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 mi xture at a pressure of 35.7 Torr. Boron doping of diamond has been ach ieved in-situ by using a solid boron source while growing the diamond in the CVD process. Electrochemical polarization measurement in the Ta fel 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. Diamo nd has shown the highest corrosion resistance and is better than the p recious materials. Cyclic voltammetry has been used to evaluate the pr esence of pinholes in the diamond films grown on molybdenum substrates in 1 M KNO3 solution. AC impedance has been used to determine the dou ble-layer parameters and to fit the experimental data to validate the equivalent circuit corresponding to molybdenum/solution and diamond/so lution interface. (C) 1997 Elsevier Science Ltd.