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1.
The thermochemistry of well-characterized synthetic K-H3O, Na-H3O and K-Na-H3O jarosites was investigated. These phases are solid solutions that obey Vegard’s law. Electron probe microanalyses indicated lower alkali and iron contents than predicted from the theoretical end-member compositions, in agreement with thermal analyses, suggesting the presence of hydronium and “additional” water. The standard enthalpies of formation (ΔH°f) of K-H3O, Na-H3O and K-Na-H3O jarosites were determined by high-temperature oxide melt solution calorimetry. These enthalpies vary linearly with the K/H3O, Na/H3O and K/Na ratio, respectively. The enthalpy of formation of pure hydronium jarosite was also determined experimentally (ΔH°f = −3741.6 ± 8.3 kJ.mol−1), and it was used to evaluate ΔH°f for the end-members KFe3(SO4)2(OH)6 (ΔH°f = −3829.6 ± 8.3 kJ.mol−1) and NaFe3(SO4)2(OH)6 (ΔH°f = −3783.4 ± 8.3 kJ.mol−1). Finally, enthalpies of dehydration (loss of the “additional” water) of some jarosites were determined and found to be near the enthalpy of vaporization of water, suggesting that the “additional” water is weakly bonded in the structure.  相似文献   

2.
We report rates of oxygen exchange with bulk solution for an aqueous complex, IVGeO4Al12(OH)24(OH2)128+(aq) (GeAl12), that is similar in structure to both the IVAlO4Al12(OH)24(OH2)127+(aq) (Al13) and IVGaO4Al12(OH)24(OH2)127+(aq) (GaAl12) molecules studied previously. All of these molecules have ε-Keggin-like structures, but in the GeAl12 molecule, occupancy of the central tetrahedral metal site by Ge(IV) results in a molecular charge of +8, rather than +7, as in the Al13 and GaAl12. Rates of exchange between oxygen sites in this molecule and bulk solution were measured over a temperature range of 274.5 to 289.5 K and 2.95 < pH < 4.58 using 17O-NMR.Apparent rate parameters for exchange of the bound water molecules (η-OH2) are kex298 = 200 (±100) s−1, ΔH‡ = 46 (±8) kJ · mol−1, and ΔS‡ = −46 (±24) J · mol−1 K−1 and are similar to those we measured previously for the GaAl12 and Al13 complexes. In contrast to the Al13 and GaAl12 molecules, we observe a small but significant pH dependence on rates of solvolysis that is not yet fully constrained and that indicates a contribution from the partly deprotonated GeAl12 species.The two topologically distinct μ2-OH sites in the GeAl12 molecule exchange at greatly differing rates. The more labile set of μ2-OH sites in the GeAl12 molecule exchange at a rate that is faster than can be measured by the 17O-NMR isotopic-equilibration technique. The second set of μ2-OH sites have rate parameters of kex298 = 6.6 (±0.2) · 10−4 s−1, ΔH‡ = 82 (±2) kJ · mol−1, and ΔS‡ = −29 (±7) J · mol−1 · K−1, corresponding to exchanges ≈40 and ≈1550 times, respectively, more rapid than the less labile μ2-OH sites in the Al13 and GaAl12 molecules. We find evidence of nearly first-order pH dependence on the rate of exchange of this μ2-OH site with bulk solution for the GeAl12 molecule, which contrasts with Al13 and GaAl12 molecules.  相似文献   

3.
The energetics of multicomponent diffusion in molten CaO-Al2O3-SiO2 (CAS) were examined experimentally at 1440 to 1650°C and 0.5 to 2 GPa. Two melt compositions were investigated: a haplodacitic melt (25 wt.% CaO, 15% Al2O3, and 60% SiO2) and a haplobasaltic melt (35% CaO, 20% Al2O3, and 45% SiO2). Diffusion matrices were measured in a mass-fixed frame of reference with simple oxides as end-member components and Al2O3 as a dependent variable. Chemical diffusion in molten CAS shows clear evidence of diffusive coupling among the components. The diffusive flux of SiO2 is significantly enhanced whenever there is a large CaO gradient that is oriented in a direction opposite to the SiO2 gradient. This coupling effect is more pronounced in the haplodacitic melt and is likely to be significant in natural magmas of rhyolitic to andesitic compositions. The relative magnitude of coupled chemical diffusion is not very sensitive to changes in temperature and pressure.To a good approximation, the measured diffusion matrices follow well-defined Arrhenius relationships with pressure and reciprocal temperature. Typically, a change in temperature of 100°C results in a relative change in the elements of diffusion matrix of 50 to 100%, whereas a change in pressure of 1 GPa introduces a relative change in elements of diffusion matrix of 4 to 6% for the haplobasalt, and less than 5% for the haplodacite. At a pressure of 1 GPa, the ratios between the major and minor eigenvalues of the diffusion matrix λ1/λ2 are not very sensitive to temperature variations, with an average of 5.5 ± 0.2 for the haplobasalt and 3.7 ± 0.6 for the haplodacite. The activation energies for the major and minor eigenvalues of the diffusion matrix are 215 ± 12 and 240 ± 21 kJ mol−1, respectively, for the haplodacite and 192 ± 8 and 217 ± 14 kJ mol−1 for the haplobasalt. These values are comparable to the activation energies for self-diffusion of calcium and silicon at the same melt compositions and pressure. At a fixed temperature of 1500°C, the ratios λ1/λ2 increase with the increase of pressure, with λ1/λ2 varying from 2.5 to 4.1 (0.5 to 1.3 GPa) for the haplodacite and 4 to 6.5 (0.5 to 2.0 GPa) for the haplobasalt. The activation volumes for the major and minor eigenvalues of the diffusion matrix are 0.31 ± 0.44 and 2.3 ± 0.8 cm3 mol−1, respectively, for the haplodacite and −1.48 ± 0.18 and −0.42 ± 0.24 cm3 mol−1 for the haplobasalt. These values are quite different from the activation volumes for self-diffusion of calcium and silicon at the same melt compositions and temperature. These differences in activation volumes between the two melts likely result from a difference in the structure and thermodynamic properties of the melt between the two compositions (e.g., partial molar volume).Applications of the measured diffusion matrices to quartz crystal dissolution in molten CAS reveal that the activation energy and activation volume for quartz dissolution are almost identical to the activation energy and activation volume for diffusion of the minor or slower eigencomponent of the diffusion matrix. This suggests that the diffusion rate of slow eigencomponent is the rate-limiting factor in isothermal crystal dissolution, a conclusion that is likely to be valid for crystal growth and dissolution in natural magmas when diffusion in liquid is the rate-limiting factor.  相似文献   

4.
Formation of aqueous aluminate-borate complexes was characterized at 25°C using 27Al NMR spectroscopy, and at 50-200°C via measurements of gibbsite and boehmite solubility in the presence of boric acid. 27Al spectra performed at pH = 9 in Al-B solution with m(B) = 0.02 show the presence of two peaks at 80.5 and 74.5 ppm which correspond to Al(OH)4− and a single Al-substituted Q1Al dimer, Al(OH)3OB(OH)2−, respectively. In 0.08 m and 0.2 m borate solution, a third peak appears at 68.5 ppm which can be assigned to the Q2Al trimer Al(OH)2O2(B(OH)2)2−. These chemical shifts are close to those measured for Al(OH)3OSi(OH)3− and Al(OH)2O2(Si(OH)3)2− (74 and 69.5 ppm, respectively; Pokrovski et al., Min. Mag.62a (1998), 1194) which demonstrates the similar structure of Al-B and Al-Si complexes formed in alkaline solutions. Gibbsite and boehmite solubility were measured in weakly basic solutions as a function of boric acid concentration at 50°C and 78 to 200°C, respectively. Equilibrium was reached within several days at m(B) = 0.01-0.1, but more slowly at higher boron concentrations, and at 50°C and m(B) = 0.2, Al concentration increased continuously during at least 3 months as a result of the sluggish formation of Al-polyborates. The equilibrium constant of the reaction Al(OH)4− + B(OH)30(aq) = Al(OH)3OB(OH)2− + H2O decreases very slowly with increasing temperature to 200°C. The log K values are 1.58 ± 0.10, 1.46 ± 0.10, 1.52 ± 0.15, and 1.25 ± 0.15 at 50, 78, 150 and 200°C, respectively, which result in the following values of the standard thermodynamic properties for this reaction: ΔrG0 = −9.22 ± 3.25 kJ/mol, ΔrH0 = −4.6 ± 2.5 kJ/mol, ΔrS0 = 15.5 ± 6.9 J/mol K. The thermodynamic data generated in this study indicate that Al-B complexes can dominate aqueous aluminum speciation in solutions containing ≥0.7 g/L of boron at temperature to at least 400°C.  相似文献   

5.
The AlOx1-3 (Ox = oxalate) species were identified in 0.6 M aqueous NaCl by 13C nuclear magnetic resonance (NMR). Rate constants and activation parameters for intramolecular cis/trans isomerization of the Werner-type AlOx2− complex (k(298 K) = 5 s−1, ΔH# = 67 ± 5 kJ mol−1, ΔS# = −6 ± 6 J mol−1 K−1, the rate determining step could be the breaking of the Al-O(C=O) bond) and a very slow intermolecular ligand exchange reaction of AlOx33− complex and the free ligand (k30(298 K) = 6.6 · 10−5 s−1, ΔH# = 164 ± 17 kJ mol−1, ΔS# = 225 ± 51 J mol−1 K−1, D/Id mechanism) were determined by dynamic 1D and 2D 13C NMR measurements. Mixed complexes, AlFOx, AlFOx22-, AlF2Ox−, and AlF2Ox23-, with overall stability (logβ) of 11.53 ± 0.03, 15.67 ± 0.03, 15.74 ± 0.02, and 19.10 ± 0.04 were measured by potentiometry using pH- and fluoride-selective electrodes and confirmed by 13C and19F NMR. The role of these complexes in gibbsite dissolution was modeled. The mixed Al(III)-Ox2--F− complexes have to be considered as the chemical speciation of Al(III) in natural waters is discussed.  相似文献   

6.
Summary The crystal structure of hydrothermally grown NaFe[SeO4]2 was determined by single crystal X-ray diffraction methods: space group C2/m, a = 8.231(1)Å b = 5.425(1)Å, c = 7.176(1)Å, = 92.44(1)°, V = 320.14Å3, Z = 2; 767 unique data, measured up to 20 = 70° (Mo Kx radiation); R,RW= 0.042, 0.055.NaFe[SeO4]2 is isotypic with yavapaiite, KFe[SO4]2. FeO6 and NaO6 form chains of edge-sharing distorted octahedra with mean Me-O bond lengths of 2.001Å and 2.496Å, respectively, linked via tetrahedral SeO4 groups [
Die Kristallstruktur von NaFe[SeO4]2, einer Verbindung des Yavapaiit-Typsre]19921030
Zusammenfassung Die Kristallstruktur von hydrothermal gezüchtetem NaFe[SeO4]2 wurde mittels Einkristallröntgenmethoden bestimmt: Raumgruppe C2/m, a = 8.231(1)Å, b = 5.425(1)Å, c = 7.176(1)Å, = 92.44(1)°, V = 320.14Å3, Z = 2; 767 unabhängige Intensitätsdaten, Meßbereich bis 20 = 70° (Mo K-Strahlung); R,RW = 0.042, 0.055.NaFe[SeO4]2 ist isotyp mit Yavapaiit, KFe[SO4]2. FeO6 und NaO6 bilden Ketten von kantenverknüpften, verzerrten Oktaedern mit mittleren Me-O Bindungslängen von 2.001Å bzw. 2.496Å, die über tetraedrische SeO4 Gruppen verbunden sind [ = 1.639Å].

Dedicated to Prof. Josef Zemann on the occasion of his 70th birthday

With 3 Figures  相似文献   

7.
The thermochemistry of jarosite-alunite and natrojarosite-natroalunite solid solutions was investigated. Members of these series were either coprecipitated or synthesized hydrothermally and were characterized by XRD, FTIR, electron microprobe analysis, ICP-MS, and thermal analysis. Partial alkali substitution and vacancies on the Fe/Al sites were observed in all cases, and the solids studied can be described by the general formula K1-x-yNay(H3O)xFezAlw(SO4)2(OH)6-3(3-z-w)(H2O)3(3-z-w). A strong preferential incorporation of Fe over Al in the jarosite/alunite structure was observed. Heats of formation from the elements, ΔH°f, were determined by high-temperature oxide melt solution calorimetry. The solid solutions deviate slightly from thermodynamic ideality by exhibiting positive enthalpies of mixing in the range 0 to +11 kJ/mol. The heats of formation of the end members of both solid solutions were derived. The values ΔH°f = −3773.6 ± 9.4 kJ/mol, ΔH°f = −4912.2 ± 24.2 kJ/mol, ΔH°f = −3734.6 ± 9.7 kJ/mol and ΔH°f = −4979.7 ± 7.5kJ/mol were found for K0.85(H3O)0.15Fe2.5(SO4)2(OH)4.5(H2O)1.5, K0.85(H3O)0.15Al2.5(SO4)2(OH)4.5(H2O)1.5, Na0.7(H3O)0.3Fe2.7(SO4)2(OH)5.1(H2O)0.9, and Na0.7(H3O)0.3Al2.7(SO4)2(OH)5.1(H2O)0.9 respectively. To our knowledge, this is the first experimentally-based report of ΔH°f for such nonstoichiometric alunite and natroalunite samples. These thermodynamic data should prove helpful to study, under given conditions, the partitioning of Fe and Al between the solids and aqueous solution.  相似文献   

8.
Atmospheric carbon dioxide is widely studied using records of CO2 mixing ratio, δ13C and δ18O. However, the number and variability of sources and sinks prevents these alone from uniquely defining the budget. Carbon dioxide having a mass of 47 u (principally 13C18O16O) provides an additional constraint. In particular, the mass 47 anomaly (Δ47) can distinguish between CO2 produced by high temperature combustion processes vs. low temperature respiratory processes. Δ47 is defined as the abundance of mass 47 isotopologues in excess of that expected for a random distribution of isotopes, where random distribution means that the abundance of an isotopologue is the product of abundances of the isotopes it is composed of and is calculated based on the measured 13C and 18O values. In this study, we estimate the δ13C (vs. VPDB), δ18O (vs. VSMOW), δ47, and Δ47 values of CO2 from car exhaust and from human breath, by constructing ‘Keeling plots’ using samples that are mixtures of ambient air and CO2 from these sources. δ47 is defined as , where is the R47 value for a hypothetical CO2 whose δ13CVPDB = 0, δ18OVSMOW = 0, and Δ47 = 0. Ambient air in Pasadena, CA, where this study was conducted, varied in [CO2] from 383 to 404 μmol mol−1, in δ13C and δ18O from −9.2 to −10.2‰ and from 40.6 to 41.9‰, respectively, in δ47 from 32.5 to 33.9‰, and in Δ47 from 0.73 to 0.96‰. Air sampled at varying distances from a car exhaust pipe was enriched in a combustion source having a composition, as determined by a ‘Keeling plot’ intercept, of −24.4 ± 0.2‰ for δ13C (similar to the δ13C of local gasoline), δ18O of 29.9 ± 0.4‰, δ47 of 6.6 ± 0.6‰, and Δ47 of 0.41 ± 0.03‰. Both δ18O and Δ47 values of the car exhaust end-member are consistent with that expected for thermodynamic equilibrium at∼200 °C between CO2 and water generated by combustion of gasoline-air mixtures. Samples of CO2 from human breath were found to have δ13C and δ18O values broadly similar to those of car exhaust-air mixtures, −22.3 ± 0.2 and 34.3 ± 0.3‰, respectively, and δ47 of 13.4 ± 0.4‰. Δ47 in human breath was 0.76  ± 0.03‰, similar to that of ambient Pasadena air and higher than that of the car exhaust signature.  相似文献   

9.
Enthalpies of formation of ferrihydrite and schwertmannite were measured by acid solution calorimetry in 5 N HCl at 298 K. The published thermodynamic data for these two phases and ε-Fe2O3 were evaluated, and the best thermodynamic data for the studied compounds were selected.Ferrihydrite is metastable in enthalpy with respect to α-Fe2O3 and liquid water by 11.5 to 14.7 kJ•mol−1 at 298.15 K. The less positive enthalpy corresponds to 6-line ferrihydrite, and the higher one, indicating lesser stability, to 2-line ferrihydrite. In other words, ferrihydrite samples become more stable with increasing crystallinity. The best thermodynamic data set for ferrihydrite of composition Fe(OH)3 was selected by using the measured enthalpies and (1) requiring ferrihydrite to be metastable with respect to fine-grained lepidocrocite; (2) requiring ferrihydrite to have entropy higher than the entropy of hypothetical, well-crystalline Fe(OH)3; and (3) considering published estimates of solubility products of ferrihydrite. The ΔG°f for 2-line ferrihydrite is best described by a range of −708.5±2.0 to −705.2±2.0 kJ•mol−1, and ΔG°f for 6-line ferrihydrite by −711.0±2.0 to −708.5±2.0 kJ•mol−1.A published enthalpy measurement by acid calorimetry of ε-Fe2O3 was re-evaluated, arriving at ΔH°f (ε-Fe2O3) = −798.0±6.6 kJ•mol−1. The standard entropy (S°) of ε-Fe2O3 was considered to be equal to S° (γ-Fe2O3) (93.0±0.2 J•K−1•mol−1), giving ΔG°f (ε-Fe2O3) = −717.8±6.6 kJ•mol−1. ε-Fe2O3 thus appears to have no stability field, and it is metastable with respect to most phases in the Fe2O3-H2O system which is probably the reason why this phase is rare in nature.Enthalpies of formation of two schwertmannite samples are: ΔH°f (FeO(OH)0.686(SO4)0.157•0.972H2O) = −884.0±1.3 kJ•mol−1, ΔH°f (FeO(OH)0.664(SO4)0.168•1.226H2O) = −960.7±1.2 kJ•mol−1. When combined with an entropy estimate, these data give Gibbs free energies of formation of −761.3 ± 1.3 and −823.3 ± 1.2 kJ•mol−1 for the two samples, respectively. These ΔGf° values imply that schwertmannite is thermodynamically favored over ferrihydrite over a wide range of pH (2-8) when the system contains even small concentration of sulfate. The stability relations of the two investigated samples can be replicated by schwertmannite of the “ideal” composition FeO(OH)3/4(SO4)1/8 with ΔG°f = −518.0±2.0 kJ•mol−1.  相似文献   

10.
The first natural occurrence of a high-pressure polymorph of chromite has been discovered in the shock-metamorphosed Suizhou meteorite. The composition of this high-pressure polymorph is identical to that of the precursor chromite. The Raman spectrum of this polymorph is distinct from that of chromite. Synchrotron X-ray diffraction analysis revealed that this polymorph has an orthorhombic CaTi2O4- type structure. The cell parameters are: a = 9.462(6) Å, b = 9.562(9) Å, c = 2.916(1) Å, V = 263.8(4) Å3 (Z=4), space group = Bbmm, and the density = 5.63 g/cm3 (the numbers in parentheses are standard deviations on the last significant digits). This polymorph is 11.5% denser than chromite. The P-T conditions for the phase transformation from chromite to the CaTi2O4-structured polymorph are estimated at 20-23 GPa and 1800 to 2000 °C, respectively. This dense CaTi2O4-structured FeCr2O4 phase could be a host phase for Cr, Al, Fe, Mg and Mn and other metallic elements in the deep Earth.  相似文献   

11.
The rate of spinel (MgAl2O4) growth at the interface between MgO and Al2O3 was investigated systematically at temperatures of 1200° to ∼2000°C and pressures between 1.0 and 4.0 GPa with a solid-media, piston-cylinder apparatus. As reported in previous 1-atm studies, the thickness (ΔX) of the spinel layer increases linearly with the square root of time for experiments differing only in duration, irrespective of pressure-temperature (P-T) conditions. The reaction rate constant (k = ΔX2/2t) is log-linear in 1/T and also in pressure. The apparent activation energy of 410 kJ/mol is independent of pressure; the apparent activation volume increases systematically with increasing temperature. Electron microprobe traverses across the spinel layer reveal a significant Al excess and charge-compensating Mg deficit near the spinel/corundum interface. This nonstoichiometry is promoted by high temperatures (>1500°C), suppressed by high pressures and varies linearly across the spinel to a near-stoichiometric composition at the interface with periclase. The Al and Mg composition gradients can be used to extract interdiffusion coefficients for Al ↔ Mg exchange through the spinel, which are described by D?=2.5×10−6 exp(−28200/T) m2sThese diffusivities differ substantially from the reaction rate constant k, reflecting the fact that k is a combination of the diffusivity and the reaction potential as indicated by the difference in spinel composition across the spinel layer (i.e., coexisting with corundum vs. coexisting with periclase). A simple model can be used to separate the two effects and show that the reaction potential (i.e., the MgO-Al2O3 phase diagram) is sensitive to changes in both temperature and pressure, whereas the governing diffusivity depends only on temperature.  相似文献   

12.
The diffusion coefficients of Fe2+ and Mg in aluminous spinel at ∼20 kb, 950 to 1325°C, and at 30 kb, 1125°C have been determined via diffusion couple experiments and numerical modeling of the induced diffusion profiles. The oxygen fugacity, fO2, was constrained by graphite encapsulating materials. The retrieved self-diffusion coefficients of Fe2+ and Mg at ∼20 kb, 950 to 1325°C, fit well the Arrhenian relation, D = D0exp(−Q/RT), where Q is the activation energy, with D0(Fe) = 1.8 (±2.8) × 10−5, D0(Mg) = 1.9 (±1.4) × 10−5 cm2/s, Q(Fe) = 198 ± 19, and Q(Mg) = 202 ± 8 kJ/mol. Comparison with the data at 30 kb suggests an activation volume of ∼5 cm3/mol. From analysis of compositional zoning in natural olivine-spinel assemblages in ultramafic rocks, previous reports concluded that D(Fe-Mg) in spinel with Cr/(Cr + Al) ≤0.5 is ∼10 times that in olivine. The diffusion data in spinel and olivine have been applied to the problems of preservation of Mg isotopic inhomogeneity in spinel within the plagioclase-olivine inclusions in Allende meteorite and cooling rates of terrestrial ultramafic rocks.  相似文献   

13.
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14.
To understand possible volcanogenic fluxes of CO2 to the Martian atmosphere, we investigated experimentally carbonate solubility in a synthetic melt based on the Adirondack-class Humphrey basalt at 1-2.5 GPa and 1400-1625 °C. Starting materials included both oxidized and reduced compositions, allowing a test of the effect of iron oxidation state on CO2 solubility. CO2 contents in experimental glasses were determined using Fourier transform infrared spectroscopy (FTIR) and Fe3+/FeT was measured by Mössbauer spectroscopy. The CO2 contents of glasses show no dependence on Fe3+/FeT and range from 0.34 to 2.12 wt.%. For Humphrey basalt, analysis of glasses with gravimetrically-determined CO2 contents allowed calibration of an integrated molar absorptivity of 81,500 ± 1500 L mol−1 cm−2 for the integrated area under the carbonate doublet at 1430 and 1520 cm−1. The experimentally determined CO2 solubilities allow calibration of the thermodynamic parameters governing dissolution of CO2 vapor as carbonate in silicate melt, KII, (Stolper and Holloway, 1988) as follows: , ΔV0 = 20.85 ± 0.91 cm3 mol−1, and ΔH0 = −17.96 ± 10.2 kJ mol−1. This relation, combined with the known thermodynamics of graphite oxidation, facilitates calculation of the CO2 dissolved in magmas derived from graphite-saturated Martian basalt source regions as a function of P, T, and fO2. For the source region for Humphrey, constrained by phase equilibria to be near 1350 °C and 1.2 GPa, the resulting CO2 contents are 51 ppm at the iron-wüstite buffer (IW), and 510 ppm at one order of magnitude above IW (IW + 1). However, solubilities are expected to be greater for depolymerized partial melts similar to primitive shergottite Yamato 980459 (Y 980459). This, combined with hotter source temperatures (1540 °C and 1.2 GPa) could allow hot plume-like magmas similar to Y 980459 to dissolve 240 ppm CO2 at IW and 0.24 wt.% of CO2 at IW + 1. For expected magmatic fluxes over the last 4.5 Ga of Martian history, magmas similar to Humphrey would only produce 0.03 and 0.26 bars from sources at IW and IW + 1, respectively. On the other hand, more primitive magmas like Y 980459 could plausibly produce 0.12 and 1.2 bars at IW and IW + 1, respectively. Thus, if typical Martian volcanic activity was reduced and the melting conditions cool, then degassing of CO2 to the atmosphere may not be sufficient to create greenhouse conditions required by observations of liquid surface water. However, if a significant fraction of Martian magmas derive from hot and primitive sources, as may have been true during the formation of Tharsis in the late Noachian, that are also slightly oxidized (IW + 1.2), then significant contribution of volcanogenic CO2 to an early Martian greenhouse is plausible.  相似文献   

15.
Giester  G. 《Mineralogy and Petrology》1995,53(1-3):165-171
Summary The crystal structure of synthetic KMn[SeO4]2 was determined by single crystal X-ray diffraction methods in space group , a = 4.827(2) Å, b = 4.988(2) Å, c = 7.981(3) Å, = 83.18(1)°, = 85.32(2)°, = 67.92(1)°, V = 176.66 Å3, Z = 1; 1564 unique data, measured up to 2 = 70° (MoK-radiation); R, R(I)w = 0.034, 0.074.KMn[SeO4]2 is closely related to monoclinic yavapaiite, KFe[SO4]2, and isotypic compounds. Jahn-Teller distorted MnO6 octahedra are alternately linked with KO10 polyhedra along [001]. The mean values of the Mn-O and Se-O distances are 2.007 Å and 1.637 Å, respectively.
Die Kristallstruktur vonKMn 3+[SeO4]-einem triklin verzerrten Vertreter der Yavapaiite-Familie
Zusammenfassung Die Kristallstruktur von synthetisch dargestelltem KMn[SeO4]2 wurde mittels Einkristallröntgenmethoden in der Raumgruppe bestimmt: a = 4.827(2) Å, b = 4.988(2) Å, c = 7.981(3) Å, = 83.18(1)°, = 85.32(2)°, = 67.92(1)°, V = 176.66 Å3, Z = 1; 1564 unabhängige Daten bis 2 = 70° (MoK-Strahlung); R, R(I)w = 0.034, 0.074.KMn[SeO4]2 ist eng mit dem monoklinen Mineral Yavapaiit, KFe[SO4]2 und einer Reihe damit isotyper Verbindungen verwandt. Jahn-Teller verzerrte MnO6 Oktaeder sind alternierend mit KO10 Polyedern parallel [001] verbunden. Die Mittelwerte der Mn-O und Se-O Abstände sind 2.007 Å bzw. 1.637 Å.

With 1 Figure  相似文献   

16.
We experimentally determined the boron partitioning and boron isotope fractionation between coexisting liquid and vapor in the system H2O−NaCl−B2O3. Experiments were performed along the 400 and 450°C isotherms. Pressure conditions ranged from 23 to 28 MPa at 400°C and from 38 to 42 MPa at 450°C. Boron partitions preferentially into the liquid. Its overall liquid-vapor fractionation is, however, weak: Calculated boron distribution coefficients DBliquid-vapor are < 2.5 at all run conditions. With decreasing pressure (i.e. increasing opening of the solvus) DBliquid-vapor increases along the individual isotherms. Extrapolation to salt saturated conditions yields maximum boron liquid-vapor fractionations of DBliquid-vapor = 1.8 at 450°C and DBliquid-vapor = 2.7 at 400°C. 11B preferentially fractionates into the vapor. Calculated Δ11Bvapor-liquid = {[(11B/10B)vapor - (11B/10B)liquid]/(11B/10B)NBS 951}*1000 are small and range from 0.2 (± 0.7) to 0.9 (± 0.5) ‰ at 450°C and from 0.1 (± 0.6) to 0.7 (± 0.6) ‰ at 400°C. The data indicate increasing isotopic fractionation with decreasing pressure (i.e. increasing opening of the solvus). Extrapolation to salt saturated conditions yields maximum boron isotope liquid-vapor fractionations of Δ11Bvapor-liquid = 1.5 (± 0.7) ‰ at 450°C and Δ11Bvapor-liquid = 1.3 (± 0.6) ‰ at 400°C. The weak boron isotope fractionation suggests similar trigonal speciation in liquid and vapor. Although the boron and boron isotope fractionation between liquid and vapor is only weak, mass balance calculations indicate that for high degrees of fractionation liquid-vapor phase separation in an open system can significantly alter the boron and boron isotope signature of low-salinity hydrous fluids in hydrothermal systems. Comparing the model calculations with natural oceanic hydrothermal fluids, however, indicate that other processes than fluid phase separation dominate the boron geochemistry in oceanic hydrothermal fluids.  相似文献   

17.
Polythionates (SxO62−) are important in redox transformations involving many sulfur compounds. Here we investigate the oxidation kinetics and mechanisms of trithionate and tetrathionate oxidation between pH 0.4 and pH 2 in the presence of Fe3+ and/or oxygen. In these solutions, Fe3+ plus oxygen oxidizes tetrathionate and trithionate at least an order of magnitude faster than oxygen alone. Kinetic measurements, coupled with density functional calculations, suggest that the rate-limiting step for tetrathionate oxidation involves Fe3+ attachment, followed by electron density shifts that result in formation of a sulfite radical and S3O30 derivatives. The overall reaction orders for trithionate and tetrathionate are fractional due to rearrangement reactions and side reactions between reactants and intermediate products. The pseudo-first order rate coefficients for tetrathionate range from 10−11 s−1 at 25°C to 10−8 s−1 at 70°C, compared to 2 × 10−7 s−1 at 35 °C for trithionate. The apparent activation energy (EA) for tetrathionate oxidation at pH 1.5 is 104.5 ± 4.13 kJ/mol. A rate law at pH 1.5 and 70°C between 0.5 and 5 millimolar [Fe3+] is of the form:
  相似文献   

18.
The solubility of cyclooctasulfur in water and sea water at various temperatures in the range between 4 and 80 °C was determined. Cyclooctasulfur in equilibrium with rhombic sulfur reacted with hot acidic aqueous potassium cyanide to form thiocyanate anion which was measured by anion chromatography. Sulfur solubility in pure water was found to increase with temperature by more than 78 times: from 6.1 nM S8 at 4 °C to 478 nM S8 at 80 °C. The following thermodynamic values for solubilisation of S8 in water were calculated from the experimental data: K° = 3.01 ± 1.04 × 10−8, ΔGr° = 42.93 ± 0.73 kJ mol−1, ΔHr° = 47.4 ± 3.6 kJmol−1, ΔSr° = 15.0 ± 11.7 J mol−1 K−1). Solubility of cyclooctasulfur in sea water was found to be 61 ± 13% of the solubility in pure water regardless of the temperature.  相似文献   

19.
Equilibrium in the chabazite-H2O system was investigated by isothermal thermogravimetric analysis over a large range of temperatures (from 23 to 315°C) and H2O-vapor pressures (from 0.03 to 28 mbar). Thermodynamic analysis of the phase-equilibrium data revealed the existence of three energetically distinct types of H2O, referred to as S-1, S-2, and S-3. At 23°C and 26 mbar of H2O-vapor pressure, chabazite has maximum H2O occupancies of 8.2, 11.1, and 3.1 wt.% for S-1, S-2, and S-3, respectively. During dehydration, S-1 H2O is lost first, followed by S-2 H2O and then S-3 H2O, with significant overlap for S-1 and S-2 as well as S-2 and S-3. The thermodynamics of chabazite-H2O were modeled using three independent equilibrium formulations for S-1, S-2, and S-3. These formulations yielded standard-state molar Gibbs free energy of hydration of −21.8 ± 0.6, −52.1 ± 1.8, and −111.7 ± 6.7 kJ/mol for S-1, S-2, and S-3. Standard-state molar enthalpies of hydration for each type of H2O are −65.6 ± 0.5, −100.1 ± 1.6, and −156.9 ± 6.2 kJ/mol, respectively. Integral molar values for the Gibbs free energy of hydration for each type of H2O are −19.0 ± 0.7, −40.1 ± 2.1, and −76.9 ± 9.6 kJ/mol, respectively. Integral molar values for the enthalpy of hydration for each type of H2O are −62.8 ± 0.6, −88.1 ± 1.9, and −122.2 ± 9.3 kJ/mol, respectively. Integration of the predicted total partial molar enthalpy of hydration for all three types of H2O over the full H2O content of chabazite gave an integral molar enthalpy of −39.65 ± 9.3 kJ/mol relative to liquid water. The thermodynamic data obtained for the hydration of natural chabazite were used to predict the hydration state of chemically similar chabazites under various temperatures and PH2O, ranging from 25 to 400°C and from 10−5 to 104 bars.  相似文献   

20.
Ammonia (NH3) is the major intermediate phase in the pathway of nitrogen (N) transfer from the fixed N phases (e.g., in crustal material) to free N2 (e.g., in natural gas reservoirs and volcanic gases). Yet the N isotopic behavior during these N-cycling processes remains poorly known. In an attempt to contribute to the understanding of N cycling using N isotopes, we carried out laboratory experiments to investigate the N isotopic effect associated with thermal decomposition of ammonia (2NH3 → N2 + 3H2). Pure NH3 (with initial δ15NNH3 of ∼ −2‰, relative to air standard) was sealed into quartz tubes and thermally decomposed at 600, 700 or 800 °C from 2 hours to 500 days. With the progress of the reaction, the δ15N of the remaining NH3 and the accumulated N2 increased from −2 to +35‰ and from −20 to −2‰, respectively. The differences of the N-isotope fractionations at the three temperatures are not significant. Modeling using the Rayleigh distillation model yielded similar kinetic N-isotope fractionation factors (αN2-NH3) of 0.983 ± 0.002 for 600, 700 and 800 °C. Applied to geological settings, this significant isotope discrimination (∼17‰) associated with partial decomposition of NH3/NH4+ from crustal sources (δ15Naverage ∼ +6.3‰) can produce mantle-like (i.e. ∼ −5‰) or even lower δ15N values of N2. This may explain the large variation of δ15N (−20 to +30‰) of N2 in natural gas reservoirs. It can also possibly explain the extreme 15N-depletion of N2 in some volcanic gases. This possibility has to be carefully considered when using N isotopes to trace geological N cycling across subduction zones by analysis of volcanic N2.  相似文献   

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