Efficacy Of Zinc Salts To Protect Glass Against Atmospheric Alteration. Part Ii: Possible Passivation Mechanisms

To investigate the origin of the protection effect of zinc salts against glass atmospheric alteration, the speciation of Zn2+ ions on glass according to the deposit protocol and the Zn2+ surface concentration, and its change over time, was investigated in the light of the respective performances of the treatments. In that respect, a combination of various characterization methods of the glass surface and near-surface was used before and after aging experiments (temperature, relative humidity (RH) control) of the Zn-treated glass. Different Zn-species could be observed on the surface of the treated glass: chemisorbed species, physisorbed species and precipitated hydroxide phases, their respective distribution being highly dependent on the nature of the treatment and on the Zn2+ surface concentration. GI-XAS (Zn K-edge) and ToF-SIMS experiments pointed out the conversion by thermal activation of these surface species into chemisorbed species inserted in the glass network in the near-surface. The chemisorbed species appear to be the most effective ones for the glass protection, possibly by making the surface less soluble, less hydrophilic and even by acting as a diffusion barrier.