Volume 18, Issue 2, 2000
5th March, 2010
Medium Effects on the Dissociation Reactions of Adipic Acid in Ethanol-Water Mixtures
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by G. A. El-Naggar, M. El-Batouti, A. A. Zaghloul
71-87
DOI: 10.4152/pea.200002071
The first and second dissociation constants of adipic acid have been determined by a precise emf method in water and in aqueous binary mixtures of ethanol, over a wide range of solvent composition (0-70%(w/w) ethanol). Measurements were conducted at different temperatures ranging from 30 °C to 60 °C at intervals of 10 °C, by emp measurements. The thermodynamic parameters (∆H°, ∆G° and ∆S°) for the first and second dissociation reactions have been computed, analyzed and discussed in terms of solute-solvent interactions. The pK values have been correlated with the mole fraction of the organic solvent and the effect of dielectric constant on the dissociation processes was then discussed.
Role of Thiourea on the Electrochemical Behaviour of Zinc Glycine Complexes
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by S. Shabanna Begum, C. Siva Kumar, S. A. Mayanna, V. S. Muralidharan
89-98
DOI: 10.4152/pea.200002089
Electrochemical behaviour of zinc-glycine complex has been studied in the presence of thiourea on platinum by cyclic voltammetric technique. The obtained results revealed that zinc-glycine complex undergoes successive reduction to zinc with the formation of monovalent zinc complex in a slow step. Thiourea in the plating bath solution hindered both the deposition and dissolution processes. Hydrogen evolution reaction was hindered by the adsorption of thiourea, which strengthened the M-H(ads) bond and raised the hydrogen over voltage.
Use of 1-Phenylamino-3-(4-Phenylthiosemi carbazone)-Butane-I,3-dione Derivatives as Corrosion Inhibitors for C-Steel in Acidic Chloride Solutions
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by A. K. Mohamed, H. A. Mostafa, G. Y. El-Ewady, A. S. Fouda
99-111
DOI: 10.4152/pea.200002099
The corrosion inhibition of nitrogen, oxygen and sulphur containing compounds in acidic chloride solutions was studied by chemical and electrochemical techniques. The percentage inhibition efficiency was calculated from both methods is in good agreement. The corrosion rate was found to be a function of the nature, concentration and temperature of the medium. The increase in temperature was found to increase the corrosion rate. The inhibitors are adsorbed on the C-steel surface according to the Langmuir isotherm. Some thermodynamic functions were computed and discussed. Quantum data were calculated and the results of HOMO and LUMO showed that the increase in energy of HOMO corresponds to an increase in the inhibition efficiency.
Photochemical Study of Passive Films Formed on Stainless Steels; Influence of the Alloying Elements
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by N. E. Hakiki, A. M. P. Simões, M. G. S. Ferreira, M. da Cunha Belo
113-128
DOI: 10.4152/pea.200002113
The study of the electronic structure of the passive films formed on high purity Fe-Cr, Fe-Cr-Ni and Fe-Cr-Ni-Mo stainless steels was carried out by photoelectrochemical measurements. Bandgap energy and quantum efficiency are associated with the changes promoted by the alloying elements in the bilayer structure of the passive films. The analysis of the photocurrent as a function of the applied potential reveals a Poole-Frenkel effect. The donor densities extracted from photoelectrochemical measurements are compared to those obtained in previous works from capacitance measurements.
