B.H Liu
,
Y Zhang
,
S.X. Ouyang
,
and H.C. Gu (Research Institute of Technical Chemical Physics
,
East China University of Science and Technology
,
Shanghai 200237
,
China)(Department of Materials Physics
,
University of Science and Technology Beijing
,
Beijing 100083
,
China)(State Key Laboratory for Synthesis and Processing of Advanced Materials
,
Wuhan University of Technology
,
Wuhan 430070
,
China)
金属学报(英文版)
Titanium nitride powder was synthesized by microwave carbothermal reduction of titanium oxide. The mechanism and thermal dynamics of the reaction process were studied. The results show that the microwave carbothermal reduction technology has unique advantages over the conventional reduction methods. It can not only lower the reaction temperature, shorten the synthesis cycle, but also refine the product particles,as well as improving the reactivity of the powder.
关键词:
TiN microwave
,
null
Applied Physics Letters
We developed an ambient pressure chemical vapor deposition (CVD) for rapid growth of high-quality graphene films on Cu foils. The quality and growth rate of graphene films are dramatically increased with decreasing H(2) concentration. Without the presence of H(2), continuous graphene films are obtained with a mean sheet resistance of < 350 Omega/sq and light transmittance of 96.3% at 550 nm. Because of the ambient pressure, rapid growth rate, absence of H(2) and readily available Cu foils, this CVD process enables inexpensive and high-throughput growth of high-quality graphene films. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3512865]
关键词:
Applied Surface Science
Hydrogenated nanocrystalline silicon (nc-Si:H) films were prepared using diluted tetrachlorosilane (SiCl4) with various hydrogen flow rates (Hf) by plasma enhanced chemical vapor deposition (PECVD) at a constant substrate temperature (Ts) as low as 120 degrees C. Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), infrared spectra (IR) and spectroscopic ellipsometry (SE) were employed to investigate the microstructure and hydrogen bonding of the nc-Si: H films. Our results showed that the microstructure and hydrogen content of the films could be effectively tailored by the hydrogen flow rates, and a distinct transition from amorphous to nanocrystalline phase was observed with an increase of Hf. At an optimal preparation condition, a deposition rate was as high as 3.7 nm/min and the crystallinity reached up to 64.1%. In addition, the effect of hydrogen on the low-temperature growth of nc-Si:H film was proposed in relation to the surface reaction of radicals and the hydrogen diffusion in the surface growing region. (C) 2011 Elsevier B.V. All rights reserved.
关键词:
Nanocrystalline silicon;PECVD;Microstructure;Raman spectra;hydrogenated amorphous-silicon;thin-films;raman-spectroscopy;solar-cells;mechanism;sih2cl2
Journal of the American Ceramic Society
Fabrication of C/SiC composites by using the heaterless chemical vapor infiltration (HCVI) technique, which is an improved technology based on the conventional chemical vapor infiltration, is reported for the first time in this paper. In the HCVI process, a gradient temperature field formed in the fiber preform overcomes the problems of slow diffusion and restricted permeability of gaseous reactant species to some extent, and the electro-deposition is necessary to accelerate the SiC deposition rates. The highest linear deposition rates of SiC matrix within inter-fiber pores are 0.33 mu m/h. Microstructures of the C/SiC composites are uniform, and the inter-fiber and inter-ply pores can be well infiltrated. The longitudinal and circumferential microcracks are found in the composites.
关键词:
deposition;behavior
Y.Chen X.Chen A.M.Guo D.X.Luo
,
B.F.Xu
,
Z.X.Yuan
,
P.H.Li
,
S.K.Pu
,
S.B.Zhou
金属学报(英文版)
The different chemical composition of silicon and manganese as well as different re-tained austenite fraction ranged from 4to 101163326174f the high strength and high elon-gation steels were studied in the paper.The dislocations and carbon concentration in retained austenite were observed by a transmission electron microscope and an electric probe analyzer,respectively.The experimental results showed that silicon and manganese are two fundamental alloying elements to stabilize austenite effectively but retaining austenite in different mechanis-↑ms.Meanwhile,the cooling processing played an important role in controlling the fraction of retained austenite of the hot-rolled high strength and high plasticity steels.
关键词:
high strength
,
null
,
null
Journal of Alloys and Compounds
Carbon-coated Fe and Co nanocapsules have been synthesized by a chemical vapor condensation process using carbon monoxide as carrier gas. The characterization and magnetic properties of carbon-coated Fe and Co nanocapsules are investigated and compared. The core/shell structure of the Fe(C) nanocapsules is similar to that of the Co(C) nanocapsules, consisting of an amorphous shell and a metallic core. The phases of the Co(C) nanocapsules are composed of f.c.c.-Co, h.c.p.-Co and cobalt carbides regardless of the decomposition temperature and the CO gas flow rate. The phases of the Fe(C) nanocapsules change with changing decomposition temperature and CO gas flow rate. The majority phases of the Fe(C) nanocapsules are alpha-Fe and Fe3C when the decomposition temperature is between 500 and 1000 degreesC, but for 700 degreesC only Fe3C exists alpha-Fe, gamma-Fe and Fe3C phases coexist after preparation at 1100 degreesC. The saturation magnetization of the Co(C) nanocapsules increases with increasing decomposition temperature, while that of the Fe(C) nanocapsules is less dependent on the phases formed. The cobalt nanocapsules reach 90% of the value of the saturation magnetization of bulk cobalt, while the iron nanocapsules obtained at 400 and 1100 degreesC reach 75 and 33 % of the saturation magnetization of bulk iron. The carbon-coated Fe and Co nanocapsules are shown to be ferromagnetic with a ratio of the remnant magnetization to saturation magnetization M-r/M-s of 0.3-0.4. (C) 2003 Elsevier B.V. All rights reserved.
关键词:
nanostructured materials;vapour deposition;crystal structure;magnetic;measurements;transmission electron microscopy (TEM);coated fe-co(c) nanocapsules;arc-discharge;nanoparticles;fe;co;methane
Electrochemistry Communications
The results of this work prove that electrochemical reactions are involved in the whole corrosion process of pure Fe with a solid NaCl deposit in water vapor at 600 degrees C. The interaction of chemical and electrochemical reactions accelerates the corrosion rate of pure Fe significantly. The electrochemical reaction is coupled with a preceding chemical reaction process (ce), in which Fe first reacts chemically with NaCl and water vapor to generate HCl(g). And then, the electrochemical reaction proceeds via a one-electron electrochemical reduction to form H(2). (C) 2009 Elsevier B.V. All rights reserved.
关键词:
Solid NaCl;Water vapor;Medium temperature;Chronopotentiometry;EIS;behavior;500-700-degrees-c
Journal of Central South University of Technology
The ablation properties of C/C composites with four different needled preforms prepared by isothermal chemical vapor infiltration (ICVI), which are super-thin mat lay-up, 0 degrees/90 degrees weftless fabric lay-up, 0 degrees/45 degrees weftless fabric lay-up and 0 degrees/45 degrees twill fabric lay-up, were quantitatively evaluated by performing the ablation tests with an engine torch. And their ablation discrepancies were analyzed according to the surface characteristic, porosity and thermal diffusivity. The results show that the 0 degrees/45 degrees weftless composite has a flat eroded surface with no obvious macroscopic pits. Its thickness and mass erosion rates are decreased by about 46.8% and 34.8%, 25.0% and 27.5%, and 17.5% and 19.4% compared with those of the mat, the 0 degrees/90 degrees weftless and the 0 degrees/45 degrees twill composites, respectively. The ablation properties are mainly controlled by the thermo-chemical effect (oxidation), and a little by the thermo-mechanical effect (mechanical denudation). The needling fiber bundles play an important role in accelerating the ablation process and resulting in the heterogeneous ablation.
关键词:
C/C composites;ablation;fiber architecture;isothermal chemical vapor;infiltration;thermal diffusivity;carbon-carbon;cfrc composites
