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    Wyświetlanie 1-6 z 6
    Tytuł:
    Influence of modifiers on thermal and optical properties of TeO2–P2O5–ZnO–PbF2 glasses
    Autorzy:
    Reben, Manuela
    Burtan-Gwizdała, Bożena
    Cisowski, Jan
    Grelowska, Iwona
    El Sayed, Yousef
    Bukalska, Julita
    Powiązania:
    https://bibliotekanauki.pl/articles/173964.pdf
    Data publikacji:
    2019
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    fluorotellurite
    thermal stability
    refractive index
    luminescence
    Judd-Ofelt theory
    Opis:
    A series of fluorotellurite glasses based on 70TeO2–5MxOy–10P2O5–10ZnO–5PbF2 in mol%, where MxOy = (WO3, Nb2O5) doped with 2400 ppm of Er2O3 have been prepared by the conventional melt quenching method. The influence of modifiers on thermal and optical properties of glasses has been analyzed. Thermal characteristics of glasses like the glass transition temperature Tg, the temperature for the crystallization onset Tx, the maximum crystallization temperature Tc, and the thermal stability parameter were determined by the DSC method. The ellipsometric data have provided Sellmeier-type dispersion relations of the refractive index of the investigated glasses. The optical parameters are used to calculate the molar refractivity, molar polarizability, oxide ion polarizability, molar cation polarizability, and a number of polarizable atoms per unit volume for every glass composition in order to interpret the refractive index of these glasses.
    Źródło:
    Optica Applicata; 2019, 49, 3; 403-413
    0078-5466
    1899-7015
    Pojawia się w:
    Optica Applicata
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Characteristics of natural and synthetic molecular sieves and study of their interactions with fragrance compounds
    Autorzy:
    Kasperkowiak, M.
    Strzemiecka, B.
    Voelkel, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/110548.pdf
    Data publikacji:
    2016
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    molecular sieves
    fragrance compounds
    adsorption properties
    thermodynamic parameters
    thermal stability
    Opis:
    Structural, physicochemical and adsorption properties of two natural and one synthetic molecular sieves were investigated by various techniques: X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, low-temperature nitrogen adsorption and inverse gas chromatography. The influence of these properties on the ability to adsorb two model fragrances: p-cymene and menthol was studied. The free enthalpy, entropy and Gibbs free energy of adsorption of fragrance molecules on the surface of zeolite and zeolite-like materials were estimated by using inverse gas chromatography. Also, the influence of temperature on the stability of solid-fragrance compound systems as well as the release of the adsorbed fragrance compounds was studied. The obtained results exhibit that both porosity and chemical composition of molecular sieves influence the size and strength of adsorption of fragrance compounds. The study indicated different release characteristics for p-cymene and menthol.
    Źródło:
    Physicochemical Problems of Mineral Processing; 2016, 52, 2; 789-802
    1643-1049
    2084-4735
    Pojawia się w:
    Physicochemical Problems of Mineral Processing
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Activated lignin and aminosilane-grafted silica as precursors in hybrid material production
    Autorzy:
    Klapiszewski, L.
    Szalaty, T. J.
    Zdarta, J.
    Jesionowski, T.
    Powiązania:
    https://bibliotekanauki.pl/articles/951851.pdf
    Data publikacji:
    2016
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    SiO2/lignin hybrids
    silica
    lignin
    lignin activation
    thermal stability
    hybrid material
    Opis:
    Functional inorganic-organic hybrids were synthesized using as a precursor silica with the addition of an appropriate amount of lignin as components. Three types of silica were applied as the support: the commercial silicas Syloid 244 and Aerosil 200, and hydrated silica precipitated in a polar system. The silicon dioxide was initially functionalized with aminosilane to activate the surface, and then the silica-based material was combined with lignin oxidized using hydrogen peroxide. The obtained inorganic-organic hybrids underwent physicochemical and dispersive-morphological analysis, with comparison of the results depending on the composition of the test samples. In addition, particle size distributions were determined and the surface structure of the products assessed by scanning electron microscopy. The presence of functional groups was also determined by FTIR spectroscopy. The thermal analysis of the silica/lignin materials was also performed, as well as the elemental and colorimetric analyses, which indirectly confirmed the correctness of the synthesis process. Hybrid materials with the most favorable dispersive and morphological properties were obtained by adding a small amount of biopolymer. The thermogravimetric analysis of the SiO2/lignin hybrids indicated their good thermal stability. With increasing quantity of lignin per 100 parts by weight of silica matrix, progressive deterioration in the thermal stability of the materials was observed.
    Źródło:
    Physicochemical Problems of Mineral Processing; 2016, 52, 1; 459-478
    1643-1049
    2084-4735
    Pojawia się w:
    Physicochemical Problems of Mineral Processing
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hybrid nanobiocomposites based on poly(3-hydroxybutyrate) : characterization, thermal and mechanical properties
    Autorzy:
    Zarzycka, Iwona
    Czerniecka-Kubicka, Anna
    Szyszkowska, Agnieszka
    Pyda, Marek
    Frącz, Wiesław
    Byczyński, Łukasz
    Sedlarik, Vladimir
    Powiązania:
    https://bibliotekanauki.pl/articles/306831.pdf
    Data publikacji:
    2020
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    nanoglinka
    stabilność termiczna
    właściwości mechaniczne
    hybrid nanobiocomposites poly(3-hydroxybutyrate)
    nanoclay
    linear polyurethanes
    thermal stability
    mechanical properties
    Opis:
    Poly(3-hydroxybutyrate) is a biopolymer used to production of implants in the human body. On the other hand, the physical and mechanical properties of poly(3-hydroxybutyrate) are compared to the properties of isotactic polypropylene what makes poly(3-hydroxybutyrate) possible substitute for polypropylene. Unfortunately, the melting point of poly(3-hydroxybutyrate) is almost equal to its degradation temperature what gives very narrow window of its processing conditions. Therefore, numerous attempts are being made to improve the poly(3-hydroxybutyrate) properties. In the present work, hybrid nanobiocomposites based on poly(3-hydroxybutyrate) as a matrix with the use of organic nanoclay – Cloisite 30B and linear polyurethane as a second filler have been manufactured. The linear polyurethane was based on diphenylmethane 4,4′-diisocyanate and diol with imidazoquinazoline rings. The obtained nanobiocomposites were characterized by X-ray diffraction, scanning and transmission electron microscopies, thermogravimetry, differential scanning calorimetry and their selected mechanical properties were tested. The resulting hybrid nanobiocomposites have intercalated/exfoliated structure. The nanobiocomposites are characterized by a higher thermal stability and a wider range of processing temperatures compared to the unfilled matrix. The plasticizing influence of nanofillers was also observed. In addition, the mechanical properties of the discussed nanobiocomposites were examined and compared to those of the unfilled poly(3-hydroxybutyrate). The new-obtained nanobiocomposites based on poly(3-hydroxybutyrate) containing 1% Cloisite 30B and 5 wt. % of the linear of polyurethane characterized the highest improvement of processing conditions. They have the biggest difference between the temperature of degradation and the onset melting temperature, about 100 °C.
    Źródło:
    Acta of Bioengineering and Biomechanics; 2020, 22, 1; 97-110
    1509-409X
    2450-6303
    Pojawia się w:
    Acta of Bioengineering and Biomechanics
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Characterization of amino-, epoxy- and carbonyl-functionalized halloysite and its application in the immobilization of aminoacylase from Aspergillus melleus
    Autorzy:
    Kołodziejczak-Radzimska, Agnieszka
    Jesionowski, Teofil
    Powiązania:
    https://bibliotekanauki.pl/articles/110662.pdf
    Data publikacji:
    2019
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    functionalized halloysite
    physicochemical and structural evaluation
    immobilization
    thermal and chemical stability
    reusability
    Opis:
    Functionalized halloysite was used as a support for the immobilization of an enzyme. The surface of halloysite was modified with amino (–NH), epoxy (–C(O)C) and carbonyl (–C=O) groups. Both unmodified and modified forms of the support underwent a comprehensive physicochemical and structural evaluation, including morphological, structural, thermogravimetric and spectroscopic analysis. Aminoacylase from Aspergillus melleus was used as the enzyme in the immobilization process. The process of immobilization by adsorption was performed for 1, 6 and 24 h using different concentrations of enzyme solution (0.5, 1 and 3 mg/cm3). The quantity of aminoacylase loaded onto the support was calculated by the Bradford method. Free and immobilized aminoacylase were used to catalyze the deacetylation of N-acetyl-L-methionine. Additionally, the thermal and chemical stability of the obtained biocatalytic systems were evaluated, as well as the reusability of the immobilized systems. The biocatalytic system with amino groups demonstrated activity above 70% in the pH range 4–9 and 60% in the temperature range 30–70 °C. Aminoacylase immobilized on amino-functionalized halloysite also retains around 50% of its initial activity after five reaction cycles.
    Źródło:
    Physicochemical Problems of Mineral Processing; 2019, 55, 1; 128-139
    1643-1049
    2084-4735
    Pojawia się w:
    Physicochemical Problems of Mineral Processing
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Global stability for thermal convection in a couple-stress fluid with temperature and pressure dependent viscosity
    Autorzy:
    Choudhary, S. S.
    Bharti, P. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/178230.pdf
    Data publikacji:
    2013
    Wydawca:
    Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
    Tematy:
    konwekcja
    konwekcja cieplna
    stabilność
    płyn nieniutonowski
    convection
    thermal convection
    stability
    non-Newtonian fluid
    Opis:
    We show that the global nonlinear stability threshold for convection in a couple-stress fluid with temperature and pressure dependent viscosity is exactly the same as the linear instability boundary. This optimal result is important because it shows that linearized instability theory has captured completely the physics of the onset of convection. It has also been found that the couplestress fluid is more stable than the ordinary viscous fluid and then the effect of couple-stress parameter (F) and variable dependent viscosity (Γ) on the onset of convection is also analyzed.
    Źródło:
    Studia Geotechnica et Mechanica; 2013, 35, 3; 85-102
    0137-6365
    2083-831X
    Pojawia się w:
    Studia Geotechnica et Mechanica
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-6 z 6

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