Abstract
Carbon materials were fully covered with a molten silicate glass in order to improve their steam oxidation resistance and thermal cyclic fatigue. The wettability of the carbon to molten glass was modified by soaking in a Si-N precursor solvent followed by thermal decomposition. When glass coating was performed under higher N2 partial pressure, the molten glass completely sealed the carbon substrate and infiltrated into the interior without the production of cristobalite due to the oxidation of the pyrolyzed species. However, coating under a lower N2 partial pressure, such as an Ar atmosphere, led to the formation of cristobalite at the interface between the carbon substrate and silicate glass. In this case, the glass covered only the surface of the substrate and many pores formed at the interface. The pores formed as a result of the production of large amounts of CO from oxidation of the carbon substrate. The structural changes of the interface, resulting from differences in the N2 partial pressure during sealing with glass, are in good agreement with thermodynamic considerations. The coating of molten glass on carbon substrates under higher N2 partial pressure significantly improved the thermal cyclic fatigue of the carbon substrates in addition to the steam oxidation resistance.
