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AN INTRINSICALLY CONDUCTING POLYMER-BASED COATING SYSTEM FOR CORROSION PROTECTION OF STEELS
Title
AN INTRINSICALLY CONDUCTING POLYMER-BASED COATING SYSTEM FOR CORROSION PROTECTION OF STEELS
Creator
Yu, Qifeng
Date
2016, 2016-12
Description
Among the various corrosion protection strategies for structural steels, coating techniques provide the most cost-effective protection and...
Show moreAmong the various corrosion protection strategies for structural steels, coating techniques provide the most cost-effective protection and have been used as the primary mode for corrosion protection. Existing coating techniques have been used mainly for their barrier capability and all have a limited service life. In this research work, a waterborne two-strand polyaniline: poly (acrylic acid) complex was synthesized and utilized to fabricate the primer layer of a two-layer coating system. The techniques of Scanning Kelvin Probe Force Microscopy (SKPFM) and Electrochemical Impedance Spectroscopy (EIS) were used to evaluate the anti-corrosion capability of the polymeric complex when mixed in an epoxy matrix and coated on steel samples as the primer layer. The evaluation results show that coating systems including a PANi-based primer has measurable anticorrosion capability and the anti-corrosion capability of PANi-based primer depends on the usage of PANi and the type of matrix material of the primer layer. In the laboratory condition, a prototype two-layer coating system including the PANi-based primer and a polyurethane topcoat was manufactured. The ASTM Salt-Spray Test and EIS were used to prove the anti-corrosion performance of the prototype using a two-layer, polyurethane-over-epoxy system (no PANi) as the control system. After the proof of concept, a non-waterborne epoxy was used to fabricate a different PANi-based primer. The two types of primers and two other commercial primers (a zinc-rich primer and an epoxy-only primer) were used to make a total of eight two-layer coating systems using two widely used topcoats. Salt-Spray Test, Cyclic Salt Fog/UV Exposure Test, Pull- Off Adhesion Test, and the techniques of EIS, SKPFM, and Scanning Electron Microscope (SEM) were used to evaluate the long-term performance of the eight systems. Based on the laboratory-based recommendations, six groups of two-layer coating systems were then subjected to the outdoor-exposure test to evaluate their anti-corrosion durability at two testing sites. The field durability of the coating systems was evaluated in terms of their surface gloss reduction, color change, adhesion change and surface deteriorations. The matrix material in which the PANi is mixed plays an important role in the longterm anti-corrosion performance of coatings. The waterborne epoxy is effective in dispersing PANi nano-particles and has zero VOC; however, it does not bond to the steel surface as strongly as the regular non-waterborne epoxy. The topcoat material also plays an important role in the long-term anti-corrosion performance of coatings; polyurethane has higher durability than epoxy as a topcoat material. The PANi-based systems possess long-term corrosion protection comparable to the performance of the conventional zincrich three-layer system based on the one-year field evaluation.
Ph.D. in Civil Engineering, December 2016
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