Insight into the structure and chemical durability of Cr-bearing lead crystal glass

The scientific understanding and demonstration of the immobilization of heavy metals (notably lead and chromium) in food contact materials is crucial for the safety of environment and humans. To tackle this issue lead crystal glasses doped between 50 and 2000 ppm of chromium oxide were carried out under severe aqueous alteration conditions (acetic acid 4% (v/v), pH 2.4, 70°C, 330 days). The increase in Cr leads to a decrease in the Pb release into the solution. The leached Cr content was lower than Pb, itself much lower than alkali ones. Structural characterization before and after alteration points out the presence of Cr(III) exclusively, with no redox changes in the course of alteration. Cr and Pb are partially retained during alteration near cationic domains, less accessible to protonated species. Cr favors the Si recondensation in the rich non-bridging oxygen (NBO) mixing sites, leading in an increase of glass polymerization within the altered layer.