Nickel-molybdenum, cobalt-molybdenum, and iron-molybdenum alloys have been electrodeposited, from aqueous solutions containing sodium molybdate, the sulfate of the codeposited metal, sodium citrate, and ammonium hydroxide. Typical baths were made up with 0.3 M/1 of the codepositing metal sulfate, 0.3 M/1 of sodium citrate, varying amounts of sodium molybdate, and ammonium hydroxide to pH about 10.5. The maximum amount of molybdenum in the electrodeposited alloys depends on the alloying metal. When a typical bath was used, nickel alloys were found to contain up to 20% molybdenum, cobalt alloys contained up to 40% molybdenum, and iron alloys contained about 50% molybdenum. The cathode current efficiency in the above cases ranged from 75-85% for the nickel-molybdenum bath, 50-60% for cobalt-molybdenum, and 10-20% for iron-molybdenum. The effects of pH, concentration, temperature, and cathode current density on cathode current efficiency and alloy composition were studied.These electrodeposited molybdenum alloys were metallic and either bright or light gray in appearance, with a large number of cracks in the bright deposits. Adherence of the deposit to well-cleaned flat cathodes seemed to be good, but adherence to tubing or rods was poor; usually these deposits could be brushed off in flake or powder form.

Cathode potential measurements are used to explain the cathode reactions that result in the electrodeposition of molybdenum alloys. Potentials were measured by the direct method during the electrolysis of aqueous ammoniacal citrate solutions containing sodium molybdate and the sulfate of a codepositing metal, iron, nickel, or cobalt. The results indicate that the reduction of molybdate ion in this type of bath is probably not accomplished in one step with six electrons, but with one, two, or three electrons depending on the codepositing metal and its oxidation state in the bath. The results also indicate that hydrogen is involved in the molybdate reduction process. A two‐step mechanism for the reduction of molybdate ion in the presence of a codepositing metal is proposed and an explanation of why this metal must be iron, cobalt, or nickel rather than such metals as chromium, manganese, copper, or zinc is presented.

A "catalytic reduction" theory is proposed to explain the electrolytic reduction of aqueous tungstate solutions in the presence of codepositing metals such as iron, nickel, and cobalt. Two cathode reactions are suggested as being essential to the reduction process:Reaction A proceeds until the cathode is covered with a thin deposit of metal, IV[, which then acts as a catalyst for reaction B. When this metal catalyst is covered with a layer of tungsten reaction B stops and reaction A again proceeds to give a new catalyst surface; thus alternate layers of metal (Ni, Co, or Fe) and tungsten are deposited on the cathode. Evidence for this postulated mechanism is based in part OR polarographic studies, cathode potential measurements, and the laminated structure of the cathode deposits.

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A new aqueous citrate plating bath for the electrodeposition of alloys of molybdenum with cobalt, iron, and nickel is described. This type of plating solution contains the sulfate of the codepositing metal citric acid, and sodium molybdate. Ammonium hydroxide is used for adjusting the pH of the solution. A bath temperature of about 25 C is preferred. Experimental results, obtained by using the Hull cell for qualitative information and regular plating procedures for quantitative data, show the effect of bath pH, concentration of sodium molybdate, and cathode current density on the performance of the plating baths. The highest percentage of molybdenum (about 50% and more) is obtained with iron as the codepositing metal, and the lowest is with nickel.