Passivation Of Iron In Solutions Research Articles

Passivation of iron in solutions containing borate using rotating ring-disc measurements

The electrochemical behavior of iron in neutral solutions of perchlorate and low borate concentrations was investigated using cyclic voltammetry and the rotating ring-disc electrode techniques. In solutions containing just perchlorate, iron passivation was observed at potentials higher than the potential of an anodic peak corresponding to the active range at which the dissolution of Fe2+ and Fe3+ species was detected. When borate is added to the solution, this anodic peak decreased as well as the amount of the active soluble species. The increase of pH, keeping the borate and perchlorate concentrations constant, was found to be less effective at promoting iron passivation than the increase of borate concentration. The results demonstrated that the interaction between borate ion and the electrode surface occurs by chemical adsorption according to the Langmuir isotherm.

The passivation of iron in solutions of hydrogen chloride in dimethylsulphoxide

The passivation of polycrystalline iron electrodes in solutions of HCl in DMSO has been studied. Steady current/potential curves were determined and potential-sweep voltammetry has been applied. Passivation onset is due to a porous type film and its occurrence can be explained by means of a reaction sequence which involves various partial steps already analysed in the anodic dissolution of active iron.

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.

THE ANODIC PASSIVATION OF IRON

A study was made of the anodic passivation of iron in solutions of 0.1 M sodium sulphate at a pH of 3.0. A mass balance of iron equivalent to coulombs required for passivation and iron found in solution after passivation showed that approximately 0.002 coulomb/cm2 is involved in the passive layer. À Flade arrest does not appear in decay traces of anodic potential unless a potential of at least 1.2 v (EH) is achieved on charging the electrode, indicating incomplete coverage by the passive layer below 1.2 v. Partial cathodic reduction followed by anodic reformation of the passive layer at the Flade arrest showed that the first charging current involved in reformation is highly efficient even when as much as 70% of the Flade arrest is reduced. These results support the view that only a fraction of the passive layer is represented by coulombs involved in the Flade arrest and that after partial reduction the remainder of the passive layer disintegrates spontaneously. Addition of chelating agents to the electrolyte has an adverse effect on passivation by chelation of ferrous ion.