Presentation Information
[P2-53]Effect of Bi addition on Decomposition Temperature of Sm-Fe-N
*Shusuke Okada1, Kenta Takagi1 (1. National Institute of Advanced Industrial Science and Technology (AIST) (Japan))
Keywords:
Sm-Fe-N,reduction-diffusion,Bi addition
Since Sm-Fe-N magnet has a very high anisotropy and a high Curie temperature compared to Nd-Fe-B magnet, it is expected to be applied as a heat-resistant magnet. On the other hand, the decomposition temperature of Sm-Fe-N is low, around 600 ℃. In addition, the coercivity of Sm-Fe-N decreases even when sintered below the decomposition temperature, making it difficult to fabricate high-density sintered magnet. 1) So, if the decomposition temperature can be improved and the sintering temperature can be raised, the possibility of realizing high-density sintered magnets can be greatly enhanced. Sugimoto et al. investigated the decomposition temperature of various elements added Sm-Fe-X-N and reported that Cr addition improves the decomposition temperature. 2) In this study, we prepared Sm-Fe-Bi-N powder, which is difficult to prepare with conventional melting process because the boiling point of Bi is equivalent to the Fe melting point, by using a reduction-diffusion (R-D) process and investigated the effect of Bi addition on the decomposition temperature.
Sm-Fe-Bi oxide powder was synthesized by coprecipitation method in which potassium hydroxide aqueous solution was dropped into aqueous solutions of iron nitrate, samarium nitrate and bismuth nitrate. The oxide powder was then subjected to hydrogen reduction, calcium reduction-diffusion, nitridation in NH3-H2, washing with water, drying, and dehydrogenation to synthesize Sm-Fe-Bi-N magnet powder. 3) The effect of Bi addition on the decomposition temperature of the synthesized powder was investigated using a TG-DSC-MASS simultaneous analysis.
The results of DSC and MASS (Molecular weight 28(N2) gas) measurements with and without Bi addition are shown in Figure 1. In the DSC measurement of Sm-Fe-N powder (without Bi addition), exothermic reactions were observed from around 600 ℃, which is known as the decomposition temperature of Sm2Fe17N3, and also from around 400 ℃ on the low temperature side. In the MASS measurement, N2 gas emissions were observed at each temperature, so it is thought that the exothermic reaction on the low temperature side is also due to the decomposition of Sm-Fe-N. On the other hand, in the case of Sm-Fe-Bi-N powder, there was no N2 emission on the low temperature side, and it was stable up to around 600 ℃. When the particle surface layer of Sm-Fe-Bi-N powder was dissolved by acetic acid treatment, the nitrogen emission at the low temperature side was confirmed. So, it is thought that the addition of Bi suppresses the formation of unstable Sm-Fe-N on the particle surface.
References
1) R. Soda, K. Takagi, M. Jinno, W. Yamaguchi and K. Ozaki, AIP Advances, 6 (11) (2016), 115108
2) S. Sugimoto, H. Nakamura, M. Okada, and M. Homma, in Proc. 12th Int. Workshop RE Perm. Magnets and Appl. (1992), 216-226
3) S. Okada, K. Suzuki, E. Node, K. Takagi, K. Ozaki and Y. Enokido, J. Alloys Compd., 695 (2017), 1617-1623
Sm-Fe-Bi oxide powder was synthesized by coprecipitation method in which potassium hydroxide aqueous solution was dropped into aqueous solutions of iron nitrate, samarium nitrate and bismuth nitrate. The oxide powder was then subjected to hydrogen reduction, calcium reduction-diffusion, nitridation in NH3-H2, washing with water, drying, and dehydrogenation to synthesize Sm-Fe-Bi-N magnet powder. 3) The effect of Bi addition on the decomposition temperature of the synthesized powder was investigated using a TG-DSC-MASS simultaneous analysis.
The results of DSC and MASS (Molecular weight 28(N2) gas) measurements with and without Bi addition are shown in Figure 1. In the DSC measurement of Sm-Fe-N powder (without Bi addition), exothermic reactions were observed from around 600 ℃, which is known as the decomposition temperature of Sm2Fe17N3, and also from around 400 ℃ on the low temperature side. In the MASS measurement, N2 gas emissions were observed at each temperature, so it is thought that the exothermic reaction on the low temperature side is also due to the decomposition of Sm-Fe-N. On the other hand, in the case of Sm-Fe-Bi-N powder, there was no N2 emission on the low temperature side, and it was stable up to around 600 ℃. When the particle surface layer of Sm-Fe-Bi-N powder was dissolved by acetic acid treatment, the nitrogen emission at the low temperature side was confirmed. So, it is thought that the addition of Bi suppresses the formation of unstable Sm-Fe-N on the particle surface.
References
1) R. Soda, K. Takagi, M. Jinno, W. Yamaguchi and K. Ozaki, AIP Advances, 6 (11) (2016), 115108
2) S. Sugimoto, H. Nakamura, M. Okada, and M. Homma, in Proc. 12th Int. Workshop RE Perm. Magnets and Appl. (1992), 216-226
3) S. Okada, K. Suzuki, E. Node, K. Takagi, K. Ozaki and Y. Enokido, J. Alloys Compd., 695 (2017), 1617-1623
