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Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture.Rust consists of hydrous iron(III) oxides (Fe 2 O 3 ·nH 2 O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH) 3), and is typically associated with the corrosion of refined iron.
Corrosion is a natural process that converts a refined metal into a more chemically ... corrosion of concrete-covered steel and iron can cause the concrete to ...
Corrosion of iron nail with coiled copper in medium with ferroxyl indicator. Ferroxyl indicator, or rust indicator, is a solution containing potassium hexacyanoferrate(III), phenolphthalein and sodium chloride. It turns blue in the presence of Fe 2+ ions, and pink in the presence of hydroxide (OH-) ions.
In this case, sacrificial anodes work as part of a galvanic couple, promoting corrosion of the anode, while protecting the cathode metal. In other cases, such as mixed metals in piping (for example, copper, cast iron and other cast metals), galvanic corrosion will contribute to accelerated corrosion of parts of the system.
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:
Selective corrosion on cast iron. Magnification 100x Selective corrosion on cast iron. Magnification 500x. Graphitic corrosion is selective leaching of iron, from grey cast iron, where iron is removed and graphite grains remain intact. Affected surfaces develop a layer of graphite, rust, and metallurgical impurities that may inhibit further ...
A broader term for this class of corrosion is lamellar corrosion. Alloys of iron are susceptible to lamellar corrosion, as the volume of iron oxides is about seven times higher than the volume of original metal, leading to formation of internal tensile stresses tearing the material apart. Similar effect leads to formation of lamellae in ...
Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic (oxidation reaction) while an unknown but potentially vast area becomes cathodic (reduction reaction), leading to ...