Thermal conductivity Thermally Conductive is a measure of a material's ability to transfer heat. Materials with high thermal conductivity can transfer heat efficiently and readily absorb it from the environment. A poor thermal conductor will impede the flow of heat and slowly acquire heat from its surroundings. According to the S.I (System International) guidelines, the thermal conductivity of a material is measured in watts per metre per kelvin (W/m-K).
The top 10 thermally conductive materials measured and their values are summarised below. As the thermal conductivity varies depending on the equipment used and the environment in which the measurements are obtained, these conductivity values are average values.
Naturally occurring thermally conductive materials
1. Diamond - 2000 - 2200 W/m-K
Diamond is nature's best thermal conductivity material, with a conductivity measurement 5 times higher than that of copper, the most manufactured metal in the USA. Diamond atoms consist of a simple carbon skeleton, making it the ideal molecular structure for efficient heat transfer. Typically, the materials with the simplest chemical composition and molecular structure have the highest thermal conductivity values.
Diamond is an important component of many modern handheld electronic devices. Their role in electronics is to promote heat dissipation and to protect sensitive computer components. The high thermal conductivity of diamonds has also proved useful when determining the authenticity of gemstones in jewellery. The inclusion of small amounts of diamond in tools and technology can have a dramatic impact on thermal conductivity.
2. Silver - 429 W/m-K
Silver is a relatively cheap and abundant conductor of heat. Silver is an integral part of many electrical appliances and is one of the most versatile metals due to its malleability. Thirty-five per cent of silver manufactured in the USA is used in power tools and electronics (US Geological Survey Mineral Community 2013). A by-product of silver, silver paste, is in increasing demand due to its use as an environmentally friendly energy alternative. Silver paste is used in the production of photovoltaic cells, which are a major component of solar panels.
3. Copper - 398 W/m-K
Copper is the most commonly used metal for the manufacture of conductive appliances in the United States. Copper has a high melting point and a medium corrosion rate. It is also a very efficient metal for minimising energy loss during heat transfer. Metal pans, hot water pipes and car radiators are all appliances that make use of copper's conductive properties.
4. Gold - 315 W/m-K
Gold is a rare and expensive metal used for specific conductive applications. Unlike silver and copper, gold rarely tarnishes and can withstand heavily corrosive conditions.
5, Aluminium Nitride - 310 W/m-K
Aluminium nitride is often used as a replacement for beryllium oxide. Unlike beryllium oxide, aluminium nitride does not pose a health hazard to manufacturing, but still shows similar chemical and physical properties to beryllium oxide. Aluminium nitride is one of the few materials with high thermal conductivity and electrical insulation properties. It has exceptional resistance to thermal shock and acts as an electrical insulator in mechanical chips.
6. Silicon carbide - 270 W/m-K
Silicon carbide is a semiconductor that consists of a balanced mixture of silicon and carbon atoms. When manufactured and fused together, silicon and carbon combine to form an extremely hard and durable material. This mixture is commonly used as a component of automotive brakes, turbines and steel mixtures.
7. Aluminium - 247 W/m-K
Aluminium is often used as a cost effective alternative to copper. Although less conductive than copper, aluminium is abundant and easy to work with because of its low melting point. Aluminium is an important component of L.E.D. lamps (Light Emitting Diodes). Copper-aluminium mixtures are becoming increasingly popular because they can take advantage of the properties of both copper and aluminium and can be manufactured at a lower cost.
8, Tungsten - 173 W/m-K
Tungsten has a high melting point and low vapour pressure, making it an ideal material for appliances exposed to high intensity electricity. Tungsten's chemical inertness allows it to be used as an electrode as part of an electron microscope without altering the current. It is also frequently used in components for light bulbs and cathode ray tubes.
9. Graphite 168 W/m-K
Graphite is a resourceful, low cost and lighter weight alternative to other carbon isomers. It is often used as an additive to polymer blends to enhance their thermal conductivity. Batteries are a common example of appliances that utilise the high thermal conductivity of graphite.
10. Zinc 116 W/m-K
Zinc is one of the few metals that can be easily combined with other metals to form a metal alloy (a mixture of two or more metals). Twenty per cent of zinc appliances in the USA are made from zinc alloys. Galvanising uses 40% of manufactured pure zinc. Galvanising is the process of applying a zinc coating to steel or iron to protect the metal from weathering and rusting.
Artificial surface treatment materials
DLC Diamond Like Coating - a nano coating manufactured using the vacuum coating technique, PVD process. Has good insulation and thermal conductivity
Al2O3 aluminium oxide coatings - nano-coatings produced by the CVD process. It is the more common composite functional film with good insulation + thermal conductivity. Film thickness control and bonding will have significant advantages over thermal spray. However, the high price is hardly popular. Thermal conductivity: 23-32 (W/m*k)
HBN hexagonal boron nitride coating - 33 (W/m*k), the best ceramic coating for thermal conductivity above 500°C ambient. Also the best ceramic insulating material at high temperatures (breakdown voltage 3kv/mm). Conventionally chemically inert, low friction coefficient of 0.16 Oxidation resistant, 900°C with oxygen, 2000°C without oxygen. NAXICO's TiB2 composite vacuum coating process allows for customised super temperature resistant and super hard nano coatings.
BeO beryllium oxide - similar thermal conductivity to purple copper. Powder is highly toxic. volatilisation starts at 1000°C. Starting to be phased out.
