Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Zhu, Jesse

2nd Supervisor

Zhang, Hui

Co-Supervisor

Abstract

Organic coatings are the most widely applied method for protection of metallic materials. Liquid coatings still dominate the coating industry, but powder coatings are capturing more of the liquid coatings market due to their economical, ecological, environmental, and energy-saving benefits.

Ultrafine powder coatings have been reported to show higher surface smoothness, gloss, and represent one of the future development directions of powder coatings. However, the mechanisms behind surface improvements and the anti-corrosion abilities of ultrafine powder coatings are still uncertain. Therefore, we fabricated ultrafine powder coatings (~ 20 µm in size), compared with coarse ones (>30 µm), and found that the ultrafine powder coatings had lower surface roughness, fewer inner voids, higher barrier properties, and narrower salt spray creepage (~ 30% decrease).

Zinc-rich powder coatings (ZRPCs) are important for heavy duty anti-corrosive applications, but current ZRPCs have a too low zinc content (≤70 wt.%), indicating limited anti-corrosive ability, to be used for higher anti-corrosive requirements. We fabricated ZRPCs by employing a press and the zinc dust content reached 85 wt.%. The fabricated ZRPCs with 80 wt.% zinc had a higher zinc utilization and a more uniform dispersion of zinc particles, and in turn, slightly longer cathodic protection period and narrower creepage (1.3 mm) than the extruded sample (1.5 mm) after 2500 h salt spray tests.

Another challenge for ZRPCs is how to decrease zinc content while maintaining the corrosion protection. We incorporated iron phosphide to replace part of zinc in zinc-rich polyester powder coatings and found that iron phosphide, due to its conductive nature and electrochemical catalysis activities, can replace 10 wt.% zinc in 75 wt.% zinc-rich coatings with maintained cathodic protection (87 days) and significantly decreased corrosion creepage (from 1.78 to 1.42 mm) and localized corrosion.

In addition, applying superhydrophobic surfaces is a recently developing approach for corrosion protection. However, there are very few reports about superhydrophobic powder coatings and their anti-corrosion abilities. We fabricated robust superhydrophobic powder coatings by incorporating polytetrafluoroethylene (PTFE) particles and achieved tunability of hydrophobicity, with the water contact angle varying from 80° to over 160°. The coatings demonstrated multifunction, multifaceted durability, and robustness against corrosion.

Summary for Lay Audience

Corrosion naturally occurs and causes damage to metal structures. Organic coatings are the most widely applied method for protecting metallic materials from corrosion. Liquid coatings still dominate the coating industry, but they involve large amount of organic solvents, which contributes to environmental pollution. In recent decades, powder coatings are occupying more of the liquid coatings market due to their economical, ecological, environmental, and energy-saving benefits.

In this study, improvements on powder coatings include four subprojects. The first subproject is ultrafine powder coatings, which have higher surface smoothness and gloss than regular coatings and promise wider applications. But the mechanisms behind ultrafine powder coatings and their effects on anti-corrosion abilities are still uncertain. Therefore, ultrafine powder coatings (~ 20 µm in size) were fabricated, and it was found that the ultrafine powder coatings had better anti-corrosive properties due to denser structures.

The second one is zinc-rich powder coatings (ZRPCs), which are mainly used for heavy duty corrosion protection. However, traditional ZRPCs have low zinc content (≤70 wt.%), indicating a shorter protection time. We replaced the traditional extrusion process with a press bonding process and fabricated ZRPCs in which the zinc dust content reached about 85 wt.%. In addition, the press-bonded zinc-rich coatings with 80 wt.% zinc had a higher zinc utilization and, in turn, higher corrosion protection than the extruded.

The third one is to reduce zinc content in ZRPCs while maintaining the corrosion protection. Iron phosphide was used to replace part of zinc in zinc-rich polyester powder coatings. It was found that iron phosphide, not only can replace 10 wt.% zinc in 75 wt.% ZRPCs, but also increase the original protection abilities.

In addition, applying superhydrophobic surfaces is a recently developed approach for corrosion protection. However, there are very few reports about superhydrophobic powder coatings and their anti-corrosion abilities. In this section, robust superhydrophobic powder coatings were fabricated by incorporating Teflon particles into regular powder coatings. The fabricated superhydrophobic coatings demonstrated mechanical and chemical robustness and multifunction including anti-corrosion.

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Available for download on Tuesday, September 01, 2026

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