Evidence of depolymerisation of amorphous silica at medium- and short-range order: XANES, NMR and CP-SEM contributions

This work reports medium- and short-range order of changes of amorphous silica submitted to chemical degradation. Structural changes were studied, using X-ray absorption near edge structure (XANES), nuclear magnetic resonance 29Si NMR-MAS and controlled pressure scanning electron microscope (CP-SEM). The depolymerisation of amorphous SiO2 compounds mainly induces the formation of Q3 species and alkali-rich domains. The XANES Si K-edge spectra demonstrate the presence of different environments of silicon: one with four oxygen atoms and the other with a number of oxygen lower than four in agreement with previous studies.