Corrosion of glasses and its significance for glass coating

Abstract

Combination of concentration profiling with electrochemical experiments yielded time-dependent local ion distributions in subsurface ranges of oxidic glasses and information on the dynamics of glass corrosion. In solutions, the first step of corrosion is based on the phase boundary equilibrium of glass surface groups with ions in the solution, whose activities determine, besides the potential of the glass, their relative concentrations bound to the surface groups. The resulting concentration gradients below the glass surface cause an interdiffusion of these ions against the ions of the glass, which is either a proton/alkali ion interdiffusion accompanied by a hydrolytic attack and dissolution of the glass network and resulting in a steady state leached layer and in incongruent glass dissolution or an alkali/alkali interdiffusion with congruent glass dissolution. Corrosion in wet gases is different in that the products resulting from the interdiffusion are accumulated at the surface and the network is not dissolved so that an ion-exchanged layer with growing thickness develops. The mechanisms are presented for a general understanding of glass corrosion and may help to select appropriate substrate glasses and their modes of storage and cleaning, which depend on the requirements of the coatings.