Investigations of the Mechanism of Corrosion Inhibition by Polyaniline. Polyaniline-Coated Stainless Steel in Sulfuric Acid Solution

Abstract

The objective of this work was to elucidate the mechanism by which polyaniline ͑PANI͒ films passivate stainless steel surfaces in highly corrosive H 2 SO 4 solution. A variety of experimental methods, including measurements of the open-circuit potential, Auger depth profiling, and the scanning reference electrode technique ͑SRET͒, was used. These studies have shown that passivation is achieved because the oxidized and protically doped emeraldine-salt form of PANI holds the potential of the underlying stainless steel electrode in the passive region. Because of this electrostatic mechanism of corrosion inhibition, the entire stainless steel surface does not have to be coated with PANI in order to achieve passivation. Auger depth profiling experiments show that, in analogy to the case of a bare stainless steel surface whose potential is potentiostatically maintained in the passive region, the stainless steel surface beneath the PANI film is enriched in Cr after exposure to the H 2 SO 4 solution. Finally, SRET was used to explore passivation of the stainless steel in regions exposed to solution by pinholes intentionally cut through the PANI film. SRET shows that the PANI film surrounding the pinhole can heal the stainless steel in the pinhole region.Polyaniline ͑PANI͒ is one of the most intensively investigated of the electronically conductive polymers. 1-7 In 1985, DeBerry found that PANI films electrodeposited on stainless steel passivated the surface to corrosion in sulfuric acid solution. 8 Since then there have been numerous studies of the corrosion inhibition properties of PANI 9-14 and other electronically conductive polymers. 15 Nevertheless, there is no universally agreed upon mechanism by which these polymers provide anticorrosion properties. We have investigated corrosion inhibition by chemically synthesized PANI films coated onto stainless steel surfaces in aqueous sulfuric acid solution. The emeraldine-base form of the polymer was coated onto the electrode surface; however, exposure to the H 2 SO 4 solution converted this to the protically doped emeraldine salt form.A variety of experimental methods, including measurements of the open-circuit potential ͑OCP͒ Auger depth profiling, and the scanning reference electrode technique ͑SRET͒, was used to explore the mechanism by which the PANI film passivates the underlying stainless steel surface. These studies have shown that passivation is achieved because the PANI film holds the potential of the underlying stainless steel electrode in the passive region. The Auger results lend especially strong support to this conclusion. In analogy to the case of a bare stainless steel surface whose potential is potentiostatically maintained in the passive region, the stainless steel surface beneath the PANI film is enriched in Cr after exposure to the H 2 SO 4 solution. Because the PANI film passivates the electrode by simply holding the potential in the passive region, the entire stainless steel surface does not have to be coated with PANI in order to achieve passivation;...

Polyaniline-coated iron: studies on the dissolution and electrochemical activity as a function of pH

“…The oxalate system was used to electrodeposit polyaniline at iron, while the sulphate medium was used in the electroformation of the polymer at the platinum electrodes. The electrochemical activity and anodic polarization measurements were carried out in alkaline pH 10 Electrochemical experiments were carried out using an EG&G Potentiostat, Model 263, a Solartron 1250 frequency response analyser and a Solartron EI 1287 electrochemical interface. The polymers were formed using potential cycling at a scan rate of 10 mV s À 1 .…”

“…These conducting properties enable oxidation and passivation of the substrate. Indeed, Kinlen et al [9] have shown, using a scanning vibrating reference electrode technique that doped polyaniline induces the passivation of steel at pinhole defects in the coating, while Gašparac and Martin [10] have concluded that polyaniline coatings induce passivation of a stainless steel surface even though the surface is not completely coated with the polymer.…”

Corrosion Studies on Stainless Steel (FE6956) in Hydrochloric Acid Solution

“…Increasing competitive price of stainless steel could add to its advantages over the usage of other forms of steels. According to several authors, the excellent corrosion resistance of stainless steel in many aqueous solution results from its ability to protect itself from the corrosive environment via formation of a thin passive film [3]- [7] which consists of a mixture of iron and chromium oxides, with the hydroxide and watercontaining compounds located at the outermost region of the passive film while the chromium oxide enrichment is found at the metal/film interface [8]. This film varies in composition from alloy to alloy and also temperature dependent.…”

Polypyrrole Coating on Zinc for Corrosion Prevention of Zinc-coated Steels

“…1) He reported that stainless steel covered by PANI layer was kept passive state in sulfuric acid solution for long time period. Other authors also presented the corrosion prevention of stainless steel by PANI coating [2][3][4] as well as PPy coating. 5,6) Since the conducting polymer coatings could be electrochemically formed on various metals, 7,8) they were applied to corrosion prevention of the metals of Cu, 9) Zn, 10) Al, 11) Ti, 12) CuNi.…”