Gas-phase combustion synthesis of aluminum nitride powder

Abstract

Due to its combined properties of high electrical resistivity and high thermal conductivity, aluminum nitride (AIN) is a highly desirable material for electronics applications. Methods are being sought E'er 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 novel approach involves reacting A1CI3, NHa, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AIN, NaC!, and Hi. The NaCI by-product is used to coat the/tiN particles in situ. The coating 'allows for control of AIN 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 AICla and NHa were premixed with HCI and then reacted with Na vapor. X-ray diffraction (X.RD) spectra of as-produced powders show only NaCI ['orthe first case and NaCI and AIN 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 AIN. Aluminum metal was also produced in the co-flow flame by reacting AICIawith Na. XRD spectra of as-produced powders show the products to be only NaCI and elemental aluminum. Introduction Background on AIN

Aluminum nitride. Preparation methods

“…According to data in [46] it is also possible to obtain AlN by combustion in a gas phase AlCl 3 + NH 3 + 50Ar = AlN + 3HCl.…”

Chemical and Physical Processes of Combustion

“…-165-EXPERIMENTAL While previous work was carried out with a non-premixed laminar jet flame (DuFaux and Axelbaum, 1995;Axelbaum et al, 1996Axelbaum et al, ,1997, this work was conducted with a non-premixed turbulent jet flame. Changing the system from a laminar facility to a turbulent facility allows significantly larger production rates to be attained thereby demonstrating the scalability of the process.…”

“…While hard agglomerates are acceptable for many end uses of powders commercially produced in flames, they must be avoided in nanopowders that are to be consolidated into structural materials. The presence of hard agglomerates in the powder leads to the formation of pores in the consolidated body which act as crack formation sites and ultimately reduce the strength of the consolidate.Recently, a sodium/halide flame synthesis process, conceptually similar to commercial flame processes, was extended to allow the production of unagglomerated, non-oxide nanopowders (DuFaux and Axelbaum, 1995;Axelbaum et al, 1996Axelbaum et al, , 1997. This technique employs an encapsulation step during the aerosol growth stage to control particle size, prevent the formation of hard agglomerates and protect the powders from oxidation/hydrolysis during post-synthesis handling.…”

“…Finally, use of a turbulent jet allows the synthesis of ceramic materials without premixing the metal and non-metal precursors. This has proved beneficial in the synthesis of A1N where the aluminum and nitrogen precursors cannot be premixed without undesirable reaction (Axelbaum et al, 1997).The reactants in Eq.(1) are delivered through a series of three concentric tubes. The metal chloride/inert mixture issues through a central tube with a jet diameter of 0.51 mm.…”

Thermal properties of AlN polycrystals obtained by pulse plasma sintering method

“…In the form of monocrystal or polycrystal, AlN is used in electronic devices, thus squeezing out conventional materials like SiO 2 , Al 2 O 3 or BeO, which are harmful for human body [1,2]. AlN is applied for sensors and heat exchangers to improve their sensitivity and efficiency [3].…”