Investigation of Nanometer- and Submicron-Size Dispersed Phases in Titanium Pseudo- β -Alloys using Scattering and Diffraction of Neutrons,Electrons, and X-Ray Radiation

Metal Science and Heat Treatment - The size and volume fraction of fine particles of secondary β -phase formed during hardening heat treatment of pseudo-β-titanium alloy VT22 are...     

Phase transformations in highly disperse powders during their rapid heating and cooling

Phase transformations in particles of ultrafine powders of graphite, hexagonal boron nitride, and quartz during rapid heating and cooling by passage through a laser beam were investigated. A continuous infrared laser with a wavelength of 10.6 μm was used as a heat source through which the powders were recycled several times. Methods of concentrating the product phases are described. Particles of diamond, carbides, cubic boron nitride, koesite and stishovite were obtained in the mixed products.     

Uranium(III) in aqueous solutions: Preparation,properties, synthesis of solid compounds

Published data on the preparation procedures, stability, and complexation of U(III) in aqueous solutions are summarized and correlated. Reactions with inorganic and organic free radicals studied by the flash radiolysis method, the spectroscopic properties, the extraction and ion-exchange behavior of U(III), and methods for isolation of solid U(III) compounds from aqueous solutions are discussed.     

Nuclear-chemical synthesis of tritium-labeled phenyl-substituted picoline derivatives

Ion-molecule reactions of free phenyl cations with six-membered nitrogen-containing heterocyclic compounds: α-, β-, and γ-picolines, were studied. Phenyl cations were generated by tritium β-decay in double-labeled benzene. The mechanism of competing reactions of electrophilic addition to the nitrogen heteroatom in the ring and electrophilic substitution of the C-H bond in the pyridine ring was examined. The effect of methyl substituent in the pyridine molecule on the reaction pathway was evaluated. A one-step procedure for nuclear-chemical synthesis of tritium-labeled N-phenylpicolinium salts and phenyl-substituted picolines was developed.     

Solubility of Pu(IV) in Weakly Alkaline Solutions (pH 9-14) Containing Silicate Anions

Behavior of hydrated ^238-242Pu(IV) oxide in 0.09-0.9 M NaOH containing 1 ×10^{- 3} M Na2SiO3 and in 0.1-0.2 M NaClO₄ containing 1×10^{- 3}-0.09 M Na2SiO3 (pH 11 and 9) was studied radiometrically with the aid of a scintillation counter. In alkaline solutions with pH 13.8-11 and high Na₂SiO₃ content, the Pu(IV) solubility increases owing to the reaction Pu(IV) + nSiO₃ ^{2 -} = Pu^{I V}(SiO₃ ^{2 -}) _n . At pH 9, Na₂SiO₃ has virtually no effect on the Pu(IV) solubility.     

Uranyl and Thorium(IV) Sorption from Dilute Nitric Acid Solutions with Dodecavanadic Acid

Sorption of uranyl on dodecavanadic acid proceeds by the ion-exchange mechanism at relatively low metal concentrations in the range (0.8-2.0) ×10^{- 3} M. Sorption of Th(IV) is practically pH-independent over the pH range 1.5-2.5, but depends significantly on the initial Th(IV) concentration. The maximal capacities of DDVA for uranyl and Th(IV) remarkably differ from each other (9 and 6.3 mg-equiv g^{- 1}, respectively). The uranyl compound formed on contacting DDVA with concentrated uranyl nitrate solution was identified by X-ray diffraction as UO₂(VO₃)₂·nH₂O.     

Structural strength of frozen soils during thawing

Conclusions Frozen clayey soils of semi-hard and hard consistency and sandy soils of medium density have a structural strength equal to the value of the actual pressure under complete saturation, and, consequently, the suspending effect of water, and their deformation is determined by the presence of ice striations and the extent to which the macropores that form after their complete thawing are interconnected. From The Editorial Office: Problems that are extremely interesting from the scientific and practical standpoint are touched upon in the paper. The authors, however, do not always adequately substantiate their own assumptions. Making note of the influence exerted by the suspending action of water on the settlement of frozen soils, the authors fail to cite data on comparison of the results of settlement computation with allowance for and with disregard of the suspending effect of water and actual settlement; this would impart greater persuasiveness to their assumptions. The authors' conclusions on the structural strength of soils are also insufficiently founded — neither physicomechanical characteristics of the soils under consideration nor geologic sections are cited, and there is no comparison made between computed and actual settlements.By publishing the paper "in order of discussion," therefore, the editorial office hopes that other specialists will participate in the solution of these critical problems.Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 5, pp. 17–18, September–October, 1989.     

Integrated method of measuring the transverse thermal conduction and diffusion in a turbulent liquid stream

A new integrated method is described for measuring the transverse diffusion and thermal conductivity coefficients of a parallel turbulent liquid stream. The method differs from other methods in a number of ways: the location of the temperature or impurity-concentration sensors outside and not inside the medium under study; simplicity of implementation; speed of measurements; and applicability to finely divided porous media as well as to large bundles of tubes, lattices, and charges, and to free turbulent streams. On the basis of experimental data we establish a limiting law of mixing of a liquid in porous media and the previously known interrelation of turbulent diffusion and thermal conductivity with the hydraulic resistance of the porous medium.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 51–53, July, 1994.     

Kinetics of the reaction of Np(VI) with iminodiacetic acid

The stability of Np(VI) in 5–200 mM iminodiacetic acid (H₂IDA) solutions at 23.5–55°С was studied by spectrophotometry. In a solution with pH 2 and excess Np(VI), 1 mol of H₂IDA reduces 2 mol of Np(VI) to Np(V). In 1 and 0.5 M HClO₄ solutions containing 200 mM H₂IDA and 1 mM Np(VI), no more than 36 and 65% of Np(VI), respectively, is reduced at 44.5°С. Complete reduction of Np(VI) is observed in solutions containing 0.2 M HClO₄ and less. In the examined ranges of H2IDA concentrations and temperatures, Np(VI) is consumed in accordance with the first-order rate law. The reduction mechanism involves formation of a Np(VI) iminodiacetate complex, which is followed by intramolecular charge transfer. The generated radical reduces Np(VI). The activation energy is 107 ± 3 kJ mol^–1.     

Oxidation of Np(V) with Xenon Trioxide in an HClO<Subscript>4</Subscript> Solution

Oxidation of Np(V) to Np(VI) with xenon trioxide in a 0.5–1.4 M HClO₄ solution was studied by spectrophotometry. The reaction rate is described by the equation–d[Np(V)]/dt = k[Np(V)][XeO₃], where k = 4.6 × 10^–3 L mol^–1 s^–1 in 1 M HClO₄ at 92°С. The activation energy is close to 92 kJ mol^–1. The activated complex is formed in contact of NpO ₂ ⁺ and ХеО₃ without participation of Н⁺ ions. The activated complex transforms into NpO ₂ ²⁺ and the products: ОН, Хе, and О₂. The ОН radical oxidizes Np(V). Admixtures of Со²⁺ and especially Fe³⁺ accelerate the Np(V) oxidation.