Overview

Lead is a dense, soft, ductile, low-melting heavy metal (atomic number 82). It has the highest density of any common engineering metal except gold, tungsten, and depleted uranium — making it valuable for weight, radiation shielding, and vibration damping. Its use has declined due to toxicity concerns, but lead remains critical in specific applications where its unique properties are irreplaceable.

ρ = 11,340 kg/m³ (11.34 g/cm³) — about 1.4x denser than steel (7850 kg/m³) and 4.5x denser than aluminum

Mechanical Properties (pure lead, room temperature)

Property	Value
Density	11,340 kg/m³ (0.410 lb/in³)
Young's Modulus	16 GPa (very low — 8% of steel)
Yield Strength	5 MPa (extremely low — lead is nearly plastic at room temperature)
Ultimate Tensile Strength	15-18 MPa
Elongation at Break	30-50%
Hardness (Brinell)	4-6 BHN (very soft — easily scratched by a fingernail)
Poisson's Ratio	0.44
Melting Point	327°C (very low; easily cast)
Boiling Point	1750°C

Lead Creeps at Room Temperature

Lead is so soft that it undergoes measurable creep (slow plastic deformation under its own weight) at room temperature. Lead sheet on roofs will gradually flow downhill over decades; lead pipes sag without support. This is unusual among common metals — most have creep thresholds well above ambient temperature. Lead must be mechanically supported for long-term installations.

Physical Properties

Property	Value
Thermal Conductivity (20°C)	35 W/m·K
Specific Heat	129 J/kg·K
Coefficient of Thermal Expansion	29 × 10⁻⁶ /°C (high)
Electrical Resistivity	20.8 × 10⁻⁸ Ω·m (higher than copper; poor conductor)
Crystal Structure	FCC (face-centered cubic)
Speed of Sound	1200 m/s (slow — good vibration damping)

Key Properties

High density: 11.34 g/cm³ — exceptional for weight, ballast, and radiation shielding
Corrosion resistance: Lead forms insoluble protective films (sulfates, carbonates, oxides) in many environments; stable underground and in sulfuric acid
Low melting point: 327°C — easily cast, melted, and formed; used in low-melting alloys
Softness/ductility: Can be hammered, rolled, extruded at room temperature
Radiation absorption: Excellent attenuation of X-rays and gamma rays (high atomic number Z=82)
Damping capacity: Excellent for sound and vibration isolation
Chemical resistance: Resistant to sulfuric acid, chromic acid, phosphoric acid (basis of lead-acid battery)

Applications

Lead-Acid Batteries (largest use, ~85% of production)

SLI batteries (Starting, Lighting, Ignition) for automobiles
Deep-cycle batteries for golf carts, forklifts, solar/UPS backup
Grid alloy plates (Pb-Sb or Pb-Ca) in sulfuric acid electrolyte
Density critical to current capacity per volume

Radiation Shielding

Sheet lead, lead bricks, leaded glass for X-ray rooms, nuclear facilities
Lead aprons (typically 0.25-0.5 mm lead equivalent) for medical/dental personnel
Lead-lined plywood/drywall in radiology departments
Container shielding for radioactive materials
Effective against photons; high-Z material attenuates via photoelectric/Compton interactions

Historical/Industrial (declining due to toxicity)

Lead pipe (plumbing — Latin plumbum gives lead its symbol Pb; largely banned for potable water)
Solder (traditional tin-lead alloys; lead-free solders now mandated in electronics and plumbing)
Lead sheet for roofing, flashing (long-lived, easily formed; replaced by copper/aluminum)
Paint pigment (white lead, red lead — banned in most countries since 1970s)
Lead shot and ammunition (partially restricted for waterfowl due to ingestion poisoning)
Cable sheathing (electrical cables, historically for moisture protection)
Lead wheel weights (being replaced by steel/zinc in many jurisdictions)
Bearing alloys (lead babbitt for heavy low-speed bearings)

Specialty Uses

Ballast/weights: keels of sailboats, aircraft ballast, counterweights, scuba diving weight belts
Cryogenic/chemical tank linings (lead is impervious to many corrosives)
Fusible alloys (solder, fire sprinklers, safety plugs — Wood's metal, Rose's metal contain lead)
Anodes for cathodic protection (impressed current systems)
Sound/vibration damping: lead sheet in partitions and machinery bases

Lead is Toxic

Lead is a cumulative neurotoxin with no safe exposure threshold. Its use is heavily regulated: banned in gasoline, paint, plumbing solder, and food containers in most countries. Always wear PPE when machining or melting lead; provide ventilation; wash hands thoroughly; never eat/smoke around lead work. Collect and recycle scrap lead (recycling is efficient and reduces primary mining).

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Lead Alloys

Alloy	Composition	Use
Pure lead	99.9+% Pb	Chemical processing, sheet, anodes
Hard lead (antimonial)	Pb + 1-10% Sb	Batteries, higher strength, castings
Lead-calcium	Pb + 0.05-0.15% Ca	Maintenance-free battery grids
Tin-lead solder	63Sn-37Pb (eutectic, 183°C)	Electronics solder (being replaced)
Babbitt metal	Pb + Sn + Sb	Sleeve bearing material
Type metal	Pb + Sn + Sb	Printing (historical)

Summary

Lead (density 11,340 kg/m³) is the most versatile heavy metal — dense, corrosion-resistant, easily cast, soft, and an excellent radiation shield. Despite toxicity restrictions on historical uses (plumbing, paint, solder), it remains irreplaceable for lead-acid batteries (85% of demand), radiation shielding, and specialty high-density applications. Its low strength (5 MPa yield) and creep at room temperature distinguish it from structural metals — lead is used for its density and chemical properties, never for strength.

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