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  • 1.
    Iftekhar, ANM Shahriar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Structure-Property-Composition Correlations in Rare-Earth Alumino-silicate Glasses2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Rare earth (RE) alumino-silicate (AS) glasses exhibit favorable physical, mechanical and optical properties, such as high values of the glass transition temperature, Vickers hardness, and refractive index. RE2O3-Al2O3-SiO2 glasses have found several industrial applications, for example as components of optical amplifiers and lasers. Many of these features stem from the high cation field-strength (CFS) of the trivalent RE ions (proportional to the valence of the ion divided by the square of its radius), which affects not only the physical properties of the glass, but also their structures.

    This thesis deals with investigations of four different RE2O3-Al2O3-SiO2 systems, where RE represents either of La, Y, Lu or Sc. The glass forming regions of the latter two were reported by us for the first time. Within each system, glasses were prepared for variable RE, Si and Al contents.

    The glass structures were investigated by solid-state 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy that informs about the local Si and Al environments in the glass network, which is built from interlinked SiO4 and AlO4 groups. Higher Al coordination numbers were also revealed by 27Al NMR: their amounts were observed to increase markedly as the CFS of the RE ion increases, i.e., along the series La<Y<Lu<Sc. This thesis discusses such structure/composition relationships, as well as the correlations between the glass composition and its physical properties of density, molar volume, compactness, glass transition temperature, Vickers hardness and refractive index. Some of these properties, for example the glass transition temperature and Vickers hardness, were observed to enhance as the RE3+ CFS increased.

  • 2.
    Iftekhar, Shahriar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Edén, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Composition–property relationships of the La2O3–Al2O3–SiO2 glass system2010Inngår i: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 356, nr 20-22, s. 1043-1048Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report physical properties of density, glass transition temperature, Vickers hardness and refractive index for 15 La–Al–Si–O glasses within the compositional region 10–28 mol% La2O3, 11–30% Al2O3 and 45–78% SiO2. The glass transition temperature varies only slightly between 871 and 883 °C. Both the density (3.25–4.33 g cm−3) and refractive index (1.59–1.70) display similar compositional dependencies and are primarily dictated by the La2O3 content. The hardness (6.4–9.0 GPa) increases with decreasing SiO2 content and to a minor extent also with the amount of La2O3 of the glass. The physical properties, in particular the hardness, are discussed with reference to glass structure. The similarity in the observed properties between the present oxide-based glasses and those of analogous rare-earth (RE) element-containing RE–Si–(Al)–O–N oxynitride glasses is highlighted and discussed in relation to the apparent, but hitherto largely neglected, role of RE-ions to primarily control many enhanced physical properties of oxynitride glasses.

  • 3.
    Iftekhar, Shahriar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Gunawidjaja, Philips N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Edén, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Glass Formation and Structure–Property–Composition Relations of theRE2O3–Al2O3–SiO2 (RE = La, Y, Lu, Sc) Systems2011Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 94, nr 8, s. 2429-2435Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the glass-forming regions of the ternary Lu2O3–Al2O3–SiO2 and Sc2O3–Al2O3–SiO2 systems. The density, molarvolume, compactness, Vickers hardness, refractive index, aswell as the glass transition (Tg) and crystallization temperatureare compared for two series of RE–Al–Si–O (RE=La, Y, Lu,Sc) glasses that display a constant molar ratio nAl/nSi=1.00,whereas nRE/nSi is equal to either 0.62 or 0.94. Several glassproperties scale roughly linearly with the cation field strength(CFS) of the rare-earth (RE3+) ion, except for the Tg values ofthe Sc-bearing glasses that are significantly lower than expected.Magic-angle spinning 29Si and 27Al nuclear magneticresonance (NMR) reveal enhanced network disorder and increasedrelative populations of AlO5 and AlO6 polyhedra in thealuminosilicate glasses for increasing RE3+ CFS, but overallsimilar Si and Al local environments (chemical shifts and quadrupolarcouplings) in all samples associated with a constant nRE/nSi ratio, except for unexpectedly shielded 29Si NMR signalsobserved from the Sc–Al–Si–O glasses.

  • 4.
    Iftekhar, Shahriar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Svensson, Gunnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Lööf, J.
    Jarmar, T.
    Botton, G.
    Andrei, C.
    Engqvist, H.
    Phase formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures2008Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 28, nr 4, s. 747-756Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Calcium aluminate is the main constituent in calcium aluminate cements, used in a wide range of applications in construction and mining industries and recently also as biomedical implant. In applications that demand very precise reaction features, such as the biomedical ones, the phase purity is of very high importance.

    In this paper the formation of CaAl2O4 from CaCO3–Al2O3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 °C. Phase formation was studied in samples both quenched from the holding temperatures and in samples slowly cooled. Samples were characterized by X-ray powder diffraction (XRPD), using Guinier-Hägg film data and the Rietveld method, and scanning (SEM) and transmission (TEM) electron microscopy. Samples for TEM with very high site accuracy were produced using focused ion beam microscopy.

    In addition to CA (CaAl2O4) the samples contained major amounts of CA2 (CaAl4O7), C12A7 (Ca12Al14O33) and minor amounts of un-reacted A (Al2O3). Trace amounts of C3A (Ca3Al2O6) were observed only for samples heated to 1500 °C. The amount of the Ca-rich phase C12A7 was found to decrease with time as it reacts with A and, to a less degree, CA2 to form CA. In agreement with previous studies the amount of CA2 formed decreases comparatively slowly with time. Its un-reactivity is due to that it is concentrated in isolated porous regions of sizes up to 100 μm. The formation of the Ca aluminates is found to be in response to local equilibriums within small inhomogeneous regions, with no specific phase acting as an intermediate phase. Samples quenched from 1500 °C were found to contain smaller amounts of poorly crystallized phases. A reaction between C and A takes place already at 900 °C, forming a meta-stable orthorhombic modification of CA. The orthorhombic unit cell with a = 8.732(2) Å, b = 8.078(2) Å, c = √3·a = 15.124(4) Å was verified by electron diffraction, revealing frequent twinning and disorder of the crystallites.

  • 5.
    Iftekhar, Shahriar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Leonova, E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Edén, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Structural Characterizations of Lanthanum Aluminosilicate Glasses by 27Al and 29Si Solid State NMR2009Inngår i: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 355, nr 43-44, s. 2165-2174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the network structures of LaSiAlO glasses by 29Si magic-angle-spinning (MAS) nuclear magnetic resonance (NMR). Their compositions span most of the glass-forming region of the ternary La2O3Al2O3SiO2 system at 1600 °C. The 29Si NMR resonances narrow and become progressively deshielded when Al substitutes for Si in the network, as well as for increasing La-content of the glass, which leads to network depolymerization. We compare experimental and calculated center of gravities of the 29Si NMR peaks, the latter generated from different simplified models for the distributions of Al and Si as well as bridging oxygen (BO) and non-bridging oxygen (NBO) atoms over the networks. The data do not permit accurate quantifications and may only be interpreted in limiting scenarios. However, they indicate that both distributions are essentially randomized, implying a clear deviation of the Al/Si ordering from that according to a Loewenstein Al-avoidance, coupled with a nearly uniform partitioning of the NBO atoms between Al and Si tetrahedra.

  • 6.
    Iftekhar, Shahriar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Pahari, Bholanath
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Okhotnikov, Kirill
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Jaworski, Aleksander
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Stevensson, Baltzar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för oorganisk kemi och strukturkemi.
    Eden, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Properties and Structures of RE2O3-Al2O3-SiO2 (RE=Y, Lu) Glasses Probed by Molecular Dynamics Simulations and Solid-State NMR: The Roles of Aluminum and Rare-Earth Ions for Dictating the Microhardness2012Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 34, s. 18394-18406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By combining molecular dynamics (MD) simulations with Si-29 and Al-27 magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we present a comprehensive structural report on rare-earth (RE) aluminosilicate (AS) glasses of the RE2O3-Al2O3-SiO2 (RE = Y, Lu) systems, where the latter is studied for the first time. The structural variations stemming from changes in the glass composition within each RE system as well as the effects of the increased cation field-strength (CFS) of Lu3+ relative to Y3+-are explored and correlated to measured physical properties, such as density, molar volume, glass transition temperature, and Vickers hardness (H-V). Si-29 NMR reveals a pronounced network ordering for an increase in either the RE or Al content of the glass. Al mainly assumes tetrahedral coordination, but significant AlO5 and AlO6 populations are present in all structures, with elevated amounts in the Lu-bearing glasses compared to their Y analogues. The MD-derived oxygen speciation comprises up to 3% of free O2- ions, as well as non-negligible amounts (4-19%) of O-[3] coordinations (oxygen triclusters). While the SiO4 groups mainly accommodate the nonbridging oxygen ions, a significant fraction thereof is located at the AlO4 tetrahedra, in contrast to the scenario of analogous alkali- and alkaline-earth metal-based AS glasses. The average coordination numbers (CNs) of Al and RE progressively increase for decreasing Si content of the glass, with the average CN of the RE3+ ions depending linearly on both the amount of Si and the fraction of AlO5 groups in the structure. The Vickers hardness correlates strongly with the average CN of Al, in turn dictated by the CFS and content of the RE3+ ions. This is to our knowledge the first structural rationalization of the well-known compositional dependence of H-V in RE bearing AS glasses.

  • 7.
    Pahari, Bholanath
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Iftekhar, Shahriar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Jaworski, Aleksander
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Okhotnikov, Kirill
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Jansson, Kjell
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Stevensson, Baltzar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Grins, Jekabs
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Edén, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Composition-property-structure correlations of scandium aluminosilicate glasses revealed by multinuclear 45Sc, 27Al and 29Si solid-state NMR2012Inngår i: Journal of The American Ceramic Society, ISSN 0002-7820, E-ISSN 1551-2916, Vol. 95, nr 8, s. 2545-1553Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Many features of aluminosilicate glasses incorporating a rare-earth (RE) ion are dictated by its mass and cation field strength (CFS). ScAlSiO glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass-transition temperature (Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2O3Al2O3SiO2 system. The glasses exhibit uniform and unexpectedly low Tg-values (similar to 875 degrees C), but a high microhardness (approximate to 9.3 GPa) that correlates with the Sc2O3 content. 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy shows enhanced deshielding and a minor glass-network ordering as either the Al or Sc content of the glass increases. 27Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%35%) and AlO6 (approximate to 5%) polyhedra are present in all ScAlSiO glass structures. 45Sc isotropic chemical shifts (similar to 92 ppm) derived from MAS and 3QMAS (triple-quantum MAS) NMR experiments are consistent with ScO6 environments.

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