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Journal of the Society of Powder Technology Japan

Thermophoresis of ultra-fine SiO2 particles formed in a flame was experimentally investigated by setting an adhering surface perpendicular to a flame axis.The following results were obtained. 1) Near the adhering surface, the number density of particles is considered to increase up to almost twice that in a flame. This is because the approaching velocity of particles decreased to about half of its original value keeping the cross sectional area of the flowing region constant. 2) The thermophoresis velosity was 1.0-1.4cm/s. 3) A particle diameter corresonding to the thermophoresis velocity is 0.4-0.8μm, which is larger than a particle diameter measured in a flame, that is, 50-60nm. 4) Particles are considered to adhere to each other in the vicinity of the surface. 5) A main mechanism of particle adhesion is thermophoresis, and the effect of inertia can be neglected.

Thermophoresis velocity of SiO2 ultra-fine particles in a flame.