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Electrodeposition and electrochemical charging of hybrid organic/inorganic films composed of the poly͑3,4-ethylenedioxythiophene͒, PEDOT, conducting polymer matrix, and Keggin type polyoxometallate, phosphododecamolybdate (PMo 12 O 40 3Ϫ) or phosphododecatungstate (PW 12 O 40 3Ϫ ), redox centers, are described under conditions of aqueous solutions. The systems are electropolymerized through potential cycling as thin and moderately thick ͑m level͒ films on electrode surfaces. They are capable of fast charge propagation during redox reactions in strong acid medium ͑0.5 mol dm Ϫ3 H 2 SO 4 ). The high overall physicochemical stability of PEDOT is explored to produce a robust, conductive, matrix for such polynuclear mixedvalence inorganic nanostructures as PMo 12 O 40 3Ϫ and PW 12 O 40 3Ϫ . The composite ͑hybrid͒ materials are stabilized due to the existence of electrostatic attraction between anionic phosphomolybdate or phosphotungstate units and positively charged conducting polymer ͑oxidized͒. Charge transport is facilitated by the fact that the reversible and fast redox reactions of polyoxometallate appear in the potential range where PEDOT is conductive. The effective diffusion coefficients are on the level 4 ϫ 10 Ϫ8 cm 2 s Ϫ1 . The whole concept may lead to the fabrication of composite ͑hybrid͒ films that are capable of effective accumulation and propagation of charge in redox capacitors.

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Robust, polyaniline-based, multilayer composite films containing Prussian blue and hexacyanoferrate anions are considered here for the protection of stainless steel (SS) against pitting corrosion in strongly acid media. Polyaniline serves as a stable host matrix for large inorganic anions. At the interface formed by a composite film with SS, the interaction of normalhexacyanoferratefalse(II,III)− with iron(II,III), and some chromium(III), results in the formation of a thin insoluble metal hexacyanoferrate (mostly Prussian blue) layer. This phenomenon leads to improved passivation of the steel, and it strongly inhibits metal dissolution even in the chloride acid media. Because the metal hexacyanoferrate deposits are electronically conducting, further electropolymerization of dense and adherent composite polyaniline layers with hexacyanoferrate has been readily achieved. Due to the existence of electrostatic repulsion between negatively charged hexacyanoferrate sites and pitting-causing chloride anions, their transport through the composite film and access to the surface of SS are largely blocked. © 2003 The Electrochemical Society. All rights reserved.

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This study presents arc surface remelting of three types of sintered stainless steels carried out in order to constitute a homogeneous microstructure in the surface layer which is free from open and interconnected porosity. The main aim of this treatment was to improve functional properties of the sinters analysed, especially their resistance to pitting corrosion. The sinters were obtained from powders of 316 L and 434 L steels. The PM austenitic-ferritic stainless steels are used mainly in the automotive industry, but their general application is still limited due to relatively poor corrosion properties when compared to casts or wrought components. This study used the gas tungsten arc welding (GTAW) process as a method of economical surface treatment. The effect of surface treatment was evaluated based on macro-and microstructural observations, energy-dispersive X-ray spectroscopy (EDX) analysis, X-ray phase analysis, measurements of surface roughness and electrochemical examinations. It was found that a cellular or mixed cellular and dendritic structure was formed in the remelted zone of the sinters after remelting. X-ray analysis demonstrated that application of remelting contributes to formation of the austenitic phase in the surface layer. The corrosion resistance of the remelted surface layers was evaluated using polarization tests in 0.5 M NaCl solution. It was found that arc surface remelted layers exhibit much better anticorrosive properties than sinters without surface treatment. Microstructural observations of the surface of specimens after electrochemical tests showed only a few single pits in the remelted layer, while the surface of initial sinters was much more corroded.

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