Félix Echeverría

Copper Corrosion Originated by Propionic Acid Vapors

Copper corrosion originated by propionic acid vapors (CH 3 CH 2 COOH ), ranging from 10 to 300 ppm, at 100% relative humidity. was studied. At 300 ppm pollutant level, the copper corrosion rate was 3.3 mg/dm 2 day. The cathodic reduction technique showed that the amount of corrosion products grew with both exposure time and pollutant level. Corrosion products were also characterized using X-ray diffraction and Fourier transform infrared techniques, and their morphology was observed by scanning electron microscope methodology. The main compounds identified were cuprite (Cu 2 O), copper hydroxide [Cu(OH) 2 ], and a copper propionate compound. Important amounts of an organic copper compound were observed at propionic acid vapor concentrations higher than 50 ppm.

Osseointegration improvement by plasma electrolytic oxidation of modified titanium alloys surfaces

Titanium (Ti) is a material frequently used in orthopedic applications, due to its good mechanical properties and high corrosion resistance. However, formation of a non-adherent fibrous tissue between material and bone drastically could affect the osseointegration process and, therefore, the mechanical stability of the implant. Modifications of topography and configuration of the tissue/material interface is one of the mechanisms to improve that process by manipulating parameters such as morphology and roughness. There are different techniques that can be used to modify the titanium surface; plasma electrolytic oxidation (PEO) is one of those alternatives, which consists of obtaining porous anodic coatings by controlling parameters such as voltage, current, anodizing solution and time of the reaction. From all of the above factors, and based on previous studies that demonstrated that bone cells sense substrates features to grow new tissue, in this work commercially pure Ti (c.p Ti) and Ti6Al4V alloy samples were modified at their surface by PEO in different anodizing solutions composed of H2SO4 and H3PO4 mixtures. Treated surfaces were characterized and used as platforms to grow osteoblasts; subsequently, cell behavior parameters like adhesion, proliferation and differentiation were also studied. Although the results showed no significant differences in proliferation, differentiation and cell biological activity, overall results showed an important influence of topography of the modified surfaces compared with polished untreated surfaces. Finally, this study offers an alternative protocol to modify surfaces of Ti and their alloys in a controlled and reproducible way in which biocompatibility of the material is not compromised and osseointegration would be improved.

CHARACTERIZATION OF DEPOSITS FORMED IN A WATER DISTRIBUTION SYSTEM

The development of unwanted deposits in any water distribution system is unavoidable under standard conditions. Knowing the composition of such deposits will help to establish the causes of deposit formation and consequently to be able to keep water quality as high as possible. This paper presents the results of an extensive study of deposits found in a water distribution system of a tropical city. Characterization of materials collected across the system was made by infrared spectroscopy (IR), X ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). Analysis of the samples taken at several sites of the system reveals the presence of three predominant deposits: a brown coloured deposit, tubercles and white deposits. Aluminosilicates and humic acids were found to be main constituents in brown deposits. Tubercles were mostly mixtures of magnetite, goethite and in some cases lepidocrocite. White deposits were formed by calcite, aluminosilicates and quartz. Organic matter as volatile solids were 14.0 ± 5.0% for brown deposits and 11.2 ± 2.0% for tubercles.

Tripigmented anticorrosive coatings based on lamellar zinc as inhibitor

SummariesThe objective of this work was to study the behaviour of zinc primers, containing either lamellar zinc alone or lamellar zinc mixed with an extender or with an extender/inhibitor mixture. Several formulations of coatings were designed. Accelerated tests were carried out by means of a salt-spray (fog) chamber and a 100% relative humidity cabinet. A statistical analysis was performed considering simultaneous ways of dry-film blistering resistance and anticorrosive behaviour. Results indicated that it was possible to incorporate an extender of high-oil absorption as a spacer of the lamellar zinc particles and also an inhibitor to improve the performance.RésuméLe but de cette uvre était d’etudier le comportement des apprêts de zinc qui contenaient ou bien du zinc lamellaire tout seul, ou bien du zinc lamellaire mélangé avec un extendeur ou avec un melange extendeur/inhibiteur. Plusieurs formulations de revêtement ont été conçues. Des essais accélérés ont été effectués grâce à une enceinte d’essais à brouillard salin et à une enceinte 100% humidité relative. On a fait une analyse statistique qui considérait simultanément des moyens d’améliorer la résistance au boursouflage des films secs et le comportement anticorrosif. Les résultats ont indiqué qu’il était possible d’incorporer un extendeur de haute absorption d’huile comme « spacer » entretoise des particules du zinc lamellaire aussi bien qu’un inhibiteur pour améliorer la performance.ZusammenfassungDàs Ziel dieser Arbeit war, das Verhalten von Zinkgrundierung die entweder lamellaren Zink allein oder lamellaren Zink mit einem Verlängerungsmittel oder einer Verlänergungsmittel/Inhibitor-Mischung enthielten. Verschiedene Lackformulierungen wurden hegestellt und beschleunigte Tests in einem Salzspray- (Nebel) Zimmer und einem 100% Luftfeuchtigkeitsraum durchgeführt. Die gleichzeitige Resistenz des Lackes zu Trockenfilmblasenbildung und Korrosion wurde statistisch bewertet. Die Ergebnisse zeigen, das es möglich ist, ein stark ölaufnehmendes Verlängerungsmittel sowohl als Platzhalter für die lamellaren Zinkpartikel als auch als leistungsverbessernden Inhibitor zu verwenden.

Examination of Cross Sections of Thin Films by Atomic Force Microscopy

Procedures are described for the examination in cross section of thin films by atomic force microscopy (AFM), with reference to anodic films on III-V semiconductors and aluminium as examples of possible applications. It is shown that by preparing cross-sectional surfaces with a diamond knife, the thickness and morphology of anodic films can be disclosed by AFM at a resolution approaching that of transmission electron microscopy, with features such as local nonuniformity of film thickness and layering of the film being revealed.

Carboxilic acids in the atmosphere and their effect on the degradation of metals

Metallic atmospheric corrosion is due to deposition of the pollutants found in the different phases of the atmosphere (especially in clouds, spray, rain and fog) onto the metallic surface, reacting with the substrate and leading to corrosion. Those pollutants are either organic or inorganic. Within the inorganic pollutants found in the atmosphere are NO 2 , SO 2 , NH 3 , HCI, CO 2 and O 3 . The organic compounds in the atmosphere, also known as volatile organic compounds (VOC), are several hydrocarbons and vapours of organic acids such as formic, acetic and propionic. In general, most of the pollutants contribute to the total acidity of rain in urban areas and it is estimated that the contribution of organic acids is about 35% of the total. VOC emissions can be either anthropogenic or biogenic; the average contents measured in the atmosphere for formic, acetic and propionic acids are about 8, 9 and 0.3 ppb respectively. On the other hand, organic acids appear related to corrosion products of lead, zinc, nickel and copper. A review of the published results on the effect of organic acids on corrosion of metals is presented.

Direct Observation of Anodic Films Formed on Gallium Phosphide in Aqueous Tungstate Electrolyte

The growth of anodic films on gallium phosphide has been investigated by transmission electron microscopy using ultramicrotomed sections of anodized specimens and Rutherford backscattering spectroscopy. The films were grown at constant current density, either 450 or 850 μA cm -2 , in aqueous 0.1 M sodium tungstate electrolyte at 293 K. Two-layered amorphous films, consisting of an outer layer composed of Ga 2 O 3 and an inner layer composed of units of Ga 2 O 3 and P 2 O 5 in the ratio of about 1:3.0, are formed by outward migration of cation species and inward migration of O 2 ions. For film formation at 100% efficiency, the outer layer represents about 34% of the film thickness. The layering is developed due to the faster migration outward of Ga 3- ions compared with that of P 5+ ions. The films are highly soluble in the tungstate electrolyte at the termination of anodizing. However, following the initial period of film nucleation, the films are formed at relatively high efficiency, probably due to the presence of a protective gel layer, composed of hydrated WO 3 at the film/electrolyte interface.

Formation of protective anodic oxides on aluminium by low voltage anodising in sulphuric acid with cerium nitrate and tartaric acid additions

Abstract The effects of the anodising potential and of the combined addition of tartaric acid and cerium nitrate to a sulphuric acid anodising bath on the corrosion behaviour of high purity aluminium and on AA2024T3 aerospace aluminium alloy have been systematically investigated. It is found that the anodising potential is critical in determining the anticorrosion performance; lower potential generates finer pores that provide enhanced corrosion protection compared with the larger pores generated at higher potentials. At both anodising potentials, the addition of cerium nitrate alone to the sulphuric acid bath does not increase significantly the anticorrosion performance. Conversely, the addition of tartaric acid alone is generally beneficial. Finally, when cerium nitrate is added in combination with tartaric acid a further improvement of the corrosion resistance is observed.

Corrosion mitigation of buried structures by soils modification

Carbon steel samples were buried in loamy soil modified with lime, fly-ash and Portland cement in ratio of 5 and 10% during 60 days. Corrosion attack was assessed by electrochemical impedance spectroscopy. Loamy soil without modification was taken as reference. The corrosion products in rust were characterized by Raman spectroscopy. It was found that soil with fly-ash and Portland cement can develop corrosion protection to bare steel due to the changing of formed rust on steel samples. Lepidocrocite and Goethite were found as major constituents in formed rust on buried steel in soil modified with fly-ash and cement, while Magnetite was found in formed rust on buried steel in soil without addition of cementitious materials and modified with lime. According to the electrochemical results, the soil with 5% of fly-ash exhibited the anticorrosive best performance.

Modification of titanium alloys surface properties by plasma electrolytic oxidation (PEO) and influence on biological response

Surface characteristics can mediate biological interaction improving or affecting the tissue integration after implantation of a biomaterial. Features such as topography, wettability, surface energy and chemistry can be key determinants for interactions between cells and materials. Plasma electrolytic oxidation (PEO) is a technique used to control this kind of parameters by the addition of chemical species and the production of different morphologies on the surfaces of titanium and its alloys. With the purpose to improve the biological response, surfaces of c.p titanium and Ti6Al4V were modified by using PEO. Different electrolytes, voltages, current densities and anodizing times were tested in order to obtain surfaces with different characteristics. The obtained materials were characterized by different techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and glow discharge optical emission spectroscopy (GDOES). Wettability of the obtained surfaces were measured and the corresponding surface energies were calculated. Superhydrophilic surfaces with contact angles of about 0 degrees were obtained without any other treatment but PEO and this condition in some cases remains stable after several weeks of anodizing; crystal phase composition (anatase—rutile) of the anodic surface appears to be critical for obtaining this property. Finally, in order to verify the biological effect of these surfaces, osteoblast were seeded on the samples. It was found that cell behavior improves as SFE (surface free energy) and coating porosity increases whereas it is affected negatively by roughness.Graphical abstractTechniques for surface modification allow changes in the coatings such as surface energy, roughness and porosity. As a consequence of this, biological response can be altered. In this paper, surfaces of c.p Ti and Ti6Al4V were modified by using plasma electrolytic oxidation (PEO) in order to accelerate the cell adhesion process.