J. Alcántara

Environmental conditions for akaganeite formation in marine atmosphere mild steel corrosion products and its characterization

The corrosion of mild steel in chloride-rich atmospheres is a highly topical issue. The formation of the oxyhydroxide akaganeite (β-FeOOH) in this type of atmosphere leads to a notable acceleration...

Hollow mesoporous silica nanoparticles loaded with phosphomolybdate as smart anticorrosive pigment

Recent developments in surface science and technology open up new opportunities for the development of smart pigments through the integration of nanoscale containers loaded with active components into coatings. Regarding the external factor to trigger the inhibitor release, a change in pH is a very interesting stimulus since corrosion activity leads to local changes in pH. Although several types of nanocontainers and encapsulation approaches have been proposed and studied to meet this goal, mesoporous silica nanoparticles (MSNs) are especially interesting as they retain their solid properties as long as pH of the surrounding medium does not exceed ~11. On the other hand, the use of hollow mesoporous silica nanoparticles (HMSNs) with a large cavity inside each original mesoporous silica nanoparticle has recently gained increasing interest due to the higher loading capacity. In the present work, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, sodium phosphomolybdate, has been successfully loaded and encapsulated on HMSNs. The pH-dependent release of the corrosion inhibitor from the loaded/encapsulated HMSNs has been confirmed. In addition, an improved anticorrosive behavior of the coatings formulated with loaded/encapsulated HMSNs has been observed by Scanning Kelvin Probe (SKP).

Wet/dry accelerated laboratory test to simulate the formation of multilayered rust on carbon steel in marine atmospheres

ABSTRACT The prolonged exposure of carbon steel in marine atmospheres with high chloride deposition rates and long times of wetness of the metallic surface leads to the formation of thick multilayered rust. The present work proposes an accelerated cyclic laboratory test based on immersion (4.2 min) in a 3.5% NaCl solution followed by drying (12 min) under infra-red lamps in the laboratory atmosphere. The carbon steel corrosion process is thus accelerated, giving rise to the generation of thick rust layers in relatively short times. The rust phases and the structure of the rust layers formed offer a good approximation to the multilayered rust formed in marine atmospheres. The study includes a gravimetric evaluation of the magnitude of corrosive attack and a characterisation of the rust phases and corrosion layers formed using XRD, optical microscopy and SEM.

Scanning electron microscopy/micro-Raman: A very useful technique for characterizing the morphologies of rust phases formed on carbon steel in atmospheric exposures

The morphological structures displayed by iron oxides present a very wide range of shapes and sizes, reflecting to a large extent the growth environment where the iron has been exposed. However, the structure of the rust phases formed on carbon steel in atmospheric exposure includes many imperfections, and real component structures appear to diverge from the ideal crystallographic structure of typical iron oxides. Rigorous information on the morphology of the rust phases formed in atmospheric exposure is very scarce, and there are even fewer studies of analytical information on the chemical compounds corresponding to these rust morphologies. The aim of this paper is to advance this field using scanning electron microscopy (SEM)/micro-Raman spectroscopy to perform a more direct and rigorous characterization of the main rust phases. The equipment used consists of a fully integrated confocal Raman microscopy module, which includes an optical video microscope and a high-resolution XY stage on top of the SEM m...

Anticorrosive behavior study by localized electrochemical techniques of sol–gel coatings loaded with smart nanocontainers

In the present work, sodium phosphomolybdate, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, has been loaded and encapsulated in mesoporous silica nanoparticles without and with a hollow core in order to produce different smart nanocontainers. These nanocontainers have been designed to allow controlled release of the inhibitor in response to an external stimulus, thereby achieving more efficient and more economical use of the active substance. Corrosion activity leads to local changes in pH, and this work considers such changes as a signal of great interest. The nanocontainers respond to a pH of 10 or higher by increasing the release rate of the encapsulated active material. The smart nanocontainers have been incorporated into hybrid organic–inorganic sol–gel coatings and applied on carbon steel substrates. Mechanical defects have been made in the organic coating, reaching through to the metallic substrate, in order to study anticorrosive behavior in the affected area. A characterization study has been carried out at the defects and in their surroundings by means of two different localized electrochemical techniques: Scanning Kelvin Probe and Localized Electrochemical Impedance Spectroscopy. The results have shown significant improvement in the anticorrosive behavior of sol–gel coatings when formulated with smart nanocontainers loaded with sodium phosphomolybdate compared to a reference sol–gel coating.