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1.
A pyroxene with composition LiNiSi2O6 was synthesized at T = 1,473 K and P = 2.0 GPa; the cell parameters at T = 298 K are a = 9.4169(6) Å, b = 8.4465(7) Å, c = 5.2464(3) Å, β = 110.534(6)°, V = 390.78(3) Å3. TEM examination of the LiNiSi2O6 pyroxene showed the presence of h + k odd reflections indicative of a primitive lattice, and of antiphase domains obtained by dark field imaging of the h + k odd reflections. A HT in situ investigation was performed by examining TEM selected area diffraction patterns collected at high temperature and synchrotron radiation powder diffraction. In HTTEM the LiNiSi2O6 was examined together with LiCrSi2O6 pyroxene. In LiCrSi2O6 the h + k odd critical reflections disappear at about 340 K; they are sharp up to the transition temperature and do not change their shape until they disappear. In LiNiSi2O6 the h + k odd reflections are present up to sample deterioration at 650 K. A high temperature synchrotron radiation powder diffraction investigation was performed on LiNiSi2O6 between 298 and 773 K. The analysis of critical reflections and of changes in cell parameters shows that the space group is P-centred up to the highest temperature. The comparative analysis of the thermal and spontaneous strain contributions in P21/c and C2/c pyroxenes indicates that the high temperature strain in P-LiNiSi2O6 is very similar to that due to thermal strain only in C2/c spodumene and that a spontaneous strain contribution related to pre-transition features is not apparent in LiNiSi2O6. A different high-temperature behaviour in LiNiSi2O6 with respect to other pyroxenes is suggested, possibly in relation with the presence of Jahn–Teller distortion of the M1 polyhedron centred by low-spin Ni3+.  相似文献   

2.
The influence of oxygen fugacity (fO2) and temperature on the valence and structural state of iron was experimentally studied in glasses quenched from natural aluminosilicate melts of granite and pantellerite compositions exposed to various T-fO2 conditions (1100–1420°C and 10?12–10?0.68 bar) at a total pressure of 1 atm. The quenched glasses were investigated by Mössbauer spectroscopy. It was shown that the effect of oxygen fugacity on the redox state of iron at 1320–1420°C can be described by the equation log(Fe3+/Fe2+) = k log(fO2) + q, where k and q are constants depending on melt composition and temperature. The Fe3+/Fe2+ ratio decreases with decreasing fO2 (T = const) and increasing temperature (fO2 = const). The structural state of Fe3+ depends on the degree of iron oxidation. With increasing Fe3+/Fe2+ ≥ 1, the dominant coordination of Fe3+ changes from octahedral to tetrahedral. Ferrous iron ions occur in octahedral (and/or five-coordinated) sites independent of Fe3+/Fe2+.  相似文献   

3.
Current models for the formation of natural diamond involve either oxidation of a methane-bearing fluid by reaction with oxidized mantle, or reduction of a carbonate-bearing fluid (or melt) by reaction with reduced mantle. Implicit in both models is the ability of the mantle with which the fluid equilibrates to act as an oxidizing or reducing agent, or more simply, to act as a source or sink of O2. If only redox reactions involving iron are operating, the ability of mantle peridotite to fulfill this role in diamond formation may not be sufficient for either model to be viable. Using the recent experimental recalibration of olivine–orthopyroxene–garnet oxybarometers of Stagno et al. (2013), we re-evaluated the global database of ~200 garnet peridotite samples for which the requisite Fe3+/Fe2+ data for garnet exist. Relative to the previous calibration of Gudmundsson and Wood (1995), the new calibration yields somewhat more oxidized values of Δlog fO2 (FMQ), with the divergence increasing from <0.5 units of log fO2 at ~3 GPa to as much as 1.5 units at 5–6.5 GPa. Globally, there is a range of ~4 log units fO2 for samples from the diamond stability field at any given pressure. Most samples are sufficiently reduced such that diamond, rather than carbonate, would be stable, and CHO fluids at these conditions would be H2O-rich (>60 mol%), with CH4 being the next most abundant species. To ascertain the capacity for mantle peridotite to act as a source or sink of O2, we developed a new model to calculate the fO2 for a peridotite at a given P, T, and Fe3+/Fe2+. The results from this model predict 50 ppm or less O2 is required to shift a depleted mantle peridotite the observed four log units of fO2. Coupled with the observed distribution of samples at values of fO2 intermediate between the most reduced (metal-saturated) and most oxidized (carbonate-saturated) possible values for diamond stability, these results demonstrate that peridotites are very poor sinks or sources of O2 for possible redox reactions to form diamond. A corollary of the poor redox buffering capacity of cratonic peridotites is that they can be employed as faithful indicators of the redox state of the last metasomatic fluid that passed through them. We propose that diamond formation from CHO fluids is a predictable consequence either of isobaric cooling or of combined cooling and decompression of the fluid as it migrates upward in the lithosphere. This establishes a petrological basis for the observed close connection between subcalcic garnet and diamond: based on high solidus temperatures of harzburgite and dunite effectively precluding dilution of CHO fluids through incipient melts, such highly depleted cratonic peridotites are the preferred locus of diamond formation. Due to a rapid increase in solidus temperature with increasing CH4 content of the fluid, diamond formation related to reduced CHO fluids may also occur in some cratonic lherzolites.  相似文献   

4.
Large-scale melting of the Earth’s early mantle under the effect of global impact processes was accompanied by the generation of volatiles, which concentration was mainly controlled by the interaction of main N, C, O, and H gas-forming elements with silicate and metallic melts at low oxygen fugacity (fO2), which predominated during metallic segregation and self-oxidation of magma ocean. The paper considers the application of Raman and IR (infrared) Fourier spectroscopy for revealing the mechanisms of simultaneous dissolution and relative contents of N, C, O, and H in glasses, which represent the quench products of reduced model FeO–Na2O–Al2O3–SiO2 melts after experiments at 4 GPa, 1550°C, and fO2 1.5–3 orders of magnitude below the oxygen fugacity of the iron—wustite buffer equilibrium (fO2(IW)). Such fO2 values correspond to those inferred for the origin and evolution of magma ocean. It was established that the silicate melt contains complexes with N–H bonds (NH3, NH 2 + , NH 2 - ), N2, H2, and CH4 molecules, as well as oxidized hydrogen species (OH– hydroxyl and molecular water H2O). Spectral characteristics of the glasses indicate significant influence of fO2 on the N–C–O–H proportion in the melt. They are expressed in a sharp decrease of NH 2 + , NH 2 - (O–NH2), OH–, H2O, and CH4 and simultaneous increase of NH 2 - (≡Si–NH2) and NH3 with decreasing fO2. As a result, NH3 molecules become the dominant nitrogen compounds among N–C–H components in the melt at fO2 two orders of magnitude below fO2(IW), whereas molecular СН4 prevails at higher fO2. The noteworthy feature of the redox reactions in the melt is stability of the ОН– groups and molecular water, in spite of the sufficiently low fO2. Our study shows that the composition of reduced magmatic gases transferred to the planet surface has been significantly modified under conditions of self-oxidation of mantle and magma ocean.  相似文献   

5.
The analysis of available data on the Fe3+/Fe2+ ratio of impact-produced glasses showed that tektites and some other types of impact glasses are reduced compared with the precursor target material. Possible reasons for the change in the degree of iron oxidation in the impact process are still debatable. Based on the analysis of redox reactions in relatively simple systems with iron in different oxidation states (Fe-O and SiO2-FeO-Fe2O3) and the available data on the influence of temperature, oxygen partial pressure (pO2), and total pressure (P tot) on the Fe3+/Fe2+ ratio of silicate melts, a model was proposed suggesting that the lower Fe3+/Fe2+ values of tektites formed in the impact process compared with the initial target material could be related to the characteristics of oxygen regime during the decompression stage following shock compression. One of the main prerequisites for the occurrence of reduction reactions involving iron and other elements is the attainment of high temperatures (>1800–2000°C) at a certain stage of decompression, providing the complete melting and partial evaporation of the material. When the vapor pressure in the system becomes equal to the total pressure during adiabatic decompression, a further decrease in P tot will be inevitably accompanied by a decrease in pO2 and, correspondingly, partial reduction of Fe3+ to Fe2+ in the melt. The reactions of decompression reduction occur under closed-system conditions and do not require oxygen removal from the system. The higher the temperature and Fe3+/Fe2+ ratio of the melt, the more extensive iron reduction can be observed during the final stages of decompression. If the temperatures attained during decompression after an impact event are sufficient (>2500–3000°C) for the complete evaporation of the material, the melt produced during subsequent condensation must be significantly more reduced than the initial material. The final stage of the impact process is characterized by a catastrophic expansion of the explosion cloud, condensation, and rapid cooling. During this stage, the system is already not closed. The quenched glasses of this stage record the redox state of earlier melts. In addition, they can contain microinclusions of the products of nonequilibrium vapor condensation with iron compounds of different oxidation states, including metallic iron and iron oxides (wüstite, magnetite, and hematite).  相似文献   

6.
A new potassium uranyl selenate compound K(UO2)(SeO4)(OH)(H2O) has been synthesized for the first time using the technique of evaporation from water solution. Its crystal structure has been solved by direct methods (monoclinic, P21/c,a = 8.0413(9) Å, b = 8.0362(9) Å, c = 11.6032(14) Å, β = 106.925(2)°, V = 717.34(14) Å3) and refined to R 1 = 0.0319 (wR 2 = 0.0824) for 1285 reflections with |F 0| > 4σ F . The structure consists of [(UO2(SeO4)(OH)(H2O)]? chains extending along axis b. In the chains, the uranyl pentagonal bipyramids are linked via bridged hydroxyl anions and tetrahedral oxoanions [SeO4]2?. Potassium ions are situated between these chains. No chains of that type have been observed in uranyl compounds earlier, but they had been detected in the structures of butlerite, parabutlerite, uklonskovite, fibroferrite, and a number of synthetic compounds.  相似文献   

7.
The crystal structure of synthetic stepanovite, Na[Mg(H2O)6][Fe(C2O4)3]·3H2O, and zhemchuzhnikovite, Na[Mg(H2O)6][Al0.55Fe0.45(C2O4)3]·3H2O, has been determined by single-crystal X-ray diffraction methods. The compounds are isotypic to each other and to the previously reported Na[Mg(H2O)6][M(C2O4)3]·3H2O (M: Cr, Al). They crystallize in the trigonal P3c1 space group with Z = 6 molecules per unit cell and (hexagonal axes) a = 17.0483(4), c = 12.4218(4) Å for the iron compound, and a = 16.8852(5), c = 12.5368(5) Å for the Al/Fe solid solution. Comparison of our crystallographic results with previous X-ray diffraction and chemical data of type stepanovite and zhemchuzhnikovite minerals provides compelling evidence that these natural materials possess the same crystal and molecular structure as their synthetic counterparts. It is shown that the originally reported unit cell for stepanovite represents a pronounced sub-cell and that the correct unit cell and space group are based on weak superstructure reflections. The infrared and Raman spectra of both synthetic analogs were also recorded and are briefly discussed.  相似文献   

8.
Stable isotope data of precipitation (δ18Op and deuterium excess), drip water (δ18Od), and modern calcite precipitates (δ18Oc and δ13Cc) from Yongxing Cave, central China, are presented, with monthly sampling intervals from June 2013 to September 2016. Moderate correlations between the monthly variation of δ18Op values (from ??11.5 to ??0.7‰) and precipitation amount (r = ??0.59, n?=?34, p?<?0.01) and deuterium excess (r?=?0.39, n?=?31, p?<?0.01) imply a combined effect of changes in precipitation amount and atmospheric circulation. At five drip sites, the δ18Od values have a much smaller variability (from ??9.1 to ??7.5‰), without seasonal signals, probably a consequence of the mixing in the karst reservoir with a deep aquifer. The mean δ18Od value (??8.4‰) for all drip waters is significantly more negative than the mean δ18Op value (??6.9‰) weighted by precipitation amount, but close to the wet season (May to September) mean value (??8.3‰), suggesting that a threshold of precipitation amount must be exceeded to provide recharge. Calculation based on the equilibrium fractionation factor indicates that the δ18Oc values are not in isotopic equilibrium with their corresponding drip waters, with a range of disequilibrium effects from 0.4 to 1.4‰. The δ18Oc and δ13Cc values generally increase progressively away from the locus of precipitation on glass plates. The disequilibrium effects in the cave are likely caused by progressive calcite precipitation and CO2 degassing related to a high gradient of CO2 concentration between drip waters and cave air. Our study provides an important reference to interpret δ18Oc records from the monsoon region of China.  相似文献   

9.
(Ca x ,Sr1?x )ZrO3 and Ca(Sn y ,Zr1-y )O3 solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO3 perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO6 octahedra, slightly increases with decreasing y content in Ca(Sn y ,Zr1?y )O3 compounds and strongly decreases with decreasing x content in (Ca x ,Sr1?x )ZrO3 compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca x ,Sr1?x )ZrO3 compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm?1 mode (?ν/?r = ?60.1 cm?1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn y ,Zr1?y )O3 compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm?1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm?1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.  相似文献   

10.
Titanomagnetite–melt partitioning of Mg, Mn, Al, Ti, Sc, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Hf and Ta was investigated experimentally as a function of oxygen fugacity (fO2) and temperature (T) in an andesitic–dacitic bulk-chemical compositional range. In these bulk systems, at constant T, there are strong increases in the titanomagnetite–melt partitioning of the divalent cations (Mg2+, Mn2+, Co2+, Ni2+, Zn2+) and Cu2+/Cu+ with increasing fO2 between 0.2 and 3.7 log units above the fayalite–magnetite–quartz buffer. This is attributed to a coupling between magnetite crystallisation and melt composition. Although melt structure has been invoked to explain the patterns of mineral–melt partitioning of divalent cations, a more rigorous justification of magnetite–melt partitioning can be derived from thermodynamic principles, which accounts for much of the supposed influence ascribed to melt structure. The presence of magnetite-rich spinel in equilibrium with melt over a range of fO2 implies a reciprocal relationship between a(Fe2+O) and a(Fe3+O1.5) in the melt. We show that this relationship accounts for the observed dependence of titanomagnetite–melt partitioning of divalent cations with fO2 in magnetite-rich spinel. As a result of this, titanomagnetite–melt partitioning of divalent cations is indirectly sensitive to changes in fO2 in silicic, but less so in mafic bulk systems.  相似文献   

11.
The Al-rich region of the CaO-MgO-Al2O3-SiO2 system was experimentally studied at pressures of 1.0–2.8 GPa and temperatures of 1300–1535°C. The slopes of the lines of the monovariant reactions An + Sp = Cpx + Cor + (Ga) and L = Cpx + Ga + Cor + Sp and the compositions of the phases involved in these reactions are determined. The results are utilized in the topological analysis of the aluminous region of the CaO-MgO-Al2O3-SiO2 system. On this basis, the principal structure of the phase diagram is analyzed, and a phase diagram is constructed for the junction region of the quaternary system and the CaO-Al2O3-SiO2 ternary system. A continuous series of the monovariant eutectic: L = Cpx + Opx + Fo + An, L = Cpx + Opx + An + Sp, L = Cpx + (Ga) + An + Sp, L = Cpx + Cor + (Ga) + An, L = An + Ga + Cpx + Ky and L = Ga + Cpx + Ky + Qz is examined within the pressure range from atmospheric to 3.0 GPa and higher. Analogous “telescoped” eutectic series are of fundamental character for interpreting the evolution of magmatic melts. A physicochemical model is suggested for the evolution of magmatic melts that produce rocks of the calc-alkaline series, with this model underlain by the fact that a change in the composition of magmatic melt at a pressure decrease should correspond to the minimum melting temperatures, i.e., to melts in the fundamental series of eutectic reactions. The comparison of our physicochemical model and rocks of the calc-alkaline series shows that the compositions of rocks of the calc-alkaline series are close to the compositions determined for the eutectic equilibria, and the mineralogical composition of xenoliths and megacrysts in volcanic and dike varieties of the rocks are similar to the subsolidus phases of the established fundamental eutectic system.  相似文献   

12.
In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic studies of orthorhombic CaFe2O4-type β-CaCr2O4 chromite were carried out up to 16.2 and 32.0 GPa at room temperature using multi-anvil apparatus and diamond anvil cell, respectively. No phase transition was observed in this study. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a zero-pressure volume of V 0 = 286.8(1) Å3, an isothermal bulk modulus of K 0 = 183(5) GPa and the first pressure derivative of isothermal bulk modulus K 0′ = 4.1(8). Analyses of axial compressibilities show anisotropic elasticity for β-CaCr2O4 since the a-axis is more compressible than the b- and c-axis. Based on the obtained and previous results, the compressibility of several CaFe2O4-type phases was compared. The high-pressure Raman spectra of β-CaCr2O4 were analyzed to determine the pressure dependences and mode Grüneisen parameters of Raman-active bands. The thermal Grüneisen parameter of β-CaCr2O4 is determined to be 0.93(2), which is smaller than those of CaFe2O4-type CaAl2O4 and MgAl2O4.  相似文献   

13.
Protohematite (Fe2?x/3(OH) x O3?x 1 ≤ x < 0.5) and hydrohematite (Fe2?x/3(OH) x O3?x 0.5 ≤ x < 0) are iron-defective phases containing hydroxyl groups in their structures. These species were described in prior studies mainly with the aid of X-ray diffraction and Infrared spectroscopy. The existence of these phases in soils might have influence in redox processes, and they were considered as a possible water reservoir in Martian soils. In this study, we have used for the first time the Karl Fischer titration method to determine the amount of water released after heating several synthetic samples of goethite, hematite and natural iron ores at 105, 400, 600 and 900 °C. It was found that heating at 105 °C did not remove all moisture from the samples, and higher temperatures were necessary to completely remove all the absorbed water. The water contents determined at 400, 600 and 900 °C were found to be the same within the experimental errors, suggesting the inexistence of both protohematite and hydrohematite in the investigated samples. Therefore, the above-mentioned effects of these phases in soils might have to be reevaluated.  相似文献   

14.
Syntans are synthetically prepared tanning agents from phenols that play an important role in leather making by enhancing the filling, grain characteristics and dyeing property. A considerable amount of syntan emanated in waste water contributes high pollution load with other heterocyclic aromatic compounds and causes serious environmental impact resulting in high oxygen demand. In order to overcome this, suitable biodegradation techniques have been developed using laccase from Penicillium chrysogenum. The influence of different environmental parameters on the biodegradation has also been studied which reveals that the maximum syntan degradation was obtained at pH 5.0, temperature at 32 °C for the duration of 48 h. Maximum biodegradation was found to be 96 and 94% for samples containing phenolic and melamine syntan. Ultraviolet spectra showed the peaks at around 280 nm for the presence of phenolic (DI) syntan and at 220 nm for melamine syntan which were disappeared later in the experimental sample indicating complete degradation of syntans. Fourier spectral analysis indicated that the peaks at the region between 1443–1574 and 1176 cm?1 correspond to C=C stretching and C–H bending for aromatic region which were later disappeared in the experimental sample. Ultrapressure liquid chromatography elution profiles of syntans showed relatively shorter retention time indicating formation of oxidized products. Syntans, namely DI and FB6, showed reduction in chemical oxygen demand up to 87.71 ± 4 and 83.38 ± 5%, respectively, while total organic carbon reduction was achieved up to 82.37 and 80.72%, respectively. Toxicity studies revealed that seeds were well germinated using the treated (biodegradation) samples by crude laccase .  相似文献   

15.
Understanding and characterizing organics in aquatic environments is a great challenge for environmental monitoring, especially for the oil sands industry due to the complexity and potential toxicity of dissolved organics in water. To date, significant efforts have been made in investigating the toxicity of naphthenic acids, although other compounds may also contribute to the toxicity of oil sands process-affected water (OSPW). Here, we present a case study showing a systematic approach for profiling the organic composition of OSPW and environmental water samples by concentrating and separating dissolved organics through complementary liquid–liquid extractions followed by positive- or negative-ion mode ultrahigh resolution mass detection. Our comparative investigation shows clear differences in the composition of dissolved organics (homologues particularly) not only between OSPW samples and environmental water samples, but also differences among oil sands operators. Sulfur-containing compounds (especially the SO n classes) appear to have great potential to be used for evaluating the impact of OSPW, while our understanding of oxygen-only containing compounds should not be limited to O2 (i.e., classic naphthenic acids), but rather can be broadened to include many other compound classes (for instance O n , n = 1–9). Systematic profiling of water samples should be more widely implemented for monitoring the origin and transport of organics in aquatic ecosystems of the oil sands development region, northeastern Alberta, Canada.  相似文献   

16.
The geochemical study of siliciclastic rocks from the Lower Cambrian of Parahio Valley has been studied to describe the provenance, chemical weathering and tectonic setting. The K2O/Al2O3 ratio and positive correlation of Co (r=0.85), Ni (r=0.86), Zn (r=0.82), Rb (r=0.98) with K2O reflects that the presence of clay minerals control the abundances of these elements and suggests a warm and humid climate for this region. The chondrite normalized REE pattern of the samples is equivalent to upper continental crust, which reflects enriched LREE and flat HREE with negative Eu anomaly. The tectonic setting discriminant diagram log[K2O/Na2O] vs. SiO2; [SiO2/Al2O3] vs. log[K2O/Na2O]; [SiO2/20] – [K2O+Na2O] – [TiO2+Fe2O3+MgO] indicates transitional tectonic setting from an active continental margin to a passive margin. The discriminant function plot indicates quartzose sedimentary provenance, and to some extent, the felsic igneous provenance, derived from weathered granite, gneissic terrain and/or from pre-existing sedimentary terrain. The CIA value indicates low to moderate degree of chemical weathering and the average ICV values suggests immature sediments deposited in tectonically active settings. The A–CN–K diagram indicates that these sediments were generated from source rocks of the upper continental crust.  相似文献   

17.
A Cs-bearing polyphase aggregate with composition (in wt%): 76(1)CsAlSi5O12 + 7(1)CsAlSi2O6 + 17(1)amorphous, was obtained from a clinoptilolite-rich epiclastic rock after a beneficiation process of the starting material (aimed to increase the fraction of zeolite to 90 wt%), cation exchange and then thermal treatment. CsAlSi5O12 is an open-framework compound with CAS topology; CsAlSi2O6 is a pollucite-like material with ANA topology. The thermal stability of this polyphase material was investigated by in situ high-T X-ray powder diffraction, the combined P–T effects by a series of runs with a single-stage piston cylinder apparatus, and its chemical stability following the “availability test” (“AVA test”) protocol. A series of additional investigations were performed by WDS–electron microprobe analysis in order to describe the P–T-induced modification of the material texture, and to chemically characterize the starting material and the run products. The “AVA tests” of the polyphase aggregate show an extremely modest release of Cs+: 0.05 mg/g. In response to applied temperature and at room P, CsAlSi5O12 experiences an unquenchable and displacive Ama2-to-Amam phase transition at about 770 K, and the Amam polymorph is stable in its crystalline form up to 1600 K; a crystalline-to-amorphous phase transition occurs between 1600 and 1650 K. In response to the applied P = 0.5 GPa, the crystalline-to-amorphous transition of CsAlSi5O12 occurs between 1670 and 1770 K. This leads to a positive Clapeyron slope (i.e., dP/dT > 0) of the crystalline-to-amorphous transition. When the polyphase aggregate is subjected at P = 0.5 GPa and T > 1770 K, CsAlSi5O12 melts and only CsAlSi2O6 (pollucite-like; dominant) and Cs-rich glass (subordinate) are observed in the quenched sample. Based on its thermo-elastic behavior, P–T phase stability fields, and Cs+ retention capacity, CsAlSi5O12 is a possible candidate for use in the immobilization of radioactive isotopes of Cs, or as potential solid hosts for 137Cs γ-radiation source in sterilization applications. More in general, even the CsAlSi5O12-rich aggregate obtained by a clinoptilolite-rich epiclastic rock appears to be suitable for this type of utilizations.  相似文献   

18.
Crystals of lead oxychloride Pb13O10Cl6 have been synthesized on the basis of high-temperature solid-state reactions. The Pb13O10Cl6 structure was studied using X-ray single-crystal diffraction analysis. The compound is monoclinic, and the space group is C2/c; the unit-cell dimensions are a = 16.1699(14), b = 7.0086(6), c = 23.578(2) Å, β = 97.75°, and V = 2647.6(4) Å3. The structure has been solved by direct methods and refined to R 1 = 0.0505 for 2671 observed unique reflections. The structure is a 3D framework consisting of OPb4 tetrahedrons. Chlorine atoms are located in the framework channels. The structure contains seven symmetrically independent Pb atoms, which are coordinated by 2 to 4 O2? and 2 to 4 Cl? anions. The synthesized compound is compared with other natural and synthetic lead oxyhalides.  相似文献   

19.
We experimentally investigated the dissolution of forsterite, enstatite and magnesite in graphite-saturated COH fluids, synthesized using a rocking piston cylinder apparatus at pressures from 1.0 to 2.1 GPa and temperatures from 700 to 1200 °C. Synthetic forsterite, enstatite, and nearly pure natural magnesite were used as starting materials. Redox conditions were buffered by Ni–NiO–H2O (ΔFMQ = ??0.21 to ??1.01), employing a double-capsule setting. Fluids, binary H2O–CO2 mixtures at the P, T, and fO2 conditions investigated, were generated from graphite, oxalic acid anhydrous (H2C2O4) and water. Their dissolved solute loads were analyzed through an improved version of the cryogenic technique, which takes into account the complexities associated with the presence of CO2-bearing fluids. The experimental data show that forsterite?+?enstatite solubility in H2O–CO2 fluids is higher compared to pure water, both in terms of dissolved silica (mSiO2?=?1.24 mol/kgH2O versus mSiO2?=?0.22 mol/kgH2O at P?=?1 GPa, T?=?800 °C) and magnesia (mMgO?=?1.08 mol/kgH2O versus mMgO?=?0.28 mol/kgH2O) probably due to the formation of organic C–Mg–Si complexes. Our experimental results show that at low temperature conditions, a graphite-saturated H2O–CO2 fluid interacting with a simplified model mantle composition, characterized by low MgO/SiO2 ratios, would lead to the formation of significant amounts of enstatite if solute concentrations are equal, while at higher temperatures these fluid, characterized by MgO/SiO2 ratios comparable with that of olivine, would be less effective in metasomatizing the surrounding rocks. However, the molality of COH fluids increases with pressure and temperature, and quintuplicates with respect to the carbon-free aqueous fluids. Therefore, the amount of fluid required to metasomatize the mantle decreases in the presence of carbon at high P–T conditions. COH fluids are thus effective carriers of C, Mg and Si in the mantle wedge up to the shallowest level of the upper mantle.  相似文献   

20.
For petrological calculations, including geothermobarometry and the calculation of phase diagrams (for example, P–T petrogenetic grids and pseudosections), it is necessary to be able to express the activity–composition (a–x) relations of minerals, melt and fluid in multicomponent systems. Although the symmetric formalism—a macroscopic regular model approach to a–x relations—is an easy-to-formulate, general way of doing this, the energetic relationships are a symmetric function of composition. We allow asymmetric energetics to be accommodated via a simple extension to the symmetric formalism which turns it into a macroscopic van Laar formulation. We term this the asymmetric formalism (ASF). In the symmetric formalism, the a–x relations are specified by an interaction energy for each of the constituent binaries amongst the independent set of end members used to represent the phase. In the asymmetric formalism, there is additionally a "size parameter" for each of the end members in the independent set, with size parameter differences between end members accounting for asymmetry. In the case of fluid mixtures, for example, H2O–CO2, the volumes of the end members as a function of pressure and temperature serve as the size parameters, providing an excellent fit to the a–x relations. In the case of minerals and silicate liquid, the size parameters are empirical parameters to be determined along with the interaction energies as part of the calibration of the a–x relations. In this way, we determine the a–x relations for feldspars in the systems KAlSi3O8–NaAlSi3O8 and KAlSi3O8–NaAlSi3O8–CaAl2Si2O8, for carbonates in the system CaCO3–MgCO3, for melt in the melting relationships involving forsterite, protoenstatite and cristobalite in the system Mg2SiO4–SiO2, as well as for fluids in the system H2O–CO2. In each case the a–x relations allow the corresponding, experimentally determined phase diagrams to be reproduced faithfully. The asymmetric formalism provides a powerful and flexible way of handling a–x relations of complex phases in multicomponent systems for petrological calculations.  相似文献   

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