Mechanisms for Changes in Surface Composition of Float Glass and Its Effects on the Mechanical Properties

Abstract

Changes in the mechanical properties on the top and the bottom faces of float glass by weathering were compared, and factors governing these properties were investigated. The resistance to the formation of radial cracks was shown to improve by the weathering, and the level of its improving was significantly high for the top face compared with that for the bottom face. Secondary ion mass spectrometry (SIMS) depth profiles have shown that the hydrated layer, which originates from the ion exchange reaction between Na⁺ and H⁺, easily forms on the top face compared with the bottom face on weathering. The significantly improved resistance to the formation of radial cracks for the top face can be explained by the low hardness of the hydrated layer. Furthermore, it has been proved that the Sn²⁺ ion suppresses the ion exchange reaction between Na⁺ and H⁺ in the glass surface. Consequently, the thinner hydrated layer on the bottom face compared with that on the top face can be ascribed to the existence of polarizable Sn²⁺ ion, which penetrates into the bottom face of float glass during the float process. These results indicate the successful control of the ion exchange reaction important for controlling the mechanical properties of float glass.