Design guidelines for Al-12%Si latent heat storage encapsulations to optimize performance and mitigate degradation

We provide detailed insight into the growth kinetics of intermetallic layers formed at the interface of molten Al-12%Si with cylindrical encapsulations of 316L stainless steel. This knowledge is relevant for the design and operation of high-temperature latent heat storage and energy harvesting devices at application-relevant conditions. Our continuous experiments on iron-aluminide deposition rates at 600 °C and 700 °C lasted up to 120 days. The layer thickness was determined in metallographic cross sections by light microscopy. We observed deviations from standard growth models, including a delayed layer growth onset at 600 °C and strongly non-parabolic kinetics at 700 °C. We developed a numerical diffusion model that accommodated temperature dependent kinetics and was able to explain the observed deviations by incorporating de-passivation and dissolution phenomena. Numerical fitting of the model to the experiments provided optimized mobility parameters that agree with those reported for the Fe2Al5 compound, whose presents was confirmed by energy dispersive X-ray elemental analysis. Differential scanning calorimetry revealed reductions in heat of fusion and melting temperature, of -10 % and -10 K, respectively, after 120 days at 700 °C. Fe concentration in the melt increased from