Portugaliae
Electrochimica Acta

Corrosion inhibition of 3-phenyl hydrazonoacetyl acetone derivatives on electrodeposited tellurium and palladium in nitric acid was measured by using electrochemical method. Polarization curves showed that these compounds are cathodic inhibitors. The inhibition appears to function through general adsorption following the Flory-Huggins adsorption isotherm. The rate of corrosion depends on the nature of the inhibitor and its concentration, mode of interaction with the metal surface, molecular size, formation of complexes and the active center in the molecules and its electron charge density. Also, ΔGoads. values were calculated. The reaction rate was found to be proportional to the absolute value of the Hammett constant (s).

Formation of complexes of alkaline-earth cations with crown ethers containing an anthraquinone unit (AQ18C6 and AQ21C7) was investigated in methanol and acetonitrile solutions. Stability constants of the resulting complexes were estimated by means of potentiometric methods. The results obtained show the formation of complexes of the LM2+ type for all alkaline-earth ions; for the larger cations, (Sr2+ and Ba2+) and in excess of ligand, L2M2+ complexes were also detected. The most stable complexes were obtained with Ba2+ cation and for both ligands. The binding strength for the cations towards AQ18C6 and AQ21C7 ligands and in both solvents, increased in the order, Mg2+ < Ca2+ < Sr2+ < Ba2+. The results of this study suggest that on the 1:1 complexes, the size of the cation and its fit into the macrocyclic internal cavity of the ligand was a dominant factor on the coordination binding. The number of donor atoms in the ring of the macrocycle does not affect the binding strength and the AQ18C6 complexes have larger stability than the corresponding AQ21C7 complexes. The presence of an anthraquinone unit on the structure of the crown ether induced a decrease of the cation binding strength. The external carbonyl group of the ligand molecules was not involved on the coordination to the cation. Considering the two solvents, the complexes were more stable on acetonitrile, the solvent of weaker solvating capacity.

The corrosion behavior of pure copper rotating cylinder electrode (RCE) exposed to 3% NaCl or artificial seawater prepared as Vätäänen nine salt solution (VNSS) has been studied using electrochemical impedance spectroscopy (EIS) and polarization techniques. EIS experiments for copper RCE were carried out at different rotation rate from 0 rpm to 1600 rpm. Polarization resistance (Rp) values were obtained from both EIS and polarization experiments. Excellent agreement between impedance and polarization data is observed. RCE experiments demonstrated that Ecorr and corrosion rate for copper depend linearly on rotation speed r0.7. The results obtained showed that EIS is a powerful electrochemical method to follow the change of corrosion mechanisms.

A few 1-aryl-2,5-dithiohydrazodicarbonamides and their triphenyltin and dibutyltin complexes have been studied as corrosion inhibitors for mild steel in dimethyl sulphoxide containing HCl at 25 ºC using electrochemical polarisation technique. Among dithiohydrazodicarbonamides, ethoxyphenyl derivative exhibited maximum inhibition efficiency (IE) followed by benzyl and phenyl analogues. The same order of IE was observed in their corresponding organotin complexes; however, IE of a complex was found to be significantly higher than that of the constituents ligand. All organotin complexes behaved predominantly as cathodic inhibitors. Triphenyltin complexes proved to be better corrosion inhibitors than their dibutyltin analogues.

The objective of the present work is the study and optimization of a voltammetric methodology to determine palladium traces and ultratraces, with the purpose of being able to establish the environmental levels of this element and to verify if a contamination takes place starting from the gases of escape of the vehicles equipped with catalytic converters. The voltammetric determination of palladium is based in the formation of a complex of palladium with dimethylglyoxime that adsorbes actively on the surface of a hanging mercury drop electrode, for then to be reduced when making the square wave potential sweep. The quantification is made by the method of standard additions. The study of interferences demonstrated that Na+, Mg2+, K+, Ca2+, Zn2+, Cu2+ and Al3+ are not even interferences at the level of 10 mg/L. The detection and quantification limits of the methodology are respectively 10 ng/L and 33 ng/L, with a sensibility of (4.3±0.8)*102 nA L/ng.

Studies of the corrosion evaluation of SS-304 stainless steel exposed in aqueous lithium bromide solution have been carried out applying the electrochemical noise technique, polarization curves and the weight loss method. The test temperatures were 50, 60 and 70 °C, and the exposure time was for fifteen days. The main objective was to determine the corrosion rates and the type of corrosion that SS-304 suffers under the mentioned conditions with the purpose of evaluating its application to heat pumps/transformers. The results showed that at the three test temperatures the type of corrosion was a mixed and pitting process. At 60 °C, it was observed some anodic peaks at the fifth day of exposure, indicating pitting nucleation. From 7 to 12 days a regular and continue pitting process was observed, and then the corrosion process became in generalized type. At 70 °C, some isolated and medium intensity peaks were observed, presenting behaviour of some mixed and pitting corrosion. The resistance noise was calculated through a statistical analysis, and then the Stern-Geary equation and Faraday Law were applied to determine the mass loss, which was compared to that obtained from weight loss method. Tafel slopes were determined from experimental polarization curves. To support the metallic oxidation carried out on the stainless steel surface, atomic absorption analysis was made to the solution corrosion products.

One of the main limiting factors of the electrocoagulation, as a process of treatment for remotion of contaminants from residual waters, is not knowing the degree of interaction of some variables which could significantly affect the system. The electrode passivation is one of them once its presence limits the emission of metallic ions and consequently the treatment time is increased as well as cost, and remotion efficiency is decreased. In the present work potentiodynamic and potentiostatic curves were used to observe the behaviour of current density vs. pH, electrical conductivity, distance between electrodes, auxiliary electrode area and applied potential difference. We found out that all the above variables influence the current density, that passivation is at 50 mV, independently of all the other variables, and that at 2000 mV, only is observed when pH = 2 and high electrical conductivities.

The electrochemical behaviour of five different complexes of cobalt with 2,4-bis(trimethylsilylethynyl)thiophene was studied, concluding that the presence of aromatic ligands gives rise to electronic communication effects that allow to define them as molecular wires. The stability of the compounds and of the products of oxidative and reductive charge transfers increases at a temperature of -30 °C.

Inconel 600 has been designed to heat resistance. It is used in the chemistry industry, food industry and, of course, in the production of electric energy, among others. The goal of this project was to decrease the costs in the equipments and pipes deterioration by prolonging their lifetime, controlling and preventing their deterioration by means of appropriated and programmed maintenance, but above all knowing the mechanism and kinetic of corrosion that affects them. We used polarization curves to evaluate the effect of wild culture isolated from a traditional thermoelectric plant located northern Mexico. The studied culture was isolated by enrichment cultures in two phases, in a selective medium for sulfate-reductive bacteria in environmental temperature. It was selected for being thermo resistant and promising the largest influence in the corrosion rate. Inconel 600 keeps a multiple protection control until week 7, then it becomes an anodic protection control and later it becomes unstable to these cultures.

For stainless steel 316 evaluation, reinforced concrete samples (12x12x25 cm), using four carbon steel bars and/or 316 stainless steel and two graphite reference electrodes were carried out. The concrete has resistance of 00 Kg/cm2 and a water/cement ratio of 0.65. The samples were exposed to an artificial environment of 5% of saline concentration and carbon dioxide, evaluating periodically the state of the samples in each environment. Electrochemical evaluations, such as potential measurement vs. Cu/CuSO4 electrode and polarization resistance were carried out. In addition, the cyclical polarization of stainless steel samples in pore solution (pH = 13.40) with different chloride concentration (0%, 0.5% and 5% chloride concentration) were evaluated. Stainless steel exposed for 6477 hours in saline environments showed very low corrosion rate for stainless steel, while carbon steel showed corrosion rate from moderate to high. Galvanic couples (stainless steel-carbon steel) showed intermediate corrosion rate. In carbonation environments low corrosion rate were detected for both materials. With cyclical polarization with 5% NaCl, corrosion products and pitting were observed.

Poly-N-vinylcarbazole (PNVCz) can be obtained by two different ways: when the reaction takes place through the vinyl group of the monomer, a white, linear-chain polymer, with interesting photoconducting properties, is obtained. When the polymerization occurs through the aromatic rings, the main product is a green, cross-linked polymer. Polymerization of N-vinylcarbazole (NVC) is possible by electrochemical oxidation. Direct anodic oxidation leads mainly to the green form of the polymer. Protons released from the initial oxidation of the aromatic rings, induce the polymerization through the vinyl group. Indirect electrolysis, making use of an intermediate to achieve oxidation of the monomer, is also possible. In particular, the electrochemical generation of Ce(IV) allows to increase selectivity towards the linear-chain polymer, and can be the basis for the development of a new process, involving the anodic oxidation, in aqueous phase, of Ce(III) to Ce(IV), which will activate the polymerization reaction through the vinyl group. This work presents results from initial characterization, by cyclic voltammetry, of the reacting system. The anodic polymerization of the monomer (NVC) was carried out in acetonitrile, using sodium perchlorate as supporting electrolyte, in the presence and in the absence of cerium salts. The voltammetric response of Ce(III) in aqueous phase, as a possible initiator for the polymerization, is also presented.

In the present study we have made the numeric simulation by finite elements of the cathodic protection by printed current system for the buried duct. The built model was based on the steel carbon type SAE-AISI 1015, and this steel is the constituent material of the duct. This work allowed analyzing the potential distribution in the proposed project and the parameters that more influence the variation of this potential. Those parameters were such as resistivity of the soil, distance between cathode and anode, position of the anode, potential and diameter of the cathode. As a result it was verified that the resistivity of the electrolyte and the distance cathode/anode influence significantly the distribution of the potential of the projected system of cathodic protection.

The reinforced concrete is a versatile and resistant material and it is used in several construction projects; for this reason the improvement of concrete properties and protection of the reinforced steel against corrosion is an active research area. Diverse methods are applied on the steel or on the concrete to protect them. The present investigation is directed towards the development and performance evaluation against corrosion of the reinforcement concrete, containing two different fly ash and blast furnace slag mixtures, in saline environments, and the corrosive evaluation was performed by electrochemical noise technique. The results show an improvement of the steel reinforcement corrosion resistance.

The development of mathematical models and the simulation of cathodic protection systems applied to buried tubing are presented. The solution of partial differential equations is obtained by numerical methods like finite elements and boundary elements. The purpose is developing a quantitative method of potential distribution prediction on the surface of the buried structure, covering aspects like selection of materials, geometric configuration and design of the system. As verification problems were used the problem of the square tank, and the problem of the cylindrical container. Finally two cases of buried structures are presented.

Fue evaluado un método voltamperométrico con preconcentración adsortiva y catálisis, utilizando el electrodo de gota suspendida de mercurio, para la determinación simultánea de ultratrazas de platino y rodio. Las condiciones óptimas establecidas fueron obtenidas luego de la optimización secuencial, consiguiéndose obtener una linealidad hasta los 6.00 ng/L de platino y los 0.7 ng/L de rodio. Los límites de detección y de cuantificación obtenidos son 4.0 ng/L y 10 ng/L para platino y 1.0 ng/L y 3.0 ng/L para el rodio.

It was developed and validated an analytical methodology able to quantify aluminium in haemodialysis fluids, based on the reaction of aluminium with cupferrron (ammonium salt of N-nitroso phenyl hydroxyl amina), on the adsorption of the complex on a hanging drop mercury electrode, and on the measurement of the reduction current of the complex. Parameter validation was done using square wave voltammetry for accumulation potential, time of accumulation, frequency, pulse amplitude, equilibrium time, cupferron concentration, optimum pH. Performance parameters of the method were established: detection limit, quantification limit, reliability, lineal interval for the calibration curves. The method was applied to haemodialysis mineralized fluids, being done the quantification of the aluminium presented.

In the present paper we have carried out a study in order to determine the grade of corrosion affectation in concrete structures reinforced by the incorporation of additives, using electrochemical techniques and analyzing the respective effect on their mechanical properties. Quantitative and qualitative determination of their properties has been done (chemical analysis of the additives and steel, resistance to the compression, and flexural strength, porosity, and water permeability). The methodology was carried out according to ASTM standards and the action of the admixtures was evaluated using corrosion potentials and corrosion rates. The carbonatation and penetration of chlorides were also determined. The study was supplemented with a morphologic characterization by means of a scanning electron microscope. Specimens with and without reinforcement were elaborated, three of each being tested in order to obtain an average. Prismatic specimens without reinforcement were also casted with the following chemical additives: air-entraining, plasticizers, retardants, accelerating, coloring and fly ash. After curing, they were exposed to an aggressive atmosphere with sodium chloride. The general performance of the specimens after the period of exposition is good, since practically all of them developed very low corrosion rates, between 0.55 × 10-4 and 4.76 × 10-4 mA/cm2.

The objective of this paper is the establishment of the better instrumental conditions of analysis for the determination and quantification of mercury in environmental samples by potentiometric stripping analysis. This determination is based in the deposition of mercury into a thin gold film, previously deposited onto a glassy carbon electrode, and then stripped back to the work solution by means of an added oxidant agent. We carried out tests to determine the oxidant concentration, electrolysis potential, support electrolyte and its concentration, potassium chloride concentration and the detection / quantification limits, having in mind to determine in a precise, reliable and reproducible form the presence of mercury, its further quantification, previous mineralization by microwave digestion and its preconcentration by cation exchange column chromatography, to eliminate interferences from metallic ions. The quantification was carried out by the standard additions method. This work shows a detection limit of 5 μg/L and quantification limit of 17 μg/L.

It was developed a sensitive analytical methodology to determine iron in water samples and other matrixes. It was used a differential pulse cathodic stripping voltammetry technique and adsorptive preconcentration with KSCN as a ligand and NaNO2 as a catalytic agent. The methodology has a linear range between 0.7 mg/L and 10.0 mg/L, a detection limit of 0.2 mg/L and a quantification limit of 0.7 mg/L. The averaged sensitivity is 344 nA/(mg/L). The accuracy has a recovery of 102% for 1.0 mg/L of iron with a variation coefficient of 4%. Also it was studied the linearity of the Fe-cathecol system, which has an average sensitivity of 4 nA/(mg/L), much lower than the one of the Fe-KSCN system, and a wider linear range from 2.4 mg/L to 50.0 mg/, a detection limit of 0.7 mg/L and quantification limit of 2.4 mg/L, with a variation coefficient of 8% and recoveries near 100% at different concentration levels.

To evaluate the electrochemical parameters of the reinforced concrete specimens at laboratory level there is no problem at all, because one can use any well-known electrochemical technique, but in site monitoring, there are few techniques being able to obtain these parameters. In this work a viable alternative is presented for the electrochemical evaluation of the reinforced concrete specimens in laboratory or in site monitoring. In order to have a reference of the corrosion rate obtained with the electrochemical noise technique and to be able to establish if these are real ones, measurements with commercial equipment were made applying the polarization resistance technique.