Properties of Si3N4 Produced by Nitriding Slip-Cast Si Containing Si3N4 Grog Additions

The properties of Si3N4 compositions produced by nitriding slip-cast Si bodies containing up to 16% Si3N4 grog were determined. The introduction of grog consistently lowered the densities, the room- and high-temperature strengths, and the resistance to oxidation. The open structure of the grog-containing mixes favored low-temperature gas-phase reactions leading to α-Si3N4 formation. In higher-density compositions containing predominantly Si, gas-liquid-solid reactions at higher temperatures produced a relatively greater content of the β phase.