High-temperature Sintering Technique Research Articles

Preparation and characterization of sintered polycrystalline diamond (PCD) with 15 wt% Nb binder

This study aimed to obtain and characterize a polycrystalline diamond body (PCD) sintered with 15 wt% Nb binder, through the high-pressure high-temperature (HPHT) sintering techniques at three different temperatures of 1650 °C, 1750 °C, and 1850 °C, with a pressure of 7.7 GPa. Characterizations on the starting powders were performed before and after high energy ball milling, and then the obtained mixture was sintered. The results showed that niobium could perform as a good binder for the sintering PCD at the specified concentration, achieving relative densities in the range of 96% to 100% for all three sintering temperatures. Also, analyses of the electron micrographs and the Raman spectrograms showed that there was no graphitization, a common problem in this type of material, and there was uniform dispersion of the niobium at the interfaces of the diamond particles, and no cracking.

Optimum in the thermoelectric efficiency of nanostructured Nb-doped TiO2 ceramics: from polarons to Nb-Nb dimers.

Rutile is the most common and stable polymorph form of titanium oxide TiO2 at all temperatures. The doping of rutile TiO2 with a small amount of niobium is reknown for being responsible for a large increase of the electrical conductivity by several orders of magnitude, broadening its technological interest towards new emerging fields such as the thermoelectric conversion of waste heat. The electronic conduction has been found to be of a polaronic nature with strongly localized charges around the Ti3+ centers while, on the other side, the relatively high value of the thermal conductivity implies the existence of lattice heat carriers, i.e. phonons, with large mean free paths which makes the nanostructuration relevant for optimizing the thermoelectric efficiency. Here, the use of a high-pressure and high-temperature sintering technique has allowed to vary the grain size in rutile TiO2 pellets from 300 to 170 nm, leading to a significant reduction of the lattice thermal conductivity. The thermoelectric properties (electrical conductivity, Seebeck coefficient and thermal conductivity) of Nb-doped rutile nanostructured ceramics, namely NbxTi1-xO2 with x varying from 1 to 5%, are reported from room temperature to ∼900 K. With the incorporation of Nb, an optimum in the thermoelectric properties together with an anomaly on the tetragonal lattice constant c are observed for a concentration of ∼2.85%, which might be the fingerprint of the formation of short Nb dimers.

Phase-structures, thermophysical properties of Sm3Ce7Ta2O23.5 and Gd3Ce7Ta2O23.5 oxides for thermal barrier coating applications

Two types of rare earth tantalite oxides, Sm3Ce7Ta2O23.5 and Gd3Ce7Ta2O23.5, were synthesised using a high-temperature sintering technique. The phase-structures, micro-morphologies, element compositions, thermal conductivities, and thermal expansion performances were investigated. The final conclusions show that these two ceramics are approximately composed of 2RETa0.5Ce2.5O8.25 and RETaCe2O7. The relative densities are above 90%, and the interfaces between grains are clear. Owing to the relatively high total atomic weights, complicated element compositions, and many more oxygen vacancies, the obtained oxides exhibit lower thermal conductivities than RE2Zr2O7 and YSZ. The coefficients of thermal expansion for Sm3Ce7Ta2O23.5 and Gd3Ce7Ta2O23.5 above 1473 K are greater than those of La2Zr2O7 and YSZ. The thermal expansion coefficients and conductivities of the obtained oxides satisfy the requirements for thermal barrier coating applications.

Exploring the effects of boron nitride coating on the thermal stability and photoluminescence properties of molybdenum disulfide nanospheres

Here, we sprang up a novel approach to synthesize molybdenum disulfide nanoparticles coated by hexagonal boron nitride via high-temperature sintering technique under floating ammonia gas at 900 °C for 3 h MoS2-BN nanocomposites have significant thermal stability with an oxidation temperature of 715 °C, indicating that its antioxidant performance increased by 217% compared with the pure MoS2 nanospheres. Additionally, the strong red PL signal of MoS2-BN characterized by Steady state transient fluorescence spectrometer appears at ~678 nm at room temperature, its strength has reached 3.14 × 106 CPS, while the original MoS2 nanospheres shows almost no characteristics, demonstrating that the nanocomposites have excellent luminescent properties. Therefore, the improved properties of molybdenum disulfide materials encapsulated by hexagonal boron nitride (h-BN) expand the applications of MoS2 nanospheres in high temperature and optoelectronic devices, which could pave way for the h-BN encapsulated transition metal dichalcogenides (TMDCs).

Covalent interfacial coupling for hybrid solid-state Li ion conductor

Solid electrolyte is the key component of any practical solid-state batteries. Although inorganic Li3PS4 electrolyte has been widely studied, this material is highly unstable in air, reactive towards Li metal, and difficult to process. These undesirable features have limited its application in solid state lithium batteries. In this work, a hybrid solid state electrolyte composed of β-Li3PS4 and poly(glycidyl methacrylate) is prepared through a controlled interfacial reaction between the polymer and the Li3PS4. The resulting hybrid electrolyte shows a good processability, i.e. it can be processed through simple slurry coating rather than conventional cold pressing or high-temperature sintering techniques. Furthermore, it exhibits improved air stability and decreased interfacial resistance with metallic lithium as compared with pure Li3PS4 electrolytes. More interestingly, this hybrid electrolyte exhibits a high ionic conductivity of 1.8 × 10−4 S/cm at room temperature, which is even slightly higher than the ionic conductivity of the pure β-Li3PS4. The new type of hybrid electrolyte will be highly promising for future applications in solid state batteries.

FeCoNi alloy-encapsulated graphene nanoplatelets with excellent magnetic properties, thermal stability and electrochemical performances

Typical magnetic three-phase alloys-modificated graphene nanoplatelets (GNPs) synthetic nanocomposites (FeCoNi@GNPs) were prepared by liquid-phase reduction method and precursor-assisted high-temperature sintering technique. FeCoNi@GNPs nanocomposites exhibit superior magnetic properties with the saturation magnetization and coercive force 58.4 emu/g and 197.25 Oe, respectively. Furthermore, the GNPs encapsulated by FeCoNi increase of 48.2% in antioxidation performance compared with original GNPs due to surface passivation layers. Additionally, it also shows superior electrochemical performances with a capacitance of 538 F/g at 1 A/g, which provides great application in the fields of magnetocaloric device, high-temperature heat-insulating coatings, electromagnetic material and electrochemical sensors, etc.

Synthesis, microstructure and thermal stability of graphene nanoplatelets coated by hexagonal boron nitride (h-BN)

Abstract Graphene nanoplatelets/Boron nitride (GNPs/BN) nanocomposites were prepared by precursor-assisted high-temperature sintering technique using carbamide (CH4N2O) and boric acid (H3BO3) at the temperature as low as 950 °C. The multilayer and single BN coverage combine with GNPs through van der Waals interplanar interaction without damaging the structures of GNPs. Specifically, GNPs/BN with oxidation temperature of 730 °C shows remarkable thermal stability compared to the original GNPs, indicating an increase of 31% in antioxidant performance, which provides great potential for GNPs in high-temperature heat-insulating coatings, inorganic refractories and heat-resisting binder, etc.

Direct Comparison of Electron Transport and Recombination Behaviors of Dye-Sensitized Solar Cells Prepared Using Different Sintering Processes

Flexible dye-sensitized solar cells on plastic substrates have achieved a conversion efficiency of 8.6% with the hot compression technique (<150 °C). However, the value of efficiency is only 70% of that achieved using glass substrates with high-temperature sintering technique (500 °C). Investigating the origin of this difference is a critical step for further improving the performance of plastic dye-sensitized solar cells. In this study, an optimized ternary viscous titania paste without the addition of organic binders enables the fabrication of efficient dye-sensitized solar cells with a low-temperature process. Therefore, the electron-transport behavior of dye-sensitized solar cells can be directly compared with those prepared with the high-temperature sintering technique. In addition to the structural and optical differences, the hot compressed photoanode of dye-sensitized solar cells have an electron diffusion coefficient that is 2 times smaller and a recombination time that is 6 times shorter than th...

Effects of High-Pressure High-Temperature Sintering on the Band Gap and Thermoelectric Properties of PbSe

In this study, PbSe bulk samples were prepared by a high-pressure high-temperature (HPHT) sintering technique, and the phase compositions, band gaps and thermoelectric properties of the samples were systematically investigated. The sintering pressure exerts a significant influence on the preferential orientation, band gap and thermoelectric properties of PbSe. With increasing pressure, the preferential orientation decreases, mainly due to the decreased crystallinity, while the band gap first decreases and then increases. The electrical conductivity and power factor decrease gradually with increasing pressure, mainly attributed to the decreased carrier concentration and mobility. Consequently, the sample prepared by 2 GPa shows the highest thermoelectric figure-of-merit, ZT, of 0.55 at ∼ 475 K. The ZT of the HPHT-sintered PbSe could be further improved by properly doping or optimizing the HPHT parameters. This study further demonstrates that the sintering pressure could be another degree of freedom to manipulate the band structure and thermoelectric properties of materials.

A new class of magnetorheological elastomers based on waste tire rubber and the characterization of their properties

This paper proposes a new type of magnetorheological elastomer (MRE) using rubber from waste tires and describes its performance characteristics. In this work, scrap tires were utilized as a primary matrix for the MRE without incorporation of virgin elastomers. The synthesis of the scrap tire based MRE adopted a high-temperature high-pressure sintering technique to achieve the reclaiming of vulcanized rubber. The material properties of the MRE samples were investigated through physical and viscoelastic examinations. The physical tests confirmed several material characteristics—microstructure, magnetic, and thermal properties–while the viscoelastic examination was conducted with a laboratory-made dynamic compression apparatus. It was observed from the viscoelastic examination that the proposed MRE has magnetic-field-dependent properties of the storage modulus, loss modulus, and loss tangent at different excitation frequencies and strain amplitudes. Specifically, the synthesized MRE showed a high zero field modulus, a reasonable MR effect under maximum applied current, and remarkable damping properties.

Experimental investigation on pressure drop and heat transfer in metal foam filled tubes under convective boundary condition

Heat transfer under convective boundary condition is common in heat exchangers. This paper presented the experimental results of air flow and heat transfer through three stainless steel foam filled tubes under convection boundary condition. The air flow velocity inside the tube is relatively high, which varied from 7.0 to 26.0m/s. The stainless steel foam filled tubes, manufactured using high-temperature metallic sintering technique, are of different pore densities (10, 30 and 70 PPI) but have the same porosity of 0.93.The air pressure drop through the stainless steel foam filled tubes was measured. It was found that the inertial drag is the dominant part of the pressure drop at higher velocity. The pressure drop experimental data under high velocity were compared to the predictions by the correlations obtained under relatively low velocity and great discrepancies have been found. A new correlation for the pressure drop through metal foams under high velocity was presented. The effect of the boundary condition on the heat transfer performance was addressed by the comparison of Nusselt number obtained in the present study with that obtained under constant heat flux boundary condition in the published investigation. It was found that the Nusselt number obtained under convective boundary condition is much lower than that obtained under constant heat flux boundary condition. A new correlation for Nusselt number under convective boundary condition was developed.

Metallic nickel hollow fiber membranes for hydrogen separation at high temperatures

Metallic nickel dense hollow fiber membranes were fabricated by a combined spinning and high-temperature sintering technique. Hydrogen permeation through the nickel hollow fiber membranes was measured at high temperatures up to 1000°C using H2-containing gas mixtures fed on the shell side and N2 as the sweep gas in the fiber lumen. The experimental results indicated the sintering should be carried out at around 1400°C for 3h, under a hydrogen-containing atmosphere so as to reach the required densification of the nickel hollow fiber membranes. Hydrogen permeation through the dense nickel hollow fiber membranes is controlled by H-atom diffusion through the membrane bulk, and can be well described by the Sieverts’ equation with the activation energy of 51.07kJmol−1. For the hollow fiber with wall thickness of 256μm, the hydrogen permeation flux value reached up to 7.66×10−3molm−2s−1 at 1000°C with 100% H2-permselectivity. The Ni hollow membrane exhibits high stability in CO2, CO or steam containing atmospheres, and demonstrates a potential use in hydrogen production by high temperature hydrocarbon reforming reactions.

Enhancing the efficiency of dye-sensitized solar cells by adding diatom frustules into TiO2 working electrodes

In this study, diatom frustules were added into TiO2 paste to prepare a TiO2-diatom paste mixture. Spin-coating and high-temperature sintering techniques were then used to fabricate working electrodes for dye-sensitized solar cells (DSSCs). Mixing the diatom frustules with the TiO2 paste improved the light-trapping effect and scattering properties of the incident light in the TiO2-diatom working electrodes, thereby enhancing the power conversion efficiency of the DSSCs. In this study, a high-speed centrifugal processing technology and sedimentation-rate separation techniques were first used to obtain the diatom frustules, which were then mixed with the TiO2 paste at a weight ratio of 1:50; a spin-coating technique was then used to fabricate the working electrodes. Finally, a high-temperature sintering process (500°C) was performed. In this study, optical microscopy, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and a surface profiler and spectrometer were used to analyze the characteristics of the working electrodes. The TiO2 or TiO2-diatom working electrodes were prepared under various spin-coating conditions for fabricating and analyzing the characteristics of the DSSCs. The results indicated that under identical conditions, the power conversion efficiency of the DSSCs was 3.81% when coated three times with a conventional TiO2 paste, and 5.26% when coated once with the TiO2-diatom paste before being coated twice again with the TiO2 paste, indicating a 38% increase in efficiency.

Magnetron formation of Ni/YSZ anodes of solid oxide fuel cells

Physico-chemical and structural properties of nanocomposite NiO/ZrO2:Y2O3 (NiO/YSZ) films applied using the reactive magnetron deposition technique are studied for application as anodes of solid oxide fuel cells. The effect of oxygen consumption and magnetron power on the discharge parameters is determined to find the optimum conditions of reactive deposition. The conditions for deposition of NiO/YSZ films, under which the deposition rate is maximum (12 μm/h), are found and the volume content of Ni is within the range of 40–50%. Ni-YSZ films reduced in a hydrogen atmosphere at the temperature of 800°C have a nanoporous structure. However, massive nickel agglomerates are formed in the course of reduction on the film surface; their amount grows at an increase in Ni content in the film. Solid oxide fuel cells with YSZ supporting electrolyte and a LaSrMnO3 cathode are manufactured to study electrochemical properties of NiO/YSZ films. It is shown that fuel cells with a nanocomposite NiO/YSZ anode applied using a magnetron sputtering technique have the maximum power density twice higher than in the case of fuel cells with an anode formed using the high-temperature sintering technique owing to a more developed gas-anode-electrolyte three-phase boundary.

TiN–TiB2 composites prepared by various sintering techniques

TiN–TiB2 composites were prepared by pressureless, Spark Plasma Sintering (SPS) and high pressure–high temperature (HP–HT) sintering techniques. Powder mixtures, in wt.%, 70 TiN–30 TiB2 and 50 TiN–50 TiB2, were based on commercial TiN and TiB2 micropowders. Parameters of sintering processes were optimized for density, hardness and Young's modulus. Young's moduli were in the range 422–460GPa for the 70–30 composite and for the 50–50 composite they were in the range 416–482GPa. Vickers hardnesses were ~15GPa for the 70–30 composite and in the range 16.4–17.5GPa for the 50–50. Relative density ranged from 95.7% (HP–HT, 50–50 composite) to 99.0% (SPS, 70–30 composite). HP–HT composites had lower densities and Young's moduli, because of microcrack's. Nitrogen contents, lattice constants and analyzed microstructures depended on the method of sintering. The smallest grain growth, of TiN particles, from 1.2μm to 2.5μm, without the size changing for the TiB2 particles, was observed for the HP–HT TiN–TiB2 composite, when there was crushing of TiB2 particles. In pressureless sintered composites the growth of TiN grains was from about 1.2μm to 4.9μm. Materials prepared using the pressureless sintering method were characterized by the highest fracture toughness: 6.38 and 6.89MPa·m1/2 for the 70 TiN–30 TiB2 and 50 TiN–50 TiB2 composites, respectively. The pressureless sintered TiN–TiB2 composites had the best combination of physical and mechanical properties.

Three‐Dimensional Nitrogen and Boron Co‐doped Graphene for High‐Performance All‐Solid‐State Supercapacitors

carbide-derived carbon, [ 12 ] carbon nanotubes (CNTs), [ 14–17 ] and graphene, [ 6 , 7 , 10 , 18 , 19 ] possess notable features including high surface area, high electrical conductivity, and good chemical stability, and therefore they have been widely explored as thinfi lm electrode materials for ASSSs. However, the fabrication of ASSSs generally involves complex solution processing, highpressure pressing, high-temperature sintering, and sputtering techniques. [ 11 , 12 , 14–17 ] Moreover, polymer binders and conductive additives are required to enhance the adhesion between electrode materials and substrates as well as to improve the conductivity of the electrode, which unavoidably leads to decreased energy density of the devices. [ 6 , 20 ] Therefore, several challenges remain in developing ASSSs, such as to: i) explore high-performance electrode materials, ii) enhance the interfacial compatibility between electrode and solid-state electrolyte, and iii) simplify the device fabrication process. Graphene aerogels (GAs) represent a new class of ultralight and porous carbon materials that are associated with high

Preparation and Characterization of Porous Acicular Mullite Ceramics

Acicular mullite porous ceramics were synthesis by high-temperature sintering technique. In the present work, Kaolin and industrial aluminum hydroxide were selected as raw materials, AlF3 used as catalyst. XRD and SEM were used to detect the crystal type and microstructure of prepared mullite ceramics, respectively. The influences of sintering temperature on the growth of crystal, the apparent porosity and compressive strength of the resulting porous ceramics were investigated. The results indicate when sintering temperature ranges from 1250 ~ 1400°C, much acicular mullite crystal appeared in the resulting ceramics. The apparent porosity, the compressive strength and the morphology of the mullite whisker changed obviously with the sintering temperature. When sintering temperature is 1400°C, the porous ceramics showed the maximum compressive strength of ~28 MPa and the maximum apparent porosity of ~63%.

Application to temperature sensor based on Er&lt;sup&gt;3 +&lt;/sup&gt;-doped barium borosilicate glasses at visible band

The process of preparing Er 3+ -doped barium borosilicate glass samples with different dopant concentrations using a high-temperature sintering technique is discussed. Under a 978-nm semiconductor laser excitation, the energy transfer from 2 H11/2 to 4 I15/2 and 4 S3/2 to 4 I15/2 caused by the transitions of Er 3+ ions yields a 534- and a 549-nm green fluorescence. The relationship between the absolute temperature T and the fluorescence intensity ratio R of these two up-conversion photo- luminescence spectra is discussed and fitted to the exponential func- tion R = 1.782exp(−328/T) in the temperature range of 298 to 698 K. The sensitivity of the samples descends monotonously from 0.00219 to 0.00075 K −1 with the temperature increase from 298 to 698 K. The data are of undoubted repeatability, and the proposed doped glass is suitable for sensitive, high-temperature measurement. C 2011 Society of Photo-Optical

Effective thermal conductivity of Cu/diamond composites containing connected particles

An analytical model for the thermal conductivity of Cu/diamond composites with connected particles is presented by replacement of a cluster of connected particles with an equivalent polycrystal subsequently using a multiple effective medium approach. By applying this model to the measured thermal conductivity of Cu/diamond composites prepared by high pressure high temperature sintering technique reported in the literature, we show that it quite well describes the observed thermal conductivity enhancement induced by the connected particles. We estimate the value of connected particle loading in real composites and show that large particles are easier to form the bonding contact than small particles. The present work also demonstrates that the sensitivity of thermal conductivity contribution from the connected particles strongly depends on the particle size, and their pronounced thermal conductivity enhancement should lie within the certain particle size range.

Synthesis, characterization and in vitro bioactivity of magnesium-doped sol–gel glass and glass-ceramics

Bioactive glass and glass-ceramics in the system CaO–MgO–SiO 2–P 2O 5 have been prepared by the sol–gel and high temperature sintering techniques. The obtained samples were characterized by thermogravimetric and differential thermal analysis (TG/DTA), N 2-adsorption measurement, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). In vitro bioactivity tests were also conducted in simulated body fluid (SBF). The studies of crystallization kinetics under non-isothermal conditions showed the activation energy for crystallization to be 381 kJ/mol and the crystallization mechanism gradually changed from three-dimension growth to two-dimension crystallization with the increase of heating rate. Sintering temperature had great influence on the samples texture and structure. In addition, the apatite-formation on glass and glass-ceramics was confirmed by in vitro tests, and crystallization decreased the samples bioactivity.