Behavior of fluorine coatings on steel bridges at different temperatures upon exposure to a direct heat source

Protective coatings are commonly used for the corrosion protection of steel structures. To protect steel bridges from weather and unexpected damage (e.g., fires or explosions), fluorine-based coatings are commonly applied as a top layer. Although the safety of infrastructure should be considered via risk assessment and maintenance, few studies have been conducted on the degradation of organic coatings under harsh environments and accidental events. Therefore, we examined the effect of direct heat exposure on organic (fluorine-based) coatings. To simulate the conditions produced by an explosion, specimens were subjected to surface temperatures of 100, 200, 300, 400, and 500 °C for 10 s through direct exposure to heat. Surface changes to the post-exposure fluorine coats were characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, nanoindentation, gloss, color differentiation, laser microscopy, and thermogravimetric analysis. Overall characterization of the coatings through electrochemical impedance spectroscopy revealed that surface changes began to occur at 300 °C and detachment of the bulk coating occurred at 400 °C or higher. Our results successfully clarify the behavior of fluorine coatings under different temperatures to a degree that is relevant to critical public safety issues in civil infrastructure.