In this study, production and characterization of acrylic based polyurethane-nanosilica clear coats on carbon steel substrates were investigated. For this purpose, two different types of nanosilica (fume and precipitate) were employed as fillers. To enhance the dispersion of nanopaticles in polymer matrix, magnetic and high speed mixers were used. Physical properties of coatings such as particle dispersion and viscosity were measured with Zeta sizer analyzer and rotational viscosimeter. Optical properties such as turbidity, gloss and UV/Vis absorption studied by Turbidimeter and spectrophotometer. The results indicated that both nanosilica with smaller particle size than visible light wavelength, excellent dispersion and refractive index close to the polyurethane matrix, had smallest effect on the traarency and gloss but obviously enhanced the viscosity, weather stability, adhesion, microhardness, toughness, scratch and abrasion resistance of coatings. SEM photographs of wear track and wear debris illustrated that surface fatigue was the predominant wear mechanism. Also, corrosion resistance of nanocomposite coatings in salt spray was better compared with that of pure coatings because of improvement in adhesion and cohesive strength of nanocomposite types. Finally, it was found that the cheaper precipitated nanosilica could to replace with expensive fumed nanosilica in clear coats.
