Mechanism of Np(VI) oxidation with ozone in alkaline solutions

Bubbling of an ozone-oxygen mixture containing 0.1?C0.5 vol % O₃ at a rate of 15?C20 l h^?1 through 13 ml of a 2 × 10^?5?1 × 10^?4 M solution of Np(VI) in 0.1 and 1 M LiOH leads to the formation of Np(VII). The initial rate increases approximately in proportion to [Np(VI)] and [O ₃ ^gas ]^0.5. Up to 80% of Np(VI) is oxidized at maximum. At the O₃ concentration in the gas phase increased to 1?C4 vol %, Np(VI) is oxidized completely. Under the same conditions, Np(VI) in a concentration of (1?C5) × 10^?3 M is oxidized to almost 100%. Analysis of published data and additional experiments on the reaction of O₃ with Np(VI) ions in LiOH solutions allow a conclusion that the ozonation involves the reactions O₃ + OH^? = HO ₂ ^? + O₂, O₃ + HO ₂ ^? + OH^? = O ₃ ^? + O ₂ ^? + H₂O, and O₃ + O ₂ ^? = O ₃ ^? + O₂, followed by O ₃ ^? + NpO₂(OH) ₄ ^2? = O₂ + NpO₄(OH) ₂ ^3? + H₂O. In addition, HO ₂ ^? reduces Np(VII) and Np(VI) and reacts with O ₃ ^? . Certain contribution is made by the reaction Np(VI) + O₃ = Np(VII) + O ₃ ^? . The dependence of the Np(VII) accumulation rate on [O ₃ ^gas ]^0.5 was interpreted in terms of the concept of a heterogeneous-catalytic process.     

Interaction of tetravalent actinides and Np(V) with some hydroxy carboxylic acids

Interaction of actinides(IV) with hydroxyisobutyric acid (HHIB) in aqueous solutions and in the course of crystallization of solid compounds was studied. The complexes ML _n ^(4-n)+ (M = U, Np, Pu; L^? is hydroxyisobutyrate anion; n = 1, 2, 3) exist in solution. Their apparent stepwise stability constants K?? _i were measured, and the overall concentration stability constants ??₃ of the complexes ML ₃ ⁺ were calculated. For U(IV) and Np(IV), log??₃ is close to 13.3?C13.4, and for Pu(IV), log??₃ = 14.5 ± 0.9 (ionic strength I = 0.1?C0.3). In the course of crystallization in air, complexes of U(IV) with hydroxyisobutyric acid, as well as those with citric acid, undergo oxidative degradation, which can be accompanied by complete oxidation of U(IV). The crystalline compounds formed in the process are oxalates of U(IV) or U(VI). The complexation of Np(V) with HHIB was studied. NpO ₂ ⁺ forms with HHIB the complexes NpO₂L and NpO₂L ₂ ^? . Their concentration stability constants are logK ₁ = 2.04 ± 0.15 and logK ₂ = 0.71 ± 0.10 (I = 0.4), i.e., log??₂ = 2.75 ± 0.25.     

Particle Concentration Measurements in Process Liquids Using Light-Scattering Techniques

A mathematical model is presented to compensate for the optical coincidence of particles in a liquid particle counter (LPC) detector, which detects particles by means of light scattering. It compensates for the optical coincidence of particles (1) belonging to the same size category, (2) belonging to different size categories, or (3) promoted from two particles to a single particle, which belongs to the larger particle size category. With this improved method, particle concentration decays are studied in a continuous stirred tank reactor where the liquid is recirculated and filtered. Furthermore, it is found that the latex sphere-calibrated LPC makes large errors in particle sizing, which is caused by the differences between the refractive index (n) of the particles under study: polystyrene latex spheres (0.112–0.204 µm), silica (0.16 and 0.33 µm), and Si₃ N₄ (< 0.4 µm). This implies that many particle-removal studies based on light-scattering detection methods become unreliable.     

A single crystal X-ray diffraction study of Na4(UO2)4(i-C4H9COO)11(NO3)·3H2O

Synthesis and the results of IR and single crystal X-ray diffraction study of Na₄(UO₂)₄(i-C₄H₉COO)₁₁·(NO₃)·3H₂O are reported. The crystals are monoclinic; the unit cell parameters at 100 K are as follows: a = 13.697(2), b = 20.285(3), c = 15.991(3) Å, β = 103.760(3)°, space group P2₁, Z = 2, R = 0.0650. The uraniumcontaining structural units are mononuclear moieties [UO₂(i-C₄H₉COO)₃]^? and [UO₂(NO₃)(i-C₄H₉COO)₂]^?, belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = i-C₄H₉COO^? and NO ₃ ^? ) of uranyl complexes. The IR data are consistent with the results of the single crystal X-ray diffraction study. The influence of the carboxylate ligand volume on the structure of Na[UO₂L₃]·nH₂O crystals (L = acetate, n-butyrate, isovalerate ion) is analyzed.     

Dipole moment of water clusters and the greenhouse effect

The dipole moments of neutral water clusters (H₂O) _n (n ≤ 100) have been simulated using the molecular dynamics method within the framework of the Stillinger-David polarization model. The spectral characteristics of emission from clusters have been calculated. It is shown that water clusters generated by flying vehicles in the Earth’s troposphere can initiate a trigger mechanism that enhances the greenhouse effect via the reactions CO ₂ ^* + (H₂O) _n → CO₂ + (H₂O) _n ^(*) → CO₂ + (H₂O) _n + hv.     

Behavior of Pu(VI) and Np(VI) in malonate solutions

Complexation of PuO ₂ ²⁺ in solutions containing malonate anions C₃H₂O ₄ ^2? (L^2?) is studied by spectrophotometry. Mono-and bimalonate complexes are formed. The monomalonate complex was isolated as PuO₂L · 3H₂O. It is isostructural to UO₂L · 3H₂O and forms rhombic crystals with the unit cell parameters a = 9.078(2), b = 7.526(2), and c = 6.2005(15) Å, space group Pmn2₁. The electronic absorption spectrum of the monomalonate complex is characterized by a strong band at 843 nm. In malonate solutions, Pu(VI) is slowly reduced to the pentavalent state even in the cold. The reduction of Np(VI) is considerably faster and more sensitive to increasing temperature. Some kinetic features of the reduction are discussed.     

Effect of nonideality on the collisional recombination coefficient in an ultracold plasma

The effect of nonideality on the dependence of the collisional recombination coefficient α in an ultracold plasma on the temperature T _e and density n _e of electrons is discussed. It has been shown that the dependence of the recombination coefficient on the density and temperature α ? n _e ² T _e ^?9/2 characteristic of a weakly nonideal plasma is transformed to α ? n _e ^1.2 T _e ^?2 when the ratio of the potential energy to the kinetic energy of an electron (nonideality parameter) reaches unity. As the nonideality parameter increases, the temperature dependence disappears and the density dependence becomes n _e ^1/2 . The existing theoretical results for various physical models have been analyzed and compared to the experimental data.     

Non-Newtonian Fluids in Spout-Fluid Beds: Mass Transfer Coefficient at Low Reynolds Numbers

Following on from the work of Anabtawi et al. (2003) Anabtawi, M. Z., Hilal, N. and Al Muftah, A. E. 2003. Volumetric mass transfer coefficient in non-Newtonian fluids in spouted-fluid beds: Part I. Chem. Eng. Technol., 26: 759–764.  [Google Scholar], this study examined how the volumetric liquid-phase mass transfer coefficient, k _L a, of oxygen in air in three-phase spout-fluid beds was affected by varying the system parameters of bed height, bed diameter, gas velocity, and liquid velocity. The liquid used was 0.1% CMC solution, displaying a pseudo-plastic rheology, with 1.75 mm glass spheres as packing. The values of the Sherwood number were lower than in previous studies (Anabtawi et al., 2003 Anabtawi, M. Z., Hilal, N. and Al Muftah, A. E. 2003. Volumetric mass transfer coefficient in non-Newtonian fluids in spouted-fluid beds: Part I. Chem. Eng. Technol., 26: 759–764.  [Google Scholar]), in the range 9,000–186,000. Gas velocity had a similar effect on k _L a as in a bubble column, with results also giving good agreement with previous work on two-phase and three-phase spouted bed systems. The correlation obtained for the effect of liquid velocity on k _L a compared well with that of Schumpe et al. (1989) Schumpe, A., Deckwer, W. and Nigam, K. D. P. 1989. Gas-liquid mass transfer in three- phase fluidized beds with viscous pseudoplastic liquids. Can. J. Chem. Eng., 67: 873–877. [Crossref] , [Google Scholar]. An increase in the height of packing increased k _L a to the power of 0.319, with an increase in column diameter also causing an increase in k _L a, which is in agreement with the results of Akita and Yoshida (1973) Akita, K. and Yoshida, F. 1973. Gas hold-up and volumetric mass transfer coefficient in bubble columns. Ind. Eng. Chem. Process Des. Dev., 12: 76–80. [Crossref] , [Google Scholar].     

Cation-cation interaction in mixed-valent An(IV)/Np(V) tribromoacetates [An(NpO2)(H2O)3(CBr3COO)5]·CBr3COOH·nH2O,An = Th(IV), Np(IV)

The structure of new mixed-valent An(IV)/Np(V) compounds [An(NpO₂)(H₂O)₃(CBr₃COO)₅]·CBr₃COOH·nH₂O, where An(IV) = Th and Np, was studied. Two independent Np(V) atoms have the coordination surrounding in the form of pentagonal bipyramids with the O atoms of NpO ₂ ⁺ dioxocations in apical positions; the equatorial planes of the bipyramids are constituted by the O atoms of five CBr₃COO^? ions. Two independent An(IV) atoms have the oxygen surrounding in the form of distorted tricapped trigonal prisms (CN = 9) constituted by the O atoms of four CBr₃COO^? ions, two NpO ₂ ⁺ cations, and three water molecules. Eight of ten independent CBr₃COO^? anions link the An⁴⁺ and NpO ₂ ⁺ cations in the bidentate bridging fashion into electrically neutral chains [An(NpO₂)(H₂O)₃(CBr₃COO)₅]n, and two CBr₃COO^? anions interact with two independent NpO ₂ ⁺ dioxocations in the monodentate fashion. CBr₃COOH and water molecules are located between the layers. In the [An(NpO₂)(H₂O)₃(CBr₃COO)₅]n chains, NpO ₂ ⁺ cations alternate with An⁴⁺ cations, and mixed-valent An(IV)/Np(V) cation-cation interaction arises, in which each NpO ₂ ⁺ cation acts as a bidentate ligand and An⁴⁺ acts as coordination center for two dioxocations. [Th(NpO₂)(H₂O)₃(CBr₃COO)₅]·CBr₃COOH·2H₂O is the first example of a Th(IV) compound in which cation-cation bonds with the NpO ₂ ⁺ ions are present.     

Measuring production yield for processes with multiple quality characteristics

Process yield is an important criterion used in the manufacturing industry for measuring process performance. Methods for measuring yield for processes with single characteristic have been investigated extensively. However, methods for measuring yield for processes with multiple characteristics have been comparatively neglected. In this paper, we develop a generalized yield index, called TS _pk,PC , based on the index S_pk introduced by Boyles (Journal of Quality Technology, 23, 17–26, 1991 Boyles, RA. 1991. The Taguchi capability index. J. Qual. Technol., 23: 17–26. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) using the principal component analysis (PCA) technique. We obtained a lower confidence bound (LCB) for the true process yield. The proposed method can be used to determine whether a process meets the preset yield requirement, and make reliable decisions. Examples are provided to demonstrate the proposed methodology.     

Mechanism of cerium(III) oxidation with ozone in sulfuric acid solutions

The kinetics of Ce(III) oxidation with ozone in 0.1–3.2 M H₂SO₄ solutions was studied by spectrophotometry. The reaction follows the first-order rate law with respect to each reactant. The rate constant k slightly increases with an increase in the acid concentration, which is associated with an increase in the O₃/O ₃ ^? oxidation potential. The activation energy in the range 17–35°C is 46 kJ mol^?1. With excess Ce(III), the stoichiometric coefficient Δ[Ce(IV)]/Δ[O₃] increases from 1.6 to 2 in going from 0.1 to 1–3.2 M H₂SO₄. The extent of the Ce(III) oxidation is 78% in 0.1 M H₂SO₄ and reaches 82% in 1 M H₂SO₄. The ozonation involves the reactions Ce(III) + O₃ → Ce(IV) + O ₃ ^? , O ₃ ^? + H⁺ → HO₃, HO₃ → OH + O₂, OH + HSO ₄ ^? → H₂O + SO ₄ ^? , OH + Ce(III) → OH^? + Ce(IV), and SO ₄ ^? + Ce(III) → SO_4/2? + Ce(IV). Low stoichiometric coefficient of the Ce(III) oxidation is associated with the hydrolysis of Ce(IV). The excited Ce(IV) ion arising from oxidation of Ce(III) with OH radical forms with the hydrolyzed Ce(IV) ion a dimer whose decomposition yields Ce(III) and H₂O₂. After the ozonation termination, Ce(IV) is relatively stable in sulfuric acid solution, with only 5–7% of Ce(IV) disappearing in 24 h.     

Sublimation study of BiBr3

Steady-state sublimation vapour pressures of anhydrous bismuth tribromide have been measured by the continuous gravimetric Knudsen-effusion method from 369.3 to 478.8 K. Additional effusion measurements have also been made from 435.4 to 478.6 K by the torsion—effusion method. Based on a correlation of Δ_sub H ₂₉₈ ⁰ and Δ_sub S ₂₉₈ ⁰ , a recommended p(T) equation has been obtained for BiBr₃(s) $$\alpha - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\alpha /T - 12.294log{\text{ }}T + 5.79112 \times 10^{ - 3} {\text{ }}T + 47.173$$ with Cα=(Δ _subH ₂₉₈ ⁰ +20.6168)/1.9146×10^-2 $$\beta - {\rm B}i{\rm B}r_3 :log{\text{ }}p = - C\beta /T - 23.251log{\text{ }}T + 1.0492 \times 10^{ - 2} {\text{ }}T + 77.116$$ with Cβ=(Δ _subH ₂₉₈ ⁰ +46.2642)/1.9146×10^-2 where p is in Pa, T in Kelvin, Δ _sub H ₂₉₈ ⁰ in kJ mol^?1. Condensation coefficients and their temperature dependence have been derived from the effusion measurements.     

Synthesis and crystal structure of a new Np(V) oxalate, Na4(NpO2)2(C2O4)3·6H2O

A new oxalate complex, Na₄(NpO₂)₂(C₂O₄)₃·6H₂O, with the Np:C₂O₄ ratio of 2:3 was synthesized and studied by single crystal X-ray diffraction. In the crystal, the NpO ₂ ⁺ cations and oxalate anions are bound in open networks [(NpO₂)₂(C₂O₄)₃] _n ^4n- parallel to the bc plane. The Na(1) cations are accommodated in large voids of the neptunyl oxalate networks with the formation of crimped mixed-cation layers of the composition [Na₂(NpO₂)₂(C₂O₄)₃] _n ^2n- . The negative charge of the layers is compensated by the Na(2) cations arranged between the layers. The Np atoms have a pentagonal bipyramidal coordination surrounding with the equatorial plane formed by the oxygen atoms of three oxalate anions. The structure contains tridentate-bridging and tetradentate-bridging oxalate anions.     

Effect of annealing temperature on magnetoresistivity, activation energy, irreversibility and upper critical field of the Cu-diffused MgB2 bulk superconductors

This study manifests the change of the pinning mechanism, superconducting and physical properties of Cu-diffused MgB₂ superconductors prepared at different annealing temperature from 650 to 850 °C by means of the magnetoresistivity measurements conducted at several applied magnetic fields in a range of 0–7 T as a function of temperature from 15 to 50 K. The onset (T _c ^onset ) and offset (T _c ^offset ) critical temperatures, activation energies (U₀), irreversibility fields (μ₀H_irr), upper critical fields (μ₀H_c2), residual resistivity ratios (R_R), cross-sectional area fractions (A_F), penetration depths (λ), coherence lengths (ξ) and electronic mean free path ( $ \ell $ ) of the samples are evaluated from the magnetoresistivity curves. Thermally activated flux creep (TAFC) model is used for the determination of the U₀ values; likewise, the μ₀H_irr and μ₀H_c2 values are obtained by resistivity criteria of 10 and 90 % normal-state resistivity, respectively. At absolute zero temperature (T = 0 K), the extrapolation of the μ₀H_irr(T) and μ₀H_c2(T) curves is used to find the μ₀H_irr(0) and μ₀H_c2(0) values of the samples. Moreover, the ξ values are deduced from the μ₀H_c2(0) values when the λ values are calculated from the Ginzburg–Landau parameter ( $ \kappa $ ). It is found that the superconducting and physical properties of the samples improve with the increment of the diffusion-annealing temperature; however, the presence of the magnetic field leading to the decrease of the flux pinning in the samples causes the reduction of these properties. Namely, the T _c ^onset and T _c ^offset values are found to increase from 38.4 to 39.3 K and 36.9 and 38.3 K with the enhancement in the diffusion-annealing temperature at zero filed. Similarly, the U₀ values increase significantly with the increase of the annealing temperature. In fact, the U₀ of 9,162 K belonging to the sample annealed at 850 °C is determined to be the maximum activation energy value. On the other hand, the minimum T _c ^onset of 30.9 K, T _c ^offset of 27.6 K and U₀ of 1,365 K at 7 T applied magnetic field are obtained for the pure sample, indicating that the sample annealed at 850 °C obtains much stronger flux pinning, better crystallinity and connectivity between grains compared to the other samples prepared. Based on these results, the superconducting and physical properties of the MgB₂ superconductors produced in this work are observed to enhance with the increase of the diffusion-annealing temperature as a result of the improvement of pinning abilities, crystallinity and connectivity between grains. The magnetic field and temperature dependence of the activation energy are also discussed.     

Sorption of Np(V) on montmorillonite from solutions of MgCl2 and CaCl2

The Np(V) distribution coefficients between montmorillonite and solutions of MgCl₂ and CaCl₂ were determined experimentally. The Np sorption decreases with increasing concentration of the supporting electrolyte. The sorption is very fast within the first several hours after the start of the experiment and then decelerates, reaching the equilibrium in approximately two weeks. The constants of binary ion exchange NpO ₂ ⁺ -Mg²⁺ and NpO ₂ ⁺ -Ca²⁺ on montmorillonite determined by fitting the experimental results are $\log K_{NpO_2^ + - Mg^{2 + } } = 0.083 \pm 0.03$ and $\log K_{NpO_2^ + - Ca^{2 + } } = 0.106 \pm 0.014$ .     

Synthesis and structure of Cs3[UO2(CH3COO)3]2(NCS)·H2O

The compound Cs₃[UO₂(CH₃COO)₃]₂(NCS)·H₂O (I) was synthesized and studied by IR spectroscopy and single crystal X-ray diffraction. Compound I crystallizes in the monoclinic system with the following unit cell parameters: a = 7.8286(9), b = 19.892(2), c = 20.050(2) Å, β = 94.527(2)°, space group P2₁/c, Z = 4, R = 0.0387. The uranium-containing structural units in crystals of I are mononuclear complexes [UO₂(CH₃COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?) of uranyl complexes.     

Photonics of UO 2 2+ complexes with tryptophan: 2. Competition of electron phototransfer from higher excited electronic and vibration-rotation levels of tryptophan to UO 2 2+ with nonradiative relaxation

The possibility of competition of photochemical reaction of tryptophan (Trp) (intraspheric electron phototransfer from Trp to UO ₂ ²⁺ and formation of hydrated electron) in higher singlet S _n and vibrational S _n ^v states with nonradiative vibration-rotation (S _n ^v → S _n ), internal (S _n → S _n?1), and solvation (S _n → S _n ^r ) relaxation was considered. The influence of the excitation wavelength of Trp on the quantum yield of fluorescence, the Stern-Volmer constant of quenching of Trp fluorescence with uranyl ion, and the activation energy of thermal quenching of Trp fluorescence was studied. The monotonic change in the constant of quenching of Trp fluorescence with uranyl ion is due to the fact that intrashperic electron phototransfer from the vibronic S _n ^v states is faster than the vibration-rotation relaxation. The experimental dependence of the activation energy of thermal quenching of the Trp fluorescence on the excitation wavelength strongly suggests that the photo-induced electron transfer occurs mainly from the higher relaxed S _n ^r states with the stable solvation shell rather than from the Franck-Condon S _n levels of tryptophan.     

Crystal structure of Rb3[UO2(CH3COO)3]2[UO2(CH3COO)(NCS)2(H2O)]

The structure of Rb₃[UO₂(CH₃COO)₃]₂[UO₂(CH₃COO)(NCS)₂(H₂O)] was studied by single crystal X-ray diffraction. The compound crystallizes in the monoclinic system with the unit cell parameters (at 100 K) a = 18.387(3), b = 16.398(3), c = 12.460(2) Å, β = 92.837(5)^°, V = 3752.4(11) ų, space group C2/c, Z = 4, R = 0.0390. The uranium-containing structural units of the crystals are isolated mononuclear groups [UO₂(CH₃COO)₃]^? and [UO₂(CH₃COO)(NCS)₂(H₂O)]^?, belonging to crystal-chemical groups AB ₃ ⁰¹ and AB⁰¹M ₃ ¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?, M¹ = NCS^? and H₂O) of uranyl complexes, respectively. The uranium-containing complexes are linked in a framework by hydrogen bonds and by electrostatic interactions with Rb⁺ cations.     

A novel approach for measuring the maximum process-loss information in multiple production line conditions

The process-loss index L_e , the expected value of the ratio of the quadratic loss function to the square value of half specification width, proposed by Johnson (1992 Johnson, T. 1992. The relationship of C_pm to squared error loss. Journal of Quality Technology, 24(4): 211–215. [Taylor &; Francis Online], [Web of Science ®] , [Google Scholar], The relationship of C_pm to squared error loss. Journal of Quality Technology, 24 (4), 211–215), has been widely used in a variety of industries to provide a numerical loss measure for assessing the performance of their production processes. However, the sampling distribution of its uniformly minimum variance unbiased estimator (UMVUE), obtained from traditional approaches involving unknown parameters, is able neither to form classical confidence intervals (CCIs) nor to provide justifiable process-loss information in practice. To tackle this disadvantage, in this paper a novel approach known as generalised confidence intervals (GCIs) is adopted. Instead of Monte Carlo simulations that were popularly utilised in implementing the GCIs method for assessing production process performance, we theoretically derive analytical forms of upper confidence bounds (L _e -GUCB) for L _e and program them to provide the maximum process-loss information for the manufacturing processes. Two common manufacturing scenarios are presented in order to work out: (1) whether the underlying production process loss is capable (or whether products received from one supplier are acceptable); and (2) whether the maximum process-loss information existing in multiple production line conditions is acceptable (or whether products received from several suppliers are acceptable). The applicability of the results is demonstrated by two examples.