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Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion. [1] [2]
Under anoxic conditions, the mechanism for corrosion requires a substitute for oxygen as the oxidizing agent in the redox reaction. [1] For abiotic anaerobic corrosion, that substitute is the hydrogen ion produced in the dissociation of water and the proceeding reduction of the hydrogen ions into diatomic hydrogen gas. [1]
Metals can be exposed to hydrogen from two types of sources: gaseous hydrogen and hydrogen chemically generated at the metal surface. Gaseous hydrogen is molecular hydrogen and does not cause embrittlement, though it can cause a hot hydrogen attack (see below). It is the atomic hydrogen from a chemical attack which causes embrittlement because ...
The key reaction is the reduction of oxygen: O 2 + 4 e − + 2 H 2 O → 4 OH −. Because it forms hydroxide ions, this process is strongly affected by the presence of acid. Likewise, the corrosion of most metals by oxygen is accelerated at low pH. Providing the electrons for the above reaction is the oxidation of iron that may be described as ...
High temperature oxidation is generally occurs via the following chemical reaction between oxygen (O 2) and a metal M: [2]. nM + 1/2kO 2 = M n O k. According to Wagner's theory of oxidation, oxidation rate is controlled by partial ionic and electronic conductivities of oxides and their dependence on the chemical potential of the metal or oxygen in the oxide.
The Schikorr reaction can occur in the process of anaerobic corrosion of iron and carbon steel in various conditions. Anaerobic corrosion of metallic iron to give iron(II) hydroxide and hydrogen: 3 (Fe + 2 H 2 O → Fe(OH) 2 + H 2) followed by the Schikorr reaction: 3 Fe(OH) 2 → Fe 3 O 4 + 2 H 2 O + H 2. give the following global reaction:
Some bacteria are able to utilize hydrogen formed during cathodic corrosion processes. Bacterial colonies and deposits can form concentration cells, causing and enhancing galvanic corrosion. [3] Bacterial corrosion may appear in form of pitting corrosion, for example in pipelines of the oil and gas industry. [4]
Susceptible alloys, especially steels, react with hydrogen sulfide (H 2 S), forming metal sulfides (MeS) and atomic hydrogen (H •) as corrosion byproducts. Atomic hydrogen either combines to form H 2 at the metal surface or diffuses into the metal matrix. Since sulfur is a hydrogen recombination poison, the amount of atomic hydrogen which ...