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A Comparison of Titania Nanoparticles Production in Two Different Reactors by MOCVD Method
Moravec, Pavel ; Smolík, Jiří ; Schwarz, Jaroslav ; Vodička, Petr ; Levdansky, V.V. ; Koštejn, Martin
Nanoparticles (NP's) have attracted considerable attention, because they show a quantum size effect, for which the physical and chemical properties are strongly dependent on particle size. This change of properties can also affect the toxicity and therefore NP's cannot be treated the same way as bulk material. In spite of that, inhalation studies of NP's are still rather rare. Recently, an exposure system for inhalation experiments was constructed in the Institute of Analytical Chemistry AS CR and the first experience with this system were reported by Večeřa et al., 2012. For these studies, a method of continual long-term generation of NP's in the gas phase is necessary. Methods for long-term generation of MnOx and Pb/PbOx NP's have recently been reported. The next task was to test the method for long-term generation of TiO2 NP's suitable for subsequent inhalation experiments.
Plný tet: SKMBT_C22014102013554 -  PDF
Plný text: content.csg - PDF
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Impact of Size Effects on Formation of Nanoparticles from Supersaturated Vapor
Levdansky, V.V. ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
The mechanism of nanoparticle formation in condensation of a supersaturated vapor is of interest for different kinds of atmospheric phenomena and processes of nanotechnology (e.g. manufacture of nanoparticles). Homogeneous nucleation is the initial stage of nanoparticle formation. The critical cluster size is one from the main parameters in the classical nucleation theory. The value of the critical cluster size is usually found from the Kelvin equation which does not depend on the condensation coefficient. In the general case the size dependence of the condensation coefficient can influence the critical cluster size (Levdansky, 2002). The size dependence of the cohesive energy in the nanoparticle can also affect the size of the critical cluster. Below we consider the joint influence of above-mentioned size effects on the critical cluster size, the rate of nucleation and the growth rate of arising nanoparticles.
Plný tet: SKMBT_C22014102013552 - PDF
Plný text: content.csg - PDF
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Influence of Size Effect on Evaporation of Aerosol Nanoparticles
Levdansky, V.V. ; Smolík, Jiří ; Ždímal, Vladimír
Evaporation of nanoscale particles plays a significant role in many branches of nanotechnology and also in the atmospheric physics and chemistry. The classical approach to the description of evaporation of small (nanoscale) aerosol particles is usually based on the Kelvin equation. The mentioned equation was used in (Nanda et al., 2003) to interpret the results of experiments related to evaporation of free Ag nanoparticles. The authors of the above-mentioned paper assume that the surface tension of free Ag nanoparticles can be significant greater than the mentioned value for bulk matter. It is worth noting that this assumption is in contradiction with the Tolman theory (Tolman, 1949). Below we consider the influence of the size dependence of the cohesive energy in the nanoparticle on its evaporation.
Plný tet: SKMBT_C22013101814594 - PDF
Plný text: content.csg - PDF
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Size Dependence of Incorporation of Gas Molecules into Aerosol Nanoparticles
Levdansky, V.V. ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
The influence of size effects on the physicochemical transformations and transfer phenomena in the heterogeneous systems with nanoobjects attracts increasing attention of researchers. These problems are of interest for nanotechnology and atmospheric physics. Size effects can influence the cohesive energy as well as the activation energies of vacancy formation and diffusion of atoms in the nanoscale particles (Vanithakumari and Nanda, 2008). Phase transitions in aerosol systems with nanoscale particles (clusters) also depend on the nanoparticle size (Levdansky et al., 2010). Hear we discuss the size dependence of the mass accommodation coefficient in the aerosol system with nanoparticles.
Plný tet: SKMBT_C22013091912290 - PDF
Plný text: content.csg - PDF
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Size Dependence of Reactive Uptake Coefficient in Chemical Reactions on Aerosol Nanoparticles
Levdansky, Valerij Vladimirovič ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
Chemical reactions in aerosol systems play a significant role in formation of new aerosol particles and their growth in the atmosphere and in various areas of nanotechnology. In the case of nanoscale aerosol particle the size effects can sufficiently affect the rate of chemical reactions both inside the particle and on its surface. The size dependence of a chemical reaction occurring on the nanoparticle surface can be related to the size dependence of the intrinsic activation energy for a chemical reaction and the adsorption kinetics of reactant molecules. Here we consider some aspects of the possible influence of the mentioned effects on the reactive uptake coefficient in the Eley-Rideal mechanism of a chemical reaction.
Plný tet: SKMBT_C22012102615344 - PDF
Plný text: content.csg - PDF
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Mass Accomodation Coefficient for Nanoscale Aerosol Particles
Levdansky, Valerij Vladimirovič ; Smolík, Jiří ; Ždímal, Vladimír ; Moravec, Pavel
The influence of size effects on physicochemical transformations and transfer processes in the heterogeneous systems with nanoobjects attracts increasing attention of researchers. These problems are of interest for nanotechnology and atmospheric physics. Size effects can influence the cohesive energy as well as the activation energies of vacancy formation and diffusion of atoms in the nanoscale particles (Vanithakumari and Nanda, 2008). Phase transitions (including nucleation) in aerosol systems with nanoscale particles (clusters) also depend on the nanoparticle size (Levdansky et al., 2010). Hear we discuss the size dependence of the mass accommodation coefficient gama in the gas–nanoparticle system.
Plný tet: SKMBT_C22012102615343 - PDF
Plný text: content.csg - PDF
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Nanoparticle Formation by Thermal Decomposition and Oxidation of Manganese(II) Acetylacetonate
Moravec, Pavel ; Smolík, Jiří ; Bakardjieva, Snejana ; Levdansky, V.V.
Over the last decade, Mn and MnOx nanoparticles has been extensively investigated due to their great importance in catalysis, electrochemistry, ion exchange materials, batteries and other areas (Si et al., 2005; Han et al., 2006). This work describes preliminary experiments producing manganese nanoparticles by metal organic chemical vapor deposition (MOCVD) using manganese(II) acetylacetonate (MnAA) as a precursor.
Plný tet: SKMBT_C22012102615333 - PDF
Plný text: content.csg - PDF
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