Raman spectroscopy, a non-destructive solution to the study of glass and its alteration

This paper presents the potential of Raman spectroscopy, a non-destructive technique which can be applied in-situ, for the analyses of glass and their alteration. Recent analytical developments are summarised for different glass composition and practical examples are given. The paper describes how to extract compositional information from the glass, first based on the spectra profile to distinguish rapidly alkali silicate from alkaline-earth alkali silicate and lead alkali silicate glass, then using the spectral decomposition and correlations to extract quantitative data. For alkali silicate glasses, that are most prone to alteration, the spectral characteristics are described to interpret the alteration process (selective leaching or dissolution of the glass) from the Raman spectra of the altered glass. These developments have greatly widened the potential of the technique and supplement well its ability to measure the thickness of the altered layer and identify the crystalline deposits

Experimental determination of the role of diffusion on Li isotope fractionation during basaltic glass weathering

International audienceIn order to use lithium isotopes as tracers of silicate weathering, it is of primary importance to determine the processes responsible for Li isotope fractionation and to constrain the isotope fractionation factors caused by each process as a function of environmental parameters (e.g. temperature, pH). The aim of this study is to assess Li isotope fractionation during the dissolution of basalt and particularly during leaching of Li into solution by diffusion or ion exchange. To this end, we performed dissolution experiments on a Li-enriched synthetic basaltic glass at low ratios of mineral surface area/volume of solution (S/V), over short timescales, at various temperatures (50 and 90°C) and pH (3, 7, and 10). Analyses of the Li isotope composition of the resulting solutions show that the leachates are enriched in 6Li (δ7Li = +4.9 to +10.5‰) compared to the fresh basaltic glass (δ7Li = +10.3 ± 0.4‰). The δ7Li value of the leachate is lower during the early stages of the leaching process, increasing to values close to the fresh basaltic glass as leaching progresses. These low δ7Li values can be explained in terms of diffusion-driven isotope fractionation. In order to quantify the fractionation caused by diffusion, we have developed a model that couples Li diffusion with dissolution of the glassy silicate network. This model calculates the ratio of the diffusion coefficients of both isotopes (a=D7/D6), as well as its dependence on temperature, pH, and S/V. a is mainly dependent on temperature, which can be explained by a small difference in activation energy (0.10 ± 0.02 kJ/mol) between 6Li+ and 7Li+. This temperature dependance reveals that Li isotope fractionation during diffusion is low at low temperatures (T 120°C), the dissolution rate of basaltic glass is also high and masks the effects of diffusion. These results indicate that the high δ7Li values of river waters, in particular in basaltic catchments, and the fractionated values of hydrothermal fluids are mainly controlled by precipitation of secondary phases

Quantifying Li isotope fractionation during smectite formation and implications for the Li cycle

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Alteration of stained glasses in an atmospheric environment: impact of the Mn-oxidiser bacteria strain Pseudomona putida

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Effect of marine aerosols on the alteration of silicate glasses

This work is focused on the effect of marine aerosols on soda-lime, potash-lime and lead silicate glass samples. Two kinds of tests were carried out, the first one under laboratory controlled condition during 36 days to evaluate the alteration of glass surface by NaCl aerosols, and the second one in a marine atmosphere in Cabo Vilano (Galicia, Spain) for up to three months. Both tests showed similar results. NaCl aerosols acted as condensation nuclei in high humidity environments favoring the lixiviation of the alkaline and alkaline-earth ions from the glass surface and the solubilization of atmospheric gases (CO2, SO2). Marine aerosols could also accelerate the corrosion attack inducing the loss of the surface hydrogen bonds and the opening of the network accelerating the corrosion mechanism. Results also confirmed that high humidity favored the alteration of the glass surface and the formation of new crystalline phases. Soda-lime silicate and lead silicate glasses were the most durable ones, whereas potash-lime silicate glass presented a fissured alteration layer due to the hydrolytic attack of the surface. New crystalline phases including chlorides, carbonates and sulfates were detected on the glass surfaces which can be related to marine aerosols, environmental particles and the reaction of the cations lixiviated from the glass with the atmospheric gases.This work was initiated during a short stay financed by the Erasmus + staff mobility program and has been partially funded by the Fundação do Ministério de Ciência e Tecnologia de Portugal (Project ref. UID/EAT/00729/2013 and Post-doctoral grant ref. SFRH/BPD/108403/2015) and GEOMATERIALES 2-CM Program Ref. S2013/MIT-2914. Professional support from Techno-Heritage (Network on Science and Technology for the Conservation of Cultural Heritage) is also acknowledged.Peer Reviewe

Lithium isotopes in hydrothermally altered basalts from Hengill (SW Iceland)

International audienceThe Li isotope signatures of hydrothermal fluids are remarkably constant (View the MathML sourceδLi7=8.0±1.9‰) irrespective of the water/rock ratio (W/RW/R), permeability, temperature or fluid involved (seawater or meteoric). High temperature hydrothermal fluids represent the second most significant source of Li to the ocean, yet the homogeneity of the Li isotopic signatures of this source remains to be explained and in this context, the lack of data for the corresponding altered phases is problematic. We measured Li contents and Li isotope signatures (as well as mineralogy, composition and local fluid temperature) in hyaloclastites collected from a borehole in the Hellisheidi geothermal system (Iceland) which have been altered by high temperature aqueous fluids (from 170 to 300 °C). Li is more enriched in the solid phases than the other alkali metals, highlighting its greater ability to be incorporated into secondary phases, especially at high temperatures (>250 °C). Mass balance calculations show that the low Li concentrations in hydrothermal fluids are best explained by a high water/rock ratio and a high permeability of this system. The Li isotopic signature of the altered hyaloclastites (View the MathML sourceδLi7 between +1.9 and +4.0‰+4.0‰) remains close to the fresh basalt at deep levels and high temperatures (290–300 °C) (as measured View the MathML sourceδLi7 range between +3.7 and +4.0‰+4.0‰), and decreases at shallower depths and lower temperatures (150–270 °C) (View the MathML sourceδLi7 between +1.9 and +3.1‰+3.1‰). A mass balance model involving basalt dissolution, secondary phase formation, and successive isotope equilibrium during the migration and the cooling of the percolating fluid was developed. The corresponding apparent mineral-fluid Li isotope fractionation factors resulting from precipitation of secondary phases (View the MathML sourceΔLiminerals-fluid7) range between 0‰ at 300 °C and −8.5‰−8.5‰ at 170 °C and highlight a key role of chlorite. Applying the same approach to mid-ridge oceanic hydrothermal systems allows the relatively homogeneous isotope signatures of high temperature fluids of various locations to be explained

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

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