Aluminum nitride (AlN) has attracted great attention due to its high electrical conductivity and insulating properties. In addition, it is also a highly effective piezoelectric material for surface acoustic wave sensors. It is a useful material for micromachined ultrasound transducers and RF filters used in mobile phones.
Aluminum nitride is synthesized by carbothermal reduction, chemical vapor deposition (CVD), and direct nitridation methods. It can be produced in a variety of densities, including technical-grade materials.
Carboxothermal reduction method The most widely used synthesis method is carbothermal reduction, which uses carbon as a reducing agent in the temperature range from 600 to 800 degC under nitrogen or ammonia gas streams. However, this method is uneconomic and has many limitations. In particular, the oxidation of the Al during carbothermal reduction causes the purity of the product to decrease significantly.
The addition of NH4Cl to the Al-nitridation reaction can be a very efficient way to reduce the reaction time and improve the purity of the product. In the present study, Al powder with 70 wt % NH4Cl was heated under a nitrogen stream to temperatures ranging from 500 to 1000 degC for 1 h and then X-ray diffraction patterns were observed.
In addition to the advantages of reduced heating time, the nitridation reaction is also more complete, as indicated by the absence of peaks corresponding to the unreacted Al powder. Moreover, the addition of NH4Cl also significantly improves the thermal resistance of the final AlN material.