The Synthesis And Properties Characterization Of Al-Si/Al₂O₃-SiC Core-shell Micro-particles

Phase change materials has the function of storing energy and controllingtemperature. Compared to other phase change materials, Al-Si alloy has theproperty of high density of energy storage, high thermal stability, smallundercooling, high thermal conductivity, rich material sources, low manufacturingcost. It is a kind of promising phase change and energy storage materials. However,its high causticity and incompatibility are primary problems obstructing itsapplication, when Al-Si alloy changes from solid phase to liquid at hightemperatures. Therefore, it is very significant for the practical applications toachieve the effective encapsulation of Al-Si melt under high temperature conditions.Based on the micro-encapsulation technology of Al-Si/Al₂O₃core-shell structureparticles, SiC particles with high inertness and thermal conductivity wereintroduced into the Al₂O₃shell in order to improve its thermal conductivity whichis a useful method to improve the heat storage speed of Al-Si alloy so as to enhancethe effect of energy storage.Some of experiments and analysis methods, such as Zeta potentialmeasurement, transmission electron microscope（TEM）, were adopted to researchthe dispersion and modification of SiC nano-meter powders in order to analyze thepreparation mechanism of Al₂O₃-SiC composite shell. When SiC powders weredispersed by KH550, only a small amount of sol particles were adhered on theresurface. After dispersed by sodium dodecyl benzene sulfonate （SDBS）, however,SiC powders were wrapped by the alumina sol particles on the surface. The reasonis that the surface of SiC powder dispersed by SDBS is negatively charged, whichis benefit to attract positively charged Al₂O₃sols to form Al–O–Si bonds. Thus, itis more effective to to graft compounds on the surface of SiC powders so as tosynthesize the modified SiC nano-meter powders.The morphology and phase analysis of Al-Si/Al₂O₃-SiC core-shell particles atdifferent heat treatment temperatures were performed by means of scanningelectron microscopy （SEM） and X-ray diffraction （XRD）. With the increasing ofsintering temperature, the shell becomes much denser. After sintering at1200℃,Al-Si/Al₂O₃-SiC core-shell structure materials possess on integrate dense surface. The components of the shell contain-Al₂O₃and a small amount of SiC. Becausethe amount of the SiC nanometer powders are small and the modified SiC nano-meter powders are inevitably followed with agglomeration, it can be ascertainedthat SiC particles dispersed in the shell are not uniform.The latent heat of the Al-Si/Al₂O₃-SiC core-shell particles were obtained bymeans of differential scanning calorimetry （DSC）. The results showed that there is acertain deviation between the experimental data and theoretical values. On one hand,it is attributed to the breakage of the shell during the process of heat treatmentwhich leads to the leakage and oxidation of Al-Si alloy. On the other hand, thesegregation and enrichment of Si elements results in componential non-uniform.The latent heat of Al-Si/Al₂O₃-SiC core-shell particles is reduced based on thesetwo reasons. The thermal conductivitiy of the core-shell particles with differentadding amounts of SiC particles were characterized. The results revealed that asSiC contents increases, the value of thermal conductivity increase. The contrastexperiment on thermal leakage resistance bewteen Al-Si/Al₂O₃-SiC core-shellparticles and original Al-Si alloy particles showed that core-shell particles areprovided with good thermal leakage resistance performance.