| Magnetic refrigeration is a new method of realizing the refrigeration by using the magnetic effect of the magnetic material.Compared with the traditional compression refrigeration,the magnetic refrigeration technology has the advantages of environmental protection,energy saving and silence,and it is expected to replace the traditional compression refrigeration technology.At present,the magnetic refrigeration technology has been applied to low temperature refrigeration,but the room temperature magnetic refrigeration technology has just started,and faced with many problems,such as induced phase transition occurred in the magnetic field is too large,the thermal and magnetic hysteresis is large,phase change Temperature is small and so on.Ni Mn-based Heusler alloy is a new type of magnetic refrigeration material.During the cooling process,the alloy undergoes a phase transition from the high temperature austenite to the low temperature martensitic phase and is accompanied by a sudden change in the magnetization.Belongs to the first-order phase transition,studies have shown that the magnetization of the mutation can produce a larger magnetic entropy change,to achieve giant magnetic heat corresponding.Magnetocaloric effect is a kind of inherent characteristics of magnetic materials.In magnetic refrigeration technology,the magnetic entropy is the most important,the magnetic entropy change of the magnetic material,accompanied by endothermic and exothermic phenomenon in order to achieve the cooling effect,but the existence of lattice entropy and electronic entropy reduce the refrigeration efficiency.In this paper,all alloys were prepared by arc-melting method,and their structure,magnetic and magnetocaloric properties were discussed in detail.Moreover,we also compared with the effects of different substitutions of atoms on alloys and details are as follows:?1?The first and second chapters introduce the principle of magnetic refrigeration,the entropy of magnetic refrigeration and the development status,preparation method and material performance of room temperature magnetic refrigeration materials.?2?In the third chapter,the Ni50-xCoxMn36Sn14?x = 0,0.5,1.5,2,3?alloys were studied.It was found that the temperature and magnetic field induced anti-martensite transformation in the alloy were investigated.Phase change temperature,improve Curie temperature.The magnetocaloric effect study shows that the alloy has a large magnetic entropy change near the martensitic transformation point,so the alloy has a considerable cooling capacity.It was also found that the phase transition temperature of the alloy could be adjusted with the doping of Co.The magnetic entropy of the sample in the sample Ni49.5Co0.5Mn36Sn14 reached 18.8 J/?kg K?,and the larger half-width was obtained in the sample Ni48.5Co1.5Mn36Sn14,made a larger refrigerating capacity,and the maximum reached 290.4 J/Kg.?3?In the fourth chapter,the crystal structure of Ni50-xCoxMn36In14?x = 2,3,4,5?alloy is analyzed and studied.The results show that with the increase of Co atoms,The magnification of the martensite transformation increased first and then disappeared,and the magnetization of the alloy was found to be significantly improved.Based on the thermodynamic theory,the isothermal entropy change of the alloy is calculated.Up to 22.7J /?kg K?.?4?Chapter fifth studies the Ni50-xCoxMn38Al12?x = 4,6,8?alloys.The martensitic transformation from ferromagnetic austenite to weak magnetic martensite is realized in the alloy,and the magnetic field induced reverse martensitic phase transformation is obtained.And the change of magnetization and magnetic entropy change in the reverse martensite transformation is obtained.By calculating the magnetocaloric effect of the sample,we obtained a large magnetic entropy change in the sample Ni44Co6Mn38Al12,reaching 22.3J /?kg K?.?5?Chapter sixth is the summary of the above content and perspective according to the present research are prospected. |
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