Preparation Of β-Sialon From Kaolin-hydrazine Intercalation Complex

The preparation of β-Sialon powders from kaolin intercalation complex by carbothemal reduction and simultaneous nitration were studied. The aim of the try is that Nitrogen which was needed in the nitration would be from the entraining agents disassembled, and to make the temperature of the preparation down. This method would reduce the cost and predigest the equipments of the preparation, accelerate the preparation of β-Sialon go to the industrialization. Kaolin is one of the abundant nonmetal mineral resources,which has special layer structure. The organic molecule can intercalate in the layers of kaolin, combine the characteristic of the slime mineral and organic compound, widen and improve the application field of kaolin. The study of the intercalation of kaolin can be tracked to early 1960s. More than 300 kaolin derivatives have been reported. Among the large number of compounds that have in the interlayer of kaolin minerals, only a few of polar compounds can intercalate kaolin directly. These compounds are termed entraining agents. Example entraining agents include formamide, dimethyl sulfoxide (DMSO), hydrazine and urea, imidazole, and potassium acetate in solution. Hydrazine is one of the most commonly used entraining agents and it intercalates kaolin faster than most other compounds do. Furthermore, hydrazine can be disjoining into N2 and NH3, which would join the nitration of the preparation to synthesize β-Sialon powders. Sialon is composed of Si,Al,O and N, it has the same structure as Si3N4, and in the structure some Al and O replace the points of Si and N. Sialon have several diverse phases, such as α-Sialon,β-Sialon and Ο-Sialon et al, due to the different content of Al and O. The capability of β-Sialon on high temperature is excellent. So it is as the new fire-resistant material in 21th to empolder. β-Sialon can be bond with other materials, for example, corundum and SiC et al. The compounds have the strongpoint of the two materials. The cost was so highly, it is the biggest hindrance on the far-ranging application of β-Sialon. So it was studied wildly, after somebody found the method, synthesize β-Sialon by carbothemal reduction and simultaneous nitration clay and carbon. Kaolin is the fit material to synthesize β-Sialon of all the clays, because it has the same Si/Al rate as β-Sialon. There many reports about the preparation of β-Sialon from kaolin, but the studies did not solve some problems all the same. The temperature of the preparation is high, can not mix the stuffs equably, and so on. Someone used the kaolin intercalation complex to successfully synthesize β-Sialon powders; the organic matter in the layers of kaolin provided the carbon in the carbothemal reduction reaction. The temperature of the preparation was reduced. Consider the experiences of the reporters previously; we used kaolin-hydrazine intercalation complex to synthesize β-Sialon powders. The entraining organic matter can disjoin N2 and NH3 to join the nitration reaction, when it was heated. After analyze the results, the conclusions are that: Ⅰ. Hydrazine monohydrate solution (50%) as entraining agents, react in the solution, kaolin-hydrazine intercalation complex was made. β-Sialon whiskers were composed from kaolin-hydrazine intercalation complex and kaolin respectively by carbothemal reduction and simultaneous nitration at 1000℃. But the production was compound, include mullite and cristobalite. The sample from kaolin is including Si3N4, because the reaction is not completed. In the same reaction environment, the rate of the reaction is different, the rate of the sample from kaolin-hydrazine intercalation complex higher than the other. Ⅱ. Nitrogen come from the abruption of Hydrazine is not enough to complete the nitration reaction, so there is not Sialon or Si3N4 in the production. This result is perhaps due to at low temperature Hydrazine was disappearing for its abruption. Ⅲ. In the reductive atmosphere, the samples composed from kaolin-hydrazine intercalation complex at 1280℃and 1450℃, which FTIR spectra have absorption bands due to Si-N vibrations. The reason is maybe that the ammonium nitrate in the...