CHARACTERISTICS OF THE LIQUID FLAME SPRAY PROCESS

Liquid flame spraying (LFS) is a new thermal spray process. Liquid fee dstock is injected and atomized in an oxygen-hydrogen flame where the liquid phase is evaporated and thermochemical reactions are completed to produce fine particles. Production of nanoparticles requires a thor ough understanding of the process. Therefore, various process stages w ere studied; i.e., the atomization of Liquid feedstock, and characteri zation of the flame and flame-droplet interactions. Experimental techn iques included laser diffraction anemometry for droplet size distribut ion, laser doppler velocimetry for particle velocity, pulsed laser Ray leigh back scattering for flame temperature and Schlieren photography for flame structure. Atomization is optimized with an organic solvent, such as isopropanol, nebulized with hydrogen gas at a high flow rate. Liquid droplets injected into the flame are subjected to a maximum te mperature of 2600 degrees C and are accelerated to about 160 m s(-1), The flame length call be controlled by flame velocity and the solvent type. Water produces a shorter name whereas isopropanol extends the fl ame. Injection of the aerosol produces a ''pencil-like'' region which does not experience turbulence for most of the flame length. Experimen tation with manganese nitrate and aluminium isopropoxide or aluminium nitrate showed conversion to a manganese oxide and alumina, respective ly. (C) 1997 Elsevier Science S.A.