凝胶注模成型制备Si_3N_4-SiC材料

Preparation of Si_3N_4-SiC material by gelcasting

以SiC颗粒(3.36～0.15 mm)、SiC细粉(≤19μm)、改性Si粉(≤26μm)、改性Al粉、α-Si3N4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Si3N4-SiC材料,并研究了SiC系悬浮体的流变特性以及氮化烧成后Si3N4-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-0.450 3,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-3;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Si3N4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。

Suspension with 75 vol% solid loading was prepared using SiC particles （3.36-0. 15 mm）, SiC fines（ ≤19 lam） ,modified Si powder（ ≤26 pm） ,modified AI powder,and 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： I ） the suspension exhibits shear thinning characteristic in the shear rate range from 10 s to 160 s-1, which meets the requests of the gelcasting process;the rheological characteristics accord with Sisko model,and the rheological equation is r/ = 4. 625 4 ＋ 2 172.9,y-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;Si3 N4 crystals are well developed, forming a uniform structure where SigN4 crystals intertwines SiC particles.