• Journal of Magnetics
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• v.4 no.4
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• pp.123-127
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• 1999

The Ga-stabilised $Sm_2Fe_{17-}$type alloy can hardly be disproportionated under ordinary HDDR condition. The HDDR characteristics of Ga-substituted $Sm_2Fe_{17-}$type alloy were examined, and, in particular, the effect of particle size on the disproportionation of the Ga-substituted alloy was investigated in detail. The reaction characteristics of the $Sm_2Fe_{17-}$type alloys with or without Ga-substitution with methane (CH4) gas are also examined. The Ga-stabilised $Sm_2Fe_{17-}$type alloy was able to be disproportionated significantly on heating up to 80$0^{\circ}C$ under hydrogen with normal pressure. The particle size influenced significantly on the disproportion-ation of the Ga-substitute alloy, and the materials with finer particle size (<40 ${\mu}{\textrm}{m}$) was fully disproportionated on heating up to around 80$0^{\circ}C$ under hydrogen gas with normal pressure. The Ga-substituted alloy has a very sluggish recombination kinetics with respect to the alloy without Ga-substitution. The $Sm_2Fe_{17}C_{x-}$type carbide was stabilised significantly by the Ga-substitution for Fe in the parent alloy. While the $Sm_2Fe_{17}C_x$ was disproportionated below 80$0^{\circ}C$ the Ga-stabilised $Sm_2Fe_{14}Ga_2C_x$ carbide remained intact even on heating up to 80$0^{\circ}C$.

• Journal of Magnetics
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• v.14 no.4
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• pp.150-154
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• 2009

The effect of Ga and, Nb addition on the kinetics and mechanism of the disproportionation of a Nd-Fe-B alloy were investigated by isothermal thermopiezic analysis (TPA) using $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ (x=0 and 0.3, y= 0 and 0.2) alloys. The addition of Ga and Nb retarded the disproportionation kinetics of the Nd-Fe-B alloy significantly, and increased the activation energy of the disproportionation reaction. The disproportionation kinetics of the $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ alloys measured under an initial hydrogen pressure of 0.02 MPa were fitted to a parabolic rate law. This suggested that during the disproportionation of $Nd_{12.5}Fe_{(81.1-(x+y))}B_{6.4}Ga_xNb_y$ alloys with an initial hydrogen pressure of 0.02 MPa, a continuous disproportionation product is formed and the overall reaction rate is limited by the diffusion of hydrogen atoms (or ions).

• Journal of the Korean Magnetics Society
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• v.7 no.1
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• pp.44-48
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• 1997

The nanocrystalline Nd-Fe-B alloys with low Nd content were prepared by rapid solidification technique. The alloys consist of both$\alpha$-Fe as the main phase and $Nd_2Fe_{14}B_1$ as a secondary phase and have an ultrafine grain structure of about 30 nm. The addition of Ga in $Nd_4Fe_{82}B_{10}Mo_3Cu_1$ alloy increases remanence up to 1.29 T and improves squareness. The nanocrystalline $Nd_5Fe_{81}B_9Mo_3Cu_1Ga_1$ alloy has a volume fraction of $Nd_2Fe_{14}B_1$ phase of around 35% due to the increase of Nd content and shows an improved coercivity. The remanence, coercivity and energy product of optimally annealed nanocrystalline $Nd_5Fe_{81}B_9Mo_3Cu_1Ga_1$ alloy are 1.24 T, 257.4 kA/m (3.23 kOe), and 100.3 kJ/ ㎥ (12.6 MGOe), respectively.

• Journal of Magnetics
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• v.16 no.3
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• pp.229-233
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• 2011

Phase evolution during the hydrogen-assisted disproportionation of $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ alloy was investigated mainly by using a magnetic balance-type thermomagnetic analyser (TMA). In order to avoid any undesirable phase change in the course of heating for TMA, a swift TMA technique with very high heating rate (around 2 min to reach $800^{\circ}C$ from room temperature) was adopted. The hydrided $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ alloy started to be disproportionated in hydrogen from around $600^{\circ}C$, and the alloy after the early disproportionation (from 600 to $660^{\circ}C$) has been partially disproportionated. The partially disproportionated alloy consisted of a mixture of $NdH_x$, $Fe_3B$, ${\alpha}$-Fe, and the remaining undisproportionated $Nd_2Fe_{14}BH_x$-phase. During the subsequent heating to $800^{\circ}C$ in hydrogen, two additional phases of $Fe_{23}B_6$ and $Fe_2B$ were formed, and the material consisted of a mixture of $NdH_x$, $Fe_{23}B_6$, $Fe_3B$, $Fe_2B$, and ${\alpha}$-Fe phases. During the subsequent isothermal holding at $800^{\circ}C$ for 1 hour, the phase constitution was further changed, and one additional unknown magnetic phase was formed. Eventually, the fully disproportionated $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ alloy consisted of $NdH_x$, $Fe_{23}B_6$, $Fe_3B$, $Fe_2B$, ${\alpha}$-Fe, and one additional unknown magnetic phase.

• Korean Journal of Materials Research
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• v.15 no.6
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• pp.388-392
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• 2005

The $Zr_{57}V_{36}M_7$ getter alloy was prepared by Fe substituting Ga or Y for Fe on $Zr_{57}V_{36}M_7$ getter alloy(St707), and the activation temperatures and the hydrogen a sorption speeds of these alloys were investigated. The activation temperatures of these alloys were estimated from the ultimate pressure-temperature curve and lowered about $100\~200\;K$ compared to $Zr_{57}V_{36}M_7$, fetter alloy(St707). However, final pressures at fully activated temperature were increased with substitution of Fe by Ga and Y on $Zr_{57}V_{36}M_7$ getter alloy. The hydrogen sorption speeds of these alloys measured by an orifice method were decreased about $0.460\~0.586liter/sec$ g compared to $Zr_{57}V_{36}M_7$ getter alloy.

• Journal of Magnetics
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• v.4 no.4
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• pp.131-135
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• 1999

The HDDR characteristics of the Nd-Fe-B-type isotropic and anisotropic HDDR alloys were investigated using three types of alloys: alloy A $(Nd_{12.6}Fe_{81.4}B_6), alloy B (Nd_{12.6}Fe_{81.3}B_6Zr_{0.1}), and alloy C (Nd_{12.6}Fe_{68.8}Co_{11.5}B_6Ga_{1.0}Zr_{0.1}$). The alloy A is featured with the isotropic HDDR character, while alloy B and C are featured with the anisotropic HDDR character. Hydrogenation and disproportionation characteristics of the alloys were examined using DTA under hydrogen gas. Recombination characteristics of the alloys were examined by observing the coercivity variation as a function of recombination time. The present study revealed that the alloy C exhibits slightly higher hydrogenation and disproportionation temperatures compared to the alloy A and B. Recombination of the anisotropic alloy B and C takes place more rapidly with respect to the isotropic alloy A. The intrinsic coercivities of the recombined materials rapidly increased with increasing the recombination time and then showed a peak, after which the coercivities decreased gradually. The degraded coercivity was, however, recovered significantly on prolonged recombination treatment. Compared with the isotropic HDDR alloy A the anisotropic HDDR alloy B and C are notable for their greater recovery of coercivity. The significant recovery of coercivity was accounted for the in terms of the development of well-defined smooth grain boundary between the recombined grains on prolonged recombination.

• Proceedings of the Korean Magnestics Society Conference
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• 1998.05a
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• pp.92-93
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• 1998

• Journal of Magnetics
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• v.10 no.4
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• pp.152-156
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• 2005

Effects of the disproportionating hydrogen pressure and alloy composition on the texture in the HDDR-treated Nd-Fe-B particles were examined using the $Nd_{12.6}Fe_{81.4}B_6$ and $Nd_{12.6}Fe_{68.7}B_6Co_{11.0}Ga_{1.0}Zr_{0.l}$ alloys. Disproportionation kinetics of the $Nd_2Fe_{14}B$ phase in the Nd-Fe-B alloy was retarded significantly by the addition of Co, Ga and Zr. The retarded disproportionation kinetics of the $Nd_2Fe_{14}B$ phase ensured a wider processing win­dow in terms of disproportionating hydrogen pressure for achieving a texture in the HDDR-treated Nd-Fe-B alloy particles.

• Journal of Magnetics
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• v.18 no.3
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• pp.240-244
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• 2013

The influences of Gallium doping on the magnetic microstructures and corrosion behaviors of Nd-Fe-B-Ti-C alloys are investigated. The cooling rate for obtaining fully amorphous structure is raised, and the glassforming ability is improved by the Ga addition. The High Resolution Transmission Electron Microscopy image shows that the ${\alpha}$-Fe and $Fe_3B$ soft magnetic phases become granular surrounded by the $Nd_2Fe_{14}B$ hard magnetic phase. The rms and $({\Delta}{\varphi})_{rms}$ value of Nd-Fe-B-Ti-C nanocomposite alloy thick ribbons in the typical topographic and magnetic force images detected by Magnetic Force Microscopy(MFM) decreases with 0.5 at% Ga addition. The corrosion resistances of $Nd_9Fe_{73}B_{12.6}C_{1.4}Ti_{4-x}Ga_x$ (x = 0, 0.5, 1) alloys are enhanced by the Ga addition. It can be attributed to the formation of more amorphous phases in the Ga doped samples.

• Proceedings of the Korean Magnestics Society Conference
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• 1999.04a
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• pp.68-69
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• 1999