Structure and protective properties of Si-Ti-epoxy organic–inorganic hybrid film

Sol–gel method was used to prepare a Si-Ti-epoxy organic–inorganic hybrid composite sol, which was cured on the carbon steel surface at room temperature to obtain a transparent film. Based on the scanning electron microscopic image, the microscopic morphology of the film is flat, smooth, and dense. The atomic force microscopic image shows a nanometer scale morphology, and the structure of the Si-Ti-epoxy hybrid film is more uniform and denser than that of the Si-epoxy hybrid film. The film/carbon steel attenuated total reflection infrared spectrum presents a Si-O-Fe absorption peak at 831 cm⁻¹, which indicates the chemical bonding of the organic–inorganic hybrid film and the carbon steel substrate. The contact angle of the film is greater than 90°, indicating hydrophobicity. The dense nanostructure of the film and the chemical combination with the metal substrate confer the film with excellent electrochemical protection performance. The low-frequency impedance modulus (|Z|_0.01Hz =10¹⁰Ω∙cm²) of the Si-Ti-epoxy hybrid film (15–20μm) is an order of magnitude higher than the double-thick epoxy film (30–35μm). The corrosion current density (10⁻¹¹A/cm²) obtained by the polarization curve is two orders of magnitude lower than the double-thick epoxy film.