Uranium formate, decomposition

The disproportionation into forms with different oxo-content has been observed for the derivatives of uranium (VI) even at room temperature. Thus on reaction of U02C12 with KOBu inTHF it was U3O4(OBu )10 that was isolated and not the dioxocomplex. The authors of [277] supposed that its formation takes place due to decomposition of the initially formed U02(0Bu )2 according to the following scheme ... 

After reaction was complete and the inert gas sparge had removed the remaining NO2, the supernate was clear and colorless. The melt temperature was then lowered to 275°C, and nitric acid vapor was added to the melt as previously described. The uranium completely dissolved. The temperature was slowly increased to 420°C over one hour. The formation of solids was first apparent at 300°C to 320°C. Formation of the solids produced a large quantity of NO2 sparging removed this gaseous product. When the thermal decomposition was complete, the melt was again clear and colorless. 

Plutonium Dioxide in Molten Equimolar Sodium-Potassium Nitrate. The behavior of plutonium dioxide in molten alkali metal nitrates is an area of major concern. Claims that alkali metal plutonates are formed (1, 2, 3, 5, 6) are not substantiated by definitive analytical results. In some cases (5, 6), sodium peroxide was added as an oxidant to either an alkali metal nitrate melt (6) or to an alkali metal hydroxide melt (5). If the temperature is great enough, for example above 700°C, thermal decomposition of the nitrate melt produces peroxide species. Other studies (4, , 12, 17) do not claim formation of a plutonate species, but only state that an insoluble plutonium-containing compound exists. However, in all the references cited, the results were given for mixed uranium-plutonium dioxide definitive analytical results were not given. 

Removal of Residual Nitrate From UO Uranium trioxide produced by thermal decomposition of uranyl nitrate solution in a fluidized-bed contains a small amount (usually about 0.4 to 1.0 wt%) of residual nitrate. If UO is to be converted to UF for feed to a gaseous diffusion enrichment plant, the nitrate content of the UO must be reduced to meet UF purity specifications. Fluorination of UO in the presence of nitrate results in formation of nitrosyl and nitryl hexafluorouranates and heptafluorou-ranates (NO UF where x = 1 or 2 and y = 6 or 7) (2). These compounds form potentially troublesome solids. 

The decomposition of uranium(IV) formate in a marginally lower temperature interval could be described by the linear law with = 119 kJ mol and at 553 K ... 

Chemiluminescence of the uranium is observed not only in solution but also in the solid phase. For instance, solid-phase decomposition of the uranyl or europium (III) persulfate leads to the formation of U02 in excited state by energy transfer mechanism, whereas electron transfer is responsible for the uranyl ion excitation (through the intermediary uranium (V)) in the oxidation of U(S04)2 by XeFj. 

Unlike the stable uranium hexafluoride, which has a negative free energy of formation, plutonium hexafluoride is thermodynamically unstable. It dissociates to Fj and the relatively nonvolatile PUF4, althou the rate of thermal decomposition is very low at room temperature. If the specific alpha activity of plutonium is equivalent to that of Pu, the rate of decomposition of solid PuF at room temperature is controlled by radiolytic decomposition, amoimting to 1.5 percent per day [W2]. 

The reaction is reversible, and uranium hexafluoride is evolved on heating it is this factor that makes the addition compound useful for the recovery or purification of uranium hexafluoride. The dissociation pressure of the complex compound in the temperature range 80-320° is given by the equation log p = 10.88 — (5.09 X 103/ T), where p is the partial pressure of UF6 in millimeters of mercury, and T is the absolute temperature. A decomposition pressure of 1 atm is calculated to occur at 363°, and an enthalpy of formation of —23.2 kcal/mole of UF6 is deduced for the formation of the complex. The kinetics of the reaction between uranium hexafluoride and sodium fluoride have been studied by Massoth and Hensel (60, 61). The reaction appears to proceed initially at a rate determined by the surface area of the sodium fluoride, and then to become diffusion limited, The rate of the reaction is given by the expression k = 5.0 X 106 exp (—13,000// r) per hour the activation energy is thus 13,1 zk 0.2 kcal/mole of uranium hexafluoride. 

The decomposition of UFg with formation of metalhc uranium is a strongly endothermic process ... 

The reduction of U(COT)2 by hydrogen in the presence of the palladium catalyst (Pd/C) does not take place even after long periods, while the reaction of this compound with LiAlH4 in tetrahydrofuran solution for three days gives (after decomposition) a mixture of cyclooctatriene and COT in the ratio of 2/3 (Table 11.1, reference /). The oxidation reaction of [U(COT)2] leads to the formation of inorganic uranium compounds and free COT. 

Catalysis by chromium(n) involves the formation of a Cr —OH—Cr hydroxo-bridged species. Some preliminary data are also reported for the analogous nicotinamide system. A similar study involves the decomposition of a uranium(v)-chromium(ra) dinuclem complex in the presence of excess chromium(n). Approximate rate data for the uncatalysed reactions are shown in Table 12. 

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