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Stoichiometry of Fluorotopaz and of Mullite Made from Fluorotopaz
Author(s) -
Moyer John R.,
Rudolf P. R.
Publication year - 1994
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1994.tb07275.x
Subject(s) - mullite , whiskers , stoichiometry , solid solution , materials science , classification of discontinuities , mineralogy , analytical chemistry (journal) , diffraction , chemistry , composite material , ceramic , metallurgy , mathematics , chromatography , mathematical analysis , physics , optics
Mixtures of alumina and silica containing 68–78 wt% alumina react above 600°C with 0.5 mol of SiF 4 per mole of alumina to form fluorotopaz. High‐resolution X‐ray powder diffraction data were used to determine very accurate cell parameters of fluorotopaz as a function of 1 wt% compositional increments. The samples containing 69–76 wt% A1 2 O 3 were found to have a linear cell parameter relationship. Compositions outside that range show discontinuities in the cell parameters, indicating solid solution behavior between 69 and 76 wt% alumina. Within this range the composition of fluorotopaz may be written 2A1 2 O 3 · x SiO 2 · SiF 4 where 1.07 x 1.53. Pyrolysis of all compositions of fluorotopaz solid solution yields mullite whiskers containing 76.1 wt% alumina (65.2 mol%).