Dynamic compression and volatile release of carbonates

Particle velocity profiles upon shock compression and adiabatic release were measured for polycrystalline calcite (Solenhofen limestone) to 12–24 GPa and for porous calcite (Dover chalk, ρ_o = 1.40 g/cm^3, 49% porosity) to between 5 and 11 GPa. The electromagnetic particle velocity gauge method was used. Upon shock compression of Solenhofen limestone, the Hugoniot elastic limit was determined to vary from 0.36 to 0.45 GPa. Transition shocks at between 2.5 and 3.7 GPa, possibly arising from the calcite II-III transition, were observed. For the Solenhofen limestone, the release paths lie relatively close to the Hugoniot. Evidence for the occurrence of the calcite III-II transition upon release was observed, but no rarefaction shocks were detected. Initial release wave speeds suggest retention of shear strength up to at least 20 GPa, with a possible loss of shear strength at higher pressures. The measured equation of state is used to predict the fraction of material devolatilized upon adiabatic release as a function of shock pressure. The effect of ambient partial pressure of CO_2 on the calculations is demonstrated. P_(CO_2) should be taken into account in models of atmospheric evolution by means of impact-induced mineral devolatilization. Mass fractions of CO_2 released expected on the basis of a continuum model are much lower than determined experimentally. This discrepancy, and radiative characteristics of shocked calcite, indicate that localization of thermal energy (shear banding) occurs under shock compression even though no solid-solid transitions occur in this pressure range. Release adiabatic data indicate that Dover chalk loses its shear strength when shocked to 10 GPa pressure. At 5 GPa the present data are ambiguous regarding shear strength. For Dover chalk, continuum shock entropy calculations result in a minimum estimate of 90% devolatilization upon complete release from 10 GPa. For calcite, isentropic release paths from calculated continuum Hugoniot temperatures cross into the CaO (solid) + CO_2 (vapor) field at improbably low pressures (for example, 10 GPa for a shock pressure of 25 GPa). However, calculated isentropic release paths originating from PT points corresponding to previous color temperature under shock measurements cross into the melt plus vapor field at pressures greater than 0.5 GPa, suggesting that devolatilization is initiated at the shear banding sites

Lunar mining of oxygen using fluorine

Experiments during the first year of the project were directed towards generating elemental fluorine via the electrolysis of anhydrous molten fluorides. Na2SiF6 was dissolved in either molten NaBF4 or a eutectic (minimum-melting) mixture of KF-LiF-NaF and electrolyzed between 450 and 600 C to Si metal at the cathode and F2 gas at the anode. Ar gas was continuously passed through the system and F2 was trapped in a KBr furnace. Various anode and cathode materials were investigated. Despite many experimental difficulties, the capability of the process to produce elemental fluorine was demonstrated

Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: Implications for planetary accretion

Impact-induced devolatilization of porous serpentine was investigated using two independent experimental methods, the gas recovery and the solid recovery method, each yielding nearly identical results. For shock pressures near incipient devolatilization, the hydrogen isotopic composition of the evolved H2O is very close to that of the starting material. For shock pressures at which up to 12 percent impact-induced devolatilization occurs, the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H2O to H2 in gases recovered at these higher shock pressures, probably caused by reaction of evolved H2O with the metal gas recovery fixture. Gaseous H2O-H2 isotopic fractionation suggests high temperature isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition. Bulk gas-residual solid isotopic fractionations indicate nonequilibrium, kinetic control of gas-solid isotopic ratios. Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can strongly affect the long-term planetary isotopic ratios of planetary bodies, leaving the interiors enriched in deuterium. Depending on the model used for extrapolation of the isotopic fractionation to devolatilization fractions greater than those investigated experimentally can result from this process

Prediction of silicate melt viscosity from electrical conductivity : a model and its geophysical implications

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 1685–1692, doi:10.1002/ggge.20103.Our knowledge of magma dynamics would be improved if geophysical data could be used to infer rheological constraints in melt-bearing zones. Geophysical images of the Earth's interior provide frozen snapshots of a dynamical system. However, knowledge of a rheological parameter such as viscosity would constrain the time-dependent dynamics of melt bearing zones. We propose a model that relates melt viscosity to electrical conductivity for naturally occurring melt compositions (including H2O) and temperature. Based on laboratory measurements of melt conductivity and viscosity, our model provides a rheological dimension to the interpretation of electromagnetic anomalies caused by melt and partially molten rocks (melt fraction ~ >0.7).We acknowledge partial support under NASA USRA subaward 02153–04, NSF EAR 0739050, and the ASU School of Earth and Space Exploration (SESE) Exploration Postdoctoral Fellowship Program.2013-12-1

Caustic Waste-Soil Weathering Reactions and Their Impacts on Trace Contaminant Migration & Separation - Final Report

Studies of the reactivity of radionuclides (Cs, Sr, I) in STWL with model clays and natural sediments were conducted by coupling macroscopic sorption-desorption experiments with spectroscopic and microscopic investigations over a wide range of reaction times. Three experimental systems were studied: (1) model clay minerals, (2) products of homogeneous precipitation from STWL, and (3) representative Hanford sediments, with (1) and (3) reacted with STWL from 1 h to 369 d. The clay minerals included illite, vermiculite, smectite and kaolinite, which constitute a sequence of micaceous weathering products with variable reactivity toward Cs+, Sr2+ and I-. Coarse and fine sediments collected from the Hanford formation (HC and HF, respectively) and Ringold Silt (RS) were studied in batch experiments and Warden silt loam was used in batch and column experiments. Solutions were analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). Solid products (referred to here as ''secondary phases'' relative to the initial reactant minerals) were analyzed for time-dependent changes in mineralogy and modes of contaminant bonding by a variety of methods, including X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) with energy dispersive spectrometry (EDS), thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR), X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analysis, and Fourier-transform infrared spectroscopy (FTIR)

Shock-induced devolatilization of calcium sulfate and implications for K-T extinctions

The devolatilization of calcium sulfate, which is present in the target rock of the Chicxulub, Mexico impact structure, and dispersal in the stratosphere of the resultant sulfuric acid aerosol have been suggested as a possible mechanism for the Cretaceous-Tertiary extinctions. We measured the amount of SO_2 produced from two shock-induced devolatilization reactions of calcium sulfate up to 42 GPa in the laboratory: CaSO_4 + SiO_2 → CaSiO_3 + SO_3↑ CaSO_4 → CaO + SO_2↑ + 1/2O_2↑ We found both to proceed to a much lower extent than calculated by equilibrium thermodynamic calculations. Reaction products are found to be ∼ 10^(−2) times those calculated for equilibrium. Upon modeling the quantity of sulfur oxides degassed into the atmosphere from shock devolatilization of CaSO_4 in the Chicxulub lithographic section, the resulting 9 × 10^(16) to 6 × 10^(17) g (in sulfur mass) is lower by a factor of 10–100 than previous upper limit estimates, the related environmental stress arising from the resultant global cooling and fallout of acid rain is insufficient to explain the widespread K-T extinctions

Shock-induced volatile loss from a carbonaceous chondrite: implications for planetary accretion

Solid-recovery impact-induced volatile loss experiments on the Murchison C2M meteorite indicate that for an impact of a given velocity, H_2O and total volatiles are driven from the sample in the same proportion as present initially. We infer that the volatiles other than H_2O driven from the meteorite also have the same bulk composition as those of the starting material. Thus, the early bulk composition of an impact-induced atmosphere of a planet growing by accretion from material like Murchison would be the same as the volatile composition of the incident planetesimals. Incipient devolatilization of Murchison occurs at an initial shock pressure of about 11 GPa and complete devolatilization occurs at a pressure of about 30 GPa. If an Earth-sized planet were formed from the infall of planetesimals of Murchison composition, incipient and complete devolatilization of accreting planetesimals would occur when the planet reached approximately 12% and 27%, respectively, of its final radius. Thus, impact-induced devolatilization of accreting planetesimals and of the hydrated surface would profoundly affect the distribution of volatiles within the accreting planet. For example, for a cold, homogeneous accretion of a planet, prior to metallic core formation and internal differentiation, the growing planet would have a very small core with the same volatile content as the incident material, a volatile-depleted “mantle”, and an extremely volatile-rich surface

Shock-induced devolatilization and isotopic fractionation of H and C from Murchison meteorite: some implications for planetary accretion

Incipient shock-induced devolatilization of Murchison meteorite occurs upon subjecting samples to a minimum shock stress, or pressure, of about 5 GPa. This pressure is similar to that required to initiate devolatilization of 20% porous serpentine. Upon low velocity impact (61.5 km/s) the solid shocked products were combusted and isotopic analysis of the resulting H_2O and CO_2 was performed. H and ^(13)C are partitioned preferentially over D and ^(12)C, respectively, into the released gas suggesting that the inorganic (mineral) portion of Murchison is devolatilized preferentially over the organic (kerogen) fraction (which is relatively enriched in D and ^(12)C) at the shock pressures studied. These results are combined with previous results on serpentine devolatilization to derive an empirical H fractionation versus devolatilization relation that is used to evaluate the extent of impact-induced isotopic fractionation during planetary accretion. During accretion of the Earth, impact-induced devolatilization and formation of the early primitive atmosphere would have begun at a point where the `growing' Earth achieved a radius in the 480-800 km range. The present experimental results suggest that the Earth's early atmosphere would have been enriched in hydrogen (relative to D) compared to the residual solid, with a fractionation factor of -18 to -23‰. Assuming that current planetary atmospheres have resulted from degassing of planetary interiors after loss of the earliest H-enriched atmosphere, the above degree of isotopic fractionation is not sufficient by itself to explain the large positive δD values of the present Martian and Venusian atmospheres. However, this mechanism in conjunction with tectonic recycling over geologic time could contribute to preferential H loss for Earth and Mars

Impact-induced devolatilization and hydrogen isotopic fractionation of serpentine: Implications for planetary accretion

The degree of impact-induced devolatilization of nonporous serpentine, porous serpentine, and deuterium-enriched serpentine was investigated using two independent experimental methods, the gas recovery method and the solid recovery method, yielding consistent results. The gas recovery method enables determination of the chemical and hydrogen isotopic composition of the recovered gases. Experiments on deuterium-enriched serpentine unambiguously identify the samples as the source of the recovered gases, as opposed to other possible contaminants. For shock pressures near incipient devolatilization (P_(initial) = 5.0 GPa), the hydrogen isotopic composition of the evolved gas is similar to that of the starting material. For higher shock pressures the bulk evolved gas is significantly lower in deuterium than the starting material. There is also significant reduction of H_2O to H_2 in gases recovered at higher shock pressures, probably caused by reaction of evolved H_2O with the metal gas recovery fixture. The hydrogen isotopic fractionation between the evolved gas and the residual solid indicates nonequilibrium, kinetic control of gas-solid isotopic ratios. In contrast, gaseous H_2O-H_2 isotopic fractionation suggests high temperature (800–1300 K) isotopic equilibrium between the gaseous species, indicating initiation of devolatilization at sites of greater than average energy deposition (i.e., shear bands). Impact-induced hydrogen isotopic fractionation of hydrous silicates during accretion can affect the distribution of hydrogen isotopes of planetary bodies during accretion, leaving the interiors enriched in deuterium. The significance of this process for planetary development depends on the models used for extrapolation of the observed isotopic fractionation to devolatilizations greater than those investigated experimentally and assumptions about timing and rates of protoatmosphere loss, frequency of multiple impacts, and rates of gas-solid or gas-melt isotopic re-equilibration. A simple model indicates that substantial planetary interior enrichments of D/H relative to that of the incident material can result from impact-induced hydrogen fractionation during accretion