Water In Silicate Glasses Research Articles

Relative abundance of subsurface hydroxyl and molecular water species in silicate and aluminosilicate glasses

The interaction of water with glass has a profound impact on its mechanical, chemical, and kinetic properties. Water can enter the glass network either as molecular form (H2O) or hydroxyl species (OH). The resulting impact of water on glass properties depends on the relative concentrations of hydroxyl to molecular species. While attenuated total reflection infrared (ATR-IR) spectroscopy can be used to determine the presence of these species in the subsurface region of glass, there is currently no approach to characterize their relative abundance in the glass surface. In this paper, we propose a calculating method for quantifying the ratio of hydroxyl to molecular water in silicate glasses based on a combination of ATR-IR spectroscopy and secondary ion mass spectrometry (SIMS). The technique is applied to leached soda lime silicate and sodium aluminosilicate glasses under a variety of process conditions. The method presented in this paper offers a new avenue for understanding the multiple roles of water in silicate glass network structure and topology.

Accounting for the species-dependence of the 3500 cm−1H2Otinfrared molar absorptivity coefficient: Implications for hydrated volcanic glasses

Fourier transform infrared (FTIR) spectroscopy can be used to determine the concentration and speciation of dissolved water in silicate glasses if the molar absorptivity coefficients (e) are known. Samples that are thin and/or water-poor typically require the use of the mid-IR 3500 cm–1 total water (H2Ot) and 1630 cm–1 molecular water (H2Om) absorbance bands, from which hydroxyl water (OH) must be determined by difference; however, accurate determination of H2Ot and OH is complicated because e3500 varies with water speciation, which is not usually known a priori. We derive an equation that uses end-member e3500 values to find accurate H2Ot and OH concentrations from the 3500 cm–1 absorbance for samples where only the H2Om concentration need be known (e.g., from the 1630 cm–1 band). We validate this new species-dependent e3500 method against published data sets and new analyses of glass standards. We use published data to calculate new end-member e3500 values of e3500OH = 79 ± 11 and e3500H2Om = 49 ± 6 L/mol∙cm for Fe-bearing andesite and e3500OH = 76 ± 12 and e3500H2Om = 62 ± 7 L/mol∙cm for Fe-free andesite. These supplement existing end-member values for rhyolite and albite compositions. We demonstrate that accounting for the species-dependence of e3500 is especially important for hydrated samples, which contain excess H2Om, and that accurate measurement of OH concentration, in conjunction with published speciation models, enables reconstruction of original pre-hydration water contents. Although previous studies of hydrous silicate glasses have suggested that values of e decrease with decreasing tetrahedral cation fraction of the glass, this trend is not seen in the four sets of end-member e3500 values presented here. We expect that future FTIR studies that derive end-member e3500 values for additional compositions will therefore not only enable the species-dependent e3500 method to be applied more widely, but will also offer additional insights into the relationship between values of e and glass composition.

Water and magmas: insights about the water solution mechanisms in alkali silicate melts from infrared, Raman, and 29Si solid-state NMR spectroscopies

Degassing of water during the ascent of hydrous magma in a volcanic edifice produces dramatic changes in the magma density and viscosity. This can profoundly affect the dynamics of volcanic eruptions. The water exsolution history, in turn, is driven by the water solubility and solution mechanisms in the silicate melt. Previous studies pointed to dissolved water in silicate glasses and melts existing as molecules (H2Omol species) and hydroxyl groups, OH. These latter OH groups commonly are considered bonded to Si4+ but may form other bonds, such as with alkali or alkaline-earth cations, for instance. Those forms of bonding influence the structure of hydrous melts in different ways and, therefore, their properties. As a result, exsolution of water from magmas may have different eruptive consequences depending on the initial bonding mechanisms of the dissolved water. However, despite their importance, the solution mechanisms of water in silicate melts are not clear. In particular, how chemical composition of melts affects water solubility and solution mechanism is not well understood. In the present experimental study, components of such information are reported via determination of how water interacts with the cationic network of alkali (Li, Na, and K) silicate quenched melts. Results from 29Si single-pulse magic-angle spinning nuclear magnetic resonance (29Si SP MAS NMR), infrared, and Raman spectroscopies show that decreasing the ionic radius of alkali metal cation in silicate melts results in decreasing fraction of water dissolved as OH groups. The nature of OH bonding also changes as the alkali ionic radius changes. Therefore, as the speciation and bonding of water controls the degree of polymerization of melts, water will have different effects on the transport properties of silicate melts depending on their chemical composition. This conclusion, in turn, may affect volcanic phenomena related to the viscous relaxation of hydrous magmas, such as for instance the fragmentation process that occurs during explosive eruptions.

Sensitive high resolution ion microprobe – stable isotope (SHRIMP-SI) analysis of water in silicate glasses and nominally anhydrous reference minerals

Water concentrations in geological reference materials are evaluated with the new SHRIMP SI ion microprobe.

Heat capacity of hydrous basaltic glasses and liquids

We determined the heat capacities of four series of glasses and liquids of basaltic and basaltic andesite compositions from remelted volcanic rock samples and Fe-free synthetic analogues. The samples are low-alkali, Ca- and Mg-rich aluminosilicates with non-bridging oxygen to tetrahedrally-coordinated cation ratios (NBO/T) ranging between 0.33 and 0.67. Differential scanning calorimetry measurements were performed at atmospheric pressure between room temperature and ~100K above the glass transition for hydrous samples and up to ~1800K for dry samples. The water contents investigated range up to 5.34wt.% (16.4mol%). Water does not measurably affect the heat capacity of glasses. We derived a new value of the partial molar heat capacity of water in silicate glasses of C¯P,H2Oglass=82.804+10−3T−48.274×10−5T−2 (J/molK) using our new data in combination with literature data on more and less polymerized compositions. The increase in heat capacity at the glass transition is of the order of ~30–40% and generally increases with increasing water content. The onset of the glass transition in hydrous samples occurs below the Dulong–Petit limit of 3R/g atom. The configurational heat capacity, i.e., the magnitude of the change in heat capacity observed at the glass transition, generally increases as polymerization decreases and as water content increases. We obtained a partial molar heat capacity of water in silicate liquids of basaltic composition of ~86J/molK. This value is comparable to the partial molar values for the major oxides which range from ~79 to 230J/molK. The partial molar heat capacity of water in silicate liquids appears to be compositionally-dependent, increasing as melt polymerization decreases. Such a dependence is certainly linked to the speciation and structural roles of water in complex silicate melts, however, a single value of ~93J/molK could reproduce the heat capacity of hydrous liquids of a wide range of NBO/T (0–1.51) at temperatures up to ~100K above the glass transition and water contents of 0–3.76wt.% with a root-mean square deviation of only 3.23J/molK.

Amorphous Materials: Properties, Structure, and Durability: Compositional dependent compressibility of dissolved water in silicate glasses

The sound velocities and elastic properties of a series of hydrous rhyolite, andesite, and basalt glasses have been determined by Brillouin scattering spectroscopy at ambient conditions to elucidate the effect of glass composition on the compressibility of dissolved water. Both the adiabatic bulk (K S ) and shear modulus (μ) of the dry glasses decrease with increasing silica content (K S,basalt > K S,andesite > K S,rhyolite and μ basalt > μ andesite > μ rhyolite ). For each composition, the shear modulus systematically decreases with increasing water content. Although the addition of up to 14 mol% water decreases the K S of andesite and basalt glasses by up to 6%, there is no discernable effect of water on the K S of the rhyolite glasses. The partial molar KS of dissolved water (K S ) in rhyolite, andesite, and basalt glasses are 37 ± 5, 19 ± 7, and 40 ± 3 GPa, corresponding to partial molar isothermal compressibilities (β̅ T ) of 0.029 ± 0.005, 0.042 ± 0.004, and 0.026 ± 0.002 GPa −1 , respectively. These results indicate that the compressibility of dissolved water strongly depends on the bulk composition of the glass; hence, the partial molar volume of water cannot be independent of the bulk composition at elevated pressure. If the compressibility of dissolved water also depends on composition in the analog melts at high temperature and pressure, these observations will have important consequences for magmatic processes such as magma mixing/unmixing and fractional crystallization.

Characterization of water in synthetic rhyolitic glasses and natural melt inclusions by Raman spectroscopy

Raman spectroscopy was used to analyze quantitatively water in silicate glasses and melt inclusions and to monitor H2O–OH speciation. Calibration is based on synthetic glasses with various water contents (0.02–7.67% H2O); water determination and OH–H2O differentiation on the area of the Si–O broad band at 468 cm–1 and the asymmetric O–H band at 3,550 cm–1. Each Raman spectrum has been decomposed into four Gaussian + Lorentzian components centered at 3,330, 3,458, 3,560, and 3,626 cm–1 using the Levenberg–Marquardt algorithm. These components are interpreted to be two different types of H2O molecule sites. The influence of the temperature on the loss of water is more important for molecular water than for the hydroxyl groups. The H2O–OH partition confirms the typical evolution of water speciation in rhyolitic glasses as a function of the bulk water content. Method limitations have been studied for the application to natural melt inclusions.

Ab initio Calculation of the 17O and 1H NMR Parameters for Various OH Groups: Implications to the Speciation and Dynamics of Dissolved Water in Silicate Glasses

Ab initio molecular orbital calculations have been carried out for silicate, aluminosilicate, and aluminate clusters to study the NMR characteristics of various types of hydroxyls (OH) that are possibly present in hydrous silicate glasses and melts. The clusters have been optimized with the density functional theory (B3LYP/6-311+G(2df,p)) and their NMR parameters calculated at HF/6-311+G(2df,p). Our calculations suggest that the 17O and 2H quadrupolar coupling constants (CQO and CQH) and 1H chemical shift (δiH) of SiOH, AlOH, and bridging OH's (Si(OH)Al, Al(OH)Al) all show good correlation with the O−H and O−H···O distances. The calculated CQO, CQH, and δiH values agree well with those of the experimental data for OH groups with similar O−H···O distances in crystalline phases. Hydroxyls with stronger hydrogen bonding tend to yield smaller CQO and CQH and larger δiH. SiOH and bridging OH's of comparable hydrogen-bonding strengths give similar 17O and 1H (2H) NMR parameters. AlOH have a tendency not to form...

The effect of water on the structure of silicate glasses — A neutron diffraction study

The first neutron diffraction study of water in silicate glasses is reported. Deuterated sodium tetrasilicate glasses, Na2Si4O9 · χD2O (χ = 5, 10 wt%), as well as a protonated glass, Na2Si4O9 · 10 wt%H2O, were prepared in rapid-quench high pressure autoclaves. Infrared (IR) measurements show, in accordance with results for other proton-containing glasses, the presence of both molecular H2O and OH species. Line shape analysis of the first sharp diffraction peak (FSDP) indicates a gradual decrease of the medium-range order with increasing total water (H2O + OH) content. A structural mechanism explaining the observed changes in the FSDP is proposed. Combined least-squares fits, using Gaussian functions, of the first SiO, NaO and OO peaks in the corresponding total pair correlation functions, T(r), indicate that the short-range order of the silicate network is not affected by the presence of water. However, the root mean square displacements of the Na atoms decrease, suggesting that the NaO coordination becomes more ordered in hydrous silicate glasses. The first-difference of the correlation functions, D(r), for the glasses with 10 wt% total water content is obtained. The OH contributions are identified and indicate, in accordance with the analysis of the FSDP, that the OH groups lead to significant changes in the silicate network on the 3–5 A scale. The average OH distance determined from the total pair correlation functions is 0.99 A. Three types of hydrous species (H2O and / or OH), participating in hydrogen-bonding, are observed in the IR spectra with average OH...O bond lenghts, equal to 3.0, 2.65 and 2.55 A, respectively.

Ion microprobe determination of water in silicate glasses: methods and applications

Ion probe measurements offer the advantage of in situ determination of water content with a few micrometres spatial resolution. After a brief review of ion microprobe procedures used for the determination of water concentration in silicates, we examine three important effects on analytical precision: (1) the effect of energy filtering on the background; (2) the variation of the H/Si ratio with time; and (3) the dependence of the H/Si ratio on the composition of the matrix, which requires the use of standards close in chemical composition to the unknowns. Finally, applications of this method to the determination of water in glasses quenched from water-saturated melts, to experimental products consisting of a mixture of glass and crystals, and to natural melt inclusions illustrate the advantages and the limitations of the ion microprobe.

The influence of bulk composition on the speciation of water in silicate glasses

Infrared spectroscopy was used to determine the concentrations of molecular water and hydroxyl groups in hydrous rhyolitic, orthoclasic, jadeitic, and Ca−Al-silicate glasses synthesized by quenching of melts from elevated presure and temperature. The rhyolitic glasses and some of the Ca−Al-silicate glasses were quenched from water-vapor-saturated melts and used to determine the solubility of water in melts of these compositions. For all compositions studied, hydroxyl groups are the dominant hydrous species at low total water contents, whereas molecular water dominates at elevated water contents. Although the trends in species concentrations in all these compositions are similar, the proportions of the two hydrous species are influenced by silicate chemistry: increasing silica content and K relative to Na both favor molecular water over hydroxyl. Results on rhyolitic glass demonstrate that molecular water is also favored by decreasing temperature at T<850°C. For rhyolitic glasses quenched from vapor-saturated melts, the mole fraction of molecular water is proportional to water fugacity for P(H2O)≤1500 bars, demonstrating that the behavior of molecular water is approximately Henrian at total water contents up to at least several weight percent. Data on water solubility for albitic, orthoclasic, and Ca−Al-silicate melts to higher pressures can also be fit by assuming Henrian behavior for molecular water and can be used to set constraints on the partial molar volume of water in these melts. The demonstration of Henry's law for molecular water in these liquids provides a link between spectroscopic measurements of microscopic species concentrations and macroscopic thermodynamic properties.

Quantitative NMR studies of water in silicate glasses

The state of water in volcanic and synthetic silicate glasses is characterized by a number of different solid state NMR techniques. 1H solid echo NMR is used to quantitate total water contents reliably down to levels of 0.1 wt%. High-speed 1H magic-angle spinning NMR can be used to obtain relative species concentrations of OH and H 2O groups in glasses free from paramagnetic impurities. Similar results are obtained from deuterium quadrupolar echo NMR difference spectroscopy, utilizing the different spin-lattice relaxation times of OD and D 2O species. The results demonstrate that the percentage of water present in the form of molecular H 2O species increases with increasing total water content. The H 2O groups are anisotropically constrained, but undergo 180° flips about the bisector axis at rates greater than 10 5 s −1. The hydrous species are not clustered and are subjected to a distribution of hydrogen bonding strengths. A distribution function of O-D·O distances obtained from infrared results, shows good compatibility with the experimental 2H NMR lineshapes. The relative merits of the different experimental approaches are discussed in detail.

ChemInform Abstract: Water in Silicate Glasses: Quantitation and Structural Studies by 1H Solid Echo and MAS‐NMR Methods.

AbstractIt is demonstrated that high‐power 1H solid‐echo and high‐speed MAS NMR techniques can provide new information of the bonding state of the hydrous species in glasses.

Water in silicate glasses: quantitation and structural studies by proton solid echo and magic angle spinning NMR methods

^(1)H wideline and magic angle spinning (MAS) NMR results are reported for water in a series of synthetic and naturally occurring silicate glasses containing from 0.04 to 9.4 wt % H_(2)0. For glasses free of paramagnetic metal ions, the absolute water contents can be accurately determined by a solid echo ^(1)H NMR technique with pyrophyllite, A1_(2)Si,0_(10)(OH)_2, as an intensity reference. The MAS-NMR spectra can be interpreted as superpositions of the individual spectra of OH and anisotropically constrained H_(2)0 groups, the latter giving rise to spinning sidebands extending over ca. 100 kHz. Two methods are described to obtain percentages of OH and H_(2)0 groups from the relative intensities of the centerband and the spinning sidebands in these glasses. The MAS-NMR results are consistent with previous IR analyses indicating that low levels of water (<2-4 wt %) are mainly present as OH groups whereas at higher concentrations molecular H_(2)0 species dominate. Simulations of the MAS-NMR spectra based on the individual spectra of compounds in which the hydrogen-bearing species are structurally isolated (OH in tremolite and H_(2)0 in analcite) accurately reproduce the experimental spectra, indicating that the OH or H_(2)0 groups in the glasses are not preferentially clustered. The MAS-NMR centerband line shapes are dominated by a distribution of isotropic chemical shifts. The well-established linear dependence of ^(1)H chemical shifts on the O-H•••O distance (a measure of the hydrogen bonding strength) leads to average distances of 290 ± 1.5 pm in all synthetic glasses except silica, 293 ± 1.5 pm in the volcanic rhyolite glasses, and 298 pm in silica glass. This value does not depend on the total water contents, indicating that the hydrogen-bonding characteristics of OH and H_(2)0 species in the glasses are similar. The ^(1)H wideline NMR procedure above yields underestimates of the total water content for synthetic and volcanic glasses containing ca. 1 wt 5% iron, presumably due to extreme signal broadening by the strong dipolar fields from the electron spins of the paramagnetic ions. These dipolar couplings also affect the line shape of the observable portion of the hydrogen resonance and produce intense spinning sidebands in the MAS-NMR spectra which invalidate determinations of OH/H_(2)0 ratios in these cases.

Water in silicate glasses: An infrared spectroscopic study

Infrared and near-infrared transmission spectra have been taken on 19 volcanic and synthetic silicate glasses with known H2O contents (0.06–6.9 wt. %). Absorption peaks were observed at wavelengths of 1.41 μm, 1.91 μm, 2.22 μm, 2.53 μm, and 2.8 μm. These peaks have been attributed to the first overtone of the OH stretching vibration, the combination stretching+bending mode of H2O molecules, the combination stretching+bending mode of X-OH groups, a combination mode of the fundamental OH stretch+a low energy lattice vibration, and the fundamental OH stretching mode, respectively. Molar absorptivities of the peaks have been determined to be 0.2, 1.8, 1.0, 0.9, and 67 l/mol-cm. These values apply over the full range of glass compositions studied (albite, rhyolite, basalt).

The influence of the distribution of water in silicate glasses on mechanical relaxation

When the internal friction of an alkali silicate glass is measured at a constant frequency and as a function of temperature, three major absorption regions are found. Little doubt exists about the mechanisms responsible for the low temperature peak or for the high mechanical loss observed at higher temperatures. On the other hand, the mechanism causing the peak observed at intermediate temperatures is still open to debate. Possible mechanisms responsible for this peak are reviewed and discussed.