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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Surface chemistry, microstructure and friction properties of some ferrous-base metallic glasses at temperatures to 750 C

X-ray photoelectron spectroscopy analysis, transmission electron microscopy, diffraction studies, and sliding friction experiments were conducted with ferrous-base metallic glasses in sliding contact with aluminum oxide at temperatures from room to 750 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on the friction properties, surface chemistry, and microstructure of metallic glasses. The relative concentrations of the various constituents at the surface of the sputtered specimens were very different from the normal bulk compositions. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and silicon oxide at 350 C and boron nitride above 500 C. The coefficient of friction increased with increasing temperature to 350 C. Above 500 C the coefficient of friction decreased rapidly. The segregation of contaminants may be responsible for the friction behavior.

Miyoshi, K.↗
NASA NTRS1984

Microscopic aspects of the effect of friction reducers at the lubrication limit

An attempt is made to analytically model the physicochemical properties of lubricants and their capacity to reduce friction. A technique of frozen fracturing of the lubricants was employed to study the dispersion of additives throughout a lubricant. Adsorption was observed at the liquid-solid interface, which was the region where the solid and lubricant met, and the molecular dispersion of the additive enhanced the effectiveness of the lubricant. The electrically conductive characteristics of the lubricant at the friction interface indicated the presence of tunneling effects. The Bethe model was used to examine the relationship between the coefficient of friction and the variation of interface thickness. The electron transport permitted an inelastic tunnel electron spectroscopic investigation of the molecular transformations undergone by the additive during friction episodes.

Mansot, J. L.↗
NASA NTRS1982

Surface chemistry, friction and wear of Ni-Zn and Mn-Zn ferrites in contact with metals

X-ray photoelectron and Auger electron spectroscopy analysis were used in sliding friction experiments. These experiments were conducted with hot-pressed polycrystalline Ni-Zn and Mn-Zn ferrites, and single-crystal Mn-Zn ferrite in contact with various transition metals at room temperature in both vacuum and argon. The results indicate that Ni2O3 and Fe3O4 were present on the Ni-Zn ferrite surface in addition to the nominal bulk constituents, while MnO2 and Fe3O4 were present on the Mn-Zn ferrite surface in addition to the nominal bulk constituents. The coefficients of friction for the ferrites in contact with metals were related to the relative chemical activity of these metals. The more active the metal, the higher is the coefficient of friction. The coefficients of friction for the ferrites were correlated with the free energy of formation of the lowest metal oxide. The interfacial bond can be regarded as a chemical bond between the metal atoms and the oxygen anions in the ferrite surfaces. The adsorption of oxygen on clean metal and ferrite does strengthen the metal-ferrite contact and increase the friction. The ferrites exhibit local cracking and fracture with sliding under adhesive conditions. All the metals transferred to he surfaces of the ferrites in sliding.

Miyoshi, K.↗
NASA NTRS1983

Surface chemistry, friction, and wear of Ni-Zn and Mn-Zn ferrites in contact with metals

X-ray photoelectron and Auger electron spectroscopy analysis were used in sliding friction experiments. These experiments were conducted with hot-pressed polycrystalline Ni-Zn and Mn-Zn ferrites, and single-crystal Mn-Zn ferrite in contact with various transition metals at room temperature in both vacuum and argon. The results indicate that Ni2O3 and Fe3O4 were present on the Ni-Zn ferrite surface in addition to the nominal bulk constituents, while MnO2 and Fe3O4 were present on the Mn-Zn ferrite surface in addition to the nominal bulk constituents. The coefficients of friction for the ferrites in contact with metals were related to the relative chemical activity of these metals. The more active the metal, the higher is the coefficient of friction. The coefficients of friction for the ferrites were correlated with the free energy of formation of the lowest metal oxide. The interfacial bond can be regarded as a chemical bond between the metal atoms and the oxygen anions in the ferrite surfaces. The adsorption of oxygen on clean metal and ferrite does strengthen the metal-ferrite contact and increase the friction. The ferrites exhibit local cracking and fracture with sliding under adhesive conditions. All the metals transferred to the surfaces of the ferrites in sliding. Previously announced in STAR as N83-19901

Miyoshi, K.↗
NASA NTRS1967

Dynamical friction.

Chandrasekhar dynamical friction theory for star in cluster adapted to Fokker-Plank electron in two-component plasma theory and including multiple encounters

STAR CLUSTER↗
NASA NTRS1998

A Transport Model for Non-Local Heating of Electrons in ICP Reactors

A new model has been developed for non-local heating of electrons in ICP reactors, based on a hydrodynamic approach. The model has been derived using the electron momentum conservation in azimuthal direction with electromagnetic and frictional forces respectively as driving force and damper of harmonic oscillatory motion of electrons. The resulting transport equations include the convection of azimuthal electron momentum in radial and axial directions, thereby accounting for the non-local effects. The azimuthal velocity of electrons and the resulting electrical current are coupled to the Maxwell's relations, thus forming a self-consistent model for non-local heating. This model is being implemented along with a set of Navier-Stokes equations for plasma dynamics and gas flow to simulate low-pressure (few mTorr's) ICP discharges. Characteristics of nitrogen plasma in a TCP 300mm etch reactor is being studied. The results will be compared against the available Langmuir probe measurements.

Chang, C. H.↗
NASA NTRS1973

Adhesion, friction, and wear of a copper bicrystal with (111) and (210) grains

Sliding friction experiments were conducted in air with polycrystalline copper and ruby riders sliding against a copper bicrystal. Friction coefficient was measured across the bicrystal surface, and the initiation of adhesive wear was examined with scanning electron microscopy. Results indicate a marked increase in friction coefficient as the copper rider crossed the grain boundary from the (111) plane to the (210) plane of the bicrystal. Adhesion, friction, and initiation of adhesive wear was notably different in the adjacent grains of differing orientation. A slip-band adhesion-generated fracture mechanism for wear particle formation is proposed.

Brainard, W. A.↗
NASA NTRS1996

Kinetic Space Weather: Toward a Global Hybrid Model of the Polar Ionosphere-Lower Magnetosphere Plasma Transport

During the indicated period of performance, we had a number of publications concerned with kinetic polar ionosphere-lower magnetosphere plasma transport. For the IUGG 1991-4 Quadrennial Report, we reviewed aspects of U.S. accomplishments concerned with polar plasma transport, among other issues. In another review, we examined the computer simulations of multiple-scale processes in space plasmas, including polar plasma outflow and transport. We also examined specifically multiscale processes in ionospheric outflows. We developed a Generalized Semi-Kinetic(GSK) model for the topside-lower magnetosphere which explored the synergistic action of wave heating and electric potentials in the formation of auroral Ion conics, in particular the "pressure cooker" mechanism. We extended the GSK model all the way down to 120 km and applied this code to illustrate the response of the ionosphere- magnetosphere to soft-electron precipitation and convection-driven frictional ion heating, respectively. Later, the convection-driven heating work was extended to a paper for the Journal of Geophysical Research. In addition to the above full published papers, we also presented the first developments of the coupled fluid-semikinetic model for polar plasma transport during this period. The results from a steady-state treatment were presented, with the second presentation being concerned with the effects of photo-electrons on the polar wind, and the first garnering an outstanding student paper award from the American Geophysical Union. We presented the first results from a time-dependent version of this coupled fluid-semikinetic model.

Horwitz, James L.↗
NASA NTRS1991

Kinetic friction attributed to enhanced radiation by cyclotron maser instability

Along the auroral field lines, a fraction of the energetic electrons injected from the magnetotail is reflected by the earth's convergent geomagnetic field. The reflected loss-cone electrons are unstable with respect to the cyclotron maser instability, resulting in the auroral kilometric radiation. This paper investigates the kinetic friction force exerted on the energetic electrons by the enhanced radiation field. It is found that the enhanced radiation results in a deceleration of reflected electrons, thereby providing an effective resistivity. In addition, the rate of decrease (increase) of effective perpendicular (parallel) kinetic temperatures is also evaluated. The analysis is carried out over various physical parameters such as the degree of loss cone, average particle energy, and the ratio of plasma frequency to cyclotron frequency.

Yoon, Peter H.↗
NASA NTRS1976

Effect of adsorbed films on friction of Al2O3-metal systems

The kinetic friction of polycrystalline Al2O3 sliding on Cu, Ni, and Fe in ultrahigh vacuum was studied as a function of the surface chemistry of the metal. Clean metal surfaces were exposed to O2, Cl2, C2H4, and C2H3Cl, and the change in friction due to the adsorbed species was observed. Auger electron spectroscopy assessed the elemental composition of the metal surface. It was found that the systems exposed to Cl2 exhibited low friction, interpreted as the van der Waals force between the Al2O3 and metal chloride. The generation of metal oxide by oxygen exposures resulted in an increase in friction, interpreted as due to strong interfacial bonds established by reaction of metal oxide with Al2O3 to form the complex oxide (spinel). The only effect of C2H4 was to increase the friction of the Fe system, but C2H3Cl exposures decreases friction in both Ni and Fe systems, indicating the dominance of the chlorine over the ethylene complex on the surface

Pepper, S. V.↗
NASA NTRS1973

Scanning electron microscope study of polytetrafluoroethylene sliding on aluminum single crystals

Friction experiments were conducted in air with polytetrafluoroethylene (PTFE) sliding on aluminum single crystals. Mechanical scoring of the crystals with (110) and (100) orientations was observed with a single pass of the PTFE slider. No scoring was observed on the (111). The degree of scoring of the crystals is related to the hardness, with the hardest surface (111) showing no damage and the softest surface (110) showing the most severe scoring. Scoring is caused by work-hardened pieces of aluminum which, as a consequence of the adhesion between PTFE and aluminum, were pulled out of the bulk and became embedded in the PTFE polymer.

Brainard, W. A.↗
NASA NTRS1999

Diffusion, Fluxes, Friction Forces, and Joule Heating in Two-Temperature Multicomponent Magnetohydrodynamics

The relationship between Joule heating, diffusion fluxes, and friction forces has been studied for both total and electron thermal energy equations, using general expressions for multicomponent diffusion in two-temperature plasmas with the velocity dependent Lorentz force acting on charged species in a magnetic field. It is shown that the derivation of Joule heating terms requires both diffusion fluxes and friction between species which represents the resistance experienced by the species moving at different relative velocities. It is also shown that the familiar Joule heating term in the electron thermal energy equation includes artificial effects produced by switching the convective velocity from the species velocity to the mass-weighted velocity, and thus should not be ignored even when there is no net energy dissipation.

Chang, C. H.↗
NASA NTRS1983

Friction and wear of some ferrous-base metallic glasses

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminum oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Miyoshi, K.↗
NASA NTRS1984

Friction and wear of some ferrous-base metallic glasses

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminium oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Miyoshi, K.↗