Effect of LiF addition on the phase transition of sinterable β-spodumene precursor powders prepared by a sol-gel process

Abstract

β-Spodumene (Li₂O · Al₂O · 4SiO₂, LAS₄) precursor powders were obtained through a sol-gel process using Si(OC₂H₅)₄, Al(OC₄H₉)₃, and LiNO₃ as starting materials and LiF as a sintering aid. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy with a wavelength dispersive spectrometer, and electron diffraction analysis were utilized to study the phase transition of the β-spodumene glass–ceramics prepared from the gel-derived precursor powders with LiF additive. For the LAS₄ precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4.0 wt% LiF and sintered at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution and β-eucryptite (Li₂O · Al₂O₃ · 2SiO₂, LAS₂) solid solution. When the LiF content was 5.0 wt% and the sintering process was carried out at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution, β-eucryptite solid solution (triclinic), and eucryptite [rhombohedral (hex.)]. When the LiF addition attains 3.0 wt%, the fully densified grains are formed, accompanied with an increase in grain size for LiF addition. At the triple junction of grain boundaries a second phase segregates which is identified to be β-spodumene solid solution. In the sintering period of LAS₄ precursor powders with LiF additive, the grains converted to β-eucryptite solid solution and β-spodumene solid solution remains at the grain boundaries.