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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

A study of the electrical properties of p-n junctions formed by ion-implantation into gallium arsenide

In the process of ion implantation, ion beams bombard the surface and create undesirable surface effects. The surface effects were investigated, and surface leakage currents were shown to be reduced by surface treatment. I-V characteristics and C-V measurements were obtained for the Zn-GaAs and Zn-(In,Ga)As junction is considered as a p-i-n heterojunction, without generation-recombination current. The Zn-GaAs junction is considered as a p-n homojunction with appreciable generation-recombination currents.

Lin, A. H.↗
NASA NTRS1981

Effect of Surface Roughness on Hydrodynamic Bearings

A theoretical analysis on the performance of hydrodynamic oil bearings is made considering surface roughness effect. The hydrodynamic as well as asperity contact load is found. The contact pressure was calculated with the assumption that the surface height distribution was Gaussian. The average Reynolds equation of partially lubricated surface was used to calculate hydrodynamic load. An analytical expression for average gap was found and was introduced to modify the average Reynolds equation. The resulting boundary value problem was then solved numerically by finite difference methods using the method of successive over relaxation. The pressure distribution and hydrodynamic load capacity of plane slider and journal bearings were calculated for various design data. The effects of attitude and roughness of surface on the bearing performance were shown. The results are compared with similar available solution of rough surface bearings. It is shown that: (1) the contribution of contact load is not significant; and (2) the hydrodynamic and contact load increase with surface roughness.

Majumdar, B. C.↗
DOE OSTI2022

Support Effect and Surface Reconstruction in In 2 O 3 / m- ZrO 2 Catalyzed CO 2 Hydrogenation

Here, we investigate the chemical and structural dynamics at the interface of In 2 O 3 /m-ZrO 2 and their consequences on the CO 2 hydrogenation reaction (CO 2 HR) under reaction conditions. While acting to enrich CO 2 , monoclinic zirconia (m-ZrO 2 ) was also found to serve as a chemical and structural modifier of In 2 O 3 that directly governs the outcome of the CO 2 HR. These modifying effects include the following: (1) Under reaction conditions (above 623 K), partially reduced In 2 O 3 , i.e., InO x (0 < x < 1.5), was found to migrate in and out of the subsurface of m-ZrO 2 in a semireversible manner, where m-ZrO 2 accommodates and stabilizes InO x by serving as a reservoir. The decreased concentration of surface InO x under elevated temperatures coincides with significantly decreased selectivity toward methanol and a sharp increase of the reverse water–gas shift reaction. The reconstruction-induced variation of InO x concentration appears to be one of the most important factors contributing to the altered catalytic performance of CO 2 HR at different reaction conditions. (2) The strong interactions and reactions between m-ZrO 2 and In 2 O 3 result in the activation of a pool of In–O bonds at the In 2 O 3 /m-ZrO 2 interface to form oxygen vacancies. On the other hand, the high dispersity of In 2 O 3 nanostructures onto m-ZrO 2 prevents their over-reduction under catalytically relevant conditions (up to 673 K), when bare In 2 O 3 is unavoidably reduced into the metallic phase (In 0 ). The relationship between the extent of reduction of In 2 O 3 and catalytic performance (CO 2 conversion, CH 3 OH selectivity, or yield of CH 3 OH) suggests the presence of an optimum coverage of surface InO x and oxygen vacancies under reaction conditions. The conventional model that links catalytic performance solely to the coverage of oxygen vacancies appears invalid in the present case. In situ analysis also allows the observation of surface reaction intermediates and their interconversions, including the reduction of CO 3 * into formate, a precursor for the formation of methanol and CO. The combinative ex situ and in situ study sheds light on the reaction mechanism of the CO 2 HR on In 2 O 3 /m-ZrO 2 -based catalysts. Our findings on the large-scale surface reconstructions, support effect, and the reaction mechanism of In 2 O 3 /m-ZrO 2 for CO 2 HR may apply to other related metal oxide catalyzed CO 2 reduction reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

Effect of Surface Impulsive Thermal Loads on Fatigue Behavior of Constant Volume Propulsion Engine Combustor Materials

The development of advanced high performance constant-volume-combustion-cycle engines (CVCCE) requires robust design of the engine components that are capable of enduring harsh combustion environments under high frequency thermal and mechanical fatigue conditions. In this study, a simulated engine test rig has been established to evaluate thermal fatigue behavior of a candidate engine combustor material, Haynes 188, under superimposed CO2 laser surface impulsive thermal loads (30 to 100 Hz) in conjunction with the mechanical fatigue loads (10 Hz). The mechanical high cycle fatigue (HCF) testing of some laser pre-exposed specimens has also been conducted under a frequency of 100 Hz to determine the laser surface damage effect. The test results have indicated that material surface oxidation and creep-enhanced fatigue is an important mechanism for the surface crack initiation and propagation under the simulated CVCCE engine conditions.

Zhu, Dongming↗
NASA NTRS1968

Effects of surface preparation on quality of aluminum alloy weldments

Study of surface preparations and surface contamination effects on the welding of 2014 aluminum involves several methods of surface analysis to identify surface properties conducive to weld defects. These methods are radioactive evaporation, spectral reflectance mass spectroscopy, gas chromatography and spark emission spectroscopy.

Kizer, D.↗
DOE OSTI2022

Effects of Surface Hydrophobicity on Catalytic Transfer Hydrogenation of Styrene with Formic Acid in a Biphasic Mixture

Transfer hydrogenation (TH) of unsaturated hydrocarbons with formic acid (FA) is an attractive processing pathway for the reduction of lignocellulosic pyrolysis oils. The low solubility of hydrophobic bio-oil species in water and FA in oil necessitates the use of a biphasic system as the reaction environment. Here, we report the effects of Pd/silica catalyst surface wettability on the TH reaction rate. Modification of the surface with short chain (C1–C4) alkyl silanes resulted in an increase in the reaction rate as compared to the unmodified catalyst. In contrast, modification of the surface with sulfonate (hydrophilic) and C18 alkyl silanes (hydrophobic) resulted in a decrease in the reaction rate as compared to the unmodified catalyst. Here, the results are discussed in terms of the catalyst interfacial activity and relative affinity of the reagents to the Pd active sites. An observed change in the apparent reaction order in styrene for a hydrophilic catalyst suggests that changing catalyst surface wettability from hydrophilic to hydrophobic resulted in a switch from a transport-limited to a kinetic-limited reaction regime.

09 BIOMASS FUELS↗
DOE OSTI2025

Surface and sub-surface porosity effects on the initial free surface expansion in shocked single crystal aluminum

Defects and roughness at a material’s surface can allow for the formation of a material jet when a shockwave reaches a surface. The formation of a jet can lead to significant material damage of the shocked material, as well as the downstream material that the jet impacts. Here, we utilize planar shocks in single crystal aluminum to assess initial jetting formation for surface notches and sub-surface porosity. In the case of surface notches, we find that changing the width of the notch can cause the shock breakout response to transition from a standard jetting mechanism to an atomic atomization at high velocities. This transition occurs due to the mechanisms associated with lateral relaxations within the notch and how this interacts with the shock focusing event that induces jetting. For sub-surface pores, the pore collapse induces a re-shock, localized near the pore, that is stronger than the initial shock, but unsupported. Changing the pore dimensions and location relative to the surface influences the strength of the shock that emanates from its collapse when it reaches the surface, leading to a variety of different breakout conditions including jetting and localized material failure.

36 MATERIALS SCIENCE↗