NEW Si₃N₄ CERAMICS WITH SUPERIOR HIGH-TEMPERATURE PROPERTIES

The high-temperature properties of Si₃N₄ ceramics with non-toxic, non-oxide additives AlN, AlN-ZrN, ZrN were investigated and compared with those of Si₃N₄ ceramics with additives MgO, MgO·Al₂O₃ and BeSiN₂. It is shown that the utilization of composite additive AlN-ZrN instead of BeSiN₂ avoids toxicity and enhances the room-temperature(RT)properties of the Si₃N₄ ceramics. AlN-ZrN as additive of Si₃N₄ instead of MgO·Al₂O₃ enhances the high-tempera-ture properties of the ceramics significantly:the oxidation rate constant at 1400℃ is two orders lower, while the ratio of bending strength at 1400℃ to bending strength at RT improves from 41.5%(for Si₃N₄+ MgO·Al₂O₃) to 71%(for Si₃N₄+ZrN-AlN)and the thermal shock resistance of the new ceramics is rather good(△Tc ≥ 900℃). It is prospective to use these new Si₃N₄ ceramics for high-temperature, high-stressed conditions.