火焰合成TiO2纳米颗粒的相变机理及晶型调控研究

This project aims to investigate the phase transformation kinetics during the process of flame synthesis TiO2 nanoparticles, from the perspective of mesoscopic particle scale. Break through the powder particle limitation that existed in traditional phase transformation kinetic investigations, this work focuses on highly dispersed aerosol particles. The size of single particle and aggregate, surface area and phase compositions are directly analyzed, which greatly improves the experimental precision. Moreover, the size effect of phase transformation can be fully considered as well as the effects of particle aggregation and sintering on phase transformation. Based on the systematically designed experiments, advanced measurement and characterization techniques, and reliable data analysis methods, attentions will be lay on single particle thermodynamic phase transformation and aggregate sintering induced phase transformation. Effect of thermodynamic item in the kinetic rate equation will be considered. Using the surface free energy released by particle sintering acts as the driving force of phase transformation, general dynamic model and parameters of the transformation from anatase to rutile can be established. Applying the obtained phase transformation model to PBMC, coupling with CFD, finally realize the tracking and prediction of multi-parameters (particle size, surface area and phase composition) during the process of flame synthesis TiO2 nanoparticles. On the basis of CFD-PBMC model based orthogonal experiments, the technological parameters can be designated and optimized. In this sense, scientific basis and technical proposal can be attained for process control and product functional design of flame synthesis TiO2 nanoparticles.

本项目旨在研究火焰合成TiO2纳米颗粒的相变动力学，在介观的颗粒层次上探究TiO2的相变机理。突破传统相变动力学研究采用粉末样品的局限，本项申请着眼于高度分散的气溶胶颗粒，直接分析单颗粒和团聚体的尺度、表面积和相组成，大幅度提高了实验的精准度，能够充分考虑相变的尺度效应，以及辨识颗粒团聚、烧结对相变的影响。基于系统的实验设计、先进的测量表征技术和可靠的数据分析方法，聚焦于单颗粒的热力学相变和团聚体的烧结诱导相变，在动力学速率方程中考虑热力学项的影响，颗粒烧结释放的表面自由能作为相变驱动力，构建锐钛矿向金红石转变的通用动力学模型及参数。将得到的相变模型应用于颗粒群平衡随机模拟(PBMC)，并与计算流体力学(CFD)耦合，实现火焰合成产品的多参数(颗粒尺度、表面积和相组成)跟踪和预测。基于CFD-PBMC模型的正交试验设计优化工艺参数，为火焰合成的过程控制和产品功能设计提供科学依据和技术方案。

本项目旨在研究火焰合成TiO2纳米颗粒的相变动力学，在介观的颗粒层次上探究TiO2的相变机理。提出TiO2纳米单颗粒缩核相变动力学模型，研究开发的CFD-PBMC模型能够准确有效地描述火焰流场和跟踪多个颗粒动力学过程，包括火焰的温度分布和速度分布，颗粒的成核、凝并、烧结和相变等。针对火焰合成过程的温度测量，研究热电偶结点和偶丝之间的非稳态传热过程，发现了偶丝对结点的热量补偿效应。提出单点时差双重热泳取样方法，针对火焰的辐射特性设计热泳探针，实现火焰合成纳米颗粒过程的多参数联合测量，包括火焰流速、颗粒尺度分布和分形维数等。研究稀释取样探头对火焰造成的干扰以及准确地定量稀释比，开发出了一种无水冷的双层折流同心管式取样探头。