Ying LI
,
Yunfa CHEN
,
Jianghong GONG
材料科学技术（英）
The ac conductivities of Y2O3 or CaO-stabilized cubic zirconias were obtained from complex impedance measurements in the temperature range from 373 to 473 K. By analyzing the temperature-dependence of the resultant dc conductivities, it was shown that the activation energies for conduction are lower than those reported previously for the same materials at high temperatures. Comparing the activation energy data with the theoretically estimated values revealed that there may exist a certain, although very small, amount of free oxygen vacancies in the test samples at low temperatures and the conduction in the test samples is a result of the migration of these free oxygen vacancies.
关键词:
Ionic conductivity
,
null
,
null
,
null
Xiao Si
材料科学技术（英）
This study reports the significantly enhanced aluminizing behaviors of a low carbon steel at temperatures far below the austenitizing temperature, with a nanostructured surface layer produced by surface mechanical attrition treatment (SMAT). A much thicker iron aluminide compound layer with a much enhanced growth kinetics of η-Fe2Al5 in the SMAT sample has been observed relative to the coarse-grained steel sample. Compared to the coarse-grained sample, a weakened texture is formed in the aluminide layer in the SMAT sample. The aluminizing kinetics is analyzed in terms of promoted diffusivity and nucleation frequency in the nanostructured surface layer.
关键词:
Nanostructured materials
International Journal of Hydrogen Energy
The stoichiometric reactions of ammonia borane (NH3BH3, AB) and selected alkali or alkaline-earth metal hydrides produce metal amidoboranes, which possess dehydrogenation property advantages over their parent AB. However, the losses of hydrogen capacity and chemical energy in the preparation process make metal amidoboranes less energy-effective for hydrogen storage application. In the present study, by combining the M+-Mg2+ double cations remarkably lowers the reactivity of the alkali metal hydrides toward AB. As a result, the starting Mg-based ternary hydrides MMgH3 (M = Na, K, Rb) and AB phases are largely stable in the mechanical milling process, but transform to the corresponding mixed-cation amidoboranes in the subsequent heating process. Importantly, when the post-milled 3AB/MMgH3 mixtures are isothermally heated at above 60 degrees C using water bath, the formation and decomposition processes of the mixed-cation amidoboranes can be favorably combined, giving rise to rapid and efficient dehydrogenation performances at the mild temperatures (60-80 degrees C). The results acquired may provide a generalized reactions coupling strategy for designing and synthesis other potentially efficient hydrogen storage system. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
关键词:
Hydrogen storage;Ammonia borane;Metal amidoborane;Hydride;Reactivity;ammonia borane dehydrogenation;thermal-decomposition;storage material;catalyzed dehydrogenation;crystal-structure;boron-nitride;amidoborane;lithium;amidotrihydroborate;hydrides
Materials Letters
Low cycle isothermal mechanical fatigue testing K40S cobalt-base superalloy was carried out at 700 and 900degreesC with total strain amplitude from +/-0.1 to +/-1.0 pct. Correlations between microscopic cyclic deformation and cycle stress response with various microstructural phenomena were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the deformation substructure and carbide precipitation. The results show that K40S superalloy exhibited cyclic stress response of cyclic hardening at 700degreesC, and of initial hardening followed by softening at 900degreesC. In addition, at both temperatures, cyclic hardening during cycle deformation increased with increasing strain amplitude, while the fatigue lifetime decreased. The cyclic stress response behavior can be rationalized based on the mechanisms associated with dislocation-dislocation interactions, dislocation-precipitate (M23C6) interactions and interactions between solute atoms and dislocations. (C) 2002 Elsevier Science B.V. All rights reserved.
关键词:
K40S cobalt-base alloy;isothermal cyclic deformation;cyclic stress;response;room-temperature;behavior;alloy;mechanisms
Journal of Coatings Technology and Research
Vitreous enamel coating is a promising candidate as a high temperature protective coating for titanium (Ti)-based alloys due to its high thermo-chemical stability, compatibility, and matching thermal expansion coefficient to the substrates. Vitreous enamel coating is economically attractive because of its low cost and easy handling. The oxidation behavior of Ti6Al4V (at 700 degrees C) and Ti-48Al (at 800-900 degrees C), with and without the vitreous enamel coating exposed to air, are investigated in this article. The results show that the vitreous enamel coating could markedly protect the substrate (Ti6Al4V and Ti48Al) from oxidation at elevated temperatures. In comparison, the TiAlCr coating might not provide long-term protection for the Ti6Al4V alloys due to the heavy interfacial interdiffusion at high temperatures, although a protective Al2O3 scale could form at the initial oxidation stage. The vitreous enamel coating remains intact, uniform, compact, and adhesive to the substrate, however, with undetectable interfacial reaction after oxidation. It is also worth noting that some new phases form in the coating during oxidation at 900 degrees C, although the protectiveness of the coating seems to be unaffected.
关键词:
Ti6Al4V;TiAl;enamel coating;oxidation;interfacial reaction;hot corrosion behaviors;intermetallic compound;titanium aluminides;ti60 alloy;resistance
材料科学技术（英）
Creep testing was conducted on K40S alloy. The detailed creep deformation and fracture mechanisms under constant load were studied. The results show that the stress exponent ranges between 7 and 14.4 at elevated temperature 973similar to1173 K, and that the activation energy is approximately 449.1 kJ/mol. During creep, the grain boundary sliding cut off primary carbides at the boundary, generating the "O" model cracks. The creep failure mode of K40S alloy is transgranular ductile and cracks originate at the primary carbides. A long carbide and matrix interface is often a preferential path for crack propagation. The creep mechanism is discussed in light of the creep microstructure, the stress exponent and the activation energy.
关键词:
K40S alloy;creep;fracture;crack propagation;activation-energies;superalloy;term
肖胜
,
徐克西
,
刘石香
,
付华明
低温物理学报
doi:10.3969/j.issn.1000-3258.2002.04.009
从磁通运动图象出发,推导了YBa2Cu3O7-δ(YBCO)颗粒膜的I-V特性关系式,并从实验上加以验证,结果表明:在TI-V表现出很强的非线性,样品主要是非欧姆损耗;在T>TKT时,I-V呈线性关系,样品以欧姆损耗为主;而在T=TKT时,I-V将出现突变,这跟K-T相变模型所描述的一致.
关键词:
Physical Review B
We calculate the temperature dependence of resistivity to second order of the interaction between the conduction electrons (extended) and fractons (excitations in a fractal lattice). The result shows that the resistivity rho varies as [1n(HBAr-omega(F)/kT-HBAR-omega(c))]2 (omega(F) the fraction Debye frequency and omega(c) the phonon-fraction crossover frequency). It is demonstrated that resistivity minima at low temperatures in weak-scattering metallic glasses might be due to a competition between negative temperature coefficients of resistivity (TCR's) resulting from the electron-fracton interaction and a positive TCR from the regular electron-phonon interaction.
关键词:
disordered-systems;thermal-conductivity;percolation clusters;amorphous materials;nonradiative decay;alloys;resistance;relaxation;states
