Effect of Al addition on creep resistance of the fired SiC-MgAl2O4 composite refractories

Abstract

SiC-MgAl2O4 composite refractories were prepared by using SiC particles, MgAl2O4 powders, α-Al2O3 micro-powders and metal Al powders as raw materials under flowing nitrogen at 1450 °C. The creep test was conducted at 1400 °C under 0.2 MPa for 50 h and the effects of Al addition on the creep resistance of SiC-MgAl2O4 composite refractories were investigated. The results show that the creep rate of samples without Al addition increases gradually as time prolonging while the samples with Al addition has a better creep resistance and the creep rate always contains a low creep rate. The mechanism for improving creep resistance of the samples with Al addition could be concluded as follow. During the creep test, the samples have a oxygen concentration from surface areas to the inner areas. (Al2OC)x-(AlN)(1-x) whiskers (generated during the sintering process) at the surface area preferentially reacts with oxygen to form Al2O3 and a little SiC oxidizes to SiO and even SiO2, the formed Al2O3 and SiO/SiO2 can react with the MgAl2O4 matrix to generate mullite, cordierite and MgO. MgO and SiO/SiO2 could also transfer and react with Al2O3 to generate new MgAl2O4 particles and even plate β-Sialon dispersed in pores where (Al2OC)x-(AlN)(1-x) whiskers ever existed. The formation of mullite, cordierite, MgAl2O4 particles and plate β-Sialon had a synergistic effect to improve the creep resistance. Besides, these new phases could fill the pores and inhibit the diffusion of oxygen inside the samples. With a relative low oxygen partial pressure inside, most of the (Al2OC)x-(AlN)(1-x) whiskers still existed in samples with a network structure and only partly oxidized to Al2O3, the oxidation of SiC was inhibited and formation of liquid was avoided. Thus, the creep resistance of the sample was further enhanced.