Non-stoichiometric crystal nucleation in a spodumene glass containing TiO2 as seed former: Effects on the viscosity of the residual melt

A spodumene glass (LiAlSi2O6), doped with 4 mol% TiO2 as a nucleating agent, was synthesized by containerless melting. Its accurate viscosity characterization by micropenetration viscometry or calorimetry is shown to be very challenging in the vicinity of the glass transition, due to the unpreventable occurrence of thermally activated non-stoichiometric crystal nucleation, closely overlapping the relaxation into the liquid state. TiO2 crystal nucleation brings about a compositional modification of the residual melt, with an associated increase in measured viscosity by up to 2 log units. A careful experimental approach and a profound understanding of seed formation are essential to circumvent or at least minimize such inaccuracies, getting as close as possible to the viscosity of the parent homogeneous melt.