The Study On Preparation And Phase Change Heat Storage Properties Of Inorganic Salt/Forsterite Composite Materials

The properties, structure, preparation and application of composite phase changeheat storage materials are introduced briefly in this paper. Through the discussion onthe process of synthesizing forsterite in inorganic salt medium, inorganic salt/forsterite composite phase change heat storage materials are prepared by in-situreaction sintering process. The influences of the technological parameter on theperformance of the composite phase change heat storage materials are studied.Furthermore, the distribution of the temperature and heat-stress during the phasetransformation of the phase change materials are also simulated.In this paper, we firstly discuss the formation mechanism of forsterite powders ininorganic salt medium using MgO and SiO2nanoparticles as raw materials. Then,inorganic salt/forsterite composite phase change heat storage materials are preparedby in-situ reaction sintering method, using the industrial materials sintered magnesiaand silica as raw materials and inorganic salt as phase change materials. Meanwhile,we study how the sintering temperatures, holding time, inorganic salt contents andmole ratios affect the properties of heat storage materials in order to obtain the bestpreparation process. Also, the phase compositions, micro structures and thermalproperties of composite phase change heat storage materials are characterized byXRD, SEM and TG-DSC. Afterwards, we test the thermal conductivity by the planetable thermo and measure the refractoriness under load, flexural strength and elasticmodulus at high temperature. In order to analyze the thermal stability, the heat storagematerials are heated cycling for several times. Finally, the distribution of thetemperature and heat-stress are simulated by COMSOL Multiphysics4.3a. Based onthe aforementioned analysis and discussion, the following conclusions are obtained.(1) Single-phase forsterite powders can be prepared with non-stoichiometric ofMgO/SiO2molar ratio of2:1.3at700℃in inorganic salt media, and the nucleationand growth process of the powder particles depend on the synthetic temperatures. Thecrystal size and morphology could be controlled by regulating the salt/powdersweight ratio and inorganic salt system. Furthermore, the dissolution-precipitationmechanism dominates the formation of Mg2SiO4in inorganic salt media.(2) Forsterite porous ceramic substrate with certain strength can be prepared byin-situ reaction sintering method in inorganic salt media. And the apparent porosityand the pore size of the porous ceramic substrate increase with the increasing of thecontent of inorganic salts. The apparent porosity is up to65%and the compressivestrength is about6MPa when the content of inorganic salts is40%. (3) The prepared materials have better overall performance with phase changelatent heat of80.1kJ/kg, heat storage density of263.19kJ/kg(ΔT=100℃), thermalconductivity of0.43~0.37W/(m·K) at400~800℃under the condition of sintering at1000℃for5hours with inorganic salt content of40%, using NaCl-KCl as phasechange materials. The refractoriness under load is up to1145℃, and the flexuralstrength and elastic modulus of the prepared materials at high temperature can satisfythe operating temperature of600~700℃. Furthermore, after recycling heating forseveral times, the mass change rate of the heat storage material is very small and thephase compositions and micro-structures are basically unchanged, indicating that theprepared materials have good thermal stability.(4) The temperature and heat-stress during the endothermic/exothermicprocesses of samples are simulated based on the experimental datas. The resultsindicate that the higher inorganic salt content, the lower thermal conductivity, as wellas the bigger phase change latent heat, which results in the more slowly internal heattransfer, and the greater the temperature difference, the larger the internal thermalstress.