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

点击翻译按钮获取中文摘要

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.