Papers by Author: Xosé R. Nóvoa

Abstract: The mass transfer coefficients at different axial positions in a bubble column have been measured using a conductivity method. Measurements of CO2 absorption in methyldiethanolamine solutions were carried out in a prismatic column 0.06 m side and 1.03 m height. Five electrode pairs were placed at various axial positions in the column. Measurements were conducted at different gas flow rates and amine concentration. It was found that the local mass transfer varied in the axial direction. An experimental model was developed to obtain the absorption rate values using the electrochemical method data. The model agrees quite well with the experimental obtained data.

Abstract: The behaviour of hybrid sol-gel coatings doped with hydrotalcite-like compound applied on AA2024-T3 alloy was investigated in the present work. The hybrid sol-gel coatings were prepared by copolymerization of 3-Glycydoxypropyltrimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (TPOZ). Three different surface finishing on the aluminium alloy AA-2024-T3, grounded, chemical etching and degreased were studied. A sol-gel film with hydrotalcite 5% w/w was deposited by dip coating procedure. The presence of hydrotalcite particles was confirmed by means of X-ray diffraction technique. The different surface morphologies were characterised using mechanical profilometry. The corrosion resistance properties were studied by means of electrochemical impedance spectroscopy and salt fog spray cabinet. The results show higher barrier properties in grounded aluminium substrates.

Abstract: Hydrotalcite-like compound that belongs to anionic clay family was prepared by classical co-precipitation method using magnesium and aluminium nitrates as precursors. Different weight percentages of hydrotalcite with Mg/Al ratio of 2.5 was added (1, 5 and 10 % wt.) to hybrid sols prepared by copolymerization of 3-Glycydoxypropyltrimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (TPOZ). The aim of this work was to study the effect of the hydrotalcite incorporation to hybrid sol-gel coatings on aluminium alloys as substitution of chromate inhibitors. Hybrid sol-gel coatings were deposited by dip coating method on AA2024-T3 substrates. By Scanning Electron Microscopy (SEM) and mechanic profilometry it was possible to see the distribution of HTCP agglomerates which varies from nanometres to micrometers. The corrosion performance was evaluated by the accelerated test salt fog spray chamber (SSFC) and by Electrochemical Impedance Spectroscopy (EIS). The obtained results show the corrosion resistance improvement at higher weight percentages of HTCP.

Abstract: Two austenitic stainless steels have been implanted at 150 keV with Mo at a fluence of 3.5x1015 ions/cm2. The effects of ion implantation in the chemical composition of the passive films was evaluated by x-ray photoelectron spectroscopy (XPS) and glancing angle x-ray diffraction (GAXRD) was used to determine the induced structural modifications. The results of the pitting corrosion studies carried out in neutral chloride medium as well as the morphology of the localized attack are discussed.

Abstract: Surface analysis techniques (XPS and grazing incidence X-ray diffraction GIXRD) and electrochemical techniques have been combined to elucidate the effect resulting from Cr+ and N+ co-implantation in the formation and evolution of passive layers generated on two different stainless steels (AISI 430 and AISI 304L) in alkaline medium. The results show that the nitrides formed on AISI 430, identified as (Cr,Fe)2N1-x, are less resistant to dissolution while the nitride phase formed in AISI 304L, NCr with nanocrystalline structure, allows the compact growth of the oxide film.