Phase-specific optical in situ detection of iron-based nanoparticle aerosols

氧化铁以不同的晶相存在，具有明显不同的物理性质。气相纳米颗粒合成是一种很有前途的方法，通过改变温度曲线和氧化物质的浓度，有望产生具有有用的催化或磁性的特定材料相。然而，到目前为止，还没有办法在反应器中形成过程中原位确定FexOy的相（以及因此FexOy的组成），并且单独分析产物是不够的，因为最终产物的途径仍然不清楚。在这个项目中，我们将开发一种方法，利用不同的氧化铁相（磁铁矿（Fe 3 O 4）：深棕色，赤铁矿（α-Fe 2 O3）：红色，磁赤铁矿（γ-Fe 2 O3）：红棕色）和金属铁纳米颗粒（灰色）的独特光学特性，使其形成过程中的各个阶段的定量原位测量。纳米颗粒气溶胶的相位相关光学性质导致特定的光谱吸收和热发光。光谱特性将使用气溶胶化的非原位表征模型材料进行分析。然后将新方法应用于在微波等离子体反应器中使用五羰基铁作为前体产生的纳米颗粒气溶胶，根据添加的氧气，从金属到完全氧化。在轴对称流中的吸收和发射测量的数据分析支持从空间1维分辨的吸收和发射测量的层析重建。基于激光的方法（LIBS和拉曼）支持原位测量。所得到的纳米粒子相的原位检测方法将支持过程的理解和设计，并使从经验试错法到有针对性的合成的步骤。

Iron oxide exists in different crystal phases with distinctly different physical properties. Gas-phase nanoparticle synthesis is a promising method promising for producing specific material phases with useful catalytic or magnetic properties by varying the temperature profile and concentration of the oxidizing species. To date, however, there is no way to determine the phase (and thus the composition of FexOy) in situ during their formation in the reactor, and analysis of the product alone is not sufficient because the pathways to the final product remain unclear. In this project, we will develop an approach that takes advantage of the distinct optical properties of different iron oxide phases (magnetite (Fe3O4): dark brown, hematite (alpha-Fe2O3): red, maghemite (gamma-Fe2O3): reddish brown) and metallic iron nanoparticles (gray) to enable quantitative in situ measurements of the respective phases during their formation. The phase-dependent optical properties result in specific spectral absorption and thermal light emission in nanoparticle aerosols. The spectral properties will be analyzed using aerosolized model materials characterized ex situ. The new method is then applied to nanoparticle aerosols that are produced in a microwave plasma reactor using iron pentacarbonyl as precursor, ranging from metallic to fully oxidized depending on the oxygen added. Data analysis of absorption and emission measurements in axially symmetric flows is supported by tomographic reconstruction from spatially 1-dimensional resolved absorption and emission measurements. The in situ measurements are supported by laser-based methods (LIBS and Raman). The resulting method for in situ detection of nanoparticle phases will support process understanding and design and enable the step from empirical trial-and-error approaches to targeted synthesis.