The thermal decomposition of bis(trispyrrolidino phosphine oxide) tetranitrato uranium(IV)

Abstract

The thermal properties of U(NO 3) 4 · 2 L (L = trispyrrolidino phosphine oxide) have been examined using thermogravimetry, differential scanning calorimetry and evolved gas analysis by repetitive gas chromatography. Decomposition of single crystals begins around 360 K, approximates to U(NO 3) 4 · 2 L(s) → UO 2(NO 3) 2 · 2 L(s) + gases and is strongly exothermic (Δ H = −154 ± 4 kJ mole −1). The shape of the exotherm is dependent upon sample mass and self-heating which induces melting. Most consistent results were obtained by reducing self-heating by crimping sample pans and using helium as carrier gas. Grinding of the crystals altered the shape of the exotherm and reduced the value of Δ H to −108 ± 6 kJ mole −1. From EGA results it is concluded that the gaseous products contain N 2, N 2O, NO AND NO 2 as well as some H 2O and CO 2. It is suggested that the primary decomposition product is NO 2 and that this oxidizes some ligand, L, to produce the H 2O and CO 2 and to form the lower oxides of nitrogen. The apparent activation energy for the initial stages of decomposition of crystals (360–385 K) was estimated from isothermal DSC curves as 157 ± 5 kJ mole −1. For ground material (<100 mesh) the activation energy (370–395 K) was increased to 185 ± 14 kJ mole −1.