Surface and volume nucleation and growth in TiO 2–cordierite glasses

Abstract

Systematic measurements and analyses of surface nucleation and growth of μ-cordierite on diamond-polished surfaces and on fractured surfaces of cordierite glasses containing 0.3, 1.2, 3.4, 6.2 and 8.1 wt% TiO 2 were carried out. All the glasses exhibit surface nucleation, however, the glass having 8.1 wt% TiO 2 also exhibits volume nucleation. The maximum surface nucleation rate is located at a temperature considerably higher than the maximum volume nucleation rate. Both surface and volume crystallization occur by heterogeneous nucleation. The average nucleus/substrate wetting angles, θ, were estimated from surface and volume nucleation measurements. The widely different values of θ indicate that the active catalyzing sites are different for surface and volume crystallization. It is likely that Al 2TiO 5 crystals induce volume crystallization of μ-cordierite, while surface crystallization is affected by TiO 2, defects and relicts of polishing power. Nucleation on fractured surfaces was induced mainly by solid particles, most likely by broken glass particles. The crystal growth velocity of μ-cordierite crystals is well fitted by the 2D-surface nucleation growth model.