Basic research on durability of Mn-based magneto-caloric material for Magnetic Heat Pump

In order to put a room temperature magnetic heat pump into practical use, the reliability of the heat pump device has to be confirmed. Recently, magnetocaloric materials (MCMs) mainly made of iron have been developed, but it is necessary to contact some liquid with MCMs for heat exchange, so it is important to evaluate the durability of the MCMs against contact with some liquid. In order to evaluate the durability of Mn-based MCMs, we added some kind of anti-rust agent to water and conducted an experiment to investigate the corrosion occurrence situation. In the experiment, the material for crushing was immersed in liquid for up to 4 weeks at room temperature, its change over time was observed, and the change in properties was periodically measured. As a result, it was observed that when rust preventives were not added, rust occurred after a few days, whereas the addition of rust inhibitors prevented rust formation. It was also confirmed that no characteristic change occurred by selection of an appropriate rust preventive agent. In addition, a durability evaluation test was conducted to see whether changes in the mechanical strength and magnetization characteristics of the Mn-based MCMs can be seen by repeatedly changing the magnetic field. Mechanical strength was measured with a Micro Vickers hardness tester. The magnetization measurements were carried out in a magnetometer equipped with a superconducting quantum interference device. In the magnetic field change of 0 to 1 T of about 400,000 times, the results are not particularly noticeable for the deterioration of magnetic properties and the change in mechanical strength.