Abstract:
In this paper we report, for the first time, a new approach for synthesis of high quality faceted microcrystalline coatings
of molybdenum (Mo), tungsten (W), their carbides and composites. These studies are carried out using Hot Filament
Chemical Vapor Deposition (HF-CVD) method wherein parent materials (Mo and/or W) are taken in the form of wires
(~0.5 mm dia) and are heated to a high temperature (TF ~ 1500 - 2000C), in ambient of “oxygen (O2) diluted hydrogen
(H2) gas”. Due to high filament temperature (TF), a series of pyrolytic reactions take place. Firstly, the gasification of
wire material (Mo and/or W) occurs in the form of its oxide. The oxide molecules reach the substrate which is kept underneath
the filament assembly. Secondly, molecular hydrogen gets dissociated into atomic hydrogen and subsequently
reaches the substrate to react with oxide molecules, finally leading to the precipitation of a pure metal. This method can
also be used, in situ, to convert metallic coatings into their carbides and/or composites. The method offers many other
attractive features, which can not be rendered by the conventional CVD/PVD methods. The results are discussed in
terms of temperature induced “Red-ox” reactions.
