Nanocomposites offer a promising approach to the incorporation of nanostructured constituents into bulk thermo- electric materials. The 0.7-at% Bi-doped Mg2Si nanocomposites are prepared by spark plasma sintering of t...
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Nanocomposites offer a promising approach to the incorporation of nanostructured constituents into bulk thermo- electric materials. The 0.7-at% Bi-doped Mg2Si nanocomposites are prepared by spark plasma sintering of the mixture of nanoscale and microsized 0.7-at% Bi-doped Mg2Si powders. Microstructure analysis shows that the bulk material is composed of nano- and micrograins. Although the nanograin hinders electrical conduction, the nanocomposite struc- ture is more helpful to reduce thermal conductivity and increase the Seebeck coefficient, hence improving thermoelectric performance. A dimensionless figure of merit of 0.8 is obtained for the 0.7-at% Bi-doped Mg2Si nanocomposite with 50-wt % nanopowder, which is about twice larger than that of the sample without nanopowder.
This thesis designs embedded control system for Consumable DE-GMAW, the system based on 32bits ARM7 microcontroller LPC2124 could real time collect and display welding parameters, and the system could control bypass a...
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This thesis designs embedded control system for Consumable DE-GMAW, the system based on 32bits ARM7 microcontroller LPC2124 could real time collect and display welding parameters, and the system could control bypass arc and metal current, ensure welding process stability. All modules of the system could perform serial communication based on RS-485 interface and Modbus protocol. This design has been simulated by the Proteus software, the system could output require PWM waveform in simulation process. Simulation result principally proves that design scenario of Consumable DE-GMAW embedded control system is practicable, and it can work well in simulation platform, lay the foundation for reality process control.
In this paper, Mo and Cu were welded together by diffusion welding with or without a Ni interlayer. SEM, EDS, EPMA, XRD were used to characterize the structure and the element distribution of the interface zone. The r...
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In this paper, Mo and Cu were welded together by diffusion welding with or without a Ni interlayer. SEM, EDS, EPMA, XRD were used to characterize the structure and the element distribution of the interface zone. The results showed that the Mo/Cu joint combined homogeneously by diffusion welding, the diffusion layer formed at the interface due to Mo atoms and Cu atoms inter-diffusion. There were some micro-voids on the copper side of the joint due to the role of kirkendall effect, and the voids reduced the performance of the joint. For the Mo/Ni/Cu joint, Mo/Ni and Ni/Cu interface were linked together, and the tensile strength of the Mo/Ni/Cu joint was higher than the Mo/Cu joint, because the added nickel eased the thermal stress of the joint. A solid solution was formed at the Mo/Ni interface where a joint brittle fracture took place.
The band structure of Mg2Si1−xSnx solid solutions with 0.250 ⩽ x ⩽ 0.875 is calculated using the first-principles pseudopotential method. It is found that the low-lying light and heavy conduction bands converge and th...
The band structure of Mg2Si1−xSnx solid solutions with 0.250 ⩽ x ⩽ 0.875 is calculated using the first-principles pseudopotential method. It is found that the low-lying light and heavy conduction bands converge and the effective mass reaches a maximum value near x = 0.625. Using the semiclassical Boltzmann transport theory and relaxation-time approximation, we find that the system with x = 0.625 exhibits both higher Seebeck coefficient and higher electrical conductivity than other solid solutions at intermediate temperatures. By fitting first-principles total energy calculations, a modified Morse potential is constructed, which is used to predicate the lattice thermal conductivity via equilibrium molecular dynamics simulations. Due to relatively higher power factor and lower thermal conductivity, the Mg2Si0.375Sn0.625 is found to exhibit enhanced thermoelectric performance at 800 K, and additional Sb doping is considered in order to make a better comparison with experiment results.
The effect of calcination temperatures on the active species of WO 3 /SiO 2 catalysts for propylene production from metathesis of ethylene and 2-butene was studied to elucidate the structure-reactivity *** influence o...
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The effect of calcination temperatures on the active species of WO 3 /SiO 2 catalysts for propylene production from metathesis of ethylene and 2-butene was studied to elucidate the structure-reactivity *** influence of calcination temperatures on catalyst physicochemical properties,relating to the active species,was summarized from an array of characterization *** has been found that the surface tetrahedral tungsten species with high metal support interaction were formed on the catalyst calcined at 550℃ as confirmed by Raman,UV-Vis and H 2-TPR spectra,respectively.
DE-GMAW (Double Electrode Gas Metal Arc Welding) is a novel welding technology. Based on the research of physical phenomena of DE-GMAW process, a new hybrid heat source model suitable for DE-GMAW was proposed. The hyb...
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DE-GMAW (Double Electrode Gas Metal Arc Welding) is a novel welding technology. Based on the research of physical phenomena of DE-GMAW process, a new hybrid heat source model suitable for DE-GMAW was proposed. The hybrid heat source consisted of a body heat source and a surface heat source, where the body heat source simulated the heat added into workpiece by molten welding wire and surface heat source simulated the heat added into workpiece generated by arc. The simulated results show that the new surface-body hybrid heat source can reflect the characteristics of DE-GMAW accurately. With the increase of bypass current, the temperature of weld center decreased gradually. Compared with the traditional welding method, DE-GMAW can reduce the heat input of base metal effective. The maximum tens ile stress and compressive stress near weld had a trend of decline and residual tensile stress of weld after welding decreased obviously.
High purity anatase nano-TiO2 powders with high photocatalytic activity were prepared by a hydrothermal synthesis method. X-ray diffraction （XRD）, field emission transmission electron microscopy （FETEM）, ultraviol...
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High purity anatase nano-TiO2 powders with high photocatalytic activity were prepared by a hydrothermal synthesis method. X-ray diffraction （XRD）, field emission transmission electron microscopy （FETEM）, ultraviolet-visible （UV-Vis） light absorption spectrum and photoluminescence （PL） spectrum were adopted to characterize the catalyst. Effects of temperature, time and sol concentration of hydrothermal synthesis on particle size and phases were investigated. Photocatalytic activities in the degradation of Rhodamine B Dye were studied. The experimental results indicated that photocatalytic activity of the nano-TiO2 powers was much higher than that of P25 （Degussa）.
Compounds Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 with filled tetragonal tungsten bronze structure were prepared,and the dielectric characteristics and ferroelectric transition were *** ceramics displayed weak frequency de...
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Compounds Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 with filled tetragonal tungsten bronze structure were prepared,and the dielectric characteristics and ferroelectric transition were *** ceramics displayed weak frequency dependence in room temperature dielectric constant,which decreased from 125 to 118 for Sr4Eu2Ti4Nb6O30,from 206 to 195 for Sr5EuTi3Nb7O30 in the frequency range of 10 kHz to 1 *** present ceramics showed a diffuse ferroelectric phase *** frequency independent transition temperature （Tm） indicated the above compounds had no relaxor *** diffuseness （γ） was 1.45 and 1.64 for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 *** weak ferroelectric of the present materials are indicated from the P-E hysteresis loops,and a small 2Pr of 0.596 μC/cm2 and 0.068 μC/cm2 were observed for Sr4Eu2Ti4Nb6O30 and Sr5EuTi3Nb7O30 respectively.
LaSrMnO（LSMO） has recently shown promising features as a metal-insulator material over a limited range of Sr doping（x=0.175 to 0.25）. Its thermal property has been commonly measured through the very expensive calo...
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LaSrMnO（LSMO） has recently shown promising features as a metal-insulator material over a limited range of Sr doping（x=0.175 to 0.25）. Its thermal property has been commonly measured through the very expensive calorimetric method. In this paper, a considerably more convenient thermal investigation approach to this issue through the thermal irradiation theory is proposed. LSMO compounds were synthesized with a wide range of x（0.15 to 0.5） using the precisely controlled Pechini sol-gel method. XRD phase structure analysis and XPS composition and chemical state study were adopted for quality assurance of the compounds. Resistance and infrared reflectance of the samples were measured respectively with the help of the four probe technique in temperature range of 150 K to 380 K and an infrared spectrometer over a temperature range of 153 K to 544 K. Investigations showed a good correlation between these two measures approving the metal-insulator characteristic of all the samples. Calculation of the total normal emittance(ε（T）) of the compounds was innovatively simplified using the measured reflectivity data through the thermal irradiation theory for graybody. Moreover, the results showed that every x ratio fabricated through the precisely controlled Pechini method presented a unique ε（T） characteristic with a different metal-insulator transition temperature.
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