Jiuxing Zhang

Beijing University of Technology, Peping, Beijing, China

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Publications (39)51.8 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: The single-phase n-type Mg2(Si0.4−xSbxSn0.6) (0≤x≤0.025) solid solutions were prepared by an induction melting and Spark Plasma Sintering method using buck of Magnesium, Silicon, Tin and Antimony. The unique multiple nanostructures of samples containing nanoscale precipitates and mesoscale grains are formed by the non-equilibrium preparing technique, resulting in remarkably decreasing of lattice thermal conductivities, particularly for samples with the nanoscale precipitates having the size of 20–30 nm. Meanwhile, the electrical properties were increased by Sb-doping. The thermoelectric performance of Sb doped samples with the nanostructures are remarkably improved, and the dimensionless figure of ZT for Mg2(Si0.38Sb0.02Sn0.6) sample shows highest value of 1.30 at 773 K, which is very much higher than that of the non-doped sample.
    Materials Letters. 01/2014; 123:31–34.
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    ABSTRACT: n-type Mg2(Si0.4Sn0.6)Bix (0 ≤ x ≤ 0.04) solid solutions with minute amounts of Bi were prepared by induction melting, melt spinning (MS), and spark plasma sintering (SPS) method, namely the non-equilibrium technique MS-SPS, using bulks of Mg, Si, Sn, Bi as raw materials; the phase components, microstructures as well as the thermoelectric properties were systematically investigated. The multiple localized nanostructures within the matrix containing nanoscale precipitates and mesoscale grains were formed, resulting in remarkably decreasing of lattice thermal conductivities, particularly for samples with the nanoscale precipitates having the size of 10–20 nm. Meanwhile, the electrical resistivity was reduced and the Seebeck coefficient was increased by Bi-doping, causing improved electrical performance for the Mg2(Si0.4Sn0.6)Bix (0 ≤ x ≤ 0.04) compounds. The dimensionless figure of merit ZT was significantly improved and the maximum value reaches 1.20 at 573 K for the Mg2(Si0.4Sn0.6)Bi0.03 sample, greatly higher than that of the non-doped samples.
    Applied Physics Letters 08/2013; 103(6). · 3.79 Impact Factor
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    ABSTRACT: The inherently high magnetic anisotropy and nanoscale grain size in a SmCo compound result in an intrinsic coercivity far higher than those of known Sm-Co compounds prior to orientation treatment. The combination of ultrahigh intrinsic coercivity, high Curie temperature and low coercivity temperature coefficient of nanocrystalline SmCo as a single phase material shows it to be a very promising compound to develop outstanding high-temperature permanent magnets.
    Nanoscale 02/2013; 5(6):2279-84. · 6.23 Impact Factor
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    ABSTRACT: The rare earth Pr doped Ca1−xPrxMnO3 (x=0, 0.06, 0.08, 0.1, 0.12, and 0.14) compound bulk samples were prepared to study the effect of Pr doping on thermoelectric transport properties of CaMnO3 compound system. The doped samples exhibited single phase composition within the experimental doping range, with condensed bulk microstructure and small porosities. The electrical resistivity was remarkably reduced for doped samples, on account of the enhanced carrier concentration; the absolute value of Seebeck coefficient was deteriorated mainly due to enhanced electron carrier concentration. The electrical performances of the doped samples reflected by resistivity and Seebeck coefficient fluctuations were optimistically tuned, with an optimized power factor value of 0.342 mW/(m·K2) at 873 K for x=0.08 sample, which was very much higher comparing with that of the un-doped sample. The lattice thermal conduction was really confined, leading to distinctly repressed total thermal conductivity. The thermoelectric performance was noticeably improved by Pr doping and the dimensionless figure of merit ZT for the Ca0.92Pr0.08MnO3 compound was favorably optimized with the maximum value 0.16 at 873 K.
    Journal of Rare Earths 01/2013; 31(9):885–890. · 1.36 Impact Factor
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    ABSTRACT: The Ba-, La- and Ag-doped polycrystalline Ca2.9M0.1Co4O9 (M=Ca, Ba, La, Ag) thermoelectric bulk samples were prepared via citrate acid sol-gel synthesis method followed by spark plasma sintering technique. The bulk samples were characterized and analyzed with regard to their phase compositions, grain orientations as well as microstructures. The high temperature thermoelectric transport properties of the bulk samples were studied in detail. All bulk samples were found to be single-phased with modified body texture. The electrical resistivity was modulated as a result of carrier concentration modification, however the carrier transport process was not influenced; the Seebeck coefficient was deteriorated simultaneously. The total thermal conductivity was remarkably reduced, on account of the decreasing of phonon thermal conductivity. The thermoelectric properties of the Ba-, La-, and Ag-doped bulk samples were optimized, and the Ba-doped Ca2.9Ba0.1Co4O9 system was found to have the highest dimensionless figure of merit ZT 0.20 at 973 K, which was remarkably higher than that of the un-doped sample.
    Journal of Rare Earths 01/2013; 31(8):778–783. · 1.36 Impact Factor
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    ABSTRACT: Polycrystalline Cr-doped higher manganese silicides (HMSs) Mn1−x Crx Si1.80 (x = 0 to 0.03) were prepared by the in situ spark plasma sintering method. The phase structure and microstructure of the bulk samples were investigated, and their thermoelectric (TE) properties were measured from 473 K to 873 K. x-Ray diffraction patterns show that almost all of the Cr-doped samples possess single-phase HMS structure. However, minor amounts of MnSi phase can be observed in scanning electron microscopy images. The electrical conductivity increases continuously with increasing Cr substitution, and is enhanced by up to 15% for bulk Mn0.97Cr0.03Si1.80 over the entire measurement range from 473 K to 873 K. Meanwhile, the Seebeck coefficient is slightly depressed, so that the power factor is increased by about 10%. Cr doping affects the thermal conductivity negatively, and the overall dimensionless TE figure of merit of all the samples decreases slightly due to the higher thermal conductivity.
    Journal of Electronic Materials 12/2011; 41(6). · 1.64 Impact Factor
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    ABSTRACT: The paper is focused on understanding the densification characteristics of WC–Co composite powders by the spark plasma sintering (SPS) technique, especially the essential mechanisms for the distinct differences of the effects of WC particle size on the densification behavior between the SPS and the conventional sintering technologies. For the particular combination and contacting state between WC and Co after ball milling in which Co forms thin films coating the WC particles, a model that quantitatively describes the densification process of SPS WC–Co powders with different WC particle sizes has been developed. The calculated results show that both the actual temperature in the Co film and the melting temperature of the Co film increase with the increase of the WC particle size. As a result, the formation and growth of the sintering necks due to the rapid melting and solidification of the Co films turn to be weakly influenced by the WC particle size, and hence the SPS densification is almost independent of the WC particle size. The model calculations are consistent with the experimental findings that in the SPS processes the temperatures corresponding to the start of the densification and the peak of the displacement rate, respectively, are nearly the same for the WC–Co powders with different WC particle sizes.
    Journal of the American Ceramic Society 06/2010; 93(10):3153 - 3158. · 2.11 Impact Factor
  • Nianduan Lu, Xiaoyan Song, Jiuxing Zhang
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    ABSTRACT: The single-phase ultrafine nanocrystalline SmCo(3) compound with a high coercivity of 33 kOe and a Curie temperature of 925 K was prepared using a simple and efficient method, which took advantages of the concurrent processes of nanocrystallization and densification during spark plasma sintering. The crystal structure of the nanocrystalline SmCo(3) compound was constructed. As compared with the conventional microcrystalline SmCo(3) compound, a large axial ratio c/a = 4.920 and an expansion of the unit cell volume of 2.97% were obtained in the lattice structure of the nanocrystalline SmCo(3). The relationship between the magnetic properties and the nanocrystalline structure was analyzed. A specific magnetic transition from the weak ferromagnetic to the strong ferromagnetic state was discovered in the nanocrystalline SmCo(3) compound, which was considered to be related to the large anisotropic strain in the crystal lattice.
    Nanotechnology 02/2010; 21(11):115708. · 3.84 Impact Factor
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    ABSTRACT: The single-phase Sm2Co17 alloys with amorphous and nanocrystalline structures were prepared separately by a simplified route combining high-energy ball milling and spark plasma sintering. The microstructure evolution, as well as the phase transformation, were investigated for the prepared Sm2Co17 alloys. It was found that the nanocrystalline Sm2Co17 alloy has a stable hexagonal crystal structure at the room temperature, which shows different phase stability from the conventional polycrystalline Sm2Co17 alloys. In contrast with the coarse-grained Sm2Co17 ingot that shows very weak permanent magnetic properties, the amorphous and nanocrystalline Sm2Co17 alloys exhibit apparently improved magnetic properties. The first-principles calculations show that a much higher spin polarization is achieved in the nanocrystalline Sm2Co17, as compared with the coarse-grained polycrystalline counterpart. Due to the intense spin polarization at the Fermi level, the exchange interaction between Sm(4f) and Co(3d) electrons is enhanced, which results in the strong magnetism in the nanocrystalline Sm2Co17 alloy.
    Intermetallics 01/2010; 18(6):1180-1184. · 1.86 Impact Factor
  • Acta Metallurgica Sinica - ACTA METALL SIN. 01/2010; 46(8):973-978.
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    ABSTRACT: A novel route for the preparation of the single-phased Sm2Co17 nanocrystalline bulk with ultrafine grain sizes was proposed. It was found that the nanocrystalline Sm20Co17 has a hexagonal crystal structure at the room temperature, which shows a different thermal stability from the conventional polycrystalline alloy. The intrinsic coercivity of the nanocrystalline Sm2Co17 with a hexagonal crystal structure was greatly increased as compared with the single-phased polycrystalline alloy with a rhombohedral structure. The microhardness and the elastic modulus of the nanocrystalline Sm2Co17 bulk were increased as high as 1.8 and 2.6 times, respectively, when compared with the polycrystalline parent alloy.
    Journal of Nanoscience and Nanotechnology 09/2009; 9(9):5141-4. · 1.15 Impact Factor
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    ABSTRACT: A rapid route of synthesizing WC–Co composite powder by in situ reduction and carbonization reactions of metal oxides and carbon was proposed. The effects of a series of processing parameters on the preparation of the pure-phase and ultrafine composite powder were studied systemically. It is found that the phase constitution in the prepared composite powder is influenced by the carbon addition content in the starting powders, the milling time, the vacuum pressure, and the reaction temperature. The long-time ball milling, low reaction temperature and short holding time are favorable to obtain the fine and homogeneous composite powder particles.
    International Journal of Refractory Metals & Hard Materials - INT J REFRACT MET HARD MATER. 01/2009; 27(1):115-120.
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    Journal of Applied Crystallography - J APPL CRYST. 01/2009; 42(4):691-696.
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    ABSTRACT: The spark plasma sintering (SPS) behavior of binder-free WC was investigated by a series of experiments. The appropriate contents of carbon addition to form dominant WC phase were determined corresponding to different sintering parameters. By optimizing the processing parameters, with 0.1wt% carbon addition and sintered at 1460°C, the WC cemented carbides of high density and a fine microstructure with grain sizes less than 350nm were obtained. By means of TEM and high-resolution transmission electron microscope (HRTEM) observations, the clean WC grain boundaries were found, and the orientation relationship between neighbouring WC grains was studied. The advantages, as well as the mechanisms of SPS sintering binder-free WC, were also discussed.
    Journal of Alloys and Compounds 01/2009; 479(1):427-431. · 2.39 Impact Factor
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    ABSTRACT: Ultrafine-grained WC-Co bulk materials were prepared by a new method that contains pretreatment of the milled powder mixture and subsequent spark plasma sintering (SPS). Ball milling parameters and the pretreatment temperature have significant effects on the microstructure and properties of WC-Co cermets. The prepared cermets have a mean grain size of less than 0.5 μm even with a pretreatment temperature as high as 1300°C. The WC-10wt.%Co cermet bulk prepared by the optimized milling, pretreatment, and SPS processing achieves excellent mechanical properties with a Vickers hardness of HV 1643, a fracture toughness of 13.1 MPa·m1/2 and a transverse rapture strength of 3100 MPa.
    Rare Metals 01/2009; 28(4):391-395. · 0.49 Impact Factor
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    ABSTRACT: A series of rare earth bulks with the ultrafine nanocrystalline structure were prepared by applying an “oxygen-free” (an environmental oxygen concentration less than 0.5 ppm) in-situ synthesis system, where the inert-gas condensation was combined with the spark plasma sintering technology into an entirely closed system. The thermal and mechanical properties of the prepared ultrafine nanocrystalline bulks were characterized and compared with those of the raw polycrystalline bulks. It was found that the specific heat capacity, the microhardness, and the elastic modulus of the ultrafine nanocrystalline rare earth bulks were significantly increased from the conventional polycrystalline bulks.
    Journal of Rare Earths - J RARE EARTH. 01/2009; 27(6):961-966.
  • Nianduan Lu, Xiaoyan Song, Jiuxing Zhang
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    ABSTRACT: The nanoparticles and nanocrystalline bulk of pure gadolinium (Gd) were prepared by a novel route. The nanostructures of the single particle and the bulk of Gd were investigated, and the crystal structure was characterized. The fundamental properties, namely the physical, thermal, and mechanical characteristics, were studied for the prepared Gd bulk with an ultrafine nanograin structure. As compared with the conventional polycrystalline metal, the ultrafine nanocrystalline Gd has greatly enhanced functional and structural properties. The physical background for the changes of the fundamental properties with the reduction of the grain size to the nanoscale was analyzed.
    Materials Letters - MATER LETT. 01/2009; 63(12):1089-1092.
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    ABSTRACT: Abnormal crystal structure stability is discovered in the single-phase nanocrystalline Sm2Co17 permanent magnet. Three kinds of crystal structures, namely the rhombohedral Th2Zn17-type (2:17 R), the hexagonal TbCu7-type (1:7 H), and the hexagonal Th2Ni17-type (2:17 H), are claimed to exist at room temperature in the Sm2Co17 alloy system. The strong dependence of the magnetic properties on the structure characteristics in the single-phase Sm2Co17 alloy is interpreted in view of the atom space occupancy and the exchange coupling between substructures especially in the nanocrystalline alloy.
    Applied Physics Letters 01/2009; 94. · 3.79 Impact Factor
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    ABSTRACT: The WC–Co cermet bulks were prepared by spark plasma sintering (SPS) using powder mixtures with different-scaled WC particles. The SPS densification process was studied by calculating the current distribution between the powder sample and the die in the SPS system. The microstructures were characterized and compared for different samples by the WC grain size, Co mean free path and contiguity of WC grains. In spite of a weak effect of WC particle size on the SPS densification stages, the WC particle size plays a significant role in the homogeneity of the cermet microstructure. Good mechanical properties of the SPSed cermet were obtained with an optimized WC and Co particle-size combination. The effects of scale combination of WC and Co particles on the microstructure hence the properties of the SPSed cermet were discussed.
    International Journal of Refractory Metals and Hard Materials 01/2009; 27(6):1014-1018. · 1.86 Impact Factor
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    ABSTRACT: The thermodynamics of mechanisms of the reactions in the synthesis processes of WC–Co composite powder by WO3, Co3O4 and carbon as original reactants was investigated. By the thermodynamic calculations, the initiation of the in situ reduction and carbonization reactions, the formation sequence and the relative stability of the reaction products, can be quantitatively described. The formation sequence of the reaction products, and the fact that WC–Co composite powder with pure phases, homogeneous and ultrafine particles can be synthesized at 1323 K in the vacuum condition, as found in experiments, verified the thermodynamic predictions. The thermodynamic analysis performed in the present work is significant to control the preparation processes and to optimize the parameters of fast synthesizing pure-phased WC–Co composite powder.
    Materials Chemistry and Physics. 06/2008;