Investigation On Magnetocaloric Effect And Microstructure Of Gd And Gd-based Alloys

Magnetic refrigeration technology at the room temperature has attracted more and more people's attention due to its advantages involving in energy saving, environmental protection. To be key issue, magnetic refrigeration material has played an important role in the technology.Firstly the article briefly introduces the basic principle, the key technology of magnetic refrigeration and the development of magnetic refrigerants. We have researched some questions and made some progress in this research. The article includes three parts: i) directly and indirectly measure the magnetocaloric effect of the different purity Gd under low magnetic field (<1.5T) , and verify the measured accuracy of the magnetocaloric effect adopting heat capacity. The result indicates that the magnetocaloric effect is reduced with increase of the impurity, Curie temperature decreased, ii) Gd5Si2Ge2 and Gd5Si1.9Ge2Sn0.1 alloy are heat-treated. The result indicates magnetocaloric effect of the alloy ingot have been greatly improved by heat treatment at high temperature, especially they has more three times than the former through heat treated by liquid nitrogen holding 1200℃ for 3h. iii) The microstructure of as-cast and heat-treated Gd5Si1 9Ge2Sn0.1 alloy are watched by SEM and XRD in order to find the cohesive relation between the microstructure and properties. The result indicates the alloy easily forms the second phase by the slower cooling during heat treatment, and makes more easily forming the single phase by holding temperature at high temperature and quicker cooling to improve the magnetocaloric effect.