Investigation of ultrafine titanium dioxide aerosol size and structure during anatase-to-rutile transformation

We have studied the ultrafine TiO2 particle morphology and phase transformation from anatase to rutile in aerosol reactor. The particles were prepared via aerosol decomposition of titanium tetraisopropoxide (TTIP) droplets. Aerosol was produced by dispersing precursor solution by aerosol nebulizer and subsequently evaporating the propanol solvent. The TTIP droplets were size selected using a differential mobility analyzer (DMA). The 45 nm mobility size fraction was transported to a tube reactor in air carrier gas with a flow rate of 1.0 lpm. Experimental runs were made between 600 and 900 °C. In the flow reactor the TTIP droplets were thermolyzed to TiO2 particles. The particle size was measured with a second DMA downstream of the flow reactor. Particle microstructure was investigated with transmission electron microscope (TEM). Computer simulations of the reactor temperature and flow fields were made. The tandem-DMA results show how particle size is reduced during the aerosol decomposition and subsequently by TiO2 densification and phase change. The original TTIP droplet size is reduced by 30 % at 700 °C reactor temperature and finally by 35 % at 900 °C to reach 30 nm rutile particle size. The high resolution TEM (HR-TEM) and electron diffraction (ED) results of the nanosized TiO2 particles reveal the crystallite size and phase transformation at different reactor temperatures.