Gas-phase combustion synthesis of aluminum nitride powder

Due to its combined properties of high electrical resistivity and high thermal conductivity, aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This movel approach involves reacting AlCl₃, NH₃, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H₂. The NaCl by product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl₃ and NH₃ were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powerds show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775°C under dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl₃ with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.