Portugaliae
Electrochimica Acta

This study is related to the electrochemical polymerisation of aniline in the presence of hydrochloric acid at DC voltages from 1.1 V to 2.1 V with platinum, stainless steel electrodes of uniform cross section. 1 M of acid and 0.1 M of monomer are taken. Efforts are concentrated on the importance of polyaniline deposited on the working electrode and the collection of pure samples out of it from forty trials each. Each trial runs for one hour. Double distilled water is used for the filtering of polyaniline. Due to the presence of mono basic acid, the FTIR peaks are well defined and their presence indicates the definite vibrational modes of the elements. The acid affects the polymerization of aniline and the results are in reasonable agreement with earlier reports. At 1.7 V the conductivity is well exhibited by HCl doped PANI. It is found that the applied DC voltage plays a role on the synthesis of polyaniline using HCl.

CR2032 button cells were fabricated in the laboratory with chemically prepared MnO2 cathode and lithium anode containing LiAlCl4 in PC (propylene carbonate) as electrolyte. These cells where discharged at various currents (15 mA, 20 mA, 25 mA, 30 mA, 35 mA and 40 mA) for various temperatures (0, 10, 30, 40, 50 and 60 °C) galvanostatically. The results are discussed in detail.

The inhibitory effect of diethanolamine (DEA) on corrosion of mild steel in 0.5 M H2SO4 was investigated by various corrosion monitoring techniques. Galvanostatic polarization study revealed that this compound is a very good inhibitor. The inhibition efficiency (I%) varies in the range of 88.7% to 55.3 % for a concentration range of 10-3 M to 10-7 M at 303 K, respectively. A study of corrosion potential (Ecorr) reveals that DEA is a mixed type inhibitor. DEA inhibited mild steel corrosion due to physical adsorption of the inhibitor on the metal surface. The study at higher temperatures indicates that the inhibition efficiency decreases with the increase in temperature. The adsorption of DEA on the mild steel surface in 0.5 M H2SO4 follows the Frumkin’s adsorption isotherm. The results of potentiostatic polarization study revealed that DEA is a strong passivating additive. The results of infra red (IR) spectroscopy, scanning electron microscopy (SEM) and quantum chemical study supplement the results of the electrochemical techniques.

The effect of addition of nano size fumed silica on the conductivity and viscosity behaviour of polymer gel electrolytes containing polyethylene oxide (PEO), ammonium hexafluorophosphate (NH4PF6) and propylene carbonate (PC) has been studied. The addition of PEO increases the viscosity of electrolytes alongwith a small increase in conductivity and polymer gel electrolytes with conductivity higher than the corresponding liquid electrolytes have been obtained. Increase in conductivity with the addition of PEO and fumed silica has been explained to be due to the dissociation of ion aggregates, which is also supported by FTIR results. The thermal stability of polymer gel electrolytes improves marginally with the addition of fumed silica. The conductivity of nano dispersed gels does not show much change over 20-100 ºC temperature range and also remains constant with time.

The use of some -aminoketone derivatives as corrosion inhibitors for nickel in 2 M acid chloride solution was investigated by gravimetric and galvanostatic polarization techniques. It was found that the investigated compounds behave as inhibitors for nickel dissolution and their inhibition efficiencies increase by the addition of iodide ions. Also, the adsorption isotherms were studied and it was found to follow the Frumkin's adsorption isotherm. By increasing the temperature of the corrosive medium containing different concentrations of the tested inhibitors, the corrosion rate of nickel increases, indicating that these inhibitors are physically adsorbed on the metal surface. Finally, some quantum chemical quantities such as HOMO, LUMO and dipole moment of the inhibitors were calculated and correlated with the rate of corrosion.

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%.