吊顶窑用α-SiC结合SiC拱顶砖的服役行为研究

Service behavior ofα-SiC bonded SiC dome bricks for movable roof kilns

为解决燃气吊顶窑拱顶用耐火材料的污染和膨胀问题,以碳化硅颗粒和细粉为主要原料,水溶性树脂为结合剂,依次按三者质量比为65∶35∶4.5配料,机压成型为240 mm×170 mm×140 mm的坯体,在2400℃真空条件下保温3 h制备了α-SiC结合SiC砖。将该砖用于国内某氧化铝陶瓷棍棒公司的燃气吊顶窑拱顶,累计使用46窑次(合计276 h)后,该砖断裂严重。为此,对用后砖进行取样,借助热力学分析,检测了其距热面不同距离处的性能,分析物相组成和显微结构,并与原砖进行对比。结果表明:1)用后α-SiC结合SiC砖比原砖的显气孔率降低,体积密度增大,因为用后砖中生成了12%~14.2%(w)的方石英,由α-SiC结合转变为方石英结合,气孔孔径变小。2)用后砖与原砖比,常温抗折强度和荷重软化开始温度变化不大,推测材料断裂不是自身力学性能失效所致,而是因温度升降而频繁受到剪切力引起。

In order to solve the problem of pollution and expansion of refractories for the dome of gas-fired movable roof kilns,a piece ofα-SiC bonded SiC brick was prepared using silicon carbide particles and fine powder as the main raw materials,and water-soluble resin as the binder with the mass ratio of 65∶35∶4.5,forming a 240 mm×170 mm×140 mm green body by mechanical pressing,and holding at 2400℃for 3 h in vacuum.The brick was used in the dome of a gas-fired movable roof kiln of an alumina ceramic stick company in China.After 46 heats(276 h in total),the brick fractured seriously.The used brick was sampled,and the properties at different distances from the hot surface were tested and thermodynamically analyzed.The phase composition and the microstructure were analyzed and compared with those of the original brick.The usedα-SiC bonded SiC brick has lower apparent porosity and higher bulk density than the original brick,because 12%-14.2%cristobalite is formed in the used brick,transforming fromα-SiC bonding to cristobalite bonding,and decreasing the pore size.Compared with the original brick,the cold modulus of rupture and the refractoriness-under-load do not change much.It is speculated that the fracture of the material is not caused by the failure of its own mechanical properties,but by the shear force due to the temperature fluctuation.