Effect of Silica Coating on Geothite Dehydration Process

The dehydration process of SiO₂ coated α-FeOOH has been investigated by DTA, TG, HTXRD and TEa measurementS. The kinetic parameters caculated from DTA and TG curves indicate that the dehydstien proess of SiO₂ coatde α-FeOOH is about first order reaction, and its apparent activation energy is higher than that of the untreated α-FeOOH. The results from HTXRD and TEM measurements show that the thermal decomposition of α-FeOOH into α-Fe₂O₃ leads to the simultaneous formation of the crystal nuclei and of the slit—shaped micropores, which may be the main reason to broad X-ray diffraction lines. With the temperature increasing, the microporous texture is changed into a mesoporous or macroporous texture, and it almost disappears at the temperature above 800℃ or so. In the case of silica coated αFeOOH, its thermal variation temperature shifts to the high temperature.