Abstract:

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 (1 150,1 350,and 1 550 ℃) 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 1 550 ℃;the ideal service temperature of the silicon nitride fiber material shall be lower than 1 150 ℃;(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.

Key words: silicon nitride fiber, silicon powder, foaming method, oxidation resistance

摘要：

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。

关键词: Si₃N₄纤维, Si粉, 发泡法, 抗氧化性