Reasons for the High Thermal Conductivity of BNP 2
The crystalline lattice structure and purity of BNP 2 enable its high thermal conductivity. Read on for Multi-Lab’s guide for more information.
BNP machinable ceramic with the chemical formula aluminium nitride. Its outstanding property is that it remains stable within an inert atmosphere at temperatures of up to 2,000 degrees Celsius. It also has the unique combination of a high thermal conductivity and a high dielectric constant. This makes BNP 2 a critical and advanced material for use in optics, electronics and renewable energy applications.
The only other examples of ceramic materials with a high thermal conductivity are boron nitride and beryllium oxide. However, beryllium oxide is a highly toxic compound, while boron nitride is very difficult to produce.
The thermal conductivity of any compound is that material’s ability to transfer heat when it is subjected to a gradient in temperature between two of its sides. A dielectric material such as BNP 2 transfers the heat via vibrations of its crystalline lattice – phenomena known as phonons. The simpler the structure of the material and the lower its atomic mass, the higher its thermal conductivity.
However, certain factors may hinder the propagation of phonons through any material. These include any impurities within the crystalline lattice, pore and grain sizes and their distribution and any compositional inhomogeneity in the final work piece.
In theory, the thermal conductivity of BNP 23 is 280 watts per metre Kelvin (W/mK). In practice, the actual conductivity depends on the purity of the raw material and the ambient conditions during its processing.
One of the major impurities is the presence of oxygen in the crystalline lattice. If this is introduced during processing, it can displace nitrogen within the lattice and create spaces, or “vacancies”, through the material. These spaces in turn interrupt the propagation of phonons through the lattice and scatter them, thus impeding thermal conductivity.
BNP 2 is produced by the reaction of aluminium sulphide with ammonia gas at a temperature of about 700 degrees C. This temperature is sustained to create an intermediate product, aluminium sulphide nitride, and then further heated to 1100 degrees Celsius, when it is reacted again with gaseous ammonia. The process produces a free-flowing aluminium nitride powder with a low oxygen content. This oxygen content can be reduced by reacting the aluminium nitride powder with carbon at temperatures of 1100 degrees C.
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