Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Mg2SiO4”

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.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Hydration-driven stabilization and volume collapse of grain boundaries in Mg2SiO4 forsterite predicted by first-principles simulations

Grain boundaries in mantle minerals are of critical importance to geophysical and geochemical processes of the Earth’s interior. One of the fundamental issues is to understand how the water (H 2 O) component influences the properties of grain boundaries in silicate materials. Here, we report the results of the structure and stability of several tilt grain boundaries in Mg 2 SiO 4 forsterite over the pressure range 0 to 15 GPa using density functional theory-based first-principles simulations. Here, the results suggest greater energetic stability and hydration-driven volume collapse (negative excess volume) at zero pressure for the majority of hydrous grain boundaries relative to the anhydrous (dry) ones. All the hydrous grain boundaries become increasingly favorable at elevated pressures as the calculated hydration enthalpy systematically decreases with increasing pressure. The hydrous components at the interfacial regions are predominantly in the hydroxyl form and, to a lesser extent, in the molecular H 2 O form. Their calculated ratio ranges from 1.6 to 8.7 among the different grain boundary configurations. Our structural analysis also reveals that the hydroxyls are bound to either both Mg and Si or to Mg only. In comparison, the molecular species are bound only to Mg sites. Besides direct oxygen-hydrogen bonding, intermolecular hydrogen bonding becomes important with compression. On the basis of our results, we suggest that local atomic rearrangements caused by dissociative adsorption of water facilitate efficient compaction of the boundary interfaces, which, in turn, results in greater relative stability of hydrous grain boundaries. This means that water prefers to be incorporated within the grain boundaries over the bulk of silicate materials.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1976

The origin of chondrules - Experimental investigation of metastable liquids in the system Mg2SiO4-SiO2

Laser-melted magnesium silicate droplets were supercooled 400-750 C below their equilibrium liquidus temperatures before crystallization and their texture was compared with that of meteoritic and lunar chondrules. Crystal morphology, width and texture were studied in relation to nucleation temperature and bulk composition. It was found that the only phase to nucleate from the forsterite-enstatite normative melts was forsterite. Highly siliceous glass, about 65% SiO2 by weight, was identified interstitially to the forsterite crystals in seven of the MgSiO4 spherules and was thought to be present in all.

Blander, M.↗
NASA NTRS1982

Olivine flotation and settling experiments on the join Mg2SiO4-Fe2SiO4

Results are presented of a study of some unusual density relations between olivine and coexisting liquid in the system fosterite-fayalite. At 1 atmosphere pressure it is found that olivine floats on its coexisting liquid for intermediate compositions on this binary because of extreme partitioning of Fe into the melt phase. At 20 kilobars, the usual behavior of olivine settling is found to occur because the partitioning of Fe in the melt is reduced, aided possibly by the dissolution of CO2 in the melt from the use of a graphite container. It is determined that olivine flotation and settling are rapid in a time period of only a few hours because viscosities are slightly greater than that of paraffin oil at room temperature. Some adcumulate textures with good triple junction grain boundaries are found to be developed. Observations of differentiated magmatic systems suggest that the mechanisms by which magmas can differentiate vary considerably in the ultramafic to tholeiitic compositional range.

Herzberg, C. T.↗
NASA NTRS1978

An experimental investigation of the condensation of silicate grains

Results are presented for a series of laboratory experiments designed to investigate the nucleation of small silicate grains from a vapor of astrophysically significant elements and compounds. In the experiments, magnesium silicate grains were condensed by simultaneously evaporating Mg and SiO solids into an atmosphere of argon or hydrogen at a pressure of a few torr. The results show that at low temperatures (up to a few hundred degrees C) the condensates are amorphous grains and have widely varying stoichiometries. The thermodynamically most stable compounds (Mg2SiO4, MgSiO3, SiO2) do not form readily, but all initial condensates can be converted to crystalline forsterite (Mg2SiO4) by heating to 1000 C in vacuum. At higher temperatures (above 700 K) it becomes more difficult to nucleate any silicates, and those that do form are amorphous, indicating that surface energies and kinetic effects are very important in determining under what conditions condensation will occur. The IR spectra of the experimentally produced magnesium silicates are found to have a strong resemblance to those observed in many astronomical clouds.

Day, K. L.↗
NASA NTRS1980

Infrared spectra of olivine polymorphs - Alpha, beta phase and spinel

The infrared absorption spectra of several olivines (alpha phase) and their corresponding beta phase (modified spinel) and spinel (gamma) high-pressure polymorphs are determined. Spectra were measured for ground and pressed samples of alpha and gamma A2SiO4, where A = Fe, Ni, Co; alpha and gamma Mg2GeO4; alpha Mg2SiO4; and beta Co2SiO4. The spectra are interpreted in terms of internal, tetrahedral and octagonal, and lattice vibration modes, and the spinel results are used to predict the spectrum of gamma Mg2SiO4. Analysis of spectra obtained from samples of gamma Mg2GeO4 heated to 730 and 1000 C provides evidence that partial inversion could occur in silicate spinels at elevated temperatures and pressures.

Jeanloz, R.↗
DOE OSTI2021

Thin Water Films Enable Low-Temperature Magnesite Growth Under Conditions Relevant to Geologic Carbon Sequestration

Injecting supercritical CO2 (scCO2) into basalt formations for long-term storage is a promising strategy for mitigating CO2 emissions. Mineral carbonation can result in permanent entrapment of CO2; however, carbonation kinetics in thin H2O films in humidified scCO2 is not well understood. We investigated forsterite (Mg2SiO4) carbonation to magnesite (MgCO3) via amorphous magnesium carbonate (AMC; MgCO3·xH2O, 0.5 < x < 1), with the goal to establish the fundamental controls on magnesite growth rates at low H2O activity and temperature. Experiments were conducted at 25, 40, and 50 °C in 90 bar CO2 with a H2O film thickness on forsterite that averaged 1.78 ± 0.05 monolayers. In situ infrared spectroscopy was used to monitor forsterite dissolution and the growth of AMC, magnesite, and amorphous SiO2 as a function of time. Geochemical kinetic modeling showed that magnesite was supersaturated by two to three orders of magnitude and grew according to a zero-order rate law. The results indicate that the main drivers for magnesite growth are sustained high supersaturation coupled with low H2O activity, a combination of thermodynamic conditions not attainable in bulk aqueous solution. This improved understanding of reaction kinetics can inform subsurface reactive transport models for better predictions of CO2 fate and transport.

Kerisit, Sebastien N.↗
DOE OSTI2020

Liquid-Vapor Coexistence and Critical Point of Mg 2 SiO 4 From Ab Initio Simulations

Hypervelocity impact-driven vaporization is characteristic of late-stage planet formation. Yet the behavior and properties of liquid-vapor mixtures of planetary materials of interest are typically unknown. Multiphase equations of state used in hydrodynamic simulations of planet impacts therefore lack reliable data for this important phenomenon. Here, we present the first constraints on the liquid-vapor critical point and coexistence phase boundary of Mg2SiO4 computed from ab initio molecular dynamics simulations. We found that the vapor is depleted in magnesium and enriched in silica and oxygen, while the coexisting liquid is enriched in magnesium and depleted in oxygen, from which we infer vaporization is incongruent. The critical point was estimated from an equation of state fit to the data. The results are in line with recent calculations of MgSiO3 and together confirm that extant multiphase equation of state (EOS) models used in planetary accretion modeling significantly underestimate the amount of supercritical material postimpact.

58 GEOSCIENCES↗
NASA NTRS1974

EPR measurement of the effect of glass composition on the oxidation states of europium

An investigation was conducted concerning the dependence of the concentration ratio of Eu(2+) to Eu(3+) on composition for silicate liquids whose compositional end members are CaAl2Si2O8 and MgSiO3, MG2SiO4, CaMgSi2O6, CaMgSiO4, CaSiO3, or Ca2SiO4. The liquids were quenched to produce glasses. An electron paramagnetic resonance spectrometer was used to determine the concentration ratios of Eu(2+) to Eu(3+) in the glasses.

Morris, R. V.↗
NASA NTRS1975

The effect of C/O ratio on the condensation of planetary material

The condensation temperatures of refractory silicates and oxides in a gas of cosmic composition are strongly dependent on the C/O ratio. As the ratio increases from 0.4 to 0.9, condensation temperatures of compounds such as Al2O3, Ca2Al2SiO7, MgAl2O4, Mg2SiO4, and MgSiO3 decrease by 50-100 degrees. As C/O increases from 0.9 to 1.0, these temperatures drop an additional 300-400 degrees. Other chemical differences result when C/O approximately equals or exceeds 0.9. A new suite of high-temperature minerals appears (graphite, CaS, Fe3C, SiC and TiN); the reaction CO + 3H2 yields CH4 + H2O proceeds to the right at higher temperatures; and iron, whose condensation temperature is unaffected, condenses at higher temperatures than any silicate or oxide.

Larimer, J. W.↗
NASA NTRS1980

Chemical and isotopic fractionation by grain size separates

Fractionation of refractory elements according to grain size is argued to occur during their growth. Two major modes should exist: (1) during thermal condensation sequences whenever the condensing phase (e.g. Mg2SiO4) does not alloy with the precondensed phase (e.g. MgAl2O4); (2) during accretion of gaseous atoms in the nonequilibrated interstellar medium. Processes dynamically sorting grains according to size (e.g. sedimentation) therefore are potentially capable of achieving fractionations normally attributed to separations of dust and gas. This paper considers the first mode during supernova condensation; however, it also can occur in an equilibrium solar condensation sequence owing to an overlooked freedom in that simplified description.

Clayton, D. D.↗
NASA NTRS1983

Temperatures of shock-induced shear instabilities and their relationship to fusion curves

New emission spectra for MgO and CaAl2Si2O8 (glass) are observed from 430 to 820 nm. Taken with previous data, it is suggested that transparent solids display three regimes of light emission upon shock compression to successively higher pressures: (1) characteristic radiation such as observed in MgO and previously in other minerals, (2) heterogeneous hot spot (greybody) radiation observed in CaAl2Si2O8 and previously in all transparent solids undergoing shock-induced phase transformations, and (3) blackbody emission observed in the high pressure phase regime in NaCl, SiO2, CaO, CaAl2Si2O8, and Mg2SiO4. The onset of the second regime may delineate the onset of shock-induced polymorphism whereas the onset of the third regime delineates the Hugoniot pressure required to achieve local thermal equilibrium in the shocked solid. It is also proposed that the hot spot temperatures and corresponding shock pressures determined in the second regime delineate points on the fusion curves of the high pressure phase.

Schmitt, D. R.↗
NASA NTRS1987

Thermally induced phase changes, lateral heterogeneity of the mantle, continental roots, and deep slab anomalies

Factors which influence the lateral heterogeneity in density and seismic velocity with depth in the upper earth mantle are discussed. It is emphasized that most of the increases in density and seismic velocity with depth are caused by pressure-induced solid-solid phase changes in the high-density high-velocity phases of mineral assemblage, due to variations in temperature. In particular, the ilmenite form of MgSiO3 and the gamma-spinel form of Mg2SiO4 have broad stability fields in cold mantle and are not stable in hotter mantle. It is emphasized that the density and velocity anomalies associated with temperature-induced phase changes in mineral assemblage must be taken into account in the thermal models of the slabs; when these effects are accounted for, the geoid and seismic anomalies associated with subducted slabs are consistent with slab confinement to the upper mantle and with layered models of mantle convection.

Anderson, Don L.↗
NASA NTRS1988

Laser action in chromium-doped forsterite

This paper reports on pulsed laser operation obtained in chromium-activated forsterite Cr(3+):Mg2SiO4 at room temperature. The spectrum of the free-running laser peaks at 1235 nm and a bandwidth of about 22 nm. The spectral range of the laser emission is expected to extend from 850 to 1300, provided the parasitic impurity absorption may be minimized by improved crystal growth techique.

Petricevic, V.↗
NASA NTRS1989

Nonradiative relaxation and laser action in tunable solid state laser crystals

Room-temperature pulsed laser action was obtained in chromium-activated forsterite (Cr:Mg2SiO4) for both 532 and 1064 nm pumping. Free running laser emission in both cases is centered at 1235 nm and has a bandwidth of approximately 30 nm. Slope efficiency as high as 22 percent was measured. Using different sets of output mirrors and a single birefrigent plate as the intracavity wavelength selecting element tunability over the 1167 to 1268 nm spectral range was demonstrated. Continuous wave laser operation at room temperature was obtained for 1064 nm pumping from a CW Nd:YAG laser. The output power slope efficiency is 6.8 percent. The gain cross section is estimated to be 1.1 x 10 to the 19th sq cm. Spectroscopic studies suggest that the laser action is due to a center other than the trivalent chromium (Cr 3+), presumably the tetravalent chromium (Cr 4+) in a tetrahedrally coordinated site.

Petricevic, V.↗