Avaliação da resistência à corrosão do aço carbono com revestimento nanocerâmico à base de zircônio

Abstract

Classical industrial pre-treatment systems based on phosphate and chromates are used to improve corrosion resistance and provide good adhesion properties for organic coatings. However, they have several drawbacks for environment because they produce a lot of solid waste with organic matter and heavy metals. To reduce the impacts, new process are being studied. Among there, there are obtained by dipping metal substrate in solutions containing ions of zirconium, and they are usually named as nanoceramic due to its ceramic properties and thickness in order of nanometers. In this context, the present study evaluated the corrosion resistance of carbon steel with a commercial nanoceramic conversion coating based on zirconium (0,6% and 3,5%) and compared with phosphate and carbon steel without treatment. The study was carried out by corrosion tests (salt spray, humidity and immersion). The corrosion process was monitored by electrochemical impedance spectroscopy. Additionally, characterization tests by scanning electron microscopy with energy dispersive spectroscopy, adhesion test (Pull-off test) and scanning vibrating electrode were carried out. The nanoceramic coatings showed better anti-corrosion performance. However, only the NT1® improved paint adhesion to the carbon steel substrate. The highest concentration of hexafluoroziconium acid did not contribute significantly to the corrosion protection and adhesion properties. The application of pre-treatment hinders the electrolyte spread under the paint film, but they have not self-healing properties.