Preparation And Heat Exchange Process Simulation Of Cu/Gd-Si-Ge Composite

In this paper, the defects, such as brittle and weak heat conductivity, Gd₅(Si_xGe_1-x)₄ series alloys which exhibit GMCE(Giant Magnetocaloric Effect) are analyzed when they are in practical used as magnetic refrigerants in a magnetic refrigerator at room temperatures. To solve this problem, the author suggest to composite Gd₅Si_3.2Ge_0.8 in Gd₅(Si_xGe_1-x)₄ series alloy and high heat conduction metal. This paper introduces the method and results of joining Gd₅Si_3.2Ge_0.8 of Gd₅(Si_xGe_1-x)₄ series alloys and high heat conduction Cu. Because heat exchange efficiency can't be calculated at present for granular composites specifically by means of analytical method, the author simulated the heat exchange process of composites and Gd₅Si_3.2Ge_0.8 individually by means of numerical simulation analyse, and found that composites are superior to matrix alloy in heat exchange feature.In this paper, compositing method is vacuum sintering base on the principle of vacuum diffusion welding. Cu film was sputtered on surface of Gd₅Si_3.2Ge_0.8 particles by means of method of DC magnetron sputtering technology to increase wettability of Cu and matrix alloy. Then the sputtered Gd₅Si_3.2Ge_0.8 particles and Cu powder were mixed. At last, the mixed mass was placed in vacuum sinter furnace to prepare samples by controlling processing parameters. Diffusion of the elements, phase structure and adiabatic temperature changes of samples were measured and analysed by utilizing SEM,XRD and adiabatic temperature changes system. The results of heat exchange time of granular composites and GdSiGe with different dimensions and different weight percentage Cu were obtained by means of ANSYS software individually, base on working condition of magnetic refrigerator under some assumptions.Experiment results indicate that some Cu atoms have diffused into matrix alloy sintered samples. Cu presents as a mesh structure surrounding matrix alloy particles, leading to join effectively matrix alloy particles, as a result, the brittleness of Gd₅Si_3.2Ge_0.8 was improved. Compared with pure Gd₅Si_3.2Ge_0.8, the adiabatic temperature changesΔT_ad of composites has a little drop, which fall into reasonable error band and doesn't affect its use in magnetic refrigerators. Its Curie Point T_c basically keeps normal with Gd₅Si_3.2Ge_0.8 corresponding to the measurement of adiabatic temperature changesΔT_ad. Simulation results show that heat exchange time of composites is shorter than identical volume GdSiGe when composites and GdSiGe are identical temperature drop during heat exchange with heat exchange medium. Heat exchange time of small particle samples is less than big particles. Heat exchange time decreasing percentageμof composites to matrix alloy increase with weight percentage Cu increasing when dimension of matrix alloy in composites is fixed. Temperature drops effect heat exchange time of composites dramatically. If weight percentage Cu is fixed,μbecomes large when temperature drop is small, contrarily,μvalue is small. If the composites is used in a magnetic refrigerator, heat exchange frequency of the machine will increase because heat exchange frequency and heat exchange time are inverse ratio, as the result, the power of magnetic refrigerator would increase because power of magnetic refrigeration and heat exchange frequency are direct ratio. The results mentioned above demonstrate that it is adoptable that the composites of Cu and GdSiGe by vacuum diffusion welding sintering process and the heat conductivity of the composites are improved compared to matrix alloy. This research supplies a new method for brittle magnetic refrigeration material used as magnetic refrigerants at room temperature.