Clay/phosphate-based ceramic materials for thermal energy storage - Part I: Effect of synthetic phosphate content on microstructure, thermo-physical and thermo-mechanical properties

Fired clay ceramics are promising materials for TES, thanks to their thermal stability, availability worldwide, low cost and easy shaping and handling. However, their thermo-physical and thermo-mechanical properties have to be improved. For the first time, clay-phosphate ceramics, with synthetic calcium hydroxyapatite (TCP, Ca10(PO4)6(OH)2) as additive, were developed in view of TES application. A parametric study was carried out for different clay/TCP mixtures, wherein the TCP percentage varies from 0 to 16.7 wt%. The best material containing 4.7 wt% TCP allowed increasing up to 20% of the thermal conductivity and 23% of the mechanical strength. Moreover, it was thermally stable up to 1000 degrees C. These original results demonstrate the suitability of these new materials for heat storage in energy systems such as in a concentrated solar power (CSP) plant, or in a unit of heat recovery from an industrial waste heat source.