Thermolysis mechanism of chromium nitrate nonahydrate and computerized modeling of intermediate products
- 246 Downloads
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.
- 1.Melnikov P, Nascimento VA, Zanoni Consolo LZZ. Thermal decomposition of gallium nitrate hydrate and modeling of thermolysis products. J Therm Anal Calorim. 2011;135:1117–21.Google Scholar
- 3.Melnikov P, Nascimento VA, Arkhangelsky IV, Zanoni Consolo LZZ. Thermal decomposition mechanism of aluminum nitrate octahydrate and characterization of intermediate products by the technique of computerized modeling. J Therm Anal Calorim. 2012. doi: 10.1007/s10973-012-2566-1.
- 9.NIST Chemistry WebBook, NIST Standard Reference Database Number 69: www.http//webbook.nist/chemistry. Accessed 12 Dec 2012.
- 11.Young DC. Computational chemistry: a practical guide for applying techniques to real-world problems. New York: Wiley; 2001.Google Scholar
- 12.http://www.avogadro.openmolecules.net/. Accessed 21 Nov 2012.
- 13.Wesley WW, Roger GS. The fusion temperatures of the rare earth chloride and nitrate hydrates. Texas J Sci. 1961;8:231–4.Google Scholar
- 15.Komissarova LN. Inorganic and analytical chemistry of scandium. Moscow: URSS; 2001.Google Scholar
- 17.Rao JR, Gayatri R, Rajaram R, Nair BU, Ramasami T. Chromium(III) hydrolytic oligomers: their relevance to protein binding. Biochim Biophys Acta. 1999;1492:595–602.Google Scholar
- 18.Speight J. Lange`s handbook of chemistry, 16th ed. McGrow-Hill, 1999.Google Scholar
- 19.Gray RJ. The normal oxidation-reduction potentials of the system hexavalent-trivalent chromium-tetravalent chromium. PhD Thesis, Faculty of Pure Science, Columbia University. N.Y. 1940.Google Scholar
- 20.Rao CNR, Rao GVS, Transition metal oxides. Crystal chemistry, phase transition and related aspects, U.S. Department of Commerce, National Bureau of Standards, U.S. Government Printing Office. Washington, 1974.Google Scholar
- 21.Wells AF. Structural Inorganic Chemistry. 5th ed. London: Clarendon, Oxford University Press; 1984.Google Scholar
- 22.Hammond Ch. The Basics of crystallography and diffraction. 3rd ed. London: Oxford University Press; 2009.Google Scholar