He Ruitian, Luo Kai H
Department of Mechanical Engineering, University College London, Torrington Place, London WC1E 7JE, UK.
Shanghai Institute for Advanced Study, Zhejiang University, Shanghai 201203, China.
Nanoscale. 2024 Aug 29;16(34):16119-16126. doi: 10.1039/d4nr00592a.
Microexplosion has been extensively studied in the context of fuel spray and droplet evaporation in engines, while its existence, impact and atomistic insight have rarely been explored in the context of flame synthesis of nanoparticles. In this study, reactive force-field molecular dynamics simulations are performed to elucidate the mechanisms of pyrolysis and oxidation of an isolated lithium nitrate nanodroplet. During the pyrolysis process, the nucleation and growth of a bubble are observed inside the droplet, which should be ascribed to the release of nitrogen and oxygen gases from the decomposition of lithium nitrate, ultimately leading to rapid droplet fragmentation (microexplosion). To demonstrate the role of microexplosion with various intensities, altering ambient temperature and addition of oxygen gas into the environment, thorough analyses of bond reactions, droplet morphology and compounds of the synthesized lithium nanoparticles are carried out. With elevated ambient temperature, the droplet substantially expands due to bubble growth and the time required for droplet disruption is shortened, which implies the enhanced strength of microexplosion. Simultaneously, the connection between the lithium and other atoms becomes weak, as evidenced by a decrease in the number of lithium bonds. These give rise to a reduction in the quantity of large-sized lithium agglomerates and simultaneously an increase in the amount of fine lithium nanoparticles. To further clarify the reaction mechanism for a lithium-containing droplet under various ambient conditions, three reaction modes, , core-shell diffusion-controlled, microexplosion-accelerated and microexplosion-dominated, are distinguished based on the intensity of microexplosion and the quality of synthesized lithium nanoparticles. Fine lithium-containing nanoparticles are expected to be produced in the microexplosion-dominated mode under high temperature conditions.
微爆炸在发动机燃料喷雾和液滴蒸发的背景下已得到广泛研究，而在纳米颗粒火焰合成的背景下，其存在、影响和原子层面的见解却鲜有探索。在本研究中，进行了反应力场分子动力学模拟，以阐明孤立的硝酸锂纳米液滴的热解和氧化机制。在热解过程中，观察到液滴内部有气泡的成核和生长，这应归因于硝酸锂分解释放出的氮气和氧气，最终导致液滴迅速破碎（微爆炸）。为了证明不同强度微爆炸的作用，通过改变环境温度和向环境中添加氧气，对合成锂纳米颗粒的键反应、液滴形态和化合物进行了全面分析。随着环境温度升高，由于气泡生长，液滴大幅膨胀，液滴破裂所需时间缩短，这意味着微爆炸强度增强。同时，锂与其他原子之间的连接变弱，锂键数量减少证明了这一点。这些导致大尺寸锂团聚体数量减少，同时细锂纳米颗粒数量增加。为了进一步阐明不同环境条件下含锂液滴的反应机制，根据微爆炸强度和合成锂纳米颗粒的质量，区分了三种反应模式，即核壳扩散控制模式、微爆炸加速模式和微爆炸主导模式。在高温条件下，预计在微爆炸主导模式下会产生细的含锂纳米颗粒。
