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  • 11
    Electronic Resource
    Electronic Resource
    Hydrolysis-polycondensation in binary phosphorus alkoxides—TEOS system studied by GC-MS (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 59-63 
    Details
    ISSN: 1573-4846
    Keywords: SiO2−P2O5 sol-gel system ; P-precursor reactivity ; GC-MS investigations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract It is well known that various phosphorus precursors exhibit different reactivities towards hydrolysis-polycondensation in acidic media. The hydrolysis-condensation in binary P-alkoxides—TEOS system was studied by GC-MS, in relation to the mentioned reactivity. As P-precursors, the following reagents were used: PO(OMe)3, PO(OEt)3, PO(OBu)3, P(OEt)3 and HOP(OMe)2. PO(OMe)3, PO(OEt)3 and PO(OBu)3 do not hydrolyze, but change the TEOS hydrolysis-polycondensation ratio. P(OEt)3 partially hydrolyzes and transforms into a very stable HOP(OEt)2 form, while HOP(OMe)2 reacts very fast with nonparental solvent and undergoes transesterification. Si−O−P bonds have not been observed in early stages of hydrolysis-polycondensation. However, the gelling tendency is strongly influenced by the P-precursor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436818
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  • 12
    Electronic Resource
    Electronic Resource
    TiO2-based porous materials obtained from gels, in different experimental conditions (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 249-253 
    Details
    ISSN: 1573-4846
    Keywords: porous materials ; TiO2 films ; titanium isopropoxide ; sol-gel method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The gels which are precursors of TiO2 porous materials are prepared by the controlled hydrolysis-condensation of titanium isopropoxide by polymeric method. In the present work, a study of the influence of different experimental conditions (water/alkoxide ratio, solvent/alkoxide ratio and temperature) on the structure and texture of the polymeric gels obtained with the same type of alkoxide has been investigated. The structural and textural modifications for the unsupported materials have been detected using DTA/TGA, XRD, specific surface area and pore size computerized measurements. The optical properties of the supported materials deposited on silicon wafers have been investigated using ellipsometric method. Supported and unsupported porous materials with different structure and texture have been obtained depending on different experimental and thermal treatment conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436848
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  • 13
    Electronic Resource
    Electronic Resource
    Contributions to the gelling process in the Bi−Sr−Ca−Cu−O system, via acetate route (1997)
    Springer
    Journal of sol gel science and technology 8 (1997), S. 681-684 
    Details
    ISSN: 1573-4846
    Keywords: sol-gel ; acetates ; Bi-based superconductors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Metal acetates represent suitable precursors in the sol-gel method. Generally, acetates are used in multicomponent systems with alkoxides or other carboxylic salts. However, Bi−Sr−Ca−Cu−O superconductors have been obtained by the sol-gel method starting only from acetate mixture. This work was intended to study the gelling process of acetates involved in the formation of bismuth-based superconducting phases, both individually and in the bi-and multicomponent systems. Probably, copper acetate is mainly responsible for the gel formation in these systems. The gelling process was monitored by measuring the pH, density and viscosity changes. The gels obtained were characterized by UV-VIS and IR spectra, DTA/TGA and powder X-ray diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02436922
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  • 14
    Electronic Resource
    Electronic Resource
    Medium range order in high surface area amorphous silicas (1990)
    Springer
    Journal of materials science 25 (1990), S. 2095-2099 
    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 Medium-range order (MRO) in amorphous (a-) SiO2 can be defined as the degree of orientational correlation between neighbouring SiO4/2 tetrahedra. Analysis of X-ray diffraction data on high surface area a-silicas shows that the MRO can be characterized quantitatively by means of (a) the first peak position in the interference function and (b) the ratio between O-O(II) and Si-O(II) coordination heights in the pair distribution function. These two quantities are physically related.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01045771
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  • 15
    Electronic Resource
    Electronic Resource
    Assessing stacking faults in Bi-Sr-Ca-Cu-O phases by X-ray diffraction (1991)
    Springer
    Journal of materials science 26 (1991), S. 4136-4141 
    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 A Hendricks-Teller analysis of the X-ray diffraction line shifts in Bi-Sr-Ca-Cu-O phases allows an estimate of the stacking fault probabilities (missing or extra Cu-O layers). The probability values suggest some conclusions about the mutual relationships of the 2201, 2212 and 2223 phases and the kinetics of their formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02402958
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  • 16
    Electronic Resource
    Electronic Resource
    Assessing stacking faults in Bi-Sr-Ca-Cu-O phases by X-ray diffraction (1991)
    Springer
    Journal of materials science 26 (1991), S. 4136-4141 
    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 A Hendricks-Teller analysis of the X-ray diffraction line shifts in Bi-Sr-Ca-Cu-O phases allows an estimate of the stacking fault probabilities (missing or extra Cu-O layers). The probability values suggest some conclusions about the mutual relationships of the 2201, 2212 and 2223 phases and the kinetics of their formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00553500
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  • 17
    Electronic Resource
    Electronic Resource
    Structure and phase diagram of the Na2B4O7-Na3AlF6 system (1999)
    Springer
    Journal of materials science 34 (1999), S. 3923-3929 
    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 A complex study was carried out on Na2B4O7-Na3AlF6 binary system by means of differential thermal analyses (DTA), X-ray diffraction as well as infrared (IR), and Raman spectroscopy. Although the system exhibits a simple eutectic at 83 wt % Na2B4O7 and Te = 642°C, interesting structural changes of borate glasses formed have been evidenced by means of IR and Raman spectroscopy. Over 80–100 wt % Na2B4O7 range AlF6 3− anions are diluted in the vitreous matrix without significant structural changes while the further increase of Na3AlF6 content diminishes the concentration of BO4 groups and promotes the appearance of complex anions AlFx (x−3)− (x = 6, 5, 4) as well as the possible new BF4 − and/or BO3F4− species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004635109184
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  • 18
    Electronic Resource
    Electronic Resource
    Hydrolysis-condensation of tetraethoxysilane in nonparental solvents studied by GC-MS (1994)
    Springer
    Journal of sol gel science and technology 2 (1994), S. 43-49 
    Details
    ISSN: 1573-4846
    Keywords: tetraethoxysilane ; hydrolysis ; nonparental solvents ; GC-MS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Gas-chromatography coupled with mass spectrometry was used to investigate the hydrolysis and condensation of tetra-ethoxysilane (TEOS) in nonparental solvents (MeOH and nPrOH). In the presence of nonparental solvents, the reaction that advanced at highest rate is alkoxy group scrambling, that changes the precursor at the molecular level. Subsequent stages of hydrolysis-polycondensation process are essentially determined by the reactivity of the new molecular species formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00486211
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  • 19
    Electronic Resource
    Electronic Resource
    Solid State Phase Formation in the Bi2O3-PbO-CaO System (1999)
    Springer
    Journal of thermal analysis and calorimetry 56 (1999), S. 125-130 
    Details
    ISSN: 1572-8943
    Keywords: Bi2O3-PbO-CaO system ; DTA ; solid-state reactions ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Following our previous research, this work is dedicated to the study of phase formation in the subsolidus domain of the Bi2O3-PbO-CaO system. Former investigations performed by DTA/TGA and XRD have pointed out that under non-isothermal conditions only the formation of binary compounds occurs. Under such conditions these compounds could be non-equilibrium phases. In order to establish the conditions of formation of equilibrium phases, a study of the Bi2O3-PbO-CaO system, in isothermal conditions, was carried out. The results obtained in isothermal conditions have confirmed the presence of Bi2O3-rich solid solutions and Ca2PbO4 as main equilibrium phases. An attempt to represent the phase relations of the mentioned system at 700°C should be equally mentioned.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010199728644
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  • 20
    Electronic Resource
    Electronic Resource
    SiO2-Sm2O3 vitreous films via the sol-gel method (1993)
    Springer
    Journal of materials science 28 (1993), S. 4435-4441 
    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 SiO2-Sm2O3 vitreous films 120 nm thick were obtained via the sol-gel method. Infrared, energy-dispersive analysis of X-rays, spectroscopic ellipsometry and absorption spectroscopy showed a total inclusion of samarium in the silica matrix, which remains amorphous up to 1000 °C. The inclusion of the samarium ion increases the porosity. The optical properties of films were investigated by spectro-ellipsometry, and the parameters obtained were compared with those obtained by other techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01154953
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