Effect of excess MgO on microstructure and thermal properties of cordierite ceramics for high-temperature thermal storage

Cordierite ceramics for high-temperature sensible thermal storage were prepared using Lincang kaolin, calcined talc and alpha-Al2O3 by solid-state method. The effects of excess MgO on phase compositions, microstructure and thermal properties were investigated in detail. Differential thermal analysis and hot stage microscopy revealed that the excess MgO promoted liquid formation and decreased the liquid viscosity and softening temperatures of cordierite ceramics. By increasing the liquid content, the excess MgO accelerated the dissolution of tubular kaolin particles and facilitated microstructure densification of cordierite ceramics to obtain the lowest water absorption as 5.26%. The excess MgO was also advantageous for cordierite crystallization and 1 wt% MgO addition decreased the coefficient of thermal expansion (CTE) of cordierite ceramics to 2.13 x 10(-6) degrees C-1 (room temperature-600 degrees C). The extra glassy phase increased the CTE to 2.48 x 10(-6) degrees C-1 when the excess MgO content was larger than 1 wt%. The excess MgO could also increase the thermal conductivity of cordierite ceramics to 3.03 W (m k)(-)(1) by reducing the amount of pores. Cordierite ceramics synthesized by using Lincang kaolin show good potentials for high-temperature thermal storage applications in concentrated solar power plants due to the low CTE, relatively high thermal conductivity and high thermal storage capacity.