The Effects of HCrO₂ Seed Crystals, Water and Oxygen Pressure on the Dissociation of CrO₃

Abstract

With DTA, TGA and X-ray diffraction analysis of the phases obtained in a closed vessel in the temperature range 300-600°C, it was postulated that the dissociation sequence of chromium trioxide into intermediate chromium oxides was CrO₃→Cr₃O₈→X-phase→Cr₂O₅→CrO₂→Cr₂O₃. Although the X-phase was not characterized enough, it was considered to be a new intermediate phase (Cr:O=1:2.49) different from Cr₂O₅.
Seed crystal (HCrO₂), water and oxygen pressure had effects on the reaction. With water, phase of Cr₂O₅ was stabilized At elevated oxygen pressure beforehand (up to 10kg/cm²), phase of Cr₃O₈ was stabilized and formation of Cr₂O₃ was retarded.
Adding HCrO₂ for seed crystals gave rise to change in the reaction sequence, the sequence being CrO₃→Cr₂O₅→CrO₂→Cr₂O₃. Further, seed crystals decreased the effects of water and oxygen pressure on the reaction.