Near-surface crystallization of cordierite glass

A special type of surface crystallization of cordierite glass was recently observed. Although the process starts close to the surface, there remains an amorphous film, covering the crystalline core. We explain this observation by taking into account two competing effects: a part of the energy, caused by the elastic deformations, dissipates near the surface. On the other hand, because of chemical corrosion, the surface layers are depleted of some components. These effects contribute to the supersaturation for crystallization Deltamu(z) and make it dependent on distance, z, from the surface. Moreover, there is a certain distance, z(0), at which the sign of the supersaturation changes, i.e. a layer very close to the surface (z < z(0)) will remain amorphous. It is demonstrated that the thickness of the amorphous cover is proportional to the width L of the corroded region and inversely proportional to supersaturation in the interior, i.e. z(0) = k(B)TL/ (C) 2002 Elsevier Science B.V. All rights reserved.