Experimental investigations on the thermal stability of Na2CO3–K2CO3 eutectic salt/ceramic composites for high temperature energy storage

Abstract

In this study, eutectic salt/ceramic composites with MgO serving as supportingmaterial and Na2CO3–K2CO3 eutectic salt acting as thermal absorbing materials were prepared by the form-stable technique. As additives, effects of both Kaolin and graphite on the thermal stability of composites were investigated. The microstructures of the composites before and after thermal cycling tests were detected by X-ray diffraction and scanning electron microscope techniques. The thermal stability and thermal properties including latent heat, specific heat capacity, thermal conductivity, etc. were measured using differential scanning calorimetry, laser thermal instrument and thermogravimetric analysis, etc. The results showed the composite phase change materials had good thermal reliability and chemical stability. No obvious damages were found in the samples with thermal cycles reaching 1500 times. Kaolin can improve the stability of the sample by restraining the volatilization of molten salt, but it can reduce the phase transition enthalpy of the composite. In comparison with kaolin, carbon can improve thermal cycle life due to its favorable shock resistance. But it suffers severe oxidation at high temperature, which might be a possible reason for its decay in thermal cycling life. These studies suggest the thermal life of the composite can be controlled by adding proper materials.