Chromium electroplating from trivalent chromium baths as an environmentally friendly alternative to hazardous hexavalent chromium baths: comparative study on advantages and disadvantages

摘要

In this communication, we present a generalization of our investigations concerning current state in the development of trivalent chromium baths as an environmentally friendly alternative to hazardous electroplating baths containing extremely toxic hexavalent chromium compounds. The main technological properties of sulfate trivalent chromium baths containing carbamide and formic acid as organic additives are described and compared to those typical of common Cr(Ⅵ) plating bath. It is shown that thick nanocrystalline chromium-carbon deposits may be obtained from the Cr(Ⅲ) electrolytes under study, with some physicochemical and service properties of such coatings exceeding those of "usual" chromium deposits. The proposed trivalent chromium baths are distinguished by their high current efficiency and electrodeposition rate. The covering power of the Cr(Ⅲ) baths is poorer than in case of hexavalent chromium baths; it may be improved by applying basic chromium sulfate (chrome tanning agent) instead of chromium sulfate as a source of Cr(Ⅲ) ions in solution. There is no need to utilize toxic lead anodes in Cr(Ⅲ) deposition processes. It is noted that a grave shortcoming of trivalent baths is their low conductivity in comparison with the hexavalent ones.