Fixation mechanism between zeolite and some radioactive elements

Fixation of some fission products and actinide elements from aqueous solutions on zeolite was investigated. Studies showed that the interaction between the radionuclides and zeolite followed the exchange and the adsorption mechanisms. The relative importance of each depends on the type, the nature, and the size of the radioelement.     

The chemical nature of electron waves in metals — A basis for the study of heterogeneous catalysis

The tight-binding method is used to describe the electronic waves of metals in the atomic orbital language familiar to chemists. It is shown that (in both fcc and bcc crystals) k vectors with components (0, 0, 1) or (1, 1, 1) carry hybrids between the s waves and Z² waves whose axis Z is parallel to the direction of the wave vector. In particular the higher-energy hybrid waves are strongly pointed along the wave vector direction. Furthermore, using the finite cube model, with excellent analytical approximations to the orbitals, the existence of privileged wave vector directions perpendicular to the surface approached by an incoming substrate is demonstrated. A preliminary discussion of the favorable conditions for catalysis emphasizes the extremely favorable role of such pointed hybrids if their sub-band lies (empty) just above the Fermi level of the metal.     

Two-electron,one-photon transitions in nickel

The two emission lines, Kα₁α₃^h and Kα₂α₃^h resulting from the two-electron transitions $\text{1s}{}^{\mathrm{?2}}\text{→ 2s}{}^{\mathrm{?1}}\text{2p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ and $\text{1s}{}^{\mathrm{?2}}\text{→ 2s}{}^{\mathrm{?1}}\text{2p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$ were resolved for elemental nickel. Their measured energies agree well with calculations. Their relative intensity $\text{I(Kα}{}_1\text{α}{}_3{}^{\mathrm{h}}\text{)/I(Kα}{}_2\text{α}{}_3{}^{\mathrm{h}}\text{) ≈}\text{3}\text{4}$ and their intensity relative to that of the Kα diagram lines is about 10^?4. This is some 10⁴ times larger than both theoretical results and the results of ion-atom collision experiments.     

Spectrum of relaxation times for ising spin clusters in random fields

Summary Exact results on the single-spin-flip Glauber dynamics of six-coupled random field Ising spins with the coordination number of four are presented. Two distributions of random fields (RF), binary (BD) and Gaussian (GD) ones, are investigated. The effects of the static magnetic field are discussed. In the zero-magnetic-field case, the number of diverging relaxation times is equal to the number of energy minima minus one. This rule breaks in the presence of a magnetic field. The longest relaxation times in the absence of the field verify the Arrhenius law with the energy barrier determined by the energy needed to invert the ground-state spin configuration. At low temperature, according to the Arrhenius law, the spectrum of relaxation times shows a two-peaked distribution on a logarithmic scale. In the GD case of RF, the energy barrier distribution is continuous, while it is quasi-discrete in the BD case.     

Iron(II)-bis (salicyladimine) Schiff-base complexes catalyzed decomposition of hydrogen peroxide

The tetradentate Schiff-base ligands, N,N′-bis(salicylidene)-ethylenediamine (Salen), N,N′-bis(salicylidene) butylenediamine (Salbut), and N,N′-bis(salicylidene)-o–phenylenediamine, (sal-o-phen) are very strongly sorbed by cation exchange resin (Dowex-50W) with Fe²⁺ ions as a counter ion, forming stable complexes. The kinetics of the catalytic decomposition of H₂O₂ using these complexes was studied in ethanolic medium. The reaction was first-order with salen and sal-o-phen and second-order with salbut with respect to [H₂O₂]. The rate of the H₂O₂ decomposition increased either from salen to salbut or from salen to sal-o-phen. Also, the k (per g dry resin) values decreased with increasing both the particle size and the degree of resin cross-linkage. The active species formed at the beginning of the reaction, had an inhibiting effect on the reaction rate. The corresponding activation parameters were calculated from a least-squares fit of the temperature dependence of the rate constant. A reaction mechanism is proposed. © 1994 John Wiley & Sons, Inc.     

High performance liquid chromatographic analysis of tetroxoprim and sulphadiazine in serum and urine.

Quantitative determination of tetroxoprim and sulphadiazine in serum and urine was performed using reversed phase high performance liquid chromatography. Protein precipitation using 10% perchloric acid was utilized for purification of serum samples while urine samples were diluted prior to analysis. The mobile phase consisted of triethylammonium acetate buffer (85%), acetonitrile (12%) and methanol (3%), with a final pH of 4.2. The eluent was monitored at 280 nm. Benzoic acid was used as an internal standard. Standardization, validation and application of the method is described.