Precursor Gas Comparison for the Growth of Silicon Carbide Fibers Via Laser Chemical Vapor Deposition PDF Download
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Author: Mia Catherine Matt
Publisher:
ISBN:
Category :
Languages : en
Pages : 168
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Book Description
Laser chemical vapor deposition (LCVD) is a processing technique that can be used to grow fibers. In this study, the relationships between deposited SiC fiber composition, fiber microstructure, and fiber mechanical properties (ambient temperature failure stress in tension) were compared using two different precursor gases - Tetramethylsilane (TMS) and Dimethylsilane (DMS) 0́3 using laser chemical vapor deposition (LCVD). Each set of fibers was grown at 2, 4 and 6 bar at a growth rate of 50 um/s. Furthermore, each set of fibers contained a nanocrystalline core. In some cases, the presence of nodular structures were noted, but these features were comprised of nanocrystalline grains. The crystalline structure for both fibers were indexed by X-ray diffraction as the 3C-SiC cubic phase. The fibers were carbon-rich. In general, the TMS fibers had generally higher average stress at failures that were 2280 MPa as compared to the average DMS fibers being 1150 MPa. Considerable spread in the tensile strength at failure was noted for the DMS fibers and is contributed to residual stresses, as they fibers were qualitatively more delicate to handle. A Weibull analysis revealed that the fibers had a low Weibull modulus, which is an indication of a large and unpredictable variation of flaws within the fibers.
Author: Mia Catherine Matt
Publisher:
ISBN:
Category :
Languages : en
Pages : 168
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Book Description
Laser chemical vapor deposition (LCVD) is a processing technique that can be used to grow fibers. In this study, the relationships between deposited SiC fiber composition, fiber microstructure, and fiber mechanical properties (ambient temperature failure stress in tension) were compared using two different precursor gases - Tetramethylsilane (TMS) and Dimethylsilane (DMS) 0́3 using laser chemical vapor deposition (LCVD). Each set of fibers was grown at 2, 4 and 6 bar at a growth rate of 50 um/s. Furthermore, each set of fibers contained a nanocrystalline core. In some cases, the presence of nodular structures were noted, but these features were comprised of nanocrystalline grains. The crystalline structure for both fibers were indexed by X-ray diffraction as the 3C-SiC cubic phase. The fibers were carbon-rich. In general, the TMS fibers had generally higher average stress at failures that were 2280 MPa as compared to the average DMS fibers being 1150 MPa. Considerable spread in the tensile strength at failure was noted for the DMS fibers and is contributed to residual stresses, as they fibers were qualitatively more delicate to handle. A Weibull analysis revealed that the fibers had a low Weibull modulus, which is an indication of a large and unpredictable variation of flaws within the fibers.
Author: Rajesh Balachandran
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 115
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Book Description
Ceramic matrix composites (CMC) constitute a category of composite materials widely used in the aerospace industry as they satisfy the thermal, chemical and mechanical requirements of a good composite material with the drawback being in the high processing costs. Chemical vapor deposition is a process long known for its importance in aerospace and structural applications. Chemical vapor deposition can be used to develop thin interfacial coatings on fibers, which are reinforced in to a matrix according to the application. The interfacial layers are useful for preventing reactions between the fibers and the matrix material at high temperatures. Interfacial coatings can also deflect crack propagation once the composite is put into service. This work focuses on developing a suitable gas phase and surface kinetics model for obtaining the deposition profiles in the chemical vapor deposition of pyrocarbon on silicon carbide fibers at the given conditions of temperature, pressure and feed rate. The model uses an existing gas phase mechanism (National Institute for Standards and Technology and Gas Research Institute). There are combinations of species in the gas phase, but all of them do not lead to the deposition of pyrocarbon. This raises a question as to which of them would affect the rate of deposition and why. For the given conditions of temperature, pressure and flow rate and from the information available in different literature sources acetylene is assumed to be the major depositing specie of pyrocarbon Also, the gas phase mechanism was modified to simplify and suit the needs of the given conditions. The importance behind modeling the surface kinetics is that it could help understand the actual process in the formation of pyrolytic carbon. The mechanism of the pyrocarbon deposition could be important in knowing the type of carbon being deposited, which is of utmost importance in its applications. The modeling data is validated by means of using data obtained from experiments.
Author: Justin Lee Rife
Publisher:
ISBN:
Category :
Languages : en
Pages : 186
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Book Description
Laser Chemical Vapor Deposition (LCVD) is a promising new processing technique by which freestanding structures, such as fibers, can be deposited. The deposition of carbon fibers by use of ethylene as a precursor gas can be easily achieved and has been investigated as a way to complement or even replace current carbon fiber production techniques. The properties of carbon fibers deposited from ethylene via LCVD have been investigated for low precursor pressures thus far. However, deposition rates for low precursor pressures are limited and rates that are orders of magnitude faster can be achieved by use of higher precursor pressures. No detailed studies on properties of fibers processed at these higher pressures have been conducted. This thesis fills this knowledge gap by exploring the relationships between processing conditions, growth behavior, microstructure and mechanical properties of carbon fibers deposited from ethylene at hyperbaric pressures. It is found that the fiber growth rates are limited by surface reaction kinetics at low temperatures, while they are mass transport limited or gas phase nucleation limited at high temperatures. When grown under mass transport limited conditions, fibers exhibit drastic changes in morphology and microstructure. The tensile strengths of the carbon fibers grown by LCVD are generally found to be poor due to the nature of graphitic carbon deposits. However, the Weibull modulus among the LCVD grown carbon fibers is found to be high. Trends in mechanical properties with processing conditions and microstructure are observed.
Author: National Aeronautics and Space Adm Nasa
Publisher:
ISBN: 9781730991448
Category :
Languages : en
Pages : 102
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Book Description
A process for development of clean silicon carbide fiber with a small diameter and high reliability is presented. An experimental evaluation of operating conditions for SiC fibers of good mechanical properties and devising an efficient technique which will prevent welding together of individual filaments are discussed. The thermodynamic analysis of a different precursor system was analyzed vigorously. Thermodynamically optimum conditions for stoichiometric SiC deposit were obtained. Revankar, Vithal and Hlavacek, Vladimir Unspecified Center...
Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 1102
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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 1148
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Author: Gladys Felton
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ISBN:
Category :
Languages : en
Pages : 216
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Author: Abebe Mesfin
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ISBN:
Category :
Languages : en
Pages : 84
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Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 492
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Author: Brandy Kay Burkland
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ISBN:
Category :
Languages : en
Pages : 166
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