Hard chromium electrodeposition from a trivalent chromium bath containing water-soluble polymer

摘要

The effect of polyvinylpyrrolidones (PVPs) with different molecular weights as polymeric additives to a sulfate trivalent chromium bath was ascertained. Introduction of PVPs to the plating bath was stated to result in improvement in the surface appearance of chromium deposits and stabilization of current efficiency value in long-term electrolysis. The rate of metal deposition is practically independent of the deposition time. Thus, using PVP additive allows one to obtain high-quality Cr-coatings with a thickness of several tens of micrometers. It is found by means of turbidimetric analysis that the polymer additive has an accelerating effect on the aggregation of particles of the chromium (Ⅲ) hydroxide sol formed in the near-electrode layer.