Oxidation of cobalt(II) with air oxygen in aqueous ethylenediamine solutions

Oxidation of aqueous Co(NO₃)₂–ethylenediamine (En) solutions with air oxygen was investigated at 20 °C and pH 5.2–7.0, with and without mechanical stirring, by measuring the Co^II concentration, pH and redox potential on an Au electrode. In most cases, the oxidation rate was proportional to the concentration of CoEn ²⁺ _n (n = 2, 3) complexes, and the influence of the solution pH on the rate of reaction was accounted for by the pH dependence of the Co^II complex distribution. It was found that sulphate inhibits and bromide accelerates the oxidation process. Possible oxidation routes are discussed. The oxidation process is limited to some extent by O₂ transport from the air to the bulk solution.     

Polarographic investigation of Cu(II) complexes with N,N,N',N'-tetrakis-(2-hydroxypropyl)-ethylenediamine

During investigation of the formation of Cu(2+) ion complexes with N,N,N',N'-tetrakis-(2-hydroxypropyl)-ethylenediamine (Quadrol-Q) by means of constant current polarography (20 degrees C, ionic strength J = 3 mol l(-1)), the possibility of the formation of two complex compounds; CuQ(2+) and CuQ(2+)(2), was shown within the pH range from 6 to 8. The logarithms of the stability constants for these compounds are 10.6 +/- 0.5 and 14.6 +/- 0.4 respectively. Cu(II) complexation increases sharply when the pH increases from 8 to 10. It was shown that the data at a pH of greater than 10 are in accordance with the existence of the hydroxy complexes CuQ(OH)(2) and CuQ(2)(OH)(2), the logarithms of the stability constants being 26.9 +/- 0.5 and 29.1 +/- 0.3.     

Electron transport in semiconductors in the presence of impact ionization

The development of impact ionization in semiconductors has been considered. A transport equation for the electron distribution function in the presence of impact ionization has been derived. It has been found that the collison integral of this equation is nonlinear with respect to the distribution function. The relation between the solutions of this equation and the usual Boltzmann equation have been determined. A Monte Carlo method for numerical calculations in the presence of impact ionization has been developed. The results of numerical calculations carried out using a simplified model of indium antimonide are presented.     

Feature extraction algorithms for constrained global optimization I. Mathematical foundation

Nonconvex mixed integer nonlinear programming problems arise quite frequently in engineering decision problems, in general, and in chemical process design synthesis and process scheduling applications, in particular. These problems are characterized by high dimensionality and multiple local optimal solutions. In this work, a novel approach is developed for determining the global optimum in nonlinear continuous and discrete domains. The mathematical foundations of the feature extraction algorithm are presented and the properties of the algorithm discussed in detail. The algorithm uses a partition and search strategy in which the problem domain is successively partitioned and a statistical approximation approach is used to characterize the objective function values and the constraint feasibility over a partition. Specifically, the general joint distribution function representing the objective function values is relaxed to a separable form and approximated using an expansion in terms of Bernstein functions. The coefficients of the expansion are determined by solving a small linear program. Feasibility is established by computing upper and lower bounds for the inequality constraint functions, while equality constraints are explicitly or numerically eliminated. Estimates of the volume averaged values of objective function and constraint feasibility are used to select efficient partitions for further investigation. These are refined successively so as to focus the search on the most promising decision regions. An alternative, constant resolution partitioning strategy is also developed using a suitably modified genetic search algorithm. Illustrative examples are used to demonstrate the key computational features of the method.     

Impact-ionized electron-hole plasma instability in GaAs

The possibility of the excitation of impact-ionized electron-hole plasma oscillatory instability in GaAs with frequency up to 10¹² Hz is shown. The linear and nonlinear stages of the instability are investigated.     

A comparison of computational strategies for geometric programs

Numerous algorithms for the solution of geometric programs have been reported in the literature. Nearly all are based on the use of conventional programming techniques specialized to exploit the characteristic structure of either the primal or the dual or a transformed primal problem. This paper attempts to elucidate, via computational comparisons, whether a primal, a dual, or a transformed primal solution approach is to be preferred.The authors wish to thank Captain P. A. Beck and Dr. R. S. Dembo for making available their codes. This research was supported in part under ONR Contract No. N00014-76-C-0551 with Purdue University.     

A new strategy for fabrication Fe2O3/SiO2 composite coatings on the Ti substrate

We report here on the synthesis of homogenous, well-adherent composite film of Fe₂O₃/SiO₂, up to 7 μm thick, on the titanium substrate by anodic treatment optimized for an aqueous suspension of K₂O·SiO₂ and Fe₂O₃ powder under galvanostatic conditions. The end products were characterized by scanning electron microscopy, energy-dispersive X-ray, X-ray powder diffractometry, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy, concluding that the formation of composite coating at the SiO₂ to Fe₂O₃ ratio of approximately 1:1 proceeds just after formation of a thin TiO₂ layer with Fe₂O₃ particle inclusions without transformations via an electrophoresis deposition of negatively charged Fe₂O₃ species enveloped by silica ions.     

Electrochemical fabrication and characterization of lepidocrocite (γ-FeOOH) nanowire arrays

We report on the fabrication of γ-phase iron oxyhydroxide (γ-FeOOH, lepidocrocite) nanowire (nw) arrays within the alumina pores by electrodeposition. An aqueous solution, friendly to alumina matrix, was generated and applied in this study for uniform deposition of γ-FeOOH nw arrays directly through the alumina barrier layer using an alternating current (ac) mode. As-deposited nanowired products were characterized using ⁵⁷Fe Mössbauer spectroscopy (MS), atomic absorption spectrophotometry analysis, field-emission scanning electron microscopy, UV-vis transmission spectroscopy, transmission electron microscopy and X-ray diffraction. The formation of pure lepidocrocite nw arrays in the alumina pores with the average Ø_pore of 45 and 150 nm was verified by transmission MS at cryogenic temperatures.     

Studies of oxidation of iron nanowires encased in porous aluminium oxide template

The transformations of phase composition of iron nanowires deposited into porous alumina template when annealing in the air were studied. The samples of iron nanowires of different diameter (8, 13, 15, 30 nm) were annealed for 1.5 h at temperature up to 600°C. In addition, for nanowires of 15 nm diameter the dependence of phase composition on annealing time was investigated. The phases were determined by applying Mössbauer spectroscopy. New Fe(II) and Fe(III) contributions to Mössbauer spectra were found and those were indentified as caused by the formation of hercynite FeAl₂O₄ and (Fe _x Al_1???x )₂O₃ with small x values (x?≤?0.15). It has been found that though initially the Fe(II) compound forms rapidly, afterwards its formation rate becomes lower than that of Fe(III) and after longer annealing time the Fe(III) content exceeds Fe(II) one.