Development of Two-Line Atomic Fluorescence for 2D-Temperature Measurement in the Flame Synthesis of Nanoparticles

本计画旨在发展双谱线原子荧光（TLAF）光学量测技术，以量测奈米粒子火焰合成过程中的温度与浓度影像。这些工艺用于从气相中生产具有特定物理和化学性质的各种功能性纳米颗粒，它们代表了一种通用且具有成本效益的制造工艺。火焰内的温度-时间曲线是影响颗粒性质如颗粒尺寸、形态和结晶度的最重要因素之一。因此，有关在这种火焰中的温度分布的详细信息是特别感兴趣的这些属性的调整，并作为数值模拟的基础。现有的火焰合成过程中的温度测量方法受到颗粒存在的巨大影响（例如，拉曼散射），局限于逐点测量（例如，汽车光谱）或需要显著的时间积分（例如，傅立叶变换红外光谱）。因此，不可能检测不稳定火焰，特别是湍流火焰中的温度分布，因为它们用于例如可广泛应用的火焰喷雾热解过程。在这里，TLAF技术，这是已经成功地用于炭黑火焰，将进一步发展，并首次直接应用于纳米粒子的火焰合成过程的调查。在该项目的第一阶段，工作将侧重于铟基粒子系统。选择铟一方面是因为该材料由于其有利的光学性质已经用于温度测量的其他应用中，另一方面是因为如此生产的材料氧化铟（III）（In 2 O3）的高技术和经济相关性。火焰中铟原子的浓度分布除了温度分布的测量外，还将被确定。到目前为止，染料激光器、窄带二极管激光器或顺序激励光学参量振荡器（OPO）被用来获得铟原子激发所需的波长。本方法的一个显著优点是准同时使用两个OPO。因此，湍流火焰的时间分辨率是可能的。通过使用窄带二极管激光器来稳定固态激光器的波长，可以同时实现高激光能量和窄光谱线宽。这种方法产生了足够高的荧光信号，用于二维单次信号检测，在成功地开发和应用本技术到铟基粒子系统之后，将在项目的第二阶段扩展到其他材料。

This project aims at the development of the optical measurement technique of two-line atomic fluorescence (TLAF) for temperature and concentration imaging in flame synthesis processes of nanoparticles. These processes are used to produce various functional nanoparticles from the gas phase with defined physical and chemical properties, and they represent a versatile and cost-effective manufacturing process. The temperature-time profile within the flame is one of the most important factors that influence particle properties such as particle size, morphology and crystallinity. Therefore, detailed information concerning the temperature distribution in such flames is of specific interest for the adjustment of these properties and serves as a basis for numerical simulations. Existing approaches for temperature measurement in flame synthesis processes are massively influenced by the presence of particles (e.g. Raman scattering), limited to pointwise measurements (e.g. CARS spectroscopy) or require a significant temporal integration (e.g. Fourier-transformed infrared spectroscopy). Therefore it is not possible to detect a temperature distribution in unsteady and especially turbulent flames as they are used e.g. in the versatilely applicable flame spray pyrolysis process.The present project shall overcome these limitations. Here, the TLAF technique, which is already successfully used in sooting flames, will be further developed and for the first time directly applied for the investigation in flame synthesis processes of nanoparticles. In a first phase of the project, the work will focus on indium-based particle systems. Indium is chosen on the one hand as this material is already used in other applications for temperature measurement due to its advantageous optical properties and on the other hand because of the high technical and economical relevance of the so produced material indium-(III)-oxide (In2O3). Concentration distributions of atomic indium in the flame will be determined additionally to the measurement of temperature distributions.Up to now dye lasers, narrowband diode lasers or sequentially exited optical parametric oscillators (OPO) are used to achieve the required wavelengths for the excitation of indium. One significant advantage of the present approach is the quasi-simultaneous usage of two OPOs. Thereby a temporal resolution of turbulent flames is possible. High laser energies and a narrow spectral linewidth can be realized at the same time by usage of narrowband diode lasers for wavelength stabilization of solid-state lasers. This approach results in sufficiently high fluorescence signals for a two-dimensional single-shot signal detection.After successful development and application of the present technique to indium-based particle systems an extension to other materials shall be implemented in a second phase of the project.