Vestigation On Magnetic Entropy Change Properties Of Lacefesi And Nimnsn Magnetocaloric Materials

The 21st centuty is a green, highly effective, safe utilization of high-tech time. The magnetic refrigeration technology makes use of magnetocaloric effect of magnetic materials, achieving cool by decalescence and exothermic reaction in magnetization and demagnetization process. It would not release any harmful gases which may destroy ozone. Special harmless, low noise, highly efficiency makes it would be one of the most potential refrigeration technologes in future. Looking for magnetocaloric materials with large magnetic entropy change is the key of exploiture the technology.In this dissertation, we explained the principle of magnetic refrigeration materials, presented the phylogeny and related theory. Then, shown the preparation, heat treatment, structure and magnetic measurement and so on. After analysing the results, we came to a conclution about Curie temperature, phase transition temperature, magnetocaloric effect. The incestigation details were summarized as follows:Firstly, polycrystalline materials of La0.8Ce0.2Fe11.4-xMxSi1.6(M=Mn, Cr, Ni) were prepared in high vacuum arc melting furnace. The alloys were annealed at 1373 K for 5 days and quenched in cool water. Then NaZn13 phase was obtained in all alloys. The magnetic measurement shown that, the substitution of Mn atoms for Fe ones could attain the constant refrigeration capacity, widen the range of refrigeration temperature and decrease Curie temperature. The replacement of Cr atoms increased the alloys mangnetic entropy change to 106 J/kg.K in 2 T magnetic field. In the alloys for Ni in place of Fe, the phase transfered from First-Order to Second-Order. Cure temperature was improved, while thermal lag and magnecit hysteresis was decreased to 0.Secondly, the Heusler alloys of Ni43Mn46VxSn11, Ni43Mn46Sn11Six and Ni43Mn46Sn11Alx were prepared by high vacuum arc melting furnace. The alloys were annealed in 1173 K for 2 days and quenched in cool water. The results shown that, the series were L2Ⅰphase structre. In the cooling process,all alloys would undergo structure transition between austenite and martensite. The substitution of V for Mn, declined the phase transion temperature, but improved magnetocloric effect. Under 3 T external field, refrigeration capacity of Ni43Mn46V1.5Sn11was 164 J/kg, only including a little average magnetic hysteresis loss of 12.0 J/kg. The addition of Si atoms depressed the phase transition temperature and the spans of hysteresis temperatures. Then hysteresis loss capacity was reduced to a low value. In the alloys of Al introducing, the Ni43Mn46Sn11Al0.6 alloy improved phase transition temperature to 202.5 K. The most magnetic entropy change was 23.6J/kg.K. Working temperatures and magnetic entropy change were enhanced at the same time.Thirdly, La0.8Ce0.2Fe11.4Si1.6 alloys were prepared in high vacuum arc melting furnace by two different methods, one is arc-melting and subsequently annealed for 5 days, and the other is rapid quenching by copper mould casting and subsequently annealed for 2 hours. In comparing, samples obtained good grain stucture, wide temperature spans, big refrigeration capacity, which prepared by copper mould casting. In addition, copper mould casting will save much time and energy. La0.8Ce0.2Fe11.4Si1.6Bx were prepared by copper mould casting. The results exhibited high Curie temperature, low hysteresis loss, weak First-Order phase transition. It is good for the application of magnetocaloric materials.