Radiation chemistry of aqueous solutions of hydrazine at elevated temperatures Part 2.—Solutions containing oxygen

Abstract

The rate of reaction for has been measured by pulse radiolysis up to 110°C in aqueous solutions of hydrazine having a pH of 10.3 at room temperature. The values of the kinetic parameters are k ₁ =(3.8±0.1)×10 ⁸ dm3 mol ^-1 s ^-1 at 20°C and E _act =5.6±2.1 kJ mol ^-1 . This small activation energy is interpreted in terms of the formation of an intermediate adduct N ₂ H ₃ O ₂ which is in a pre-equilibrium with the reactants and whose stability with respect to dissociation back to the reactants decreases with increasing temperature. The rate of the thermal reaction has also been determined up to 110°C by measuring the decrease in k ₁ with increasing age of the oxygenated hydrazine solution in order to monitor the depletion of [O ₂ ]. The kinetic parameters are k ₁₂ =(1.2±0.8)×10 ^-3 dm3 mol ^-1 s ^-1 at 20°C and E _act =70±5 kJ mol ^-1 . γ-Radiolysis studies show that N ₂ H ₄ is destroyed in a short chain reaction in oxygenated hydrazine solutions with G(-N ₂ H ₄ )∝(dose rate) ^-0.5 , indicating chain termination by radical–radical reactions. Added EDTA shortens the chain but does not alter the form of the rate law, indicating that metal ions present as impurities accelerate the chain-propagating reactions more than the termination steps. In each case the chain length increases as ca. [N ₂ H ₄ ] ^0.5 .