Thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate. Part 1. Mechanism

The thermal decomposition of aqueous manganese nitrate solutions in air or nitrogen proceeds in three steps: (i) partial evaporation of water to a concentrated solution containing equimolar amounts of water and Mn(NO3)2, (ii) a first decomposition step in which the residual water evolves and part of the Mn(NO3)2 decomposes to MnO2, and (iii) a second decomposition step in which the remaining Mn(NO3)2 decomposes to MnO2. Decomposition of part of the Mn(NO3)2 in the first step is caused by the presence of water (vapour) which accelerates the decomposition of anhydrous Mn(NO3)2 and lowers the temperature at which this reaction starts. Without water [anhydrous Mn(NO3)2] only one decomposition step occurs. Off-gas analysis with mass spectrometry, IR spectroscopy and chemiluminescence showed NO2 to be the main gaseous product, NO being formed in much smaller amounts. amounts.