Abstract Fluorides, bromides, and iodides, despite being less common than chlorides, are present in various environments of industrial relevance. Stainless steels suffer pitting corrosion in solutions of all halides except fluorides, which can be understood considering that fluoride is the anion of a weak acid. The aggressiveness of the rest of the halides for pitting corrosion is on the order Cl− > Br− > I− for stainless steels with Mo content below 3 wt.%. Mo is not as effective in inhibiting Br− pitting corrosion as it is for inhibiting Cl− pitting corrosion. Most of those observations were rationalized based on the effect of anions on pit growth kinetics. Sensitized austenitic stainless steel suffers stress corrosion cracking (SCC) in solutions of all halides, albeit chlorides seem to be the most aggressive. Fluoride SCC is relevant for SCC under insulation of stainless steels, and standards and regulations developed to mitigate this problem consider this ion as aggressive as chloride. For the solubilized stainless steels, aggressiveness toward SCC is in the order Cl− > Br−. The SCC of solubilized stainless steels was not observed in solutions of F− and I−, and the possible reasons for this fact are discussed.

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Localized corrosion and stress corrosion cracking of stainless steels in halides other than chlorides solutions: a review

We used the electrochemical techniques to study the effect of the addition of four salts, K+,Cl−, K+,Br−, K+,I− and C8H17Ph3P+,I−, on the corrosion behaviour of nickel when submitted to 1M sulphuric acid medium. After one hour of immersion time, we noted an acceleration of nickel corrosion process after the addition of K+,Cl− and K+,Br− in the 1M H2SO4 electrolyte. K+,I− exhibited an inhibition of the anodic Ni corrosion process whereas the phosphonium iodine (R+,I−) acts simultaneously on both processes: it is a mixed inhibitor. Such result is due to the adsorption of the alkyl group C8H17 which limited oxygen diffusion.



EIS characterization of Ni exhibited surfaces after iodine salts addition allowed us simulating the resulting interfaces by electrical equivalent circuits. We concluded that (K+,I−) addition decreased the material corrosion rate without changing the alteration mechanism. That result is due to the formation of NiI at the electrode surface. On the other hand, phosphonium iodine addition modifies the interface behaviour. In fact, the alkyl part of the organic iodine adsorbs at the surface preserving it against the corrosive action of the sulfuric acid.

Effect of (R+, X–) salts addition on nickel corrosion in 1M sulfuric acid medium

https://hal.archives-ouvertes.fr/hal-00875485/document

Influence of the oxyanion nature of the electrolyte on the corrosion/passivation behaviour of nickel

Solubilisation of nickel from powders at near-neutral pH and the role of oxide layers

Erosion-corrosion characteristics of spark plasma sintered pure nickel in simulated mine water

The electrochemical behaviour of pure nickel in H2SO4 solutions has been potentiodynamically investigated. The effects of the following factors on the anodic dissolution and passivation of the metal are discussed: potential scan rate, successive cyclic voltammetry and progressive additions of Cl−, Br− and I− ions. Increasing the potential scan rate increases the critical current density icc, denoting that the active dissolution of nickel in H2SO4 is a diffusion controlled process. Cyclic voltammetry shows that the reverse excursion does not restore the anode to its active state. On successive cycling, the height of icc decreases; this could be attributed to the decrease in the reduction efficiency of passivating oxide film during the cathodic half cycles.



The presence of the halogen ions below a certain concentration specific to each anion inhibits the anodic dissolution both in the active and passive states. The inhibitive action of these additives decreases in the order I−, Br−, Cl−. Beyond the specific concentrations, the halogen ions accelerate the anodic dissolution and shift the active passive transition to more positive values. The aggressiveness of these anions decreases in the sequence Cl−, Br−, I−, Further increase in the halogen ion concentrations can lead to breakdown of the passive film and initiate pitting. The susceptibility of nickel to pitting attack enhances with increasing H2SO4 concentration.



Elektrochemisches Verhalten von Nickelanoden in Schwefelsaurelosungen und Einflus von Halidionen



Das elektrochemische Verhalten von reinem Nickel in Schwefelsaure wurde potentiodynamisch untersucht. In diesem Zusammenhang werden die Einflusse der folgenden Faktoren auf die anodische Auflosung und Passivierung des Metalls erortert: Potentialvorschubgeschwindigkeit, zyklische Voltammetrie und steigende Zusatzmengen von Chlorid, Bromid und Jodid. Erhohen der Potentialvorschubgeschwindigkeit erhoht die kritische Stromdichte icc, was ein Indiz dafur ist, das die aktive Auflosung von Nickel in Schwefelsaure diffusionskontrolliert ist. Die Ergebnisse der zyklischen Voltammetrie zeigen, das beim Durchlauf in Gegenrichtung die Anode nicht wieder aktiviert wird. Bei mehrfachem Durchlaufen des Zyklus nimmt die kritische Stromdichte ab; dieser Effekt konnte der Abnahme des Reduktionswirkungsgrades fur den passivierenden Oxidfilm wahrend der kathodischen Halbzyklen zugeschrieben werden.



Halogenionen unterhalb einer bestimmten Konzentration (die fur jedes Anion spezifisch ist) hemmen die anodische Auflosung sowohl im Aktiv- als auch im Passivbereich. Die hemmende Wirkung dieser Zusatze nimmt in der Reihe Jodid – Bromid – Chlorid ab. Oberhalb dieser spezifischen Konzentrationen wirken Halogenionen beschleunigend auf die anodische Auflosung und verschieben den Aktiv/Passiv-Ubergang in Richtung von positiven Werten. Die Aggressivitat dieser Anionen nimmt in der Reihenfolge Chlorid – Bromid – Jodid ab. Weiteres Erhohen der Halogenionenkonzentration kann zum Durchbruch der Passivschicht fuhren und Lochkorrosion auslosen. Die Anfalligkeit von Nickel fur Lochkorrosion nimmt mit der Schwefelsaurekonzentration zu.

E. A. Abdel Maguid

Papers

Electrochemical behaviour of nickel anode in H2SO4 solutions and the effect of halide ions