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Abrupt change of acoustic impedance at the interfaces of step gradient composites is the main reason which hinder their further improving of bulletproof performance. Eliminating these interfaces is an effective method to fundamentally solve this problem. In this study, continuous gradient Ti/TiB–TiB2 composite was fabricated by spark plasma sintering (SPS) combined with tape casting. Interfaces between the different thin tape layers were successfully eliminated through the growth of rod-like TiB crystals during SPS sintering. High speed impact test indicates the continuous gradient Ti/TiB–TiB2 composite not only possesses excellent anti-penetration performance, but also has the ability to resist a second strike.

Dense silicon nitride (Si3N4) ceramics were prepared using Y2O3 and MgF2 as sintering aids by spark plasma sintering (SPS) at 1650 °C for 5 min and post-sintering annealing at 1900 °C for 4 h. Effects of MgF2 contents on densification, phase transformation, microstructure, mechanical properties, and thermal conductivity of the Si3N4 ceramics before and after heat treatment were investigated. Results indicated that the initial temperature of liquid phase was effectively decreased, whereas phase transformation was improved as increasing the content of MgF2. For optimized mechanical properties and thermal conductivity of Si3N4, optimum value for MgF2 content existed. Sample with 3 mol.% Y2O3 and 2 mol.% MgF2 obtained optimum flexural strength, fracture toughness and thermal conductivity (857 MPa, 7.4 MPa m1/2 and 76 W m−1 K−1, respectively). It was observed that excessive MgF2 reduced the performance of the ceramic, which was caused by the presence of excessive volatiles.

Thermochemical energy storage based on CaO/CaCO3 cycles is a promising technique used in concentrated solar power plant. The high global efficiency can be achieved under high carbonation pressure and temperature. In this work, limestone and carbide slag were chosen as the representatives of Ca-based natural and waste materials, respectively. The thermochemical energy storage performances of the limestone and the carbide slag under high carbonation pressure condition (>1.0 MPa) during CaO/CaCO3 cycles were studied in a pressurized dual fixed-bed reactor. The effects of carbonation temperature, calcination temperature and number of energy storage cycles under high carbonation pressure condition were also researched. The energy storage capacities of two Ca-based materials are enhanced significantly with increasing the carbonation pressure. The carbonation conversion and energy density of the limestone carbonated under 1.3 MPa are about 0.83 and 2626 kJ/kg after 10 cycles, respectively, which are 1.76 times as high as those carbonated under 0.1 MPa. The carbide slag carbonated under high pressure exhibits higher cyclic stability than the limestone during long-term energy storage cycles. In addition, the optimum temperatures for the energy storage of the limestone and the carbide slag carbonated under 1.3 MPa are 850–900 °C and 800–850 °C, respectively. High carbonation pressure can mitigate the sintering and pore-plugging of CaO. The average grain size of CaO carbonated under higher pressure increases more slowly with the number of energy storage cycles. The microstructure of the Ca-based material carbonated under high pressure appears more porous than that carbonated under atmospheric pressure. Increasing carbonation pressure is an effective method to improve the energy storage capacity of Ca-based material. The carbide slag is also a good candidate for long-term thermochemical energy storage under high pressure.

TaC/SiC composites with 20 vol.% SiC addition were densified by spark plasma sintering at 1600–1900 °C for 5 min under 40 MPa. Effects of sintering temperatures on the densification, microstructures and mechanical properties of composites were investigated. The results showed the materials achieved >98% of theoretical density at a temperature as low as 1600 °C. While the TaC grains grew slightly with the sintering temperature increasing, the SiC particles in materials decreased in size. Equiaxed to elongated grain morphology transformation was observed in the SiC phase in the 1900 °C material to obtain a higher flexural strength and fracture toughness of 715 MPa and 6.7 MPa m 1/2 , respectively. Lattice enlargement of the TaC phase in the 1900 °C material suggested possible Si diffusion into TaC grains. Ta was also detected in SiC grains by energy dispersive spectroscopy. Glassy pockets present at multi-grain junctions explained the enhanced densification.

Single phase hexagonal α-Ta 2 C ceramics were synthesized by spark plasma sintering and using TaC and Ta as the starting powders. Effects of sintering temperatures and holding times on the densification process, phase formation, microstructure development, and mechanical properties of the α-Ta 2 C ceramics were investigated. Densification occurred in the temperature range of 1520–1675 °C in less than 2.5 min. But completion of the Ta 2 C formation took about 40 min at 1500 °C, and 5 min at 1900 °C. The materials sintered at 1500 °C consisted of fine equiaxed grains. The Ta 2 C grains grew anisotropic to form an elongated self-toughening microstructure at 1700 °C. At 1900 °C, the neighboring Ta 2 C individual crystals coalesced to form large Ta 2 C blocks to entrap the residual pores. Although higher flexural strength and fracture toughness were reached at 1700 °C, the unstable microstructures of the Ta 2 C materials indicated limited applications at high temperatures.

A series of intergrowth bismuth-layered ferroelectric Bi7Ti4NbO21 materials are reactive-sintered at 1050 to 1150 °C from Bi3TiNbO9 and Bi4Ti3O12 parent phases to infer their structural characters and microstructure relations. Various types of stacking faults are revealed in the intergrowth structure with extra Bi3TiNbO9 or Bi4Ti3O12 layer(s) by high-resolution transmission electron microscopy; some faults with even spacing form locally new intergrowths of Bi10Ti5Nb2O30 and Bi11Ti7NbO33. Co-growth of Bi7Ti4NbO21 epitaxially grown onto the remaining Bi4Ti3O12 grains is found in the low temperature sintered samples, while the Bi4Ti3O12 co-growth onto the intergrowth grains is also found in the high temperature samples. Both co-growths are created from intergranular melts during a solution-precipitation process, which is consistent with the anisotropic growth of the intergrowth structure and the presence of a Bi-rich intergranular phase. The populations of different stacking faults are found to decrease with the increase of their thickness and also with the increase of sintering temperature, indicating that they are remnants survived from dissolution to imbed via precipitation into the intergrowth structure, which should be created from the smaller but much abundant one-layered remnants of the parent phases. This leads to a new model of structural reorganization by such one-layered units to form the intergrowth structure in this solution-precipitation process. Such incomplete dissolution is initiated by the preferential melting of interleaved [Bi2O2]2+ sheets to enable the exfoliation of perovskite layers to re-order into the intergrowth structure. This reorganization model re-defines the reactive sintering as an evolution process of Bismuth-layered structures.

Yttria (8 mol %)-stabilized zirconia electrolyte tubes with thin walls, which are 266 mm in length, 0,4-0.9 mm in thickness, and 96.7% in relative density, were prepared with an improved slip casting method. The microstructure and electrical properties of the samples sintered at different temperatures were studied using SEM and a.c. impedance spectroscopy. The effects of sintered density, grain and grain boundary on the electrical properties of samples were analyzed. The results show that the densification of samples increases gradually with increasing sintering temperatures. The microstructure of samples strongly influences their electrical properties, and with increasing sintered density, the electrical properties of samples are enhanced. The ionic conductivity of grain and grain boundary is improved as the sintering temperatures increase. The grain boundary resistance of samples sintered at 1650degreesC is higher than that of samples sintered at 1600degreesC. Better sinterability of samples was obtained at a sintering temperature of 1650degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.