Portugaliae Electrochimica Acta

Adsorption and Inhibitive Properties of Lincomycin for the Corrosion of Zinc in 0.01 - 0.05 M H₂SO₄

Inhibition of the corrosion of zinc in various concentrations of H2SO4 by lincomycin was studied using weight loss and hydrogen evolution methods. The results obtained indicated that lincomycin is a good adsorption inhibitor for the corrosion of zinc in H2SO4 solutions. The inhibition efficiencies of lincomycin for the corrosion of zinc in H2SO4 were found to range from 70.90 to 80.32 %, 69.25 to 77.70 % and from 52.11 to 67.49 % at 303, 313 and 323 K, respectively. The inhibition efficiencies decreased with increase in temperature and with increasing concentration of H2SO4 but increased with increase in the concentration of lincomycin. The adsorption of lincomycin on Zn surface is endothermic, spontaneous and is best described by Langmuir adsorption isotherm. Base on the trend in the variation of inhibition efficiency with temperature and the calculated values of the activation and free energies of adsorption, a physical adsorption mechanism is proposed for the adsorption of lincomycin on the surface of zinc.

The Polarographic Reduction and Electrode Kinetics of Anti-depressant Drug Bupropion Hydrochloride

The electroreduction of the antidepressant drug Bupropion hydrochloride has been studied in aqueous media at dme. Single well defined wave was obtained in different supporting electrolytes, like, KNO3, ammonium citrate buffer, acetate buffer, B. R. buffer, etc. The effect of pH on this reduction has been studied in B. R. buffer in the pH range 3.13 - 11.0. The Bupropion hydrochloride is best reduced in slightly acidic medium. This behavior was attributed to the reduction of >C=O group present in the drug. The effect of concentration and temperature on half wave potential has also been investigated. The reduction of drug was found to be irreversible and diffusion controlled, hence kinetic parameters (K0fh, αn) are evaluated using Meites Israel and Gaur Bharagav,s method. Further, with increase in temperature the values of K0fh also increase, showing that irreversibility of the system decreases on increasing the temperature.

Inhibition of Uniform and Pitting Corrosion Processes of Al Induced by SCN^- anions - Part I. Effect of Glycine

As a first step towards inhibition of uniform and pitting corrosion processes of Al in SCN- solutions, glycine (Gly) was used. Full immersion tests, using inductively coupled plasma atomic emission spectroscopy (ICP-AES) method of chemical analysis were used to monitor rates of corrosion. The results obtained from the ICP method have been verified by electrochemical assays based on linear and cyclic polarization measurements. Monitoring the open circuit potential (OCP) of the system as a function of immersion time and Gly concentration was also carried out. SEM and EDX examinations of the electrode surface revealed the adsorption of Gly molecule on the surface. Results showed that the presence of Gly in aggressive SCN- solutions decreased the corrosion and passive currents and shifted the pitting potential to more noble values. Thus Gly inhibited uniform and pitting corrosion processes. The inhibition efficiency of Gly enhanced with its concentration. The potential of zero charge (PZC) of the Al electrode has been studied in 0.04 M KSCN solutions without and with Gly and the mechanism of adsorption is discussed. The adsorption of Gly precluded significant adsorption of the aggressive SCN- anions, and hence the corrosion rate was diminished.

Study of the Anticorrosive Properties of Different Bi-Layers of Polypyrrole - BTSE on Carbon Steel Immersed in NaCl Media

To improve the corrosion resistance of mild steel, in this work, bi-layers of BTSE (bis-(triethoxysilyl) ethane) and Ppy coatings have been deposited via adsorption and electrodeposition, respectively. The anticorrosive properties of these bi-layers have been evaluated in an aggressive medium like 3% NaCl, and compared with the layers of BTSE and Ppy in a separate way. In spite of the aggressive solution, it was evaluated a poor behaviour of both Ppy and BTSE coatings using potential measurements, EIS and SEM techniques. A better behaviour was expected because the preparation of the bi-layers Ppy/BTSE and BTSE/Ppy showed a protective behaviour using SEM and salt spray tests. However, EIS results predicted an evolution of these coatings for long immersion times being evident the oxidation of the steel.

Removal of Heavy Metals Fe³⁺, Cu²⁺, Zn²⁺, Pb²⁺, Cr³⁺ and Cd²⁺ from Aqueous Solutions by Using Eichhornia Crassipes

The adsorption capacity of Eichhornia Crassipes towards metal ions such as Fe3+, Cu2+, Zn2+, Pb2+, Cr3+ and Cd2+, was studied. The adsorption capacity was investigated by batch experiments. The results showed that the removal percentages increased as the weight of sorbent increased, except for Fe3+ and Zn2+. The effect of contact time was also studied and the results showed that the removal percentages increased as the contact time increased for Cr3+, Zn2+ and Pb2+, but for Fe3+, Cu2+ and Cd2+ the removal decreased. The effect of pH of the solution was also studied and the removal percentages increased as pH increased. Also the effect of the initial concentration of metal ions was studied at four different concentrations (5, 10, 30, 50 mg/L); in case of metal ions (Cu2+, Zn2+ and Cd2+) the removal percentages increased by increasing initial concentration. But, for the other metal ions it decreased by increasing initial concentration over 30 mg/L. The order of increasing removal percentages of metal ions at pH=4.86, initial concentration of metal ions 30 mg/L, and after four hours of shaking was: Cu2+< Cr3+

Electrochemical Evaluation of Wrought Titanium -15 Molybdenum Alloy for Dental Implant Applications in Phosphate Buffer Saline

Ti-15Mo alloy has been evaluated for its electrochemical behavior in phosphate buffer saline solution at the physiological temperature of 37 ºC. A two time constant model of a duplex oxide layer has been used to assess the corrosion behavior of the Ti-15Mo alloy-solution interface using electrochemical impedance spectroscopy (EIS). Interfacial characteristics of the inner barrier layer and the outer porous layer have been studied to understand the role of the alloy as an implant. Ti-15Mo alloy shows a very high barrier layer resistance and a tendency to resist localized corrosion.