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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

This paper describes a new method for the destruction of chlorofluorocarbons (CFCs). The process consists of mixing vapor-phase CFCs and sodium at atmospheric pressure in an exothermic single-pass process leading to the mineralization of the carbon and halogen components. The process has demonstrated high destruction efficiencies for a surrogate CFC (CF 4 ) as well as high efficiency for the formation of the equilibrium-predicted products of reaction: benign salt-coated carbon aerosols, large enough to be filtered with existing filtering technologies, with no volatile products. The rapidity of the chemistry and condensation process and the low cost of sodium should enable the construction of industrial-scale reactors that are fairly small and economical to build and operate. The application of this chemistry would be toward destruction of CFC stockpiles and as a treatment of the effluent of plasma reactors used in semiconductor processing.

A gas-phase flame process for synthesizing unagglomerated nanoparticles of metals, intermetallics, ceramics, and composites is described. Employing this process, titanium and titanium boride have been synthesized by the vapor-phase reaction of sodium with titanium tetrachloride and a 1:2 mixture of titanium tetrachloride and boron trichloride, respectively. To minimize agglomeration and protect the particles from postflame oxidation, the NaCl by-product is allowed to condense onto the particles in situ, yielding NaCl-encapsulated particles. In this way, stable, unagglomerated Ti and TiB 2 nanoparticles have been produced and the encapsulated powders have been handled in air without oxidation. Particle size has also been varied with the encapsulation process, and titanium particles with mean sizes of 10 and 60 nm have been produced by varying operating conditions. The NaCl has been removed by water washing as well as vacuum annealing. Thermodynamic results show that the sodium/halide process is applicable for synthesis of many materials, with yields approaching 100 pct under a wide range of operating conditions. Similarly, the encapsulation process is generally applicable, making the sodium/halide flame and encapsulation process a viable one for large-scale synthesis of environmentally insensitive nanopowders.

This study focuses on the optical characterization of a novel method of forming nanoscale titanium and boron particles, which can be used to form ceramic precursors such as TiB2. TiCl4 or BCl3 reacts with heated Na vapor in a counterflow diffusion flame reactor. After Na strips the Ti or B of its Cl atoms, nanosize Ti or B particles form and become encased in NaCl, which helps to prevent agglomeration and oxidation. The two-dimensional spatial distribution of the Na dimer has been optically interrogated using planar laser-induced fluorescence (PLIF) to clarify the influence of the concentration distributions and transport on particle formation rates.