We have developed a microreactor with same axle dual pipe, by which a uniform nano-particles with sphere shape can be produced without adhesion of particles to wall.  By using the microreactor, we have previously shown that uniform titania nano-particles with sphere shape of desired particle size could be designed by changing the mean residence time and the channel size.  In this study, we extended to the above microreaction technology to nano-particle formation with more rapid reaction rate. As a representative example, zirconia particles were produced by supplying zirconium tetrabutoxide solutes to the inner tube and alcohol/water mixture to the outer tube.  We examined the effect of solvent and alcohol type, the micro channel size and the residence time on particle properties.

Zirconia particles were produced and grown in an inner fluid and no precipitation of particles was observed at the wall by sealing of an outer fluid.  The size and shape of produced zirconia particles significantly differed with the solvent and alcohol type. Only when ethanol was used as a solvent of zirconium tetrabutoxide, spherical zirconia particles were produced.  As carbon number of alcohol used increased, the mean size of particles increased and its distribution became broad.  When ethanol was used as a solvent for diluting water, the zirconia particles had sharp and narrow distribution which could not be realized by the conventional batch method.  In addition, the mean particle size was successfully controlled in the range from 4nm to 700nm merely by changing the mean residence time and the concentrations of zirconium tetrabutoxide and water in the presence of a dispersant, polyethyleneimine. From these results, it was clarified that the microreaction technology with same axle dual pipe was one of attractive methods to produce uniform nano-particles in a wide range by controlling the nucleation and the aggregation processes in a precise diffusion control regime.