Process Modifications and Additives for Anticorrosive Powder Coatings
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.