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Decomposition Pathways for Aqueous Hydroxylammonium Nitrate Solutions: a DFT Study

Izato Y., Koshi M., Miyake A.

Central European Journal of Energetic Materials

2017

Vol. 14, no. 4

888--916

Hydroxylammmonium nitrate (hydroxylamine nitrate, HAN) is one of the most promising candidates as a replacement for commonly used liquid mono-propellants such as hydrazine. The reaction pathways involved in the initial and the catalytic decomposition of HAN in aqueous solution were determined using quantum chemistry calculations incorporating solvent effects. Optimized structures were obtained for the reactants, products and transition states at the ωB97XD/6-311++G(d,p)/SCRF = (solvent = water) level of theory and the total electron energies of these structures were calculated at the CBS-QB3 level of theory. In the initial decomposition, the ion-neutral NH3OH+-HNO3 reaction, the neutral-neutral NH3O-HNO3 reaction and the HNO3 self-decomposition pathways were all found to have reasonable energy barriers, with values of 91.7 kJ/mol, 88.7 kJ/mol and 89.8 kJ/mol, respectively. The overall reaction resulting from any of these pathways can be written as: HAN → HONO + HNO + H2O. The ionic reaction is dominant during the initial decomposition of HAN in aqueous solution because NH3OH+ and NO3– are the major species in such solutions. We also developed six catalytic mechanisms and each of these schemes provided the same global reaction: NH2OH + HONO → N2O + 2H2O. The t-ONONO2 oxidizing scheme is the most plausible based on the energy barrier results.

Zastosowanie metod kwantowych w badaniu ścieżek reakcji w CVD

Tkacz-Śmiech K., Jonas S.

Inżynieria Materiałowa

2011

Vol. 32, nr 4

776-780

Praca podejmuje problem termodynamicznych aspektów reakcji chemicznych, jakie decydują o przebiegu procesów CVD. Opisano sposób wyznaczania parametrów termochemicznych z zastosowaniem metod kwantowych. Przedstawiono teoretyczne podstawy metody obliczeń z uwzględnieniem kluczowego znaczenia funkcji sumy statystycznej. Wskazano przyczynki do energii cząsteczki, które należy uwzględnić w obliczeniach ciepła i energii swobodnej reakcji. Przykładowe obliczenia wykonano z zastosowaniem programu Gaussian03W dla wybranych reakcji o istotnym znaczeniu dla procesów CVD. Pokazano również, że metody kwantowe stanowią efektywne narzędzie w przewidywaniu ścieżek reakcji.

This article concerns thermodynamic aspects of chemical reactions which determine CVD processes. A way of calculation of thermochemical parameters with application of quantum methods is presented. Theoretical basis of computational model are described and key role of partition function is discussed. The contributions to the molecular total energy which are to be included into reaction heat and free energy calculations are indicated. Exemplary results of calculations performed with use of Gaussian03W program for some typical CVD reactions are presented. It is also shown that quantum methods provide effective tool in predicting reaction pathway.