Jerónimo Agrisuelas

The cleaning process kinetics of metallic surfaces has been studied by means of digital video monitoring. Two theoretical models based on experimental observations are proposed for two possible cleaning kinetics mechanisms and two practical cases that can be adapted to these models are analyzed. As a kinetic parameter, the duration of the cleaning of a metallic surface is defined from the time evolution of the color intensities and their variance. These times allow us to characterize and to optimize the cleaning process procedure. Apparent activation energies are estimated from the characteristic times at different temperatures.

The cleaning process of metallic surfaces has been studied by means of digital video monitoring. Two theoretical models based on experimental observations are proposed for two possible cleaning mechanisms and two practical cases that can be adapted to these models are analyzed. As a kinetic parameter, the duration of the cleaning of a metallic surface is defined from the time evolution of the color intensities and their variance. These times allow us to characterize and to optimize the cleaning process procedure. Apparent activation energies are estimated from the characteristic times at different temperatures.

Methylene blue was electropolymerized on the surface of stainless steel 316. The addition of sodium oxalate and working at a pH near 11 allowed us to obtain steel electrodes coated with an electroactive polymer. This polymer shows electrochromic properties like those of the monomer, but also exhibits electroactivity at more positive potentials, which is associated with the active centers in the bridges between monomeric units. A digital video electrochemistry study allowed us to simultaneously quantify, on the one hand, the color changes on the entire surface of the stainless steel and on the other to separate the contribution of the active centers of the phenothiazine ring and of the inter-monomer bonds to the overall polymer response by means of assessing the mean color intensities. A reduction mechanism for the polymer, compatible with the pH variation of the observed electrochemical behavior, was proposed.

The electrical percolation of alternating current through two-phase polyethylene/graphite composite electrodes with different contents of graphite microparticles immersed in aqueous KCl solutions has been studied. Above the graphite content of the first percolation threshold, the electrochemical impedance response of this electrode is associated with an equivalent circuit of resistance Ru in series with a constant phase element CPE. An insulator material+conductive filler model is proposed in which the electroactive surface is considered as the intersection of the percolation cluster through the solid and the cluster associated with the interfacial region. CPE is analyzed assuming a distribution of micro-capacitors of the graphite particles in contact with the dielectric solution and inside the dielectric polymeric phase.

Methylene blue has been electropolymerized on the surface of a stainless steel 316. The addition of sodium oxalate and working at a pH near 11 has allowed to obtain steel electrodes coated with electroactive polymer. This polymer shows electrochromic properties similar to those of the monomer, but also appears electroactivity at more positive potentials which is associated to the active centers in the bridges between monomeric units. The study by means of digital video electrochemistry has allowed on the one hand, to quantify the color changes on the entire surface of the stainless steel simultaneously and by means of the mean color intensities to separate the contribution to the overall polymer response of the active centers of the phenothiazine ring and of the inter-monomer bonds. A reduction mechanism for the polymer compatible with the pH variation of the observed electrochemical behavior is proposed.

The quality of metal electrodeposits on different surfaces depends on the configuration and composition of the electrochemical bath, but also on the control of experimental variables that can affect the electrode processes taking place. In this work, we have studied the electrodeposit of nickel on a polypropylene|graphite|copper (PP|G|Cu) ternary composite electrode. Together with the resistive behavior of the electrode, the nickel electrodeposition presents extra difficulties as a low reduction potential and numerous and possible chemical reactions with the medium to form passive layers or aqueous complexes. The use of digital video electrochemistry (DVEC) has allowed detecting some issues during the electrodeposition and electrodissolution processes such as the non-uniform growth of Ni due to the electrode configuration, secondary and oscillatory electrochemical reactions caused by the subproducts in the auxiliary electrode or the effect of the formation of hydrogen bubbles. The estimation of electrodeposition efficiency from DVEC and a possible electrodissolution mechanism are discussed.