Microstructure and Thermal Shock Resistance of Molten Glass‐Coated Carbon Materials Fabricated by Interfacial Control

Carbon substrates were coated completely with a molten silicate glass, where the wettability of carbon to glass was improved by infiltration and pyrolysis of perhydropolysilazane. Microstructures of the carbon–glass interface were dependent on Pn2 during coating. Coating at lower Pn2 induced the formation of cristobalite at the carbon–glass interface. When the coating was performed at higher Pn2, the glass and carbon were strongly adhered, without the formation of cristobalite. Coating at higher Pn2 improved the thermal shock resistance of the glass layer, because crack initiation was not induced by the phase transformation of cristobalite during the cooling process. In the case of coating at higher Pn2, an oxynitride glass layer was formed at the glass subsurface by dissolution of N2. A porous glass subsurface layer with uniform spherical micro-pores could be produced by soaking near the glass transition temperature in a steam environment. The porous layer with fine and homogeneous microstructure acts as a thermal shock absorbing layer, so that glass-coated carbon with a porous glass layer has excellent thermal shock resistance in addition to steam oxidation resistance.