J. L. Guiñón

Effect of pH and chloride concentration on the removal of hexavalent chromium in a batch electrocoagulation reactor

In this work, the effect of pH and chloride ions concentration on the removal of Cr(VI) from wastewater by batch electrocoagulation using iron plate electrodes has been investigated. The initial solution pH was adjusted with different concentrations of H(2)SO(4). The presence of chloride ions enhances the anode dissolution due to pitting corrosion. Fe(2+) ions formed during the anode dissolution cause the reduction of Cr(VI) to form Cr(III), which are co-precipitated with Fe(3+) ions at relatively low pH. The reduction degree of Cr(VI) to Cr(III) and the solubility of metal hydroxide species (both chromic and iron hydroxides) depend on pH. At higher concentrations of H(2)SO(4), the reduction of Cr(VI) to Cr(III) by Fe(2+) ions is preferred, but the coagulation of Fe(3+) and Cr(III) is favoured at the lower H(2)SO(4) concentrations.

Corrosion of carbon steels, stainless steels, and titanium in aqueous lithium bromide solution

Abstract Effects of lithium bromide (LiBr) concentration, pH, temperature, exposure time, and the action of some inhibitors on corrosion of several carbon (C) steels, stainless steels (SS), and a titanium (Ti) alloy were studied. Corrosion rates were determined by the polarization resistance method and compared to rates determined by weight-loss measurements. Pitting potentials (Ep) were evaluated in neutral LiBr solution and with different inhibitors. Pit density and average pit depth depended on the metal tested, with lowest values for Ti, the next lowest values for type 316 SS (UNS S31600), and the highest values for UNS G41350 tempered steel.

Corrosion Behavior and Galvanic Coupling of Stainless Steels, Titanium, and Alloy 33 in Lithium Bromide Solutions

Abstract The corrosion resistance and galvanic behavior of three stainless steels (SS), Alloy 33, and titanium were analyzed in commercial lithium bromide (LiBr) heavy brine solutions used in heating and refrigerating systems, with and without additives, using potentiodynamic anodic polarization measurements. Corrosion rates were determined from the Tafel slopes and inhibitor effects were also analyzed. The highest corrosion currents were obtained in the less-concentrated LiBr solution and the most negative corrosion potentials were obtained in a chromate-inhibited LiBr brine. The most effective action of the inhibitor was observed on titanium while it was least effective for Alloy 33. Critical potentials were calculated at 100 μA/cm2, and it was observed that the chromate inhibitor did not improve the resistance of SS to pitting corrosion. Galvanic current and mixed potentials were calculated for all possible combinations of the tested materials from polarization curves according to the mixed potential t...

Galvanic Studies of Copper Coupled to Alloy 33 and Titanium in Lithium Bromide Solutions

Abstract Galvanic influence of Alloy 33 (UNS R20033) and titanium (Grade 2) on copper was studied in lithium bromide (LiBr) solutions (400, 700, and 850 g/L chromate containing commercial solution). Temperature effect was also analyzed by imposing a heating/cooling cycle to the samples during a 10-h period (from 25°C to 80°C at 0.5°C/min), during a 2-h period (from 80°C to 25°C at 0.5°C/min), and during the last 2 h (maintained at 25°C). The galvanic potential and the galvanic current were measured with a zero-resistance ammeter (ZRA) during the temperature cycle. Images of the electrode surfaces were captured simultaneously with the recorded electrochemical signal caused by corrosion processes without disturbing the electrochemical system. The experimental device consists of an electrochemical system with an horizontal electrochemical cell coupled to a microscope, camera, and a system of image acquisition. Copper is always the anodic element of the Cu-Alloy 33 pair; however, it behaves cathodically or an...

Corrosion of copper in aqueous lithium bromide concentrated solutions by immersion testing

Abstract The corrosion rate of copper produced by lithium bromide (LiBr) concentrated solutions of 400 g/L and 700 g/L (4.61 M and 8.06 M) at room temperature, 70°C, and 110°C was studied using imm...

A new technique for online visualization of the electrode surface under electrochemical corrosion processes

A new method for the online visualization of corrosion processes has been developed. It relates two techniques, electrochemical studies (potentiodynamic, potentiostatic, chronoamperometric etc.) and image processing. The main advantage of this method is that it is possible to relate the morphological changes of the electrode surfaces to the electrochemical signal measured without disturbing the electrochemical system. The online visualization technique is based on a horizontal electrochemical cell. The cell allows observation of the surface of the electrodes in a horizontal position by means of a triocular microscope–stereoscope assembled to an image acquisition system. The methodology was applied to the study and understanding of the surface changes of a copper and an AISI 316L electrode, respectively, when their potentiodynamic curves were taken in a lithium bromide solution. The corroded area of an AISI 316L electrode was determined by image processing in order to calculate the local current density in a potentiostatic test. The visualization method proposed can be used to gain a better understanding of electrochemical corrosion processes.

Pourbaix Diagrams for Nickel in Concentrated Aqueous Lithium Bromide Solutions at 25°C

Abstract Pourbaix diagrams (electrode potential-pH diagrams) for the Ni-Br−-H2O system at 25°C were developed in 400-g/L, 700-g/L, and 850-g/L (4.61-M, 8.06-M, and 9.79-M) lithium bromide (LiBr) solutions, which are common concentrations found in different parts of absorption devices. The diagrams were compared with the simple Ni-H2O system at 25°C. Pourbaix diagrams were constructed from standard Gibbs free energy of formation (ΔGfo) data at 25°C for all the species considered. Conventional procedures were followed to calculate the electrochemical and chemical equilibria from ΔGfo data Equilibria for the Ni-Br−-H2O system at 25°C were determined for bromide ion activities of 15.61, 194.77, and 650.06, which corresponded to the 400-g/L, 700-g/L, and 850-g/L LiBr solutions, respectively. Activities of all the dissolved species containing nickel were plotted for 10−6, 10−4, 10−2, and 100. Comparison of the simple Ni-H2O system at 25°C with the diagrams illustrating the effect of Br− activity showed that the...

Online Visualization of Corrosion Processes of Zinc and a Cu/Zn Galvanic Pair in Lithium Bromide Solutions

Abstract A new method has been developed for online visualization of corrosion processes. The system allows surface images of the tested electrode to be captured simultaneously with the recorded electrochemical signal caused by corrosion processes without disturbing the electrochemical system. The experimental device consists of an electrochemical system with a horizontal electrochemical cell coupled to optical equipment. The horizontal position of the electrodes tested permitted the direct observation of surface modifications with time and of the experimental conditions by means of a triocular microscope stereoscope assembled to an image acquisition system. The new methodology was applied in the study of zinc corrosion and galvanic behavior when coupled to copper in lithium bromide (LiBr) media. Zinc exfoliation was observed in potentiodynamic tests. Zero-resistance ammetry was the electrochemical technique used to evaluate the galvanic corrosion in the Cu/Zn pair. The online visualization of the electro...

Galvanic Study of Zinc and Copper in Lithium Bromide Solutions at Different Temperatures

Abstract Galvanic corrosion of pure zinc coupled to pure copper was investigated in three different lithium bromide (LiBr) solutions (400 g/L, 700 g/L, and 850 g/L additive commercial solution) at different temperatures. The galvanic potential and the galvanic current were measured simultaneously by a zeroresistance ammeter (ZRA) at a rate of 2 Hz during a period of 24 h at 25°C, following a heating-cooling cycle from 25°C to 85°C at 0.5°C/min, during 2 h at 85°C, from 85°C to 25°C at 0.5°C/min and maintained at 25°C during the last 3 h. From the electrochemical data obtained and their subsequent statistical analysis in terms of mean values and standard deviation, it was concluded that copper-zinc coupling generated higher galvanic current in 400 g/L LiBr than in 700 g/L LiBr solution. The passivating character of the additives added to the commercial solution reduced the galvanic effect considerably. The temperature cycle imposed to the copper-zinc coupling showed that the galvanic current values at the ...

Analysis of mass and momentum transfer in an annular electrodialysis cell in pulsed flow

An analysis of mass and momentum transfer in an annular pulsating electrodialysis cell has been made. The mass and momentum balance equations are solved numerically for the case of reversing and non-reversing oscillatory flow. The numerical mass transfer is compared with the experimental results obtained from the determination of the limiting current density in an electrodialysis cell. From the numerical calculations and the experimental results, an enhancement of mass transfer due to superimposed pulsation can take place in the case of reversing flow. Increases in frequency and amplitude of pulsation improve the mass transfer coefficient, the effect of frequency being greater.