Studies On The Massive Preparation Technology And The Performance Of Mn-Fe Based Magnetic Refrigeration Materials

Recently years, the studies of room-temperature magnetic refrigerationmaterials have made much progress, of which the Mn-Fe based alloys becomeone of the best candidate materials for large scale preparation due to theirlarge magnetocaloric effect （MCE）, low cost and simple preparation. Thework in my thesis was carried out on the basis of the previous studies, useingindustry purity raw materials, and to use polycrystalline Si to replace the toxicelement As and the expensive element Ge. By changing the ratio of P:Si, itcan be obtained a better material with larger MCE for application.Furthermore, we prepared the alloys with phosphorsiderite and summarizedthe large scale preparation work of Fe₂P type materials.By means of the different measurement system, we have studied thecrystal structure and magnetic properties of Mn_1.27Fe_0.68P_0.44Si_0.56alloy, whichwas prepared by using pulverisette-6type high-energy milling machine. Theresult shows that the alloy mainly crystallizes in the type of Fe₂P hexagonalstructure with P62m space group. It can be observed from the temperaturedependence of magnetization （M-T）, the Curie temperature （TC） of the alloy is297K with a thermal hysteresis （ΔThys） of2K. According to the curves ofisothermal magnetization in a field change from0to1.5T, the maximalentropy change of the alloy is5.0J/（kg·K）, higher than that of Gd. Form theDSC measurement, it can be easily observed that the curve of DSC appears anendothermic peak at the temperature of295K, and the ΔThysis2.1K byextrapolation. The two results from magnetic and DSC measurement arealmost same. For this paper batch preparation to do some research work.To one-time can be more consistent with the sample performance, weusing pulverisette-5four cans of high-energy ball mill batch prepared a seriesof Mn_1.27Fe_0.68P_1-xSi_x（x=0.50,0.52,0.54,0.56） alloys and studied the crystalstructural and magnetic properties of them. The alloys mainly crystallizes in the type of Fe₂P with P62m space group, and with a second phase of Fe₃Siwhen x equals0.50,0.52and0.56. From the ratio adjustment of P:Si, the TCof the alloys can be made across the room temperature. With the increasing ofx, the TCof the alloys increased linearly from230K to310K, which makessense to the room temperature magnetic refrigeration. In addition, the ΔThysdecreases from4.7K to2.4K when x increases from0.50to0.56, and themaximal entropy change is14.2J/（kg K） which is higher than the report ofGd when x=0.52. It has been proved that the preparation process of them isvery simple, and for the low cost of raw materials, the alloys should be mostideal magnetic refrigerant.In order to make a further effort to reduce the cost, we have used threedifferet purity phosphosiderite which is very cheap and enriched with Fe andP, studied their influence on the MCE of the alloys. The result shows that thealloys made with phosphosiderite, exhibit better properties, all three alloyscrystallized in Fe₂P-type with the space group of P62m, and the TCincreasedby the adding of iron （Fe）, but the TCis higher than before when comparedwith previous work, maybe influenced by the impurities of phosphosiderite.The ΔThysis about4K, appears no obvious change, and the maximal entropychange is5.8J/（kg·K）,4.5J/（kg·K）,5.7J/（kg·K） respectively, only can beone half of the previous work. When studied the alloys in differentphosphosiderite content and compared with previous work, found that thealloys made with phosphosiderite also appeared a stable properties ofmagnetic, and with a considerable MCE. So, by using phosphosiderite, thealloys can be much cheaper and benefit for large scale preparation andcommercialization.