• Energy Research

Abstract Anodic and cathodic polarization curves have been determined in the current density range of 0.005 to 1 A/cm 2 and in the temperature range of 40 to 80°C in 30% KOH, using a measuring method that allows direct ohmic drop correction at zero distance from the electrode surface. Tafel linearity has been confirmed on all the materials tested, as well as the presence of films whose considerable ohmic resistance depends on temperature but remains unchanged throughout the cd range investigated. The possible nature of such films, whose resistance is to be included among the basic parameters of electrode performance, is discussed.

Coating electroaccretion on galvanized iron and aluminum 1100 under cathodic polarization in artificial and natural seawaterwas investigated through electrochemical tests and optical imaging techniques. Biofilm affects the current density and the morphologies of gas evolution, particularly the maximum size of the gas bubbles and the interaction between gas evolution and calcareous deposit. Coating mineral composition is related to the type of metallic material and can be different according to growth in natural or artificial seawater. On galvanized iron in ASTM and natural seawater at potential -1.2V versus Ag/AgCl. Coatings grown on aluminum 1100 are different from those on galvanized iron. In ASTM seawater, the coating on aluminum 1100 is composed of aluminum oxide and Mg4Al2(OH)14·2H2O; in natural seawater, only of aluminum oxide. On specimens coupled with magnesium anode, the coating does not contain brucite and is composed of aragonite with Mg6Al2(OH)18·4H2O islands.

The chemical dissolution of anodically grown Si oxides in acidic fluoride medium has been studied in-situ with the Bending Beam Method (BBM). Current and deflection transients were recorded after switching the electrode from the given polarization conditions to zero applied field and monitoring the etchback process. Oxide stress values estimated with this approach are free from contributions due to film electrostriction and to changes in surface tension. Transients recorded after polarization in the regime of current or potential oscillations show dissolution patterns which contain information on the properties of oxide film along its depth profile.

Spectral, grey-scale and colour chemiluminescence measurements of C 2* and CH* radicals' emission are carried out on the flame front of a methane-air premixed flame at different equivalence ratios. To this purpose, properly spatially resolved optical equipment has been implemented in order to reduce the background emission from other burned gas regions. The grey-scale (ICCD + interference filters) and RGB colour (commercial digital camera) approaches have been compared in order to find a correspondence between the C2* and the green component, as well as the CH* and the blue component of the emission intensities. The C2*/ CH* chemiluminescence ratio has been investigated at different equivalence ratios and a good correlation has been obtained, showing the possibility of sensing the equivalence ratio in practical systems. The grey-scale and colour chemiluminescence analysis has then been applied to a meso-scale not premixed swirl combustor fuelled with a methane-air mixture and operating at 0.3 MPa. 2D results are presented and discussed in this work.