Anhydrous Glass Research Articles

Effects of effluent pressure on the thermal cracking of crude oil: insights from thermal simulation experiments and phase analysis

This study discusses the anhydrous glass tube isothermal pyrolysis simulation for a crude oil, in order to explore the effects of effluent pressure on crude oil cracking. The results of gas chromatograph indicate that effluent pressure promotes the cracking of crude oil, increasing yields of C1–C5 saturates but inhibiting the generation of olefins. According to the calibration result of Soave–Redlich–Kwong equation of state, fluid phase transitions occur at very high effluent pressures, resulting in constant effluent pressure with no further increase in cracking efficiency and with invariant yields of pyrolysates. This study suggests that fluid phase transitions should be considered in petroleum exploration, which can help us to precisely determine the type of petroleum resources.

Novel approach to study diffusion of hydrogen bearing species in silicate glasses at low temperatures

Diffusion of hydrogen bearing species in glasses plays a significant role in numerous applications in commercial as well as scientific domains. The investigation of diffusion of water in glasses at low temperatures led to experimental and analytical difficulties in the past. We present a new approach that lets us overcome these complications. Diffusion couples of An50Di50 glass (mol %, NBO/T = 0.67) were produced by coating anhydrous glass substrates with thin films of hydrated glass (~200 nm, ~2 wt% H2O) using pulsed laser deposition (PLD). Bonding the diffusant to the glass matrix of the thin film instead of using free water at the interface during experiments precludes other glass altering processes such as dissolution and precipitation. This allows us to confidently interpret the measured profiles to be a result of diffusion only. Nanoscale concentration profiles that result from diffusion at low temperatures on experimentally feasible time scales were measured with the Nuclear Resonance Reaction Analysis (NRRA, 1H(15N,αγ)12C). The non-destructive nature of NRRA enables us to observe and better understand the evolution of diffusion profiles with time within one sample. Evaluation of the sample quality by EPMA, SEM, optical microscopy, Rutherford backscattering spectroscopy (RBS), and NRRA was performed and confirmed the suitability of the samples for diffusion studies. Experiments at 1 atm in a box furnace and at 2 kbar in a CSPV (pressure medium = water) and an IHPV (pressure medium = Argon) prove that the diffusion couples can be used under various experimental conditions. We present diffusion profiles that were measured in experiments carried out in these devices and discuss the distinct features of each that result from different boundary conditions in the experiments.

Water makes glass elastically stiffer under high-pressure

Because of its potentially broad industrial applications, a new synthesis of elastically stiffer and stronger glass has been a long standing interest in material science. Various chemical composition and synthesis condition have so far been extensively tested to meet this requirement. Since hydration of matter, in general, significantly reduces its stiffness, it has long been believed that an anhydrous condition has to be strictly complied in synthesis processes. Here we report elastic wave velocities of hydrous SiO2 glass determined in-situ up to ultrahigh-pressures of ~180 gigapascals, revealing that the elastic wave velocities of hydrous glass unexpectedly show the rapid increase with pressure and eventually become greater than those of anhydrous glass above ~15 gigapascals. Furthermore, anomalous change in the velocity gradient at ~100 gigapascals, probably caused by the change in Si-O coordination number from 6 to 6+, was also found at ~40 gigapascals lower pressure condition than that previously reported in anhydrous silica glass, implying that water is a highly effective impurity to make SiO2 glass much denser. This experimental discovery strongly indicates that hydration combined with pressurization is highly effective to synthesize elastically stiffer glass materials, which offers a new insight into the fabrication of industrially useful novel materials.

Reactivity of Glass Powder in Aqueous Medium

Recycled glass powder (GP) has recently been widely used as a complementary cementitious material to replace a part of the Portland cement in concrete. However, unlike the chemistry of the Portland cement hydration, more studied and mastered, the mechanism of GP reaction that occurs in-situ during the mixture hydration, is less studied. To overcome this, a first study was focused on the reactivity of the anhydrous glass powder surface over time and its effect on physico-chemical and mechanical properties of concrete. The results showed a very good stability of GP surface. Actually, Portland cement mortars incorporating 20% GP at different ages exhibited the same required properties. The second step, which is the subject of this paper, consists of studying the behavior of GP alone in water and identifying species likely to involve in the hydration reaction in presence of the cement. pH of suspensions and chemical composition of leachates were monitored respectively by pH-meter and inductively coupled plasma mass spectrometry (ICP-MS) as a function of contact time, water-to-solid mass ratio (W/S) and GP particle size. Results reveal an instantaneous increase of pH after mixing GP with water resulting in the passage of surface alkali ions in the solution. Moreover, an enhancement of silicon content in solution is observed suggesting a partial dissolution of the glass network. The dissolution rate increases with increasing W/S ratio and decreasing particle size. Thus, dissolved silica species would react with portlandite from cement hydration explaining good mechanical properties generally observed in concrete containing GP at long term. Accordingly, due to its high amorphous silica content, GP could be an excellent alternative for conventional supplementary cementitious materials such as fly ashes which are not locally available.

Nucleation rates of spherulites in natural rhyolitic lava

The rates of nucleation and crystal growth from silicate melt are difficult to measure because the temperature–time path of magma is often unknown. We use geochemical gradients around spherulites in obsidian glass to estimate the temperature–time interval of spherulite crystallization. This information is used in conjunction with new high-resolution X-ray computed tomography (HRXCT) data on the size distributions of spherulites in six samples of rhyolite obsidian lava to infer spherulite nucleation rates. A large data set of geochemical profiles indicate that the lavas cooled at rates of 10 −2.2 to 10 −1.2 °C/h, and that the spherulites grew at rates that decreased exponentially with time, with values of 10 −0.70 to 10 0.30 μm/h at 600 °C. Spherulites are estimated to have begun nucleating when undercooling [Δ T , = liquidus T (≈800 °C) minus nucleation T ] reached 100–277 °C, and stopped when Δ T = 203–365 °C, with exact values dependent on assumed cooling and growth rates. Regardless of rates, we find that spherulites nucleated within a ~88–113 °C temperature interval and, hence, began when Δ T ≈ 0.65–0.88 × T L , peaking when Δ T ≈ 0.59–0.80 × T L . A peak rate of nucleation of 0.072 ± 0.049 cm −3 h −1 occurred at 533 ± 14 °C, using cooling and growth rates that best fit the data set of geochemical profiles. While our inferred values for Δ T overlap those from experimental studies, our nucleation rates are much lower. That difference likely results from experimental studies using hydrous melts; the natural spherulites grew in nearly anhydrous glass.

Effect of the addition of chlorhexidine and miswak extract on the clinical performance and antibacterial properties of conventional glass ionomer: an in vivo study.

Antibacterial restorations can increase the success rate of minimum invasive dentistry especially in young permanent molars with deep carious lesions as an attempt to preserve maximum dental structure and avoid pulp exposure. Further research is warranted to evaluate different antibacterial agents. This study aimed to evaluate the efficacy of adding chlorhexidine gluconate (CHX) or aqueous miswak (Salvadora persica) extract on the clinical performance and in vivo antibacterial activity of conventional anhydrous glass ionomer cement (GIC). The study was a randomized clinical trial. Sixty young permanent molars, with deep carious lesions in 6- to 9-year-old children were included. After randomization, atraumatic restorative treatment (ART) or stepwise excavation was performed followed by bacterial sampling from the center of the remaining carious dentine in the floor of the pulp. GIC powder was mixed with 0.5% chlorhexidine gluconate liquid in group I; with 100% aqueous miswak in group II; and with deionized water in group III (control). Clinical performance for all groups was assessed at 3, 6, and 9 months. After 9 months, restorations were removed and a second bacterial sample was collected for Streptococcus mutans (S. mutans) quantification and analysis by real-time polymerase chain reaction (PCR) test. Results showed no statistically significant difference in the success rate of the three groups at the 3-month interval. At 6 and 9 months, however, restoration success was 75% then 60% in group I, 100% then 90% in group II, and 95% then 85% in control group. Group II and the control group showed statistically significant higher survival rates than group I. All groups showed reduction in S. mutans counts in underlying dentine, but the percent reduction was significantly higher in group I. (P < 0.001). The addition of CHX and miswak to GIC showed superior antibacterial properties than conventional GIC, without seriously affecting the clinical performance of the restoration until the 6-month follow-up, but failure significantly increased in terms of marginal defects at 9 months with CHX (group 1).

Effect of water on the high-pressure structural behavior of anorthite-diopside eutectic glass

We employed in situ high pressure Raman spectroscopy to examine structural variations in hydrous versus anhydrous aluminosilicate glasses as a function of pressure. Raman spectra of anhydrous and water-saturated (6.7wt% H2O) eutectic anorthite – diopside (An-Di) glasses were collected at pressures up to 10GPa in a diamond anvil cell (DAC). Both glasses exhibited a distinct change in compression mechanism at about 2.5GPa. From 0 to 2.5GPa each glass depolymerizes. Above 2.5GPa the anhydrous glass becomes less polymerized, whereas the hydrous glass becomes more polymerized as pressure is increased up to 10GPa. These differences are explained in terms of Al-coordination and formation of triclusters. For the dry glass, at pressures below 2.5GPa, depolymerization occurs by means of tricluster (OT3) formation in which bridging oxygens (BO) become triply coordinated to a third network forming cation, preferentially IVAl, thereby increasing the coordination to VAl. At pressures >2.5GPa compression induced coordination to non-bridging oxygens (NBO) causes tetrahedral IVAl to become highly coordinated V,VIAl. Network modifying cations (Ca and Mg) coordinated to NBO at ambient conditions become charge-balancing cations for V,VIAl at elevated pressure, resulting in decreased polymerization. For the wet glass, compression up to 2.5GPa causes protons in H2O to depolymerize Al tetrahedra into Al-OH. At pressures >2.5GPa most of the highly coordinated Al is present as VIAl and network polymerization increases with the formation of M-OH (M=Ca, Mg) groups that enable Si-O-Si bonds (BO). Bulk modulus measurements support increased polymerization with the wet glass (K0=16±2GPa) shown to be more compressible than the dry glass (K0=52±5GPa).

4.6-billion-year-old aragonite and its implications for understanding the geological record of Ca-carbonate.

Owing to its diagenetic instability, aragonite is rare in the geological record and almost entirely absent from pre-carboniferous sedimentary rocks. The former presence of this mineral in older deposits has to be inferred from petrographic, chemical or isotopic proxies. Crystals of aragonite that formed around 4563 million years ago occur in carbonaceous chondrite meteorites, showing that under certain conditions, the orthorhombic polymorph of Ca-carbonate can survive essentially indefinitely. Together with other carbonate minerals, phyllosilicates and sulphides, this aragonite formed by low-temperature water-mediated alteration of anhydrous minerals and glass in the interior of the meteorite’s parent asteroid(s). The survival of aragonite for such a long time can be attributed to the loss of free water by its incorporation into phyllosilicates, and to the very low permeability of the fine-grained and organic-rich rock matrix that prevented the ingress of fresh solutions via intergranular flow. By analogy with these meteorites, terrestrial aragonite is likely to survive where it has been similarly isolated from liquid water, particularly in organic-rich mudrocks, and such deposits may provide important new evidence for deducing the original mineralogy of skeletal and non-skeletal carbonates in deep-time.

Thermal Dehydration of Magnesium Acetate Tetrahydrate: Formation and in Situ Crystallization of Anhydrous Glass

The kinetics and mechanism of the thermal dehydration of magnesium acetate tetrahydrate were investigated as a typical example of the glass formation process via the thermal decomposition of solids. Formation of an intermediate fluid phase was identified as the characteristic phenomenon responsible for the formation of anhydrous glass. Thermal dehydration from the surface fluid layer regulates the zero-order-like rate behavior of the mass-loss process with an apparent activation energy E(a) ≈ 70-80 kJ mol(-1). Because of variations in the mechanism of release of the water vapor with changes in the reaction temperature range, the mass-loss behavior is largely dependent on the particle size of the sample and heating conditions. The formation of hollow anhydrous glass is the novel finding of the present study. The mechanism of formation is discussed in terms of complementary interpretations of the morphological changes and kinetic behavior of the thermal dehydration. On further heating, the as-produced anhydrous glass exhibits a glass transition phenomenon at approximately 470 K with an E(a) ≈ 550-560 kJ mol(-1), and subsequently crystallizes via the three-dimensional growth of nuclei controlled by diffusion. The crystallization process is characterized by an E(a) ≈ 280 kJ mol(-1) and an enthalpy change ΔH = -13.3 kJ mol(-1), resulting in the formation of smaller, rounded particles of crystalline anhydrate.

Hydroxyl and molecular H2O diffusivity in a haploandesitic melt

H2O diffusion in a haploandesitic melt (a high-silica and Fe-free andesitic melt, NBO/T=0.173) has been investigated at 1GPa in a piston-cylinder apparatus. We adopted a double diffusion couple technique, in which one couple was composed of a nominally anhydrous glass with 0.01wt.% H2O and a hydrous glass with 5.7wt.% H2O, and the other contained the same nominally anhydrous glass and a hydrous glass with 3.3wt.% H2O. Both couples were annealed in a single experimental run and hence experienced exactly the same P–T history, which is crucial for constraining the dependence of H2O diffusivity on water content. H2O concentration profiles were measured by both Fourier transform infrared (FTIR) microspectroscopy and confocal Raman microspectroscopy. Nearly identical profiles were obtained from Raman and FTIR methods for profile length >1mm (produced at 1619–1842K). By contrast, for profile lengths <100μm (produced at 668–768K), FTIR profiles show marked convolution effects compared to Raman profiles. A comparison between the short FTIR and Raman profiles indicates that the real spatial resolution (FWHM) of FTIR analyses is about 28μm for a 7μm wide aperture on ∼200μm thick glasses.While the short profiles are not reliable for quantitative modeling, the long diffusion profiles at superliquidus temperatures can be fit reasonably well by a diffusivity model previously developed for felsic melts, in which molecular H2O (H2Om) is the only diffusive species and its diffusivity (DH2Om) increases exponentially with the content of total water (H2Ot). However, there is noticeable misfit of the data at low H2Ot concentrations, suggesting that OH diffusivity (DOH) cannot be neglected in this andesitic melt at high temperatures and low water contents. We hence develop a new fitting procedure that simultaneously fits both diffusion profiles from a single experimental run and accounts for the roles of both OH and H2Om diffusion. With this procedure, DOH/DH2Om is constrained to be 0.1–0.2 at 1619–1842K as H2Ot concentration approaches zero. The obtained OH diffusivity is similar to fluorine diffusivity but is much higher than Eyring diffusivity.

Infrared spectroscopy used to evaluate glycosylation of proteins

Infrared (IR) spectroscopy is used for studying the carbohydrate moieties of glycosylated proteins. IR spectra of mono- and disaccharides in the fingerprint region are specific to each sugar and to the environment of the sugar molecules (i.e., aqueous solution or anhydrous glass phase). The IR spectra of glycosylated proteins (mucin, soybean peroxidase, collagen IV, and avidin) were compared with those of the constituent sugars and cytochrome c (a protein with no glycosylation). Our results demonstrate that the IR absorption spectra of glycosylated proteins show distinct absorption bands for the sugar moiety, the protein amide group, and water. Therefore, IR can be used to detect glycosylation.

Thermal dehydration of dipotassium tetraborate tetrahydrate and crystallization of amorphous dehydration product

As one of the typical examples of producing an amorphous dehydration product, the thermal dehydration process of K2B4O7·4H2O was subjected to thermoanalytical and morphological studies. An anhydrous glass was formed via three distinguished dehydration stages. The overall thermal dehydration process was characterized as a self-induced sol-gel process to form anhydrous glass. The as produced anhydrous glass exhibited glass transition at around 700 K and subsequently crystallized via two consecutive exothermic peaks at around 770 and 900 K. The final crystallization product, triclinic K2B4O7, melted at 1072 K.

Contrasting interactions of sodium and potassium with H2O in haplogranitic liquids and glasses at 200 MPa from hydration–diffusion experiments

This study examines hydration–diffusion in the metaluminous haplogranite system at 200 MPa H2O and 800–300°C. At 800°C hydration is accompanied by melting and uphill diffusion of sodium from anhydrous glass toward the region of hydration and melting, whereas potassium diffuses away from the hydration front and into anhydrous glass. Silicon and aluminum are simply diluted upon hydration. There is no change in molecular Al/(Na + K) throughout the entire hydration-diffusion aureole and, therefore, (1) there is no loss of alkalis to the vapor, and (2) K migrates to replace Na in order to maintain local charge balance required by IVAl. Alkali diffusion occurs over a viscosity contrast from 104.1 Pa s in hydrous liquid to ≈1011.8–1013.5 Pa s in anhydrous glass. From these results, we interpret that: (1) Na is structurally or energetically favored over K as a charge-balancing cation for IVAl in hydrous granitic liquids, whereas the opposite behavior has been observed for anhydrous melts, and (2) the diffusion of alkalis through silicate melts is largely independent of viscosity. Results from 600°C are similar to those at 800°C, but hydration at 300°C involves a loss of Na and concomitant increase in molar Al/(Na + K) in the hydration zone due to hydrogen-alkali exchange between fluid and glass. Hydration behavior at 400°C is transitional between those at 300°C and 600°C, suggesting that the change in hydration mechanism occurs near the glass transition.

Amorphization of crystalline orthoboric acid on a vitreous B2O3 substrate

Time-resolved x-ray diffraction measurements were carried out during and after the exposure of anhydrous boron oxide glass films to humid air. B(OH)3 crystals grew on the glass substrate with planar sheets of B(OH)3 molecules aligned parallel to the surface. After the space above the sample was evacuated, the crystal peaks began to disappear. During the decay, new crystals of orthoboric acid grew with the orientation of the B(OH)3 sheets perpendicular to the substrate. Then crystals with all orientations decayed completely, and an amorphous scattering pattern remained. The water acquired by the sample during the exposure eventually reacted with the anhydrous B2O3 glass to produce amorphous BO(3+y)/2Hy. The decay of the crystals took from one to several days, depending on the length of the exposure to humid air. Measurements of the metastable equilibrium phases in the B2O3–H2O binary system showed that at room temperature the amorphous phase could reach the composition BO1.85H0.7. At higher water concentrations this saturated amorphous phase coexisted with crystalline B(OH)3. This result is consistent with the instability of the crystalline B(OH)3 film in contact with anhydrous glass, and we present a thermodynamic model for this process. In the present case, amorphization is driven by the outdiffusion of water from a crystalline phase rather than interdiffusion in conventional solid-state amorphization.

Hydration in Alkali-silicate Glasses Studied by Two Dimensional Multi-Quantum Magic Angle Spinning

The hydration in Na2O-3SiO2 glass was studied by 23Na Magic Angle Spinning (MAS) and 2D MQMAS NMR spectroscopy. It was found that one-dimensional MAS spectra for the hydrated glasses with more than 8.4 wt% water consist of two signals at around -10 and -40 ppm. On the other hand, anhydrous glass and glass with low water content (2.8 wt%) give a single resonance line at around -10 ppm. From 2D MQMAS spectra, the isotropic chemical shift ( δiso) and the quadrupole coupling frequency (VQ) for two sites (Na(1) and Na(2)) were estimated: δiso = 4.2 ppm and VQ = 0.6 MHz for Na(1) and δiso = 10.2 ppm and VQ = 1.3 MHz for Na(2). These results are discussed together with our previous results of 29Si and 1H NMR, and infrared spectra. It is speculated that Na(1) may exist in a similar environment as that in anhydrous sodium-silicate glasses, while Na(2) may be attached directly to water molecules

MULTIFUNCTIONAL BASES AND LINERS

Three one-minute techniques are presented using anhydrous resin modified glass isonomer, an antibacterial and multifunctional base and liner. The isonomer is placed in deep areas of caries, as insurance, and to desensitize the tooth and fill gaps. The anhydrous glass accepts water from the dentin to fill potential contraction gaps from polymerization shrinkage of the composite fill.

Stability of phlogopite in granitic melts, an experimental investigation

Water-saturated and water-undersaturated experiments (a H2 O = 1.0 and 0.5) were performed in the temperature range 780–1040°C at 2 and 5 kbar in order to determine the upper thermal stability of phlogopite in granitic melts. Starting compositions were: (A) subaluminous mixtures of 20 wt % synthetic phlogopite and 80 wt % synthetic anhydrous haplogranitic glass; (B) peraluminous mixtures (normative corundum = 4 %) of 20 wt % synthetic phlogopite and 80 wt % synthetic anhydrous peraluminous haplogranitic glass. The molar quartz: albite: orthoclase ratio of the glasses of the 2␣kbar runs was 35:39:26 and that of the 5 kbar runs 30:42:28. In the subaluminous system, phlogopite is stable up to 820°C at a H2 O = 1.0 and up to 780°C at a H2 O = 0.5. At higher temperatures, it is replaced by enstatite. In the peraluminous system phlogopite has a remarkably higher thermal stability (up to 1000°C at 5 kbar and a H2 O = 1.0) and there is a temperature interval of 80°C at a H2 O = 1.0, and 90–100°C at a H2 O = 0.5 between the first appearance of enstatite and the disappearance of phlogopite. In the peraluminous system, phlogopite is a solid solution (ss) of phlogopite, muscovite, talc and eastonite components. The crystalline product of the phlogopitess breakdown reaction is an aluminous enstatite. The MgO-content of the melt depends on the normative corundum content of the starting material and the run temperature. It is independent of pressure. In the subaluminous system, the MgO-content ranges between 0.05 and 0.3 wt % in the temperature interval 780–880°C at both investigated water activities. The MgO-content of the peraluminous melts at a H2 O = 1.0 ranges between 0.4 and 1.7 wt % and at a H2 O = 0.5 between 0.2 and 1.4 wt % in the temperature range 780–980°C.

Experimental Determination of Trace Element Partitioning Between Pargasitic Amphibole and Hydrous Silicate Melt

Our starting material is similar to that used by Mysen (1978), and is broadly analogous to a Kand Fe-free andesite. At the run conditions of our experiments (1.5GPa, 1000~ nearly H20-saturated), pargasite and subordinate clinopyroxene are the liquidus phases. Starting materials were synthesized from oxides and carbonates; trace elements were added as dilute nitrate solutions. The samples were sealed in Pt capsules with 10 wt.% H20, and run in a piston cylinder apparatus (fo2 ~ QFM) using a P-T history designed to promote equilibrium growth of a few large crystals. Electron microprobe analyses of the run products used a 20ttm, defocussed beam and a 10hA or 5hA beam current on crystals and glass, respectively. Trace elements were measured using a Cameca IMS-3F ion microprobe using a 15-50nA Oprimary beam. For each sample, multiple spots on each phase were analyzed, and the results for each phase were averaged. Isobaric molecular interferences were minimized by the use of an energy-filtering technique. Trace element concentrations were determined by comparing the 3~ isotopic ratios of the samples to those of silicate mineral and glass standards. Our quench glass contains > 10% H20, and ion yields relative to 3~ were higher in this hydrous glass than in an anhydrous glass of the same composition. The enhancement in yield is largest for Rb (+39%), Sr (+17%), and Ba (+ 20%). For the other elements we report, the enhancement is < 10%. All glass analyses were corrected for this effect. The estimated combined error in the trace element concentrations is -+20%. Partition coefficients were calculated from the ratio of the average 3~ count rate of an isotope in the amphibole to the average ~~ count rate in the glass, correcting for the differences in Si contents and the difference in ion yields due to the effect noted above. Reported errors reflect propagation of the larger of the counting statistics errors or the lt~ variability of the spot analyses.

Change in pH during setting of polyelectrolyte dental cements

The change in pH during setting has been studied for five different glass polyalkenoate (ionomer) cements and for two different zinc polycarboxylate cements using a flat-headed combination electrode on both the fresh cement and on a slurry of the set cement. The results show that the pH of the glass ionomers was slightly lower in the early stages of setting than was the pH of the zinc polycarboxylates and also that the pH of glass ionomers rises more slowly. For anhydrous cements (i.e. those formulated from dried polymer) pH was found to rise quicker than for hydrous cements (i.e. those prepared from aqueous solutions of polymer). Previous workers have assumed that anhydrous cements undergo slower rises in pH than hydrous ones. Our results clearly refute this assumption, and also suggest that the reported pulpal irritation associated with the use of anhydrous glass ionomers may be due to something other than low pH.

A model for H 2O solubility mechanisms in albite melts from infrared spectroscopy and molecular orbital calculations

Infrared spectra of H 2 O- and D 2 O- NaAlSi 3 O 8 (albite) glasses were measured and contain two major differences from the anhydrous glass spectra. The first is the presence of a number of bands above 3000 cm −1 arising from O-H stretching modes. The second change in hydrous glass spectra is the appearance of a shoulder at approximately 900 cm −1. No frequency shift of the 900 cm −1 shoulder was detected with H-D substitution. We conclude, based on our infrared spectra and molecular orbital calculations as well as previous NMR ( Kohn et al., 1989) and Raman ( Mysen and Virgo, 1986a) spectra, that the 900 cm −1 band in the vibrational spectra of H 2O-albite glass arises from an Al-(OH) stretching vibration in an Al Q 3 site. The model proposed in this paper is that below 30 mol% [H 2O] tot, molecular water interacts with the network A1 3+ to produce Al-(OH) and a minor concentration of Si-(OH) bonds. Above 30 mol% [H 2O] tot, the dominant species is molecular H 2O and H + exchanges with Na + at the charge-balancing site to produce molecular NaOH or hydrated Na +( H 2 O) n , complexes in the melt.