Plasma Sintering Method Research Articles

Thermoelectric Properties of Silicon Germanium Alloy Nanocomposite Fabricated by Mechanical Alloying and Spark Plasma Sintering

High dense p-type Si95Ge5 doped with nanoSi70Ge30B5particles thermoelectric materials were firstly fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) method. The effects of different nanoSi70Ge30B5 doping content on the thermoelectric and phase properties were studied. A dimensionless thermoelectric figure-of-merit (ZT) of 0.47 at 710K in p-type nanocomposite bulk silicon germanium (SiGe) alloys is achieved. The enhancement of ZT is due to a large reduction of thermal conductivity caused by the increased grain boundaries of the numerous nanograins that effectively scatter long wavelength phonons.

Spark plasma sintering of doped (Kx Na1-x)NbO3 piezoceramics

ABSTRACTIn this work, “pure” and doped (K0.48 Na0.52)NbO3 ceramics (KNN) were prepared by using Spark Plasma Sintering (SPS) method. In order to investigate the influence of doping elements on the microstructural, structural and dielectric properties of KNN, Cu2+ and Li1+ doping elements were added. The results revealed the viability to produce highly dense “pure” and doped KNN ceramics with good crystallization in the perovskite phase. Densities around 96% and 99% of the theoretical one were reached. In relation to pure KNN, it was verified that Cu2+ addition reduced significantly the sintering temperature, revealing a better microstructure with a more homogeneous grain size distribution and structure with well-defined splitting of the XRD peaks. In comparison to pure KNN, the addition of both doping elements decreased both the dielectric constant the dielectric losses as well.

Ceramic Matrix Composites Reinforced with Carbon Nanotubes: Spark Plasma Sintering, Modeling, Optimization

The method of spark plasma sintering is used to obtain an α-Al2O3-based nanocomposite reinforced with many-walled carbon nanotubes in amounts up to 50 vol.%. A mathematical model is constructed to describe the change in porosity during the sintering operation. The model accounts for the physico-chemical essence of the processes which take place during spark plasma sintering. Results obtained from experimental studies and mathematical modeling are used to determine the optimum sintering regime, which makes it possible to obtain a composite that has zero porosity and a carbon-nanotube content up to 50 vol.%.

Synthesis and reactivity of single-phase Be17Ti2 intermetallic compounds

To investigate feasibility for application of Be17Ti2 as a neutron multiplier as well as a refractory material, single-phase Be17Ti2 intermetallic compounds were synthesized using an annealing heat treatment of the starting powder and a plasma sintering method. Scanning electron microscopic observations and X-ray diffraction measurements reveal that the single-phase Be17Ti2 compounds were successfully synthesized. We examined the reactivity of Be17Ti2 with 1% H2O and discovered that a larger stoichiometric amount of Ti resulted in the formation of TiO2 on the surface at high temperatures. This oxidation may also contribute to an increase in both weight gain and generation of H2. This suggests that the formation of the Ti-depleted Be17Ti2−x layer as a result of oxidation facilitates an increased reactivity with H2O. To evaluate the safety aspects of Be17Ti2, we also investigated the hydrogen positions and solution energies based on the first principle. The calculations reveal that there are 10 theoretical sites, where 9 of these sites have hydrogen solution energies with a positive value (endothermic) and 1 site located at the center of a tetrahedron comprising two Be and two Ti atoms gives a negative value (exothermic).

Spark Plasma Sintering of Bi1.65Pb0.35Sr2Ca2Cu3O10+δ Superconducting Samples: Evaluation of Microstructure and Mechanical Properties

Powders of single-phase Bi1.65Pb0.35 Sr2Ca2Cu3O10+δ (Bi-2223) were consolidated by the spark plasma sintering (SPS) method at 750 ∘C. The SPS samples exhibited very high density, but are oxygen deficient, as inferred from magnetization, M(T), data. Therefore, the samples were then subjected to a post-annealing heat treatment in air, at 750 ∘C for 5 min. From the combined data of X-ray diffraction, microstructures observed by SEM, and Vickers microhardness measurements, we have found that SPS post-annealed samples showed the presence of an extra phase. According to the EDS analysis and X-ray diffraction results, the extra was identified as an infinite layer compound with general formula Ca1−x Sr x CuO2. Irrespective of the presence of this additional phase, the superconducting properties of post-annealed SPS samples are optimized when they are heat treated in air, at 750 ∘C for just 5 min. We have also observed a decrease in the Vickers as well as different indentation features in post-annelaed samples when compared with SPS ones. The occurrence of a decohesion of grains has been also observed, a feature similar to that found previously in the same material. On the other hand, a pile up formation occurred throughout the indentation in the sample, in which the annealing was carried out. 3-D profilometer characterizations confirmed these results, which are close related to the occurrence of the extra phase Ca1−x Sr x CuO2.

Effect of Y<sub>2</sub>O<sub>3</sub> on Microstructure and Properties of cBN/SiAlON Composite

cBN/SiAlON composites were prepared by spark plasma sintering (SPS) method using Si3N4, AlN, Al2O3,cBN and Y2O3 powders as raw materials. The sintering process is at the temperature of 1500°C holding for 5 min. Effect of the Y2O3 content on phase composition, microstructure, bulk density, hardness and fracture toughness of the cBN/SiAlON composite was investigated. The experimental results showed that when the Y2O3 content was 0.2 wt. % the bulk density and fracture toughness of the composite had the maximum values of 3.0 g/cm3 and KIC = 5.7 MPa∙m1/2, respectively. The cBN/SiAlON composite with 0.8 wt. % Y2O3 addition got the maximum hardness of 16.4 GPa.

The Analysis of Microstructure and the Properties of the Metallic-Matrix Composite on the Basis of the Copper and Aluminum Oxide

The article is devoted to the analysis of the possibilities to obtain gradient materials by the method of spark plasma sintering. Pure copper powders consisting of particles with the average particle size 100 microns and the nanodispersed powder of aluminum oxide were used in this study. Two powder compositions - pure copper powder and a mixture of copper powder and aluminum oxide powder were sintered:. As a result of the sintering process a sample with a double-area structure has been formed with a well-defined boundary between these areas. After sintering the copper powder porosity remained at the initial level. But having been mixed and sintered, the aluminum oxide powder particles agglomerated up to the average particle size of 80 – 100 microns.

The Analysis of Microstructure and the Properties of the Metallic-Matrix Composite on the Basis of the Copper and Aluminum Oxide

The article is devoted to the analysis of the possibilities to obtain gradient materials by the method of spark plasma sintering. Pure copper powders consisting of particles with the average particle size 100 microns and the nanodispersed powder of aluminum oxide were used in this study. Two powder compositions - pure copper powder and a mixture of copper powder and aluminum oxide powder were sintered:. As a result of the sintering process a sample with a double-area structure has been formed with a well-defined boundary between these areas. After sintering the copper powder porosity remained at the initial level. But having been mixed and sintered, the aluminum oxide powder particles agglomerated up to the average particle size of 80 – 100 microns.

Characteristics of Nanophase WC and WC-3 wt% (Ni, Co, and Fe) Alloys Using a Rapid Sintering Process for the Application of Friction Stir Processing Tools

Microstructures and mechanical characteristics of tungsten carbide- (WC-) based alloys, that is, WC, WC-3 wt% Ni, WC-3 wt% Co, and WC-3 wt% Fe, fabricated using a spark plasma sintering (SPS) method for the application of friction stir processing tools were evaluated. The sintered bodies with a diameter of 66 mm showed relative densities of up to 99% with an average particle size of 0.26~0.41 μm under a pressure condition of 60 MPa with an electric current for 35 min without noticeable grain growth during sintering. Even though no phase changes were observed after the ball milling process the phases of W2C andWC1-xappeared in all sintered samples after sintering. The Vickers hardness and fracture toughness of the WC, WC-3 wt% Ni, WC-3 wt% Co, and WC-3 wt% Fe samples ranged from 2,240 kg mm2to 2,730 kg mm2and from 6.3 MPa·m1/2to 9.1 MPa·m1/2, respectively.

On fabrication of functionally graded thermoelectric materials by spark plasma sintering

A process of fabrication of thermoelectrics by the spark plasma sintering (SPS) method to obtain materials with advanced properties is simulated. The effect of the die dimensions and geometry on the temperature field distribution inside the sintered sample is analyzed. The feasibility of fabrication of functionally graded materials by the SPS process using dies of special configuration is demonstrated.

Different-Oxides Nanoceramics Microhardness

With help of the method of the spark plasma sintering (SPS), the fine-grained (of micron approximately) ceramics based on various alumina nanopowders had created. A comparison of microhardness of ceramic samples obtained from 11 alumina nanopowders and 2 their composites was held. Microhardness of the ceramics obtained both by SPS, and by the traditional method (at successive pressing and sintering) is compared. The dependence of ceramics microhardness on the phase composition of the initial nanopowder and the average size of its particles was investigated. Besides alumina nanopowders ( Al 2 O 3), there were compared microhardness of ceramics from other 10 nanopowders of oxides ( SiO 2, ZnO , Fe 3 O 4, Gd 2 O 3, CuO , WO 3, TiO 2, Y 2 O 3, ZrO 2, MgO ) obtained both by SPS, and by the traditional method. It is obtained that the microhardness of the ceramics created on the method of the spark plasma sintering, is significantly higher than a microhardness of the ceramics obtained by the traditional method; at the SPS method the average size of grain in ceramics decreases (to 1 micron and less).

Multiscale microstructures and improved thermoelectric performance of Mg2(Si0.4Sn0.6)Sbx solid solutions

A series of Sb -doped Mg 2( Si 0.4 Sn 0.6) Sb x (0 ≤ x ≤ 0.025) solid solutions were prepared by an induction melting, Melt Spinning (MS) and Spark Plasma Sintering (SPS) method, namely the non-equilibrium technique MS–SPS, using bulks of Magnesium, Silicon, Tin, and Antimony as raw materials. The non-equilibrium technique generates the unique multiscale microstructures of samples containing micronscale grains and nanoscale precipitates, the multiscale microstructures remarkably make the lattice thermal conductivities decreased, particularly for samples with the nanoscale precipitates having the size of 10–20 nm. Meanwhile, Sb -doping greatly increased the electrical performance of samples. Consequently, the Sb -doping combined with the multiscale microstructures strategy remarkably improves the overall thermoelectric (TE) performance of Sb doped samples, and a high dimensionless figure of merit (ZT) value of up to 1.25 at 723 K is obtained with Mg 2( Si 0.4 Sn 0.6) Sb 0.02 sample in a relatively wide temperature range.

Blanket material and technology developments toward DEMO under the Broader Approach framework

In the Broader Approach (BA) framework, research and development on blanket related materials and technologies have been carried out between the EU and Japan. Those activities are implemented mainly at the Rokkasho BA site in collaboration with universities in Japan. In the R&D on SiCf/SiC composites for an advanced blanket material, mechanical properties of chemically vapor infiltrated (CVI) SiCf/SiC composites have been obtained in high temperature vacuum environment up to 1000°C. As to R&D on the tritium technology, tritium retention of the fine-grained re-crystallized tungsten has been evaluated. On reduced activation of ferritic/martensitic (RAFM) steels as the blanket structural material, a 20-ton heat of the F82H RAFM steel has been successfully produced in an electric arc furnace. Advanced neutron multiplier pebbles of beryllide (beryllium–titanium alloy) have been fabricated using a dedicated rotating electrode apparatus followed by annealing from the beryllide rod produced with the plasma sintering method. Also advanced tritium breeder pebbles of lithium-rich lithium titanate have been fabricated by an emulsion method, where the grain size, confirmed by SEM, was less than 5μm. Tritium recovery tests of advanced tritium breeder pebbles will be investigated under 14MeV neutron irradiation as one of the new activities.

The Influence of Anisotropy and Nanoparticle Size Distribution on the Lattice Thermal Conductivity and the Thermoelectric Figure of Merit of Nanostructured (Bi,Sb)2Te3

Two factors that are important for proper estimation of the thermoelectric figure of merit of bulk nanostructured materials based on bismuth telluride and its solid solutions have been investigated. First, the anisotropy of the thermoelectric properties of nanostructured (Bi,Sb)2Te3 fabricated by the spark plasma sintering (SPS) method was studied experimentally as a function of sintering temperature and pressure. Two measuring methods were used: (a) the Harman method and (b) separate measurements of electrical conductivity, Seebeck coefficient, and thermal conductivity (laser flash method). Anisotropy and transport property values obtained by these methods are compared. Secondly, the influence of the nanoparticle size distribution on the lattice thermal conductivity was taken into account theoretically for scattering of phonons both on nanoprecipitates with different compositions and orientations and on grain boundaries. The results of estimations based on different theoretical approaches (relaxation-time approximation, Monte Carlo simulations, and effective medium method) are compared using typical size distribution parameters from available experimental data.

Investigation on Dynamic Compressive Properties of Carbon Fiber Cloth-Reinforced Titanium Alloy

Cu-coated carbon fiber cloth/Ti-6Al-4V composite (Cu-Cf/TC4) and uncoated-Cf/TC4 were fabricated by spark plasma sintering (SPS) method. The microstructure and dynamic compression properties of the Cf/TC4 composites were investigated. Results show that the matrix-fiber interfacial bonging in uncoated-Cf/TC4 is weaker than in Cu-Cf/TC4. Moreover, lamellar TiC exists throughout the TC4 matrix in uncoated-Cf/TC4, while there is no TiC generated in TC4 matrix of Cu-Cf/TC4. Dynamic compressive tests indicate the stress-strain curves of Cu-Cf/TC4 and uncoated-Cf/TC4 show no difference at a strain rate of 2500 s-1, while show significant difference at a strain rate of 4800 s-1. Further investigations find: (1) at a strain rate of 2500 s-1, the reinforcement effect of Cf on Cu-Cf/TC4 is similar to TiC on uncoated-Cf/TC4, explaining the exact similarity in compressive property of Cu-Cf/TC4 and uncoated-Cf/TC4; (2) at a strain rate of 4800 s-1 the reinforcement effect of Cf on Cu-Cf/TC4 is far more than TiC on uncoated-Cf/TC4, explaining the higher compressive strength of Cu-Cf/TC4; moreover, multiple debonding of carbon fiber and its squeezing into TC4 matrix constitute an important energy absorption mechanism for uncoated-Cf/TC4, explaining the better plasticity of uncoated-Cf/TC4.

Microstructure Control of Potassium Niobate Porous Ceramics and their Sensor Properties

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by spark plasma sintering (SPS) method using carbon black (CB, 5 μm). First, the powders of raw materials were mixed in ethanol by ball milling, and then calcined. Obtained KN powders with CB were sintered by SPS in argon atmosphere. Their piezoelectric properties were measured and a relationship between porosity, pore size, and sensor properties was studied. It was found that d33 increased as pore size decreased. Thus, pore size was important for the improvement of value of g33/ρ.

Oxidation resistance of Be12Ti fabricated by plasma-sintering method

Titanium beryllium intermetallic compounds (beryllides), such as Be12Ti, are alternatives to metallic beryllium as the neutron multiplier for the fusion reactor blanket. Be12Ti is known to have advantages over metallic beryllium, which includes a high melting point, lower swelling and higher chemical stability. This work examined the oxidation resistance of Be12Ti samples fabricated by a plasma-sintering. Metallic beryllium and Be12Ti samples were placed under a flow of an argon gas containing 10,000ppm of water vapor at the temperature of 1273K for 24h. The Be12Ti sample fabricated was shown to have higher oxidation resistance than metallic beryllium.

Optimization of synthesis conditions for plasma-sintered beryllium–titanium intermetallic compounds

Abstract Plasma sintering method has been newly suggested as a synthesis method for beryllium–titanium intermetallic compounds (beryllides) as an advanced neutron multiplier in a system of water cooled solid breeder demonstration fusion reactors. Not only synthesis of the beryllide but joining the beryllide could be successfully fabricated. We report on the optimization of the main sintering conditions, on the sinterability of the plasma-sintered beryllides in the light of sinterability, as well as consolidation to the Be 12 Ti phase. The optimum sintering temperature for consolidation to the Be 12 Ti phase was 1273 K and the area fraction of the Be 12 Ti phase obtained when sintering at 1273 K, was approximately 83%. To increase the fraction of the Be 12 Ti phase, increasing the sintering time was inevitable and this led to an increase in the Be 12 Ti phase corresponding to 97.5%. However, as the sintering time increased, variation in grain size of the beryllides was observed. With regard to the sintering pressure, the higher the sintering pressure applied, the higher the sinterability, even though lower pressure may lead to better consolidation with respect to the absence of the Be 2 Ti phase.

Novel granulation process of beryllide as advanced neutron multipliers

Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. In order to fabricate the beryllide pebbles, beryllide with shapes of block and/or rod is necessary when a melting granulation process is applied such as a rotating electrode method. A plasma sintering method has been proposed as new technique which uses a non conventional consolidation process. It was clarified that the beryllide could be simultaneously synthesized and jointed by the plasma sintering method in the insert material region between two beryllide blocks. Beryllide rod of Be12Ti with 10mm in diameter and 60mm in length has been successfully fabricated by the plasma sintering method. Using this plasma-sintered beryllide rod, fabrication of prototype beryllide pebble was performed by a rotating electrode method as one of the melting methods. The prototype pebbles of Be12Ti with 1mm in average diameter were successfully fabricated.

Preliminary characterization of plasma-sintered beryllides as advanced neutron multipliers

Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. The plasma sintering method has been selected as a new synthesis method for beryllides because this method is very simple and easy to control. Plasma sintering is a non-conventional consolidation process. The plasma sintering results in starting-powder particle surface activation that enhances sinterability and reduces high temperature exposure. The sintering properties of beryllides were evaluated. Results show that intermetallic beryllide compounds such as Be12Ti, Be17Ti2 and Be2Ti can be directly synthesized by the plasma sintering method from mixed elemental powders of Be and Ti at a temperature below the melting point. The preliminary characterization of plasma-sintered Be–Ti beryllide was carried out including examination of oxidation with water vapor, microstructure analysis, irradiation effects, and deuterium retention compared with beryllium (Be) metal. The preliminary characterization revealed that the plasma-sintered Be–Ti beryllide sample performs well as a neutron multiplier. This beryllide sample has better oxidation resistance, higher radiation resistance and lower deuterium retention than Be metal.