Study on thermophysical properties and phase evolution in Nd doped Li2O-Al2O3-SiO2 glass nucleated by multiple nucleating agents

Abstract

Lithium aluminium silicate (LAS) glasses of compositions (wt%) (1) LASa: 59SiO2-19Al2O3-3.5Li2O-5B2O3-1.5ZnO-1MgO-2TiO2-2ZrO2-7P2O5 and (2) LASb: 58SiO2-19Al2O3-3.5Li2O-5B2O3-1.5ZnO-1MgO-2TiO2-2ZrO2-7P2O5-1Nd2O3 were prepared by melt-quench technique and converted to glass-ceramics. In glass samples, addition of Nd2O3 showed an increase in the glass transition temperature (Tg) and crystallization temperature. Thermo-mechanical analysis (TMA) showed that crystallized samples have very low thermal expansion coefficient (α) of value around 2.5×10−6/°C (30–300). The microhardness and density values of crystallized samples were found to be higher than the base glasses. XRD and SEM techniques were employed to see nature of phases and their microstructures in glass/glass ceramic samples. From XRD formation of β-spodumene (LiAlSi2O6) as major crystalline phase while Berlinite (AlPO4)and Srilankite (TiZrO4) were identified as minor crystalline phases after heat treatment at 850°C.·The microstructure of LASa and LASb samples heat treated at 675°C showed formation of nanocrystals (size <50nm) of TiZrO4 within the glass matrix, whereas samples heat treated at maximum 850°C showed formation of shell type/spherical particles structure which support the three dimensional or bulk crystallization in these samples. Micro-laser Raman spectroscopy was carried out to confirm presence of TiZrO4 phase after heat treatment at 675°C. Crystallization kinetics study was carried out by recording DTA traces at different scanning rate. Activation energy (E) and Avrami parameter (n) were calculated by using Kissinger and Marotta methods and Augis-Bennett equation. Activation energy of crystallization for LASa and LASb were found to be 263kJ/mol and 270kJ/mol, respectively whereas the Avrami parameter (n) for LASa and LASb glass was found to be greater than 2 and greater than 4, respectively. Avrami parameter greater than 2 indicates near three dimensional growth of spodumene phase, which is also confirmed by microstructural analysis and parameter greater than 4 indicated interfacial controlled growth.