Thermal outgassing of vacuum glazing

Vacuum glazing consists of two sheets of glass separated by a narrow evacua ted space. In this article we describe investigations of the causes of ther mally induced degradation of vacuum glazing. It is shown that the rate of i ncrease of pressure within the glazing during high temperature aging is mai nly determined by the diffusion of water out of near-surface regions in the glass. In addition, adsorption of water molecules onto the internal surfac es influences the temperature dependence of the pressure in a degraded glaz ing. A prediction is made of the likely upper limit of the thermally induce d degradation of vacuum glazing, and hence its properties as a thermal insu lator, for a given production schedule and under conditions representative of practical applications. (C) 1999 American Vacuum Society. [S0734-2101(99 )04503-0].