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  • 1
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    Preparation of Nitrogen-Doped Mullite Fiber by Nitridation of Silica–Alumina Gel Fiber in Ammonia (2013)
    Wiley
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    Publication Date: 2013-06-11
    Description: Nitrogen-doped mullite fibers were first synthesized through the nitridation of Al 2 O 3 – SiO 2 gel fibers in NH 3 . The results showed that nitrogen take-up began at 800°C, reached the maximum at 900°C, and then decreased with increasing temperature. The ceramic fibers nitridated at 900°C were essentially amorphous, but contained a small amount of nano-sized Al – Si spinel crystals. Mullite was formed after nitridation at 1200°C, accompanied by crystallization of χ- SiAlON and δ- Al 2 O 3 . The incorporation of nitrogen resulted in the formation of a variety of nitrogen-containing crystalline phases. The grain size of the mullite fibers can be adjusted by changing of the nitrogen content.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 2
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    Dense SiCf/MoSi2 composite via liquid silicon infiltration (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract Silicon carbide fiber reinforced MoSi2 matrix composite (SiCf/MoSi2) is prepared by liquid silicon infiltration at 1450°C. SiC fiber preform is first impregnated with phosphomolybdic acid (PMA) solution in ethyl alcohol. After calcinations, the PMA is converted into MoO3. Following the heating in hydrogen atmosphere, the MoO3 is reduced into metallic Mo, leading to a porous SiCf/Mo. The porous preform is then infiltrated with liquid silicon above silicon melting point to produce SiCf/MoSi2. The microstructure evolution and the underlying mechanism are studied. It is found that MoSi2 is formed by dissolution‐precipitation. Through multiple impregnation‐calcination cycles, a fully dense SiCf/MoSi2 can be obtained with MoSi2 as the continuous matrix phase. The presence of Mo is found to significantly reduce the attack of liquid silicon the silicon carbide fiber reinforcements.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 3
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    Effects of laser fluence on silicon modification by four-beam laser interference (2015)
    American Institute of Physics (AIP)
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    Publication Date: 2015-12-18
    Description: This paper discusses the effects of laser fluence on silicon modification by four-beam laser interference. In this work, four-beam laser interference was used to pattern single crystal silicon wafers for the fabrication of surface structures, and the number of laser pulses was applied to the process in air. By controlling the parameters of laser irradiation, different shapes of silicon structures were fabricated. The results were obtained with the single laser fluence of 354 mJ/cm 2 , 495 mJ/cm 2 , and 637 mJ/cm 2 , the pulse repetition rate of 10 Hz, the laser exposure pulses of 30, 100, and 300, the laser wavelength of 1064 nm, and the pulse duration of 7–9 ns. The effects of the heat transfer and the radiation of laser interference plasma on silicon wafer surfaces were investigated. The equations of heat flow and radiation effects of laser plasma of interfering patterns in a four-beam laser interference distribution were proposed to describe their impacts on silicon wafer surfaces. The experimental results have shown that the laser fluence has to be properly selected for the fabrication of well-defined surface structures in a four-beam laser interference process. Laser interference patterns can directly fabricate different shape structures for their corresponding applications.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Rapid Preparation of SiC Fibers Using a Curing Route of Electron Irradiation in a Low Oxygen Concentration Atmosphere (2015)
    Wiley
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    Publication Date: 2015-05-29
    Description: Polycarbosilane (PCS) fiber was irradiated by electron beam at low dose in a flowing N 2 /O 2 mixture with O 2 concentration of 1%. After the pyrolysis of the irradiated precursor fibers, SiC fibers with high strength of 2.4 GPa were obtained. Microstructural evolutions of the resultant fibers were explored. It was found that during the irradiation, free radicals were formed in the PCS and were oxidized by oxygen as Si–OH groups. The Si–OH groups then transformed into Si–O–Si linkage and resulted in further cross-linking of the PCS during pyrolysis. A remarkable structure gradient along the fiber diameter was formed under the coupled effects of irradiation and oxidation. The content of oxygen decreased from the fiber surface to the core, whereas the crystallinity of β-SiC increased in the same direction. The electrical resistivity of the as-prepared ceramic fiber was 80.7 Ω cm, showing good potential for being as electromagnetic wave absorber.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 5
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    Method for Comparative Analysis of Ribonucleic Acids Using Isotope Labeling and Mass Spectrometry (2012)
    American Chemical Society (ACS)
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    Publication Date: 2012-10-04
    Description: Analytical Chemistry DOI: 10.1021/ac301638c
    Print ISSN: 0003-2700
    Electronic ISSN: 1520-6882
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society (ACS)
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  • 6
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    EDTA-Assisted Self-Assembly of Fluoride-Substituted Hydroxyapatite Coating on Enamel Substrate (2011)
    American Chemical Society (ACS)
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    Publication Date: 2011-11-04
    Description: Crystal Growth & Design DOI: 10.1021/cg101708y
    Print ISSN: 1528-7483
    Electronic ISSN: 1528-7505
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by American Chemical Society (ACS)
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  • 7
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    Effect of Temperature on the Microstructure of Boron Nitride Formed In Situ on Chemical Vapor-Deposited Boron in Ammonia Gas (2011)
    Wiley
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    Publication Date: 2011-01-29
    Description: Boron nitride thin layers are in situ fabricated on chemical vapor-deposited boron in ammonia gas. Characterization by X-ray photoelectron spectroscopy and transmission electron microscopy reveals that the nitridation is dominated by different processes with varying temperatures. Below 1300°C the surface reaction is in control and leads to the formation of uniformly thin layer with mostly sp 3 boron nitride. As the temperature rises, the nitridation is gradually turned as a diffusion-determining process, after which a thicker but uneven layer with hexagonal sp 2 boron nitride is produced.
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 8
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    A robust approach to time-to-depth conversion and interval velocity estimation from time migration in the presence of lateral velocity variations (2014)
    Wiley
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    Publication Date: 2014-11-08
    Description: ABSTRACT The problem of conversion from time-migration velocity to an interval velocity in depth in the presence of lateral velocity variations can be reduced to solving a system of partial differential equations. In this paper, we formulate the problem as a non-linear least-squares optimization for seismic interval velocity and seek its solution iteratively. The input for the inversion is the Dix velocity, which also serves as an initial guess. The inversion gradually updates the interval velocity in order to account for lateral velocity variations that are neglected in the Dix inversion. The algorithm has a moderate cost thanks to regularization that speeds up convergence while ensuring a smooth output. The proposed method should be numerically robust compared to the previous approaches, which amount to extrapolation in depth monotonically. For a successful time-to-depth conversion, image-ray caustics should be either nonexistent or excluded from the computational domain. The resulting velocity can be used in subsequent depth-imaging model building. Both synthetic and field data examples demonstrate the applicability of the proposed approach.
    Print ISSN: 0016-8025
    Electronic ISSN: 1365-2478
    Topics: Geosciences , Physics
    Published by Wiley
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  • 9
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    Synthesis of β-SiAlON Nanopowder by Ammonolysis of Alumina–Silica Gel (2013)
    Wiley
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    Publication Date: 2013-11-29
    Description: A simple method for synthesis of β- SiAlON powder by nitridation of alumina–silica gel in ammonia was provided. Precursor was obtained from a mixture of nanosized alumina and colloidal silica. Nitridation reactions took place at 1100°C and conversion to β- SiAlON was achieved at 1300°C for 2–3 h. The synthesized β- SiAlON powder was nanocrystalline in size (〈100 nm).
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 10
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    Quantifying Aerosol Direct Effects from Broadband Irradiance and Spectral Aerosol Optical Depth Observations (2014)
    Wiley
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    Publication Date: 2014-04-24
    Description: We outline a methodology using broadband and spectral irradiances to quantify aerosol direct effects on the surface diffuse shortwave (SW) irradiance. Best Estimate Flux (BEF) data spans a 13–year timeframe at the Department of Energy Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) site. Screened clear–sky irradiances and aerosol optical depth (AOD), for solar zenith angles ≤ 65°, are used to estimate clear–sky diffuse irradiances. We validate against detected clear-sky observations from SGP's Basic Radiation System (BRS). BRS diffuse irradiances were in accordance with estimates, producing a root mean square (RMSE) and mean bias errors (MBE) of 4.0 W/m 2 and −1.4 W/m 2 , respectively. Absolute differences show 99% of estimates within ±10 W/m 2 (10%) of the mean BRS observations. Clear–sky diffuse estimates are used to derive quantitative estimates of aerosol radiative effects, represented as the aerosol diffuse irradiance (ADI). ADI is the contribution of diffuse SW to global SW, attributable to scattering of atmospheric transmission by natural plus anthropogenic aerosols. Estimated slope for the ADI as a function of AOD indicates an increase of ~22 W/m 2 in diffuse SW for every 0.1 increase in AOD. Such significant increases in the diffuse fraction could possibly increase photosynthesis. Annual mean ADI is 28.2 W/m 2 and heavy aerosol loading at SGP provide up to a maximum increase of 120 W/m 2 in diffuse SW over background conditions. With regard to seasonal variation, the mean diffuse forcing's are 17.2, 33.3, 39.0, and 23.6 W/m 2 for winter, spring, summer, and fall, respectively.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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