Zhang Qingjie

Phase transition and high temperature thermoelectric properties of copper selenide Cu 2-x Se （0 ≤ x ≤ 0.25）

With good electrical properties and an inherently complex crystal structure, Cu2−xSe is a potential “phonon glass electron crystal” thermoelectric material that has previously not attracted much interest. In this study, Cu2−xSe (0 ≤ x ≤ 0.25) compounds were synthesized by a melting-quenching method, and then sintered by spark plasma sintering to obtain bulk material. The effect of Cu content on the phase transition and thermoelectric properties of Cu2−xSe were investigated in the temperature range of 300 K–750 K. The results of X-ray diffraction at room temperature show that Cu2−xSe compounds possess a cubic structure with a space group of F m3m (#225) when 0.15 < x ≤ 0.25, whereas they adopt a composite of monoclinic and cubic phases when 0 ≤ x ≤ 0.15. The thermoelectric property measurements show that with increasing Cu content, the electrical conductivity decreases, the Seebeck coefficient increases and the thermal conductivity decreases. Due to the relatively good power factor and low thermal conductivity, the nearly stoichiometric Cu2Se compound achieves the highest ZT of 0.38 at 750 K. It is expected that the thermoelectric performance can be further optimized by doping appropriate elements and/or via a nanostructuring approach.

Dynamic response, buckling and collapsing of elastic-plastic straight columns under axial solid-fluid slamming compression. I : Experiments

Abstract The dynamic behavior of straight elasto-plastic columns subjected to axial solid-fluid slamming compression is investigated experimentally in the present study. Two classes of columns are tested: large slenderness columns with the static Euler strain e crE smaller than the yield strain e y and middle slenderness ones with the e crE close to the e y . Three critical conditions for each of the columns are observed from the experiments: plastic incipience, buckling, and plastic collapse. These conditions are defined by introducing three critical loading strains: plastic, buckling, and collapse axial loading strains. The three critical strain values for each tested column are reported in the paper. The results indicate that: (1) the plasticity in a column appears first at the center and the plastic region is always at the middle length; (2) according to the buckling definition, the type 1 columns buckle elastically while the type 2 buckle plastically: (3) the columns load-carrying capacity is insensitive to the elasto-plastic loading histories (sequences) which the structure experiences before the plastic collapse occurs and is essentially governed by the dynamic post-buckling elasto-plastic behavior in one slamming: and (4) at the critical buckling loading magnitudes the columns response becomes dominated by motion in the fundamental mode.

Fast preparation and thermal transport property of TiCoSb-based half-Heusler compounds

TiCoSb-based half-Heusler compounds with the substitution of Zr for Ti have been prepared quickly by combining high-energy ball milling method with spark plasma sintering technique, and their thermal transport properties have been investigated. With the increase of the concentration of Zr, the thermal conductivity of Ti1-xZrxCoSb compounds decreases significantly. Compared with the thermal conductivity of TiCoSb compound, that of Ti0.5Zr0.5CoSb decreases by 200% at 1000 K.

Quick preparation and thermal transport properties of nanostructured β-FeSi2 bulk material

This paper reports that the nanostructured β-FeSi2 bulk materials are prepared by a new synthesis process by combining melt spinning (MS) and subsequent spark plasma sintering (SPS). It investigates the influence of linear speed of the rolling copper wheel, injection pressure and SPS regime on microstructure and phase composition of the rapidly solidified ribbons after MS and bulk production respectively, and discusses the effects of the microstructure on thermal transport properties. There are two crystalline phases (α-Fe2Si5 and -FeSi) in the rapidly solidified ribbons; the crystal grains become smaller when the cooling rate increases (the 20 nm minimum crystal of e-FeSi is obtained). Having been sintered for 1 min above 1123 K and annealed for 5min at 923 K, the single-phase nanostructured β-FeSi2 bulk materials with 200–500 nm grain size and 98% relative density are obtained. The microstructure of β-FeSi2 has great effect on thermal transport properties. With decreasing sintering temperature, the grain size decreases, the thermal conductivity of β-FeSi2 is reduced remarkably. The thermal conductivity of β-FeSi2 decreases notably (reduced 72% at room temperature) in comparison with the β-FeSi2 prepared by traditional casting method.

Crystal Structures and Thermoelectric Properties of Sm-Filled Skutterudite Compounds Smy Fex Co4 - x Sb12

Abstract Polycrystalline samples of Sm partially filled skutterudites Sm y Fe x Co 4 - x Sb 12 were prepared by melting and Spark Plasma Sintering technique. The results of Rietveld refinement showed that the obtained Sm y Fe x Co 4 - x Sb 12 samples possessed filled skutterudite structures. The thermal parameter ( B ) of Sm is larger than that of Sb, Fe, and Co, indicating that Sm “rattled” in Sb-icosahedron voids. The effects of filling atom Sm on thermoelectric properties of these compounds were investigated. With the increase of Sm filling fraction ( y ), electrical conductivity decreased, Seebeck coefficient increased and had a maximum value when y was 0.38; thermal conductivity reduced and had a minimum value when y was 0. 32. At 750 K, the highest figure of merit of 0.68 was obtained for Sm 0.32 Fe 1.47 Co 2.53 Sb 12 .

Preparation and characterization of monodisperse nickel nanoparticles by polyol process

Polymer-protected monodisperse nickel nanoparticles were synthesized by a modified polyol reduction method in the presence of poly (N-vinyl-2-pyrrolidone). These nanoparticles were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), as well as vibrating sample magnetometer (VSM). The experimental results show that the addition of PVP and the concentration of NaOH have strong influences on the size, agglomeration and uniformity of nanoparticles. In the presence of PVP and NaOH with low concentrations, monodisperse nickel nanoparticles with average diameters about 42 nm were obtained and characterized to be pure nickel crystalline with fee structure. Secondary structures such as clusters, loops, and strings resulted from magnetic interactions between particles were observed. The chemical interaction between the PVP and nickel nanoparticles was found by FTIR. The saturation magnetization (Ms), remarem magnetization (Mr) and coercivity (HC) of these nickel nanoparticles are lower than those of balk nickel.

Breaking and characteristics of Ganoderma lucidum spores by high speed entrifugal shearing pulverizer

The spores of Ganoderma lucidum were ground and broken to ultrafine particles by high speed centrifugal shearing(HSCS) pulverizer. The characteristics of Ganoderma lucidum spores were analyzed by scanning electron microscope (SEM), Fourier transform infrared spectrophotometry (FTIR). Ultraviolet-visible pectrophotometer was used to determine the extraction ratio of aqueous solubility polysaccharide between the raw and broken spores. The immunological function on the mice before and after the breaking of spores was investigated. The experimental results show that after being ground, the sporoderm-broken ratio reachs 100%, the original active ingredients of ganoderma lucidum spores do not change, and the extraction ratio of aqueous solubility polysaccharide is greatly increased by 40.08%. The broken spores show much higher immunological activity comparing with original spores of Ganoderma lucidum.

Optimization of p-type Segmented Bi2Te3/CoSb3 Thermoelectric Material Prepared by Spark Plasma Sintering

A kind of p-type segmented Bi2Te3/CoSb3 thermoelectric material was prepared by spark plasma sintering (SPS). When the segmented materials were used at the temperature ranging from 300 Koto 800K, the junction temperature was optimized, which is about 500 K, and the corresponding length ratio of CoSb3 to Bi2Te3 is about 15∶2. The measured maximum power output of segmented materials is about 320 W·m−2, which is about 1.8 times as high as that of monolithic material CoSb3 under the same measuring conditions.

XRD and HRTEM analyses of the ball milled nanocrystalline FeCo alloy

The nanostructures of the ball milled FeCo particles were characterized as functions of the ball milling time (t) using quantitative X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) analysis techniques. The results show that the nanocrystalline bcc FeCo particles are available using carbonyl iron and cobalt powders as the start materials during the high-energy ball milling. At the early stage of ball milling, Co powders are easily mashed into nanocrystalllites, by which the surface of the larger Fe particles of about 80–150 nm is coated. With t increasing, the refinement of grain size and the incorporation of defects including dislocations, disclinations and grain boundaries happen, and then FeCo alloy with a certain layered structure is formed, finally the layered structure disappears with the formation of isotropic grains having a steadystate grain size in the nanometer regime after a certain period of t.

A new theoretical model about shear stress in magnetorheological fluids with small shear deformation

Based on the single-chain structure model of magnetorheological fluids, a formula for the calculation of shear stresses was established. The interaction force of two magnetic particles in an infinite single-chain was deduced using a new theoretical model which is founded on Ampere’ molecular current hypothesis, dipole theory and Ampere’ law. Furthermore, the resultant force on a particle was then deduced by taking into account of the action caused by all the other particles in the single-chain. A predictive formula for shear stresses was made corresponding to the case that MR fluids were sheared by a small angle and the calculating results fit well on the order with the yield stresses of the commercial MR fluids.