0 a n d SiS04.(r\”4)2S0,.6H,0. F r o m t h e above table i t is apparent t h a t t h e solubilities of cobalt a n d nickel sulfates are n o t very different. These, however, do n o t lend themselves t o satisfactory plating solutions without adding various other compounds t o t h e m . On t h e other h a n d . cobalt-ammonium sulfate is approximately 2 . j times as soluble as nickel-ammonium sulfate. As will be shovcn in t h e sequel! from t h e experiments performed. The saturated solution of this cobaltammonium sulfate offers a n extremely rapid a n d satisfactory plating b a t h . CTRREST DENSITIES Unless specifically s t a t e d t o t h e contrary, the current densities given in t h e tables t o follow and throughout the t e s t are cathode current densities: t h a t is, t h e y were compu:ed by dividing t h e total current b y t h e cathode area. -In approximate notion of t h e anode current density m a y be obtained from t h e following s t a t e m e n t , although it is impossible t o compute it with a n y degree of accuracy: At t h e beginning of each experiment! the anode was smooth a n d of approximately the same area a s t h e cathode (see above), b u t as t h e experiment proceeded, t h e anode gradually increased in effectil-e area, due t o unequal corrosion of its surface. At the cnd of some of our experiments t h e anode 3 83 area m a y have been more t h a n tn-ice t h a t of t h e cathode. I n our conclusions a n d through t h e t e s t of this paper we speak of allowable current densities with t h e various solutions, a n d we recommend certain ranges of current density which are permissible for t h e best plates. I n every case these are cathode current densities, b u t are. of course, only valid with a sufficient anode area. K e hal-e conducted our experiments under conditions which might be called good s t a n d a r d practice for plating shops, which means, so far as anode area is concerned, t h a t t h e anode area vias in every case greater t h a n . and in m a n y cases, tn-ice t h a t of t h e cathode area. EPFICIESCY TESTS Efficiency tests were made in t h e usual manner b y carefully weighing t h e q u a n t i t y of metal deposited in a measured t i m e a n d comparing it with t h e theoretical a m o u n t of metal which should have been deposited in accordance with Faraday‘s laws. T h e d a t a for these tests for each important solution are given in Table VI, Page 3 9 2 . AGISG TESTS With all t h e plating b a t h s which were found t o be satisfactory or promising, both aging a n d efficiency tests were r u n . T h e aging tests were for t h e purpose of ascertaining t h e constancy of t h e b a t h during continued use for plating over a considerably longer period t h a n was necessary for our experiments. The solution was analyzed for cobalt content a n d tested for acidity a n d alkalinity a t intervals of I j hours during plating runs of I O G or more hours duration. This was in addition t o t h e series of runs already made with t h e given b a t h , operating with it t o produce t h e plates studied. T h e results of these aging tests are given in Table 1-11,page 392. LA B 0 R A T 0 R Y E XP E R I ME N T S- E LE C T R 0 D E P 0 S I T 10 6 OF COBALT SERIES I-COBALT-AMMONIUM SULFATE S O L K T I O S S Langbein recommends for the nickel bath of the type 1.4, with a n electrode distance of I O cm., a n electromotive force of 3 volts; he states that this will give a current density of 0 . 3 ampere per square decimeter.’ We wished t o compare the cobalt solution I A with the corresponding nickel solution as regards their relative specific electrical conductivities or with regard t o the electromotive force necessary t o give a specific current density through each, other conditions being the same. -In experiment was tried using solution 1 4 , with which was compared the following nickelammonium sulfate solution: Sickel sulfate, WSOa 30.9 grams Ammonium sulfate, ( N H ~ ) z S O I 26.3 grams \Vater io00 cc ‘Csing the proper current t o obtain a current density of 0 . 3 amp. per sq. dm., with the cobalt solution I A , i t .was found that the potential difference between the electrodes was 0 . 8 8 volt. LVith the identical electrodes and with the same distance between them, namely I O crn., using the nickel solution, the potential difference between the electrodes was 2 . I volts. Thus we have the very great difference between 0 . S8 T-olt and z , I volts required t o give the same current density with these two solutions, other conditions being equal, which means that the cobalt solution is of very much loner specific electrical resistance than the nickel solution 1 Langbein, “Electro-Deposition p, 252. of Metals,” 6th Edition Revised, 384 T H E J O U R N A L OF I A V D r S T R I A L A N D EA’GINEERIXG C H E M I S T R Y Thus, in the first series of experiments with cobalt-ammonium sulfate and nickel-ammonium sulfate, we found a result which ran uniformly throughout our plating experiments, uiz., that the conductivity of the cobalt bath was considerably higher than t h a t of the corresponding nickel bath. The last go hours plating with Solution I A were with a current density of 0 . 6 0 amp. per sq. dm. It was, therefore, clear t h a t this solution was not changing rapidly, and t h a t the anode was dissolving satisfactorily. The slight increase in concentration was accounted for by evaporation. Very similar results were obtained with iron and steel cathodes in place of the brass ones. Bath I A was not thought sufficiently important t o warrant a similar series of experiments being made with the corresponding nickel bath for comparison, The last 90 hours plating with Solution I B were performed a t a current density of 3 . o t o 3 . j amp. per sq. dm. The cathode area was 3 4 . 0 sq. cm. This solution was neutral t o litmus paper, b u t very slightly alkaline as shown by titration with N / r o HCl and litmus indicator. The solution remained absolutely constant and the cobalt anode dissolved satisfactorily. A number of the plates from Solution I B were given a very severe bending test t o study their adhesive qualities. I n every case the plates stuck to the cathode after being bent backwards and forwards a t an angle of nearly 180’, in a manner equal to, if not better than, that of the best nickel plates with which we are familiar, subject t o a similar test. Even after the surface of the metal base had started t o break, the cobalt plate still continued t o cover the furrows and ridges formed. The d a t a of the plating experiments for Solution I B show this solution t o be remarkable for the extremely high-current densities, a t which satisfactory plates may be obtained. We find no record of nickel plating being accomplished, except under special conditions, such as with rotating cathodes, at anything like the same speed. It is fairly well recognized t h a t any improvement in the chemical composition of solutions for nickel plating, in order t h a t a faster rate of deposition may be brought about, would have t o be based upon a higher concentration of the nickel ion in the solution, The inventors of “ Prometheus,” “ Persels” and other salts for concentrated nickel solutions, no doubt had this in mind. These new baths are of comparatively recent invention, and there is considerable diversity of opinion as to their merits. The practical plater knows t h a t he can carry in his plating bath I Z oz. of double nickel salt per gallon of water in the summer, and about 9 02. of the same salt per gallon in the winter, without danger of frequent crystallization. Taking the higher of these figures, we have a bath equivalent t o about 80 grams (NH4)S04.NiS04.6H20 per liter. This solution contains approximately I . 5 per cent metallic nickel. On the other hand, using t h e Prometheus salts as bought on the market, as much as 2 lbs. may be dissolved t o the gallon of water without danger of crystallization in the summer. Since this Prometheus salt contains about 28 per cent of NiSO1, this bath will contain approximately z . 6 per cent of metallic nickel in solution. This tremendously increased metal content of the latter bath accounts for the greater speed a t which plating is possible with it. Comparing the cobalt solution I B with this, we note t h a t it contains zoo grams of CoSOd. (NH4)2S04.6Hz0 t o the liter, so t h a t its concentration in metallic cobalt is approximately 3 . o per cent. We would, therefore, expect this solution t o be a very rapid plating one, faster than the other, as we find it, b u t the figures do not account for the great difference between the solutions. It has the advantage of being free from magnesium sulfate, boric acid and the like, which are very considerable and necessary constituents of all the concentrated fast plating nickel solutions. Moreover, we find with all solutions * V O ~7,. NO. j of this type t h a t the cobalt bath is a much more rapid plating one than the nickel bath, taking them a t the same concentration. Experiments conducted under conditions of present plating practice demonstrated t h a t Solution I B was capable of plating cobalt satisfactorily a t several times the speed that the Prometheus salt was capable of plating nickel (see Series I ) . This comparison was for the best condition for each t h a t was known to the practical plater in charge of the plating establishment in question, and to us as a result of these experiments. CO~%;~I.USIO~S: I-Cobalt plates from these cobalt-ammonium sulfate solutions, on brass and iron, are firm, adherent, hard and uniform, and may be readily buffed to a satisfactorily finished surface. They take a very high polish, with a beautiful luster, which although brilliantly white, possesses a slightly bluish cast. a-The specific electrical conductivity of these cobalt-ammonium sulfate solutions is very much higher than t h a t of the corresponding nickel solutions. 3--All of these cobalt plates within the current density ranges described as satisfactory, are as smooth, adhesive and generally satisfactory as the best nickel plates. 4-Solution 1.4 does not lend itself t o extremely fast plating like IB, b u t satisfactory plates may be obtained with i t a t current densities up t o 0 . 8 0 amp. per sq. dm. j-Solution I A may be used at higher current densities t h a n the corresponding nickel solution, for which Langbein recommends a current density of 0.30 amp. per sq. dm. 6-Solution I A does not change appreciably in cobalt content or in acidity when used over long periods of time a t the recommended current densities. 7-Solution IB, which is a nearly saturated solution of cOs04.(NH4)2S04, containing zoo grams of CoS04. (NH&SOa.6H20 t o the liter of water, yields satisfactory cobalt deposits a t all current densities up t o 4 amp. per sq. dm., i. e . , 37.2 amp. per sq. ft. This very rapid plating was performed in a manner similar to that of common plating practice. 8-There is no nickel bath operating in the manner of the usual commercial plating procedure at anything like as high a current density as cobalt bath I B . More specifically, the allowable current density with which an adherent, firm, smooth, white, hard plate may be obtained with Solution IB, without sign of pitting or peeling, and yet which may be readily and satisfactorily finished, is four times t h a t for which the same results may be obtained with the fastest commercial nickel solutions. 9-Both baths I A and I B may be used for plating on the usual surface, including brass, iron and steel. N o preliminary coating of copper is necessary when plating with these baths on iron and steel. Io-Solutions I A and IB may both be used with a large proportion of rolled anodes without becoming acid or depleted in metal. 11-Solution I B does not change appreciably in cobalt content or in acidity when used over long periods of time at the high recommended current density. Iz-The current efficiency of Solution I B is extremely high a t a current density of I ampere per sq. dm. The mean of our measurements, which agree very well among themselves, gave a value of 98 .o per cent, The current efficiency of Solution I B is as high a t 3 amp. per sq. dm. as is common for the best nickel solutions t h a t are ,used in nickel plating practice at very much lower current densities. The average of three current efficiency measurements with Solution IB, a t 3, amp. per sq. dm., which measurements agreed very well among themselves, was go. j per cent. 13-Solution I C is intermediate in concentration between I A and I B and its properties, as regards speed and quality of the plates t o be obtained therefrom, are correspondingly inter- May, 191; T H E J O 1-R S .I L O F I S D 1-S T RI A L d4S D E SG1-Y E E RI T G C H E Jf I S T R I- mediate. It is not nearly so rapid or as satisfactory a t high current densities as IB. r~-Solution I B should be run neutral, for these plates are adherent, firm, smooth, white, hard, yet easily buffed to an excellent finish. IVhen operated slightly alkaline it yields plates which are grayish in color, which peel, pit, and show blisters. n’hen operated acid it yields plates that, while fairly adherent, firm and smooth, are dark and freakish ~j-Solution IB requires very little, if any, aging to put it in condition, b u t yields satisfactory plates almost from the start 16-The “throwing” power of Solution I B is remarkably satisfactory. Ii-The anodes in Solution IB are remarkahly free from the coating that characterizes nickel anodes Solution I B showed so many superior qualities that It seemed highly worth while t o develop it further, and particularly to study it under exact commercial conditions. This work is reported later under Commercial Tests,” page 394. I‘ SERIES I I - C O B A L T - A ~ l ~ ~ O S I U 3 1 SULFATE SOLUTIOXS WITH A?: EXCESS O F AMMONIUM S U L F A T E Series 11 was prepared with the view of increasing the conductivity of Solution I by adding a relatively larger amount of ammonium sulfate. Solution I1 does not give good results above 0 . 9 0 amp. per sq. dm. m’ith an unboiled solution, very dark, unsatisfactory plates were obtained at current densities between 0 . 3 0 and 0 . 6 2 amp. per sq. dm. This solution was not thought of sufficient importance to w-arrant making a series of tests with rolled anodes, or aging and efficiency tests. c o x c ~ u s ~ o ~I-Cobalt s: plates from this cobalt sulfate and ammonium sulfate solution, with an excess of ammonium sulfate, on brass and iron, are firm, adherent, hard and uniform, and may be readily buffed to a satisfactorily finished surface, within the narrow range recommended for them. They take a very high polish, with a beautiful luster, which: although brilliantly white, possesses a slightly bluish cast. z-The specific electrical conductivity of Solution I1 is considerably higher than that of the corresponding nickel solution. 3-Solution I1 is not a fast-plating solution, and can be used only a t current densities up to about 0 . 9 0 amp. per sq. dm. This bath is not. nearly so rapid nor so satisfactory as others described. 4-Solution I1 is an analog of one proposed by Langbein for nickeling, of which he says that the nickel deposit piles up, especially in the lower portion of the object; that is, the lorver part of the cathode becomes dull, burned or over-nickeled. This takes place with the nickel solution a t current densities about 0 . 3 j amp. per sq. dm., and consequently the cobalt solution is a very great improvement, as regards speed, on the corresponding nickel solution. j-Solution I1 requires to be boiled a t the outset to yield satisfactory plates. Otherwise the plates are dark, even a t low current densities. 6-Solution 11, after operating a number of hours, tends to become acid. This acid may be neutralized with ammonia, and the solution re-acidified with boric acid, to yield satisfactory plates. However, on this account and for others mentioned. this solution is not nearly as satisfactory as some others described, since it is not self-sustaining. SERIES I I I - C O B A L T - A ~ ~ I \ I O S I U J I S C L F A T E WITH AS EXCESS OF A M M O N I C X SULF.%TE A N D CITRIC A C I D A bath which W B S formerly in extended use for nickel plating is prepared by boiling 34. j grams nickel sulfate, with 5 0 . 3 3s j grams ammonium sulfate and adding 4 2 grams citric acid to the liter of water. .halogous to this, Solution 111.1 was made up, when it was found to be not very satisfactory; I , j grams sodium sulfite were added t o the liter, making Solution IIIB. No reagent was added during the experiments with the solutions of Series 111, either to neutralize them or for any other purpose. Solution IIIA was not thought to be of sufficient importance to warrant running a series of experiments with rolled anodes. The last 90 hours plating with Solution IIIB w a s a t a current density of 1 . 0 amp. per sq. dm. The cathod2 area was 3 4 . 0 sq. cm. The cobalt content and alkalinity of this solution were remaining approximately constant. For comparison with Solutions 1II.A and B, :t set of runs on the corresponding nickel bath, Solution IIIC,was made. Solution HID resembled IIIA, but was considerably less concentrated in cobalt and ammonium sulfates. Solution IIID, after being used for plating approximately 35 hours, became somewhat alkaline. In comparison, Solution IIIC, the corresponding nickel bath, was tested d t e r running with the same current for an identical time. It was found to be practically in the same condition as regards alkalinity as a t the start. Cast anodes were used in both of these baths throughout these runs, which were made partly for the purpose of testing the relative solubility of the anodes. This result confirmed a conclusion to be geneqlly drawn from a11 our experiments, that in baths of this type the cast cobalt anodes are more soluble than the cast nickel anodes. Solution IIIE is more than twice as saturated in cobalt sulfate as IIIA, and more than three times as saturated in cobalt sulfate as IIID. The last 4j hours of plating with Solution IIIE was at a current density of 3 . o amp. per sq.dm. The 4 j hours preceding this was a t a current density of 4 . 7 5 amp. per sq. dm. This solution was gradually becoming more alkaline and its cobalt content increasing. The solution was ol~viously changing too rapidly to be satisfactory, but with an increased number of rolled anodes replacing cast ones, it might he used. CONCLUSIOSS: I-Cobalt plates from the solutions of Series I11 on brass and iron, are firm, adherent, hard and uniform and may readily he buffed to a satisfactory finish, within the current density range recommended. They take :i vcrl- high polish, with a beautiful luster, which, although l~rilliantly white, posseses a slightly bluish cast. r-Solutions IIIA, B and D do not lend themselves to extremely fast plating, but satisfactory plates may be obtained from them a t current densities up to o , So, I . o and o , So amp. per sq. dm., respectively. 3-Solution IIIB maintained itself substantially constant as regards cobalt content and alkalinity during 114 hours of plating. Its current efficiency is satisfactorily high. q-Solution IIIE, which is very much more concentrated in cobalt than the other solutions of this series, yields satisfactory plates a t all current densities up to I . jamp. per sq. dm. j-Solution IIIE. when used with cast anodes, gracluallg becomes more concentrated in metallic colialt content, and iricreasingly alkaline. For this reason this solution can be used only with care, and is probably not satisfactory for general commercial plating purposes. 6-The current etxciency of Solution IIIE is extraordinarilv high as compared with that of the usual commercial nickel plating solutions. j-The current efficiencieq of a11 the solutions of Seriei I11 are high and \yell over 90 per cent a t the recommended current densities. 8--1 number of experiments with Solution IIIC and Solution IIIE were run simultaneously, with the same current density, electrode distance and electrode area The E. 11. F. across the nickel bath was from 2 t o 7 , 3 times as great as that across T H E J O U R N A L OF I N D U S T R I - 4 L A N D ENGPNEERING C H E M I S T R Y 3 86 DATA O B T A I N E D W I T H S O L U T I O N S O F S E R I E S I A N D I1 TABLE I-EXPERIXENTAL SOLUTION I B SOLUTION I C Co and NH4 in molecular proportions Co .and NHI in molecular proporC O S O ~ ( N H I ) ~ S O ~ . ~ H Water ~O tions 200g.i = 145 g. CoSOa(NHa)nSOa] 1OOOcc. COS04 ( N H ~ ) P S O Water I Bath solution saturated 40.0g. 34.0g. 10OOcc. 2.51iters No additions t o maintain neutrality Intermediate in concentration beSp. gr. a t 15’ C. = 1.053 tween 1.4 and 1.B S O L I X I O X IA Co and NH, in molecular proportions Cos04 (NHa)2SOa Water Bath 30.9 g. 26.3 g. 1000 cc. 3 liters Somewhat more t h a n 1 1 8 saturated .4nalogous t o nickel plating solution recommended by Dr. Langbein SOL. Date No. 1914 IA- IB-CAST ANODES-BR 7/17 0.75 17 1.0 21 :.u 8/ 3 1.0 7/18 1.2 22 1.2 22 1.5 30 8/ 1.5 23 24 28 28 28 31 31 1.8 2.0 2.2 2.5 2.7 3.5 4.0 3 4.5 2 z$3;

ROLLED

ASS

2::

ANODES-BRASS

g:1: . 0

27.3 27.3 27.3 2i.3 27.3 27.3 27.3 27.3 27.3 27.3

2 1 2 4 3 2 3 1 1

27.3 2i.3 2i.3 37.0 37.0 37.1

I

0

1 1

0 0

30.1

1

0

37 i ?,,I 23.7(a) 23.7 37.1 23.7(a) 23.7(a)

2 1 1 2

SOLUTION I1 Co and NH4 not in molecular pro-

portions Cos04 (NHI)PSOI Water 16.7g. 56.7g. 1OOOcc. N o t nearly saturated with Co(NHa)z-

(so&)?

Seutralized with NHrOH, if too acid Boiled in preparation and prior t o using

Cur. Dens. Electr. C a t h o d e Plating Amp. per E. M . F. dist. area time sq. dm. Volts Cm. Sq. cm. Hr. Min

ROLLED ASODES-ZINC 17 0.50

Vol. 7; No. 5

C H A R A C T E R OP’

DEPOSIT

1

30 0 0 0 0 0 0 30 30 30

Fairly bright, hard, pitted a t ittom. Light gray, somewhat pitted ‘.L bottom. Bright and smooth, not lustrous Heavy metallic, lustrous, slightly spotted. Metallic, lustrous, streaked and spotted. Metallic, uniform, not lustrous. Uniform, metallic, lustrous. Bright, smooth, bottom rough b u t not burned Uniform; lower corners burned, dull color. Uniform, extremely bright, thmoughly satisfactory surface whcn pol

1

30

1 1

15

Uniform, bright; edges slightly burned Dark; badly burned a t edges, bright in center. Burning mor- iiiarked than preceding.

15

5

;d

Exceptionally good; white, uniform. Slightly burned a t upper edges. Clean, smooth, bright; peeled upon heating in boiling water for a few minutes.

CATHODES

0.83

10

CATHODES 1.0 17 1.5 19 1.5 24 1.70 19 19 1.95 1.7 24 2.05 24 1.20

10

2.1

16 24 24

2.4 2.55

2;:

3.75 2.25 3.0 2.9 4.9 3.0 2.95

;:

24 23 22 20 20

10 10

CATHODES 0.44 10

o,55

Polished steel knife 37.1 23.7(a) 23.7(a)

~

1

Very rough surface, unlike anything obtained on brass or steel. Under microscope metal appeared to be deposited in small irregular masses a n d not t o be polished.

Bright, uniform, glossy; little buffing gave satisfactory surface. i:0 \ Good, smooth, bright plate over entire surface. ~~

Very satisfactory; hard, bright, easily buffed. Bright, uniform, glossy; little buffing gave satisfactory surface. Beautiful smooth plate over entire surface. High and low spots evenly coated. Very smooth and bright, beautiful finish after slight huffing. Uniform thickness on high a n d low spots. Plate 0.062 mm. thick. Bright, smooth, even, hard. satisfactory.

0 0 0 0

1

30

1

30

1 2

45

15

Beautiful, bright, smooth; easily buffed t o mirror surface. Beautiful finish after slight buffing.

and bright. \ Veryandsmooth low spots.

Uniform thickness on high

ii ]

Beautiful, white, hard, lustrous; no sign of burning or scaling. 25.0 22.2 }Very smooth, even, hard; white, beautiful, satisfactory finish after slight buffing. No ZO.O(a) 1 30 signs of burning. 18 ( n ) 3; 27.5 Fairly uniform and bright; darkened a t edges. Began t o peel a t one corner. 27.5 1 30 Similar t o last; burning slightly marked, b u t no peeling. 27.5 1 0 Similar t o previous; burning not quite so marked. Buffed satisfactorily; slightly pitted, due t o gas bubbles.

:z ;

26.2 26.7 37.0

:1

Smooth, uniform, white: readily buffed t o mirror surface. Very bright and metallic; split a t one place; easily removed from cathode. Plate 0.34 mm. thick a t edge, 0.24 ,mm. a t center. 9/ 2 1.0 0.77 10 27.0 1 0 Smooth, uniform, white; readily buffed t o mirror surface. 8/ 4 1.5 2.2 16 37 16 0 Beautiful, bright, smooth; began t o separate from cathode a t one corner. 9/14 2.0 1,30 10 26.5 0 45 Very even, smooth; good luster when polished. 15 3.0 1.32 10 20.0 0 20 White; good luster when polished: somewhat rough on bottom, showing heavier deposit thkre; also small furrows from gas streaks. 14 4.0 1.35 10 11.7 0 15 Splendid white deposit, cracked a short distance in one place. 15 4.0 1.35 10 11.7 0 25 Good, n-hite; rough on bottom, showing heavier deposit there; also very small furrows from gas streaks. S/ kz5 4.25 20 27 1 15 Burned, b u t not so badly as 4.5 amperes current density. 4.60 18 27 1 0 Burned along edges. IC-The electromotive force across the electrodes was progressively increased so t h a t a series of plates was obtained a t current densities from 0.30 t o 1.25 amp. per sq. dm. in t h e manner shown in t h e d a t a for Solutions I A and I B . (See descriptive text.) 5

1.6

16

24

0

t

11-CASTANODES-BRASS

9/18 0.31 18 0.56 18 0.60 18 0.75 24 0.90 25 1.0 27 1.0 This r u n immediately a n d slightly acidified with 29 1.0 6/29 1 .O

CATHODES

1

0.91 10 39.4 1 15 Good, white, even, smooth; required almost no buffing t o give fine luster. 1.18 10 33 6 1 15 1.25 10 33 6 0 45 Good, white, uniform; fine luster when polished. 1.35 10 38.7 0 45 1.27 10 38.7 4 0 Bright, evenly deposited; not lustrous. 10 38.7 3 0 Smooth and bright; somewhat spotted. 1.30 10 38.7 3 0 Dark. bright with buffing. 1.55 followed one a t current density 1.4. After’the former t h e solution was found rather too acid and was neutralized with ammonia boric acid. 2.10 20 38.7 2 0 D a r k , polished brightly. 27.3 2 0 Dark: buffed t o satisfactory brilliant surface. 2.10 20 27.3 2 0 Badly burned over entire surface. 1.4 10 7/ 1.95 20 2 i .3 2 0 Very black with rough, grainy surface. Burned a t sides and a t bottom. 13 1.0 2.05 15 39.3 2 0 Very poor; black and polished with difficulty. 14 1.0 ,, , , 1 30 Very unsatisfactory; black a n d grainy. 2.05 15 B a t h stirred by bubbling air through it. ,, , . 1 30 K o t h a r d ; burned on sides; generally unsatisfactory. 15 1.0 1.42 15 6/26 1.4 1.95 10 27.3 3 0 Dark and badly burned. (a) When cobalt plate was dissolved off in nitric acid, grooves lost their plate first, showing thinner deposit there t h a n on higher places.

; ;:;

the cobalt bath. This is evidence, as noted throughout these experiments, of the greater conductivity of the cobalt solutions. 9-Solution IIIC is very concentrated in nickel salt, and is more satisfactory than the corresponding cobalt solution of the same concentration. However, the corresponding cobalt solution is not nearly saturated. The comparison with an equally saturated similar cobalt solution, IIIE, is in favor of

the cobalt solution, for i t will operate a t higher current densities than IIIC, and yields a plate which is just as satisfactory in appearance and harder. Io-These solutions operated alike plating on iron, steel and brass, for which metals only the above conclusions apply. 11-Cobalt anodes are more readily soluble than nickel anodes in the solutions of Series 111, and consequently a larger

. IIay, 191j

T H E J O C R S -1L 0 F I S D 1-S T RI A L A S D E S G I S E E RI -YG C H E M I ST R 1-

387

A? ; '?

}

it

Q ;

,,, __

:] :} :} :1

i;::

I , . -

2,-

E

:]

3t

noticed t o marked extent throughout these plating experiments. (C) Considerably harder t h a n Ni plate run a t same time, see IIIC,J u l y 22nd. 0.50 a m p .

(f) S o t as white when removed f r o m b a t h as S i plate r u n simultaneously, see I I I C , July 73rd. 0.90 a m p . Co plate much harder t h a n corresponding Xi plate.

T H E J O C R X A L O F InTDCSTRlAL A N D E S G I N E E R I a V G C H E N I S T R Y

388

proportion of rolled cobalt anodes may be used than is t h e case with nickel. SERIES IV-COBALT-AMMOh*IUM

SULFATE, ARIMONIUM CHLORIDE

SOLUTIONS

The baths of Series 11- were prepared in a manner similar to t h a t described under Series I. It is stated in the literature' that baths containing chlorides or nitrates are not suitable for nickeling over iron. They are, however, well adapted to the rapid light nickeling of cheap brass articles. Bath IV is the cobalt analogue of one sometimes used in nickeling practice for work of this lighter kind. CONCLUSIONS: I-Solution IVA yields satisfactory cobalt plates on brass and iron a t all current densities up to about I . 5 amp. per sq. dm. a-The plates of Series IVA buffed t o a brilliant surface, similar t o t h a t described under 3 below. 3-Solution IVB gave satisfactory plates a t all current densities up t o 1.25 amp. per sq. dm. on brass and iron which are firm, adherent, hard and uniform, and may be readily buffed to a satisfactorily finished surface. They take a very high polish, with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. 4-S~lutions IVA and B are moderately rapid plating baths, but not nearly as rapid as Solutions I B and X I I I B . 5-Solution IVB is considerably more rapid t h a n the corresponding nickel bath, the latter working best a t a current density of about 0 . 5 5 amp. per sq. d n 2 6-These solutions operated alike plating on iron, steel and brass, for which metals only t h e above conclusions apply. 7-The cobalt content and t h e neutrality of Solution IVB do not change appreciably with prolonged usage. 8-The current efficiency of Solution IVB is satisfactorily high, t h e average value of three measurements, agreeing well among themselves, being 9 2 . 6 per cent. 9-Solution IVB, with boric acid, yields somewhat whiter plates than IVA, but IVA may be operated a t a somewhat higher current density. SERIES \'-COBALT

CHLORIDE, AMMONIUM CHLORIDE SOLCTIONS

A bath was prepared analogous to the nickel-ammonium chloride bath which has been largely favored for nickeling over zinc. This solution is also used for dark nickeling. C O N C L U S I O ~ ~ S : I-Solution V was not found t o be satisfactory for obtaining a bright characteristic cobalt plate a t any current density up t o 1 . 0 amp. per sq. dm., either with rolled or cast anodes, plating on brass and iron. This refers to plating in the normal manner and without agitation of the solution. This solution could be used on brass and iron if dark cobalting were required 2-Rolled anodes are required' for a satisfactory deposit with the nickel analogue of this solution. They improve the deposit in the case of cobalt, b u t it is by no means satisfactory, either in speed or quality of deposition, as compared with other solutions, such as IB and X I I I B . 3-Solution V may be used satisfactorily to cobalt on zinc, provided there is a sufficient mechanical agitation to remove hydrogen bubbles from the surface of the cathode. U'ith this provision the cobalt plates are firm, adherent,, hard and uniform, and of a polished appearance as removed from the solution SERIES VI-COBALT-AMMONIUM

SULFATE, BORIC ACID SOLUTIOKS

Solution VIA is analogous to a solution recommended by Weston for nickel baths. It has, however, never found extended 1

Langbein, "Electro-Deposition

p. 2 5 4 .

ZIbid., p. 2 5 3 .

of Metals," 6th Edition Revised,

V O ~7,, NO. 5

usage in commercial plating for the reason t h a t the nickel solution, after working faultlessly for a comparatively short time, begins to fail, yielding a blackened deposit. Solution VIB is the nickel solution corresponding to t h e cobalt solution VIA. After Solution VIA was found to be unsatisfactory, its metal content was increased by further addition of cobalt sulfate. This solution was called VIC. In addition a much more concentrated solution of the same series, VID, was prepared and studied. CONCLUSIONS: 1-Solution T'IA does not yield a satisfactory plate a t any current density, plating with cast anodes, up to 1.0 amp. per sq. dm. The plates are dark and spotted and hydrogen is evolved. -4t current densities in the neighborhood of one amp. per sq. dm. or higher, the plates are badly burned and pitted. a'ith rolled anodes there is a slight improvement a t moderate current densities, that is, in the neighborhood of 0.50 amp. per sq. dm. a-Solution VIB, which is the nickel analogue of VIA, gave very bright, clean, satisfactory plates a t current densities up t o 0 . 5 0 amp. per sq. dm. -4t current densities greater t h a n this the plates are burned. j-This nickel solution, VIB, is not nearly so f a s t as some of the cobalt solutions elsewhere described in this paper. 4-Solution VIC, which is a more concentrated solution of the type of VIA, operated satisfactorily a t a higher current density than VIA, that is, up t o 1.0 amp. per sq. dm. This conforms t o the general conclusion throughout this work t h a t t h e more concentrated cobalt solutions, which are likewise those from which plates may be obtained with the greatest speed, are the most satisfactory for practical plating purposes. 5-Solution VID is not t o be compared in speed with IB, from which i t differs only by the addition of the boric acid. Solution VID yields a satisfactory white cobalt plate a t all current densities up t o 1.25 amp. per sq. dm. 6-The current efficiencies with all solutions of Series VI are high and satisfactory, the average being better than 90 per cent. 7-These solutions operate alike plating on iron, steel and brass, for which metals only the above conclusions apply. 8-The cobalt plates from Series VI, wherever they are pronounced satisfactory, are firm, adherent, hard and uniform, and may be readily buffed t o a satisfactorily finished surface. They .take a very high polish, with a beautiful luster, which, although brilliantly wkite, possesses a slightly bluish cast. SERIES VII-COBALT-AMMONIUM SULFATE, COBALT CARBONATE, BORIC ACID SOLUTIONS

This solution was prepared by boiling cobalt-ammonium sulfate crystals and cobalt carbonate in water until the evolution of C 0 2 gas ceased, and until the solution was no longer acid t o blue litmus. ilfter settling, any undissolved cobalt carbonate was removed by filtration or decantation, and the boric acid added. After further boiling for a short time, the solution was allowed to cool and was ready for plating purposes. If the solution is too acid it may be neutralized with ammonia. Solution VI1 can be used with rolled anodes, or rolled anodes with a small proportion of cast ones. The proportion of cast to rolled anodes used in this bath can be established by frequent testing of the acidity of the bath. For this purpose the following should be noted: Blue litmus paper should always be reddened, indicating the presence of boric acid; congo paper should not be turned blue, for if i t does, i t indicates the presence of free sulfuric acid in the bath. Red litmus paper should remain red for if i t turns blue the bath has become alkaline and further addition of boric acid is required. After plates from Solution VIIA were found to be unsatisfactory, yielding dark deposits a t current densities in the neighborhood of I amp. per sq. dm., sodium sulfite was added t o the

'

Z‘IIE J O C R z V A 4 LO F I S D C S T R I A L . 4 S D E S G I L V E E R I J Y G C H E M I S T R Y

?day, 1 9 1 j

389

T.iBLE 111-EXPERIhlENTAL DAT.1 O B T A I S E D XVITH S O L U T I O S S O F S E R I E S V, V I i l S D VI1 G. Der 1. U-ater SOL. T-1.4 T’IC \-ID ( I B T Boric Acid) VIB SOLUTION VIIA VIIB G. per I. water CoSOi.. . . . . . . . . . . . . 1 4 . 8 3 8 . 6 Co(h7H;)2(SO~):.6K?O 14.8 g. S i S O i 63.5 200.0 12.6 Co(NHd2 (SOdz.6HzO 6 3 . 5 32.9 fSH6)nSOi.. . . . . . . . 1 2 . 6 5.3 37.2 18.8 COCO3. . . . . . . . . . . . . .. 5 . 3 Boric a c i d . . . . . . . . . . 1 8 . 8 38.8 31.7 Boric a c i d . . , . . , , . . , , . 3 1 . 7 2 . 5 .ill boric acid dissolved 2.5 Total bath (1.). , . . , . 2 5 1.4 b y continued agitation r o n e Sa?S03.. . . . . . . . . . . S o n e .idditions . . . . . . . . . ?;one Sone Perlectly clear after standT o t a l b a t h (1.) . . . . . . . 3 . 5 3.5 ?;one ing several days Additions. . . . . . . . . . .. None Cur. Dens. Electr. Cathode Plating SOL. D a t e A m p per E. 11. F. dist. area time S o . 1914 sq. d m . I-olts Cm. Sq. cm. Hr. Min. CHARACTER U F D E P O S I T SOI,17TIOS \’

V-CAST

.INODES--BRASS

6 17

CATHODES

0.30 0.30 0(1.37 .37 0.50 0 50 0.90 1.0

2i

18 18 XI 21 ZY 7,15

0.96

z::;

0.66

10 10

27.3

7

20

27.1

$;:; 7 30 :I 10 27.3 10 77.3 27.3 37 3 2 2 20 30 0 i: 0.75 0 6Y 1.76 70 1.15 11 0.i0 10 1 0 1 1 1i 1 2 0 20 ] Dark gray. D a r k , even; huffed satisfactorily. Dull gray, spotted and rough. Dark a n d spotted. H t a v y black; buffed satisfactorily. Very d a r k . slightly pitted; huffed satisfactorily. Somrwhat dull; buffed satisfactorily. ROLLED ASOI)ES 2 1, 8 7 0 5 0 0 8 1 0 1; Iron, 4 5 . 4 15 Brass, 2 7 , 3 16.5 27.3 10 I r o n , 41 . 2 1.0 1.1 Very smooth, bright, d a r k g r a y ; readily buffed t o mirror. Smooth. bright, slightlr pitted a t bottom. Smooth, uniform, dark. Bright after buffing. Smooth, dull gray, somewhat p i t t e d ; no sign of burning. Polished readily t o mirror. 0 CATHODES stirred mechanically 10 Cast, 2 6 . 6 1 10 26.6 1 10 26.6 1 10 26.6 1 10 Sheet. 2 8 . 8 1 VI.4 2.3 1 0 0.95 I0 24 74 14 22 1 0 1 0 0 9s 10 10 1.0 2 0 0.Y5 -CAST ANODES-BRASS 61.3 .30 0.30 0.60 0.63 0.90 1 .0 I5 1.0 15 27 .3n 0.95 1.48 0.5 16 0.8 0.8 16 VIC--CAST AKODBS-BR.4SS i ‘20 2.3 8 4 5 VID--BRASS 025 25 26 10: 1 I 1 9,28 28 79 in, 2 0.50 0 . 70 1.0 1.5 26.6 26.6 26.6 26.6 1 0 1 CATHODES 0.96 io 10 IO 1.i0 1.25 3.5 3.27 3.6 ROLLED AXCJDES-BRASS 7/16 10 10 Cast, 26.6 t o keep off hydrogen bubbles 30 Bright, almost a s if buffed when removed from solution. 15 Good rvhite. uniform. Readily buffed t o mirror. 0 S o agitation, poor plate. crystalline. 15 Smooth, uniform, looked almost a s if buffed when removed from solution. 0 Verv smooth on portion of cathode where aEitation removed hydrogen bubbles; rough on . p&t away f r o m agitation where hydrogen-clung. 0 K e p t free of gas bubbles by rubbing for 10 min. Plate satisfactory a n d smooth. A t end of hour without further brushing off of bubbles, plate rough and crystalline. Solution stirred mechanically t o keep off H bubbles, b u t in spite of this, a t this current density, gas pits appeared a t top and bottom. 30 Decidedly crystalline; very poor. G a s formed a n d adhered t o cathode. 20 20 15 1 20 20 30 0 0 30 Lustrous, b u t d a r k ; not very smooth. Lustrous, b u t s p o t t e d ; hydrogen gas given off freely. Smooth, fairly lustrous. b u t dark. Split on edges. Unsatisfactory, pitted and burned. Badly burned a n d unsatisfactory. Current density too great Badly burned a t edges. 1 30 Bright, smooth, uniform plate. Unsatisfactory, burned along edges, peeled. 27.3 27.3 39.3 27.3 2 2 1 2 0 0 30 0 Very smooth, bright. satisfactory; required very little buffing t o finish. Dull metallic color; buffed satisfactorily. Showed few pits near b o t t o m G r a y , b u t readily buffed t o satisfactory finish. Dull a n d burned in places. 35.5 1 1 1 0 Good, even, uniform, g r a y ; good luster when buffed. 30 Smooth, uniform; good luster when polished. 0 .\ 27.3 Zi.3 31.5 27.3 27.3 24.0 2 2 2 2 2 3i.3 37.3 CATHODES 2,0 2 . .3 2.5 15 13 15 2i.1 CATHODES 0.94 1.12 1.95 2.15 10 1.0 1.3s 2.85 1.25 1.4 1.38 1.35 I Y2 1 87 10 10 10 10 10 10 10 IO 10 in 10 10 IO 10 E CATHODES 0.51 0 .7 5 1 0 1.o 1 25 1 75 1.5 1.5 1 5 1.5 2 1.75 VIB--CAST . 4 1 O D E S - - B R A S S i 15 0.30 15 0.50 29 0.60 1.74 2.11 34.1 34.3 34.3 32.6 34.6 35.3 37.5 33.8 33.8 17.8 \Good, smooth, uniform, g r a y ; good luster when polished 0 . n Uniform, dull white; tendency t o split a t bottom a n d edges. i 30 Uniform, smooth, g r a y ; tendency t o peel a t edges. 1 0 Uniform, light g r a y ; split a t edges. 1 0 Uniform, rough, gray a n d porous; impossible t o buff. 0 30 Uniform, g r a y ; badly gas-pitted. 1 i CATHODES 1.55 7.0 ’ 77 10 10 10 27.3 27.3 39.3 39.3 39.3 2 2 1 2‘) 0.80 7 36 10 1 28 1 .(I 3.01 10 1 V 1 1 . 4 - c ~ ~I ~ NODES-BRASS CATHODES 7 ’ 3 0.35 20 27.3 2 3 0.50 1.5(1 20 27.3 2 Y 0.50 1.5s 20 39.3 2 10 0.50 39.3 1.53 20 2 4 0.70 2 7 20 27.3 2 2 1.0 2.S 10 27 3 2 / 1.0 7 7 15 2; 3 2 i I 0 3.30 I5 39.3 9 1.0 3.25 1s 39.3 11 1.0 4 15 2 15 27.3 Solution rapidly becoming more alkaline with use. VIIB-CAST A K O D E - B R A S S CATHODE 7/11 1.0 2.05 I5 27.3 2 Solution rapidly becomina more alkaline. R O L L E D ANODES-BR.4SS 0 0 30 30 30 Very white, even; so glossy when removed from solution almost n o buffing required. Very bright, even, with no trace of burning. Bright in center b u t signs of burning a t edges. Bright in center b u t burned a t edges and corners. I’ery d a r k a n d grainy. 1Iarked burning over entire surface, especially a t edges. 0 0 30 30 0 0 Bright, even, without flaw; bufftd satisfactorill-. Very bright. smooth plate without flaws, buffed brightly. Surface granular; unsatisfactory. Rough a n d unsatisfactory; did not polish readily. Smooth, flawless, w h i t t b u t not lustrous. Buffed satisfactorily Burned a t sides a n d bottom. unsatisfactory. Current density too great. Burned a t edges, unsatisfactory. Current density too great. H e a v y b u t dull and granular. Burned. Burned and unsatisfactory. Scaly and unsatisfactory. 0 30 30 0 0 TVhite, even, somen h a t burned a t edges 0 Even and satisfactory Satisfactory, bright. requiring little buffing. Satisfactory and bright. Black. burned. CATHODES 1: 030 1.21 10 I, 17 (L50 0.80 10 18 0.Y0 1.15 1.95 2.20 in 10 27.3 27.3 27.3 2i.3 2 2 2 2 0 o 0 bath to see if the deposit would be brighter. This latter solution is Bath T’IIB. C O P ; C L ~ S I O X S : I-Solution YII.4 gives bright, satisfactory plates, a t low current densities in the neighborhood of 0.3j amp. per sq. drn., as is true of the corresponding nickel solution. 2-Solution VII.4 does not lend itself for rapid plating; a t current densities ox-er 0 . 8 0 amp. per sq. tim., the plates are burned. 3-The addition of sodium sulfite t o Solution VIIA, a s in Solution T’IIB. does not materially increase the current density a t which satisfactory bright plates may be obtained. These solutions are not t o be compared for rapid plating with some of the others described and styled satisfactory, as I B and X I I I B . 4-The solutions of Series VI1 become alkaline so rapidly with cast anodes that rolled anodes should preferably be used with them. I n general, cobalt solutions improved by addition of sodium sulfite are not sufficiently constant with prolonged use to have the self-supporting characteristic required by most plating establishments. T H E J O C R S d L OF I S D C - S T R I A L A S D ESGIiVEERING C H E M I S T R Y 3 90 T A B L E IV-EXPERISIEKTAL Vol. 7, No. 5 D A T A O B T A I N E D W I T H S O L U T I O N S O F S E R I E S V I I I , IX, X , X I A N D X I 1 G. per 1. water SOL. VIIIA V I I I B SOLUTION Grams per liter Total SOLUTION Grams per liter water cos04. . . . 2 6 . 3 40.5 IX COHPOI iXarP207 bath XI.. cos04 h-Hd t a r t r a t e ”H4C1.. . . . 17.6 17.6 i .58 66.1 3 . 5 1. 25.0 41.7 Potassium citrate. . . . 1 7 . 6 1 7 . 6 X Cos01 (NHI)?SOI hfgSO4 X I I . . . . . . . . . . Cos01 Tartaric acid T o t a l b a t h (l.).. ... , , 2 . 5 1.0 26.6 22.6 33.8 2 . 5 1. 52.7 27.8 Cur. Dens. Electr. Cathode Plating SOL. Date Amp. per E . hf. F. dist. area time No. 1914 sq. dm. Volts Cm. Sq. cm. Hr. hlin. CHARACTER O F DEPOSIT \TII.~-cAsT ANODES-BRASS CATHODES 10/1 0 ., 35 00 0 10 33 43 ., 81 0 o ., 69 77 Good, uniform, bluish white, buffed readily t o mirror. 6/30 0.50 1.95 20 27.3 3 0 Beautiful bright, hard, smooth, a f t e r polishing. 7/15 0.50 1.15 13 37.1 1 30 Dark, buffed satisfactorily. 10/ 2 0.95 1.50 10 40.8 I 30 Smooth, uniform, gray, readily buffed t o mirror. 2 1.0 1.36 10 34.1 I 0 Smooth, uniform, gray, buffed satisfactorily. 15 1.5 15 1.75 2 . 04 Uniform, gray, showing burning. VIIIB-CAST ZINC CATHODE 9/22 0.26 0.95 10 26.6 2 0 Crystalline in most parts, with small patches of smooth plat;. .. Tannic acid 0.28 Total bath 3 . 5 1. KOH 6.8 3.5 I. ’2 00 ] tt i;:: A 4g 1 10 10 10 10 10 10 10 39.6 34.7 34, 33.4 35.0 34.8 34.8 BRASS C A T H O D E S 10/ 2 9/22 10/ 1 1 9/23 IO/ 1 2 0.50 1.0 1.0 1.25 1.5 1.5 1.75 CAST Z I N C CATHODES 5 0.20 Mechanical agitation 10 0.50 6 0.75 9/21 1.0 I x- -CAST ANODES-BRASS 7/ 3 0.50 9/29 0.50 30 0.75 7/ y:;o ~ 2 7 9/30 X-CAST 1.0 1.0 ANODES-BRASS 1.07 1.97 1.4 1 .75 2.67 2.15 2.35 10 26.6 near cathode. in 25 6 io 25.6 10 26.6 0.80 of solution 1.03 0.95 1.4 10 10 10 10 10 20 10 27.3 33.4 34.1 27.3 27.3 27.3 40 . O 10 10 15 39.3 36.6 32.2 35.2 48.1 0.30 0.30 0.40 0.50 0.50 16 29 9/30 7/ 7 0.50 0.50 0.60 0.70 1.1 1.15 1.17 1.i0 14 10 10 15 37.1 46,6 34.3 48.1 9/30 0.70 1.34 1.30 2.25 2.25 2.05 2.10 10 15 15 15 15 15 34.8 48.1 37.1 48.1 39.3 39.3 7 7 9 ROLLED 1.0 1.0 ANODES-BRASS 0.5 0.8 1.0 1.0 0 1 0 30 0 0 .. I 1 :] 3 2 - n- 3 1 0 0 1 1 30 0 0 0 30 45 30 1 30 ( Uniform, smooth, gray, readily buffed t o mirror. Good, smooth, uniform, somewhat dark, taking a good polish when buffed. Uniform, smooth, white, buffing t o mirror. Good, smooth, uniform, dark gray, taking a good polish. Slightly burn-d a t edges Uniform, smooth, white, slightly pitted a t top and burned at edges. Not rcndily buffed Smooth, uniform, gray, slightly burned on edges and difficult t o buff. Smooth, uniform, metallic, dark gray. Buffed readily t o mirror. , Very rough, scaly. unsatisfactory. N o agitation. Poor, very decidedly crystalline. CATHODES 3.30 3.03 3.68 3.65 4.80 5.0 4.35 CATHODES 0.70 0.75 0.87 1.03 1.54 7/29 9/29 30 30 7/ 6 2:; 1.0 2 10 10 2 2 2 1 1 2 2 1 2 1 2 1 2 Coated with precipitate which easily washed off. Satisfactory and readily buffed Dark streaked. Gelatinous cobalt compound precipitate on surface of cathode. Dark, lustrous, streaked. Gelatinous precipitate as in last. Bright, satisfactory except f o r few black spots, which buffed off easily. Smooth, even, covered with bluish precipitate. Satisfactorily buffed. Black, streaked and unsatisfactory. Dark, streaked and unsatisfactory. Gelatinous precipitate on cathode. :!. 30 0 \ 30 0 30 0 1 1 30 30 0 I 30 1i 0 3 0 1 White, metallic, easily buffed t o mirror. Good, white, uniform; readily buffed t o mirror. Bright, evenly coated, except few streaks in metal portion. Readily buffed to satisfactory mirror. Bright, uniform, over entire surface. Readily buffed t o satisfactory mirror. White, metallic and easily buffed t o mirror. Bright, uniform over entire surface. Readily buffed t o satisfactory mirror. Bright, evenly coated, except few streaks in middle portion. Readily buffed t a satisfactory mirror. Good, uniform, white, requiring little buffing. Satisfactory. white, smooth and even. Readily buffed t o satisfactory mirror Bright and smooth a t center, somewhat burned at edges. Bright. rough a n d uneven on lower portion, no burning apparent Very thick, rough, dark, full of small holes, b u t adherent. Pitted a n d somewhat burned. CATHODES 16 1.0 14 37. 1 2 0 Bright, smooth, uniform, over entire surface. 16 1.05 15 37.1 1 0 Bright, smooth, over entire surface. 17 2.25 1, 37.1 1 0 Fairly smooth and bright, not very uniform in appearance, some parts darker t h a n others. 17 2.15 17 37. I 1 0 Very smooth, bright and uniform. XI-BRASS CATHODE 7/ 7 0.30 1.5 25 41.2 1 30 Dark, absolutely unsatisfactory. Solution X I continually precipitated a cobalt compound both when in use a n d upon standing idle. It gave t h e same unsatisfactory deposit as in t h e run shown above, a t t h e several current densities tried. XII-CAST AXODES-BRASS CATHODES 1.17 20 37.1 2 0 7/ 6 0.30 White, uniform and velvety. Readily buffed t o mirror. 10/ 1 0.30 1.25 10 39.5 2 0 9/29 1.25 10 33.6 2 0 0.39 Smooth, uniform, d a r k ; buffed t o satisfactory mirror. 2 0 30 0.50 1.45’ 10 34.6 101 1 0.50 1.40 10 34.8 2 0 Uniform, smooth, gray; buffed t o satisfactory finish 2 0.50 1.53 io 41.2 2 0 9/30 2.03 io 39.1 I 30 0.75 Uniform, smooth, gray; buffed satisfactorily. 7/13 3.6 1.0 15 37.0 I 30 1.0 2.18 10/ 2 10 32.6 1 0 2 1.25 2.55 10 32.9 1 10 ) Very even, smooth, and Satisfactory 3 1.50 2.86 10 30.9 0 45 15 1.50 3.5 IO 34.5 1 n 15 1.96 4.25 10 30.) 0 30 12 3.87 6.0 10 34.0 0 15 12 4.0 3.95 10 14.2 0 30 15 5.0 .... 10 13.0 0 20 Good, smooth, white, nearly polished as removed from solution. 16 6.0 .... 10 13.0 0 15 I 16 7.0 6.0 10 9.9 0 10 17 6 4.0 9 17 180..00 J Burned a t edges. 17 12.0 5.5 10 11.5 0 5 Badly burned at edges-splitting. 17 15.6 5.8 10 9.3 0 .5 ROLLED ANODES-BRASS CATHODES Smooth a n d uniform, h u t dark. Solution from which this plate was taken had been operated 7/16 1.0 3.0 14 37.0 1 30 for 48 hours. ] [ , ;; ;E:, ;; s-The solutions of Series VI1 operated alike plating on iron, steel and brass, for which metals only the above conclusions apply. 6-The cobalt plates from Series VII, wherever they are pronounced satisfactory, are firm, adherent, hard and uniform, a n d may be readily buffed to a satisfactory finished surface. They take a v e r y high polish, with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. SERIES VIII-COBALT SULFATE, POTASSIUM NIUM CHLORIDE SOLUTIONS CITRATE, AMMO- This bath is analogous t o one recommended by Langbein,’ C . H. Proctor,* and 1%‘. P f a n h a ~ s e r ,and ~ which is reported to be particularly satisfactory for plating on copper and zinc. 1 2 3 Langbein, “Electro-Deposition of Metals,” 6 t h Edition Revised. Melo1 I n d u s k y , 1911, p. 353. I\‘. Pfanhauser. “Elektroplattiring.” 1900. 7 TIIE JOUR-VAL OF IXDGSTRI:IL A S U E S G I S E E R I S G CHEVIS1'RY Xay, 191j 39= T.XB1.11 V - E X P E R I X E P i T A L D A T A O B T . 1 I S E D W I T H S O L U T I O S S O F S E R I E S X I I I , XIT', X V A S D X\'I Total G . per 1. xy-ater SOL. X\-IA X\-IB XVIC G. per 1. water So!. X l l I - 1 X I I I B X I I I C SOL. Grams per liter of water . . . , 161.2 312.5 312.5g.SiSO4 XI\-Cos04 (SH;)?SO1 1IgSO; H;BOI b3a. t5h1. CoSOi .S.O. .;.. ,. ,. .. ,. 90.7 9 0 ..6i ISiSOi) 150.0 3 7 , ~ 2 1 . 7 1 . 3 1 2 . 1 ( X H ~ I 2 7 . 6 2 7 150.0 X a C l . . . . . . , . . . , 11.35 19.6 19.6 CoSOa 37. 8 Kearly t o saturation 11.3 g. XI' Co(C2Hs)n(SOd? SalSOa S H a C l Boric acid . . . . . . 1.5 .... 1.25 .... 100.0 10.0 I.il 2.0 I. -1ddition. , . . , , , X-HcOH t o neutrality (see text) o Yes .. .. Electr. Cathode Plating C u r Dens. area tirnr SOL. D a t e .Imp. per E . X I . F. dist. \.olts Cm. Sq. c m . Hr. Sfin. .;~IL.\RACTER i DSPOSIT No. 11114 sq. d m . XIII.1-C.iST AXODES-BRASS CATHODES i,lO 0.iO 1.5G 23 37.1 1 30 Rather d a r k ; little buffing required to fi Ai satisfactorily; greatly rcsernblcd S i in IO 0.70 1.56 23 37.1 1 30 color. I5 3i.l 2 0 10 0.9i 2.0 0 Fairly smooth and uniiorm, b u t dar:; 2 16 3i, II 1.0 1.8 I1 1.0 1.87 15 37. 1 1 0 Good, smooth, uniform, bright, some\\hat streaked on upper half of plate. 1.45 10 37.1 1 20 14 1.0 0 Very smooth and uniform on I o n c ~ rhalf; badly streaked in upper portion. 1 1 0 ,65 14 1 1 I 0 1.7 13 37. 1 1 0 Solution stirred continuously by bubbling air through near c a t h d e . P.,ite brighter and more metallic looking than last runs, b u t badly split and peeled. I5 1 0 1.9 12 37. 1 0 45 Very poor, d a r k streaked and peeling. SII113-- B R A S S CATHODES IO 2 0.50 1. O ? 10 33.6 3 0 t-niform, rough, dark. Imposiible t o polish without grinding. 1 7.1 IO 32.6 1 30 Smooth, uniform, gray, bufied t o satisfactory finish x i t h diWcult?. 2 (1 75 "'O 1 1 0 1. 5 3 Uniform, d a r k gray, difficult t o bui?. i 1 ,? 1.75 10 34.0 1 ,?j 10 32.0 Uniform, smoDth gray, buffed more readily t h a n preceding platrr Tilth thls solution h l.50 5.5 10 34.8 0 30 Good, smooth, >\hit?,buffed rcadily t o mirror. 6 N: .46 D ti 0 10 32.2 IO (1.15 6.0 10 32.' ]Good, smooth, white, buffed readily t o mirror. .\iter bevere aging test described below 8 8 0 4.83 10 17.6 ,i Good, smooth. white, buffed readily t o mirror. This plate was given a ievere bending teat, ,o Iron, 2 0 , 0 '> 8 . 0 6.0 being doub!ed on itself backward5 a n d forxvards t o a n angle of 180 degrees. The metal v 8.0 6.0 Iron* 20.0 lo \ furrowed and split on suriace and end, b u t plate clung absolutely. 8 8.8 6.5 10 I r o n , 2 2 . 5 0 i2 Good, smooth, x h i t e , buffed readily t o mirror. 10 B r a s s . 2 0 . 0 0 15 IO 8.88 5.90 Alter severe aging test. 8 '9,ii 6.5 6.3 10 li 10.7 x 10.0 , , . . 10 Brass, 1 7 . 6 0 8 14.6 6.5 10 14.7 0 Best obtained with this solution t o date, although all plates a t current densities from 6 amperes u p were good. 5.7 13 16.5 Good, smooth, white, readily buffed t o mirror. Excellent plate. 6,85 6 17.5 B R A S S CATHODES-HEAVY PLATE 6-7 5.35 6.0 10 32.8 15 15 Firm, adherent, massive, showing no tendency t o split or curl. Smooth in center, with nod-. ules a t edges. Weight approximately 3 i grams, thickness approximately 1 mm. T h e area of t h e effective cathode increased from 32.8 sq. cm. a t t h e s t a r t , t o approximately 40.0 sq. cm. a t the end of the run. T h i s latter figure is n o t sufilciently accurate t o admit of exact computation, b u t t h e figures show in a general way t h a t t h e current efficiency was very high. 7 16.5 5.5 10 10.0 17 30 Firm, adherent, massive, showing no tendency to split or curl. Weight, about 30 grams. 13 5.26 6.0 10 Circular, 18.9 67 0 Firm, adherent, massive. showing no tendency t o split or curl; about 5 mm. thick. Plate o i l brass cathodes with gyooz1es. depth 1.62 mm. lo 7.0 m m . to study "throwing" p v o p e r t y o j l h i s solution. 7 9.0 5.5 10 18.3 CoSO; , . . . 1 } ] ' 2 ;g } iz,6 Good, smooth, uniform, white. All grooves satisfactorily covered. and satisfactorily buffed 5.5 t o mirror finish. total surface 3.83 5.5 I n last two, grooves faced toward anode, b u t entire block, back a s well as grooves, satisfactorily covered t o admit of severe and satisfactory buffing a f t e r only 10 minutes' plating. XIIIC-BRASS CATHODES 5 3 10 33.8 0 20 Good, smooth, uniform. nearly polished as removed from solution. 10/15 3.95 3.7 I5 Smooth, white. b u t splitting a t edges. , , , , 15 ,. i G XIV-CAST AI\'ODES---BRASS CATHODES 32.4 lo/ 1 0.50 1.05 10 1 1.25 1.92 10 35.3 2 1.50 2:20 10 35.3 18.5 4: Uniform, smooth, \.!lite. readily buffed to mirror. 2 1.75 1 .68 10 11.1 1 30 1 2 2.0 1.55 10 11.3 1 30 , I 2.5 Lii 10 3 3.0 2.47 10 17.2 0 30 ) 19.6 0 20 Uniform. smooth, white, slightly burned on edges. 5 3.0 3.32 10 3 3.51 2.88 10 16.8 0 30 Uniform, smooth, white. readily buffed t o mirror. 5 4.0 2.98 10 13.3 0 20 Uniform, smooth, w-hite. slightly burned o n edges. SV-A number of cobalt depositions were made with Solution XV a t various current densities, both with and without mechanical agitation a n d for varying lengths of time. Mechanical agitation caused t h e plates t o crack. One of t h e iepositions wa5 continued f o r a period of eight 24-hour days. a uniform, dense, h a r d . satisfactory plate v a s found. T h i s deposit mas made on a plste approximately half a millimeter thick a t a current density'of 0.30 amp. per sq. dm. It was, of course, not as hard a deposit as some of t h e heavy plates deposited from Bath X I I I B a t very much higher current densities. X V I d and XVIB-Solution XV1.4 a n d its nickel analogue X V I B , in a n extended series 01 experiments were found t o give satisfactory plates a t low current densities. b u t t o fail b y splitting and burning when current densities of 1.0 a m p . per sq dm. or more were reached. Solution X V I C was found t o precipitate a red compound on the anode. A very much greater hardness of t h e cobalt plate t h a n t h e nickel plate wa5 particularly noticeable throughout. 7 3.77 7 1.2 i: ; ti 1 ? 1 A I Langbein specifies for the nickel solution on copper and copper alloys a current density of 0 . 4 j amp. per sq. dm., and on zinc a current density of 0 . 8 to I amp. per sq. dm. CO?~CLLWOSS: I-Cobalt plates from the solutions of Series Y I I I , on brass and iron, are firm, adherent, hard and uniform, and may b e readily buffed t o a satisfactorily finished surface. Thev take a very high polish, with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. z--Seither Solution V I I I A nor B lends itself t o fast cobalt plating like Solutions IB and XIIIB. Solution VIIIA yields satisfactor>- deposits a t all current densities up t o 1 . 0amp. per sq. d m . . while S'IIIB, which is more concentrated in cobalt sulfate. yields satisfactory plates a t all concentrations up t o I . 2 j amp. per sq. dm. These figures are for plating on brass and iron. 3--Solution \?IIIB may be used for plating on zinc a t low current densities up to 0.50 amp. per scl. dm., particularly if the solution near the cathode is agitated. SERIES IX--COBALT PHOSPHATE, SODIUM PYROPHOSPHATE SOLCTIOSS Langbeinl recommends a solution containing nickel phosphate I j . 8 grams, sodium pyrophosphate 6 6 . I grams, and water 1000 cc. for dark nickeling upon iron, brass and copper. This is supposed to be particularly serviceable where darker tones of nickel are required for decorative purposes. I t was found in trying to prepare the analogous cobalt phosphate solution that the soluhility of the cohalt phosphate was lower than that of nickel phosphate. Langbein, "Electro-Deposition of p. 758. Xetals," 6th Edition Revised, T H E J O l - R S A L OF I S D L - S T R I A L A S D ESGINEERISG CHEMISTRY 392 Solution IX is saturated in cobalt phosphate. The cobalt phosphate prepared for this bath was made by mixing two solutions, one containing 3 0 . 0 grams CoSOa.7HzO in 3 . 4 liters of warm water, and the other containing 2 4 . 9 grams sodium phosphate in 3 . 4 liters of warm water. These two solutions were mixed, with constant stirring, and the precipitated cobalt phosphate filtered off. These quantities yielded I j . 8 grams TABLZVI-CURRENT EFFICIEXCY TESTS-ALL CATHODESBRASS Current density Average Amp. a m - GRAMSC O B A L T Current ~SL-MBER OF R u n per Cathode peres DEPoSIT~D Solulasted sq. area through b Series tion R u n M i n . d m . Sq.cm. b a t h Theory -4ctual P e r c e n t 1 . 0 2 9 . 2 0.300 0.331 I B l ( a ) 60 60 l,o 4 7 , 4 o , 4 i j o , 5 2 3 0o .,352133 3 9 97 8 ., 7 2 ToI. 7 , NO. j with the nickel analogue of Solution X was not found with the cobalt solution. On the contrary, the plates are beautifully white and hard. 3-The specific electrical conductivity of Solution X is very much higher than that of the corresponding nickel solution. 4--All of the cobalt plates deposited a t current densities between 0 . 2 j and 0 . 7 5 are as smooth, adhesive and generally satisfactory as the best nickel plates. j-Solution X does not lend itself t o extremely fast plating as do Solutions I B and XIIIB, but satisfactory plates may he obtained with it a t current densities up t o 0 . 7 5 amp. per sq. dm. Solution X may be used a t very higher current densities than the corresponding nickel solution, for which a current density of 0 . 2 0 amp. per sq. dm. is recommended. effitiy:y 3 4 III VI B 3.0 3.0 29.5 20.0 0.907 0.599 ::iz: ,": 7:; 1.0 1.0 1.0 0.80 0.80 32.6 24.2 40.0 40.0 40.0 0.328 0,242 0.400 0.321 0.321 0 . 3 6 1 0.3563 0 . 2 6 6 0.2473 0 . 4 4 0 0.4063 0 . 2 6 5 0.2619 0 . 3 5 3 0.3514 :: :g ;E : E 1 2 60 60 60 45 60 B :(a) 3 1 2 60 45 60 0.50 0.50 1 2 3 4 1 2 60 60 60 60 60 60 0.50 1.0 1.0 1.2 1.0 C XI11 :(a) 2 60 60 B 2; A:1:2. 0 25:1 . 0 f:: 0.911 0.5952 E : ;z:g ::::!::;;;?;: 40.0 40.0 0.512 0.563 0 . 2 0 0 0.165 0 . 2 0 1 0.221 0.5144 0.1397 0.2133 i2.0 39..2 40.0 35.0 32.4 0.357 0.361 0.394 0,402 0.435 0.324 0.3723 0.3717 0.4097 0.4184 0.4812 0.3563 2; g:0:. 5 0 2;7:;2 . 0 2: XIV 0.996 0.659 if:: 91.5 90.3 g; : 98.6 92.8 92.2 98.8 99.4 z::: 91.2 84.8 96.4 :::::;::::::::?::;:: 0.393 0.397 0.433 0.442 0.478 0.356 ::::: &!:A 94.6 93.i 94.6 94.6 100.0 100.0 z;:: 2 60 1.0 4 0 . 0 0 . 4 0 2 0 . 4 4 2 0.4255 96.3 ( a ) Asphaltum on back of cathode, all others polished on both sides. cobalt phosphate. The final bath was prepared by dissolving t h e sodium pyrophosphate in warm water, and adding the cobalt phosphate, which dissolved up t o the quantity indicated in Bath IX as determined by analysis b u t not up to the quantity recommended by Langbein for nickel. CONCLUSIONS: I-Solution I X is more satisfactory than t h e corresponding nickel phosphate solution for the purpose of ,SERIES XI-COBALT SULFATE, AMIMOSIUM TARTRATE, TASNIC ACID SOLrTIONS Neutral ammonium-tartrate is obtained by saturating 3 solution of tartaric acid with ammonia. The cobalt salt should also be neutral. The solution was prepared by dissolving the ingredients in .water, boiling for about fifteen minutes, adding water t o make desired quantity and filtering. COSCLUSION: Solution X I is not satisfactory for cobalt plating under the usual conditions of plating practice. SERIES XII-COBALT SULFATE, POTASSIC?d TARTRATE, TARTARIC ACID SOLUTIONS The cobalt sulfate, tartaric acid and caustic potash were dissolved in water and then mixed, adding sufficient water to make the bath. COSCLOSIOXS: 1-Cobalt plates from Solution XIT, which is simple cobalt sulfate in the presence of potassium tartrate with an excess of tartaric acid, on brass and iron, are firm, adherent, hard and uniform and may be readily buffed t o a satisfactorily finished surface. They take a very high polish with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. TABLES 1 TO v S O L U T I O X XIIIB .4t cur. Hrs. Grams dens. 'G.Co Date After G. Co. Acidity 4 f t e r G . Co. After G. Co. After G. Co. A f t e r G . Co. plating per plating per plating per plating per of plating per Octo- additional cobalt Amp. per per deposited sa. d m . 100 cc. her run Hrs. 100 c c . Hrs. 100 cc. solution Hrs. 100 cc. Hrs 100 cc. Hrs. 100 cc. 80 2.54 24 1.11 26 1.72 Neutral 16 0.i6 2 . .. .... 8,55 31 0.94 1.81 Very sl. alk. 31 0.80 151 8 3; 5,35 8.40 95 2.58 46 0.94 39 1.10 41 1.95 SI. alk. 46 0.74 8 17.5 30 16.5 8.20 41 0.95 110 2.52 54 1.14 56 2 . 12 Neutral .. .... 8 5 min. ., 15.4 (0) 2.55 69 1.10 71 76 0.94 125 1.95 SI. alk. 6! 0 75 9 15 40 11 0 30 1 11 86 Diluted t o original volume R7 0 96 140 2 S~. R 'Si 1.12 101 ii 0.96 10 16 .. 5.0 f.95 1.99 >Alk. 5.26 7.59 2.11 >Alk. .. .... 13$7 .. 99 1.13 116 102 0.9i 155 2;60 13 3 min. 16.25 (0) > Alk. 2. l i 114 1.14 131 lli 0.99 170 2.62 Strongly acid t o liimus throughout tests \$eutrai 'thioughS'ery slightly al.h-eutral solutions throughout tests ont (a) kaline throughout ( a ) Solution IVR was neutral t o litmus paper a n d slightly' alkaline by titration with S / 1 0 HC1 a n d litmus indicator. ( b ) Good, smooth, white plate obtained; buffed readily t o a mirror surface. (Note severe anode current densities a n d good behavior of solution.)

TABLE VII-AGING TESTSO F BEST PLATIXG SOLUTIONS. D A T A (EXCEPTXIIIB) S O L U T I O N I.4 S O L U T I O S IB SOLUTIOS I I I B SOLUTIOS I I I E

BEGUN

ON

A U G . 2 6 T H AFTER R u X S RECORDED IN

SOLUTIOP.; I V B

'

5

~~~

~

dark cobalting for decorative purposes. The voltage required for moderate current densities is extremely high as compared with that required for other cobalt solutions described as satisfactory. a-Cobalt phosphate, in the presence of sodium pi-rophosphate, as indicated in Solution IX, is less soluble than the corresponding nickel salt. This is the only case among those studied in which the cobalt bath could not be made more concentrated i n metallic cobalt than the corresponding nickel bath, with consequent greater electrical conductivity and correspondingly higher permissible current density for plating. SERIES X-COBALT-AMMONIUM

SULFATE, MAGNESICM S O L U T I O S S

I-Cobalt plates from Solution X on brass a n d iron are firm, adherent, hard and uniform, and may be readily buffed to satisfactory mirror surface. They take a very high polish with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. a-The soft yellowish tinge which is observed when plating CONCLUSIONS:

2--All of the cobalt plates from this solution within the current density ranges described as satisfactory, are as smooth, adhesive and generally satisfactory as the best nickel plates. 3-Solution X I 1 is a n extremely fast-plating solution when compared with the fastest nickel solutions. It yields satisfactory plates a t all current densities up t o I I . o amp. per sq. dm. 4-Solution XI1 may be used for plating on brass, iron and steel, for which cathodes alone these conclusions apply. j-There is, no nickel bath, of which we are aware, operating in the manner of the usual plating practice a t anything like as high a current density as the cobalt solution XII. SERIES XIII-COBALT

SULFATE, COBALT CHLORIDE, BORIC A C I D SOLUTIOSS

Solution XIIIA-l is analogous t o one suggested t o us by Llr. \V, S . Barroivs, foreman of the plating department, Russell LIotor Car Company, Toronto. Ontario, as being satisfactory and rapid for nickel plating.

'

M a y , 1915

*

T H E J O U R N A L O F I X D I ‘ S T R I A L A X D EiTGINEERIXG CHEMISTRE’

COXCLUSIOXS:I-The estreme importance of proper concentration of cobalt sulfate solutions is shown by the results of this series. Solution XIIIA is unsatisfactory for plating purposes a t all current densities tried. Solution X I I I B , which is a more concentrated solution of the same type, is the most completely satisfactory solution, for a great variety of purposes, which we have found. \Ye know of no solution, plating with nickel, which begins t o compare with Solution X I I I B for the range of work which it will do, and for the extreme high current densities a t which it will operate. I t is possible t o get a plate in three minutes or less with Solution X I I I B , which will stand all the usual physical commercial tests, and which will buff as satisfactorily as a plate which has taken one hour in the usual nickel-plating baths. 2-Cobalt plates from this simple cobalt sulfate solution in t h e presence of sodium chloride and boric acid, Bath X I I I B , on brass and iron, are firm, adherent, hard and uniform, and may be readily buffed t o a satisfactorily finished surface. They take a yery high polish, with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. 3-The specilic electrical conductivity of Solution X I I I B is much higher than t h a t of the corresponding nickel solution. 4-Solution X I I I B does not yield the best cobalt plates a t low current densities, that is, in the neighborhood of 0 . j o to I .oamp. per sq. d m . , which is a common range for nickel-plating work. Solution X I I I B begins t o plate most satisfactorily a t a current density in the neighborhood of 3 . j amp. per sq. dm., and continues to give satisfactory plates a t all current densities up to 2 6 . 4 amp. per sq. dm. This is equivalent to a current density of ox-er 240 amp. per sq. it., and even a t this speed, the limit of the solution has not yet been reached. j--All of these cobalt plates within the wide current density range described as satisfactory for Solution X I I I B , are as smooth, adhesive and generally satisfactory as the best nickel plates. 6-Solution X I I I B does not change appreciably in cobalt content nor in acidity when used over long periods of time a t current densities as high as I amp. per sq. dm. It showed only a very gradual diminution in cobalt content under the most severe conditions of the aging test described in Table V I I . TVe know of no other cobalt solution and of no nickel solution which would stand up under the conditions of this aging test. ?-There is no nickel bath of which we are aware operating in the manner of the usual commercial plating procedure a t anything like as high current density as Bath X I I I B . S---Solution XIIIA may lie used for plating on brass, iron a n d steel, for xhich cathodes the above conclusions apply. 9--Solution X I I I B may be used t o deposit a heavy cobalt plate. These plates may apparently be deposited to any desired thickness, and they are firm, adherent, massive, of extreme hardness and show no tendency t o curl or split. ro-Heavy plates may be obtained from Solution X I I I B t o much better adT-antage than from Solution XY, which has been particularly patented for the purpose with nickel; that is, heax-y deposits may be obtained from Solution X I I I B a t current densities of j or 6 amp. per sq. dm., whereas Solution XI- must be operated a t low current densities in the neighborhood of 0 . 3 0 amp. per sq. dm. If a current density of above 6 amp. per sq. d m . i,; used with Solution X I I I B for heal-y deposits, under the conditions in dimension of our baths, it was found t h a t trees were formed on the cathode. I I-Our esperiments show that Solution XITIB throws” very satisfactorily. I z--.%mong the satisfactory properties of this remarkable solution should be mentioned a n estremely high current efficiency, which we found a t I .o and j .o amp. per sq. dm. t o be almost IOO per cent. 13-Solution XIIIC, which is the nickel analogue of Solution X I I I B , yielded satisfactory plates to about j amp. per sq. ‘ I

393

dm., b u t showed splitting a t current densities greater than t h a t . hTickel solution XI11 C does not possess the remarkable qualities of its cobalt analogue X I I I B , although in many respects it is a n improvement on standard nickel solutions. 14-Solution X I I I B requires very little aging: it operates satisfactorily almost from the start. I j-Solution X I I I B is so remarkable in its properties that it was thought highly worth while t o develop it further under p. 394, el seg. commercial conditions. See COM>fERCIAL TESTS, SERIES XIV-COBALT

SCLFATE, A M N O N I C M SULFATE, MAGSESlt:>l

SULFATE, BORIC ACID SOLUTIONS

plates from Solution XI\-, on brass CONCLUSIONS : 1-Cobalt and iron, are firm, adherent, hard and uniform, and may be readily buffed to a satisfactory mirror surface. They take a very high polish with a beautiful luster, which, although brilliantly white, possesses a slightly bluish cast. 1-Solution XIY yields satisfactory plates a t all currcnt densities up to about 3 amp. per sq. dm. 3-The current efficiency of Solution XIIT is satisfactorily high, being in the neighborhood of 96 t o 97 per cent under the conditions of our experiments. 4---411 of the cobalt plates from Solution XI\- within the current density range described as satisfactory are as smooth, adhesive and generally satisfactory as the best nickel plates. SERIES XV-COBALT

ETHYLSULFATE,

SODIUM SULFATE,

AMMO-

SICM CHLORIDE SOLL’TIOSS

This solution is the cobalt analogue of a nickel solution patented by Dr. G. Langbein & Co., Leipzig, Germany.’ The inventor claims for this solutiom t h a t very dense, hard, uniforn. deposits of nickel may be obtained from it, and particularly “deposits of any desired thickness can be produced if the bath be constantly agitated by mechanical means or by the introduction hydrogen.” It, of course, is not permissible to agitate this bath with air, as that would cause oxidation. CONCLCSIOXS : I-Dense, hard, uniform deposits of cobalt may be obtained from a cobalt-ethylsulfate solution made up like Solution XV, without mechanical agitation, provided that the current density be low, not exceeding o , 3 o amp. per sq. d m . 2-For heavy depositions of cobalt, where density, hardness and speed of deposition are important, Solution XI- is not nearly as satisfactory as Solution X I I I B . However, the cobalt-ethylsulfate solution deposits cobalt more satisfactorily than the cor responding nickel-ethylsulfate solution deposits nickel. SERIES XVI--COBALT

SCLFATE, AMSIONIUM SULFATE, AM310SICJI

CHLORIDE, B O R I C ACID S O L C T I O S S

I n making this solution it was reasoned, as in many instances already reported, that a greater current density might be used if the metal content were increased. This solution, contrary t o a number of others reported, would not, hot very great increase in cobalt content without giving disturbing effects of crystallization in the bath. Current efficiency runs were made with these solutions, which show them to be in the neighborhood of 90 per cent, but they xere not thought of sufficient importance to warrant a careful study. COSCLUSIOWS: x-Plates from Solution XT’IA and the corresponding nickel solution are both satisfactory a t current densities below I amp. per sq. dm. -4t higher current densities both solutions fail. 2-A solution of the type of Series XS’I cannot be prepared in much greater concentration than XS‘IA, without obtaining troublesome crystallization. Therefore. Series XVI does not offer a highly concentrated rapid plating cobalt solution. 3-Cobalt plates from Solution XTI.1, on brass and iron, are firm, adherent, hard and uniform, and may be readily buffed 1

1902.

Kaiserliches Patenamt, Pntentschriff. h-o. 134,736 €348~1, Sept. 1 8 ,

T H E JOCRLYAL OF I N D U S T R I A L A N D E;Z'GISEERISG C H E M I S T R Y

3 94

V O ~7,. NO.j

2

.

~

8

3.7

2

5

12

vincing

test.

Good color, buffed easily t o splendid finish; bending, hammering, twisting did n o t crack nor loosen plate. 8 4.2 3.5 8 Sheet steel 52 1 0 90 T h e cathode consisted of six pieces steel hooked to wire frame. Plate good color, smooth, hard; did n o t crack when bent o r twisted. Buffed t o good finish. D mro t -heean current densitv of 30 amo. oer sa. it. a n d eraduallv in14 4.5 4 8 Steel 72 1 0 . 90 _ -s-i - ~ - - -with creased t o 42. .