Effects of synthesis temperature and raw materials composition on preparation of β-Sialon based composites from fly ash

β-Sialon based composites were successfully prepared from fly ash and carbon black under nitrogen atmosphere by carbothermal reduction-nitridation process. Effects of heating temperature and raw materials composition on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by X-ray diffraction and scanning electronic microscopy. The results show that increasing heating temperature or mass ratio of carbon black to fly ash can promote the formation of β-Sialon. The β-Sialon based composites can be synthesized at 1723 K for 6 h while heating the sample with mass ratio of carbon black to fly ash of 0.56. The as-received β-Sialon in the composites exists as granular with an average particle size of 2-3 μm. The preparation process of β-Sialon based composites includes the formation of O′-Sialon, X-Sialon and β-Sialon as well as the conversion processes of O′-Sialon and X-Sialon to β-Sialon.

Preparation and Microstructure of Bauxite-Based Sialon by Reduction Nitridation

The phase composition and microstructure of Sialon prepared from Chinese bauxite have been studied. The use of Si powder is more effective than that of activated carbon for reduction-nitridation. For bauxite specimens with 40～50% Si addition, more than 90% of Sialon may be obtained when nitrided at 1450～1500℃; the main crystalline phase is O′-Sialon (Z=0.2).

Fabrication of β-Sialon/ZrN/ZrON composites using fly ash and zircon

β-Sialon/ZrN/ZrON composites were successfully fabricated by an in-situ carbothermal reduction？nitridation process with fly ash, zircon and active carbon as raw materials. The effects of raw materials composition and holding time on synthesis process were investigated, and the formation process of the composites was also discussed. The phase composition and microstructure of the composites were characterized by means of XRD and SEM. It was found that increasing carbon content in a sample and holding time could promote the formation of β-Sialon, ZrN and ZrON. The proper processing parameters to synthesize β-Sialon/ZrN/ZrON composites were mass ratio of zircon to fly ash to active carbon of 49：100：100, synthesis temperature of 1550 °C and holding time of 15 h. The average grain size ofβ-Sialon and ZrN（ZrON） synthesized at 1550 °C for 15 h reached about 2 and 1μm, respectively. The fabrication process ofβ-Sialon/ZrN/ZrON composites included the formation ofβ-Sialon and ZrO2 as well as the conversion of ZrO2 to ZrN and ZrON.

矾土碳热还原氮化合成Ca-α-Sialon及热力学研究

从热力学上分析了Ca-α-Sialon相的合成过程。研究了以高铝矾土为原料,碳热还原氮化合成Ca-α-Sialon的影响因素,包括还原剂的用量、氮化温度和时间等。结果表明:以矾土为原料,1550°C碳热还原氮化反应可以合成Ca-α-Sialon,适当过量的碳有利于Ca-α-Sialon的氮化还原合成。