Portugaliae
Electrochimica Acta

This paper proposes the application of the Double Pulse Potential Chronoamperometry (DPPC) technique to modify the ITO electrode surface in order to increase the electrode activity for chlorophenol detection. This technique consists in the application of two sets of potential pulses (anodic and cathodic). We used Ni-triethylenediamine as the electrode-modifying agent. We characterized the modified electrodes using SEM and Cyclic Voltammetry (CV), and determining the amount of film immobilized over the electrode area. We also applied CV to detect 2,4-dichlorophenol using the chemically modified electrodes (CMEs). The application of DPPC led to CMEs with a higher capacity to detect 2,4-DCP than that of the CMEs obtained by Chemisorption and CV.

A new amperometric biosensor for copper determination in food samples was developed through the immobilization of glucose oxidase (GOx) in polyacrylamide gel. The response time for the reaction was studied by observing the percentage inhibition with time at 0.0125 ppm concentration of Cu2+. 2.30 minutes was the optimized response time for the estimation of Cu2+ ion in the solution. Linear range for the detection of Cu2+ by the biosensor was between 0.0125-0.1 ppm. Bioprobe was operationally stable for five days followed by a fall in activity.

The corrosion inhibition of mild steel in 1M H2SO4 by polyvinyl pyrrolidone (PVP) and the synergistic effect of iodide ions were investigated using weight loss and hydrogen evolution methods in the temperature range of 30 – 60 oC. The corrosion rates of mild steel decreased with the increasing concentration of PVP, while the inhibition efficiency (%I) increased. The inhibition efficiency of PVP decreased with rise in temperature, suggesting a physical adsorption mechanism, which was found to follow Freundlich and Temkin adsorption isotherms. The inhibition mechanism was further collaborated by the values of kinetics/thermodynamic parameters obtained from the experimental data. The inhibiting action of PVP was considerably enhanced in the presence of iodide ions and values of the synergism parameter (S1) obtained point to synergistic interactions between PVP and iodide ions.

Electrochemical oxidation of some dyes making wastewater assisted by transition metal (Co, Cu) modified kaolin in an electrolytic cell with graphite plates as electrodes was investigated. H2O2, produced on the surface of porous graphite cathode reacts with the (Co, Cu) modified kaolin catalyst to form strong oxidant (hydroxyl radicals HO*) that can in turn degrade the pollutants adsorbed on the surface of kaolin. Series of experiments were done to prove the synergetic effect of the combined oxidation system and to find out the optimal operating conditions such as initial solution pH, current density, time of electrolysis, and amount of modified kaolin catalyst. It was found that when the initial pH was 3, current density of 40 mA/cm2, electrolysis time of 40 minutes and catalyst dose of 15 g/L, the COD (chemical oxygen demand) removal could reach up to about 100% for the two investigated dyes.

Liquid lead-bismuth eutectic (LBE) may see extensive use as a coolant fluid, and perhaps also as a spallation target, in the next generation nuclear energy system. However, it is very corrosive to the common steels used in nuclear installations. This corrosion problem can be prevented by the formation of a protective oxide layer on the exposed surface of steel. For this purpose, accurately measuring and controlling the oxygen concentration in liquid LBE is very important. Electrochemical oxygen sensors with In/In2O3 and Bi/Bi2O3 reference systems can be used as in situ devices for measuring the oxygen concentration in liquid LBE. YSZ (Yttria Stabilized Zirconia) oxygen sensor with molten bismuth saturated with oxygen as a reference, has been selected to measure the oxygen concentration in LBE coolant system. The oxygen concentration difference across the solid electrolyte and the resultant oxygen ion conduction inside the electrolyte establish an electromagnetic force (EMF) that is used to measure the ppb level of dissolved oxygen concentration in liquid LBE. In this paper, the sensitivity of an YSZ oxygen sensor has been evaluated. Sensor calibration curves in liquid LBE at 450 ºC have been obtained.

Kinetic parameters and stability constants of [Mn – sulfonamides – cephalothin] system were reported at pH = 7.30 ± 0.01 in 1.0 M NaClO4 at 25 ºC. The sulfonamides were sulfadiazine, sulfisoxazole, sulfamethaxyzole, sulfamethazine, sulfathiazole, sulfacetamide and sulfanilamide as primary ligands, and cephalothin as secondary ligand. Values of transfer coefficient (α) varied from (0.41 to 0.59), showing that transition state behaves between oxidant and reductant response to applied potential and it adjusts itself in such a way that the transition state is located midway between dropping mercury electrode and solution interface. The rate constants (k) varied from 3.61 x 10-3 cm.sec.-1 to 9.93 x 10-3 cm.sec.-1, confirming that the electrode processes were quasi reversible. Small changes in potential not only affect the rate of the electrochemical reaction, but also strongly affect the rate constant. Values of stability constants (log β) varied from 1.75 to 9.13, showing that these drugs or their complexes could be used against Mn toxicity.

Diffusion models capable of describing the ionic diffusion inside host materials, e.g. oxides, during intercalation processes, have been reported in the literature. However, the majority of the models do not succeed in establishing a good correlation between diffusion and structural environment. What is frequently described is the influence of an addition solid state reaction. In this paper we discuss about such additional reaction and its influence on the diffusion. The responses were evaluated by means of impedance patterns analyzed in (Snx,Ti1-x)O2 binary systems whose structural disorder control provides a way to evaluate how such structural disorder influences the global diffusion.

The performance of two resin combinations, such as acrylic polyol – aromatic isocyanate and polyester polyol – aromatic isocyanate as durable and effective rebar coatings for steel in concrete has been examined by studying their mechanical properties and by using accelerated tests such as salt spray test and electrochemical impedance spectroscopy. It is found that polyester polyol-aromatic isocyanate combination performs better than acrylic polyol-aromatic isocyanate combination. Incorporation of fly ash in the coating is found to influence the performance of the coating.

Repair and rehabilitation of deteriorated concrete structures are essential not only to utilize them for their intended service life, but also to assure the safety and serviceability of the associated components. A good repair improves the function and performance of the structure, thus prevents ingress of aggressive species to the steel/concrete interface and improves its durability. It is important to evaluate the performance of repair materials available for repairing the deteriorated concrete structures. This investigation was carried out to evaluate the durability characteristics of five types of modified cement based repair mortars. The corrosion resistance of the repair materials was evaluated by conducting various tests such as water absorption, rapid chloride ion penetration test, impressed voltage, 90 days ponding test, macro cell corrosion test, weight loss measurement, etc. Details of the test and their results were discussed. It is concluded that the modified cement based repair mortars formulated with different mineral admixtures (fly ash and/or silica fume) showed improved corrosion resistance.

Acid catalyzed reactions of three proton pump inhibitors (PPIs), namely omeprazole, lansoprazole and pantoprazole, have been investigated and monitored by direct current polarography at dropping mercury electrode (D.M.E) in phosphate buffer (0.1 M) of pH 3-7.5. This gives well defined current-time profiles of individual electroactive degradation products along with their starting materials. The investigation shows that the order of stability of three PPIs can be written as: pantoprazole  omeprazole  lansoprazole. The rate of degradation of PPIs decreases with decreasing the basicity of the corresponding benzimidazole nitrogen of PPIs, as predicted by the effect of individual substituents on each of the benzimidazole rings. At pH 7.5 all three PPIs are almost stable and the observed half wave potentials (E1/2 ) are –1.07 V for omeprazole, –1.25 V for lansoprazole and –1.32 V for pantoprazole. On decreasing the pH from 7.5 to 3.0 the anodic shift in E1/2 values were observed along with degradation of the PPIs and simultaneous appearance of degradation products. The present study may provide an insight for designing more potent new proton pump inhibitors.

The work presented in this paper deals with the investigations on the effect of Cu and Ni on the corrosion behavior of carbon steel under different experimental conditions. Electrochemical techniques like potentiodynamic polarization, linear polarization resistance and AC impedance have been used to investigate the effect of Cu and Ni on the corrosion behavior of carbon steel. The important experimental conditions which include the nature of aqueous medium, metal ion concentration and pH have been taken into account. The instantaneous corrosion parameters as computed by potentiodynamic polarization, linear polarization resistance and AC impedance show an increase in corrosion rates of carbon steel with increasing Cu and Ni concentrations. However, the corrosion parameter as computed by AC impedance for an extended period of one month follows an interesting trend. The presence of Cu and Ni in the aqueous medium produces almost identical effect on the corrosion behavior of carbon steel. The microscopic examination of the test samples, under controlled laboratory conditions, did not show the evidence of localized attack on carbon steel in presence of different concentrations of Cu and Ni.

Erratum to Port. Electrochim. Acta 2008, 26(4), 315-324

Cathodic stripping voltammetric determination of losartan using hanging mercury drop electrode HMDE was described. The method was based on adsorptive accumulation of the species at HMDE and at pH 7, followed by alternating current AC sweep. The behavior of adsorptive stripping response was studied under various experimental conditions, e.g. type of supporting electrolyte, pH, accumulation time, scan rate and mode of sweep (direct current DC, differential pulse DP, square wave SW and AC). In Britton-Robinson buffer solution, pH 7, a quasi-reversible reaction took place. The reduction response was more sensitive than the oxidation one and it was linear over the concentration range of 0.16-1.2 microg/mL. The determination of the cited compound in oral dosages was achieved using the standard addition method. The average of determinations obtained by square wave adsorptive voltammetric method with its standard deviation was 100.1±3%.

A voltammetric procedure optimized by experimental design for glyphosate determination in soil, water and vegetable samples is described. The voltammetry experiments were performed using a hanging mercury drop electrode (HMDE). The DPV variables involved in the optimization process were: voltage step, pulse amplitude, pulse interval, voltage step time and concentration of the supporting electrolyte. A full 25 factorial design was chosen to evaluate these effects. From the results obtained by the factorial design the three most important factors were determined. These variables were evaluated with a central composite design. Under the optimized conditions, the operational range was from 0.050 to 100.0 mg dm-3 and the detection and quantification limits were 14 and 48 µg dm-3, respectively. The optimized method was successfully applied to glyphosate determination in soil, water and vegetables after purifying with an ion exchange resin and derivation.

The influence of phosphate of aluminum (PA) on the corrosion inhibition of mild steel in phosphoric acid solution was studied using the weight-loss method. The electrochemical performance of the inhibitors was also investigated through potentiodynamic polarisation and EIS measurements. The inhibition efficiency of inhibitor increases with concentration to attain 84 % at 10-2M of PA in 0.33 M H3PO4. Polarization studies show that PA is a mixed-type inhibitor and acts both on the cathodic and anodic reactions without changing the mechanism of the hydrogen evolution reaction. The inhibition efficiency of PA is temperature-dependent in the range 298 - 363 K, the associated activation energy has been determined. PA adsorbs on the steel surface according to a Langmuir isotherm adsorption model.

The computational simulation of the Bray-Liebhafsky (BL) oscillating chemical reaction by differential kinetic methodology is carried out in this work. According to the mechanism of Treindl and Noyes involving 10 reaction steps, the changes of the concentrations of I2 and O2 in solution are simulated. When the control parameters are alpha = 0.55, beta = 0.2882 and delta ＜ 0.6, the differential equations present periodic solution, and the oscillations can be observed in 150 min. If , alpha and beta are taken as the control parameters, respectively, the bifurcation points would be observed in the processes of control parameters, changing successively with the critical values of alpha = 0.55，beta = 0.2882，and delta = 0.6. The acidity of solution on the nonlinear phenomena is also investigated in detail.

Nickel-diamond composite coatings are produced by electro deposition using sedimentation techniques on mild steel substrate at various cathode current density, pH and temperature. Electro deposition was carried out from a conventional Watts bath. Natural diamond powder of 6-12 m size was used in the study. The volume percent incorporation of diamond on the coated specimens was measured gravimetrically. Artificial Neural Network (ANN) and regression models (a mathematical model) were used to predict the volume percent incorporation of diamond in the Ni-diamond metal matrix. In this work, Volume fraction of diamond deposition (Vfd) was taken as response variable (output variable) and current density, pH and temperature were taken as input variables. The prediction of response variable was obtained with the help of empirical relation between the response variable and input variables using ANN and also through DOE. The predicted values of the responses by ANN and regression models were compared with the experimental values and their closeness with the experimental values was determined.

The calculation with rotational elliptic coordinates of the streaming potential in the vicinity of a disk-shaped sample rotating in an electrolytic solution is presented. The measurement of this streaming potential is used to determine the zeta potential of planar surfaces. Rotational elliptic coordinates are favored in relation to integral transform methods because only simple mathematical methods are employed to explain the theory of this technique.