Metals are materials characterized by high electrical and thermal conductivity, malleability, and a distinctive luster. These properties stem from their atomic structure, where valence electrons are shared among all atoms, enabling the efficient movement of heat and charge. Due to the vast range of applications, metals are categorized based on composition, performance, and practical use. The three primary types focus on their base composition and resulting industrial roles.
Ferrous Metals
Ferrous metals are characterized by their high iron content, which provides unique mechanical properties, high tensile strength, and durability. The presence of iron also makes these metals generally magnetic, making them the backbone of heavy industry. However, iron-based materials are susceptible to rusting, a type of electrochemical corrosion that occurs when iron reacts with oxygen and water. The resulting rust layer is flaky and porous, offering no protective barrier to the underlying metal.
The most widespread ferrous metal is steel, an alloy primarily composed of iron and carbon, often with other elements to modify its properties. Carbon steel is the most common form, valued for its strength in construction applications like building frameworks and bridges. Cast iron contains a higher carbon content, which improves its castability and wear resistance but makes it more brittle. Stainless steel is a notable exception to corrosion, incorporating a minimum of 10.5% chromium that forms a thin, self-healing oxide layer on the surface.
Non-Ferrous Metals
Non-ferrous metals are defined by the absence of iron as a primary component. These materials exhibit superior resistance to corrosion and rust because they do not undergo the same oxidation process as iron. Many non-ferrous metals also possess a lower density, resulting in lightweight materials with an excellent strength-to-weight ratio. These properties make them indispensable for applications where weight and environmental exposure are important.
Aluminum is a lightweight non-ferrous metal that immediately forms a hard, electrically insulating oxide film when exposed to air, providing exceptional corrosion resistance. Copper is valued for having the highest electrical and thermal conductivity of all non-precious metals, making it the standard for electrical wiring and heat exchangers. Copper’s surface develops a protective green patina when exposed to the atmosphere, shielding the underlying metal from further degradation.
Other examples include:
- Zinc, which is primarily used to coat and protect steel in a process called galvanizing.
- Lead, which is prized for its high density in radiation shielding applications.
Precious Metals
Precious metals are characterized by their rarity, high economic value, and extraordinary chemical stability, often referred to as nobility. These metals are highly resistant to chemical attack and do not readily react with oxygen or sulfur in the atmosphere. This inherent inertness means they do not tarnish or corrode easily.
Gold is the most famous example, valued for its unique luster and exceptional malleability, allowing it to be drawn into extremely thin wires or sheets. Silver possesses the highest electrical and thermal conductivity of all known elements, making it essential for high-performance electrical contacts and circuit boards. The Platinum Group Metals (PGMs), including platinum and palladium, are chemically stable and used extensively in catalytic converters to reduce automotive emissions. Due to their scarcity and stability, these metals serve a dual role as industrial raw materials for high-tech electronics and as a store of value for investment.