Reactions of the precursors for spray-flame of nanoparticles during partial evaporation of the spray

喷雾火焰合成法是制备功能纳米材料的一种很有前途的方法。喷雾用于将低挥发性前体引入气相中。喷雾火焰的热结构和化学结构表明，在不同的火焰区，化学反应在实质上不同的反应条件下发生。本项目的工作集中在位于火焰中心的喷雾形成区的溶剂和前体的化学转化。在该区域中，仅达到低于1000 °C的中等温度，并且化学基质由氧气、溶剂和少量水和前体主导。喷雾形成和蒸发过程与溶剂和前体的化学转化相一致。 在喷雾火焰合成的这一子过程中的未决问题是在喷雾蒸发期间哪些反应发生在液相中，哪些反应发生在气相中。这些反应的反应产物影响随后的反应途径，包括纳米颗粒的形成途径。这些纳米颗粒通常通过两种主要的反应途径形成，液滴-颗粒途径和气体-颗粒途径。在第二个项目期间，将研究三个子过程：将通过电喷雾质谱法和气相色谱法对溶液的组成进行详细的化学分析，确定在缓慢加热液体溶剂/前体溶液期间发生的液相反应。该实验将确定哪些前体已经在液相中反应，即水解或氧化，并且可能通过不太有利的液滴至颗粒途径反应。将在管式反应器中研究喷雾部分蒸发过程中发生的反应。在这个简化的过程中，热前体反应与火焰中的自由基反应分离，取代了喷雾的点燃和随后的燃烧热的释放，通过反应器的外部加热。这些实验提供了关于前体和溶剂在喷雾蒸发过程中如何化学相互作用的信息，并确定了气相中存在的相互作用产生的中间体。随后的反应形成的中间体的前体与火焰气体将在一个组合良好的搅拌和活塞流反应器中进行研究。这些实验确定了从分子中间体到簇，然后到纳米颗粒的反应模式。所有实验都依赖于质谱诊断来进行物种识别和浓度测量。当使用盐溶液喷雾时，将使用特殊的取样和转移程序来识别带电物质。该项目的化学见解用于制定反应机理，并支持SPP内的全局火焰喷雾合成过程的模拟。

Spray-flame synthesis is a promising option for the production of functional nanomaterials. The spray is used to introduce low-volatility precursors into the vapor phase. The thermal and chemical structure of the spray flames indicates that chemical reactions occur at substantially different reaction conditions in the different flame zones.The work in this project concentrates on the chemical transformations of the solvent and the precursor in the spray formation zone which is located in the center of the flame. In this zone, only moderate temperatures below 1000 °C are reached and the chemical matrix is dominated by oxygen, the solvent and small amounts of water and precursor. Spray formation and evaporation processes coincide with chemical transformations of the solvent and precursors. Open questions in this sub-process of spray flame synthesis are which reactions happen in the liquid phase and which reactions occur in the gas phase during spray evaporation. The reaction products of these reactions influence subsequent reaction pathways, including the formation pathways of nanoparticles. Those nanoparticles will typically be formed by two main reaction pathways, the droplet-to-particle route and the gas-to-particle route. In the second project period, three sub-processes will be investigated: Liquid phase reactions that occur during slow heating of the liquid solvent/precursor solution will be identified through a detailed chemical analysis of the composition of the solution by electrospray mass spectrometry and gas chromatography. This experiment will determine which precursors already react, i.e. hydrolyze or oxidize, in the liquid phase and are likely to react by the less favorable droplet-to-particle route. Reactions occurring during the partial evaporation of the spray will be investigated in a tubular reactor. In this simplified process, the thermal precursor reactions are separated from radical reactions in the flame by replacing the ignition of the spray and subsequent release of combustion heat by external heating of the reactor. These experiments provide information on how the precursor and solvent interact chemically during the evaporation of the spray and identify the intermediates resulting from the interactions that are present in the gas phase. Subsequent reactions of the intermediates formed from the precursors with flame gases will be investigated in a combined well-stirred and plug-flow reactor. These experiments identify the reaction patterns that lead from molecular intermediates to clusters and then nanoparticles. All experiments rely on mass spectrometric diagnostics for species identification and concentration measurements. A special sampling and transfer procedure will be used to identify charged species when sprays of salt solutions are used.The chemical insights from this project are used to formulate reaction mechanism and support the simulation of the global flame spray synthesis process within the SPP.