In a nutshell, passivation is the process of treating or coating a metal in order to reduce the chemical reactivity of its surface. A “passive” substrate is one that the environment affects or corrodes less than others. In passivation, a chemical reaction with the base material creates an outer layer of shield material.
Passivation is used in a number of industries and is especially useful in the automotive industry, where aluminum pigments are used in coatings to enhance the appearance of automobiles. The use of aluminum pigments continues to grow in this market space, with the global aluminum powders, paste and flake market growing at a 6-percent compound annual growth rate (CAGR).
When Aluminum Meets Water
Most of the automotive industry has moved to water-based coatings to meet environmental regulations. The problem—aluminum and water don’t get along. When they meet, there is an unstable reaction, which has two negative outcomes:
- Aesthetic issue—the reaction leads to a dulling of the aluminum pigment, and consequently can end with the coating looking gray.
- Safety issue—the reaction also releases hydrogen gas, which is flammable and very dangerous.
Surface passivation prevents hydrogen evolution and dulling of aluminum pigment. Achieving surface passivation requires aluminum passivators used at the correct dosage.
Lubrizol has developed very effective passivator additives that solve the challenges inherent with passivation of aluminum pigments. Lubrizol® 2062H and Lubrizol® 2063H are hydrophobic phosphate esters. With these performance additives, the phosphate binds to the aluminum and prevents water from penetrating, acting as a surface protector.
Dosage and pH
Dosage is extremely important when using aluminum passivator additives. Different levels of the additive need to be optimized to achieve the correct level of passivation. As pH levels increase, more hydrogen is evolved. The challenge comes in finding the right balance of dosage and pH. Lubrizol can assist with optimizing dosage and pH to enable complete passivation of the aluminum while eliminating the hydrogen.
Contact us to learn more about Lubrizol’s high performing aluminum passivator technology.