| Magnetic refrigeration technology is a new refrigeration technology which has the advantages of environmental protection,high efficiency,low noise and high reliability,thus has broad application prospects.The key of magnetic refrigeration technology is magnetic refrigeration materials.NaZn13 typed La(Fe,Si)13 alloy has become one of the most promising magnetic refrigeration materials because of its non-toxicity,harmlessness,low cost of raw materials,large magnetocaloric effect and so on.However,it has low Curie temperature(about 200 K),poor mechanical properties and thermal conductivity,which can not meet the needs of the application of refrigeration at room temperature.It has been found that the Curie temperature of La(Fe,Si)13 compounds can be improved to room temperature by incorporating interstitial H atoms.The traditional gas hydrogenation technology has the potential disadvantages of high energy consumption,cumbersome process and poor mechanical properties of finished products.In order to solve these problems,a solid-state hydrogen permeation method is proposed in this paper.Sm5Mg41Hx,La(Fe,Si)i3 based powder and solder powder were homogeneously mixed for cold-pressed and low-temperature hot-pressed treatment,and then hydrogen permeation treatment was carried out at a higher temperature to achieve the effect of hydrogen permeation at the same time the material was formed,so as to improve the mechanical properties and the density of material.The main conclusions are as follows:Composite samples(LaFe11.65S11.35+Sm5Mg41Hx)were prepared as the following steps:homogeneous mixing of LaFe11.65Si1.35 and Sm5Mg41Hx powders in the mass ratio of 9:1,cold m oulding and heat-treated under different temperatures.Curie temperature(Tc)of the composite samples increased by around 150 K.Besides,they maintained large magnetic entropy change and cooling capacity while the hysteresis of the material is reduced.Compared with LaFe11.65Si1.35 samples,to a certain extent the temperature span of the composite samp,les also increased,which showed that LaFe11.65Si1.35Hx magnetic refrigeration material with high magnetocaloric effect can be prepared by solid hydrogenation.Among them,when the heat treatment temperature is 783 K,(LaFe11.65Si1.35+Sm5Mg41Hx)composite samples have the best comprehensive properties.Based on the results above,La0.8Ce0.2Fe11.47Mn0.23Si1.3 material was selected as research object,and the addition of Ce and Mn elements improved the magnetic entropy change and the stability of hydride.La0.8Ce0.2Fe11.47Mn0.23Si1.3 and Sm5Mg41Hx hydrogen storage alloy were mixed in the mass ratio of 20:1,15:1,10:1 and 5:1 for cold-pressed solid hydrogenation.The effects of different proportion of hydrogen storage alloys on the properties of La0.8Ce0.2Fe11.47Mn0.23Si1.3 magnetic refrigeration materials were studied.All composite samples'Curie temperature increased,while their magnetic hysteresis decreased significantly,maintaining high magnetocaloric effect.In addition,the composite material was treated by dehydrogenation failure treatment and secondary hydrogen permeation treatment.And the experimental results showed that the samples prepared by solid hydrogenation can be repaired by re-hydrogenation without destroying the integrity of the samples.According to the increase of additive amount of hydrogen storage alloys,the Curie temperature can be increased from 152 K to 298 K,and the restored samples all maintained good magnetocaloric properties.In order to further improve the mechanical properties of the alloy,10 wt.%,20 wt.%and 30 wt.%solder powders were added into the mixed powders of La0.8Ce0.2Fe11.47Mn0.23Si1.3 and Sm5Mg41Hx hydrogen storage alloys,respectively.The samples were cold-pressed and heat-treated at 783 K.The results showed that the Magnetocaloric Properties and mechanical properties of the samples were improved after heat-treated,and the mechanical properties of the composites were the best with the solder powder content of 20 wt%.The composite sample with 20 wt.%solder powder was hot-pressed near the melting point of solder powder(217 ?)and then heat-treated.The results show that the hot-pressed sample has higher mechanical properties,density and magnetocaloric properties. |
PDF Full Text Request