Studies on phase evolution, microstructure and crystallization kinetics in Nd2O3 doped Li2O-Al2O3-SiO2 glass system

Nd ₂O ₃ doped Lithium Alumino Silicate (LAS) glass of composition (wt.%) 57SiO ₂–19Al ₂O ₃–3.5Li ₂O-7P ₂O ₅–11.5X–2Nd ₂O ₃ ( X = B ₂O ₃, MgO, ZnO, TiO ₂, ZrO ₂) was synthesized and transformed into glass ceramic. X Ray Diffraction (XRD) showed formation of TiZrO ₄ nano crystalline phase at 948 K and major phase β -spodumene (β-LiAlSi ₂O ₆) along with some minor phases at temperatures >1073 K. In the intermediate temperature range, γ-spodumene /Li _xAl _xSi _3-xO ₆ (0< x<1)/Virgilite was identified as a major phase which was shown to get converted into stable β-spodumene phase at elevated temperature. Micrographs of heat treated samples revealed nanocrystals of size (<25 nm) of Titanium Zirconate phase at 948 K and shell type microstructure of β-spodumene phase at temperature >1073 K. Decrease in thermal expansion coefficient (α) from 5.5×10 ⁻⁶/K to 2.98×10 ⁻⁶ /K (303–573 K) was observed for sample crystallized at around 1073 K. Non isothermal DTA data showed two exothermic peaks, indicating crystallization of two different phases in temperature range of 993 to 1223 K. Activation energy for crystallization (Ea) of first peak was found to be 168±20 kJmol ⁻¹ and 187±20 kJmol ⁻¹ using Kissinger and Marotta methods, respectively. Model free kinetics was used to find more accurate kinetic parameters such as Ea and predict isothermal reaction progress.