Diamond Properties : Thermal Conductivity

Thermal conductivity is the quantity of heat transmitted, due to unit temperature gradient, in unit time under steady conditions in a direction normal to a surface of unit area, when the heat transfer is dependent only on the temperature gradient .

Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding within the crystal. Most natural blue diamonds contain boron atoms which replace carbon atoms in the crystal matrix, and also have high thermal conductivity.

Specially purified synthetic diamond has the highest thermal conductivity (2000–2500 W/(m·K), five times more than copper) of any known solid at room temperature. Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating.

Diamonds are called "ice" with good reason. Objects feel cold not only because they are at a lower temperature than our bodies, but also because they can extract or conduct the heat away from us. When you touch a diamond to your lips, it feels ice-cold because it robs your lips of their heat.

The capacity of diamond to conduct heat distinguishes it readily from other gems and exceeds that of copper, an excellent thermal conductor, by about 4 times at room temperature. This exceptional property of diamond is increasingly being used for extracting heat from electronic devices to make them smaller and more powerful.

Metals usually conduct heat much better than transparent substances, because they have loose electrons that act as packets for carrying heat in much the same way they move electricity. Nonmetals conduct heat solely by atomic vibrations, a less efficient mechanism than moving electrons. In diamond, however, vibrational energy travels through the crystal along the strong internal chemical bonds. Thus, diamond's superlative strength provides excellent thermal conduction as well.

Thermal conductivity of diamond

Typical values (at 293 K):

• Type Ia 600-1000 Wm-1K-1
• Type II 2000-2100 Wm-1K-1

• Type Ia 2000-4000 Wm-1K-1
• Type IIa up to 1.5 x 104 Wm-1K-1

Thermal expansion (linear)

At 293 K 0.8 + 0.1 x 10-6
193 K 0.4 + 0.1 x 10-6
400-1200 K 1.5 - 4.8 x 10-6
Gruneisen's Law obeyed between 420 K and 1200 K.

Other Properties of Diamond.