Two techniques are described for synthesizing nanometer-sized TiB 2 particles by gas-phase combustion reactions of sodium vapor with TiCl 4 and BCl 3 : a low-pressure, low-temperature burner and a high-temperature flow reactor. Both methods produce TiB 2 particles that are less than 15 nm in diameter. The combustion by-product, NaCl, is efficiently removed from the TiB 2 by water washing or vacuum sublimation. Material collected from the low-temperature burner and annealed at 1000 ± C consists of loosely agglomerated particles 20 to 100 nm in size. Washed material from the high-temperature flow reactor consists of necked agglomerates of 3 to 15 nm particles. A thermodynamic analysis of the Ti͞B͞Cl͞Na system indicates that near 100% yields of TiB 2 are possible with appropriate reactant concentrations, pressures, and temperatures.TiCl 4 1 2BCl 3 1 10Na°! TiB 2 1 10NaCl . (1) Calcote and Felder 9,10 have recently proposed producing metals and nonoxide ceramics from reactions of 948

No 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

No abstract

No abstract