Natural Glasses Research Articles

Properties of compression moulded new fully biobased thermoset composites with aligned flax fibre textiles

The development of aligned natural fibre reinforced composites utilising biobased thermosets is an essential step towards the manufacture of ecofriendly composite systems. In many cases, the matrix system, which is usually oil based in nature, is disregarded. Therefore, a new fully biobased thermoset composite with aligned flax fibre textiles was developed using a bioderived matrix resin. The thermoset furan resin has recently received interest due to its good environmental profile containing no petrochemicals, using water as solvent and biomass as raw material. The new resin also shows good mechanical performance and excellent fire resistance. In the present study, aligned natural fibre textiles, randomly oriented natural fibre textiles and glass fibre textiles have been hand laid up and impregnated with the furan resin to form prepregs. After precuring, the prepregs were consolidated into composites using an industrial scale compression moulding machine, and their material properties were analysed. The density was calculated by using a computed microtomography system, and tensile tests were carried out. Besides the mechanical properties, the burning and the moisture absorption behaviour have been determined.

Microtextures, microchemistry, and mineralogy of basaltic glass alteration, Jeju Island, Korea, with implications for elemental behavior

The meteoric alteration of basaltic glass in hyaloclastite (0.55 to 0.2 Ma) from Jeju Island, Korea, was examined using high-resolution electron microscopy, in situ sample preparation using focused ion beam, and microchemical analysis. The glass particles showed a sequential development of alteration textures toward the glass interior as follows: oscillatory zoning of smectite and amorphous bands/hemispheres, congruent dissolution of glass with smectite infilling in interparticle pore, and the replacement of nanogranular amorphous aggregate (NAA) for porous leached glass (LG) followed by a partial crystallization of smectite. Chemical compositions of LG widely varied from partial to complete leaching of almost all kinds of cations, to a preferred leaching of Na only. The order of leaching in LG followed Na + >Mg 2+ >Ca 2+ = Fe 2+ >Al 3+ >Ti 4+ . Leached cations were removed from the hyaloclastite-water system or incorporated into secondary phases. Sodium was all but removed from the system. Magnesium was largely lost with partial incorporation into smectite. Calcium was significantly retained in NAA, partly incorporated into the smectite interlayer, and partly lost. Iron and Al were partitioned between NAA and smectite. Titanium was mostly retained in NAA and Ti-rich silicates. The molar ratio of major cations to Si was reversed from Ca 2+ >Mg 2+ >Na + in basaltic glass to Na + >Mg 2+ >Ca 2+ in groundwater. The geochemical evolution of pore water was influenced by the microtextural and microchemical evolution of glass particles, and vice versa. Systematic microtextural, microchemical, and mineralogical analyses of natural glass alteration are critical to understanding the long-term behavior of glass alteration.

Onboard calibration igneous targets for the Mars Science Laboratory Curiosity rover and the Chemistry Camera laser induced breakdown spectroscopy instrument

Accurate characterization of the Chemistry Camera (ChemCam) laser-induced breakdown spectroscopy (LIBS) on-board composition targets is of prime importance for the ChemCam instrument. The Mars Science Laboratory (MSL) science and operations teams expect ChemCam to provide the first compositional results at remote distances (1.5–7 m) during the in situ analyses of the Martian surface starting in 2012. Thus, establishing LIBS reference spectra from appropriate calibration standards must be undertaken diligently. Considering the global mineralogy of the Martian surface, and the possible landing sites, three specific compositions of igneous targets have been determined. Picritic, noritic, and shergottic glasses have been produced, along with a Macusanite natural glass. A sample of each target will fly on the MSL Curiosity rover deck, 1.56 m from the ChemCam instrument, and duplicates are available on the ground. Duplicates are considered to be identical, as the relative standard deviation (RSD) of the composition dispersion is around 8%. Electronic microprobe and laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) analyses give evidence that the chemical composition of the four silicate targets is very homogeneous at microscopic scales larger than the instrument spot size, with RSD < 5% for concentration variations > 0.1 wt.% using electronic microprobe, and < 10% for concentration variations > 0.01 wt.% using LA ICP-MS. The LIBS campaign on the igneous targets performed under flight-like Mars conditions establishes reference spectra for the entire mission. The LIBS spectra between 240 and 900 nm are extremely rich, hundreds of lines with high signal-to-noise, and a dynamical range sufficient to identify unambiguously major, minor and trace elements. For instance, a first LIBS calibration curve has been established for strontium from [Sr] = 284 ppm to [Sr] = 1480 ppm, showing the potential for the future calibrations for other major or minor elements.

Efficiency of perlite as a low cost adsorbent applied to removal of Pb and Cd from paint industry effluent

Among the major environmental concerns worldwide is release of heavy metals in the environment. Different studies have demonstrated that natural volcanic glass has high capacity in removal of divalent heavy metal ions. Perlite is a volcanic rock with high porosity and specific surface area which costs much lower in comparison with the other adsorbents. In this study, the removal of lead and cadmium from Binalood paint industry (Kerman, Iran) effluent by perlite is investigated in batch conditions. Lead and cadmium measurements are carried out with atomic absorption spectrophotometeric methods adapted from standard methods applied to the examination of water and wastewaters. In this regard, the effect of pH, dosage and contact time is also determined and Langmuir and Freundlich isotherms are obtained. Results show that adsorption process follows Freundlich adsorption isotherm model. The maximum obtained removal efficiency at pH = 7 are close to 100% and 97.7% for lead and cadmium, respectively. These efficiencies are achieved in 10 g/l perlite and recommended contact time is 1.5 h. Finally, perlite is recommended as a low cost and accessible adsorbent to remove lead and cadmium from municipal and industrial wastewaters.

Spectroscopic Studies on Sulfur Speciation in Synthetic and Natural Glasses

Spectroscopic methods are powerful means to obtain information on the electronic or local structure of materials. By these methods, constraints can be provided on the chemical state, crystal chemistry or, in non-crystalline materials, the coordination environment or complexation of a given element. In this chapter, we focus on spectroscopic techniques that provide direct insight into the sulfur (S) species present in glasses and melts and which are applicable at the sulfur concentrations usually found in glasses (mostly below 1–2 wt%). Methods that are potentially suitable for this task are i) the wavelength analysis of X-ray emission spectra (mostly using the electron microprobe), ii) X-ray absorption spectroscopy, iii) 33S NMR and iv) Raman spectroscopy. For compounds such as sulfides or sulfates, containing S as a major component, further methods such as optical absorption spectroscopy in the UV-visible frequency range (UV-VIS) or electron spin/paramagnetic resonance (ESR or EPR) spectroscopy (e.g., Ross 1974; Wincott and Vaughan 2006) are useful. However, these two techniques provide only an indirect view on sulfur because they actually probe the cations, which are often transition metals. In compounds where S is a major component, these data also provide information on the sulfur species, because the cations are linked to S as an anion. In glasses, where S is only a minor component and cations are mostly coordinated by oxygen, it is difficult to link the observations made on the cation to the S species. Nevertheless, there are some studies on glasses where the additional information by UV-VIS or ESR spectroscopy was used to constrain possible species of sulfur in the glass (e.g., Beerkens 2003; Bingham et al. 2010). Here, only very brief introductions to the spectroscopic techniques will be provided. For a more detailed introduction to the spectroscopic techniques introduced here the reader is …

Oceanic Volcanism from the Low-velocity Zone – without Mantle Plumes

We develop a model for oceanic volcanism that involves fracturing of the seismic lithosphere to access melts from the partly melted seismic low-velocity zone. Data on global seismic shear-wave velocities are combined with major-element compositions of global mid-ocean ridge basalt glasses, Hawaiian basalt glasses, and phase relations in the CaO-MgO-Al2O3-SiO2-CO2 and CaO-MgO-Al2O3-SiO2-Na2O-FeO systems at pressures from 1 atm to 6 GPa. We use these data to constrain the pressure–temperature conditions for melt extraction at Hawaii and mid-ocean ridges (including Iceland), and to evaluate the existence of hot mantle plumes. In the low-velocity zone, the maximum reduction and maximum anisotropy of seismic shear-wave velocity (maximum melt fraction) occurs at a depth of ∼140–150 km for crustal ages >∼50 Ma, and a depth of ∼65 km at the East Pacific Rise axis. Seismic data indicate a smooth depth transition between these extremes. Experimental phase-equilibrium data, when combined with natural glass compositions, show that pressure–temperature conditions of tholeiitic melt extraction at Hawaii (∼4–5 GPa, 1450–1500°C) and the global oceanic ridge system (∼1·2–1·5 GPa, 1250–1280°C) are an excellent match for the two depth ranges of maximum melting indicated by seismic shear-wave data. At Hawaii, magmas escape to the surface along a fracture system that extends through the lithosphere into the low-velocity zone. This allows eruption of progressively deeper melts from the low-velocity zone, which exist at equilibrium along a normal geotherm. No significant decompression melting occurs. This produces the characteristic sequence at each volcano of initial low-volume alkalic magmas, then voluminous tholeiitic magmas that show low-pressure olivine-controlled crystallization, and final low-volume alkalic magmas from extreme depths. At the East Pacific Rise, the more shallow depth of magma extraction is caused by a perturbed ridge geotherm that grazes the lherzolite solidus within the thermal boundary layer. This results in an absence of olivine-controlled crystallization. Hawaii is not a hot plume. Instead, it shows magmas characteristic of normal mature-ocean thermal conditions in the low-velocity zone. We find no evidence of anomalously high temperatures of magma extraction and no role for hot mantle plumes anywhere in the ocean basins.

Matrix effects in the analysis of Mg and Si isotope ratios in natural and synthetic glasses by laser ablation-multicollector ICPMS: A comparison of single- and double-focusing mass spectrometers

We report composition-dependent matrix effects in the in-situ measurement of Mg and Si isotope ratios by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) in natural and synthetic silicate glasses. These were determined using two 193nm wavelength excimer laser ablation-multicollector ICPMS systems, one employing a double-focusing mass spectrometer (ThermoFinnigan Neptune) and one employing a single-focusing mass spectrometer with a hexapole/collision cell (GV Instruments IsoProbe). Observed matrix effects in isotopic measurements by LA-ICPMS range from subtle (i.e., less than ≈0.7‰ per amu for Si isotope measurements in natural and synthetic glasses in all instrumental configurations) to significant but mass-dependent (i.e., less than 1.2‰ per amu for Mg isotope measurements performed using the Neptune) to large and significantly non-mass-dependent (i.e., up to 6‰ mass dependent/3‰ non-mass dependent for Mg isotope measurements of natural glasses made with the IsoProbe). Composition-dependent differences in the magnitude and direction of within-run isotopic fractionation (particularly for Mg isotope measurements) suggest that isotopic fractionation at the site of ablation is the main source of matrix effects in measurements employing the double-focusing mass spectrometer. However, the large and significantly non-mass dependent (but systematic and reproducible) matrix effects affecting LA-ICPMS Mg isotope data obtained using the single-focusing IsoProbe appear to be largely due to non-linear scattering processes occurring in the hexapole/collision cell as Mg becomes increasingly diluted by matrix elements.

Vesiculation and Microlite Crystallization Induced by Decompression: a Case Study of the 1991–1995 Mt Unzen Eruption (Japan)

Isothermal decompression experiments were performed to simulate magma ascent at Unzen volcano from the depths of magma storage to shallow crustal levels, corresponding to pressure decrease from 300 to 50MPa. A partially crystallized synthetic rhyodacitic magma (representing equilibrium conditions at 8508C and 300MPa) was used as a starting material; this has a composition identical to the groundmass of Unzen rocks erupted in 1991^1995. Decompression rates were varied from 0·0002 to 20MPa s . Experiments conducted with decompression rates 0·1MPa s 1 were decompressed continuously; a multi-step decompression approach was used at decompression rates 0·1MPa s . The experiments were fluid-saturated, either containing only water as a fluid component (H2O-bearing) or containing a water and carbon dioxide mixture (H2OþCO2; initial mole fraction of H2O in the fluid 0·6).The experimental products of the H2O-bearing experiments consist of amphibole, pyroxenes, oxides and glass. Plagioclase microlites nucleated and grew only in experiments with the two lowest decompression rates of 0·0005 and 0·0002MPa s . The length of those plagioclases is up to 200^250 mm, which is consistent with the size of plagioclase microlites observed in the natural samples.The experimental products of the H2OþCO2-bearing system are composed of pyroxenes, oxides, glass and plagioclase. Plagioclase microlites in the H2OþCO2-system were already present in the starting assemblage and grew to a maximum size of 80 mm. Equilibrium concentrations of water in the residual glasses at the final pressure of 50MPa are reached at decompression rates 1MPa s 1 for the H2OþCO2-bearing system and 0·1MPa s 1 for the H2O-bearing system. The bubble number density (BND) values range from 10 to 10 mm 3 in the H2O-bearing system and from 10 4·6 to 10 mm 3 in the H2OþCO2-bearing systems. In both systems, BND values decrease with decreasing decompression rate from 20 to 0·01MPa s , and increase with decreasing decompression rates50·01MPa s , which is interpreted to reflect predominant bubble growth and bubble nucleation, respectively.The onset of crystallization, observed from changes in the chemical composition of the residual melt, occurs at decompression rates 50·1MPa s . At the lowest decompression rate (0·0002MPa s ) the chemical composition of the residual melt in the H2OþCO2-bearing system becomes similar to the natural matrix glass composition. There is no significant variation of the microlite number density (MND) value as a function of the decompression rate. The MND values for plagioclases-only range from 10 to 10 mm , whereas the MND values for the other phases range from 10 to 10 mm . Our experimental MNDPl values are in the range of those from natural samples (10^10 mm ).We show that the size of microlites nucleating and crystallizing during decompression (plagioclase in our experimental dataset) is useful to constrain magma ascent rates at the onset of the crystallization of the corresponding phase. Based on the size of plagioclase microlites and on the composition of the residual melts, the average magma ascent rates of Unzen magmas in the pressure range 200 to 50MPa is estimated to be 10^50 m h .

The H2O solubility of alkali basaltic melts: an experimental study

Experiments were conducted to determine the water solubility of alkali basalts from Etna, Stromboli and Vesuvius volcanoes, Italy. The basaltic melts were equilibrated at 1,200°C with pure water, under oxidized conditions, and at pressures ranging from 163 to 3,842 bars. Our results show that at pressures above 1 kbar, alkali basalts dissolve more water than typical mid-ocean ridge basalts (MORB). Combination of our data with those from previous studies allows the following simple empirical model for the water solubility of basalts of varying alkalinity and fO2 to be derived: $$ {\text{H}}_{ 2} {\text{O}}\left( {{\text{wt}}\% } \right) = {\text{ H}}_{ 2} {\text{O}}_{\text{MORB}} \left( {{\text{wt}}\% } \right) + \left( {5.84 \times 10^{ - 5} *{\text{P}} - 2.29 \times 10^{ - 2} } \right) \times \left( {{\text{Na}}_{2} {\text{O}} + {\text{K}}_{2} {\text{O}}} \right)\left( {{\text{wt}}\% } \right) + 4.67 \times 10^{ - 2} \times \Updelta {\text{NNO}} - 2.29 \times 10^{ - 1} $$ where H2OMORB is the water solubility at the calculated P, using the model of Dixon et al. (1995). This equation reproduces the existing database on water solubilities in basaltic melts to within 5%. Interpretation of the speciation data in the context of the glass transition theory shows that water speciation in basalt melts is severely modified during quench. At magmatic temperatures, more than 90% of dissolved water forms hydroxyl groups at all water contents, whilst in natural or synthetic glasses, the amount of molecular water is much larger. A regular solution model with an explicit temperature dependence reproduces well-observed water species. Derivation of the partial molar volume of molecular water using standard thermodynamic considerations yields values close to previous findings if room temperature water species are used. When high temperature species proportions are used, a negative partial molar volume is obtained for molecular water. Calculation of the partial molar volume of total water using H2O solubility data on basaltic melts at pressures above 1 kbar yields a value of 19 cm3/mol in reasonable agreement with estimates obtained from density measurements.

Composition effects on synthetic glass alteration mechanisms: Part 1. Experiments

Alteration of nuclear waste glasses and silicate minerals is governed by complex processes regulated by several coupled mechanisms. Among these processes is reactive mass transfer through the amorphous gel layer (known as the passivating reactive interphase (PRI) in case of a rate-limiting effect) located between the pristine glass and the bulk solution. In order to assess the influence of the glass composition and the pH on the properties of the PRI, and thus on the nuclear glass durability, an experimental leaching study was performed on borosilicate glass samples with or without Ca, Al, and Zr. Experiments were conducted to understand the influence of the pH and glass composition on the solvated cation diffusion coefficient within the PRI and to generate data for calibration of a PRI solubility model (not presented here). All the experiments were carried out at high S/ V ratios so that silicon rapidly reached apparent saturated conditions and the PRI could form: in such conditions glass alteration is controlled only by diffusion of water and dissolved species through the PRI and by precipitation of crystallized secondary phases. The constituents in the PRI and the crystallized secondary phases depend to a large extent on the glass composition and pH. Alkali metal (Na) or preferentially alkaline earth (Ca) elements are retained in the PRI for charge compensation of Al and Zr. The apparent diffusion coefficient calculated from the release of boron, a good tracer, varies with the pH from less than 4 × 10 −22 to 9 × 10 -18 m 2 s −1 in the studied glasses. These very low diffusion coefficients decrease as the pH increases. Concerning the PRI composition we show that Si, Al, Ca and Zr have strong interactions and thus major consequences on the glass durability. Our findings indicate that the SiO 2aq activity is relatively constant and independent of the pH below pH 9, followed by a drop at pH 10. In addition, the activity of SiO 2aq is affected by the glass composition, and especially by aluminum and zirconium. As soon as dissolved silicon reaches steady state in solution the aluminum and zirconium concentrations start to decrease, probably due to silicon, aluminum and zirconium interactions with retention in the PRI. The formation of crystallized secondary phases is observed at pH 10 for aluminum-free glasses, which diminishes the saturation state of amorphous silica in solution. In these glasses the saturation index indicates that the solution is oversaturated with respect to calcium silicate hydrates (ex: tobermorite, gyrolite). Moreover, the formation of crystallized secondary phases causes dissolution of the PRI and the glass, which sustains renewed alteration. This study leads to the conclusion that modeling nuclear glass dissolution kinetics over a wide pH range (typically from pH 7 to pH 10) must take into account (1) PRI composition variations and relations between the PRI composition and properties (solubility, diffusion coefficient); and (2) crystallized secondary phases that can consume elements from the PRI. Applying PRI modeling concepts to other kinds of natural glasses or even multi-oxide minerals might prove useful for enhancing our understanding of alteration mechanisms.

The determination of sulfate and sulfide species in hydrous silicate glasses using Raman spectroscopy

Raman spectroscopy is used to identify the sulfur speciation (sulfur valence state) in “technical” iron-free soda-lime and potassium-silicate glasses and in “natural” glass compositions such as basalt, andesite, and rhyodacite. The presence of sulfate (S6+) is marked in Raman spectra of oxidized synthetic and natural glasses by bands at ~990 and ~1000 cm-1, respectively. The presence of sulfide (S2-) in the reduced technical glasses is marked in Raman spectra by a band at 2574 cm-1 indicating that S2- is present as HS- in these Fe-free glasses. Such a band is absent in the Raman spectra of reduced basaltic, andesitic, and rhyodacitic glasses. However, an additional band at ~400 cm-1 appears in the Raman spectra of the reduced S-bearing “natural” glasses when compared to that of S-free reduced “natural” reference glasses indicating that S2- is most likely complexed with Fe in these glasses. Thus, the dissolution mechanism of S2- appears to be different in Fe-free and Fe-bearing glasses and S2- is dissolved as either HS--species or Fe-S complexes, respectively. The data shown here demonstrate the potential of Raman spectroscopy in identifying the sulfur valence state in silicate glasses. In addition, S2- is dissolved as completely different complexes when comparing “technical” iron-free and “natural” iron-bearing, hydrous silicate glass compositions.

A cooling rate bias in paleointensity determination from volcanic glass: An experimental demonstration

The suitability of volcanic glass for paleointensity determinations is the basis of many studies. The dominant single domain (SD) magnetic remanence carriers, the pristine character of volcanic glass, and the possibility to correct paleointensity data for cooling rate dependence using relaxation geospeedometry are all arguments that have been made in favor of this technique. In the present study the validity of cooling rate correction is tested using remelted volcanic glass. To obtain a stable multicomponent glass, with ideal magnetic properties, a natural phonolitic glass from Tenerife was remelted in air to avoid heterogeneity and degassing in later experiments. Further, it was tempered for altogether 10 hours at 900°C to yield a sufficient concentration of magnetic remanence carriers. To exclude nucleation or crystallization, six samples were then heated to about 60°C above the calorimetric glass transition temperature (≈660°C) and quenched at different rates from 0.1 to 15 K/min. Rock magnetic measurements show that low titanium titanomagnetite in the SD range is the main remanence carrier. After performing paleointensity experiments using a modified Thellier method, the dependence of the thermoremanence on cooling rate was investigated. Using the synthesis cooling rates and the experimentally determined magnetic cooling rate dependencies we were able to correct the data and obtained a mean paleointensity of 46.9 ± 1.3μT, which reflects the ambient field of 48μT within error. The uncorrected mean paleointensity corresponds to a 18% larger value of 56.5 ± 0.9μT. Therefore, application of a cooling rate correction is essential to obtain the correct ancient magnetic field intensity from SD assemblages in volcanic glass.

Sulfur K-edge XANES analysis of natural and synthetic basaltic glasses: Implications for S speciation and S content as function of oxygen fugacity

XANES analyses at the sulfur K-edge were used to determine the oxidation state of S species in natural and synthetic basaltic glasses and to constrain the fO 2 conditions for the transition from sulfide (S 2−) to sulfate (S 6+) in silicate melts. XANES spectra of basaltic samples from the Galapagos spreading center, the Juan de Fuca ridge and the Lau Basin showed a dominant broad peak at 2476.8 eV, similar to the spectra obtained from synthetic sulfide-saturated basalts and pyrrhotite. An additional sharp peak at 2469.8 eV, similar to that of crystalline sulfides, was present in synthetic glasses quenched from hydrous melts but absent in anhydrous glasses and may indicate differences in sulfide species with hydration or presence of minute sulfide inclusions exsolved during quenching. The XANES spectra of a basalt from the 1991 eruption of Mount Pinatubo, Philippines, and absarokitic basalts from the Cascades Range, Oregon, USA, showed a sharp peak at 2482.8 eV, characteristic of synthetic sulfate-saturated basaltic glasses and crystalline sulfate-bearing minerals such as hauyne. Basaltic samples from the Lamont Seamount, the early submarine phase of Kilauea volcano and the Loihi Seamount showed unequivocal evidence of the coexistence of S 2− and S 6+ species, emphasizing the relevance of S 6+ to these systems. XANES spectra of basaltic glasses synthesized in internally-heated pressure vessels and equilibrated at fO 2 ranging from FMQ − 1.4 to FMQ + 2.7 showed systematic changes in the features related to S 2− and S 6+ with changes in fO 2. No significant features related to sulfite (S 4+) species were observed. These results were used to construct a function that allows estimates of S 6+/ΣS from XANES data. Comparison of S 6+/ΣS data obtained by S Kα shifts measured with electron probe microanalysis (EPMA), S 6+/ΣS obtained from XANES spectra, and theoretical considerations show that data obtained from EPMA measurements underestimate S 6+/ΣS in samples that are sulfate-dominated (most likely because of photo-reduction effects during analysis) whereas S 6+/ΣS from XANES provide a close match to the expected theoretical values. The XANES-derived relationship for S 6+/ΣS as a function of fO 2 indicates that the transition from S 2− to S 6− with increasing fO 2 occurs over a narrower interval than what is predicted by the EPMA-derived relationship. The implications for natural systems is that small variation of fO 2 above FMQ + 1 will have a large effect on S behavior in basaltic systems, in particular regarding the amount of S that can be transported by basaltic melts before sulfide saturation can occur.

Spectroscopic analysis (FTIR, Raman) of water in mafic and intermediate glasses and glass inclusions

Micro-Raman spectroscopy, even though a very promising technique, is not still routinely applied to analyse H 2O in silicate glasses. The accuracy of Raman water determinations critically depends on the capability to predict and take into account both the matrix effects (bulk glass composition) and the analytical conditions on band intensities. On the other hand, micro-Fourier transform infrared spectroscopy is commonly used to measure the hydrous absorbing species (e.g., hydroxyl OH − and molecular H 2O) in natural glasses, but requires critical assumptions for the study of crystal-hosted glasses. Here, we quantify for the first time the matrix effect of Raman external calibration procedures for the quantification of the total H 2O content (H 2O T = OH − + H 2O m) in natural silicate glasses. The procedures are based on the calibration of either the absolute (external calibration) or scaled (parameterisation) intensity of the 3550 cm −1 band. A total of 67 mafic (basanite, basalt) and intermediate (andesite) glasses hosted in olivines, having between 0.2 and 4.8 wt% of H 2O, was analysed. Our new dataset demonstrates, for given water content, the height (intensity) of Raman H 2O T band depends on glass density, reflectance and water environment. Hence this matrix effect must be considered in the quantification of H 2O by Raman spectroscopy irrespective of the procedure, whereas the parameterisation mainly helps to predict and verify the self-consistency of the Raman results. In addition, to validate the capability of the micro-Raman to accurately determine the H 2O content of multicomponent aluminosilicate glasses, a subset of 23 glasses was analysed by both micro-Raman and micro-FTIR spectroscopy using the band at 3550 cm −1. We provide new FTIR absorptivity coefficients ( ε 3550) for basalt (62.80 ± 0.8 L mol −1 cm −1) and basanite (43.96 ± 0.6 L mol −1 cm −1). These values, together with an exhaustive review of literature data, confirm the non-linear decline of the FTIR absorptivity coefficient ( ε 3550) as the glass depolymerisation increases. We demonstrate the good agreement between micro-FTIR and micro-Raman determination of H 2O in silicate glasses when the matrix effects are properly considered.

Amorphous Materials: Properties, Structure, and Durability: Arsenic enrichment in hydrous peraluminous melts: Insights from femtosecond laser ablation-inductively coupled plasma-quadrupole mass spectrometry, and in situ X-ray absorption fine structure spectroscopy

Despite the ubiquity of arsenic in hydrothermal-magmatic environments, its abundance, distribution, and chemical and structural status in natural silicate melts and glasses remain poorly known. Here we report the first in situ measurements of the redox state and molecular structure of As, using X-ray absorption fine structure (XAFS) spectroscopy, in a rhyolitic peraluminous glass from Macusani (SE Peru) that is representative of anatectic melts derived from metasedimentary crustal protoliths. Arsenic abundances as well as the concentrations of other trace elements were measured in the glass using a femtosecond laser ablation-inductively coupled plasma-quadrupole mass spectrometry (LA-ICP-QMS). The glass shows enrichments, by factors of 10 to 100, in comparison with the mean continental crust values, for As and other incompatible trace elements (e.g., Be, B, Rb, Sn, Sb, and Ta), and by factors of 100 to 200 for Li, Cd, and Cs. Arsenic is present in the peraluminous glass in trivalent state in the form of oxy-hydroxide complexes like AsO(OH) 2 - and/or As(OH) 3 , similar to those dominant in the aqueous fluid vapor phases at hydrothermal-magmatic conditions. The similar As chemical speciation between the fluid and the melt is consistent with As fluid/melt partitioning coefficients close to one, as observed in experiments on rhyolite-water systems. The depolymerized melt structure caused by elevated H 2 O, F, and P contents is likely to allow accomodation of high concentrations of metalloid hydroxide/hydrated complexes. Consequently, hydrous silicate melts may be important transporting media in shallow magmatic-hydrothermal settings for As and similar elements like B and Sb due to their high affinity to water and hydroxide ligands

Resilience and alternative equilibria in a mire plant community after experimental disturbance by volcanic ash

Following disturbance events vegetation can either be resilient and return to its original state, or there can be shifts in vegetation composition and abundance patterns that may indicate alternative equilibiria. We conducted a long-term field experiment that simulated impact by aerially transported volcanic ejecta (tephra) in a Sphagnum-dominated plant community in order to test the effects of this type of large-scale disturbance. Sixty plots of 1.4 x 1.4 m were established at Sarobetsu mire in northern Hokkaido, Japan and subjected to seven treatments (including the control) with natural tephra or ground glass shards differing in grain size, layer thickness and season of application. Water chemistry and vegetation were surveyed before tephra application and during five and eight years after the perturbation, respectively. Leaching of ions from fine-grained glass shards caused a sustained increase of soil water pH and electric conductivity. Under coarser materials water quality differed little from the control, but a short-lived peak of potassium suggested that mechanisms like nutrient release from decomposing plant material may influence water chemistry after volcanic disturbance. The perturbation initially reduced the cover of the dominant functional group (Sphagnum mosses) in all treatments; vascular plants were less affected. All species were able to recover by growing through the tephra, and open tephra surfaces were colonized by ubiquitous cryptogams, but not by spermatophytes. In contrast to the overall resilient behaviour of the vegetation, in some plots that received natural tephra an alternative state with high cover of the dwarf shrub Myrica gale developed. The patterns indicated that physical and chemical properties of the tephra determined the initial effects on plants, but that stochastic processes contributed to subsequent succession. These are likely to have effects on ecosystem functioning, e.g. hydrological processes and carbon sequestration.

Durable Glass for Thousands of Years

The durability of natural glasses on geological time scales and ancient glasses for thousands of years is well documented. The necessity to predict the durability of high‐level nuclear waste (HLW) glasses on extended time scales has led to various thermodynamic and kinetic approaches. Advances in the measurement of medium‐range order in glasses has led to the understanding that the molecular structure of a glass, and thus the glass composition, controls the glass durability by establishing the distribution of ion exchange sites, hydrolysis sites, and the access of water to those sites. During the early stages of glass dissolution, a “gel” layer resembling a membrane forms through which ions exchange between the glass and the leachant. The hydrated gel layer exhibits acid/base properties, which are manifested as the pH dependence of the thickness and nature of the gel layer. The gel layer ages into clay or zeolite minerals by Ostwald ripening. Zeolite mineral assemblages (higher pH and Al3+rich glasses) may cause the dissolution rate to increase, which is undesirable for long‐term performance of glass in the environment. Thermodynamic and structural approaches to the prediction of glass durability are compared versus Ostwald ripening.

Investigation of inclusions trapped inside Libyan desert glass by Raman microscopy

Several specimens of Libyan desert glass (LDG), an enigmatic natural glass from Egypt, were subjected to investigation by micro-Raman spectroscopy. The spectra of inclusions inside the LDG samples were successfully measured through the layers of glass and the mineral species were identified on this basis. The presence of cristobalite as typical for high-temperature melt products was confirmed, together with co-existing quartz. TiO(2) was determined in two polymorphic species rutile and anatase. Micro-Raman spectroscopy proved also the presence of minerals unusual for high-temperature glasses such as anhydrite and aragonite.

Long-term modeling of alteration-transport coupling: Application to a fractured Roman glass

To improve confidence in glass alteration models, as used in nuclear and natural applications, their long-term predictive capacity has to be validated. For this purpose, we develop a new model that couples geochemical reactions with transport and use a fractured archaeological glass block that has been altered for 1800 years under well-constrained conditions in order to test the capacity of the model. The chemical model considers three steps in the alteration process: (1) formation of a hydrated glass by interdiffusion, whose kinetics are controlled by a pH and temperature dependent diffusion coefficient; (2) the dissolution of the hydrated glass, whose kinetics are based on an affinity law; (3) the precipitation of secondary phases if thermodynamic saturation is reached. All kinetic parameters were determined from experiments. The model was initially tested on alteration experiments in different solutions (pure water, Tris, seawater). It was then coupled with diffusive transport in solution to simulate alteration in cracks within the glass. Results of the simulations run over 1800 years are in good agreement with archaeological glass block observations concerning the nature of alteration products (hydrated glass, smectites, and carbonates) and crack alteration thicknesses. External cracks in direct contact with renewed seawater were altered at the forward dissolution rate and are filled with smectites (400−500 μm). Internal cracks are less altered (by 1 or 2 orders of magnitude) because of the strong coupling between alteration chemistry and transport. The initial crack aperture, the distance to the surface, and sealing by secondary phases account for these low alteration thicknesses. The agreement between simulations and observations thus validates the predictive capacity of this coupled geochemical model and increases more generally the robustness and confidence in glass alteration models to predict long-term behavior of nuclear waste in geological disposal or natural glass in the environment.

Lithium isotope analysis of natural and synthetic glass by laser ablation MC-ICP-MS

This contribution presents the first laser ablation multicollector ICP-MS (LA-MC-ICP-MS) technique for the measurement of Li isotopes. A Nu Instruments NuPlasma HR operating at 6 kV and fitted with a non-standard “low-mass, high abundance” skimmer cone is used, coupled to a NewWave UP213 213 nm laser ablation unit operating under a He atmosphere. Asymmetric tuning of the quad lenses on the NuPlasma allows the simultaneous measurement of 7Li and 6Li on a Faraday-ion counter configuration. Use of the standard-bracketing technique for analysis of unknowns obviates any cross calibration between Faraday cup and ion counter. Use of a natural glass as bracketing standard (e.g. BCR-2G) yields accurate Li isotope data with external, measured 2σ δ7Li precision of <1‰ at Li concentrations of 3–35 ppm.