Vapor Saturation Pressures Research Articles

Quantitative in situ Raman spectroscopy investigation on HSO4− dissociation at high pressures (up to 420 MPa) and its geological implication

Sulfate-bearing hydrothermal fluids are widespread in crustal environments, and recent papers highlight a possible important role of sulfate as an agent for mass and electron transfers in subduction zone. The geochemical characters of sulfate-bearing fluids (e.g., ability of complexing with ore-forming elements) depend largely on the dissociation behavior of HSO4−. However, the dissociation of HSO4− was only investigated at vapor saturation pressures and the pressure dependence of the dissociation behavior is thus unclear. In this study, we modified the fused silica capillary capsule (FSCC) method to explore the dissociation behavior of HSO4− quantitatively via in situ Raman spectroscopy experiments. We designed a new heating stage that can accommodate a 7 cm-long FSCC, and we show that thick-walled FSCCs with high degrees of filling can withstand pressures up to 645 MPa at temperatures to 450 °C. The sulfate concentrations in Cs2SO4–H2SO4 solutions were measured using Raman spectroscopy with increasing pressures and temperatures (P–T). The sulfate concentrations were calibrated using Cs2SO4 solutions with known concentrations, and the concentrations of HSO4− were determined by mass balance. According to our experimental results, increasing pressure increases the dissociation of HSO4− into SO42− and H+ while increasing temperature promotes ion association, which means that HSO4− dissociation is favored in high-density fluids. Comparisons between our experimental results with those of thermodynamic predictions using currently available thermodynamic properties indicate that the dissociation of HSO4− is stronger than previously thought in high-density fluids, especially at high pressures. We then optimized the thermodynamic properties of HSO4− based on our experimental results, and used them to simulate the S(VI) speciation in slab-derived fluids. Similar with our experimental results, the simulations also predict that the HSO4− will largely dissociate into SO42− and H+ in fluids with high P–T conditions, causing the SO42− as the predominant S(VI) speciation in subduction zone.

Germanium speciation in experimental and natural sphalerite: Implications for critical metal enrichment in hydrothermal Zn-Pb ores

The critical metal germanium (Ge) is recovered as a by-product of mining other commodities, such as zinc and thermal coal. We investigated the Ge incorporation mechanism in sphalerite synthesized under hydrothermal conditions like those of sediment-hosted Zn-Pb deposits. Sphalerite ± galena ± barite formed via reactions of Ge ± Fe ± Cu ± Ba-bearing brine with calcite and reduced sulfur at 200 °C and water vapor-saturated pressure. The products were examined using backscattered electron (BSE) imaging, electron probe microanalysis (EPMA), electron backscattered diffraction (EBSD), synchrotron X-ray fluorescence (SXRF) and micro-X-ray absorption near-edge structure (μ-XANES). We show that Ge(IV) is incorporated into sphalerite and bonded with reduced sulfur, both in the experimental sphalerite and in natural zinc ore samples from the MacArthur River Zn-Pb-Ag deposits, Australia. Copper K-edge XANES spectra show that copper occurs as Cu(I) in the experimental sphalerite, consistent with previous studies on Cu in natural sphalerite. The experiments reveal that Ge(IV) substitution in sphalerite occurs with and without the presence of other metal ions (e.g., Cu(I)), indicating that Ge(IV) substitution can be accommodated via charge balance by vacancies as well as by coupled substitution in the synthesized sphalerite. Ab initio quantum chemical simulations confirm that sphalerite can readily accommodate Ge, with the crystal structure and average Zn-S, Zn-Zn, S-S distances retained when replacing > 3 mol% of the Zn sites with Ge(IV), Ge(II), Cu(I) or Fe(II), demonstrating the resilience and flexibility of the sphalerite crystal structure. These Ge incorporation mechanisms explain the previous observations of multiple ways of Ge incorporation in natural sphalerite. The study provides experimental and molecular simulation insights for understanding the processes related to the formation and extraction of Ge in zinc ores.

Copper mobilization via seawater-volcanic rock interactions: New experimental constraints for the formation of the iron oxide Cu-Au (IOCG) mineralization

The involvement of modified seawater and/or basinal brine in IOCG mineralization was documented by numerous geologic studies. Still, this process remains poorly understood. In this study, we reacted seawater with andesite and basalt, the most common arc volcanic rocks, at 150 and 240 °C and water vapor-saturated pressure to assess the Cu leaching capacity and fluid evolution due to the seawater-volcanic rock interactions. The experimental results show that Mg, Fe, Al, and SO42− in the modified seawater decreased significantly, accompanied by an increased Ca concentration. The fluid pH also decreased from 8.3 of the initial seawater to ∼7.5 and ∼7.0 after 150 and 240 °C experiments, respectively. The incongruent calcsilicate (e.g., plagioclase) dissolution and anhydrite precipitation were observed in the reacted rock samples. Thermodynamic modeling confirmed the trends of those concentration changes but predicted several alteration minerals that were not observed in the experiments. Our experiments show that Cu-leaching efficiency is much higher from the andesite than from the basalt, also higher at 240 °C than at 150 °C. The andesite contains more Cu than the basalt samples, and abundant Cu-rich (average 106 ppm) plagioclase-hosted silicate melt inclusions and Cu-bearing (average 59 ppm) groundmass are identified in the original andesite sample but not in the original basalt sample, which is considered to be the cause of the Cu-leaching differences between the two rock samples. The δ34S value of resultant fluids is dominated by seawater sulfate with a minor contribution of magmatic sulfur from the rock. Thermodynamic modeling combined with recent experimental studies show that deposition of Cu sulfides is the most effective when Cu-bearing fluids react with early-stage pyrite. Our results suggest that the seawater/(brine)-volcanic rock reactions at 150–250 °C can produce Cu-bearing fluids, which in turn can form IOCG deposits, and that Cu mineralization with sulfides zonation can result from replacement reactions between the Cu-bearing fluids and Fe-rich minerals in precursor iron ore bodies.

The petrologic and degassing behavior of sulfur and other magmatic volatiles from the 2018 eruption of Kīlauea, Hawaiʻi: melt concentrations, magma storage depths, and magma recycling

Kīlauea Volcano’s 2018 lower East Rift Zone (LERZ) eruption produced exceptionally high lava effusion rates and record-setting SO2 emissions. The eruption involved a diverse range of magmas, including primitive basalts sourced from Kīlauea’s summit reservoirs. We analyzed LERZ matrix glasses, melt inclusions, and host minerals to identify melt volatile contents and magma storage depths. The LERZ glasses and melt inclusions span nearly the entire compositional range previously recognized at Kīlauea. Melt inclusions in Fo86-89 olivine from the main eruptive vent (fissure 8) underwent 70–170 °C cooling during transport in LERZ carrier melts, causing extensive post-entrapment crystallization and sulfide precipitation. Many of these melt inclusions have low sulfur (400–900 ppm) even after correction for sulfide formation. CO2 and H2O vapor saturation pressures indicate shallow melt inclusion trapping depths (1–5 km), consistent with formation within Kīlauea’s Halemaʻumaʻu and South Caldera reservoirs. Many of these inclusions also have degassed δ34S values (− 1.5 to − 0.5‰). Collectively, these results indicate that some primitive melts experienced near-surface degassing before being trapped into melt inclusions. We propose that decades-to-centuries of repeated lava lake activity and lava drain-back during eruptions (e.g., 1959 Kīlauea Iki) recycled substantial volumes of degassed magma into Kīlauea’s shallow reservoir system. Degassing and magma recycling from the 2008–2018 Halemaʻumaʻu lava lake likely reduced the volatile contents of LERZ fissure 8 magmas, resulting in lower fountain heights compared to many prior Kīlauea eruptions. The eruption’s extreme SO2 emissions were due to high lava effusion rates rather than particularly volatile-rich melts.

Formation of Mg-carbonates and Mg-hydroxides via calcite replacement controlled by fluid pressure

Reactive fluid flow can control the mineralogical, mechanical and chemical evolution of the Earth’s crust. When rocks are exposed to differential stresses (i.e., vertical stress ≠ horizontal stress ≠ pore-fluid pressure (Pf)) during reactive fluid flow, effective pressure is usually assumed to control the overall reaction process. Here, we show that fluid pressure can play an important role in mineral replacement reactions. We conducted experiments in which calcite (CaCO3) grains (fraction size 53–150 µm) reacted with a Mg-rich solution at ~ 200 °C both in a closed system and under reactive fluid flow conditions with different fluid flow rates and fluid pore pressures, but with similar confining pressure (σn = 10 or 20 MPa) and effective pressure (Pe). Under closed system, vapor-saturated pressures, the magnesite formed with large pores between the magnesite and the calcite. In the open system flow-through experiments, however, brucite (Mg(OH)2) or magnesite (MgCO3) formed, depending on pore-fluid pressure. The main reaction product was brucite at low pore-fluid pressure (0.2 MPa), but magnesite at higher pore-fluid pressures (≥ 1 MPa). Calcite dissolution and precipitation of the product mineral increased concomitantly with flow rate, but the flow rate did not affect the nature of the products. The permeability of the reacting rock was related to the reaction pathway, i.e. the nature of the products. Magnesite replaced the pristine calcite in a pseudomorphic manner, and mantled the pristine calcite with 10–100 µm wide pores. In contrast, tabular and/or platy brucite blocked the porosity and resulted in a decrease in permeability. Our results show that the pore-fluid pressure can be a significant parameter controlling the reaction products and reaction processes in volatile-rich (e.g., CO2, HCl, H2S and SO2) systems at conditions close to phase separation; these conditions occur for example in epithermal and porphyry hydrothermal systems, and in carbonate-replacement and some metamorphic environments.

A segmented fuel cell unit with functionally graded distributions of platinum loading and operating temperature

Desired electrochemical reaction and mass transport rates vary in the operation of PEM fuel cells due to the inhomogeneous spatial distribution of reactants and products. A segmented fuel cell unit was manufactured and a comprehensive model was developed to study the effect of the graded distributions of platinum loading and operating temperature, to simultaneously save the usage of platinum, improve the cell performance and maintain the homogeneity of current density. The increase of temperature towards the cathode outlet improved the reaction kinetics and reduced the liquid water content along the gas flow direction, which decreased the required platinum loading. A large temperature gradient may lead to membrane/ionomer dehydration and oxygen starvation near the cathode outlet due to the increase in the saturation pressure of vapor and the dilution of the increased vapor content. A systematical design of the gradients of platinum loading and temperature achieved an improved cell performance and saved the usage of Pt-based catalysts without worsening the homogeneity of current density.

Thermodynamic Properties of Aqueous Sodium Nitrate Solutions Under Superambient Conditions

Use has been made of the Pitzer ion-interaction or virial coefficient approach to estimate the pressure dependence of the osmotic and activity coefficients of aqueous solutions of sodium nitrate (NaNO3) up to 423.15 K and 6.0 mol·kg−1 using published volumetric data on NaNO3(aq). In particular, volumetric Pitzer ion-interaction parameters have been evaluated from a mathematical fit of published apparent molar volume data with the appropriate Pitzer equation. The Pitzer parameters were then fitted as a function of temperature and pressure. These results were then used to calculate the change in the osmotic and activity coefficients in going from the state of an initial pressure p1 to one of a final pressure p2. These pressure dependences have been combined with the osmotic and activity coefficient values of NaNO3(aq) at 0.1 MPa or vapor-saturation pressures (psat) obtained from the model of Archer to yield a comprehensive set of thermodynamic parameters for NaNO3(aq) at temperatures from 293.15 K through 423.15 K, at pressures of (5, 10, 15, 20) MPa, and molalities to 6.0 mol·kg−1.

Environmental Significance of the Stable Isotopes in Precipitation at Different Altitudes in the Tuolai River Basin

Precipitation samples and meteorological data were collected simultaneously during individual precipitation events at Tuole station (3367 m a.s.l.) and Jiayuguan station (1658 m a.s.l.) in the Tuolai River Basin. A study of temporal variation, Local Meteoric Water Lines, and altitude change on precipitation stable isotopes was conducted. The relationships between precipitation stable isotopes and temperature, precipitation, average vapor pressure, and relative humidity were determined in order to explore the environmental significance of the stable isotopes at different altitudes in the middle reaches of the Qilian Mountains. The analysis indicated that the stable isotopes of the precipitation in Tuole and Jiayuguan station were characterized by pronounced seasonal variation, with Tuole having higher δ18O values in summer and autumn and lower δ18O values in spring and winter, while Jiayuguan displays higher δ18O values in spring and lower in other seasons. The d-excess was correlated negatively with δ18O, and the correlation coefficients between δ18O and d-excess decreased with increasing altitude due to weakening sub-cloud evaporation. The slope and intercept of the Local Meteoric Water Lines from Jiayuguan to Tuole rose significantly, showing an increasing trend from low altitude to high altitude. For the precipitation events above 10℃, δ18O of Tuole was positively correlated with the temperature, but the Jiayuguan results indicated the opposite. Sub-cloud evaporation weakened with high precipitation events in Jiayuguan. δ18O and d-excess were positively correlated with the average vapor pressure, which declined from Tuole to Jiayuguan. Since the water vapor pressure and saturated water vapor pressure increased, it was difficult to form precipitation with decreasing altitude. The local strong sub-cloud evaporation caused δ18O and δD was positive at low altitude, while the effect of moisture recycling is obvious, such that δ18O and δD are negative in high altitude areas. There is no significant positive correlation between the δ18O and the relative humidity of the precipitation in Jiayuguan, while Tuole displays an opposite pattern. The results of the study will provide a scientific basis for further study of precipitation isotopes in the Tuolai River basin.

Effect of Latent Heat Released by Freezing Droplets during Frost Wave Propagation.

Frost spreads on nonwetting surfaces during condensation frosting via an interdroplet frost wave. When a supercooled condensate water droplet freezes on a hydrophobic or superhydrophobic surface, neighboring droplets still in the liquid phase begin to evaporate. Two possible mechanisms govern the evaporation of neighboring water droplets: (1) The difference in saturation pressure of the water vapor surrounding the liquid and frozen droplets induces a vapor pressure gradient, and (2) the latent heat released by freezing droplets locally heats the substrate, leading to evaporation of nearby droplets. The relative significance of these two mechanisms is still not understood. Here, we study the significance of the latent heat released into the substrate by freezing droplets, and its effect on adjacent droplet evaporation, by studying the dynamics of individual water droplet freezing on aluminum-, copper-, and glass-based hydrophobic and superhydrophobic surfaces. The latent heat flux released into the substrate was calculated from the measured droplet sizes and the respective freezing times ( tf), defined as the time from initial ice nucleation within the droplet to complete droplet freezing. To probe the effect of latent heat release, we performed three-dimensional transient finite element simulations showing that the transfer of latent heat to neighboring droplets is insignificant and accounts for a negligible fraction of evaporation during microscale frost wave propagation. Furthermore, we studied the effect of substrate thermal conductivity on the transfer of latent heat transfer to neighboring droplets by investigating the velocity of ice bridge formation. The velocity of the ice bridge was independent of the substrate thermal conductivity, indicating that adjacent droplet evaporation during condensation frosting is governed solely by vapor pressure gradients. This study not only provides key insights into the individual droplet freezing process but also elucidates the negligible role of latent heat released into the substrate during frost wave propagation.

When does eruption run-up begin? Multidisciplinary insight from the 1999 eruption of Shishaldin volcano

During the run-up to eruption, volcanoes often show geophysically detectable signs of unrest. However, there are long-standing challenges in interpreting the signals and evaluating the likelihood of eruption, especially during the early stages of volcanic unrest. Considerable insight can be gained from combined geochemical and geophysical studies. Here we take such an approach to better understand the beginning of eruption run-up, viewed through the lens of the 1999 sub-Plinian basaltic eruption of Shishaldin volcano, Alaska. The eruption is of interest due to its lack of observed deformation and its apparent long run-up time (9 months), following a deep long-period earthquake swarm. We evaluate the nature and timing of recharge by examining the composition of 138 olivine macrocrysts and 53 olivine-hosted melt inclusions and through shear-wave splitting analysis of regional earthquakes. Magma mixing is recorded in three crystal populations: a dominant population of evolved olivines (Fo60–69) that are mostly reversely zoned, an intermediate population (Fo69–76) with mixed zonation, and a small population of normally zoned more primitive olivines (Fo76–80). Mixing-to-eruption timescales are obtained through modeling of Fe–Mg interdiffusion in 78 olivines. The large number of resultant timescales provides a thorough record of mixing, demonstrating at least three mixing events: a minor event ∼11 months prior to eruption, overlapping within uncertainty with the onset of deep long-period seismicity; a major event ∼50 days before eruption, coincident with a large (M5.2) shallow earthquake; and a final event about a week prior to eruption. Shear-wave splitting analysis shows a change in the orientation of the local stress field about a month after the deep long-period swarm and around the time of the M5.2 event. Earthquake depths and vapor saturation pressures of Raman-reconstructed melt inclusions indicate that the recharge magma originated from depths of at least 20 km, and that mixing with a shallow magma or olivine cumulates occurred in or just below the edifice (<3 km depth). Deformation was likely outside the spatial and temporal resolution of the satellite measurements. Prior to eruption magma was stored over a large range of depths (∼0–2.5 km below the summit), suggesting a shallow, vertical reservoir that could provide another explanation for the lack of detectable deformation. The earliest sign of unrest (deep long-period seismicity) coincides temporally with magmatic activity (magma mixing and a change in the local stress state), possibly indicating the beginning of eruption run-up. The more immediate run-up began with the major recharge event ∼50 days prior to eruption, after which the signs of unrest became continuous. This timescale is long compared to the seismic run-up to other basaltic eruptions (typically hours to days). Other volcanoes classified as open-system, based on their lack of precursory deformation, also tend to have relatively long run-up durations, which may be related to the time required to fill the shallow reservoir with magmas sourced from greater depth.

Spreading rate‐dependent variations in crystallization along the global mid‐ocean ridge system

AbstractWe investigate crustal accretion at mid‐ocean ridges by combining crystallization pressures calculated from major element contents in mid‐ocean ridge basalt (MORB) glasses and vapor‐saturation pressures from melt inclusions and MORB glasses. Specifically, we use established major element barometers and pressures estimated from 192 fractional crystallization trends to calculate crystallization pressures from &gt;9000 MORB glasses across the global range of mid‐ocean ridge spreading rates. Additionally, we estimate vapor‐saturation pressures from &gt;400 MORB glasses from PETDB and &gt;400 olivine‐hosted melt inclusions compiled from five ridges with variable spreading rates. Both major element and vapor‐saturation pressures increase and become more variable with decreasing spreading rate. Vapor saturation pressures indicate that crystallization occurs in the lower crust and upper mantle at all ridges, even when a melt lens is present. We suggest that the broad peaks in major element crystallization pressures at all spreading rates reflects significant crystallization of on and off‐axis magmas along the base of a sloping lithosphere. Combining our observations with ridge thermal models we show that crystallization occurs over a range of pressures at all ridges, but it is enhanced at thermal/rheologic boundaries, such as the melt lens and the base of the lithosphere. Finally, we suggest that the remarkable similarity in the maximum vapor‐saturation pressures (∼3 kbars) recorded in melt inclusions from a wide range of spreading rates reflects a relatively uniform CO2 content of 50–85 ppm for the depleted upper mantle feeding the global mid‐ocean ridge system.

The solubility of fluorite in Na-K-Cl solutions at temperatures up to 260 °C and ionic strengths up to 4 mol/kg H2O

The solubility of fluorite in hydrothermal conditions is important in ore forming and geothermal processes and groundwater utilization. However, a quantitative description of the geochemical behavior of fluorite under hydrothermal conditions has not been previously reported. In this work, the solubility of fluorite in Na-K-Cl solutions at temperatures up to 260 °C and ionic strengths up to 4 M was determined by experiments and modeling. The solubility products obtained in this work at 30 and 50 °C under ambient pressure and those from literature were used to regress the density model parameters for fluorite solubility product calculation at high temperature. The Pitzer interaction model was adopted to calculate the activity coefficient. The fluorite solubility determined in KCl solution at 250 °C under vapor saturated pressure and that from the literature were combined with the low-temperature thermodynamic properties of heat capacity and osmotic coefficient to obtain the binary parameters of NaF and KF at temperatures up to 260 °C. A thermodynamic model was then developed for calculating the fluorite solubility in Na-K-Cl solution at temperatures up to 260 °C, under vapor saturated pressure and ionic strengths up to 4 M. As calculated from this model, fluorite solubility measured at 200 °C and 0.1 M NaCl was well predicted. Both temperature and ionic strength had significant effects on fluorite solubility, and fluorite exhibited a similar dissolution pattern in both NaCl and KCl solution. When the concentration was lower than 2 M, the solubility of fluorite first increased with temperature, reached a maximum at approximately 100 °C, and then decreased. When the concentration was higher than 2 M, the solubility of fluorite increased monotonically with temperature.

Influence of temperature, pressure, and fluid salinity on the distribution of chlorine into serpentine minerals

Serpentinization produces serpentine minerals that have abundant water and fluid-mobile elements (e.g., Ba, Cs, and Cl). The dehydration of serpentine minerals produces chlorine-rich fluids that may be linked with the genesis of arc magmas. However, the factors that control the distribution of chlorine into serpentine minerals remain poorly constrained. We performed serpentinization experiments at 80–500°C and pressures from vapor saturated pressures to 20kbar on peridotite, orthopyroxene, and olivine with <5% pyroxene. The results show that the concentrations of chlorine in serpentine minerals were up to 1.2wt% at 200°C, whereas they decreased slightly at 311–400°C and 3.0kbar and became significantly lower at 485°C and 3.0kbar, ∼0.1wt%. Fluid salinity greatly decreased chlorine concentrations of olivine-derived serpentine produced at 400°C and 3.0kbar, which was associated with a decrease in silica mobility during serpentinization. By contrast, influence of fluid salinity at 311°C and 3.0kbar is minor. Moreover, chlorine distribution into serpentine can be influenced by primary minerals of serpentine. Serpentine formed in olivine-only experiments at 311°C and 3.0kbar had 0.08±0.03wt% Cl, which is significantly lower than chlorine concentrations of serpentine minerals (0.49±0.36wt%) produced in orthopyroxene-only experiments. By contrast, for experiments at 311°C and 3.0kbar, olivine- and orthopyroxene-derived serpentine had comparable amounts of chlorine. In particular, olivine-derived serpentine had 0.16±0.09wt% Cl that was slightly higher than chlorine concentrations of serpentine formed in olivine-only experiments, whereas orthopyroxene-derived serpentine had significantly lower chlorine concentrations than that formed in orthopyroxene-only experiments. The contrast may be associated with releases of aluminum and silica from pyroxene minerals, which possibly results in a decrease in chlorine concentrations of serpentine. The concentrations of chlorine in serpentine formed in experiments at 311°C and 3.0kbar were slightly lower than those in serpentine produced at 300°C and 8.0kbar, which may be associated with influence of pressure on the mobility of iron and silica. The experimental results of this study indicate that serpentine minerals are important carriers of chlorine in subduction zones. It also suggests that chlorine is significant for the redistribution of cations during serpentinization.

Properties of lithium under hydrothermal conditions revealed by in situ Raman spectroscopic characterization of Li2O-SO3-H2O (D2O) systems at temperatures up to 420 °C

Lithium (Li) is an important component of hydrothermal fluids, especially submarine hydrothermal fluids. Investigation of the species and ion complexation of Li+ at elevated temperature and pressure can improve our knowledge on the behavior of Li under hydrothermal conditions. In this study, in situ optical and Raman spectroscopic experiments were conducted on the Li2SO4-H2SO4-H2O system and its D2O analogue at temperatures≤420°C. An unexpected liquid-liquid phase separation (immiscibility) was observed at temperatures above 336.5°C; the aqueous phase was separated into a sulfate-rich heavy liquid phase and a sulfate-poor light liquid phase at vapor-saturation pressures. The liquid-liquid phase separation temperature decreased as the Li2SO4 concentration increased in dilute solutions (≤1.25 m), increased as the Li2SO4 concentration increased in concentrated solutions (>1.25 m), and exhibited a lower critical solution temperature (LCST) at ~336.5°C. The presence of excess H2SO4 (or D2SO4) increased the liquid-liquid phase separation temperature at a constant Li2SO4 concentration. Liquid-liquid phase separation is common in organic-bearing solutions, and LCST is considered to be a macro-scale property of polymer solutions, indicating complicated ion pairing between Li+ and SO42− at high temperature. In situ Raman spectra of the v1(SO42−) band indicated the presence of “free” SO42−, LiSO4−, possible Li2SO40 and other poly-ion associations. The Li+-SO42− association increased with increasing temperature at a constant Li2SO4 concentration. These results indicate that Li+ can form contact ion pairs with ligands despite its strong hydration tendency.In submarine hydrothermal systems, various contact ion pairs should be important Li species during the high-temperature leaching of Li from basalts (e.g., >200°C). The formation of strong and various Li+-SO42− pairs can enhance the leaching of Li because the mobility and diffusion of the Li+-SO42− complex has been reported to be stronger than that of “free” ions. During the low-temperature (e.g., <150°C) uptake of Li+ into secondary minerals (e.g., clays), free Li+ and outer-sphere ion pairs are the dominant Li+ species. Contact ion pairs are also important Li species during the hydrothermal alteration/precipitation of Li-rich minerals in pegmatite systems. Moreover, liquid-liquid phase separation was found to play important roles in the formation of low-temperature minerals (e.g., calcite). However, similar crystallization pathways have rarely been documented for inorganic systems under high temperatures. Anhydrous Li2SO4 was observed to precipitate within the dense liquid phase at ≥360°C in 1.5 m Li2SO4, confirming that the immiscible dense liquid phase can serve as a precursor for the crystallization of sulfates and other minerals under hydrothermal conditions. The possible processes for the dense-liquid-based crystallization by particle attachment can be summarized as (1) strong and reversible ion association induces liquid-liquid phase separation, (2) nucleation and crystallization within the dense liquid phase, and (3) continued growth on the surface of early formed solid phase. Submarine hydrothermal fluids often contain low-dielectric components such as methane and other organic components, which lower the dielectric constant of hydrothermal fluids and promote ion association. Therefore, liquid-liquid phase separation may occur in submarine hydrothermal fluids and can play important roles in the precipitation of sulfates and other minerals.

Mechanisms of Serpentinization Utilizing Olivine–Plagioclase–H2O System under Hydrothermal Conditions

Silica activity influences the reaction pathways that may occur during serpentinization. At the crust–mantle boundary, silica activity and mass transfer are expected to increase. In this study, hydrothermal ‘tube-in-tube’ experiments utilizing the olivine–plagioclase–H2O system were conducted to assess silica-related mechanisms of hydrothermal alternation at the crust–mantle boundary. Experimental conditions were 230 ˚C and 2.80 MPa (i.e., vapor–saturated pressure) with run times up to 7,980 hours.Reaction products in the olivine zone varied with increasing distance from the olivine–plagioclase boundary, primarily changing from Al–serpentine to serpentine ± brucite + magnetite. No secondary minerals were apparent in the plagioclase zone. Total H2O content in the products was greatest at the boundary compared to the inner tube, where total H2O became homogeneous after the appearance of brucite at 3,184 h. During the experiments, olivine hydration and metasomatic reactions proceeded simultaneously. In contrast to talc-forming metasomatic reactions in olivine–quartz experiments, metasomatic reactions involving plagioclase–buffered fluids led to a decrease in fluid pressure. These reactions suggest that contrasting effects between quartz-buffered and plagioclase-buffered fluids on the chemical and mechanical behavior of the crust–mantle boundary.

Numerical investigation of the interaction, transport and deposition of multicomponent droplets in a simple mouth-throat model

A basic analysis of inhaled multicomponent droplet-vapor interaction and subsequent aerosol deposition is very important for the understanding of natural phenomena as well as for health-care related applications. Employing a highly idealized mouth-throat (MT) model as a test bed, the transport and deposition mechanisms of a water-droplet are simulated, considering ethanol, sodium chloride and fluorescein as components. The flow-field equations are solved with a validated transition SST model which can predict the effects of flow rate, relative humidity (RH), and wet vs. dry airway walls on aerosol deposition efficiency (DE). The simulation results indicate that the hygroscopic growth of sodium chloride particles is sensitive to the saturation pressure of water vapor. A high flow rate decreases the RH in the airways as well as the average growth ratios of deposited and escaped droplets; but, still increases the DE. When compared to a dry boundary condition, the wet airway-wall increases the DE up to 4.6% when RH=30% and the flow rate is 60L/min. It also increases the average growth ratio of deposited droplets notably, i.e., larger than 0.5 for most conditions, while its effect on the average growth ratio of deposited droplets is not apparent. A high inlet RH can significantly enhance the hygroscopic growth of the droplets and DE, especially when it is larger than the RH threshold for the hygroscopic component. Besides, it can elevate the growth ratios of deposited and escaped droplets at the same time, which could be utilized to reduce the deposition of submicron hygroscopic aerosol in the upper airway.

An experimental study on two-phase frictional pressure drop for R-407c in smooth horizontal tubes

This work presents an experimental study on two-phase flow pressure drop for R-407C in a smooth copper tube, alternating a 4.5 mm with a 8.0 mm inner diameter. Data set were collected in different experimental conditions, such as adiabatic and diabatic (4 kW.m−2), evaporation pressures (10.0 bar and 12.0 bar), mass flux (from 180 kg.m−2s−1 to 500 kg.m−2s−1). As a consequence of the experiments and the database from literature review, the effects of vapor qualities, diameters, mass fluxes and saturation pressures on the two-phase flow pressure drop were studied. The present experimental data was compared against 18 different correlations. Results showed that Cicchitti et al. and Sun and Mishima correlations provide the best results.

Water‐rich and volatile‐undersaturated magmas at Hekla volcano, Iceland

AbstractOlivine‐hosted melt inclusions from four eruptions at Hekla volcano in Iceland were analyzed for their dissolved H2O, CO2, S, and Cl contents. A positive correlation among the repose interval, magmatic evolution, and volatile contents of magmas is revealed. H2O is the dominant volatile species; it behaves as an incompatible component, increasing in concentration over time as a result of fractional crystallization in the magma. The full suite of H2O contents ranges from a low of 0.80 wt % in basaltic andesites to a maximum of 5.67 wt % in rhyolites. Decreasing H2O/K2O at fixed major element compositions suggests that syneruptive degassing reduces H2O contents significantly. Hekla magmas are CO2 poor, with very low concentrations present only in the most evolved compositions (∼20–30 ppm or less). The decrease in S content from basaltic andesite to rhyolite demonstrates that sulfide saturation is attained when the melt composition reaches basaltic andesite, resulting in the precipitation of pyrrhotite. Low CO2/Nb ratios suggest that vapor saturation is most likely reached during an early period of cooling and solidification in the crust. Fresh injections of mafic magma interact with previously solidified intrusives, producing new melts that are volatile undersaturated. Vapor saturation pressures obtained using the most volatile‐rich melt inclusions suggest the presence of a magma chamber at a minimum depth of ∼7 km. This is in agreement with geophysical observations from recent small‐volume eruptions, but given the possibility of volatile‐undersaturated melts, some of the magmas may reside at greater depths.

In situ observations of liquid–liquid phase separation in aqueous ZnSO4 solutions at temperatures up to 400 °C: Implications for Zn2+–SO42− association and evolution of submarine hydrothermal fluids

Liquid–liquid immiscibility is gaining recognition as an important process in hydrothermal fluid activity. However, studies of this complex process are relatively limited. We examined liquid–liquid immiscibility in aqueous ZnSO4 solutions at temperatures above ∼266.5°C and at vapor-saturation pressures. The homogeneous aqueous ZnSO4 solution separated into ZnSO4-rich (L1) and ZnSO4-poor (L2) liquid phases coexisting with the vapor phase. The L1–L2 phase separation temperature decreased with increasing ZnSO4 concentration up to 1.0mol/kg, and then increased at greater ZnSO4 concentrations, showing a typical lower critical solution temperature (LCST) of ∼266.5°C. Gunningite (ZnSO4·H2O) precipitated in 2.0mol/kg ZnSO4 solution at 360°C. The L1–L2 phase separation resulted mainly from the strong Zn2+–SO42− association at high temperatures. The major results of this study are: (1) the discovery of the LCST in these systems, a macroscale property associated with polymeric mixtures; (2) analyses of the peak area ratios of the v1(SO42−) and OH stretching bands, which suggest that the sulfate concentration increases with increasing temperature in L1, especially above 375°C; (3) a new Raman v1(SO42−) mode at ∼1005cm−1 observed only in the L1 phase, whose fraction increases with increasing temperature; and (4) the shape of the OH Raman stretching band, which indicates that water molecules and solute interact much more strongly in L1 than in the coexisting L2 phase, suggesting that water molecules fit into the framework formed by various Zn2+–SO42− pairs and chain structures in L1. These results have potential implications for understanding transport and reduction of seawater-derived sulfate in submarine hydrothermal systems. The formation of an immiscible sulfate-rich liquid phase can favor the circulation of sulfate within mid-ocean ridge basalt because the sulfate-rich liquid density is higher than that of the coexisting fluid. The reduction of sulfate could also be accelerated because sulfate is locally concentrated and strong Zn2+–SO42− association increases the reactivity of sulfate.

Competitive hydration and dehydration at olivine–quartz boundary revealed by hydrothermal experiments: Implications for silica metasomatism at the crust–mantle boundary

Serpentinization occurs via interactions between mantle peridotite and water that commonly passes through the crust. Given that such a fluid has a high silica activity compared with mantle peridotite, it is thought that serpentinization and silica metasomatism occur simultaneously at the crust–mantle boundary. In this study, we conducted hydrothermal experiments in the olivine (Ol)–quartz (Qtz)–H2O system at 250 °C and vapor-saturated pressure under highly alkaline conditions (NaOHaq, pH = 13.8 at 25 °C) to clarify the mechanism of silica metasomatism at the crust–mantle boundary. Composite powders consisting of a Qtz layer and an Ol layer were set in tube-in-tube vessels. After the experiments, the extents of serpentinization and metasomatic reactions were evaluated as a function of distance from the Ol–Qtz boundary.The mineralogy of the reaction products in the Ol-hosted region changed with increasing distance from the Ol–Qtz boundary, from smectite + serpentine (Smc zone) to serpentine + brucite + magnetite (Brc zone). Olivine hydration proceeded in both zones, but the total H2O content in the products was greater in the Brc zone than in the Smc zone. Mass balance calculations revealed that olivine hydration occurred without any supply of silica in the brucite zone. In contrast, the Smc zone was formed by silica metasomatism via competitive hydration and dehydration reactions. In the Smc zone, smectite formed via the simultaneous progress of olivine hydration and serpentine dehydration, and around the boundary of the Smc and Brc zones, serpentine formation occurred by olivine hydration and brucite dehydration. The relative extent of hydration and dehydration reactions controlled the along-tube variation in the rate of H2O production/consumption and the rate of volume increase. Our findings suggest that the competitive progress of serpentinization and silica metasomatic reactions would cause fluctuations in pore fluid pressure, possibly affecting the mechanical behavior of the crust–mantle boundary.