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How does the silica-glass layer protect silicon carbide heating elements?

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Figure 1: Schematic diagram of a zirconia oxygen sensor used to monitor automobile exhaust gases. The sensor, approximately the size of a spark plug, is fitted into the exhaust manifold of an automobile engine. The thimble-shaped zirconia sensor, sandwiched between thin layers of porous platinum, is exposed on its interior to outside air and on its exterior to exhaust gas passing through slits in the sensor shield. The two platinum surfaces serve as electrodes, conducting a voltage across the zirconia that varies according to the difference in oxygen content between the exhaust gas and the outside air.
conductive ceramics Figure 1: Schematic diagram of a zirconia oxygen sensor used to monitor automobile exhaust gases. The sensor, approximately the size of a spark plug, is fitted into the exhaust manifold of an automobile engine. The thimble-shaped zirconia sensor, sandwiched between thin layers of porous platinum, is exposed on its interior to outside air and on its exterior to exhaust gas passing through slits in the sensor shield. The two platinum surfaces serve as electrodes, conducting a voltage across the zirconia that varies according to the difference in oxygen content between the exhaust gas and the outside air.

Silicon carbide (SiC) is a conductive ceramic frequently utilized as a heating element in electric furnaces due to its effectiveness in high-temperature, oxidizing environments.1

When exposed to these oxidizing atmospheres, silicon carbide forms a protective surface layer of silica-glass (silicon dioxide). This layer acts as a barrier that prevents further oxidation of the underlying material, allowing the heating element to maintain its integrity and performance at temperatures up to 1,500 °C (2,730 °F).12