Production of nanometer-sized metal oxide particles by gas phase reaction in a free jet.

摘要

Nanosized metal oxide particles were produced by injecting precursor vapor as a free jet into a methane/air flame. The influence of process conditions (temperature, volume loading and velocity) and material properties (solid state diffusion coefficient) on particle and agglomerate characteristics was studied. Particles formed in the initial region of the jet and grew by a collision-coalescence mechanism. The aerosol characteristics are determined by the characteristic particle collision and coalescence times. The collision time was controlled by varying the aerosol volume loading which ranged from 10;Experiments were made at four jet velocities. The Reynolds number at the highest velocity was 3600, corresponding to a turbulent flow. The other Reynolds numbers were 330 (laminar) and 1020 and 1880 (transitional). The aerosol production rate ranged from 0.05 to 1.0 g/hr. Primary particle size increased with volume loading, solid state diffusion coefficient and maximum temperature. Larger particles were also obtained by decreasing the jet velocity. The number of particles per agglomerate increased with volume loading, and decreased with solid state diffusion coefficient and maximum temperature.;Several metal oxides were produced under the same process conditions to study the effect of solid state diffusion on aerosol characteristics. Niobium oxide (largest diffusion coefficient) formed the largest particles with geometric volume mean diameters between 5.7 and 33.7 nm. Titania (mid-range diffusion coefficient) and alumina (lowest diffusion coefficient) formed particles with geometric volume mean diameters ranging from 3.8 to 21.3 nm and 2.8 to 10.7 nm, respectively. The standard deviation for the metal oxide particles was about 1.2.;A model was developed, based on the collision and coalescence times, to predict particle sizes in the coalescence limited regime by dividing agglomerates into domains in which coalescence occurs. The calculated particle sizes compared well with measured particle diameters.