Spherulitic textures in glassy and crystalline rocks
Cooling history of magma containing spherulite growth forms on basis of morphological variations in glassy and crystalline rocks
Lofgren, G.↗
SEARCH · Search NASA
Results for “glassy”
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Biaxial stress relaxation in glassy polymers - Polymethylmethacrylate.
Biaxial stress relaxation studies were performed on glassy polymethylmethacrylate in combined torsion-tension strain fields using a specially designed apparatus with exceptionally high stiffness and low cross talk between the torsional and tensile load measuring transducers. It was found that at low strain levels uniaxial tension relaxation is slower than pure torsion relaxation; tensile-component relaxation rates are unaffected by the level of torsional strain; torsional-component relaxation rates decrease as tensile strain is increased; uniaxial tension relaxation rates approach the pure torsion rates at higher strains (about 2%). A phenomenological treatment is presented which shows that relaxation rates can be coupled to the strain fields in which they are observed and yet be consistent with the concepts of linear viscoelasticity and the Boltzmann superposition integral.
Sternstein, S. S.↗
Surface temperatures and glassy state investigations in tribology, part 1
The research in this report is divided into two categories: (1) lubricant rheological behavior, and (2) thermal behavior of a simulated elastohydrodynamic contact. The studies of the lubricant rheological behavior consists of high pressure, low shear rate viscosity measurements, viscoelastic transition measurements, by volume dilatometry, dielectric transitions at atmospheric pressure and light scattering transitions. Lubricant shear stress-strain behavior in the amorphous glassy state was measured on several fluids. It appears clear from these investigations that many lubricants undergo viscoplastic transitions in typical EHD contacts and that the lubricant has a limiting maximum shear stress it can support which in turn will determine the traction in the contact except in cases of very low slide-roll ratio. Surface temperature measurements were made for a naphthenic mineral oil and a polyphenyl ether. The maximum surface temperature in these experiments was approximately symmetrical about the zero slide-roll ration except for absolute values of slide-roll ratio greater than about 0.9. Additional surface temperature measurements were made in contacts with rough surfaces where the composite surface roughness was approximately equal to the EHD film thickness. A regression analysis was done to obtain a predictive equation for surface temperatures as a function of pressure, sliding speed, and surface roughness. A correction factor for surface roughness effects to the typical flash temperature analysis was found.
Winer, W. O.↗
Scanning Electron Microscopy and Petrography of Glassy Particles Produced by Lava Fountain Eruptions
A conceptual model of a lava fountain consists of a vent, spatter ramparts, fountain column, downwind plume and associated pumice deposits. Glassy particles produced by lava fountain eruptions consist primarily of sideromelane glass and minor to moderate amounts of vesicles and crystals. Particles are classified on the basis of morphology as: (1) spherical, (2) elongate, (3) glass-coated mineral grain, (4) shard, (5) reticulite, (6) composite particle, and (7) lithic fragment.
Ladle, G. H.↗
Sublimate morphology on 74001 and 74002 orange and black glassy droplets
SEM-EDX analysis of the surface morphology of the 74001 and 74002 orange and black glassy droplets has revealed the presence of ubiquitous micromound coatings. Assuming that the diameter of an individual micromound is an indication of total coating thickness, then the thickness of this volatile and metal-rich layer ranges from less than 20 A to over 300 A in thickness. On rare droplets the micromound coating is partially covered by a sparse population of crystals and masses that are essentially NaCl in composition. Additionally, an irregular mass on the surface of one black droplet may contain free sulfur. Amoeboid masses of iron, some with incipient crystal faces, are also present on a few droplet surfaces. The above features, i.e., halite crystals, sulfur-rich masses and amoeboid iron, are rare; the more common occurrence of metals and volatiles is in the micromound coating. Based on our observations of several hundred spheres from both Apollo and Luna missions, the classic micromound coating is unique to the Apollo 15 green and Apollo 17 orange and black droplets. Although some investigators have proposed various impact sequences to produce these unique droplets, the volcanic fire fountain origin is favored.
Clanton, U. S.↗
Metallic particles in the glassy constituents of three lunar highland samples 65315, 67435 and 78235
Electron probe microanalysis and analytical electron microscopy techniques were employed to obtain structural and chemical analyses of metal particles in the size range of less than 1000 A and greater than 5 microns from the glassy constituents of 3 lunar highland samples 65315, 67435 and 78235. Most of the micron size metal particles in the glass coatings of the three samples are of meteoritic Co-Ni content. The Ni content of submicron metal often differs significantly from the micron size metal in the same glass. This difference can be explained by one of 3 reasons: (a) the presence of metal of different sizes and Ni contents in the rock prior to the shock event, (b) the presence of metal particles in the lunar soil of meteoritic or variable Ni content which were incorporated when the glass formed and (c) the production of submicroscopic Fe metal from the reduction of Fe(+2) in the shock produced melt.
Mehta, S.↗
Mechanisms of devitrification of grain boundary glassy phases in Si3N4 materials
Changes in the grain boundary (g.b.) phases of Si3N4 are analyzed, the effects of composition and thermal history on devitrification of the g.b. phases are determined, devitrification of the g.b. phases of Si3N are related to mechanical behavior and oxidation sensitivity of the material. The phase relationships that occur within the grain boundaries of Si3N4 containing various densification aids are reviewed. Comparisons of the effects of MgO, Y2O3, CeO2, and Y2O3 + AL2O3 are made in terms of the phase equilibria of the Si3N4 + SiO2 + additive compositional system. Two new equilibrium phase diagrams for the Si3N4-SiO2 and Y2O3 and Si3N4-SiO2-Ce2O3 systems are preented. The effects of Y2O3 vs CeO2 densification aids on the fracture surfaces of Si3N4 are compared. Auger electron spectroscopy shows that both oxides are concentrated within the fracture surface. Scanning electron microscopy shows evidence that Si3N4 with CeO2 formed an intergranular structure of fine grained oxynitride reaction products, as predicted by phase quilibria, whereas the Y2O3 containing sample shows evidence of an intergranular glassy phase.
Hench, L. L.↗
Crystallization of the glassy phase of grain boundaries in silicon nitride
Three types of hot-pressed silicon nitride specimens (containing 5wt% Y2O3 and 2wt% Al2O3 additives) which were subjected to different temperature heat treatments were studied by X-ray diffraction, X-ray microanalysis and high resolution electron microscopy. The results indicated that there were phase changes in the grain boundaries after heat treatment and the glassy phase at the grain boundaries was crystallized by heat treatment.
Jefferson, D. A.↗
Absorption Of Gases By Glassy Polymers
Report discusses solubility of gas in glassy polymer, both above and below glass-transition temperature (Tg). Thermodynamic arguments brought to bear on previously-developed mathematical models, result being new model that enables calculation of infinite-dilution partial molar volume of solvent in glass or liquid solvent from data on pressure, volume, and temperature of solute in equilibrium with solvent.
Fedors, Robert F.↗
Equation of state of heated glassy carbon
New Hugoniot data are presented for glassy carbon preheated to 1550 K and shocked to 20 GPa. The high-temperature Hugoniot is very similar to the principal Hugoniot. This results argues against the diffusional mechanism for the shock-induced transformaton of amorphous carbon to diamond, although the present results are obviously limited to below 20 GPa. This study provides the first Higoniot data for carbon preheated to significantly high temperatures.
Sekine, Toshimori↗
Free Volume in Glassy Poly(arylene Ether Ketone)s
Amorphous polyarylene ether ketones were examined in the glassy state by positron annihilation lifetime spectroscopy ( PALS ) and in the melt by standard rheological techniques. Specimens were well-characterized fractions of two isomeric structures. PALS clearly shows that the polymer with meta linkages in its backbone contains larger voids (greater than 0.25 nm radius). Thus despite their similar bulk densities, the two materials must pack very differently on a local scale. On the other hand, the free volumes inferred from the WLF treatment of melt viscosity data are practically identical in both materials ca. 4% at T(sub g). The comparison between techniques sheds some light on the distribution of free volume.
Hinkley, J. A.↗
A Novel Method for Electroplating Ultra-High-Strength Glassy Metals
A novel method for electroplating ultra-high-strength glassy metals, nickel-phosphorous and nickel-cobalt-phosphorous, has been developed at NASA Marshall Space Flight Center, cooperatively with the University of Alabama in Huntsville. Traditionally, thin coatings of these metals are achieved via electroless deposition. Benefits of the new electrolytic process include thick, low-stress deposits, free standing shapes, lower plating temperature, low maintenance, and safer operation with substantially lower cost.
Ramsey, Brian↗
Potential of Glassy Carbon and Silicon Carbide Photonic Structures as Electromagnetic Radiation Shields for Atmospheric Re-entry
During high-velocity atmospheric entries, space vehicles can be exposed to strong electromagnetic radiation from ionized gas in the shock layer. Glassy carbon (GC) and silicon carbide (SiC) are candidate thermal protection materials due to their high melting point and also their good thermal and mechanical properties. Based on data from shock tube experiments, a significant fraction of radiation at hypersonic entry conditions is in the frequency range from 215 to 415 THz. We propose and analyze SiC and GC photonic structures to increase the reflection of radiation in that range. For this purpose, we performed numerical optimizations of various structures using an evolutionary strategy. Among the considered structures are layered, porous, woodpile, inverse opal and guided-mode resonance structures. In order to estimate the impact of fabrication inaccuracies, the sensitivity of the reflectivity to structural imperfections is analyzed. We estimate that the reflectivity of GC photonic structures is limited to 38% in the aforementioned range, due to material absorption. However, GC material can be effective for photonic reflection of individual, strong spectral line. SiC on the other hand can be used to design a good reflector for the entire frequency range.
Komarevskiy,Nikolay↗
Memory and rejuvenation in glassy systems
Here, the memory effect in a single crystal spin glass (Cu 0.92 Mn 0.08 ) has been measured using 1 Hz ac susceptibility measurements over a reduced temperature range of 0.4 - 0.7 T g and a model of the memory effect has been developed. A double-waiting-time protocol is carried out where the spin glass is first allowed to age at a temperature below T g , T w$_{1}$ , followed by a second aging 4 K lower, T w$_{2}$ . The 4 K separation is sufficient to ensure rejuvenation has occurred. The model is based on calculating overlaps between the growth of the correlation lengths at the two temperatures. It accounts for the absolute magnitude of the memory effect as a function of both waiting times and temperatures. The data can be explained by the memory loss being a function of the relative change in the correlated volume at the first waiting temperature due to growth in the correlations at the second waiting temperature.
36 MATERIALS SCIENCE↗
Unveiling the structural transformations in glassy solid electrolyte adapted to high-stress cycles
Brittleness of glass–ceramic and ceramic ion conductors is considered as a main roadblock for their implementation as electrolytes in solid-state batteries where the fractures often occur due to the pressure exerted by metallic lithium. In this regard, nano- and micro-scale ductility of the solid electrolyte allows reducing such pressure without formation of cracks. Among different types of solid state ion conductors, phosphate invert glasses seem to be promising in achieving such ductility. We report the mechanical behavior of lithium phosphorous oxynitride (LiPON) invert glass probed by static and cyclic nanoindentation. Repeated application of high intensity stress results in densification and shear deformation of material allowing LiPON to accommodate the ~ 22% nominal strain imposed by the nanoindenter without cracking. Ability to do this under repeated loading indicates robustness of LiPON when used in lithium metal batteries under cyclic charge and discharge. Using Raman spectroscopy with unsupervised K-means clustering we reveal pressure-induced formation of P 2 O 7 units which migrate to the periphery of the residual hardness impressions with cycling resulting in surface morphology of LiPON superficially similar to that of deformed bulk metallic glass.
36 MATERIALS SCIENCE↗