Papers by Keyword: Nitrogenation

Abstract: Nitrides of ‘2:17’ - type based on rare earth metals and iron are of interest as promising magnetic materials for the development of high-energy permanent magnets. The magnetic properties and phase composition of the starting compound Sm_1.8Er_0.2Fe₁₇, nitride Sm_1.8Er_0.2Fe₁₇N_2.1 and its crushed powders have been investigated. The magnetic measurements of the samples were studied in magnetic fields up to 70 kOe at room temperature. It was found that the introduction of nitrogen atoms into the crystal lattice of the substituted composition (Sm,Er)₂Fe₁₇ in combination with the effect of high-energy milling of nitride leads to an increase in the saturation magnetization (σ_S) and coercive force (H_C).

Abstract: Influence of nanoflakes and melt-spun ribbons on the nitrogenation temperature f Sm₂Fe₁₇ was investigated. The microstructure, phase structure, properties of the specimens before and after nitrogenation have been discussed. It is interesting found that hard magnetic Sm₂Fe₁₇N₃ flakes have been synthesized by surfactant-assisted high energy ball milling and nitriding Sm2Fe17 in 3 psi of N2 gas at lower temperature 300 °C and 350 °C for 3 h. The synthesized Sm₂Fe₁₇N₃ flakes still retained nanostructure and obtained a coercivity of 3.56 kOe. For the melt-spun ribbons, it needs a higher nitrogenation temperature and longer time to obtain the same coercivity values as the nanoflakes.

Abstract: Calciothermic reduction-diffusion (CRD) method was employed to prepare the Sm2Fe17 powder. By using CRD method, single-phase Sm2Fe17 powders were successfully made and no α-Fe phase detected. And Subsequent suitable nitrogenation treatment after CRD process enabled us to obtain Sm2Fe17Nx magnetic powders. However, the magnetic performance of the powders was below expectation due to their large particle size. Further study on effective milling process is needed.

Abstract: The sintering of Sm2Fe17 compound prior to the nitrogenation process is studied as an alternative process to produce dense Sm2Fe17N3 hard magnets with higher maximum energy products (BH)max than conventional polymer bonded magnets. In order to optimize sintering and nitrogenation processes, powders made from alloys, with different compositions, in the as-cast as well in the as-homogenized state were used. It could be shown that the amount of α-Fe, formed in the casting process, was reduced during sintering and that Sm selective loss is restricted to the surface up to a depth of 100 +m. Moreover the density of the sintered samples was not much affected by the initial composition or by the prior homogenization of the alloys. Although the nitrogenation process was successful in producing the Sm2Fe17N3 as proved by the mass gain, magnetic properties measurements and X-Ray diffraction, the hard magnetic properties were much lower than expected, indicating that other variables, which are discussed in the text, must be considered.

Abstract: The calciothermic reduction-diffusion (CRD) process is a alternative preparation route for Nd15Fe77B8, NdFe11Ti, NdFe10.5Mo1.5 and NdFe10.75Mo1.25 alloys, which eliminates the need for long homogenizing heat treatment; in addition, the resulting alloy is already in powder form. We have examined the effect of various processing variables in the preparation of mother alloys. Compacts made of NdCl3, Fe, Ti, Mo and Fe-B powders and Ca granules were heated under argon for different times and temperatures. The alloys as-prepared contained mostly the hard magnetic phase. The NdFe11Ti, NdFe10.75Mo1.25 and NdFe10.5Mo1.5 alloys have been successfully nitrogenated by heating a mixture of powdered alloys with sodium azide (NaN3) at temperatures between 330 and 450 oC.