Steel structures in the fields of architecture, bridge construction and shipbuilding must not lose strength or safety, not even over the course of many years, which is why the steel plates and beams used must be durably and extensively protected against corrosion. Particularly atmospheric oxygen, water vapour and salts attack steel. Zinc-phosphate coatings are usually applied to phosphated metal surfaces to prevent the corrosive substances penetrating.
Researchers at the INM have developed special, flake-shaped metal-phosphate particles to improve passivation and increase the diffusion barrier to corrosive substances. Manganese-phosphate flakes are available in addition to zinc phosphate. The flake-shaped particles are produced in a controlled precipitation process, and their anisotropy means that they are more readily soluble than corresponding spherical particles of the same composition. This allows the coating to provide more phosphate ions as needed, thereby ensuring improved and more rapid repassivation when metal surfaces are exposed due to mechanical damage. The shingle-like layering of the particles lengthens the path the corrosive gas molecules must take through the protective coating. In standardised corrosion tests, the coatings with flake-shaped phosphate particles outperformed coatings with spherical phosphate particles around tenfold.