Yves Laurent

Aqueous alteration of lanthanum alumino-silicate glasses

Abstract The aqueous alteration behavior of glasses in the system Y–La–Al–Si–O–N has been investigated using the Soxlhet test. The altered surface was then studied by means of solid and solution analyses. In the case of La–Al–Si–O–N glasses, the formation of a crystallized lanthanum hydroxycarbonate was determined by X-ray diffraction (XRD) analysis. In the case of Y–La–Al–Si–O–N, X-ray photoelectron spectroscopy analysis (XPS) reveals a complete disappearance of silicon and aluminum at the glass surface (depth analyzed: 20 A). Rutherford backscattering spectrometry (RBS) gives some evidence that the glass surface is covered with a phase consisting mainly of yttrium and lanthanum compounds. Solution and solid analyses provide evidence that yttrium increases the chemical durability of the glass. Nitrogen seems to enhance glass corrosion by increasing the pH of the solution.

Diffuse reflectance infrared (DRIFTS) and mass spectrometry study of thermal stability of aluminophosphate oxynitrides (AlPON)

Aluminophosphate oxynitrides (AIPON) are new materials showing a very interesting catalytic behaviour. In their synthesis, impregnation and calcination stages are involved. AIPON suffers surface hydrolysis and moderate thermal decomposition. We have analysed the influence of temperature combining diffuse reflectance (DRIFTS) and mass spectrometry. Nitrogen is eliminated as NH3 in two stages. The first one, at low temperature (100-130 degrees C), is accompanied by water and corresponds to NH3 desorption from Lewis and Bronsted sites. The second stage at 330 degrees C is due to terminal (-NH2) removal upon reaction with water.

Cerium SiAlON Glasses as a Model for the Immobilisation of Nuclear High Level Wastes

The synthesis and characterisation of model glasses for the stabilisation and immobilisation of high level nuclear wastes is described. The introduction of nitrogen into the anionic network of aluminosilicate glasses greatly influences the mechanical properties and leaching characteristics of the glasses resulting in better performance. The redox properties of nitride ions also favour the stabilisation of the low oxidation states of radionuclides which significantly affects the dispersion of radioactive elements by interaction with colloidal particles.