At high temperatures, steam reacts with the iron in the carbon steel of steam boilers. This leads to the formation of a thin layer of magnetite, an iron(II,III) oxide, which passivates the steel surface protecting it against further corrosion (Schikorr reaction).
Under unfavorable conditions, the inhibiting magnetite layer can flake off, which leads to elevated iron concentrations in the water-steam circuit. A regular iron determination enables monitoring of not only corrosion processes but also the formation and destruction of the protective magnetite layer.
Adsorptive stripping voltammetry (AdSV) provides fast and sensitive detection of iron in process waters of the water-steam circuit (boiler feed water, makeup water, condensate) in power plants. This is achieved by adding suitable complexing agents to convert the iron into adsorbable complexes that are reduced on the electrode surface after a defined preconcentration time. Detection limits in the lower μg/L range can be achieved using 2,3-dihydroxynaphthalene (DHN) as the complexing agent.