以电熔尖晶石、Si粉和鳞片石墨为主要原料,木质磺酸钙溶液(1.25 g/mL)为成型结合剂,在氮气气氛下1450℃分别保温1、2、3和4h原位生成β-Sialon结合MgAl2O4-C材料,研究了保温时间对材料的物相组成、β-Sialon的显微结构及常规物理性能的影响,并对该复合材料进行氧化动力学研究.结果表明:当保温时间从lh增加到4h,试样的物相变化规律基本相同,Si单质相消失,完全转化为SiC、Si3N4和β-Sialon(Si3A13O3N5).当保温时间为3h时,生成的β-Sialon(Si3A13O3N5)为完整圆柱状晶粒,尺寸分布均匀,交错成网络结构.随着保温时间的增加,试样内部产生较多的SiO气体,导致试样的显气孔率增加,体积密度下降,耐压强度和抗折强度先增加后下降,当保温时间为3h时,耐压强度和抗折强度达到最大.氧化动力学研究表明,氧化过程随着时间的推移分为化学反应控制阶段、化学反应和扩散共同控制阶段及扩散控制三个阶段.
A β-Sialon bonded MgAl2O4-C refractory was prepared in-situ by fused spinel,silicon powder,flake graphite as raw materials,and calcium lignosulfonate with the concentration of 1.25 g/mL as the binder.The samples were sintered under N2 atmosphere at 1450℃ for 1,2 3 and 4 h,respectively.The effects of holding time on the conventional physical properties,phase compositions and microstructure of MgA12O4-C refractory were investigated.The phase composition and microstructure of the sintered samples were investigated by X-ray diffraction (XRD) and Scanning Electron Microscope (SEM),respectively.XRD patterns showed that there were no evident differences on the phase compositions and the silicon phase had completely disappeared to form SiC,Si3N4 or β-Sialon (Si3A13O3N5).The 3-Sialon crystals had columned microstructure stagger on each other when holding time was 3 h.With the holding time increasing from 1 h to 4 h,the increased SiO gas lead to an increase of apparent porosity and a decrease of bulk density.In addition,the cold crushing strength and flexural strength of the samples sintered at 1450C for 3 h reach the highest.Research on oxidation kinetics of composite material indicates that oxidation process can be divided into three stages:chemical reaction rate controlling stage,diffusion rate controlling stage,and co-effect controlling of chemical reaction and diffusion rate stage.
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