Accounting for hydrolysis in the modeling of titanium dioxide nanoparticle synthesis in laminar TiCl 4 flames

International audienceThe description of TiO 2 synthesis in TiCl 4 flames is most often based on phenomenological models that qualitatively reproduce experimental trends in terms of final production but they do not provide chemical insights into the actual kinetic pathways. Alternatively, thermodynamically-consistent detailed TiCl 4 oxidation kinetics are available. However, since they have been developed under dry conditions they still need to be challenged and validated when employed for flame synthesis where the presence of water molecules may potentially activate TiCl 4 hydrolysis. To derive accurate chemical descriptions for TiO 2 flame synthesis, it is essential to evaluate the possible contribution of TiCl 4 hydrolysis. For this, numerical simulations of TiO 2 flame synthesis in laminar flames are performed in this article using different chemical descriptions for TiCl 4 conversion into TiO 2. Detailed oxidation kinetics neglecting hydrolysis are shown to predict an extremely slow formation of TiO 2 particles in flames when O 2 concentration is small. As a consequence, a significant underestimation of the conversion yield is observed compared to experimental evidences and to trends deduced from phenomenological models. To correct this behaviour, a new scheme is proposed by combining a detailed oxidation kinetics with a five-reaction mechanism describing the first steps of TiCl 4 hydrolysis. Conversion of TiCl 4 is found to be faster and more efficient with this new combined scheme, leading to log-normal particle size distributions in agreement with the experimental data for nanoparticles flame synthesis