Large scale melt synthesis in an open crucible of Na-fluorohectorite with superb charge homogeneity and particle size

• Published in: Applied clay science 2010-03, Vol.48 (1), p.39-45
• Main Authors: Kalo, Hussein, Möller, Michael W., Ziadeh, Mazen, Dolejš, David, Breu, Josef
• Format: Article
• Language: English
• Subjects: CHARGE DENSITY; Charge homogeneity; Crucibles; FABRICATION; FLUORIDES; Fluorohectorite; FLUXING; Homogeneity; Large scale synthesis; Melt synthesis; Melts; Particle size; PARTICLE SIZE AND SHAPE; SCANNING ELECTRON MICROSCOPY; Synthesis
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2009.11.014

Sodium fluorohectorite Na 0.6[Mg 2.4Li 0.6]Si 4O 10F 2 was synthesized from the melt in an open glassy carbon crucible at 1265 °C under argon flow. A glass (Na 2O–Li 2O–SiO 2) precursor was used as a fluxing agent in order to maintain a low vapor pressure of volatile fluorides and sustain a low silica activity, which inhibits the formation of silicon fluoride gases and promotes the fluorine solubility in the melt. To minimize the loss of volatile fluorine compounds the pre-synthesized alkali silicate glass was heated together with additional raw materials needed in a high frequency induction furnace rapidly from 800 °C up to 1265 °C and then kept at this temperature for a short period of time (15 min). The synthesis method can easily be scaled to batches larger than 1 kg. The Na 0.6-fluorohectorite obtained stands out by (i) phase purity as checked by X-ray powder diffraction (PXRD), (ii) a superb homogeneity of the charge density as demonstrated by stepwise hydration behavior followed by in-situ PXRD in a humidity chamber and the Lagaly method with alkylammonium exchange ( Mermut and Lagaly, 2001), (iii) a high cation exchange capacity (CEC) of 136 meq/100 g as determined by the copper complex ([Cu(trien)] 2+) method, and (iv) extreme lateral extensions with a median value of the particle size of 45 μm as measured by static laser light scattering (SLS) which was confirmed by scanning electron microscopy (SEM).