Modeling The Nucleation And Growth Process And Size Distribution Of Nano-TiO₂ Synthesized By RF-plasma CVD

As one of the CVD method, RF-PCVD (Radio-Frequency plasma chemical vapor deposition) method is well suited to generation of high pure, good dispersity and narrow size distribution nanoparticles. This method is widespread used in synthesis research of heat-resisting and metal materials, such as oxide(TiO2,WO3), carbide(TiC) and nitride(TiN). As one of the important industrial chemicals, nano-TiO2 is widespread used in the field of energy, chemical engineering, semiconductor material, Photo catalytic materials and fine ceramics. In the preparation process of nanoparticles, the technology aim is obtained by altering technology condition and improving the equipment in most research. So the systematic theory research about the preparation process is meaningful to the designing and controlling of average size, size distribution and crystal form. In this paper, the preparation of TiO2 by TiCl4 oxidation was chosen in order to lay the theory foundation of the preparation of nano-powder by RF-PCVD through preliminary research in temperature distribution, flow state, nucleation and growth process.According to the assumptions about the RF-Plasma reactor, the reactor model was simplified to a steady two-dimension axial symmetry columnar reactor model. The flow state was considered in the model and the temperature distribution equation was obtained by energy transfer equation, which is a second-order partial differential equation. The temperature distribution was computed by solving the equation with the Crank-Nicholson finite difference method in matlab. According to the collision growth theory of homogeneous nucleation, the kinetic equation of nucleation and growth process was obtained by simplification and making hypothesis, which is a first-order ordinary differential equation. The kinetic equations of particle growth was calculated by fourth and fifth order Runge-Kutta method along each gas streamline which are chosen in the temperature field. According to the particle diameter result along the radial distance which was obtained above, the average diameter and diameter distribution of the nanoparticals were gained by disperse and simulation method. By the comparison of the result of simulation and experiment on condition of different input concentrations, the conclusions can be made:(1) The average size result of simulation and experiment are simply the same on the aspect of numerical value and variation trend. When the input concentration are respectively 0.0657 mol/m3,0.266 mol/m3 and 0.356 mol/m3, the simulation result are respectively 27.38 nm,48.78nm and 54.85 nm, and the experiment result are respectively 25.0nm,45.0nm and 50.0nm. The size distribution result of simulation and experiment are close. As the increase of the input concentration, both size distribution ranges are wider and the variation trends are simply the same. So the conclusion can be made that the model could predict the average size and distribution of nano-TiO2 well.(2) The flow state and concentration of the model are both in ideal condition and the final simulation size distribution can't predict the experiment result very well. The actual flow state, mass transfer factors and perfection of the kinetic equations of particle nucleation and growth should be considered to perfect the model.