In-situ synthesis of a cordierite-andalusite composite for solar thermal storage

Abstract

An innovative thermal storage material, in-situ synthesised cordierite combined andalusite (Al2O3·SiO2), was prepared via semi-dry pressing followed by pressureless sintering. The samples were mainly composed of andalusite (the main raw material), with in-situ synthesised cordierite added to improve the thermal shock resistance. The results indicate that the formula L4 (70% andalusite, 13% talcum, 13% kaolin and 4% γ-Al2O3) sintered at 1400°C has the best thermal stock resistance, physical properties and chemical properties. The L4 sample can withstand 30 thermal shock test cycles without cracking (wind cooling from 1100°C to 25°C), and the bending strength after the thermal shock cycle test increased 26.20% rather than decreasing. Other properties are as follows: apparent porosity: 22.95%; water absorption: 10.71%; bulk density: 2.14g/cm3; bending strength: 92.74MPa; coefficient of thermal expansion: 4.11×10−6/°C; specific heat capacity: 0.95kJ·(kgK)−1; thermal conductivity coefficient: 0.58×10−2cm2s−1; and thermal conductivity: 1.17W·(mK)−1. The examination of the phase composition indicates that cordierite, mullite, sillimanite, cristobalite and α-quartz are the main phase elements. Analysis of the microstructure shows that the cordierite crystals were formed during the sintering process and were dispersed evenly in the mullite crystals, which gave the samples a favourable thermal shock resistance. It was concluded that the ceramic material, a combination of cordierite and andalusite, is an excellent candidate for solar thermal storage material due to its high thermal shock resistance, temperature resistance and strength.