首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
 The chemical bonding in the ring silicate mineral dioptase is investigated on the basis of accurate single-crystal X-ray diffraction data. A multipole model is used in the refinements. Static deformation electron density is mapped for the silicon tetrahedron, Cu-octahedron and water molecule in different sections. The silicon tetrahedron exhibits peaks resulting from σ-bonds between Si–sp3 hybrid orbitals and O–p orbitals. The excess density is located on bonds between the Si atom and bridge (in ring) O(1)-, O(1′)-oxygens and across the interior of the Si–O–Si angle. In the Jahn-Teller distorted Cu octahedron, in addition to peaks which result from single Cu–O σ-bonds, there are peaks which are due to 3d electrons. The analysis of crystal-field influence on the Cu charge distribution is made using the tetragonal D 4 d approximation for the low-symmetry (C1) Cu octahedron. The calculation of the occupancies of the 3d atomic orbitals shows that the Cu non-bonding orbitals are most populated (˜20%) and the bonding orbitals least populated (14%), as is typical for the Jahn-Teller octahedron. The effective atomic charge on the Cu atom in dioptase determined from the multipoles is +1.23e: closer to the Cu+1 than to the Cu+2 state. The charge on the Si atom has a value +1.17e, which is in the range typical for Si atoms already determined by this method. The accumulation of density on bridge oxygens and across the interior of the Si–O–Si angle may be explained by additional strain in the bond with the decrease of the Si–O–Si angle in dioptase to 132°. The same effect was found earlier in coesite. A single-crystal neutron diffraction study shows that dioptase becomes antiferromagnetic below a Néel temperature of 15.9(1) K, in contrast to the previously reported specific heat anomaly at 21 K. The magnetic propagation vector is (0, 0, 3/2) on the hexagonal triple cell or (1/2, 1/2, 1/2) in rhombohedral indices. The relation between the antiferromagnetic and the charge-density models for dioptase is discussed. The less occupied Cu d x2−y2 orbitals are responsible for the magnetic properties. These lie in the Cu–O squares, which are approximately perpendicular to c hex, but which are alternately inclined to it by a small angle. The magnetic moments of 0.59(1)μ B on the Cu ions in the same level are ordered ferromagnetically, but between ions in alternate levels the coupling is antiferromagnet. Within experimental error the magnetic moments are perpendicular to the square planes, which make an angle ±13(3)° to the triad axis. Received: 8 June 2001 / Accepted: 10 January 2002  相似文献   

2.
The ∞ 2 [Si2O 5 2− ] frame in phyllosilicate minerals is distorted through the rotation and tilting of the silicate tetrahedra and interacts with octahedral cations through its apical oxygens. Qualitative perturbation theory and extended Hückel band structure calculations demonstrate that rotation and tilting distortions of the ∞ 2 [Si2O 5 2− ] frame have little influence on orbital interactions within the frame. The effects which are observed can be traced to next-nearestneighbor, oxygen-oxygen interactions. Analysis of band widths and crystal-orbital-overlap-populations demonstrate the importance of O(2s) orbitals in the silicate bond. Interactions between Si(3s, 3p) and O(2s) atomic orbitals account for about half of the bonding overlap in the Si-O bond. Crystal orbitals within the ∞ 2 [Si2O 5 2− ] frame are perturbed in kaolinite, lizardite, pyrophyllite and talc through interactions of the apical oxygens with octahedrally coordinated Al(III) and Mg(II). These interactions appear to involve states that are non-bonding in an isolated frame, having little effect on the Si-Oapical bond while significantly reducing the apical-oxygen atomic population.  相似文献   

3.
 Synchrotron excited X-ray photoelectron spectra (SXPS) of hexagonal pyrrhotite reveal three distinct Fe 3d-derived photopeaks within its outer valence band. The t 2gα band (majority spin) is centered at about 2.5 eV, the e g α band at about 1.0 eV and the t 2gβ (minority spin) contribution at about 0.25 eV. From these data the ligand field splitting energy is 1.5 (±0.2) eV and the majority spin pairing energy is 2.25 (±0.2) eV. These are the first such XPS measurements for this mineral. S 3p-derived bonding and non-bonding bands are identified, with the former centred at about 6.5 eV and the latter near 4.5 eV. The XPS results are remarkably consistent with SCF-Xα scattered wave molecular orbital calculations. Although the calculations and the collected spectra are consistent, they differ from a recent interpretation of the pyrrhotite valence band. An explanation for the discrepant results is provided. Auger resonant enhancement of Fe 3d photopeaks at 60 eV photon energy results in the t 2gα emission (at 2.5 eV) being strongly enhanced and broader than the t 2gβ emission (0.25 eV). The explanation of these observations requires the presence of weak Fe–Fe π and π* crystal (molecular) orbitals located near 2.5 eV, and separated by no more than about 0.5 eV. The π-bonded crystal orbitals are derived from weak mixing of adjacent Fe t 2g atomic orbitals along the c crystallographic axis. Received: 15 June 2000 / Accepted: 11 June 2001  相似文献   

4.
 Solid solutions of (Fe,Mn)TiO3 were synthesized, mostly at 0.10 XMn intervals, at 1 bar, 900°C and log f O 2 = –17.50. Analysis by EMP indicate an ideal stoichiometry for the Fe-Mn ilmenites with (Fe+Mn) = Ti = 1.000 when normalized to 3 oxygens. Their unit cell volume increases linearly with XMn. The composition of Fe-Mn ilmenite coexisting with metallic Fe and rutile was reversed at 1 bar, 700–900°C and fixed f O 2 in a gas-mixing furnace. Oxygen fugacity was controlled by mixing CO2 and H2 gas and was continuously monitored with an yttrium-stabilized zirconia electrolyte. Solution properties of Fe-Mn ilmenite were derived from the experimental data by mathematical programming (Engi and Feenstra, in preparation) including notably the results of Fe-Mn exchange experiments between ilmenite and garnet (Feenstra and Engi, submitted) and anchoring the standard state properties to the updated thermodynamic dataset of Berman and Aranovich (1996). The thermodynamic analysis resulted in positive deviations from ideality for (Fe,Mn)TiO3 ilmenite, which is well described by an asymmetric Margules model with WH FeFeMn = –9.703 and WH FeMnMn = –23.234 kJ/mol, WS FeFeMn = –19.65 and WS FeMnMn = –22.06 J/(K·mol). The excess free energy for Fe-Mn ilmenite derived from the redox reversals is larger than in the symmetric ilmenite model (WG FeMn = +2.2 kJ/mol) determined by O'Neill et al. from emf measurements on the assemblage iron-rutile-(Fe,Mn)ilmenite. Received: 10 January 1996 / Accepted: 11 July 1996  相似文献   

5.
Polarized absorption spectra, σ and π, in the spectral range 30000–400 cm−1 (3.71–0.05 eV) were obtained on crystal slabs // [001] of deep blue rutile at various temperatures from 88 to 773 K. The rutile crystals were grown in Pt-capsules from carefully dried 99.999% TiO2 rutile powder at 50 kbar/1500 °C using graphite heating cells in a belt-type apparatus. Impurities were below the detection limits of the electron microprobe (about 0.005 wt% for elements with Z≥13). The spectra are characterized by an unpolarized absorption edge at 24300 cm−1, two weak and relatively narrow (Δν1/2≈3500–4000 cm−1), slightly σ-polarized bands ν1 at 23500 cm−1 and ν2 at 18500 cm−1, and a complex, strong band system in the NIR (near infra red) with sharp weak peaks in the region of the OH stretching fundamentals superimposed on the NIR system in the σ-spectra. The NIR band system and the UV edge produce an absorption minimum in both spectra, σ and π, at 21000 cm−1, i.e. in the blue, which explains the colour of the crystals. Bands ν1 and ν2 are assigned to dd transitions to the Jahn-Teller split upper Eg state of octahedral Ti3+. The NIR band system can be fitted as a sum of three components. Two of them are partly π-polarized, nearly Gaussian bands, both with large half widths 6000–7000 cm−1, ν3 at 12000 cm–1 and the most intense ν4 at 6500 cm−1. The third NIR band ν5 of a mixed Lorentz-Gaussian shape with a maximum at 3000 cm−1 forms a shoulder on the low-energy wing of ν4. Energy positions, half band widths and temperature behaviour of these bands are consistent with a small polaron type of Ti3+Ti4+ charge transfer (CT). Polarization dependence of CT bands can be explained on the basis of the structural model of defect rutile by Bursill and Blanchin (1983) involving interstitial titanium. Two OH bands at 3322 and 3279 cm−1 in σ-spectra show different stability during annealing, indicating two different positions of proton in the rutile structure, one of them probably connected with Ti3+ impurity. Total water concentration in blue rutile determined by IR spectroscopy is 0.10 wt-% OH. The EPR spectra measured in the temperature interval 20–295 K show the presence of an electron centre at temperatures above 100 K and Ti3+ ions in more than one structural position, but predominantly in compressed interstitial octahedral sites, at lower temperatures. These results are in good agreement with the conclusions based on the electronic absorption data. Received: 24 March 1997 / Revised, accepted: 14 October 1997  相似文献   

6.
 The stability of pargasite in the presence of excess quartz has been determined in the range of 0.5–6.0 kbar and 500–950 °C in the system Na2O– CaO–MgO–Al2O3–SiO2–H2O, using synthetic minerals. The experimental results from this study indicate the presence of two distinct mineral assemblage regions: (1) a high temperature supersolidus region containing tremolitic amphibole+melt+quartz; (b) a low temperature subsolidus region consisting of Al-rich amphibole+plagioclase+enstatite+quartz. Compositional reversals have been determined for the following three equilibria: (a) 2 pargasite+9 quartz=tremolite+4 plagioclase (An50)+1.5 enstatite+H2O, (b) 2 pargasite+10 quartz=tremolite+4 plagioclase (An50)+talc, and (c) pargasite+diopside+5 quartz=tremolite+2 plagioclase (An50). These experiments indicate a continuous change of amphibole composition from pargasite to tremolite with increasing temperature, and an opposite effect with increasing pressure. The third equilibria is used to constrain a site-mixing model for the pargasitic amphiboles, which favor a single-coupled NaA-AlT1 site mixing. The thermochemical data for pargasite estimated from the reversal data of the three equilibrium reactions is estimated as for ΔG 0 f ,Pg=−12022.11±5.2 kJ mole-1, and S 0 Pg=591.7 ±7.9 JK-1 mole-1. Received: 31 July 1995/Accepted: 3 June 1996  相似文献   

7.
 The magnetic behavior of the Jahn-Teller structure braunite, (Mn2+ 1−yM y )(Mn3+ 6− x Mx)SiO12, is strongly influenced by the incorporation of elements substituting manganese. Magnetic properties of well-defined synthetic samples were investigated in dependence on the composition. The final results are presented in magnetic phase diagrams. To derive the necessary data, ac susceptibility and magnetization of braunites with the substitutional elements M = Mg, Fe, (Cu+Ti) and Cu were measured. Whereas the antiferromagnetic ordering temperature, T N , of pure braunite is hardly affected by the substitution of nonmagnetic Mg, it is rapidly suppressed by the substitution of magnetic atoms at the Mn positions. Typically for a concentration (x, y) ≥ 0.7 of the substituted elements, a spin glass phase occurs in the magnetic phase diagrams. Additionally, for the braunite system with Fe3+ substitutions, we observe in the concentration range 0.2 < x< 0.7 a double transition from the paramagnetic state, first to the antiferromagnetic state, followed by a transition to a spin glass state at lower temperatures. The unusual change of the magnetic properties with magnetic substitution at the Mn positions is attributed to the peculiar antiferromagnetic structure of braunite, which has been resolved recently. Received: 19 April 2001 / Accepted: 6 September 2001  相似文献   

8.
Copper contamination in soils and vegetables in the vicinity of an abandoned copper mine in China was investigated. The Cu concentrations of 93 soil samples ranged from 30.4 to 3,191 mg kg−1 soil for a mean of 816.8 mg kg−1 soil. Among 15 samples from a 0 to 20-cm soil layer used for the toxicity characteristic leaching procedure (TCLP) test, the highest value of Cu-TCLP was 133.8 mg kg−1 soil and the TCLP values were positively correlated with the total Cu content of the soils. The sequential extraction of soils in the 0–20-, 20–40-, and 40–60-cm soil layers showed that Cu existed mainly in the Fe–Mn oxide fraction, sulfide/organic fraction, and residual fraction. The copper contamination of 21 species of vegetables from in situ sampling was also examined. Cu concentrations in the edible portions of Brassica chinensis and Solanum melongena were higher than the FAO/WHO standard (40 mg kg−1 DW). The health risk of copper for local inhabitants from consuming these vegetables was assessed on the basis of the target hazard quotient. Enriched concentrations of copper were also found in situ in eight cultivars of B. chinensis planted in the fields, with two levels of Cu concentration. The results showed that there is severe copper contamination in this mine area, and the pollutant in soils show a high risk of leaching into the groundwater and diffusing through the food chain.  相似文献   

9.
Oxyphlogopite is a new mica-group mineral with the idealized formula K(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2. The holotype material came from a basalt quarry at Mount Rothenberg near Mendig at the Eifel volcanic complex in Rhineland-Palatinate, Germany. The mineral occurs as crystals up to 4 × 4 × 0.2 mm in size encrusting cavity walls in alkali basalt. The associated minerals are nepheline, plagioclase, sanidine, augite, diopside, and magnetite. Its color is dark brown, its streak is brown, and its luster is vitreous. D meas = 3.06(1) g/cm3 (flotation in heavy liquids), and D calc = 3.086 g/cm3. The IR spectrun does not contain bands of OH groups. Oxyphlogopite is biaxial (negative); α = 1.625(3), β = 1.668(1), and γ = 1.669(1); and 2V meas = 16(2)° and 2V calc = 17°. The dispersion is strong; r < ν. The pleochroism is medium; X > Y > Z (brown to dark brown). The chemical composition is as follows (electron microprobe, mean of 5 point analyses, wt %; the ranges are given in parentheses; the H2O was determined using the Alimarin method; the Fe2+/Fe3+ was determined with X-ray emission spectroscopy): Na2O 0.99 (0.89–1.12), K2O 7.52 (7.44–7.58), MgO 14.65 (14.48–14.80), CaO 0.27 ((0.17–0.51), FeO 4.73, Fe2O3 7.25 (the range of the total iron in the form of FeO is 11.09–11.38), Al2O3 14.32 (14.06–14.64), Cr2O3 0.60 (0.45–0.69), SiO2 34.41 (34.03–34.66), TiO2 12.93 (12.69–13.13), F 3.06 (2.59–3.44), H2O 0.14; O=F2 −1.29; 99/58 in total. The empirical formula is (K0.72Na0.14Ca0.02)(Mg1.64Ti0.73Fe0.302+ Fe0.273+Cr0.04)Σ2.98(Si2.59Al1.27Fe0.143+ O10) O1.20F0.73(OH)0.07. The crystal structure was refined on a single crystal. Oxyphlogopite is monoclinic with space group C2/m; the unit-cell parameters are as follows: a = 5.3165(1), b = 9.2000(2), c = 10.0602(2) ?, β = 100.354(2)°. The presence of Ti results in the strong distortion of octahedron M(2). The strongest lines of the X-ray powder diffraction pattern [d, ? (I, %) [hkl]] are as follows: 9.91(32) [001], 4.53(11) 110], 3.300(100) [003], 3.090(12) [112], 1.895(21) [005], 1.659(12) [−135], 1.527(16) [−206, 060]. The type specimens of oxyphlogopite are deposited at the Fersman Mineralogical Museum in Moscow, Russia; the registration numbers are 3884/2 (holotype) and 3884/1 (cotype).  相似文献   

10.
 Synthetic aegirine LiFeSi2O6 and NaFeSi2O6 were characterized using infrared spectroscopy in the frequency range 50–2000 cm−1, and at temperatures between 20 and 300 K. For the C2/c phase of LiFeSi2O6, 25 of the 27 predicted infrared bands and 26 of 30 predicted Raman bands are recorded at room temperature. NaFeSi2O6 (with symmetry C2/c) shows 25 infrared and 26 Raman bands. On cooling, the C2/c–P21/c structural phase transition of LiFeSi2O6 is characterized by the appearance of 13 additional recorded peaks. This observation indicates the enlargement of the unit cell at the transition point. The appearance of an extra band near 688 cm−1 in the monoclinic P21/c phase, which is due to the Si–O–Si vibration in the Si2O6 chains, indicates that there are two non-equivalent Si sites with different Si–O bond lengths. Most significant spectral changes appear in the far-infrared region, where Li–O and Fe–O vibrations are mainly located. Infrared bands between 300 and 330 cm−1 show unusually dramatic changes at temperatures far below the transition. Compared with the infrared data of NaFeSi2O6 measured at low temperatures, the change in LiFeSi2O6 is interpreted as the consequence of mode crossing in the frequency region. A generalized Landau theory was used to analyze the order parameter of the C2/c–P21/c phase transition, and the results suggest that the transition is close to tricritical. Received: 21 January 2002 / Accepted: 22 July 2002  相似文献   

11.
The Tongshankou Cu–Mo deposit, located in the westernmost Daye district of the Late Mesozoic Metallogenic Belt along the Middle-Lower reaches of the Yangtze River, eastern China, consists mainly of porphyry and skarn ores hosted in the Tongshankou granodiorite and along the contact with the Lower Triassic marine carbonates, respectively. Sensitive high-resolution ion microprobe zircon U–Pb dating constrains the crystallization of the granodiorite at 140.6 ± 2.4 Ma (1σ). Six molybdenite samples from the porphyry ores yield Re–Os isochron age of 143.8 ± 2.6 Ma (2σ), while a phlogopite sample from the skarn ores yields an 40Ar/39Ar plateau age of 143.0 ± 0.3 Ma and an isochron age of 143.8 ± 0.8 Ma (2σ), indicating an earliest Cretaceous mineralization event. The Tongshankou granodiorite has geochemical features resembling slab-derived adakites, such as high Sr (740–1,300 ppm) and enrichment in light rare earth elements (REE), low Sc (<10 ppm), Y (<13.3 ppm), and depletion in heavy REE (<1.2 ppm Yb), and resultant high Sr/Y (60–92) and La/Yb (26–75) ratios. However, they differ from typical subduction-related adakites by high K, low MgO and Mg#, and radiogenic Sr–Nd–Hf isotopic compositions, with (87Sr/86Sr) t  = 0.7062–0.7067, ɛ Nd(t) = −4.37 to −4.63, (176Hf/177Hf) t  = 0.282469–0.282590, and ɛ Hf(t) = −3.3 to −7.6. The geochemical and isotopic data, coupled with geological analysis, indicate that the Tongshankou granodiorite was most likely generated by partial melting of enriched lithospheric mantle that was previously metasomitized by slab melts related to an ancient subduction system. Magmas derived from such a source could have acquired a high oxidation state, as indicated by the assemblage of quartz–magnetite–titanite–amphibole–Mg-rich biotite in the Tongshankou granodiorite and the compositions of magmatic biotite that fall in the field between the NiNiO and magnetite–hematite buffers in the Fe3+–Fe2+–Mg diagram. Sulfur would have been present as sulfates in such highly oxidized magmas, so that chalcophile elements Cu and Mo were retained as incompatible elements in the melt, contributing to subsequent mineralization. A compilation of existing data reveals that porphyry and porphyry-related Cu–Fe–Au–Mo mineralization from Daye and other districts of the Metallogenic Belt along the Middle-Lower reaches of the Yangtze River took place coevally in the Early Cretaceous and was related to an intracontinental extensional environment, distinctly different from the arc-compressive setting of the Cenozoic age that has been responsible for the emplacement of most porphyry Cu deposits of the Pacific Rim.  相似文献   

12.
 Time-resolved luminescence spectra of natural and synthetic hydrous volcanic glasses with different colors and different Fe, Mn, and H2O content were measured, and the implications for the glass structure are discussed. Three luminescence ranges are observed at about 380–460, 500–560, and 700–760 nm. The very short-living (lifetimes less than 40 ns) blue band (380–460 nm) is most probably due to the 4T2(4D) →6A1(6S) and 4A1(4G) →6A1(6S) ligand field transitions of Fe3+. The green luminescence (500–560 nm) arises from the Mn2+ transition 4T1(4G) →6A1(6S). It shows weak vibronic structure, short lifetimes less than 250 μs, and indicates that Mn2+ is tetrahedrally coordinated, occupying sites with similar distortions and ion–oxygen interactions in all samples studied. The red luminescence (700–760 nm) arising from the 4T1(4G) →6A1(6S) transition of Fe3+ has much longer lifetimes of the order of several ms, and indicates that ferric iron is also mainly tetrahedrally coordinated. Increasing the total water content of the glasses leads to quenching of the red luminescence and decrease of the distortions of the Fe3+ polyhedra. Received: 30 July 2001 / Accepted: 15 November 2001  相似文献   

13.
Summary The crystal structure of arsentsumebite, ideally, Pb2Cu[(As, S)O4]2(OH), monoclinic, space group P21/m, a = 7.804(8), b = 5.890(6), c = 8.964(8) ?, β = 112.29(6)°, V = 381.2 ?3, Z = 2, dcalc. = 6.481 has been refined to R = 0.053 for 898 unique reflections with I> 2σ(I). Arsentsumebite belongs to the brackebuschite group of lead minerals with the general formula Pb2 Me(XO4)2(Z) where Me = Cu2+, Mn2+, Zn2+, Fe2+, Fe3+; X = S, Cr, V, As, P; Z = OH, H2O. Members of this group include tsumebite, Pb2Cu(SO4)(PO4)(OH), vauquelinite, Pb2Cu(CrO4)(PO4)(OH), brackebuschite, Pb2 (Mn, Fe)(VO4)2(OH), arsenbracke buschite, Pb2(Fe, Zn)(AsO4)2(OH, H2O), fornacite, Pb2Cu(AsO4)(CrO4)(OH), and feinglosite, Pb2(Zn, Fe)[(As, S)O4]2(H2O). Arsentsumebite and all other group members contain M = M–T chains where M = M means edge-sharing between MO6 octahedra and M–T represents corner sharing between octahedra and XO4 tetrahedra. A structural relationship exists to tsumcorite, Pb(Zn, Fe)2(AsO4)2 (OH, H2O)2 and tsumcorite-group minerals Me(1)Me(2)2(XO4)2(OH, H2O)2. Received June 24, 2000; revised version accepted February 8, 2001  相似文献   

14.
In order to avoid the pollution of trace metals in marine environment, it is necessary to establish the data and understand the mechanisms influencing the distribution of trace metals in marine environment. The concentration of heavy metals (Fe, Mn, Cr, Cu, Ni, Pb, Zn, Co and Cd) were studied in sediments of Ennore shelf, to understand the metal contamination due to heavily industrialized area of Ennore, south-east coast of India. Concentration of metals shows significant variability and range from 1.7 to 3.7% for Fe, 284–460 μg g−1 for Mn, 148.6–243.2 μg g−1 for Cr, 385–657 μg g−1 for Cu, 19.8–53.4 μg g−1 for Ni, 5.8–11.8 μg g−1 for Co, 24.9–40 μg g−1 for Pb, 71.3–201 μg g−1 for Zn and 4.6–7.5 μg g−1 for Cd. For various metals the contamination factor (CF) and geoaccumulation index (I geo) has been calculated to assess the degree of pollution in sediments. The geoaccumulation index shows that Cd, Cr and Cu moderately to extremely pollute the sediments. This study shows that the major sources of metal contamination in the Ennore shelf are land-based anthropogenic ones, such as discharge of industrial wastewater, municipal sewage and run-off through the Ennore estuary. The intermetallic relationship revealed the identical behavior of metals during its transport in the marine environment.  相似文献   

15.
Heavy metal pollution and their fractionations in the sediments of Changjiang River in Nanjing Reach was monitored for cadmium (Cd), lead (Pb), zinc (Zn), chromium (Cr), and copper (Cu). Moreover, the biological enrichment of metals by riverine plants was studied. The results demonstrated there were highly significant variations among different sampling stations for the concentrations of tested metals. The highest range was for Cu (38.8–120.4 mg kg−1), followed by Cr (74.4–120.0 mg kg−1), Zn (80.9–121.1 mg kg−1), Ni (26.0–55.5 mg kg−1), Pb (15.8–46.7 mg kg−1) and Cd (0.28–0.48 mg kg−1). Cd was the element with highest biological enrichment factor (BEF). The highest BEF of Cd in Erigeron bonariensis reached 3.0, indicating a significant Cd enrichment in this aquatic plant. In addition, 60% of Cd was found in reducible fraction and exchangeable and acid-soluble fraction, which was consistent with its high mobility. The consistency of Cd fraction in sediment and suspended particle indicated they came from the same source. Accumulated Cd concentration calculated according to the release curve showed significant relativity with the total Cd concentration in the sediment.  相似文献   

16.
In order to assess the geothermometric potential of the Na2(Mn2−2x Fe1+2x )(PO4)3 system (x = 0–1), which represents the compositions of natural weakly oxidized alluaudites, we performed hydrothermal experiments between 400 and 800°C, at 1 kbar, under an oxygen fugacity (f(O2)) controlled by the Ni–NiO (NNO), Fe2O3–Fe3O4 (HM), Cu2O–CuO (CT), and Fe–Fe3O4 (MI) buffers. When f(O2) is controlled by NNO, single-phase alluaudites crystallize at 400 and 500°C, whereas the association alluaudite + marićite appears between 500 and 700°C. The limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites, because marićite has never been observed in these geological environments. Because alluaudites are very sensitive to variations of oxygen fugacity, the field of hagendorfite, Na2MnFe2+Fe3+(PO4)3, has been positioned in the f(O2)–T diagram, and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate.  相似文献   

17.
 Infrared spectroscopy provides a reliable method for rapid, non-destructive quantitative analysis of volatile species in silicate glasses, with applications to geochemistry and volcanology. The technique has been extensively calibrated for transmission measurements, in which the species concentration present is correlated with the height or area of characteristic absorption peaks, for doubly polished samples of known thickness. There are several drawbacks associated with this method, including the need for double polishing of parallel faces on thin samples, the errors associated with sample thickness measurement, and total absorption of the IR beam intensity for samples with high volatile content. We have tested an alternative method for quantitative IR determination of volatile concentrations in silicate glasses, based on analysis of the IR reflectivity signal. The reflectivity method requires preparation of a single polished glass surface, and no thickness measurement of the sample is necessary. The technique is applied easily as a microbeam technique using apertures as small as a few μm in diameter. The method should be particularly useful for volatile analysis of glass inclusions in phenocrystals, or standard samples in thin section. We have developed the methodology for the technique using a series of basanite and leucitite glasses with high carbonate contents (>1 wt% CO2), which could not be easily analyzed via IR transmission. We have used SIMS to standardize the technique. Two features observed in the reflectance spectra near 1400 cm–1 and 1500 cm–1 are due to resonance of the infrared beam with the asymmetric stretching vibrations of carbonate groups. The contribution of these species to the total reflectivity is directly correlated with the carbon abundance in the samples. This forms the basis for an empirical quantitative analysis. The optical constants, including the IR absorption coefficients associated with the CO3 2– stretching vibrations, have been extracted by Kramers-Kronig analysis of the reflectivity data. The molar extinction coefficients are 1119 ± 138 L mol–1 cm–1 and 1198 ± 145 L mol–1 cm–1 for the 1400 and 1500 cm–1 bands, respectively, in excellent agreement with results of previous transmission studies, after orientation effects are taken into account. Received: 29 September 1995 / Accepted: 17 May 1996  相似文献   

18.
The crystal structure of Bi2Al4−x Fe x O9 compounds (x = 0–4) has striking similarities with the crystal structure of mullite. A complete substitution of Al by Fe3+ in both octahedral and tetrahedral sites is a particular structural feature. The infrared (IR) spectra of the Bi2M4O9 compounds (M = Al, Fe3+) are characterised by three band groups with band maxima in the 900–800, 800–600 and 600–400 cm−1 region. Based on the spectroscopic results obtained from mullite-type phases, the present study focuses on the composition-dependent analysis of the 900–800 cm−1 band group, which is assigned to Al(Fe3+)–O stretching vibrations of the corner-sharing MO4 tetrahedra. The Bi2Al4O9 and Bi2Fe4O9 endmembers display single bands with maxima centred at 922 and 812 cm−1, respectively. Intermediate Bi2Al4−x Fe x O9 compounds exhibit a distinct splitting into three relatively sharp bands, which is interpreted in terms of ordering effects within the tetrahedral pairs. Thereby the high-energy component band of the band triplet relates to Al–O–Al conjunctions and the low-energy component band to Fe–O–Fe conjunctions. The intermediate band is assigned to stretching vibrations of Al–O–Fe or Fe–O–Al configurations of the corner-sharing tetrahedral pairs. Bands in the 800–600 cm−1 range are assigned to low-energy stretching vibrations of the MO4 tetrahedra and to M–O–M bending vibrations of the tetrahedral pairs. Absorptions in the 600–400 cm−1 range are essentially determined by M–O stretching modes of the M cations in octahedral coordination.  相似文献   

19.
The elastic properties of coexisting natural 3T and 2M 1 phengite samples (Cima Pal, Sesia Zone; Val Savenca; Western Alps, Italy) with similar chemical compositions have been studied by room temperature–high pressure powder diffraction, using synchrotron radiation on the ID9A beam-line at ESRF (Grenoble, France). The P–V curves have been modelled by the Birch–Murnaghan model; a third-order expansion fitted to the experimental data yields for 3T and 2M 1 K 0=60.4(±0.7) GPa, K′=5.79(±0.11) at V 0=703.8851 Å3, and K 0=57.3(±1.0) GPa, K′=6.97(±0.24) at V 0=938.8815 Å3, respectively. The relative stability of 3T vs. 2M 1 has been explored as a function of pressure and temperature in terms of configuration and deformation contributions to the Gibbs energy, using the elastic properties determined here and other thermodynamic parameters from earlier investigations. The results presented agree with the hypothesis of stability of the 3T polytype in the high pressure regime.  相似文献   

20.
Interpretation of Ni2p XPS spectra of Ni conductors and Ni insulators   总被引：1，自引：0，他引：1  
Ni2p3/2 X-ray photoelectron spectral peak binding energies of Ni metal, NiS, and NiAs (all conductors) span a range of about 0.5 eV and are, consequently, insensitive to formal Ni oxidation state and to the nature of the ligand to which Ni is bonded, relative to other metals (e.g., Fe). Ni2p3/2 peak structures and binding energies reflect two energetic contributions. The major contribution is that associated with the electrostatic field produced by ejection of the Ni(2p) photoelectron, the minor contribution is the relaxation energy associated with filling unoccupied, conduction band 3d9 and 4s Ni metal orbitals. These conduction band orbitals become localized on the Ni photoion (and sometimes filled) in response to the field created by the photoemission event. Because only the core Ni2p electron and nonbonding orbitals of predominantly metallic character are affected, the main peak of all three conductors are affected similarly, leading to similar Ni2p3/2 main peak binding energies. NiO, Ni(OH)2, and NiSO4 are insulators in which Ni is divalent and is bonded to oxygen. Although Ni is bonded to oxide in these phases, Ni2p binding energies differ substantially, and reflect primarily the nature of the ligand (O2−, OH−, SO4 2−) to which Ni is bonded. The influence of the ligand is the result of charge (electron) transfer from valence band bonding orbitals of dominantly ligand character, to unoccupied conduction band orbitals localized on Ni photoions. Relaxation energy resulting from charge transfer is acquired by the emitted photoelectron, thus Ni2p3/2 photopeak binding energies of these insulators reflect the nature of the ligand to which Ni is bonded. The Ni2p main peak binding energy of these conductors and insulators is a poor guide to Ni oxidation states. The Ni2p3/2 binding energies of insulators reflect, however, the nature of the ligand in the first coordination sphere of Ni. The intensity of the Doniach–Sunjic contribution to Ni2p XPS spectra of NiS and NiAs is dependent on the nature of the ligand. The Doniach–Sunjic contribution to ligand XPS core-level photopeaks (e.g., S2p of NiS and As3d of NiAs) has not been explained and is poorly understood. Received 24 May 1999 / Revised, accepted: 30 June 1999  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号