Mechanism of alteration of the surface of lead crystal glass in contact with food: A chemical study of the surface layer

Abstract

Lead crystal glass (24 wt% PbO) is one of the tableware materials that can release lead into the environment. A deep knowledge of the release of lead (Pb) due to food contact is necessary to control and minimize the human exposure to this heavy metal. The Pb leaching was characterized by elemental analysis (ICP-AES) of the 4 vol% acetic acid solution to simulate the food contact versus leaching time. The analysis of the subsurface layer (SIMS, STEM) allows to understand the change of composition and morphology. After an initial period of rapid leaching, the diffusion of lead out of the glass slows down, due to the formation of a blocking barrier of diffusion in the subsurface layer of lead crystal glass. Experiments, carried out with a D218O solution, highlight the different mechanisms of hydrolysis, then condensation of the silanol groups, explaining the decrease of the diffusion coefficient of Pb2+ by the formation of a “passive” sub-layer. This protective sub-layer can be reinforced by successive leaching processes or by the storage of lead crystal glass at high temperature after leaching.