Terumi Tanaka

Effects of additives on hydrogenation, disproportionation, desorption and recombination phenomena in Nd2Fe14B compounds

Hydrogenation, desorption, disproportionation and recombination (HDDR) phenomena are very attractive for the production of anisotropic Nd-Fe-B powders with high coercivity. HDDR phenomena are closely related to the characteristics of hydrogen absorption and desorption which correspond to the disproportionation and recombination reactions respectively. The effects of additional elements on these characteristics have been studied. According to the results for Nd 12.6 Fe 81.4 B 6.0 alloys, Nd 2 Fe 14 B compounds disproportionate into a mixture of NdH 2 , α-Fe and Fe 2 B phases at around 650 °C, which recombine to give the original compound at around 1050 °C under atmospheric pressure of hydrogen. The Nd 2 Fe 14 B compound exhibits two hydrogen desorption peaks corresponding to the recombination reaction. Judging from this result, it is considered that the recombination reaction occurs by a two-stage process. The temperature of the hydrogen absorption peak corresponding to the disproportionation reaction shifts to a higher value on the addition of Zr. Alloys with Co or Ga added show lower optimum temperatures of the recombination reaction than those of the alloy without additional elements. It can be said that Zr addition makes the disproportionation reaction sluggish, and Co or Ga addition enhances the recombination reaction in HDDR phenomena.

Effects of additional elements on hydrogen absorption and desorption characteristics of Sm2Fe17 compounds

Abstract Effects of additional elements on hydrogen absorption and desorption characteristics of Sm2Fe17 compounds have been studied. On heating the Sm2Fe17 compound under an atmospheric pressure of hydrogen, the Sm2Fe17 compound disproportionates into a mixture of SmH2 and α-Fe at around 550 °C; this mixture recombines to form the original compound above 1000 °C. Zr or Nb addition makes the disproportionation reaction sluggish. Co or Ga addition decreases the temperature of the recombination reaction under an atmospheric pressure of hydrogen. It can be said that Co or Ga addition is effective for enhancing the recombination reaction in hydrogenation, disproportionation, desorption and recombination phenomena.

Temperature dependence of the effective permeability of heat treated Sendust alloys

The temperature dependence (-10°C-70°C) of the effective permeability (μ eff ) of Sendust alloys (Fe-9-10 wt% Si-5-7 wt% Al) quenched at a room temperature from the various temperatures (400°C-700°C) was investigated at every 2°C in the temperature range of -10°C to 70°C. Most of the studied alloys gave a peak of μ eff in the studied temperature range. The peak temperature (Tp) giving the peak μ eff varied with different alloy composition. The alloys of Tp = 20°C are supposed to correspond to the alloys of the zero magnetocrystalline anisotropy constant (K 1 = 0) at 20°C. The deduced K 1 = 0 lines at various temperatures (-10°C-50°C) were obtained for an Fe-Si-Al ternary system. The values of peak μ eff at the same Tp were different, depending on alloy composition, This difference is due to the difference in the polycrystalline magnetostriction constant (λ s) of the alloys. The peak temperatures of the studied alloys vary with the different heat treatments. This variation is due to the variation of K 1 , induced by the change in microstructures of the alloys. The variation of the values of peak μ eff with heat treatments was small compared to the difference of those in the alloys of different composition. It seems that the variation of the λ s with heat treatments would be small. Both the compositional dependence of μ eff at 20°C and the temperature sensitivity (Δμ eff /ΔT) were obtained for both the alloys cooled continuously to room temperature and those quenched at room temperature from 400°C.

The effects of the heat treatments on the soft magnetic properties of the Sendust alloys

The effects of heat treatments on the soft magnetic properties and the temperature dependency of the properties of the Sendust alloys (Fe-9∼10wt%Si-5∼7 wt%A1 ternary alloys) were investigated. The quenching from the various temperatures(400°C∼800°C) was performed on the samples control-cooled(100°C/h) after homogenization(1100°C × 5h). It is found that the quenching temperature considerably affected the soft magnetic properties, and that the quenching temperature giving the good properties was varied with the alloy composition. The obtained highest initial permeability at 20°C was 380 000 for an Fe-9.7wt%Si-5.4wt%A1 alloy when it was quenched from 400°C. This value is about ten times higher than that of conventional Sendust alloys, and superior to 220 000 of Permalloy (Fe-79wt%Ni-5wt%Mo).