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Magnetocaloric effect and H gradient in bulk La(Fe,Si)13Hy magnetic refrigerants obtained by HDSH

2015; Elsevier BV; Volume: 386; Linguagem: Inglês

10.1016/j.jmmm.2015.03.068

1873-4766

Henrique Neves Bez, Bruno G.F. Eggert, Jaime A. Lozano, C.R.H. Bahl, Jader R. Barbosa, Cristiano da Silva Teixeira, Paulo A.P. Wendhausen,

Rare-earth and actinide compounds

Results are reported on the preparation of bulk parts of La(Fe,Si)13Hy via the Hydrogen-Decrepitation-Sintering-Hydrogenation (HDSH) process. Net shape parts for application in room-temperature magnetic refrigeration have been produced in only 8 h of heat treatment which is considerably faster than the conventional ingot homogenization heat treatment of 7 days. The samples produced by HDSH showed higher amounts of hydrogen than the parts hydrogenated by the conventional method of thermal homogenization (20 h at 1423 K), milling to fine powder and subsequent hydrogenation. Hydrogenation parameters play an important role for the stability of the desired La(Fe,Si)13 phase during the process. Hydrogen desorption was seen to occur at two temperature ranges as a result of internal gradients. Dissimilar amounts of α-Fe were precipitated for different hydrogenation times. As a result, parts produced via HDSH with 2 and 4 h of hydrogenation exhibited different magnetocaloric behaviours. For a hydrogenation step of 4 h, parts with a demagnetization factor of 0.49 showed an adiabatic temperature change (ΔTad) higher than 1 K for a temperature range of 40 K with a maximum value of 1.57 K for an applied magnetic field of 1.75 T. As the duration of the hydrogenation step of the HDSH process decreased to 2 h, ΔTad was larger than 1 K for a temperature range of 24 K. However the maximum value of ΔTad at 328 K was 2.2 K, which is 37.5% larger than the maximum value for a hydrogenation period of 4 h.