How do elevated temperatures affect Chem Film?
Hexavalent chemical film conversion coating is actually a gel on a microscopic level. This gel contains water known as “waters of hydration” and this water is what imparts the “self healing” characteristics of the coating. Self healing is the process of the chem film flowing back into areas which have been scratched to protect the exposed substrate. Over time, the waters of hydration are lost and eventually the chemical film coating loses its ability to self heal. The coating becomes chalky, powdery and can be abraded off somewhat easily at this point. On a microscopic level the coating is cracked much like dried out mud. These cracks are the in roads to the base metal where corrosive agents can find their way to attack the substrate. Chemical film coatings can however have this process sped up dramatically by exposure to elevated temperatures. As a rule, coatings should not be exposed to temperatures above 150 degrees F. The dehydration of the coating is a function of time and tempera
