Estudo das condições de obtenção do filme viniltrietoxisilano na proteção contra a corrosão do aço galvanizado

Abstract

Galvanized steel is obtained by immersing the carbon steel in a molten zinc bath widely employed in the automotive, petrochemical, chemical, marine, aeronautical and white-good appliances. It has higher corrosion resistance than carbon steel when exposed to corrosive environments. To increase its durability and corrosion resistance, it undergoes a surface treatment that is adherent to its surface. For this reason, phosphatization and chromatization are currently used as an after treatment to galvanization, both with environmental restrictions and human health. Due to the presence of toxic and carcinogenic products – in the chromatization or phosphatization - and to minimize the impact on the environment, the development of silane films as alternative pretreatments have been studied due to their good physical barrier properties against diffusion of oxygen to the metal interface and improve corrosion resistance. The aim of this work is to evaluate a corrosion resistance performance of galvanized steel coated with vinyltriethoxysilane (VS) film under hydrolysis conditions: silane concentration (2%, 3% and 4% %v) and hydrolysis time (30 min, 45 min and 60 min). The fixed variables were: the solvent solution used was water/ethanol (50% v/v) at pH 4.0, the curing time of 120 min and the curing temperature of 150°C in an oven. The corrosion resistance of pre-treated galvanized steel with VS silane film was evaluated by the following electrochemical techniques: open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), linear polarization resistance (Rp) and potentiodynamic polarization curves in 0.1 mol.L-1 NaCl solution. The chemical properties of films were analyzed by infrared spectroscopy technique (IR). The galvanized steel and the film surface morphology were observed by scanning electron microscopy (SEM) and X-ray energy dispersion spectroscopy (EDX). The electrochemical results indicated the formation of an efficient corrosion protection film when galvanized steel is treated with film obtained at 4% silane concentration and 60 min hydrolysis time. SEM images revealed less corrosion product formation when galvanized steel is treated with silane film and EDS spectra showed Si peaks indicating the adhesion of the film to the galvanized steel surface. The spectra in the IR region showed bands of Sicontaining compounds that reveal the presence of silane film on the substrate surface.