相变介质组成对粉煤灰基高温定形复合相变材料蓄热性能的影响

分别以Al粉、Al-12Si、Al-20Si合金粉为相变介质,粉煤灰为基体材料,采用混合烧结法在空气、真空两种烧结氛围下制备金属/陶瓷基高温定形复合相变材料,探讨相变介质中硅铝相对含量及烧结氛围对材料蓄热性能的影响。结果表明:分别用三种金属粉制备复合相变材料时,Al的氧化难以避免,致使Si的相对含量均超过共晶点组成,凝固时其状态点始终处于共晶相+Si相的两相区,未被氧化的Al都转变成为Al-Si共晶相。空气中烧结有利于Al形成致密氧化膜从而阻止其进一步反应,材料的密度、相变潜热都比真空中烧结高。三种复合相变材料中,由Al粉制备的热稳定性最差,由Al-12Si合金粉制备的相变潜热、保留率最高,热稳定性及蓄热性能突出。

Influence of Phase Change Medium Composition on Heat Storage Performance of Fly Ash-Based High-Temperature Shaped Composite Phase Change Materials

Using Al powder, Al-12 Si and Al-20 Si alloy powder as phase change medium and fly ash as matrix material, metal/ceramic based high-temperature shaped composite phase change materials were prepared by mixed sintering method under air and vacuum sintering atmosphere. The effects of the Al-Si relative content and sintering atmosphere on the heat storage performances of materials were investigated. The results show that the oxidation of Al is inevitable when the three kinds of metal powders are used to prepare composite phase change materials, the relative content of Si exceeds the eutectic point composition. The state point during solidification is always in the two-phase zone of eutectic phase and Si phase, and the unoxidized Al transforms into Al-Si eutectic phase. Sintering in air is beneficial for Al to form a dense oxide film and prevent its further reaction. The density and latent heat of phase change of materials sintered in air are higher than those sintered in vacuum. Among the three kinds of composite phase change materials, Al powder composite phase change material has the worst thermal stability, while Al-12 Si composite phase change material has the highest latent heat of phase change and retention rate, and outstanding thermal stability and heat storage performance.