J.T. Bell

Plutonium polymerization—I A spectrophotometric study of the polymerization of plutonium(IV)☆

Abstract Standard spectra of the Pu species have been observed and then used in the calculations of the distribution of Pu(III), (IV), (V), (VI) and polymeric Pu(IV) in solutions containing ∼ 0·009M total Pu at initial acidities of 0·1, 0·075, 0·06 and 0·04M HNO3, and at 25°, 50° and 75°C. the distributions of the Pu species are given for the four acidities at 25°C, and the distributions are given for the initial acidity of 0·075M HNO3 at 25°, 50° and 75°C. In these studies the polymer is not formed when the initial acidity is 0·1M and the temperature is 25°C, but the degree of polymerization continuously increases at the lower acidities and is almost quantitative when the initial acidity is 0·04M. The effect of an increasing temperature is to increase the rate of polymerization at the expense of the ionic Pu species. The amount of polymer formed at 75°C is ∼ 3·5 times as great as the amount at 25°C when the initial acidity is 0·075M.

Spectrophotometric studies of dioxouranium(V) in aqueous media. I. The perchlorate medium

The spectrum of UO2+ in aqueous perchlorate medium is described as two absorption bands at 9400 and 7380 A, with higher energy absorption beginning at ∼ 6500 A and increasing at shorter wavelengths to at least 5000 A. Thermodynamic values of K, ΔF°, ΔH° and ΔS° for the disproportionation of UO2+ were determined to be 7 × 104, −6·6 kcal, −18·6 kcal and −40 e.u., respectively. The value of S° for UO2+ was determined to be −11 e.u.

Photoreduction of the uranyl ion with laser light and ethanol—I: Quantum yields and medium effects☆

Abstract The photoreduction of the uranyl ion in sulfuric acid with laser light and ethanol is discussed. Quantum yields of ∼0·6 and 0·5 were measured for the production of U(IV) with an argon ion laser and with the neon laser, respectively. The effects of ethanol and sulfuric acid concentrations to increase the quantum yields are discussed.

Continuities in the spectra and structure of the actinyl ions

Abstract The band positions of the uranyl absorption spectrum have been diagramed to indicate the relative energy levels of the nonbonding orbitals for a molecular orbital model for the uranyl ion which has been defined as the actinyl core. The band positions of the transuranium actinyl spectra have been compared with the spacings between the positions of the uranyl bands. The results indicate that a single molecular orbital model can represent any of the actinyl ions when the uranyl ion is assumed to have the bonding orbitals exactly filled, and the transuranium actinyl ions are represented with the actinyl core and a progressive increase of electrons in the first two orbitals lying above the bonding orbitals.

Photoreduction of the uranyl ion with laser light and ethanol—II: The effects of temperature and uranyl concentration on the uranyl-ethanol reaction

Abstract The effects of temperature and UO 2 2+ concentration on the quantum yield for the photochemical reduction of UO 2 2+ to U 4+ with laser light and ethanol are described. As the temperature was increased, the quantum yield decreased through a minimum for the lower UO 2 2+ concentrations ( 2 2+ concentrations (≥0·5 M). The quantum yield at each temperature in the range 25 to 87°C was strongly dependent on UO 2 2+ concentrations less than 0·2 M, and almost independent of UO 2 2+ concentrations greater than 0·3 M. The essential considerations of the UO 2 2+ -ethanol dark reaction and of various effects on the UO 2 2+ absorbance at the specific argon laser wavelengths are also discussed. The UO 2 2+ -ethanol reaction will occur in the dark, especially at the higher temperatures, and the activation energy for the reaction was determined to be 10·2 kcal. The equilibrium quotient at 25°C for the UO 2 2+ -ethanol dark reaction was calculated to be ∼ 10 −7 . The effects of temperature and of UO 2 2+ concentration on the UO 2 2+ absorbance at the laser wavelengths are not equivalent to the same effects on the absorption at the peak wavelengths. It is suggested that the photochemical reduction of the U(V) intermediate plays a primary role in the mechanism for the photochemical reduction of UO 2 2+ to U 4+ .

Photoreduction of the uranyl ion with argon laser light and ethanol—III: The photochemical reduction of dioxouranium(VI) to dioxouranium(V)

Abstract The photochemical reduction of UO 2 2+ to UO 2 + wit argon laser light and ethanol was studied at 25 and 45°C. Quantum yields for the reduction were determined to be near unity for each temperature, and the yields were compared with those for the photochemical reduction of UO 2 2+ to U 4+ under similar experiment conditions. The results of experiments designed to photochemically reduce UO 2 + were inconclusive.

Plutonium polymerization—II Kinetics of the plutonium polymerization☆

Abstract Experimental data for the distribution of Pu(III), Pu(IV), Pu(V), Pu(VI) and Pu(IV) polymer have been used to calculate the rates of polymerization of Pu(IV). The rate of formation of Pu(IV) polymer is proportional to the first power of the Pu(IV) concentration and to the inverse square of the acidity as long as the solution contains a detectable amount of Pu(IV). When the concentration of Pu(IV) is not detectable, the rate of polymerization is proportional to the product of the square roots of the Pu(V) and (III) concentrations. When the concentrations of both the Pu(IV) and (III) are not detectable, the rate of polymerization is proportional to the product of the squares of the Pu(V) and the acid concentrations and to the inverse first power of the Pu(VI) concentration.

Plutonium polymerization—III The nitrate precipitation of Pu(IV) polymer☆

Abstract The precipitation of aged Pu(IV) polymer by HNO3, LiNO3, Al(NO3)3 and NaNO3 has been observed. With the exception of LiNO3, the precipitation of 0·00678M Pu(IV) polymer was independent of the source of NO3−, and the maximum amount of precipitated polymer occurred at 1·8 NO3−. Further addition of NO3− redissolved the polymer. The nitrate precipitation of Pu(IV) polymer has been analyzed according to the solubility product principle and has been found to closely resemble a solubility product mechanism.

A spectrophotometric study of the formation of americium thiocyanate complexes

Abstract The results of a spectrophotometric study of the formation of Am(III) thiocyanate complexes at an ionic strength of 1·0 M enabled calculation of β1 = 5·79 (σ = 0·33) and β2 = 6·77 (σ = 1·05) for Am(SCN)2+ and Am(SCN)2+, respectively. Additional studies of Am(III)in KSCN solutions of variable ionic strength suggested that Am(III) is strongly complexed and provided qualitative evidence for the existence of anionic complexes in 5–10 M KSCN. The “effective stability constant” approach was applied to the data at low KSCN concentrations to calculate β 1 ∗ = 7·6 (σ =2·5) for Am(SCN)2+.

Photochemical reactions of aqueous plutonium systems—II☆

Abstract The photochemical shift of the Pu 4+ disproportionation equilibrium in aqueous perchloric acid solutions has been measured and shown to be reversible. Ratios of equilibrium quotients between light and dark conditions have been measured for 0.01 M Pu ion concentrations in 0.53 to 1.24 N acid solutions exposed to 0.5 Watt of UV light. The photodecomposition of time- and temperature-aged Pu(IV) polymers in perchloric and nitric acid solutions have been examined as a function of aging conditions. Effects similar to those seen previously for fresh polymers have been observed in the aged perchloric acid solutions.