Simultaneous acid exposure and erosive particle wear of thermoset coatings

Handling acidic chemicals is a challenge in the chemical industry, requiring a careful choice of contact material. Certain thermoset organic coatings are applicable in low pH environments, but when particulate erosion is also present the performance demand is increased. This is the case in, e.g., stirred tanks for agitated leaching of copper ore, where sulfuric acid is mixed with an erosive slurry. A pilot-scale agitated leaching tank was designed and constructed to explore the performance of selected thermoset coatings in such an environment. For reference, simple immersion experiments were conducted. Coating durability was estimated by observing the film thickness change during exposure. It was found to be a function of film swelling and film contraction, due to chemical exposure, as well as the “polishing” caused by erosive wear. Film reduction rates varied with radial position in the tank bottom-placed coating samples. Maximum rates were found about halfway between the reactor center and wall. Polishing rates also varied significantly with acid concentration, most likely due to chemical reactions taking place between the acid and the coatings, damaging surface mechanical properties, similar to the erosion/corrosion-type phenomena found in metals. A vinyl ester-based coating was the most resistant to the simultaneous erosive/acidic exposure, with a maximum polishing rate of 3.24±0.61 μm/week, while novolac epoxy and polyurethane coatings showed high polishing rates of 11.7±1.50 and 13.4±0.57μm/week, respectively.