Accelerated aging of zinc-rich powder coatings containing different conductive pigments
Powder zinc-rich primers (ZRPs) may be subjected to mechanical defects during their service. To evaluate their protective capability, accelerated tests (salt spray, free corrosion potential [Ecor] versus time in the presence of an artificial defect) were monitored for different ZRP systems containing carbon black (CB) and/or polyaniline (PANI) as conductive pigments, with a polyester topcoat.
Accelerated aging tests are frequently used to evaluate and compare the anticorrosive properties of many new formulations of organic coatings developed by the industry. To be realistic, an accelerated aging test for an organic coating should reproduce the most important environmental factors affecting the organic coating properties during its service life (that is, solar irradiation, thermal aging, mechanical damage, water permeation, and so on). This has led to the development of a number of weathering tests and methods often standardized, such as salt-spray chamber exposure, prohesion test, ultraviolet (UV) weathering, thermal cycling, and others. It can be noted that the accelerated tests could be a combination of these factors1,2. As an example, an interesting accelerated aging test is represented by the thermal cycle developed by Bierwagen and co-workers3.4. However, even if some criticisms can be formulated in terms of representativeness of the reality5, the salt-spray chamber remains the main tool used in industry because it’s simple to use. As an example, according to Munger6, a coating that withstands a salt-spray test for 1,000 hours without coating damage or metal corrosion should possess good resistance to moist air conditions in the field.