As far as this theme is concerned, the laboratory's longstanding and recognised skills in thermodynamics and surface characterisation have led to considerable progress in understanding the structure of passive films on stainless steel observed by XPS and, in particular, to a new "island" model structure being proposed for the carbonated contamination layer on stainless steels. This research is supported by Arcelor Mittal in the context of the ongoing partnership agreement signed in 1991 between Usinor and the ENSEEG.
Over the past few years, the SIR group has broadened its work to functionalisation studies and has developed the concept of TiO2-SiO2 dual-phase superhydrophilic layers, the properties of which, exacerbated by UV illumination, persist several weeks following illumination. The aim of these studies is to optimise the cleanability of surfaces coated with TiO2-SiO2 films. This system, introduced in the framework of a Franco-Thai partnership (PAI) (thesis by S. Permpoon, 2006), has been patented in collaboration with Arcelor Mittal. A second thesis (M. Houmard, 2009) in collaboration with the LMGP and again supported by Arcelor Mittal, was devoted to the optimisation of composite films containing nanograins of anatase TiO2 set in an amorphous SiO2 matrix of controlled reactivity, and to the development of cleanability experiments performed in a laminar flux cell.
Wetting Condensation of liquid water on the hydrophobic fibers of a PEMFC
A new theme has been studied for more than two years, namely characterisation of the chemistry and wettability properties of functionalised materials. At the request of CEA LITEN, we have been involved in the characterisation of materials for low-temperature proton exchange membrane fuel cells through two ANR-Pan-H projects (CHAMEAU 2007 and POLIMPAC 2007). Wettability characterisations are performed mainly on gas diffusion layer media (composite carbon fibre-PTFE materials transporting both the liquid and gas phases).
Other research being carried out in partnership with Becton Dickinson in the context of a CIFRE thesis (J .Haguet) aims to optimise an injection system by choosing suitable materials for the mobile part (piston) and lubricant (silicone between the piston and the body of the device). The model chosen, based on the behaviour of a viscoelastic silicone (Maxwell fluid), gives a suitable representation of the experimental results (force-distance curve).
In observing the high-temperature behaviour of various FeCrAl grades with different titanium contents, we had the idea of developing a surface treatment process for alloy strip involving the application of TiO2 in powder form (slurry coating) or as a gel (sol-gel coating). This treatment is particularly effective in inhibiting the formation of transition aluminas, which are responsible for excessively rapid consumption of aluminium in the alloy, and in promoting the alpha-Al2O3 variety that offers highly efficient protection without consuming too much aluminum from the fine substrate (thesis by R. Chegroune and Oxid. Met. 2008).