Schikorr reaction

The primary reaction in the corrosion of boiler steel is the formation of ferrous hydroxide and its subsequent decomposition to magnetite and hydrogen - the Schikorr reaction (Section 4.4). This is demonstrated by the products of corrosion encountered throughout the whole range of boiler operating pressures, but the details are influenced by other factors, i.e. the water quality, heat flux, and the boiler operating conditions. 

Alkaline hydrolysis of Fe" sulphate solution to give Fe(OH)2 followed by heating the product at ca. 100 °C (Schikorr reaction, Schikorr, 1929), i.e. 

The subsequent formation of magnetite from the metastable Fe(OH)2(s), describing the Schikorr reaction ... 

At lower temperatures (e.g., room temperature to about 100°C) and probably at higher temperatures before a relatively thick surface film develops, experiments show that Fe(OH)2 is the initial reaction product and not Fc304 [15]. The mechanism of corrosion in this temperature range follows that described for anode and cathode interaction on the plane of the metal surface in contact with an electrolyte. Ferrous hydroxide eventually decomposes, at a rate depending on temperature, into magnetite and hydrogen in accord with a reaction first described by Schikorr (Schikorr reaction) [16]... 

It takes place only at relatively high temperatures, typically 150 C, and it results in the formation of compact layers of magnetite, that provide good corrosion protection. In practice, the Schikorr reaction plays a role for the corrosion protection of steam condenser tubes made of steel. 

The Schikorr reaction (9.5) describes corrosion of iron in contact with water vapor at temperatures up to 600 °C. 

The Schikorr reaction results in the formation of a compact layer of magnetite whose growth governs the kinetics of corrosion. Below 300 °C, the rate of film growth is very slow and the magnetite film effectively protects against further corrosion (Section 8.1). 

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