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Results for “ALUMINUM OXIDE”

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Reactively Deposited Aluminum Oxide and Fluoropolymer Filled Aluminum Oxide Protective Coatings for Polymers

Reactive ion beam sputter deposition of aluminum simultaneous with low energy arrival of oxygen ions at the deposition surface enables the formation of highly transparent aluminum oxide films. Thick (12 200 A), adherent, low stress, reactively deposited aluminum oxide films were found to provide some abrasion resistance to polycarbonate substrates. The reactively deposited aluminum oxide films are also slightly more hydrophobic and more transmitting in the UV than aluminum oxide deposited from an aluminum oxide target. Simultaneous reactive sputter deposition of aluminum along with polytetrafluoroethylene (PTFE Teflon) produces fluoropolymer-filled aluminum oxide films which are lower in stress, about the same in transmittance, but more wetting than reactively deposited aluminum oxide films. Deposition properties, processes and potential applications for these coatings will be discussed.

Rutledge, Sharon K.↗
NASA NTRS1983

Photodeposition of aluminum oxide and aluminum thin films

Uniform films of Al2O3 have been photodeposited using an excimer laser operating at 248 nm (KrF) or at 193 nm (ArF) and trimethylaluminum and N2O as the reactants. Deposition rates were typically 2000 A/min and the physical, chemical, and electrical properties of the photodeposited Al2O3 films are comparable to films deposited using conventional techniques. Properties of photodeposited aluminum films are also presented.

Solanki, R.↗
NASA NTRS1979

Energy dependence of the trapping of uranium atoms by aluminum oxide surfaces

The energy dependence of the trapping probability for sputtered U-235 atoms striking an oxidized aluminum collector surface at energies between 1 eV and 184 eV was measured. At the lowest energies, approximately 10% of the uranium atoms are not trapped, while above 10 eV essentially all of them stick. Trapping probabilities averaged over the sputtered energy distribution for uranium incident on gold and mica are also presented.

Librecht, K. G.↗
NASA NTRS1987

Analysis of mid-tropospheric Space Shuttle exhausted aluminum oxide particles

Aluminum oxide particles from the exhaust of the Space Shuttle were collected immediately after the launch of the SEPEX mission and during the descent over the altitude interval of 7.6-4.6 km. The SEM examination revealed that the particles were spherical and ranged in diameter from about 0.1 micron to 10 microns. Results from the energy dispersive analysis (by an X-ray method) and of the particle chemistry (by electron spectroscopy) confirmed that the particles were predominantly composed of aluminum and oxygen. The particle size distribution of the Al2O3 was bimodal, with one observed peak centered near 2.0 microns; the other distribution mode centered at a diameter of less than 0.3 micron, but could not be accurately located. A mass median diameter was slightly less than 2 microns. Evaluation of ice nucleation activity revealed only a small fraction (about 1 ppm) of active ice nuclei among the Al2O3 particulates.

Cofer, Wesley R., III↗
NASA NTRS1972

An experimental investigation of radiative properties of aluminum oxide particles.

The radiative properties of aluminum oxide at high temperatures were determined at various wavelengths. Absorption cross-sections of aluminum oxide particles averaged over a particle size distribution were determined by measuring the radiative emission from the particles in a flame and by determining the particle number density and size distribution from measurements of the scattering of laser light incident on the particles in this flame. From these values of average absorption cross-section, the imaginary part of the refractive index was deduced. Results indicate that the absorption cross-section and the imaginary part of the refractive index increase as the temperature increases in the range from 1920 to 2610 K, and that these properties decrease with increasing wavelength in the interval from 0.35 to 1.2 micron, indicating a nongray-body behavior.

Mularz, E. J.↗
NASA NTRS1985

Thermal and sputtered aluminum oxide coatings for high temperature electrical insulation

Aluminum oxide coatings have been investigated as electrically insulating layers for mounting thin film Pt-Pt/Rh thermocouples on gas turbine blade and vane alloys (MAR M200 + Hf and MAR M509). Thermal oxides were grown directly onto NiCoCrAlY and FeCrAlY coatings on these alloys at temperature between 1300 and 1400 K in oxygen partial pressures 10 to the -7th to 2 x 10 to the 4th Pa. Although these thermal oxides exhibited good adherence, analytical characterizations using electron and optical microscopy, as well as X-ray photoelectron spectroscopy showed that they had defects and impurities which limited their insulating ability. The insulating quality of the coating was greatly improved however by reactively sputtering an aluminum oxide film over the thermal oxide. Results are presented on the electrical performance of the 2-5 micron thick composite layers for temperatures up to 1300 K.

Kreider, K. G.↗
NASA NTRSDate not supplied

Measuring the Wear and Abrasive Resistance of Air Plasma Sprayed Aluminum Oxide for Lunar Exploration

Lunar regolith, especially finer dust particles traveling at high velocities, can cause significant wear and abrasive damage to structural components that ensure a prolongated presence on the surface of the Moon. With the absence of an atmosphere and lower gravity than on Earth, regolith particles maintain high velocities at large distances from where they were generated, for example next to lunar landers. Wear-resistant ceramic and ceramic composite materials can improve the durability of spacecraft components during long missions on the Moon’s surface. Aluminum oxide coatings are lightweight, have multifunctional properties, and have high strength including high hardness and wear resistance. These properties can help improve the durability of structures used in space exploration. Air plasma sprayed (APS) aluminum oxide coatings have demonstrated the potential to protect critical structures. This study investigated the abrasive wear resistance of APS aluminum oxide coatings via Taber abrasion experiments. Taber abrasion offers the advantage of quantifying the abrasive wear behavior of particles with different shapes on a surface. In this work, an abrasive wheel made of silicon carbide was utilized to evaluate wear properties of specimens progressively over 5000 cycles. This experiment focused on testing two series of specimens to determine whether a bond coat composed of nickel, chromium, aluminum, and yttrium (NiCrAlY) improved the protective behavior of the APS aluminum oxide coating. The specimens varied in topcoat thickness and were made with and without an approximately 100 µm bond coat layer. The mass of the specimens was measured at 400 cycles, 800 cycles, 3800 cycles, and 5000 cycles. Increasing thickness was found to result in higher wear for samples with and without a bond coat. Increased mass loss in samples with a bond coat was observed indicating a need for further studies on the overall impact of the use of a bond coat on the protective behavior of the coatings. To continue designing wear resistant coatings for structural protection in space missions, the multifunctional properties of the APS aluminum oxide coating will be studied. Future experiments will determine whether the APS aluminum oxide coating can protect the structures from other aspects of the harsh space environment, such as extreme temperature variations and ionizing radiation.

aluminum oxide↗
NASA NTRS1989

Surface composition of solid-rocket exhausted aluminum oxide particles

Particulate samples of aluminum oxide were collected on Teflon filters from the exhaust plume of the Space Shuttle (STS-61A, October 30, 1985) over the altitude interval 4.6-7.6 km immediately after launch. These particles were analyzed using SEM, energy-dispersive X-ray analysis, electron spectroscopy for chemical analysis, X-ray fluorescent spectroscopy, and conventional wet-chemical techniques. The samples were 0.6-1.0 percent surface-chlorided (chlorided meaning predominantly aluminum chlorides and oxychlorides, possibly including other adsorbed forms of chloride) by weight. This level of chloriding is about one-third of the amount determined previously from laboratory-prepared alumina and surface site samples of solid-rocket-produced alumina (SRPA) after both had been exposed to moist HCl vapor at temperatures down to ambient. This level is equivalent to previous laboratory results with samples exposed to moist HCl at temperatures above the boiling point of water. It is suggested that the present lower chloriding levels, determined for samples from a 'dry' Shuttle exhaust cloud, underscore the importance of a liquid water/hydrochloric acid phase in governing the extent of surface chloriding of SRPA. The reduced chloriding is not trivial with respect to potential physical/chemical modification of the SRPA particle surfaces and their corresponding interaction with the atmosphere.

Cofer, Wesley R., III↗
NASA NTRS1976

Heterogeneous reaction of ozone with aluminum oxide

Rates and collision efficiencies for ozone decomposition on aluminum oxide surfaces were determined. Samples were characterized by BET surface area, X-ray diffraction, particle size, and chemical analysis. Collision efficiencies were found to be between 2 times 10 to the -10 power and 2 times 10 to the -9 power. This is many orders of magnitude below the value of 0.000001 to 0.00001 needed for appreciable long-term ozone loss in the stratosphere. An activation energy of 7.2 kcal/mole was found for the heterogeneous reaction between -40 C and 40 C. Effects of pore diffusion, outgassing and treatment of the aluminum oxide with several chemical species were also investigated.

Keyser, L. F.↗
NASA NTRS1984

The Strength of the Metal. Aluminum Oxide Interface

The strength of the interface between metals and aluminum oxide is an important factor in the successful operation of devices found throughout modern technology. One finds the interface in machine tools, jet engines, and microelectronic integrated circuits. The strength of the interface, however, should be strong or weak depending on the application. The diverse technological demands have led to some general ideas concerning the origin of the interfacial strength, and have stimulated fundamental research on the problem. Present status of our understanding of the source of the strength of the metal - aluminum oxide interface in terms of interatomic bonds are reviewed. Some future directions for research are suggested.

Pepper, S. V.↗
NASA NTRS1994

Depth Profiling Analysis of Aluminum Oxidation During Film Deposition in a Conventional High Vacuum System

The oxidation of aluminum thin films deposited in a conventional high vacuum chamber has been investigated using x-ray photoelectron spectroscopy (XPS) and depth profiling. The state of the Al layer was preserved by coating it with a protective MgF2 layer in the deposition chamber. Oxygen concentrations in the film layers were determined as a function of sputter time (depth into the film). The results show that an oxidized layer is formed at the start of Al deposition and that a less extensively oxidized Al layer is deposited if the deposition rate is fast. The top surface of the Al layer oxidizes very quickly. This top oxidized layer may be thicker than has been previously reported by optical methods. Maximum oxygen concentrations measured by XPS at each Al interface are related to pressure to rate ratios determined during the Al layer deposition.

Kim, Jongmin↗