相变介质粒径对粉煤灰基高温定形复合相变材料蓄热性能的影响

Effects of Particle Size of Phase Change Medium on Thermal Storage Performance of Fly Ash-based High Temperature Formstable Composite Phase Change Material

以Al-Si共晶合金粉为相变介质、粉煤灰为基体材料,采用混合烧结法制备高温定形复合相变材料,通过密度和增重率的测定及DSC,SEM和XRD分析,探讨烧结过程中导致合金粉性质发生变化的原因,研究合金粉粒径对材料蓄热性能的影响规律。结果表明:烧结过程中,合金粉中Al被氧化并与基体中SiO_2发生反应,破坏了部分合金粉的原有性能,导致相变潜热降低。合金粉粒径越小,自身氧化及与基体间的反应程度越高,材料更为致密但相变潜热偏低。合金粉粒径越大,材料的相变潜热越高但密度偏低。通过调整合金粉中大粒径(40≤d≤74μm)颗粒的含量,可实现相变潜热与密度之间的适度平衡。当合金粉中40≤d≤74μm颗粒质量分数调整为44%时,材料的相变潜热为94.9J/g,密度为1.37g/cm^3,与用原始合金粉所制备的材料相比,相变潜热增加了114%而密度仅降低了3.5%,复合材料的综合性能得以改善,尤其是蓄热性能大幅度提升。

High temperature form-stable composite phase change materials were prepared by mixed sintering method with Al-Si eutectic alloy powder as phase change medium and fly ash as matrix material.The density,weight gain rate,DSC,SEM and XRD were measured and characterized to study the effect of particle size of phase change media on material properties.The reason for the properties change of the alloy during sintering was discussed.The results show that during the sintering process,Al in the alloy powder is oxidized and reacts with SiO 2 in the matrix,which destroys the original properties of the alloy powder and results in the decrease of latent heat of phase change.The smaller the particle size of the alloy powder,the greater the degree of oxidation and reaction with the matrix,leading to more compact compound but lower latent heat of phase change.On the contrary,larger particle size of the alloy powder contributes to higher latent heat but lower density.Therefore,The appropriate balance between latent heat and density can be achieved by adjusting the content of large particle size(40μm<d<74μm)in alloy powder.When the mass fraction of large particle(40μm≤d≤74μm)of the alloy powder is 44%,the latent heat of the compound material is 94.9 J/g,and the density is 1.37 g/cm 3.Compared with the composite prepared by the original alloy powder,the latent heat of phase change is increased by 114%,and the density is only reduced by 3.5%.The overall performance of the composite material is improved,especially the heat storage performance is greatly increased.