Nanometer Particles and Their Agglomerates

Nanometer sized metal oxide particles were produced by a collision-coalescence mechanism in a free jet generator. Particle and agglomerate characteristics were controlled by varying the process conditions and material properties. Metal oxides with diffusion coefficients varying over several orders of magnitude produced different sized particles under the same process conditions. Primary particle size increased with volume loading, maximum temperature and aolid state diffusion coefficient. Particle size also increased by decreasing the jet velocity. The number of particles per agglomerate increased with volume loading and decreased with maximum temperature and solid state diffusion coefficient. The collision time was varied by changing the volume loading from 10- 7 to 10-6. The coalescence time for a given material was varied by changing the precursor jet and flame gas exit velocities from 4.8 to 53.2 m/sec and from 0.14 to 0.51 m/sec, respectively. The flow rates produced jet temperature profiles with maximum temperatures ranging from 1050 to 1920°K. The mass production rate under the conditions studied ranged from 0.05 to 1.0 g/hr. Niobium oxide (largest diffusion rate) produced the largest particles with mean diameters ranging from 5.7 to 33.7 nm. Titania (mid range diffusion coefficient) and alumina (lowest diffusion coefficient) produced particles with mean diameters ranging from 3.8 to 21.3 nm and 2.8 to 10.7 mn, respectively. The standard deviation for the metal oxide particles was about 1.2.