Preparation and Characterization of Cr-Co-P Alloy Coating Electrodeposited from Trivalent Chromium Solution

Abstract

Cr-Co-P alloy coating was prepared from trivalent chromium bath and the appearance and performances of the coating were characterized. The Cr-Co-P alloy electroplating bath was prepared through orderly adding cobalt chloride, sodium hypophosphite monohydrate, urea, sodium format, ammonium citrate tribasic, boric acid, and ammonium brome into distilled water. Optimum plating crafts were determined as follows: pH value 1.5~3.0, temperature 25~45°C, plating time 1~15 minutes, and current density 5~25A·cm-2. Reticulate iridium dioxide coating electrode or highly pure graphite electrode were adopted as anode. And electro deposition experiments were carried out with air disturbance. The surfaces of deposited coatings are silvery white, bright and smooth. The Cr-Co-P alloy coatings were characterized by scanning electronic microscope (SEM). The results proved that P is favour to the improvement of deposit corrosion resistance. In addition, Cobalt atoms are in favor of enhancing throwing power and cover power of plating baths. Via adjusting plating bath, the electro-deposition rate could reach at 1.0~1.3μm·min-1, and the contents of P and Co could be controlled in 15~25% and 10~65%.