Corrosion studies of CVD diamond coated molybdenum, evaluation of equivalent circuit and the effect of pinholes in diamond film on cyclic voltammetric behavior

Boron-doped diamond films have been deposited on molybdenum substrates by a microwave plasma CVD process using a methane and hydrogen gas mixture at a pressure of 35.7 Torr. Boron doping of diamond has been achieved in-situ by using a solid boron source while growing the diamond in the CVD process. Electrochemical polarization measurement in the Tafel regime have been used to evaluate the boron-doped diamond, undoped diamond, molybdenum, platinum, palladium, gold, and silver electrode materials for corrosion resistance characteristics in terms of charge-transfer coefficients and corrosion rate in 0.5 M NaCl solution. Diamond has shown the highest corrosion resistance and is better than the precious materials. Cyclic voltammetry has been used to evaluate the presence of pinholes in the diamond films grown on molybdenum substrates in 1 M KNO3 solution. AC impedance has been used to determine the double-layer parameters and to fit the experimental data to validate the equivalent circuit corresponding to molybdenum/solution and diamond/solution interface. (C) 1997 Elsevier Science Ltd.