Abstract In this report, a flame spray pyrolysis setup has been examined with various in situ extraction methods of particle samples along the flame axis. First, two precursor formulations leading to the formation of iron oxide nanoparticles were used in a standardized SpraySyn burner system, and the final particle outcome was characterized by a broad range of established powder characterization techniques (TEM/HRTEM, SAXS, XRD, BET). The characterization of the powder products evidenced that mostly homogeneous gas-to-particle conversion takes place when applying an acidic precursor solution, whereas the absence of the acid leads to a dominant droplet-to-particle pathway. Our study indicates that a droplet-to-particle-pathway could be present even when processing the acidic formulation. However, even if a secondary pathway might take place in this case as well, it is not dominant and nearly negligible. Subsequently, the in situ particle structure evolution was investigated for the dominant gas-to-particle pathway, and particles were extracted along the flame axis for online SMPS and offline TEM/HRTEM analysis. Due to the highly reactive conditions within the flame (high temperatures, turbulent flow field, high particle number concentrations), the extraction of representative samples from spray flames is challenging. In order to handle the reactive conditions, two extraction techniques were tailored in this report. To extract an aerosol sample within the flame for SMPS measurement, a Hole in a Tube probe was adjusted. Thus, the mobility particle diameter as well as the corresponding distribution widths were obtained at different heights above the burner along the flame axis. For TEM/HRTEM image analysis, particle samples were collected thermophoretically by means of a tailored shutter system. Since all sampling grids were protected until reaching the flame axis and due to the low sampling time, momentary captures of local particle structures could be extracted precisely. The particle morphologies have clearly shown an evolution from spherical and paired particles in the flame center to fractal and compact agglomerates at later synthesis stages.

中文翻译：

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通过定制的原位颗粒取样技术检查火焰喷雾热解中氧化铁纳米颗粒的演变

摘要在本报告中，火焰喷雾热解装置已通过沿火焰轴的颗粒样品的各种原位提取方法进行了检查。首先，在标准化的 SpraySyn 燃烧器系统中使用了两种导致氧化铁纳米粒子形成的前体配方，最终粒子结果通过广泛的已建立的粉末表征技术（TEM/HRTEM、SAXS、XRD、BET）进行表征。粉末产品的表征证明，当应用酸性前体溶液时，大部分均质的气体到颗粒的转化发生，而没有酸导致主要的液滴到颗粒途径。我们的研究表明，即使在处理酸性配方时，也可能存在液滴到颗粒的途径。然而，即使在这种情况下也可能发生次要途径，它也不是占主导地位的，几乎可以忽略不计。随后，研究了主要气体到粒子路径的原位粒子结构演变，并沿火焰轴提取粒子用于在线 SMPS 和离线 TEM/HRTEM 分析。由于火焰内的高反应条件（高温、湍流流场、高粒子数浓度），从喷雾火焰中提取代表性样品具有挑战性。为了处理反应条件，本报告定制了两种提取技术。为了在火焰内提取气溶胶样品以进行 SMPS 测量，调整了管探针中的孔。因此，沿火焰轴线在燃烧器上方不同高度处获得了流动性粒径以及相应的分布宽度。对于 TEM/HRTEM 图像分析，通过定制的快门系统以热泳方式收集颗粒样品。由于所有采样网格在到达火焰轴之前都受到保护，并且由于采样时间短，因此可以精确提取局部粒子结构的瞬时捕获。粒子形态清楚地显示了从火焰中心的球形和成对粒子到后期合成阶段的分形和致密团聚体的演变。由于所有采样网格在到达火焰轴之前都受到保护，并且由于采样时间短，因此可以精确提取局部粒子结构的瞬时捕获。粒子形态清楚地显示了从火焰中心的球形和成对粒子到后期合成阶段的分形和致密团聚体的演变。由于所有采样网格在到达火焰轴之前都受到保护，并且由于采样时间短，因此可以精确提取局部粒子结构的瞬时捕获。粒子形态清楚地显示了从火焰中心的球形和成对粒子到后期合成阶段的分形和致密团聚体的演变。