LaAl添加对放电等离子烧结LaFeSi磁体微观结构和磁热效应的影响

Microstructure and Magnetocaloric Effect of Spark Plasma Sintered LaFeSi Magnets with LaAl Addition

摘要:

使用LaFe_11.3Si_1.7薄带合金为前驱体粉末，研究了低熔点La_0.77Al_0.23合金添加对放电等离子烧结磁体微观结构和磁热性能的影响。研究发现，适量低熔点LaAl合金的添加能够促进包晶反应，制得了具有较高1:13相含量的LaFeSi磁体。磁体中观察到有微弱的巡游电子变磁转变现象的存在。热处理工艺研究显示，退火时间的增加会使得磁体的磁性转变由一级向二级变化，这主要归因于Al向1:13相内部的扩散。1000 ℃/6 h热处理工艺条件下，其在0~5 T磁场变化下的磁熵变最大，达12.40 J?kg^-1?K^-1，而1000 ℃/10 h条件下所获得磁体的制冷能力最强，为318.40 J?kg^-1。

Abstract:

Using LaFe_11.3Si_1.7 and La_0.77Al_0.23 alloys as precursors, the bulk LaFeSi samples with excellent magnetocaloric performance were synthesized through the spark plasma sintering (SPS) technology. The results show that the La_0.77Al_0.23 compound with a low melting point is helpful in facilitating peritectic reaction, and NaZn₁₃-type phase with high content can be achieved. A slight itinerant-electron-metamagnetic transition is observed. The increased thermal annealing time facilitates magnetic transition from the first order to the second order, which is ascribed to the excessive Al diffusion into the 1:13 phase. Under the thermal treatment condition of 1000 °C/6 h, the maximum entropy change (-ΔS_M) ^max of 12.40 J?kg^-1?K^-1 can be obtained, and the highest refrigerating capacity, up to 318.40 J?kg^-1, is achieved under thermal annealing condition of 1000 °C/10 h.