Thermal decomposition characteristics of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide-tri n-butyl phosphate–nitric acid systems

Abstract

Thermal stability of neat octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OΦD[IB]CMPO) and TRUEX solvent composition (0.2M OΦD[IB]CMPO-1.2M tri n-butyl phosphate-in n-dodecane) in the presence and absence of nitric acid has been studied in ambient air in a closed vessel, employing an adiabatic calorimeter. Enthalpies and kinetic parameters for the decomposition reaction were derived wherever possible and are reported for the first time. Neat OΦD[IB]CMPO was found to be thermally stable up to 633 K and exhibited an exothermic decomposition later. It decomposed at lower temperatures (376–386 K) depending on the nitric acid concentration. The exothermic rise in temperature and pressure increased exponentially, while activation energies exhibited exponential decrease for the decomposition reactions with increase in nitric acid content. TRUEX solvent was found to be stable up to 661 K in the absence of nitric acid while in the presence of 8 and 4M HNO3, it decomposed between 387 and 413 K. All these samples on decomposition formed incompressible gases and viscous black liquids. The results also indicate that the neat OΦD[IB]CMPO and the TRUEX solvent are thermally more stable than neat tri n-butyl phosphate (TBP), PUREX solvent (1.1M TBP/n-DD), neat diamyl amyl phosphonate (DAAP) and 1.1M DAAP/n-DD, triisoamyl phosphate (TiAP) and 1.1M TiAP/n-DD.