OPTICAL AND MODELING STUDIES OF SODIUM HALIDE REACTIONS FOR THE FORMATION OF TITANIUM AND BORON NANOPARTICLES/

This study focuses on the optical characterization of a method for the formation of nanoscale titanium and boron particles. This versatile m ethod can also be used to form a variety of metals as well as ceramic powders such as TiB2. The gas-phase chemical process, given by (mn)Na + (n)MCl(m) --> (M)(n) + (mn)NaCl, should be generic to many metal chl orides or mixtures of metal chlorides. In this study, either TiCl4 or BCl3 is reacted with Na vapor in a counterflow diffusion flame reactor . After the Cl is stripped from the metal chloride by the Na vapor, na nosize Ti or B particles form and, under certain thermodynamic circums tances, become encased in NaCl, which helps to prevent agglomeration a nd postflame oxidation. The two-dimensional spatial distribution of Na -2 has been optically interrogated using planar laser-induced fluoresc ence under various conditions to clarify the influence of concentratio n and transport on particle formation. Reactant concentration and time available for reaction were found to dramatically influence the react ive flow. Simulations using a counterflow diffusion flame model show t hat formation of TiB2 likely occurs by gas-phase clustering reactions involving both precursors. The model indicates that experimental resul ts are consistent with the proposed chlorine abstraction mechanism wit h near-collisional reaction rates.