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1.
The borate polyhedra BO 3 3? , B(OH)3, BO 4 5? , and B(OH) 4 ? are studied using the ab initio and multiple scattering Xα quantum mechanical methods. The ab initio self-consistent-field (SCF) molecular orbital (MO) method, at the minimum basis set level, predicts equilibrium B-O distances within 0.04 Å of their average values in solids so long as the polyhedron charge is small. Orbital energies from double zeta basis set ab initio calculations and analogies with isoelectric compounds are used to assign the X-ray spectra of BO 3 3? and to predict the valence region spectra of BO 4 5? . Contour maps of the difference between molecular and superimposed free atom electron densities show charge buildup along the B-O bond which is only slightly smaller than that observed in CO 3 2? .  相似文献   

2.
Hydrotalcite-like solid solutions have been synthesized by coprecipitation in basic solutions with variable SO 4 2? /CO 3 2? ratios. Chemical determination of CO 3 2? in the interlayer was impossible because of the presence of minor hydromagnesite. SO 4 2? was determined both by chemical analysis and X-ray photoelectron spectroscopy (XPS), the two methods giving similar results. A Raman spectrometry gave additional data on the SO 4 2? /CO 3 2? ratio. Then, the stoichiometry of the anionic interlayers, X s , X c , and X OH were determined, and the influence of X s on the c′ parameter (increasing from c′=7.97 Å to c′=8.63 Å between X s =0 and X s =1) was characterized. In addition, a partitioning curve of SO 4 2? and CO 3 2? between aqueous solutions and hydrotalcite-like compounds was established. Its general shape strongly suggests a miscibility gap between a sulfate-rich end and a carbonate-rich solid solution (maximum SO 4 2? /CO 3 2? about 0.2). This result explains why most of the hydrotalcites synthesized during experimental alteration of basaltic glasses by sea-water (a sulfate-rich solution) are CO 3 2? -rich solid solutions.  相似文献   

3.
An experimental study of the particulars of the solubility and crystallization of brushite Ca(HPO4) · 2H2O from aqueous solution in conditions of a variable pH (6.0–3.0) and the contents of impurity ions (K+, Na+, NH 4 + , Mg2+, SO 4 2? , CO 3 2? ) has been conducted. It is established that brushite solubility markedly rises with a decrease in pH from 6 to 3 and slightly rises with an increase in Mg2+ and SO 4 2? concentrations. The enrichment in K+, Na+, and NH 4 + does not affect brushite solubility. The changeable chemistry of the medium results in variation of the synthetic crystal habit, from rhombic tabular to thickened prismatic crystals.  相似文献   

4.
A new Cu-rich variety of lyonsite has been found from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia). The empirical formula is Cu4.33Fe 2.37 3+ Ti0.26Al0.26Zn0.07(V5.85As0.07Mo0.07P0.01S0.01)O24. The crystal structure was studied on single crystal using synchrotron radiation, R = 0.0514. The mineral is orthorhombic, Pnma, a = 5.1736(7), b =10.8929(12), c = 18.220(2) Å, V = 1026.8(2) Å3, and Z = 2. The structural formula is (Cu0.6Ti0.3Al0.3Fe 0.2 3+ □0.6)Σ2Cu2(Fe 2.2 3+ Cu1.8)Σ4(V5.8As0.1Mo0.1)Σ6O24. It is proposed to recast the simplified formula of lyonsite as Cu3+x (Fe 4?2x 3+ Cu2x )(VO4)6, where 0 ≤ x ≤ 1.  相似文献   

5.
Hydrogeochemical studies have been carried out in a coastal region, using multivariate statistical model, for better understanding the controlling processes that influence the aquifer chemistry. Two principal components (PC1 and PC2) are extracted from the data set of chemical variables (pH, TDS, Ca2+, Mg2+, Na+, K+, HCO 3 ? , Cl?, SO 4 2? , NO 3 ? and F?), which account for 79% of the total variation in the quality of groundwater. The PC1 (salinity controlled process) includes the concentrations of TDS, Mg2+, Na+, K+, Cl?, SO 4 2? and NO 3 ? , while the PC2 (alkalinity controlled process) comprises the concentrations of pH, HCO 3 ? and F?. The spatial distribution of PC scores identifies the locations of high salinity and alkalinity processes. The first process corresponds to the influences of geogenic, anthropogenic and marine sources, and the second one to the influence of water-soil-rock interaction. Thus, the present study shows the usefulness of multivariate statistical model as an effective means of interpretation of spatial controlling processes of groundwater chemistry.  相似文献   

6.
Molecular orbital calculations are presented for the copper-sulfur polyhedral clusters CuS 4 7? , CuS 4 6? , CuS 3 5? and CuS 3 4? , which occur in many minerals. Calculated and experimental optical and X-ray energies are found to be in good agreement. The crystal field orbitals of Cu+ in tetrahedrally coordinated sulfides are found to be less tightly bound than the S3p nonbonding orbitals by about 2–3 eV whereas the e and t 2 crystal field orbitals are split by about 1 eV. The crystal field splitting of Cu2+ in tetrahedral coordination is about 0.7–0.8 eV while the separation of the S3p nonbonding orbitals and the partially filled t 2 crystal field orbital is about 2 eV. In triangular coordination both the Cu+ and Cu2+ crystal field orbitals are more stable than in tetrahedral coordination, more widely split and more strongly mixed with the S3p orbitals. CuS is shown to be unstable as the mixed oxidation state compound Cu2+III (Cu+IV)2S2?(S 2 2? ); rather each Cu is predicted to have a fractional oxidation state and partially-empty crystal field orbitals.  相似文献   

7.
Electric dipole polarizabilities have been calculated from first principles of quantum mechanics for the BO 3 3? , CO 3 2? , NO 3 ? series and for NO 2 ? and LiNO3(g). Calculated trends in average polarizability and polarizability anisotropy in the BO 3 3? -NO 3 ? series are in agreement with experiment and can be qualitatively interpreted in terms of the varying energies of the a1′, a2″ and e′ symmetry unoccupied MO's of the oxyanions. Embedding a CO 3 2? ion in a D3h symmetry array of divalent cations reduces both the average polarizability and its anisotropy, particularly when diffuse s and p functions are included in the calculation. Calculations on the gas phase LiNO3 molecule and on the free NO 3 ? ion in the distorted geometry found in LiNO3(g) allow us to separate polarizability contributions internal to the NO 3 ? and Li+ ions from those which arise from the Li+-NO 3 ? interaction. The Li+-NO 3 ? interaction term so obtained is much smaller than the NO 3 ? contribution but is in turn larger than the Li+ contribution, suggesting that the inclusion of this interaction term is essential for obtaining accurate results for ion pairs. Although static polarizabilities are in reasonable agreement with experiment for NO 3 ? the wavelength dispersion of the polarizability is underestimated by about a factor of two, apparently as a result of inadequacies in the quantum mechanical method. Calculated values are also presented for 14N NMR shieldings in the nitrogen oxyanions but these are in only qualitative agreement with the experimental values. Similarly, calculated values of magnetic susceptibility are in only qualitative agreement with experiment although trends along the BO 3 3? -NO 3 ? series are properly reproduced.  相似文献   

8.
Based on the expert review of literature data on the thermodynamic properties of species in the Cl-Pd system, stepwise and overall stability constants are recommended for species of the composition [PdCl n ]2 ? n , and the standard electrode potential of the half-cell PdCl 4 2? /Pd(c) is evaluated at E 298,15° = 0.646 ± 0.007 V, which corresponds to Δ f G 298.15° = ?400.4 ± 1.4 kJ/mol for the ion PdCl 4 2? (aq). Derived from calorimetric data, Δ f H 298.15° PdCl 4 2? (aq) = ?524.6 ± 1.6 kJ/mol and Δ f H 298.15° Pd2+(aq) = 189.7 ± 2.6 kJ/mol. The assumed values of the overall stability constant of the PdCl 4 2? ion and the standard electrode potential of the PdCl 4 2? /Pd(c) half-cell correspond to Δ f G 298.15° = 190.1 ± 1.4 kJ/mol and S 298.15° = ?94.2 ± 10 J/(mol K) for the Pd2+(aq) ion.  相似文献   

9.
Electron paramagnetic resonance (EPR) measurements of natural anhydrite CaSO4, celestite SrSO4 and barite BaSO4 have revealed the presence of PO 3 2? and SO 3 ? radicals. Hyperfine structure from33S has been detected and measured for the first time. Low-symmetry effects, which are manifested in noncoincidence of g and hyperfine axes, were observed for SO 3 ? . The dynamics of one of the two SO 3 ? types in anhydrite has been investigated. Variations of spin Hamiltonian parameters with temperature have been attributed to thermally induced jumps between the two magnetically inequivalent sites of this center.  相似文献   

10.
The temperature dependence of the lattice parameters of pure anorthite with high Al/Si order reveals the predicted tricritical behaviour of the \(I\bar 1 \leftrightarrow P\bar 1\) phase transition at T c * =510 K. The spontaneous strain couples to the order parameter Q° as x i∝S xQ i Q°2 with S xQ 1 =4.166×10?3, S xQ 2 =0.771×10?3, S xQ 3 =?7.223×10?3 for the diagonal elements. The temperature dependence of Q° is $$Q^{\text{o}} = \left( {1 - \frac{T}{{510}}} \right)^\beta ,{\text{ }}\beta = \tfrac{{\text{1}}}{{\text{4}}}$$ A strong dependence of T c * , S xQ i and β is predicted for Al/Si disordered anorthite.  相似文献   

11.
The solubility of all possible Zn and Pb species in aqueous chloride fluids was evaluated by means of thermodynamic simulations in systems ZnO(PbO)-aqueous solution of NaCl (KCl, NaCl + HCl) within broad ranges of temperature (600–900°C), pressure (0.7–5 kbar), and chloride concentrations, under parameters corresponding to the crystallization and degassing of granitoid magmas in the Earth’s crust. Our simulation results demonstrate that the addition of Cl to the fluid phase in the form of Na(K)Cl and HCl significantly increases the concentrations of Cl-bearing Zn and Pb complexes and the total concentration of the metals in the solutions in equilibrium with the solid oxides. In Zn-bearing fluids, the Zn(OH) 2 0 , ZnOH+, and Zn(OH) 3 ? —hydroxyl complexes and the ZnCl 2 0 , and ZnCl+ chlorocomplexes, which are predominant at low Cl concentrations (CCl < 0.05–0.1 m) give way to ZnCl 4 2? with increasing CCl, which becomes the predominant Zn species of the fluid at CCl > 0.1–0.5 m throughout the whole temperature range in question and pressures higher than 1 kbar. For Pb-bearing fluids, the T-P-X region dominated by the Pb(OH) 2 0 , and Pb(OH) 3 ? hydroxyl complexes is remarkably wider than the analogous region for Zn, particularly at elevated temperatures (≥700°C) in alkaline solutions. An increase in CCl is associated with an increase in the concentration and changes in the speciation of Pb chlorocomplexes: PbCl 2 0 → PbCl 3 ? → PbCl 4 2? . The concentrations of Zn and Pb chlorocomplexes increase with increasing pressure, decreasing temperature, and decrease pH with the addition of HCl to the system. It is demonstrated that the solubility of ZnO at any given T-P-X in alkaline solutions with low chloride concentrations are lower than the solubility of PbO. The Zn concentration increases more significantly than with the Pb concentration with increasing CCl and decreasing pH, so that the Zn concentration in acidic solutions is higher than the Pb concentration over broad ranges of temperature, pressure, and Cl concentration. Chloride complexes of Zn (ZnCl 2 0 , and ZnCl 4 2? ) and Pb (PbCl 2 0 , and PbCl 3 ? are proved to be predominant within broad T-P-X-pH ranges corresponding to the parameters under which magmatic fluid are generated. Our simulation results confirm the hypothesis that chlorocomplexes play a leading role in Zn and Pb distribution between aqueous chloride fluids and granitic melts. These simulation results are consistent with experimental data on the Zn and Pb distribution coefficients (D(Zn)f/m and D(Pb)f/m, respectively) between aqueous chloride fluids and granitic melts that demonstrated that (1) D(Zn)f/m and D(Pb)f/m increase with increasing Na and K chloride concentrations in the aqueous fluid, (2) both D(Zn)f/m and D(Pb)f/m drastically increase when HCl is added to the fluid, and (3) (D(Zn)f/m is higher than D(Pb)f/m at any given T-P-X parameters. The experimentally established decrease in D(Zn)f/m and D(Pb)f/m with increasing pressure (at unchanging temperature and Cl concentration) is likely explained by an increase in the alkalinity of the aqueous chloride fluid in equilibrium with granite melt and, correspondingly, a decrease in the Zn and Pb solubility in this fluid.  相似文献   

12.
This paper presents the point-defect thermodynamics for fayalite and olivine solid solutions (Fe x Mg1?x )2SiO4. By means of thermogravimetry, the metal-to-oxygen ratio of these silicates has been determined as a function of oxygen potential, compositionx and temperature. Experiments were performed in the range of 1,000° C≦T≦1,280° C and 0.2≦x≦1.0. It is found that V Me ″ , Fe Me · and the associate {Fe′ Si ′ Fe Me · } are the majority defects. With this knowledge it is possible to calculate the nonstoichiometry at given temperature as a function of \(p_{O_2 } \) and \(a_{SiO_2 } \) . The cation vacancy concentration shows a \(p_{O_2 }^{1/5} \) -dependence (forx≧0.2) and increases at givenT and \(p_{O_2 } \) almost exponentially with compositionx. In the composition range studied here, the silicates show an oxygen excess, and FeO is more soluble in the olivine than SiO2.  相似文献   

13.
Hydrogeochemical investigations were carried out around Fetzara Lake, Northeast Algeria, to assess the quality of groundwater for its suitability for drinking and irrigation purposes. The groundwater chemistry is mainly controlled by the water?Crock interactions, but also influenced by other processes such as evapotranspiration and ion exchange. Groundwater samples collected, during two periods (1993 and 2007) from wells in the area were analyzed for pH, EC, TDS, Ca2+, Mg2+, Na+, K+, CO 3 2? , HCO 3 ? , Cl?, SO 4 2? , and NO 3 ? . The chemical relationships in Piper??s diagram and Gibbs??s diagram suggest that groundwaters mainly belong to noncarbonate alkali type and Cl? group and are controlled by evaporation dominance, respectively, due to the sluggish drainage conditions, greater water?Crock interaction, and anthropogenic activities. A comparison of the groundwater quality in relation to drinking water quality standards proves that most of the water samples are not suitable for drinking. US Salinity Laboratory??s and Wilcox??s diagrams and %Na+ used for evaluating the water quality for irrigation suggest that the majority of the groundwater samples are not good for irrigation.  相似文献   

14.
Absorption bands are determined in polarized optical spectra of vivianite Fe3(PO4)2·8H2O, recorded at room and low temperatures. These bands are caused by spin-allowed d-d transitions in structurally nonequivalent Fe A 2+ (～11000 cm-1 (γ-polarization) (and) ～12000 cm-1 (β-polarization)) (and) Fe B 2+ (～8400 cm-1 (γ, α-polarization) and ～11200 cm-1 (α-polarization)) ions. A charge transfer band (CTB) Fe B 2+ +Fe B 3+ →Fe B 2+ +Fe B 2+ (～15000 cm-1) also determined, has polarizing features giving evidence of a change in the Fe B 2+ -Fe B 3+ bond direction, when compared with Fe B 2+ -Fe B 2+ . Bands of exchange-coupled Fe3+-Fe3+ pairs (～19400, ～20400, ～21300 and ～21700 cm-1) which appear on oxidation of Fe2+ in paired Fe B octahedra are also characterized.  相似文献   

15.
The dissolution of H2O and CO2 in structurally dense, nominally anhydrous and non-carbonate oxide matrices such as MgO and CaO is reviewed. H2O and CO2 are treated as gaseous oxide components which enter into solid solution with the refractory oxide hosts. They form anion complexes associated with cation vacancy sites. Evidence is presented that OH? pairs which derive from the dissolution of H2O are subject to a charge transfer (CT) conversion into peroxy moieties and molecular hydrogen, O 2 2? ... H2. Because the O 2 2? moiety is small (O?-O? distance ≈ 1.5 Å) high pressure probably favors the CT conversion. Mass spectroscopic studies show that molecular H2 may be lost from the solid which retains excess oxygen in the form of O 2 2? , leading to the release of atomic O. The dissociation of O 2 2? moieties into a vacancy-bound O? state and an unbound O? state can be followed by measuring the internal redox reactions involving transition metal impurities, the transient paramagnetism of the O? and their effect on the d.c. conductivity. Evidence is presented that CO2 molecules dissolve dissociatively in the structurally dense oxide matrix, as if they were first to dissociate into CO+O and then to form separate solute moieties CO 2 2? and O 2 2? , both associated with cation vacancy sites. In the CO 2 2? moiety (C-O? distance 1.2–1.3 Å, OCO angle ≈ 130°) the C atom probably sits off center. The transition of the C atom into interstitial sites is accompanied by dissociation of the CO 2 2? moiety into CO? and O?. This transition can be followed by infrared spectroscopy, using OH? as local probes. Further support derives from magnetic susceptibility, thermal expansion, low frequency dielectric loss and low temperature deformation measurements. The recently observed emission of O and Mg atoms besides a variety of molecules such as CO, CO2, CH4, HCN and other hydrocarbons during impact fracture of MgO single crystals is presented and discussed in the light of the other experimental data.  相似文献   

16.
Groundwater, surface water, soil and river sediment samples, and information on land use in the Nanfei River basin (NRB) of China have been analyzed to study the geochemistry, distribution, and mobilization of phosphorus. The distribution of phosphate (PO 4 3??/sup> ) and the relationships between PO 4 3??/sup> and several constituents in groundwater were studied. Partial correlation analysis relating PO 4 3??/sup> to types of land use was conducted using the data analyzing tool SPSS 15.0. The processes controlling the transport of PO 4 3??/sup> are discussed. The conclusions from this study are: (1) urban land use has obvious impact on PO 4 3??/sup> in groundwater, the average concentration of PO 4 3??/sup> being 4.37?mg/L, greater than that resulting from farmland and mixed land use, which have average PO 4 3??/sup> concentrations of 0.10 and 0.18?mg/L, respectively; (2) the partial correlation between PO 4 3??/sup> and types of land use is significant with a coefficient of 0.760; (3) the PO 4 3??/sup> concentrations in surface water are generally higher than those in groundwater, and the total phosphorus (TP) concentrations in river sediments are generally higher than those in soil samples; (4) groundwater is a carrier of PO 4 3??/sup> and is likely responsible for the redistribution of PO 4 3??/sup> in different regions of NRB.  相似文献   

17.
In the lattice energy expression of forsterite, based on a Born-Mayer (electrostatic+repulsive+dispersive) potential, the oxygen charge z o, the hardness parameter ρ and the repulsive radii r Mg and r Si appear as unknown parameters. These were determined by calculating the first and second partial derivatives of the energy with respect to the cell edges, and equalizing them to quantities related to the crystal elastic constants; the overdetermined system of equations was solved numerically, minimizing the root-mean-square deviation. To test the results obtained, the SiO 4 4? ion was assumed to move in the unit-cell, and the least-energy configuration was sought and compared with the experimental one. By combining the two methods, the optimum set of parameters was: z o=?1.34, ρ=0.27 Å, r Mg=0.72 Å, r Si=0.64 Å. The values ?8565.12 and ?8927.28 kJ mol?1 were obtained, respectively, for the lattice energy E Land for its ionic component E L 0 ,which accounts for interactions between Mg2+ and SiO 4 4? ions only. The charge distribution calculated on the SiO 4 4? ion was discussed and compared with other results. Using appropriate thermochemical cycles, the formation enthalpy and the binding energy of SiO 4 4? were estimated to be: ΔH f(SiO 4 4? )=2117.6 and E(SiO 4 4? )=708.6 kJ mol?1, respectively.  相似文献   

18.
Ionic conductivity of polycrystalline calcite containing varying amounts of PO 4 3? ions was measured in the pressure range of 1–6 GPa and at room temperature. Electrical conductivity increased with pressure corresponding to the phase transition of calcite I to calcite II. The conductivity in calcite III decreased exponentially with pressure. Calculated activation volumes of the conductivity varied with PO 4 3? content in the range of 0.94–5.34 cm3/mol. This variation corresponded to the lattice parameter change of calcite I due to PO 4 3? incorporation and indicated the contribution of CO 3 2? -vacancies associated with PO 4 3? ions to the conductivity.  相似文献   

19.
Given the direction cosines a i ′ = (a 1 i , a 2 i , a 3 i )corresponding to a set of pspherically projected fabric poles, an initial estimate x′ = (x1, x2, x3, x4)for the angular radius x4,and direction cosines of the center of the least-squares small circle which minimizes the sum of the squares of the angular residuals $$r = \sum\limits_p {\left[ {x_4 - \cos ^{ - 1} \left( {a_1^i x_1 + a_2^i x_2 + a_3^i x_3 } \right)} \right]} ^2 $$ can be iteratively improved by taking xj+1 = xj + Δxwhere xj is the value of xat the jth iteration and $$\Delta x = - H_j^{ - 1} \left[ {q_j + x_j \left( {x'_j H_j^{ - 1} x_j } \right)\left( {q_j - x'_j H_j^{ - 1} q_j } \right)} \right],$$ where As an initial approximation for xwe have found it convenient to ignore the fact that the data are constrained to lie on the surface of the reference sphere and to use the parameters of a least-squares plane through the given poles. Generalization of this approach to fitting variously constrained great and small circles is easily made. The relative merits of differently constrained fits to the same data can be tested approximately if it is assumed that the errors in the location of the poles are isotropic and normally distributed. It is thus possible to statistically assess the relative significance of conflicting structural models which predict different geometrical patterns of fabric elements.  相似文献   

20.
A number of experimental CO2 solubility data for silicate and aluminosilicate melts at a variety of P- T conditions are consistent with solution of CO2 in the melt by polymer condensation reactions such as SiO 4(m 4? +CO2(v)+Si n O 3n+1(m) (2n+1) ?Si n+1O 3n+4(m) (2n+4)? +CO 3(m )2? . For various metalsilicate systems the relative solubility of CO2 should depend markedly on the relative Gibbs free change of reaction. Experimental solubility data for the systems Li2O-SiO2, Na2O-SiO2, K2O-SiO2, CaO-SiO2, MgO-SiO2 and other aluminosilicate melts are in complete accord with predictions based on Gibbs Free energies of model polycondesation reactions. A rigorous thermodynamic treatment of published P- T-wt.% CO2 solubility data for a number of mineral and natural melts suggests that for the reaction CO2(m) ? CO2(v)
  1. CO2-melt mixing may be considered ideal (i.e., { \(a_{{\text{CO}}_{\text{2}} }^m = X_{{\text{CO}}_{\text{2}} }^m \) );
  2. \(\bar V_{{\text{CO}}_{\text{2}} }^m \) , the partial molal volume of CO2 in the melt, is approximately equal to 30 cm3 mole?1 and independent of P and T;
  3. Δ C p 0 is approximately equal to zero in the T range 1,400° to 1,650 °C and
  4. enthalpies and entropies of the dissolution reaction depend on the ratio of network modifiers to network builders in the melt. Analytic expressions which relate the CO2 content of a melt to P, T, and \(f_{{\text{CO}}_{\text{2}} } \) for andesite, tholeiite and olivine melilite melts of the form
$$\ln X_{{\text{CO}}_{\text{2}} }^m = \ln f_{{\text{CO}}_{\text{2}} } - \frac{A}{T} - B - \frac{C}{T}(P - 1)$$ have been determined. Regression parameters are (A, B, C): andesite (3.419, 11.164, 0.408), tholeiite (14.040, 5.440,0.393), melilite (9.226, 7.860, 0.352). The solubility equations are believed to be accurate in the range 3<P<30 kbar and 1,100°<T<1,650 °C. A series of CO2 isopleth diagrams for a wide range of T and P are drawn for andesitic, tholeiitic and alkalic melts.  相似文献   

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