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1.
The response of magnesiochloritoid to pressure has been studied by single crystal X-ray diffraction in a diamond anvil cell, using crystals with composition Mg 1.3Fe 0.7Al 4Si 2O 10(OH) 4. The unit cell parameters decrease from a = 9.434 (3), b = 5.452 (2), c = 18.136 (5) Å, β = 101.42° (2) (1 bar pressure) to a = 9.370 (7), b = 5.419 (5), c = 17.88 (1) Å, β = 101.5° (1) (42 kbar pressure), following a slightly anisotropic compression pattern (linear compressibilities parallel to unit cell edges: β a = 1.85, β b = 1.74, β c = 3.05 × 10 ?4 kbar ?1) with a bulk modulus of 1480 kbar. Perpendicular to c, the most compressible direction, the crystal structure (space group C2/c) consists of two kinds of alternating octahedral layers connected via isolated SiO 4 tetrahedra. With increasing pressure the slightly wavy layer [Mg 1.3Fe 0.7AlO 2(OH) 4] tends to flatten. Furthermore, the octahedra in this layer, with all cations underbonded, are more compressible than the octahedra in the (A1 3O 8) layer with slightly overbonded aluminum. Comparison between high-pressure and high-temperature data yields the following equations: $$\begin{gathered} a_{P,T} = 9.434{\text{ }}{\AA} - 174 \cdot 10^{ - 5} {\text{ }}{\AA}{\text{kb}}^{{\text{ - 1}}} \cdot P \hfill \\ {\text{ }} + 9 \cdot 10^{ - 5} {\text{ }}{\AA}^\circ C^{ - 1} \cdot (T - 25^\circ C) \hfill \\ b_{P,T} = 5.452{\text{ }}{\AA} - 95 \cdot 10^{ - 5} {\text{ }}{\AA}{\text{kb}}^{{\text{ - 1}}} \cdot P \hfill \\ {\text{ }} + 5 \cdot 65 \cdot 10^{ - 5} {\text{ }}{\AA}^\circ C^{ - 1} \cdot (T - 25^\circ C) \hfill \\ c_{P,T} = 18.136{\text{ }}{\AA} - 549 \cdot 10^{ - 5} {\text{ }}{\AA}{\text{kb}}^{{\text{ - 1}}} \cdot P \hfill \\ {\text{ }} + 16 \cdot 2^{ - 5} {\text{ }}{\AA}^\circ C^{ - 1} \cdot (T - 25^\circ C) \hfill \\ \end{gathered} $$ with P in kbar and T in °C. These equations indicate that the unit cell and bond geometry of magnesiochloritoid at formation conditions do not differ greatly from those at the outcrop conditions, e.g. the calculated unitcell volume is 917.3 Å 3 at P = 16 kbar and T=500 °C, whereas the observed volume at room conditions is 914.4 Å 3. In addition, they show that the specific gravity increases from formation at depth to outcrop at surface conditions. 相似文献
2.
The solubility of pentatungstate of sodium ( PTS) Na 2W 5O 16 · H 2O and sodium tungsten bronzes ( STB) Na 0.16WO 3 in acid chloride solutions containing 0.026, 0.26, and 3.02 m NaCl have been studied at 500°C, 1000 bar, given fO 2 (Co-CoO, Ni-NiO, PTS-STB buffers), and constant NaCl/HCl ratio (Ta 2O 5-Na 2Ta 4O 11 buffer). Depending on experimental conditions, the tungsten content in the solutions after experiments varied from 10 −3 to 2 × 10 −2 mol/kg H 2O. Obtained data were used to calculate the formation constants of predominant tungsten complexes (VI, V): H 3W 3VIO 123−, W 3VO 93−, [W VW 4VIO 16] 3−, for reactions
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$
\begin{gathered}
3H_2 WO_4^0 \leftrightarrow H_3 W_3 O_{12}^{3 - } + 3H^ + \log K_p = - 7.5 \pm 0.1, \hfill \\
3H_2 WO_4^0 \leftrightarrow W_3 O_9^{3 - } + 1.5H_2 O + 3H^ + + 0.75O_2 \log K_p = - 25.7 \pm 0.2, \hfill \\
5H_2 WO_4^0 \leftrightarrow \left[ {W^V W_4^{VI} O_{16} } \right]^{3 - } + 3H^ + + 3.5H_2 O + 0.25O_2 \log K_p = - 4.6 \pm 0.1 \hfill \\
\end{gathered}
$
\begin{gathered}
3H_2 WO_4^0 \leftrightarrow H_3 W_3 O_{12}^{3 - } + 3H^ + \log K_p = - 7.5 \pm 0.1, \hfill \\
3H_2 WO_4^0 \leftrightarrow W_3 O_9^{3 - } + 1.5H_2 O + 3H^ + + 0.75O_2 \log K_p = - 25.7 \pm 0.2, \hfill \\
5H_2 WO_4^0 \leftrightarrow \left[ {W^V W_4^{VI} O_{16} } \right]^{3 - } + 3H^ + + 3.5H_2 O + 0.25O_2 \log K_p = - 4.6 \pm 0.1 \hfill \\
\end{gathered}
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3.
Oxygen diffusion in albite has been determined by the integrating (bulk 18O) method between 750° and 450° C, for a P H2O of 2 kb. The original material has a low dislocation density (<10 6 cm ?2), and its lattice diffusion coefficient ( D 1), given below, agrees well with previous determinations. A sample was deformed at high temperature and pressure to produce a uniform dislocation density of 5 × 10 9 cm ?2. The diffusion coefficient ( D a) for this deformed material, given below, is about 0.5 and 0.7 orders of magnitude larger than D 1 at 700° and 450° C, respectively. This enhancement is believed due to faster diffusion along the cores of dislocations. Assuming a dislocation core radius of 4 Å, the calculated pipe diffusion coefficient ( D p), given below, is about 5 orders of magnitude larger than D 1. These results suggest that volume diffusion at metamorphic conditions may be only slightly enhanced by the presence of dislocations. $$\begin{gathered} D_1 = 9.8 \pm 6.9 \times 10^{ - 6} (cm^2 /\sec ) \hfill \\ {\text{ }} \cdot \exp [ - 33.4 \pm 0.6(kcal/mole)/RT] \hfill \\ \end{gathered} $$ $$\begin{gathered} D_a = 7.6 \pm 4.0 \times 10^{ - 6} (cm^2 /\sec ) \hfill \\ {\text{ }} \cdot \exp [ - 30.9 \pm 1.1(kcal/mole)/RT] \hfill \\ \end{gathered} $$ $$\begin{gathered} D_p \approx 1.2 \times 10^{ - 1} (cm^2 /\sec ) \hfill \\ {\text{ }} \cdot \exp [ - 29.8(kcal/mole)/RT]. \hfill \\ \end{gathered} $$ 相似文献
4.
Spatial factor analysis (SFA) is a multivariate method that determines linear combinations of variables with maximum autocorrelation at a given lag. This is achieved by deriving estimates of auto-/cross-correlations of the variables and calculating the corresponding eigenvectors of the covariance quotient matrix. A two-point spatial factor analysis model derives factors by the formation of transition matrix U comparing auto-/cross-correlations at lag 0, R
0, with those at a specified lag d, R
d, expressed as U
d= R
0
–1
R d. The matrix U
d can be decomposed into its spectral components which represent the spatial factors. The technique has been extended to include three points of reference. Spatial factors can be derived from the relationship: |
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5.
Experiments at high pressure and temperature indicate that excess Ca may be dissolved in diopside. If the (Ca, Mg) 2Si 2O 6 clinopyroxene solution extends to more Ca-rich compositions than CaMgSi 2O 6, macroscopic regular solution models cannot strictly be applied to this system. A nonconvergent site-disorder model, such as that proposed by Thompson (1969, 1970), may be more appropriate. We have modified Thompson's model to include asymmetric excess parameters and have used a linear least-squares technique to fit the available experimental data for Ca-Mg orthopyroxene-clinopyroxene equilibria and Fe-free pigeonite stability to this model. The model expressions for equilibrium conditions \(\mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Mg}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction A) and \(\mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{opx}}} = \mu _{{\text{Ca}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{\text{6}} }^{{\text{cpx}}} \) (reaction B) are given by: 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Mg}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ W_{21} [2(X_{{\text{Ca}}}^{{\text{M2}}} )^3 - (X_{{\text{Ca}}}^{{\text{M2}}} ] \hfill \\ {\text{ + 2W}}_{{\text{22}}} [X_{{\text{Ca}}}^{{\text{M2}}} )^2 - (X_{{\text{Ca}}}^{{\text{M2}}} )^3 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{Wo}}}^{{\text{opx}}} )^2 \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = {\text{RT 1n}}\left[ {\frac{{(X_{{\text{Ca}}}^{{\text{opx}}} )^2 }}{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Ca}}}^{{\text{M2}}} }}} \right] - \frac{1}{2}\{ 2W_{21} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^2 - (X_{{\text{Mg}}}^{{\text{M2}}} )^3 ] \hfill \\ {\text{ + W}}_{{\text{22}}} [2(X_{{\text{Mg}}}^{{\text{M2}}} )^3 - (X_{{\text{Mg}}}^{{\text{M2}}} )^2 + \Delta {\text{G}}_{\text{*}}^{\text{0}} (X_{{\text{Mg}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} )\} \hfill \\ {\text{ + W}}^{{\text{opx}}} (X_{{\text{En}}}^{{\text{opx}}} )^2 \hfill \\ \hfill \\ \end{gathered} $$ where 1 $$\begin{gathered} \Delta \mu _{\text{A}}^{\text{O}} = 2.953 + 0.0602{\text{P}} - 0.00179{\text{T}} \hfill \\ \Delta \mu _{\text{B}}^{\text{O}} = 24.64 + 0.958{\text{P}} - (0.0286){\text{T}} \hfill \\ {\text{W}}_{{\text{21}}} = 47.12 + 0.273{\text{P}} \hfill \\ {\text{W}}_{{\text{22}}} = 66.11 + ( - 0.249){\text{P}} \hfill \\ {\text{W}}^{{\text{opx}}} = 40 \hfill \\ \Delta {\text{G}}_*^0 = 155{\text{ (all values are in kJ/gfw)}}{\text{.}} \hfill \\ \end{gathered} $$ . Site occupancies in clinopyroxene were determined from the internal equilibrium condition 1 $$\begin{gathered} \Delta G_{\text{E}}^{\text{O}} = - {\text{RT 1n}}\left[ {\frac{{X_{{\text{Ca}}}^{{\text{M1}}} \cdot X_{{\text{Mg}}}^{{\text{M2}}} }}{{X_{{\text{Ca}}}^{{\text{M2}}} \cdot X_{{\text{Mg}}}^{{\text{M1}}} }}} \right] + \tfrac{1}{2}[(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} )(2{\text{X}}_{{\text{Ca}}}^{{\text{M2}}} - 1) \hfill \\ {\text{ + }}\Delta G_*^0 (X_{{\text{Ca}}}^{{\text{M1}}} - X_{{\text{Ca}}}^{{\text{M2}}} ) + \tfrac{3}{2}(2{\text{W}}_{{\text{21}}} - {\text{W}}_{{\text{22}}} ) \hfill \\ {\text{ (1}} - 2X_{{\text{Ca}}}^{{\text{M1}}} )(X_{{\text{Ca}}}^{{\text{M1}}} + \tfrac{1}{2})] \hfill \\ \end{gathered} $$ where δG E 0 =153+0.023T+1.2P. The predicted concentrations of Ca on the clinopyroxene Ml site are low enough to be compatible with crystallographic studies. Temperatures calculated from the model for coexisting ortho- and clinopyroxene pairs fit the experimental data to within 10° in most cases; the worst discrepancy is 30°. Phase relations for clinopyroxene, orthopyroxene and pigeonite are successfully described by this model at temperatures up to 1,600° C and pressures from 0.001 to 40 kbar. Predicted enthalpies of solution agree well with the calorimetric measurements of Newton et al. (1979). The nonconvergent site disorder model affords good approximations to both the free energy and enthalpy of clinopyroxenes, and, therefore, the configurational entropy as well. This approach may provide an example for Febearing pyroxenes in which cation site exchange has an even more profound effect on the thermodynamic properties. 相似文献
6.
A unifying theory of kinetic rate laws, based on order parameter theory, is presented. The time evolution of the average order parameter is described by $$\langle Q\rangle \propto \smallint P(x)e^{^{^{^{^{^{^{ - xt} } } } } } } dx = L(P)$$ where t is the time, x is the effective inverse susceptibility, and L indicates the Laplace transformation. The probability function P(x) can be determined from experimental data by inverse Laplace transformation. Five models are presented: - Polynomial distributions of P(x) lead to Taylor expansions of 〈Q〉 as $$\langle Q\rangle = \frac{{\rho _1 }}{t} + \frac{{\rho _2 }}{{t^2 }} + ...$$
- Gaussian distributions (e.g. due to defects) lead to a rate law $$\langle Q\rangle = e^{ - x_0 t} e^{^{^{^{^{\frac{1}{2}\Gamma t^2 } } } } } erfc\left( {\sqrt {\frac{\Gamma }{2}} t} \right)$$ where x 0 is the most probable inverse time constant, Γ is the Gaussian line width and erfc is the complement error integral.
- Maxwell distributions of P are equivalent to the rate law 〈Q〉∝e?k√t .
- Pseudo spin glasses possess a logarithmic rate law 〈Q〉∝lnt.
- Power laws with P(x)=x a lead to a rate law: ln〈Q〉=-(α + 1) ln t.
The power spectra of Q are shown for Gaussian distributions and pseudo spin glasses. The mechanism of kinetic gradient coupling between two order parameters is evaluated. 相似文献
7.
Equilibrium Zn isotope fractionation was investigated using first-principles quantum chemistry methods at the B3LYP/6-311G* level. The volume variable cluster model method was used to calculate isotope fractionation factors of sphalerite, smithsonite, calcite, anorthite, forsterite, and enstatite. The water-droplet method was used to calculate Zn isotope fractionation factors of Zn 2+-bearing aqueous species; their reduced partition function ratio factors decreased in the order \(\left[ {{\text{Zn}}\left( {{\text{H}}_{2} {\text{O}}} \right)_{6} } \right]^{2 + } > \left[ {{\text{ZnCl}}\left( {{\text{H}}_{2} {\text{O}}} \right)_{5} } \right]^{ + } > \left[ {{\text{ZnCl}}_{2} \left( {{\text{H}}_{2} {\text{O}}} \right)_{4} } \right] > \left[ {{\text{ZnCl}}_{3} \left( {{\text{H}}_{2} {\text{O}}} \right)_{2} } \right]^{ - } > {\text{ZnCl}}_{4} ]^{2 - }\). Gaseous ZnCl 2 was also calculated for vaporization processes. Kinetic isotope fractionation of diffusional processes in a vacuum was directly calculated using formulas provided by Richter and co-workers. Our calculations show that in addition to the kinetic isotope effect of diffusional processes, equilibrium isotope fractionation also contributed nontrivially to observed Zn isotope fractionation of vaporization processes. The calculated net Zn isotope fractionation of vaporization processes was 7–7.5‰, with ZnCl 2 as the gaseous species. This matches experimental observations of the range of Zn isotope distribution of lunar samples. Therefore, vaporization processes may be the cause of the large distribution of Zn isotope signals found on the Moon. However, we cannot further distinguish the origin of such vaporization processes; it might be due either to igneous rock melting in meteorite bombardments or to a giant impact event. Furthermore, isotope fractionation between Zn-bearing aqueous species and minerals that we have provided helps explain Zn isotope data in the fields of ore deposits and petrology. 相似文献
8.
Dialysis and chemical speciation modelling have been used to calculate activities of Fe 3+ for a range of UK surface waters of varying chemistry (pH 4.3–8.0; dissolved organic carbon 1.7–40.3 mg l −1) at 283 K. The resulting activities were regressed against pH to give the empirical model: . Predicted Fe 3+ activities are consistent with a solid–solution equilibrium with hydrous ferric oxide, consistent with some previous studies
on Fe(III) solubility in the laboratory. However, as has also sometimes been observed in the laboratory, the slope of the
solubility equation is lower than the theoretical value of 3. The empirical model was used to predict concentrations of Fe
in dialysates and ultrafiltrates of globally distributed surface and soil/groundwaters. The predictions were improved greatly
by the incorporation of a temperature correction for , consistent with the temperature dependence of previously reported hydrous ferric oxide solubility. The empirical model,
incorporating temperature effects, may be used to make generic predictions of the ratio of free and complexed Fe(III) to dissolved
organic matter in freshwaters. Comparison of such ratios with observed Fe:dissolved organic matter ratios allows an assessment
to be made of the amounts of Fe present as Fe(II) or colloidal Fe(III), where no separate measurements have been made.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
9.
Equilibrium alumina contents of orthopyroxene coexisting with spinel and forsterite in the system MgO-Al 2O 3- SiO2 have been reversed at 15 different P-T conditions, in the range 1,030–1,600° C and 10–28 kbar. The present data and three reversals of Danckwerth and Newton (1978) have been modeled assuming an ideal pyroxene solid solution with components Mg 2Si 2O 6 (En) and MgAl 2SiO6 (MgTs), to yield the following equilibrium condition (J, bar, K): $$\begin{gathered} RT{\text{ln(}}X_{{\text{MgTs}}} {\text{/}}X_{{\text{En}}} {\text{) + 29,190}} - {\text{13}}{\text{.42 }}T + 0.18{\text{ }}T + 0.18{\text{ }}T^{1.5} \hfill \\ + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP = 0,} \hfill \\ \end{gathered} $$ where $$\begin{gathered} + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP} \hfill \\ = [0.013 + 3.34 \times 10^{ - 5} (T - 298) - 6.6 \times 10^{ - 7} P]P. \hfill \\ \end{gathered} $$ The data of Perkins et al. (1981) for the equilibrium of orthopyroxene with pyrope have been similarly fitted with the result: $$\begin{gathered} - RT{\text{ln(}}X_{{\text{MgTs}}} \cdot X_{{\text{En}}} {\text{) + 5,510}} - 88.91{\text{ }}T + 19{\text{ }}T^{1.2} \hfill \\ + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP = 0,} \hfill \\ \end{gathered} $$ where $$\begin{gathered} + \int\limits_1^P {\Delta V_{T,P}^{\text{0}} dP} \hfill \\ = [ - 0.832 - 8.78{\text{ }} \times {\text{ 10}}^{ - {\text{5}}} (T - 298) + 16.6{\text{ }} \times {\text{ 10}}^{ - 7} P]{\text{ }}P. \hfill \\ \end{gathered} $$ The new parameters are in excellent agreement with measured thermochemical data and give the following properties of the Mg-Tschermak endmember: $$H_{f,970}^0 = - 4.77{\text{ kJ/mol, }}S_{298}^0 = 129.44{\text{ J/mol}} \cdot {\text{K,}}$$ and $$V_{298,1}^0 = 58.88{\text{ cm}}^{\text{3}} .$$ The assemblage orthopyroxene+spinel+olivine can be used as a geothermometer for spinel lherzolites, subject to a choice of thermodynamic mixing models for multicomponent orthopyroxene and spinel. An ideal two-site mixing model for pyroxene and Sack's (1982) expressions for spinel activities provide, with the present experimental calibration, a geothermometer which yields temperatures of 800° C to 1,350° C for various alpine peridotites and 850° C to 1,130° C for various volcanic inclusions of upper mantle origin. 相似文献
10.
The equilibrium partitioning of Fe 2+ and Mg between olivine and liquid along a liquid line of descent has been determined for a calc-alkaline system, ranging in composition from picritic to andesitic. Experiments were conducted between 1000–1450° C and 1 bar to 30 kbar. Within the compositional range investigated
and
, the compositional dependence of the Fe 2+ and Mg partitioning is a function of the Mg-content of the liquid. The Mg-content of the liquid correlates strongly with temperature. The variation of the Fe 2+ and Mg partitioning were therefore evaluated individualy as functions of composition and temperature alone. The composition dependence of the cation-partitioning coefficients (Kd) is given by the following two equations: |
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11.
The non-ideal regular Mg-Fe binary in cordierite has been derived through multivariate linear regression of the expression RT InK D +(P- 1)ΔVK 1 0 , 298 along with updated subfegular mixing parameter of almandine-pyrope solution (Hackler and Wood 1989; Berman 1990). The data base used for multivariate analyses consists of published experimental data (n = 177) on Mg-Fe partitioning between garnet and cordierite in the P-T range 650–1050°C and 4–12 K bar. The non-ideality can be approximated by temperature-dependent Margules parameters. The retrieved values of ΔH <T> o and ΔH <T> o of exchange reaction between garnet and cordierite and enthalpy and entropy of mixing of Mg-Fe cordierite were combined with recent quaternary (Fe-Mg-Ca-Mn) mixing data in garnet to obtain the geothermometric expressions to determine temperature (T Kelvin): $$\begin{gathered} T(WH) = 6832 + 0.031(P - 1) - \{ 166(X_{Mg}^{Gt} )^2 - 506(X_{Fe}^{Gt} )^2 + 680X_{Fe}^{Gt} X_{Mg}^{Gt} + 336(X_{Ca} + X_{Mn} ) \hfill \\ (X_{Mg} - X_{Fe} )^{Gt} - 3300X_{Ca}^{Gt} - 358X_{Mn}^{Gt} \} + 954(X_{Fe} - X_{Mg} )^{Crd} /1.987\ln K_D + 3.41 + 1.5X_{Ca}^{Gt} \hfill \\ + 1.23(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ \end{gathered} $$ $$\begin{gathered} T(Br) = 6920 + 0.031(p - 1) - \{ 18(X_{Mg}^{Gt} )^2 - 296(X_{Fe}^{Gt} )^2 + 556X_{Fe}^{Gt} X_{Mg}^{Gt} - 6339X_{Ca}^{Gt} X_{Mg}^{Gt} \hfill \\ - 99(X_{Ca}^{Gt} )^2 + 4687X_{Ca}^{Gt} (X_{Mg} - X_{Fe}^{Gt} ) - 4269X_{Ca}^{Gt} X_{Fe}^{Gt} - 358X_{Mn}^{Gt} \} + 640(X_{Fe} - X_{Mg} )^{Crd} \hfill \\ + 1.90X_{Ca}^{Gt} (X_{Mg} - X_{Ca} )^{Gt} . \hfill \\ \end{gathered} $$ 相似文献
12.
Experiments were conducted to determine CO 2 solubilities in alkali basalts from Vesuvius, Etna and Stromboli volcanoes. The basaltic melts were equilibrated with nearly
pure CO 2 at 1,200°C under oxidizing conditions and at pressures ranging from 269 to 2,060 bars. CO 2 solubility was determined by FTIR measurements. The results show that alkalis have a strong effect on the CO 2 solubility and confirm and refine the relationship between the compositional parameter Π devised by Dixon (Am Mineral 82:368–378,
1997) and the CO 2 solubility. A general thermodynamic model for CO 2 solubility in basaltic melts is defined for pressures up to 2 kbars. Based on the assumption that O 2− and CO 32− mix ideally, we have:
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_boxclose_3^2 - ^m (P,T)X_^2 - ^m f__2 (P,T) K(P,T) = X__3^2 - ^m (P,T) ( X_^2 - ^m f__2 (P,T) ). \begin{gathered} K(P,T) = {\frac{{X_{{{\text{CO}}_{3}^{2 - } }}^{m} (P,T)}}{{X_{{{\text{O}}^{2 - } }}^{m} \times f_{{{\text{CO}}_{2} }} (P,T)}}} \hfill \\ K(P,T) = {{X_{{{\text{CO}}_{3}^{2 - } }}^{m} (P,T)} \mathord{\left/ {\vphantom {{X_{{{\text{CO}}_{3}^{2 - } }}^{m} (P,T)} {\left( {X_{{{\text{O}}^{2 - } }}^{m} \times f_{{{\text{CO}}_{2} }} (P,T)} \right).}}} \right. \kern-\nulldelimiterspace} {\left( {X_{{{\text{O}}^{2 - } }}^{m} \times f_{{{\text{CO}}_{2} }} (P,T)} \right).}} \hfill \\ \end{gathered} 相似文献
13.
Synthetic spinel harzburgite and lherzolite assemblages were equilibrated between 1040 and 1300° C and 0.3 to 2.7 GPa, under
controlled oxygen fugacity ( f
O
2). f
O
2 was buffered with conventional and open double-capsule techniques, using the Fe−FeO, WC-WO 2-C, Ni−NiO, and Fe 3O 4−Fe 2O 3 buffers, and graphite, olivine, and PdAg alloys as sample containers. Experiments were carried out in a piston-cylinder apparatus
under fluid-excess conditions. Within the P-T-X range of the experiments, the redox ratio Fe 3+/ΣFe in spinel is a linear function of f
O
2 (0.02 at IW, 0.1 at WCO, 0.25 at NNO, and 0.75 at MH). It is independent of temperature at given Δlog( f
O
2), but decreases slightly with increasing Cr content in spinel. The Fe 3+/ΣFe ratio falls with increasing pressure at given Δlog( f
O
2), consistent with a pressure correction based on partial molar volume data. At a specific temperature, degree of melting
and bulk composition, the Cr/(Cr+Al) ratio of a spinel rises with increasing f
O
2. A linear least-squares fit to the experimental data gives the semi-empirical oxygen barometer in terms of divergence from
the fayalite-magnetite-quartz (FMQ) buffer:
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14.
Boron is known to interact with a wide variety of protonated ligands(HL) creating complexes of the form B(OH) 2L -.Investigation of the interaction of boric acid and bicarbonate in aqueoussolution can be interpreted in terms of the equilibrium $B(OH)_3^0 + HCO_3^ - \rightleftharpoons B(OH)_2 CO_3^ - + H_2 O$ The formation constant for this reaction at 25 °C and 0.7 molkg -1 ionic strength is $K_{BC} = \left[ {B(OH)_2 CO_3^ - } \right]\left[ {B(OH)_3^0 } \right]^{ - 1} \left[ {HCO_3^ - } \right]^{ - 1} = 2.6 \pm 1.7$ where brackets represent the total concentration of each indicatedspecies. This formation constant indicates that theB(OH) 2 $CO_3^ - $ concentration inseawater at 25 °C is on the order of 2 μmol kg -1. Dueto the presence of B(OH) 2 $CO_3^ - $ , theboric acid dissociation constant ( $K\prime _B $ ) in natural seawaterdiffers from $K\prime _B $ determined in the absence of bicarbonate byapproximately 0.5%. Similarly, the dissociation constants of carbonicacid and bicarbonate in natural seawater differ from dissociation constantsdetermined in the absence of boric acid by about 0.1%. Thesedifferences, although small, are systematic and exert observable influenceson equilibrium predictions relating CO 2 fugacity, pH, totalcarbon and alkalinity in seawater. 相似文献
15.
Reversed phase equilibrium experiments in the system (Ca, Mg, Fe) 2SiO4 provide four tielines at P?1 bar and 1 kbar and 800° C–1,100° C. These tielines have been used to model the solution properties of the olivine quadrilateral following the methods described by Davidson et al. (1981) for quadrilateral clinopyroxenes. The discrepancy between the calculated phase relations and the experimentally determined tielines is within the uncertainty of the experiments. The solution properties of quadrilateral olivines can be described by a non-convergent site-disorder model that allows for complete partitioning of Ca on the M2 site, highly disordered Fe-Mg cation distributions and limited miscibility between high-Ca and low-Ca olivines. The ternary data presented in this paper together with binary solution models for the joins Fo-Mo and Fa-Kst have been used to evaluate two solution parameters: $$\begin{gathered} F^0 \equiv 2(\mu _{{\rm M}o}^0 - \mu _{{\rm K}st}^0 ) + \mu _{Fa}^0 - \mu _{Fo}^0 = 12.660 (1.6) kJ, \hfill \\ \Delta G_*^0 \equiv \mu _{{\rm M}gFe}^0 + \mu _{FeMg}^0 - \mu _{Fo}^0 - \mu _{Fa}^0 = 7.030 (3.9) kJ. \hfill \\ \end{gathered} $$ . Ternary phase quilibrium data for olivines tightly constrain the value of F 0, but not that for ΔG * 0 which describes nonideality in Fe-Mg mixing. From this analysis, we infer a function for the apparent standard state energy of Kst: $$\begin{gathered} \mu _{{\rm K}st}^0 = - 102.79 \pm 0.8 - (T - 298)(0.137026) \hfill \\ + (T - 298 - T1n(T/298))(0.155519) \hfill \\ + (T - 298)^2 (2.8242E - 05)/2 \hfill \\ + (T - 298)^2 (2.9665E + 03)/(2T(298)^2 ) kJ \hfill \\ \end{gathered} $$ where T is in Kelvins and the 298 K value is relative to oxides. 相似文献
16.
Sogdianite, a double-ring silicate of composition
( \text Zr0. 7 6 \text Ti0. 3 84 + \text Fe0. 7 33 + \text Al0.13 ) \Upsigma = 2 ( \square 1. 1 5 \text Na0. 8 5 ) \Upsigma = 2 \text K[\text Li 3 \text Si 1 2 \text O 30 ] ( {\text{Zr}}_{0. 7 6} {\text{Ti}}_{0. 3 8}^{4 + } {\text{Fe}}_{0. 7 3}^{3 + } {\text{Al}}_{0.13} )_{\Upsigma = 2} \left( {\square_{ 1. 1 5} {\text{Na}}_{0. 8 5} } \right)_{\Upsigma = 2} {\text{K}}[{\text{Li}}_{ 3} {\text{Si}}_{ 1 2} {\text{O}}_{ 30} ] from Dara-i-Pioz, Tadjikistan, was studied by the combined application of 57Fe M?ssbauer spectroscopy and electronic structure calculations. The M?ssbauer spectrum confirms published microprobe and
X-ray single-crystal diffraction results that indicate that Fe 3+ is located at the octahedral A-site and that no Fe 2+ is present. Both the measured and calculated quadrupole splitting, Δ E
Q, for Fe 3+ are virtually 0 mm s −1. Such a value is unusually small for a silicate and it is the same as the Δ E
Q value for Fe 3+ in structurally related sugilite. This result is traced back to the nearly regular octahedral coordination geometry corresponding
to a very symmetric electric field gradient around Fe 3+. A crystal chemical interpretation for the regular octahedral geometry and the resulting low Δ E
Q value for Fe 3+ in the M?ssbauer spectrum of sogdianite is that structural strain is largely “taken up” by weak Li–O bonds permitting highly
distorted LiO 4 tetrahedra. Weak Li–O bonding allows the edge-shared more strongly bonded Fe 3+O 6 octahedra to remain regular in geometry. This may be a typical property for all double-ring silicates with tetrahedrally
coordinated Li. 相似文献
17.
Recent improvements to experiments and modelling of batch dissolution in a turbulent reactor, based upon the shrinking object model, are extended to middle loadings of gypsum, that is, in the region between low and high loadings, which lead, respectively, to high under-saturation or saturation with a great excess of solid left undissolved. Dissolved calcium sulphate concentration was monitored by change in electrical conductivity. This investigation uses an improved, ion-pair model for CaSO 4 0 to allow for the presence of calcium or sulphate added as common ions. The study demonstrates that the full dissolution curve for 5.82 mM loadings of 106-μm particles of gypsum (~1.00 g L ?1) in de-ionised water barely changed in the presence of either 4.64 or 8.09 mM calcium chloride, or 4.39 mM sodium sulphate. However, this masked a doubling of dissolution rate imposed by comparable increases in ionic strength from sodium chloride. The results are consistent with the ion pair, CaSO 4 0 , being the key species in the rate-determining step of the back-reaction, and perhaps all salt dissolutions, including calcium carbonate. In this case, the rate equation is as follows: \( {\frac{{{\text{d}}c}}{{{\text{d}}t}}} = \frac{S}{V} \cdot (k_{1} - k_{2}^{\prime } \cdot [{\text{CaSO}}_{ 4}^{0} ]) \), where k 1 and k 2′ are rate constants. The reported observations are interpreted as effects of ionic strength and common ion concentrations upon the formation equilibrium for the ion pair. This rate equation readily transforms mathematically to one involving the product of [Ca 2+] and [SO 4 2?] in the back-reaction. The parallel of this with the well-known PWP equation used in calcium carbonate dissolution is discussed, with the CaHCO 3 + ion pair of the equation being replaced by that of CaCO 3 0 . Meanwhile, the earlier use of the product, [Ca 2+] ½ × [CO 3 2?] ½, in the back-reaction term of another dissolution rate equation for calcite is shown to be incorrect. Finally, it is argued that the shrinking object model should be repositioned as a logical derivative of the hydrodynamical approach to dissolution. 相似文献
18.
New data concerning glaucophane are presented. New high temperature drop calorimetry data from 400 to 800 K are used to constrain the heat capacity at high temperature. Unpublished low temperature calorimetric data are used to estimate entropy up to 900 K. These data, corrected for composition, are fitted for C p and S to the polynomial expressions (J · mol ?1 · K ?2) for T> 298.15 K: $$\begin{gathered} C_p = 11.4209 * 10^2 - 40.3212 * 10^2 /T^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} - 41.00068 * 10^6 /T^2 \hfill \\ + 52.1113 * 10^8 /T^3 \hfill \\ \end{gathered} $$ $$\begin{gathered} S = 539 + 11.4209 * 10^2 * \left( {\ln T - \ln 298.15} \right) - 80.6424 * 10^2 \hfill \\ * \left( {T^{ - {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} - 1/\left( {298.15} \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} } \right) + 20.50034 * 10^6 \hfill \\ * \left( {T^{ - 2} - 1/\left( {298.15} \right)^2 } \right) - 17.3704 * 10^8 * \left( {T^{ - 3} - \left( {1/298.15} \right)^3 } \right) \hfill \\ \end{gathered} $$ IR and Raman spectra from 50 to 3600 cm ?1 obtained on glaucophane crystals close to the end member composition are also presented. These spectroscopic data are used with other data (thermal expansion, acoustic velocities etc.) in vibrational modelling. This last method provides an independent way for the determination of the thermodynamic properties (C p and entropy). The agreement between measured and calculated properties is excellent (less than 2% difference between 100 and 1000 K). It is therefore expected that vibrational modelling could be applied to other amphiboles for which spectroscopic data are available. Finally, the enthalpy of formation of glaucophane is calculated. 相似文献
19.
Thorium(IV) sorption onto hematite (-Fe 2O 3) was examined as a function of pH and ionic strength. Sorption behaved Langmuirian over an eleven order of magnitude range in adsorption densities, : 10 –12 to 10 –1 moles Th sorbed per mole hematite sites, indicating that the overall free energy of Th adsorption is independent of adsorption density. Modeling of Th sorption was conducted with the Triple Layer Model of Davis and Leckie; reactions considered included solution-phase hydroxy and carbonato complexes of thorium, and carbonate/hematite surface complexes. The entire Th sorption isotherm can be modeled with a single surface complex formation reaction |
相似文献
20.
Interaction of freshly precipitated silica gel with aqueous solutions was studied at laboratory batch experiments under ambient
and near neutral pH-conditions. The overall process showed excellent reversibility: gel growth could be considered as an opposite
process to dissolution and a linear rate law could be applied to experimental data. Depending on the used rate law form, the
resulting rate constants were sensitive to errors in parameters/variables such as gel surface area, equilibrium constants,
Si-fluxes, and reaction quotients. The application of an Integrated Exponential Model appeared to be the best approach for
dissolution data evaluation. It yielded the rate constants k
dissol ∼ (4.50 ± 0.68) × 10 −12 and k
growth ∼ (2.58 ± 0.39) × 10 −9 mol m −2 s −1 for zero ionic strength. In contrast, a Differential Model gave best results for growth data modeling. It yielded the rate
constants k
dissol ∼ (1.14 ± 0.44) × 10 −11 and k
growth ∼ (6.08 ± 2.37) × 10 −9 mol m −2 s −1 for higher ionic strength ( I ∼ 0.04 to 0.11 mol L −1). The found silica gel solubility at zero ionic strength was somewhat lower than the generally accepted value. Based on the
and standard Gibbs free energy of silica gel formation was calculated as and −850,318 ± 20 J mol −1, respectively. Activation energies for silica gel dissolution and growth were determined as and respectively. An universal value for growth of any silica polymorph, is not consistent with the value for silica gel growth, which questions the hypothesis about one unique activated complex
controlling the silica polymorph growth. 相似文献
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