Liquid H2O Research Articles

Nonprecious Catalyst for Three-Phase Contact in a Proton Exchange Membrane CO2 Conversion Full Cell for Efficient Electrochemical Reduction of Carbon Dioxide

Development of a cost-effective and highly efficient electrocatalyst is essential but challenging in order to convert carbon dioxide to value-added chemicals at ambient conditions. In the current work, the activity of a full electrochemical cell has been demonstrated, utilizing a proton exchange membrane CO2 conversion cell that can selectively convert carbon dioxide to a value-added chemical (formic acid) at room temperature and pressure. A cost-effective, nonprecious-metal-based electrocatalyst, nitrogen-doped carbon nanotubes encapsulating Fe3C nanoparticles (Fe3C@NCNTs), has been reported to exhibit superior catalytic activity toward the electrochemical CO2 reduction reaction (CO2RR). A facile one-step synthesis procedure has been undertaken to synthesize Fe3C@NCNTs. CO2 adsorption takes place via sharing of charge between the nucleophilic anchoring site (Fe3C) and the electrophilic C site of CO2, as shown by the DFT studies. The porous architecture, unique tubular structure, high graphitization degree, and appropriate doping of the Fe3C-encapsulating NCNTs allow better three-phase contact of CO2 (gas), H2O (liquid), and catalyst (solid), which can enhance the electrocatalytic activity of the cell, as demonstrated by the experimental findings. The cell was tested under a continuous flow of CO2 gas and has been demonstrated to produce a good amount of formic acid (HCOOH). The production of formic acid was examined by utilizing UV-vis spectroscopy and high-performance liquid chromatography (HPLC). A series of designed experiments disclosed that the maximum yield of formic acid was as high as 90% with Fe3C@NCNTs as both anode and cathode catalysts. Technology to scale up the reduction procedure has also been proposed and shown in this particular work. These unique observations open a route for the development of cost-effective and highly active platinum-free electrocatalysts for the CO2RR.

High-Temperature Evolution of Point Defect Equilibria in Hydrous Forsterite Synthesized at 1100 °C and up to 4 GPa

Water distribution in the deep Earth represents one of the most important topics in the field of geodynamics due to its large impact on the physical and chemical properties of the Earth’s mantle, such as electrical conductivity, seismic anisotropy, diffusion, and rheology. In this study, we synthesized hydrous forsterite at 1100 °C and up to 4 GPa with either a piston-cylinder or multianvil apparatus. As a starting material, we used synthetic forsterite, unbuffered by SiO2, obtained by thermo-mechanical activation of talc and magnesium carbonate hydroxide. Hydration was carried out using liquid H2O as hydrogen source. Samples were polycrystalline in an effort to distribute H2O throughout the sample both rapidly and homogeneously. Using the Paterson calibration, we observed total water content concentrations ranging between 100 and 500 ppm wt H2O. Multiple absorption bands are found in the frequency range between 3400 and 3650 cm−1, identifying at least seven peaks in all samples. Vibrational bands were centered at 3476, 3535, 3550, 3566, 3578, 3605, and 3612 cm−1, in good agreement with experimental studies conducted on both hydrous forsterite and single crystals of olivine. The stronger OH stretching peaks can be attributed to vibrational modes associated with the hydrogarnet defect 4 H Si x in which four protons occupy a vacant tetrahedral site. None of the OH bands observed are found at frequencies associated with hydrogen occupying vacant octahedral sites. High-temperature FTIR spectroscopy was used to evaluate the evolution of IR spectra as a function of temperature, up to 500 °C. The complete reversibility of peak absorption vs. temperature in the OH stretching region confirms that no water loss occurred during heating. We observe an overall a decrease in total absorption with increasing temperature, and a prominent decrease in the relative intensities of the higher frequency bands (>3600 cm−1) with respect to lower frequency bands. We have assigned a series of equilibrium expressions based on the variation of relative peak areas with temperature and find that enthalpies of these processes range between 0.047–0.068 eV (4.5–6.5 kJ/mol), very low in comparison to activation energies observed for electrical conduction in hydrous olivine. Major changes in the vibrational spectrum are expected to be related to configurational changes of the same fully protonated hydrogarnet defect species. However, the complexity of the FTIR spectra may also be related to partially protonated defects, such as the associate defect 3 H Si ′ + H i • generated by a dissociation reaction of the hydrogarnet species.

Beta-NMR of short-lived nucleus 17N in liquids

The β-ray detected nuclear magnetic resonance (β-NMR) of a short lived-nucleus 17N (I = 1/2, T1/2 = 4.173 s) in liquid H2O and CH3NO2 has been performed. A π-pulse method was applied to obtain sharp NMR lines, from which the ratio of the Larmor frequencies of 17N in CH3NO2 and 1H was determined to be ν[17N in CH3NO2]/ν[1H2O] = 0.1265751 ± 0.0000019. Two resonance lines were observed for 17N in H2O with the relative frequency shifts of –(2.33 ± 0.37) × 10−4 and (2.91 ± 0.27) × 10−4 referenced to 17N in CH3NO2.

Three-Phase Photocatalysis for the Enhanced Selectivity and Activity of CO2 Reduction on a Hydrophobic Surface.

The photocatalytic CO2 reduction reaction (CRR) represents a promising route for the clean utilization of stranded renewable resources, but poor selectivity resulting from the competing hydrogen evolution reaction (HER) in aqueous solution limits its practical applicability. In the present contribution a photocatalyst with hydrophobic surfaces was fabricated. It facilitates an efficient three‐phase contact of CO2 (gas), H2O (liquid), and catalyst (solid). Thus, concentrated CO2 molecules in the gas phase contact the catalyst surface directly, and can overcome the mass‐transfer limitations of CO2, inhibit the HER because of lowering proton contacts, and overall enhance the CRR. Even when loaded with platinum nanoparticles, one of the most efficient HER promotion cocatalysts, the three‐phase photocatalyst maintains a selectivity of 87.9 %. Overall, three‐phase photocatalysis provides a general and reliable method to enhance the competitiveness of the CRR.

Opportunities for Electrochemical and Catalytic Processes That Support Human Activity on Mars

Supporting human activity on Mars requires working with available resources, which include low-pressure CO2 (P CO2 » 5.8 mbar) even lower pressure N2 (P N2 » 0.12 mbar), sub-surface ice, and solar insolation (up to 300 W/m2 at the surface). Supporting life on Mars requires sustained production of O2, liquid H2O, food, heat, and fuel for rockets and mobility. This presentation explores electrochemical and chemical processes based on catalytic membrane reactors that can enable production of value-added products and/or their precursors from the in-situ resources. Many practical chemical technologies require H2 as a feedstock, which can be produced by steam electrolysis that also produces O2. An attractive approach to electrolysis uses proton-conducting ceramic membrane such as (BCZYYb) at intermediate temperatures (between 450 and 650 °C) [1-3]. Proton-conducting ceramics electrochemical cells (PCEC) provide advantages compared to liquid-based polymer electrolyte membrane electrolysis in that they can operate without the need for high-purity liquid H2O and they can incorporate carbonaceous feedstocks for combining electrolysis with other chemistries. In addition to producing H2, the electrolysis cell can be operated as an integrated H2 electrochemical compressor. Several viable catalytic hydrogenation processes can react H2 from the electrolysis cell with CO2 to produce fuels and chemicals. The Sabatier reaction for producing CH4 from CO2 and electrolysis derived H2 has been well studied with an optimal operating temperature around 400 °C [4]. More selective catalysts and novel membrane reactors can be developed to produce valuable fuels and chemicals that include methanol, ethylene, dimethyl ether, formic acid, etc. The desired product streams depend on selective catalysts and on operating pressures and temperature. In some cases, process performance may depend on the development of novel bi-functional catalysts and/or selective membranes. In addition to carbon-based products, applications such as fertilizers need ammonia. Available N2 in the atmosphere could react with H2 to synthesize NH3 via Haber-Bosch process. Many of these relevant catalytic processes require high pressure (at least tens of bar) and modest elevated temperature (300-500 ˚C). Depending on the product yield, downstream separations and purifications may be needed. Assuming limited space and need to high efficiency, process intensification [5] will likely play important roles in the development of in-situ resource utilization. This paper explores the opportunities and challenges for developing critical electrochemical processes for production of a variety of chemicals to support future human Martian activity. Fig.1. Cartoon illustration of a H2 membrane coupled catalytic reactor for CO2 hydrogenation to chemicals References C. Duan, J. Tong, M. Shang, S. Nikodemski, M. Sanders, S. Ricote, A. Almansoori, and R. O’Hayre. Science, 349:1321–1326, 2015.H. Zhu, S. Ricote, C. Duan, R.P. O’Hayre, and R.J. Kee. J. Electrochem. Soc., 165:F845–F853, 2018.C. Duan, R.J. Kee, H. Zhu, N. Sullivan, L. Zhu, L. Bian, D. Jennings, and R.P. OHayre. Nature Energy, 4:230240, 2019.K.P. Brooks, J. Hu, H. Zhu, R.J. Kee, “Methanation of carbon dioxide by hydrogen reduction using the Sabatier process in microchannel reactors”, Chem. Eng. Sci., 62(4):1161-1170, 2007.R.J. Kee, C. Karakaya, H. Zhu, “Process intensification in the catalytic conversion of natural gas to fuels and chemicals,” Proc. Combust. Inst., 36:51–76, 2017 Figure 1

Abiotic methane synthesis and serpentinization in olivine-hosted fluid inclusions

The conditions of methane (CH4) formation in olivine-hosted secondary fluid inclusions and their prevalence in peridotite and gabbroic rocks from a wide range of geological settings were assessed using confocal Raman spectroscopy, optical and scanning electron microscopy, electron microprobe analysis, and thermodynamic modeling. Detailed examination of 160 samples from ultraslow- to fast-spreading midocean ridges, subduction zones, and ophiolites revealed that hydrogen (H2) and CH4 formation linked to serpentinization within olivine-hosted secondary fluid inclusions is a widespread process. Fluid inclusion contents are dominated by serpentine, brucite, and magnetite, as well as CH4(g) and H2(g) in varying proportions, consistent with serpentinization under strongly reducing, closed-system conditions. Thermodynamic constraints indicate that aqueous fluids entering the upper mantle or lower oceanic crust are trapped in olivine as secondary fluid inclusions at temperatures higher than ∼400 °C. When temperatures decrease below ∼340 °C, serpentinization of olivine lining the walls of the fluid inclusions leads to a near-quantitative consumption of trapped liquid H2O. The generation of molecular H2 through precipitation of Fe(III)-rich daughter minerals results in conditions that are conducive to the reduction of inorganic carbon and the formation of CH4 Once formed, CH4(g) and H2(g) can be stored over geological timescales until extracted by dissolution or fracturing of the olivine host. Fluid inclusions represent a widespread and significant source of abiotic CH4 and H2 in submarine and subaerial vent systems on Earth, and possibly elsewhere in the solar system.

Microthermometric evidence for the formation of Permian VHMS deposits in Tasik Chini area, Central Belt of Peninsular Malaysia

The VHMS deposits of Tasik Chini area are located in the Pahang State of Central Belt, Peninsular Malaysia. The deposits occur in a package of Permian volcanics within mixed volcano-sedimentary sequence, and have been exploited from the Bukit Botol and Bukit Ketaya deposits. They have many similarities with Kuroko-style massive sulfide deposits. The host rocks at both deposits are felsic volcanic rocks of rhyolitic to rhyodacitic composition. Mineralization occurs as distinct ore zonation forming a stringer to massive sulfide zone at the footwall followed by barite lenses and exhalite layers (Fe + Mn ± Si ore) at the stratigraphic top. The sulfide phases are characterized by pyrite as the major sulfide mineral, with subordinate chalcopyrite, sphalerite and rare galena; traces of gold, silver- and Sn-bearing minerals occur in the massive sulfide and barite ores. Primary fluid inclusions within quartz and barite occur as two types: (1) type I: two phase, liquid-vapour inclusions without daughter minerals, and (2) type II: three phase, liquid CO2-bearing carbonic inclusions. These three phase inclusions include liquid H2O, liquid CO2 and vapour CO2, with variable CO2 content, and often decrepitate before complete homogenization. Microthermometric measurements of the type I inclusions show that the temperature of homogenization (Th) varies between 180 °C and 310 °C with salinities ranging from 1.0 to 15.0 wt% NaCl equivalent in the quartz samples. Homogenization temperatures (Th) of 190 °C to 300 °C and salinities between 1.0 and 13.0 wt% NaCl equivalent are recorded from the barite samples. Type II inclusions have an initial melting temperature range of −57.1 °C to −57.5 °C, clathrate melting temperature (Tmclathrate) of 7.4 °C to 8.0 °C and CO2 homogenization temperature (ThCO2) between 30.1 °C and 30.3 °C, and salinity ranging from 4.0 to 5.1 wt% NaCl equivalent. Densities, pressure and depth of ore forming fluids range from 0.711 to 0.970 g/cm3, 12 to 93 bars, and ∼1500 m depth of seawater. Laser Raman spectroscopic analysis shows the presence of CO2 in the carbonic inclusions. The fluid inclusion results suggest that the main ore fluid during the formation of the Tasik Chini VHMS deposit is a seawater-dominated fluid, but contribution from a modified seawater or possibly magmatic origin is also indicated by higher salinities relative to seawater (3.2 wt% NaCl) and the presence of CO2. Taking into account the regional geodynamic evolution, it is also concluded that the formation of VHMS deposits in the Tasik Chini area occurred in a back-arc geotectonic setting.

A Smooth Dissipative Particle Dynamics method for nonisothermal liquid and gas flows in bounded domains

A Smoothed Dissipative Particle Dynamics formulation with dynamic virtual particle allocation (SDPD-DV) is developed for the simulation of mesoscale nonisothermal flows with non-slip, constant temperature and constant heat flux boundary conditions. For liquids, the particle internal energy is evaluated through a first-order expansion from an initial volume and entropy state. For liquids, the particle pressure and temperature are evaluated using the coefficients of adiabatic compressibility, volumetric thermal expansion and heat capacity. For monatomic and diatomic gases, the fluid particle internal energy is evaluated through a Sackur-Tetrode type of equation. For both liquids and gases, the viscosity and thermal conductivity are modeled by a power law. Integration of position and momentum equations is performed with a velocity-Verlet method and bounce-forward reflection. Integration of the entropy equation is performed with a Runge-Kutta method. Verification of SDPD-DV is performed for planar isothermal Couette, planar Fourier, and planar nonisothermal Couette flows of liquid H2O and gaseous N2, and for a nonisothermal planar Poiseuille flow of a fluid with an exponential temperature-depended viscosity. SDPD-DV simulations for liquid H2O, gaseous Ar and N2 systems under thermal equilibrium assess the impact of the ratio of particle mass (mi) over the real molecular mass and the size of smoothing length (h) on fluid properties, hydrodynamic fluctuations and transport coefficients. For liquid systems the density fluctuations exhibit scatter about the analytical estimates and the temperature fluctuations follow the analytical estimates for mass ratios smaller than 10,000. The velocity fluctuations are in excellent agreement with theoretical estimates. For gases, the density fluctuations exhibit scatter about the analytical estimates and the pressure fluctuations agree with the analytical estimates for mass ratios smaller than 10,000. The temperature and velocity fluctuations are in excellent agreement with the analytical estimates. The self-diffusivity evaluated from SDPD-DV simulations for liquid and gases is shown to increase with smoothing length for a given mass ratio, scales with h2/mi and is in excellent agreement with analytical estimates. The shear viscosity evaluated from SDPD-DV simulations for liquid and gases exhibits scatter around the experimental values and is shown to be scale free.

Co2 Separation from Ambient Air by Novel CeO2-Based Adsorbent

CO2 direct air capture is a process for CO2 negative emission to prevent global warming. To consider an application for CO2 direct air capture using temperature swing adsorption process, CeO2-based and zeolite-based adsorbent were investigated for their CO2 adsorption and desorption characteristics under atmospheric conditions. The CeO2-based adsorbent exhibited a larger CO2 adsorption amount than zeolite-based adsorbents at atmospheric CO2 concentration under dry conditions. Remarkably, under wet conditions, the CO2 adsorption amount of the CeO2-based adsorbent remained large while the zeolite-based adsorbents exhibited almost no CO2 adsorption. A CO2 adsorption isotherm study revealed that CO2 adsorption of the CeO2-based adsorbent was stable at a low CO2 partial pressure, indicating strong CO2 chemical adsorption. The CO2 desorption of the CeO2-based adsorbent was observed at relatively low temperatures below 200 °C under both dry and wet conditions. The CO2 desorption temperature under dry conditions was lower than that under wet conditions. In situ Fourier transform infrared spectroscopy indicated that in spite of the different CO2 desorption temperatures, the CO2 adsorbed on the CeO2 formed bidentate carbonate species under both dry and wet conditions. Temperature dependence analysis of the spectra revealed that CO2 desorption was accelerated under wet conditions after liquid H2O desorption occurred, indicating that CO2 and H2O had an attractive interaction, which led to a higher CO2 desorption temperature.

Characterization of Choked Conditions Under Subsonic to Supersonic Flow in Single‐Phase (Supercritical to Gaseous CO2 or Liquid H2O) and Multiphase (CO2 and H2O) Transport

AbstractIn geologic media, fluids exist in gas, liquid, and supercritical phases, generating multiphase and multicomponent systems. As fluids migrating through geologic fractures reach the speed of sound, choked flow can be developed in microfractures. To elucidate such choked flow, thermodynamic analysis and numerical simulations were conducted with CO2, H2O, and CO2‐H2O mixtures at various phases ranging from supercritical to gaseous CO2 and liquid H2O. Compressible CO2, with a relatively low speed of sound (~225 m/s at 31.1 °C and 7.38 MPa), demonstrated significant changes in thermodynamic properties with small pressure and temperature variations. In contrast, H2O, having a relatively high speed of sound (1,524 m/s), showed little thermodynamic variation. For CO2‐H2O mixtures, a small addition of CO2 (or H2O) dramatically reduced the speed of sound relative to those for pure H2O or CO2. For an idealized converging‐diverging microfracture with CO2 flow, choked flow and a shock wave were generated as outlet pressure was decreased to less than 6.8 MPa. The H2O flow did not generate choked flow at any outlet pressures. For CO2‐H2O mixtures, choked flow was generated when the CO2 void fraction was greater than 0.7 with an outlet pressure of 6.5 MPa, indicating that presence of H2O inhibited occurrence of choked flow. Choked flow and shock waves can occur in various geologic environments including geologic CO2 sequestration, geothermal energy development, geysers, and volcano eruptions.

Prebiotic Chemistry of Pluto.

We present the case for the presence of complex organic molecules, such as amino acids and nucleobases, formed by abiotic processes on the surface and in near-subsurface regions of Pluto. Pluto's surface is tinted with a range of non-ice substances with colors ranging from light yellow to red to dark brown; the colors match those of laboratory organic residues called tholins. Tholins are broadly characterized as complex, macromolecular organic solids consisting of a network of aromatic structures connected by aliphatic bridging units (e.g., Imanaka et al., 2004; Materese et al., 2014, 2015). The synthesis of tholins in planetary atmospheres and in surface ices has been explored in numerous laboratory experiments, and both gas- and solid-phase varieties are found on Pluto. A third variety of tholins, exposed at a site of tectonic surface fracturing called Virgil Fossae, appears to have come from a reservoir in the subsurface. Eruptions of tholin-laden liquid H2O from a subsurface aqueous repository appear to have covered portions of Virgil Fossae and its surroundings with a uniquely colored deposit (D.P. Cruikshank, personal communication) that is geographically correlated with an exposure of H2O ice that includes spectroscopically detected NH3 (C.M. Dalle Ore, personal communication). The subsurface organic material could have been derived from presolar or solar nebula processes, or might have formed in situ. Photolysis and radiolysis of a mixture of ices relevant to Pluto's surface composition (N2, CH4, CO) have produced strongly colored, complex organics with a significant aromatic content having a high degree of nitrogen substitution similar to the aromatic heterocycles pyrimidine and purine (Materese et al., 2014, 2015; Cruikshank et al., 2016). Experiments with pyrimidines and purines frozen in H2O-NH3 ice resulted in the formation of numerous nucleobases, including the biologically relevant guanine, cytosine, adenine, uracil, and thymine (Materese et al., 2017). The red material associated with the H2O ice may contain nucleobases resulting from energetic processing on Pluto's surface or in the interior. Some other Kuiper Belt objects also exhibit red colors similar to those found on Pluto and may therefore carry similar inventories of complex organic materials. The widespread and ubiquitous nature of similarly complex organic materials observed in a variety of astronomical settings drives the need for additional laboratory and modeling efforts to explain the origin and evolution of organic molecules. Pluto observations reveal complex organics on a small body that remains close to its place of origin in the outermost regions of the Solar System.

Pressure tolerance of Artemia cysts compressed in water medium

ABSTRACTThe high pressure tolerance of cysts of Artemia salina was investigated up to several GPa in water. No survival was observed after exposure to 1.0 GPa for 15 min. After exposure to 2.0 GPa for the same time duration, the hatching rate had recovered to 33%, but decreased to 8% following compression at 7.5 GPa. This contrasts with results using Fluorinert™ as the pressure-transmitting medium where 80–88% recovery was observed. The lower survival rate in water is accompanied by swelling of the eggs, indicating that liquid H2O close to the ice-VI crystallization pressure penetrated inside the eggs. This pressure exceeds the stability limit for proteins and other key biomolecules components within the embryos that could not be resuscitated. Rehydration takes several minutes and so was not completed for all samples compressed to higher pressures, prior to ice-VI formation, resulting in renewed survival. However H2O penetration inside the shell resulted in increased mortality.

Performance simulation on an integrated natural gas-, N2- and organic fluid-cycle thermal power plant

Seeking for a low-cost carbon capture method and recovering waste heat of the flue gas are the effective ways to improve the thermal efficiency of power plants with carbon capture. A novel oxy-fuel combustion nature gas (NG) power plant integrated the gas turbine (GT), N2 Brayton cycle (NBC), Organic Rankine cycle (ORC), CO2 capture and cold energy utilization of liquefied natural gas (LNG) is proposed in this paper. NBC combined with GT to generate electricity can simplify heat transfer process and provide a utilization path of N2 to reduce the cost of air separation unit (ASU). ORC is used to recover low temperature waste heat of the sulfur-free flue gas with improving system efficiency. LNG cold energy is utilized to achieve low-cost carbon capture. O2/CO2 combustion and O2/H2O combustion are investigated to determine the suitable diluent. The result shows that GT and NBC have better performance in the O2/CO2 cycle compared to O2/H2O cycle, while ORC is more potential in the O2/H2O cycle. Taking into account the energy consumption of ASU and CO2 capture, the result shows that the liquid H2O is not suitable to be used to moderate the combustion temperature because the recycled H2O is vaporized in the combustor and consumes a large amount of heat. In the O2/CO2 atmosphere, the net power generation efficiency of integrated system can reach 56.57%.

T–P–X Phase Diagram of the Water–Hydrogen System at Pressures up to 10 kbar

The stability field of the C0 hydrogen hydrate in the pressure–temperature phase diagram of the water–hydrogen system is studied by volumetry under hydrogen excess. This stability field is confined by the sII hydrate stability field at the low-pressure side; by the liquid stability field at the high-temperature side; and by the C1 hydrate stability field at the high-pressure side. The pressure of the C0 ↔ C1 phase equilibrium is temperature-independent in the studied temperature range from −20 to +18 °C. The corresponding equilibrium line in the phase diagram terminates at the nonvariant quadruple point “C0 hydrate + C1 hydrate + liquid H2O + H2 gas” (or Q3) at 7.7(3) kbar and +22(2) °C. The volume change accompanying the C0 → C1 phase transition, and the dTdPH2 slopes of the melting lines of the C0 and C1 hydrates are measured by volumetry. Thermodynamic considerations are used to estimate the hydrogen content H2/H2O ≈ 0.53(5) and 0.23(5) of the C0 and C1 hydrates, respectively, near the Q3 point.

Analyzing the role of interfacial water on sulfate formation on present Mars

This work investigates a realistic scenario for sulfate formation on Mars that may have occurred under conditions representative to the whole Amazonian period. The process, according to reaction kinetics, works without the necessity of elevated temperature and is due to volcanic eruptions. Theoretical modeling utilizing a heterogeneous pathway leading to sulfates in the presence of microscopic subzero-temperature liquid H2O layer is presented for the first time. The process takes place via the following steps: 1. explosive volcanic eruption with gas, vapor and ash particle release; 2. adsorption of volcanic SO2 and H2O on grains in the volcanic cloud, and formation of interfacial H2O layer between the ice–grain boundary; 3. chemical reactions in the microscopic liquid H2O film forming HSO3–(aq); 4. oxidation to HSO4–(aq); 5. acid-sulfate reaction yielding SO4–-bearing minerals. Steps 1 and 2 happen in the atmosphere, steps 3 and 4 may occur both in the atmosphere and after deposition on the surface, while step 5 takes place on the surface. According to the findings the heterogeneous pathway is an important one, therefore future models should consider them besides homogeneous gas-phase reactions. Furthermore, microscopic liquid H2O could produce specific zonal distribution of sulfate content on the surface.

Thermodynamics of Sea Ice Phase Composition Revisited

AbstractPure ice, brine and solid minerals are the main contributors to sea ice mass. Constitutional changes with salinity and temperature exert a fundamental control on sea ice physical, chemical, and biological properties. However, current estimation methods and model representations of the sea ice phase composition suffer from two limitations—in a context of poorly quantified uncertainties. First, salt minerals are neglected. Second, formulations are inconsistent with international standards, in particular with the International Thermodynamic Equation of Seawater (TEOS‐10). To address these issues, we revisit the thermodynamics of the sea ice phase composition by confronting observations, theory, and the usual computation methods. We find remarkable agreement between observations and the Gibbs‐Pitzer theory as implemented in FREZCHEM, both for brine salinity (RMSE = 1.9 g/kg) and liquid H2O mass fraction (RMSE = 8.6 g/kg). On this basis, we propose expanded sea ice phase composition equations including minerals, expressed in terms of International Temperature Scale 1990 temperature and absolute salinity, and valid down to the eutectic temperature (−36.2 °C). These equations precisely reproduce FREZCHEM, outcompeting currently used calculation techniques. We also suggest a modification of the TEOS‐10 seawater Gibbs function giving a liquidus curve consistent with observations down to the eutectic temperature without changing TEOS‐10 inside its original validity range.

Cycle Stability and Hydration Behavior of Magnesium Oxide and Its Dependence on the Precursor-Related Particle Morphology.

Thermochemical energy storage is considered as an auspicious method for the recycling of medium-temperature waste heat. The reaction couple Mg(OH)2–MgO is intensely investigated for this purpose, suffering so far from limited cycle stability. To overcome this issue, Mg(OH)2, MgCO3, and MgC2O4·2H2O were compared as precursor materials for MgO production. Depending on the precursor, the particle morphology of the resulting MgO changes, resulting in different hydration behavior and cycle stability. Agglomeration of the material during cyclization was identified as main reason for the decreased reactivity. Immersion of the spent material in liquid H2O decomposes the agglomerates restoring the initial reactivity of the material, thus serving as a regeneration step.

Kinetics of D/H isotope fractionation between molecular hydrogen and water

At equilibrium, the D/H isotope fractionation factor between H2 and H2O (αH2O-H2(eq)) is a sensitive indicator of temperature, and has been used as a geothermometer for natural springs and gas discharges. However, δDH2 measured in spring waters may underestimate subsurface temperatures of origin due to partial isotopic re-equilibration during ascent and cooling. We present new experimental data on the kinetics of D–H exchange for H2 dissolved in liquid water at temperatures below 100 °C. Comparing these results with published exchange rates obtained from gas phase experiments (100–400 °C), we derive a consistent activation energy of 52 kJ/mol, and the following rate expressions;lnk=9.186-6298/Tandk1=9764.61[H2O]e-6298/Twhere T is absolute temperature (K), k is the universal rate constant ([L/mol]/hr), and k1 is a pseudo-first-order constant (hr−1) applicable to water-dominated terrestrial systems by constraining [H2O] as the density of H2O (in mol/L) at the P-T of interest. The density-dependent rate constant accounts for the kinetic disparity of D–H exchange with H2 when dissolved in liquid H2O relative to a gas/steam phase, exemplifed by 1/k1 at 100 °C of ∼2 days in liquid, versus ∼7 yrs in saturated steam. This difference may explain the high variability of δDH2 observed in fumarolic gases. Fluids convecting in the crust frequently reach T > 225 °C, where isotopic equilibrium is rapidly attained (<1 hr). We compare fractionation factors measured in natural fluids (αOBS) with values expected for equilibrium at the T of acquisition. Where these values differ, we use kinetic models to estimate cooling rates during upward advection that account for the observed disequilibrium. Models fit to fluids from Yellowstone Park and the Lost City (deep-sea) vent field, both recovered at ∼90 °C, require respective transit times of ∼7 hrs and ∼11 days between higher temperature reaction zones and the surface. Using estimates of subsurface depths of origin, however, suggests similar mean fluid flow rates (10 s of meters/hr). Additional complications must be considered when interpreting the δDH2 of lower-temperature effluent. When applied to data from deep-sea hydrothermal systems, our kinetic models indicate microbial catalysis accelerates D–H exchange once fluids cool below ∼60 °C. The H2 measured in both continental alkaline springs and fracture fluids from Precambrian shield rock is likely produced at T < 100 °C, through processes such as serpentinization. In these settings, δDH2 values appear closer to equilibrium with H2O than those from geothermal systems. Considering kinetic isotope effects may yield H2 that is out of equilibrium when generated at lower temperatures, we calculate maximum (isothermal) times to apparent isotopic equilibrium of 1.3 yrs at 50 °C, 9 yrs at 25 °C, and 35 yrs at 10 °C. A similar calculation applied to Antarctic brines (−13 °C), where measured δDH2 is far from equilibrium, yields ∼350 yrs. This time is shorter than the fluids have been isolated (2.8 ka), suggesting kinetic isotope effects associated with H2 destruction or loss via diffusion may also be possible.

Temperature and polarization dependent Raman spectra of liquid H2O and D2O

AbstractPolarized Raman spectra of liquid H2O and D2O have been measured over the entire 100 to 4,000 cm−1 vibrational frequency range and 280 to 360 K temperature range. The measured spectra are corrected for wavelength‐dependent detector quantum efficiency and are provided in numerical form to facilitate comparisons with theoretical predictions. Self‐modeling curve resolution is used to decompose the measured spectra into a linear combination of two spectral components whose relative intensities change with temperature but whose shapes are approximately temperature independent. The component whose intensity increases with decreasing temperature contains prominent features in both the high‐frequency OH stretch band region and low‐frequency OH⋯O hydrogen bond stretch band region that resemble those observed in single crystal ice Ih and clathrate hydrates.

Intrusion-related gold-bismuth deposits of North-East Russia: PTX parameters and sources of hydrothermal fluids

Intrusion-related Au-Bi deposits of North-East Russia are related to Late Mesozoic orogenic S- and I-type granites of ilmenite series. The studied deposits differ in their position relatively to the plutons, alteration, ore body morphology and sulphide content in ores. Based on mineral composition of ores, studied deposits are divided into bismuth-sulphotelluride-quartz, bismuth-arsenide-sulpharsenide and bismuth-siderite-polysulphide types. Bismuth-sulphotelluride-quartz deposits (Levo-Dybinskoe, Kurum, Ergelyakh, Tuguchak, Basugunya) are characterised by low-sulphide (≤3 vol%) mineralisation. Native gold associates with bismuth minerals (bismuthinite, sulphotellurides and tellurides, maldonite, jonassonite, native bismuth). Bismuth-arsenide-sulpharsenide deposits (Myakit, Chepak, Dubach, Chistoe, Kandidatskoe) host As-rich mineralisation. Löllingite and arsenopyrite are main minerals, and their contents vary from 5 to 60 vol% (commonly ∼10%). The intergrowths of native gold with bismuth minerals (sulphotellurides, tellurides, native bismuth) occur mainly in arsenopyrite. Bismuth-siderite-polysulphide (Arkachan) type is characterised by high-sulphide (5–15 vol%) and high-carbonate (up to 35 vol%) ores. Native gold associates with bismuthinite and other sulphobismuthites. Minerals of tellurium are rare. Fluid inclusion and stable isotope study of samples from eighteen Au-Bi deposits constrains the fluid composition, formation temperatures, pressures, and fluid sources. Four types of fluid inclusions (FI) were revealed: (I) two-phase FI, consisting of H2O liquid and CO2 vapour, and three-phase FI with H2O liquid, CO2 vapour and CO2 liquid; (II) vapour-rich CO2 one- or two-phase FI with minor (rarely dominant) CH4 and N2, sometimes with a thin liquid rim; (III) two-phase liquid-vapour aqueous inclusions; (IV) three- or multiphase FI, consisting of H2O liquid, gas bubble and one or more daughter minerals. Au-Bi mineralisation formed at 437–200 °C (mainly from 400 to 250 °C) and 0.1–1.9 kbar from a H2O-CO2-NaCl fluid, which forms an immiscible brine and CO2-bearing vapour at low pressure (≤1.3 kbar) as well as low- to moderate salinity CO2-H2O mixtures without brines at higher pressure (≥1.3 kbar). The studied deposits formed at shallow (Ergelyakh, Tuguchak, Arbatskoe at 1–2 km, Kurum, Levo-Dybinskoe at 2–3 km) and deep (Chuguluk, Shkolnoe, Arkachan at ∼4 km, Dubach at >5 km) depth. Bismuth-sulphotelluride-quartz deposits commonly occur at shallow depth, whereas bismuth-arsenide-sulpharsenide and bismuth-siderite-polysulphide deposits are mainly formed in deeper environment. The stable isotope data suggest predominantly magmatic source of gold-bearing fluids, but magmatic fluid was enriched in light O, C and S isotopes as a result of fluid immiscibility. The magmatic source is consistent with the overlap in lead isotope compositions of ores and related intrusions, as well as synchronism of magmatism and hydrothermal activity according to geochronology data.