A.C. Bastos

Effect of uniaxial strain on the protective properties of coil-coatings

The effect of uniaxial deformation on coil-coated galvanised steel was investigated. Samples with several degrees of uniaxial elongation were exposed to a corrosive solution and the loss of protective properties was monitored by electrochemical impedance spectroscopy (EIS). Protection rapidly decreased with the degree of elongation. After 16% the coating degradation introduced by elongation was so high that EIS was not able to distinguish different strained samples. The loss of protection was interpreted in terms of the morphological changes experienced by the coated system as a consequence of strain, supported by scanning electron microscopy (SEM) observations.

Nanocontainer-based corrosion sensing coating

The present paper reports on the development of new sensing active coating on the basis of nanocontainers containing pH-indicating agent. The coating is able to detect active corrosion processes on different metallic substrates. The corrosion detection functionality based on the local colour change in active cathodic zones results from the interaction of hydroxide ions with phenolphthalein encapsulated in mesoporous nanocontainers which function as sensing nanoreactors. The mesoporous silica nanocontainers are synthesized and loaded with pH indicator phenolphthalein in a one-stage process. The resulting system is mesoporous, which together with bulkiness of the indicator molecules limits their leaching. At the same time, penetration of water molecules and ions inside the container is still possible, allowing encapsulated phenolphthalein to be sensitive to the pH in the surrounding environment and outperforming systems when an indicator is directly dispersed in the coating layer.The performed tests demonstrate the pH sensitivity of the developed nanocontainers being dispersed in aqueous solutions. The corrosion sensing functionality of the protective coatings with nanocontainers are proven for aluminium- and magnesium-based metallic substrates. As a result, the developed nanocontainers show high potential to be used in a new generation of active protective coatings with corrosion-sensing coatings.

Control of crystallite and particle size in the synthesis of layered double hydroxides: Macromolecular insights and a complementary modeling tool

Zinc-aluminum layered double hydroxides with nitrate intercalated (Zn(n)Al-NO3, n=Zn/Al) is an intermediate material for the intercalation of different functional molecules used in a wide range of industrial applications. The synthesis of Zn(2)Al-NO3 was investigated considering the time and temperature of hydrothermal treatment. By examining the crystallite size in two different directions, hydrodynamic particle size, morphology, crystal structure and chemical species in solution, it was possible to understand the crystallization and dissolution processes involved in the mechanisms of crystallite and particle growth. In addition, hydrogeochemical modeling rendered insights on the speciation of different metal cations in solution. Therefore, this tool can be a promising solution to model and optimize the synthesis of layered double hydroxide-based materials for industrial applications.

Active sensing coating for early detection of corrosion processes

A corrosion sensing coating based on specially developed polymeric microcapsules with a pH-indicator is reported. The synthesis of the microcapsules is designed in a way to ensure their optimal compatibility with the polyurethane protective coatings and to allow release of the indicator at higher pH values. The obtained polyurea microcapsules have a regular and microsized morphology and a loading content of 12 wt%. The developed sensing coating applied on aluminium and magnesium alloys is able to indicate initiation of corrosion processes through a pink coating coloration, as a result of local pH increase in the cathodic areas.

Synthesis and electrochemical study of a hybrid structure based on PDMS-TEOS and titania nanotubes for biomedical applications

Metallic implants and devices are widely used in the orthopedic and orthodontic clinical areas. However, several problems regarding their adhesion with the living tissues and inflammatory responses due to the release of metallic ions to the medium have been reported. The modification of the metallic surfaces and the use of biocompatible protective coatings are two approaches to solve such issues. In this study, in order to improve the adhesion properties and to increase the corrosion resistance of metallic Ti substrates we have obtained a hybrid structure based on TiO₂ nanotubular arrays and PDMS-TEOS films. TiO₂ nanotubes have been prepared with two different diameters by means of electrochemical anodization. PDMS-TEOS films have been prepared by the sol-gel method. The morphological and the elemental analysis of the structures have been investigated by scanning electron microscopy and energy dispersive spectroscopy (EDS). Electrochemical impedance spectroscopy (EIS) and polarization curves have been performed during immersion of the samples in Kokubos simulated body fluid (SBF) at 37 °C to study the effect of structure layers and tube diameter on the protective properties. The obtained results show that the modification of the surface structure of TiO₂ and the application of PDMS-TEOS film is a promising strategy for the development of implant materials.

Catalyst-free growth of carbon nanotube arrays directly on Inconel® substrates for electrochemical carbon-based electrodes

Vertically aligned carbon nanotubes (VACNTs) were grown directly on a pretreated Inconel® metallic substrate by thermal chemical vapor deposition without the need of catalyst addition. This experimental approach allows the substrate surface to act as both the catalyst and support for the CNTs growth therefore enhancing the connection between the two. It was found that uniformly dispersed and densely packed nano-sized, intrinsic catalytic particles, generated during the annealing pretreatment, allow the growth of the vertically aligned CNTs. Scanning electron microscopy, transmission electron microscopy and Raman spectroscopy were used to assess the quality and the nature of the formed CNTs. Electrochemical measurements were performed to evaluate the possibility to use the Inconel/VACNTs system as an electrode material. As a proof of concept, the capacitive behavior of the VACNTs arrays coupled to the Inconel substrate as the active electrode material and the current collector, respectively, in supercapacitors is demonstrated.

Extending the Lifetime of Weldable Primers by Means of Chemical Inhibitors

Pre-painted metal sheets (coil-coatings) are widely used in casings of household appliances, roofs and side walls in buildings and body parts for the automotive industry. One of the main problems of this type of material is the difficulty to weld it. In an attempt to overcome this problem weldable organic coatings are being experimented. Primers with heavy loads of zinc powder are being employed with success to spot-weld different components of an article. These primers may also present an anticorrosive effect through the galvanic protection offered by the zinc powder. However in aggressive conditions the zinc containing primers can corrode very fast and be consumed in a short period of time. Work has been undertaken in order to extend the lifetime of these primers but maintaining the welding and anticorrosive capabilities. The approach followed here was the modification of primers by corrosion inhibitors that can provide additional active protective effect. A set of organic and inorganic corrosion inhibitors was tested in order to partially passivate the primer. The inhibition of corrosion of zinc and iron was also investigated. Electrochemical testing was done with Electrochemical Impedance Spectroscopy (EIS) and the Scanning Vibrating Electrode Technique (SVET). Results showed that soluble inorganic salts of Ce(III) and La(III) and organic inhibitors like benzotriazole and mercaptobenzothiazole are good candidates to increase the service life of weldable primers.

Monolithic porous carbon materials prepared from polyurethane foam templates

Monolithic carbon foams with hierarchical porosity were prepared from polyurethane templates and resol precursors. Mesoporosity was achieved through the use of soft templating with surfactant Pluronic F127, and macroporosity from the polyurethane foams was retained. Conditions to obtain high porosity materials were optimized. The best materials have high specific surface areas (380 and 582 m2 g–1, respectively) and high electrical conductivity, which make them good candidates for supports in sensors. These materials showed an almost linear dependence between the potential and the pH of aqueous solutions.

Effect of Strain on the Protective Properties of Organic Coatings

The effect of strain on the corrosion protection performance of organic coatings was tested using coil-coated galvanised steel subjected to uniaxial strain. The protective properties were followed by the coating resistance and the double layer capacitance in the delaminated areas, determined by Electrochemical Impedance Spectroscopy (EIS) during immersion in NaCl solution. The degradation increased with the elongation of the sample until a value of 16%.