Henryk Bala

Protection of Steel Against Corrosion in Aggressive Medium by Surface Modification with Multilayer Polyaniline-Based Composite Film

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 hexacyanoferrate(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.

Electrochemical corrosion characteristics of RETiCo11 compounds

Abstract The corrosion behaviour of six RETiCo11 permanent magnet compounds (RE = Y, Pr, Nd, Sm, Gd or Dy) in sulphate solutions with pH = 0–4 and in acetic acid salt spray were investigated. It was found that the tested RETiCo11 magnets were much more corrosion resistant than the alternative NdFeB and SmCo material. The kind of RE element in the magnet composition has practically no influence on the corrosion rates in the tested environments.

Electrochemical corrosion characteristics of ZrNi5-xCox alloys

Abstract The electrochemical corrosion behaviour of a series of ZrNi 5− x Co x alloys with x =0–4 has been tested using potentiokinetic polarisation technique. The polarisation curves were measured in deaerated 0.5 M sulphate solutions with pH=0.2–7 and in strong alkaline solution of KOH (pH=15). It is shown that the presence of greater amounts of Co in the alloy ( x ⩾2) worsens the passivating properties of the alloy in acidified sulphate solutions. On the other hand, in strong alkaline solutions, both low- and high-cobalt alloys undergo stable passivation. The degree of Ni substitution by Co in the alloys does not generally affect the shape of cathodic polarisation curves.

Hydrogenation and Corrosion Properties of LaNi4.5Co0.5-Based Alloy Doped with 1.7 at% Sn

Effect of small addition of tin (1.7 at.%) into LaNi4.5Co0.5 alloy on gas phase and cathodically charged hydrogen absorption ability as well as its corrosion resistance in 6M KOH solution is discussed. To reveal the effect of Sn doping three alloys have been selected: LaNi4.5Co0.5 (precursor), LaNi4.5Co0.5Sn0.1 and LaNi5 - as a parent compound. The room temperature p-C isotherms indicate to beneficial effect of Sn addition which causes decrease of H2 equilibrium pressure and does not limit atomic hydrogen solubility. Discharge capacities (Qdisch), exchange current densities of H2O/H2 system () as well as corrosion rates () have been determined for the tested alloys on the basis of cyclic galvanostatic measurements (at –0.5C/+0.5C rates). It has been shown that for N > 3 cycle the discharge capacity of LaNi4.5Co0.5 is ca twofold greater than that for LaNi5 reference. Addition of 1.7 at.% Sn into Co-containing alloy expands the discharge capacity by 30-40%. The Co containing alloys reveal twice as great exchange current densities of H2O/H2 system compared to LaNi5, however, Sn addition slightly decreases the , especially for latest cycles. The partial cobalt substitution for Ni accelerates alloy corrosion in alkaline solution, however, tin addition fully eliminates this effect.

Corrosion resistance of stainless steel covered by 4-aminobenzoic acid films

AbstractThe protective, anticorrosion properties of 4-aminobenzoic acid (4-ABA) films are evaluated in the paper. The 4-ABA films were electrodeposited on the surface of both X20Cr13 stainless steel and glassy carbon electrodes by galvanostatically and cyclic voltammetry methods. The protective properties of the resulting films on stainless steel were investigated in the aggressive medium of acidified (pH=4) 0.25 mol dm−3 K2SO4 in the absence and with the presence of 0.5 mol dm−3 KCl. Morphology of the 4-ABA films was examined using scanning electron microscopy.

Corrosion depth profiles of nitrided titanium alloy in acidified sulphate solution

AbstractThick (400 µm) glow-discharge nitrided layers, TiN+Ti2N + αTi(N) type, have been produced on the Ti-1Al-1Mn titanium alloy. Using a progressive thinning method, the polarization characteristics at different depths of nitrided layers have been measured. From the plots of obtained potentiodynamic polarization curves the depth profiles of characteristic anodic and cathodic currents (at potentials corresponding to (a) hydride formation, (b) hydrogen evolution, (c) primary passivation, (d) oxygen evolution and (e) secondary passivation) as well as polarization resistance have been determined in 0.5 M Na2SO4 solution acidified to pH = 2. The anomalously high slope of the polarization curves in the cathodic region has been ascribed to the formation of titanium hydride. It has been shown that outer nitrided layers (up to 25 µm) exhibit excellent acid corrosion resistance owing to strong inhibition of the anodic process by TiN phase. Corrosion resistance of deeper situated layers gradually decreases and at depths of 250–370 µm the corrosion process is accelerated by presence of TiO2 precipitations. Nitrided layers, unlike the alloy core, allow oxygen evolution on the oxy-nitrided surface at potential of +1.6 V and at more positive potentials gradual transformation of the surfacial film into TiO2 takes place. Secondary passivation on nitrided titanium is less efficient than that in the absence of Ti-N species.

Hydrogen Absorption by Co-Substituted Nd-Fe-B High Coercivity Magnetic Material

The present paper aims at explanation of the advantageous role of partial substitution of iron by cobalt in Nd-Fe-B magnet for distinct inhibition of mechanically assisted corrosion phenomena. The hydrogen uptake by Nd16Fe76B8 and Nd16Fe56Co20B8 sintered materials have been compared with the use of charge/discharge method in terms of the alloys corrosion behavior in strong alkaline solution. For initial cycles, the hydrogen discharge capacity of Co-containing alloy is 5-10 times lower than that for the Nd16Fe76B8 reference alloy. After 6-7 cycles both alloys reveal comparable hydrogen capacity. Also the plots of polarization curves testify to comparable corrosion resistance for both materials. The unusual resistance of Nd16Fe56Co20B8 sinter to pulverization should be ascribed to strong inhibition of hydrogen absorption at initial steps of corrosion process.