NANOSCALE UNAGGLOMERATED NONOXIDE PARTICLES FROM A SODIUM COFLOW FLAME

A coflow burner has been developed to react sodium vapor with gaseous halides in a flame configuration similar to the hydrocarbon coflow fla me, and produce metals, composites, and nonoxide ceramics. Nanometer-s ized particles of elemental titanium and titanium diboride were succes sfully produced with this burner as indicated by XRD. In a novel appro ach, the flame is operated under conditions that lead to condensation of the NaCl byproduct onto the particles. The NaCl coating acts to con trol size and eliminate agglomeration of the particles in the flame be cause the particles are encapsulated in NaCl. The coating was also fou nd to be highly effective at limiting oxidation during postflame handl ing of Ti powders. TEM analysis indicates that the as-received product s are composed of individual nanoparticles in an NaCl matrix. The NaCl coating has been efficiently removed from the TiB2 particles by both water washing and sublimation at 800 degrees C under vacuum. It is pro posed that this method of encapsulation, with a removable coating-mate rial, is a general method of obtaining unagglomerated nanoparticles in a flame. Other applications and coating materials need to be explored .