Electrochemical behaviour of iron in alkaline sulphide solutions

Abstract

Cyclic voltammograms and galvanostatic polarisation curves were traced for the iron electrode in alkaline solutions containing sulphide species. In sulphide free NaOH solution, the galvanostatic anodic polarisation curves are characterised by two well defined steps before tending finally to values characteristic for the oxygen evolution reaction. However, using cyclic voltammetry technique, three anodic peaks are distinct. On the other hand, the cathodic half cycles using both techniques are characterised by two cathodic reduction steps before hydrogen evolution commences. In the presence of increasing sulphide content the polarisation curves are characterised by the presence of several anodic and cathodic regions. The anodic regions correspond to the simultaneous formation and oxidation of different Fe sulphide and oxide species. A mechanism is thus proposed for the formation and reduction of iron sulphide species.

Effect of Additional Sulfide and Thiosulfate on Corrosion of Q235 Carbon Steel in Alkaline Solutions

“…The mechanism of steel corrosion and formation of the passive film have been always studied by many scholars [4][5][6]. The role of sulfide in the highest concentrations of alkaline solution like white liquor has been studied on the corrosion behavior of carbon steel [7][8][9]. But in the higher concentrations of caustic solution sulfur-contained species like alumina industry the research of the role of sulfide on steel corrosion is too sparse and corrosion behavior of 16MnR low alloy steel in sulfide-containing Bayer solutions was researched by Xie and Chen [3].…”

Chloride-initiated corrosion in alkali activated reinforced concrete

“…The C 3 A content in PC concrete produces Ca 6 Al 2 O 6 .CaCl 2 .10H 2 O (Friedel's salt) which accounts for its high chloride binding capacity [23]. The presence of gypsum in AACM concrete increases solubility of ions leading to the release of sulfate ions into its pore solution [15]. Halite is soluble in water and releases chloride into the pore fluid [37].…”

“…Furthermore, oxidized sulfide was suggested to produce elemental sulfur which accumulates at the pores of the depleted passive film resulting in its repair [12], particularly at sufficiently high sulfide concentration [13]. Alternatively, Tromans [14] suggested a reduction in the passive film due to the attraction of sulfide by magnetite resulting in the disintegration of the passive film [15], thereby, promoting higher corrosion rates. Blast furnace slag has high sulfide content which produces redox potentials of negative values compared to PC concrete [12].…”

“…The change over from the submerged state (cycle 1) to the dry curing state (cycle 2) increased the oxygen concentration required for the cathodic reaction as well as the oxidation of the sulfide, thus producing elemental sulfur deposits on the steel surface embedded in AACM concrete as seen in Fig 15…”

Electrochemical Formation of a Failure Preventing Film on Nickel Surface in Borate Solutions

“…However, the film dissolution is counterbalanced by a protective film formation. The rates of these two processes are nearly the same at the steady-state polarization, so as to keep the thickness of the protective film nearly constant [24,25]. Finally, the current is suddenly increased due to oxygen evolution.…”