| Sm2Fe17N3has excellent intrinsic magnetic properties, which is supposedto replace Nd-Fe-B. The Curie temperature of Sm2Fe17Nxis200K higher than that ofNd-Fe-B, while the anisotropy field in Sm2Fe17Nxis almost three times to that ofNd-Fe-B. However, when the temperature exceed to773K, Sm2Fe17N3decomposesto SmN, Fe4N and Fe. This paper attempts to explore the use of high N2pressureheat-treatment technique to solve the decomposition problem. In theory, highnitrogen pressure can inhibit the decomposition and increase the nitrogen content ofthe product. In addition, we prepared Mn-N powders under high gas pressure andstudied its effect on the structure and magnetic properties.We report on a novel method for preparation of high purity Sm2Fe17phase byremoving the liquid impurity phase from the Sm-rich precursor during thehigh-temperature reduction process. The magnetic properties of Sm2Fe17N3from theatomic-number proportion of2.4:17（Sm:Fe） is relatively good.We developed two high gas-pressure heat-treatment devices. For one, theworking pressure is up to300atm and the working temperature is up to800℃. Thebasic principle is that some gas is cooled by liquid nitrogen, then heated in a closedspace to achieve high gas pressure. For the other, the working pressure is up to1000atm and the working temperature is up to1000℃，using gas booster achieves highgas pressure continuously.We do some research on the effect of hydrogenation process. It is found thathydrogenation can reduce SmFe3to improve the purity of the ingot and magneticproperties.Sm2Fe17N3was prepared by melt-spun method with liquid-N2-cooling andnitrogen absorption under N2gas pressures up to25MPa. The structure andmagnetic properties of the products prepared under varied temperatures, N2pressuresand nitrogen absorption time have been investigated systematically. The melt-spun method and high N2pressure improve the magnetic properties. The sample preparedat743K under nitrogen pressure of20MPa for5h, which shows Hcj=190.3kA/m,Br=0.223T, Hcb=82.44kA/m,（BH）max=4.4kJ/m3.We have studied the structure and the magnetic properties of the productsnitrided from Sm2(Fe0.8Co0.2)17under varied high N2pressures systematically.Withthe increase of pressure from10MPa to25MPa, Brand （BH）maxgoes up firstly thengoes down. The optimium values for magnetic properties are: Hcj=229.7kA/m,Hcb=174.4kA/m, Br=0.635T,（BH）max=39.16kJ/m3.We report on the structural transformation and unique magnetic properties ofthe manganese nitrides prepared by nitriding Mn under N2pressures up to25MPawith varying temperatures. High N2pressure not only makes nitridation moreefficient at lower temperatures, but also enhances the N-content in the nitride lattices.The N-rich nitrides, including ε-Mn4N, ζ-Mn6N2.58and η-Mn3N2, exhibit uniquethermal behaviors. The N-rich ε-Mn4N exhibits much larger coercivity, which is44656A/m, in comparison with the same phase prepared under ambient N2pressures,which is18069A/m. The coercivity of the N-rich ζ-Mn6N2.58reaches up to45054A/m, which is antiferromagnetic.The saturation magnetization of η-Mn3N2is31Am2/kg. |
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