Fluidal pyroclasts reveal the intensity of peralkaline rhyolite pumice cone eruptions

This work is a contribution to the Natural Environment Research Council (NERC) funded RiftVolc project (NE/L013932/1, Rift volcanism: past, present and future) through which several of the authors are supported. In addition, Clarke was funded by a NERC doctoral training partnership grant (NE/L002558/1).Peralkaline rhyolites are medium to low viscosity, volatile-rich magmas typically associated with rift zones and extensional settings. The dynamics of peralkaline rhyolite eruptions remain elusive with no direct observations recorded, significantly hindering the assessment of hazard and risk. Here we describe uniquely-preserved, fluidal-shaped pyroclasts found within pumice cone deposits at Aluto, a peralkaline rhyolite caldera in the Main Ethiopian Rift. We use a combination of field-observations, geochemistry, X-ray computed microtomography (XCT) and thermal-modelling to investigate how these pyroclasts are formed. We find that they deform during flight and, depending on size, quench prior to deposition or continue to inflate then quench in-situ. These findings reveal important characteristics of the eruptions that gave rise to them: that despite the relatively low viscosity of these magmas, and similarities to basaltic scoria-cone deposits, moderate to intense, unstable, eruption columns are developed; meaning that such eruptions can generate extensive tephra-fall and pyroclastic density currents.Publisher PDFPeer reviewe

CEMS study of tin in the hot end coatings of glass containers

Tin oxide coatings are applied to glass containers as adhesion promoters for the organic lubricants. In this article, room temperature conversion electron M\uf6ssbauer spectroscopy (CEMS) is used to analyse a range of tin oxide coated containers. Readable CEMS curves could be obtained even for the thinnest (30 CTU or about 6 nm) coatings. The hyperfine parameters calculated from the spectral curves show that tin is tetravalent in crystalline form with a preferential grain orientation, which is reduced on annealing. The presence of tin in other oxidation states and dissolved in the matrix was excluded

SAXS study of the micro-inhomogeneity of industrial soda lime silica glass

The microstructure of a variety of industrial multicomponent soda lime glasses for container and glazing and of a lead alkali silicate glass for pressed tableware articles was analyzed using small angle X-ray scattering (SAXS). No inhomogeneity with size >0.5 nm was found in the industrial samples, while ternary soda lime glass samples with a suitable composition when heat treated developed a phase separation which SAXS detected without difficulty. The results obtained disprove earlier reports which attributed problems of rheology and strength affecting container production ('bad workability') to microstructure formation. © 1994

SAXS study of the micro-inhomogeneity of industrial soda lime silica glass.

The microstructure of a variety of industrial multicomponent soda lime glasses for container and glazing and of a lead alkali silicate glass for pressed tableware articles was analyzed using small angle X-ray scattering (SAXS). No inhomogeneity with size >0.5 nm was found in the industrial samples, while ternary soda lime glass samples with a suitable composition when heat treated developed a phase separation which SAXS detected without difficulty. The results obtained disprove earlier reports which attributed problems of rheology and strength affecting container production ('bad workability') to microstructure formation

Behaviour of self-cleaning glass in urban atmosphere

International audienceIn order to analyse the self-cleaning mechanism of TiO$_2$-coated window float glass, a field experiment was conducted in Paris, at a site representative of background urban pollution. Two hydrophilic photocatalytic TiO$_2$-coated industrial glasses and a traditional float glass (reference) were exposed in unsheltered and sheltered condition for various time duration. The sheltered exposure allowed to study the soiling and self-cleaning mechanism without the disturbing effect of rain washing. In parallel, air filtrations were carried out in order to assess the chemical composition of airborne particulate.Analytical measurements were performed on the deposit and on the weathered glass layer. The analyses of the deposit on glass and of atmospheric particles on filters consisted in the determination of the organic fraction (organic carbon, particulate organic matter, water-soluble organic carbon), elemental carbon and the inorganic soluble fractions. The impairment of glass optical properties was followed by haze measurements. Investigation of the weathered surfaces was performed using EPMA and scanning electron microscopy (SEM)/EDX. Only a moderate weathering of the glass surfaces after 24 months of exposure was detected. The self-cleaning mechanism was evidenced by a significant decrease of the organic fraction in the deposit on the TiO$_2$-coated glasses