کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
144047 438921 2014 20 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Agglomerates and aggregates of nanoparticles made in the gas phase
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی مهندسی شیمی (عمومی)
پیش نمایش صفحه اول مقاله
Agglomerates and aggregates of nanoparticles made in the gas phase
چکیده انگلیسی


• Aerosol nanoparticles form agglomerates (physically-) and aggregates (chemically-bonded).
• Such clusters exhibit self-similarity and can be characterized with power-law scalings.
• They have different equivalent sizes that can easily differ up to a factor of two.
• Fractal-like particles reach self-preserving size distributions similar to spheres.
• They can restructure and break-up by ultrasonication, dispersion, impaction or condensation.

Gas-phase (aerosol) technology is used widely in manufacture of various nanostructured commodities at tons/hour today. So it is quite promising for synthesis of sophisticated nanoparticles motivating basic and applied research. Frequently such nanoparticles are made as clusters of primary particles (PPs) by chemical reaction, aerosol coagulation, sintering, surface growth and even fragmentation. When PPs are bonded by strong chemical forces, they are termed aggregates. As such they are sought in catalysis, lightguide preform manufacture and, most importantly, as components in electronic devices (sensors, batteries). When PPs and aggregates are held together by rather weak, physical forces, they form agglomerates. These are attractive in nanocomposites and fluid suspensions (paints, nanofluids, bioimaging). Such clusters may have also distinct health effects, beyond those of equivalent spherical particles.Agglomerates and aggregates are characterized by microscopy, electromagnetic scattering and mass mobility measurements in terms of their volume-equivalent radius, radius of gyration and/or mobility radii in the free molecular and continuum regimes along with the corresponding power laws (fractal dimension, Df). Coagulation and sintering largely determine nanoparticle structure. Coagulation of PPs leads to agglomerates of Df = 1.78 and 1.91 in the continuum and free-molecular regimes, respectively. The coagulation rate of agglomerates is higher than that of volume-equivalent spheres in the free molecular regime. Agglomerates attain also a self-preserving size distribution by coagulation facilitating process design for their manufacture. Mesoscale simulations elucidate the sintering (or coalescence) of agglomerates to aggregates and narrowing of their PP size distribution. Once agglomerates start to sinter, they follow a power law to aggregates and eventually to compact (spherical) particles, regardless of composition and initial PP size distribution. Aggregate properties are in-between those of the initial agglomerate and the fully coalesced sphere. Finally the stability of agglomerates under ultrasonication, stretching, fluid dispersion, impaction and capillary condensation is highlighted.

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ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Advanced Powder Technology - Volume 25, Issue 1, January 2014, Pages 71–90
نویسندگان
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