Melting of reactive packings

Un article de Surface du verre et interfaces.

Julien Grynberg (PhD 2009-2012), Emmanuelle Gouillart.

To elaborate glass, raw materials as silica and carbonates are heated up to 1600°C. These materials consist of grains, which melt as a result of heat and chimical reactions between silica and carbonates. A "refining phase" is then necessary to obtain a homogeneous glass without bubbles and unmelted grains.

The idea behind this research on the melting of reactive packings is to understand at the grain scale the first steps of transformation, and thereby may be able to skip a refining phase which requires a lot of energy and pollutants. Is it possible to elaborate a more homogeneous glass with fewer defects in the early stages of the liquid formation ?

Several stages in the processing of a granular packing in a viscous liquid (the glass) can be distinguished, which are as many lines of research (see diagram above).

A first study examines the initial granular pile, in which the grains are still in a solid state and distinguishable by their chemical species (silica or carbonates). What are the contact properties between grains of different species ? What are the optimal size and distribution to promote a reaction path? How does the packing structure respond to a sudden rise in temperature ?

 

As a response to a chemical and thermodynamic process, grains melt during the heating, changing the structure and the rheology of the packing.

From a structure originally solid, liquids will first appear during the heating. We can consider the distribution of these early fluids and how they are incorporated into the granular packing, which is the question of blending liquids with grains. Therefore, the study focuses on a complex two-phase system in which the liquid fraction increases as the solid phase decreases - as a result of the dissolution of grains. A simple question may be raised, however, is the geometry of the original structure influence the homogeneity of the liquid phase formed? It's the whole purpose of this study.

Collaborations

• Michael Toplis : Observatoire Midi Pyrenées - Dynamique Terrestre et Planétaire (UMR5562)
• L. Salvo et M. Suéry : Science et Ingénierie des Matériaux et Procédés (SIMaP), Grenoble.