THESIS BY CHARLOTTE GALLOIS*
The production of alumina catalyst supports involves a series of individual operationsa during which the solid fraction of the material varies, from a dispersed state (colloidal fluid) to a porous solid state.
This gradual densification reflects a change in the structural organization of solid particles on a mesoscopic scale.
The arrangements adopted depend both on:
- the physicochemical properties of the initial alumina suspensions,
- and the densification processes employed.
It is crucial to identify and understand the mechanisms at play during densification, since they determine the finished product properties.
A study of colloidal fluid drying was carried out in partnership with the Phenix laboratory at UPMC. A droplet of alumina suspension, applied to a solid hydrophobic substrate and placed in controlled drying conditions, was examined by rapid X-ray microtomography (on Paul Scherer Institute synchrotron).
These experiments demonstrated that:
- a droplet of liquid suspension collapses in the final stages of its drying, due to an accumulation of particles on the outside surface of the drop (particularly at triple line levelb),
- whereas a droplet of a suspension in gel state is deformed in a homothetic manner(1-2).
This research will be applied to the study of industrial formulations and be continued in more severe drying conditions.
%20au%20cours%20de%20son%20s%C3%A9chage%20-%20visualisation%20de%20l%E2%80%99accumulation%20de%20solide%20(vert%20fonc%C3%A9)%20en%20p%C3%A9riph%C3%A9rie.PNG)
during drying: visualization of the solid accumulation
(dark green) around the edges.
a- Synthesis of boehmite, filtration and washing, shaping, calcination.
b- Solid-liquid-gas interface.
* Thesis entitled “Study of the physicochemical properties of boehmite. Application to catalytic supports”
(1) C. Gallois, E. Rosenberg, L. Barré, A. Bonnin, D. Frot, E. Lécolier, P. Levitz, Drying of sessile droplets of anisotropic colloids dispersions. In the process of being drafted.
(2) C. Gallois, D. Frot, E. Lécolier, P. Levitz, Colloidal boehmite dispersions under osmotic stress: an in situ DLS investigation of gelation. In the process of being drafted.
Scientific contact: eric.lecolier@ifpen.fr