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 flame, and produce metals, composites, and nonoxide ceramics. Nanometer-sized particles of elemental titanium and titanium diboride were successfully produced with this burner as indicated by XRD. In a novel approach, the flame is operated under conditions that lead to condensation of the NaCl byproduct onto the particles. The NaCl coating acts to control size and eliminate agglomeration of the particles in the flame because the particles are encapsulated in NaCl. The coating was also found to be highly effective at limiting oxidation during postflame handling of Ti powders. TEM analysis indicates that the as-received products 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°C under vacuum. It is proposed that this method of encapsulation, with a removable coating-material, is a general method of obtaining unagglomerated nanoparticles in a flame. Other applications and coating materials need to be explored.