Aluminum Nitride

This chapter describes the preparation and applications of aluminum nitride (AlN). The development of AlN ceramic materials has been largely driven by the demand for a high-thermal-conductivity material that is also an electric insulator. This combination is for applications such as substrates and housings in hybrid circuits, power electronics, or microwave tubes. In commercial AlN ceramic materials, the content of secondary phases such as glass or crystallized sintering additives is always below 2–3 vol.%. The commercial production route for AlN powder mainly involves the carbonitridation of A12O3. The problems with this reaction are the high temperatures involved and the fact that all impurities dissolved in the carbon or in the alumina tend to contaminate the final A1N powder product. Residual oxygen and carbon from unreacted Al2O3 and carbon can also be found in the final powder. A1N powders are densified by pressureless sintering or hot pressing. The sintering mechanism during densification by pressureless sintering is influenced by additive melt formation and by the solution-reprecipitation of the A1N. The mobility and the density of lattice vacancies are major factors in determining densification rate during hot pressing.