Study of anti-corrosive mechanisms of metal-rich silicates (silica) in paint

Abstract

The anti-corrosive effectiveness and mechanisms of a number of the synthetic amorphous calcium rich silicates (silica), and zinc rich silicates contained in a white water-based interior acrylic paint formulation and applied to mild steel plates, have been studied primarily using Scanning Electron Microscopy, Energy Dispersive X-ray Analysis, Transmission Electron Microscopy and Image Quantitative Analysis. The samples were provided from a previous study that involved synthesizing the metal-silicates (silica), incorporating them into a paint film on mild steel plates and exposing the plates to a natural weathering atmosphere for several months. In this study the nature and extent of the corrosion in the system mentioned above was studied and a mechanism for the corrosion protection afforded by the amorphous calcium rich silicates (silica), and zinc rich silicates has been developed. The extent of corrosion was determined by the development of a rust area ratio parameter based on the results of Image Quantitative Analysis. Energy Dispersive X-ray Analysis and Element Mapping have been used to determine the distribution and migration of calcium, zinc and silicon in the paint film. Transmission Electron Microscopy was used to identify the structure of calcium compound deposited on the corroded surface of mild steel plates. The results suggest different mechanisms for the amorphous calcium rich silicate (silica) and for the amorphous zinc rich silicate in paint film. The amorphous calcium rich silicates (silica) in paint film acts as a cathodic inhibitor. The amorphous zinc rich silicates appear to bond with the paint base together to form a high density, high weathering resistance and relatively pore-free coating which more impervious to water.