Overview

Copper is one of the oldest engineering metals, valued for its exceptional electrical and thermal conductivity, natural corrosion resistance, ductility, and antimicrobial properties. It is reddish-orange in color, easily formed and joined, and widely used in electrical wiring, plumbing, heat exchangers, and roofing.

ρ = 8960 kg/m³ · Thermal conductivity k = 401 W/m·K (second only to silver among common metals)

Mechanical Properties

Property	Value
Density	8,960 kg/m³ (0.324 lb/in³)
Young's Modulus	117 GPa (17 × 10⁶ psi)
Yield Strength (annealed)	70 MPa (10,000 psi)
Ultimate Tensile (annealed)	220 MPa (32,000 psi)
Ultimate Tensile (hard drawn)	380 MPa (55,000 psi)
Elongation at break	45-50% (annealed)
Hardness	40-50 BHN (annealed)
Melting Point	1085°C

Thermal & Electrical Properties

Property	Value
Thermal Conductivity (20°C)	401 W/m·K
Specific Heat	385 J/kg·K
Coefficient of Thermal Expansion	16.5 × 10⁻⁶ /°C
Electrical Resistivity	1.72 × 10⁻⁸ Ω·m
Electrical Conductivity	58 MS/m (100% IACS)

Why Copper is the Electrical Standard

Copper is the international reference standard for electrical conductivity (100% IACS = International Annealed Copper Standard). Aluminum has only 61% of copper's conductivity but is much lighter, making it preferred for overhead power lines where weight matters more than cross-sectional area.

Common Alloys

Alloy	UNS	Key Properties	Applications
C11000 (ETP)	C11000	101% IACS, pure copper	Electrical wire, bus bars
C12200 (DHP)	C12200	Deoxidized, weldable	Plumbing tube, refrigeration
Brass (Cu-Zn)	C2xxx	Higher strength, machinable	Valves, fittings, hardware
Bronze (Cu-Sn)	C5xxx	Higher strength, corrosion resistant	Bearings, gears, marine
Cu-Ni 90/10	C70600	Seawater corrosion resistance	Marine piping, condensers

Applications

Electrical: Building wiring, motor windings, transformers, bus bars, printed circuits
Plumbing: Water supply tubing (Type L/M/K), refrigerant lines, gas distribution
Heat transfer: Heat exchanger tubes, radiators, air conditioning coils, solar collectors
Roofing & architecture: Long-lasting green patina, flashing, gutters, decorative elements
Marine: Cu-Ni piping for seawater service, propellers, hull antifouling coatings
Industrial: Chemical process equipment (non-sparking, corrosion resistant)

Copper vs Aluminum for Wiring

Copper is preferred for building wiring due to higher conductivity per unit area, more reliable terminations, and lower thermal expansion. Aluminum requires larger conductors, antioxidant compound at joints, and proper torque to avoid loosening from thermal cycling.

Corrosion Resistance

Copper naturally forms a protective green patina (basic copper carbonate/sulfate) in outdoor environments, which stops further corrosion. It resists:

Fresh water and most non-oxidizing acids
Atmospheric exposure (centuries-long service life for roofing)
Neutral/alkaline soils

Copper is attacked by:

Oxidizing acids (nitric acid, concentrated sulfuric)
Ammonia and ammonium compounds (stress corrosion cracking)
Sulfides and high-sulfur environments
Highly acidic water (pH < 6)

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Summary

Copper (density 8960 kg/m³) is the standard for electrical conductivity and a preferred material for plumbing and heat transfer. Its high thermal conductivity (401 W/m·K), ductility, corrosion resistance, and antimicrobial properties make it irreplaceable in many applications. It costs significantly more than carbon steel but its performance justifies the premium in electrical and heat-transfer service.