Thermal Conductivity
Also: heat conduction, thermal conduction, λ (lambda)
Thermal conductivity describes how well a material transports heat energy through itself and is expressed in watts per metre per kelvin (W/(m·K)).
Thermal conductivity (symbol λ, unit W/(m·K)) is a material property that states how fast a solid, liquid or gas carries heat energy from a warmer to a cooler zone. The higher the λ value, the more efficiently the material conducts heat. Precious metals are among the very best thermal conductors known — a property as sought-after in industry as it is relevant when valuing alloys with the melt-value calculator.
The physical background
Heat transport in metals occurs mainly through free electrons, not through lattice vibrations (phonons) alone. That is why good electrical conductors are usually good thermal conductors too — a relationship captured by the Wiedemann-Franz law:
λ / sigma = L · T
Here sigma is the electrical conductivity, T the absolute temperature (in kelvin) and L the Lorenz number (≈ 2.44 × 10⁻⁸ W·Ω/K²). The law holds reasonably well for pure metals at room temperature.
Precious metals compared
Silver tops the ranking of pure metals at 429 W/(m·K), making it the best metallic thermal conductor of all. Copper follows just behind at 401 W/(m·K) — which is why copper dominates heat sinks and heat exchangers as the cheaper alternative. Gold reaches 318 W/(m·K) and is used where corrosion resistance takes priority, for example in aerospace or microelectronics. Platinum and palladium sit much lower, at around 72 W/(m·K), but score through their resistance at high temperatures.
| Metal | λ in W/(m·K) | Main thermal application |
|---|---|---|
| Silver | 429 | Contacts, paste, soldering |
| Copper | 401 | Heat sinks, heat exchangers |
| Gold | 318 | Microchips, aerospace |
| Platinum | 72 | Thermocouples, high-temp. |
| Palladium | 72 | Catalysts, electrodes |
Practical significance
In electronics, thermal conductivity determines how effectively processors and power semiconductors are cooled. Silver-bearing thermal pastes and sintered layers are considered state of the art for high-performance chips. In the jewellery and alloy field, every alloying partner alters the λ value: sterling silver (925) conducts noticeably worse than pure silver, because lattice defects disrupt electron movement.
Thermal conductivity also underpins the so-called ice-melt test for silver: pure silver conducts heat so well that an ice cube on a silver bar melts distinctly faster than on most other metals — a simple plausibility check for home use.
In brief
Silver is the best metallic thermal conductor of the known elements; copper and gold follow a little behind. This property makes precious metals indispensable materials in high-performance electronics, aerospace and heat engineering — far beyond their role as an investment precious metal.