The primary products of iron corrosion in water include ferrous hydroxide (Fe(OH)2) and hydrated iron(III) oxides (like Fe2O3.H2O), which form the familiar red-brown rust.
When iron corrodes in water, particularly in the presence of oxygen, it undergoes a series of chemical reactions. The initial step often involves the oxidation of iron to ferrous ions (Fe²⁺). These ions then react with water and other substances present.
Initial Corrosion Product
According to the provided reference, the initial, or primary corrosion product, of iron in water is Fe(OH)2 (ferrous hydroxide). The reference also notes this is "more likely FeO. nH2O," which represents hydrated ferrous oxide. This product is typically greenish or white initially.
Formation of Rust
However, Fe(OH)2 is unstable in the presence of oxygen. The action of oxygen and water further oxidizes the ferrous hydroxide to ferric compounds. This process yields other products, which often have different colors.
The reference specifically states that Fe2O3. H2O (hydrous ferrous oxide, sometimes written as Fe(OH)3), is the principal component of red-brown rust. This is the most common form of rust observed on iron exposed to the environment. The 'nH2O' indicates that the exact amount of water incorporated into the structure can vary.
Summary of Key Products
Based on the reference, the key products formed during iron corrosion in water are:
- Fe(OH)2 (Ferrous Hydroxide) or FeO.nH2O (Hydrated Ferrous Oxide): The primary, initial corrosion product.
- Fe2O3.H2O (Hydrated Ferrous Oxide) or Fe(OH)3: The principal component of the characteristic red-brown rust, formed through further reaction with oxygen and water.
These compounds are complex and the exact composition of rust can vary depending on the environmental conditions, such as the amount of oxygen, presence of salts, and pH level of the water.
