The purpose of this paper is to develop a corrosion resistant zinc‐free coating for interstitial free steel.
The objective was achieved by developing a titania‐silica hybrid coating through a sol‐gel process by incorporating a dye molecule. The role of dye molecules was particularly important for enhancing the anti‐corrosion properties of the coating. The approach of current research was to develop a low‐temperature coating process that can bring similar performance to that obtained in case of zinc coating. Titania and silica precursors were mixed by stirring under a nitrogen atmosphere at 80°C to formulate a low‐temperature coating. The dye molecules were added before addition of water for subsequent hydrolysis. This complete formulation was applied over steel sheets using a roll coater as the application method.
The ranking order of improved corrosion resistance was found to be PATMS>EETMS>GPTMS and the addition of trace amount of tartrazine dye (60‐65 mg/l of liquid) in PATMS increased the corrosion service life in saline environments from 168 to 216 h, thus showing a promising improvement. Scanning Kelvin Probe results indicated that the corrosion reaction is controlled cathodically in presence of dye and, electrochemical impedance spectroscopy results exhibited a charge transfer resistance (Ct) of coating with dye of 419Ω cm2, which was higher than that of a similar coating without dye (360Ω cm2), indicating increased corrosion protection.
This coating had improved barrier protection but lacked cut edge protection. Future work will focus on adding sacrificial protection by introducing compatible corrosion inhibitors, especially dye molecules, which are photosensitive.
This coating has huge potential for use in the automotive sector, especially for certain automotive parts (i.e. helm flanges), which suffer from poor durability in salty and high‐humidity atmospheres.
Since this coating formulation utilises a partially aqueous base, some environmental impact cannot be avoided, but it will have less impact than a complete solvent base formulation.
The novelty of the work was the introduction of dye molecules as the corrosion inhibitor and their compatibility in the hybrid coating system.
