23 research outputs found
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A MODULATED MOLECULAR BEAM STUDY OF THE ENERGY OF SIMPLE GASES SCATTERED FROM PYROLYTIC GRAPHITE
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A MODULATED MOLECULAR BEAM STUDY OF THE ENERGY OF SIMPLE GASES SCATTERED FROM PYROLYTIC GRAPHITE
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Reactivity of hydrogen with uranium in the presence of Pt
The surface-reaction of di-hydrogen with uranium in the presence of Pt clusters has been studied using scanning tunneling microscopy (STM). Uranium was deposited on highly oriented pyrolytic graphite (HOPG) and annealed at temperatures up to 1200{degrees}C to obtain atomically pyrolytic flat surfaces. Pt clusters were then formed using evaporation from a Pt source onto the surface and subsequent annealing. Hydrogen mainly attacked uranium in the vicinity of Pt clusters and formed hydride. The hydride formation probability is almost constant at 2.3x10{sup -4} over the range of exposures studied
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Modeled heating and surface erosion comparing motile (gas borne) and stationary (surface coating) inert particle additives
The unsteady, non-similar, chemically reactive, turbulent boundary layer equations are modified for gas plus dispersed solid particle mixtures, for gas phase turbulent combustion reactions and for heterogeneous gas-solid surface erosive reactions. The exterior (ballistic core) edge boundary conditions for the solutions are modified to include dispersed particle influences on core propellant combustion-generated turbulence levels, combustion reactants and products, and reaction-induced, non-isentropic mixture states. The wall surface (in this study it is always steel) is considered either bare or coated with a fixed particle coating which is conceptually non-reactive, insulative, and non-ablative. Two families of solutions are compared. These correspond to: (1) consideration of gas-borne, free-slip, almost spontaneously mobile (motile) solid particle additives which influence the turbulent heat transfer at the uncoated steel surface and, in contrast, (2) consideration of particle-free, gas phase turbulent heat transfer to the insulated surface coated by stationary particles. Significant differences in erosive heat transfer are found in comparing the two families of solutions over a substantial range of interior ballistic flow conditions. The most effective influences on reducing erosive heat transfer appear to favor mobile, gas-borne particle additives
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Predamage threshold electron emission from insulator and semiconductor surfaces
Predamage electron emission shows a dependence on fluence, bandgap and wavelength consistent with multiphoton excitation across the bandgap and inconsistent with avalanche ionization and thermionic emission models. The electron emission scales with pulselength as 1/..sqrt..T. 6 references, 8 figures, 1 table
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MOLECULAR BEAM STUDY OF HYDROGEN-DEUTERIUM EXCHANGE ON LOW AND HIGH MILLER INDEX PLATINUM SINGLE CRYSTAL SURFACES
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THE THERMAL AND ION-ASSISTED REACTIONS OF GaAs(100) WITH MOLECULAR CHLORINE
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