Ishaq A. Zaafarany

Kinetics of Corrosion Inhibition of Aluminum in Acidic Media by Water-Soluble Natural Polymeric Pectates as Anionic Polyelectrolyte Inhibitors

Corrosion inhibition of aluminum (Al) in hydrochloric acid by anionic polyeletrolyte pectates (PEC) as a water-soluble natural polymer polysaccharide has been studied using both gasometric and weight loss techniques. The results drawn from these two techniques are comparable and exhibit negligible differences. The inhibition efficiency was found to increase with increasing inhibitor concentration and decrease with increasing temperature. The inhibition action of PEC on Al metal surface was found to obey the Freundlich isotherm. Factors such as the concentration and geometrical structure of the inhibitor, concentration of the corrosive medium, and temperature affecting the corrosion rates were examined. The kinetic parameters were evaluated and a suitable corrosion mechanism consistent with the kinetic results is discussed in the paper.

Further evidence for detection of short-lived transient hypomanganate(V) and manganate(VI) intermediates during oxidation of some sulfated polysaccharides by alkaline permanganate using conventional spectrophotometric techniques.

Spectrophotometric evidence for the formation of hypomanganate(V), [CAR-Mn(V)O43-], and manganate(VI), [CAR-Mn(VI)O42-], intermediate complexes has been confirmed during the oxidation of iota- and lambda-carrageenan-sulfated polysaccharides (CAR) by alkaline permanganate at pHs 12 using a conventional spectrophotometer. These short-lived intermediate complexes were identified and characterized. A reaction mechanism in good consistence with the experimental results is suggested.

Synthesis of some aromatic nitro compounds and its applications as inhibitors for corrosion of carbon steel in hydrochloric acid solution

The inhibition effect of some synthetic aromatic nitro compounds on the corrosion of carbon steel in 1 M HCl solution was studied using galvanostatic and potentiodynamic anodic polarization measurements. The percentage inhibition efficiency was found to increase with increasing the concentration of inhibitors and decreasing of temperature. Polarization data indicated that the additives acted as mixed-type inhibitors meaning that these compounds reduced the anodic dissolution of carbon steel and retard the cathodic hydrogen evolution reaction. Inhibition was interpreted in view of formation of insoluble complex adsorbed on the metal surface. The formation of complex was confirmed by UV-spectra. The adsorption of these compounds was found to obey Langmuir adsorption isotherm. Activation energy and some activated thermodynamic parameters were computed and discussed. It was found that these additives provide good protection to carbon steel against pitting corrosion in chloride-containing solution.

A Revisit to the Corrosion Inhibition of Aluminum in Aqueous Alkaline Solutions by Water-Soluble Alginates and Pectates as Anionic Polyelectrolyte Inhibitors

The corrosion behavior of aluminum (Al) in alkaline media in presence of some natural polymer inhibitors has been reinvestigated. The inhibition action of the tested inhibitors was found to obey both Langmuir and Freundlich isotherms models. The inhibition efficiency was found to increase with increasing the inhibitors concentration and decrease with increasing the temperature, suggesting physical adsorption mechanism. Factors such as the concentration and geometrical structure of the inhibitor, concentration of the corrosive medium, and temperature affecting the corrosion rates were examined. The kinetic parameters were evaluated, and a suitable corrosion mechanism consistent with the kinetic results obtained is suggested and discussed.

Spectrophotometric determination of bismuth after solid-phase extraction using amberlite XAD-2 resin modified with 5-(2′-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione

Abstract A highly selective and sensitive spectrophotometric method has been developed for the determination of trace amounts of bismuth in various samples. The method is based on the adsorption of Bi(III) after complexation with 5-(2′-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (BPAHPD) in a pH range of 2.0–2.5 on amberlite XAD-2 resin in the presence of emulsifier-OP. The retained analyte on the resin recovered with 5.0 mL of 2.0 mol L−1 hydrochloric acid and bismuth was analyzed spectrophotometrically at λmax 579 nm. Beer’s law is obeyed in the concentration range of 0.1–7.5 μg mL−1 Bi(III) in the measured solution. For more accurate results, the Ringbom optimum concentration range was determined to be 0.25–7.25 μg mL−1. The linear regression equation was A = 0.123C (μg mL−1) + 0.002 (r = 0.9996). The molar absorptivity was calculated to be 2.56 × 105 L mol−1 cm−1 at 579 nm, and the Sandell sensitivity was determined to be 8.15 ng cm−2. Various parameters, such as the effect of pH, reagent concentration, surfactant, and flow rate, were studied. The interference of various metal ions on the determination of bismuth has been studied in detail to optimize the conditions for the determination of bismuth in biological samples (i.e., National Institute for Environmental Studies (NIES, No. 5 human hair, NIES, No. 7 tea leaves)) and water samples (i.e., spring water, river water, underground water, and sea and tap water).

Physicochemical Studies on some Cross-linked Trivalent Metal-alginate Complexes especially the Electrical Conductivity and Chemical Equilibrium related to the Coordination Geometry

The electrical conductivity of cross-linked lanthanum(III)- and cerium(III)-alginate complexes in the form of circular discs has been studied as a function of temperature. The Arrhenius plots of log σ versus 1/ T showed a sharp increase in the electrical conductivity values at elevated temperatures, whereas no changes in σ values were observed at lower temperatures (< 450 K). This behavior was explained by the degradation of the complexes at higher temperatures to give rise to metal oxide products at the final stages. The heterogeneous chemical equilibrium for exchange of La 3+ and Ce3+ metal ions by H+ ions has been investigated complexometrically and titrimetrically. The X-ray diffraction pattern indicated that these complexes are amorphous in nature. Infrared absorption spectra indicated the presence of chelated La3+ and Ce3+ metal ions with alginate macromolecular chains. A geometrical structure for chelation of lanthanum(III) and cerium(III) to the carboxylate and hydroxyl functional groups of the alginate macromolecule is suggested and discussed in terms of complex stability.

Kinetics and mechanism of oxidation of chondroitin-4-sulfate polysaccharide by chromic acid in aqueous perchlorate solutions

The kinetics of chromic acid oxidation of chondroitin-4-sulfate polysaccharide as sulfated carbohydrates at a constant ionic strength of 4.0 mol dm(-3) has been investigated, spectrophotometrically. The reaction kinetics showed a first-order dependence in chromic acid and fractional-first-order kinetics with respect to the chondroitin-4-sulfate concentration. The influence of [H(+)] on the reaction rates showed that the oxidation process is acid-catalyzed. Added Mn(2+) ions indicated the formation of Cr(IV) as intermediate species. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The kinetic parameters have been evaluated and a tentative reaction mechanism in good consistent with the kinetic results obtained is discussed.

Kinetics and mechanism of permanganate oxidation of iota- and lambda-carrageenan polysaccharides as sulfated carbohydrates in acid perchlorate solutions.

The kinetics of oxidation of iota- and lambda-carrageenan as sulfated carbohydrates by permanganate ion in aqueous perchlorate solutions at a constant ionic strength of 2.0 mol dm(-3) have been investigated spectrophotometrically. The pseudo-first-order plots were found to be of inverted S-shape throughout the entire courses of reactions. The initial rates were found to be relatively slow in the early stages, followed by an increase in the oxidation rates over longer time periods. The experimental observations showed first-order dependences in permanganate and fractional first-order kinetics with respect to both carrageenans concentration for both the induction and autoacceleration periods. The results obtained at various hydrogen ion concentrations showed that the oxidation processes in these redox systems are acid-catalyzed throughout the two stages of oxidation reactions. The added salts lead to the prediction that Mn(III) is the reactive species throughout the autoacceleration periods. Kinetic evidence for the formation of 1:1 intermediate complexes was revealed. The kinetic parameters have been evaluated and tentative reaction mechanisms in good agreement with the kinetic results are discussed.

Kinetics and Mechanistic Approach to Palladium (II)-Catalyzed OxidativeDeamination and Decarboxylation of Leucine and Isoleucine byAnticancer Platinum (IV) Complex in Perchlorate Solutions

Oxidations of two aliphatic α-amino acids (AA), namely, leucine and isoleucine by hexachloroplatinate (IV) as an anticancer platinum (IV) complex has been studied using a spectrophotometric technique in perchlorate solutions in the presence of palladium (II) catalyst at a constant ionic strength of 1.0 mol dm-3 and at 25°C. The reactions did not proceed in the absence of the catalyst. The reactions of both amino acids showed a first order dependence on both [PtIV] and [PdII], and less than unit order dependences with respect to both [AA] and [H+]. Increasing ionic strength and dielectric constant of the reactions medium increased the rates of the reactions. A probable oxidations mechanism has been suggested and the rate law expression has been derived. Both spectral and kinetic evidences revealed formation of 1:1 intermediate complexes between AA and PdII before the rate-controlling step. The oxidation products of the investigated amino acids were identified as the corresponding aldehyde, ammonium ion and carbon dioxide. The activation parameters of the second order rate constants were evaluated and discussed

Kinetics and Mechanism of Oxidation of Vanillin by Chromium(VI) inSulfuric Acid Medium

The kinetics of oxidation of vanillin (VAN) by chromium(VI) in sulfuric acid medium was studied by a spectrophotometric technique. The reaction exhibited a first order dependence with respect to [Cr(VI)] and fractionalfirst orders with respect to [VAN] and [H+]. Varying ionic strength or dielectric constant of the reaction medium had no significant effect on the oxidation rate. The proposed mechanism includes an intermediate complex formation between vanillin and chromium(VI) before the rate-determining step. The final oxidation product of vanillin was identified by both spectral and chemical analysis as vanillic acid. The suitable rate law has been deduced. The reaction constants included in the various steps of the suggested mechanism have been evaluated. The activation parameters of the rate constant of the rate-determining step of the mechanism and the thermodynamic quantities of the equilibrium constant have been evaluated and discussed.