Theoretical Single-Droplet Model for Particle Formation in Flame Spray Pyrolysis

Abstract

In the current work, we develop a single droplet model to describe particle formation in multicomponentliquid droplet combustion. Both the gas-to-particle conversion and droplet-to-particle conversion routes of different solution properties are investigated, together with the population balance model and the droplet drying model. For multi-component droplets without precursors, the droplet combustion is limited by the species diffusion in the liquid phase. The model can well predict the droplet shrinkage history observed by previous PDA measurements. For the precursor with a low boiling point than its thermal decomposition temperature, the precursor in the droplet can then transform into nanoparticles through the gas-to-particle conversion route. The population balance model reveals that the generated nanoparticle size relies on both the precursor mass fraction and the residence time, which is consistent with the vaporfed aerosol flame synthesis. For the precursor that tends to decompose or precipitate in the liquid, it then undergoes the droplet-to-particle conversion route. The droplet behavior can be classified by the ratio of droplet evaporation time and precursor reaction or precipitation time. For small droplets with short evaporation time, the nanoparticle formation obeys the one-droplet-one-particle rule. For large droplets with long evaporation time, the competition among precipitation, thermal decomposition, and evaporation determines the final nanoparticle morphology. The single droplet model established in this study can potentially guide the precursor design and be coupled with the turbulent flame simulation of the whole flame spray pyrolysis burner.

Structural Characterization of Ceria-Supported Pt Nanoparticles by Flame-Assisted Spray Pyrolysis Using a Burner Diffusion Flame

“…The presence of large spherical and small agglomerated CeO 2 particles indicates that mainly two particle formation routes coexist in this experiment, which has also been reported in previous FSP studies. , Large particles may have formed by a droplet-to-particle route, in which precursor droplets do not completely evaporate, while the small ones may have formed by a gas-phase reaction, with completely evaporated precursors (gas-to-particle route) . It is considered that at higher F O 2 , the flame temperature becomes higher (Figure b) and evaporation of precursor droplets is enhanced, resulting in the shift of particle formation route from droplet-to-particle to gas-to-particle …”

“…13 It is considered that at higher F O 2 , the flame temperature becomes higher (Figure 4b) and evaporation of precursor droplets is enhanced, resulting in the shift of particle formation route from droplet-to-particle to gas-to-particle. 31 of around 3 to 20 nm, which was observed as dark black dots (confirmed in Figure 9a), were found in a CeO 2 particle. In the case of Nos.…”

Numerical Modelling of Formation of Highly Ordered Structured Micro- and Nanoparticles – A Review

“…Model based on heat and mass balances equations has been also applied for simulation of FSP method (Ren et al, 2021). Similarly as in work by Mezhericher group, authors of this works considered single droplet and assumed its spherical symmetry.…”

Virtual Special Issue of Recent Advances in Gas-Phase Synthesis of Functional Materials for Energy

“…show microscopic molecular dynamics simulations to investigate the initial crystal formation of Y 2 O 3 nanoparticles as a function of the temperature. Ren et al present a single-droplet model to describe multicomponent droplet combustion with the consideration of micro explosion, precursor reaction, and particle formation, aiming to elucidate the droplet-to-particle conversion route in spray-flame synthesis of nanoparticles.…”

“…Liu et al9 show microscopic molecular dynamics simulations to investigate the initial crystal formation of Y 2 O 3 nanoparticles as a function of the temperature. Ren et al10 present a single-droplet model to describe multicomponent droplet combustion with the consideration of micro explosion, precursor reaction, and particle formation, aiming to elucidate the droplet-to-particle conversion route in spray-flame synthesis of nanoparticles.Three papers demonstrate the outstanding possibilities provided by gas-phase synthesis for the generation and applications of tailored materials. Angel et al11 present the synthesis of LaMnO 3+δ nanoperovskites in spray flames and demonstrate excellent catalytic activity for selective CO oxidation.…”