Effects of lithium oxide on the crystallization kinetics of Na2O·2CaO·3SiO2 glass

Abstract The crystal nucleation ( I ) and growth ( U ) rates of Na 2 O·2CaO·3SiO 2 glasses with increasing additions of Li 2 O were measured for the primary crystalline phase over wide and overlapping temperature intervals. A partial section of the phase diagram Na 2 O·2CaO·3SiO 2 –Li 2 O was constructed via DSC analysis and shows a narrow range of solid solution formation that is close to that of Na 2 O·2CaO·3SiO 2 . In the four-component system (Na 2 O–Li 2 O–CaO–SiO 2 ), a pseudo-binary eutectic system of Na 2 O·2CaO·3SiO 2 –Li 2 O·SiO 2 exists. The role of Li 2 O in the formation of the crystalline phases was investigated using DSC and X-ray analyses. The addition of Li 2 O results in decreases in the glass transition ( T g ) and liquidus ( T L ) temperatures. With increasing Li 2 O content, both the reduced glass transition temperature T gr ( T gr = T g / T L ) and the fragility index, m , pass through a minimum. These findings extend and confirm the known inverse correlation between T gr and I max (lower values of T gr correspond to higher values of I max ) and provide evidence for a similar correlation between m and I max . When using the low temperature data for the crystal growth rate ( U ) the viscosity (η) and diffusivity ( D ) were decoupled at T T g . Next, a parameter ( U ·η at T g ) that characterized the decoupling phenomenon was proposed.