STRUCTURAL CHARACTERIZATION OF LITHIUM ALUMINOSILICATE GLASS AND GLASS-CERAMICS DERIVED FROM SPODUMENE MINERAL

Lithium aluminosilicate (LAS) glass and glass ceramics derived from sp odumene mineral have been studied by transmission electron microscopy (TEM), x-ray diffraction (XRD), positron annihilation lifetime spectro scopy (PALS) and solid state nuclear magnetic resonance (NMR) as as-ca st glass, as partially crystallized glasses, and as fully crystalline glass ceramics. The nucleation and growth of the crystalline phases at 725 degrees C up to 1000 degrees C have been studied as functions of varying time and temperature. Both TEM and PALS are effective tools fo r studying the development of the nanophase structure in the partially crystallized glass. TEM observation established the size and number o f crystallites present in the glassy matrix, whilst the PALS component attributed to orthopositronium (oPs) pickoff annihilation was remarka bly sensitive to the nucleation and growth of the crystalline phases i n the glass ceramic. This oPs component was associated either with the nuclei/glass interface or with the nuclei structure. XRD and NMR were used to study the evolution of the two crystalline phases which form from the glass in the temperature range 725 degrees C to 1000 degrees C, the beta-quartz solid solution (ss) phase below 900 degrees C and t he beta-spodumene ss phase above 900 degrees C. The Si-29 NMR spectra of both beta-quartz ss and beta-spodumene ss phases show structures as sociated with the next nearest neighbour configurations of the central SiO4 units. The Si-29 and Al-27 NMR spectra of alpha-spodumene minera l and beta-spodumene ss phase formed by annealing alpha-spodumene are compared to the spectra for the glass and crystalline phases formed fr om the melt.