SHI Xiumei ^{1, 2}, CUI Hong ¹, CAO Jianwu ², WANG Jinghui ², LI Guobin ², GUO Jianbin ², ZHANG Lijun ², TANG Jiayun ²
(1. Northwestern Polytechnical University, Xi’an 710072, Shaanxi, China; 2. Ningbo Branch of China Academy of
Ordnance Science, Ningbo 315103, Zhejiang, China)

Abstract: Silicon carbide ceramics were prepared by pressureless sintering. The effects of different sintering temperatures, doping amounts of carbon and particle sizes on the structures and properties of the silicon carbide ceramics were investigated. The research shows the distribution of carbon in the ceramics is more homogeneous, the density and the mechanical properties of SiC ceramics increase when the amount of the carbon additive (phenolic resin) increases. When the content of the phenolic resin additive reaches 2.0wt.%, the ceramics achieve the highest density and the strongest bending strength, which are 3.17 g/cm³ and 507 Mpa respectively. When the content of the phenolic resin additive is more than 2.0wt.%, the abnormal growth of SiC grains and pores appears inside the ceramics, the bending strength and density of the SiC ceramics decrease. The density and shrinkage of SiC ceramic initially increase with the increase of the sintering temperature up to 2150 ℃, but stop increasing with the temperature further increased. The optimum bulk density and bending strength are 3.18 g/cm³ and 507 MPa after sintering at 2150°C in Ar gas. Under the conditions of sintering at 2150 ℃ and preparing with 2.0wt.% phenolic resin additive, two types of SiC powders were obtained for the study on the impact of different particle sizes. One type is single size particles which average 1.0 μm and 2.0 μm, respectively, and the other type is the particles of mixed sizes (the mixing ratio is 4:1); the relative bulk density and bending strength of the SiC ceramics prepared with the mixed powders were better than those of the samples prepared with the single-sized powders.

Key words: silicon carbide; pressureless sintering; sintering aids