Corrosion resistance

Corrosion resistance is the ability of a material to resist being eaten away by air, water or chemicals. Malay: ketahanan kakisan · Chinese: 抗腐蚀性.

Corrosion is the slow chemical attack that damages a material from its surface, and rusting is the most familiar example, in which iron is eaten away by water and oxygen. A material with good corrosion resistance keeps its strength and appearance far longer in wet or chemically harsh conditions, which is why it is so valued in industry. This property can be built in during manufacture: alloying a metal with the right elements, or choosing a non-metal material that does not react, gives a product that lasts. It is one of the main reasons, alongside greater hardness, that metals are turned into alloys rather than used pure.

Example. Stainless steel resists rusting because it is an alloy of iron with chromium and nickel, so it is used for cutlery and surgical instruments. Fibreglass does not corrode, so it is used for boat and car bodies that are constantly exposed to water. In both, corrosion resistance is the deciding property.

Confusion to avoid. Do not treat corrosion resistance as the same thing as hardness or strength. Alloying can improve all of these, but they are distinct properties: a material can be hard yet still corrode, and corrosion resistance is specifically about resisting chemical attack from the surroundings.

When a question asks why a particular material was chosen, corrosion resistance is often part of the answer, so name it explicitly rather than saying only that the material is strong or hard. Stating clearly that it resists being eaten away by air, water or chemicals is the wording that earns the mark, especially for stainless steel and fibreglass.

Corrosion resistance links the alloys and composites of this chapter to the rusting you will meet again later, and it is a recurring reason-for-choice in SPM Chemistry.