The Synthesis And Phase Change Properties Of Al-Si/Al₂O₃Core-shell Micro-particles

Al-Si eutectic alloy is an ideal high temperature phase change material （PCM）because of its high latent heat value. Molten Al-Si alloy, however, possesses highcorrosion, which is the main reason of its restriction application. It is valuable toexplore a new effective method to encapsulate Al-Si alloy particles. In this paper, amethod of micro-packing Al-Si particles was investigated. The structure and phaseproperties of Al-Si/Al₂O₃core-shell micro-particles were analyzed.Based on the theory of sol-gel method, Al-Si/Al₂O₃core-shell micro-particleswere synthesized by direct-packed sol-gel method, coupling agent modified sol-gelmethod and coupling agent modified Al-Si particles method. The results show thatthe shell prepared by the direct-packed method is not dense and there are someconnected dots among the core/shell particles. Those prepared by coupling agentmodified method show little connected dots, but the shell is easily broken duringthe drying course. Those synthesized by coupling agent modified particle methodexhibit the best core-shell structures, such as dense core-layer, intact and noconnected dots among particles.The influences of synthesis parameters were studied to prepare Al-Si/Al₂O₃core-shell micro-particles by coupling agent modified Al-Si particles method. Adense layer of coupling agent is found on the surface of the modified Al-Si particles.Compared with the rough surface of the raw Al-Si particles, the smooth surface isobtained. The integrated shell is formed when the mole radio of aluminum tri-sec-butoxide and water is1:80. The drying temperature at30℃is suitable to reducethe crack on the surface of the shell. The dense and smooth shell is obtained afterheating treatment at1200℃, while porous shell is formed at700℃and900℃. Thephase of shell layer is-Al₂O₃after the particles are sintered at1200℃. It isapparent that core-shell structure is formed by the means of SEM. The shell isdense, integral and possesses single layer without crack and pores. The componentof shell layer is Al₂O₃that mainly originates from alumina sol in the course of thesol-gel.The results of heat storage of Al-Si/Al₂O₃core-shell micro-particles show thattheir phase temperature is572℃that is consistent with the raw Al-Si alloy particles. The latent heat reduces to307.2J/g. High temperature recycling experimentexhibits that after15times thermal treatment circles, Al₂O₃shell is still dense,integrated and no obvious cracks. After20times thermal treatment circles, its latentheat decays to215J/g and the mass increases3.75wt.%because of the oxidation.The gap between Al-Si alloy core and Al₂O₃shell is one of the reasons preventingthe shell to be broken during the course of phase change from solid state to liquid.The results of thermal conductive simulation reveal that when d=0.4, themulti-layer structure shows the most obvious thermal insulation effect, after Al-Si/Al₂O₃core-shell particles are added into multi-layer insulation as PCM. Thereasonable design of PCM located in the multi-layer insulation is a key step forrealizing the action of PCM.