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1.
Water solubility mechanism in hydrous aluminosilicate glasses: information from Al MAS and MQMAS NMR
New 27Al NMR data are presented in order to clarify the discrepancies in the interpretation of the previous 27Al Magic Angle Spinning (MAS) spectra from hydrous aluminosilicate glasses. The 27Al MAS data have been collected at much higher magnetic field (14.1 and 17.6 T) than hitherto, and in addition, multiple quantum (MQ) MAS NMR data are presented for dry and hydrous nepheline glasses and NaAlSi7.7O17.4 glass that, according to the model of Zeng et al. (Zeng Q., Nekvasil H., and Grey C. P. 2000. In support of a depolymerisation model for water in sodium aluminosilicate glasses: Information from NMR spectroscopy. Geochim. Cosmochim. Acta64, 883-896), should produce a high fraction (up to 30%) of Al in Al Q3-OH on hydration. Although small differences in the MAS spectra of anhydrous and hydrous nepheline glasses are observed, there is no evidence for the existence of significant (>∼2%) amounts of Q3 Al-OH in these glasses in either the MAS or MQMAS data. 相似文献
2.
Sedimentary biogenic silica from Redeyef in Gafsa basin (southern Tunisia) was analysed for its 29Si and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra and complemented by X-ray diffraction and SEM observations. The 29Si MAS NMR spectrum is characterized by the abundance of hydroxylated silicon, displayed in resonance intensities and reflects a clear tendency towards dissolution of diatomaceous amorphous silica and the occurrence of the hydrated silica, which is the main component that ensures the diagenetic transition via the mechanism of dissolution–precipitation to other more crystalline silica phases, after the lost of its hydroxyls groups (water) by heating (burial). 27Al MAS NMR reveals two coordinations of Al; the octahedrally coordinated Al suggests the presence of clay relics trapped during crystal growth or a microcrystalline zeolite (clinoptilolite detected by SEM observations), while the tetrahedrally coordinated Al suggests the presence of minor quantities of minerals with tetrahedral Al, such as an Al-rich fluid and/or minerals such as feldspars. 相似文献
3.
Kimberly E. Kelsey Jonathan F. Stebbins Gordon E. Brown Jr. Jed L. Mosenfelder 《Geochimica et cosmochimica acta》2009,73(13):3914-2191
We examined aluminosilicate glasses containing a variety of network modifying to intermediate cations (Li, La, Sc, and Fe), quenched from melts at 1 atm to 8 GPa, to further investigate the role of cation field strength in Al coordination changes and densification. 27Al Nuclear Magnetic Resonance Spectroscopy (NMR) reveals that the mean Al coordination increases with increasing pressure in the Li-containing glasses, which can be explained by a linear dependence of fractional change in Al coordination number on cation field strengths in similar K-, Na-, and Ca-containing aluminosilicate glasses (K < Na < Li < Ca). Measured recovered densities follow a similar linear trend. In contrast, the La-containing glasses have significantly lower mean Al coordination numbers at given pressures than the cation field strength of La and glass density would predict. La L3 X-ray absorption fine structure (XAFS) spectroscopy results indicate a significant increase with pressure in average La-O bond distances, suggesting that La and Al may be “competing” for higher coordinated sites and hence that both play a significant role in the densification of these glasses, especially in the lower pressure range. However, in Na aluminosilicate glasses with small amounts of Sc, 45Sc NMR reveals only modest Sc coordination changes, which do not seem to significantly affect the mean Al coordination values. For a Li aluminosilicate glass, 17O MAS and multiple quantum magic angle spinning (3QMAS) NMR data are consistent with generation of more highly coordinated Al at the expense of non-bridging oxygen (NBO), whereas La aluminosilicate glasses have roughly constant O environments, even up to 8 GPa. Finally, we demonstrate that useful 23Na and 27Al MAS NMR spectra can be collected for Ca-Na aluminosilicate glasses containing up to 5 wt.% Fe oxide. We discuss the types of structural changes that may accompany density increases with pressure and how these structural changes are affected by the presence of different cations. 相似文献
4.
We describe here high-field 17O magic-angle-spinning (MAS) and triple-quantum MAS (3QMAS) NMR spectra for several alkali silicate and Na, K, and Ca aluminosilicate glasses containing up to 10 wt.% water. The H2O site appears to have a large quadrupolar coupling constant, and its chemical shift increases from Na- to K- glasses, suggesting significant cation-H2O interactions. In 17O one-pulse MAS and 3QMAS and 27Al one-pulse NMR experiments, major differences were seen between spectra for anhydrous and hydrous calcium aluminosilicate glasses. The changes in the 17O MAS spectra can be explained by the addition of an H2O peak and to the disappearance of an Al-O-Al peak from the 17O NMR spectrum for the hydrous glass. The 27Al results are consistent with this interpretation. 相似文献
5.
Structural interaction between dissolved fluorine and silicate glass (25°C) and melt (to 1400°C) has been examined with 19F and 29Si MAS NMR and with Raman spectroscopy in the system Na2O-Al2O3-SiO2 as a function of Al2O3 content. Approximately 3 mol.% F calculated as NaF dissolved in these glasses and melts. From 19F NMR spectroscopy, four different fluoride complexes were identified. These are (1) Na-F complexes (NF), (2) Na-Al-F complexes with Al in 4-fold coordination (NAF), (3) Na-Al-F complexes with Al in 6-fold coordination with F (CF), and (4) Al-F complexes with Al in 6-fold, and possibly also 4-fold coordination (TF). The latter three types of complexes may be linked to the aluminosilicate network via Al-O-Si bridges.The abundance of sodium fluoride complexes (NF) decreases with increasing Al/(Al + Si) of the glasses and melts. The NF complexes were not detected in meta-aluminosilicate glasses and melts. The NAF, CF, and TF complexes coexist in peralkaline and meta-aluminosilicate glasses and melts.From 29Si-NMR spectra of glasses and Raman spectra of glasses and melts, the silicate structure of Al-free and Al-poor compositions becomes polymerized by dissolution of F because NF complexes scavenge network-modifying Na from the silicate. Solution of F in Al-rich peralkaline and meta-aluminous glasses and melts results in Al-F bonding and aluminosilicate depolymerization.Temperature (above that of the glass transition) affects the Qn-speciation reaction in the melts, 2Q3 ⇔ Q4 + Q2, in a manner similar to other alkali silicate and alkali aluminosilicate melts. Dissolved F at the concentration level used in this study does not affect the temperature-dependence of this speciation reaction. 相似文献
6.
Harris E. Mason Robert S. Maxwell Susan A. Carroll 《Geochimica et cosmochimica acta》2011,75(20):6080-6093
We present the results of a series of experiments designed to probe the interactions between Al and the amorphous silica surface as a function of thermodynamic driving forces. The results from 27Al single pulse magic angle spinning (SP/MAS) and 27Al{1H} rotational echo double resonance (REDOR) allow us to identify the reaction products and constrain their structure. In all cases, despite low Al and Si concentrations we observe the formation of metastable aluminosilicates. Results from low temperature experiments indicate that despite thermodynamic driving forces for the formation of gibbsite we observe the precipitation of separate octahedrally coordinated Al (Al[6]) and tetrahedrally coordinated Al (Al[4]) silicate phases. At higher temperatures the Al[4] silicate phase dominates the speciation. Structural models derived from the NMR data are also proposed, and the results are discussed as they relate to previous work on Al/Si cycling. 相似文献
7.
A. Ninh Pham 《Geochimica et cosmochimica acta》2006,70(3):640-650
The kinetics of Fe(III) precipitation in synthetic buffered waters have been investigated over the pH range 6.0-9.5 using a combination of visible spectrophotometry, 55Fe radiometry combined with ion-pair solvent extraction of chelated iron and numerical modeling. The rate of precipitation, which is first order with respect to both dissolved and total inorganic ferric species, varies by nearly two orders of magnitude with a maximum rate constant of 16 ± 1.5 × 106 M−1 s−1 at a pH of around 8.0. Our results support the existence of the dissolved neutral species, Fe(OH)30, and suggest that it is the dominant precursor in Fe(III) polymerization and subsequent precipitation at circumneutral pH. The intrinsic rate constant of precipitation of Fe(OH)30 was calculated to be allowing us to predict rates of Fe(III) precipitation in the pH range 6.0-9.5. The value of this rate constant, and the variation in the precipitation rate constant over the pH range considered, are consistent with a mechanism in which the kinetics of iron precipitation are controlled by rates of water exchange in dissolved iron hydrolysis species. 相似文献
8.
Ingvi Gunnarsson Stefán Arnórsson Sigurethur Jakobsson 《Geochimica et cosmochimica acta》2005,69(11):2813-2828
Magnesium silicate precipitation experiments were carried out in alkaline solutions in the temperature range 39°C-150°C. Titrations were carried out at room temperature where the pH of an aqueous solution containing magnesium and silica was raised to bring about precipitation of a magnesium silicate. The precipitation of the magnesium silicate was rapid. Equilibrium between the solution and the precipitate was attained in a period of less than one hour up to a month at around 90°C, depending on the initial degree of oversaturation. Relative magnesium and silica depletion in the experimental solutions and IR spectra of the precipitate show that the magnesium silicate resembles poorly developed antigorite (p-antigorite). Values for its solubility constant were obtained and an equation describing its solubility in the temperature interval 0°-200°C calculated. The equation is: log Ksp = 9303/T + 3.283, where T is in K, and it is valid for the following reaction:
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10.
We have taken a systematic approach utilizing advanced solid-state NMR techniques to gain new insights into the controversial issue concerning the dissolution mechanisms of water in aluminosilicate melts (glasses). A series of quenched anhydrous and hydrous (∼2 wt% H2O) glass samples along the diopside (Di, CaMgSi2O6)—anorthite (An, CaAl2Si2O8) join with varying An components (0, 20, 38, 60, 80, and 100 mol %) have been studied. A variety of NMR techniques, including one-dimensional (1D) 1H and 27Al MAS NMR, and 27Al → 1H cross-polarization (CP) MAS NMR, as well as two-dimensional (2D) 1H double-quantum (DQ) MAS NMR, 27Al triple-quantum (3Q) MAS NMR, and 27Al → 1H heteronuclear correlation NMR (HETCOR) and 3QMAS/HETCOR NMR, have been applied. These data revealed the presence of SiOH, free OH ((Ca,Mg)OH) and AlOH species in the hydrous glasses, with the last mostly interconnected with Si and residing in the more polymerized parts of the structure. Thus, there are no fundamental differences in water dissolution mechanisms for Al-free and Al-bearing silicate melts (glasses), both involving two competing processes: the formation of SiOH/AlOH that is accompanied by the depolymerization of the network structure, and the formation of free OH that has an opposite effect. The latter is more important for depolymerized compositions corresponding to mafic and ultramafic magmas.Aluminum is dominantly present in four coordination (AlIV), but a small amount of five-coordinate Al (AlV) is also observed in all the anhydrous and hydrous glasses. Furthermore, six-coordinate Al (AlVI) is also present in most of the hydrous glasses. As Al of higher coordinations are favored by high pressure, AlVIOH and AlVOH may become major water species at higher pressures corresponding to those of the Earth’s mantle. 相似文献
11.
Isothermal evaporation experiments were carried out on an acidic (pH 2), partially oxidized (Fe2+/FeT ∼0.5) brine with a cation composition consistent with derivation from the chemical weathering of martian basalt. During evaporation, the brine composition evolved to a highly acidic (un-scaled pH −1.3) Mg-Fe-SO4-Cl brine depleted in Ca, Al and K. Evaporite minerals identified throughout the course of the experiment include (in order of crystallization): gypsum, Mg-rich voltaite, (Mg0.7, )SO4·7H2O and rhomboclase. The solid solution compositions of voltaite and (Mg0.7, )SO4·7H2O, although uncommon in analogous environments on Earth, result from the distinct chemistry of evaporating martian surface fluids. Analysis of brine compositions with available thermodynamic models indicates that, although gypsum and rhomboclase precipitate at equilibrium saturation, kinetic controls on the precipitation of copiapite-group minerals affect the subsequent sulfate mineralogy and evolving chemistry of the entire system. In addition, geochemical simulations of the experimental evaporation process suggest that the appearance of voltaite and rhomboclase indicate a “metastable” evaporation pathway for martian fluids whereby bilinite and copiapite-group minerals did not form despite thermodynamic saturation. Comparison of the experimentally-produced assemblage to available observations of saline minerals at the martian surface represents a step toward systematically characterizing evaporite mineralogy as a function of Fe-oxidation in the initially dilute fluid. Deconvolving the complexity of Fe-sulfate formation in martian environments ultimately will help to exploit the sensitivity of these minerals to pH and redox conditions present at the ancient martian surface. 相似文献
12.
B.H.W.S. de Jong Charles M. Schramm Victor E. Parziale 《Geochimica et cosmochimica acta》1983,47(7):1223-1236
The coordination of aluminum with oxygen in crystalline and amorphous alumina, aluminates, and aluminosilicates has been determined with magic angle spinning 27Al nuclear magnetic resonance. The 27Al NMR spectra of crystalline materials show that VIAl and IVAl can readily be distinguished. The same is not the case for amorphous aluminosilicates due to the superposition of a narrow peak, characteristic of IVAl, on a broad band. Our spectroscopic results indicate that Al coordination is not the determining factor in explaining differences in devitrification behavior of albite and anorthite glasses. The coordination of Al in aqueous solutions seems to prevent precipitation of the three common Al(OH)3 polymorphs (VIAl) at pH above 10. There is clear evidence to suggest that, in solutions containing Si as well as Al, aluminum coordination is related to the type of precipitate formed in acid (clays, VIAl, IVAl), and basic (zeolites, IVAl) environments. Zeolites can be precipitated in near neutral pH environments at higher temperatures, reflecting an increase in IVAl under these conditions. The Al avoidance principle for aluminosilicates does not seem to be a hard principle. It is likely that the validity of this principle depends on the type of modifying cation present in the aluminosilicate framework. 相似文献
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16.
Frédéric Angeli Marina Gaillard Thibault Charpentier 《Geochimica et cosmochimica acta》2006,70(10):2577-2590
A multinuclear solid-state NMR investigation of the structure of the amorphous alteration products (so called gels) that form during the aqueous alteration of silicate glasses is reported. The studied glass compositions are of increasing complexity, with addition of aluminum, calcium, and zirconium to a sodium borosilicate glass. Two series of gels were obtained, in acidic and in basic solutions, and were analyzed using 1H, 29Si, and 27Al MAS NMR spectroscopy. Advanced NMR techniques have been employed such as 1H-29Si and 1H-27Al cross-polarization (CP) MAS NMR, 1H double quantum (DQ) MAS NMR and 27Al multiple quantum (MQ) MAS NMR. Under acidic conditions, 29Si CP MAS NMR data show that the repolymerized silicate networks have similar configuration. Zirconium as a second nearest neighbor increases the 29Si isotropic chemical shift. The gel porosity is influenced by the pristine glass composition, modifying the silicon-proton interactions. From 1H DQ and 1H-29Si CP MAS NMR experiments, it was possible to discriminate between silanol groups (isolated or not) and physisorbed molecular water near Si (Q2), Si (Q3), and Si (Q4) sites, as well as to gain insight into the hydrogen-bonding interaction and the mobility of the proton species. These experiments were also carried out on heated samples (180 °C) to evidence hydrogen bonds between hydroxyl groups on molecular water. Alteration in basic media resulted in a gel structure that is more dependent on the initial glass composition. 27Al MQMAS NMR data revealed an exchange of charge compensating cations of the [AlO4]− groups during glass alteration. 1H-27Al CP MAS NMR data provide information about the proximities of these two nuclei and two aluminum environments have been distinguished. The availability of these new structural data should provide a better understanding of the impact of glass composition on the gel structure depending on the nature of the alteration solution. 相似文献
17.
Bjorn O. Mysen 《Geochimica et cosmochimica acta》2007,71(7):1820-1834
Solubility and solution mechanisms of H2O in depolymerized melts in the system Na2O-Al2O3-SiO2 were deduced from spectroscopic data of glasses quenched from melts at 1100 °C at 0.8-2.0 GPa. Data were obtained along a join with fixed nominal NBO/T = 0.5 of the anhydrous materials [Na2Si4O9-Na2(NaAl)4O9] with Al/(Al+Si) = 0.00-0.25. The H2O solubility was fitted to the expression, XH2O=0.20+0.0020fH2O-0.7XAl+0.9(XAl)2, where XH2O is the mole fraction of H2O (calculated with O = 1), fH2O the fugacity of H2O, and XAl = Al/(Al+Si). Partial molar volume of H2O in the melts, , calculated from the H2O-solulbility data assuming ideal mixing of melt-H2O solutions, is 12.5 cm3/mol for Al-free melts and decreases linearly to 8.9 cm3/mol for melts with Al/(Al+Si) ∼ 0.25. However, if recent suggestion that is composition-independent is applied to constrain activity-composition relations of the hydrous melts, the activity coefficient of H2O, , increases with Al/(Al+Si).Solution mechanisms of H2O were obtained by combining Raman and 29Si NMR spectroscopic data. Degree of melt depolymerization, NBO/T, increases with H2O content. The rate of NBO/T-change with H2O is negatively correlated with H2O and positively correlated with Al/(Al+Si). The main depolymerization reaction involves breakage of oxygen bridges in Q4-species to form Q2 species. Steric hindrance appears to restrict bonding of H+ with nonbridging oxygen in Q3 species. The presence of Al3+ does not affect the water solution mechanisms significantly. 相似文献
18.
The local configurations around sodium ions in silicate glasses and melts and their distributions have strong implications for the dynamic and static properties of melts and thus may play important roles in magmatic processes. The quantification of distributions among charge-balancing cations, including Na+ in aluminosilicate glasses and melts, however, remains a difficult problem that is relevant to high-temperature geochemistry as well as glass science.Here, we explore the local environment around Na+ in charge-balanced aluminosilicate glasses (the NaAlO2-SiO2 join) and its distribution using 23Na magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy at varying magnetic fields of 9.4, 14.1, and 18.8 T, as well as triple-quantum (3Q)MAS NMR spectroscopy at 9.4 T, to achieve better understanding of the extent of disorder around this cation. We quantify the extent of this disorder in terms of changes in Na-O distance (d[Na-O]) distributions with composition and present a structural model favoring a somewhat ordered Na distribution, called a “perturbed” Na distribution model. The peak position in 23Na MAS spectra of aluminosilicate glasses moves toward lower frequencies with increasing Si/Al ratios, implying that the average d(Na-O) increases with increasing R. The peak width is significantly reduced at higher fields (14.1 and 18.8 T) because of the reduced effect of second-order quadrupolar interaction, and 23Na MAS NMR spectra thus provide relatively directly the Na chemical shift distribution and changes in atomic environment with composition. Chemical shift distributions obtained from 23Na 3Q MAS spectra are consistent with MAS NMR data, in which deshielding decreases with R. The average distances between Na and the three types of bridging oxygens (BOs) (Na-{Al-O-Al}, Na-{Si-O-Al}, and Na-{Si-O-Si}) were obtained from the correlation between d(Na-O) and isotropic chemical shift. The calculated d(Na-{Al-O-Al}) of 2.52 Å is shorter than the d(Na-{Si-O-Si}) of 2.81 Å, and d(Na-{Al-O-Al}) shows a much narrower distribution than the other types of BOs. 23Na chemical shifts in binary (Al-free) sodium silicate glasses are more deshielded and have ranges distinct from those of aluminosilicate glasses, implying that d(Na-NBO) (nonbridging oxygen) is shorter than d(Na-BO) and that d(Na-{Si-O-Si}) in binary silicates can be shorter than that in aluminosilicate glasses. The results given here demonstrate that high-field 23Na NMR is an effective probe of the Na+ environment, providing not only average structural information but also chemically and topologically distinct chemical shift ranges (distributions) and their variation with composition and their effects on static and dynamic properties. 相似文献
19.
The composition of carbonate minerals formed in past and present oceans is assumed to be significantly controlled by temperature and seawater composition. To determine if and how temperature is kinetically responsible for the amount of Mg incorporated in calcite, we quantified the influence of temperature and specific dissolved components on the complex mechanism of calcite precipitation in seawater. A kinetic study was carried out in artificial seawater and NaCl-CaCl2 solutions, each having a total ionic strength of 0.7 M. The constant addition technique was used to maintain [Ca2+] at 10.5 mmol kg−1 while [] was varied to isolate the role of this variable on the precipitation rate of calcite.Our results show that the overall reaction of calcite precipitation in both seawater and NaCl-CaCl2 solutions is dominated by the following reaction:
20.
An experimental study of oxygen isotope fractionation between inorganically precipitated aragonite and water at low temperatures 总被引：1，自引：0，他引：1
Gen-Tao Zhou 《Geochimica et cosmochimica acta》2003,67(3):387-399
To determine oxygen isotope fractionation between aragonite and water, aragonite was slowly precipitated from Ca(HCO3)2 solution at 0 to 50°C in the presence of Mg2+ or SO42−. The phase compositions and morphologies of synthetic minerals were detected by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The effects of aragonite precipitation rate and excess dissolved CO2 gas in the initial Ca(HCO3)2 solution on oxygen isotope fractionation between aragonite and water were investigated. For the CaCO3 minerals slowly precipitated by the CaCO3 or NaHCO3 dissolution method at 0 to 50°C, the XRD and SEM analyses show that the rate of aragonite precipitation increased with temperature. Correspondingly, oxygen isotope fractionations between aragonite and water deviated progressively farther from equilibrium. Additionally, an excess of dissolved CO2 gas in the initial Ca(HCO3)2 solution results in an increase in apparent oxygen isotope fractionations. As a consequence, the experimentally determined oxygen isotope fractionations at 50°C indicate disequilibrium, whereas the relatively lower fractionation values obtained at 0 and 25°C from the solution with less dissolved CO2 gas and low precipitation rates indicate a closer approach to equilibrium. Combining the lower values at 0 and 25°C with previous data derived from a two-step overgrowth technique at 50 and 70°C, a fractionation equation for the aragonite-water system at 0 to 70°C is obtained as follows: