Definition - What does Sacrificial Pigment mean?
A sacrificial pigment is a material that not only changes the color of a coating, but also protects the base material onto which it is applied. A sacrificial pigment coating provides this protection by shielding the base material from the atmosphere and by being more reactive than the base material.
Corrosionpedia explains Sacrificial Pigment
Adding a sacrificial pigment to a coating provides increased corrosion protection to a base material. A coating normally shields the base material from the atmosphere and corrosive environments. When a sacrificial pigment is added to the coating, not only will the base material be shielded from corrosive environments, it will also be less likely to corrode because the sacrificial pigment has a higher reactivity. This higher reactivity causes any oxidation to occur to the sacrificial pigment rather than to the base material.
Zinc dust is the most common sacrificial pigment for paints that are applied to steel. Zinc is more reactive than steel, which makes the sacrificial zinc pigment the anode when in contact with steel. This corrosion protection method provided by a sacrificial pigment is also known as cathodic protection because the base material is the cathode in the chemical reaction.
In order for a sacrificial pigment to be effective, it must be more reactive than the base material. For example, zinc would be effective for a steel base material but less effective for a magnesium base material.