Precursor release in nanoparticle producing spray flames: Single droplet investigation of multicomponent mass transfer (within SPP 1980)

SPP的目的是对整个火焰喷雾热解过程进行基本的理解和理论建模。要建立这样一个喷雾火焰合成纳米颗粒的预测过程模型，需要了解许多方面和机理。包括从液滴相到气相的多组分传质，以及包括氧化物形成、成核、冷凝、凝聚、聚合和烧结在内的颗粒生长。在第一个项目阶段，我们可以证明液滴微爆炸效应对利用火焰喷雾热解前驱体制备纳米颗粒的均匀性的重要性。微爆炸特别被发现是在工业中利用廉价氮化物前体的一个重要机制。在最后一个项目阶段，单液滴实验取得了很大进展，这表明微爆炸对有效生产均质纳米粒子具有重要意义。对不同前驱体-溶剂体系的燃烧和颗粒合成进行了实验研究，推导了液滴微爆炸的概念性机理。为了研究双液滴燃烧和微爆炸，研制了一种新的双液滴发生器和基于两个时间同步高速摄像机的三维测量技术。利用彩虹折射仪测量了前驱体/溶剂液滴单液滴燃烧过程中液滴温度和组成的变化。建立了一个多组分扩散限制模型来推算内部温度和浓度分布。搭建了数字同轴全息实验装置。对非燃烧液滴进行了全息成像和数值再现。对前驱体溶液的单液滴燃烧进行了初步的全息实验。首次测量了单个孤立微爆燃烧液滴在液滴表面以上的发光火焰位置(火焰阻隔率)。我们项目提案的主要目标是通过单液滴实验研究火焰喷雾热解过程中微爆炸在有效合成纳米粒子过程中的机理和作用。为了实现这一目标，我们将拓宽我们的分析工具，开发和集成用于单液滴实验的化学发光、测温、激光诱导荧光技术。我们将与SPP的其他研究小组密切合作，为前体从液滴释放到气相的多组分传质模型开发和提供验证数据，其中包括前体分解、气泡成核、壳层形成、液滴微爆炸和向气相的质量传递。

The aim of the SPP is a fundamental understanding and theoretically modelling of the entire flame spray pyrolysis process. To develop such a predictive process model for the spray flame synthesis of nanoparticles requires the understanding of many aspects and mechanisms. These include the multicomponent mass transfer from the liquid droplet phase to the gas phase and particle growth that includes oxide formation, nucleation, condensation, coagulation, coalescence and sintering.In the first project phase we could demonstrate the importance of the droplet micro-explosion effect on the homogeneity of nanoparticle production using flame spray pyrolysis precursors. Micro-explosions were especially found to be a vital mechanism for utilizing cheap nitride precursors in industry. In the last project phase strong progress was achieved in single droplet experiments that show the great importance of micro-explosions for effective production of homogeneous nanoparticles. The combustion and particle synthesis of different precursor-solvent systems were experimentally investigated and conceptual mechanism of droplet micro-explosion were deduced. A new double droplet generator and a 3D measurement technique using two time-synchronized high-speed cameras were developed to study double droplet combustion and micro-explosions. Rainbow refractometry was used to measure droplet temperature and composition changes during single droplet combustion of precursor/solvent droplets. A multicomponent diffusion limited model was developed to infer the internal temperature and concentration profiles. The experimental setup of digital in-line holography was constructed. The hologram formation and numerical reconstruction of non-burning droplets were developed. Preliminary holography experiments on single droplet combustion of precursor solutions were conducted. For the first time the luminous flame position above the droplet surface (flame standoff ratio) of single isolated burning droplets with micro-explosions was measured. The primary goal of our project proposal is to study the mechanism and role of micro-explosions in effective synthesis of nanoparticles in the flame spray pyrolysis process using single droplet experiments. To achieve this goal, we will broaden our analysis tools and develop and integrate chemiluminescence, pyrometry, laser-induced fluorescence techniques for single droplet experiments. In close collaboration with other research groups of the SPP we will develop and provide validation data for multicomponent mass transfer models for the precursor release from droplets into the gas phase that includes precursor decomposition, bubble nucleation, shell formation, droplet micro-explosions and mass transfer into the gas phase.