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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 4 (1993), S. 127-131 
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: It has been proposed that a hydrated silica plays an important role in forming a biologically active apatite layer on the surfaces of bioactive glasses and glass-ceramics in the body. Recent experiments have shown that a silica hydrogel actually induces apatite formation on its surface in a simulated body fluid (SBF). In the present study the process of apatite formation on silica gel was investigated by means of thin-film X-ray diffraction, Fourier-transformed infrared reflection spectroscopy and scanning electron microscopic observation of the surface of the silica gel, as well as the measurement of changes in the ion concentration of the fluid. It was found that the induction period for the apatite nucleation on the surface of the silica gel was about 6 days. Once the apatite nuclei were formed they grew, taking a spherulitic form by consuming the calcium and phosphate ions from the surrounding fluid. Each spherulite consisted of a lot of flake that clustered into a petal-like morphology. The flake was carbonate-containing hydroxyapatite of small-crystallites and/or defective structure. The Ca/P ratio of the apatite was estimated as 1.5–1.6. Thus, the apatite formed was able to induce secondary nucleation of the apatite.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bone-like apatite on their surfaces. It has been shown that even a pure silica gel forms the bone-like apatite on its surface in a simulated body fluid. In the present study, pore structure of silica gels prepared by hydrolysis and polycondensation of tetraethoxysilane in an aqueous solution containing polyethylene glycol was modified by 1M HNO3, and 0.1M and 1M NH4OH solution treatments. The three kinds of resultant gels all contained large amounts of silanol groups and trisiloxane rings, but differ greatly in pore structure of nanometre pore size. Irrespective of these differences, all the gels formed the bone-like apatite on their surface in the simulated body fluid. It was speculated that a certain type of structural unit of silanol groups, which is easily formed in the presence of the polyethylene glycol, is effective for the apatite formation. © 1998 Chapman & Hall
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 8 (1997), S. 547-552 
    ISSN: 1573-4846
    Keywords: silicon alkoxide ; phase separation ; double pore structure ; liquid chromatography ; Van Deemter equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica gels retaining double pore structure in the size ranges of micrometer and nanometer have been applied to the rod-shaped monolithic column for liquid chromatography. The macropore structure was designed by controlling the phase separation process induced by the hydrolysis and polycondensation of alkoxysilane, whereas the mesopore structure was tailored by the solvent exchange treatments on wet gels. The size exclusion chromatograms on polystyrene standards exhibited almost similar features for octadecyl-modified rod and conventional packed beads columns. The dependence of plate height on the velocity of mobile phase determined for amylbenzene was by far weaker in the rod column than in the packed beads column, suggesting that additional geometrical factors should be considered in describing the separation mechanism in the rod column.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 13 (1998), S. 163-169 
    ISSN: 1573-4846
    Keywords: silica gels ; phase separation ; pore size distribution ; liquid chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Utilizing the concurrence of polymerization-induced phase separation and sol-gel transition in the hydrolytic polycondensation of alkoxysilanes, a well-defined macroporous structure is formed in a monolithic wet gel. By exchanging the fluid phase of the wet gel with an appropriate external solution, the nanometer-range structure of the wet gel can be reorganized into structures with larger median pore size essentially without affecting the macroporous framework. The double-pore structure thus prepared is characterized by open pores distributed in discrete size ranges of micrometers and nanometers. A new type of chromatographic column (silica rod) has been developed using monolithic double-pore silica instead of packed spherical gel particles. Typical silica rod columns had significantly reduced pressure drops and improved analytical efficiencies which do not deteriorate even at higher sample flow rates, both arising from a greater macropore volume than particle packed columns.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 8 (1997), S. 547-552 
    ISSN: 1573-4846
    Keywords: silicon alkoxide ; phase separation ; double pore structure ; liquid chromatography ; Van Deemter equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Silica gels retaining double pore structure in the size ranges of micrometer and nanometer have been applied to the rod-shaped monolithic column for liquid chromatography. The macropore structure was designed by controlling the phase separation process induced by the hydrolysis and polycondensation of alkoxysilane, whereas the mesopore structure was tailored by the solvent exchange treatments on wet gels. The size exclusion chromatograms on polystyrene standards exhibited almost similar features for octadecyl-modified rod and conventional packed beads columns. The dependence of plate height on the velocity of mobile phase determined for amylbenzene was by far weaker in the rod column than in the packed beads column, suggesting that additional geometrical factors should be considered in describing the separation mechanism in the rod column.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 17 (1998), S. 1063-1065 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 27 (1992), S. 2623-2626 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Four samples of YBa2Cu3O7−x with different values of x were prepared and characterized, and their elastic properties from 80 K to room temperature were investigated. It was found that an anomalous softening of the elastic moduli G, K, and E temperatures slightly higher than T c appeared only on the specimens with the superconducting orthorhombic phase. As the value of x became small and the transition width ΔT c became narrower, the softening became remarkable. The elastic constants also showed a thermal hysteresis at low temperatures. Relationships between this behaviour and proposed structural and domain changes are discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 27 (1992), S. 3365-3371 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The elastic modulus of polycrystalline (La, Sr)2CuO4 and YBa2Cu3O7−δ with copper replaced by iron has been measured in the temperature range from room temperature to 4.2 K using the cube resonance method. For the former system, 0.5% Cu is displaced by iron and the content of strontium is varied. The incorporation of iron gives rise to an apparent coexistence of magnetic order and superconducting order in samples La2−x Sr x (Cu, Fe)O4 withx=0.15 and 0.3, which is reflected in the temperature dependence of Young's modulus. For samples withx=0 and 0.05, an anomalous behaviour of Young's modulus, which is thought to correspond to orthorhombic-monoclinic transition, is observed. For the YBa2(Cu1−γFeγ)3O7−δ system, softening and a thermal hysteresis loop are observed in the temperature dependence of shear modulus of the sample withγ=0. The softening also appears in the temperature variation of Young's modulus. The degree of softening becomes smaller as the iron content which displaces copper is increased. These phenomena are discussed on the basis of the microstructure of the samples and the change of crystal structure with the iron content.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 31 (1996), S. 3541-3547 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Transparent glass-ceramics containing LiGa5O8∶Cr3+ crystallites have been prepared by heat treatment of Li2O-Ga2O3-SiO2-Cr2O3 glassy material. Average crystallite size evaluated from the full-width at half-maximum of the X-ray diffraction lines varies from about 3–7 nm as the heat-treatment temperature increases from 650 °C to 800 °C. The ligand field strength of the Cr3+ ion estimated from optical absorption measurements increases with an increase in the heat-treatment temperature. The fluorescence spectra of the glass-ceramics resemble that of LiGa5O8∶ Cr3+ polycrystal. In particular, for the specimen containing a crystallite of 7 nm, intense emission due to the 2E→4A2 transition has been observed. These optical measurements demonstrate that the Cr3+ ions are incorporated into LiGa5O8 microcrystals in the present glass-ceramics. For the transparent glass-ceramics and LiGa5O8∶Cr3+ polycrystal, the temperature dependence of the peak position of the zero-phonon line (R-line) has been analysed assuming that the electronic transition is described by the Raman process and the vibrational density of state is expressed by the Debye model. The Debye temperature of the transparent glass-ceramics is slightly lower than that of LiGa5O8∶ Cr3+ polycrystal, indicating that the softening of the phonon occurs in the LiGa5O8∶Cr3+ microcrystal precipitated in the transparent glass-ceramics.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 4 (1985), S. 759-760 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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