Mixed alkali effect on crystallization kinetics of xNa2O:(50 −x)Li2O:50P2O5

The main aim of the present study is to investigate the effect of second glass modifier Na2O on the crystallization kinetics and thermal stability of the mol% xNa2O:(50 −x)Li2O:50P2O5 glasses, where Li+ ions are progressively substituted with Na+ ions, using differential scanning calorimetry. The DSC studies showed the classical ‘mixed alkali effect’ on the glass transition temperature, with the Tg minima for the glass composition of [Na+/(Li++ Na+)] = 0.5 i.e. x = 25 mol%. The crystallization temperature decreases as Na+ ions completely replaces Li+ ions. The presence of small concentration of second alkali (either the guest ion or host ion) tends to enhance the thermal stability, S, against devitrification as observed for 5 ≤ x ≤ 15 and 37.5 ≤ x ≤ 45. The ‘mixed alkali effect’ tends to thermally stabilize the intermediate compositions of mol% xNa2O:(50 −x)Li2O:50P2O5 as these compositions exhibited high S parameter, high activation energy for crystallization and low enthalpy of crystallization, ΔHc.