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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Dual photon effects in nitrogen dioxide photolysis

A previous study demonstrated two-photon consecutive absorption as being the most probable mechanism for the photodissociation of NO2 using a pulsed ruby laser at 6943 A. Additional data discussed here confirmed this and also examined an associated phenomenon, that of multiphoton induced fluorescence. The dissociation of NO2 by ON-O bond cleavage requires 3.4 eV, while the laser energy corresponds to 1.785 eV. The pooling of the energy of two photons would give more than enough energy to dissociate the NO2 into NO + O. Several mechanisms including (1) simultaneous absorption of two photons; (2) reaction of two singly excited NO2; (3) reaction of a singly excited NO2 with a ground state NO2; and (4) consecutive absorption of two photons were examined.

Hakala, D.↗
NASA NTRS1974

Pyrolysis of amino acids - Mechanistic considerations

Pyrolysis of several structurally different amino acids in a column at 500 C showed differences in the mechanisms and final products. The aliphatic protein amino acids decompose mainly by simple decarboxylation and condensation reactions, while the beta amino acids undergo deamination to unsaturated acids. Alpha amino acids with alpha alkyl substituents undergo an unusual intramolecular SN1 reaction with the formation of an intermediate alpha lactone which decomposes to yield a ketone. The alpha alkyl substituents appear to stabilize the developing negative charge formed by partial heterolytic cleavage of the alpha carbon - NH3 bond. The gamma and delta amino acids give 2-pyrrolidinone and 2-piperidone respectively, while the epsilon acids yield mixed products.

Ratcliff, M. A., Jr.↗
NASA NTRS1974

Social cost considerations and legal constraints in implementing modular integrated utility systems

Social costs associated with the design, demonstration, and implementation of the Modular Integrated Utility System are considered including the social climate of communities, leadership patterns, conflicts and cleavages, specific developmental values, MIUS utility goal assessment, and the suitability of certian alternative options for use in a program of implementation. General considerations are discussed in the field of socio-technological planning. These include guidelines for understanding the conflict and diversity; some relevant goal choices and ideas useful to planners of the MIUS facility.

Lede, N. W.↗
NASA NTRS1975

Fractography of the high temperature hydrogen attack of a medium carbon steel

Microscopic fracture processes were studied which are associated with hydrogen attack of a medium carbon steel in a well-controlled, high-temperature, high-purity hydrogen environment. Exposure to a hydrogen pressure and temperature of 3.5 MN/m2 and 575 C was found to degrade room temperature tensile properties with increasing exposure time. After 408 hr, yield and ultimate strengths were reduced by more than 40 percent and elongation was reduced to less than 2 percent. Initial fissure formation was found to be associated with manganese rich particles, most probably manganese oxide, aligned in the microstructure during the rolling operation. Fissure growth was found to be associated with a reduction in carbide content of the microstructure and was inhibited by the depletion of carbon. The interior surfaces of sectioned fissures or bubbles exhibit both primary and secondary cracking by intergranular separation. The grain surfaces were rough and rounded, suggesting a diffusion-associated separation process. Specimens that failed at room temperature after exposure to hydrogen were found to exhibit mixed mode fracture having varying amounts of intergranular separation, dimple formation, and cleavage, depending on exposure time.

Melson, H. G.↗
NASA NTRS1974

Comparison of fracture mechanisms for carbon-epoxy composites under tensile loading

The effects of oxidative surface treatments and differences in resin crack sensitivity on the tensile properties of carbon-epoxy composites have been investigated. A comparison of the fracture mechanisms for two different fiber batches was made in both model and engineering composites, using unmodified and modified epoxy resin. It has been observed that two distinct characteristics occur in the fracture surfaces of most engineering composites; first, fibers which fracture at the surface result in cleavage failure and, second, those which have fractured elsewhere and pulled out. A detailed discussion of these observations is contained in this paper.

Mazzio, V. F.↗
NASA NTRS1975

Experimental shock metamorphism of maximum microcline

A series of recovery experiments are conducted to study the behavior of single-crystal perthitic maximum microcline shock-loaded to a peak pressure of 417 kbar. Microcline is found to deform in a manner similar to quartz and other alkali feldspars. It is observed that shock-induced cleavages occur initially at or slightly below the Hugoniot elastic limit (60-85 kbar), that shock-induced rather than thermal disordering begins above the Hugoniot elastic limit, and that all types of planar elements form parallel to crystallographic planes of low Miller indices. When increasing pressure, it is found that bulk density, refractive indices, and birefringence of the recovered material decrease and approach diaplectic glass values, whereas disappearance and weakening of reflections in Debye-Sherrer patterns are due to disordering of the feldspar lattice.

Robertson, P. B.↗
NASA NTRS1976

Rolling-contact deformation of MgO single crystals

Magnesium oxide single crystals were used as a model bearing material and deformed by rolling contact with a steel ball 0.64 cm in diameter. A dependence of depth of slip on rolling velocity which persisted with increasing numbers of rolling-contact cycles was discovered. The track width, track hardness and dislocation interactions as observed by transmission electron microscopy all increased in a consistent manner with increasing cycles. The rolling-contact state of stress produces a high density of dislocations in a localized zone. Dislocation interaction in this zone produces cleavage-type cracks after a large number of rolling-contact cycles. The orientation of the crystal influences the character of dislocation accumulation.

Dufrane, K. F.↗
NASA NTRS1977

Friction, deformation and fracture of single-crystal silicon carbide

Friction experiments were conducted with hemispherical and conical diamond riders sliding on the basal plane of silicon carbide. The results indicate that, when deformation is primarily elastic, the friction does not depend on crystallographic orientation and there is no detectable fracture or cracking. When, however, plastic deformation occurs, silicon carbide exhibits anisotropic friction and deformation behavior. Surface fracture crack patterns surrounding wear tracks are observed to be of three types. The crack-geometries of two types are generally independent of orientation, the third crack, however, depends on the orientation. All surface cracks extend into subsurface. Anisotropic friction, deformation and fracture on the basal plane are primarily controlled by the slip system and cleavage.

Miyoshi, K.↗
NASA NTRS1977

Friction and deformation behavior of single-crystal silicon carbide

Friction and deformation studies were conducted with single-crystal silicon carbide in sliding contact with diamond. When the radius of curvature of the spherical diamond rider was large (0.3), deformation of silicon carbide was primarily elastic. Under these conditions the friction coefficient was low and did not show a dependence on the silicon carbide orientation. Further, there was no detectable cracking of the silicon carbide surfaces. When smaller radii of curvature of the spherical diamond riders (0.15 and 0.02 mm) or a conical diamond rider was used, plastic grooving occured and the silicon carbide exhibited anisotropic friction and deformation behavior. Under these conditions the friction coefficient depended on load. Anisotropic friction and deformation of the basal plane of silicon carbide was controlled by the slip system. 10101120and cleavage of1010.

Miyoshi, K.↗
NASA NTRS1976

Photoionization and ion cyclotron resonance studies of the ion chemistry of ethylene oxide

The formation of the ethylene oxide molecular ion and its subsequent ion-molecule reactions leading to the products C2H5O(+) and C3H5O(+) have been studied using time-resolved photoionization mass spectroscopy, ion cyclotron resonance spectroscopy, and photoelectron spectroscopy. An examination of the effects of internal energy on reactivity shows that the ratio of C3H5O(+) to C2H5O(+) increases by an order of magnitude with a single quantum of vibrational energy. The formation of (C2H4O/+/)-asterisk in a collision-induced isomerization is found which yields a ring-opened structure by C-C bond cleavage. The relaxed ring-opened C2H4O(+) ion reacts with neutral ethylene oxide by CH2(+) transfer to yield an intermediate product ion C3H6O(+) which gives C3H5O(+) by loss of H.

Corderman, R. R.↗
NASA NTRS1978

Friction and wear behavior of single-crystal silicon carbide in sliding contact with various metals

Sliding friction experiments were conducted with single-crystal silicon carbide in contact with various metals. Results indicate the coefficient of friction is related to the relative chemical activity of the metals. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to silicon carbide. The chemical activity of the metal and its shear modulus may play important roles in metal transfer, the form of the wear debris and the surface roughness of the metal wear scar. The more active the metal, and the less resistance to shear, the greater the transfer to silicon carbide and the rougher the wear scar on the surface of the metal. Hexagon shaped cracking and fracturing formed by cleavage of both prismatic and basal planes is observed on the silicon carbide surface.

Miyoshi, K.↗
NASA NTRS1978

Wear of single-crystal silicon carbide in contact with various metals in vacuum

Sliding friction experiments were conducted in vacuum with single crystal silicon carbide (0001) surface in contact with transition metals (tungsten, iron, rhodium, nickel, titanium, and cobalt), copper, and aluminum. The hexagon shaped cracking and fracturing of silicon carbide that occurred is believed to be due to cleavages of both the prismatic and basal planes. The silicon carbide wear debris, which was produced by brittle fracture, slides or rolls on both the metal and silicon carbide and produces grooves and indentations on these surfaces. The wear scars of aluminum and titanium, which have much stronger chemical affinity for silicon and carbon, are generally rougher than those of the other metals. Fracturing and cracking along the grain boundary of rhodium and tungsten were observed. These may be primarily due to the greater shear moduli of the metals.

Miyoshi, K.↗
NASA NTRS1978

Microstructure and mechanical properties of quenched and tempered 300M steel

Type 300M steel, which is being used for the landing gear on the space shuttle orbiter, was subjected to a wide range of quenched and tempered heat treatments. The plane-strain fracture toughness and the tensile ultimate and yield strengths were evaluated. Cryogenic mechanical properties were obtained for conventionally heat-treated steel. The microstructure of all heat-treated test coupons was studied both optically and by transmission electron microscopy. Fracture surfaces were studied by means of scanning electron microscopy. Results indicate that substantial improvement in toughness with no loss in strength can be accomplished in quenched and tempered steel by austenitizing at 1255 K or higher. Low fracture toughness in conventionally austenitized 300M steel (1144 K) appears to be caused by undissolved precipitates, seen both in the submicrostructure and on the fracture surface, which promote failure by quasi-cleavage. The precipitates appeared to dissolve in the range 1200 to 1255 K.

Youngblood, J. L.↗
NASA NTRS1978

Mechanistic possibilities in prebiotic thiophosphate chemistry

The two types of thiophosphate reactivities were studied in a system that involves reactions of 5'-substituted adenosine derivatives. In this system, both nucleophilic displacement on carbon and P-S cleavage are possible. The products and possible mechanisms of cyclization experiments involving different leaving groups are reported. The data indicate superior reactivity of the 3'-OH of the ribonucleoside, although in most other systems the 2'-OH is found to show superior reactivity. It is suggested that thiophosphates might play a role in prebiotic activation and phosphorylation reactions.

Kapovits, I.↗
NASA NTRS1978

Quasi-microscope concept for planetary missions - Stereo

The quasi-microscope has been used for stereo pictures using a small aperture placed at the right and left over the entrance aperture. A 16-degree stereo view angle yields an enhanced stereo effect. When viewed upward through a transparent support, all grains come into focus. The technique may be used for determining mineral constituents on the basis of cleavage and fracture patterns, grain details, and surface slopes used in estimating single-particle albedo and the illumination of scattering profiles.

Burcher, E. E.↗
NASA NTRS1978

Friction and wear behavior of single-crystal silicon carbide in sliding contact with various metals

Sliding friction experiments were conducted with single-crystal silicon carbide in contact with various metals. Results indicate the coefficient of friction is related to the relative chemical activity of the metals. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to silicon carbide. The chemical activity of the metal and its shear modulus may play important roles in metal-transfer, the form of the wear debris and the surface roughness of the metal wear scar. The more active the metal, and the less resistance to shear, the greater the transfer to silicon carbide and the rougher the wear scar on the surface of the metal. Hexagon-shaped cracking and fracturing formed by cleavage of both prismatic and basal planes is observed on the silicon carbide surface.

Miyoshi, K.↗
NASA NTRS1978

Anisotropic friction and wear of single-crystal manganese-zinc ferrite in contact with itself

Sliding friction experiments were conducted with manganese-zinc ferrite (100), (110), (111), and (211) planes in contact with themselves. Mating the highest-atomic-density directions, (110), of matched crystallographic planes resulted in the lowest coefficients of friction. Mating matched (same) high-atomic-density planes and matched (same)crystallographic directions resulted in low coefficients of friction. Mating dissimilar crystallographic planes, however, did not give significantly different friction results from those with matched planes. Sliding caused cracking and the formation of hexagonal- and rectangular-platelet wear debris on ferrite surfaces, primarily from cleavage of the (110) planes.

Miyoshi, K.↗
NASA NTRS1979

Friction and wear of single-crystal manganese-zinc ferrite

Sliding friction experiments were conducted with single crystal manganese-zinc ferrite in contact with itself and with transition metals. Results indicate mating highest atomic density directions (110) on matched crystallographic planes exhibit the lowest coefficient of friction, indicating that direction is important in the friction behavior of ferrite. Matched parallel high atomic density planes and crystallographic directions at the interface exhibit low coefficients of friction. The coefficients of friction for ferrite in contact with various metals are related to the relative chemical activity of these metals. The more active the metal, the higher the coefficient of friction. Cracking and the formation of hexagon- and rectangular-shaped platelet wear debris due to cleavages of (110) planes are observed on the ferrite surfaces as a result of sliding.

Miyoshi, K.↗