A FLAME PROCESS FOR SYNTHESIS OF UNAGGLOMERATED, LOW-OXYGEN NANOPARTICLES - APPLICATION TO TI AND TIB2

A gas-phase flame process for synthesizing unagglomerated nanoparticle s of metals, intermetallics, ceramics, and composites is described. Em ploying this process, titanium and titanium boride have been synthesiz ed by the vapor-phase reaction of sodium with titanium tetrachloride a nd a 1:2 mixture of titanium tetrachloride and boron trichloride, resp ectively. To minimize agglomeration and protect the particles from pos tflame 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 TiB2 nanoparticles have been produced an d the encapsulated powders have been handled in air without oxidation. Particle size has also been varied with the encapsulation process, an d titanium particles with mean sizes of 10 and 60 nm have been produce d by varying operating conditions. The NaCl has been removed by water washing as well as vacuum annealing. Thermodynamic results show that t he sodium/halide process is applicable for synthesis of many materials , with yields approaching 100 pet under a wide range of operating cond itions. 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.