The Electrodeposition of Cobalt-Tungsten-Molybdenum Alloys from Aqueous Citrate Solutions

Abstract

The electrodeposition of cobalt‐tungsten‐molybdenum alloys is described. The aqueous plating bath was prepared from sodium tungstate, sodium molybdate, cobalt sulfate, and citric acid. The pH of the solution was adjusted by the addition of either ammonium hydroxide or dilute sulfuric acid. A Hull cell and regular plating procedures were used to determine optimum bath concentrations and electrolysis conditions. It was found that a bath containing 0.23 mole per liter of cobalt sulfate, a total of 0.23 mole per liter of sodium tungstate and sodium molybdate (W:Mo mole ratio of 7:3), and 0.31 mole per liter of citric acid gave satisfactory performance. When this plating solution was adjusted to pH 4 and maintained at 25°C, electrolysis at 5 amp/dm² gave a cathode deposit containing 66 per cent cobalt, 21 per cent molybdenum, and 13 per cent tungsten with a cathode current efficiency of 73 per cent.