Effect of some nucleating agents on crystallizing phases and microstructure in Li2O–BaO–Al2O3–SiO2 system

Different concentrations of LiF and Cr2O3 were incorporated in Li, Ba aluminosilicate glass to establish their effects on the crystallisation process. The kinetics of phase transformations, the final crystalline phase assemblages and the microstructures formed depended on the types and concentration of the nucleant involved. Cr2O3 increased the melting temperature and favoured crystallisation of beta-spodumene ss hexacelsian and traces of monoclinic celsian. It also favoured volume crystallisation of finer grained microstructure. LiF decreased the melting temperature and favoured crystallisation of beta-spodumene ss and monoclinic celsian. LiF in low concentrations greatly facilitated the crystallisation process, the beta-eucryptite ss/beta-spodumene ss transformation and hexacelsian/monoclinic celsian transformation. It also stimulated surface crystallisation with holocrystalline coarse non-uniform textures. The effects of various Cr2O3 concentrations are discussed on the basis of the increased viscosity and separation of Cr2O3 and/or chromium spinel phases. The role of LiF was attributed to the role of fluorine ions in reducing the viscosity of the glasses, consequently facilitating crystallisation of the structurally more complex silicate in addition to helping to reach thermodynamic equilibrium.