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    Wyświetlanie 1-6 z 6
    Tytuł:
    The Influence of Steric Stabilization on Process of Au, Pt Nanoparticles Formation
    Autorzy:
    Luty-Błocho, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/356030.pdf
    Data publikacji:
    2019
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    gold
    platinum
    nanoparticles
    kinetic
    nucleation growth
    steric stabilization
    Opis:
    Nanoparticles are very fascinating area of science not only due to their unique properties but also possibility of producing new more complex materials, which may find an application in modern chemistry, engineering and medicine. In process of nanoparticles formation very important aspect is a rate of individual stage i.e. reduction, nucleation and autocatalytic growth, because this knowledge allows for proper materials design, morphology manipulation, stability. The last one aspect can be realized using proper electrostatic, steric and electrosteric stabilization. However until now nobody reports and measures kinetic rates of all stages during process of particles formation in the presence of steric stabilizers. Thus, the main contribution of this paper is determination of individual rate constants for nanoparticles formation in the presence of steric stabilizers and their comparison to the system without stabilizer. For this purpose, an aqueous solution of Au(III) and Pt(IV) ions were mixed with steric stabilizers like PVA and PVP, and reduced using L-ascorbic acid as a mild and sodium borohydride as a strong reductant. As a results stable nanoparticles were formed and process of their formation was registered spectrophotometrically. From obtained kinetic curves the values of observed rate constants for reduction metal ions, slow nucleation and fast autocatalytic growth were determined using Watzky-Finke model. It was found that the addition of polymer affects the rate of the individual stages. The addition of steric stabilizers to gold ions reduced with L-ascorbic acid causes that the process of nucleation and autocatalytic growth slows down and the value of observed rate constants for nucleation changes from 3.79·10-3 (without polymer) to 7.15·10-5 s-1 (with PVA) and for growth changes from 1.15·103 (without polymer) to 0.48·102 s-1 M-1 (with PVA). However, the rate of the reduction reaction of Au(III) ions is practically unchanged. In case of using strong reductant the addition of polymer effects on the shape of kinetic curve for reduction of Au(III) and it suggests that mechanism is changed. In case of Pt(IV) ions reduction with L-ascorbic acid, the process speeds up a little when PVA was added. Determined values of observed rate constants for nucleation and growth platinum nanoparticles decrease twice comparing to the system without polymer. The reduction of Pt(IV) ions with sodium borohydride accelerates when PVP was added and slows down when PVA was used. Moreover, the size of obtained colloidal gold and platinum was also analysed using DLS method. Obtained results (rate constants) may be useful in the process of nanomaterials synthesis, in particular in microflow.
    Źródło:
    Archives of Metallurgy and Materials; 2019, 64, 1; 55-63
    1733-3490
    Pojawia się w:
    Archives of Metallurgy and Materials
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigation on Nucleation Kinetics, Growth and Nonlinear Optical Properties of L-Cystine Hydrochloride Crystal
    Autorzy:
    Manivannan, D.
    Kirubavathi, K.
    Selvaraju, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/1029827.pdf
    Data publikacji:
    2018-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    crystal growth
    nucleation kinetics
    optical materials
    NLO
    Opis:
    The semiorganic nonlinear optical crystal of amino-carboxyl acid family, L-cystine hydrochloride (LCHCl) was successfully grown from its aqueous solution by the slow evaporation solution growth method. The solubility, metastable zone width and induction period were determined for the first time experimentally and there by the possibility of growing bulk crystals of LCHCl using deionized water as solvent. The induction period was recorded for the different supersaturation ratios (S=1.2, 1.3, 1.4, and 1.5), which reveals that the induction period of LCHCl decreases with increase in supersaturation. The nucleation kinetic parameters such as critical free energy, change of volume free energy, critical radius, number of molecules in the critical nucleus and nucleation rate have been evaluated for LCHCl crystals. The interfacial energy values of LCHCl were determined for different supersaturation ratio by means of varying temperatures. The single crystal X-ray diffraction gives the lattice parameters value of the grown crystals. The second harmonic generation efficiency was confirmed by the Kurtz-Perry powder method. The laser damage threshold energy of the grown crystal indicates that grown crystal has excellent resistance to laser radiation also compared with known other nonlinear optical crystals.
    Źródło:
    Acta Physica Polonica A; 2018, 133, 1; 63-67
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Modelling and identification of voids nucleation and growth effects in porous media plastic flow
    Autorzy:
    Nowak, Z.
    Stachurski, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/970581.pdf
    Data publikacji:
    2003
    Wydawca:
    Polska Akademia Nauk. Instytut Badań Systemowych PAN
    Tematy:
    optymalizacja globalna
    regresja nieliniowa
    programowanie nieliniowe
    plastic flow of voided media
    material functions identification
    global optimization
    nonlinear regression
    nonlinear programming
    Akaike and FPE tests for nested models
    Vuong test for nonnested models
    Opis:
    In the paper the effects of nucleation and growth of voids in the plastic porous media are investigated. Three different forms of the model are considered: the augmented Gurson model (total porosity model) with variable nucleation and growth material function, the same model with constant growth material function and the separated porosity model. The identification of the material functions parameters is based on Fischer's experimental data set for axisymmetric tension of steel specimens and formulated as a typical nonlinear regression problem using the least squares approach. The resulting minimization problem is solved by means of our own implementation of the Boender at al. global minimization method. Calculations and statistical analysis (Akaike, FPE and Vuong tests) have led to a conclusion that the growth material function in the uniaxial tension for steel may be assumed to be constant although not necessarily equal to one.
    Źródło:
    Control and Cybernetics; 2003, 32, 4; 819-849
    0324-8569
    Pojawia się w:
    Control and Cybernetics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Optimisation of LT-GaN nucleation layer growth conditions for the improvement of electrical and optical parameters of GaN layers
    Autorzy:
    Wośko, Mateusz
    Powiązania:
    https://bibliotekanauki.pl/articles/174388.pdf
    Data publikacji:
    2019
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    GaN
    nucleation
    recrystallization
    metalorganic chemical vapor deposition
    nitrides
    LED
    MSM
    MESFET devices
    Opis:
    In this work we present the influence of low temperature gallium nitride (LT-GaN) nucleation layer deposition and recrystallization conditions on the electrical and optical properties of buffer and active layer of metal–semiconductor field-effect transistor (MESFET) structure. MESFET structures were used to investigate the properties of bulk materials that determine also the performance of many type GaN based devices, like light emitting diodes (LEDs), high electron mobility transistors (HEMTs) and metal–semiconductor–metal (MSM) detectors. The set of n-GaN/u-GaN/sapphire structures using different nucleation LT-GaN layers thickness and different annealing times was deposited using AIXTRON CCS epitaxial system. In contrast to typical procedure, the high resistive GaN buffer layer was not obtained by intentional Fe/Mg doping, but by specific adjustment of GaN nucleation conditions and recrystallization process parameters that introduce carbon atoms in epitaxial layers, that serve as donors. Generally, low pressure (below 200 mbar) in a reactor chamber, during initial stages of nucleation and recrystallization as well as HT-GaN epitaxy, promotes the growth of high resistive material. Obtained results show that annealing/recrystallization time of LT-GaN has a significant impact on the electrical and optical properties of GaN buffer layers. Longer annealing periods tend to promote crystallization of material with higher electron mobility and higher Si dopant incorporation/activation while maintaining high resistivity in u-GaN buffer area. It was shown that the dimensions of the GaN islands, that could be influenced by the duration of an annealing step of LT-GaN growth, have no impact on the HT-GaN buffer layer coalescence process and material resistivity, but influences mainly electrical properties of active n-GaN layer. Author suggests that the key parameters that are determining the buffer resistivity are the pressure and temperature during LT-GaN annealing and buffer layer coalescence. The influence of GaN island diameters, after LT-GaN annealing, on the u-GaN resistivity was not confirmed.
    Źródło:
    Optica Applicata; 2019, 49, 1; 167-176
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Reduction of Industrial Nickel Oxides with a Hydrogen Bearing Gas Between 523 and 673K
    Autorzy:
    Plascencia, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/352276.pdf
    Data publikacji:
    2018
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    nickel oxides reduction
    hydrogen reduction
    Avrami-Erofeyev kinetic model
    nucleation and growth
    activation energy
    Opis:
    Reduction of three industrial nickel oxides (Goro, Tokyo and Sinter 75) with a hydrogen bearing gas was revisited in the temperature interval from 523 to 673 K (250 to 400°C). A pronounced incubation period is observed in the temperature interval tested. This period decreases as the reduction temperature increases. Thermogravimetric data of these oxides were fitted using the Avrami-Erofeyev kinetic model. The reduction of these oxides is controlled by a nucleation and growth mechanism of metallic nickel over the oxides structure. Rate kinetic constants were re-evaluated and the activation energy for the reduction of these oxides was re-calculated.
    Źródło:
    Archives of Metallurgy and Materials; 2018, 63, 2; 781-789
    1733-3490
    Pojawia się w:
    Archives of Metallurgy and Materials
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nucleation and Crystal Growth of Cu on Ir Tips Under Ultra-High Vacuum and in the Presence of Oxygen
    Autorzy:
    Zuber, S. M.
    Ciszewski, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2013288.pdf
    Data publikacji:
    2000-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.16.Fk
    81.15.Ef
    68.35.Bs
    Opis:
    Results concerning the morphology of Cu adsorption layers deposited from vapor under ultrahigh vacuum on Ir tip and the influence of oxygen on this morphology are reported. The method employed was field electron emission microscopy. It was found that the presence of oxygen decreases the copper wettability of iridium. Preadsorption of oxygen on the Ir surface is followed by an increase in cohesion interaction between atoms of the Cu deposited onto the tip at room temperature. Coadsorption of Cu and O on the Ir tip surface at liquid nitrogen temperature, when followed by gradually heating the adlayer, results in crystallization of the deposit in the temperature range from 430 K to about 700 K. Some evidence indicates the formation of Cu$\text{}_{2}$O with a high degree of crystallinity under these conditions. Cu and O coadsorption on the Ir surface at a temperature higher than 1090 K leads to selective accumulation of Cu on the {111} faces and to formation of epitaxial crystals which are oriented to the substrate in the same manner as the Cu crystals grown at ultra-high vacuum from Cu flux containing no oxygen. Oxygen incorporated into the Cu beam interact preferentially with {011} and {001} Ir faces, where it can produce oxide layers.
    Źródło:
    Acta Physica Polonica A; 2000, 97, 4; 681-692
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-6 z 6

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