Corrosion-resistant Zeolite Coatings

Zeolite films are well-known as molecular sieves for membrane applications, but they may also be useful as nontoxic, corrosion-resistant coatings to replace chromate-based materials, according to Yushan Yan and colleagues at the University of California, Riverside (Angew. Chem. Int. Ed. 2008, 47, 525). Hydrothermal zeolite coating methods require high process pressures, which the authors say are difficult for the surface-finishing industry to adopt commercially. To make the coatings at ambient pressure, Yan and coworkers adapted a technique normally used to prepare zeolite powders.Their method relies on an "environmentally benign" ionic liquid solvent rather than water or an organic solvent. The researchers used the approach to coat a corrosion-susceptible aluminum alloy commonly used in aerospace and defense applications with the silicoaluminophosphate zeolite SAPO-11. When deposited, the zeolite showed good resistance to pitting corrosion, especially when topped with a silane sealant.