Long-time aging of La(Fe,Si,Mn)13Hz microparticles using different fluids for magnetic refrigeration systems

Abstract

La(Fe,Si,Mn)13Hz alloys are promising solid-state refrigerant candidates for room-temperature magnetocaloric refrigeration due to their giant magnetocaloric effect, adjustable Curie temperature (TC) and low rare-earth content. For enhanced efficiency, the magnetocaloric material (MCM) is configured into an active magnetic regenerator (AMR), a porous, layered component with a chemically-tuned TC gradient. The porous structure facilitates heat exchange with a working fluid. It is crucial to preserve the thermomagnetic properties, such as TC and the magnetocaloric effect intensity, during refrigeration cycles. This study conducts a systematic investigation of the stability of three batches of La(Fe,Si,Mn)13Hz magnetocaloric microparticles, each with different values of TC. The commercially available microparticles (average size about 620 µm), which simulate AMR applications, underwent a 1-year immersion in deionized water and three water mixtures with corrosion inhibitors: Entek FNE (2 % vol.), ME-1 (5 %. vol.) and ME-3 (5 % vol.). Optical and scanning electron microscopy revealed surface changes within the first week of immersion in water and later in two fluids. The TC shifted towards higher temperatures (up to 13 K) after immersion, especially in water and in the ME-3-containing medium. After 40 weeks, the Entek FNE mixture caused some damage to the magnetocaloric materials. The lattice parameter of the La(Fe,Si,Mn)13Hz magnetocaloric phase changed, and magnetic entropy decreased for most aqueous media. Only ME-1 proved effective in preserving magnetocaloric microparticle properties for all TCs over a year, making it a potential candidate for long-term prototypes and commercial products.