Determination of the water content in muscovites containing large amounts of fluorine by karl fischer titration after fusion with silicon dioxide

Abstract

Complete release of water (or of hydrogen in the lattice which is finally released as water) from muscovite containing a large amount of fluorine, requires heating above 1500°C or addition of an appropriate flux. Experimental data from differential thermal analysis, x-ray diffraction patterns and dehydration curves showed that silicon dioxide is a useful flux. Samples are mixed with a 3 : 1 (weight) ratio of silicon dioxide in a platinum crucible and heated inductively in a nitrogen stream at 1200°C. The water released is absorbed in anhydrous (1 + 1) methanol—1, 2-ethanediol and titrated by the Karl Fischer method. For a representative muscovite sample, the water contents were 4.26 ± 0.03% at 1300—1400°C and 4.35 ± 0.08% above 1500°C in the absence of silicon dioxide. When silicon dioxide was added as described, the mean result was 4.33 ± 0.01% at 1200°C (95% confidence level) with a standard deviation of 0.015 and a coefficient of variation of 0.35%.