An experimental study of controlled gas phase synthesis of nanosize TO2 powders
Recently there has been an increased interest in the generation of ceranlic powders composed of nanosize particles with a narrow size-distribution and high purity. It has been shown that ceramics sintered from these ultrafine partic1es exhibit improved mechanical and electrical properties. The present research has attempted to control the growth of the ceramic particles in a relatively simple continuous flow process by placing charges on the forming particles and controlling their evolution with an electric field.
Nanosize TiO₂ powder was produced using a multi-stream, co-annular reactor. The heat source was a cylindrical H₂/0₂ diffusion flame located around the outside of reaction zone. The effect on the powder size, shape, and size distribution due to particle charging, applied electric fields, and varying reactant concentrations were investigated.
The temperature field within the reaction zone was uniform radially and ramped axially from 600 to 1100 K. The reactant stream passed through a 10 millicurie Po-21 0 alpha source within the burner with the intention of creating a bipolar ion concentration. In the presence of an electric field, this ionization can lead to either a unipolar-negative or unipolar-positive particle charging environment. The electric field across the reaction zone was varied in an attempt to control particle residence time.