L. Maldonado

Corrosion resistance and microstructure of electrodeposited Zn and Zn alloy coatings

The nature of electrodeposited zinc coating corrosion inhibition by alloying with Fe group metals is not fully understood, because it depends on several factors including the microstructure. The crystallographic texture and lattice cell parameters were determined for nonchromated Zn, Zn-Co, Zn-Fe and Zn-Ni coatings, deposited from alkaline baths, and the results have been used to explain the observed differences in their corrosion behaviour in aerated chloride solutions and in neutral salt spray tests. The presence of Ni or Co in the zinc matrix increases the Zn coating corrosion resistance, while Fe has no effect. It has been suggested that the lower Zn-Ni alloy corrosion rate is due to the predominant presence in this layer of crystallographic planes with a higher packing density. The lower Zn-Co alloy corrosion rate compared with that of Zn and Zn-Fe has been associated with the lower values of its lattice cell parameter c/a (axial ratio).

CHARACTERIZATION OF THE CORROSION BEHAVIOUR OF Zn AND Zn ALLOY ELECTRODEPOSITS: ATMOSPHERIC AND ACCELERATED TESTS

The corrosion behaviour of unchromated Zn. Zn-Co (0.6%). Zn-Fe (0.4%) and Zn-Ni (1 2%) coatings deposited from alkaline cyanide free solution was studied in a humid tropical climate and in accelerated chloride and sulfur dioxide cabinet tests. The presence of Ni or Co in the Zn matrix increases Zn coating corrosion resistance. while Fe does not chanse it. The statistical analysis of the data obtained showed that the specimens corrosion losses can be represented as an exponential equation as a function of time of wetness. In such case the corrosion losses in one year of wetness can be approx~mated as a linear function of accumulated CI and SO: pollutant deposition. The data indicate a more significant SO1 influence on the coating corrosion rate that is due to C1-. (: 1998 Elsevier Science Ltd. All rights reserved

Characterization of Activated Titanium Solid Reference Electrodes for Corrosion Testing of Steel in Concrete

Abstract Small bars of Ti activated with mixed-metal oxide (commercially produced for permanent impressed-current anodes in cathodic protection) were used as embedded reference electrodes (RE) in c...

An electrochemical investigation of passive layers formed on electrodeposited Zn and Zn- alloy coatings in alkaline solutions

Abstract Data on the corrosion behaviour of pure Zn, Zn-0.4%Fe, Zn-0.6%Co and Zn-12%Ni coatings deposited from an alkaline cyanide-free solution, studied by salt spray test and anodic polarization curves in a nearly neutral NaCl solution are presented. The Zn-12%Ni and Zn-0.6%Co alloys show higher corrosion resistance than the two other systems. An attempt has been made to correlate the observed corrosion resistance of these two coatings with the electrochemical behaviour of anodically formed passive layers on them in alkaline solutions, investigated by Electrochemical Impedance Spectroscopy. Analysis of the electrochemical impedance data in the frequency range 1 Hz–10 kHz obtained for anodic passive films on the four systems in 0.1 M NaOH at different potentials in the passive region suggest that the passive films on Zn-Ni and Zn-Co present deviations from the ideal Mott-Shottky behaviour which were attributed to the introduction of deep donor levels by the doping elements Co and Ni. These doping elements seem to play an important role in the anodic control of the corrosion process which involves ionic transport processes through the oxide films.

Mechanism of copper patina formation in marine environments

Data analysis of the initial superficial layers of copper patina formed in several marine environments, using X-ray diffraction and cathodic reduction techniques, are presented. It was observed that cuprite phase decreases and the paratacamite phase increases, as corrosion develops on the surface of copper. The data presented show good agreement with previously published eletrochemical reactions of copper corrosion in marine environments.

Atmospheric corrosivity in the Caribbean area

This paper presents the first results of a parallel evaluation of the aggressivity of atmospheric corrosion in three Caribbean countries: Cuba, Mexico and Venezuela. The temperature-humidity complex and contamination parameters were determined in order to explain the differences in atmospheric corrosivity. For the Caribbean coastal stations, chloride deposition is the predominant factor for determining the steel corrosion rate after one years exposure. In this region, it is common to find corrosion values exceeding the ones established in Standard ISO 9223. It is therefore recommended that a new Corrosion Aggressivity Scale be added to allow the inclusion of coastal zones in tropical areas. A different influence of chlorides on steel atmospheric corrosion was determined for Eastern and Western Caribbean. Differences are explained based on temperature-humidity-rain regime.

Corrosivity category maps of a humid tropical atmosphere: the Yucatán Peninsula, México

Fourteen test sites were established in the tropical humid atmosphere of the Yucatan Peninsula and the Mexican Caribbean area. In each environment sulfur dioxide and chloride deposition rates were measured and the corrosion rates of flat plate samples (low carbon steel, copper and zinc) determined. In selected locations open helix samples of copper, and low carbon steel were also tested. In two typical test sites (a rural-urban and a marine-coastal) the time-of wetness and temperature were registered, then their influence on the metallic corrosion rates discussed. The obtained data were used for classification of atmospheric aggressivity, according to ISO 9223. It was observed that the aggressivity categories of marine coastal zones are C5, the highest one, while the rural and rural-urban sites classify as C2, C3 and C4. No appreciable difference in category classification is observed, when flat plates or open helix samples are used. Korrosivitatsklassenkarten einer feuchten, tropischen Atmosphare: die Yucatan Halbinsel, Mexiko Vierzehn Versuchsstellen wurden in der tropischen, feuchten Atmosphare der Yucatan Halbinsel und der mexikanischen Karibikzone errichtet. In jeder dieser Umgebungen wurden die Schwefeldioxid- und Chlorid-Ablagerungsraten gemessen und die Korrosionsgeschwindigkeiten an Hand von Flachproben (niedriglegierter Stahl, Kupfer und Zink) bestimmt. An ausgewahlten Orten wurden auch offene Spiralproben aus Kupfer und niedriglegiertem Stahl untersucht. An zwei typischen Versuchsstanden (landlich-stadtische Atmosphare sowie Meereskusten-Atmosphare) wurde die Zeitdauer der Benetzung und die Temperatur registriert. Ihr Einflus auf die Korrosionsgeschwindigkeiten wird diskutiert. Mit den erhaltenen Daten wurde entsprechend ISO 9223 eine Klassifizierung der atmospharischen Aggressivitat vorgenommen. Es wurde festgestellt, das die Meereskustenzone mit C5 die hochste Aggressivitatsklasse aufweist, wahrend die landlichen und landlich-stadtischen Orte mit C2, C3 und C4 klassifiziert wurden. Zwischen den Flachproben und den offenen Spiralproben wurden keine nennenswerte Unterschiede hinsichtlich der Korrosivitatsklassen beobachtet.

Study of chloride diffusion as a corrosive agent in reinforced concrete for a tropical marine environment

Abstract Diffusion of chloride ions through 7.5 cm × 15.0 cm concrete cylinders was studied. The cylinders were immersed for 30 days in a tank containing distilled water and a sodium chloride solution. Five water/cement (w/c) ratios and three curing times ( t c ) were tested. It is suggested that coarse aggregate is a barrier which blocks chloride ion diffusion. A model considering a homogeneous and porous concrete was used to describe the influence of high w/c ratios and t c . A dependence between t c and the chloride concentration at the concrete surface ( C 0 ) for high w/c ratios was found. Dispersion in the results was minimized by using a large number of specimens.

Sputtered thin film YBa2Cu3On

This study was carried out to determine the effect of substrate temperature, target to substrate angle, and the partial pressure of oxygen in the sputtering atmosphere on the stoichiometry of the deposition. Films were deposited by a planar magnetron sputtering of stoichiometric 1:2:3 pressed and sintered targets on MgO, ZrO2 (Y) and ZrO2 coated Al2O3 substrates. EDX and WDS were used to determine the chemical composition of the thin films. X‐ray diffraction was used to identify the structure after film crystallization at 1175 K and oxidation at 800 K. The partial pressure of oxygen appears to have the most profound effect on the stoichiometry by lowering the barium content. Negative ion resputtering of the growing film apparently also slows film growth rate. Films deposited on alumina circuitboard with a ZrO2 barrier layer have demonstrated sharp transitions to superconducting behavior at 95 K when the stoichiometric ratio is preserved.

Electrochemical, gravimetric and X-ray characterization of low carbon steel corrosion rate and products after atmospheric exposure in the Caribbean area

Rust scales of commercially available low carbon steels from Venezuela (AlSI 1010), Mexico and Cuba (AISI 1019) were characterised after exposure at two typical atmospheres in the Caribbean region: Merida (rural-urban; RU) and Progreso (marine-coastal; MC). Low carbon steel surfaces rusting in those atmospheres formed mainly the oxyhydroxides lepidocrocite (y-FeOOH), goethite (a-FeOOH) and akaganeite (β-FeOOH). Different amounts of lepidocrocite, goethite and akaganeite and the oxide phases hematite (α-Fe 2 O 3 ), magnetite (Fe 3 O 4 ) and maghemite (γ-Fe 2 O 4 ) were found, depending on the deposition rates value of air-borne salinity, time-of-wetness (TOW) and temperature present in every particular test site. The rust scale composition and air pollution are used to explain the corrosion rates and corrosion behaviour of the exposed low carbon steels in the tests sites.