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  • phosphate xerogels  (2)
  • phosphates  (1)
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  • 1
    ISSN: 1573-4846
    Keywords: thorium ; tin ; phosphate xerogels ; EPR ; DSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Different transparent phosphate xerogels were synthesized usingconcentrated solutions of metal chlorides and phosphoric acid with aproper mole ratio of both components. By this method we prepared bulksamples of thorium and tin(IV) phosphate xerogels by drying at room temperature or at 350 K. Some properties of these amorphous materialswere studied by means of differential scanning calorimetry (DSC) andelectron paramagnetic resonance (EPR) techniques. Depending on moleratio $$\frac{{{\text{metal}}}}{{{\text{phosphate}}}}$$ , these xerogels show, near 180 K, inflection points which we interpret as T g . Samples dried at 425 K lose their transparency and have no T g . Thus, it seems that the “glassy” state is due to water molecules remaining in the material. The same properties wereconfirmed by EPR studies of the xerogels doped with Cr3+ andFe3+ ions as probes. These results show the existence of twodifferent phases in the xerogels: a liquid-like one, in the range from190 K to 350 K and a solid-like one, in the range from 4 K to 190 K.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4846
    Keywords: thorium ; tin ; phosphate xerogels ; EPR ; DSC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Different transparent phosphate xerogels were synthesized using concentrated solutions of metal chlorides and phosphoric acid with a proper mole ratio of both components. By this method we prepared bulk samples of thorium and tin(IV) phosphate xerogels by drying at room temperature or at 350 K. Some properties of these amorphous materials were studied by means of differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) techniques. Depending on mole ratio metal/phosphate, these xerogels show, near 180 K, inflection points which we interpret asT g . Samples dried at 425 K lose their transparency and have noT g . Thus, it seems that the “glassy” state is due to water molecules remaining in the material. The same properties were confirmed by EPR studies of the xerogels doped with Cr3+ and Fe3+ ions as probes. These results show the existence of two different phases in the xerogels: a liquid-like one, in the range from 190 K to 350 K and a solid-like one, in the range from 4 K to 190 K.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of sol gel science and technology 2 (1994), S. 787-789 
    ISSN: 1573-4846
    Keywords: phosphates ; optical properties ; refractive index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have developed the chemical conditions to prepare highly concentrated mixtures of different metallic chlorides (Sn, Al, Cr) and phosphoric acid. We let them dry at room temperature for bulk materials, but for films the temperature of drying can reach 400°C. The structure of bulk compounds have been examined through elastic neutron diffraction experiments correlated with X ray diffraction at large angle. These compounds are amorphous and we observed, using the differential scanning calorimetry at low temperature, that T g values can be determined at more than 100 K below room temperature. This material could be considered as a “liquid glass” at room temperature. Several other metallic elements are under progress to determine if this behavior is depending on the nature of the element. Bulk materials have been codoped with a dye (oxazine) and trivalent erbium ion. By UV excitation of the dye we observed the absorption spectrum Er3+ in the emission band of oxazine, that is an evidence of the energy transfer effect. Films made by spin coating technique have been doped with Dispersed Red 1 (DR 1). We studied the effect of organic additives (hydrosolubles polymers like PVP) on the kinetics of photoisomerisation of DR 1. Films are also used as waveguide. Several modes have been observed and their refractive index values determined.
    Type of Medium: Electronic Resource
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