Ph.D. Student, National University of Singapore (NUS)
Prediction of the durability of industrial protective coatings in corrosive environments
Paint is applied to protect steel structures from corrosion effectively. The long-term performance of a coating is influenced significantly by its ability to adhere to the material to which it is applied. This is not only because the coating might flake away or detach from the surface, but also because poor adhesion will allow moisture or corrosion products to undercut the coating film from areas of damage. Among the many types of paints, zinc rich paints are the prime choice for use in aggressive environments, such as offshore and industrial plants, because of their unique property of protecting the metal even when there is a degree of mechanical damage to the coating. The identification of the corrosion products that form in the damaged area is essential for a better understanding of the mechanism of corrosion protection and predicting the durability of the paint system. However, the analysis of the durability of the zinc paint system is still underrated and disregarded, unlike steels where failure analysis and life assessment methods are well established. The lack of knowledge in predicting the durability of zinc paints may be due to four reasons:
• Firstly, the mechanism of protection of substrate by zinc paints has not been well studied over the different stages of service life. • Secondly, there is a lack of information on the healing action mechanism of zinc paints within the scratches or mechanical damages. • Thirdly, the nature of the corrosion products under zinc paints have not been well characterized. • Fourthly, there is a lack of simulations or models for zinc paint failures. In order to predict the durability of zinc paints, the fastest and least expensive way is likely to be via models.
Therefore, The main scope of our research falls into three phases: First phase: Characterization of the corrosion products under zinc rich paints Second phase: Understanding the protectiveness mechanism of zinc rich paints over different stages of service life Third phase: Modelling the corrosion mechanisms of zinc rich paints
Abstract: The corrosion behavior of a semi-automatic gas tungsten arc welded joint in 3Cr steel was investigated in a CO2-containing environment. Assessment of the galvanic corrosion interactions of the different regions in the joint was carried out through microelectrochemical measurements and immersion tests. The weld zone (WZ) was determined to be the most cathodic region while the base metal (BM) was the most anodic region. The heat affected zone (HAZ) underwent little galvanic interaction, as its free potential was close to the coupled potential. The galvanic coupling effects theoretically derived from the corrosion current densities before and after coupling were in good agreement with the results of the immersion tests.
Pub.: 20 May '16, Pinned: 26 Aug '17
Abstract: The initial pH effect on the dissolution of zinc-magnesium coated steel is investigated with or without chlorides for long immersion periods. The coating is characterized by TEM, SEM and GDOES. With immersion time, the alloy electrochemical behaviour is investigated by EIS and the corrosion products are analysed using ICP-OES and XPS. In alkaline medium, the formation of zincite is inhibited and chlorides do not hinder a passive layer formation. In chloride electrolyte at natural pH, chlorides are not detected on the metal surface. Chemical composition of corrosion products and their protective effect depend on the initial pH and its evolution.
Pub.: 03 Mar '16, Pinned: 26 Aug '17
Abstract: This study investigates the electrochemical characterization of carbon nanotube and zinc-rich epoxy primers (CNT-ZRPs) on carbon steel in simulated concrete pore (SCP) solutions in the presence of chloride ions. The mechanistic performance of CNT-ZRPs was characterized by adding different zinc content. The electrochemical results indicated a dominant barrier protection effect for the coating with 60 wt% Zn while there was a mixed corrosion protection mechanism for the coating with 70 wt% Zn and a dominant cathodic protection mechanism for coatings with higher zinc content (80 wt% and 90 wt% Zn). These barrier and cathodic protection control mechanisms were characterized quantitatively by electrochemical and high-resolution techniques.
Pub.: 31 Mar '16, Pinned: 26 Aug '17
Abstract: This work presents the synthesis of nanostructured hollow polyaniline (PANI) capsules and their application for encapsulation of corrosion inhibitor 2-Mercaptobenzothiazole (MBT). The pH-triggered release of MBT from the capsules was evidenced using UV–vis and Surface Enhanced Raman Spectroscopy (SERS). Incorporation of MBT loaded PANI capsules into epoxy ester coating on AA2024-T3 resulted in a protective system with self-healing ability confirmed by Electrochemical Impedance Spectroscopy (EIS) and Scanning Vibrating Electrode Technique (SVET). The results showed that the incorporation of MBT-loaded PANI capsules into the coating has significantly improved its corrosion protection performance due to the interesting smart characteristics of PANI capsules.
Pub.: 06 Jul '16, Pinned: 26 Aug '17
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