In-situ high temperature monitoring of structural and optical properties of silicate glasses and liquids

Start Date
23-11-2017 10:00
03-1-13 ExpHall
Speaker's name
Florent Michel
Speaker's institute
Contact name
Sabine Schreiber
Host name
Gilles Renaud
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In-situ high temperature monitoring of structural and optical properties of silicate glasses and liquids

Reducing energy consumption in flat glass furnace or optimization of thermal insulation of glass fibers are strong economic and environmental challenges driven by radiative properties of silicate glass/liquid. However, the laws governing the structure-radiative properties relationships are largely unknown in silicate melts and glasses. In this seminar, we present how in-situ techniques can show in temperature how the optical absorption properties are connected to the liquid/glass structure.

We are dealing firstly with alkali boro-silicates, corresponding to glass fibers, to understand the role of boron at high temperatures. We then examine the role of iron in the fusion of sheet glass for soda-lime/alumino-silicate matrices.

In the alkali boro-silicate liquid fiberglass, trigonal boron absorbs infrared at 10 µm, which corresponds to the max emitted thermal radiation of a building at 25 °C. In-situ neutron scattering reveals that the trigonal boron proportion increases by 40 % when the temperature increases from 25 °C to 1200 °C. We show that a rapid quench of the borosilicate liquid would maximize the trigonal boron proportion as well as the thermal insulation properties of the fiberglass.

Fusion of soda-lime/alumino-silicate sheet glass is mainly done by radiative transfer in furnaces, mainly in the near infrared domain. In order to follow those radiative transfer in temperature, we obtained in-situ near infrared absorption spectra for different glasses/melts. One of the most spectacular change being observed on these spectra is for the main Fe2+ absorption bands, the intensity of which decreases from glass to melt in most compositions. Those results show an increase of radiative transfer up to 1400°C in the glass batch within the furnace. In order to understand structural origin for this evolution of optical properties, Fe2+ K-edge XANES and EXAFS spectra were investigated in-situ in the melts using an original furnace setup allowing a control of the atmosphere to prevent Fe-oxidation. The evolution of pre-edge features and EXAFS-derived Fe-O distances provide information on the evolution of Fe2+ coordination. These data will be discussed with the evolution of the optical absorption spectra and the relationships with the way radiative heat transfer occurs inside melts.

Keywords: melts, UV/Visible/Near Infra-Red spectroscopy, X-ray Absorption Spectroscopy, glass fiber, window glass.

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