采用Si粉发泡氮化制备Si3N4纤维材料的抗氧化性研究

Oxidation resistance of Si3N4 fibers synthesized by foaming and nitriding of Si powder

采用发泡法将气孔引入Si坯体,使体积分别增加0、1、2、3倍,经原位氮化制备出显气孔率分别为49%、74%、81%和87%的Si3N4纤维材料,研究了氧化温度(1 150、1 350和1 550℃)和显气孔率对Si3N4纤维材料抗氧化性的影响。结果表明:1)温度是影响Si3N4纤维材料抗氧化性的关键因素,随温度升高试样氧化后生成SiO2的量逐渐增多。孔中Si3N4纤维因具有较大的比表面积,1 550℃氧化后全部转化为串珠状SiO2结构,Si3N4纤维材料理想的使用温度应低于1 150℃;2)试样显气孔率由49%提高至87%,氧化后生成SiO2的量变化不大;3)发泡法引入的气孔可部分吸收孔壁上Si3N4氧化产生的体积效应,避免孔壁在氧化中产生裂纹。同时,Si3N4氧化产生的体积膨胀可使孔壁结构致密化,有利于提高材料强度。

The foaming method was used to introduce pores into Si bodies to increase the volume by 0,1,2,and 3 times,respectively.Si3N4 fiber materials were produced by in-situ nitridation with porosity of 49%,74%,81%,and 87%,respectively.The effects of the oxidation temperature(1150,1350,and 1550℃)and the apparent porosity on the oxidation resistance of the Si3N4 fiber materials were studied.The results show that:(1)the temperature is a key factor affecting the oxidation resistance of Si3N4 fiber materials;as the temperature increases,the amount of the SiO2 produced by the oxidation gradually increases;since the silicon nitride fiber in the pores has large specific surface area,it is converted into beaded SiO2 structure after oxidation at 1550℃;the ideal service temperature of the silicon nitride fiber material shall be lower than 1150℃;(2)the apparent porosity of the samples increases from 49%to 87%,and the amount of the SiO2 generated after oxidation does not change much;(3)the pores introduced by the foaming method can partially absorb the volume effect generated by the oxidation of Si3N4 on the pore walls to avoid cracks in the pore walls during oxidation;at the same time,the volume expansion caused by the oxidation of silicon nitride can densify the pore wall structure,which is beneficial to improving the strength of the materials.