The process of heat transfer through direct contact is called thermal conduction, and it occurs when warmer molecules with greater kinetic energy collide with adjacent, cooler molecules. Some materials allow this energy to diffuse very quickly, meaning they are highly effective thermal conductors. The speed at which this transfer happens depends entirely on the substance through which the heat must pass.
Defining Thermal Conductors
A thermal conductor is defined as a material that permits heat energy to pass through it easily and quickly. This ability is quantified by a material’s thermal conductivity value, typically measured in Watts per meter-Kelvin (W/m·K). Heat flows spontaneously along a temperature gradient, moving from a region of higher temperature to one of lower temperature until both areas reach thermal equilibrium. The mechanism for this energy transfer in solids happens through two main processes: the vibration of atoms and the movement of free electrons.
In non-metallic materials, heat is transferred primarily by the vibration of atoms in the material’s lattice structure, which pass energy along through collisions. Metals, however, are exceptionally good conductors because they contain a large number of mobile, or “free,” electrons that are not bound to individual atoms. These electrons move rapidly throughout the material, efficiently carrying thermal energy and accelerating the rate of heat transfer.
Common Material Examples
Metals like silver, copper, and aluminum are the most widely recognized examples of high-quality thermal conductors. Silver is technically the most conductive metal, boasting a thermal conductivity value of approximately 429 W/m·K. However, its high cost limits its use to specialized applications like electrical contacts and thermal pastes.
Copper follows closely, with a conductivity of around 398 W/m·K, making it the most common metal used in manufacturing conduction technologies. It is favored for applications like cookware and hot water pipes due to its combination of high performance, moderate corrosion resistance, and reasonable cost. Aluminum, with a value of about 237 W/m·K, is a lightweight and cost-effective alternative frequently used in heat sinks and radiators, often combined with copper to balance performance and expense.
While metals dominate the list, the non-metal material diamond holds the title for the single best known thermal conductor, with values reaching 2000–2200 W/m·K. Diamond’s simple, rigid carbon structure allows atomic vibrations to travel through it with extreme efficiency, making it five times more conductive than silver. This property makes it valuable for specialized heat dispersion in sensitive, high-power electronic devices.
The Science of Thermal Insulators
In contrast to conductors, thermal insulators are materials that resist and slow the flow of heat. Materials with low thermal conductivity are classified as insulators, and their effectiveness is often measured by their thermal resistance, or R-value. They function by impeding the movement of heat energy, either by lacking free electrons or by possessing a complex structure.
Many common insulators rely on trapping pockets of air or other gases within their structure, which significantly lowers their overall conductivity. Gases like air have a very low conductivity value, and trapping them prevents the larger-scale heat transfer that occurs through convection. Examples of materials that utilize this principle include fiberglass, Styrofoam, and mineral wool, which are employed to reduce heat loss in buildings and appliances.
Practical Uses of Conductivity
Highly conductive materials are utilized when the goal is to quickly move heat away from a source or into an object. This is evident in the design of cooking utensils, where metal pots and pans ensure that heat from the stove is rapidly and evenly transferred to the food.
In electronics, high conductivity is necessary for thermal management, where materials like copper or aluminum are formed into heat sinks to pull waste heat away from sensitive components such as computer processors. Conversely, in situations requiring thermal isolation, materials with low conductivity are chosen to prevent heat transfer. This application is seen in the walls of thermos bottles, residential insulation, and the handles of metal cookware, where the goal is to keep the heat in or out.