Li, Haipeng
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Item-typ:Veröffentlichung, Flame spray pyrolysis for synthesizing functional nanoparticles: Fundamental investigations on single and double droplet combustion(2021-11-12); ; ; In this thesis ‘‘Flame spray pyrolysis for synthesizing functional nanoparticles: Fundamental investigations on single and double droplet combustion’’, experimental studies on droplet combustion and explosions to fundamentally understand the particle formation from liquid droplets and droplet interactions in the nanofabrication process of flame spray pyrolysis (FSP) are shown. FSP is one promising and versatile flame aerosol technique for fast synthesis of functional and engineering nanomaterials. This gas-phase synthesis nanomaterial process is famous and attractive for its reproducibility and scalability, and thus has potential applications for commercial scale-up production in industry. Gas-to-particle conversion and droplet-to-particle conversion are two particle formation routes in FSP, which decide the quality of produced particles. The particle formation mechanism is associated with the mass transfer of the precursor from liquid droplet to gas phase. Therefore, it is necessary and important to investigate droplet combustion behavior of precursor solutions, for providing fundamental insights into the mechanisms of droplet combustion and particle formation in FSP. The focus of this work is divided into three parts. Single droplet combustion and FSP synthesis of iron oxide nanoparticles using low- and high-volatility precursors were done, aiming to investigate the mechanism and occurrence condition of droplet micro-explosions, nanoparticle formations in single droplet combustion and FSP, as well as the promotion of homogeneous nanoparticle synthesis from low-volatility precursors. The influences of precursor choices, precursor concentrations and solvent compositions on droplet combustion behaviors, rainbow signals and the synthesis of iron oxide particles were experimentally investigated. The mechanism and occurrence conditions of droplet micro-explosions were discussed and summarized, which could be used to trigger explosions of droplets containing metal nitrates. The synthesized particles were characterized using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), as well as low- and high-resolution transmission electron microscopy (TEM and HRTEM) techniques. The similarity of nanoparticles prepared from single droplet combustion and FSP was explained. It is found that the secondary-atomization of droplets induced by micro-explosions efficiently promotes the production of homogeneous nanoparticles. Three-dimensional measurements of double droplet combustion of the pure solvent and the precursor solution were conducted, targeting to study the influence of a neighboring droplet on combustion behaviors (droplet interactions), and the occurrence of double droplet explosions. The developed three-dimensional measurement technique using two highly time-synchronized high-speed cameras could provide highly time-resolved information including droplet diameters, flame diameters, droplet 3D trajectories, droplet 3D velocities, and the center distances between the two burning droplets. Droplet interactions in the pure oxygen atmosphere as well as in the mixture of oxygen and nitrogen atmosphere were investigated. Droplet micro-explosions were first observed during double droplet combustion experiments of precursor solutions. The occurrence of double droplet explosions is affected by droplet interactions. Digital in-line holography measurements of single droplet combustion were performed, and the focus is to detect the size of non-burning droplets and to estimate the refractive index gradient surrounding the burning droplet. The constructed experimental setup and the developed imaging processing method are able to obtain clear hologram signals. The developed methods for hologram formation and numerical reconstruction have shown their abilities to detect droplet size. The influence of the surrounding flame on hologram signals are experimentally identified, which is proposed to estimate the refractive index gradient surrounding burning droplets. This thesis shows the capability of using droplet combustion experiments to provide fundamental information of droplet combustion, explosion and interaction for FSP. These investigations could be used to explore low-cost precursor-solvent systems for producing homogeneous nanoparticles, to figure out the interaction between burning droplets, as well as to understand the droplet flame.Dissertation568 278 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Rare-Earth-Doped Y4Al2O9 Nanoparticles for Stable Light-Converting Phosphors(American Chemical Society, 2019-12-24); ; ; ; The ternary mixed metal oxides with high specific surface area are industrially important for sensors, catalysis, energy storage, and optoelectronics. However, synthesis of such metal oxides is always challenging, especially when multicomponent mixtures occur due to very narrow formation temperature windows. Flame spray pyrolysis is one of the best known techniques which enable formation of pure phases optimizing the temperature profile via control over the fuel/oxidizer ratio. Here, Y4Al2O9 (monoclinic phase of yttrium aluminum oxide, also known as YAM) and Y4–xEuxAl2O9 (x = 0.05–1.0) were strategically synthesized with specific precursor–solvent chemistry. While the hydrated yttrium nitrate with 28.2% water was unsuitable for the formation of crystalline Y4Al2O9 particles, the use of organic precursor–solvent combinations (Y/Al 2:1) resulted in 16 nm phase pure, highly crystalline Y4Al2O9 particles. All the materials were characterized by using X-ray diffraction with Rietveld refinement, Raman spectroscopy, and transmission electron microscopy. To develop a stable light-converting phosphor, the Y4Al2O9 host was doped with Eu to investigate the photoluminescence properties of Y4–xEuxAl2O9 (x = 0.05–1.0). The results indicated increased photoluminescence intensity with increasing Eu3+ concentration up to x = 0.5, i.e., Y3.5Eu0.5Al2O9, and a subsequent drop or decrease in intensity for x ≥ 0.7. Hence, Y3.5Eu0.5Al2O9 is proposed for a potential light-converting phosphor.Wissenschaftlicher ArtikelBand:3Heft:116 10 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Reference data set for three-dimensional measurements of double droplet combustion of p-xyleneIn order to provide fundamental information for droplet interactions in the versatile and promising flame spray pyrolysis (FSP) technique, double droplet combustion experiments of p-xylene have been conducted via an improved piezoelectric droplet-on-demand generator. Using a steel nozzle plate with two laser-drilled nozzles, the generator can simultaneously generate two upwards-flying droplets with initial diameters of around 100 µm. A three-dimensional (3D) measurement technique using two time-synchronized high-speed cameras has been developed to detect double droplet combustion processes. Droplet diameters, flame diameters, droplet 3D trajectories, droplet 3D velocities, and the center distances between the two burning droplets are highly time-resolved measured, and then visualized via 3D videos and images. Flame spacing, as a new definition, is proposed to describe the interactions between the two flame fronts. The influences of the flame spacing and the oxygen concentration in the ambience on double droplet combustion were experimentally investigated. The obtained 3D data can serve as an ideal validation case for modeling and simulating droplet interactions during combustion as well as a highly time-resolved reference data set in the future.Wissenschaftlicher ArtikelBand:38Heft:216 17