The influence of Sahara sand on the degradation behavior of float glass surfaces

To guarantee a long life span and high quality performance of glass including devices, a deep understanding of glass corrosion processes is required. The influence of adhering particles on the degradation behavior of glass surfaces is little investigated yet. Studies of particle-glass surface interaction are of practical interest when it comes to several technical applications implying particle exposition besides natural weathering and storage. Sahara sand was chosen for the investigation of the influence of adhering particles on glass corrosion as one example of harsh environmental conditions. The scope of this work is on chemical changes and crystallization effects that are induced by the adhering sand. Soda-lime-silicate glass produced in a float process and sand collected in the Moroccan Sahara have been investigated in this study. The glasses were weathered in a climate chamber (80 °C, 80% relative humidity) for up to 8 days - half of them with a thin sand layer, the other half without and subsequently compared to each other. The following investigation of the samples included optical and atomic force microscopy (AFM) as well as X-ray diffraction (XRD). Furthermore, X-ray photoelectron spectroscopy (XPS) combined with stepwise sputtering was used to generate element depth profiles and to investigate chemical changes of the glasses. The sand was examined with XRD and energy dispersive X-ray spectroscopy (EDX). The study shows that the adhering sand drastically enhances the leaching of the network modifiers Na and Ca and furthermore adsorbs them. It also effects crystallization processes: For sand-free weathered glasses the formation of dendritic trona and massive sodium bicarbonate layers could be verified within this study. While sand-weathering the formation of carbonates is suppressed due to the adsorption of network modifiers by the sand and the formation of aluminosilicates on the glass surface is observed. These aluminosilicates would lead in ongoing weathering to more drastic corrosion damages than carbonates due to their high alkalinity. Hence, sand is not an inert material only lowering the light transmittance of glasses when covering them. It actively changes the properties of glass surfaces and fastens their degradation.