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Gd-Tb-Ga and Gd-Bi-Sb ternary phase diagrams and magnetic refrigeration performance
Author: ZuoYongXi
Tutor: LiJunQin
School: Shenzhen University
Course: Materials Physics and Chemistry
Keywords: Gd-Tb-Ga system Gd-Bi-Sb system Magnetic refrigeration Phase diagram CALPHAD
CLC: TG113.14
Type: Master's thesis
Year: 2006
Downloads: 176
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Abstract
Magnetic refrigeration technology with high efficiency, low noise, high reliability and environmental pollution, etc., experts recognized as high-tech green refrigeration technology. The magnetic refrigeration lies in magnetic refrigeration materials. Looking for each temperature zone, especially ideal magnetic refrigeration near room temperature materials and preparation techniques is the research focus of scientists. These room-temperature magnetic refrigeration materials, in order to study the magnetic refrigeration at room temperature Gd-Bi-Sb and Gd-Tb-Ga ternary materials preparation technology and elements doping phase diagram of these two systems in this article, The phase structure and room temperature magnetic refrigeration materials doped system. Gd-Tb-Ga system confirmed eight binary compounds: Gd 5 Ga 3 the Gd 3 ' 2 , GdGa, GdGa 2 , Tb 5 Ga 3 , TbGa, TbGa 2 and TbGa 3 the presence of and is not found that the ternary compound. 500 ℃ isothermal section of the Gd-Tb-Ga ternary alloy phase diagrams were measured. Such isothermal section consists of seven single-phase region, eight two-phase region and two-phase regions. The Gd and Tb, Gd , 5 Ga 3 and the Tb 5 Ga 3 GdGa and TbGa GdGa 2 and TbGa 2 form a continuous solid solution. 500 ℃, Ga the largest solid solution of (Gd, Tb, Ga) is 5at% GdGa 2 evenness range is 20 to 33at% Ga. Found no discernible degree of solid solution of Ga in the other single-phase. This work studies the room temperature magnetic refrigerant materials Gd 60 the Tb 40-x (x = 0, 1, 3, 5), the Ga x series alloys magnetic refrigeration performance. Because there is a certain degree of solid solution of Ga in the (Gd, Tb), these alloys are single phase compound, Ga into the (Gd, Tb) to the crystal lattice, thus affecting its magnetic refrigeration performance. The experiments show that the Curie temperature of the alloy first increased with increasing the Ga doping amount of x when x = 3, reached the maximum (297K), and then declined, while the magnetic entropy change is first and then decreased. Corresponding to x = 0,1,3,5, the Curie temperature of the alloy were as follows: 272.5,283.5,297 and 272.5K, while the maximum magnetic entropy change were: 5.15,4.43,3.32 and 4.58J / (kg · K) . Wherein x = 3 when the Curie temperature of the highest, while when x = 0 the magnetic entropy change of the maximum. Gd-Sb-Bi system, confirmed the seven binary compounds: the Gd 5 Sb 3 of Gd 4 Sb 3 , GdSb, Gd 16 Sb 39 , Gd 5 Bi 3 , Gd 4 Bi 3 and GdBi the existence of ternary compounds not found. Measured cross-section of the room-temperature phase diagram of the Gd-Sb-Bi ternary alloy system. These isothermal section consists of six single-phase region, six two-phase region, and a three-phase regions. Sb and Bi GdSb and the GdBi, Gd 4 Sb 3 and Gd of 4 Bi 3 Gd 5 Sb 3 and Gd of 5 Bi 3 form a continuous solid solution. Confirmed that there is no Gd-Bi binary system GdBi 2 compounds. Gd (Sb, Bi), the maximum degree of solid solution is 7.5at%, while Gd no discernible degree of solid solution in the other solid solution. Although Gd 4 Sb 3 and Gd 4 Bi 3 to form a continuous solid solution, but Gd Gd 4 of (Sb, Bi) of 3 in the degree of solid solution is small and Bi, SB of volatile easily lead to deviate from the alloy composition, so the arc melting is difficult to obtain the pure phase, but the use of high-frequency melting is easy to obtain the pure phase The room-temperature magnetic refrigeration materials. The room temperature magnetic refrigerant materials Gd 4 (Sb 1-x Bi x ) 3 (x = 0, 0.5) performance of P-doped the impact. Show that the P added conducive Gd 5 (Sb, Bi) 3 phase formation and not conducive to Gd 4 (Sb, Bi) 3 phase formation, the magnetic transition temperature of the master alloy has little effect, but reduce the maximum magnetic entropy change. This work was supported by CALPHAD method and corresponding phase diagrams and thermodynamic data of the Gd-Sb binary system phase diagram thermodynamic optimization using the Redlich-Kister polynomial to describe the liquid phase, hcp A 3 (αGd) phase and bcc A 2 (βGd) and other solid solution phase excess Gibbs energy the sublattice model describes the intermediate compound Gd 5 Sb 3 and Gd 4 the Sb 3 htGdSb, rtGdSb and Gd 16 Sb 39 to obtain a reasonable, reliable, self-consistent thermodynamic parameters.
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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Metallographic microstructure and properties of the (metal ) > Organization of the metal > State diagram ( phase diagram )
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