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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Tribological properties of boron nitride synthesized by ion beam deposition

The adhesion and friction behavior of boron nitride films on 440 C bearing stainless steel substrates was examined. The thin films containing the boron nitride were synthesized using an ion beam extracted from a borazine plasma. Sliding friction experiments were conducted with BN in sliding contact with itself and various transition metals. It is indicated that the surfaces of atomically cleaned BN coating film contain a small amount of oxides and carbides, in addition to boron nitride. The coefficients of friction for the BN in contact with metals are related to the relative chemical activity of the metals. The more active the metal, the higher is the coefficient of friction. The adsorption of oxygen on clean metal and BN increases the shear strength of the metal - BN contact and increases the friction. The friction for BN-BN contact is a function of the shear strength of the elastic contacts. Clean BN surfaces exhibit relatively strong interfacial adhesion and high friction. The presence of adsorbates such as adventitious carbon contaminants on the BN surfaces reduces the shear strength of the contact area. In contrast, chemically adsorbed oxygen enhances the shear strength of the BN-BN contact and increases the friction.

Miyoshi, K.↗
NASA NTRS2012

Is Water a Universal Solvent for Life?

There are strong reasons to believe that the laws, principles and constraints of physics and chemistry are universal. It is much less clear how this universality translates into our understanding of the origins of life. Conventionally, discussions of this topic focus on chemistry that must be sufficiently rich to seed life. Although this is clearly a prerequisite for the emergence of living systems, I propose to focus instead on self-organization of matter into functional structures capable of reproduction, evolution and responding to environmental changes. In biology, most essential functions are largely mediated by noncovalent interactions (interactions that do not involve making or breaking chemical bonds). Forming chemical bonds is only a small part of what living systems do. There are specific implications of this point of view for universality. I will concentrate on one of these implications. Strength of non-covalent interactions must be properly tuned. If they were too weak, the system would exhibit undesired, uncontrolled response to natural fluctuations of physical and chemical parameters. If they were too strong kinetics of biological processes would be slow and energetics costly. This balance, however, is not a natural property of complex chemical systems. Instead, it has to be achieved with the aid of an appropriate solvent for life. In particular, potential solvents for life must be characterized by a high dielectric constant to ensure solubility of polar species and sufficient flexibility of biological structures stabilized by electrostatic interactions. Among these solvents, water exhibits a remarkable trait that it also promotes solvophobic (hydrophobic) interactions between non-polar species, typically manifested by a tendency of these species to aggregate and minimize their contacts with the aqueous solvent. Hydrophobic interactions are responsible, at least in part, for many self-organization phenomena in biological systems, such as the formation of cellular boundary structures or protein folding. Strengths of electrostatic and hydrophobic interactions are similar and can be balanced over a wide range of temperatures, which considerably increases the repertoire of interactions that can be used to modulate biological functions. Some properties of water, e.g. its chemical activity against polymerization reactions, are considered as unfavorable to life. In actuality, this might be a favorable trait because life requires a balance between constructive and destructive processes. For example, molecules synthesized in response to specific conditions must be degraded once these conditions change. Otherwise regulation of biological processes would be virtually impossible. Water might not be the only liquid with favorable properties for supporting life. It has been proposed that formamide, which might be present elsewhere in the universe in sufficient quantities to warrant interest, could be a potential alternative to water for the origin of life. However, this will remain highly hypothetical until it is demonstrated in further studies on its physical, chemical and biological properties it is capable of mediating self-organization of matter and providing proper balance between different types of non-covalent interactions.

Pohorill, Andrew↗
NASA NTRS2005

Incorporation of a Chemical Equilibrium Equation of State into LOCI-Chem

Renewed interest in development of advanced high-speed transport, reentry vehicles and propulsion systems has led to a resurgence of research into high speed aerodynamics. As this flow regime is typically dominated by hot reacting gaseous flow, efficient models for the characteristic chemical activity are necessary for accurate and cost effective analysis and design of aerodynamic vehicles that transit this regime. The LOCI-Chem code recently developed by Ed Luke at Mississippi State University for NASA/MSFC and used by NASA/MSFC and SSC represents an important step in providing an accurate, efficient computational tool for the simulation of reacting flows through the use of finite-rate kinetics [3]. Finite rate chemistry however, requires the solution of an additional N-1 species mass conservation equations with source terms involving reaction kinetics that are not fully understood. In the equilibrium limit, where the reaction rates approach infinity, these equations become very stiff. Through the use of the assumption of local chemical equilibrium the set of governing equations is reduced back to the usual gas dynamic equations, and thus requires less computation, while still allowing for the inclusion of reacting flow phenomenology. The incorporation of a chemical equilibrium equation of state module into the LOCI-Chem code was the primary objective of the current research. The major goals of the project were: (1) the development of a chemical equilibrium composition solver, and (2) the incorporation of chemical equilibrium solver into LOCI-Chem. Due to time and resource constraints, code optimization was not considered unless it was important to the proper functioning of the code.

Cox, Carey F.↗
NASA NTRS1997

Metamorphism of Cosmic Dust: Processing from Circumstellar Outflows to the Cometary Regolith

Nucleation is a non-equilibrium process: the products of this process are seldom the most thermodynamically stable condensates but are instead those which form fastest. It should therefore not be surprising that grains formed in a circumstellar outflow will undergo some degree of metamorphism if they are annealed or are exposed to a chemically active reagent. Metamorphism of refractory particles continues in the interstellar medium (ISM) where the driving forces are sputtering by cosmic ray particles, annealing by high energy photons and grain destruction in supernova generated shocks. Studies of the depletion of the elements from the gas phase of the interstellar medium tell us that if grain destruction occurs with high efficiency in the ISM, then there must be some mechanism by which grains can be formed in the ISM. Various workers have shown that refractory mantles could form on refractory cores by radiation processing of organic ices. A similar process may operate to produce refractory inorganic mantles on grain cores which survived the supernova shocks. Most grains in a cloud which collapses to form a star will be destroyed; many of the surviving grains will be severely processed. Grains in the outermost regions of the nebula may survive relatively unchanged by thermal processing or hydration. It is these grains which we hope to find in comets. However, only those grains encased in ice at low temperature can be considered pristine since a considerable degree of hydrous alteration might occur in a cometary regolith if the comet enters the inner solar system. Some discussion of the physical, chemical and isotopic properties of a refractory grain at each stage of its life cycle will be attempted based on the limited laboratory data available to date. Suggestions will be made concerning the types of experimental data which are needed in order to better understand the processing history of cosmic dust.

Nuth, Joseph A., III↗
NASA NTRS1993

Magmatic volatiles and the weathering of Mars

The sources for volatiles on Mars have been the subject of many hypotheses for exogenous influences including late accretion of volatile-enriched material, impact devolatilization to create massive early atmospheres, and even major bombardment by comets. However, the inventory of chemically active volatiles observable at the contemporary surface of Mars is consistent with domination by endogenous, subsequent planetary processes, viz., persistent magmatic outgassing. Volcanism on Mars has been widespread in both space and time. Notwithstanding important specific differences between the mantles of Earth and Mars, the geochemical similarities are such that the suite of gases emitted from Martian volcanic activity should include H2O, CO2, S-containing gases (e.g. H2S and/or SO2), and Cl-containing gases (e.g., Cl2 and/or HCl). H2O and CO2 exist in the atmosphere of Mars. Both are also present as surface condensates. However, spectroscopic observations of the Martian atmosphere clearly show that the S- and Cl-containing gases are severely depleted, with upper limits of less than or equal to 10(exp -7) the abundance of CO2. Likewise, there is no evidence of polar condensates of compounds of these elements as there is for CO2 and H2O. Within the soil, on the other hand, there has been direct measurement of incorporated H2O and abundant compounds containing S and Cl. Barring some as yet implausible geochemical sequestering process, the S/Cl ratio of about 6:1 in Martian soils implies a limit of 5% on the contribution of matter of solarlike composition (e.g., carbonaceous chondrite or cometary material) to these volatiles. Hence, exogenous sources are minor or not yet observed. From analysis of elemental trends in Martian soils, it has been recently shown that a simple two-component model can satisfy the Viking in situ measurements. Component A includes Si and most or all the Al, Ca, Ti, and Fe. Component B, taken as 16 +/- 3% by weight of the total, contains S and most or all the Cl and Mg. These results constrain several models of Martian soil mineralogy but are consistent with a mixture of silicates (such as Fe-rich clays and accessory minerals and soluble salts). The overall element profile is notably like shergottites, with significant incorporation of chemically reactive atmospheric gases from magmatic degassing.

Clark, B. C.↗
NASA NTRS1966

Lubricants, bearings and seals

Extreme temperature, vacuum, and chemically active fluid effects on bearing and sealing materials and lubricants

BEARING↗
NASA NTRS1968

Pyrotechnic device provides one-shot heat source

Pyrotechnic heater provides a one-shot heat source capable of creating a predetermined temperature around sealed packages. It is composed of a blend of an active chemical element and another compound which reacts exothermically when ignited and produces fixed quantities of heat.

Haller, H. C.↗
NASA NTRS1972

Adhesion of metals to a clean iron surface studied with LEED and Auger emission spectroscopy.

Discussion of the results of adhesion experiments conducted with various metals contacting a clean iron surface. The metals included gold, silver, nickel, platinum, lead, tantalum, aluminum, and cobalt. Some of the metals were examined with oxygen present on their surface as well as in the clean state. The results indicate that, with the various metals contacting iron, the cohesively weaker will adhere and transfer to the cohesively stronger. The chemical activity of the metal also influenced the adhesive forces measured. With oxygen present on the metal surface, the adhesive forces measured could be correlated with the binding energy of the metal to oxygen.

Buckley, D. H.↗
NASA NTRS1973

Friction, wear, and transfer of carbon and graphite to copper, chromium, and aluminum metal surfaces in vacuum

Sliding friction experiments were conducted with amorphous and fully graphitized carbons sliding on copper and on films of chromium and aluminum on copper. Auger emission spectroscopy analysis was used to monitor carbon transfer to the metal surfaces. Friction and wear were also measured. Metal surfaces were examined both in the clean state and with normal oxides present. Results indicate that different metals have an important effect on friction, wear, and transfer characteristics. With amorphous carbon, the least chemically active metal gave the highest wear and amount of carbon transfer. Both forms of carbon gave lower friction and wear and lower transfer rates when in contact with clean, as opposed to oxide-covered, chromium surfaces. With copper, the reverse was true; cleaning was detrimental.

Buckley, D. H.↗
NASA NTRS1973

Friction and wear behavior of glasses and ceramics

Adhesion, friction, and wear behavior of glasses and ionic solids are reviewed. These materials are shown to behave in a manner similar to other solids with respect to adhesion. Their friction characteristics are shown to be sensitive to environmental constituents and surface films. This sensitivity can be related to a reduction in adhesive bonding and the changes in surficial mechanical behavior associated with Rehbinder and Joffe effects. Both friction and wear properties of ionic crystalline solids are highly anisotropic. With metals in contact with ionic solids the fracture strength of the ionic solid and the shear strength in the metal and those properties that determine these will dictate which of the materials undergoes adhesive wear. The chemical activity of the metal plays an important role in the nature and strength of the adhesive interfacial bond that develops between the metal and a glass or ionic solid.

Buckley, D. H.↗
NASA NTRS1974

Relation between surface slip topography and stress corrosion cracking in Ti-8 wt % Al

The deformation behavior of Ti-8 wt % Al has been investigated in an inert environment (air), and an aggressive environment (salt water). Details of surface slip geometry were examined by high resolution surface replicas at various stages of deformation in both environments. Specimens aged to contain a fine dispersion of Ti3Al precipitates failed by subcritical crack growth in salt water, whereas specimens in the single phase condition showed no effects of environment on the yield or fracture characteristics. The Ti3Al precipitates produce little change in strength level or slip character compared to the single phase alloy, and there is no evidence of any effects of environment on the character of surface slip. Rather, the presence of trenches along slip bands on the surface of aged specimens suggest that the specific effect of the Ti3Al precipitates is to render the surface slip steps chemically active relative to the surrounding matrix by slip induced dissolution of the particles.

Boyd, J. D.↗
NASA NTRS1975

Friction behavior of members of the platinum metals group with gold

The adhesion and friction behavior of the platinum metals group was examined with clean surfaces and surfaces selectively contaminated with oxygen, vinyl chloride (C2H3Cl), and methyl mercaptan (CH3SH). A pin or disk specimen configuration was used with the pin being a single crystal of gold of the (111) orientation and with the platinum metal disks also being single crystals of the (111) or (0001) orientation. Loads applied ranged from 1 to 10 g and a sliding velocity of 0.7 mm/min was employed. Results indicate adhesion and transfer of gold to all of the platinum metals. Despite this observation friction differences existed among the metals in the group. These differences are related to surface chemical activity. Adsorption of various friction reducing species was selective. With some adsorbates present strong adhesive forces between metals were still observed.

Buckley, D. H.↗
NASA NTRS1976

Rolling-element fatigue life with two synthetic cycloaliphatic traction fluids

The life potential of two synthetic cycloaliphatic hydrocarbon traction fluids in rolling element fatigue was evaluated in a five ball fatigue tester. Life comparisons with a MIL-L-23699 qualified tetraester oil showed that the traction test oils had good fatigue life performance, comparable to that of the tetraester oil. No statistically significant life differences between the traction fluids and the tetraester oil were exhibited under the accelerated fatigue test conditions. Erratic operating behavior was occasionally encountered during tests with the antiwear additive containing traction fluid for reasons thought to be related to excessive chemical activity under high contact pressure. This behavior occasionally resulted in premature test termination due to excessive surface distress and overheating.

Loewenthal, S. H.↗
NASA NTRS1976

The metal to metal interface and its effect on adhesion and friction

The nature of the interface, adhesion and friction properties of noble metals, platinum metals, Group IV (B) metals and transition metals were considered. The surface chemical activity of the noble and platinum metals is shown to effect metal to metal interfaces as does a valance bonding in the transition metals. With the Group IV (B) metals the degree of metallic nature of the elements is shown to effect interfacial behavior. The effect of surface segregation of alloy constituents such as silicon in iron and its influence on the metal to metal interface is discussed. In addition the effect of alloy constituents on changes in bulk properties such as transformations in tin are shown to effect interfacial adhesion and friction behavior.

Buckley, D. H.↗
NASA NTRS1976

Radical formation, chemical processing, and explosion of interstellar grains

The ultraviolet radiation in interstellar space is shown to create a sufficient steady-state density of free radicals in the grain mantle material consisting of oxygen, carbon, nitrogen, and hydrogen to satisfy the critical condition for initiation of chain reactions. The criterion for minimum critical particle size for maintaining the chain reaction is of the order of the larger grain sizes in a distribution satisfying the average extinction and polarization measures. The triggering of the explosion of interstellar grains leading to the ejection of complex interstellar molecules is shown to be most probable where the grains are largest and where radiation is suddenly introduced; i.e., in regions of new star formation. Similar conditions prevail at the boundaries between very dark clouds and H II regions. When the energy released by the chemical activity of the free radicals is inadequate to explode the grain, the resulting mantle material must consist of extremely large organic molecules which are much more resistant to the hostile environment of H II regions than the classical dirty-ice mantles made up of water, methane, and ammonia.

Greenberg, J. M.↗
NASA NTRS1976

The metal to metal interface and its effect on adhesion and friction

The paper considers the interface between two bulk metals and the effect of this interface on adhesive bonding, resistance to tangential displacements, friction and the interfacial transport from one surface to another. Using Auger emission spectroscopy, field ion microscopy, and low energy electron diffraction techniques, the influence of surface orientation, lattice registry, crystal lattice structure and defects, metal surface chemistry and alloying on the characteristics of the interface was studied for noble, platinum, transition, and Group 4B metals. With dissimilar metals in contact, epitaxial transfer of the cohesively weaker to the cohesively stronger metal has been observed. Surface chemical activity of the noble and platinum metals is shown to affect interfacial behavior as does a valence bonding in the transition metals, and the degree of metallic nature in the Group 4B elements. Alloying elements, e.g., Si and Fe, can alter interfacial behavior by segregation to the surface of metals or by altering bulk properties such as crystal transformation kinetics.

Buckley, D. H.↗