Leached layer formation on float glass surfaces in the presence of acid interleave coatings

Acid interleave coatings are routinely used in the float glass industry to inhibit corrosion during transport and storage in hot, humid environments. It is well recognized that acid interleave coatings neutralize surface alkalinity, and thereby delay the onset of etching, dissolution, and permanent staining (so-called Stage II corrosion). However, the effect of acid interleave coatings on leached layer formation (so-called Stage I corrosion) has not been reported. For many applications of float glass, the presence of a shallow leached layer may be of little consequence, but in other applications, there can be nanoscale effects on scratch resistance, optical properties, adsorption, adhesion, and interface stability. In this study, complementary techniques of X-ray photoelectron spectroscopy (XPS) sputter depth profiling and infrared reflection spectroscopy were used to evaluate the thickness of leached layers in float glass samples weathered in a controlled manner, both with and without acid interleave coatings applied. The results reveal that acid interleave coatings do, in fact, enhance leaching during both cyclic and static weathering. This confirms that the acid not only neutralizes the alkaline reaction products of weathering but also reacts with the glass itself by ion exchange. The concentration of acid in the coating influences the thickness of the resultant leached layer, but this effect depends on the weathering conditions (cyclic versus static) and the duration of the exposure; boric acid and adipic acid coatings performed similarly. An excellent correlation was found between the more direct method of XPS depth profiling of the sodium leaching profile and the less direct, but perhaps more convenient, method of infrared reflection spectroscopy.