Differential pulse voltammetry as an in situ monitoring technique for the thermal-decomposition kinetics of nitrate melts

Abstract

Differential pulse voltammetry has been used to detect NO^–₂ at trace level in fused nitrates. A detection limit of 10 ppb was estimated. The technique was employed for studying the thermal-decomposition kinetics of molten nitrates under controlled experimental conditions. A pseudo-zero-order kinetic process was found, characterized by a kinetic constant of 7.6 × 10^–11 mol kg^–1 s^–1 at 538 K and by an apparent activation energy of 39 ± 2 kJ mol^–1 in the temperature range 510–620 K.

The suggested reaction mechanism is 2 NO^–₃⇌ NO^–₃+ NO^–*₃ NO^–*₃→ NO^–₂+½O₂ where the first reaction seems to represent an equilibrium prior to the second rate-determining reaction.

The equilibrium constant and the value of ΔH for the reaction NO^–₃= NO^–₂+½O₂ were also calculated from equilibrium data and compared with previous literature parameters estimated by indirect or approximate methods.