Abstract
Materials used in nuclear energy (fuel, packaging matrix, structural materials...) are subject to significant stresses due to the creation of defects that modify their properties. Several studies have shown that interfaces can act as a sink for defects caused by irradiation, which suggests that nanomaterials could have a higher resistance to irradiation than materials with a "micrometric" structure. Simultaneously, mesoporous silica materials have grown in popularity in recent years and are becoming more involved in the domain related to radiation conditioning, such as the prospective use of conditioning for nuclear waste. While research has begun to focus on the behavior of non-porous silica materials when exposed to radiation, no extensive investigations have been conducted on the behavior of mesoporous silica when exposed to radiation, particularly at electronic irradiation regime.This thesis aims to comprehend and explain the radiation-induced changes in mesoporous silicas under electronic regimes. This work quantified the evolution of physical (pore volume, pore diameter and distribution...) and structural (polymerization of the network, creation of defects...) properties of mesoporous silica irradiated with high-energy ion beams with stopping powers ranging from 1 keV/nm to 12 keV/nm, and with electron beams (10 - 300 keV and 0.6 - 2.4 MeV). Post-irradiation characterization methods (X-ray reflectivity, gas adsorption, SAXS, FTIR, etc.) have been used, as well as in-situ pore structure monitoring using electron microscopes. The experimental findings indicated that pore structures were susceptible to a certain degree of irradiation-induced shrinking. In contrast, evidence shows that the silica network itself does not alter much in porous silica compared to non-porous silica. Meanwhile, a 3DTS (3D thermal spike) model has been successfully applied to describe and explain the observed pore contraction behavior in response to ionic irradiation. Additionally, the mechanism of pore contraction under electron irradiation has been delineated according to the domain of incident electron energies. When compared to non-porous silica, this research has demonstrated that the existence of nanoscale pores reduces the accumulation of damage induced by irradiation. In conjunction with this effect, the pore contracts until it completely disappears under the impact of irradiation. This characteristic could, from an applicative point of view, be of interest to practitioners in the context of new methods of treating radioactive effluents, such as through the use of a "separation/conditioning" strategy, or in the context of the self-healing of porous gel layers formed on the surface of vitrified waste packages whose final destination is deep geological disposal.