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1.
Thermal and Electrical Conductivity of Amorphous and Graphitized Carbide‐Derived Carbon Monoliths
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Andreas M. Kern Bodo Zierath Joachim Haertlé Tobias Fey Bastian J. M. Etzold 《化学工程与技术》2016,39(6):1121-1129
The influence of graphitization and composition of carbide‐derived carbon (CDC) monoliths on the electrical and thermal conductivity was investigated. Carbon monoliths with varying porosities were synthesized employing biomorphous macroporous TiC and SiC as precursors. Graphitization was carried out in situ during high‐temperature chlorination with and without addition of nickel, iron, and cobalt chloride to the carbide. The graphitized monoliths showed improved properties. The results demonstrate that despite graphitic carbon also glass‐like carbon, stemming from the carbide synthesis, increases the thermal and electrical conductivity significantly. 相似文献
2.
《应用陶瓷进展》2013,112(7):409-417
ABSTRACTThe silicon carbide (SiC) ceramics containing multilayer graphene derived from graphite exfoliation were successfully prepared by pressureless sintering, and the effect of graphene content on the sintering behaviours, microstructure, mechanical, tribological, electrical and thermal properties was investigated in detail. The bulk density, bending strength and hardness of the composite ceramics gradually decrease with the increase of graphene content, but the friction, conductance and thermal conductance properties are improved obviously. When the graphene content reaches 5?wt-%, the dry friction coefficient of 0.22, electrical conductivity of 2724.14 S?1?m?1 and thermal conductivity of 8.5?W?(m?1?K?1) can be obtained, indicating good comprehensive mechanical, tribological, electrical and thermal properties. This multilayer graphene reinforced silicon carbide ceramic is a promising seal material instead of SiC seal materials containing graphite to be applied in next-generation mechanical seals. 相似文献
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以溶剂热法合成聚对亚苯基/LiNi0.5Fe2O4纳米复合材料,分别对放电等离子烧结时不同保温时间制备的样品的电导率和热导率进行了研究。发现,保温时间不同对聚对亚苯基/ LiNi0.5Fe2O4纳米复合材料的电导率没有明显的影响,但对热导率具有一定的影响,保温时间越长热导率越大。保温时间延长,导致铁氧体晶粒长大,使材料体系的声子平均自由程增加,因此声子热导率增加,从而导致总热导率的增加。由于铁氧体具有较差的电输运特性,因此晶粒长大对电导率大小没有明显的影响。 相似文献
5.
The effect of nanocrystals with preferred orientation on the thermal conductivity of carbon films is studied. During graphitization, the presence of biaxial compressive stress results in the formation of preferred orientation in the microstructure of graphitic nanocrystals if the corresponding activation energy is supplied. This formation of preferred orientation leads to the orientation of graphitic basal planes perpendicular to the substrate. Due to the high thermal conductivity of graphite in the basal planes, there is a significant increase in thermal conductivity of textured nanocrystalline films compared to amorphous film. 相似文献
6.
《Ceramics International》2019,45(12):14555-14561
Processing metallic powders by electrical resistance sintering requires the use of insulating ceramics dies. Selecting the appropriate ceramic material according to the electrical, thermal and mechanical properties is a need. Dies produced with several ceramic materials have been tested during the production of cemented carbide in order to check their behaviour in the process and final product properties. Tialite/mullite, zircon/mullite, zirconium phosphate based ceramic, yttria-stabilized zirconia and sialon, in most cases with modified compositions and shaping processes in order to achieve a high density, have been tested. Dry powder processing by cold isostatic pressing and furnace sintering resulted to be the better process for dies production. The effect of die properties on the produced cemented carbide, and the behaviour and life of the die during the production have been analysed. Very smooth die surface increases the number of cycles withstood during metallic parts production, because of lower extraction stresses, as checked for sialon dies. Zirconium phosphate based dies, with low thermal conductivity, show the most densified hard metal parts surface. 相似文献
7.
《Journal of the European Ceramic Society》2020,40(2):241-250
Dense silicon carbide/graphene nanoplatelets (GNPs) and silicon carbide/graphene oxide (GO) composites with 1 vol.% equimolar Y2O3–Sc2O3 sintering additives were sintered at 2000 °C in nitrogen atmosphere by rapid hot-pressing technique. The sintered composites were further annealed in gas pressure sintering (GPS) furnace at 1800 °C for 6 h in overpressure of nitrogen (3 MPa). The effects of types and amount of graphene, orientation of graphene sheets, as well as the influence of annealing on microstructure and functional properties of prepared composites were investigated. SiC-graphene composite materials exhibit anisotropic electrical as well as thermal conductivity due to the alignment of graphene platelets as a consequence of applied high uniaxial pressure (50 MPa) during sintering. The electrical conductivity of annealed sample with 10 wt.% of GNPs oriented parallel to the measuring direction increased significantly up to 118 S·cm−1. Similarly, the thermal conductivity of composites was very sensitive to the orientation of GNPs. In direction perpendicular to the GNPs the thermal conductivity decreased with increasing amount of graphene from 180 W·m−1 K−1 to 70 W·m−1 K−1, mainly due to the scattering of phonons on the graphene – SiC interface. In parallel direction to GNPs the thermal conductivity varied from 130 W·m−1 K−1 up to 238 W·m−1 K−1 for composites with 1 wt.% of GO and 5 wt.% of GNPs after annealing. In this case both the microstructure and composition of SiC matrix and the good thermal conductivity of GNPs improved the thermal conductivity of composites. 相似文献
8.
《Journal of the European Ceramic Society》2023,43(9):3855-3874
Silicon carbide (SiC) exhibits excellent thermal conductivity. Recently, thermal conductivity that amounts to 261.5 W/m-K has been obtained in polycrystalline SiC ceramic liquid-phase sintered (LPS) with Y2O3-Sc2O3 additives at 2050 °C under a nitrogen atmosphere. From the additive used to the sintering atmosphere selected, many factors affect the thermal conductivity of the SiC. In this review, important factors that are known to determine the thermal conductivity of LPS-SiC (lattice oxygen/nitrogen content, porosity, grain size, grain boundary structure, phase transformation, and additive composition) have been evaluated. While reviewing the impact of each factor on thermal conductivity, hidden correlations among different factors are also discussed. Among the factors that are claimed to be important, we suggest a few factors that are more critical to thermal conductivity than others. Based on the most critical factors on the thermal conductivity of LPS-SiC, a complete engineers’ guide for high thermal conductivity LPS-SiC is proposed. 相似文献
9.
Jose Manuel Ramos-Fernández Manuel Martínez-Escandell Francisco Rodríguez-Reinoso 《Journal of the European Ceramic Society》2013,33(3):583-591
This work reports the synthesis of nanoTiC–graphite composites using mesophase pitch containing titanium as TiC or TiO2 nanoparticles. NanoTiC–graphite composites have been prepared using Ti-doped self-sintering mesophase powders as starting materials without using any binders or a metal carbide-carbon mixing stage. The effect of manufacture variables on the graphite compacts properties was studied. Graphites were characterised using XRD and Raman spectroscopy, SEM and TEM, as well as by their mechanical, electrical and thermal properties. The presence of TiC promotes graphitisation producing materials with larger crystal sizes. The kind of titanium source and mesophase content of the starting pitch affects to the final properties. Mesophase pitch with higher amount of mesophase content produces graphites with higher degree of graphitisation. The incorporation of TiC nanoparticles to the graphites composites improved thermal conductivity more than four times, and mechanical properties are not significantly modified by the presence of TiC. 相似文献
10.
Possible Electrical Double-Layer Contribution to the Equilibrium Thickness of Intergranular Glass Films in Polycrystalline Ceramics 总被引:1,自引:0,他引:1
David R. Clarke Thomas M. Shaw Albert P. Philipse Roger G. Horn 《Journal of the American Ceramic Society》1993,76(5):1201-1204
The plausibility of the entropic repulsion of electrical double layers acting to stabilize an equilibrium thickness of intergranular glass films in polycrystalline ceramics is explored. Estimates of the screening length, surface potential, and surface charge required to provide a repulsive force sufficiently large to balance the attractive van der Waals and capillary forces for observable thicknesses of intergranular film are calculated and do not appear to be beyond possibility. However, it has yet to be established whether crystalline particles in a liquid-phase sintering medium possess an electrical double layer at high temperatures. If they do, such a surface charge layer may well have important consequences not only for liquid-phase sintering but also for high-frequency electrical properties and microwave sintering of ceramics containing a liquid phase. 相似文献
11.
Epoxy composites doped with different content of graphene nanoplatelets (GNPs) and/or carbon nanotubes (CNTs) have been manufactured. Their chemical, thermal, electrical, and mechanical behaviors have been studied, evaluating also their performance as coatings of glass fiber composite substrates. It is confirmed that the graphitic nanofillers present different efficiency as nanofillers as a function of their geometry. CNTs are much higher efficient electrical nanofillers than graphene, but an important synergetic effect is determined in the electrical conductivity of hybrid GNP/CNT/epoxy composites. In contrast, the thermal conductivity scarcely depends on the geometry of graphitic nanofillers but on the graphitic nanofiller content. Adding up to 12 wt% GNP and 1 wt% CNT, the thermal conductivity of the epoxy resin can be increased more than 300%. GNP presents high efficiency to increase the barrier properties, reducing the water absorption up to 30%. The stiffness of nanocomposites proportionally increases with graphitic addition, up to 50%, regard to the modulus of the neat epoxy resin. The adherence of coatings over glass fiber composite substrates increases by nanofiller addition due to the nanomechanical anchoring. However, the water uptake induces a higher weakening on nanodoped composites due to the preferential water absorption by the interface. 相似文献
12.
Silicon carbide ceramics with BeO as an additive exhibit unusually high electrical resistivity and thermal conductivity compared to conventional SiC ceramics. Studies concerning the effects of carrier concentration in the SiC grains on electrical properties and thermal conductivity are described. The low carrier concentration in this ceramic is responsible for the high electrical resistivity. The thermal conductivity, however, decreases gradually with increasing impurity concentration. 相似文献
13.
Jie Xu Xiaobing Zhou Shunrui Zou Lu Chen Peter Tatarko Jian-Qing Dai Zhengren Huang Qing Huang 《Journal of the American Ceramic Society》2022,105(9):5576-5584
A novel Pr3Si2C2 additive was uniformly coated on SiC particles using a molten-salt method to fabricate a high-density SiC ceramics via liquid-phase spark plasma sintering at a relatively low temperature (1400°C). According to the calculated Pr–Si–C-phase diagram, the liquid phase was formed at ∼1217°C, which effectively improved the sintering rate of SiC by the solution–reprecipitation process. When the sintering temperature increased from 1400 to 1600°C, the thermal conductivity of SiC increased from 84 to 126 W/(m K), as a consequence of the grain growth. However, an increasing amount of the sintering additive increased the interfacial thermal resistance, resulting in a decrease of thermal conductivity of the materials. The highest thermal conductivity of 141 W/(m K) was obtained for the material having the largest SiC grains and an optimized amount of the additive at the grain boundaries and triple junctions. The proposed Pr3Si2C2-assisted liquid-phase sintering of SiC can be potentially used for the fabrication of SiC-based ceramic composites, where a low sintering temperature would inhibit the grain growth of SiC fibers. 相似文献
14.
Rohit Malik Hyun-Min Kim Young-Wook Kim Kwang Joo Kim 《Ceramics International》2018,44(14):16394-16399
SiC–BN composites were fabricated by conventional hot-pressing from β-SiC and h-BN nanopowders with 2?vol% yttria as a sintering additive. Electrical and thermal properties of the composites were investigated as a function of initial BN content. Owing to the nanosize of the starting powders, the grain-growth-assisted N-doping of the SiC lattice was significantly enhanced during liquid-phase sintering, yielding the highest-reported electrical conductivity of ~124 (Ω?cm)?1 for a SiC–4-vol% BN composite. The typical values of electrical resistivity and thermal conductivity of the SiC–4-vol% BN composite at room temperature were 8.1?×?10?3 Ω?cm and 92.4?W?m?1 K?1, respectively. 相似文献
15.
Thermal conductivity and microstructure of Ti-doped graphite 总被引:2,自引:0,他引:2
Ti doped and Si-Ti doped graphites have been developed. The influence of the dopants on the properties and microstructure of doped graphites was analyzed. Test results reveal that Ti doped graphite has excellent bending strength and high thermal conductivity, with highest values reaching 50.2 MPa and 424 W m−1 K−1 for a Ti concentration of 15 wt% in the raw materials. Si added simultaneously with Ti promotes the growth of graphite crystals resulting in an increased thermal conductivity. A kind of Si-Ti doped graphite has been developed with thermal conductivity as high as 494 W m−1 K−1 by optimizing the compositions. Correlation between the content of dopant and the properties and microstructure of doped graphites was studied, and catalytic graphitization mechanism of dopants is also discussed. 相似文献
16.
Guo-Dong Zhan Mamoru Mitomo Rong-Jun Xie Amiya K. Mukherjee 《Journal of the American Ceramic Society》2001,84(10):2448-2450
This study investigates the thermal and electrical properties of SiC ceramics with a combination of Y2 O3 and rare-earth-oxide additions as sintering additives, by comparing four types of SiC starting powders varying in particle size and chemical composition. The powder mixtures were plasma-activation sintered to full densities and then annealed at high temperatures for grain growth. The thermal conductivity and electrical resistivity of the SiC ceramics were measured at room temperature by a laser-flash technique and a current–voltage method, respectively. The results indicate that the thermal conductivity and electrical resistivity of the SiC ceramics are dependent on the chemical composition and particle size of the starting powders. The thermal conductivities observed for all of the annealed materials with a rare-earth La2 O3 sintering additive were >160 W·(m·K)−1 , although low electrical resistivity was observed for all materials, in the range 3.4–450 Ω·cm. High thermal conductivity, up to 242 W·(m·K)−1 , was achieved in an annealed material using a commercial 270 nm SiC starting powder. 相似文献
17.
《Journal of the European Ceramic Society》2014,34(14):3413-3419
In the present study, boron carbide matrix composites were manufactured by hot-pressing method. In order to reduce the boron carbide sintering temperature and to improve the mechanical properties, such as bending strength, critical stress intensity factor and hardness, chromium carbide, because of its low melting point and high thermal expansion coefficient, was added in various volume quantities. In order to prepare the material for cutting tool or ceramics sealing applications hexagonal boron nitride in quantities ranging from 2 and 8 vol.% was added to reduce the friction coefficient. The sinters were subjected to the abrasive test and to elastic properties examinations. Computer simulations of thermal stresses were prepared. The measured mechanical properties were supported by phase analysis and microstructural observations. Because the carrying out of heat is very important for mechanical properties of materials the influence of additives on thermal conductivity was also presented. 相似文献
18.
A number of anisotropic and near-isotropic graphites were irradiated at 300° to 1500°C to fluences of up to 1.5 × 1022n/cm2 (E > 0.18 MeV). The maximum volume contraction of the graphites ranged from 4 to 9 per cent at 4 to 6 × 1021 n/cm2 at 1175° to 1280°C, and the maximum expansions ranged from 11 to 50 per cent at 1.5 × 1022 n/cm2. Pores, located between crystallite clusters, were identified and are shown to be those eliminated by c-axis expansion during densification while intercrystallite pores formed. The rate of elimination of the pores located between crystallite clusters increases while the rate of formation of intercrystallite pores decreases with increasing temperature. During expansion new pores form between filler particles increasing the bulk volume expansion. The dimensional and microstructural changes are correlated with the distribution of apparent crystallite sizes in the graphites; a predominance of highly graphitic structure in each material causes maximum contraction strain and higher expansion rates after turnaround. The thermal expansivity of materials, composed predominantly of anisotropic and highly graphitic structure, increases by a factor of 2, whereas the thermal expansivity of materials predominant in isotropic structure decreases by a factor of 2. Thermal expansivity changes coincide with volume expansions. A graphite with evenly balanced volumes of isotropic and anisotropic structures shows no change in thermal expansivity with fluence. The thermal expansivity changes follow the same correlation with apparent crystallite size and distribution of crystallite sizes as does the maximum volume contraction and expansion rates of the graphites. Near-isotropic graphites that contain a narrow range of crystallite sizes are more stable under fast neutron irradiation at high temperatures than are anisotropic materials which have a wide range of crystallite sizes. The addition of semigraphitic isotropic carbon structure to an anisotropic material improves its stability and reduces the magnitude of the increase in thermal expansivity. 相似文献
19.
Christophe Lorrette Adrien Réau Laurent Briottet 《Journal of the European Ceramic Society》2013,33(1):147-156
Silicon carbide based materials are foreseen candidates for next generation nuclear applications due to a combination of the following properties: high temperature strength, high thermal conductivity and low nuclear activation. Their main drawback lies in their too low toughness. A promising route to enhance such mechanical properties is to reduce the grain size down to the nanosize range. Enabling a quite low sintering time, the spark plasma sintering technique has been used to process nano size monolithic Silicon carbides with several grain sizes and with or without boron additives. The mechanical properties, including Young modulus, flexural strength and toughness, of these materials have been measured from room temperature to 1300 °C and compared to those of a commercially sintered α-SiC. The results are carefully discussed in correlation with the microstructure. Despite a lower density, the obtained flexural strength and toughness properties of the nano grain silicon carbide are very promising when processed without boron additives. Thus, efforts should be focused on the processing of large size nanograins SiC components by SPS without boron and with high density. 相似文献
20.
Ulrich Schmitt-Radloff Frank Kern Rainer Gadow 《Journal of the European Ceramic Society》2018,38(10):3585-3594
Hot pressing and spark plasma sintering were applied to manufacture electrical discharge machinable ZTA-TiC ceramics containing 17?vol.% zirconia (1.5Y) and 24?vol.% titanium carbide in an alumina matrix. Sintering was carried out at 1450–1600?°C and 40?MPa pressure with 2?h dwell for HP and 10?min for SPS. The influence of sintering conditions on mechanical properties, microstructure, phase composition and electrical conductivity was investigated. Both sintering technologies lead to fully densified samples with similar strength and toughness. Hardness was generally lower for SPS. SPS samples develop a finer microstructure. HP samples the TiC grains tend to merge at high sintering so that HP materials reach significantly higher conductivities. Productivity and energy consumption per piece can be significantly decreased by shifting to SPS. Both types of material were ED-machinable. Hot pressed ceramics showed better cutting performance and improved surface quality in trimming operations. 相似文献