(07A927) Effect of carbon on magnetocaloric effect of LaFe_(11.6)Si_(1.4) compounds and on the thermal stability of its hydrides

摘要

La(Fe,Si)_(13) alloys display a giant magnetocaloric effect when a magnetic field is applied near the Curie temperature T_C. However, to use these alloys for domestic refrigeration based on magnetic cooling, it is vital to increase T_c near to the room-temperature range while simultaneously maintaining a large magnetocaloric effect. With this aim, we studied the effect of interstitial carbon on the microstructure and magnetocaloric effect in LaFe_(11.6)Si_(1.4)C_x (X= 0-0.4). The investigation was carried out in cast samples annealed for seven days at 1323 K. The study of microstructure shows that annealing led to about 90wt. % of 1:13 magnetocaloric phase. Magnetization data revealed that the addition of carbon leads to an increase in T_c and a decrease of the thermal hysteresis width. For x > 0.2, the magnetic transition changes from first-order to second-order, with a corresponding reduction in magnetocaloric effect. A small amount of C (x up to 0.2) improves the magnetocaloric properties of the parent alloy La(Fe,Si)_(13), and, furthermore, the carbon addition leads to an increase in the thermal stability of hydrided LaFe_(11.6)Si_(1.4)C_x The onset of hydrogen desorption increases from 460 K for the x — 0 (carbon-free alloy) to 500 K and 540 K, respectively, for x = 0.1 and x = 0.2.