NaZn13型La-Fe-Si(H,C)泡沫材料的制备、磁性和磁热效应研究

NaZn13-typed La-Fe-Si and their interstitial compounds have attracted much attention due to the low cost and their large magnetocaloric effect. The magnetic, thermal hysteresis and the large internal stress induced by its first order phase transition nature, howerver, are not conducive to its application in magnetic refrigerator. The microstructure has significant effects on the phase transition nature. The heat exchange efficiency between the refrigerant and the cold storage fluid will be improved in the foamed materials, which is very improtan in the application of the magnetic refrigeration technology. . Through this project, we would try to prepare the La-Fe-Si and their interstitial compounds with a foam structure by the replication processe. Through the measurements and analysises about the microstructure and magnetic, thermal properties of the foamed and bulk materials, the effects of microstructure such as porosity , pore size etc. on the phase transition, magnetocaloric effect, magnetic and thermal hysteresis, internal stress and other properties as well as the heat exchange efficiency of refrigerant with cold storage fluid will be studied. We try to find out the relationship between the microscopic structure and the phase transition, the large magnetocaloric effect, and reveal its physical mechanism. NaZn13-typed La-Fe-Si and their interstitial compounds with a foam sturcture and the large magnetocaloric effect around room temerature would be prepared. This work will not only help the development of China's independent intellectual property rights of the magnetic refrigeration materials for magnetic refrigeration technology, but also have important influence on application and basic research of magnetic refrigeration technology.

高铁含量的NaZn13型La-Fe-Si及其间隙化合物因价格低廉、磁热性能优良而备受关注。但一级相变过程引起的磁和热滞后以及较大的内应力不利于其在磁制冷样机中的应用。而微观结构对相变性质有较大影响；理论计算表明：泡沫结构可有效提高磁制冷工质与蓄冷液间的热交换效率。我们将尝试采用铸造复制和粉末冶金造孔剂法制备具有泡沫结构的La-Fe-Si（H,C）新材料，通过微观结构、磁和热等性能的测量、分析，并结合La-Fe-Si块体材料已有研究成果，澄清微观结构特征如孔隙率、孔隙大小等对材料相转变、磁热效应、磁和热滞后、内应力、制冷工质与蓄冷流体间热交换效率等的影响。揭示微观结构、相变性质、磁（热）滞后之间的联系。成功制备在中高温区尤其是温区附近具有大磁热效应、制冷性能优良的La-Fe-Si泡沫材料，对发发展具有我国自主知识产权的磁制冷新材料，对磁制冷技术的应用和基础研究都将具有非常重要的意义。

优良磁制冷材料的研究与开发对磁制冷技术的发展至关重要。本项目我们拟尝试采用铸造复制和粉末冶金造孔剂法制备具有泡沫结构的La-Fe-Si（H,C）化合物，研究其结构、磁性和磁热效应。并探索了其它系列材料的磁性和磁热效应。 . 制备了单相性较好的NaZn13型La-Fe-Si块材及条带并探讨了块材NaZn13型化合物La-Fe-Si的居里温度机制。探索了制备La-Fe-Si泡沫材料的工艺条件和技术参数，结果发现热压结合粘接法制备的材料性能较好。并研究其磁性能和微观结构，结果表明颗粒间被孔隙和环氧树脂分割，颗粒度大小从60-200微米不等。在此基础上调节La-Fe-Co-Si成分，制备了居里温度在室温附近（320K）的LaFe10.7Co0.8Si1.5泡沫材料，磁熵变在室温附近保持了近15J.kg-1.K-1的较大值，可应用于室温区磁致冷。. 研究了Pr2CuSi3和Gd2CuSi3 化合物、Mn42Al50−xFe8+x 合金的结构、磁性和磁热效应。通过成分调节, Mn42Al50−xFe8+x 居里温度在室温附近一宽温区连续可调。研究了Ni2In-型化合物FeMn1-xNixGe的磁热效应和临界现象，居里温度在160 -320 K可调， 0-5T外磁场变化下化合物可在室温附近呈现4J/kg K 的等温磁熵变。用平均场理论结合Arrott曲线讨论了居里温度附近相变的临界行为。研究了重稀土基非晶合金制备条件的不同对合金磁性和磁热效应的影响。不同冷却速度导致不同微观结构（即不同程度的短程序和中程序），相变过程与微观结构有一定关系，0-5T 的磁场变化下，等温磁熵变峰值可达11J.kg-1.K-1,制冷效率为 670J.kg-1