Kinetics and mechanism of the nickel electrode—II. Acid solutions containing a high concentration of sulphate and nickel ions

The kinetics of the Ni electrode in acid solutions with a high sulphate and nickel ion concentration has been investigated in the range of 25–75°C. The active dissolution and the passive regions and the active-passive transition phenomena have been studied employing different potential perturbation techniques using both still and stirred solutions. Two electrochemical processes are competing within the prepassive film potential region, namely, the active Ni dissolution to Ni(II) ions and the Ni(OH)2 film formation. Nickel passivation is explained by reaction pathways involving successive electrochemical and chemical steps implying the occurrence of hydroxo- and oxo-species as reactions intermediates. The advanced mechanism is based upon a positively charged Ni surface structure and attributes the onset of the complete passivity to a particular surface oxide species.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Kinetics and mechanism of the nickel electrode—II. Acid solutions containing a high concentration of sulphate and nickel ions

The kinetics of the Ni electrode in acid solutions with a high sulphate and nickel ion concentration has been investigated in the range of 25–75°C. The active dissolution and the passive regions and the active-passive transition phenomena have been studied employing different potential perturbation techniques using both still and stirred solutions. Two electrochemical processes are competing within the prepassive film potential region, namely, the active Ni dissolution to Ni(II) ions and the Ni(OH)2 film formation. Nickel passivation is explained by reaction pathways involving successive electrochemical and chemical steps implying the occurrence of hydroxo- and oxo-species as reactions intermediates. The advanced mechanism is based upon a positively charged Ni surface structure and attributes the onset of the complete passivity to a particular surface oxide species.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Las academias nacionales y la educación de la sociedad

El mundo está cambiando rápidamente como consecuencia del desarrollo científico y tecnológico. La veloz acumulación de conocimiento científico y el desarrollo de sus aplicaciones técnicas está facilitada por la gran capacidad y velocidad de las computadoras y por la rapidez de las comunicaciones. Sin embargo, la realidad global es que muchas innovaciones no alcanzan a beneficiar a aquellos que más las necesitan, y las ventajas del desarrollo ciéntífico no son compartidas en el planeta. La comunidad internacional ha atendido inadecuadamente a las necesidades de capacitación en ciencia y técnica de los pueblos. Esta es una omisión crítica que influye en la disponibilidad de suficiente personal capacitado, de adecuada infraestructura e inversión y dificulta el establecimiento de reglas de juego claras para conducir la investigación científica y el desarrollo tecnológico. El mundo de los negocios no ha considerado como problema propio la diferencia entre las naciones en función de su desarrollo, antes bien ha usufructuado esa diferencia ayudando a establecer un círculo vicioso que acentúa la diferencia en el desarrollo científico y técnico entre las naciones. Esta disparidad continuará aumentando en la medida en que las naciones industrializadas continúen siendo dueñas del equipamiento y de las invenciones, tanto por lo que generan como porque captan un número apreciable de los científicos más destacados de las naciones en desarrollo.Facultad de Ciencias Exacta

Scanning tunneling microscopy and electrochemistry

The experimental gap existing between surface science and heterogeneous chemical kinetics applies also to electrochemistry. Difficulties for modelling the electrode surface topography under equilibrium and non-equilibrium conditions, particularly for solid electrodes, are presented. Attention is focussed on structural problems of metal/solution interfaces encountered in corrosion and passivation of metals and in electrocatalysis, although the analysis also extends to metal electrodeposition and to semiconductor/solution interfaces. STM has already provided important imaging of preferred oriented platinum electrode surfaces as well as large surface area platinum electrodes exhibiting practically no diffusional and ohmic polarization effects. Possible applications of STM to underpotential deposition of metals and to chemically modified electrodes are envisaged among others. Some future perspectives of STM for electrochemistry are advanced.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The diffusion of ferro- and ferricyanide ions in aqueous solutions of sodium hydroxide

The diffusion of ferri- and ferrocyanide ions in sodium hydroxide solutions has been studied by means of a platinum rotating disk electrode. Results were obtained at variable concentrations an in the range of temperature between 24 and 40°C. The product Dɳ/T was approximately constant and independent of temperature in the range studied. The dependence of D on the total ionic strength is mainly due to the change of viscosity at large ionic concentration.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

Kinetic and Structural Consequences Derived from Ageing Effects on Electrochemically Formed Layers

The influence of different ageing processes on electrochemical reactions is analysed. Three main types of ageing processes are described: open circuit ageing, potentiostatic ageing and potentiodynamic ageing. The data derived from different electrode processes show that the films are composite systems themselves. They involve various nonequilibrated species which accordingly react to attain either a single equilibrium configuration or a configuration involving equilibria among the various surface species. Surface restructuring and cluster-type reactions are important contributions toward understanding the dynamic behaviour of electrochemical interfaces.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The diffusion of ferro- and ferricyanide ions in aqueous solutions of sodium hydroxide

The diffusion of ferri- and ferrocyanide ions in sodium hydroxide solutions has been studied by means of a platinum rotating disk electrode. Results were obtained at variable concentrations an in the range of temperature between 24 and 40°C. The product Dɳ/T was approximately constant and independent of temperature in the range studied. The dependence of D on the total ionic strength is mainly due to the change of viscosity at large ionic concentration.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

The kinetics and mechanism of the nickel electrode—III. The potentiodynamic response of nickel electrodes in alkaline solutions in the potential region of Ni(OH)₂ formation

The electrochemical behaviour of nickel in alkaline aqueous solutions within the anodic potential range yielding Ni(OH)2 and under different potentiodynamic perturbations profiles has been investigated. The formation of Ni(OH)2 is characterized by an irreversible anodic current peak which is quantitatively interpreted in terms of a complex reaction pathway involving different hydroxoadsorbed species.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

The potentiodynamic behaviour of iron in alkaline solutions

The potentiodynamic behaviour of iron in alkaline solutions under carefully controlled perturbation conditions reveals that the overall electrochemical process is more involved than was thought earlier. The electrochemical characteristics of the systems are explained through a series of successive conjugated redox couples principally involving Fe(OH), Fe(OH)2 and FeOOH as limiting stoichiometric species. The yield of soluble species such as either FeO2−2 or HFeO−2 increases with the pH. Ageing effects of reactants and products are also distinguished through the potentiodynamic E/I records.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA)Facultad de Ciencias Exacta

The electroformation and electroreduction of anodic films formed on silver in 0.1 M sodium hydroxide in the potential range of the Ag/Ag2O couple

The complex electrochemical reactions related to the electroformation and electroreduction of silver(I) oxide films in base electrolyte were investigated by means of combined potentiodynamic techniques and potential steps. The anodic process involves the initial fast OH− ion discharge yielding OH-adsorbed species and later continues to form the silver(I) oxide layer. The latter behaves as a duplex structure anodic layer with a degree of hydration changing with depth. The electroreduction characteristics of the anodic film depend both on potential sweep and anodic charge, and the relationships of the corresponding kinetic parameters fit qualitatively with those predicted by nucleation and growth mechanisms. Activity increases of silver caused by the potential sweeps are interpreted by the simultaneous contribution of the increase in the concentration of silver active surface sites and the change in size distribution of silver electrodeposited from silver(I) oxide.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta