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1.
The vibrational interactions of oxide tetrahedra and the correlation off vibrational bands with structural entities in variously polymerized idealized silicate structural units have been investigated with normal-coordinate calculations. Raman and infrared intensities as well as frequencies were calculated, yielding good qualitative agreement with observed glass and crystal spectra. Structures considered include those in the binary metal-oxide-silica systems, and analogous structures with Al or Ge replacing every other Si. The fitted force constants for stretching of bonds from Si to bridging oxygens (Obr) and non-bridging oxygens (Onb) show close correlation with bond lengths in crystals. In all-silicate units the high-frequency Raman modes due to symmetric T-Onb stretching show essentially no coupling between unlike types of tetrahedra (O-types), classified on the basis of numbers of Obr versus Onb. Calculated spectra of units with more than one O-type (e.g. double chain) have multiple high-frequency Raman modes. Interconnection of different O-types in glasses is very probable on the basis of unsplit low/mid-frequency Si-Obr stretching bands in the measured spectra of all-Si glasses. In Si-Al and Si-Ge structures oscillation of bridging oxygens may play an important role in the high-frequency Raman. There may be more high-frequency modes than there are different types of tetrahedra, and behavior in such modes is complex, not readily described by “one-mode/two-mode” terminology. High frequency antisymmetric (both infrared- and Raman-active) and low- to mid-frequency symmetric (Raman active) T-O stretching modes may sometimes be identified with individual T-O-T groups, although this depends on the degree of polymerization.  相似文献   

2.
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3.
Enthalpies of solution in molten 2PbO · B2O3 at 985 K are reported for series of glasses xCa0.5AlO2-(1?x)SiO2 (O ≤ x ≤ 0.99) and xNaAlO2-(1?x)SiO2 (0 ≤ x ≤ 0.56). The data are compared to values for the corresponding crystalline aluminosilicates and to preliminary data for systems containing KAlO2 and Mg0.5AlO2. The enthalpies of mixing of glasses become more exothermic with increasing basicity of the mono- or divalent oxide. The tendency toward immiscibility on the silica-rich side, indicated by the shape of the heat of mixing curve between x = 0 and x = 0.4, is pronounced in the calcium aluminate system, but not in the sodium aluminate system. The shape of the heat of mixing curve, which is roughly symmetrical about x = 0.5, can be rationalized in terms of glass structure by considering essentially random substitution of Si and Al on a continuous three dimensional tetrahedral framework, with stabilization arising from electrostatic interactions between aluminum and the nonframework cation balancing the destabilizing effects arising from perturbation of the aluminosilicate framework by the nonframework cation. These trends are consistent with the variation of physical properties of aluminosilicate melts.  相似文献   

4.
Estimation of the framework connectivity and the atomic structure of depolymerized silicate melts and glasses (NBO/T > 0) remains a difficult question in high-temperature geochemistry relevant to magmatic processes and glass science. Here, we explore the extent of disorder and the nature of polymerization in binary Ca-silicate and ternary Ca-aluminosilicate glasses with varying NBO/T (from 0 to 2.67) using O-17 NMR at two different magnetic fields of 9.4 and 14.1 T in conjunction with quantum chemical calculations. Non-random distributions among framework cations (Si and Al) are demonstrated in the variation of relative populations of oxygen sites with NBO/T. The proportion of non-bridging oxygen (NBO, Ca-O-Si) in the binary and ternary aluminosilicate glasses increases with NBO/T. While the trend is consistent with predictions from composition, the detailed fractions apparently deviate from the predicted values, suggesting further complications in the nature of polymerization. The proportion of each bridging oxygen in the glasses also varies with NBO/T. The fractions of Al-O-Si and Al-O-Al increase with increasing polymerization as CaO is replaced with Al2O3, while that of Si-O-Si seems to decrease, implying that activity of silica may decrease from calcium silicate to polymerized aluminosilicates (XSiO2=constant). Quantum chemical molecular orbital calculations based on density functional theory show that a silicate chain with Al-NBO (Ca-O-Al) has an energy penalty (calculated cluster energy difference) of about 108 kJ/mol compared with the cluster with Ca-O-Si, consistent with preferential depolymerization of Si-networks, reported in an earlier O-17 NMR study [Allwardt, J., Lee, S.K., Stebbins, J.F., 2003. Bonding preferences of non-bridging oxygens in calcium aluminosilicate glass: Evidence from O-17 MAS and 3QMAS NMR on calcium aluminate glass. Am. Mineral.88, 949-954]. These prominent types of non-randomness in the distributions suggest significant chemical order in silicate glasses that leads to a decrease in silica activity coefficient and will be useful in modeling transport properties of melts.  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.
In order to decipher information about the local coordination environments of Na in anhydrous silicates from 23Na nuclear magnetic resonance spectroscopy (NMR), we have collected 23Na magic angle spinning (MAS) NMR spectra on several sodium-bearing silicate and aluminosilicate crystals with known structures. These data, together with those from the literature, suggest that the 23Na isotropic chemical shift correlates well with both the Na coordination and the degree of polymerization (characterized by NBO/T) of the material. The presence of a dissimilar network modifier also affects the 23Na isotropic chemical shift. From these relations, we found that the average Na coordinations in sodium silicate and aluminosilicate liquids of a range of compositions at 1 bar are nearly constant at around 6–7. The average Na coordinations in glasses of similar compositions also vary little with Na content (degree of polymerization). However, limited data on ternary alkali silicate and aluminosilicate glasses seem to suggest that the introduction of another network-modifier, such as K or Cs, does cause variations in the average local Na coordination. Thus it appears that the average Na coordination environments in silicate glasses are more sensitive to the presence of other network-modifiers than to the variations in the topology of the silicate tetrahedral network. Further studies on silicate glasses containing mixed cations are necessary to confirm this conclusion.  相似文献   

7.
Liquation structures were described in ultrahigh-pressure impact glasses of the Kara astrobleme (Pay-Khoy) with differentiation into the bisilica, aluminosilicate, and ore components for the first time. The sequence of differentiation of mineral phases upon solidification of an ultrahigh-pressure impact melt was established: coesite, silicate glass, augite, aluminosilicate glass of albite composition, and pyrite. The discovered impact glasses are highly resistant to postimpact alterations.  相似文献   

8.
Normal coordinate calculations, producing synthetic infrared and Raman spectra, were carried out on melilites, pyroxenes, silica polymorphs and feldspars. Atomic motions are complex in the high-frequency Raman modes of melilites and aluminous pyroxenes. The symmetric T-Onb stretching vibrations of Si and Al tetrahedra with different numbers of bridging oxygens are separate from each other, but may combine individually with oscillation of bridging oxygens between Si and Al tetrahedra. The latter type of vibration tends to dominate as Al/Si increases. The frequencies of these vibrational components and the degree of such intermixing depend on T-O force constants, which vary greatly depending on local bonding configurations; individual bands in the high-frequency Raman cannot in general be assigned to single structural entities or fixed combinations thereof. Calculations confirm that in some Al-Si glasses such as jadeite and spodumene, i.e. those in which all Al can be tetrahedral without non-bridging oxygens, Al-O-Al linkages or linkage of more than two tetrahedra by a single oxygen, aluminum is predominantly in tetrahedral coordination. Other Al-Si glasses which are richer in aluminum or which have non-bridging oxygens may contain Al tetrahedral triclusters, non-tetrahedral Al, or both. On the basis of distinctive 450–750 cm?1 infrared bands, both silica and feldspar glasses resemble tridymite and related stuffed derivatives, not other crystalline silica polymorphs or feldspars. Either these glasses have a structure like that of tridymite on a local scale, or the disorder of the glasses causes drastic modification to the vibrations in question.  相似文献   

9.
The Raman spectra of albite glasses with 4.5 and 6.6 weight percent water have been obtained, and are compared with that of a dry sample. The hydrous glasses show bands near 3600 cm?1 due to O-H stretching, and a previously unreported weak band near 1600 cm?1 due to bending of molecular H2O. Other weak spectral features are discussed, and the effect of dissolved water on the aluminosilicate framework vibrations is considered.  相似文献   

10.
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   

11.
We have compiled water solubility data for a wide range of natural and synthetic aluminosilicate melts in a search for correlations between melt composition and solubility. The published data reveal some interesting systematics. For example, molar water solubility increases with decreasing silica content in binary and pseudobinary silicates, and much higher solubilities are associated with alkali systems compared to alkaline earth silicate melts. Water solubility increases regularly with decreasing silica content along the silica-nepheline join. From the limited data available for potassium and calcium aluminosilicate melts, these systems appear to behave differently to sodium aluminosilicates. The compiled data are not nearly extensive enough to begin to understand the effects of melt composition on solubility. We suggest that many more systematic studies for a wide range of aluminosilicate melts will be necessary before we can systematize and understand the compositional dependence of water solubility. We have also examined results of experiments designed to probe the details of the water dissolution mechanism, and discuss the present state of interpretation of these data. We conclude that although considerable progress has been made, the water dissolution process is still not well understood at the molecular level, and remains an important research problem.  相似文献   

12.
Revealing the atomic structure and disorder in oxide glasses, including sodium silicates and aluminosilicates, with varying degrees of polymerization, is a challenging problem in high-temperature geochemistry as well as glass science. Here, we report 17O MAS and 3QMAS NMR spectra for binary sodium silicate and ternary sodium aluminosilicate glasses with varying degrees of polymerization (Na2O/SiO2 ratio and Na2O/Al2O3 ratio), revealing in detail the extent of disorder (network connectivity and topological disorder) and variations of NMR parameters with the glass composition. In binary sodium silicate glasses [Na2O-k(SiO2)], the fraction of non-bridging oxygens (NBOs, Na-O-Si) increases with the Na2O/SiO2 ratio (k), as predicted from the composition. The 17O isotropic chemical shifts (17O δiso) for both bridging oxygen (BO) and NBO increase by about 10-15 ppm with the SiO2 content (for k = 1-3). The quadrupolar coupling products of BOs and NBOs also increase with the SiO2 content. These trends suggest that both NBOs and BOs strongly interact with Na; therefore, the Na distributions around BOs and NBOs are likely to be relatively homogenous for the glass compositions studied here, placing some qualitative limits on the extent of segregation of alkali channels from silica-enriched regions as suggested by modified random-network models. The peak width (in the isotropic dimension) and thus bond angle and length distributions of Si-O-Si and Na-O-Si increase with the SiO2 content, indicating an increase in the topological disorder with the degree of polymerization. In the ternary aluminosilicate glasses [Na2O]x[Al2O3]1−xSiO2, the NBO fraction decreases while the Al-O-Si and Al-O-Al fractions apparently increase with increasing Al2O3 content. The variation of oxygen cluster populations suggests that deviation from “Al avoidance” is more apparent near the charge-balanced join (Na/Al = 1). The Si-O-Si fraction, which is closely related to the activity coefficient of silica, would decrease with increasing Al2O3 content at a constant mole fraction of SiO2. Therefore, the activity of silica may decrease from depolymerized binary silicates to fully polymerized sodium aluminosilicate glasses at a constant mole fraction of SiO2.  相似文献   

13.
Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structural studies of aluminosilicate glasses. Both techniques are sensitive to small-scale (<15 Å) structural features that amount to units of several SiO4 tetrahedra. Application of IR spectroscopy has, however, been limited by the more complex nature of the IR spectrum compared with the Raman spectrum, particularly at higher frequencies (1200–800 cm?1) where strong antisymmetric Si-O and Si-O-Si absorptions predominate in the former. At lower frequencies, IR spectra contain bands that have substantial contributions from ‘cage-like’ motions of cations in their oxygen co-ordination polyhedra. In aluminosilicates these bands can provide information on the structural environment of Al that is not obtainable directly from Raman studies. A middle frequency envelope centred near 700 cm?1 is indicative of network-substituted AlO4 polyhedra in glasses with Al/(Al+Si)>0·25 and a band at 520–620cm?1 is shown to be associated with AlO6 polyhedra in both crystals and glasses. The IR spectra of melilite and melilite-analogue glasses and crystals show various degrees of band localization that correlate with the extent of Al, Si tetrahedral site ordering. An important conclusion is that differences in Al, Si ordering may lead to very different vibrational spectra in crystals and glasses of otherwise gross chemical similarity.  相似文献   

14.
利用钾长石粉体水热合成13X沸石分子筛的晶化过程   总被引：2，自引：1，他引：1  
章西焕  马鸿文  白峰 《现代地质》2007,21(3):584-590
实验研究了以钾长石粉体为原料水热合成13X沸石分子筛的晶化过程,确定了晶化过程的诱导期、晶化期和沸石晶体的平均生长速率。以钾长石焙烧熟料为前驱物合成13X沸石,反应混合物首先转变为铝硅酸钠（钾）凝胶,再逐步水热晶化为13X沸石;在反应物未完全转变为铝硅酸钠（钾）凝胶之前,13X沸石已开始结晶。13X沸石晶体的生成主要发生在凝胶相内部,是凝胶结构逐步趋于有序化的过程。13X沸石晶体生成是由凝胶相内的[TO4]四面体相互连接,互套构成笼状结构。推测13X沸石形成机理为：硅酸根离子和铝酸根（+铁酸根）离子发生聚合反应,生成次级结构单元双六元环;双六元环进一步缩合,生成方钠石型笼;最后,方钠石型笼进一步相互联结,生成13X型沸石分子筛的硅铝骨架结构。  相似文献   

15.
Simple model calculations show that the reversible temperature effects reported for broad OH-stretching bands in infrared spectra of silica, aluminosilicate, and similar glasses can be explained, in essentials, by homogeneous thermal broadening of the ν(OH) envelope constituents and a decrease in intensity with increasing temperature taking place uniformly across the band. This means that these effects are reasonably consistent with the temperature behaviour of narrow ν(OH) bands of crystalline OH-bearing minerals. These findings leave little room for the previously agreed interpretation in terms of a change in hydrogen-bonding strength, although the dependence of integrated intensity on temperature still remains to be understood. Received: 16 April 1999 / Accepted: 4 April 2000  相似文献   

16.
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   

17.
A new approach was developed to measure the water content of silicate glasses using Raman spectroscopy, which is independent of the glass matrix composition and structure. Contrary to previous studies, the compositional range of our studied silicate glasses was not restricted to rhyolites, but included andesitic, basaltic and phonolitic glasses. We used 21 glasses with known water contents for calibration. To reduce the uncertainties caused by the baseline removal and correct for the influence of the glass composition on the spectra, we developed the following strategy: (1) application of a frequency-dependent intensity correction of the Raman spectra; (2) normalization of the water peak using the broad T–O and T–O–T vibration band at 850–1250 cm−1 wavenumbers (instead of the low wavenumber T–O–T broad band, which appeared to be highly sensitive to the FeO content and the degree of polymerization of the melt); (3) normalization of the integrated Si-O band area by the total number of tetrahedral cations and the position of the band maximum. The calibration line shows a ±0.4 wt% uncertainty at one relative standard deviation in the range of 0.8–9.5 wt% water and a wide range of natural melt compositions. This method provides a simple, quick, broadly available and cost-effective way for a quantitative determination of the water content of silicate glasses. Application to silicate melt inclusions yielded data in good agreement with SIMS data.  相似文献   

18.
Single-crystal Raman and infrared reflectivity data including high pressure results to over 200 kbar on a natural, probably fully ordered MgAl2O4 spinel reveal that many of the reported frequencies from spectra of synthetic spinels are affected by disorder at the cation sites. The spectra are interpreted in terms of factor group analysis and show that the high energy modes are due to the octahedral internal modes, in contrast to the behavior of silicate spinels, but in agreement with previous data based on isotopic and chemical cation substitutions and with new Raman data on gahnite (～ ZnAl2O4) and new IR reflectivity data on both gahnite and hercynite (～Fe0.58Mg0.42Al2O4). Therefore, aluminate spinels are inappropriate as elastic or thermodynamic analogs for silicate spinels. Fluorescence sideband spectra yield complementary information on the vibrational modes and provide valuable information on the acoustic modes at high pressure. The transverse acoustic modes are nearly pressure independent, which is similar to the behavior of the shear modes previously measured by ultrasonic techniques. The pressure derivative of all acoustic modes become negative above 110 kbar, indicating a lattice instability, in agreement with previous predictions. This lattice instability lies at approximately the same pressure as the disproportionation of spinel to MgO and Al2O3 reported in high temperature, high pressure work.  相似文献   

19.
We have measured in-situ Raman spectra of aluminosilicate glasses and liquids with albite (NaAlSi3 O8) and anorthite (CaAl2Si2O8) compositions at high temperatures, through their glass transition range up to 1700 and 2000 K, respectively. For these experiments, we have used a wire-loop heating device coupled with micro-Raman spectroscopy, in order to achieve effective spatial filtering of the extraneous thermal radiation. A major concern in this work is the development of methodology for reliably extracting the first and second order contributions to the Raman scattering spectra of aluminosilicate glasses and liquids from the high temperature experimental data, and analyzing these in terms of vibrational (anharmonic) and configurational changes. The changes in the first order Raman spectra with temperature are subtle. The principal low frequency band remains nearly constant with increasing temperature, indicating little change in the T-O-T angle, and that the angle bending vibration is quite harmonic. This is in contrast to vitreous SiO2, studied previously. Above Tg, intensity changes in the 560–590 cm?1 regions of both sets of spectra indicate configurational changes in the supercooled liquids, associated with formation of additional Al-O-Al linkages, or 3-membered (Al, Si)-containing rings. Additional intensity at 800 cm?1 reflects also some rearrangement of the Si-O-Al network.  相似文献   

20.
Information about the state of sulfur in silicate melts and glasses is important in both earth sciences and materials sciences. Because of its variety of valence states from S2− (sulfide) to S6+ (sulfate), the speciation of sulfur dissolved in silicate melts and glasses is expected to be highly dependent on the oxygen fugacity. To place new constraint on this issue, we have synthesized sulfur-bearing sodium silicate glasses (quenched melts) from starting materials containing sulfur of different valence states (Na2SO4, Na2SO3, Na2S2O3 and native S) using an internally heated gas pressure vessel, and have applied electron-induced SKα X-ray fluorescence, micro-Raman and NMR spectroscopic techniques to probe their structure. The wavelength shift of SKα X-rays revealed that the differences in the valence state of sulfur in the starting compounds are largely retained in the synthesized sulfur-bearing glasses, with a small reduction for more oxidized samples. The 29Si MAS NMR spectra of all the glasses contain no peaks attributable to the SiO4-nSn (with n > 0) linkages. The Raman spectra are consistent with the coexistence of sodium sulfate (Na2SO4) species and one or more types of more reduced sulfur species containing S-S linkages in all the sulfur-bearing silicate glasses, with the former dominant in glasses produced from Na2SO4-doped starting materials, and the latter more abundant in more reduced glasses. The 29Si MAS NMR and Raman spectra also revealed changes in the silicate network structure of the sulfur-bearing glasses, which can be interpreted in terms of changes in the chemical composition and sulfur speciation.  相似文献   

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