Nucleation inhibitors—The effect of small concentrations of Al2O3, La2O3 or TiO2 on nucleation and crystallization of lithium disilicate

Stoichiometric lithium disilicate glasses were doped with small amounts of Al2O3, TiO2 and La2O3. During thermal treatment lithium disilicate was precipitated. The steady state nucleation rate, the induction period and the crystal growth velocities were determined as a function of temperature using in situ optical hot stage microscopy. All additives are most suitable to decrease the nucleation rates and to increase the induction period. The nucleation rates show a pronounced maximum at a temperature around 10 °C above Tg. The crystal growth velocities decrease if Al2O3 or La2O3 are added, but remain unchanged if the samples are doped with TiO2.These effects are much more pronounced than expected from the increase in the viscosities. Hence the deceleration of the crystallization process if adding Al2O3 or La2O3 is predominantly due to the hindered nucleation and not to a decrease of the crystal growth velocity.In summary: nucleation inhibitors really exist.