Effect of the nucleating agents Cr2O3 and LiF on crystallizing phases and microstructures of glass-ceramics prepared by using some industrial wastes

Glass-ceramics in the system diopside - anorthite - orthoclase were prepare d using the waste known as the by-pass cement dust in the amount or 36% of the batch constituents. The effects of addition of the nucleating agents Cr 2O3, LiF, and mixtures of them on the crystallizability, phase assemblages, and the resultant microstructures were investigated. Low concentration of Cr2O3 (0.5 wt%) causes volume crystallization and formation of fine-grained microstructures of microcline. anorthite and aluminous pyroxene. Higher co ncentrations of Cr2O3 favor formation of leucite and aluminous pyroxene and inhibit crystallization of anorthite. LiF causes the formation of microcli ne and its transformation into orthoclase. It also increases the crystalliz ability with the formation of non-uniform coarse-grained texture. A mixture of 0.5 % Cr2O3 and 1.5 % LiF causes a synergistic effect, where fine-grain ed microstructure is formed (due to Cr2O3) with orthoclase formation (due t o LiF) in addition to aluminous pyroxene and anorthite. The effects of vari ous Cr2O3 concentrations were discussed on the bases of the increased visco sity and separation of Cr2O3 and/or chromium-spinel phases, The effects of LiF were attributed to the role of fluorine ions in reducing the viscosity of the glasses. consequently facilitating crystallization of the structural ly more complex silicate in addition to favoring reaching thermodynamic equ ilibrium.