Influence of preformed nuclei on crystal nucleation kinetics in soda–lime–silica glass

• Crystal nucleation in the glass 22.4Na2O·28.0CaO·49.6SiO2 (mol.%) is studied.
• An unusual shape of the time-dependence of the nucleated crystal number is obtained.
• The unusual step-like shape is explained by the influence of preformed crystal nuclei.
• These nuclei are formed in the course of quenching of the glass-forming melt.
• The effect of preformed nuclei is discussed using classical nucleation theory.

An unusual form of the time-dependence of the number N(t, Tn) of nucleated at a temperature Tn crystals was obtained for a soda–lime–silica glass of the composition 22.4Na2O·28.0CaO·49.6SiO2 (mol.%). The crystals are solid solutions based on the Na2O·2CaO·3SiO2 compound. The analysis of the nucleation kinetics was performed for a nucleation temperature Tn located well below the temperature of the maximum of the steady-state crystal nucleation rate. Following to the development method, supercritical clusters formed at the temperature Tn have been developed at a temperature Td > Tn in order to reach measurable sizes. A large number of crystals, N(t, Tn, Td) = No, was detected by this method already at t = 0. With an increasing nucleation time, the number of developed crystals gradually increases with a temporary tendency towards saturation. After this transient stage, the crystal number gradually increases again and a linear N(t, Tn, Td)-dependence corresponding to the steady state nucleation rate is established. These uncommon features are the consequence of the growth at the nucleation temperature of the nuclei preformed in the course of glass preparation with sizes between critical sizes corresponding to the nucleation Tn and development Td temperatures.