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  • Other Sources  (496)
  • INORGANIC AND PHYSICAL CHEMISTRY  (267)
  • COMPOSITE MATERIALS  (229)
  • 1990-1994  (496)
  • 1993  (496)
  • 1
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    Single and double charge transfer of He(2+) ions with molecules at near-thermal energies (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Rate coefficients were measured for charge-transfer reactions of He(2+) ions with H2, N2, O2, CO, CO2, and H2O. The experiments were carried out using a selected-ion drift-tube mass spectrometer. Total rate coefficients are found to be very large and are generally close to the limiting Langevin capture rate coefficients or the corresponding ADO-model (Su and Bowers, 1973) coefficients. The product-ion spectra indicate that both single and double charge transfer and possibly transfer ionization occur in these reactions.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: International Journal of Mass Spectrometry and Ion Processes (ISSN 0168-1176); p. 193-203.
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  • 2
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    Modeling the densification of metal matrix composite monotape (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We present a first model that enables prediction of the density (and its time evolution) of a monotape lay-up subjected to a hot isostatic or vacuum hot pressing consolidation cycle. Our approach is to break down the complicated (and probabilistic) consolidation problem into simple, analyzable parts and to combine them in a way that correctly represents the statistical aspects of the problem, the change in the problem's interior geometry, and the evolving contributions of the different deformation mechanisms. The model gives two types of output. One is in the form of maps showing the relative density dependence upon pressure, temperature, and time for step function temperature and pressure cycles. They are useful for quickly determining the best place to begin developing an optimized process. The second gives the evolution of density over time for any (arbitrary) applied temperature and pressure cycle. This has promise for refining process cycles and possibly for process control. Examples of the models application are given for Ti3Al + Nb, gamma TiAl, Ti6Al4V, and pure aluminum.
    Keywords: COMPOSITE MATERIALS
    Type: Acta Metallurgica et Materialia (ISSN 0956-7151); 41; 8; p. 2297-2316.
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  • 3
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    Laser flash photolysis studies of atmospheric free radical chemistry using optical diagnostic techniques (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Some recent studies carried out in our laboratory are described where laser flash photolytic production of reactant free radicals has been combined with reactant and/or product detection using time-resolved optical techniques to investigate the kinetics and mechanisms of important atmospheric chemical reactions. Discussed are (1) a study of the radical-radical reaction O + BrO yields Br + O2 where two photolysis lasers are employed to prepare the reaction mixture and where the reactants O and BrO are monitored simultaneously using atomic resonance fluorescence to detect O and multipass UV absorption to detect BrO; (2) a study of the reaction of atomic chlorine with dimethylsulfide (CH3SCH3) where atomic resonance fluorescence detection of Cl is employed to elucidate the kinetics and tunable diode laser absorption spectroscopy is employed to investigate the HCl product yield; and (3) a study of the aqueous phase chemistry of Cl2(-) radicals where longpath UV absorption spectroscopy is employed to investigate the kinetics of the Cl2(-) + H2O reaction.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: In: Optical methods in atmospheric chemistry; Proceedings of the Meeting, Berlin, Germany, June 22-24, 1992 (A93-51501 22-35); p. 2-14.
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  • 4
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    Mass spectrometric studies of SiO2 deposition in an indirect plasma enhanced LPCVD system (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Reaction pathways for the low temperature deposition of SiO2 from silane and indirect plasma-excited oxygen-nitrogen mixtures are proposed based on experimental evidence gained from mass spectrometry in an indirect plasma enhanced chemical vapor deposition chamber. It was observed that about 80-85 percent of the silane was oxidized to byproduct hydrogen and only about 15-20 percent to water. Such conversion levels have led us to interpret that silanol (SiH3OH) could be the precursor for SiO2 film deposition, rather than siloxane /(SiH3)2O/ which has generally been cited in the literature. From mass spectrometry, we have also shown the effects of the plasma, and of mixing small amounts of N2 with the oxygen flow, in increasing the deposition rate of SiO2. Free radical reaction of nitric oxide, synthesized from the reaction of oxygen and nitrogen in the plasma chamber, and an *ncrease in atomic oxygen concentration, are believed to be the reasons for these SiO2 deposition rate increases. Through mass spectrometry we have, in addition, been able to identify products, presumably originating from terminating reactions, among a sequence of chemical reactions proposed for the deposition of SiO2.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: Electrochemical Society, Journal (ISSN 0013-4651); 140; 5; p. 1430-1434.
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  • 5
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    Reaction layer formation at the graphite/copper-chromium alloy interface (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.
    Keywords: COMPOSITE MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 24A; 1; p. 53-60.
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  • 6
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    Studies on droplet evaporation and combustion in high pressures (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: High pressure droplet evaporation and combustion have been studied up to 15 MPa under normal and microgravity fields. From the evaporation studies, it has been found that in the supercritical environments, the droplet evaporation rate and lifetime take a maximum and a minimum at an ambient pressure over the critical pressure. Its maximum and minimum points move toward the lower ambient pressures if the ambient temperature is increased. It has been found from the combustion studies that the burning life time takes a minimum at an ambient pressure being equal to the critical pressure. It is attributable to both the pressure dependency of the diffusion rate and the droplet evaporation characteristics described above.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 93-0813 , AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States|; 10 p.
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  • 7
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    Transverse flexural tests as a tool for assessing damage to PMR-15 composites from isothermal aging in air at elevated temperatures (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: To date, the effect of thermo-oxidative aging on unidirectional composite mechanical properties has been monitored by the measurement of interlaminar shear strength (ILSS) and either three or four point longitudinal flexural strength (LFS) of the composites being tested. Both results are affected by the fiber-to-matrix bonding, the former being dependent on the shear resistance of the interface and the latter on the degree of load sharing by the fibers through the fiber/matrix interface. Recently, fiber/matrix interfacial bond strengths have been monitored using a transverse flexural strength (TFS) test method. This test method was used to evaluate the effect of fiber surface treatment on the fiber/matrix.
    Keywords: COMPOSITE MATERIALS
    Type: SAMPE Quarterly (ISSN 0036-0821); 24; 2; p. 49-53.
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  • 8
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    Direct numerical simulation of turbulent H2-O2 combustion using reduced chemistry (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Results of direct numerical simulations of hydrogen-oxygen combustion using a partial-equilibrium chemistry scheme in constant density, decaying, isotropic turbulence are reported. The simulations qualitatively reproduce many features of experimental results, such as superequilibrium radical species mole fractions, with temperature and major species mole fractions closer to chemical equilibrium. It was also observed that the peak reaction rates occur in narrow zones where the stoichiometric surface intersects regions of high scalar dissipation, as might be expected for combustion conditions close to chemical equilibrium. Another finding was that high OH mole fraction correspond more closely to the stoichiometric surface than to areas of high reaction rate for conditions of the simulations. Simulation results were compared to predictions of the Conditional Moment Closure model. This model was found to give good results for all quantities of interest when the conditionally averaged scalar dissipation was used in the prediction. When the nonconditioned average dissipation was used, the predictions compared well to the simulations for most of the species and temperature, but not for the reaction rate. The comparison would be expected to improve for higher Reynolds number flows, however.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: AIAA PAPER 93-0248 , ; 11 p.|AIAA, Aerospace Sciences Meeting and Exhibit; Jan 11, 1993 - Jan 14, 1993; Reno, NV; United States
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  • 9
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    On 'large-scale' stable fiber displacement during interfacial failure in metal matrix composites (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Experimental results are presented to show that interfacial failure in sapphire-reinforced niobium is characterized by 'large-scale' (5-15 microns) plasticity-controlled fiber displacements occurring under increasing loads. The results are based on the responses during thin-slice fiber pushout tests wherein the fiber is supported over a hole twice the fiber diameter. The results describe an interfacial failure process that should also occur near fiber ends during pullout when a fiber is well-bonded to a soft, ductile matrix, such that eventual failure occurs by shear within the matrix near the interface.
    Keywords: COMPOSITE MATERIALS
    Type: Scripta Metallurgica et Materialia (ISSN 0956-716X); 28; 12; p. 1583-1588.
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  • 10
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    Fiber pushout and interfacial shear in metal-matrix composites (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Recent thin-slice pushout tests have suggested that MMC matrix-fiber interface failure processes depend not only on such intrinsic factors as bond strength and toughness, and matrix plasticity, but such extrinsic factors as specimen configuration, thermally-induced residual stresses, and the mechanics associated with a given test. After detailing the contrasts in fiber-pullout and fiber-pushout mechanics, attention is given to selected aspects of thin-slice fiber pushout behavior illustrative of the physical nature of interfacial shear response and its dependence on both intrinsic and extrinsic factors.
    Keywords: COMPOSITE MATERIALS
    Type: JOM (ISSN 1047-4838); 45; 3; p. 34-37.
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