Open System Experiments Research Articles

Phyllosilicate formation on early Mars via open-system acid alteration of basaltic glass

Smectites are widespread on Mars, but the water-rich, neutral-to-alkaline pH conditions favorable for smectite formation would be expected to have also produced abundant carbonates on early Mars, which are not observed. Smectite formation from basaltic glass on Mars could occur in acidic environments unfavorable for carbonate formation. Acidic smectite formation has been previously demonstrated in batch experiments (closed hydrologic systems), however, the mechanisms and octahedral composition of smectite forming in acidic flow-through (open hydrologic systems) environments are still not fully understood. We conducted hydrothermal (190°C) alteration experiments on Stapafell basaltic glass at 0.01 and 0.25 mLmin−1 flow rates corresponding to low and high water to rock ratio (W/R) flow conditions, and initial pH (pH0) values of 2, 3, 4 and 6. A batch low W/R experiment was conducted at pH0 2 for comparison to the open system experiment. Kaolinite, montmorillonite and chlorite formed at pH0 2 at low W/R; no phyllosilicates formed at pH0 2 at high W/R; and lizardite formed at pH0 ≥ 3 at both W/R ratios. Lizardite, kaolinite, and montmorillonite in these experiments formed by precipitation from solution and chlorite likely formed through alteration of montmorillonite and/or basalt. Saponite formed at pH0 2 in batch conditions by alteration of basaltic glass. Comparison of experimental data with martian observations of phyllosilicate assemblages indicated that smectite formation on Mars likely occurred under water-limited environmental conditions. Al-rich smectite could form in low W/R open system subsurface environments under a very narrow range of pH (pH < 3) while saponite could form in closed low W/R systems under acidic to alkaline conditions. The combination of open and closed hydrological regimes could be responsible for development of clay mineral stratigraphies observed on Mars. The acidic conditions required for formation of Al-rich smectite montmorillonite were unfavorable for carbonate precipitation, but carbonate precipitation could occur together with Fe/Mg-smectite saponite in closed systems at pH > 4. The lack of widespread carbonates on Mars could not therefore be explained solely by acidic conditions. Phyllosilicate formation under acidic conditions on Mars may affect biosignature stability in martian regolith as preservation capacity is lower in phyllosilicates that formed in or experienced acidic pH.

Molecular hydrogen from organic sources in geological systems

We have recently shown that molecular hydrogen generation from organic matter occurs at high maturity levels (vitrinite reflectance 3–5%) in Lower Cretaceous shales of the Songliao Basin. To evaluate and extend these implications to a wider range of source rock types and organofacies, we report on two Paleozoic maturity suites from Australia, namely the Permian Patchawarra Formation (fluviodeltaic; Type-III; Cooper Basin) and the middle Cambrian Arthur Creek Formation (marine; Type-II; Georgina Basin), and additional mature marine source rocks from Europe and the USA.It can be inferred from high resolution mass spectrometry that rapid growth of aromatic ring systems is the major pathway for the formation of thermogenic molecular hydrogen from all organic matter types. Extensive open system pyrolysis experiments indicate that the main generation pulse occurs in the vitrinite reflectance range 3.5–5.0%. Kinetic parameters were constructed by subtracting the hydrogen associated with hydrocarbon formation from total hydrogen in the open-system experiments via adjustment factors defined by the relative yields of CH4 and H2. A cumulative H2 potential of 20 mg/g TOC is found with maximum rates of generation that are sufficient for feeding the deep biosphere. Back of the envelope calculations indicate ∼3.5E+10 tonnes of in-place accessible H2 globally, which is an order of magnitude lower than in-place shale gas resource estimates. Regionally, inferred here for the Patchawarra Formation in the Nappamerri Trough (Cooper Basin), yields per unit rock volume resemble those of economic shale gas in the Barnett Shale, Fort Worth Basin, USA.Organic particles are, at the SEM-scale (>30 nm), barren of secondary porosity in the case of terrigenous samples at all maturity stages, but show sponge-like porosity in the investigated marine source rocks exhibiting vitrinite reflectance >∼2.0%. Presence of such meso- and macropores is crucial for H2 storage in marine shales, as microporosity (<2 nm) yielding sorptive storage space for H2, is usually much higher in mature terrigenous kerogens.

Thermochemical model on the carbothermal reduction of oxides during spark plasma sintering of zirconium diboride

AbstractCarbon was used to reduce oxides in spark plasma sintered ZrB2 ultra‐high temperature ceramics. A thermodynamic model was used to evaluate the reducing reactions to remove B2O3 and ZrO2 from the powder. Powder oxygen content was measured and carbon additions of 0.5 and 0.75 wt% were used. A C–ZrO2 pseudo binary diagram, ZrO2–B2O3–C pseudo ternaries, and Zr–C–O potential phase diagrams were generated to show how the reactions can be related to an open system experiment in the tube furnace. Scanning transmission electron microscopy identified impurity phases composed of amorphous Zr–B–O with lamellar BN and a Zr–C–O ternary model was calculated under SPS sintering conditions at 1900°C and 6 Pa to understand how oxides can be retained in the microstructure.

Surface tension of dilute alcohol-aqueous binary fluids: n-Butanol/water, n-Pentanol/water, and n-Hexanol/water solutions

Surface tension of pure fluids, inherently decreasing with regard to temperature, creates a thermo-capillary-driven (Marangoni) flow moving away from a hot surface. It has been known that few high-carbon alcohol-aqueous solutions exhibit an opposite behavior of the surface tension increasing with regard to temperature, such that the Marangoni flow moves towards the hot surface (self-rewetting effect). We report the surface tensions of three dilute aqueous solutions of n-Butanol, n-Pentanol and n-Hexanol as self-rewetting fluids measured for ranges of alcohol concentration (within solubility limits) and fluid temperatures (25–85 °C). A maximum bubble pressure method using a leak-tight setup was used to measure the surface tension without evaporation losses of volatile components. It was found from this study that the aqueous solutions with higher-carbon alcohols exhibit a weak self-rewetting behavior, such that the surface tensions remain constant or slightly increases above about 60 °C. These results greatly differ from the previously reported results showing a strong self-rewetting behavior, which is attributed to the measurement errors associated with the evaporation losses of test fluids during open-system experiments.

The efficient long-term inhibition of forsterite dissolution by common soil bacteria and fungi at Earth surface conditions

San Carlos forsterite was dissolved in initially pure H2O in a batch reactor in contact with the atmosphere for 5years. The reactive fluid aqueous pH remained relatively stable at pH 6.7 throughout the experiment. Aqueous Mg concentration maximized after approximately 2years time at 3×10−5mol/kg, whereas aqueous Si concentrations increased continuously with time, reaching 2×10−5mol/kg after 5years. Element release rates closely matched those determined on this same forsterite sample during short-term abiotic open system experiments for the first 10days, then slowed substantially such that the Mg and Si release rates are approximately an order of magnitude slower than that calculated from the short-term abiotic experiments. Post-experiment analysis reveals that secondary hematite, a substantial biotic community, and minor amorphous silica formed on the dissolving forsterite during the experiment. The biotic community included bacteria, dominated by Rhizobiales (Alphaproteobacteria), and fungi, dominated by Trichocomaceae, that grew in a carbon and nutrient-limited media on the dissolving forsterite. The Mg isotope composition of the reactive fluid was near constant after 2years but 0.25‰ heavier in δ26Mg than the dissolving forsterite. Together these results suggest long-term forsterite dissolution in natural Earth surface systems maybe substantially slower than that estimated from short-term abiotic experiments due to the growth of biotic communities on their surfaces.

The Effect Of Physiological Metal Ions On The Procoagulant Enzyme-Cofactor Complexes Of The Extrinsic Pathway Of Coagulation

IntroductionThe rapid coagulation response to vascular injury is mediated by the formation of three enzyme cofactor complexes (extrinsic tenase, intrinsic tenase and prothrombinase) on membrane surfaces. A common structural feature of these proteases is their GLA domains, each of which requires the binding of divalent metal ions at multiple sites to achieve the conformation necessary for optimal membrane and cofactor binding. Both Ca2+ and Mg2+ ions have been reported to bind to GLA domain sites. However almost all studies kinetically characterizing these complexes have been done in the presence of Ca2+ (2-5 mM) as the sole metal ion, despite the relatively equivalent availability in plasma of both free Ca2+ (∼1.1 mM) and Mg2+ (∼0.6 mM) (Ca2+/Mg2+). A recent study has systematically examined the effects of various Ca2+ concentrations with and without Mg2+ on the membrane binding of activated protein C (APC) and FVIIa and enzymatic activity of APC and the extrinsic tenase complex which were enhanced in Ca2+/Mg2+ relative to Ca2+ alone (Vadivel, K., et al, 2013 JMB). In the current study we compare the effects of plasma levels of Ca2+ and Mg2+ versus Ca2+alone on the catalytic performances of the extrinsic tenase, intrinsic tenase and prothrombinase complexes individually and collectively. MethodsAll experiments were conducted in Hepes buffered saline pH 7.4 containing 0.1% PEG and either 2 mM Ca2+ or 1.1 mM Ca2+/0.6 mM Mg2+ (Ca2+/Mg2+). In closed system experiments, enzyme-cofactor complexes were assembled on phospholipid vesicles composed of a 3:1 ratio of synthetic phosphatidylcholine and phosphatidylserine (PCPS), and zymogen activation monitored via sampling into assay mixtures containing the appropriate chromogenic substrate. In open system experiments complexes were preassembled on PCPS coated capillaries, the zymogen delivered in the flowing phase and the extent of zymogen activation monitored in the effluent as described previously (Haynes, LM., et al, 2011 Biophys J). The combined interaction of the procoagulant enzyme cofactor complexes under both metal ion conditions was studied in a synthetic coagulation proteome monitoring thrombin (IIa) generation as previously described (van't Veer, C., and Mann, KG, 1997 JBC). ResultsExtrinsic tenase The extrinsic tenase complex had an approximately two-fold higher rate of FXa generation in the presence of Ca2+/Mg2+ (1.78 ±0.05 pM/s) versus Ca2+ alone (0.88 ± 0.02 pM/s) (N=3, p<0.001). Experiments were also conducted in the absence or presence of tissue factor pathway inhibitor (TFPI); in the presence of TFPI and Ca2+/Mg2+ ions the extrinsic tenase complex was three times as catalytically active compared to TFPI and Ca2+ only (N=3, p<0.05). Direct FXa inhibition by TFPI was not significantly different between the Ca2+ and Ca2+/Mg2+ containing buffers. Intrinsic tenase In closed system experiments the intrinsic tenase complex showed impaired FXa generation in the presence of Ca2+/Mg2+ (29.3 ± 3.4 pM/s) compared to Ca2+ alone (51.7 ± 3.0 pM/s) (N=3, p<0.001). Thrombin activation of FVIII was not statistically different between both buffers, however the presence of Ca2+/Mg2+ resulted in a more rapid loss of cofactor activity over Ca2+ alone. Prothrombinase Under flow, IIa generation measured from prothrombinase was not statistically different between both buffers when measured at five different shear rates (100-1000s-1, N≥2). Plasma proteome In the synthetic coagulation proteome (N=4) the presence of Ca2+/Mg2+ led to an average 31% increase in maximum IIa levels compared to Ca2+alone and an average decrease of 1 minute to reach maximum levels. ConclusionsIn summary, the presence of plasma levels of Ca2+ and Mg2+, compared to Ca2+ alone, enhances the initiation phase of the extrinsic pathway of coagulation by enhancing the rate of FXa generation from the extrinsic tenase complex while also impairing the TFPI inhibition of the extrinsic tenase complex. These procoagulant effects are potentially abrogated by the suppressive effects of Ca2+/Mg2+ on the intrinsic tenase complex, potentially caused by the increased rate of spontaneous inactivation of FVIIIa. These results highlight the importance of complementing the assessments of individual enzyme complex systems with studies of the larger complex systems in which they function to identify the net physiologic impact of metal ions that target various components in the coagulation cascade. Disclosures:Mann:Haematologic Technologies, Inc: Equity Ownership, Membership on an entity's Board of Directors or advisory committees.

Effects of open and closed system oxidation on texture and magnetic response of remelted basaltic glass

As part of an experimental and observational study of the magnetic response of submarine basaltic glass (SBG), we have examined, using ion backscattering spectrometry (RBS), transmission and scanning electron microscopy, energy dispersive X‐ray spectrometry, and surface X‐ray diffraction, the textures wrought by the controlled, open and closed system oxidation of glasses prepared by the controlled environment remelting and quenching of natural SBG. Initial compositions with ∼9 wt % FeO* were melted at 1430°C with the oxygen fugacity buffered at fayalite‐magnetite‐quartz; melts were cooled at a rate of 200°C min−1 near the glass transition (Tg = 680°C). In open system experiments, where chemical exchange is allowed to occur with the surrounding atmosphere, polished pieces of glass were reheated to temperatures both below and above Tg for times 1–5000 h; undercooled melts were oxidized at 900°C and 1200°C for 18 and 20 h, respectively. RBS demonstrates unequivocally that the dynamics of open system oxidation involves the outward motion of network‐modifying cations. Oxidation results in formation of a Fe‐, Ca‐, and Mg‐enriched surface layer that consists in part of Ti‐free nanometer‐scale ferrites; a divalent‐cation‐depleted layer is observed at depths &gt;1 μm. Specimens annealed/oxidized above Tg have magnetizations elevated by 1–2 orders of magnitude relative to the as‐quenched material; this does not appear to be related to the surface oxidation. Quenched glass (closed system, i.e., no chemical exchange between sample and atmosphere) exhibits very fine scale chemical heterogeneities that coarsen with time under an electron beam; this metastable amorphous immiscibility is the potential source for the nucleation of ferrites with a wide range of Ti contents, ferrites not anticipated from an equilibrium analysis of the bulk basalt composition.

Solubility of ThO2·xH2O(am) in carbonate solution and the formation of ternary Th(IV) hydroxide-carbonate complexes

AbstractThe solubility of X-ray amorphous Th(IV) hydroxide or hydrous oxide was determined in carbonate solution atI=0.5 M (NaHCO3-Na2CO3-NaOH-NaCl) and 22 °C. Two series of open system experiments were performed under CO2partial pressures of 1.0 and 0.1 bar at -log [H+]=4.5– 7.5. In three series of closed system experiments at constant total carbonate concentrations ofCtot=[HCO3-]+[CO32-]=0.1, 0.04 and 0.015 M, the H+concentration was varied in the range -log [H+] = 8.5–13.5. Some additional solubility data were determined in 0.25–2 M Na2CO3containing 0.1 M NaOH. There was no indication for the formation of a thorium carbonate solid.The simultaneous evaluation of the different sets of experimental data atI=0.5 M shows that Th(OH)(CO3)45-and Th(OH)2(CO3)22-are the most important ternary complexes. Further contributions to the Th(IV) solubility are coming from Th(OH)2(CO3)(aq), Th(OH)3(CO3)-and Th(OH)4(CO3)2-. Their formation constants, extrapolated toI=0 with the SIT and combined with the solubility product of logK°sp=-47.8±0.3, are calculated to be logβ°114=35.8±0.3, logβ°122=37.0±0.4, logβ°121=30.7±0.4, logβ°131=38.5±0.6 and logβ°141=40.6±0.5. Pure carbonate complexes and other ternary complexes have no significant contributions to the solubility in the present studies atI=0.5 M. Upper limits are derived for their formation constants. Using the SIT for ionic strength corrections, the evaluated set of equilibrium constants is also consistent with the solubility in Na2CO3-NaOH mixtures of higher ionic strength.

Evaporative chemical evolution of natural waters at Yucca Mountain, Nevada

The authors report results from experiments on the evaporative chemical evolution of the two major types of natural waters present at Yucca Mountain, Nevada. The first is represented by J13 well water, a dilute Na–HCO 3–CO 3 water similar to saturated horizons in volcanic tuffs across the western United States. The second is represented by Ca–C1–SO 4-rich pore water that has a higher dissolved ion content, from the unsaturated zone above the repository horizon. Data include anion and cation analysis and qualitative mineral identification for a series of open system experiments, with and without crushed tuff present, conducted at sub-boiling temperatures (75–85°C). This work is motivated by a need to characterize the chemistry of concentrated aqueous films that might form on engineered components at the potential high-level, nuclear-waste repository at Yucca Mountain, Nevada and lead to electrochemical corrosion. The experiments indicate the evolution of high pH, Na–HCO 3–CO 3 brines from J13-like waters and the evolution of near-neutral pH brines from the pore water compositions. The minerals recovered after complete evaporation of the J13 water alone experiments include amorphous silica, aragonite, calcite, halite, niter, thermonatrite and, possibly, gypsum, anhydrite and hectorite. Tachyhydrite and gypsum were observed to form in equivalent experiments with pore waters from the unsaturated zone.

Chemical Exchange Between Volcanic Ash in Seawater: Abiotic Versus Biotic, Warm vs Cold

Volcanic glass is probably chemically the most reactive material that is deposited in the oceans, as aerosol, as suspended river load from volcanic terrain, or as part of the extrusive layer of the oceanic crust. The total volume of this material is large, probably on the order of about 10~6g/a, providing the potential of very large chemical fluxes. Recent studies have shown that microbial activity plays an important role in the dissolution of glass in the marine environment, through mediation of the dissolution process, and, presumably, utilization of components of the glass freed up during this process (e.g. Thorseth et al., 1995; Fumes et al., 1996, Giovarmoni et al., 1996; Staudigel et al., 1995). The interaction between biota and volcanic glass is likely an influence on local ecology as well as on the chemical mass balance between biosphere, hydrosphere and lithosphere. We carried out a series of experiments to explore further the role of colonizing microorganisms on the dissolution of glass. All experiments were done with natural populations of microbes from surface sea water at two temperatures, under the ambient light intensity in the laboratory and in the dark. Open system experiments were done with a constant supply of fresh seawater. The closed system apparatus included 501 seawater reservoirs and a FEP Teflon column setup with approximately 150 g of glass (Staudigel et al., 1997). A closed system with autoclaved components and seawater served as an abiotic control. More recent continuous flow experiments include approximately 300 g of glass and a continuous flow of 20 1 of fresh sand-filtered seawater per day. We carried out an experiment at 60 ~ C and compared this to an experiment at 16~ Run products were analysed for major and trace elements and for changes in glass surface structure and in microbial colonization by SEM. Microbial populations were characterized with a variety of metabolic tests. Closed-system sterile control experiments remained sterile for periods exceeding 450 days showing that these experimental conditions do not allow for microbial contamination. Biologically active experiments display a diverse population of microbes, including a series of algae including Si utilizers (diatoms) and algae with aragonitic exosceletons (halimeda). In cold experiments we identified several chemolithotrophs including a rod-shaped motile sulphur-oxidizer, probably Thiobacillus sp., and two strains of rod-shaped non-motile ammoniaoxidizers. Photoautotrophs, all cyanobacteria, include Spirulina, Phormidium, Anacystis, and a sheathed, filamentous strain that is probably either Anabaena or Nostoc. 60~ experiments displayed no significant thermophile activity for the first two months of its duration. However, after about g months we could identify a diverse population of thermophilic microorganisms, including heterotrophs, sulphuroxidizers, nitrite-oxidizers and ammonia-oxidizers. These results suggest that surface seawater has the means to transport thermophilic microbial life, even though in our experiments it took between two to eight months for them to appear. Overall these results suggests that surface seawater contains a sufficiently diverse environmental microbial population that can adjust to a wide range of conditions, and newly developed hydrothermal systems do not remain abiotic for a long time after initiation. Such processes are expected to occur not only in the mixing zone of

Kinetics of petroleum generation and cracking by programmed-temperature closed-system pyrolysis of Toarcian Shales

Primary kerogen-to-petroleum and secondary oil-to-gas conversion processes in marine source rocks have been studied contemporaneously by programmed-temperature closed-system (MSSV) pyrolysis of Toarcian Shale concentrates at heating rates of 0.1, 0.7 and 5.0K min −1 in the temperature range of 300–610°C. All pyrolysates were analysed by single-step on-line gas chromatography. The cumulative evolution profiles of liquid and gaseous compounds were deconvoluted into generation curves for oil (C 6+), primary gas and secondary gas using complementary open-system experiments and simple stoichiometric relationships. The subsequent kinetic analysis resulted in potential versus activation energy distributions which turned out to be comparatively broad for oil and primary gas and rather narrow for secondary gas, indicating that the formerer are generated from more inhomogeneous precursor materials than the latter. The dominant activation energies were found to increase from 52 (217.9) (oil) to 53 (222) (primary gas) and 55 (230.5) kcal mol −1 (kJ mol −1) (secondary gas); the best-fit frequency factors were calculated around 1015 min −1. By extrapolation to a geological heating rate of 5.3K my −1 (10 −11K min −1) the onset of oil generation is predicted to occur at 90°C, the maximum oil formation rate at 140°C and the onset (peak generation) of primary and secondary gas at 110°C (165°C) and 150°C (180°C), respectively.

Noble gas studies in diamonds synthesized by shock loading in the laboratory and their implications on the origin of diamonds in ureilites

We synthesized diamonds by shock transformation from natural graphite using a single-stage propellant gun and examined the noble gas concentrations in them. The diamond yields correlated with the shock pressure and with the porosity of the starting material. Considerable amounts of noble gases were trapped in the shock-produced diamonds when the starting material was sealed inside the container (closed system experiment), but were not trapped when employing vented containers (open system experiment). The noble gases were tightly retained within the diamonds and were released only during graphitization of the diamonds. The elemental abundance patterns of noble gases are similar to that of air in the closed system experiments, suggesting that noble gases in the pore spaces within the starting material were driven into and/or dissolved in the diamonds. In the open system experiments, the elemental abundance patterns of noble gases were highly fractionated, indicating that only the gases adsorbed on the preshocked graphite surfaces were trapped in the diamonds. There was no large variation of the noble gas concentrations related to shock pressure or porosity of the starting material in the closed system experiments. These results imply that the vapor-growth model is better than the shock model as the origin of ureilite diamonds.

Carbon isotope fractionation between dissolved carbonate (CO 32−) and CO 2(g) at 25° and 40°C

Carbon isotope fractionations ε HCO 3—CO 2(g) and ε CO 3—CO 2(g) have been obtained in open system experiments. At medium-pH, measured isotopic fractionations ε between total dissolved carbonate TDC and CO 2(g) were 7.32 ± 0.07‰ and 6.15 ± 0.08‰ at 25° and 40°C, respectively. Assuming ε CO 2 *(aq)—CO 2(g) = −1.06‰ from Vogel et al. (19 [5] and ion speciation in the solution, calculated fractionations ε HCO 3—CO 2(g) are 8.21‰ at 25°C and 6.71‰ at 40°C. At high-pH, measured isotopic fractionations between TDC and CO 2(g) were 8.30 ± 0.09‰ and 6.69 ± 0.15‰ at 25° and 40°C, respectively. Considering ion speciations and the above fractionation ε HCO 3—CO 2(g) , we derived ε CO 3—CO 2(g) as equal to 8.38‰ at 25°C and 6.67‰ at 40°C.

Sulfur isotope effects associated with protonation of Hs − and volatilization of H 2S

The isotope effects associated with: (1) formation of H2S from HS − by protonation in aqueous solution; and (2) volatilization of H 2S have been experimentally determined. Both isotopic distributions in closed systems at equilibrium and differential rates of volatilization of isotopic species in open systems were measured at 22 ± 1°C. It was found that, at equilibrium, aqueous H 2S is enriched in 34S by 2.0–2.7%‰ relative to H − and that H 2S volatilized from solution is depleted in 34S by 0.5%‰ relative to dissolved H 2S. A small kinetic isotope effect accompanying volatilization of H 2S was observed in the open-system experiments.

Experimental Catastrophic Selection and Tolerances to Low Oxygen Concentration in Native Arizona Freshwater Fishes

Open— and closed—system experimental designs were used to test comparative tolerance, survival, and potential natural selection in four species subjected to low dissolved oxygen concentration–the desert pupfish (Cyprinodon macularius), long—fin dace (Agosia chrysogaster), speckled dace (Rhinichthys osculus), and Gila sucker (Catostomus clarki). Different rankings of the species resulted for tolerance (closed—air system) and survival (open air system). Open—system experiments were designed that demonstrate mechanisms by which this environmental stressor produces catastrophic selection in nature. During interspecific competition, adaptive behavior and structure as well as physiological tolerance were decisive in survival.