The electrochemical behavior and characterization of the anodic oxide film formed on titanium in NaOH solutions

Titanium dissolution and passivation were studied in NaOH aqueous solution using open-circuit potential, potentiodynamic and potentiostatic techniques. Potentiodynamic data showed that the active-passive transition involves active metal dissolution followed by formation of a poorly conducting passive oxide film that passivates the electrode. The critical current density varied with pH as d log<I> j</I><SUB>m</SUB>/d pH=-0.098 in the pH range 11.00–14.00, while the passivation potential is changed according to the following two features: at pH 10.55–13.00, d<I>E</I><SUB>m</SUB>/d pH=-0.06 V; and at pH 13.50–14.00, d<I>E</I><SUB>m</SUB>/d pH=-0.40 V. The apparent activation energy, E*, was calculated from the slope of the Arrhenius plot and was found to be 12.6 kJ mol^–1. Current-time transients showed that the growth of titanium oxide passive film is a diffusion-controlled process. XPS measurements indicated that the passive oxide film consists mainly of TiO₂ and a mixture of suboxides of Ti₂O₃ and TiO. Electronic Publication     

Organic thermal stabilizers for rigid poly(vinyl chloride). Part XIII: Eugenol (4-allyl-2-methoxy-phenol)

Eugenol (4-allyl-2-methoxy-phenol) has been examined as a thermal stabilizer and co-stabilizer for rigid PVC in air, at 180 °C. Its high stabilizing efficiency is detected by its high thermal stability value (Ts) when compared with some of the common reference stabilizers used industrially such as dibasic lead carbonate, calcium-zinc soap and octyl tin mercaptide.Blending this organic stabilizer with some of the reference stabilizers in different ratios had synergistic effect on both the induction period and the dehydrochlorination rate together with the longer extent of discolouration of PVC stabilized by eugenol as compared with the blank and the samples stabilized with reference commercial stabilizers.A probable mechanism for the stabilizing action of eugenol has been proposed. The stabilizing efficiency is attributed partially to the stabilizer's ability to intervene in the radical chain degradation process of PVC and to the replacement of the labile chlorine atoms on PVC chains by a relatively more stable moiety of the organic stabilizer.     

Synthesis and characterization of new metal complexes of thiosemicarbazone derived from 4-phenyl-3-thiosemicarbazide and chromone-3-carboxaldehyde

Summary The reaction between chromone-3-carboxaldehyde-4-phenylthiosemicarbazone (HCPT) and some hydrated metal salts of Co^II, Ni^II and Cu^II give complexes of the type [Cu(HCPT)Cl₂],[Cu(CPT)BrH₂O],[Cu(CPT)₂]·2H₂O, [Ni(CPT)₂(H₂O)₂]·2H₂O, [Co(CPT)₂(OAc)] and [Co(CPT)₂(H₂O)₂]X·2H₂O (where X=Cl or Br). The metal complexes were characterized by elemental analyses, molar conductivities, and spectal (i.r. and visible) and magnetic studies. I.r. spectra show that the HCPT coordinates in the thione or thiol form and behaves in a bidentate manner. Also, HCPT behaves as an oxidizing agent towards Co^II forming diamagnetic Co^III complexes. An octahedral structure is proposed for both Co^III and Ni^II complexes, while a square-planar structure is proposed for Cu^II complexes on the basis of magnetic and spectral measurements.     

Comparative Study of Polymer Nanoparticles on the Basis of Caprolactone–Polyvinyl Alcohol Mixtures with an Encapsulated Antitumor Preparation by Atomic Force Microscopy,X-Ray Diffraction,and Dynamic Light Scattering

Technical Physics - The morphology, structure, and optical properties of composites with biodegradable polymeric particles, which are based on poly-ε-caprolactone–polyvinyl alcohol...     

Ring Opening and Recyclization Reactions of 3‐Nitrochromone with Some Nucleophilic Reagents

The chemical reactivity of 3‐nitrochromone ( 1 ) was studied towards some nucleophilic reagents. Reaction of 3‐nitrochromone ( 1 ) with some carbon nucleophiles revealed existence of ring‐opening ring‐closure reactions, and the mode of cyclization depends on the nucleophile used. Treatment of 3‐nitrochromone ( 1 ) with malononitrile and ethyl cyanoacetate produced benzoxocinone derivatives 2 and 3 , respectively. Boiling compound 1 with cyanoacetamide and 2‐aminoprop‐1‐ene‐1,1,3‐tricarbonitrile afforded pyridine derivatives 4 and 5 , respectively. Reaction of compound 1 with 1H‐benzimidazol‐2‐ylacetonitrile, 5‐amino‐2,4‐dihydro‐3H‐pyrazol‐3‐one, and dimedone led to pyrido[1,2‐a]benzimidazole 6 , pyrazolo[3,4‐b]pyridine 7 , and chromenone 8 , respectively. Treating 3‐nitrochromone ( 1 ) with heterocyclic amines gave enaminones 11 and 12 via nucleophilic attack at C‐2 position with ring opening. The structures of the newly synthesized products were deduced on the basis of their analytical and spectral data.     

Non-linear temporal dynamics of two-mode interactions of magnetized flow

This paper considers, in the frame work of the model of two superposed layers of viscous-potential incompressible magnetic fluids, the problem on formation of resonant waves of two modes on the interface between fluids that arisen as a result of second-harmonic resonance. The fluids moving with uniform velocities parallel to their interface are stressed by a tangential magnetic field. The analysis includes the linear, as well as the non-linear effects where the analytical solutions are constructed using the method of multiple scales, in both space and time, and hence the solvability conditions correspond to the uniform (convergent) solutions are obtained. The solvability conditions are then exploited to derive a more general system of non-linear partial differential equations with complex coefficients governing the amplitudes of the resonant waves. These equations are examined for solutions corresponding to sinusoidal wavetrains consequently different kinds of instabilities are demonstrated. The stability criterion in each case is derived and discussed both analytically and graphically.     

Instability through porous media of three layers superposed conducting fluids

The instability properties of streaming superposed conducting fluids through porous media under the influence of uniform magnetic field have been investigated. The system is composed of a middle fluid sheet of finite thickness embedded between two semi-infinite fluids. The fluids are assumed to be incompressible, perfectly conducting and there are weak viscous stresses on the interfaces. The Rayleigh–Taylor and Kelvin–Helmholtz problems have been studied. Such configurations are of relevance in a variety of astrophysical and space configurations. The solutions of the linearized equations of motion together with the boundary conditions lead to deriving the dispersion equation with complex coefficients. The limiting case of the stability of one interface between two fluids has been discussed. The stability criteria are discussed theoretically and numerically in which stability diagrams are obtained. It has been found that the increase of the viscosity coefficient as well as the porosity plays a regular stabilizing role in the stability behavior, while the increase of the fluid velocity plays a destabilizing influence in the stability criteria.     

Chemical Transformations of Chromone‐3‐carbonitrile with Cyclohexanediones: Synthesis of Bis[1]chromenophenanthrolines

The chemical reactivity of chromone‐3‐carbonitrile ( 1 ) toward 1,2‐cyclohexanedione, 1,3‐cyclohexanedione, and 1,4‐cyclohexanedione was studied under different molar ratios. Three isomeric products of angular bis[1]chromenophenanthrolines were isolated. Structures of the new synthesized products were deduced on the basis of their analytical and spectral data.     

Development of an Optode for Detection of Trace Amounts of Hg2+ in Different Real Samples Based on Immobilization of Novel Tetradentate Schiff Bases Bearing Two Thiol Groups in PVC Membrane

A very sensitive and reversible optical chemical sensor based on a novel tetradentate Schiff base namely N.N^/bis(2-aminothiophenol)benzene-1,2-dicarboxaldehyde (ATBD) immobilized within a plasticized PVC film for Hg²⁺ determination is described. At optimum conditions (i.e. pH 6.0), the proposed sensor displayed a linear response to Hg²⁺ over 1.0?×?10^?10 ? 1.0?×?10^?2 mol L^?1 with a limit of detection of 7.23?×?10^?11 mol L^?1 (0.0145 μgL^?1). Moreover, the results revealed that, under batch condition, the sensor is fully reversible within a response time?~?35 s. In addition to its high stability and reproducibility, the sensor showed good selectivity towards Hg²⁺ ion with respect to common metal cations. The sensor was successfully applied for determination of Hg²⁺ ion in some real samples, including hair, urine and well water samples. The results were in good correlation with the data obtained using cold vapor atomic absorption spectrometry.     

Reactivity of Z- and E-isomers of 2-benzamido-3-phenylacrylohydrazide towards some carbon electrophiles. A comparative study

Z- and E-isomers of 2-benzamido-3-phenylacrylohydrazide 2a, 2b have different relative reactivities towards some carbon electrophiles had been discussed.The Z-isomer underwent cyclization to give imidazole derivative 3 and triazine derivative 4, whereas the latter E-isomer does not undergo such cyclization. The reaction of 2a and/or 2b with 1,2-dibenzylidene hydrazine at different reaction conditions afforded the Schiff bases 6, 8 and the triazolidine derivative 9. Reactions of 2a, 2b with formic acid and phthalic anhydride gave the different cyclization products 10–14, respectively. The structures of all the new synthesized compounds were established from their IR, ¹H-NMR and mass spectra as well as elemental analyses.