Development of chrome free coatings for white rust (corrosion) protection of galvanised steel is a key concern for scientists worldwide. The present work presents the results of an investigation on the effect of amine and thiol functional groups bearing silane coupling agents such as 3-phenyl-aminopropyl-triethoxy silane and mercapto-propyl-tri methoxysilane respectively on anticorrosion properties of a reference sol–gel solution. Anticorrosion performance of the coatings was evaluated by potentiodynamic polarisation method and AC impedance spectroscopy. Accelerated corrosion test was performed using salt spray chamber and compared with a chromate coated galvanised sheet. The results clearly revealed that the addition of silane containing thiol group to the reference coating solution produced remarkable improvement in hydrophobicity and corrosion resistance compared to amine group.
Just as the diverse as the various substrates that can be coated is the choice of several coating methods by which the coating can be applied to these pretreated surfaces. They include the manual methods, where great skills and experience is needed, on the other hand there are automated and robotics coating control methods where coating can be applied with more precise manner. Sol-gel process is one of the promising bottom up nano-coating technologies to develop thin film over various metallic substrates. The property and characteristic of the resulting film is strongly influenced by the various parameters and reaction conditions of the sol-gel process and of course on the deposition techniques. In this review, we have thrown some lights on different coating application processes covering theoretical principle, advantages, disadvantages, and special various parameters controlling the final film quality.
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