Sodium silicate assisted manganese phosphate chemical conversion coating on D2 steel at various concentration

Abstract Iron-Manganese Phosphate composite coatings are formed in order to protect the surface of D2 steel from corrosion. The coating has been established by immersion method. Addition of sodium silicate (additive) in different concentration to the phosphating solution altered the coating weight, coating time, morphology, porosity and anti-corrosion performance of phosphate chemical conversion (PCC) coatings on D2 steel were studied. The resultant coatings were characterized by Fourier-transform infrared spectroscopy, Field emission scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction measurements to ascertain the type of functional groups, morphological features, and chemical composition and phase constituents, respectively. The corrosion resistance of iron-manganese phosphate composite coated D2 steel, in 3.5% NaCl, was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. Potential-time measurement can be used to follow the phosphate coating formation and provide an indication of the completion of the coating process. The results infer that the presence of additive can formed highly corrosion resistant iron-manganese phosphate composite coatings in shorter time. The novelty is an approach to determine the optimum concentration of additive for better protective layer.