Thermoelectric properties of Bi_(0.5)Sb_(1.4-x)Na_xIn_(0.1)Te_3 alloys

The Bi_(0.5)Sb_(1.4-x)Na_xIn_(0.1)Te_3(x=0.02-0.20)alloys were fabricated by high vacuum melting and hotpressing technique.The phase structures and morphology of the bulk samples were characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM),respectively.Effects of In and Na co-doping on the electrical and thermal transport properties were studied from room temperature to 500 K.Seebeck coefficient of the Bi_(0.5)Sb_(1.5)Te_3 can be enhanced by substituting Sb with In and Na at near room temperature.The electrical conductivity of the In and Na co-doped samples is lower than that of the Bi_(0.5)Sb_(1.5)Te_3 alloy from room temperature to 500 K.In and Na co-doping of appropriate percentage optimizes the thermal conductivity of the Bi_(0.5)Sb_(1.5)Te_3 alloy.The minimum value of thermal conductivity of Bi_(0.5)Sb_(1.36)Na_(0.04)In_(0.1)Te_3 alloy is 0.45 W·m~(-1) K~(-1) at 323 K.which leads to a great improvement in the thermoelectric figure of merit(zT).The maximum zT value reaches 1.42 at 323 K.     

Crystal structure and magnetic properties of SmFe9-xCox alloys简

The crystal structure and magnetic properties of SmFe9-x Cox(x = 0, 1, 3, 5) alloys were studied by X-ray powder diffraction(XRD) and magnetic measurements. The Th2 Zn17-type structure of the as-cast state is changed to TbCu7-type structure after quenching to a rotating molybdenum roll under certain velocity(12, 20, and 32 m s-1). The(002) XRD peak appears and a-Fe phase disappears when the Co is added up to x = 5. Saturation magnetization of SmFe9 under different temperature shows 9 % change(112–102 A m2 g-1) when the temperature is higher than 200 K. The saturation magnetization is 115 A m2 g-1and coercivity is 0.304 T at 5 K for SmFe9 alloys. Increased saturation magnetization and decreased coercivity can be obtained for Co added up to x = 5 at 5 K.     

Microstructure and thermoelectric properties of Bi_(0.5)Na_(0.02)Sb_(1.48-x)In_xTe_3 alloys fabricated by vacuum melting and hot pressing

The Bi_(0.5)Na_(0.02)Sb_(1.48-x)In_xTe_3 alloys(x =0.02-0.20) were synthesized by vacuum melting and hot pressing methods at 753 K,60 MPa for 30 min.Effects of Na and In dual partial substitutions for Sb on the thermoelectric properties were investigated from 300 to 500 K.Substituting Sb with Na and In can enhance the Seebeck coefficient effectively near room temperature.The electrical resistivity of the Na and In dual-doping samples is higher within the whole test temperature range.The Bi_(0.5)Na_(0.02)Sb_(1.48-x)In_xTe_3 samples(x = 0.02,0.06) play a great role in optimizing the thermal conductivity.As for the Bi_(0.5)Na_(0.02)Sb_(1.46)In_(0.02)Te_3 alloy,the minimum value of thermal conductivity reaches 0.53 W·m~(-1)·K~(-1) at 320 K.The thermoelectric performance of the Na and In dualdoped samples is greatly improved,and a figure of merit ZT of 1.26 is achieved at 300 K for the Bi_(0.5)Na_(0.02)Sb_(1.42)In_(0.06)Te_3,representing 26%enhancement with respect to ZT = 1.0 of the undoped sample.     

Dynamic recrystallization of AZ91 magnesium alloy during compression deformation at elevated temperature

High temperature compressive tests of AZ91 Mg alloy were carried out at 573 - 723 K and strain rates of 0. 001 - 1 s^-1 . The microstructures of as-compressed samples were observed by optical microscopy and transmission electron microscopy (TEM), and the microhardness was also tested. It is shown that with the increase of temperature or the decrease of strain rate, the flow stress decreases, at the same time the dynamic recrystallization (DRX) of the alloy is more noticeable. The microstructures reveal that continuous dynamic recrystallization, which develops through conversion of low-angle grain boundaries into high-angle boundaries, occurs preferentially at the grain boundary.     

Microstructure and thermoelectric properties of Bi_(1.9)Lu_(0.1)Te_3 compound

Effect of fabrication conditions on micros tructure and thermoelectric properties of the Bi_(1.9)Lu_(0.1)Te_3 compound was studied.Starting nanopowder with mean nanoparticle size of ～37 nm was synthesized by a microwave-solvothermal method.In order to prepare samples with various micro-grained structures,the synthesized nanopowder was compacted by two methods.The first method is cold isostatic pressing with further hightemperature annealing,while the second method is spark plasma sintering at various temperatures of process(653 and 683 K).It is found that mean grain size is equal to～290,～730 and ～1160 nm for cold isostatically pressed and spark plasma sintered at 653 and 683 K samples,respectively.The micro-grained sample with maximum mean grain size shows the best thermoelectric properties.This sample is structurally inhomogeneous and has the lowest thermal conductivity and the specific electrical resistivity.Maximum dimensionless figure of merit for this sample is equal to ～0.9 for temperature range of450-500 K.     

New Steel Making Process through Reduction and Sintering of Cementite Powder

A new steel making process through reduction and sintering treatment of cementite powder was proposed, and microstructure of the material obtained by this process was examined by scanning electron microscopy and EBSP analysis.The cementite powder obtained by mechanical alloying was compacted under high pressure up to 1000MPa, and then reduced during sintering in a hydrogen (H2) gas atmosphere at elevated temperatures. The cementite compacts were completely reduced by the sintering at 1073K to 1273K for 18ks. The relative density of sintered material became 95% or more when the temperature was elevated above 1173K. The SEM observation and EBSP analysis indicated that the obtained steel has equiaxed ferrite-pearlite structure with grain size of around 5μm and the crystallographic orientations of ferrite grains are randomly distributed.     

Synthesis and characterization of LiFePO4／C composite used as lithium storage electrodes

LiFePO4/C composites with good rate capability and high energy density were prepared by adding sugar to the synthetic precursor, A significant improvement in electrode performance was achieved. The resulting carbon contents in the sample 1 and sample 2 are 3.06% and 4.95% (mass fraction), respectively. It is believed that the synthesis of LiFePO4 with sugar added before heating is a good method because the synthesized particles having uniform small size are covered by carbon. The performance of the cathodes was evaluated using coin cells. The samples were characterized by X-ray diffraction and scanning electron microscope observation. The addition of carbon limits the particles size growth and enables high electron conductivity. The LiFePO4/C composites show very good electrochemical performance delivering about 142 mAh/g specific capacity when being cycled at the C/10 rate. The capacity fade upon cycling is very small.     

Fabrication of monolithic bulk Ti3AlC2 and impurity measurement by K-value method

Polycrystalline bulk Ti3AlC2 material with high purity and density was fabricated by hot pressing from the powder mixture with the starting stoichiometric mole ratios of 2.0TiC/1.0Ti/1.1Al/0.1Si at 1 300-1 500 ℃. X-ray diffraction patterns and scanning electron microscopy photographs of the fully dense samples indicate that the proper addition of silicon is favorable to the formation of Ti3AlC2, consequently results in high purity of the prepared samples. The Ti3AlC2 hot pressed at 1 300 ℃ and 1 400 ℃ is in plane-shape with sizes of 6-8 μm and 15-20 μm in the elongated dimension, respectively. The purities of samples are measured by the K-value method, and the contents of TiC are given by a linear equation.     

Electrochemical performance of Al_2O_3 pre-coated spinel LiMn_2O_4

Al_2O_3-coated spinel LiMn_2O_4 cathode materials, presintered LiMn_2O_4(P-LMO), and calcined LiMn_2O_4(C-LMO) were synthesized by chemical deposition and thermal treating method using presintered and calcined LiMn_2O_4 as precursors. The crystal structure, morphology,the thickness of the coating layer, and particle size of prepared samples were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM), high-resolution transmission electron microscopy(HRTEM), and Malvern instruments. The average particle size of P-LMO with like-spheres(0.3 μm) is much smaller than that of C-LMO(0.5 μm). The Al_2O_3 layer of P-LMO can effectively reduce the charge transfer resistance and inhibit the Mn dissolution. The electrochemical performance of P-LMO is better than that of C-LMO. It is found that the LiMn_2O_4 cathode materials have excellent electrochemical cyclability by coated 2 mol% Al_2O_3 at the surface of presintered material. The initial discharge capacity of the material with 2 mol% Al_2O_3-coated is 114.0 m Ah·g~(-1) at 0.1 C rate and 55 ℃, and the capacity retention is 87.3 % at 0.5 C rate.     

Influences of post-annealing and internal stress on magnetoresistance properties of Ni80Fe20 films

Ni80 Fe20 films with thickness about 54 nm were deposited on K9 glass and thermally oxidized silicon substrates at ambient temperature by electron beam evaporation with deposition rate about 1.8 nm/min. The as-deposited films were annealed at 350, 450 and 570 ℃ respectively for 1 h. After annealing at 570 ℃, the anisotropic magnetoresistance ratio(RAM) of the films is greatly improved. It increases to 3%- 3.5% nearly about three times of that of the as-deposited films. The grain size increases with the annealing temperature and the [111] crystal orientation is obviously enhanced after annealing at temperature above 450 ℃. The internal stress in the films deposited on K9 glass is compressive and the resistance measurement shows that RM∥ is larger than RM⊥ in these films. However, in the films deposited at the same conditions but on oxidized silicon substrates, the internal stress is tensile and RM⊥ is larger than RM∥. The differences of RM∥ and RM⊥ in two series of specimens are discussed.     

Influences of vacancy defects on thermal conductivities of Ge thin films

The effects of vacancy defects on the thermal conductivity of Ge thin films were investigated by employing molecular dynamics(MD) simulations and theoretical analysis based on the Boltzmann equation.Both the MD and theoretical results show that the lattice thermal conductivity dramatically decreases with the increasing of vacancy concentration at 400 and 500 K.In addition,the dependence of vacancy concentration on the thermal conductivity of Ge thin films becomes less sensitive as the temperature increases.Theoretical results also confirm that the major part of the lattice thermal conductivity reduction is associated with the point-defect scattering and phonon-phonon scattering processes.     

Electrical conductivity of Na3AlF6-AlF3-Al2O3-CaF2-LiF（NaCl） system electrolyte

A PGSTAT 30 and a BOOSTER 20A were used to measure cell impedance.Electrical conductivity was gained by the Continuously Varying Cell Constant Technique.Electrical conductivity of KCl was measured for comparison.The results prove that the method is reliable and accurate.The electrical conductivity of Na3AlF6-AlF3-Al2O3-CaF2-LiF(NaCl)system was studied by this method.Activation energy of conductance was obtained based on the experiment results.The experiments show that electrical conductivity is increased greatly with NaCl and LiF added.Increasing 1%LiF(mass fraction)results in corresponding increase of 0.0276 S/cm for superheat condition of 15℃.For NaCl,it is 0.024 S/cm.Electrical conductivity is increased by 0.003 S/cm with 1℃temperature increase.The electrical conductivity is lower than that predicted by the WANG Model and higher than that predicted by the Choudhary Model.     

Experiment and Simulation for Rolling of Diamond–Cu Composites

We demonstrate an innovative preparation approach of diamond/Cu composites by powder-in-tube technique and rolling. A small copper tube was loaded with Ti-and Cu-coated diamond particles, and then the diamond particles were combined with Cu matrix by composite rolling. The morphology and element distribution of the interface between diamond and Cu were determined by scanning electron microscopy and energy-dispersive spectrometer. Finite element method(FEM) simulation was used to analyze the rolling process associated with experiment by DEFORM-3D. The final experimental results showed that homogeneous distribution of diamond particles could be observed in the center layer of the composites. According to the contrast experiments, the sample, whose diamond particle size is 0.12–0.15 mm and thickness of pre-rolling is 1.2 mm, showed relatively complete morphologies and homogeneous distribution. Experimental results indicated a poor efficacy of excessive rolling reduction. The thermal conductivity of the composites is about 453 W(m K)~(-1)by theoretical calculation. For FEM simulation, rolling strain and temperature field of the composites were simulated by DEFORM-3D. Simulation results were interpreted, and numerical results verified the reliability of the model.The simulation predicted that the local area of large strain, indicative of the strain along the thickness direction, could be intensified by adding diamond particles.     

Electronic packaging materials prepared by powder injecting molding and pressure infiltration process

AlSiCp (65 vol.% SiC) electronic packaging materials were manufactured by powder injection molding (PIM) and pressure infiltration process in order to obtain near net-shaped parts. SiCp preformed compacts obtained by pre-sintering process at 1150 K have high strength and good appearance, and the ratio of open porosity to total porosiry is nearly 98%. The relative density of composites is bigger than 99%. The thermal conductivity of AlSiCp composites fabricated by this method is 198 W·m-1·K-1, and the coefficient of thermal expansion (CTE) is 8.0 × 10-6/K (298 K).     

Ionic conductivity of infiltrated Ln(Ln=Gd,Sm,Y)-doped ceria

This work studies the ionic conductivity of nanosized Gd-, Sm-, and Y-doped ceria prepared by the infiltration/impregnation method. The nanoparticles were deposited onto porous pure ceria substrates via infiltrationheating processes, and the conductivity was determined with the electrochemical impedance spectroscopy (EIS)using the conductive model for infiltrated phases. The conductivity of the infiltrated doped ceria changes with the doping amount, and Gd_(0.25)Ce_(0.75)O_(2-δ), Sm_(0.2)Ce_(0.8)O_(2-δ),and Y_(0.15)Ce_(0.85)O_(2-δ) show the highest values of 2.56, 3.01,and 2.07×10~(-3) S·cm~(-1) at 600℃,respectively. Overall,Sm-doped samples show the highest conductivity, whileY-doped samples show the lowest conductivity. In consideration of the Bruggeman factor, the intrinsic conductivity of the infiltrated doped ceria was calculated.Compared with the bulk doped ceria, the intrinsic conductivity is higher while the activation energy is lower,which may suggest different conduction mechanisms.Besides, co-doping effects on the conductivity of the infiltrated sample are less obvious than those of the bulk sample.     

PARTICLE SIZE AND MICROSTRUCTURE OF Ni NANOPOWDERS PREPARED BY ANODIC ARC PLASMA

Pure Ni nanopowders were successfully prepared by the method of anodic arc discharged plasma with homemade experimental apparatus. The particle size, mircostructure and morphology of the particles by this process were characterized via X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED); The specific surface area and pore parameters were investigated by multi-point full analysis of nitrogen adsorption-desorption isotherms at 77K by BrunauerEmmett-Teller (BET) surface area analyzer; The chemical composition were determined by X-ray energy dispersive spectrometry (XEDS) equipped in SEM and element analyze instrument. The experiment results indicate that the samples by this method with high purity, the crystal structure of the particles is as same as the bulk material, is fcc structure, with average particle sizes about 47nm, ranging from 20 to 70nm, and distributed uniformly in spherical chain shapes, the specific surface areavis 14.23m^2/g, pore volume of pore is 0.09cm^3/g and average pore diameter is 23nm.     

Determination of isothermal sections of the Co-Nb-Ni and Ni-Mo-Re ternary systems

The isothermal sections of the Co-Nb-Ni ternary system at 1373 K and the Ni-Mo-Re ternary system at 1473 K were determined by means of diffusion triple and electron probe microanalysis (EPMA).The results indicate that there are three three-phase regions found in the Co-Nb-Ni ternary system at 1373 K:(Ni,Co) NbCo3 Ni3Nb,NbCo3 NbCo2 Ni3Nb,and NbCo2 μ Ni3Nb;and four three-phase regions found in the Ni-Mo-Re ternary system at 1473 K:Re Ni χ,Ni NiMo σ,σ χ Ni,and σ Mo NiMo.No ternary eompoond is observed in the two isothermal sections.The isothermal sections arc contrasted with the previous study.     

Thermal properties of Y_(1-x)Mg_xTaO_(4-x/2) ceramics via anion sublattice adjustment

A systematic investigation concerned with Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16 and 0.20,respectively)ceramics was fabricated by a solid-state reaction method and characterized by X-ray diffraction(XRD),Raman spectroscopy,scanning electron microscopy(SEM)and thermal analysis.XRD spectra display that all of the samples are excellently consistent with the standard XRD spectrum of monoclinic YTaO_4(PDF No.24-1415;space group:I2(5)).The Raman peaks of the samples doped with Mg~(2+)just widen slightly compared with those of pure YTaO_4,which are in agreement with the results of XRD.The thermal conductivity of dense 7 wt%–8 wt%yttria-stabilized zirconia(7–8 YSZ)ceramic is about 2.5 W·m~(-1)·K~(-1)at 900°C,while the Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16 and 0.20)ceramics possess lower thermal conductivity in the range of 1.45–1.57 W·m~(-1)·K~(-1)at 900°C,which declines by35%compared with that of 7–8 YSZ.The lower thermal conductivities of Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16and 0.20)ceramics are originated from the enhanced phonon scattering caused by oxygen vacancy and Mg~(2+)ions defect complex.However,the thermal expansion coefficients are about 9.0 9 10~(-6)–9.5 9 10~(-6)K~(-1)along with the different amounts of Mg~(2+)doping at 1200°C.Compared to the pure sample,the thermal expansion coefficient decreases slightly when the Mg~(2+)doping amount is over 20%.The systematic investigations on the phase,microstructure,elastic and thermal properties of Y_(1-x)Mg_xTaO_(4-x/2)(x=0,0.08,0.12,0.16 and 0.20)ceramics will provide guidance for its application at high temperature,especially as thermal barrier coatings.     

Enhanced thermoelectric performance of AgBi_3S_5 by antimony doping

AgBi_3S_5 is a promising n-type thermoelectric material with low lattice thermal conductivity.In this paper,polycrystalline bulk samples of n-type Ag_(1-x)Sb_xBi_3S_5(x=0-0.03) were prepared by high-temperature reaction and pressed by spark plasma sintering(SPS).Electrical conductivity of AgBi3 S5 is enhanced significantly due to the increased carrier concentration.There is a remarkable enhancement of power factor from～2.1 μW·cm~(-1)·K~(-2) for undoped AgBi_3S_5 to～3.3 μW·cm~(-1)·K~(-2) for Ag_(0.97)Sb_(0.03)Bi_3S_5.The Sb lone pair electrons,as indicated from density functional theory(DFT) calculation results,contribute to the Fermi energy and enhance the carrier effective mass.In addition,the point defects enhance phonon scattering and decrease the lattice thermal conductivity.Owing to the enhanced power factor and reduced thermal conductivity,the thermoelectric figure of merit(ZT) at 800 K for Ag_(0.97)Sb_(0.03)Bi_3S_5 reaches 0.53,which is 70% higher than that of the pristine AgBi_3S_5.     

Preparation and electrochemical properties of LiFePO4/C composite with network structure for lithium ion batteries

The bare LiFePO4 and LiFePO4/C composites with network structure were prepared by solid-state reaction. The crystalline structures, morphologies and specific surface areas of the materials were investigated by X-ray diffractometry（XRD）, scanning electron microscopy（SEM） and multi-point brunauer emmett and teller（BET） method. The results show that the LiFePO4/C composite with the best network structure is obtained by adding 10% phenolic resin carbon. Its electronic conductivity increases to 2.86 × 10^-2 S/cm. It possesses the highest specific surface area of 115.65 m^2/g, which exhibits the highest discharge specific capacity of 164.33 mA.h/g at C/IO rate and 149.12 mA.h/g at 1 C rate. The discharge capacity is completely recovered when C/10 rate is applied again.