Aqueous alteration of lanthanum alumino-silicate glasses

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 Å). 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.