Papers by Keyword: Chemical Vapor Deposition (CVD)

Abstract: Silicon carbide is one of the best materials for satellite mirror and chemical vapor deposition (CVD) is an effective method of preparing SiC whiskers and films. In this paper, SiC whiskers or films were deposited on substrates of RB-SiC in an upright chemical vapor deposition furnace of Φ150mm × 450 mm with methyltrichloride silicane (MTS) as precursor gas and H2 as carrier gas under dilute gases of different H2/Ar ratio and different deposition temperature between 1050°C and 1150°C. The morphology and composition of the CVD-SiC grown on RB-SiC substrate were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. As a result, whisker-like, worm-like or ball-like SiC can be respectively obtained dependent on different deposition conditions such as H2/Ar ratio and deposition temperature, and the composition of the productions are determined as β-SiC by XRD. Furthermore, the deposition mechanisms of different morphologies of SiC are introduced.

Abstract: Carbon fibre reinforced carbon and silicon carbide dual matrix composites (C/C-SiC) are new type of high performance brake materials, and possess a series of outstanding advantages. In the present study, the C/C-SiC brake composites were fabricated by the combination of chemical vapor infiltration with liquid silicon infiltration. The fabric preforms were prepared by three dimension needling method. Results show the SiC form inside the short-cut fabric, around the needing fibre and among the fibre bundles in the non-woven web of the C/C-SiC composites. The average static friction coefficient of the C/C-SiC materials was 0.61. The average dynamic friction coefficient were between 0.41 and 0.54 with the increase of brake speed, and the wear rates are not sensitive to the brake speed and maintained about 0.02 cm3•MJ-1 all along.

Abstract: Novel single-crystalline SnO2 zigzag nanoribbons have been successfully synthesized by chemical vapour deposition. Sn powder in a ceramic boat covered with Si plates was heated at 1100°C in a flowing argon atmosphere to get deposits on a Si wafers. The main part of deposits is SnO2 zigzag nanoribbons. They were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). SEM observations reveal that the SnO2 zigzag nanoribbons are almost uniform, with lengths near to several hundred micrometers and have a good periodically tuned microstructure as the same zigzag angle and growth directions. Possible growth mechanism of these zigzag nanoribbons was discussed. A room temperature PL spectrum of the zigzag nanoribbons shows three peaks at 373nm, 421nm and 477nm.The novel zigzag microstructures will provide a new candidate for potential application.

Abstract: TiO2/Ti-Al-MCM-41 (TAM) with high Ti content (Si/Ti=6.2) was prepared by chemical vapor deposition (CVD) of TiCl4 on Al-MCM-41 at low reaction temperature (423 K). The sample was characterized by X-ray diffraction (XRD), N2 adsorption/desorption, high resolution transmission electron microscopy (HRTEM) and diffuse reflectance ultraviolet-visible spectroscopy (DR UV-vis). The results showed that Ti atoms were in tetrahedral coordinated in the framework of Al-MCM-41. Meanwhile, higher Ti4+ ions coordination and bulk anatase titania was observed in the DR UV-vis spectra. TAM still exhibited hexagonal p6m pore architectures, large specific surface area and narrow pore distribution. Catalytic activity of TAM for polystyrene (PS) pyrolysis has been investigated. The results showed that TAM exhibited high activity for the PS pyrolysis and good selectivity to liquid hydrocarbons of C5-C12 hydrocarbons.

Abstract: Preliminary study on the preparation and performance of vapor grown carbon fibers (VGCF) reinforced cement composites was carried out. VGCF were prepared from de-oiled asphalt (DOA) by chemical vapor deposition (CVD). Results demonstrated that compressive strength and electrical conductivity of VGCF reinforced cement could be significantly enhanced with very low fiber content. The resistivity decreased and compressive strength increased of cement-matrix composites with weight fraction of VGCF increasing from 0 to 0.6% fiber in the paste. The fiber content of 0.4% by mass of cement was recommended, which yielded the resistivity of 1.49×103Ωcm. That was two orders of magnitude lower than that for the same paste without VGCF (3.25×105Ωcm). Furthermore, the compressive strength increased by 28.8% as the VGCF content increases from 0 to 0.4% by mass of cement.

Abstract: Diamond convex surface films were synthesized on molybdenum substrate using DC plasma Jet CVD (DCPJCVD), and their microstructure and topography were characterized by those techniques such as X ray diffraction, Raman spectroscopy respectively. It showed that, when the substrate was pre-treated by polishing using successive micron diamond powder (about 30～3μm), diamond film was a polycrystalline texture and (111) faces were dominant. Raman spectrum shows that high quality diamond convex surface film was prepared successfully. Meantime, We used Finite element methods (FEM) to simulate the velocity, pressure and temperature fields of reaction chamber respectively, and it indicated that the distribution of the velocity, pressure fields were fluctuant, which had negative influence on diamond film, but the temperature fields is uniform, and it is an important factor to prepare high quality diamond convex surface film.

Abstract: Stainless steel/carbon nanotubes (CNTs) nanocomposite powders were synthesized by chemical vapor deposition (CVD) method with ethanol as a carbon source. The effects of synthesis temperature and time on microstructure and chemical composition of the powders were investigated. The as-received stainless steel powders were synthesized at temperature in between 550-800°C for 30-180 min at a pressure of 10 Torr. The optimum synthesis condition was found to be 800°C for 120 min. Average diameter of CNTs grown on stainless steel particles slightly increased with increasing growth temperature. The synthesis time, however, was found to have no effect on the size of CNTs.

Abstract: In this contribution we present high resolution transmission electron microscopy (HR-TEM) and Raman studies on the synthesis of carbon nanotubes using platinum supported on MgO in alcohol - chemical vapour deposition (A-CVD). For comparison copper and iron catalysts mixed with the same metal loading in MgO and the same process parameters in A-CVD have been tested. Our findings show that the choice of catalyst utilized under the same experimental conditions strongly influences the final morphology of the carbon nanostructures. Application of Pt/MgO in CVD results in doublewalled carbon nanotubes (DWCNT) and multiwalled carbon nanotubes (MWCNT). Cu/MgO mixtures lead to the synthesis of copper filled multiwalled carbon nanotubes (Cu-MWCNT) and iron capsules surrounded by multiwalled carbon shells (Fe-MWCS), respectively. Our findings indicate that the three discussed metals interact differently with the substrate leading to the formation of different sized catalyst particles. The analysis of the particles size in the catalyst precursors and in the final products is also described in this contribution.

Abstract: We present the synthesis of carbon nanocoils using the chemical vapor deposition technique with metal catalysts on silicon substrates. The optimum synthesis conditions and coil geometry are summarized. The coils have distribution of the outside diameter of 300 nm to 1200 nm, wire diameter of 150 nm to 400 nm and the pitch of the coil of 150 nm to 1200 nm. Applications of the developed carbon nanocoils can be electro-mechanical sensing and the electro-magnetic insulation.

Abstract: Carbon nanotubes (CNTs)/hydroxyapatite (HA) nanocomposites have been successfully fabricated by a novel method for the biomedical applications, which is in situ growing CNTs in HA matrix in a chemical vapor deposition (CVD) system. The results show that it is feasible to in situ grow CNTs in HA matrix by CVD for the fabrication of CNTs/HA nanocomposites. Multi-walled CNTs with 50-80 nm in diameter have been grown in situ from HA matrix with the pretreatment of sintering at 1473K in air. The nanocomposites are composed with carbon crystals in CNTs form, HA crystallites and calcium phosphate crystallites, one of most important CaP bioceramics. And the CNTs content is about 1% proportion by weight among the composites in our experiments, which can enhance the HA mechanical properties and the CNTs content does not affect the HA performances. These CNTs/HA nanocomposites have the potential application in the biomedical fields.