Thermal stability of nitric acid solutions of acetohydroxamic acid

The thermal stability of a solution of 12 mol center dot L-1 nitric acid with 50 g center dot L-1 acetohydroxamic acid has been studied. It has been established that weak exothermic oxidation processes occur in solutions at atmospheric pressure at temperatures below the boiling point, accompanied by gas evolution. Under these conditions, the specific volume of evolved gases, the onset temperature of the exothermic reaction, the induction period, the duration of the exothermic process, and the self-heating value have been determined. In the adiabatic mode, the kinetic parameters of a thermal explosion have been determined taking into account the thermal energy compensation function, and it has been shown that under these conditions this reaction proceeds in an autocatalytic mode. Such kinetic parameters as activation energy and pre-exponential factor have been calculated. The influence of the heating rate of the solution and its exposure time on the onset temperature of the exothermic reaction has been studied. The values of heat release for the concentration of nitric acid, which simulates the initial stages of evaporation of aqueous solutions, have been determined. It has been shown that even at low concentrations of nitric acid of 1.6 and 3.2 mol center dot L-1, an exothermic reaction occurs with a noticeable heat release, while the onset temperature of the exothermic reaction of the solution with 3.2 mol center dot L-1 HNO3 is lower than its boiling point. The data obtained are necessary to assess the safe conditions for the evaporation of nitric acid solutions containing acetohydroxamic acid.