Effects of dynamic conditions in the corrosion of stainless steel and graphite with molten Al-Si alloy for transport applications

Abstract

Energy storage systems are key mechanisms for the transition to more sustainable energy sources. In the case of applications that involve heating intermittency, the use of phase change materials (PCMs) as thermal energy storage systems is of relevance. Particular metals and metallic alloys represent a promising alternative for their use as PCMs due to their high latent heat and high density, minimising the storage volume, and high thermal conductivity, allowing fast charge and discharge. However, the high operating temperatures, the reactivity of the molten metals and the periodic melting and solidification cycles promote corrosion of the container materials. Moreover, applications involving relative movement between the components (e.g. sloshing or pumping) can experience erosive-corrosive wear. In this work, a thermal energy storage system using an Al-Si alloy as PCM intended for application in electric vehicle cabin heating is analysed in terms of the compatibility with graphite and 304 stainless steel. The formation of new phases and potential reaction products at a static interface between container and molten material has been studied. Furthermore, the relative motion expected in the application has been simulated using a high temperature rheometer with cup and bob geometry. The type and extent of phases formed under dynamic conditions have been identified, exemplifying the influence of erosive-corrosive interaction as compared to static corrosion. The experimental methods, results and an appraisal of the impact of relative motion on wear in metallic phase change material systems undergoing dynamic conditions will be given.