Micro-exploding metal particles and formation of oxide nanoparticles:Development of in situ imaging techniques and advanced morphological image analysis

金属颗粒的微爆炸和氧化物纳米颗粒的形成：原位成像技术和先进形态图像分析的发展

• 批准号: 517038121
• 负责人: Dr. Niklas Jüngst
• 金额: --
• 依托单位: Department of Physics
• 依托单位国家: 德国
• 项目类别: WBP Fellowship
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/517038121?language=en
• 关键词: Micro; exploding; metal; particles; formation

Combustion of metal powders and subsequent reduction will contribute to a zero-carbon generation and storage of heat and electricity. Metal powders have a high volumetric energy density, making them more economical to transport than batteries or hydrogen. However, laboratory-scale experiments show fragmentation (also known as micro-explosion) of metal particles during combustion. This can produce metal- and metal-oxide vapor as well as metal-oxide nanoparticles. The latter are easily lost to the environment, posing health risks and impeding recycling. To better understand and control metal-particle micro-explosion and the associated phenomena, in situ diagnostics with very high spatio-temporal resolution are needed. In this project, optical imaging and image-analysis techniques will be developed and used towards two goals, (1) a detailed analysis of the micro-explosion itself, and (2) visualizing the potential metal-oxide nanoparticles produced by those. In the first step it is determined, under what conditions (e.g., ambient oxygen concentration, particle size, and gas temperature) micro-explosions occur, and if they do occur, how often, where, and when in the flame they occur. The second step is to develop an imaging measurement technique to visualize oxide nanoparticles near the fragmenting metal particles. Candidate techniques include elastic light scattering (ELS), laser-induced incandescence (LII), and phase-selective laser-induced breakdown spectroscopy (ps-LIBS). An important figure of merit in the development is how well signal contributions by the large metal particle and its fragments can be rejected. The studies are performed in a modified flat flame burner. A dispersion of metal powder and hydrogen flows through a central opening of the sintered matrix and ignites in a non-premixed flame. A microscope images the shadowgraphs of the fragmenting particles on a high-speed camera. Explicitly programmed and neural-network-based image analysis is used to process the images, to distinguish fragmenting and non-fragmenting particles, and extract their size, shape, and velocity. For ELS, selected geometric illumination-detection arrangement are tested to best suppress the scattered light from the large metal particle. For LII, the spectral excitation-detection-scheme and the choice of laser fluence are critical. Ps-LIBS needs to be optimized such that the laser excitation does not lead to significant ablation of the metal particle or breakthrough of the gas phase while detecting oxide nanoparticles with sufficient signal-to-noise ratio.

金属粉末的燃烧和随后的减少将有助于零碳发电和热量和电力的储存。金属粉末的体积能量密度很高，这使得它们的运输比电池或氢气更经济。然而，实验室规模的实验表明，金属颗粒在燃烧过程中发生破碎(也称为微爆炸)。这会产生金属和金属氧化物蒸气以及金属氧化物纳米颗粒。后者很容易流失到环境中，构成健康风险，阻碍回收。为了更好地理解和控制金属颗粒微爆炸及其相关现象，需要具有很高时空分辨率的现场诊断。在这个项目中，光学成像和图像分析技术将被开发并用于两个目标，(1)详细分析微爆炸本身，以及(2)可视化由其产生的潜在的金属氧化物纳米颗粒。在第一步中，确定在什么条件下(例如，环境氧浓度、颗粒大小和气体温度)发生微爆炸，如果确实发生微爆炸，则确定它们在火焰中发生的频率、地点和时间。第二步是开发一种成像测量技术，以可视化破碎的金属颗粒附近的氧化物纳米颗粒。候选技术包括弹性光散射(ELS)、激光诱导白炽光(LII)和位相选择性激光诱导击穿光谱(PS-LIBS)。开发中的一个重要指标是大金属粒子及其碎片的信号贡献可以被拒绝的程度。研究是在改装的平焰燃烧器上进行的。金属粉末和氢气的分散体流经烧结体的中心开口，并在非预混火焰中点火。显微镜在高速摄像机上拍摄碎裂颗粒的阴影图。显式编程和基于神经网络的图像分析用于处理图像，以区分破碎和非破碎颗粒，并提取它们的大小、形状和速度。对于ELS，测试了选定的几何照明-检测布置，以最好地抑制来自大金属颗粒的散射光。对于LII，光谱激发-检测方案和激光通量的选择是关键。PS-LIBS需要进行优化，以便在检测具有足够信噪比的氧化物纳米颗粒时，激光激励不会导致金属颗粒的显著烧蚀或气相的突破。