Aerosol Synthesis of Aluminum Nitride Powder Using Metalorganic Reactants (original) (raw)

1992, Journal of the American Ceramic Society

We describe a new laboratory-scale aerosol process for making submicrometer AIN powder by the reaction of gas phase AI(C,H,), and NH,. The process can produce spherical, near-stoichiometric AIN powder with mean particle diameter ranging from 0.07 to 0.20 pm and polydispersity index between 0.2 and 0.5. The inlet TEA concentration is found to have the greatest effect on particle size, with the furnace temperature and carrier gas flow rate having lesser influence. Our results appear to favor a LaMer-type mechanism (particle nucleation, followed by condensation growth) over fusionxoaiescence to explain particle growth. I. Introduction LUMINUM NiTRiDE is currently receiving renewed attention A within the advanced ceramic materials community. I.' Because of its high thermal conductivity, AIN is being intensively studied as a replacement for A120, in making heat-dissipating substrates for microelectronic device packaging. If sintered to high density in transparent form, AlN has potential applications in the area of electro~ptics.~ Aluminum nitride is also a potential structural material, in either monolithic or composite form, for applications ranging from severe service environments' to ballistic armor.' Many of these applications may require greater control of particle size, uniformity, and impurity composition than can be achieved by current preparation methods. Aluminum nitride is currently manufactured using either direct nitridation or carbothemal methods. '.' Direct nitridation involves heating aluminum powder in the presence of N2 or NH, at temperatures above 1473 K. Alternatively, carbothermal reduction involves reacting finely mixed Al20, and carbon powder in a N2-containing gas at temperatures between 1373 and 2023 K, usually with an intermediate oxidation step at 873-973 K to remove unreacted carbon. In both processes, the quality of the product powder is limited by the impurity level and morphology of the starting A1 or AI,O, powder. Aerosol synthesis offers a potential alternative to conventional powder preparation methods.7-"' High-purity powders can be obtained using molecular precursors as starting reactants. Narrow, uniform powder size distributions can be achieved by controlling particle nucleation and growth rates. Aerosol synthesis processes have been developed at the commercial scale for several materials (e.g., Si, carbon black, TiO,, and SiO,). Previous workers have described aerosol reactors for A1N synthesis using AICI, and NH, as gas phase reactants."-'3 Initial conversion to AlN is obtained at reaction temperatures between 873 and 1373 K. Mean particle sizes as small as 0.2 p m are obtained at the higher temperature limit. However, these studies T. M. Besmann-contributing editor tvhuscriot No.