Oxide Coating on Carbon Surface and Mechanism of Antioxidation

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In order to find out the conditions for antioxidation coating of some oxide films on carbon materials, the fundamental studies on the following two points were carried out; 1) oxide coating by using sol-gel method and 2) oxidation mechanism of metal carbides.By selecting the suitable metal alkoxides and employing a simple dipping process, the films of ZrO_2, SiO_2 and also ZrSiO_4 were coated on the carbon materials. The viscosity of the alkoxide solutions was found to govern the thickness of oxide films. In order to get homogeneous film of ZrSiO_4, it was found to be essential to control the hydrolysis rates of each alkoxide.From the kinetic studies of oxidation of TiC and ZrC the diffusion of oxygen was found to be a rate-determining process. For both carbides, a formation of intermadiate layer between carbide and oxide was observed. For TiC, this intermediate layers are supposed to consist of titanium oxycarbide and suboxides. For ZrC, the segregation of carbon was expected, possibly diamond structure. The experimental results suggest the importance of these intermediate layers for having good adhesion between carbide and oxide.