Study On Properties Of LaFe_11.65Si_1.35H_y Room Temperature Magnetic Refrigerating Materials Prepared By Solid Hydrogenation

Compared with the traditional gas compression refrigeration technology,magnetic refrigeration technology has the characteristics of environment friendship,high efficiency and energy saving.NaZn13 type intermetallic compound La(Fe,Si)13 has received extensive attention due to giant magnetocaloric effect and its low price.It has been found that La(Fe,Si)13Hy is considered to be an ideal room temperature magnetic refrigeration material.However,it is not easy to prepare homogeneous La(Fe,Si)13Hy bulks by gas phase hydrogenation,and the decomposition of La(Fe,Si)13Hy hydride is caused by the high temperature molding process.Herein,the innovative solid hydrogenation method is proposed,which posseses the merits of the uniform hydrogenation from inside and the integration of the hydrogenation process with molding process.In this paper,the solid hydrides YH2/Mg2NiYHx and LaFe11.65Si1.35 are uniformly mixed and cold-pressed,and then the vacuum heat treatment is performed above the hydride decomposition temperature to explore the feasibility of the preparation of La(Fe,Si)13Hy room temperature magnetic refrigeration materials by solid hydrogenation;next,the solder powder Sn3.0Ag0.5Cu was added to improve the mechanical properties and thermal conductivity of La(Fe,Si)13Hy room temperature magnetic refrigeration materials,The main conclusions are as follows:1.In contrast with LaFe11.65Si1.35 sample,the Curie temperature Tc of the(YH2(10 wt%)+LaFe11.65Si1.35)composite sample increases from 212 K to 254 K,and the magnetic hysteresis decreases from 3.34 J/kg to 1.10 J/kg,and the maximum magnetic entropy change reduces from 9.11 J/kg·K to 8.29 J/kg·K.It is proved that LaFe11.65Si1.35Hy magnetic refrigeration material can be prepared by the solid hydrogenation method.However,with the addition of YH2,the Curie temperature Tc of the composite sample only increased 30 K.2.In order to increase the solid-hydrogenation efficiency,we used Mg2NiYHx hydrogen storage alloy instead of YH2,which has a rich hydrogen storage and low decompositiontemperature.The Curie temperature Tc of the(Mg2NiYHx(10 wt%)+LaFe11.65Si1.35)composite sample increases from 212 K to 333 K,and the hysteresis decreases from 3.89 J/kg to 1.95 J/kg,and the magnetic entropy change reduces from 12.44 J/kg·K to 10.06 J/kg·K.It shows that the addition of hydride Mg2NiYHx increases the efficiency of solid hydrogenation.In addition,the study found that by only adding 4 wt%(even less)Mg2NiYHx,the Curie temperature Tc of the composite sample can be increased to 333 K.But the addition of Mg2NiYHx reduces mechanical properties and thermal conductivity of the composite sample.1.In order to improve the mechanical properties and thermal conductivity of composite samples,the low-melting solder powder Sn3.0Ag0.5Cu was selected.Compared with the(Mg2NiYHx+LaFe11.65Si1.35)composite sample,the Curie temperature Tc of the(Mg2NiYHx+LaFe11.65Si1.35+Sn3.0Ag0.5Cu)composite sample remains unchanged and the composite sample still maintains giant magnetocaloric effect.At the same time,the addition of 17 wt%Sn3.0Ag0.5Cu increases the compressive strength of composite sample from 18.69 MPa to 120 MPa,and the thermal conductivity from 2.778 W/(m K)to 5.691 W/(m K).It shows that the adding of Sn3.0Ag0.5Cu can improve mechanical properties and thermal conductivity of the composite sample without deteriorating the magnetocaloric performance.