Investigation of the interaction of precursor and flame chemistry

喷雾火焰合成纳米颗粒的详细数值和实验研究正在进入化学领域的“未知领域”。对火焰至关重要的物质（尤其是自由基）与金属原子和前驱体分解中间体的相互作用的理解正在缓慢增长，迄今为止只对少数材料系统进行了研究。这种相互作用的研究和机理描述是本项目的目标，也是正确模拟喷射火焰合成反应流动系统的基本前提。一个特殊的挑战是前体相互作用的研究，前体-如SPP -不能预蒸发，而是溶解在液滴中。为此，开发了一种矩阵燃烧器，它允许在层流中以尽可能简单的几何形状研究化学过程，即使是与喷雾形成、蒸发和湍流隔离的溶液基前驱体。通过分子束技术（飞行时间质谱法和粒子质谱法）和光学方法研究了在低压下操作会产生空间扩展的火焰。为了量化采样和浮力效应引起的扰动，实验伴有流动模拟。从第一个项目期间的工作中产生了一个额外的问题：许多前体需要使用燃料混合物作为溶剂，一方面防止（或控制）液滴中的沉淀，另一方面支持传质。在这里，迄今为止没有燃烧机制可用的溶液成分（例如乙基己酸或二醇）已被证明是有效的。对于这些燃料，必须开发燃烧机制-最初独立于前体-并根据火焰速度测量进行优化。第一周期的结果表明，前驱体和溶剂的初始衰变步骤通常可以通过优化的全局反应很好地映射出来。另一方面，高温动力学由详细的或骨架的子机制来表示，这些子机制也描述了与金属氧化物中间体的相互作用。在铁掺杂火焰研究的基础上，利用文献数据和新的实验，开发和优化了碱土金属与铈的相互作用机制。掺铁火焰的机理将根据数据情况不断验证和重新优化。简化（骨架）反应机制的发展为流动模拟的合成过程，这取决于直接解决的反应动力学。简化方法是基于遗传算法的，遗传算法也用于开发和优化，但具有一组适合问题的优化目标和公差。保存火焰自由基与金属氧化物中间体之间的相互作用机制是至关重要的。

The detailed numerical and experimental investigation of spray flame synthesis of nanoparticles is entering "uncharted territory" in chemistry. The understanding of the interaction of the species crucial for the flame (especially radicals) with metal atoms and precursor decomposition intermediates is growing slowly and has been studied for only a few materials systems so far. The investigation and mechanistic description of this interaction is the goal of this project and a basic prerequisite for the physically correct simulation of the reactive flow systems of spray flame synthesis.A special challenge is the investigation of the interaction in precursors, which - as in SPP - cannot be pre-evaporated but are present dissolved in droplets. For this purpose, a matrix burner was developed, which allows the chemical processes to be investigated in a laminar flow with the simplest possible geometry, even for solution-based precursors isolated from spray formation, evaporation, and turbulence. Operation at low pressure results in a spatially extended flame, which is investigated by molecular beam techniques (time-of-flight mass spectrometry and particle mass spectrometry) and optical methods. To quantify disturbances caused by sampling and buoyancy effects, the experiments are accompanied by flow simulations.An additional question has arisen from the work in the first project period: Numerous precursors require the use of fuel mixtures as solvents to prevent (or control) precipitation in the droplet on the one hand and to support mass transfer on the other hand. Here, solution components for which no combustion mechanisms have been available so far (e.g. ethylhexanoic acid or diols) have proven to be effective. For these fuels, combustion mechanisms must be developed - initially independently of the precursors - and optimized on the basis of flame velocity measurements.The results of the first period show that the initial decay steps of the precursor and solvents can often be well mapped by optimized global reactions. The high-temperature kinetics, on the other hand, are represented by detailed or skeletal sub-mechanisms, which also describe the interaction with the metal oxide intermediates. Based on the work on iron-doped flames, the interaction mechanisms for alkaline earth metals and for cerium are developed and optimized using literature data and new experiments. The mechanism for the iron-doped flames will be continuously validated and re-optimized depending on the data situation.Reduced (skeletal) reaction mechanisms are developed for the flow simulations of the synthesis process, which depend on a direct solution of the reaction kinetics. The reduction methodology is based on genetic algorithms which are also used for development and optimization, but with a set of optimization targets and tolerances adapted to the problem. It is crucial that the interaction mechanisms between the flame radicals and metal oxide intermediates are preserved.