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1.
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   

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.
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   

4.
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   

5.
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   

6.
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   

7.
In this paper we discuss the main petrogenetic models for granitic pegmatites and how these models have evolved over time. We suggest that the present state of knowledge requires that some aspects of these models to be modified, or absorbed into newer ones. Pegmatite formation and internal evolution have long supposed the need for highly water- and flux-enriched magmas to explain the differences between pegmatites and other intrusives of similar major element composition. Compositions and textural characteristics of fluid and melt inclusions in pegmatite minerals provide strong evidence for such magmas. Furthermore, we show that melt inclusion research has increased the number of potential flux components, which may include H2O, OH?, CO2, HCO 3 ? , CO 3 2? , SO 4 2? , PO 4 3? , H3BO3, F , and Cl, as well as the elements Li, Na, K, Rb, Cs, and Be, herein described as melt structure modifiers. In this paper we emphasize that the combined effect which these components have on the properties of pegmatite melts is difficult to deduce from experimental studies using only a limited number of these components. The combination and the amount of the different magmatic species, together with differences in the source region, and variations in pressure and temperature cause the great diversity of the pegmatites observed. Some volatile species, such as CO 3 2? and alkalis, have the capacity to increase the solubility of H2O in silicate melt to an extraordinary degree, to the extent that melt-melt-fluid immiscibility becomes inevitable. It is our view that the formation of pegmatites is connected with the complex interplay of many factors.  相似文献   

8.
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   

9.
The electron paramagnetic resonance (EPR) spectra of Fe3+ in a well cristallized kaolinite from Decazeville in France are well resolved. It is shown that in this sample there are mainly two slightly different spectra, well separated at low temperature and characterized at -150° C by the constants B 2 0 = 0.112 cm?1, B 2 2 = 0.0688 cm?1 for one and B 2 0 = 0.116 cm?1, B 2 2 = 0.0766 cm?1 for the second. These two spectra arise from Fe3+ substituted for Al3+ at the two octahedral positions in equal amounts. The temperature dependence of EPR spectra was studied and was explained by a modification of the octahedral sites.  相似文献   

10.
According to Koopmans' theorem, only the electrons associated with molecular levels of negative energy are stable. Many ions which cannot exist in the isolated state because certain occupied levels are positive, become stable in crystals under the stabilization effect arising from the crystal field. As examples, we have studied CO 3 2? in calcite, NO 3 ? in NaNO3, and several natural limpurities: O 3 ? in fluorite, [(OH)4]4?, [(OH)3F]4? and [(OH)2F2]4? in zircon and thorite, by means of the molecular self-consistent field, the crystal field being simulated by point charges. As expected, all the energies corresponding to the occupied levels are negative within the crystal field, contrary to what occurs in the isolated state. Informations concerning the structure and the size of the critical germ are obtained for CaCO3 and NaNO3.  相似文献   

11.
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   

12.
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   

13.
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   

14.
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   

15.
The Si, Al LII, III and OKα emission and quantum yield spectra were obtained for 24 silicates. It was found that in minerals of a homogeneous anion composition the Si LII, III line has double-humped structure, and when in addition to SiO 4 4? ions of other composition (BeO 4 6? , AlO 4 5? etc.) are present it has triple-humped structure. The process of crystal-glass transition was studied by X-ray spectroscopy. The result is that in spite of the original form of the Si LII, III line of the mineral this line changes its structure in glass and exhibits a typical double-humped structure. The CNDO/2 approach was used to calculate the electronic structure of basic structural groups of silicates from SiO 4 4? to Si5O 16 12? by replacing one or two of the Si atoms by Be, B, Al and P. A qualitative interpretation of the X-ray spectra is presented.  相似文献   

16.
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   

17.
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   

18.
Manganoan lipscombite (Fe x /2+ , M y /2+ ) Fe 3?(x +y)/3+ [OH)3?(x+y)(PO4)2] was synthesized from pure chemicals. From the study of the Mn2+/Fe2+ atomic ratio by Mössbauer spectra, solubility, and electrokinetic properties, it was found that the crystal structure of lipscombite is not changed substantially by the manganese substitution. The unit cell parameters were determined from Guinier-Hägg X-ray diffraction patterns, which are identical for both synthetic ferrous-ferric and manganoan lipscombite. The two compounds crystallize in the tetragonal system with a=5.3020±0.0005 Å and c=12.8800±0.0005 Å.  相似文献   

19.
Several additional pieces of evidence are offered in support of the recent reinterpretation (Tossell et al. 1981a, b) of the electronic and geometric structure of lollingite, FeAs2, and related minerals. This evidence consists of: (1) the experimental electron affinities of diatomic molecules such as P2 and S2, (2) an analysis of the structure and spectra of TiP2, (3) quantum mechanical calculations on FeAs6, CoAs6 and As4 polyhedra which allow prediction of the photoelectron spectra of FeAs2 and CoAs3, (4) an analysis of bimetal cluster and band calculations suggesting metallic behavior for a hypothetical Fe4+As 4 4? species and (5) qualitative molecular orbital (MO) interpretations of the stability of As 4 4? polyhedra, the interaction between adjacent As 2 2? anions in FeAs2, and the variations in <M-S-S in pyrites and in R(As-As) in diarsenides. It is suggested that previous theories of sulfide and arsenide electronic structure have put too much emphasis upon metal-metal interaction and too little upon anion-anion interaction.  相似文献   

20.
The results of X-ray fluorescence Ka 1,2 and Kβ1,β′-spectra of iron in 54 samples, including 23 minerals, are presented. Spectrum characteristics are mainly dependent on the environment of iron in the sample, the most susceptible parameter being the chemical shift δβ1. For the compounds investigated δβ1 varies between ?1.58 eV and +1.56 eV when referring to metallic iron. Chemical shifts of compounds with predominantly covalent bonds exhibit more negative values, compounds with metallic bonds nearly vanishing values and compounds with predominantly ionic bonds more positive values. The FeKβ1,β′-group of lines is actually a superposition of three lines: the long-wave line β′ and two overlapping lines β 1 5 and β 1 7 of which the superposition is conventionally denoted as β1. The relative intensity of β 1 5 increases with ionicity of the bond, while that of β 1 7 decreases. The effective charge of iron has been determined for a group of iron-bearing minerals.  相似文献   

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