β-sialon/Al_2O_3/SiO_2系材料烧结性能及反应过程研究

SINTERING PROPERTIES AND REACTION PROCESS OF β-SIALON/ALUMINA/SILICA COMPOSITE IN COKE BED AT HIGH TEMPERATURES

以 β-sialon粉、活性氧化铝微粉和氧化硅微粉为原料 ,研究了在焦碳保护下 ,β -sialon/Al2 O3/SiO2 体系材料经 15 0 0 ,160 0 ,165 0℃烧成时 ,该体系材料的烧结性能和物相变化 ,同时借助于SEM ,EDX和XRD等手段对材料的显微结构和反应过程进行了观察和分析。结果表明 ,随着温度升高 ,β -sialon/Al2 O3/SiO2 体系材料的体积密度下降 ,显气孔率增加 ,同时试样烧成前后的质量损失大大增加 ,尤其是经165 0℃烧成的试样 ,显气孔率在 5 0 %以上 ,质量损失大于 2 0 %。XRD物相分析显示 15 0 0℃时 ,产物中生成X相 (Si1 2 Al1 8O39N8)和SiC ,高于 165 0℃生成γ -AlON和SiC相 ,与热力学计算结果一致。同时高温下大量低价态的氧化铝如Al(g)及SiO( g)气相物质逸出试样表面 ,可能是导致试样质量损失 ,结构松散 ,显气孔率增加的主要原因。切开经高温烧成的试样 ,其截面由中心致密区 ,过渡区和边缘的松散区 3部分组成 ,含氮物相的形状由中心部位发育良好的柱状 ,演变成过渡区的针状或须状 ,直至松散区消失。

sialon/alumina/silica composites were calcined in coke powder bed at 1 500 ℃, 1 600 ℃ and 1 650 ℃. Their sintering properties and microstructure were investigated by SEM, EDX and XRD. It shows that the bulk density of β-sialon/alumina/silica composites decreases and their apparent porosity increases as increases of temperatures, accompanying with the large mass loss. Especially at 1 650 ℃, the apparent porosity of all the composites is more than 50%, and their mass loss is more than 20%. Also, except β-sialon and corundum, X_phase, SiC phase are produced in composites fired at 1 500 ℃, and γ-AlON and SiC phases at 1 650 ℃ which agrees with thermodynamic calculation. Simultaneously, it is supposed that plenty of gases such as Al(g), SiO(g) etc. escape from the surface of the composite at high temperatures, leading to the mass loss, loose structure and apparent porosity increasing. Correspondingly, the dense, transitional and loose areas are observed in composites from the center to the verge of the fracture section of the sample sintered at high temperature. The portion of the loose area in the profile relates to heating temperature and composite constitute. Also, well developed column and needle like grains of the nitrogen_containing phases are found in dense, transitional areas respectively, and disappear at loose area in the verge of the section.