Nanocrystallization of fresnoite glass. I. Nucleation and growth kinetics

We determined the internal nucleation, crystal growth and overall crystallization kinetics of fresnoite crystal (2BaO · TiO2 · 2SiO2) in an almost stoichiometric fresnoite glass. Due to the extremely high nucleation rates (∼1017 m−3 s−1) that limit the maximum crystal size to ∼700 nm the nucleation densities and crystal sizes were estimated by scanning electron microscopy (SEM). The volume fraction crystallized was measured by X-ray diffraction. The nucleation rates obtained directly from SEM measurements reasonably agree with those calculated from the combination of overall crystallization with crystal growth kinetics. The activation enthalpies for viscous flow, transport of structural units across the nucleus/melt interface (nucleation) and crystal growth: ΔHη, ΔHτ and ΔHU respectively, follow a similar trend to that observed for other stoichiometric silicate glasses that nucleate internally: ΔHη=294>ΔHτ=87>ΔHU=61 kJ/mol. Fresnoite glass displays the highest internal nucleation rates so far measured in inorganic glasses. These rates are comparable to some metallic glasses and can lead to nanostructured glass-ceramics.