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排序方式: 共有302条查询结果,搜索用时 15 毫秒
1.
Effect of pyrolysis temperature on the mechanical evolution of SiCf/SiC composites fabricated by PIP
《Ceramics International》2020,46(2):1297-1306
Three types of SiCf/SiC composites with a four-step three-dimensional SiC fibre preform and pyrocarbon interface fabricated via precursor infiltration and pyrolysis at 1100 °C, 1300 °C, and 1500 °C were heat-treated at 1300 °C under argon atmosphere for 50 h. The effects of the pyrolysis temperature on the microstructural and mechanical properties of the SiCf/SiC composites were studied. With an increase in the pyrolysis temperature, the SiC crystallite size of the as-fabricated composites increased from 3.4 to 6.4 nm, and the flexural strength decreased from 742 ± 45 to 467 ± 38 MPa. After heat treatment, all the samples exhibited lower mechanical properties, accompanied by grain growth, mass loss, and the formation of open pores. The degree of mechanical degradation decreased with an increase in the pyrolysis temperature. The composites fabricated at 1500 °C exhibited the highest property retention rates with 90% flexural strength and 98% flexural modulus retained. The mechanism of the mechanical evolution after heat treatment was revealed, which suggested that the thermal stability of the mechanical properties is enhanced by the high crystallinity of the SiC matrix after pyrolysis at higher temperatures. 相似文献
2.
《中国有色金属学会会刊》2020,30(3):756-764
The microstructure, dielectric and ferroelectric properties of (1–y)Ba(Zr0.1Ti0.9)O3–yBa(Zn1/3Nb2/3)O3 (y=0–0.05) ceramics prepared by traditional solid state method were investigated by X-ray diffractometer, scanning electron microscope, electric parameter testing system and ferroelectric tester. It is found that the barium zirconate titanate based ceramics are single-phase perovskites as y increases up to 0.05 and their average grain size decreases with the increase of y. The permittivity maximum εr,max is suppressed from 8948 to 1611 at 1 kHz with increasing y, and the ferroelectric–paraelectric phase transition temperature Tm decreases from 93 to –89 °C at 1 kHz as y increases. The composition-induced diffuse phase transition is enhanced with increasing y. The relaxor-like ferroelectric behavior with a strong frequency dispersion of Tm and permittivity at T<Tm accompanied by a strong diffuse phase transition is found for the system with high y value. The remnant polarization decreases with increasing y, while the coercive field decreases remarkably and then increases with the increase of y. 相似文献
3.
《Ceramics International》2020,46(9):13047-13053
Porous (Ba,Sr)(Co,Fe)O3-δ (BSCF) ceramics with high open porosity and good electrical conductivity was fabricated using Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), which shows a high mixed ionic-electronic conductivity. In general, during the fabrication of porous ceramics by the sacrificial template method using pore former particles, closed pores are easily formed unless sufficient pore former particles are added. In this study, we have devised a method using the gelatinization-retrogradation phenomena of starch for producing a porous body with an excellent percolated pore network structure. By dispersing BSCF and starch in an aqueous slurry (0–50% by weight) and heating, gelatinization of the starch occurred and the starch particles adhered to each other. Furthermore, in order to retain the percolated structure, the water solvent was removed by freeze-drying without heating to obtain a dried green body. The sintering behavior of the porous BSCF bodies prepared under various conditions was characterized by microstructural observations and relative density measurements. By optimizing the process conditions of the gelatinization and retrogradation, a porous body having an open porosity of 48.3%, and with 99% of the total pores open, was obtained. The matrix was also well connected and showed a sufficiently high conductivity which was similar to the porous bodies made by the traditional sacrificial template method. 相似文献
4.
《Journal of the European Ceramic Society》2022,42(1):169-174
In this work, we propose a modulation doping strategy for simultaneous achievement of low lattice thermal conductivity and high Seebeck coefficient in the Cu2GeSe3 compound. The Ag and In dual-doping can optimize the hole carrier concentration to balance electrical conductivity and Seebeck coefficient, achieving a high power factor of ~6.4 μW cm?1 K?2 for the Cu2GeSe3 compound. The Ag point defect makes a great contribution to blocking the propagation of phonons besides the phonon-phonon Umklapp process, yielding a minimum lattice thermal conductivity of ~0.38 W m–1 K–1. Remarkably, a maximum ZT value of ~0.97 at 723 K is achieved for Cu1.8Ag0.2Ge0.95In0.05Se3 compound, which is the highest value for the Cu2GeSe3-based systems in the temperature range of 323–723 K. 相似文献
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6.
《Journal of the European Ceramic Society》2022,42(12):5023-5028
Lithium garnet oxides with 6.5 mol Li, such as Li6.5La3Zr1.5(Ta/Nb)0.5O12, typically crystallise in cubic structure and exhibit excellent room-temperature ionic conductivity close to 1 mS cm?1. However, it is challenging to densify garnet oxides. In this work, we investigated how the co-doping of tantalum (Ta) and niobium (Nb) affects the densification of pressureless sintered garnet electrolytes with compositions of Li6.5La3Zr1.5Ta(0.5?x)NbxO12, where x = 0–0.5. The highest densification (94.5% of relative density) was achieved in Li6.5La3Zr1.5Ta0.1Nb0.4O12 (TN-LLZO) when it was sintered at 1150 °C for 6 h. This TN-LLZO garnet electrolyte delivers an ionic conductivity of 1.04 × 10?3 S cm?1 (at 22 °C) with a low activation energy of 0.41 eV. Our findings demonstrate that the content of dopants (Ta and Nb) plays a critical role in enhancing the sintering performance of garnet ceramics at ambient pressure. 相似文献
7.
The fluidization technique has advantages in rapid and high-efficiency heat transfer. Application of fluidization technology can significantly improve the productivity and product performance in the cemented carbide industries. This technique has become an attractive research topic within the issue of green and low-carbon technologies. Aiming at better understanding the principles of fluidization, in the present paper we demonstrate three typical cases of liquid–solid fluidized crystallization, bubbling bed combustion synthesis and reduction carbonization production. From these samples, we study the factors which play an important role in the fluid dynamics, fluidized state of materials and reaction thermodynamics during the process of cemented carbide production. The solutions and mechanisms of the practical problems such as the fluidized state of ultrafine particles, critical opening percentage of the distribution plate and adherent effect in multilayer bubbling bed are proposed. Moreover, the potential applications and prospects of the fluidization technology in the field of cemented carbides are presented. 相似文献
8.
The use of heat exchanger/reactors (HEX/reactors) is a promising way to overcome the barrier of poor heat transfer in batch reactors. However to reach residence time long enough to complete the chemistry, low Reynolds number has to be combined with both a plug flow behaviour and the intensification of heat and mass transfers. This work concerns the experimental approach used to characterize an innovative HEX/reactor. The pilot is made of three process plates sandwiched between five utility plates. The process stream flows in a 2 mm corrugated channel. Pressure drop and residence time distribution characterizations aim at studying the flow hydrodynamics. Identified Darcy correlations point out the transition between laminar and turbulent flow around a Reynolds number equal to 200. Moreover the flow behaves like a quasi-plug flow (Pe > 185). The heat transfer and mixing time have also been investigated. The ratio between the reaction kinetics and the mixing time is over 100 and the intensification factor ranges from 5000 to 8000 kW m−3 K−1. As a consequence, no limitations were identified which allows the implementation of an exothermic reaction. It has been successfully performed under severe temperature and concentration conditions, batchwise unreachable. Thus, it highlights the interest of using this continuous HEX/reactor. 相似文献
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10.
以Al2O3、Y2O3(质量比为2:3)为烧结助剂,在氮气氛或氩气氛中、1900~1970℃、30 MPa下热压制备SiC陶瓷.根据Archimedes原理测量烧结体的体积密度和显气孔率;采用XRD、SEM(EDS)及瞬态热导率测试仪分别对材料的物相、显微结构和热导率进行表征.研究了烧结温度、烧结气氛和烧结助剂含量对材料烧结性能和热导率的影响.结果表明,当烧结助剂质量分数为10%,获得SiC致密体(气孔率<0.30%),热导率高达182.50 W/(m·K);随着烧结助剂的质量分数降至6%,材料的致密度和热导率皆明显下降;在氩气氛中SiC与Al2O3、Y2O3具有更好的润湿性. 相似文献