What Is Copper?

Copper is a transition metal with atomic number 29 and chemical symbol Cu, valued in electrical engineering and materials science for the combination of high electrical conductivity, ductility, and thermal performance it offers at a commercially accessible cost. It is one of the oldest metals used by humans and remains central to the global electrical infrastructure, from the windings of power transformers to the microscale interconnects of semiconductor chips.

Copper draws its engineering prominence from a resistivity of approximately 16.78 nΩ·m at 20°C, the second lowest among commercially relevant metals after silver. This property, combined with its mechanical workability and the relative abundance of copper ore deposits, has made it the default conductor material for power generation, transmission, and distribution systems worldwide.

Electrical and Thermal Properties

The electrical conductivity of copper is defined as 100 percent by the International Annealed Copper Standard (IACS), a benchmark established in 1913 against which other conductor materials are measured. Highly purified oxygen-free copper (OFHC, UNS C10200) can exceed this baseline at approximately 101 percent IACS, making purity a critical parameter in applications where conductor loss must be minimized. Thermal conductivity is correspondingly high at around 400 W/(m·K), which explains copper's use as both an electrical conductor and a heat spreader in power electronics packaging. Research published in Communications Materials has examined how microstructural refinement through thermomechanical processing can simultaneously improve tensile strength and maintain this high conductivity in copper wire, addressing a longstanding trade-off in conductor design.

Metallurgy and Processing

Copper is extracted primarily from sulfide ores through flotation, smelting, and electrorefining, with the electrorefining step producing cathode copper at purities above 99.99 percent. Wrought forms include wire rod, sheet, strip, tube, and bar, produced by rolling, drawing, and extrusion. The face-centered cubic (FCC) crystal structure of copper gives it excellent ductility and ease of cold working. Work hardening increases tensile strength but reduces conductivity, so wire intended for power transmission is annealed after drawing to restore conductivity. The International Copper Association documents the range of product forms and their standard designations under the Unified Numbering System used by the electrical and automotive industries.

Corrosion and Surface Behavior

Copper develops a stable surface oxide and, in outdoor or marine environments, a characteristic green patina of copper carbonate and sulfate compounds. This patina is adherent and limits further corrosion, which accounts for the long service life of copper in architectural applications. In electrical connections, however, surface oxidation can increase contact resistance over time, particularly at jointed interfaces. Connectors may be tin or silver plated to maintain a low-resistance contact surface. The dataset of copper electrical and mechanical properties compiled in Scientific Data provides a reference baseline for both pure copper and its major alloy families, supporting materials selection in design tools.

Applications

Copper has applications across a wide range of electrical, thermal, and structural domains, including:

• Power transmission and distribution wiring, bus bars, and cable conductors
• Motor and transformer windings in rotating machines and power conversion equipment
• Printed circuit board traces and semiconductor packaging interconnects
• Heat sinks, heat exchangers, and cooling systems in power electronics
• Telecommunications infrastructure, including coaxial cable and twisted-pair wiring
• Electroplated coatings and thin-film metallization in microfabrication processes