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 |
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 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.