Structure, Magnetic Properties And Refrigeration Performance Of MnFe (P, Si) Compounds

Nowadays,the concept of advocating eco-friendly is deeply rooted in people's minds.We are constantly developing green energy to create a habitable environment.In terms of refrigeration technology,the traditional pneumatic refrigeration is widely used in refrigerators,air conditioning in daily life,it has made the huge energy consumption,and the emissions also contribute to the greenhouse effect.How to guarantee an ecological environment suitable for living,becomes a problem to be solved urgently for the world in urbanization process.The magnetic refrigeration technology in room temperature area has made great achievements in recent years.Compared with the traditional pneumatic refrigeration,it has two significant advantages,on one hand,it is highly efficient and energy-saving without the compressor equipment,on the other hand,it adopts green and environmental protection theme.In the past two decades,the research on magnetic refrigeration materials has greatly promoted the development of magnetic refrigeration technology.Among all the magnetocaloric materials,Mn-Fe based compounds are favored for its simple preparation,suitable cooling temperature and strong cooling capacity.However,this refrigerating material has never been operated in the refrigeration prototype.This paper studies its structure and magnetothermal effect,in addition,the refrigeration mechanism of the compound permanent magnet in room temperature magnetic refrigeration was also explored.The first chapter gives a systematic review of the theoretical basis and research background of magnetic refrigeration,which reveals the purpose and content of this paper.Chapter 2 introduces the experimental equipment and the data analyzing software from the research contents.Chapter 3 based on XRD-Rietveld Full-Spectrum Fitting Method to quantitative analysis of phases characterization of Mn_1.28Fe_0.67P_0.48Si_x?x=0.52,0.53,0.55?compounds.After the refinement R factor meets the requirements of the qualified judgment,in addition,the calculation spectrum and the original spectrum match high degree.It is shown that the quantitative analysis applied to such samples is highly accurate and reliable.This is the first time that the Rietveld full-spectrum fitting method has been introduced into functional materials,which helps to explore the evolution of ferromagnetic to geomagnetic phases of MnFe?P,Si?materials during phase change,while providing a new way for the fitting of its XRD map.Chapter 4 studies the structure and magnetocaloric of Mn_1.28Fe_0.67P_0.48Si_x?x=0.56,0.565,0.57,0.575?,Mn_1.28Fe_0.67P_1-xSi_x?x=0.54,0.55,0.56?,and Mn_xFe_1.93-xP_0.45Si_0.55?x=1.1,1.17,1.18,1.19,1.2?series.In chapter 5,on the basis of the research in chapter 4,Mn_1.28Fe_0.67P_0.48Si_x?x=0.56,0.565,0.57,0.575?series samples were selected to experiments in the complex permanent magnet room temperature Magnetic refrigerator of Bao Tou rare earth institute.Before the experiment,the size and sintering process of samples were studied and selected,and then the cooling data of samples were obtained in the experiment.