Conversion coatings are generally required to enhance organic coating adhesion and corrosion resistance on galvanized steel. Until a few decades ago, chromate conversion coatings were the most common conversion coatings in the industry owing to their exceptional performance in this regard. However, the adverse effects associated with hexavalent chromium as found in chromate conversion coatings and certain corrosion inhibitor pigments are now widely known. As a result, various initiatives have been deployed around the globe to restrict and regulate the use of hexavalent chromium. Finding suitable alternatives for chromate conversion coatings has therefore become one of the most pertinent research topics of the moment in the field of corrosion protection. A number of chromium-free conversion coatings have been found to show comparable corrosion resistance relative to chromate conversion coatings. For galvanized steel, conversion coatings based on zirconium and titanium have been found to be suitable alternatives to chromium. Organic additives may be incorporated in these conversion treatment solutions for galvanized steel to enhance the adhesion of organic coatings to the substrate. The effect of a given organic additive is highly dependent on the surface composition of the substrate as has been observed with the polymers polyacrylic acid (PAA), polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) on hot-dip galvanized steel and a Zn-Mg-Al alloy coated steel studied in this project. The durability of corrosion protection may also be enhanced by embedding corrosion inhibitors in the organic coating. An increased concern for sustainability and environmental-friendliness, has resulted in a global effort toward developing and using corrosion inhibitors which are safe for the environment and for human health. The electrochemical behaviour of galvanized steel in electrolytes with green inhibitors based on silicates, phosphates, zinc oxide and calcium at various concentrations are investigated. This project considers a multi-layer corrosion protection coating system comprising a conversion layer based on Zr/Ti cations and adhesion-enhancing polymer additives, and an organic coating embedded with 'green' corrosion inhibitors. The overarching aim is to investigate and establish new knowledge regarding the effect of polymer additives in conversion coatings on the adhesion of organic coatings as well as the identification of suitable green corrosion inhibitors. The outcome is an indication of which types of polymer additives and corrosion inhibitors work best for the two substrates tested – MagiZinc® and hot-dip galvanized steel, both supplied by Tata Steel BV.

Orpiment and realgar are yellow and red arsenic sulphide pigments that have been used since antiquity in works of art until the 19thcentury, when their use was restricted due to their toxicity. With time, these pigments degrade to form colourless arsenic oxide. Different oxidation states of arsenic (+3 and +5) in the degradation products have been recently found. Moreover, they have been identified throughout the whole painting layout from the panel until the varnish, suggesting the migration of degradation products through the paint layers. Besides changing the aspect, they might change the stability of the painting or painted object. Furthermore, they might represent a potential hazard for conservators when dealing with the work of art. Since a painting is in equilibrium with its environment, there is always water in motion inside the painting. It is therefore believed that the degradation products are migrating via water. However, the migration mechanism is still not well understood. This thesis aims to provide a better insight into the diffusion process of arsenites (As+3) and arsenates (As+5) in materials commonly found in paintings. For this, two different approaches were followed: In one hand, light aged painting reconstructions were analysed with FTIR microscopy and SEM-EDS to asses the effect of different grounds and relative humidity on the migration of arsenic. In all the samples, degradation products were found in the orpiment layer based on the As-O vibration, detected with FTIR microscopy. It was possible to identify arsenic in the ground layer close to the orpiment-ground interface for all samples with both techniques. However, due to the low intensity and the proximity to the interface of the arsenic found in the grounds, no conclusions could be drawn about its migration. On the other hand, in-situ ATR-FTIR spectroscopy and EIS measurements were performed on a set of samples to analyse the water, arsenates and arsenites diffusion through oil and two varnishes (dammar and mastic). The diffusion coefficients of water in oil, dammar and mastic were determined with both techniques. It was found that the water diffuses faster in oil than in the two varnishes. Despite being similar, mastic was found to be less stable than dammar since a decrease in its barrier properties with time was found. The diffusion of arsenates and arsenites in dammar and mastic was studied by EIS and the diffusion coefficients were calculated for the first time. It was found that the diffusion of arsenites in the coatings is faster than arsenates, which is in accordance to the diffusion of these species in water. EIS resulted in a promising technique in the study of diffusion of ions in coatings. Although further research is needed to fully understand the migration mechanism of arsenic in painting systems, this thesis provides a useful insight and a methodology with which the water and ion transport in coatings can be studied.