Transport phenomena in silicate melts: chemical diffusion and phase separation
Event details
| Date | 04.04.2016 |
| Hour | 13:15 › 14:15 |
| Speaker | Prof. Emmanuelle Gouillard, Saint Gobain Recherche, Aubervilliers France |
| Location | |
| Category | Conferences - Seminars |
Co-authors: Ekaterina Burov, Marie-Hélène Chopinet, Corinne Claireaux (SVI), David Bouttes et Damien Vandembroucq, PMMH (ESPCI), Michael Toplis (Observatoire Midi-Pyrénées)
In this lecture, I will present two different studies of transport phenomena conducted at high temperature in silicate melts.
The structure of silicate melts is that of a strongly polymerized network of silica tetrahedra, with additional degrees of freedom given by cations known as network modifiers. In such a constrained system, the diffusion of chemical species cannot be considered independent, and couplings between species have to be taken into account. Instead of independent diffusion coefficients, one has to consider a diffusion matrix, which relates the flux of one element to the gradients of all elements. We
studied chemical diffusion in the quaternary system Na2O - CaO - SiO2 - Al2O3, of interest to industrial glass melting as well as geochemistry. Diffusion experiments between melts of different initial compositions were realized, and chemical profiles were measured thanks to electron microprobe. The set of all chemical profiles is used to determine the complete diffusion matrix. From the diffusion matrix, eigenvectors and eigenvalues can be extracted. They are interpreted respectively as combinations of elements that rearrange cooperatively for diffusion to proceed, and as the probabilities of such exchanges. Eigenvalues of strikingly different magnitudes are found, confirming that fast and very slow diffusion processes operate simultaneously in the melts.
Secondly, we studied the kinetics and the morphology of phase-separated domains during coarsening in barium borosilicate melts, using in situ synchrotron microtomography to characterize the 3-D microstructure of the phases. Quantitative geometrical measurements and direct observations demonstrate that viscous coarsening is the dominant mechanism governing the evolution of the bicontinuous structure. This mechanism results in a linear growth of domain size with time, much faster than the t^1/3 growth associated to diffusive mechanisms, that have been observed so far in silicates. Complementary experiments show that diffusive mechanisms
are negligible compared to viscous coarsening at such high temperatures, in contrast to experiments of the literature performed closer to the glass transition. Furthermore, we observe a progressive fragmentation of one of the percolating phases, that we relate to the important viscosity contrast between phases.
Bio: Emmanuelle Gouillart is currently the head of the joint unit CNRS/Saint-Gobain Surface of Glass and Interfaces, a lab dedicated to basic research on topics relevant for the industry.
After graduating in theoretical physics at Ecole Normale Supérieure in Paris, she did her PhD on chaotic mixing in viscous fluids between Imperial College and CEA Saclay and graduated in 2007. In 2008, she joined the R&D center Saint-Gobain Recherche to work in their joint unit with CNRS (an academic lab), and start a research program on glass melting. She took over the direction of the joint unit in 2013.
Her research activities are on glass melting, phase separation and diffusion in silicate glass. She is a frequent user of synchrotron ultrafast microtomography, an imaging technique used to study the evolution of phases in materials such as silicate melts, in situ at high temperature. Her strong focus on imaging techniques led her to contribute to and develop scikit-image, a major open-source image processing library for the Python language.
In this lecture, I will present two different studies of transport phenomena conducted at high temperature in silicate melts.
The structure of silicate melts is that of a strongly polymerized network of silica tetrahedra, with additional degrees of freedom given by cations known as network modifiers. In such a constrained system, the diffusion of chemical species cannot be considered independent, and couplings between species have to be taken into account. Instead of independent diffusion coefficients, one has to consider a diffusion matrix, which relates the flux of one element to the gradients of all elements. We
studied chemical diffusion in the quaternary system Na2O - CaO - SiO2 - Al2O3, of interest to industrial glass melting as well as geochemistry. Diffusion experiments between melts of different initial compositions were realized, and chemical profiles were measured thanks to electron microprobe. The set of all chemical profiles is used to determine the complete diffusion matrix. From the diffusion matrix, eigenvectors and eigenvalues can be extracted. They are interpreted respectively as combinations of elements that rearrange cooperatively for diffusion to proceed, and as the probabilities of such exchanges. Eigenvalues of strikingly different magnitudes are found, confirming that fast and very slow diffusion processes operate simultaneously in the melts.
Secondly, we studied the kinetics and the morphology of phase-separated domains during coarsening in barium borosilicate melts, using in situ synchrotron microtomography to characterize the 3-D microstructure of the phases. Quantitative geometrical measurements and direct observations demonstrate that viscous coarsening is the dominant mechanism governing the evolution of the bicontinuous structure. This mechanism results in a linear growth of domain size with time, much faster than the t^1/3 growth associated to diffusive mechanisms, that have been observed so far in silicates. Complementary experiments show that diffusive mechanisms
are negligible compared to viscous coarsening at such high temperatures, in contrast to experiments of the literature performed closer to the glass transition. Furthermore, we observe a progressive fragmentation of one of the percolating phases, that we relate to the important viscosity contrast between phases.
Bio: Emmanuelle Gouillart is currently the head of the joint unit CNRS/Saint-Gobain Surface of Glass and Interfaces, a lab dedicated to basic research on topics relevant for the industry.
After graduating in theoretical physics at Ecole Normale Supérieure in Paris, she did her PhD on chaotic mixing in viscous fluids between Imperial College and CEA Saclay and graduated in 2007. In 2008, she joined the R&D center Saint-Gobain Recherche to work in their joint unit with CNRS (an academic lab), and start a research program on glass melting. She took over the direction of the joint unit in 2013.
Her research activities are on glass melting, phase separation and diffusion in silicate glass. She is a frequent user of synchrotron ultrafast microtomography, an imaging technique used to study the evolution of phases in materials such as silicate melts, in situ at high temperature. Her strong focus on imaging techniques led her to contribute to and develop scikit-image, a major open-source image processing library for the Python language.
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Practical information
- General public
- Free
Organizer
- Prof. Fabien Sorin
Contact
- Prof. Fabien Sorin