Phase Transformation of Rust in the Presenceof Various Tannins

Rust converters are chemical formulations that can be applied to corroded surfaces causing the passivation and elimination of possible further attack after the application of a coating. Tannins extracted from mangrove, chestnut, quebracho and mimosa as rust converters were evaluated. Two different types of pre-rusted sample preparations were adopted. The pre-rusted samples were immersed in 5 g/l of the various tannin solutions and the phase transformations were analyzed via Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The rust components were mainly lepidocrocite (γ-FeOOH) and magnetite (Fe3O4) and were found to be dependent on sample preparations. Transformation of rust components to ferric-tannates, particularly lepidocrocite, in the presence of various tannins could be observed. The relation between the partial transformation of pre-rusted samples and sample preparation is correlated.