Size-dependent High-Temperature Behavior of Bismuth Oxide Nanoparticles.
Technische Universität, Darmstadt
[Ph.D. Thesis], (2012)
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Experimental and theoretical study of size-effects in oxide nanoparticles -
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|Item Type:||Ph.D. Thesis|
|Title:||Size-dependent High-Temperature Behavior of Bismuth Oxide Nanoparticles|
Oxide nanostrucures show very strong size-dependent changes in their thermal and chemical stability and reactivity. The total energy of nanoparticles (high surface-to-volume ratio) is increased due to the imperfect bonding structure of their surface-affected atoms. This leads to the shifts in the mentioned properties. While this relationship is valid for any kind of inorganic material the degree of these changes depends on the bond-strength and bond-nature of the material at the surface: The higher the surface energy the stronger the size-dependence. These thoughts are demonstrated here by experiments with sized-selected bismuth oxide nanoparticles between 5 and 50 nm. They were synthesized by an aerosol-based evaporation-condensation process with a size-selecting method resulting in monocrystalline, spherical and monodisperse particles. Characterization at room temperature revealed a distorted Beta-Bi2O3 structure. This shows a size-driven thermodynamic crossover in phase stability below a critical particle size. Heating experiments up to the evaporation point were performed inside the synthesis-chamber as well as with in-situ TEM, in-situ XRD and a special membrane-based high-temperature nanocalorimeter. Different atmospheres were used. The results show a pronounced melting point reduction. For example 10 nm particles melted 40% below the bulk in the TEM which is a considerably stronger size-effect than for metals (approx. 5 %). These experimental results were compared with the existing models.
|Place of Publication:||Darmstadt|
|Uncontrolled Keywords:||Models for size-dependent melting point reduction, Pawlow, Buffat, evaporation, phase transformation, solid state phase transition, Phase diagram, oxides, surface enregy, surface stress, nanoparticle, nucleation, synthesis, facets shape, chip calorimetry, nanocalorimetry|
|Classification DDC:||500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften
500 Naturwissenschaften und Mathematik > 530 Physik
500 Naturwissenschaften und Mathematik > 540 Chemie
600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften
|Divisions:||11 Department of Materials and Earth Sciences > Material Science > Joint Research Laboratory Nanomaterials
11 Department of Materials and Earth Sciences > Material Science > Nonmetallic-Inorganic Materials
11 Department of Materials and Earth Sciences > Material Science > Structure Research
07 Fachbereich Chemie > Physical Chemistry
|Date Deposited:||25 Feb 2013 12:57|
|Last Modified:||25 Feb 2013 12:57|
|Referees:||Guillon, Prof. Dr. Olivier and Hahn, Prof. Dr. Horst|
|Refereed:||14 December 2012|
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