Synthesis of Room-Temperature Magnetic Refrigerants Based on La-Fe-Si by a Novel Process

In this contribution, aiming to scale-up the production of the material to be used as a magnetic refrigerant, important results are reported regarding the preparation of La(Fe, Si) $_{13}$ compounds by a novel powder metallurgical approach. Additionally, with this new processing route, near net shape components can be fabricated. Based on the ability of some rare-earth compounds to absorb and desorb hydrogen in a controllable manner, an La-based alloy, obtained by conventional casting, was used as a precursor material for this approach. Due to the high content of La-rich phase (LaFeSi), it was possible to decrepitate the ingot into small pieces via interstitial hydrogen insertion. The decrepitated material was further milled, sieved and subsequently pressed into cylinders. A further consolidation step was carried out by sintering. During sintering, simultaneously, the microstructure was homogenized and the porosity controlled. After a 6 h heat-treatment at 1423 K, the samples approached single-phase La(Fe, Si) $_{13}$ , with a relative phase amount of 99 wt%. The residual porosity, inherent of powder metallurgy, plays an important role in a final hydrogenation step necessary to tune the transition temperature. This transition-temperature, around which the magnetocaloric effect is useful for refrigeration, was verified via DSC, while direct measurements of the adiabatic temperature change, $\Delta T_{\rm ad}$ , were carried out to quantify the magnetocaloric effect.