INTERCONVERSION OF CRO2 FORMED BY DECOMPOSITION OF CHROMIUM(III) NITRATE NONAHYDRATE

The products of the decomposition of chromium(III) nitrate nonahydrate (CNN) and interconversions occurring in the system CrO2-CrOOH have been investigated using thermal analysis, mass spectrometry, X-ray powder diffraction, and magnetic resonance. The studies indicate that changes in the conditions of CNN calcination, especially in the temperature, greatly influence the ratio of Cr(IV) to Cr(III) oxides in the products. CrO2 formed during slow heating to ca. 350 degrees C is very stable and its complete transformation into Cr2O3 requires a temperature higher than 600 degrees C. The rapid crystallization of the amorphous products of CNN calcination, occurring at ca. 380 degrees C, leads to the decomposition of all intermediates during this strongly exothermal reaction, finally resulting in Cr2O3. The interconvertability of the components of the redox cycle CrO2-CrOOH was proven experimentally. Due to its unique characteristics, this redox cycle is suggested for the difficult identification of CrO2 in amorphous chromium-oxygen systems. (C) 1995 Academic Press, Inc.