ELECTROCHEMICAL-BEHAVIOR OF MOLYBDENUM COATED WITH FLAME CVD POLYCRYSTALLINE DIAMOND FILM

Although natural diamond is a complete chemically-inert material for a wide range of aggressive environments, its comparative scarcity and p roblems for coating design have hampered its utility as a corrosion pr otective coating. The recent discovery and development of chemical vap our deposition methods for growing diamond crystals and polycrystallin e diamond films has opened up a wide range of applications thanks to t heir excellent tribological, electronic and optical properties. Variou s applications are in progress for corrosion and combined wear and cor rosion protection. This paper presents the first study of the corrosio n behaviour of continuous polycrystalline diamond films using electroc hemical impedance electroscopy. Diamond films have been deposited on m olybdenum substrates by means of the acetylene flame combustion method (FCVD). Electrochemical behaviour has been studied in a 0.6 M NaCl so lution, it being seen that despite the inert character and apparent co ntinuity of the film, there are areas of the base material which are e xposed to the electrolyte. This behaviour has been modelled by means o f an equivalent circuit which allows for the corroboration of the prop osed mechanism. (C) 1997 Elsevier Science S.A.