Preparation of TiO<sub>2</sub> Particles by Means of Wire Exploding Method

Abstract

Titanium wires were exploded in air by electric discharge and properties of obtained particles were investigated. Ti wires (purity>99.5%) with diameters of 0.20, 0.508 and 0.762mm were cut to 50 or 80mm long. Exploding conditions were as follows: charged voltage 2.5-6.5kV, condenser capacity 40μF and charged energy 125-845J. Most particles formed were collected on the filter paper set in a vacuum cleaner. The powder was bluish white and consisted of spherical particles. Two types of particles were observed: large (>1μm) and very fine. These particles were identified as rutile- and anatase-type TiO2, respectively. The amount of anatase increased from 60 to 90% with an increase in the energy ratio which was defined as the ratio of heat contents required for melting and vaporizing the Ti wire to charged energy. Anatase particles were considered to be formed by a reaction between metal vapor and oxygen gas because the amount of anatase almost agreed with that of metal vapor produced in the wire explosion. On the other hand, liquid metal drops were considered to be oxidized into rutile. Particle size distributions indicated a maximum frequency at about 0.3μm, but the distribution was considerably broad and particles larger than 2μm existed in the range from 10 to 20%. The average size of particles decreased from 0.74 to 0.37μm with increasing the energy ratio mainly due to an increase in the amount of metal vapor produced.