Abstract: Si₂N₂O was synthesized using Si powder and SiO₂ micropowder as raw materials and treating at 700 ℃ in the air atmosphere and then at 1 400 ℃ in the nitrogen atmosphere.The effect of the B₄C addition (0,1.0%,2.0%,3.0% and 4.0%,extra adding,by mass) on the synthesis of Si₂N₂O was studied.With the optimal B₄C addition,Si₃N₄/Si₂N₂O bonded SiC samples were prepared after firing at 700 ℃ for 5 h in the air atmosphere and then at 1 400 ℃ for 5 h in the nitrogen atmosphere.The thermal shock resistance of the samples was evaluated by the retention ratio of the modulus of rupture after 5 cycles of thermal shock(1 300 ℃,air quenching).The phase composition and the microstructure of the samples before and after thermal shock were analyzed.The results show that:(1)the optimal B₄C addition is 3%;B₄C preferentially reacts with O₂ to generate B₂O₃ at 700 ℃ in the air atmosphere,which provides sufficient liquid phase for the formation of plate-like Si₂N₂O at 1 400 ℃ in the nitrogen atmosphere;(2)after thermal shock,the sample added with B₄C has complete Si₂N₂O bonding phase and increased strength retention ratio from 67.5% to 88.5% compared with the sample without B₄C;at the same time,B₂O₃ transforms to BN of good thermal conductivity and self-lubricating property through the carbothermal reduction nitridation reaction,which improves the thermal shock resistance and continues to protect Si₃N₄/Si₂N₂O bonded SiC materials during service.

Key words: boron carbide, Si₃N₄/Si₂N₂O bonded silicon carbide, thermal shock resistance, coke dry quenching furnace, inclined channel area

摘要： 首先以Si粉、SiO₂微粉为原料,先在700 ℃空气气氛处理,然后在1 400 ℃氮气气氛下合成Si₂N₂O,研究了B₄C添加量(外加质量分数分别为0、1.0%、2.0%、3.0%、4.0%)对Si₂N₂O合成效果的影响。然后根据B₄C最优加入量,先在700 ℃空气气氛保温5 h,然后在1 400 ℃氮气气氛保温5 h制备了Si₃N₄/Si₂N₂O结合SiC试样。采用1 300 ℃风冷5次后试样的抗折强度保持率评价其抗热震性,分析了热震前后试样的物相组成和显微结构。结果表明:1)合成Si₂N₂O的B₄C最优添加量为3%(w);在700 ℃空气处理时,B₄C优先和气氛中O₂反应生成液相B₂O₃,为1 400 ℃氮气气氛生成板片状Si₂N₂O提供充足液相。2)风冷热震后,添加B₄C的试样中Si₂N₂O结合相保持完整,强度保持率由未添加时的67.5%提高至88.5%;同时,生成的B₂O₃发生碳热还原氮化反应,生成导热性好、具有自润滑特性的BN,改善其抗热震性,并在使用过程中继续为Si₃N₄/Si₂N₂O结合SiC材料提供保护。

关键词: B₄C, Si₃N₄/Si₂N₂O结合SiC, 抗热震性, 干熄炉, 斜道区