Preparation And Thermophysical Properties Of Hitec Salt/porous Aluminosilicate Ceramic New Composite Phase Change Material

Energy storage technology can promote the development of new energy and the efficient use of traditional energy,especially the thermal energy storage(TES)system,which has the advantages of good flexibility and cost-effectiveness.The core of TES technology lies in the selection of heat storage materials,Hitec molten salt has suitable phase change temperature,large phase change latent heat,and high decomposition point,it has been caused wide attention in the field of medium temperature.However,it also has problems such as phase change leakage,corrosive and low thermal conductivity.The porous ceramic encapsulation can solve these problems of Hitec salt.Therefore,by choosing suitable porous ceramic materials to encapsulate Hitec salt,it is of great significance to prepare composite phase change material(CPCM)for medium temperature TES system.In this paper,a combination of experiment and molecular dynamics simulation was used to prepare a new type of CPCM with porous aluminosilicate ceramics(AC)as the matrix and Hitec salt as the PCM.The pore characteristics of porous AC and the influence of porous AC on the thermophysical properties of Hitec salt in CPCM were explored.Firstly,the properties of porous aluminosilicate ceramics were studied,and the porous aluminosilicate models were established using Materials Studio(MS)software with Si O₂:Al₂O₃ molecular ratio of 3:1,2:1,3:2,1:1,2:3,1:2,1:3.Using the Forcite,VAMP modules in MS to running the model and analyze the model's thermal conductivity,specific heat capacity,porosity,and specific surface area.The results show that as the proportion of Al₂O₃ increases,the specific heat capacity,thermal conductivity,specific surface area and porosity all increase,the overall thermal conductivity changes in a piecewise linear increasing trend,while the specific heat capacity and porosity at constant pressure increase slowly.In the experiment,the ratio of Si O₂:Al₂O₃ also adopted the above-mentioned molecular ratio,porous AC was prepared by adding pore former,kieselguhr,aluminum hydroxide,aluminum oxide and starch soluble were mixed in a certain proportion to prepare ceramic embryos,and it was sintered at1250?to form porous AC.Then SEM was used to observe the internal pores of the porous ceramics and the Archimedes drainage method was employed to test its porosity.The experimental results show that the increase of starch soluble raises its porosity.When the proportion of Al₂O₃increases,its porosity also increases,which is similar to the change trend of the molecular dynamic simulation data.Next,Hitec salt was prepared by static melting method at the ratio of 53wt%KNO₃:7wt%Na NO₃:40wt%Na NO₂,and Hitec molten salt was absorbed into ceramics by spontaneous melting and immersion method to form CPCM.By DSC,thermal conductivity analyzer,TG,XRD,SEM,etc.the performances(specific heat capacity,phase change temperature,phase change latent heat,thermal conductivity,decomposition point,crystal structure,microporous structure)of CPCM were studied.At the sintering temperature 1250?,DSC and thermal conductivity analyzer test found that the CPCM has the best comprehensive thermal properties when 25wt%starch soluble is added and Si O₂:Al₂O₃ is 1:2 compared with the other groups of materials.Its thermal conductivity is 2.11W/(m·K),its Cp and phase change latent heat are1.25J/(g·K)and 60.83J/g,respectively.TG research finds that porous aluminosilicate can increase the decomposition temperature of CPCM to 750°C and reduce the decomposition rate.XRD analysis shows that the addition of Al₂O₃ in porous aluminosilicate ceramics increases,the proportion of mullite inside increases,and the stability of the crystal form is enhanced.SEM observation shows that the pore diameter changes from 30-50?m to 10-30?m when the porous aluminosilicate ceramics vary from Si O₂:Al₂O₃=3:1 to Si O₂:Al₂O₃=1:2,the pores gradually become smaller and the pore diameters are more uniform.Calculations have found that the capillary action is enhanced,and the molten Hitec salt is not easy to leak.The research results in this paper provide some guidance for choosing suitable Hitec salt/porous aluminosilicate ceramic CPCM as energy storage materials for medium temperature TES systems.