Anodic Passivation Of Iron Research Articles

Effects of phenol, dioxane, and oxyethylidene diphosphonic acid on the oxide and nonoxide passivation of iron in acetate solution

Effects of phenol, dioxane, and OEDPh complexone, which form soluble complexes with Fe3+ cations, on the anodic passivation of iron in acetate solution and its nonoxide passivation, which is caused by lithium oleate, are studied by the methods of voltammetry and impedance measurements. Phenol, dioxane, and OEDPh promote the anodic dissolution of iron both in the aerated and deaerated solutions. Phenol and dioxane have no effect on the nonoxide passivation of iron. Oxygen and OEDPh disturb the nonoxide passivation, which is caused by lithium oleate.

Anodic passivity of iron in sulphuric acid

The anodic passivation of iron was examined with respect to the degree of proton hydration as well as the acid structure. The investigation was based on the electrochemical measurements, XPS study and sulphur dioxide analysis. When acid concentration is low, the passivity of iron is a result of the precipitation of an oxide layer which is formed only in the presence of water. The role of sulphate ions in passivation grows with increasing acid concentration. For a concentration of about 5 M, the passivation is observed both in water and alcohol solutions. Above this concentration the passivation may occur as an effect of S 6+ ion reduction. The experiments revealed the sulphur dioxide evolution in the active and passive range of the potential. The increase of the volume of SO 2 with the acid concentration was also observed. An in-depth XPS analysis of the oxide layer for 18 M and 10 M solutions detected a gradual decrease in the oxidation number of iron as well as the reduction of sulphate ions to sulphides and the formation of iron sulphides in the bottom part of the oxide layer.

Anodic Passivation of Iron and Steel in Solutions containing Non-oxidising Inorganic Inhibitors and Breakdown of Passivity by Chloride Ions

AbstractThe effect of 3 inhibitors on the anodic passivation of iron and steel was investigated. Values of passivation current were determined by potentiostatic and potentiodynamicmethods. In the former the break-through potential gave an indication when corrosion spots occurred.

Anodic passivation of iron in alkaline solutions containing halides

Passivation of Fe in pure NaOH solutions, and in alkaline solutions containing Cl t-, Br t-, and I t- ions has been studied by measuring the galvanostatic relations during anodic polarization to the O 2-evolution potential, followed by cathodic polarization to the H 2evolution potential. Halides decrease the charge needed for each of the two arrests observed in the anodic curve, and for the arrest in the cathodic curve. At the same halide concentration, the effect increases with increase of atomic number. However, it increases with increase of concentration for the same halide. The phenomena are explained on the basis of adsorption. The possible role of XO t- ions has been also considered. In pure NaOH solutions, the effect of pH on the potential E of the two anodic arrests is given by d E/dpH = -70 to -75 mV, in agreement with the suggested mechanisms for iron dissolution in alkaline solutions.

Anodic Passivation of Iron in Carbonate Solutions

The anodic passivation of iron in aqueous carbonate solutions, pH 11·3, at room temperature gives potentiostatic polarisation curves with two well defined current peaks. the potential of the first oxidation pea. −0·58 v., indicates that passivation is primarily due to the formation of an oxide film, probably mamly magnetite. the iron surface also becomes covered with a film containing ferrous carbonate. The second oxidation peak, at −0·22 v and less than half the size (coulombic equivalent) of the first peak, is due to the oxidation of the ferrous carbonate film to form hydrated γ-ferric oxide. The sizes of the two current peaks depend on the carbonate concentration and on pH. Dissolved oxygen in the solution has no direct effect on the passivation processes in 0·1 M sodium carbonate.

The Anodic Passivation of Iron in Solutions Of Inhibitive Anions*

The anodic passivation of iron in air-saturated and de-aerated solutions of a number of inhibitive anions has been studied by the determination of potentiostatic polarisation curves. The critical passivation potential, critical passivation current density and leakage currents through the passive films have been found to depend on pH and on the nature of the anion present in the solution. The critical passivation potential (N.H.E. scale) in solutions of anions, where passivation occurs relatively easily, varies with pH in the range 6–12 according to Ep = + 0.09 – 0.06 pH volt For the anions studied, the critical passivation current densities in de-aerated 0·1 M-solution increase (and the difficulty of passivation increases) in the order: nitrite < hydroxide < chromate < borate < phosphate < carbonate < benzoate < bicarbonate < nitrate.

Noncathodic Effects of the Permanganate Ion in the Anodic Passivation of Iron

Iron actively reduces the permanganate ion at concentrations and pH values at which both chromate and pertechnetate ions inhibit corrosion effectively. The electrostatic polarization hypothesis of inhibition by such ions suggests, however, that the permanganate ion should probably manifest the same noncathodic effects as the inhibiting ions, if its reduction at the interface could be avoided. Anodic passivation of iron in permanganate solutions has therefore been conducted at potentials too noble for the cathodic process to occur. The polarization data showed that passivation was facilitated exactly as was previously found for the chromate and pertechnetate ions. The contrasting behavior of , , and is discussed in relation to different theories of the action of the inhibitors.

A potentiokinetic polarization study of the behaviour of steel in NaOH-NaCl system

The anodic behaviour of iron and steel in N/10 and N/100 NaOH solution in the presence of chloride and sulphate ions has been studied by the potentiokinetic polarization method. Anodic passivation of iron in NaOH is revealed by a fall in the anodic current after it reaches a maximum value. Behaviour in NaOH solution in the presence of chloride ions is similar to that obtained in NaOH solution up to a Cl : OH ratio of 1 : 1 but the passivation current is increased when the chloride concentration exceeds this ratio, and a breakdown of passivity is observed only at higher chloride concentration. SO 4 staggered2− ions do not effect any change in the passivation behaviour of iron in 0·1 N NaOH up to the highest ratio studied (SO 4 staggered2− : OH − = 20: 1).

鉄および鉄合金の陽極的不働態化におよぼす水素イオンおよび硫酸イオンの影響

鉄および鉄合金の陽極的不働態化におよぼす水素イオンおよび硫酸イオンの影響

鐵の陽極酸化被膜 (第2報)

Anodic passivation of iron in H3PO4 solutions has been studied mainly from a view point of finding the effects of magnetic field.In cases the H3PO4 concentration is high passivation occurs in two steps and the magnetic field has no effect upon its first stage, while no remarkable change is observable in the case of 2nd stage too.With dilute solutions of H3PO4 only the γ-Fe2O3 type passivation occurs and the magnetic field affects the phenomena in a way which is typical of the γ-Fe2O3 type passivation.

鐵の陽極酸化被膜 (第3報)

Anodic passivation of iron in 10% H2SO4 solution has been studied and much differences have been observed in the manner the passivation phenomena sets in according to the methods of applying the current, for instance:1. by plotting the current density-voltage curve2. certain initial current density is applied3. current density is kept constant.

鐵の陽極酸化被膜 (第1報)

The meanings of the study of passivation phenomena are discussed in relation to the surface finishing on iron & steel. Anodic passivation of iron in 10% HNO3 & 10%H2SO4 solutions, especially the effects of magnetic field are studied.1) 10%HNO3: In the magnetic field perpendicular to the anode plate, the passivation time is prolonged, but in weak magnetic field parallel to the anode it is rather quickened.The passivation films made in the magnetic field above 200Oe are resistant to 10%HNO3 after switched off the current.2) 10%H2SO: In the case of ordinary vertical electrode, two steps of passivation are found: the first one is accounted for by the black Fe3O4 film which grows thick, the second one by the same transparent film of γ-Fe2O3 as that in HNO3. The effects of the magnetic field have the same tendency in both perpendicular & parallel magnetic field. That is, the Fe3O4 passivation time is not effected and γ-Fe2O3 passivation time is delayed.In the case of horizontal electrode, it is passivated muchmore readily, and in general only γ-Fe2O3 passivation is occured. The effects of magnetic field are just like the case in 10%HNO3.The films made, also in magnetic field, are weak.