M. Drogowska

Copper Dissolution in NaHCO3 and NaHCO3 + NaCl Aqueous Solutions at pH 8

The anodic oxidation of copper in 0.001 to 0.1M NaHCO 3 and NaHCO 3 +NaCl aqueous solutions at pH 8 has been studied using a rotating disk electrode. The first oxidation product is a thin porous Cu(I) oxide film formed by a solid-state mechanism. In the solutions containing low NaHCO 3 concentrations ( 0.05M, more positive anodic potentials, or longer exposure times, further oxidation of copper take place through the thin porous Cu(I) oxide film

Electrochemical behaviour of tin in bicarbonate solution at pH 8

The anodic oxidation of tin in 0.1 to 1M bicarbonate solutions at pH 8 has been studied. The process may be divided into three potential regions: (1) a short active dissolution (Tafel) region; (ii) a dissolution-precipitation region; and (iii) a large region of electrode passivity. The rate-determining step of the reaction in the active-dissolution region is attributed to the diffusion of an ionic species into the solution, the diffusing species being generated at the metal surface. In the region of the first oxidation peak, the reaction rate is controlled by diffusion of CO32− species in solution. When the potential becomes more positive than −0,1 Vsce, a highly passivating (most likely SnO2) film is formed on the electrode surface.

Electrochemical behaviour of 1024 mild steel in slightly alkaline bicarbonate solutions

The electrochemical behaviour of 1024 mild steel electrodes is investigated in the presence of 0.05–0.5 M sodium bicarbonate in aqueous solution at pH 8.9 and 25°C. Voltammograms are obtained with a rotating gold ring-mild steel electrode and the effect of the NaHCO3 concentration, the potential limits and the rotation speed of the disc electrode is considered. The voltammograms display an oxidation peak current at low potentials, a passivity region and a transpassive region at high potentials for the potential sweep in the anodic direction. The oxidation current in the passivity region is practically independent of the applied potential and the NaHCO3 concentration. The rate-determining step of the oxidation reaction in both the oxidation peak current region and the transpassive region is determined.

Influence of anions on the passivity behavior of copper in alkaline solutions

Abstract The competitive effect of the inorganic anions OH-, Cl-, Br-, I-, ClO-4, NO-3, SO2-4, CO2-3 and phosphates on the behavior of copper in alkaline aqueous solutions at pH 12 was investigated. The nature of changes occurring on the copper surface was analyzed by potentiodynamic and potentiostatic methods in conjunction with different instrumental surface analysis techniques. The influence of these anions on the anodic dissolution of copper was classified into three distinct categories. In the first group, comprising NaCl, NaBr and NaI solutions, copper(I) salts form insoluble, nonprotective films on the metal surface and the copper is expected to dissolve via the formation of CuA( n - 1 )- n complexes. In the second group, comprising NaClO4, Na2SO4 and NaNO3 solutions, substantial dissolution of copper is caused by the formation of easily soluble Cu2+ salts, and copper (II) ions precipitate as hydroxides and oxides. In the third group, the hydroxide, phosphate and carbonate passivate the copper surface. In some solutions the phosphate and carbonate inhibit the anodic dissolution of copper. The aggressive nature of the anions investigated against the passivity of copper increases in the order SO2-4

Electrooxidation of stainless steel AISI 304 in carbonate aqueous solution at pH 8

The electrochemical behaviour of stainless steel AISI 304 (SS304) has been investigated in deaerated 0.1–1 m NaHCO3 solutions at pH 8 using a rotating disc electrode. The polarization curves are characterized by a broad range of passivity at low potentials (−0.8 to 0.3 V), a depassivation region at 0.4 V vs SCE and, at high potentials (0.5 to 0.85 V), a passive region before oxygen evolution. In the low potential range, the SS304 electrode behaves like a Cr-rich metallic phase, and the dissolution of Fe2+ ions into the solution is hindered by the formation of a Cr2O3 layer. As the potential reaches 0.4V, the oxidation-dissolution of Cr(iii) oxide/hydroxide to CrO42 ions occurs, with the participation of bicarbonate/carbonate as a catalyst in the dissolution reaction. Since the chromium oxide/hydroxide dissolution and subsequent surface enrichment of iron oxides occur, the applied potential, exposure time and oxidation charge have a considerable effect on the passive film properties. At high potentials, the presence of a passive film of iron oxides/hydroxides or oxyhydroxides plays a key role in the SS304 passivity with the presence of Fe(vi) species incorporated or adsorbed into the passive films. Colouration of the SS304 surface is observed in the second passive region. A film of a uniform gold colour formed on SS304, mild steel 1024 and iron in carbonate and borate solutions at pH 8. The colour of the electrode surfaces remain unchanged in air and in solutions at positive potential but it disappears at open-circuit potential or is easily reduced in the first negative-going potential scan.

Pitting of AISI 304 stainless steel in bicarbonate and chloride solutions

Metastable and stable pitting on 304 stainless steel (SS304) in 0.1–0.5 m NaCl aqueous solution (pH ~8) has been investigated using a potentiodynamic, a potentiostatic and a weak anodic current galvanostatic techniques. The addition of bicarbonate (0.025–0.5 m) to the solution had an inhibiting effect, manifested by a shift of the pitting potentials to more positive values, a longer induction time for pitting and reduced pit nucleation. The pit nucleation frequency and growth, in the metastable and stable states, decrease as the NaHCO3/NaCl molar concentration increases and pitting is no longer observed for NaHCO3/NaCl molar ratios higher than 3 (four times larger % wt of NaHCO3). Pitting events never occurred at a potential below −0.1 V, fewer metastable events were observed at higher temperature (50°C) and none were observed in chloride free bicarbonate solutions. The inhibiting behaviour of oxyanions is discussed.

Effects of Phosphate Ions on Copper Dissolution and Passivation

The dissolution and passivation of copper was studied in the presence of phosphate and phosphate + chloride in aqueous solution at pH 8 for temperatures ranging from 5 to 60 o C. The copper oxidation current increased with (i) the concentration of phosphate ions in chloride-free solutions, (ii) the concentration of chloride ions in solution containing phosphate ions, and (iii) the temperature in both solutions. Two passivation mechanisms are postulated

Comparative study of copper behaviour in bicarbonate and phosphate aqueous solutions and effect of chloride ions

Copper oxidation in aqueous solutions of pH 8 showed some differences in the presence of bicarbonate and phosphate ions. The bicarbonate ions did not interfere with Cu2O film formation but the Cu2+ ions were stabilized by the complexing action of CO2−3anions. In phosphate solutions, copper dissolved in the range of potentials associated with the Cu(I) oxidation state and the Cu(II) compound on the surface resulted in an extensive passivation region. In both solutions, a higher ion concentration caused an increase in the anodic current, suggesting that the copper ions were stabilized by the complexing action of the electrolyte. The copper oxidation current in a bicarbonate solution was higher than that observed in a phosphate solution of the same concentration. The thickness of the Cu(II) film rather than the Cu(I) layer appears to be the important factor related to the stability of the passive layer on the copper surface. The shift in the breakdown potential toward more positive values indicates that both bicarbonate and phosphate ions inhibit localized corrosion due to the presence of chloride ions. Their protective effect depends on the concentration of each anion, although the concentration of chloride ions necessary for pitting is larger in phosphate solutions than in bicarbonate solutions. In both solutions, long-term immersion of copper under anodic polarization results in the precipitation of a protective coating.

Dissolution of tin in the presence of Cl− ions at pH 4

AbstractThe anodic dissolution of tin, investigated in an acidic solution at pH 4 containing 0.1–1 M NaCl at 25°C, displays Tafel behavior as long as the electrode surface is bare (E≤−0.5 V vs SCE). The main characteristics can be derived from the proposed dissolution mechanism, i.e