Effect Of Microstructure On Thermal Properties After High Temperature Cycling

Inorganic salt/ceramic composite phase change materials are one of the most effective technical means to solve the current energy problems.In this study,through experiments and literature,it is found that Na2CO3-K2CO3 eutectic salt has great potential for phase change material and good high temperature stability at 700℃.MgO has good thermal shock resistance,high thermal conductivity and specific heat capacity,and has good compatibility with Na2CO3-K2CO3 eutectic salt,graphite has good thermal shock resistance and high thermal conductivity and kaolin can improve the stability of molten salt.So inorganic salt/ceramic composite phase change materials consisting of Na2CO3-K2CO3 binary eutectic acting as thermal absorbing materials,MgO serving as the supporting material and Kaolin and graphite using as additive were prepared as a novel form-stable composite phase change material.The composition of the eutectic binary salt was determined with the aid of FactSage software and the prepared composite phase change materials were characterized in terms of X-ray diffraction as well as scanning electron microscope analysis,respectively.The thermal properties and thermal stability including latent heat,specific heat capacity,thermal conductivity,etc.were investigated by differential scanning calorimetry,laser thermal instrument and thermogravimetric analysis.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 attained to 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.The results of laser thermal instrument showed that adding graphite can improve the thermal conductivity of samples.The successful fabrication and performance research of Na2CO3-K2CO3/MgO、Na2CO3-K2CO3/MgO-kaolin and Na2CO3-K2CO3/MgO-C composite phase change energy storage materials not only provide necessary experiment date and theory support for its application in the industrial waste heat recovering,solar energy utilization,active and passive cooling of electronic devices,seasonal energy storage and energy-saving building materials,but also give an important reference to fabricate other inorganic salt/ceramic composite phase change energy storage materials.