Mass spectrometric characterization of the precursor chemistry and particle growth in flame reactors

在火焰反应器中由气态前驱体生成纳米颗粒是由火焰化学和前驱体化学复杂的相互作用控制的。反应条件和不同前驱体的选择会影响颗粒的粒径和其他与粒径有关的性质。子项目TP2的目标是研究在火焰合成二氧化硅和氧化铁纳米颗粒过程中前体分子向负责纳米颗粒生长的中间体的转化。过程的控制变量，如温度或自由基浓度，是通过改变火焰条件来确定的。在与TP1和TP8的合作中，这些数据被用于开发和验证在可扩展工艺中控制合成具有定制性能的复杂纳米颗粒所需的反应机制。在TP2中，火焰中的中间体使用分子束质谱（MBMS）进行鉴定。在第二个资助期，系统地应用先前开发的MBMS程序来研究火焰条件对选定含硅前驱体分解的影响。此外，火焰离子MBMS技术也得到了实质性的改进。通过这种方法，首次可以对Fe(CO)5在火焰中形成的铁中间体的氧化态过程进行追踪。根据实验数据，建立了反应机理。基于这些结果和迄今为止所获得的知识，纳米颗粒如何在火焰中形成的扩展图景出现了，这在某些方面不同于文献中公认的观点。综上所述，我们已经观察到，沿着前驱体分解和中间小分子与火焰物质反应的反应途径，可以形成蒸汽压很低的化合物，并凝结成颗粒。这种早期粒子形成的证据在铁和硅体系中都观察到了。它与文献中描述的后期反应步骤中的颗粒形成不同，化学反应最初是由小分子形成簇，然后进一步反应或凝聚成颗粒。FOR 2284在第三个项目期间的首要目标是通过淬火和涂层来稳定这些早期颗粒相，并使其可用。TP2的工作通过确定早期颗粒形成区域或条件以及获得涂层中使用的前驱体的动力学数据来支持这一目标。这些包括HMDSO， TEOS和四甲基锡。离子MBMS技术可用于分子和簇的测量，它补充了TP3和TP4中颗粒相的测量。还将测试是否有可能通过热淬火过程终止颗粒形成反应。

The generation of nanoparticles from gaseous precursors in flame reactors is governed by the complex interaction of flame chemistry and precursor chemistry. The particle size and other size-dependent properties of the particles can be influenced by the reaction conditions and the choice of different precursors. The goal of subproject TP2 is to investigate the conversion of precursor molecules to the intermediates responsible for nanoparticle growth during the flame synthesis of silica and iron oxide nanoparticles. Control variables for the process, such as temperature or radical concentrations, are identified by varying the flame conditions. In cooperation with TP1 and TP8, the data are used to develop and validate the reaction mechanisms needed for a controlled synthesis of complex nanoparticles with tailored properties in scalable processes.In TP2, the intermediates in the flames are identified using molecular beam mass spectrometry (MBMS). In the second funding period, the previously developed MBMS routines were systematically applied to study the influence of flame conditions on the decomposition of selected silicon-containing precursors. In addition, the flame ion MBMS technique was substantially improved. In this way, the progression of the oxidation state of iron intermediates formed in flames from Fe(CO)5 could be traced for the first time. Based on the experimental data, reaction mechanisms were developed. Based on the results and the knowledge gained so far, an expanded picture of how nanoparticles are formed in flames emerges, which in some aspects differs from the accepted view in the literature. In summary, it is observed that already along the reaction pathways of precursor decomposition and the reactions of small intermediate molecules with flame species, compounds with a very low vapor pressure can be formed that condense into particles. Evidence of this early particle formation is observed in both the iron and silicon systems. It differs from particle formation in later reaction steps described in the literature, where chemical reactions initially form clusters from small molecules that then further react or condense into particles. An overarching goal of FOR 2284 in the third project period is to stabilize these early particle phases by quenching and coating and to make them usable. The work in TP2 supports this goal by identifying the early particle formation zones or conditions and by obtaining kinetic data for precursors used in coatings. These include HMDSO, TEOS and tetramethyl tin. The ion MBMS technique is available for the measurement of molecules and clusters and it complements the measurements of the particle phase in TP3 and TP4. It will also be tested whether it is possible to terminate the particle formation reactions by a thermal quenching process.