Study of thermal properties of mullite porous materials

Abstract

Green ceramic bodies based on mullite were infiltrated with SiO2 (TEOS precursor) solution using a sol–gel technique and sintered at 1,300 °C. Previously, the green bodies had been prepared with the molding method, using corn flour as the pore-forming agent with a concentration in mass percent of 10, 15, and 20, and then they were sintered. Infiltrated ceramic material was evaluated to determine the relationship between, morphology, porosity, thermal properties, and crystalline characteristics by scanning electron microscopy, X-ray diffraction, porosimetry by N2 at 77 K, and thermal analysis using laser flash technique. The presence of SiO2 together with magnesium (talc powder) gives a cordierite crystalline phase, which is considered presenting thermal stability. Infiltration process changes the surface area, which is reduced by 93 %, and the pore size value reaches 1.98 nm, changing from open to closed structure. In spite of porosity change, thermal conductivity increases in the majority of the samples. This phenomenon obeys the complex system involved in the study, such as closed porosity, microstructure, tortuosity, geometry, and the anisotropy of mullite bonds, accompanied by the infiltrant liquid (SiO2).