Definition - What does Inhibitive Pigment mean?
An inhibitive pigment is a specially formulated compound used to prevent or retard corrosion reactions on a metallic substrate. Inhibitive pigments are typically found in inhibitive coatings and operate mainly by chemical/electrochemical means, where they undergo a series of reactions that disrupt the natural corrosion processes.
Corrosionpedia explains Inhibitive Pigment
Red lead and zinc chromate are two of the most well-known and commonly used inhibitive pigments.
Inhibitive pigments are usually integrated into primers or first coats, where they are in contact with the metal substrate and are most effective. These pigments reduce the rate of electrochemical corrosion by reducing the chemical reactivity of the metal's surface; this process is known as passivation.
Inhibitive pigments passivate metallic surfaces mainly by polarization. During polarization, the electrode potential of the surface is shifted to either an anodic or a cathodic state, thus causing the surface to become more electropositive or electronegative. This promotes the natural growth of the metal's protective oxide layers, rendering the substrate inert.
Inhibitive pigments can also protect against macroscopic defects by self-healing, i.e., the pigments leach out from nearby areas into the defect. This type of protection is typically associated with chromate pigments.