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    Wyświetlanie 1-3 z 3
    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:
    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:
    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
      Wyświetlanie 1-3 z 3

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