38 Search Results

New candidate materials for GenIV or fusion nuclear energy systems, e.g., nanostructured ferritic alloys, are distinguished from older-generation nuclear materials by much smaller feature sizes and complex local nanochemistry and crystallography. Established and perspective nuclear materials, e.g. reactor pressure vessel steels or plasma-facing tungsten, also form small nanoscale structures under in-reactor service. Here, we discuss recent advances in materials characterization – high-efficiency X-ray mapping combined with datamining; transmission Kikuchi diffraction; and atom probe tomography – that make it possible to quantitatively characterize these nanoscale structures in unprecedented detail, which enables advances in understanding and modelling of radiation service and degradation.

The chemistry of zeolite-supported site-isolated cobalt, rhodium, and iridium complexes that are essentially molecular was investigated with density functional theory (DFT) and the results compared with experimentally determined spectra characterizing rhodium and iridium species formed by the reactions of Rh(C₂H₄)₂(acac) and Ir(C₂H₄)₂(acac) (acac = acetylacetonate) with acidic zeolites such as dealuminated HY zeolite. The experimental results characterize ligand exchange reactions and catalytic reactions of adsorbed ligands, including olefin hydrogenation and dimerization. Two molecular models were used to characterize various binding sites of the metal complexes in the zeolites, and the agreement between experimental and calculated infrared frequencies and metal-ligand distancesmore » determined by extended X-ray absorption fine structure spectroscopy was generally very good. The calculated structures and energies indicate a metal-support-oxygen (M(I)-O) coordination number of two for most of the supported complexes and a value of three when the ligands include the radicals C₂H₅ or H. The results characterizing various isomers of the supported metal complexes incorporating hydrocarbon ligands indicate that some carbene and carbyne ligands could form. Ligand bond dissociation energies (LDEs) are reported to explain the observed reactivity trends. The experimental observations of a stronger M-CO bond than M-(C₂H₄) bond for both Ir and Rh match the calculated LDEs, which show that the single-ligand LDEs of the mono and dual-ligand complexes for CO are similar to 12 and similar to 15 kcal/mol higher in energy (when the metal is Rh) and similar to 17 and similar to 20 kcal/mol higher (when the metal is Ir) than the single-ligand LDEs of the mono and dual ligand complexes for C₂H₄, respectively. The results provide a foundation for the prediction of the catalytic properties of numerous supported metal complexes, as summarized in detail here.« less

The trinuclear triangle-shaped system [tris{3,5-bis(heptafluoropropyl)-1,2,4-triazolatosilver(I)}] (1) and the multi-armed square-shaped metalloporphyrin PtOEP or the free porphyrin base H2OEP serve as excellent octopus hosts (OEP=2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine). Coupling of the fluorous/organic molecular octopi 1 and H2OEP or PtOEP by strong quadrupole-quadrupole and metal- interactions affords the supramolecular assemblies [1PtOEP] or [1H(2)OEP] (2a), which feature nanoscopic cavities surrounding the upper triangular and lower square cores. The fluorous/organic biphasic configuration of [1PtOEP] leads to an increase in the phosphorescence of PtOEP under ambient conditions. Guest molecules can be included in the biphasic double-octopus assembly in three different site-selective modes.

AbstractTotal, static, and operating holdups have been measured for 1‐in porcelain and carbon Raschig rings and 1‐in. porcelain Berl saddles, employing aqueous solutions of calcium chloride, sorbitol, and a wetting agent as well as pure methanol and benzene. The range of variables covered by this investigation includes liquid rate, 1,000 to 10,000 1b./(hr.) (sq. ft.); viscosity, 0.6 to 185 cp.; surface tension, 23 to 86 dynes/cm.; specific gravity, 0.8 to 1.32.Equations and charts are presented for estimating holdups for all liquids. The application of holdups for estimating mass transfer coefficients, kG, and effective interfacial areas, a, is discussed.The total holdupsmore » for water, methanol, and benzene can be used to explain why mass transfer coefficients obtained by vaporization of pure liquids in packings seem to depend on gas diffusivity raised to the 0.15 power instead of the 0.67 power, as found in other mass transfer studies. The larger total holdups of nonaqueous liquids result in larger effective interfacial areas in the packing, which mask the effect of the change in gas diffusivity.« less

The reactions of the chelating reagents named in the title, with a number of metal ions, have been studied in order to evaluate the behavior of reagents containing reactive groupings analogous to those of 8-hydroxyquinoline, but so arranged as to form six-membered ring chelates with metal ions. All three reagents have been found to give less stable chelates than 8-hydroxyquinoline, indicating that for this type of reagent, six-membered ring chelates are less stable than five. 2-(o-Hydroxy-phenyl)-benzoxazole and 2-(o-hydroxyphenyl)-benzothiazole have been found to be potentially useful as organic precipitating agents for metal ions, being more selective than 8-hydroxyquinoline, which they somewhatmore » resemble in behavior. In contrast to the oxazole and thiazole, 2-(o-hydroxyphenyl)-benzothiazoline was found to react with most of the metal ions tried. Finally, because of the solubility of its chelates in organic solvents, 2-(o-hydroxyphenyl)-benzothiazoline may be a useful solvent extraction agent for metal ions.« less

Acrylamide, methacrylamide, methylene-bis-acrylamide, vinyl carbazole, vinyl stearate, acrylic acid, methacrylic acid and potassium, calcium and barium acrylates have been polymerized in the solid state by irradiation with γ-rays. Further, the molecular weight of polyacrylamide obtained at low conversion was constant over a 270-fold variation of radiation intensity and in the temperature range 20 to 65°, but increased slightly with the energy of the radiation. The polymerization rate, however, was linear with field intensity, independent of the energy of radiation and had an over-all activation energy of 4.7kcal./mole. Irradiation of acrylamide at —179° produced “frozen-in” radicals in concentrations of the ordermore » of 10^-4 molal. In the polymerization of vinyl stearate the temperature dependences of rate and molecular weight exhibit a discontinuity on passing through the melting point of the monomer. With barium acrylate there is no significant variation in polymerization rate between 10 and 65°. Crystalline maleic anhydride, allylamine hydrochloride and picrate, and stilbene did not polymerize on exposure to γ-rays.« less

Here a method is described which has been used to verify the intensity distribution in the lower fringes in a Gouy diffusion fringe pattern predicted by the general theory for the Gouy method. The position of the zeroth turning point predicted by the theory has also been shown to be correct. Two techniques for the direct recording of Gouy diffusion data for use in the actual determination of diffusion coefficients are presented briefly.

From electromotive force measurements of suitable cells, the activity coefficient of hydrochloric acid in barium chloride solutions has been computed in mixtures of 1, 2 and 3 ionic strengths. It is shown that at these concentrations, the logarithm of the activity coefficient of the acid varies linearly with the acid concentration. Finally, following a procedure adopted by Harned which employed the Gibbs-Duhem equation and considerations arising from the application of cross differentiation relations as suggested by Glueckauf, these data are subjected to a critical examination.

Following some general remarks on the present state of knowledge of the relative chemical potentials of electrolytes, some recent determinations of activity coefficients of systems containing two electrolytes in concentrated solutions will be dis-cussed. The theory of irreversible processes emphasizes the role of the gradient of the chemical potential as a “force” in causing the motions of the components of the solutions. Finally, recent results on the diffusion coefficients of electrolytes in aqueous solutions will be employed to assess the importance of this role.

The differential diffusion coefficient of cesium chloride has been determined by the conductometric method at 25° through the concentration range 0.001 to 0.012 M. At these low concentrations, the results herein are in accord with the Nernst-Onsagerand Fuoss theory.