This research was carried out as a part of the study on the synthetic topaz, (Al
2SiO
4F
x(OH)
2-x).
Mixtures of SiO
2 and Al
2O
3 gels, and AlF
3 corresponding to compositions, Al
2SiO
4F
x(OH)
2-x, where
x=1.0, 1.5 and 2.0 were treated in temperatures ranging from 400° to 1500°C in pressures ranging from 10 to 50 kbar using sqeezer and girdle type high pressure apparatus.
The treated sample was suspended in heavy solution to separate the impurities with a centrifuge.
The fluorine content of synthetic topaz crystal was increased with increasing the fluorine content of the starting mixture,
x, and with increasing the temperature and pressure of synthesis. Refractive index and lattice constants were decreased with increasing the fluorine content of topaz crystal according to the linear relationship, but specific gravity somewhat decreased.
The application of infrared spectrophotometry to the determination of OH content of synthetic topaz making use of OH spectrum at 3, 620cm
-1, was found to give a fairly good result. Results of differential thermal analysis and the heating-loss curve were found to agree very much with each other. The fluorine of topaz crystal was lost in temperatures ranging from 800° to 900°C.
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