flame synthesis
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Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6698
Author(s):  
Simon Aßmann ◽  
Bettina Münsterjohann ◽  
Franz J. T. Huber ◽  
Stefan Will

The investigation of droplet and nanoparticle formation in spray flame synthesis requires sophisticated measurement techniques, as often both are present simultaneously. Here, wide-angle light scattering (WALS) was applied to determine droplet and nanoparticle size distributions in spray flames from a standardized liquid-fed burner setup. Solvents of pure ethanol and a mixture of ethanol and titanium isopropoxide, incepting nanoparticle synthesis, were investigated. A novel method for the evaluation of scattering data from droplets between 2 µm and 50 µm was successfully implemented. Applying this, we could reveal the development of a bimodal droplet size distribution for the solvent/precursor system, probably induced by droplet micro-explosions. To determine nanoparticle size distributions, an appropriate filter and the averaging of single-shot data were applied to ensure scattering from a significant amount of nanoparticles homogeneously distributed in the measurement volume. From the multivariate analysis of the scattering data, the presence of spherical particles and fractal aggregates was derived, which was confirmed by analysis of transmission electron microscopy images. Monte Carlo simulations allowed determining the distribution parameters for both morphological fractions in three heights above the burner. The results showed relatively wide size distributions, especially for the spherical fraction, and indicated an ongoing sintering, from fractal to spherical particles.


Author(s):  
N. Hamzah ◽  
M. F. Mohd Yasin ◽  
M. T. Zainal ◽  
M. Mohd Sies ◽  
M. Z. Mohd Yusop ◽  
...  

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Hao Zhou ◽  
Qiwei Wu ◽  
Boyang Qi

A large amount of CO as hazardous emission in the iron ore sintering process has caused severe harm to the environment and human health. To control the emission of CO more effectively, the preparation of highly efficient catalysts has attracted much attention. In this study, the La1-xSrxMnO3 (0 ≤ x < 1) perovskite catalysts with different Sr2+ contents were prepared by the one-step flame synthesis method to treat CO pollutants in the iron and steel industry. The influence of Sr2+ doping on the structure and activity of catalytic were characterized and analyzed. La1-xSrxMnO3 perovskite catalysts exhibit good perovskite phases and loose spherical structures. The specific surface areas are between 4.1 and 12.0 m2 g−1. Combined with the results of H2-TPR and O2-TPD, the improvement of catalytic activity of La1-xSrxMnO3 perovskite can be attributed to the high concentration of active centers and oxygen vacancies. Significantly, the La0.4Sr0.6MnO3 catalyst presented the best reducibility and high content of absorbed active oxygen species, leading to a superior CO oxidation catalytic activity and reaches 50% CO conversion at 134.9°C and 90% at 163.2°C, respectively. The effects of water vapor and CO2 on the oxidation activity of La1-xSrxMnO3 perovskite was investigated. The flame-produced catalysts exhibit favorable catalytic stability and antisintering ability, achieving 100% CO conversion after fifth consecutive oxidation cycles.


Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4672
Author(s):  
Mario Commodo ◽  
Gianluigi De Falco ◽  
Ettore Sarnelli ◽  
Marcello Campajola ◽  
Alberto Aloisio ◽  
...  

Nanostructured films of carbon and TiO2 nanoparticles have been produced by means of a simple two-step procedure based on flame synthesis and thermophoretic deposition. At first, a granular carbon film is produced on silicon substrates by the self-assembling of thermophoretically sampled carbon nanoparticles (CNPs) with diameters of the order of 15 nm. Then, the composite film is obtained by the subsequent thermophoretic deposition of smaller TiO2 nanoparticles (diameters of the order of 2.5 nm), which deposit on the surface and intercalate between the carbon grains by diffusion within the pores. A bipolar resistive switching behavior is observed in the composite film of CNP-TiO2. A pinched hysteresis loop is measured with SET and RESET between low resistance and high resistance states occurring for the electric field of 1.35 × 104 V/cm and 1.5 × 104 V/cm, respectively. CNP-TiO2 film produced by flame synthesis is initially in the low resistive state and it does not require an electroforming step. The resistance switching phenomenon is attributed to the formation/rupture of conductive filaments through space charge mechanism in the TiO2 nanoparticles, which facilitate/hinder the electrical conduction between carbon grains. Our findings demonstrate that films made of flame-formed CNP-TiO2 nanoparticles are promising candidates for resistive switching components.


2021 ◽  
Author(s):  
Alexander Keller ◽  
Irenäus Wlokas ◽  
Maximilian Kohns ◽  
Hans Hasse

The quality of nanoparticles that are obtained by spray flame synthesis dependsstrongly on the thermophysical properties of the precursor solutions. Solutions ofiron(III)nitrate-nonahydrate (INN) in ethanol are interesting precursor solutions forthe production of iron oxide nanoparticles in these processes. However, no data onthermophysical properties of solutions of INN in ethanol are available in theliterature. Therefore, in the present work, the specific density, viscosity, thermalconductivity and molar isobaric heat capacity of solutions of INN in solvent mixturesof ethanol and water were measured at 101.3 kPa between 288.15 and 333.15 K,solvent compositions ranging from pure ethanol to pure water, and INN molalities upto 1.3 mol kg-1. Empirical correlations of the experimental data are provided.


Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3472
Author(s):  
Md Yusuf Ali ◽  
Hans Orthner ◽  
Hartmut Wiggers

A spray-flame reaction step followed by a short 1-h sintering step under O2 atmosphere was used to synthesize nanocrystalline cubic Al-doped Li7La3Zr2O12 (LLZO). The as-synthesized nanoparticles from spray-flame synthesis consisted of the crystalline La2Zr2O7 (LZO) pyrochlore phase while Li was present on the nanoparticles’ surface as amorphous carbonate. However, a short annealing step was sufficient to obtain phase pure cubic LLZO. To investigate whether the initial mixing of all cations is mandatory for synthesizing nanoparticulate cubic LLZO, we also synthesized Li free LZO and subsequently added different solid Li precursors before the annealing step. The resulting materials were all tetragonal LLZO (I41/acd) instead of the intended cubic phase, suggesting that an intimate intermixing of the Li precursor during the spray-flame synthesis is mandatory to form a nanoscale product. Based on these results, we propose a model to describe the spray-flame based synthesis process, considering the precipitation of LZO and the subsequent condensation of lithium carbonate on the particles’ surface.


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