Research On Preparation And Properties Of Porous Silicon Nitride Ceramics

With the prompt development of industry and urbanization process, nowdays, our country is faced with the severe problem of water pollution and air pollution, how to effectively use the environmental control technology is an important topic in today’s social environment and economy coordinated development. The traditional catalyst supports have the disadvantage of low strength, poor acid resistance, high temperature expansion coefficient and so on, there are inherent deficiencies in the application of exhaust gas treatment and sewage treatment. Porous silicon nitride ceramics with high corrosion resistance, thermal shock resistance and excellent mechanical properties have a broad prospect in the application of new catalyst support. So how to prepare the porous silicon nitride ceramics with higher strength and better comprehensive performance have become the key point of this research.To prepare porous silicon nitride ceramics, starch, rice husk, sawdust and Mg O, Y₂O₃, Al₂O₃, Zr O₂ were separate used as pore forming agent and sintering aids,using α-Si₃N₄ that it is the ain raw material. The effects of content and kinds of pore forming agent and sintering aids, different sintering process on the properties, phase composition and microstructure of porous silicon nitride ceramics were researched.Porous silicon nitride ceramics were prepared and properties of porous silicon nitride ceramics were researched with three kinds of pore-forming agent including starch, rice husk, sawdust as pore forming agents, and five kinds of parameters including 0%, 10%, 20%, 30%,40%. The experimental results show that with the increase of the amount of pore forming agent content, the bending strength of silicon nitride ceramics showed a decreasing trend, the apparent porosity and water absorption firstly, and then the volume density decreased and then increased. The pore forming effect of starch is best in three kinds of pore forming agent. When the starch content was 30% and the adding amount of sintering aids was 8%（Y₂O₃:A1₂O₃=6:2）, the flexural strength of porous silicon nitride ceramics was 53.2 MPa, and the porosity was 43.6%.Mg O, Y₂O₃, Al₂O₃, Zr O₂ and starch were separate used as sintering aids and the pore forming agent, the sintering mechanism of Mg O, Y₂O₃, Y₂O₃-Al₂O₃, Mg O-Al₂O₃ were analyzed, the effects of content and kinds of sintering aids on the properties, phase composition and microstructure of porous silicon nitride ceramics were researched. The experimental results show that with the increase of sintering aids content, porous ceramic flexural strength increased first and then decreased, apparent porosity decreased first and then increased. The properties of porous silicon nitride ceramics by adding composite sintering were better than single, the flexural strength of porous silicon nitride ceramics was increased by adding Zr O₂. When 6%Y₂O₃, 4%Al₂O₃, 3%Zr O₂ and starch were respectively used as a sintering aids and the pore forming agent, it can be prepared porous ceramic products that its flexural strength and significant porosity is separate 68.7 MPa and 43.7%.Porous silicon nitride ceramics were prepared by SPS sintering technology,The effect of sintering temperature and holding time on the properties of porous silicon nitride ceramics were discussed, the properties of porous ceramic products were compared by comparing with normal pressure sintering and SPS sintering process. The experimental results show that SPS sintering process can reduce the sintering temperature of silicon nitride ceramics and the sintering time, compared to the normal sintering, the density of ceramic products by SPS sintering technology were higher. The optimum sintering temperature of porous silicon nitride ceramics sintered by SPS process was around 1500℃, and the optimum holding time was about 5 min by analyzing the properties of the prepared ceramic samples. When the adding amount of sintering aids was 8%（Y₂O₃:A1₂O₃=6:2）, and the starch content was 30%, the flexural strength of porous silicon nitride ceramics was 59.6 MPa, and the porosity was 37.3% under the temperature of 1500℃ for holding 5 min.