Production of Nanometer-Sized Metal Oxide Particles by Gas Phase Reaction in a Free Jet. I: Experimental System and Results

Abstract

ABSTRACT. In a study of the effect of process conditions and material properties on aerosol characteristics, nanosized metal oxide particles were produced by injecting precursors as a free jet into a methaneair flame. 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. Metal oxides with diffusion coefficients ranging over several orders of magnitude produced different sized particles under the same process conditions (temperature profile and aerosol volume loading). 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 geometric standard deviation for the metal oxide particles was about 1.2. The properties of the primary particles and agglomerates depend on the characteristic collision and coalescence times. The collision time was controlled by varying the aerosol volume loading from 10 ' to 10 -'. The coalescence time depends strongly on the solid state diffusion coefficient which ranged over several orders of magnitude as the jet temperature changed. Maximum jet temperatures from 1050 to 1920 K were obtained by adjusting the precursor jet and flame gas exit velocities from 4.8 to 53.2 m/s and 0.14 to 0.51 m/s, respectively. The mass production rate ranged from 0.05 to 1.0 g/h for a jet orifice of 1.2 mm.

Production of Nanometer-Sized Metal Oxide Particles by Gas Phase Reaction in a Free Jet. II: Particle Size and Neck Formation—Comparison with Theory

“…The distributions of the temperature, velocity, and volume loading along the jet axis are complex because the aerosol generator includes three concentric streams (Windeler et al, 1997). The innermost stream, a high velocity precursor jet, is centered in a laminar methane flame stream which in turn is surrounded by stationary ambient air.…”

“…Part I (Windeler et al, 1997) summarized the results of an experimental study of the effect of operating conditions (temperature, volume loading, velocity) and material properties (solid state diffusion coefficient) on nanoparticle characteristics. Nanosized metal oxide particles were generated by injecting a vapor phase aerosol precursor in the form of a jet into a methane-air flame.…”

Characteristics of Titania Nanoparticles Synthesized Through Low Temperature Aerosol Process

“…Two different chemical precursors have been typically used in these investigations namely, titanium tetra chloride (TiCl 4 ) and titanium tetra isopropoxide (TTIP). In high temperature processes, particles can be synthesized either by the oxidation of TiCl 4 (Suyama and Kato 1976;Morooka et al, 1989;Akhtar and Xiong, 1991;Akhtar and Vemury, 1994;Jang and Jeong, 1995;Yang et al, 1996;Yang et al, 1997;Windeler and Friedlander, 1997), or by the hydrolysis of TiCl 4 (Akhtar and Vemury,1994;Xia et al, 1999a,b) or by the thermal decomposition of TTIP (Komiyama and Kanai, 1984;Okuyama et al, 1986;Okuyama et al, 1990) or by the hydrolysis of TTIP (Wu et al, 1998;Kirkbir and Komiyama 1988;Chan et al, 1999). Recently, considerable interest has been directed towards the synthesis of titania at low temperatures based on aqueous phase processing (Kim and Park, 1999;Park et al, 1999;Li and Fan, 2002;Yin et al, 2002;Tang and Zhang, 2002;Yang, 2003).…”

Internal pressure and surface tension of bare and hydrogen coated silicon nanoparticles

“…For example, the characteristic coalescence time calculated from a solid state diffusion model is written as 12,13,15 …”

“…The rate at which two colliding particles coalesce has been modeled by both phenomenological [12][13][14][15][16][17] and molecular dynamics methods 18 which has resulted in simple to apply kinetic laws. For example, the characteristic coalescence time calculated from a solid state diffusion model is written as 12,13,15 …”