Effect of annealing pressure on surface oxidation in annealing process for LaFe11.5Si1.5C0.13 strips

Abstract

La(Fe,Si)13-based compounds are promising refrigerants for new magnetic refrigeration technology. Cumulatively, rapid solidification is one of the most effective synthetic methods for these compounds because it requires a short annealing time. However, the strips were found to become more susceptible to external factors due to the reduced dimensionality. In this work, the effect of annealing pressure on the surface oxidation of rapidly solidified LaFe11.5Si1.5C0.13 strips during heat treatment is explored. The results show that a lower annealing pressure (5 × 10−5 Pa) leads to obvious oxidation on the surface of the strip during the heat treatment. As a result, the chemical composition of the 1:13 phase becomes nonuniform on the strips after heat treatment. By annealing the strip composed of almost the single 1:13 phase under lower annealing pressure, the 1:13 phase is also decomposed because of oxidation. On the contrary, no obvious oxide layer is observed on the surface of the strip with the increase in the annealing pressure to 1 atm during the heat treatment. Additionally, the magnetic measurements show that the maximum magnetic entropy change (|ΔS|max) becomes smaller due to surface oxidation. The strips annealed under a higher annealing pressure exhibit a higher |ΔS|max of 15.97 J/(kg K). Therefore, the higher annealing pressure (1 atm) can be helpful to fully exploit the magnetocaloric potential of La(Fe,Si)13-based strips.