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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Effect of the powder characteristics of Sisub3Nsub4 on the microstructure of sintered bodies

Silicon nitride powders sintered with the addition of 2 wt% Mg0 to 95% theoretical density after attrition milling and subsequent purification were evaluated. Preparation of the powders is described. The powder characteristics (specific surfaces, iron concentration, and oxygen content), and density, weight loss, and phase state of the sinter bodies as a function of powder preparation are presented.

Woetting, G.↗
NASA NTRS1981

Hydraulics and geology related to beach restoration in Lee County, Florida

The erosion problem on Captiva Island is discussed. It is due to a deficit in the sand budget of the littoral drift system; a system with losses due to attrition of the particles and mass losses into the lagoons, to offshore, and to lateral transport. The effect that reopening Blind Pass would have, and the placement of sediment retaining structures in the surf zone at the northern and southern limits of the Captiva beach system, wave examined. A geological approach was used to study the origin and dynamic changes that have occurred. Through hydraulic modeling, changes that will occur by reopening and stabilizing Blind Pass are predicted. It is concluded that if the island is to be stabilized, beach nourishment with proper amounts and particle size is a necessity and that jetties adequate to restrict lateral and offshore losses are essential. It is shown that the reopening of Blind Pass would have minimal effects on the passes to the north and south, and would improve the environmental conditions in the sound with no adverse effects on the beach system.

Winton, T.↗
NASA NTRS1983

Stress-corrosion behavior of aluminum-lithium alloys in aqueous environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Pizzo, P. P.↗
NASA NTRS1984

Stress-corrosion behavior of aluminum-lithium alloys in aqueous salt environments

The stress corrosion susceptibility of two powder metallurgy (P/M) alloys, Al-Li-Cu and Al-Li-Cu-Mg; two mechanically attrited (M/A) alloys, Al-Li-Cu and Al-Li-Mg; and two wrought, ingot alloys, X-2020 and AA7475, are compared. Time-dependent fracture in an aqueous sodium chloride environment under alternate immersion condition was found to vary significantly between alloys. The stress corrosion behavior of the two powder metallurgy processed alloys was studied in detail under conditions of crack initiation, static crack growth, and fatigue crack growth. A variety of stress corrosion tests were performed including smooth surface, time-to-failure tests; potentiostatic tests on smooth surfaces exposed to constant applied strain rates; and fracture mechanics-type tests under static and cyclic loads. Both alloys show surface pitting and subsequent intergranular corrosion. Pitting is more severe in the magnesium-bearing alloy and is associated with stringer particles strung along the extrusion direction as a result of P/M processing.

Pizzo, P. P.↗
NASA NTRS1984

NASA's plans for life sciences research facilities on a Space Station

A Life Sciences Research Facility on a Space Station will contribute to the health and well-being of humans in space, as well as address many fundamental questions in gravitational and developmental biology. Scientific interests include bone and muscle attrition, fluid and electrolyte shifts, cardiovascular deconditioning, metabolism, neurophysiology, reproduction, behavior, drugs and immunology, radiation biology, and closed life-support system development. The life sciences module will include a laboratory and a vivarium. Trade-offs currently being evaluated include (1) the need for and size of a 1-g control centrifuge; (2) specimen quantities and species for research; (3) degree of on-board analysis versus sample return and ground analysis; (4) type and extent of equipment automation; (5) facility return versus on-orbit refurbishment; (6) facility modularity, isolation, and system independence; and (7) selection of experiments, design, autonomy, sharing, compatibility, and integration.

Arno, R.↗
NASA NTRS1986

Fluidized-bed reactor modeling for production of silicon by silane pyrolysis

An ideal backmixed reactor model (CSTR) and a fluidized bed bubbling reactor model (FBBR) were developed for silane pyrolysis. Silane decomposition is assumed to occur via two pathways: homogeneous decomposition and heterogeneous chemical vapor deposition (CVD). Both models account for homogeneous and heterogeneous silane decomposition, homogeneous nucleation, coagulation and growth by diffusion of fines, scavenging of fines by large particles, elutriation of fines and CVD growth of large seed particles. At present the models do not account for attrition. The preliminary comparison of the model predictions with experimental results shows reasonable agreement. The CSTR model with no adjustable parameter yields a lower bound on fines formed and upper estimate on production rates. The FBBR model overpredicts the formation of fines but could be matched to experimental data by adjusting the unkown jet emulsion exchange efficients. The models clearly indicate that in order to suppress the formation of fines (smoke) good gas-solid contacting in the grid region must be achieved and the formation of the bubbles suppressed.

Dudukovic, M. P.↗
NASA NTRS1987

Aeolian abrasion on Venus: Preliminary results from the Venus simulator

The role of atmospheric pressure on aeolian abrasion was examined in the Venus Simulator with a constant temperature of 737 K. Both the rock target and the impactor were fine-grained basalt. The impactor was a 3 mm diameter angular particle chosen to represent a size of material that is entrainable by the dense Venusian atmosphere and potentially abrasive by virtue of its mass. It was projected at the target 10 to the 5 power times at a velocity of 0.7 m/s. The impactor showed a weight loss of approximately 1.2 x 10 to the -9 power gm per impact with the attrition occurring only at the edges. Results from scanning electron microscope analysis, profilometry, and weight measurement are summarized. It is concluded that particles can incur abrasion at Venusian temperatures even with low impact velocities expected for Venus.

Marshall, J. R.↗
NASA NTRS1989

Grinding Si3N4 Powder In Si3N4 Equipment

Three methods of grinding compared. Report based on study of grinding silicon nitride powder in preparation for sintering into solid ceramic material. Attrition, vibratory, and ball mills lined with reaction-bonded silicon nitride tested. Rates of reduction of particle sizes and changes in chemical compositions of powders measured so grinding efficiences and increases in impurity contents from wear of mills and media evaluated for each technique.

Herbell, Thomas P.↗
NASA NTRS1989

Simulation Of Combat With An Expert System

Proposed expert system predicts outcomes of combat situations. Called "COBRA", combat outcome based on rules for attrition, system selects rules for mathematical modeling of losses and discrete events in combat according to previous experiences. Used with another software module known as the "Game". Game/COBRA software system, consisting of Game and COBRA modules, provides for both quantitative aspects and qualitative aspects in simulations of battles. COBRA intended for simulation of large-scale military exercises, concepts embodied in it have much broader applicability. In industrial research, knowledge-based system enables qualitative as well as quantitative simulations.

Provenzano, J. P.↗
NASA NTRS1989

Age distribution among NASA scientists and engineers

The loss of technical expertise through attrition in NASA and the aerospace industry is discussed. This report documents historical age-related information for scientific and engineering personnel in general and the NASA Lewis Research Center in particular, for 1968 through 1987. Recommendations are made to promote discussion and to establish the groundwork for action.

Ciancone, Michael L.↗
NASA NTRS1989

The impact of solar cell technology on planar solar array performance

The results of a study into the potential impact of advanced solar cell technologies on the characteristics (weight, cost, area) of typical planar solar arrays designed for low, medium and geosynchronous altitude earth orbits are discussed. The study considered planar solar array substrate designs of lightweight, rigid-panel graphite epoxy and ultra-lightweight Kapton. The study proposed to answer the following questions: Do improved cell characteristics translate into array-level weight, size and cost improvements; What is the relative importance of cell efficiency, weight and cost with respect to array-level performance; How does mission orbital environment affect array-level performance. Comparisons were made at the array level including all mechanisms, hinges, booms, and harnesses. Array designs were sized to provide 5kW of array power (not spacecraft bus power, which is system dependent but can be scaled from given values). The study used important grass roots issues such as use of the GaAs radiation damage coefficients as determined by Anspaugh. Detailed costing was prepared, including cell and cover costs, and manufacturing attrition rates for the various cell types.

Mills, Michael W.↗
NASA NTRS1992

Gravity and the geoid in the Nepal Himalaya

Materials within the Himalaya are rising due to convergence between India and Asia. If the rate of erosion is comparable to the rate of uplift, the mean surface elevation will remain constant. Any slight imbalance in these two processes will lead to growth or attrition of the Himalaya. Although buried rocks, minerals and surface control points in the Himalaya are undoubtably rising, the growth or collapse or the Himalaya depends on the erosion rate which is invisible to geodetic measurements. A way to measure erosion rate is to measure the rate of change of gravity in a region of uplift. Essentially gravity should change precisely in accord with a change in elevation of the point in a free air gradient if erosion equals uplift rate. A measurement of absolute gravity was made simultaneously with measurements of GPS height within the Himalaya. Absolute gravity is estimated from the change in velocity per unit distance of a falling corner cube in a vacuum. Time is measured with an atomic clock and the unit distance corresponds to the wavelength of an iodine stabilized laser. An experiment undertaken in the Himalaya in 1991 provide a site description also with a instrument description.

Bilham, Roger↗
NASA NTRS1993

Production of Ultrafine, High-purity Ceramic Powders Using the US Bureau of Mines Developed Turbomill

Turbomilling, an innovative grinding technology developed by the U.S. Bureau of Mines in the early 1960's for delaminating filler-grade kaolinitic clays, has been expanded into the areas of particle size reduction, material mixing, and process reaction kinetics. The turbomill, originally called an attrition grinder, has been used for particle size reduction of many minerals, including natural and synthetic mica, pyrophyllite, talc, and marble. In recent years, an all-polymer version of the turbomill has been used to produce ultrafine, high-purity, advanced ceramic powders such as SiC, Si3N4, TiB2, and ZrO2. In addition to particle size reduction, the turbomill has been used to produce intimate mixtures of high surface area powders and whiskers. Raw materials, TiN, AlN, and Al2O3, used to produce a titanium nitride/aluminum oxynitride (TiN/AlON) composite, were mixed in the turbomill, resulting in strength increases over samples prepared by dry ball milling. Using the turbomill as a leach vessel, it was found that 90.4 pct of the copper was extracted from the chalcopyrite during a 4-hour leach test in ferric sulfate versus conventional processing which involves either roasting of the ore for Cu recovery or leaching of the ore for several days.

Hoyer, Jesse L.↗
NASA NTRS1993

Materials education activities

Last year, at NEW: Update '91, a panel discussion was held to address the unique difficulties of attracting and retaining minorities and women in technical studies. Unfortunately, retention in technical majors is a problem of varying proportions for the entire student population, and must be improved in order to maintain the strength of the nation's industrial base. To investigate the cause of student attrition in technical majors, in-depth interviews of both current and former (non-graduating) engineering students at four colleges and universities in Colorado were conducted by Hewitt and Seymour. They found that there was no significant difference in the level of high school preparation and undergraduate academic performance in these two groups, despite the prevailing faculty perception that most students who switch from technical to nontechnical majors were underprepared. The majority of engineering students who changed majors reported that they were turned off by science, while one-third complained of poor teaching.

Ries, Heidi R.↗
NASA NTRS1993

ASRM propellant and igniter propellant development and process scale-up

A program of formulation and process development for ANB-3652 motor propellant was conducted to validate design concepts and screen critical propellant composition and process parameters. Design experiments resulted in the selection of a less active grade of ferric oxide to provide better burning rate control, the establishment of AP fluidization conditions that minimized the adverse effects of particle attrition, and the selection of a higher mix temperature to improve mechanical properties. It is shown that the propellant can be formulated with AP and aluminum powder from various producers. An extended duration pilot plant run demonstrated stable equipment operation and excellent reproducibility of propellant properties. A similar program of formulation and process optimization culminating in large batch scaleup was conducted for ANB-3672 igniter propellant. The results for both ANB-3652 and ANB 37672 confirmed that their processing characteristics are compatible with full-scale production.

Landers, L. C.↗
NASA NTRS1992

Gravity and the geoid in the Nepal Himalaya

Materials within the Himalaya are rising due to convergence between India and Asia. If the rate of erosion is comparable to the rate of uplift the mean surface elevation will remain constant. Any slight imbalance in these two processes will lead to growth or attrition of the Himalaya. The process of uplift of materials within the Himalaya coupled with surface erosion is similar to the advance of a glacier into a region of melting. If the melting rate exceeds the rate of downhill motion of the glacier then the terminus of the glacier will receed up-valley despite the downhill motion of the bulk of the glacier. Thus although buried rocks, minerals and surface control points in the Himalaya are undoubtably rising, the growth or collapse of the Himalaya depends on the erosion rate which is invisible to geodetic measurements. Erosion rates are currently estimated from suspended sediment loads in rivers in the Himalaya. These typically underestimate the real erosion rate since bed-load is not measured during times of heavy flood, and it is difficult to integrate widely varying suspended load measurements over many years. An alternative way to measure erosion rate is to measure the rate of change of gravity in a region of uplift. If a control point moves vertically it should be accompanied by a reduction in gravity as the point moves away from the Earth's center of mass. There is a difference in the change of gravity between uplift with and without erosion corresponding to the difference between the free-air gradient and the gradient in the acceleration due to gravity caused by a corresponding thickness of rock. Essentially gravity should change precisely in accord with a change in elevation of the point in a free-air gradient if erosion equals uplift rate. We were funded by NASA to undertake a measurement of absolute gravity simultaneously with measurements of GPS height within the Himalaya. Since both absolute gravity and time are known in an absolute sense to 1 part in 10(exp 10) it is possible to estimate gravity with a precision of 0.1 mu gal. Known systematic errors reduce the measurement to an absolute uncertainty of 6 mu gal. The free air gradient at the point of measurement is typically about 3 mu gals/cm. At Simikot where our experiment was conducted we determined a vertical gravity gradient of 4.4 mu gals/cm.

Bilham, Roger↗
NASA NTRS1989

The KAPTUR environment: An operations concept

This report presents a high-level specification and operations concept for KAPTUR, a development environment based on knowledge acquisition for preservation of tradeoffs and underlying rationales. KAPTUR is intended to do what its name implies: to capture knowledge that is required or generated during the development process, but that is often lost because it is contextual, i.e., it does not appear directly in the end-products of development. Such knowledge includes issues that were raised during development, alternatives that were considered, and the reasons for choosing one alternative over others. Contextual information is usually only maintained as a memory in a developer's mind. As time passes, the memories become more vague and individuals become unavailable, and eventually the knowledge is lost. KAPTUR seeks to mitigate this process of attrition by recording and organizing contextual knowledge as it is generated.

Source record↗
NASA NTRS1994

The Effect of Polymer Char on Nitridation Kinetics of Silicon

Effects of polymer char on nitridation kinetics of attrition milled silicon powder have been investigated from 1200 to 1350 C. Results indicate that at and above 1250 C, the silicon compacts containing 3.5 wt percent polymer char were fully converted to Si3N4 after 24 hr exposure in nitrogen. In contrast, the silicon compacts without polymer char could not be fully converted to Si3N4 at 1350 C under similar exposure conditions. At 1250 and 1350 C, the silicon compacts with polymer char showed faster nitridation kinetics than those without the polymer char. As the polymer char content is increased, the amount of SiC in the nitrided material is also increased. By adding small amounts (approx. 2.5 wt percent) of NiO, the silicon compacts containing polymer char can be completely nitrided at 1200 C. The probable mechanism for the accelerated nitridation of silicon containing polymer char is discussed.

Chan, Rickmond C.↗