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

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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.