Abstract
Two layers oxidation protecting coatings of SiC and mullite were successfully created on the graphite substrate by pack cementation and plasma spray methods, respectively. Phase synthesis was studied by X-ray diffraction. Microstructure and morphology were investigated by optical and scanning electron microscopes (SEM). X-ray diffraction results of the first coating showed that the secondary SiC was completely synthesised by the heat treatment of Si, Al2O3, C and SiC at 1500°C. Alumina and kaolin reaction at 1400°C led to the formation of mullite as the second layer. The oxidation resistance of two layers coating was considerably improved in comparison with mono layer coating and raw graphite. Oxidation resistance was decreased at higher temperatures in all samples. Formation of SiO2 glassy phase improved the graphite oxidation resistance which was confirmed by SEM.
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