Research On Compatability Between PCM And Heat Storage Ceramics

Solar energy has the characteristics of clean and environment friendly.It is the most promising alternative to take over the fossil energy sources in all kinds of new energy sources.Solar thermal storage technology is that kind of technology which turns solar radiation energy into thermal energy.In the thermal storage technology,heat storage material is the key to improve the efficiency of solar energy heat utilization.This paper developed a sensible heat ceramics and the latent heat of PCMs（phase change materials）composite heat storage material,and discusses the compatibility mechanism between the PCMs and the ceramics.Based on sensible/latent composite heat heat storage subsystem in a solar thermal power generation system,we designed B1^B5 honeycomb ceramic batch formula with 300 mesh andalusite in Korla Xinjiang,Yingde Guangdong quartz,Guangxi talc,Hebi Henan calcined bauxite and Danjiangkou Hubei 325 mesh silicon carbide as main raw materials,added CMC,tung oil and water as additives,extruded honeycomb ceramics by wistra,and selected AlSi₁₂ as PCM by thermodynamic calculation.In order to guarantee sealing performance at high temperature,we designed F series sealing agents,by using the method of high temperature encapsulation,and then obtained PCM/honeycomb ceramic composite heat storage materials.On the thermal cycle test,used XRD,SEM,FESEM and EDS,TG and DSC and other means to investigate the thermal stability of the PCM,the compatibility between the PCMs and the ceramic substrate,and tried to explain its compatibility mechanism.The main conclusions are as follow:（1）Used Guiguang talc,andalusite,Yingde quartz and SiC as the main raw materials,by pressureless sintering,cordierite ceramic,mullite ceramic and SiC Ceramic was prepared.After a serials of tests such as sintering shrinkage,water absorption（Wa）and apparent porosity（Pa）,bulk density（D）,flexural strength（σ_b）,XRD and SEM,the testing results showed that:when fired at optimum temperature,B series ceramic body has a small sintering shrinkage,and its Wa is less than 0.46%,Pa is less than 2.07%,D is more than 2.42g·cm^-3,σ_b is greater than 96.12MPa,the crystal phases are cordierite,mullite and silicon carbide respectively.It has a compact structure and well crystal morphology.All crystal phases are combined with the glass phase,giving a good mechanical properties to the ceramic body,which is expected to be used as solar thermal power generation sensible heat storage material.（2）Based on the optimum batch formula of the first chapter,in order to simulate the actual application of the honeycomb ceramics,using B series formula powder as the main raw material,extruded by wistra,shaped by microwave,B serials honeycomb ceramics was prepared.The plasticity of mud,the physical properties（Wa,Pa,D,σ_a）and the XRD,SEM of honeycomb ceramics are tested.The testing results are as follow:when mix with 3%CMC,23%²6%water and 3%tung oil,the plasticity index of B series honeycomb ceramic mud is more than 22cm·kgf,which indicate it has a good molding properties,the Wa is between 1.17%and 16.11%,Pa is between 3.34%and 27.95%,D is between 1.80 g·cm^-3 and 2.8g·cm^-3,σ_a is between10.34MPa to 25.77MPa,a axial compressive strength meets the requirements of GB/T 25994-2010,all phases are combined with glass phase,making the substrate dense.Before and after the thermal shock,the phase composition and the microstructure basically have no change,which indicates it has a good thermal shock resistance and is expected to be used for solar thermal power generation ceramic substrate.（3）To encapsulate the PCMs well,designed the F1^F5 series of encapsulate agent formulas useing B serials fired ceramic powder as the main materials.By high temperature rapid packaging method,honeycomb ceramic encapsulate agents were prepared.The shear strength and SEM testing results showed that:the shear strength of the best encapsulate agent is about 2.18 MPa⁴.83MPa,SEM results indicate that the best encapsulate agent and the substrate are combined closely,which meets the shear strength requirement of the standard JC/T547-2005 and is expected to be used in sealing honeycomb ceramic substrate.（4）Used the honeycomb ceramics prepared in the third charpter as the container,F serials batch formula as the sealing agents,AlSi₁₂ as the PCM,AlSi12/honeycomb ceramic composite heat storage material was prepared.After 100 times cycling,XRD,SEM,FESEM,EDS and TG-DSC,etc,were used to test the composite materials.The testing results showed that:AlSi₁₂ was partially oxidized,the oxidation rate of it in the first and second thermal cycle reaches the largest,since then,with the increase of times of thermal shock,the oxidation rate waves in a few tenths,by the effects of the capillary force of micro pores,PCMs penetrate into the pores of the substrate,deposit and fill the pores.The oxidant（Al₂O₃）destroyed alloy sphere,at the same time,quite a number of alloy ball remained.AlSi₁₂ degradation rate is between 20.5%⁶0.3%,and presents the trend of B3<B1<B2<B4<B5,consistent with the trend of apparent porosity of the substrate material.The phase transition temperature of AlSi₁₂ is range from 574.8℃to 574.8℃,the peak temperature is 582.6℃,the peak area is-339.4J/g.After 100 times cycling,the phase change temperature of composite heat storage material range from 571.7℃to 571.7℃,the peak temperature is 578.3℃,the peak area is-24.4J/g.phase transition temperature of left-shift is 3.1℃⁷.1℃,the peak temperature deviates less than 0.7%.AlSi₁₂ degradation is mainly caused by thermal diffusion of trace elements in the substrate,which leads to AlSi₁₂ constituent fluctuations.It causes composition segregation of the alloy,Al oxidizes into Al₂O₃easily while Si gathers in an area of alloy.