Comparison of Porous Ceramic Materials with Low Thermal Expansion Coefficient Prepared with SiC and Black-Al_2O_3

摘要

Porous ceramic materials with low thermal expansion (LTE) at room temperature were prepared by heating a mixture of SiC or black-Al_2O_3, vitrified bonding material (VBM) and LiAlSiO_4 at temperatures from 850°C to 1100°C. The mixture was prepared in adequate proportions to obtain a material with LTE according to previous works made in our laboratory. It was observed that a change in temperature provoked the formation of a new phase, LiAlSi_3O_8, which appears above 900°C. The presence of this new phase did not affect the thermal expansion value, keeping LTE at room temperature. All compounds showed around 40% of porosity, and Young's modulus values of 30 GPa using black-Al_2O_3 or SiC. X-ray diffraction analysis (XRD) revealed that above 900°C the phase LiAlSi_3O_8 starts to appear as a consequence of the melting of VBM, which is reacting with the raw materials. SEM micrographs showed the presence of SiC or black-Al_2O_3 grains joined by VBM, which is acting as a bridge between them.