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

本项目旨在开发用于纳米颗粒火焰合成过程中温度和浓度成像的双线原子荧光(TLAF)光学测量技术。这些工艺用于从具有特定物理和化学性质的气相中生产各种功能纳米颗粒，它们代表了一种多功能和成本效益高的制造工艺。火焰内部的温度-时间分布是影响颗粒大小、形态和结晶度等颗粒特性的最重要因素之一。因此，关于这种火焰中温度分布的详细信息对于这些性质的调整是特别重要的，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粒子存在的很大影响(例如拉曼散射)，仅限于逐点测量(例如CARS光谱)，或者需要显著的时间积分(例如傅里叶变换红外光谱)。因此，在非稳定火焰和特别是湍流火焰中使用时，例如在通用的火焰喷雾热解过程中，不可能检测到它们的温度分布。本项目将克服这些限制。在这里，已经成功地用于燃烧火焰的TLAF技术将得到进一步发展，并首次直接应用于纳米颗粒的火焰合成过程的研究。在项目的第一阶段，这项工作将集中在基于铟的粒子系统上。选择铟一方面是因为这种材料由于其优越的光学性质已经被用于温度测量的其他应用，另一方面是因为如此生产的材料铟(III)-氧化物(In2O3)具有很高的技术和经济相关性。除了测量火焰中的温度分布外，还将测量火焰中铟原子的浓度分布。目前，人们使用染料激光器、窄带二极管激光器或顺序激发的光学参量振荡器(OPO)来获得激发铟所需的波长。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。利用窄带半导体激光器实现固体激光器的波长稳定，可以同时实现高激光能量和窄线宽。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基于铟的颗粒系统之后，将在该项目的第二阶段实施对其他材料的扩展。

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.