Preparation And Properties Of Porous Silicon Nitride Ceramics

Porous silicon nitride ceramic, a new type structural and functional ceramic manufactured in recent years, has been widely concerned for their high performance and wide application, and applied in lots of fields.In this article silicon nitride powder first prepared by direct nitriding method, then silicon nitride ceramics prepared by carbothermal reduction-pressureless sintering. And by changing the sintering system, ratio of powder and adhesive type, silicon nitride was studied from the method of the preparation and the characteristics of the porous ceramics.High performance porous silicon nitride powder was prepared by silicon powder nitrogen nitriding directly method. The mechanism was investigated by thermodynamic calculation and TG-DTA analysis, and the reaction was exthermic reaction, the Gibbs free energy was under zero at the 1400?, at this temperature the reaction was spontaneous reaction. The results of XRD, SEM and grain size showed: the silicon nitride powder was mainly composed of piece of the massive ?-Si₃N₄ grain; the product had a uniform distribution and grain combined with relatively close. The uniform particle size D₅₀ is 6.59 microns.High performance porous silicon nitride ceramic was prepared by carbonthermal reduction-pressureless sintering. By thermodynamic calculation and TG-DTA analysis, the results showed that carbonthermal reduction sintering was endothermic reaction and the Gibbs free energy decreases with the increase of temperature, the reaction started when the temperature was 1472?. The results of XRD, SEM and MIP showed that the product was mainly composed of needle-like ?-Si₃N₄ grains. It was conducive to the formation and development of ?-Si₃N₄ grains at the temperature of 1200 ? of pre-sintering system. The product had a uniform distribution and a combination of tight grains, and the ratio of length to diameter of ?-Si₃N₄ grains was higher. Pore volume and porosity of the product was 0.554 m L·g^-1 and 48.04%.The porous silicon nitride ceramic was prepared by different proportions of reaction materials. By TG-DTA, XRD, SEM and MIP analyzes, the results showed that the porous silicon nitride ceramics were mainly composed of needle-like ?-Si₃N₄ grains. The reaction material of 50 wt.% ?-Si₃N₄ was conducive to the formation and development of ?-Si₃N₄ grains. The product had a uniform distribution and a combination of tight grains, and the ratio of length to diameter of ?-Si₃N₄ grains was higher.Porous silicon nitride ceramic was prepared by different adhesives. With TG-DTA, XRD, SEM and MIP analysis, the results showed that the porous silicon nitride ceramics were mainly composed of needle-like ?-Si₃N₄ grains. The PVA was conducive to the formation and development of ?-Si₃N₄ grains. The product had a uniform distribution and a combination of tight grains, and the ratio of length to diameter of Si₃N₄ grains was higher. Pore volume and porosity of the product was 0.142 m L·g^-1 and 22.35%.