Portugaliae
Electrochimica Acta

Square-wave voltammetry was used to explore the adsorption property of cefadroxil complex with copper ions on the hanging mercury drop electrode (HMDE). By employing the adsorptive stripping voltammetric approach, a sensitive electroanalytical method for the quantitative analysis of cefadroxil antibiotic was achieved. A well-developed voltammetric peak was obtained in pH 10 Britton-Robinson buffer (B-R buffer) at -650 mV. The cyclic voltammetric studies indicated that the reduction process was irreversible and primarily controlled by adsorption. An investigation of the variation of adsorptive voltammetric peak current with supporting electrolyte, pH, accumulation time, accumulation potential, scan rate, pulse amplitude, SW frequency, working electrode area and convection rate has resulted in the recognition of optimal experimental conditions for cefadroxil analysis. The studied electroanalytical signal showed a linear response for cefadroxil in the concentration range 6E-7 - 2E-6 mol L-1 (r = 0.999). A limit of detection of 2E-9 mol L-1 with relative standard deviation of 2.783 RSD% and mean recovery of 99% was obtained. Possible interferences by several substances usually present in pharmaceutical formulation were also evaluated. The analytical quantification of cefadroxil in commercially available pharmaceutical formulation was performed and compared with data from HPLC technique.

Corrosion of the embedded steel reinforcements (rebars) in concrete is the major reason for the deterioration of concrete structures. One of the effective methods of overcoming this serious problem is by applying a barrier coating to the steel rebars. The barrier coating on steel rebars isolates the steel from the immediate environment and also acts as an insulator to prevent the corrosion. Four different coatings have been formulated using resins such as epoxy silicone-polyamide, polyester polyol-aromatic isocyanate, and acrylic polyol-aromatic isocyanate. These formulations consist of either ordinary portland cement (OPC) or fly ash as extender (pozzolanic pigments) and titanium dioxide (TiO2) and zinc phosphate as the main pigment. All these coatings have been studied for their barrier protection and other mechanical properties. Evaluation study of these coatings include Electrochemical Impedance Spectroscopy (EIS), chemical resistance tests and mechanical tests such as flexibility, impact resistance, adhesion, hardness and abrasion resistance, etc., as per ASTM standards and the results are discussed elaborately. It has been concluded from this study that the epoxy silicone-polyamide resin based coating formulation shows good mechanical properties in addition to the barrier protection to the steel rebars from the corrosive environments.

Adsorption of film forming corrosion inhibitors on metallic surfaces led to a decrease in corrosion rates, since the adsorbed organic molecules behave as chemical and physical barriers for cathodic and anodic reactions. A novel and simple methodology to characterize commercial corrosion inhibitors is proposed. Fundamental studies of film forming corrosion inhibitors adsorption on platinum and its correlation with corrosion inhibition efficiencies of steel provide useful information for quality control of film forming inhibitors.

In the present work, a study of the photoelectrochemical characteristics and chemical structure of anodic films formed onto different Sn1-xInx (0 ≤ x < 0.3) alloys in 0.2 M NaOH is presented. The electrochemical behavior of the alloys was studied by means of cyclic voltammetry. The optical band gaps of the passive films were determined by photocurrent spectroscopy, while its chemical structure was studied by Fourier transform infrared reflection-absorption spectroscopy. The experimental results indicate that the anodic films consist of hydroxylated species of the type InySn(1-y)(OH)4-y. The films are enriched in In and, for x > 0.25, In(OH)3 is the dominant component of the surface layers. The existing theoretical background was used to estimate the relative concentration of Sn and In in the films from the band gap measurements.

This work aims to investigate the electro reduction of nitrate at copper elecrode in HClO4 medium by the linear sweep voltammetry and convuctivity measurement methods. Two charge transfer steps were detected, the first one corresponding to adsorption and reduction of nitrate to nitrite and the second step consists of reducing nitrate to monoxide of nitrogen.

The effect of phenylthiourea as a corrosion inhibitor for low carbon steel at different hydrochloric acid concentrations, different temperatures and fixed speed of electrode rotation, were addressed in this work. Polarization technique was used to evaluate the corrosion rates parameters. The corrosion rate of low carbon steel increases with temperature and follows Arrhenius equation in all acid concentrations in presence and absence of the inhibitor. Detailed thermodynamic parameters of activation (ΔHact and ΔSact) for the corrosion reaction were obtained using nonlinear estimation method, while adsorption parameters (ΔGads, ΔHads and ΔSads) were obtained using graphical method. Maximum inhibitor efficiency was (96.44%) obtained at 1 M HCl at 333 K and 1 g/L inhibitor concentration.

The corrosion of zinc in 0.01 to 0.04 M H2SO4 was studied using gravimetric and gasometric methods of monitoring corrosion. The results obtained indicate that clarithromycin is a good adsorption inhibitor for the corrosion of zinc in H2SO4. The inhibition efficiency of clarithromycin increases with increasing concentration but decreases with increasing temperature. There was no significant difference between the inhibition efficiencies of clarithromycin obtained at various concentrations of H2SO4 (P>0.5), but values of inhibition efficiency tend to decrease with increasing concentration of the acid. The adsorption of clarithromycin on zinc surface is endothermic, spontaneous and is best described by Langmuir adsorption isotherm. Calculated values of activation energies and free energies of adsorption indicate that the adsorption of clarithromycin on zinc surface supports the mechanism of physical adsorption.

Influence of various carrier additives and brightener additives on the voltammetric behavior of zinc electro deposition from an alkaline non-cyanide bath was studied. Two different cathodic peaks were observed. Peak I has been attributed to hydrogen reduction / UPD of zinc and peak II to reduction of the metal. The extent of polarization of the zinc deposition to more negative potentials and the corresponding peak current decide the nature of deposits. PVA was found to be the best carrier additive. PVA chains retain zinc hydroxyl anions and control the speed of the rate determining step. Unsaturated aldehydes bring about 3-dimensional nucleation and further increase the polarization when added with PVA.