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 Wysłany: Nie 12:31, 16 Sty 2011 Temat postu: moncler daunenjacke Adding Zr and Ga on the Nd-Fe- |
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Adding Zr and Ga on the Nd-Fe-B magnets role of hydrogen treatment
Hydrogen technology commonly used in the preparation of high coercivity and anisotropy of powder. French scholars to study the hydrogen protection by induction melting method were Nd2Fe14B, Nd2Fel4B ~ Zro. 5 and Nd2Fe14B-Ga2.53 kinds of alloy ingots, the 1000 * C after homogenization 6h, broken into a powder, average particle size of 157 ± 5/_tm. X-ray diffraction samples are single phase Nd2Fe14B (phase). Extended x-ray absorption fine structure (x) of the zr and Ga added after the close order structure. 3 powder in 2kOe field, the continuous communication of hydrogen, and 10 ℃ / min heating rate to 600 * (2 ~ 750 * (2, then at the same speed cooling, measurement of magnetic powder in the hydrogenation reaction can be change. Undoped phase hydrogenation was found that with increasing temperature, due to the magnetization M phase hydrogenation increases; but the Curie point (Tc) at,[link widoczny dla zalogowanych], M rapid decline into a platform; rose to 625 * (2, due to the phase hydrogenation disproportionation increased production of free Fe and M. If the platform area to stay long enough, you can complete disproportionation disproportionation if fully cooled before the sample, the resulting mixture of disproportionation and not disproportionation. disproportionation reaction to the conversion before and after the height of Tc can be estimated at a heat treatment at the end of the disproportionation rate (rn), in the low temperature, the disproportionation started M-T curves corresponding to the platform started (t = 0 处, m = 0), the end of the platform at the height of the curve obtained by the disproportionation rrc speed ( If the reaction is completed,[link widoczny dla zalogowanych], rn = 1). with a radius r of the spherical particles of solid-state reaction-diffusion mechanism of experimental data can be seen: no doped powder in T ≤ 625 * (2, the disproportionation interface diffusion mechanism for the control of the process, its speed U unchanged. in the 625 * (2, response to comply with F (m) = 1 A (1 A m) = (u / r) · t. T> 625 \control, T = 670 ~ 2, the disproportionation follow Jander Law: G (m) = [1 a (1 A m) 32 = (k/r2) · t. where k (T) = koep (E / RT), Ea is the activation energy, R is the gas constant. Experimental results show that adding a small amount of zr in the alloy can only form a small ZrB2 precipitation (space group: P6/mmm, a = 3.168 / ~, c = 3.55oA). plus zr phase disproportionation of power can be reduced, however,[link widoczny dla zalogowanych], extend the time for increasing reaction temperature,[link widoczny dla zalogowanych], phase can be completely disproportionation. including less than 625 * (2 in the entire temperature range, the phase disproportionation of zirconium doped Jander compliance law. undoped and doped 0.7at % Zr phase of the In (k/r2) with 1 / T change is linear. obtained zirconia phase and processing phase of the activation energy E = 335kj/mo1 respectively, and (Ea) z = 228kj/mol, measured with average size of the powder was calculated diffusion coefficient ko = 3.7 × 10m2 / s (phase) and (1 【0) z = 0.56m2 / s (zr-doped sample). But measured by the Scherrer method 2 powder grain size was 70nm and 60nm. crystallite size calculated by the non-zr phase ko = 0.72m2 / s, the hydrogen in the grain boundary diffusion is faster than intracrystalline diffusion. but increases the formation of fine Zr particles in the grain boundary ZrB2 will hinder the grain boundary diffusion of hydrogen. Therefore, when heated at 740 ~ 2, no zr phase disproportionation in 0.38h completely, and add zr phase completely disproportionation need 7h. so easy to form completely before disproportionation disproportionation disproportionation and not a mixture of nanoparticles their orientation and initial phase of the corresponding crystallographic direction, when the magnet can be induced in re-oriented growth. Doped Ga can substitute Fe (4c), no diffuse particle generation, the role of hydrogen diffusion unhindered, so its behavior and no disproportionation relative to the same doping. (Zhang Tingjie) Metal Letters of 2003 l2 l3
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