Thermolysis mechanism of chromium nitrate nonahydrate and computerized modeling of intermediate products
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Thermal decomposition of chromium nitrate nonahydrate was studied by thermal analysis, differential scanning calorimetry, infrared spectroscopy, and high temperature X-ray diffraction, so that mass losses were related to the exactly coincident endothermic effects and vibrational energy levels of the evolved gases. The thermal decomposition of chromium nitrate is a complex process, which begins with the simultaneous dehydration and concurrent condensation of 4 mol of the initial monomer Cr(NO3)3·9H2O. Soon after that, the resulting product Cr4N12O36·31H2O gradually loses water and azeotrope HNO3 + H2O, and is transformed into tetrameric oxynitrate Cr4N4O16. At higher temperatures, the tetramer loses N2O3 and O2 and a simultaneous oxidation of Cr(III) to Cr(IV) occurs. The resulting composition at this stage is chromium dioxide dimer Cr4O8. Finally, at 447 °C the unstable dimer loses oxygen and is transformed into 2Cr2O3. The models of intermediate amorphous compounds represent a reasonably good approximation to the real structures and a proper interpretation of experimental data.
KeywordsChromium nitrate Thermal decomposition Computer modeling
The authors are indebted to CNPq (Brazilian agency) for financial support and to Dr. Heberton Wender for fruitful discussions and technical assistance.
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