Influence of the Citrate Solution Composition on the Autocatalytic Deposition of Nickel–Phosphorus–Tungsten Alloy

The influence of buffering additives on the tungsten and phosphorus content in chemically deposited nickel–phosphorus–tungsten alloy and coating deposition rated has been studied. It has been shown that an ammonia citrate solution fails in obtaining high-tungsten coatings. Sodium tetraborate used as a buffering additive makes it possible to raise the deposition rate and tungsten content. It has been found that when the citric acid concentration in the solution grows to 20 g/L, the alloy deposition rate increases and the tungsten content rises. However, a further increase in citric acid concentration results in a sharp drop of deposition rate without increasing the tungsten fraction in the alloy. The use of citrate–succinate solution allows one to considerably improve the deposition rate without decreasing the tungsten fraction in the alloy. As in the case of citrate solution, the deposition rate goes though a maximum as the succinic acid concentration grows.