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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis and reactivity of cristobalite obtained from the SiO2-V2O5 system (1990)
    Springer
    Journal of materials science 9 (1990), S. 484-488 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00721038
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of quantum-size cadmium-zinc sulfide particle-doped glasses by the sol-gel method (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 1043-1047 
    Details
    ISSN: 1573-4846
    Keywords: quantum size materials ; optical materials ; CdS doped silica glasses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The optical properties of extremely small particles of semiconductor materials provide a sensitive probe of the band structure in the materials. The Sol-Gel process has been applied successfully to the preparation of small particle-size CdS-doped silica glasses such that quantum size effects are significant. Transparent and colorless gels were prepared through the hydrolysis of a complex solution of Si(OC2H5)4, (CH3)2SO, Zn(CH3COO)2·2H2O and Cd(CH3COO)2·2H2O. These gels were heated at 350, 500 and 750°C. The thermal treatments of samples were established by TDA/TGA analysis. By means of shift in optical absorption spectra, quantum size effects could be inferred in glasses containing these calcogenide microcrystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436981
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  • 3
    Electronic Resource
    Electronic Resource
    Fe x Ti1−2x M x O2 (M=Nb, Ta) rutile solid solutions from gels (1994)
    Springer
    Journal of sol gel science and technology 2 (1994), S. 381-385 
    Details
    ISSN: 1573-4846
    Keywords: gel ; solid solutions ; rutile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this study, Fe x Ti1−2x M x O2 (M=Nb, Ta) rutile solid solutions have been synthesized from gels made from Fe(III) acetylacetonate, NbCl5, TaCl5, Ta(V) ethoxide, TiCl4 and Ti(IV) isopropoxide. The results obtained are compared with those obtained by the ceramic method. The solid solutions synthesized from gels were obtained at lower temperatures than these synthesized by the ceramic method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486275
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  • 4
    Electronic Resource
    Electronic Resource
    Classical ceramic colors through colloidal and from alkoxides gels (1994)
    Springer
    Journal of sol gel science and technology 2 (1994), S. 377-380 
    Details
    ISSN: 1573-4846
    Keywords: ceramic pigment ; gel ; synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Classical ceramic pigments are manufactured through the traditional method of firing a mixture of oxides previously mechanical homogeneized in a mill. From industrial overview sol-gel applied in ceramic pigments manufacture is more expensive than ceramic method because the high price of raw materials. However in some classical pigments it would be economically interesting to use a sol-gel route because raw materials in ceramic route are as well expensive and gel route give the pigment at lower firing temperature and soaking time. In this paper a discussion for several pigments is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486274
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  • 5
    Electronic Resource
    Electronic Resource
    Study of phase-transfer-catalyst influence in CaO-SiO2 Gel preparation (1994)
    Springer
    Journal of materials science 29 (1994), S. 4325-4330 
    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 Gels in a CaO-SiO2 (20∶80 wt%) system were prepared in a heterogeneous phase. The following phase-transfer catalysts were tested: 18-Crown-6, 15-Crown-5 and tetrabutylammonium hydrogenosulphate. The influences of the polarity of two non-classical solvents (toluene and dichloromethane) were also studied. The degrees of polymerization and of oxide contents were analysed by infrared spectroscopy and thermal analysis. Finally, the morphology and structure of the dry and fired gels were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414218
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of hydrolysis time and type of catalyst on the stability of tetragonal zirconia-silica composites synthesized from alkoxides (1993)
    Springer
    Journal of materials science 28 (1993), S. 5852-5862 
    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 ZrO2-transformation-toughened glass-ceramics have been prepared by the sol-gel process from either colloidal gels (CG) or polymeric gels from alkoxides (PG), using, in the latest method, a different catalyst (acid, basic and without catalyst), and different compositions in the ZrO2·SiO2 system (free ZrO2 included). The different methods of synthesis of tetragonal zirconia in SiO2 matrix were compared in order to obtain thermal stability, and a high amount of stabilized tetragonal zirconia. The effect of catalyst, hydrolysis time, chemical composition, critical particle size in ZrO2(t)→ZrO2(m) transformation, the doping with vanadium on the ZrO2(t) stability in SiO2 matrix and Vickers microhardness of samples have also been studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00365192
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of ZrO2 precursors on the synthesis of V-ZrSiO4 solid solutions by the sol-gel method (1992)
    Springer
    Journal of materials science 27 (1992), S. 351-357 
    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 The preparation of V-ZrSiO4 solid solutions starting from different ZrO2 precursors by using sol-gel methods is reported. The starting materials were hydrolysed and the dried gels were fired at a temperature between 500 and 900 °C with soaking times of 12h. The organic character of zirconia precursors was stronger, i.e. the starting material had more carbon atoms, a higher temperature was necessary to make the first crystalline phase appear (ZrO2(tetragonal)) and the temperature range for the whole phase transformation was narrower. In all dried gel samples the presence of infrared bands which might be associated with either Si-O-Zr or Si-O-V was not observed. On the other hand, some bands could be attributed to a silica network and ZrO8 groups. The main steps in V-ZrSiO4 solid solutions were confirmed. ZrO2(tetragonal) is crystallized on heating from an amorphous sample. The ZrO2(tetragonal) → ZrO2(monoclinic) phase transformation then occurs and immediately afterwards the zircon formation begins. Finer textures in samples were obtained from polymeric gels rather than for colloidal gel samples, as seen from the scanning electron micrographs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00543923
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of Cr x Ti1−2x Nb x O2O20≤x≤0.5 rutile solid solutions from alkoxides (1994)
    Springer
    Journal of materials science 29 (1994), S. 3817-3821 
    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 In this study, Cr x Ti1−2x Nb x O2 (0 ⩽ x ⩽ 0.5) rutile solid solutions have been synthesized from gels built from hydrolysis-condensation of Cr (III) acetylacetonate, NbCl5 and Ti (IV) isopropoxide mixture (polymeric gel). Characterization of these solid solutions was carried out by X-ray diffraction, ultraviolet-visible and infrared spectroscopy, differential thermal and thermogravimetric analysis and CIELAB (Commission Internationale del'Eclairage L*a*b*) parameter measurements. The results obtained by the polymeric gel method were compared with those obtained by traditional ceramic synthesis. This comparison reveals some differences with regard to synthesis temperatures and reaction mechanisms. The formation of Cr x Ti1−2x Nb x O2 (0 ⩽ x ⩽ 0.5) rutile solid solutions by the ceramic method requires temperatures of about 1200°C and soaking times of several days. These solid solutions are synthesized at 1000°C in 24 h by the polymeric gel method. In ceramic synthesis, the CrNbO4 compound with rutile structure appears as an intermediate compound in the formation of rutile solid solutions. In polymeric gel synthesis, however, the CrNbO4 rutile compound was not detected in the samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357354
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  • 9
    Electronic Resource
    Electronic Resource
    Structural and electrical conductivity studies on rutile solid solutions [FexTi1-2xMxO2 (M=Nb, Ta)] (1998)
    Springer
    Journal of materials science 33 (1998), S. 4235-4238 
    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 In this study, FexTi1-xMxO2 (M=Nb, Ta; 0≤x≤0.5) solid solutions have been synthesized from both ceramic and gel methods, and electrical and structural characterization hasbeen carried out. The solid solutions show rutile structure except for the case of FeNbO4, which forms an orthorhombic structure. The electrical behaviour of the system studied corresponds to extrinsic p-type semiconduction and it is related to the presence of Fe(II) ions. Conductivity is enhanced by local distortions of the M–O lengths associated with ordering oxidation states such as those in Fe3O4. The distortions are more frequent when the asymmetry is greater (M=Nb). No electrical changes have been detected when the synthesis method is different. © 1998 Kluwer Academic Publishers
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004434009509
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  • 10
    Electronic Resource
    Electronic Resource
    Impedance spectroscopy studies of orthorhombic FeNbO4 (1996)
    Springer
    Journal of materials science 31 (1996), S. 2043-2046 
    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 Electrical characterization of the FeNbO4 compound, with orthorhombic structure, has been carried out. Compact bodies were prepared by sol-gel and ceramic routes. Pellets for electrical measurement were sintered in air, and samples for electrical tests were electroded with platinum, gold and silver paste. Equivalent circuit models were established that fit the impedance spectroscopy data with good agreement. Comparison of impedance responses showed that samples prepared by different routes have similar electrical behaviour. These measurements, in conjunction with I–V characteristic curves, indicate the existence of a small bulk resistance, which does not change at the higher experimental temperatures considered. Interfacial impedances due to the metallic contact regions contribute the greatest part of the overall impedance. The response of the sample with different electrode materials (platinum, gold, silver) was studied. I–V characteristic curves indicate a space charge-limited current phenomenon at the platinum contact, followed by a charge avalanche process at higher voltages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356624
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