Preparation of nanometer-sized In2O3 particles by a reverse microemulsion method

Nanometer-sized indium oxide (In(2)O(3)) particles have been prepared by chemical reaction of inorganic indium compounds and ammonia gas in a reverse microemulsion system consisting of water, Triton X-100 (surfactant), n-heptanol (co-surfactant), and n-octane (oil). Precursor hydroxides precipitated in the droplets of water-in-oil (W/O) microemulsion were calcined at different temperatures to form indium oxide powder. The factors affecting the particle size have been discussed; the calcination temperature is considered to be the important factor for controlling the size. In(2)O(3) calcined at 400 degrees C had a spherical form and a narrow size distribution. Calcination at 800 degrees C led to the formation of particles not only of irregular shape, but also of a wide size distribution. With the increase in calcination temperature from 400 to 800 degrees C, the average size of the particles grew from 7 to about 40 nm. The species of reactants used in the aqueous phase had a significant effect on the size of the particles. The average diameter of In(2)O(3) particles derived from reactant InCl(3) was 7 nm; that of particles derived from In(NO(3))(3) was 15 nm. The In(2)O(3) nanoparticles were characterized by transmission electron microscopy and X-ray diffraction. The phase behavior of the microemulsions is discussed.