Studies On The Design Of Thermomagnetic Power Generator And The Properties Of Thermomagnetic Power Generation Materials

First-order phase transition （FOPT） materials MnFeP1-xAsxhave attractedmuch attention of refrigeration industry and scientists due to its largemagnetocaloric effect （MCE） and broad refrigeration-zone crossing the roomtemperature. But the existence of As makes the doubt whether the series ofcompounds could be environmentally friendly materials or not. In the past tenyears study, the element As has been successfully replaced by Ge and Si. Si isthe best element that replaced As at present, not only because it has low costbut also because it is the second most abundant element on the earth exceptfor oxygen.The FOPT materials can be used not only in the field of magneticrefrigeration, but also in the field of thermomagnetic power generation（TMPG）. In this thesis, the author reported the preparation methods, crystalstructure, MCE and TMPG performance of MnFe（P,Si） compounds. Thestudy showed that all MnFe（P,Si） prepared by using mechanical alloytechnology and solid state sinter reaction mainly crystallize in the Fe2P typehexagonal structure with P62m space group, but a minor second phase（Mn,Fe）3Si existed.Thermal hysteresis （Thys） is the most notable feature of the FOPTmaterials. In order to decrease Thysof MnFe（P,Si） compounds, the authorprepared a series of Mn_1.3Fe_0.7-xV_xP_0.45Si_0.55（x=0,0.05,0.10,0.15）,attempted to use V to substitute for iron （Fe）. The results showed that theCurie temperature （TC） of the compounds can be continuously adjusted bysubstitution, but the Thyshas no obvious change. It could be easily observed from the field dependence of the isothermal magnetic entropy change that thewidth of half peak value increases with the increase of V content. So, thesubstitution of V for iron can be used for broadening the temperature-span ofmagnetic materials and increasing the continuity of MCE.In this thesis, the author mainly reported the MCE and TMPGperformance of the series of Mn_1.1Fe_0.8P_xSi_1-x（x=0.4,0.42,0.44,0.46）compounds with TCabout340K in average. The result showed that thecompounds all crystallize in the phase of Fe2P type, and the lattice parametera, cell volume V and the Curie temperature TCdecrease with the increase of x,while the magnetic entropy change increases and the maximum is18.44J/（kg K） for x=0.46in a field change from0to1.5T. We utilized thecompound of x equals0.46for TMPG, and the results showed that themaximal induced current can be up to1.38mA/kg.In addition to the material study, the design of TMPG demonstrationdevice is also reported. The device consists of three parts: external magnet,induction coils in different turns （N=1000,1500,2000,2500,3000） andthermal circular system （hot and cold water alternative）. The experiment wasconducted in two aspects, one was the temperature dependence of inducedcurrent at different quality of the materials, and another was the temperaturedependence of induced current at different turns of induction coil. The resultshowed that the induced current increased with increasing mass of material inthe same coil, and also increased when adding the turns of the coil.