ELECTROLYTIC CO-DEPOSITION OF ilETAXS By Albert Hudiburgh A Cooper THESIS Submitted to the Faculty of Michigan State College in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Kedzie Chemical Laboratory East Lansing, Michigan 1933 ProQuest Number: 10008222 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10008222 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 1 INTRODUCTION Certain alloys are known to have higher corrosion resistant properties than those of the individual metals. It is well known chat under certain conditions it is possible to deposit two metals simultaneously from a solution containing both ions* During the last several years a large amount of investigation has "been car­ ried out in the field of alloy deposition, and a great deal of new knowledge has "been accumulated. From the literature, study of co-deposited metals by the aid of x-rays show that alloys, compounds and solid solutions,are act­ ually formed and not a simple mixture. Although certain general principles of alloy deposition are fairly well estahlished, their application involves a knowledge of so many, at present,undefined variables that the question remains, can the deposit ion of an alloy be predicted from the data for the separate metals. In electroplating many factore enter in which affect the characteristics of the deposits > current density, concentration, agitation, temperature, conductivitys metal ion concentration, hydrogen ion concentration, addition agents, and structure of the base metal. Plating of alloys, h o w e v e r , is an exceedingly complex problem, and numerous difficulties are encountered which may not be present at all, or to a much less d e g r e e ,in the plating of the elements alone. When two or more different cations deposit together, one of them may be preferred over the other, for such causes as a differ-* encesi in potentials, or in degree of hydration,mobility, valence cr mrtcxl ratio. The fundamental problem of alloy deposition is to find that compositlon of solution in which the potentials of the metals are equal, or at least, nearly so. Variables which one would expect to affect the composition of a deposit, and also the structure of the deposit arei Ratio of the metals in the bath, temperature, current density, total m e t a l concentration, addition of a common ion or oomplex ion, agitation, overvoltage, polarisation, and valence. It also sometime happens that one metal affects the deposition of the other to an unfcrseen extent. In operating conditions, a number of these factors may tend to conteract each other, the actual deposit obtained being the net result of all the factors. The purpose of this work has been to supplement this present knowledge, dealing with the behavior of solutions under varying conditions, studying the factors which affect the structure of the deposited metals, and their effects upon the composition of the co-deposited metals. With a review of the present knowledge of the subject, it is designed to point the way to a more complete correlation of the accumulated data on alloy deposition to evolve some working hypothesis to fit the facts. 2 THEORY UNDERLYING- CO-DEPOSIT ION When a metal is in contact with a solution containing ions of ;hat metal there is a certain tendency for the metal to go into t" solution to form positively'charged ions of the metal , the elects . ‘being left with a negative charge. On the other hand this " s o i u t U 1 pressure" is opposed by a certain ’’osmotic pressure” which ter.cw' ..eposit metal on the electrode from the solution. This differ - ■ce between solution and osmotic pressures, or electrode potentials may he represented by the Nernst equation, -g ST -]n^ —C-~ ^ nF 10ge p , where E- electrode potential in volts, gas constant, T= absolute temperature, n= valence of the metal ions, F= Faraday’s constant,p = "osmotic pressure” of the metal ions, P="solution pressure of m e t a l . From this it is seen qualitatively that the potential of an electrode depends upon the concentration of its ions in solution. Theoretically, metals commence to deposit at their r e v e r s i b l e potentials, but as the passing of current takes place their c a t h o d e potentials become more negative due to concentration polarization and hydrogen overvoltage. Agitation and temperature tend to reduce these effect s * When a group of metallic salts are present in solution, the metal will plate out in the largest proportion w M c h has; (l) Lowest electrode potential(most positive), (2) Ureauosz .oncentration, and (3) Highest ionic mobility. Upon passing a current deposition will occur when the cathode potential just exceeds the potential of the most positive metal. Alloy deposition will occur if ; (1) Electrode potentials are c l o s e .together and polarization is small, (2) If the difference in overvoltage brings the deposition potentials closer together than are their reversible potentials,(3) If the co ncentrat­ ion of the ions of the more noble metal is reduced. The following figure gives the current density-cathode poten­ tial curves for two metals,A and B. Theoretically, the amounts of •ach metal which will be deposited will be proportional to the current density corresponding to the intersection of the vertical line a n d the current density-electrode potential curves of the metals at a g i v e n current density. Metal A would deposit at a rate proportional to d'i and B proportional to d a. Then the frabtion-g—— '- • will be the part of the current utilized in depositing A. I+ <^ 2 The enormous variation in the electrode ^ potential of a metal which can be effected by 1 altering the relative concentration of metal and cyanide often® changes the potentials of metals which are widely separated in an acid solution , bringing them closely enough that co-deposition occurs. Increase of temperature ^ conteracts polarization and decreases hydrogen overvoltage,and electrode potentials approach their true values. Cathode Potentials when co-deposition is ppssible 3 With complex cyanides, Deposition commences at the reversible potential, but considerable polarization results, due to;^ (1) Deposition of the metal ions faster than the complex metal ions dissociate to form sjmple ions, (2) She marked increase in cathode potential may be due to even a small f jge in ratio of metal to free cyanide, (3) Cathode potential reac& the point at which hydrogen evolution can begin. When hydrogen is e v o l v ed overvoltage enters in and affects the relative amounts of metal and hydrogen deposited. In an electrolyte containing a common ion, the degree of dis­ sociation depends solely upon the concentration of the common ion, and in turn, the potentials depend upon metal ion concentration.In a solution containing several metals, in the form of the same salt, the relative ion concentrations are governed by the common ion,each metal affecting the concentration of the other. In alloy deposition the variable factors which affect the comp­ osition of the deposit also affects it structure. X-ray studies have shown that the principle difference in appearance and p h y s i c a 1 properties are caused by difference in size or shape of each metal crystal. This is,in turn, dependent upon the relative rates, of cry­ stal growth,and of crystal nuclei formation. A rapid formation of nuclei favors production of finer grained, bright and smooth plate. In solutions whose salts are highljr dissociated, rapid growth of crystals takes place during deposition. Favorable conditions for the production of fine grained deposits are obtained when only few metal ions are present, but with a high metal concentration which will furnish a fresh supply of ions almost as fast as they are re­ moved from the solution. At low current densities, the result is toward the growth of crystals, while at higher current densities, in general, the rate of nuclei formation increases, resulting in finer grained deposits. Temperature has several effects, some of which oppose one an­ other* Increase of temperature (1) Favors diffusion and convection, tending to give a uniform,fine deposit, (2) Increases conductivity, due to increased ionic mobilities, (3) Increases rate of crystal growth, tending towards the formation of coarse deposits, (4) De­ creases polarization and overvoltage and favors crystal growth. Addition agents are commonly used for producing smooth or bright deposits, by (1) Reducing metal ion concentration due to the common ion added, or (2) By hindering the growth of crystals mechanically. Any foreigh substance which is adsorbed or included in the deposit, as with colloidal addition agents, will hinder the growth of crystals and assist in the formation of finer grained depositsA similar effect is produced if two metals are deposited simultaneously. I n general, such alloys have a finer structure than either of the com­ ponents deposited separately under similar conditions, each metal acting as an addition agent, preventing the growth of the crystals of the other. 4 SURVEY OF THE LITERATURE Blum and HaringtTrans.Amer.Electrochem.Soc.,40, 287-306(1921), plated lead-tin alloy from a fluoborate solution and concluded that; (1) Lead and tin have nearly equal potentials in fluoborate solutions,(2) Composition of the deposits obtained ‘under otherwise similar conditions depends upon the metal ratio in the solutions, (3) Increasing current density in the baths of low tin content increases the tin in the deposit, (4) Increasing amounts of glue in the solution have the same effect as current density,(5)Leposits of lead-tin alloy have a finer crystalline structure than lead or tin deposited under same conditions, (6) In the presence of glue the deposits are still finer grained. Efremor ( Ann, Inst. Polytechn. Oural, 6, 111-50 (1927) claims plating of copperrcadmium alloy from cyanide solutions. He states that (1) Free cyanide content of the bath must be below .3 normal, (2) A 1 to 1 ratio of copper-cadmium in the bath gives an alloy of 62 to 7 2 percent Cadmium, (3) Temperature has but little influence on the deposit. Ferguson and Sturdevant(T r a n s . Amer. Electrochem. Soc.,38,167201(1920) in depositing brass from the cyanide solutions find that (1) An increase in the ratio of copper to zinc in the solution increases copper in the deposit, (2) Increase of temperature decr­ eases cathode polarization and consequently increases the percent of copper in the deposit, (3) Increase of current density produces a gradual decrease in percent of copper in the de po si t,(4)Alkaline substances decrease the percent of copper in the deposit,(5) Incr­ decreases the rate of copper deposition and ease of free cyanide favors a high zinc content deposit. Fink and Conrad(Trans. Amer. Electrochem. So c.,58,437-63(1930) in the deposition of lead-thallium alloy from a perchlorate bath found that (1) A high ratio of thallium to lead in the bath is necessary to co-deposit the two metals, (2) Ratio of thallium to lead in the deposit decreases as current density increases. Fink and Gerapostolou (Metal Ind. (N.Y.) 28,519-21 (1930), de­ positing silver-cadmium alloy, give the following conclusions; (1) Increase in mol ratio of cadmium to silver in the bath incr­ eases mol ratio in deposit, (2) Increase of current density incr­ eases cadmium to silver ratio in the deposit, mere marked with low cadmium silver baths, (3) Increasing the temperature decreases percent and makes the deposit more brittle, (4) Increase of free cyanide decreases the efficiency, (5) Microstructure of deposits reveals a heterogeneous mixture of at least two constituents, one of a silver rich solid solution, and the other of a cadmium r i c h solid solution. Fink and Lah (Trans. Amer. Electrochem. Soc., 58,373-85 (1930) found in depositing nickel-cobalt alloys from the sulfate-chloride bath, (1) As cobalt in the bath increases in small quantities, t h e 100 100 Lead-Tin Blum & Haring 80 60 40 40 2Q 20 Percent m 80 Tin Deposit 3 Lead-Thallium Fink & Conrad • Percent Cadmium in Deposit 0 20 40 60 §0 100 Percent (Equiv)Tin in Bath 1 t ___ ;___ i 2 3 4 5 6 Lead , G- / L i 7 100 ____ cc Lah 80 80 60 60 C-lasstone & Speakman t-1 40 ■g 40 o 20 Cobalt-Hickel 20 r- ■Cadmium ■postolon 4 6 8 Current Density in peposit 2 100 80 ' 50 'percent Co 30 percent Co Cobalt .0 60 C oba It '-Hi eke 1 G-las stone ^ - ^ 1 0 percent Co Percent 0 i 10 0 20 40 60 80 100 Percent Cobalt in Bath -p 1 0 0 •H 80 40 V 50 percent Co5 percent Co 20 0 i ■ • • 1 2 3 4 Current Density 0 20 40 60 80 Temperature, C 100 Zinc ; eo ?.r 60 Metal i- » 40 Cadmi Copper Percent Zinc Copper Percent Metal in Deposit 0 in Deposit 5 10 15 20 25 Potassium Cyanide 30 0 5 10 15 20 25 potassium Cyanide 30 100 80 1-4 4^> 60 Zinc Copper 40 Cadmium me Copper 20 i —1 0 5 10 15 20 25 Potassium Hydroxide 30 100 0 p 5 10 15 20 25 30 Potassium Hydroxide 100 •H 80 Copper 60 ■ h 60 admium 40 Copper Percent Metal -p 20 2C Zinc * 1 Zinc .3 » 4 .2 5 Current Density .6 20 30 40 50 60 70 Temperature,°C Copper-Cadmoum-Zinc Alloys Ernst A Mann 80 7 percentage of cobalt in the deposit increases rapidly, (£) As the total metal concentration increases, at a constant metal ratio, the cobalt content of the deposit increases, (3) Increase of temp­ erature decreases the cobalt content of the deposit,(4) Increasing current density increases cobalt content of the deposit,(5) I n c r ­ easing pH increases the cobalt content of the deposit. / In the electrodeposition of Chromium-Iron alloy, Fuseya and Sasaki (Trans. Amer. Electrochem. S o c . ,59,445-60 (1931), concluded that at higher current density, and lower temperature or acidity of the bath, the higher the chromium content of the deposit. Temp­ erature has the same effect as acidity. Increase of iron sulfate in the bath increases the iron content of the deposit* . Olasstone and Symes (Trans. Faraday So c .,£3,213-26 (1927), £4, 370-8 (1928), in co-depositing nickel and iron from the sulfateoxalate bath found that; (1) An increase of nickel to iron ratio in the bath increases nickel to iron ratio in the deposit, (£) An increase of the oxalate concentration of the hch increases the nickel content of the deposit,(3) Increasing temperature increases the nickel to iron ratio of the deposit, (4) Increasing current density increases the content of iron in the deposit, (5) Relative tendencies for iron and nickel to deposit as an alloy is independent of hydrogen ion concentration of the bath. In plating Cobalt-Nickel-alloys, Glasstone and Speakman(Trans. Faraday S o c . ,£6.565-74 (1930); 27,29-35 (1931), give the following information, (1) As the temperature increases, the deposition pot­ ential of nickel becomes less negative. and the proportion of nickel in the plate increases with increasing temperature, (2) As current density increases, the cathode potential of cobalt becomes more negative and the proportion of cobalt in the deposit increases rapidly toward a maximum value, (3) Alloys always contained rel­ atively more cobalt than present in the bath. With iron-cobalt, iron-nickel, and cobalt-nickel deposition, Glasstone and Speakman (Trans. Faraday Soc. 28,733-40 (1932); 29, 426-8 (1933) concluded that (1)Increase of A in the bath increases A in the deposit, (2) Increase of temperature decreases A in the deposit,(3) Increase of current density increases A in the deposit, where A is the first metal mentioned in the above pairs. Mathers and Sowder ( Trans. Amer. Electrochem. Soc., 37, 525-8 (1920), plated a oopper-tin alloy from the oxalates of copper and tin dissolved in ammomium oxalate, and also from potassium cyanide^ potassium stannate, and potassium hydroxide. Schoch(j. Amer. Chem. S o c . ,29,314- rlv lvJ7 ] ^ / e s the following conclusions on his work with nickel-zinc alloys; (l) Proportion of zinc in the deposit increases with current de nsity,(2)Eroportion of zinc in the deposit increases with increasing zinc content of the bath. While it is very difficult to deposit nickel or iron fro m cyanide baths, the work of Hineline and Cooley(T r an s. Amer. Elect- 402.00 Percent Copper in Depop. 100 2 4 6 oodrii Carbonate Percent Copper in Deposit 15 20 25 30 35 Copper, G- / L 100 -1 a5 SO •HT Cathode 60 Zinc 40 20 .0 7 17 12 Sodium Cyanide,O/L 27 7 ~1 22 Sodium Cyuu Ide , G-/L 27 Copper in Deposit 100 80 60 40 o 40 Percent | H 20 0 20 40 50 60 30 Temperature, C 70 0 4 ,6 .5 \?\-ent Density Copper-Zinc Alloys Ferguson cc Sturdevant -L J 9 rochem. Soc*,48. 61-8(1925), and of Stout,Burch and langsdorf(Ibid., 57,113-27 (1930) have shown it to he much easier to obtain their alloys. They conclude (1) The percent of copper in the deposit is always greater than that of the hath,(2) Ratio of copper to nickel on the plate increases linearly with the temperature, (3) Low current density favors deposition of high copper a l l o y s ,(4)Incr­ ease in free cyanide was found to lower the rate of deposition. Concentration of free cyanide should he low as possible.Stout shows that the relationship between copper-nickel ratio in the plate,Rp, and the copper-nickel ratio in the solution, Rs, may he of the hyperbolic type expressed by the general equation b + x = a where a and b are constants, and x(Rs) is the abeissae,and y(Rp)*ls the ordinate. From the curves, the copper to nickel ratio in the deposit increases linearly with temperature, Rp = C + K T. In their work on iron-nickel alloys, Stout and Carol (Trans. Amer. Electrochem. Soc., 53,357-72(1930), find (1) Iron content of the deposit tends to be higher than that present in the b a th ,(2) Percent nickel in the deposit increases with current density. Low temperatures minimize the changes in composition of the deposit with increasing current density. At high temperature the effect of changes in current density becomes more appreciable, (3)The nickel content of the deposit increases rapidly with an increase in temp­ erature, (4) Even with high iron content, a large excess of cyanide will give iron free deposits, (5) Potassium tartrate proved to be the ideal addition agent. Very few references to the deposition of ternary alloys are in the literature. According to Ernst and Mann (Trans. Amer. Electro­ chem, Soc., 61, 363-95 (1932). in their investigation of coppercadmium-zinc alloys, find (1) Copper has a depolarizing effect on the deposition of zinc,as has cadmium,and the alloy should deposit at a potential lower than the potential of the three metals, Zinc and cadmium are depolarized by copper. (2) The percent copper de­ creased, cadmium and zinc increased, and cathode efficiency decreased, as the amount of free cyanide increased, (3) With the addition of alkalie the percent of copper was decreased,while that of cadmium and zinc increades, resulting in coarse crystalline structure, (4) Percent of copper in the deposit increased with a decrease of temperature, while that of cadmium increases with in­ creasing temperature,(5) Percent of copper and zinc decreases with increasing current density, (6) Percent of copper and zinc incr­ eases, and cadmium decreases, with dilution. G-lasstone (J. Chem. Soc., 129, 2897-902 (1926) in his work on polarization of the iron,nickel and cobalt group, studied deposit­ ion potentials and concluded; (l)They vary directly with the metal ratios, (2) Varies directly with temperature, (3) Is independent of hydrogen ion concentration. Later in his work with the deposition of alloys of zinc with cobalt, nickel and iron (J. Chem. S o c . ,130,641-7 (1927),finds that (1) A decrease in temperature decreases the cobalt to zinc ratio, (2) The cathode potential ,at some point rises rapidly,and an alloy rich in zinc is deposited. The same phenomena has also b e en .0 -.7 H cii 40 S CD P o Ph Iron £ o SO 10 ■H CQ 0 Iron-Cobalt Alloys Glasstone esc Speaianan 10 20 30 percent Iron in in Deposit Iron Percent 40 NiSO 1 o .2 Iron-Cobalt Glasstone o <=}- •2 40 50 Bath 100 60 CoSO 4 P 0 0 SO 40 60 BO Temperature, °p 100 p ■H i 100 f o 00 Depo to •g rl 60 - O Iron-Nickel Glasstone & Byrnes Iron-Nickel Giasstone & Symes 40 P £ 20 \ g 20 p CD F4 0 20 50 40 Percent Iron \r . Bat a 0 100 80 Iron 40 20 . .i ! .! 1_____ ...... ii _____: _____ _____ _____ 20 40 60 80 100 Temperature, C. ,5 50 pe 60 Percent in Deposit 6 -P Percent in Deposit 50 .3 10 percent Fe 2 5 a m dm 2 / 1.5 ampdm2 Fe Iron - t eke . Glas 3 1 ar.e &, ovne s 0 o 4 1 Current Density ^ a o .> •Z inc Sciucli oc Hirsch 5 0 1 2 3 4 5 Hi / Zn Equiv, Ratio in Bath i; Ratio 20 Cu-Ri in Deposit 50 10 Copper-Nickel Stout Burch & lang&dorf. o 40 6 amps £ 30 Copper-Hickel Stout.Buroh 1 Lanrsdo ri Rs- 4/1 _ amps 1.5 amps 0 1 Cu-IFi Ratio in Deposit Cu / Ri Ratio in Bath 12 40 IQ O 10 Rs = 4 / 1 6 " i j [ r Iron-Copper-Rickel Stout a Faust ■r-} 80 CD P £ 8 Copper 60 Clj -+3 0 6 4 40 Rickel +3 C 0 O U Copper-Rickel Stout,Burch & Langsaorf 20 Iron 0 2 10 P4 20 30 40 Temperature, 50 60 20 C 100 jj Copper 60 100,— Iron-Copper-Rickel St out u Faust Sulfate-Boro-Citrate 80 Q £ 30 40 50 60 Temperature, C. . •H TS1 o del Iron-Copper Stout u F a u s Cyanide Baths 80 60 Metal rS 40 Percent in Deposit 100 2 3 4 5 Current Density 20 1 Rickel ^ Copper 'J o Ire 20 0- o1 Ph 0 2 4 6 8 Current Density .0 u 2 Curicut Density 12 observed with, cobalt and zinc, (3) The sudden increase of cathode potential is attributed to a decrease in the concentration of iron, nickel oer cobalt ions in the vicinity of the cathode, and with the result that an alloy richer in zinc ,and with a higher overvoltag e, is deposited. (4) The lower the temperature, the greater the pro­ portion of zinc in the deposit. In the deposition of ternary alloys of iron-copper-nicke 1, Stout and Faust (Trans. Amer. Electrochem. Soc., 60, 271-96(1931); 61, 341-62 (1932) claim, (l) Ternary alloys of copper, nickel and iron can be deposited in cyanide baths in the presence of tartrates, the presence of tartrates being necessary for the deposition of the iron. (2) Deposition of copper is favored over nickel and iron. Increase of current density more equalizes the amounts of each metal depositing, (3) Increasing temperature has the opposite influences at low current densities than it has at high current densities, (4) High concentrations of iron are required in bath in order to permit even small amounts in the deposit, (5) Increase of current density favors the deposition of nickel and iron at the ^expence of the copper, (6) Effect of free cyanide is marked, as no ternary alloy was obtained with excess cyanide, (7) Copper to nickel ratio is not affected very much by tartrate, but is necessary for the iron to deposit. (8) Composition of the deposit depends upon the relative concentrations of each metal in the bath. The Percent copper in the deposit is relatively much greater t h a n in the bath, the percent nickel in the deposit being slightly less than in the bath. Stout and Goldstein(Trans. Amer. Electrochem. Soc.,63,preprint, 21 pp (1933) deposited cadmium-zinc-antimony alloys from t h e cyanide bath, with potassium antimonyl tartrate, concluding, (1) Deposition of zinc and antimony is favored over cadmium, (2) An increase of one metal in the bath tends to increase that metal content of the deposit, (3) An increase in current density causes an increase in antimony content of the deposit when the cadmium and zinc contents of the bath are low, and a decrease when they are high. An increase in current density causes a slight decrease in zinc content, and an increase in cadmium content of the deposit, (4) Temperature has the same effect as that of current density, (5) Increasing current density increases the cadmium content more than that of zinc, (6) Alkalie reduces the zinc content,but affects that of cadmium but little, (7 ) A comparatively large cadmium conc­ entration in the bath is required to produce an appreciable amount in the deposit. EXPERIMENTAL In studying the problem of alloy deposition, the affect of the following factors were determined experimentally,(l) Metal ratio , (2) Current density,(3) Temperature,(4) Addition agents, and (5) Total metal concentration, determining the : si a'.ng effect u p o n composition of deposit, and changes in elecxroia. potentials. With a potentiometer set up, and a hydrogen reference electrode, both static equilibrium electrode potentials ,and the dynamic p o t e n t i a l during the process of plating, were measured. The results obtained on five pairs of metals , Copper-Tin; Silver-Cadmium; Silver-Tin; S i l v e r - C o p p e r ; and Cobalt-Nickel, are recorded as follows. Fe-Zn >7 Decomposiiio; 6 5 .4 Zinc Alloys Glasstone 3 40 60 80 20 Temperature C. Percent Metal in Deposit 0 10 100 12 14 16 20 ‘ Zinc 60 40 60 20 0 Atomic Percent Zn 100 Zinc fij 4-^ 40 & 20 1 in Batli ^100 •H CQ o P4 er square decimeter. Effect of Alkalie NaOft yGr / L 0 5 10 15 20 30 Composition ) Electrode Potential Decomposition Potential oi Deposit? ci m 5n m Cu 8n cu in an in Cathode Percent Cu CuCN Na2Sn02 CuCl ■ 50 % 0 aON 'ha2Sh03 CUCIT 50 % 85.6 77.2 63.7 49.3 - - - - - — —— — -.505 -.775 t 6 9 9 -.475 -.835 t 764 -.462 -.855 7775 ---- t 778 -.448 -.870 ----.435 -.885 - .499 ---7841 7862 - .450 ---7 874 ---- - .440 - .440 t 7 35 -.57 9 ---- -.590 ---- -.5§0 -.571 -.810 -.880 -.902 -.922 ------ - 15 Effect of Free Cyanide Decomposition Potentials | NaCN Composition I n DU p e r c ent uu-an naxn G / L of Deposit Tin TTathode Percent Cu Cu in CuCN Sn inEaaSn0 3 “"Copper 93.5 90.5 85.2 62.5 so 35.2 !3 Q 32.2 L Current Density 0 5 10 15 -.499 -.561 -.613 -.657 — - ~ -.662 ---- ---- ---- -. 545 -.7 20 -.805 -. 565 -.655 -.695 -.420 -.575 -.680 —— — -.840 -.870 -.715 -.7 25 -.755 -.660 -*724 -.825 -.773 -.660 0.2 amps per decimeter^ Effect of Free Cyanide on Electrode Potentials NaCN G/ L 0 !5 10 20 [30 du in CuCN -.504 -.570 -.635 -.739 -.895 Potentials Equilibrium Electrode 667. Cu-Sn 50 Cu-■Sn Bath Sn in 33 (Molal)Cu-Sn Copper Tin Tin Copper N a 2Sn 0 3 Copper Tin -.779 ------- -.780 -.775 -.778 -.445 -.692 -.847 -.888 ♦ - .638 - .737 -.765 -.785 -.795 -.458 -.623 -.698 -.7 93 - .870 -.610 -.680 -.735 -.783 -.785 -.542 -.662 -.712 -.756 - .7 90 t . 667 t 7 23 t 742 t t 760 773 Effect of Temperature D e c omposition Pb tential T e m p . Composition Electrode Potentials oc. of Deposit T u in" Sn in 'Alloy Bath Cu in Sn m Cathode m Percent Cu CuCN Na23J03 Copper Tin CuCN a «*SnO 3 Alloy Bath -.764 20 85.5 - .698 ■*736 ? 615 -. 634 -.781 -.780 40 58.8 -.762 -*764 t 653 -.675 -.786 50 -.692 51.6 -.792 •*778 t 670 -.812 60 -.716 -.816 70 -.828 - .739 -.848 t 7 94 t 7 25 64.5 t 8 22 80 76.2 Compc sition of Ba bh, 50. percent (molal) Cu-Sr1 NaCN, 10 G L Current Densit y > 0.2 amps i per Dm 2 -.810 -.877 -.890 -.780 Effect of Current Density Current Density AMp/Dm^ .05 •10 .20 .40 .50 Composition of Deposit Percent Copper Theo. CN NaCN 10 G/L 98.0 96.5 93.5 92.2 9 0 .6 710 65.8 56.0 41.2 36. 2 50 percent(molal)Cu-Sn Bath Cathode Potential Current Density Cu in CuCN Sn in MaaShQ Amp ./Dm 2 0 .0010 .0025 .0050 .0100 .0200 .0300 .0400 .0500 -.085 -.685 -.753 - .776 -.792 -.810 -.830 -.865 - .958 -.206 -.741 -.840 -.901 -.988 -1.069 -1.115 -1.145 -1.170 16 -M ■H m o Ph 1 0 0 1— i — :. voe , Cypr-,^80^. eo ~7 ^ —I d Pi (NaCN 10 G/L; •H M 0 Ph Ph O oa ■Tin(No Free Cyanide ) 5-1 0 20 40 60 Percent Copper in C a t ho de (NaCN 10 G/L) CD O Copper Pi uj 80 100 Bath 4-3 f^(NaCg AO) 0 ’1 o FreejCgr^uij ds JL 20 40 60 Q0 100 Percent Copper in Bath ■P 10C ■rH 03 O Pi 8C 0 Pi P •H 6CP 0 Pi Pi Cathode (No Free Cy Pi o n e 0 -7 -p * o +3 o 0 1 —I pp -.4 o M O © Tin(\NaCN 10 .*G/L) o *-I 0 S3 o •H 43 •0H O \ 0 *6 xS r-H i-i cj •H & (-> ! cf * h U~ •H fV Ph -'o Ph 1 —J Copper(No Free^ 4 I 20 40 60 80 100 Percent Copper in Bath O O 4-5 P 0 o M 0 Pi 50 percent Cu Bath C .J). 0.2 amp j d m 2 20 0 t1 .2 .3 .4 .5 .6 Total Metal C o n c . tM o l s / L . Cathode i —i Cj ■H jj S3 0 4-5 O Pi 0 od o m +3 O 0 I—I Copper in 4-5 •H 50 percent Cu Bath “ .5 4 .6 .1 .2 Total Metal Conc.,Mols/ L 0 O Pi 3 o 0 0 p .1 3 .4 5 Total Metal Cone.,Mols / Copper-Tin Alloys 6 1' 9 80 r—I .8 •H in Depos H 100 S3 Percent Copper 60 .7 CD -P O P4 40 50 percent Cu bath NaCN 10 G / L C.D. 0.2 amps / d m 2 20 "5 fo Sodium 0 o U ■P o 0 Copper 6 ♦5 rH iIB t SB "S5 SB So Cy anide,G/l 0 10 15 20 25 30 5 Sodium Cyanide, G/L Potential 9 .8 Cathode 80 Decomposition 7 *H 60 .6 Ph Copper o 50 percent Cu Bath NaCN 10 g / L a 40 20 4 0 1.0 0 - 5 10 15 Sodium Hydroxide,G/L 1.0 •H -p Tin Potential - 5 10 15 20 25 30 Sodium Cyanide, G/L Cathode m -H +3 Electrode Copper 0 15 5 10 Sodium Hydroxide, G/L opper 0 5 10 15 Sodium Hy dr o xi de ,G/L Copper-Tin Alloys Percent Copper in Deposit Percent Copper in Deposit 1G 100" Tin 40 7 50 percent Cu Bath C . D . 0.2 amps / d m 2 Free Cyanide 10 0 /'I 20 6 20 30 40 50 60 70 Temperature, ^C 10 80 08 60 50 40 30 Temperature,o c* 70 60 CuCN if .04 40 50 percent Copper Total Metal Cone. 0.6 Mols per liter 20 .1 .5 .2 .3 .4 Cathode Potential Current Density Copper-Tin Alloys -l.qr in Deposit Silver 20 80 100 0 Percent Copper .8 DadmiumlKCN 10 G/L) •r— I £ CD -u KCN 10 C C.D. 0.2 amp j dm 0 2 0 40 60 80 100 Percent Silver in Bath O Ph T0d o -p O 0 H eq .6 Cadmium [T h e o -Cyanide J -Silver (n c n ? o a / i A .4 o •^ Silver(Theo. Cyan 0 SO T > , rex' x t.a Silver-Cadmium Alloys i-0 60 80 100 Ivor in Bath 19 SILVER-CADMIUM ALLOYS Effect of Metal Ratio Composition of Bath Percent A g Composition Equilibrium Electrode Potential of Deposit Cadmium J Silver Percent Ag KCN i'heo. KCT i KCIT |Theo. KCN Tcc'tt " Theo. Cyan. 10 g/l 30 G/L Cyan. io/a! 300 \ Cyan. 1 0 G / L 30 a A ~r..0 0 0 0 “i. 032 ?814 t 865 10 78.8 55.0 40.7 20 88.2 7490 7375 77.0 68.5 -.441 7710 1*846 7 216 40 96.5 94.1 7657 7848 7187 7 341 7466 91.4 -.325 50 100.0 100.0 100.0 60 7487 7645 ;7854 7182 7 404 -.268 100 7 212 7635 7676 25 perce nt Sil ver-Cadm' ium Ba th i Cu:?rent DensiJby.O .2 amp. / D m * . Effect of Free Cyanide KCN Composition of1 Deposit! Electrode Potentials JD ecomposition Potential G / L 10 £ Ag Bath 25 % A s Bath) Cy-an.Ba.tfiL Alloy Bath; Y / X ' \KAglCWJLj 10 % Ag Cd Bath • Cd Ag As : Od Ag ...... . ... i 0 91.5 78.8 7 547 7 210 7135 -1.050 - I S ) §5 7 210 7325 5 7738 r343 -.748 7 540 7130 -.282 7132 10 7788 7395 55.2 82.2 -.§00 7618 7126 -.056 t 096 20 49.3 7815 7448 -.843 7680 79.6 7115 -.050 -065 30 44.5 77.5 -.860 -7 28 7839 t 48 3 -109 - .043 7060 Tot al Metal Cone entration, 1 mol a l ; Curreiit De..,, -y, 0.2 amp s/Dm * Effect of Alkalia KOH G /L Composition of Deposit Percent Ag 0 5 10 20 30 10 % A s 78.8 64.5 58.2 51.0 44 •0 Bathi KCD Electrode Potential Cd Ag “ .644 -.423 -.299 -.675 -.266 -.690 -*263 -.680 - .67 2 - .278 10 G- L* Effect of Temperature Temp. °C. Electrode Pot ential Cd j Ag | -.786 ' -.393 -.705 -.383 -.685 -.387 -.722 -.388 KCE 10 G / L Composition of Deposit Percent Ag 78.0 20 88.6 40 90. 2 §0 95. 2 70 2 5 ^ .g B a t h ; Effect of Metal Concentration Metal Cone. Mols/L .1 .2 .4 .5 Composition of Deposit Percent Ag 82.3 91.7 97 .0 97.1 25 ^ As Bath; Electrode Potential Cd Ag -.786 -.719 - .552 - .485 KCE 10 -.390 -.357 -.295 -.265 G L. Effect of Current Density Current Density Amps.per Dm 3 .1 .2 .4 .6 25 % Ag Bath; Composition of Deposit Percent Ag KCH 90.2 88.2 72.5 45.3 10 G/L in Deposit 20 100 80 10 Silver •r-i P £ Mols/l. 100 Total Metal C on e. ,Mols/L. -1. Cadmium 80 £5 percent silver Percent Silver 60 40 10 percent Silver Silver 20 0 Percent Cyanide 100 30 -.90 80 Cadmium 60 +* .80 Silver in Deposit Potassium 5 10 15 20 25 Potassium Cyanide 10 percent Silver Silver i —<2i .70 - 20 65 0 20 25 30 Potassium Hydroxide 0 5 10 15 20 25 30 Potassium Hydroxide Silver-Cadmium Alloys percent Silver in Deposit 21 100 r-» a •H P C 80 p 25 percent Silver 40 in Deposit Silver Percent Silver 0 30 40 50 60 Temperature,° C . 70 Temperature, 100 °C. 10 >5 08 P tQ c CD n 60 25 percent Ag Bath 40 06 p a .04 G) £ O 20 Cd(CN) 02 0 10Q 2 .3 .4 .5 Current Density 6 Cathode Silver*Cadmium Alloys - 1.0 .4 .6 1.0 1.2-1.4 Potential 80 +> - .6 60 Silver 25 percent Ag Bath p o G) rH P3 20 1 in Deposit o o to o xi o 60 20 Percent C "mium amp/dm Copper 40 20 -j Silver i—I 100 20 40 60 §0 Percent Silver in Bath 0 20 40 60 80 100 Percent Silver in Bath Silver-Copper Alloys 22 SILVER-C OPPER Effect Composition of Bath Molal 7 , Ag 0 5 10 15 25 50 100 NaCN of 10 G / L Metal Ratio of Bath Electrode Potentials Copper Silver Composition of Deposit Molal % Ag 0 37.1 49.3 61.0 99.7 100.0 100.0 ALLOYS Decomposition Potential — — w.— -.635 — *011 -.083 -.284 -.076 ---— — -.083 - .054 -.052 -.114 ----.618 Current Density, 0.2 amps. per -.735 -.097 -.089 ----.071 -.065 -.056 D m 2. Effect of Free Cyanide NaCN G/L 0 5 10 20 30 Composition of Deposit Electrode Potential Decomposition Molal Percent Silver Silver | Copper Potential 5 7#Ag Bath (5 percent Ag Bath) 10 % Ag Bath 27.7 29.2 37.1 68.8 80.1 Effect NaOH G/L 55.8 44.3 49.3 98. 9 100.0 -.215 -.252 -.311 -.388 -.466 -.016 -.059 -.083 -.127 -.188 of Alkalie Effect Composition of Deposit Molal Percent Silver 55.8 0 66.8 5 5 3 16 10 15 49,0 39. 9 25 lver Bath. No Free Cyanide 1 0 # Si ..Curren t Density, 0a2 amps per D m 2 of -.027 -.068 -.097 -.157 -.240 Temperature Temp. Composition of Deposit Molal Percent Ag. °C. 10 Ag Bath 5 Ag 98. 9 20 38.5 40 97 .7 36.0 50 98.2 37.5 44.7 70 100.0 NaCI 10 G / L Dms . Cur]rent Density, 9* 2 a m p s / Effect of Current Density Current Density Amp s/Dm 2 .1 .2 .3 .4 Composition of Deposit 5 7 , Ag Bath 1C ' '.g Bath NaCN 20 G/L B3,uj 00 G/L 38.0 45.6 35.2 25. 2 100.0 100.0 100.0 94. 3 Si 100 10 percent / Silver / 80 £ O o H! -1-5 60 Decomposite 5 percent Silver Free Cyanide NaCN 10 G I 20 0 20 40 60 80 100 Percent Silver in Solution 0 Sodium Cyanide, G / L Potential -.24 P4 .16 Electrode Copper 5 Percent Silver Bath 0 in Deposit 5 10 15 20 25 30 Sodium Cyanide, G / L Silver 30 -p 100 ■a 100 5 percent Silver Bath 5 percent Silver NaCN 20 G / L 80 80 60 60 Percent 5 10 15 20 25 Sodium Cyanide , G / L r~i 40 ‘ H 40 m 20 20 0 0 .1 .3 2 .4 Current Density 5 Temperature,°C Silver-Copper Alloys SILVER-TIN ALLOYS Effect of Metal Ratio Composition Composition of Deposit Electrode Potential Cathode of Bath Decom position Percent (NaCN 10 G / l ) Silver Percent Ag Theo. CN Tin Potential NaCir' 10 tyL Silver 0 0 0 5 7 9.5 80.4 10 97 .0 91.0 25 97.4 98.1 50 100.0 100.0 100 100.0 100.0 Current D«m s i t y 0*2 ar ips. per d m 2 -.662 -.327 -.313 .-.290 -.265 -.211 -.201 -.160 -.205 -.618 -.778 -2270 -.260 -.166 -. 140 -.056 Effect of Free Cyanide NaCN Composition of Deposit G/L Percent Ag* From Baths ft Ag lOJAg £5 Ag 0 79.5 97.0 97.4 5 80.0 91.8 98. 2 ;10 80.4 98.1 91.0 20 80.1 90.2 98.0 30 79.3 91.2 97.6 Cathode Electrode Potentials Decomposition (10 perc ent A g ) Potential Tin Silver Effect of Alkalie NaOH G/L Composition of Deposit Percent Ag -.089 -. 150 -.201 -.220 -.239 Effect of Metdl Concentration of Temperature Deg. Cent. 20 40 50 70 10 Ag Bat i. NaCN 10 G L Temperature Composition of Deposit Percent Ag Composition of Deposit Percent Ag Total Mols per Liter 80.2 82.6 85.7 88.5 91.2 .1 42 .3 •* 4 .5 0 97.4 5 96.3 95.2 10 15 94.0 91.3 25 No Free Cyanide Effect -.140 -.221 -.260 -.281 -.301 -.276 -.295 -.313 -.316 -.317 Effect of Current Density Current Density Amps, per Dm? 91.0 93. 9 95.2 98.2 10 .10 .15 . 20 .30 .40 .50 Ag Bath. Composition of Deposit Percent Ag 100.0 94.5 91.0 91.3 91.7 92.4 N aCN 10 G L in Dcpjj 10 80 08 -p •H Percent Silver 60 4-0 20 10 percent Silver 5 10 15 20 Sodium Hydroxide 2 25 .4 .o Cathode *8 1*0 Potential rH Free C y a n i d e , . NaCH 10 G/L C* D. 0.2 amps / dm Percent Silver in Deposit Silver-Copper Alloys 100 Tin l—I 2 1- JL 0 20 40 60 80 100 Percent Silver in Solution 0 40 20 60 80 100 Percent Silver in Solution •p 1 0 0 Potential •H 90 Decomposition 80- 60 10 perctnt Silver 50 0 20 40 60 80 100 Percent Silver in Solution Silver-Tin Total iletal Con. ,Mols /L. Alloys in Deport silver JLQO. , * ---- f---- r 1 -- 1 •2 .4 £ a -P rz o *^ 10 percent Sliver 80 70 Percent 60 in Deposit ’I .2 f-i ° O -- A -7 H 10 percent Ag. Bath & » 5 ...... 30 . i .. _i---- 1---- ! 10 15 20 25 30 Sodium Cyanide 100 92 10 percent Silver Silver Percent ' Silver^.----- Cyanide Baths Free CyanidelOC/L C*D. 0.2 amp./dm2' . , 10 percent Silver 'A 84 88 o 84 80 0 in Deposit i Tin 5 percent Silver DO --- — I-- -U----J. 1 . L. 0 > 10 15 20 25 Sodium Cyanide oilver -1 ni 90 Q Percent —n ° 5 10 15 20 Sodium Hydroxide 80 25 Current Density *• 10 08 96 ■r-i co £ .06 o 92 +3 £ o £ 10 percent Silver 88 04 AgCN 84 80 20 30 40 50 60 Temperature 70 Silver-Tin .4 .6 .8 Cathode Alloys 1.0 1.2 1.4 'ot ential 27 COBALT-NICKEL ALLOYS Effect of Metal Ratio Effect of Metal Concentration Composition Composition t Cathode of Bath of Deposit !Decomposition Percent Co Percent Co Potential Total Metal Concentration Normality 0 0 “ .595 5 15.5 10 45.6 25 74.0 -.584 50 98-5 -.582 100 100.0 -.580 .Total Metal Cone. 1 No]rmal Effect of 10 percent Co-I i Bath Ratio , Current Density Effect of Current Density Temperature Composition Decomposition °C. of Deposit Potential Molal Co Co Ni Composition Of Deposit Percent Co -.595 -.410 -.383 -.330 -.335 -.595 -. 594 -.580 -.550 (UH4 J aS04 G / L 0 10 30 60 Decomposition Potential Co Ni -.580 -.612 - .662 -.7 20 -.5 95 -.640 -.6 90 -.750 Effect og Current Density Decompo sition Pot en^bial Co Ni 0 49.2 -.580 5 -.525 15 45.6 -.508 25 41. 2 -.507 10 pt?rcent Co-Ni Bath Currcsnt Density, 1 a m p . 38.0 0.5 45.6 1.0 51.5 1.5 57.0 2.0 1 Normal Solut ions 10 percent Co- Ni Bath Current Densit y 1 amp. Dm* Dm* Effect of Boric Acid 3b o 3 Composition G/l of Deposit Molal Co "Composition of Deposit Molal Co Effect of Ammonium Sulfate Decomposition Potential Co Ni 0 44.3 -.580 5 44.5 -.573 10 45.0 15 45 * 6 -.558 3° 46.3 -.502 10 pe rcent Co-Ni B*ith . Cur re:nt Density, 1 amp. pel' h Current Density Amps, per Dm®. -.580 -.400 -.370 Effect of Ammonium Chloride NH*C1 G- / L 24.5 33.0 39.4 45.6 0. 25 0.50 0.75 1.00 Temperature 20 54.4 40 48.0 50' 60 43.3 70 80 38.8 10 percent Co-Ni Bath Composition of DepositPercent CcJ Current Density ' Amp. /15m2 c -.595 . 0^10 -.540 .0025 1 -.525 .0050 -.525 .0100 .0300 DrI s .0600 Cathode Co in C0SO4 - . 215 - - ,352 t .410 -.480 - .525 -.528 ]Potential Ni in niso4 - . 295 -.398 -.440 -.465 - .499 -602 - .6 95 00 T6 H c3 2 t 59 - \ CD 4-3 S .58 fl o ■H 57 •H CO o 56 P h a o o £ t 55 20 [ 20 40 60 80 100 Percent Cobalt in Solution 100 40 60 80 0 20 ion Percent Cobalt in Solut 100 •H CO 01 O Ph 80 CD P £ 60 ■H 2. 80 4-3 i —I a’ _a 40 o o o o 40 4-3 p CD ■£ 20 0 .20 .4 .6 .8 1.0 Total Metal C o n e . ,Normality Current 1.0 1.5 Density ■'■0 +3 P 80 T O 60 Nickel CO Jj O £ P-t CD S o 4o0 o pn ° 40 Cobalt o 20 20 0 80 20 Cobalt-Nickel Alloys 70 Percent Cobalt in Deposit 29 100 80 •H 4-3 4-3 60 40 •H 1 Normal Solutions 10 percent Co Bath *H £0 15 30 Ammonium Chloride&/1 0 10 15 20 25 30 5 Ammonium Chloride,G-/L in Deposit 40 Decomposition Potential Percent 60 Cobalt 100 4-3 60 20 Cobalt Q 35 7 10 15 20 Boric Acid, C /D 25 6 5 Potential 7 08 Nickel .04 6 u St o 5 v. 0 10 20 30 40 50 60 AmmoniniQ S’&lfate,G-/L Cathode Cobalt-Nickel Alloys 30 SUMMARY OF Copper-Tin RESULTS Alloys 1* Copper content of the deposit varies with changes in condit­ ions as foll ow s; (a) Copper has the greater tendency to deposit, increasing rapidly with increasing copper to tin ratio in “bath. (L ) Increases with increasing total metal concentration. (cj Decreases with the addition of free cyanide. (d) Decreases with the addition of alkalie. (e) Decreases with increasing temperature. (f) Decreases with increasing current density. S. Increasing Copper to Tin ratio in the bath; la) Rapidly increases copper to tin ratio in the deposit. (b) Decreases(more positive) the copper equilibrium potenr tial, while that of tin is affected very little. (c) Decreases cathode decomposition potentials. 3. Increasing total metal concentration; (a) Increases(linearly) the copper content of the deposit. (b) Increases the equilibrium electrode potential of tin, while that of copper changes but very little. (c) Increases(more negative) decompoiemtioh potentials* 4. Addition of free cyanide; (a) Rapidly decreases copper content of the deposit. (b) Rapidly increases the electrode potentials of copper, but that of tin is affected but very little. (c) Rapidly increases(more negative) the decomposition potential of copper, and that of tin ic a lesser extent. 5. Addition of alkalie; (a) Slowly decreases the copper content of the deposit. (b) Decreases the equilibrium electrode potentials of Copper, and increases that of tin* (c) Rapidly changes the decomposition potential of copper to a more pegative value, while that of tin to a more negative one. 6. Increase of temperature; (a) Decreases the copper content to a minimum value, again increasing as the temperature rises. (b) Increases the electrode potentials of both copper and tin. 7. Increasing current density decreases copper content of deposit. Silver-Cadmium Alloys 1. Silver content of the deposit varies with changes in condit­ ions. as follows; la) Silver has the greatest tendency to deposit,increasing rapidly with increasing silver to cadmium ratio of bath, (b) Increases with increasing total metal concentration. 31 (c) (dj (e) (f) Decreases Decreases Increases Decreases with with with with the addition of free cyanide* the addition of alkalie. rising temperature. increasing current density* 2. Increasing silver to cadmium ratio in the "bath; (a) Rapidly increases silver content of the deposit. (b) Increases(more negative) the qquilibrium electrode potential of silver, while that of cadmium is decreased* 3. Increasing total metal concentration of bath; (a) Increases silver content of the deposit. (b) Decreases the equilibrium electrode potentials of both silver and cadmium, but cadmium at the greater rate. 4. Addition of free cyanidei (a) Decreases the silver content of the deposit. (b) Increases the electrode potentials of both metals. 5. Addition of alkalie * » (a) Decreases the silver content of the deposit. (b) Decreases the equilibrium electrode potential of cadmium to a slight extent,but increases that of silver. 6. Increase of temperature; (a) Slowly increases the silver content of the deposit. (b) Apparantly has no effect upon the equilibrium electrode potential of silver, but rapidly lowers that of cadminm. 7. Increasing current density rapidly lowers the silver content of the deposit. Silver-Copper Alloys 1.■Silver content of the deposit varies with changes in condit­ ions, as follows; (a) Silver has the greater tendency to deposit,increasing rapidly with decreasing copper to silver ratio of the bath. (bl Increases with increasing total metal concentration. (c) At first decreases with the addition of free cyanide, but quickly passes thru a minimum and rapidly increases. (d) Decreases with the addition of alkalie, giving the reverse effect of free cyanide. (e) Increases very slowly with rising temperature. (f) Increases with increasing current density, passing thru a maximum at moderate current density,and rapidly falling off. 2. Increasing silverv to copper ratio in the bath; (a) Rapidly increases the p e r c en t'silver in the deposit. (b) Decreases the equilibrium potentials of both metals. (c) Decomposition potentials become more positive. 32 3. Increasing total metal concentration of the hath; (a) Increases the silver content of the deposit. (h) Decreases the equilibrium electrode potentials of both metals, but to a greater extent for the silver. 4. Addition of free cyanide; (a) Causes a slight drop in the silver content of the deposit, passing thru a minimum, and rapidly increasing. (b) Rapidly shifts the equilibrium electrode potentials of both silver and copper to more negative values. (c) Causes the decomposition potentials to rapidly become more negative. 5. Addition of alKalie; (a) Decreases the silver content of the deposit. (b) Decreases the equilibrium electrode potential of copper, but increases that of silver. (c) Causes the decomposition potentials to become more negative. 6. Increasing temperature; (a) Slowly increases the silver content of the deposit. (b) Increases the equilibrium electrode potential of copper , but has very little effect upon that of silver. 7. Increasing current density causes the silver content of the deposit to decrease, after passing thru a maximum value. Silver-Tin Alloys 1. Silver content of the deposit varies depending upon conditions, as follows; (a) Silver has the greater tendency to deposit,increasing very rapidly with increasing silver content of the bath. (b) Increases as the total metal concentration increases. (c) Decreases slowly upon addition of free cyanide. (d) Decreases(linearly) with addition of alkalie. (e) Rapidly decreases with increasing current density. (f) Increases slowly with temperature,as a linear function. 2. Increasing silver to tin ratio in the bath; (a) Rapidly increases the silver content of the deposit. (b) Both silver and tin equilibrium electrode potentials becomes more positive. (c) Shifts the decomposition potentials to more positive values. 3. Increasing total metal concentration of the bath; (a) Increases the silver content of the deposit. (b) Decreases the. equilibrium electrode potentials. 4. Addition of free cyanidei (a) Slightly lowers the silver content of the deposit. (b) Shifts the equilibrium electrode potentials of both silver and tin to more negative values. (c) Rapidly shifts decompositions potentials to more negative values. Addition of :1 :alie; (a) Gradually lowers the silver content ,:e a linear function. (b) Shifts doth silver and tin electrode potentials to more negative values, hut that of tin more rabidly. (c) Shifts decomposition potentials to more negative values. Increase of temperature; (a) Slowly increases silver content of deposit(linearly). (h) Causes the tin electrode p o t e n t ! t o slowly become more negative, hut that of silver is practically “unaffected. Increasing current density rapidly decreases the silver content of the deposit. Cobalt-Nickel Alloys Cobalt content of the deposit varies with changes in conditions, as follows; (a) Cobalt has the greater tendency to deposit,increasing very rapidly with increasing cobalt to nickel ratio. (b) Increases with increasing total metal concentration. (c) Slowly increases with increasing temperature. (d) Slowly increases with increasing current density. (e) Is practically unaffected by the presence of chlorides or boric acid. Increase of cobalt to nickel ratio of bath; (a) Rapidly increases cobal# content of t deposit. (b)Changes eqmilibrium electrode potentials of both cobalt and nickel but very little. Increase of total metal - concentration; ■(a) Increases cobalt content of the deposit. (b) Shifts the equilibrium electrode potentials to more negative values. Addition of ammonium chloride; (a) Has no apparent affect upon the composition of the d ep osit. (b) Slightly lowers the decomposition potentials. Addition of boric acid; (a) Slightly lowers the cobalt content of the deposit. (b) Slightly lowers the decomposition potentials. Increasing temperature; (a) Slightly decreases the cobalj; content of the deposit. (b) Rapidly decreases the decomposition potentials of both metals. Increasing current density content of the deposit. slowly increases the cobalt 34 CONCLUSIONS When two or more different cations are present in solution, deposition of one may "be preferred over that of the other, for causes such asi (1) Metal ratio in solution, (2) Total metal concr centration, (3) Degree of ionization, (4) Electrode potentials,(5) Temperature, (6) Current Density, (7) Addition agents,18) M o b i l i t y of ions, and , (9) Overvoltage. The composition of deposits obtained under otherwise similar conditions depend upon the metal ratio in the solution. I n general, an increase in a metal ratio in solution increase s that metal ratio in the deposit. The rate of increase of a metal in the deposit varies from one combination to a n o t h e r depending upon the other factors involved, such as relative degrees of ionization, which determines the ratios of m e t a l ions present, relative electrode potentials, current density, and relative mobilities of the ions. In general, with increasing total metal concentration,there is an increase in that metal deposited which ordinarily has the greater tendency to deposit. This may be attributed to; (a) The increase in the number of prefered metal ions in the vicinity of the cathode which eliminat any possibility of a shortage of these ions available. (b) Increase in resulting common ions which may, according to the law of mass action, further shift the equilibrium poten­ tials of the more negative one having the smaller degree of ion­ ization. Due to the fact that the addition of substances with a common ion, or substances which form complex ions with the metal ions, and thus reduce the concentration of the metal ions pres­ ent, according to the Nernst equation, and the equilibrium elect'ode potential is repidly shifted to a more negative ^aiue. This nay in turn reverse the relative equilibrium potentials of the two metals in question, depending upon their degree of i o n i z a t i o n , and greatly change the composition of the deposited alley. Deposited alloys, in g e n er al , have a much finer structure than either of the component metals deposited separately under similar conditions. It may be assumed th&t each metal acts as an addition agent with respect to the other, in that each metal prevents the growth of the crystals of the other. In every case, the predominating metal present in the de­ posit, is the one having the most positive ele-"trode potential. Addition of complex ions, as cyanide, or ccmnou ions, reduced the simple metal ion concentration and rapidly charged the electrode potentials. Due to relative degrees of ionization of the complex metal ions, the addition of complex i cos changes the single electrode potentials at widely different, rates and results in 35 relatively cpfhplete reversed, value. In agreement with these, m all cases, radical changes in composition of the deposited alloys resulted. As a general rule, it can be seen from the results obtained that the proportion present has a relation to the proximity of the single electrode potentials to each other. Increase of temperature, in general, tends to favor the deposition of the more negative, less preferred metal. This may be due to a combination of the following reasons, which depending upon their relative values, give different net results (a) Reduces polarization and overvoltage, favoring the deposition of the more electropositive metal. (b) Increases mobility of the ions. The resulting change in composition of the deposit is due to the difference in the change in their mobilities. (c) Increases migration of ions, due to convestion current. This results in the same effect as agitation, favoring the more electronegative metal. (d) Rise in temperature may have the affect of changing the deposition potentials of one constituent more than the other, consequently, the composition of the deposited alloy will be such that there will be an increase in the percent of the matal h a v ­ ing the lowest(most positive) potential. Increasing current density, in nearly all cases, tends to decrease the percentage of the more easily deposited metal.In other words, increased current density tends to increase the percent of the metal deposited having the more negative p o t ­ ential. Other factors which no doubt enter into the problem of alloy deposition make certain cases difficult to explain, and fit any general rule. The formation of an entirely new phase on the cathode, solid solutions, with their own^ potentials,may result in further complicated facts, rendering it almost impos­ sible to apply conclusions drawn from a study of the individual component metals. The evidence that has been submitted here, has been restric­ ted to an attempted consideration of one factor at a time. In actual practice, all of these numerous factors act together,and it is difficult to distinguish or isolate the effect of any one variable. The actual deposit is the net result of all of these factors.