A sintering study on the β-spodumene-based glass ceramics prepared from gel-derived precursor powders with LiF additive

Beta-spodumene (Li(2)O(.)Al(2)O(3)(.)4SiO(2), LAS) powders were prepared by a sol-gel process using Si(OC2H5)(4), A1(OC4H9)(3), and LiNO3 as precursors and LiF as a sintering aid agent. Dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED) were utilized to study the sintering, phase transformation, microstructure, and properties of the)beta-spodumene glass-ceramics prepared from the gel-derived precursor powders with and without LiF additives. For the LAS precursor powders containing no LiF, the only crystalline phase obtained was beta-spodumene. For the pellets containing less than 4 wt pct LiF and sintered at 1050 degreesC for 5 hours the crystalline phases were beta-spodumene and beta-eucryptite (Li(2)O(.)A1(2)O(3)(.)2SiO(2)). When the LiF content was 5 wt pct and the sintering process was carried out at 1050 degreesC for 5 hours, the crystalline phases were beta-spodumene, beta-eucryptite (triclinic), and eucryptite (rhombohedral (hex.)) phases. With the LiF additive increased from 0.5 to 4 wt pct and sintering at 1050 degreesC for 5 hours, the open porosity of the sintered bodies decrease from 30 to 2.1 pct. The grains size is about to 4 to 5 mum when pellect LAS compact contains LiF 3 wt pct as sintered at 1050 degreesC for 5 hours. The grains size grew to 8 to 25 mum with a remarkable discontinuous grain growth for pellet LAS compact contain LiF 5 wt pct sintered at 1050 degreesC for 5 hours. Relative densities greater than 90 pct could be obtained for the LAS precursor powders with LiF > 2 wt pct when sintered at 1050 degreesC for 5 hours. The coefficient of thermal expansion of the sintered bodies decreased from 8.3 X 10(-7) to 5.2 X 10(-7)degreesC (25 degreesC to 900 degreesC) as the LiF addition increased from 0 to 5 wt pct.