Silicone resin to improve corrosion resistance of Zn and ZnFe coated steel

Abstract

Chromatation pre-treatments have been widely used to improve galvanized steel corrosion resistance. However, due to the high toxicity of chromate ions, chromatation pre-treatments tend to be banned and, in last years, alternative coating systems are under investigation. Recently, polysiloxanes have been developed for application as coatings. Among them, and due to their specific properties, such as hardness, chemical resistance and hydrophobicity, silicone resins may be considered as promising substitutes for chromatation pre-treatments.In this work silicone films, obtained from the hydrolysis of a methoxy functional silicone reactive intermediate, were applied on galvanized steel and on steel electroplated with a ZnFe alloy. Electrochemical techniques were used to characterize the degradation behavior of the samples. These consisted on the monitoring of the open circuit potential (OCP), and on the potentiodynamic polarization of the samples, which was performed in a 3% NaCl aqueous solution. Additionally, electrochemical impedance spectroscopy (EIS) was used as a complementary technique for the evaluation of the corrosion mechanisms of the coating system. SEM and EDS were employed to inspect the surface of the samples before and after the electrochemical tests. EIS data was fitted to an equivalent circuit from which the electrochemical parameters were obtained.Results show the protective character of the resin films, when compared with uncovered specimens. The capacitance of the films increased with the immersion time, in accordance to the behavior expected for an organic film. The overall performance of the coating systems appears to be highly dependent on the type of metallic coating applied to the steel. During the first three days of immersion the coatings applied upon galvanized steel showed larger |Z| values when compared with those applied to the electroplated steel, indicating a superior corrosion resistance of the former. However, after that time, an abrupt drop of |Z| is observed in the film applied on galvanized steel. In comparison, the coating system involving ZnFe alloy evidences a better stability throughout the immersion time.

Inhibitor-Sandwiched Polyelectrolyte Film for Micro/Nanopore Sealing to Enable Corrosion-Resistant Self-Healing Capability

“…In addition, the absolute value of the phase angle at high-frequency (10 kHz) for the LDH coating gradually decreases from 80 to 60° as the soaking time increases (Figure b). This decrease in impedance results from the gradual degradation of the LDH layer during the soaking process. , As for the PEI/PSS/8HQ/PSS/PEI coating, after experiencing the same soaking time, the absolute value of the phase angle only decreases from 87 to 80°, indicating better corrosion resistance compared to the single LDH layer (Figure d). From the Tafel curves (Figure f), the corrosion potentials of PEI/PSS/8HQ/PSS/PEI and LDH coatings after 15 days of immersion are −0.415 and −1.100 V and the corrosion current densities are 4.66 and 10.80 nA cm –2 , respectively.…”

Synthesis and Characterization of Zn-Nix Advanced Alloys Prepared by Mechanical Milling and Sintering at Solid-State Process

“…e relative density of the green compacted Zn-Ni 5 powder alloy resulted to be about 6.20 g/cm 3 , which increases slightly to 6.52 g/cm 3 when the compacts are subjected to a sintering process, so that the alloy during the heat treatment undergoes a volumetric contraction of 0.45%, and this treatment also decreases the percentage of apparent porosity from 18.2% to 1.8%.…”

“…However, in the last quarter of the twentieth century, there has been an advancement in the characterization, analysis, and processing of metallic materials, having allowed the development of new advanced alloys. ere are several systems of metal mixtures such as nickel (Ni) base alloys in which the interest lies in their higher corrosion resistance, which is commonly used in oil-and chemical-processing industries, and for a long time, zinc (Zn) alloys have primarily been studied because of their light weight and good corrosion resistance and recently have been used as metal coatings to provide any type of surface protection for automobile parts or building materials [2,3].…”

Influência dos defeitos de solidificação na resistência à corrosão do Zamac 5 obtido por injeção sob pressão

“…Manteve-se um potencial praticamente estável por aproximadamente 1800 segundos, oscilando entre -1,000 e -1,025 V. O tempo de imersão da amostra durante a medida e a agressividade do eletrólito podem ter influenciado no resultado obtido. Observa-se, então, que os valores encontrados para Zamac 5 evidenciam que o comportamento da liga tende a assemelhar-se ao do metal puro [21][22][23]. Isso já era esperado, uma vez que a liga é formada basicamente por zinco.…”