凝胶注模成型制备Si3N4-SiC材料

摘要

Suspension with 75 vol% solid loading was prepared using SiC particles (3. 36-0.15 mm),SiC fines(≤19 μm) .modified Si powder( ≤26μm),modified Al powder,and α-Si3N4 as starting materials. Then Si3N4-SiC refractories were prepared by gelcasting the suspension and nitridation firing. The rheological characteristics of the suspension,the properties and the microstructure of the Si3N4-SiC material nitridation fired were studied. The results show that; 1) the suspension exhibits shear thinning characteristic in the shear rate range from 10 s-1 to 160 s-1,which meets the requests of the gelcasting process;the rheological characteristics accord with Sisko model,and the rheological equation is η = 4. 625 4 + 2 172.9γ-0.4503 ;the fitting rheological curve basically agrees with the experimental curve;2)the modulus of rupture and bulk density of the wet demolded green body after solidification are 16 MPa and 2.57 g · cm-3;the structure of the dried green body is dense,SiC particles are evenly wrapped by Si powders and SiC powders;3)the Si3N4 content,cold and hot modulus of rupture of the fired Si3N4-SiC refractories are all higher than those of non-gelcasting industrial products;Si3N4 crystals are well developed,forming a uniform structure where Si3N4 crystals intertwines SiC particles.%以SiC颗粒(3.36 ～0.15 mm)、SiC细粉(≤19 μm)、改性Si粉(≤26 μm)、改性Al粉、α-Si3 N4粉为原料制成固相体积分数为75％的悬浮体,采用凝胶注模成型工艺和氮化烧成工艺制备Si3 N4-SiC材料,并研究了SiC系悬浮体的流变特性以及氮化烧成后Si3 Na-SiC材料的性能和显微结构.结果表明:1)悬浮体在切变速率10～160 s-1范围内表现出剪切变稀的特征,满足凝胶注模成型的要求；其流变特征符合Sisko模型,流变方程为η=4.625 4+2 172.9γ-0.4503,拟合流变曲线与试验流变曲线基本吻合.2)脱模后湿坯的抗折强度为16 MPa,体积密度为2.57 g· cm-5；干燥后坯体结构致密,SiC大颗粒被Si粉和SiC粉均匀包裹.3)氮化烧成后试样的Si3 N4含量、常温抗折强度和高温抗折强度均高于非凝胶注模成型的工业产品；Si3N4晶体发育完整,形成了Si3N4晶体紧密环绕SiC颗粒的均匀结构.