Chemistry – Metals - Reactivity series | e-Consult

Aluminium is surprisingly resistant to corrosion, despite being a highly reactive metal. This resistance is primarily due to the formation of a thin, tenacious, and self-healing oxide layer (Al₂O₃) on its surface. This layer is crucial for aluminium's apparent unreactivity.

Properties of the Aluminium Oxide Layer:

• Strong and adherent: The oxide layer adheres very strongly to the aluminium metal. This prevents it from easily being removed by abrasion or mechanical damage.
• Impermeable: The layer is essentially impermeable to most gases and liquids. This prevents corrosive substances like oxygen, water, and salts from reaching the underlying aluminium.
• Self-healing: If the oxide layer is scratched or damaged, it rapidly reforms in the presence of oxygen. This self-healing property ensures continuous protection.
• High melting point: The high melting point of Al₂O₃ (approximately 2076 °C) contributes to its stability and resistance to degradation.

How the Oxide Layer Protects the Metal:

The oxide layer acts as a barrier, preventing the aluminium metal from reacting with its environment. For example, in air, the oxide layer prevents the aluminium from reacting with oxygen and water to form aluminium hydroxide (Al(OH)₃) or aluminium oxide (Al₂O₃) further down. Even if the oxide layer is damaged, it quickly reforms, maintaining the protective barrier. This is why aluminium is used in applications where corrosion resistance is essential, such as aircraft, food packaging, and building materials.