The Electrodeposition of Nickel‐Cobalt‐Tungsten Alloys from an Acid Plating Bath

Abstract

The electrodeposition of nickel‐cobalt‐tungsten alloys from an aqueous plating bath is reported. The most satisfactory bath was found to be a modified Fink and Lah borate type of nickel‐cobalt bath to which was added a small amount of sodium tungstate. The effect of bath temperature, bath pH and current density on the cathode current efficiency and on the composition of the alloy deposit was studied. The tungsten content of the alloy deposit on the cathode varied from less than 1% to about 10% W and was found to increase in this range with: (a) higher tungsten content of the bath; (b) higher bath pH; and (c) lower current density. The appearance of the deposits was in general improved by raising the bath temperature but the tungsten content of the alloy was somewhat less at the higher temperatures. The cathode current efficiency of the nickel‐cobalt‐tungsten bath was found to be somewhat less than the efficiency of the nickel‐cobalt bath and varied somewhat with electrolysis conditions. A bright, adherent nickel‐cobalt‐tungsten alloy was obtained on electrolysis, at a current density of 1 to 3 amp./dm. 2 , of a bath containing 240 g./L NiSO 4 . 6 H 2 O , 21 g./L NiCl 2 . 6 H 2 O , 12 g./L CoSO 4.7 H 2 O , 30 g./L H 3 BO 3 and 3.6 g./L Na 2 WO 4 . 2 H 2 O with a pH of 4 to 4.5 and a temperature of 65° C to 75° C. These Ni‐Co‐W alloy deposits were found to have no special corrosion‐resistant properties.