Nucleation Mechanism And Grain Growth Simulation Of TiO₂ Generated By Oxidation Reaction Of TiCl₄

With the development of social industrialization,titanium dioxide is widely used in industrial production due to its excellent physical and chemical properties.For example,in the fields of pigments,medical,cosmetics,semiconductors and aerospace technology.At present,the production technology of titanium dioxide mainly includes three methods:liquid phase method,sulfuric acid method and chlorination method.Among them,the chlorination method is more in line with the double standard of economy and environmental protection.In the process of producing titanium dioxide by chlorination,the reaction between TiCl₄ and O₂ belongs to the millisecond extreme.Due to the fast reaction speed,it is difficult to study the reaction process from the experimental level.Therefore,the quantum chemical calculation method is used to study its microscopic and high-speed reaction process.In this paper,the first-principles calculation method is mainly used to study the microscopic mechanism of the nucleation process of titanium dioxide.The main research theory is based on density functional theory（DFT）.The research and calculation of the microscopic mechanism of titanium dioxide nucleation is carried out through the two important modules of the Material Studio software,Castep and Dmol3.The main research contents and conclusions are as follows:（1）The deposition and adsorption of TiCl₄ on the complete rutile surface and the surface containing oxygen defects were calculated by Castep,and the change of bond length before and after adsorption,the number of electron transfer,density of state,adsorption energy,etc.were calculated.The results were analyzed and discussed,and it was concluded that the best deposition position of TiCl₄ is bottom-down deposition.The surface contains oxygen vacancies,and with the increase of oxygen vacancies,TiCl₄ electron transfer increases,making it easier for molecules to deposit on the surface.The deposition and adsorption of O₂ molecules on the surface of TiO₂（110）containing oxygen defects was further calculated,and it was concluded that the optimal adsorption site of O₂ molecules was vertical oxygen defects,and the adsorption energy of vertical oxygen defects was-10.37 k J·mol-1,The amount of charge transfer is 0.14 e V.（2）The deposition of K⁺in KCl on the surface of rutile TiO₂（110）was calculated by Castep,and the change of bond length before and after deposition,as well as the transfer of electrons,charge density,and adsorption energy,were calculated.The hydrolysis of water molecules reduces the energy barrier of hydrolysis of water molecules on the surface of TiO₂（110）,which reduces the hydrolysis energy from-1.5 e V to-3.9 e V,and hydrolyzes to generate a terminal hydroxyl group and a bridging oxygen,which makes the rutile surface present hydroxyl groups change.The hydroxylated surface increases the difficulty of deposition of TiCl₄ on the surface,making the adsorption energy larger,and it is difficult to form a stable adsorption structure,thereby inhibiting the nucleation of TiO₂.（3）The clusters between TiO₂ molecules are calculated by Dmol3,the transition state is searched to calculate the optimal reaction path,and the nucleation process of the clusters is analyzed by calculating the excited state energy,wavelength and oscillator frequency of different number of TiO₂ molecular clusters.And by analyzing the LOMO and HOMO orbits of electrons in the clustering process,and analyzing the charge transfer in the clustering process,different molecular cluster structures have different charge distribution laws and cluster energies.