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Backman Ulrika Jokiniemi Jorma K. Auvinen Ari Lehtinen Kari E.J. 《Journal of nanoparticle research》2002,4(4):325-335
We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size. 相似文献
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Unoccupied titanium 3d states due to subcluster formation in stoichiometric TiO2 nanoparticles 下载免费PDF全文
Sami Auvinen Matti Lahti Matti Alatalo 《International journal of quantum chemistry》2015,115(17):1175-1180
The source of unoccupied Ti 3d states in the case of stoichiometric anatase structured (TiO2)n clusters has been investigated using ab initio methods. These unoccupied gap states appear for example in the case of a stoichiometric (TiO2)38 cluster. We show that the origin of these gap states is related to effective subcluster formation which gives rise to empty defect‐like gap states, when these states are split off from conduction band. © 2015 Wiley Periodicals, Inc. 相似文献
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Cobalt and nickel nanoparticles were produced by hydrogen reduction reaction from cobalt or nickel chloride precursor vapour
in nitrogen carrier gas. This aerosol phase method to produce nanoparticles is a scalable one-step process. Two different
setups were introduced in particle production: a batch type reactor and a continuously operated reactor. Common feature in
these setups was hydrogen mixing in a vertical flow reactor. The process was monitored on-line for particle mass concentration
and for gas phase chemical reactions. Tapered element oscillating microbalance measured the particle mass concentration and
Fourier transform infrared spectroscopy was used to monitor relevant gas phase species. The produced cobalt and nickel particles
were characterised using transmission electron microscopy and x-ray diffraction. The produced cobalt and nickel particles
were crystalline with cubic fcc structure. Twinning was often observed in cobalt particles while nickel particles were mostly
single crystals. The cobalt particles formed typically long agglomerates. No significant neck growth between the primary particles
was observed. The primary particle size for cobalt and nickel was below 100 nm. 相似文献
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M. Ahonen M. Hirsimki A. Puisto S. Auvinen M. Valden M. Alatalo 《Chemical physics letters》2008,456(4-6):211-214
Adsorption dynamics experiments on Cu(1 0 0) at 300 K indicate that surface defects induced by 3.4 keV Ar+-ion bombardment strongly enhance the dissociative chemisorption probability of O2. Energy selective molecular beam surface scattering experiments reveal a defect induced low-barrier dissociation pathway leading to enhanced dissociation of O2 molecules with translational energy up to 60 meV. Density functional theory calculations attribute the decrease in O2 dissociation barrier to the weakening of O–O bond at Cu vacancies, thus resolving the contradiction between experimental observations and theoretical predictions of the height of the barrier to O2 dissociation on Cu(1 0 0). 相似文献
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J. Leskinen J. Joutsensaari J. Lyyränen J. Koivisto J. Ruusunen M. Järvelä T. Tuomi K. Hämeri A. Auvinen J. Jokiniemi 《Journal of nanoparticle research》2012,14(2):718
Nanoparticles are used in many applications because of their novel properties compared to bulk material. A growing number
of employees are working with nanomaterials and their exposure to nanoparticles trough inhalation must be evaluated and monitored
continuously. However, there is an ongoing debate in the scientific literature about what are the relevant parameters to measure
to evaluate exposure to level. In this study, three types of nanoparticles (ammonium sulphate, synthesised TiO2 agglomerates and aerosolised TiO2 powder, modes in a range of 30–140 nm mobility size) were measured with commonly used aerosol measurement instruments: scanning
and fast mobility particle sizers (SMPS, FMPS), electrical low pressure impactor (ELPI), condensation particle counter (CPC)
together with nanoparticle surface area monitor (NSAM) to achieve information about the interrelations of the outputs of the
instruments. In addition, the ease of use of these instruments was evaluated. Differences between the results of different
instruments can mainly be attributed to the nature of test particles. For spherical ammonium sulphate nanoparticles, the data
from the instruments were in good agreement while larger differences were observed for particles with more complex morphology,
the TiO2 agglomerates and powder. For instance, the FMPS showed a smaller particle size, a higher number concentration and a narrower
size distribution compared with the SMPS for TiO2 particles. Thus, the type of the nanoparticle was observed to influence the data obtained from these different instruments.
Therefore, care and expertise are essential when interpreting results from aerosol measurement instruments to estimate nanoparticle
concentrations and properties. 相似文献
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