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  • 1990-1994  (4)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Bleaching mechanism of silver halide photochromic glasses (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 1657-1668 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal bleaching of silver halide photochromic glasses is studied by electron paramagnetic resonance spectroscopy of photoinduced CuII centers. During exposure to ultraviolet light, the only stable CuII species is the (CuIIVAg)A center, which is a CuII-silver vacancy complex with the vacancy in a nearest position. In the dark, this center rapidly decays via two parallel channels. The first involves the dissociation of the complex by displacement of the vacancy along a [110] direction, with an activation energy E3=0.44 eV and a frequency factor k30=3.4×105 s−1. The second channel involves the conversion of the (CuIIVAg)A center into a (CuIICl−VAg)B center, where the silver vacancy is in the next nearest position along the [100] direction. This process occurs with an activation energy E1=0.44 eV and a frequency factor k10=3.1×105 s−1. The (CuIICl−VAg)B center slowly decays by a vacancy hopping mechanism, with an activation energy E2=0.22 eV and a frequency factor k20=4.6 s−1. To explain these two decay channels, it is proposed that the (CuIIVAg)A and (CuIICl−VAg)B centers annihilate via the formation of a CuI ion and a neutral complex (AgIIVAg)A which migrates to the surface of the silver halide particle, where electron-hole recombination occurs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353200
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Electron-paramagnetic-resonance study of silver halide photochromic glasses: Darkening mechanism (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1081-1090 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism of darkening of standard silver halide photochromic glass is studied by electron paramagnetic resonance (EPR) of photogenerated divalent copper ions. A time resolution of the EPR spectra was obtained by recording the evolution with the irradiation time of the EPR intensity at various magnetic-field strengths. It is shown that only one copper species is photogenerated during darkening. This species is a CuII-silver vacancy complex oriented along a [110] direction. The electron ground state has a predominantly dz2 character. The activation energy of the formation of this complex, E=0.06±0.01 eV, is controlled by the migration of interstitial silver ions. It is also shown that the silver vacancy of the complex is generated during the hole trapping by the monovalent copper ion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351400
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Glasses from aerogels (1990)
    Springer
    Journal of materials science 25 (1990), S. 3118-3126 
    Details
    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 Silica glasses are obtained by the densification of aerogels. The transformation of the material into a glass is followed by differential thermal analyis, thermo-gravimetric analysis, dilatometry and by the evolution of the structural, textural and mechanical properties of the material. The organic species and the hydroxyl groups are removed by oxidation and chlorination heat treatments in such a way as to avoid bloating and crystallization phenomena during sintering. Densification is obtained by heat treatment at a low temperature (1100 to 1300 ° C). The densified aerogel shows physical properties identical to those of molten silica. Moreover, this material is very pure and its water content is low. The same process can be extrapolated to multicomponent glasses and composite materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587660
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  • 4
    Electronic Resource
    Electronic Resource
    Glasses from aerogels (1990)
    Springer
    Journal of materials science 25 (1990), S. 3111-3117 
    Details
    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 Experiments carried out to obtain monolithic silica aerogels are reported. The different ways to synthesize silica aerogels from alkoxides are investigated. The manner by which the critical point of the solvent can be reached is discussed as a function of the nature of the solvent. Physical parameters such as the amount of additional solvent or pressure, play a very important role in the direction of the liquid-vapour interface displacement during the heating of the autoclave. Some experiments performed using hypercritical drying with CO2 liquid are also mentioned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587659
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    Paper (German National Licenses)
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