Electrochimica Acta, Vol.54, No.2, 370-375, 2008
Characterisation of electrodeposited Co-W-P amorphous coatings on carbon steel
Electrochemistry and nucleation mechanism of induced co-deposition of cobalt, tungsten and phosphorus from a citrate bath was investigated using voltammetry and chronoamperometry techniques. it was found that the induced co-deposition of the species occurred under diffusion control and followed instantaneous nucleation mechanism. Co-W-P coatings were electrodeposited potentiostatically on plain carbon steels from a citrate bath containing CoSO4, Na2WO4 and NaH2PO2. X-ray diffraction studies of the coatings revealed that the as-deposited Co81W10P9 coatings had amorphous structure. The formation of some stoichiometric compounds like Co3W, Co2P and WP2, however, was observed upon annealing at 600 degrees C. The hardness of the Co-W-P coatings increased with annealing temperature which was possibly due to the formation of these inter-elemental compounds. The corrosion resistance of the Co-W-P coatings increased with increase in annealing temperature which might also be due to the formation of the stoichiometric compounds at elevated temperatures. A comparison between coating characteristics of Co-W-P and chromium showed that the Co-W-P coatings exhibited nobler corrosion potential than chromium coatings. (c) 2008 Elsevier Ltd. All rights reserved.