共查询到20条相似文献,搜索用时 15 毫秒
1.
High-Strength Zirconium Diboride-Based Ceramics 总被引:10,自引:1,他引:10
Adam L. Chamberlain William G. Fahrenholtz Gregory E. Hilmas Donald T. Ellerby 《Journal of the American Ceramic Society》2004,87(6):1170-1172
Zirconium diboride (ZrB2 ) and ZrB2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing. Four-point bend strength, fracture toughness, elastic modulus, and hardness were measured. Modulus and hardness did not vary significantly with SiC content. In contrast, strength and toughness increased as SiC content increased. Strength increased from 565 MPa for ZrB2 to >1000 MPa for samples containing 20 or 30 vol% SiC. The increase in strength was attributed to a decrease in grain size and the presence of WC. 相似文献
2.
3.
关于氮化铝陶瓷导热性的讨论 总被引:1,自引:0,他引:1
本从声子机理出发,探讨了影响氮化铝陶瓷导热性的主要因素;提出了提高导热率的努力方向,即结构上努力减少晶格缺陷(主要是杂质固溶)和晶界缺陷(包括第二相析出,晶界玻璃相,气孔),并使相的分布尽量合理;指出了提高A1N陶瓷导热率的可能途径,即严格控制A1N粉末质量,选择合理的烧结助剂,采用还原气氛烧成等。 相似文献
4.
多孔陶瓷热导率的影响因素及其有效热导率的数值计算方法 总被引:1,自引:0,他引:1
多孔陶瓷因具有孔隙率高、体积密度小、比表面积大等独特的表面物理特性而被广泛应用于保温材料、炉膛材料、热障涂层材料、高温烟气过滤材料等,研究多孔陶瓷导热机制并给出其有效热导率的计算方法既是重点又是难点。本文总结了国内外研究的多孔陶瓷热导率的影响因素,概述了多孔陶瓷有效热导率的计算方法,并重点分析了不同显微结构的不同计算方法。针对不同的应用领域对材料热导率的不同要求,提出通过控制显微结构控制热导率是今后多孔陶瓷热导率研究得发展趋势。 相似文献
5.
W. D. KINGERY 《Journal of the American Ceramic Society》1955,38(7):251-255
Theoretical relationships and experimental data concerning thermal conductivity for a number of oxide materials have been compared over a wide temperature range. Deviations from the basic proportionality between k and 1/ T are caused by radiant-energy transmission, a high Debye temperature, a low mean free path of the thermoelastic waves, porosity, and in a few cases electronic conductivity. Extrapolation of thermal conductivity data to high temperatures is not reliable. 相似文献
6.
The hypothesis is presented that the maximum tensile thermal stresses in brittle ceramics can be reduced significantly by a redistribution of the temperature profile using a spatially varying thermal conductivity. On the basis of a hollow circular cylinder subjected to radially inward or outward steady-state heat flow, it is shown that such a spatially varying thermal conductivity can lead to significant decreases in magnitude of the maximum tensile thermal stress. Possible techniques of creating such thermal conductivity variations are discussed briefly. 相似文献
7.
EDWIN RUH 《Journal of the American Ceramic Society》1954,37(5):224-229
An instrument has been developed to measure the thermal conductivity of dense ceramic materials over the temperature range 20° to 200°C. A cylindrical ceramic specimen 1/2 in. in m diameter by 1/2 in. long is used in the instrument. hessures lower than 1μ of mercury are used to reduce heat losses and to permit rapid attainment of steady-state conditions. 相似文献
8.
Alida Bellosi Frédéric Monteverde Diletta Sciti 《International Journal of Applied Ceramic Technology》2006,3(1):32-40
This work investigated suitability and efficacy of the sintering technique known as spark plasma sintering to produce ultra-high-temperature-based Hf and Zr borides. Ceramic–matrix composites in the systems HfB2 –SiC, ZrB2 –MoSi2 , and ZrB2 –ZrC–SiC were processed by spark plasma sintering and hot pressing. The effects of processing were evaluated comparing the materials microstructure and properties. Compared with hot-pressing technique, spark plasma sintering offers the great advantage to fabricate successfully in short time (i.e., cuts in costs) poorly sinterable powder compositions without the help of any sintering activators. 相似文献
9.
The thermal conductivity of Al2 O3 , MgO, TiO2 , and CaF2 single crystals and single-phase poly-crystalline aggregates of controlled microstructure was measured between 0° and 1000°C. The conductivity of pure single-phase dense polycrystalline aggregates agrees with that of the corresponding single crystals at temperatures below the onset of radiant-heat transfer. Small amounts of impurities and the pore geometry may considerably affect the conductivity of aggregates. 相似文献
10.
Effect of Grain Thermal Expansion Mismatch on Thermal Conductivity of Porous Ceramics 总被引:1,自引:0,他引:1
Efim Litovsky Tatiana Gambaryan-Roisman Michael Shapiro Artur Shavit 《Journal of the American Ceramic Society》1999,82(4):994-1000
Many ceramics contain microcracks, which are often situated between sintered grains. These microcracks constitute thermal resistances, which may affect heat transfer through the material and its effective thermophysical properties. The thicknesses and the contact areas of the microcracks change with temperature as a result of the thermal expansion mismatch between the grains on opposite sides of the microcracks. This physical mechanism affects changes of the material's thermal conductivity, k , with temperature. The above mechanism usually plays a minor role at atmospheric pressure, where heat may flow via the gas filling the cracks. Hence, the temperature-induced changes of the crack geometry have little effect on heat transfer. However, at low gas pressures, where the heat flow between the grains occurs mainly via the contact areas, the grains' thermal expansion mismatch causes unusual temperature behavior of the material's thermal conductivity observed for several industrial refractories. In this paper, the influence of the above physical mechanism is discussed relative to other heat transfer mechanisms described in the literature. A simple physical model of the thermal expansion of grains bonded by an agent, having different thermal expansion coefficients, is developed. This model allows calculation of the contact area and the average microcrack opening between the grains as functions of the temperature, the characteristic grains sizes and their thermal expansion coefficients, and the permanent crack area. These parameters are evaluated and used to calculate the effective thermal conductivity of ceramic materials containing microcracks that appear as a result of thermal contraction of grains. The calculated thermal conductivity satisfactorily correlates with the experimental data collected for several chrome-magnesite refractories over a wide range of temperatures and gas pressures. 相似文献
11.
12.
研究了化学组成及显微结构对M1位NZP陶瓷导热系数的影响,随着M1位离子种类数的增加,NZP陶瓷的导热和降低。CMS的导热系数随着气孔率的增加而降低。 相似文献
13.
Julie Bourret Aurelie Michot Nicolas Tessier‐Doyen Benoit Naït‐Ali Fabienne Pennec Arnaud Alzina Jerome Vicente Claire S. Peyratout David S. Smith 《Journal of the American Ceramic Society》2014,97(3):938-944
A clay‐based material exhibiting high pore volume fraction and low thermal conductivity suitable for thermal insulation is described. Starting with a commercial clay containing >75% kaolinite, foams were made by mixing in water and methyl cellulose as a surfactant then beating. After drying at 70°C, the pore volume fraction >94% remains almost constant for treatments up to 1150°C. In contrast, the phases constituting the solid skeleton evolve strongly with removal of surfactant, dehydroxylation of kaolinite, and formation of mullite. The latter leads to greater mechanical strength but also an increase in thermal conductivity. Thermal treatment of the kaolin foam at 1100°C yields a suitable compromise between low thermal conductivity of 0.054 W.(m.K)?1 at room temperature with a compressive yield stress of 0.04 MPa. The radiation component in the effective thermal conductivity is <10% at 20°C increasing to >50% at 500°C. 相似文献
14.
15.
16.
17.
Processing and Mechanical Properties of Zirconium Diboride-Based Ceramics Prepared by Spark Plasma Sintering 总被引:1,自引:0,他引:1
Hailong Wang Chang-An Wang Xuefeng Yao Daining Fang 《Journal of the American Ceramic Society》2007,90(7):1992-1997
Zirconium diboride (ZrB2 ) reinforced by nano-SiC whiskers has been prepared by spark plasma sintering (SPS). Of most interest is the densification of ZrB2 –SiCw composites accomplished by SPS at a temperature as low as 1550°C. The relative density of ZrB2 –SiCw composites could reach to 97% with an average grain size of 2–3 μm. Both flexural strength and fracture toughness of the composites were improved with increasing amount of SiCw. Flexural strengths ranged from 416 MPa for monolithic ZrB2 to over 545 MPa for ZrB2 –15 vol% SiCw composites. Similarly, fracture toughness also increased from 5.46 MPa·m1/2 to more than 6.81 MPa·m1/2 in the same composition range. The relative density of ZrB2 –SiCw composites could be further improved to near 100% by adding some sintering aids such as AlN and Si3 N4 ; however, the effects of different sintering additives on the mechanical properties of the composites were different. 相似文献
18.
Weon-Ju Kim Do Kyung Kim Chong Hee Kim 《Journal of the American Ceramic Society》1996,79(4):1066-1072
The effect of the morphology of second phases in sintered microstructure on the thermal conductivity of AIN ceramics was investigated. When an Y2 O3 -doped AIN specimen was cooled down slowly at a rate of 3°C/min after sintering at 1850° or 1900°C, the second phases were concentrated in the corners of the AIN grains by an increase of dihedral angle during cooling. On the other hand, the fast-cooled specimen at a rate of 60°C/min showed a different structure of the second phases interconnected through the triple-grain junctions. The specimen with isolated second-phase morphology showed a higher thermal conductivity than those with interconnected second-phase morphology. The measured thermal conductivity of the specimens with different morphologies of the second phases agreed well with the calculated one derived from modeled microstructures. From the comparison of the measured and calculated thermal conductivity, it was shown that the thermal conductivity of the specimen with interconnected second-phase morphology decreased steeply with an increase of the amount of the second phases, assuming the content of lattice oxygen to be constant. However, the thermal conductivity of the specimen with isolated second-phase morphology was rather insensitive to an increase of the amount of the second phases. 相似文献
19.
Multiscale Genome Modeling for Predicting the Thermal Conductivity of Silicon Carbide Ceramics 下载免费PDF全文
Silicon carbide (SiC) ceramics have been widely used in industry due to its high thermal conductivity. Understanding the relations between the microstructure and the thermal conductivity of SiC ceramics is critical for improving the efficiency of heat removal in heat sink applications. In this paper, a multiscale model is proposed to predict the thermal conductivity of SiC ceramics by bridging atomistic simulations and continuum model via a materials genome model. Interatomic potentials are developed using ab initio calculations to achieve more accurate molecular dynamics (MD) simulations. Interfacial thermal conductivities with various additive compositions are predicted by nonequilibrium MD simulations. A homogenized materials genome model with the calculated interfacial thermal properties is used in a continuum model to predict the effective thermal conductivity of SiC ceramics. The effects of grain size, additive compositions, and temperature are also studied. The good agreement found between prediction results and experimental measurements validates the capabilities of the proposed multiscale genome model in understanding and improving the thermal transport characteristics of SiC ceramics. 相似文献
20.
Geng-fu Xu Tayo Olorunyolemi Yuval Carmel Isabel K. Lloyd Otto C. Wilson 《Journal of the American Ceramic Society》2003,86(12):2082-2086
A multilayer insulation configuration suitable for microwave sintering of ceramics up to 2100°C was designed and tested successfully. The configuration is based on porous, granular BN/ZrO2 fiber composite powder for packed beds and spacer cylinders. This insulation allows stable, controlled microwave sintering and can be modified to microwave process materials with different thermal, dielectric properties with improved properties. 相似文献