Formation pathway, structural characterization and optimum processing parameters of synthetic topaz – Al2SiO4(OH,F)2 – by CVD

• Published in: Journal of solid state chemistry 2015-10, Vol.230, p.350-356
• Main Authors: Trujillo-Vázquez, E., Pech-Canul, M.I.
• Format: Article
• Language: English
• Subjects: CVD; Lattice parameters; Optimal process parameters; Topaz synthesis
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2015.07.030

A novel synthesis route for topaz (Al2SiO4(OH,F)2) by chemical vapor deposition (CVD) using Na2SiF6 as solid precursor was developed. Synthesis tests were conducted with and without a flow of nitrogen, positioning the Al(OH)3 substrate at 0° and 90° with respect to the gas flow direction, at 700 and 750°C, for 60 and 90min, respectively. It was found that topaz is synthesized through two pathways, directly and indirectly, involving a series of endothermic and exothermic, heterogeneous and homogeneous reactions between Al(OH)3 and SiF4(g). Analytical structural determination confirmed existence of orthorhombic polycrystals with lattice parameters of a =4.6558Å, b=8.8451Å and c=8.4069Å. According to ANOVA, while temperature, time and interaction of substrate angular position with atmosphere (P×A) are the parameters that most significantly influence the variability in the amount of topaz formed – equivalent contributions of 31% – topaz lattice parameters are mostly impacted by the same factors (T, t, P, A), but without the interaction factor. The projected amount of topaz is in good agreement with that obtained in confirmation tests under optimal conditions: Al(OH)3 substrate compact placed at 0°, treated at 750°C for 90min in the absence of N2. [Display omitted] •Topaz synthesis as a unique phase by CVD, using solid precursor Na2SiF6 is feasible.•Two pathways, a series of endothermic/exothermic, heterogeneous/homogeneous reactions.•Crystal structure, orthorhombic polycrystals: a =4.6558 Å, b=8.8451 Å, c=8.4069 Å.•Anova: amount of topaz formed and lattice parameters are impacted by same factors.•Projection of topaz quantity in good agreement with those from confirmation tests.