ENVIRONMENTALLY ACCEPTABLE PROCESS FOR ELECTRODEPOSITION OF HARD CHROMIUM FROM CHROMIUM(III) ELECTROLYTE

In engineering applications the hexavalent chromium plating process provides excellent wear and corrosion resistant coatings (50-100 mu m). However, this process is based on the highly toxic and environmentally unacceptable chromium (VI) electrolytes. Persistent attempts over many years, have been made to deposit a thick coating of high quality chromium from environmentally more acceptable chromium (III) electrolytes to replace the chromium (VI) process. The most successful studies have shown that it is possible to produce thick coatings of chromium (III) electrolytes bur due to the very slow rate metal deposition Sailing to about 1 mu m/hr, the process is unsuitable as a commercially viable hard chromium system. The present project has developed a laboratory scale high speed electrodeposition process based on chromium (III) electrolyte. This paper reports on an investigation in to the enhanced plating rate (300 mu m/hr) using high flow rates and high current density system. Excellent quality deposits were obtained using this process. The quality, structure and properties of the deposits have been examined and related to the prevailing electrohydrometallurgical condition thereby providing quantitative and qualitative data on which to base the engineering design of an advanced environmentally acceptable plating system.