Portugaliae
Electrochimica Acta

Molecular structure of the azo-dye derived from sulfonamide was synthesized. The elucidation of ligand and complex structures were studied by electronic, infrared and 1H NMR spectroscopies. Proton-ligand constants of sulphonamid azo-derivatives and the stability constant of Mo (III), VO (II), UO2 (II) and Co (II) metal ions with sulfonamide azodye derivatives have been determined potentiometrically in 0.1 M KCl and 30% (v/v) ethanol-water mixture. The data are discussed in terms of the electronic character of the substituents and of the change in temperature. The pK1-H values have been found to increase with increasing electron donating nature of the subsituents. The evaluated dissociation processes are non spontaneous, endothermic and entropically unfavourable. The order of the stability constants of the formed complexes was found to be Mo3+ > VO2+ > UO22+ > Co2+. The influence of substituents on the stability of the complexes was examined on the basis of an electron repelling property of the substituent. The effect of temperature on the stability of the formed complexes was studied and the corresponding thermodynamic parameters (∆G, ∆H and ∆S) were evaluated and discussed. The stoichiometries of these complexes were determined conductometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes.

The inhibition efficiency (IE) of an aqueous extract of Hibiscus rosa-sinensis (white) in controlling corrosion of aluminium at pH 12 has been evaluated by weight loss method in the absence and presence of Zn2+. The formulation consisting of 8 mL flower extract (FE) and 50 ppm of Zn2+ had 98% inhibition efficiency. Polarization study revealed that this formulation functioned as cathodic inhibitor. AC impedance spectra revealed the presence of a protective film formed on the metal surface. FTIR spectra revealed that the protective film consisted of a complex formed between the active principle of the flower extract and Al3+.

Oxygen reduction reaction (ORR) was investigated on a multi-walled carbon nanotubes (MWCNTs)-modified edge plane pyrolytic graphite (EPPG) electrode using cyclic voltammetry (CV) in three kinds of room temperature ionic liquids (RTILs), i.e., 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-n-propyl-3-methylimida-zolium tetrafluoroborate (PMIBF4), and 1-n-butyl-3-methylimidazolium tetrafluoro-borate (BMIBF4). The results demonstrated that, after being modified by MWCNTs on the EPPG electrode, both the reduction peak current of oxygen and the oxidation peak current of superoxide anion were all dramatically increased, and the values of standard rate constant, κs, corresponding to ORR, were greatly enhanced. Under the same condition, in PMIBF4, MWCNTs-modified EPPG electrode exhibited the most satisfied electrocatalysis for ORR, in which standard rate constant, κs, was improved from 2.9 × 10-3 cm s-1 on a EPPG electrode, to 10.4 × 10-3 cm s-1. While in EMIBF4 and BMIBF4, after being modified by MWCNTs, the value of κs was increased from 4.3 × 10-3 to 8.3 × 10-3 and 2.3 × 10-3 to 4.2 × 10-3 cm s-1, respectively. For the catalysis of MWCNTs-modified EPPG electrode towards ORR, the enhanced surface area of electrode and the increased amount of “defect” sites on electrode were thought to be the main reasons for our obtained results.

The inhibition efficiency (IE) of K3[Fe(CN)6] in controlling corrosion of carbon steel in aqueous solution containing 60 ppm of Cl- in the presence and absence of Zn2+ has been evaluated by weight loss method. The formulation consisting of 100 ppm K3[Fe(CN)6] and 50 ppm Zn2+ offers 98% inhibition efficiency to carbon steel immersed in aqueous solution containing 60 ppm Cl-. A synergistic effect exists between K3[Fe(CN)6] and Zn2+. As immersion period increases, the inhibition efficiency of K3[Fe(CN)6]─ Zn2+ system decreases. Polarization study reveals that this formulation controls the cathodic reaction predominantly. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Prussian blue and Zn(OH)2. The film is found to be UV fluorescent.

The inhibition efficiency (IE) of an aqueous extract of beet root (BR) in controlling corrosion of carbon steel in well water in the absence and presence of Zn2+ has been evaluated by mass loss method. The formulation consisting of 4 mL of BR extract and 50 ppm Zn2+ offers 98% inhibition efficiency to carbon steel immersed in well water. A synergistic effect exists between BR extract and Zn2+. Addition of N-Cetyl-N,N,N – trimethylammonium bromide (CTAB) does not change the excellent inhibition efficiency of the BR – Zn2+ system. The BR – Zn2+ system shows excellent IE up to 7 days. Polarization study reveals that this formulation controls the cathodic reaction predominantly. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Fe2+ - betanin complex and Zn(OH)2. The film is found to be UV - fluorescent.

The corrosion inhibition of mild steel in H2SO4 in the presence of methocarbamol was studied using thermometric and gasometric (hydrogen evolution) methods. The study revealed that the corrosion rate increases with temperature, time and concentration of H2SO4. Addition of methocarbamol to the corrodent solution lowered the corrosion rate of mild steel. Inhibition efficiency (%I) of methocarbamol was found to increase with concentration and decreased with temperature. Adsorption of methocarbamol molecule on mild steel surface was found to obey the Langmuir adsorption isotherm. The phenomenon of physical adsorption is proposed from the obtained thermodynamic parameters.

The inhibition efficiency (IE) of malonic acid (MA)-Zn2+ system in controlling corrosion of carbon steel immersed in well water has been evaluated by weight-loss method. The formulation consisting of 50 ppm of MA and 50 ppm of Zn2+ has 85% IE. The influence of N-cetyl-N,N,N-trimethylammonium bromide (CTAB) and N-cetyl pyridinium chloride (CPC) on the IE of the MA- Zn2+ system has been studied. At lower pH value (pH=6) IE decreases and in alkaline medium (pH=8) IE increases. Polarization study reveals that MA-Zn2+ system functions as a mixed inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Fe2+-MA complex and Zn(OH)2.

Inhibitive and adsorption properties of ethanol extract of vernonia amygdalina for the corrosion of mild steel were studied using weight loss, thermometric, gasometric and IR methods of monitoring corrosion. The results revealed that ethanol extract of Vernonia amygdalina inhibited the corrosion of mild steel. The inhibition efficiency of the extract increased as the concentration of the extract increases. The inhibitor was found to function by being adsorbed on the surface of mild steel. The adsorption of the inhibitor followed the Langmuir adsorption isotherm. IR spectra of the corrosion product (without inhibitor), the extract and the corrosion product (with the inhibitor) confirmed that ethanol extract of vernonia amygdalina is an adsorption inhibitor. Phytochemical studies also revealed that ethanol vernonia amygdalina contains tannin, saponnins, flavanoid and anthraquinone, all of them contributing to the corrosion inhibition. Physical adsorption mechanism has been proposed from the values of some of the thermodynamic parameters obtained.

The aim of this research is to obtain electrodeposits of copper-tin over mild steel substrate. The plating parameters were studied and a model is developed using Artificial Neural Networks (ANN). The electrodeposition of copper-tin was carried out from an alkaline cyanide bath. Copper content of coatings in alloy deposition was determined by using X-ray fluorescence spectroscopy. The results were used to create a model for the plating characteristics and also for studies using ANN. The ANN model is compared with the conventional mathematical regression model for analysis.

Inhibition of the corrosion of zinc in various concentrations (0.01 to 0.05 M) of H2SO4 was studied using weight loss and hydrogen evolution methods of monitoring corrosion. The results revealed that various concentrations of azithromycin (0.0001 to 0.0005 M) inhibited the corrosion of zinc in H2SO4 at different temperatures (303 to 333 K). The concentration of H2SO4 did not exert significant impact on the inhibition efficiency of azithromycin, but inhibition efficiencies were found to decrease with increase in the concentration of the inhibitor. Values of inhibition efficiency obtained from the weight loss measurements correlated strongly with those obtained from the hydrogen evolution measurements. The activation energies for the corrosion of zinc inhibited by azithromycin were higher than the values obtained for the blank. Thermodynamic data revealed that the adsorption of azithromycin on the surface of zinc was endothermic (values of enthalpies of adsorption were positive), spontaneous (values of free energies of adsorption were negative) and was consistent with the adsorption model of Langmuir.

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.