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Spark Plasma Sintering (spark + plasma_sintering)
Terms modified by Spark Plasma Sintering Selected AbstractsSize Effect on Properties of Varistors Made From Zinc Oxide Nanoparticles Through Low Temperature Spark Plasma SinteringADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Léna Saint Macary Abstract Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8-nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at room temperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as-prepared ceramics are based on scanning electron microscopy and X-ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current,voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600,°C. [source] A Screening Design Approach for the Understanding of Spark Plasma Sintering Parameters: A Case of Translucent Polycrystalline Undoped AluminaINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 5 2010Yann Aman An experimental screening design was used to evaluate the effects of spark plasma sintering (SPS) parameters such as heating rate, sintering temperature, dwell duration, and green-shaping processing on the relative density, grain size, and the optical properties of polycrystalline alumina (PCA). It is shown that heating rate and sintering temperature are the most critical factors for the densification of PCA during SPS. Green-shaping processing could prevent grain growth at low SPS sintering temperatures. No predominant SPS parameters are observed on the optical properties. Hence, the optical properties of PCA are controlled by microstructural evolution during the SPS process. [source] Technique for Preparing Ultrafine Nanocrystalline Bulk Material of Pure Rare-Earth Metals,ADVANCED MATERIALS, Issue 9 2006X. Song Ultrafine nanocrystalline bulk material of pure rare-earth metals has been prepared using a combination of inert gas condensation and spark plasma sintering (see figure). Some of the bulk properties such as the microhardness and specific heat capacity are remarkably improved compared to the conventional polycrystalline material. This new preparation technique enables the preparation and study of a variety of other nanostructured metal materials. [source] Nanostructured La1,xSrxGa1,yMgyO3,, Ceramics Processed by Spark Plasma Sintering of Mechanosynthesized PrecursorsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Alberto Moure Nanostructured ceramics with La1,xSrxGa1,yMgyO3,, composition have been processed by spark plasma sintering of precursors obtained by mechanosynthesis. The compositions with x=0.10 and y=0.20 are single-phase ceramics even at the lowest processing temperatures of 900°C. For x=0.20, y=0.17, typical secondary phases as SrLaGaO4 and SrLaGa3O7 appear at all the processing temperatures, from 900° to 1100°C. The high reactivity of the precursors due to the prolonged milling allows highly densified ceramics (>98%) to be obtained at moderate applied pressures (100 MPa), and at temperatures for which the nanostructure scale is maintained. Single-phase ceramics present higher conductivity than those with isolating secondary phases. The nanostructure appears to break the vacancies ordering, and the conductivity is produced through random vacancies paths, diminishing the activation energy and increasing the total conductivity of the ceramics. [source] Fabrication of Silicon Nitride Nanoceramics and their Tribological PropertiesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2010Jae-Hee Kim Si2N2O secondary phase-free, fully dense nano-Si3N4 ceramics (,97% of theoretical density) were developed by combining carbothermal reduction treatment and spark plasma sintering (SPS), and their tribological properties were investigated by subjecting to self-mated sliding under unlubricated conditions. Commercially available Si3N4 nanopowder was used as a starting material and phenolic resin was used for carbothermal reduction, which was conducted at 1450°C for 10 h. Fully densified Si2N2O phase-free Si3N4 ceramics with a wide range of grain size from 90 nm to 1.5 ,m were fabricated by varying SPS temperature from 1550° to 1750°C. The microstructure of the developed Si3N4 ceramics was changed from nano equi-axed at 1550°C to large elongated bimodal grain morphology at 1700° or 1750°C. The frictional behavior was not dependent on the microstructure, but the wear rate was strongly influenced such that it decreased by an order of magnitude (from 9.7 × 10,5 to 0.88 × 10,5 mm3/N·m) with decreasing grain size. The dominant wear mechanism was changed from the delamination of tribochemical layer for the ceramics with nano equi-axed grain microstructure to the fracture and grain pull-out for the ceramics with duplex microstructure. [source] Effect of Applied Stress on IR transmission of Spark Plasma-Sintered AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Dibyendu Chakravarty The effect of applied stress on IR transmittance of nanocrystalline alumina prepared by spark plasma sintering was evaluated. Transparent alumina with maximum transmittance >80% was obtained over the entire mid-IR wavelength range of 3,5 ,m by applying a high stress of 275 MPa at 1150°C using specially designed high-strength compound dies. The transmittance observed was similar to previous reports at identical wavelengths, but at a lower sintering temperature. The transparent samples have an average grain size of 0.3 ,m and a hardness of 23 GPa. At lower stresses and sintering temperatures, transmittance reduced drastically due to remnant pores in the matrix as observed from the microstructural analysis. The effect of porosity was found to be critical in developing transparency as even a marginal decrease in porosity led to substantial increase in transmittance. [source] Blue-emitting AlN:Eu2+ Powder Phosphor Prepared by Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2010Hyoung-SeoK Do Blue-emitting AlN:Eu2+ powder phosphor was synthesized by spark plasma sintering (SPS) using AlN, Si3N4, and Eu2O3 as the starting materials, and its luminescence properties were investigated. A single-phase Eu- and Si-co-doped AlN powder was successfully fabricated by SPS in the range of 1650°,1800°C for 5 min. The AlN:Eu2+ obtained exhibited a strong blue emission at 480 nm under the excitation of ,exc=340 nm and an electron beam. The highest photoluminescence intensity was observed in the phosphor sintered at 1700°C, which was comparable to that of the phosphor prepared by gas pressure sintering at 1750°C for 4 h. [source] Alumina/Silicon Carbide Laminated Composites by Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009Vincenzo M. Sglavo Ceramic laminates composed of alumina/silicon carbide composite layers were produced by spark plasma sintering (SPS). Monolithic composite disks containing up to 30 vol% of silicon carbide were fabricated by stacking together and cosintering by SPS green layers prepared by tape casting water-based suspensions. An engineered laminate with a specific layer combination that is able to promote the stable growth of surface defects before final failure was also designed and produced. Fully dense materials with an optimum adhesion between the constituting layers and a homogeneous distribution of the two phases were obtained after SPS. Monolithic composites showed an increasing strength with SiC load, and biaxial strength values as high as 700 MPa were observed for a SiC content of 30 vol%. The engineered laminate showed a peculiar crack propagation that is responsible for the high strength value of about 600 MPa and for the evident insensitivity to surface defects. [source] Oxidation Behavior of Zirconium Diboride Silicon Carbide Produced by the Spark Plasma Sintering MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Carmen M. Carney Dense samples of ZrB2,20 vol% SiC were successfully fabricated by spark plasma sintering without the use of sintering aids. Oxidation behavior of these samples was characterized by exposing them to 1400°, 1500°, and 1600°C in an ambient atmosphere for 150 min, and by measuring the weight gains of the sample and crucible, as well as the thickness of the oxide scale and the glassy outer layer. The effects of gravity on the viscous outer layer are shown to result in significant heterogeneity within a sample. The oxidation scales were characterized by scanning electron microscopy and transmission electron microscopy with energy dispersive spectroscopy analysis. The oxide scale was found to be composed of three layers: (1) a SiO2 -rich glassy outer layer, (2) an intermediate layer of a ZrO2 matrix with interpenetrating SiO2, and (3) a layer containing a ZrO2 matrix enclosing partially oxidized ZrB2 with Si,C,B,O glass inclusions. [source] Spark Plasma Sintered Silicon Nitride Ceramics with High Thermal Conductivity Using MgSiN2 as AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Gui-hua Peng Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°,1600°C for 3,12 min, using ,-Si3N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%,-Si3N4 phase left in the sintered material. ,-Si3N4 was completely transformed to ,-Si3N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K),1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate ,-Si3N4 ceramics with high thermal conductivity when appropriate additives are used. [source] Hydrothermal Synthesis and Spark Plasma Sintering of (K, Na)NbO3 Lead-Free PiezoceramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009Nan Liu A facile hydrothermal route was adopted for synthesis of lead-free piezoceramics (K, Na)NbO3 powders. The influences of temperature and KOH/NaOH concentration on the resultant powders were investigated. Although two similar perovskite phases appeared when K/Na ratio tended toward 1:1, the two-phase coexistence tendency was weakened by increasing hydrothermal reaction temperature, and consequently only one phase could be obtained after spark plasma sintering. Reasonably good ferroelectric and piezoelectric properties were obtained for the samples after postannealing, whose piezoelectric constant (d33) reached 135 pC/N. The optimal remnant polarization (Pr) and mechanical quality factor (Qm) were 26.2 ,C/cm2 and 164, respectively, which were both twice as much as those of the samples using powders prepared from solid-state reaction. [source] Effects of La2O3 Addition and PbO Excess on the Transmittance of PbZrO3,PbTiO3,Pb(Zn1/3Nb2/3)O3 Ceramics by Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Yong Jun Wu The effects of La2O3 addition and PbO excess on the microstructures and optical properties of PbZrO3,PbTiO3,Pb(Zn1/3Nb2/3)O3 (PZ,PT,PZN) ceramics prepared by spark plasma sintering were investigated. When 1 mol% La2O3 was added, the highest transmittance of 35% at 700 nm for PZ,PT,PZN ceramics was obtained. The improved transmittance was attributed to the increased relative density and the decreased optical anisotropy. The samples containing more than 1 mol% La2O3 showed decreased transmittance, due to the appearance of secondary phases. The transmittance of PZ,PT,PZN ceramics increased slightly to 29% at 700 nm with increasing amount of excess PbO up to 10 mol% and thereafter decreased rapidly. [source] Preparation and Microstructure of a ZrB2,SiC Composite Fabricated by the Spark Plasma Sintering,Reactive Synthesis (SPS,RS) MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Yuan Zhao A mixture of Zr, B4C, and Si powders was adopted to synthesize a ZrB2,SiC composite using the spark plasma sintering,reactive synthesis (SPS,RS) method. SPS treatments were carried out in the temperature range of 1350°,1500°C under a varying pressure of 20,65 MPa with a 3-min holding time. A dense (,98.5%) ZrB2,SiC composite was successfully fabricated at 1450°C for 3 min under 30 MPa. The microstructure of the composite was investigated. The in situ formed ZrB2 and SiC phases dispersed homogeneously on the whole. The grain size of ZrB2 and SiC was <5 and 1 ,m, respectively. A number of in situ formed ultrafine SiC particles were observed entrapped in the ZrB2 grains. [source] Spark Plasma Sintering Behavior of Nano-Sized (Ba, Sr)TiO3 Powders: Determination of Sintering Parameters Yielding Nanostructured CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2006Jing Liu Nano-powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3 (BST64), and a mixture of the composition (BaTiO3)0.6(SrTiO3)04 with particle sizes in the range of 60,80 nm were consolidated by spark plasma sintering (SPS). An experimental procedure is outlined that allows the determination of a "kinetic window," defined as the temperature interval within which the densification process can be kinetically separated from the grain growth one, enabling preparation of dense nanostructured ceramics. The width of this window varied from almost zero for BST64 to 125°C for the (BaTiO3)0.6(SrTiO3)0.4 mixture. During the densification (sintering) of the (BaTiO3)0.6(SrTiO3)04 mixture, BST64 is formed. The main part of this reaction occurs in a fully densified body through which suggesting that the constitutional phase(s) have a self-pinning effect on the grain growth. [source] Novel Fabrication Route to Al2O3,TiN Nanocomposites Via Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Lianjun Wang A novel method for the preparation of Al2O3,TiN nanocomposites was developed. A mixture of TiO2, AlN, and Ti powder was used as the starting material to synthesize the Al2O3,TiN nanocomposite under 60 MPa at 1400°C for 6 min using spark plasma sintering. X-ray diffractometry, scanning electron microscopy, and transmission electron microscopy were used for detailed microstructural analysis. Dense (up to 99%) nanostructured Al2O3,TiN composites were successfully fabricated, the average grain size being less than 400 nm. The fracture toughness (KIC) and bending strength (,b) of the nanostructured Al2O3,TiN composites reached 4.22±0.20 MPa·m1/2 and 746±28 MPa, respectively. [source] Compositional Dependence of Piezoelectric Properties in NaxK1,xNbO3 Lead-Free Ceramics Prepared by Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2006Bo-Ping Zhang Lead-free piezoelectric NaxK1,xNbO3 (x=20,80 mol%) ceramics were fabricated using spark plasma sintering at a low temperature (920°C). All the NaxK1,xNbO3 ceramics showed a similar orthorhombic phase structure, while the corresponding lattice parameters decreased from the KNbO3 side to the NaNbO3 side with increasing Na content. A discontinuous change in lattice parameter close to composition of 60 mol% Na indicated the presence of a transitional area that is similar to the morphotropic phase boundary (MPB) in NaxK1,xNbO3 ceramics. The sintered density of the NaxK1,xNbO3 ceramics decreased with increasing Na content, from a relative density of 99% for the K-rich side to 92% for the Na-rich side. The piezoelectric constant d33 and planar mode electromechanical coupling coefficient kp showed a maximum value of 148 pC/N and 38.9%, respectively, due to the similar MPB effects in the PZT system. [source] Simultaneous Spark Plasma Synthesis and Densification of TiC,TiB2 CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2006Antonio M. Locci The simultaneous synthesis and densification of dense TiC,TiB2 composite has been investigated starting from Ti, B4C, and C as reactants, and using the spark plasma sintering (SPS) technique. The optimal conditions for complete conversion of the reactants to the composite were determined for different applied DC current levels. A kinetic investigation performed allows us to conclude that solid-state diffusion is the mechanism governing the synthesis process. It is seen that TiC is the first phase formed, while TiB2 formation occurs afterward. Two intermediate boride phases, i.e. TiB and Ti3B4, are also formed but, as the SPS holding time was augmented, they were gradually and completely converted to TiB2. Moreover, it is found that in order to reach relatively high dense products, an electric current needs to be applied for time intervals longer than those required for obtaining complete conversion. A pure dense product (relative density ,98%) was obtained when an electric pulsed current of 1100 A and a mechanical pressure of 20 MPa were applied for about 4 min. [source] Development of Nanocrystalline Wear-Resistant Y-TZP CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2004Bikramjit Basu The present contribution reports some interesting and new results obtained while developing yttria-stabilized tetragonal zirconia (Y-TZP) using spark plasma sintering (SPS). The experimental results clearly showed that ZrO2 -nanoceramics with high hardness(,14.5 GPa) can be processed at a lower sintering temperature of 1200°C in a short time (5 min). Another important result is that the newly developed Y-TZP nanoceramics, compared with the conventional sintered TZP, exhibit better fretting wear resistance against bearing steel. The intergranular fracture and the grain pullout were observed as the major wear mechanisms of the zirconia nanoceramics. [source] Preparation of Textured Bismuth Titanate Ceramics Using Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2004Hao Junjie Textured bismuth titanate ceramics were successfully produced using spark plasma sintering and platelike bismuth titanate particles prepared using a molten-salt method. The microstructure and dielectric properties of the samples were investigated. The results showed that the dielectric property of the textured bismuth titanate ceramics was anisotropic in various directions and that spark plasma sintering was an effective sintering technology to obtain textured, dense bismuth titanate ceramics at a low temperature. [source] Synthesis of Dense, High-Defect-Concentration B4C through Mechanical Activation and Field-Assisted CombustionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2004E. M. Heian Dense fine-grained B4C was synthesized by the spark plasma sintering (SPS) method using mechanically activated elemental powders. Relative densities of up to 95% were achieved. When characterized by X-ray line broadening methods, the grains of the resulting product were determined to be nanometric in scale. However, transmission electron microscopy (TEM) observations showed the product to be composed of a mixture of fine (nanometric) crystallites and grains in the micrometer range. The TEM images showed a highly defective structure containing a high density of twins. Their presence is the reason for the discrepancy between the X-ray and TEM results. [source] Preparation of Dense MgB2 Bulk Superconductors by Spark Plasma SinteringJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Soo-Yong Lee Fully dense MgB2 bulk specimens (,higher than 99% dense) were prepared using spark plasma sintering (SPS) at 1250°C for 15 min. Microstructure analyses revealed that faceted MgO particles of ,8% volume fraction were dispersed in the MgB2 matrix. A sharp superconducting transition with an onset temperature of 38.5 K was confirmed by both magnetization and resistivity measurements. [source] Titanium Diboride,Tungsten Diboride Solid Solutions Formed by Induction-Field-Activated Combustion SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003Masachika Shibuya Solid solutions of titanium diboride,tungsten diboride (TiB2,WB2) were synthesized by induction-field-activated combustion synthesis (IFACS) using elemental reactants. In sharp contrast to conventional methods, solid solutions could be formed by the IFACS method within a very short time, ,2 min. Solutions with compositions ranging from 40,60 mol% WB2 were synthesized with a stoichiometric ratio (Ti + W)/B =½; however, samples with excess boron were also made to counter the loss of boron by evaporation. The dependence of the lattice constants of the resulting solid solutions on composition was determined. The "a" parameter decreased only slightly with an increase in the WB2 content, whereas the "c" parameter exhibited a significant decrease over the range 40,60 mol% WB2. Solid-solution powders formed by the IFACS method were subsequently sintered in a spark plasma sintering (SPS) apparatus. After 10 min at 1800°C, the samples densified to relative density 86%. XRD analysis showed the presence of only the solid-solution phase. [source] Spark Plasma Sintering of AluminaJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002Zhijian Shen A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al2O3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al2O3 could be fully densified at a much lower temperature (1150°C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark-discharge process in the vicinity of contacting particles, and that both grain-boundary diffusion and grain-boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine-grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21,22 GPa and fracture toughness values of 3.5 ± 0.5 MPa·m1/2 were found for the compacts containing submicrometer-sized Al2O3 grains. [source] Microstructures and Pyroelectric Properties of Multicomposition 0.9PbZrO3·xPbTiO3·(0.1,x)Pb(Zn1/3Nb2/3)O3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002Yong Jun Wu The microstructures and pyroelectric properties of multicomposition 0.9PbZrO3·xPbTiO3·(0.1,x)Pb(Zn1/3Nb2/3)O3 (PZ,PT,PZN) ceramics were investigated. The PZ,PT,PZN ceramics with nearly theoretical density were prepared by spark plasma sintering at low temperature (800°C) for a very short time (10 min) from two original compositions with x= 0.025 and x= 0.050. The heat treatment was successfully used to control the diffusion between the different compositions in such ceramics. For ceramics heat-treated at 900°C, two pyroelectric peaks corresponding to the original compositions were observed. When the heat-treatment temperature was increased to 1200°C, these two pyroelectric peaks combined into one sharp pyroelectric peak, which corresponds to average composition. When the spark-plasma-sintered ceramics were heat-treated at 950°C, a high and stable pyroelectric coefficient (>100 nC·cm,2·K,1) over a wide temperature range (23°,47°C) was obtained. It was found that the pyroelectric properties strongly depended on the microstructures. [source] Preparation and Electric Properties of Dense Nanocrystalline Zinc Oxide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2002Lian Gao This communication reports on the preparation and electric properties of dense nanocrystalline ZnO ceramics. By spark plasma sintering, nanocrystalline (,100 nm) ZnO ceramics with a high density of 98.5% were obtained at a very low temperature of 550°C. Electric property measurement revealed a novel conduction nonlinearity in the sample sintered at 500°C. This phenomenon is due to the nanometerization of ZnO crystal and the grain boundary layer with an amorphous interfacial layer. [source] Distribution of Cerium Ions in Cerium-Doped ,,-SiAlON and Its Effect on Grain MorphologyJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2002Fang-Fang Xu Cerium-doped ,,-SiAlON material was prepared by spark plasma sintering at 1750°C under 30 MPa pressure for 10 min. Yttrium ,,-SiAlON seeds (1 wt%) were added to the starting powder mixture. Recent work showed that up to 45 wt% of ,,-SiAlON phases are formed in the present sintered ceramics. The material presented a microstructure, containing rodlike cerium-doped ,,-SiAlON crystals. In this paper, transmission electron microscopy and energy dispersive spectroscopy examinations of the ,,-SiAlON grains are reported. The structural analyses revealed a high density of domain boundaries, within which larger amounts of cerium ions were segregated than in the matrix. The density of the domain boundaries was proportional to the amount of incorporated cerium ions. These structural defects eventually dominated the growth habits of the ,,-SiAlON crystals, by modifying the structure of the interstices at the boundary sites. The role of yttrium ,,-SiAlON seeds also is discussed in this paper. [source] Preparation and thermoelectric properties of polycrystalline nonstoichiometric Yb14MnSb11 Zintl compoundsPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 8-9 2010C. Yu Abstract Polycrystalline nonstoichiometric Yb14MnSb11 compounds have been successfully prepared by modified induction melting and spark plasma sintering. The carrier concentration was finely tuned by changing the elemental ratio of Mn to Sb. Excess Mn decreases the electrical conductivity and increases the Seebeck coefficient. The thermal conductivity of all samples was less than 1.0 W m,1 K,1. The maximum ZT value is 0.35 K at 673 K for Yb14Mn1.05Sb11, significantly higher than that of the stoichiometric Yb14MnSb11 polycrystalline sample. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Bulk anisotropy Nd-Fe-B/,-Fe nanocomposite permanent magnets prepared by sonochemistry and spark plasma sinteringPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2007Peili Niu Abstract NdFeB/,-Fe nanocomposite magnetic powders were prepared by sonochemical process. The powders were then submitted to a hot press and subsequent hot deformation process by spark plasma sintering (SPS) technique. Effect of ,-Fe content on structure and magnetic properties of both isotropic and anisotropic magnets was investigated. For hot pressed magnets, the remanence increases with the content of ,-Fe, while the coercive force drops simultaneously. After hot deformation, the magnets with no more than 2 vol% ,-Fe exhibit obvious anisotropic characteristic. For the magnets with more ,-Fe, however, the magnetic anisotropy disappears due to the absence of (00l) crystal texture after deformation. It is, therefore, expected that ,-Fe content plays an important role in the formation of C-axis crystal texture during hot deformation process. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||