Thermal Conductivity
Also: Heat Conduction, Thermal Conductance, λ (Lambda)
Thermal conductivity describes how well a material transports thermal 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 indicates how quickly a solid, liquid, or gas transports thermal energy from a warmer to a cooler zone. The higher the λ value, the more efficiently the material conducts heat. Precious metals rank among the best thermal conductors of all – a property that is just as sought after in industry as it is relevant when using the melt value calculator for alloys.
Physical Background
Heat transport in metals occurs primarily through free electrons, not through lattice vibrations (phonons) alone. Good electrical conductors are therefore generally also good thermal conductors – a relationship described by the Wiedemann–Franz Law:
λ / σ = L · T
Here σ 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 well for pure metals at room temperature.
Precious Metals Compared
Silver heads the ranking of pure metals at 429 W/(m·K), making it the best metallic thermal conductor of all. Copper follows closely at 401 W/(m·K) – which is why copper dominates as the cheaper alternative in heat sinks and heat exchangers. Gold achieves 318 W/(m·K) and is used where corrosion resistance takes priority, such as in aerospace or microelectronics. Platinum and palladium lie at around 72 W/(m·K), but score through their high-temperature resistance.
| Metal | λ in W/(m·K) | Main thermal application |
|---|---|---|
| Silver | 429 | Contacts, thermal paste, soldering |
| Copper | 401 | Heat sinks, heat exchangers |
| Gold | 318 | Microchips, aerospace |
| Platinum | 72 | Thermocouples, high temperature |
| Palladium | 72 | Catalysts, electrodes |
Practical Significance
In electronics, thermal conductivity determines how effectively processors and power semiconductors are cooled. Silver-containing thermal pastes and sintered layers are considered state of the art for high-performance chips. In the jewellery and alloy sector, every alloying partner alters the λ value: sterling silver (925) already conducts noticeably less well than pure silver, because lattice defects impede electron movement.
Thermal conductivity also influences the so-called ice melt test for silver: pure silver conducts heat so well that an ice cube placed on a silver bar melts noticeably faster than on most other metals – a simple plausibility test for home use.
Key Takeaway
Silver is the best metallic thermal conductor among all known elements; copper and gold follow at some distance. This property makes precious metals indispensable materials in high-performance electronics, aerospace, and thermal engineering – far beyond their role as investment metals.