Molten‐Salt Corrosion of Silicon Nitride: II, Sodium Sulfate

Abstract

The corrosion mechanism of Si 3 N 4 + Na 2 SO 4 /O 2 at 1000°C was investigated. Corrosion of both pure and additive‐containing Si 3 N 4 was studied. The reaction of Si 3 N 4 + Na 2 SO 4 consists of an initial period of slow weight loss due to Na 2 SO 4 vaporization and oxidation‐dissolution. This initial period was the same for all forms of Si 3 N 4 . A second region consisted of further oxidation or near termination of reaction, depending on the additive in the Si 3 N 4 . A 5‐ to 10‐μm yttrium depletion zone was found after corrosion for the Si 3 N 4 with yttria additives. For comparison, Si and SiC were corroded under similar conditions. These materials corroded substantially faster than all forms of Si 3 N 4 .