Sticking temperature investigations of glass/metal contacts Determination of influencing parameters

Abstract

Sticking experiments between hot viscous glass and metallic Substrates have been performed with a glass press apparatus on a laboratory scale, allowing a precise determination of the sticking temperatures, Ts, versus selected experimental parameters (nature of the Substrate, composition of the glass). Complementary surface analyses have also been carried out to identify the surface and interface reaction products following the glass/metal contact. Experimental results have been compared to ternary phase diagrams, in order to test the reliability of thermodynamic calculations to predict the nature of the phases produced by the contact at high temperature. The sticking phenomenon is governed by a coupling between the rheological behaviour of the glass melt and the physicochemical reactivity of the contacting surfaces. Sticking occurs when the temperature at the interface remains sufficiently high, so that the glass viscosity remains low enough to enhance the real contact area and thus, to induce physicochemical interactions between Substrate and glass. Sticking is attributed to the presence of an interfacial oxide layer which strongly adheres onto the glass. Chemical analysis of the sticking surfaces identifies a physicochemical driving force contributing to the sticking phenomenon. The predominant reaction consists in the reduction of the sodium oxide of the glass at the expense of the oxidation of the metallic elements of the Substrate during pressing, in agreement with thermochemical calculations presented by the ternary phase diagrams. The strong chemical reactivity of the soda-lime-silica glass is thus attributed in particular to the highly reactive sodium oxide constituent.