Physical Review B
We report the electronic transport properties of a composite system comprising zero dimensional superconducting NbC(C) nanocapsules and carbon nanofiber matrix. DC susceptibility measurements of the nanocomposite indicate that the critical temperature (T-C) of NbC nanocrystals is 10.7 K. The temperature dependence of electrical resistivity of the specimen pellet follows the Mott's T-1/4 law in a temperature range between T-C of NbC and 300 K, owing to a strong degree of structural disorder in the carbon matrix. Below the T-C of NbC, when the change of its electrostatic energy Delta E is far greater than the thermal energy, an electron will be localized on an isolated NbC nanocrystal at very low temperatures, leading to "Coulomb Blockade." As a result, a collective behavior of the single-electron tunneling effect takes place in a three-dimensional granular superconductors' network composed of the NbC/carbon/NbC tunneling junctions. The superconducting gap of NbC crystals is not found in the current-voltage curves, due to the suppression of surface superconductivity through the contact between NbC and carbon shells.
关键词:
zero-dimensional superconductor;granular metal-films;particles;conduction;nanocapsules;percolation;samples
Journal of Materials Research
The oxidation behavior of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) in air has been investigated. The oxidation kinetics of bulk Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) at 900-1300 degrees C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO(2), Al(2)O(3), and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr(2)[Al(Si)](4)C(5) and Zr(3)[Al(Si)](4)C(6) has been improved compared with Zr(2)Al(3)C(4), and is much better than Zr(3)[Al(Si)](4)C(6) to larger fraction of protective oxidation products, Al(2)O(3) and aluminosilicate/mullite.
关键词:
single-crystals;thermoelectric properties;zrc/zro2 interface;zirconium carbide;high-temperatures;bulk zr2al3c4;carbon;mullite;microstructure;ceramics
Author S.R. Zhou
,
S.R. Qiao
,
S.H. Bai and C.S. Tian Faculty 401
,
Northwestern Polytechnical University
,
Xian 710072
,
ChinaManuscript received 18 October 1998
金属学报(英文版)
The tensile properties of three different carbonfiberreinforced carbon composites (C/C), mat C/C, 2D laminate and 4D C/C, were investigated under the combined influence of temperature and loading rate. From the experiments the following could be concluded: loading rate between 10-1-10 mm/min was valid; the fracture stress of the three kinds of C/C composites increased with increasing temperature in the range from room temperature to 1900, and the initial modulus of 2D laminate C/C composites increased with the increase of temperature up to 2000.
关键词:
tensile testing
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null
,
null
,
null
Journal of Materials Research
The isothermal oxidation behavior of Zr(2)Al(3)C(4) in the temperature range of 500 to 1000 inverted perpendicular C for 20 h in air has been investigated. The oxidation kinetics follow a parabolic law at 600 to 800 degrees C and a linear law at higher temperatures. The activation energy is determined to be 167.4 and 201.2 kJ/mol at parabolic and linear stages, respectively. The oxide scales have a monolayer structure, which is a mixture of ZrO(2) and Al(2)O(3). As indicated by x-ray diffraction and Raman spectra, the scales formed at 500 to 700 degrees C are amorphous, and at higher temperatures are alpha-Al(2)O(3), and t-ZrO(2) nanocrystallites. The nonselective oxidation of Zr(2)Al(3)C(4) can be attributed to the strong coupling between Al(3)C(2) units and ZrC blocks in its structure, and the close oxygen affinity of Zr and Al.
关键词:
high-temperature oxidation;zirconium carbide;behavior;kinetics;ti2alc;zr
孙乐
,
方向青
,
孟广慧
材料科学与工程学报
doi:10.14136/j.cnki.issn 1673-2812.2016.05.027
通过化学气相渗透(CVI)、树脂浸渍/碳化(I/C)的工艺制成多孔的C/C预制件,采用气体压力浸渗方法向预制体中渗入铜,制备出C/C-Cu复合材料.以高密度C/C复合材料(1.9g/cm3)作为对比样,在MM-200型磨损试验机上对其摩擦磨损性能进行测试,并对其微观结构和摩擦磨损机理进行分析.研究结果表明:C/C-Cu的摩擦系数比C/C复合材料的低,这主要与摩擦表面的摩擦膜有关,铜在摩擦力带动下填充摩擦表面的凹坑,并与碳材料共同形成摩擦膜,摩擦膜的碳含量越高,润滑效果越好.当C/C预制件密度为1.59 g/cm3时,C/C-Cu的摩擦系数和磨损量均小于C/C复合材料,摩擦磨损性能良好.
关键词:
C/C-Cu
,
摩擦磨损
,
摩擦膜
Tribology Letters
The isothermal oxidation behavior of a single-crystal (SC) Ni-base superalloy was studied over the temperature range from 900 to 1100 degrees C and analyzed by OM, TGA, XRD, EDX, SEM and EPMA. The alloy obeyed subparabolic rate law during oxidation at 900 and 1000 degrees C, whereas the alloy showed parabolic rate law at 1100 degrees C exposure. The variations in the chemical composition due to segregations, which resulted from the solidification process, led to the formation of different kinds of oxide scale on the dendritic and interdendritic area during oxidation at 900 and 1000 degrees C, while the alloy exhibited relatively uniform oxidation at 1100 degrees C. The growth mechanism of the scale was discussed.
关键词:
Ni-base single-crystal;superalloy;oxidation;microstructure;kinetics;cr-al alloys;internal nitridation;coatings
材料科学技术（英文）
Oxidation behavior of C/C-SiC gradient matrix composites and C/C composites were compared in stationary air. The results show that oxidation threshold of C-SiC materials increases with the amount of SiC particles in the codeposition matrix. Oxidation rate of C/C-SiC gradient matrix composites is significantly lower than that of C/C material. The micro-oxidation process was observed by SEM.
关键词:
carbon carbon composites
