The thermal oxidation of tetrachlorobis(N,N,N′,N′-tetramethylurea)uranium(IV)

Abstract

The thermal oxidation of UCl 4·2tmu (tmu  N,N,N′,N′-tetramethylurea) was studied in an oxygen atmosphere by using thermogravimetry and differential scanning calorimetry. Thermogravimetric results indicated that the oxidation reaction can be described as: ▪ ▪ This reaction started at ±150 °C and was completed at ±250 °C and (ii) UO 2Cl 2tmu + O 2 → U 3O 8 + volatile products over the temperature range ±260 °C to ±480 °C. Only the first reaction was studied fundamentally. The profiles of the TG and DTG curves, Fig. 1, suggested that the oxidation and dissociation reactions are occurring simultaneously. Isothermal measurements were performed over the temperature range 180–205 °C. The data suggested that the mechanism for the reaction can be described by the equation 1 - (1 - α) 1 2 = kt where α = fraction decomposed. Using this equation an apparent activation energy was calculated and found to be 164 kJ mol −1. The DSC trace obtained for the oxidation reaction gave series of exothermic peaks over the temperature range 175–500 °C. The two overlapping peaks between 178 and 275 °C were assigned to the reaction, ▪ The enthalpy of the reaction was estimated as −271 kj mol −1. The total enthalpy i.e. for the reaction ▪ was estimated as −765 kJ mol −1. Those results as well as isothermal measurements which are carried out in a argon atmosphere suggested that although the dissociation and oxidation reactions seem to occur simultaneously, the dissociation of the neutral ligand is a prerequisite for the reaction to occur.