Materials Science Forum Vols. 610-613

Abstract: In this study, we designed a suitable electrode material was designed, Cu-W alloy, which achieved a good thermal match with CoSb3 thermoelectric (TE) material. By means of spark plasma sintering (SPS), Cu-W alloy was introduced into CoSb3/Ti/Cu-W TE element successfully. Finite element analysis showed that the maximum thermal residual stress appeared at the cylindrical surface zone close to the CoSb3/electrode interface. SEM and EPMA results showed that an intermetallic compound (IMC) layer formed at the CoSb3/Ti interface and EDS analysis confirmed the IMC layer was TiSb phase. Shear tests showed that the shear strength of CoSb3/Ti/Cu70W30 joint was about 50Mpa. The potential profile of the interface area was measured by the four-probe method and the result showed no abrupt change in voltage was found around the interface. The high temperature reliability evaluation showed the joint had high thermal duration stability.

Abstract: P-type Bi0.5Sb1.5Te3 thermoelectric materials have been prepared by ultrarapid quenching method with various cooling rates. The microstructures of sample are very different from those prepared by normal cooling. The ultrarapid quenched material was obtained in the shape of foils, the thickness of which were found to vary in the range of 6-20 μm, which corresponds to a cooling rate of about 106 K/S. X-ray diffraction evidenced a microcrystalline structure of the expected composition with a (0015) plane. Increasing the cooling rate, the Seebeck coefficient increase, the electrical conductivity decrease and the power factor rise up to 4.4×10-3 Wm-1K-2 .The highest ZT value of 1.22 was achivedachieved for the materials with the copper roller roration speed 40 m/s in room temperarure.

Abstract: SiGe alloy composite material including TiN nanoparticle were prepared. The TiN nanoparticles as the inert scattering center were fabricated by Nitrogen plasma-metal reaction. The sintered samples were characterized by electrical resistivity and seebeck coefficient measurement. Adding nanophase inclusion into the SiGe alloy matrix, the Seebeck coefficient increased, the electrical conductivity decreased and the electrical power factor only slightly reduced.

Abstract: A series of Sr0.95Al2O4:Eu2+0.02, Dy3+ 0.03•nB2O3 (0≤n≤0.30) were prepared by a solid state reaction. The role of B2O3 on the photoluminescence (PL) properties of Sr0.95Al2O4:Eu2+0.02, Dy3+0.03 were evaluated with UV emission spectra and decay curves. B2O3 significantly improved the emission intensity and persistent luminescence time. The crystal environment and defects induced by B3+ doping were detected with IR spectra, thermoluminescence and positron annihilation (PA) methods. Some Al3+ were substituted by B3+ and a kind of defect complex cluster responsible for the long decay time was formed when the substitution of Al3+ by B3+ occurs.

Abstract: Flywheel rotor structure is one of essential assemblies of the flywheel system used in IPACS. It is significant to ensure the safety of metallic hub and the composite rim under high centrifugal loading induced by the rotation field and the surface pressure produced by the interface misfits. In this paper a 3-D stress analysis model of the flywheel rotor is presented with the finite element analysis software ANSYS and the failure criteria of the materials are discussed to assess the structural strength. Moreover, the key design parameters are investigated briefly to disclose their influences on the stress distribution of rotor structure. At last, an optimum mathematics model with the outer radius of metallic hub, the thickness of each composite ring and the interface misfits as the design variables is presented. Based on the optimum design platform, the series of flywheel rotor structures can be designed systematically.

Abstract: Phase change materials (PCMs) with storing and releasing energy properties have been widely used in lots of fields such as solar energy storing, smart housing, thermo-regulated fibers, and agricultural greenhouse. Here, PCMs based on polyamide 6 (PA6) blended with Polyethylene glycol (PEG) was studied. In order to improve the compatibility between PA6 and PEG, a PA6-PEG block copolymer was synthesized and added to the blends. The structure and properties of the block copolymer were determined by Fourier Transform Infrared (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and optics microscope (OM). The results of DSC analysis showed that tThe copolymer block is phase separated. DSC results also showed that the phase transition temperature of the blend is different from that of pure PEG, indicating the interaction occurrence between PEG and PA6 by using PA6-PEG block copolymer, the latent heat of PEG/PA6 blend increased with the mass percent of PEG. The results of tThermal cycling tests showed that the blend as a PCM has good long-term thermal reliability.

Abstract: By study the development situation of blast furnace smelting in china and the blast furnace operation system and technology, combined with production conditions of JISC BF, based on a large number of the production data, the comparison analysis test on JISC BF operation system and technology was did. Through continuously optimization and practice, the relatively suitable operation system and technology of JISC BF at present was explored, which could reduce the coke ratio into furnace while increasing the coal injection ratio and making great economic effect.

Abstract: Ammonia borane(BH3NH3) is a promising hydrogen storage material because of its high gravimetric (19.6 wt% H2) and volumetric hydrogen density with an accompanying moderate decomposition temperature. Previously reported structures determined by using x-ray and neutron diffraction on hydrides show differences in bond lengths and atomic coordination. Here, the crystal structures of fully and half deuterated ammonia borane were investigated as a function of temperature using powder neutron diffraction. The neutron diffraction patterns show a significant difference due to large difference in the scattering length of D and H. It is evident that an order-disorder phase transition occurs around 225 K for all compounds. At low temperature, the compound crystallizes in the orthorhombic structure with space group Pnm21 and gradually transforms to a high temperature disordered tetragonal structure with space group I/4mm at about 225K. The differential scanning calorimetry studies confirm this phase transformation and also indicate that all compounds melt and decompose at above 370 K. The c cell parameter remains unchanged in the orthorhombic phase from 16 K to 200K and increases liaa nearly above 225K. As the temperature is increased, the BH3-NH3 groups start to reorient along the c axis, and the D/H atoms become disordered, leading to the tetragonal phase transition around 225K.

Abstract: The nanocrystalline Mg-based metal hydrides offer a breakthrough in prospects for practical applications. In this work, we study experimentally the structure, electrochemical properties and surface segregation effect of nanocrystalline and microcrystalline Mg2M alloys and Mg2M/M’ (M=Cu, Ni; M’=C, Ni, Pd) nanocomposites. These materials were prepared by mechanical alloying (MA). In the nanocrystalline Mg2Cu powder, discharge capacity up to 30 mA h g-1 was measured. It was found that nickel substituting copper in Mg2Cu1-xNix alloy greatly improved the discharge capacity of studied material. In nanocrystalline Mg2Ni powder, discharge capacities up to 100 mA h g-1 were measured. Additionally, it was found that mechanically coated Mg-based alloys with graphite, nickel or palladium have effectively reduced the degradation rate of the studied electrode materials. Finally, the properties of nanocrystalline alloys and their nanocomposites are compared to that of microcrystalline samples. X-ray photoelectron spectroscopy studies showed that the surface segregation of Mg atoms and valence band width in the nanocrystalline Mg2M alloy are greater compared to those observed in microcrystalline Mg2M. Especially, a strong surface segregation of Mg atoms was observed for the Mg2Ni/M’ composites. In that case, Mg atoms strongly segregate to the surface and form a Mg based oxide layer under atmospheric conditions. The lower lying Ni and M’ atoms form a metallic subsurface layer and could be responsible for the observed relatively high hydrogenation rate. Furthermore, the valence band broadening observed in the nanocrystalline Mg2Ni alloys and Mg2Ni/M’ composites could also significantly influence their hydrogenation properties.

Abstract: Ga-substituted Ge based type-I clathrates with the general formula A8X16Y30 display promising thermoelectric performance. Using high purity elemental Sr, Ba, Ga, and Ge as starting materials, polycrystalline co-filled type-I clathrate compound (Sr,Ba)8Ga16Ge30 were successfully achieved by combining melting and Spark Plasma Sinter (SPS) method. The temperature dependence of thermal conductivity, electronic conductivity and Seebeck coefficient were reported. The calculated ZTmax is 0.28 at 700K. Enhanced thermoelectric performance would be expected through adjusting Sr/Ba ratio and framework atoms.