HSC ES Corrison

Definition of Corrosion

Defined as the process where materials (often metals) deteriorate due to chemical reactions with their environment.
Often mistaken for "rust"; however, rust specifically refers to the corrosion of iron and its alloys.
Corrosion can occur in various scenarios, each with its own specific causes and mechanisms.
Examples include visible rust on steel structures such as fencing and trusses.

A term used to describe the deterioration of concrete, often colloquially referred to as "concrete cancer" due to its appearance.
Caused by the corrosion of steel reinforcements within concrete.
Engineers can mitigate this by strategically placing reinforcing bars away from the concrete surface to reduce moisture contact.
Moisture can lead to "wet corrosion," emphasizing the porous nature of concrete.
Corrosion leads to concrete flaking and exposure of reinforcing steel.

Chemical Corrosion: Occurs in the absence of water, resulting from chemical reactions between materials (e.g., oxidation of non-ferrous metals such as aluminium).
Electrolytic Corrosion: Takes place when dissimilar metals contact in the presence of moisture, generated through oxidation processes.

Steel rebar can be elevated off the ground using rebar chairs, preventing contact with concrete and facilitating proper placement in slabs.
Protective methods include using bitumen-impregnated fabrics to impede water penetration.

Metals that do not contain significant amounts of iron, reducing the likelihood of rust formation.
Example of Ferrous Metal: Stainless steel is a ferrous metal that exhibits resistance to rust due to the presence of chromium, forming a protective oxide layer.

Use of inert linings and coatings for piping to prevent chemical reactions with transported gases.
Example: The oxidation of copper alloy leads to the green patina on the Statue of Liberty due to copper oxide formation.

Occurs when an anode and cathode are present, which may be within the same metal or across different metals in contact.
The reactivity table shows that metals like gold and silver do not corrode easily due to their inert nature in soils.
Aluminium extraction from bauxite is energy-intensive due to its resistance to oxidation.

A subtype of electrolytic corrosion, where an anode and cathode arise from the interaction of different metals or conditions.
Can occur without water, but electrolytic solutions (like saline environments) accelerate the process.
Notably affects coastal structures with increased corrosion rates.

A phenomenon where deformation of metal grains through processes like bending or drilling creates distinct electrical properties.
Stressed grains may act as anodes, while unstressed grains behave as cathodes, leading to corrosion.

Painting: Direct and straightforward; requires regular reapplication (e.g., Sydney Harbour Bridge maintenance).
Metallic Coatings: Techniques such as electroplating, cladding, and hot-dip galvanizing to protect metals.
Galvanic Protection: Use of sacrificial anodes (e.g., zinc blocks) to protect structures; anodes require periodic replacement.
Impressed Voltage Protection: Involves applying a low current to the structure that counteracts the loss of electrons during corrosion (common in fuel tank protection).

Utilized because of its sacrificial properties, effectively protecting metals against corrosion.

Timber and biological materials decay due to organic processes; polymers may degrade from UV exposure, though inhibitors help mitigate this.