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  • Articles  (259)
  • sol-gel  (259)
  • Springer  (259)
  • Blackwell Publishing Ltd
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  • Chemistry and Pharmacology  (259)
  • 1
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    Journal of inorganic and organometallic polymers and materials 8 (1998), S. 205-214 
    ISSN: 1572-8870
    Keywords: Phosphazenes ; sol-gel ; urethane ; surface functionalization ; heparin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A sol-gel precursor was prepared by the reaction of poly[bis(2-(2-hydroxyethoxy)ethoxy)phosphazene] (1) with 3-isocyanatopropyltriethoxysilane. It was then sol-gel polymerized to produce a covalently interconnected phosphazene-silicate network with urethane functionalities. Isocyanato groups were introduced on the surface of the network through coupling by allophanate formation between hexamethylene diisocyanate and urethane functionalities on the gel surface. Heparin was immobilized on the surface of the network by reacting hydroxyl or amino groups of heparin with the surface isocyanato groups. The activity of the immobilized heparin was 4.0% that of free heparin.
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  • 2
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    Journal of solution chemistry 20 (1991), S. 1149-1157 
    ISSN: 1572-8927
    Keywords: Tetraethyl orthosilicate ; ethanol ; 1-propanol ; 1-butanol ; sol-gel ; dielectric spectroscopy ; dielectric relaxation ; ceramics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dielectric properties of mixtures of 1-alcohols (ethanol, 1-butanol and 1-hexanol) and tetraethyl orthosilicate (TEOS) were determined by means of the time domain method (TDS). To all spectra were fitted a model function containing a sum of three debye relaxation terms with fixed τ2 and τ3. Initially, to 2–3 mole%, TEOS did not influence static permittivity nor main relaxation time of the alcohol. For higher concentrations there is a linear decrease in both these parameters. Qualitatively the effects of TEOS are comparable with those of a nonpolar hydrocarbon on the alcohol structure.
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  • 3
    ISSN: 1572-879X
    Keywords: alumina ; carbon monoxide oxidation ; ethylene oxidation ; platinum ; cerium ; sol-gel ; thermostability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Various alumina-based supports were prepared by adding metal elements such as alkaline and rare earths to sol-gel alumina synthesized from aluminium isopropoxide using 2-methylpentane-2,4-diol as a solvent and the influence of the additives on the thermostability of the supports was investigated. It was found that Ba and Sr are the most effective in improving the thermostability of the alumina, La is moderately effective while Zr, Mg and Ca are ineffective. The influence of the additives on the catalytic activities of Pt/CeO x /MO y -Al2O3 (M=Ba, Sr, La) after the calculation at 1273 K was also investigated. Pt/CeO x /BaO-Al2O3 and Pt/ CeO x /La2O3-Al2O3 showed higher catalytic activity than Pt/CeO x /Al2O3, while Pt/CeO x / SrO-Al2O3 showed lower catalytic activity. The activity order was Ba 〉 La = none 〉 Sr in terms of CO and C2H4 oxidation.
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  • 4
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    Catalysis letters 36 (1996), S. 41-49 
    ISSN: 1572-879X
    Keywords: sol-gel ; Ru/Al2O3 ; ethylene glycol ; characterization ; chelating agent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ru/Al2O3 catalysts were prepared by sol-gel method with an organic additive (ethylene glycol). The effect of the addition of ethylene glycol on the properties of Ru/Al2O3 was characterized by BET, XRD, EXAFS, and TGA/DTA. Ethylene glycol was effective to promote the phase transition of α-Al2O3 even at 800°C calcination with high surface area. This finding is ascribed to the modified structure of aluminum alkoxide by ethylene glycol addition in the solution state. Ethylene glycol is also effective to get small particles of ruthenium after the reduction at 500°C. The EXAFS and UV-Vis spectra of Ru complex revealed that the coordination structure of Ru depended on the additive used. The ethylene glycol sol prefers to form octahedral Ru complex. This Ru complex in alumina matrix is stable up to 200°C and forms small Ru oxide particles even at 300°C calcination. This suggests that ethylene glycol coordinates to the Ru complex as well as to aluminum ion in the initial state, which is important to control the final properties of the Ru/Al2O3 catalyst.
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  • 5
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    Journal of applied electrochemistry 28 (1998), S. 1051-1059 
    ISSN: 1572-8838
    Keywords: Carbon-Ceramic electrodes ; Li ion batteries ; intercalation ; Li salt solutions ; EIS ; sol-gel ; Ormosil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Graphite electrodes comprising silica binder were tested in ethylene carbonate–dimethyl carbonate (EC–DMC), propylene carbonate and tetrahydrofuran solutions. The electrochemical behavior of these electrodes was analyzed using chronopotentiometry, slow-scan rate cyclic voltammetry (SSCV), impedance spectroscopy and potentiostatic intermittent titration technique (PITT). The electrode morphology and integrity were studied by scanning electron microscopy (SEM). Using silica binder, graphite particles are usually embedded in the current collector in an unoriented form. Thus, the electroanalytical study of these electrodes and the comparison of their response with that of highly oriented PVDF based graphite electrodes, provided insight into the effect of particle orientation on the general electrochemical behavior of lithiated graphite anodes. In general, the higher the particle orientation and compact packing in the electrodes' active mass, the better the performance o f the Li–graphite electrodes, as the surface films developed are better passivating and the interparticle electronic contact is also better. The silica binder may have advantages over other binders such as PVDF in its ability to better retain the electrode integrity upon cycling. However, the practical use of such electrodes requires further optimization, especially in connection with particle orientation and compact packing.
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  • 6
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    Journal of inorganic and organometallic polymers and materials 6 (1996), S. 221-236 
    ISSN: 1572-8870
    Keywords: Hybrid materials ; metal oxides ; polytorganophosphazenes ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this paper the sol-gel preparation of hybrid materials made of metal oxide and polytorganophosphazenel components is described. The main problem focused on during this research was to avoid phase separation in order to get homogeneous materials. This problem was pursued looking at the formation of genuine chemical bonds between the exploited polyphosphazenes and the inorganic composite networks. Investigations on the thermal, mechanical, and electroconductive properties of the synthesized, phosphazene-containing composite materials showed that these matrices presented improved mechanical and thermal features with respect to those of the original phosphazene macromolecule, while the ionic conductivities of the prepared molecular hybrids doped with lithium or silver trillate are of the same order of magnitude as those measured for the neat, original phosphazene substrate.
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  • 7
    ISSN: 1572-9028
    Keywords: titania-silica ; mixed oxide ; sol-gel ; aerogel ; epoxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The paper provides a short overview on the various Ti- and Si-containing epoxidation catalysts, with a focus on the development and characterisation of titania-silica mixed oxides prepared by the sol-gel-aerogel method. Titania-silica aerogels, dried by semicontinuous extraction of the solvent with supercritical CO2 at low temperature, possess high surface area, an amorphous mesoporous structure, and a rather even distribution of Ti in the silica matrix. The catalytic activities of mixed oxides, silica-supported titania and Ti-substituted molecular sieves (TS-1, Ti-Β and Ti-MCM-41) are compared in the epoxidation of 1-hexene, 1-octene, cyclohexene, cyclododecene and norbornene, based on literature data. The activities (i.e. the amount of converted olefin per unit time and catalyst weight) vary in a broad range of several orders of magnitude. It is shown that the low temperature aerogel containing 20 wt% TiO2 is superior to any other Ti- and Si-containing catalyst for the epoxidation of cyclic olefins. In the epoxidation of linear alkenes TS-1 has outstanding activity. Ti-substituted large and ultra-large pore molecular sieves require further development concerning their catalytic performance.
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  • 8
    ISSN: 1572-879X
    Keywords: molybdenum oxide ; silica support ; sol-gel ; impregnation ; partial oxidation ; methane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Two kinds of MoO3/SiO2 catalysts, MoO3-I and MoO3-S, were prepared by impregnation and sol-gel method, respectively. When MoO3 loading was increased, formation of MoO3 crystals was observed to begin at a MoO3 loading of 8 and 16 wt% with MoO3-I and MoO3-S, respectively. The highest yield of formaldehyde from methane oxidation was attained also at those critical values of MoO3 loading of 8 and 16 wt% over MoO3-I and MoO3-S, respectively. It is suggested that the active species for formaldehyde formation is well dispersed molybdenum oxide clusters on SiO2 support: the optimum dispersion of the clusters affords the highest activity for formaldehyde formation.
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  • 9
    ISSN: 1572-879X
    Keywords: hydrogenation ; ruthenium/tin/alumina ; combination ; sol-gel ; impregnation ; ethyl phenylacetate ; 2-phenylethanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A ruthenium-tin-alumina catalyst, prepared by a combination of kneading and impregnation methods, which we have named the combination method, was able to selectively hydrogenate ethyl phenylacetate to 2-phenylethanol; tin oxide was used as a chloride-free tin source. For this combination catalyst, the optimum atomic ratio for Ru: Sn was found to be 1 ∶ 4. X-ray diffraction measurements showed the presence of tin particles. It appeared that the number of the tin particles had a large effect on the hydrogenation of C=O groups. However, the catalyst prepared with ruthenium oxide had a low activity, possibly owing to the ruthenium metal or ruthenium-tin alloy, which was formed and which obstructed the reaction.
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  • 10
    ISSN: 1572-879X
    Keywords: support ; cerium ; alumina ; sol-gel ; thermostability ; platinum ; three-way catalyst
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Various CeOx-Al2O3 powders were prepared and the influence of the method of support preparation on the thermostability of the mixed alumina-supported Pt catalysts and on their oxidation of CO was investigated. It was found that the complexing agent-assisted sol-gel method is effective in improving the thermostability of the mixed alumina-supported Pt catalysts. Monolith Pt-Rh three-way catalysts were prepared using these aluminas and other thermostable alumina including Ba. Activity of the catalysts was also investigated after conducting accelerated thermal engine aging in order to test their durability. Under normal operating conditions of the automobile engine, the activity of the Pt-Rh three-way catalyst using the CeOx-Al2O3 support prepared by the complexing agent-assisted sol-gel method is nearly equal to that of the catalyst using the CeOx impregnated onto BaO-Al2O3 powder prepared by the same sol-gel method.
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  • 11
    ISSN: 1572-879X
    Keywords: zeolite ; Al-TS-1 ; sol-gel ; bifunctional properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ti-containing ZSM-5 (Al-TS-1) has been synthesized by wetness impregnation of amorphous Al2O3-TiO2-SiO2 solids with TPAOH solutions and subsequent crystallization under autogenous pressure at 170°C. The cogel containing aluminum, titanium and silicon oxides used as raw material has been prepared following a two-step (acid-base) sol-gel process which leads to the formation of Si-O-Ti and Si-O-Al bonds previously to the zeolite crystallization. X-ray diffraction (XRD) confirms the high crystallinity of TS-1 and Al-TS-1 obtained by this procedure whereas thermogravimetric analysis (TGA) of TPAOH-containing samples andnC6 adsorption measurements show the purity of the different samples. Fourier transformed infrared spectroscopy (FTIR) evidences the incorporation of Ti and NH3 temperature programmed desorption confirms the acidic properties of Al-TS-1. Diffuse reflectance ultraviolet-visible spectroscopy (DR UV-VIS) shows that Ti atoms occupy tetrahedral positions in the Al-TS-1 and TS-1 lat-tices whereas bulk anastase and/or extraframework Ti species are not detected.29Si and27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy indicate the presence of Al occupying tetrahedral positions in the Al-TS-1 framework. Therefore, the simultaneous incorporation of Ti and Al provides the Al-TS-1 samples with bifunctional properties showing high catalytic activity forn-hexane oxyfunctionalization with H2O2 and for alcohols etherification reactions. When it is compared to the conventional procedures of Al-TS-1 preparation by hydrothermal crystallization of a liquid gel, the method studied here is simpler, requires a lower reaction volume and proceeds with shorter synthesis time. In addition Al-TS-1 prepared through this alternative method exhibits better catalytic properties than the material synthesized following a recipe based on hydrothermal crystallization of a liquid gel.
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  • 12
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    Microchimica acta 129 (1998), S. 149-165 
    ISSN: 1436-5073
    Keywords: silicates ; organosilicon ; sol-gel ; ORMOSIL ; solid-state lasers ; gas separation membrane ; nonlinear optics ; optical wave guides ; composite films ; chemical sensors ; gas sensors ; catalysis ; chromatographic applications
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Inorganic-organic hybrid materials prepared by the sol-gel process have become an attractive field of study due to the immense versatility associated with this method of composite material preparation. The blending of inorganic precursors with organosilicon reagents enables unique materials to be fabricated with the desired chemical and physical characteristics. The ability to control the interfacial polarity, the degree of porosity, and the chemical functionality in the matrix has been shown to be a powerful tool in the design of materials for sensor, optical, chromatographic, and catalytic applications. In this review, the preparation of the organically modified silicates (ORMOSILs) where the individual precursors are covalently bound to each other is discussed and selected examples of their potential usefulness in analytical applications is presented.
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  • 13
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    Microchimica acta 108 (1992), S. 133-141 
    ISSN: 1436-5073
    Keywords: optical sensor ; sensor material ; pH measurement ; fluorescence ; sol-gel ; optrode for pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We report on an optical sensor material suitable for fluorimetric measurement of pH in the 6–9 range using a new, fully LED-compatible fluorescent dye. Its base form has a strong absorption between 580 and 630 nm that matches the emission band of conventional yellow or orange light-emitting diodes. Two kinds of dye immobilization are reported. The first is based on covalent binding to a cellulosic matrix and the resulting material is intended for use in sensing membranes. The second involves physical entrapment of the dye in a sol-gel matrix which can be used for optical fiber tip coating as well as in evanescent wave type sensors. Both kinds of sensor materials are studied with respect to dynamic pH ranges, response times, sensitivity toward ion strength, and stability.
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  • 14
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    Journal of thermal analysis and calorimetry 48 (1997), S. 989-996 
    ISSN: 1572-8943
    Keywords: sol-gel ; TG ; thermal decomposition ; Y-Ba-Cu superconductors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A precursor of Y-Ba-Cu oxides was prepared by a modified alkoxide sol-gel method and its thermal decomposition in air was studied by on-line coupled TG-FTIR and High Resolution Thermogravimetric measurements. A continuous more or less stepwise weight loss was observed between room temperature and 600°C at which all organic compounds had evolved and were progressively oxidized as the temperature increased leaving only Y and Cu oxides and bariumcarbonate. Between 700 and 800°C a final weight loss was observed due to the decomposition of bariumcarbonate into oxide.
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  • 15
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    Journal of thermal analysis and calorimetry 48 (1997), S. 1051-1067 
    ISSN: 1572-8943
    Keywords: reaction mechanisms ; sol-gel ; superconductors ; thermoanalytical techniques
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The high temperature superconducting compound YBa2Cu3O72212;δ (Y-123) is synthesised by sol-gel process using various precursors viz., acetate, acetate-citrate, nitrate-citrate and acrylamide. The phase purity of the final product depends on the homogeneity of the gels which intern depends on the bonding of the metal ions in the gels. The samples prepared by acrylamide and nitrate-citrate gel routes yielded phase pure Y-123 compound with better superconducting properties. The mechanism of formation of Y-123 in all these four gel routes is established by characterising the gels and intermediate phases using TG, DTA and XRD techniques. Kinetic analysis is carried out on the mass loss data using the method proposed by Phadni's and Deshpande. Avrami-Erofeev nuclei growth in case of acrylamide, diffusion controlled process in nitrate-citrate and phase boundary reaction mechanisms in case of acetate-citrate gels are found to be responsible for the formation of Y-123 phase.
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  • 16
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    Journal of thermal analysis and calorimetry 60 (2000), S. 699-705 
    ISSN: 1572-8943
    Keywords: crystallization kinetics ; sol-gel ; solid solutions ; ruthenia ; titania
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of rutile type solid solutions in (TiO2)x -(RuO2)1−x system in the 0≤x ≤0.7 concentration range is described. The single phase solid solutions are formed by controlled nanocrystallization of amorphous gels prepared by the sol-gel method. The kinetics of this crystallization process has been analyzed. It was found that the crystallization does not correspond to the Johnson-Mehl-Avrami model and it can be described by the two-parameter Šesták-Berggren kinetic model.
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  • 17
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    Journal of thermal analysis and calorimetry 50 (1997), S. 105-115 
    ISSN: 1572-8943
    Keywords: BiSCCO synthesis ; fluorine substitution ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel citrate technology was used to prepare BiSCCO 2223 and 2212 superconducting phases. Fluorine in the initial mixture was shown to enhance considerably formation of the 2223 phase. Fluorine substitution of up to three F atoms per Bi(Pb)SCCO 2223 formula was achieved by treatment of the sample in 80 Torr ClF3 atmosphere. A number of experimental methods have been used to characterize the samples and to trace the phase transformations in the sol-gel process: DTA/TG, XRD, atomic absorption, potentiometry with fluoride selective electrode, magnetic susceptibility measurements.
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  • 18
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    Journal of thermal analysis and calorimetry 56 (1999), S. 7-15 
    ISSN: 1572-8943
    Keywords: ALE ; CVD ; DSC ; DTA ; EGA ; EL display ; solar cell ; sol-gel ; spray pyrolysis ; super-conductor ; TG ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Processing thin films for advanced applications, for instance in electronics and optoelectronics, involves several steps starting from precursor synthesis and ending up with the devices. Especially when optimizing the first steps of this chain of processes, thermoanalytical techniques play an important role. The review will focus on the main chemical deposition methods (CVD, ALE, spray pyrolysis, sol-gel) giving selected examples of problem-solving by thermal analysis. The techniques discussed are TG, DTA/DSC, EGA and their combinations. High-temperature X-ray diffraction (HTXRD) is also a powerful tool for in situ studies of thin films. The examples are taken from solar cell, superconductor and flat panel electroluminescent display technologies.
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  • 19
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    Journal of thermal analysis and calorimetry 56 (1999), S. 199-204 
    ISSN: 1572-8943
    Keywords: aluminium ions ; aluminosilicate gel ; mullite ; silica solution ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The mechanism of mullite formation depends upon the method of combining the silica and alumina-containing reactants. In this work, the effects of the processing variables (dilution, pH, gelling temperature and water content) on mullite formation were investigated. Monophasic gel was synthesized from aluminium nitrate nanohydrate dissolved in an absolute ethyl alcohol and silica sol mixture. The gelling was performed at room temperature and at 60°C. It was found experimentally that the temperature of mullite formation depends on the microstructure of the gel. The lowest temperature of mullite formation (970°C) was observed when the mullite gel was prepared at low pH (pH=1), low water content and high gelling temperature.
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  • 20
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    Journal of sol gel science and technology 11 (1998), S. 55-66 
    ISSN: 1573-4846
    Keywords: titania coating ; sol-gel ; coating bonding strength to substrate ; biocompatible ; bioactive
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bioactive ceramic coatings have had poor adhesion to substrate. In this study, the bond strength (tensile strength) of titania gel coating to titanium substrate was studied. In the experiments three different pretreatments were used, namely sodium hydroxide corroding, plasma cleaning and titanium nitride coating. Also the effects of heating temperature, heating in vacuum and titanium surface roughness were studied. The sol properties were altered with valeric acid addition. Samples were analysed by SEM-EDX, AES, AFM and tested by bond strength gauge. Those samples in which the titanium surface was precorroded one hour in sodium hydroxide, predeposited by titanium nitride or ground improved the bonding strengths of titania coatings to over 24 MPa. In these samples a fracture occurred at the glue-coating interface.
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  • 21
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    Journal of sol gel science and technology 11 (1998), S. 289-298 
    ISSN: 1573-4846
    Keywords: Ag/SiO2 ; Cu/SiO2 and Ag-Cu/SiO2 nanocomposite films ; sol-gel ; annealing atmospheres ; clusters growth by thermal annealing ; optical absorption ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a program on the development of metal nanoclusters in sol-gel derived thin films, attempts were made to synthesize pure and mixed metal clusters, control the cluster size and increase the volume fract f the clusters. Thus, Ag, Cu and Ag-Cu nanoclusters were prepared in silica films using dip- and spin-coating techniques. The annealing of Ag/SiO2 films in different atmospheres (air, argon and 5% H2-95% N2 gas) caused modifications of Ag nanoclusters resulting in changes in their surface plasmon resonance (SPR) peak positions. The Cu and Ag-Cu codoped films were annealed in reducing atmosphere (5% H2-95% N2 gas). In order to prepare Cu nanoclusters of different sizes, the concentrations of Cu in Cu/SiO2 composite films were varied from 8 to 30 mol% and annealed at 800°C for different times for growth. The size of the Cu nanoclusters was measured from the half band width of Cu SPR peak (appearing within 570–557 nm range) and X-ray diffraction. In this way Cu-nanoclusters of size ranges from about 3.5 to 10 nm (average diameters) were prepared . The Ag-Cu nanocluster-containing silica films show the existence of both Ag and Cu SPR peaks with some blue shifting in comparison with to their pure analogues depending on the Ag:Cu ratio.
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  • 22
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    Journal of sol gel science and technology 13 (1998), S. 289-294 
    ISSN: 1573-4846
    Keywords: sol-gel ; metal biosorption ; polysaccharide encapsulation ; column sorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this work we compared biosorbents obtained by encapsulation of polysaccharides, isolated from waste brewing biomass, in sol-gel derived silicates and an organic polymer. Biosorbents were prepared by mixing cross-linking-agents—organic or siliceous—with dried cells envelopes. Siliceous prepolymers were synthezised via transesterification and hydrolysis from tetraethoxysilane (TEOS) and methanol. Sorption of Cd2+, Cu2+ and Ag+ by biosorbent granules (0.25–0.6 mm) was examined in batch and in a packed column. The biosorbent prepared by interesterification of TEOS showed a 2–3 times higher intensity of sorption than the biosorbent cross-linked with epichlorohydrin (the most effective cross-linking organic agent) while the sorption capacity of both biosorbents was equal. The specific surface area of the silica matrix was 597 m2/g but only traces of metals were sequestered from solution with a concentration of Cd2+ of 50 mg/l. The biosorbent with a silica matrix is a heterogeneous material containing microporous matrix inclusions of thin cell walls. Its high sorption intensity and good mechanical strength will be useful in continuous metal uptake of low concentrations of metals.
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  • 23
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    Journal of sol gel science and technology 13 (1998), S. 341-346 
    ISSN: 1573-4846
    Keywords: titanium dioxide ; nanoparticles ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Titania nanoparticles and gels are synthesized in reverse micelles with either an ionic (AOT) or a non-ionic (Triton X-100) surfactant in alkanes with low water contents. Acids were in some cases dissolved in the aqueous phase. Whereas the size of the sol nanoparticles is independent of the micellar composition, the kinetics of the sol-gel transition are not. The gelation time is shorter for the non-ionic surfactant and becomes longer as the acid content in the water increases, and for smaller anions of equal charge.
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  • 24
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    Journal of sol gel science and technology 13 (1998), S. 427-432 
    ISSN: 1573-4846
    Keywords: hybrid gels ; Eu3+ spectroscopy ; polymer electrolytes ; optical probes ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Good optical quality Eu3+-doped silica-polyethyleneglycol hybrids were prepared by the sol-gel process. Thermomechanical analysis showed an increase of the glass transition temperature, due to the stiffness of the polymeric network, as the amount of Eu3+ increased. Europium luminescent properties were used to study structural evolution during the sol-gel transition. For lower doping concentrations dried gels present statistical distributions of Eu3+, typical of an amorphous environment, while for higher concentrations a crystalline-like environment of Eu3+ was observed. A broad emission band was observed in the visible part of the electromagnetic spectrum and assigned to the intrinsic emission from the hybrid polymeric network.
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  • 25
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    Journal of sol gel science and technology 13 (1998), S. 757-761 
    ISSN: 1573-4846
    Keywords: zirconia ; laser damage ; sol-gel ; depth profiling ; thin films
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel material based mirrors have been produced by forming alternate layers of high refractive index and low refractive index thin films. These mirrors have proven to have a high laser induced damage threshold [LIDT]. Using nitric acid stabilized zirconia derived from zirconium-n-propoxide and base catalyzed silica, a 16 layer mirror with a reflectivity of better than 94% at 351 nm and 45° angle of incidence was fabricated. This had an LIDT of 7.7 J/cm2 at 351 nm with a 0.7 ns pulse width. Crazing prevented further layers being deposited. Both spin and dip coating were attempted with dip coating yielding the best results. The coating structure has been analyzed using XPS depth profiling and AES. The bulk materials have been investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and TGA. High refractive index layers using Hafnia with nitric or acetic acid have also been investigated as prospective high LIDT mirrors. Alternative acidic routes to silica have been studied as a possible low index material and a route to preventing crazing.
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  • 26
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    Journal of sol gel science and technology 13 (1998), S. 821-825 
    ISSN: 1573-4846
    Keywords: thick film ; sol-gel ; PZT ; interfacial polymerization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The formation of a PZT film of 10–20 μm in thickness via an interfacial polymerization of metal-organic precursors has been studied. A commercially available PZT precursor solution developed for dip- or spin-coating was diluted with hexane containing acetylacetone as chelating agent. The solution was poured on water contained in a teflon reaction container of 88 mm inside diameter. A translucent gel film was formed at the interface of the two immiscible liquids. While floating on water it shrank as the evaporation of solvent proceeded until its diameter decreased to about 45% of its initial value. The dried gel film was almost pore free and its thickness was estimated to be about 10 μm.
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  • 27
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    Journal of sol gel science and technology 10 (1997), S. 309-316 
    ISSN: 1573-4846
    Keywords: lactate dehydrogenase ; sol-gel ; biosensor ; lactic acid
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Physical adsorption and physical entrapment techniques have been utilized for the immobilization of lactate dehydrogenase (LDH) on tetraethylorthosilicate (TEOS) derived sol-gel films. The enzyme (LDH) activity has been assayed as a function of time, temperature, pH and pyruvate concentration. The results of photometric measurements used for monitoring the reaction yield a response time of about 1 min, linearity over a concentration range of 0–1.5 × 10-3 M and detection limit of 5 × 10-5 M. The TEOS sol-gel films containing LDH have been found to be stable for about 30 days at temperatures 4 to 10°C.
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  • 28
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    Journal of sol gel science and technology 11 (1998), S. 229-240 
    ISSN: 1573-4846
    Keywords: sol-gel ; optical waveguides ; quantum dots ; optics: nonlinear
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Thin silica and silica-titania films doped with sulfide nanocrystals of controlled size were fabricated by a method based on the preparation of colloidal particles and their introduction into a glassy matrix through the sol-gel method. Colloidal sols of composition HgxCd1-xS and PbxCd1-xS (with x ranging from 0 to 1) were prepared and used to dope alkoxide solutions for the deposition of thin silica and silica-titania films. Optical absorption spectra were taken on both precursor colloidal sols and derived doped films. X-ray diffraction characterization gave structural information on the nature and size of particles in powders obtained by precipitation from colloidal sols and in doped films. The advantages and limits of the investigated systems are discussed in light of possible applications. The nonlinear properties of the most interesting PbS-doped planar waveguides have been investigated in the near-infrared, at 1.064 μm. A reversible nonlinear effect was measured, with n 2 values ranging from -5 to -20×10-9 cm2/kW.
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  • 29
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    Journal of sol gel science and technology 12 (1998), S. 181-184 
    ISSN: 1573-4846
    Keywords: sol-gel ; Sb2S3 microcrystallite doped glasses ; transmission spectrum ; second harmonic generation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The sol-gel process has been applied to the preparation of nano-size Sb2S3 crystallite doped silica glasses and thin films. Silica glasses containing 1–1.5 wt% Sb2S3 are prepared by hydrolysis of complex solution of Si(OC2H5)4, SbCl3 and SC(NH2)2, and subsequent heat treatment. The nano-size crystallite in the matrix is observed by means of TEM. The transmission spectra of the films show that the transmission valley shifts toward longer wavelengths with increasing heat treatment time and temperature. Second harmonic generation (SHG) has been observed in the glasses illuminated with intense 1.06 μm and frequency-doubled laser beams from mode-locked Nd:YAG laser.
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  • 30
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    Journal of sol gel science and technology 13 (1998), S. 735-738 
    ISSN: 1573-4846
    Keywords: sol-gel ; organic-inorganic nanocomposite ; protective coating ; nanosized particles
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Organic-inorganic nanocomposite protective coatings are prepared on aluminum substrates by the spinning technique with the concept of incorporating homogeneously nanosized particles (of AlOOH, Al2O3, ZrO2, SiC) into molecular organic-inorganic hybrid matrices. The hybrid matrices are prepared from epoxysilane and bisphenol A with imidazol as catalyst. The AlOOH particles are derived from aluminum isoprooxide and introduced into the hybrid sols directly, and Al2O3, ZrO2, SiC particles are first surface-modified with Si–OH from hydrolyzed TEOS. The coatings are dense, smooth and flexible and inhibit corrosion.
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  • 31
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    Journal of sol gel science and technology 13 (1998), S. 827-831 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; ferroelectricity ; lead zirconate titanate (PZT)
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Precursor powders for Pb(Zr1 − xTix) O3 (PZT) thin films were produced by the reaction of zirconium-and titanium-n-propoxides with acetylacetone and lead acetate trihydrate. The subsequent complete removal of volatile components yielded powders that can be handled in air. The powders are indefinitely stable under ambient conditions. High molarity (〉2m) coating sols were prepared by dissolution of the precursor powders in mixtures of 1,3-propanediol, triethanolamine (TEA) and water. Excess amounts of lead to compensate lead loss during firing were easily introduced into these solutions. The deposition of these sols on steel substrates and firing at 600°C yielded PZT films. Many physical parameters like film thickness, morphology and electrical performance could be influenced by choice of the solvent mixture composition and oxide content of the sols. Depending on the preparation dielectric permittivities, εr of up to 840 were measured at 1 kHz. By hysteresis measurements at 50 Hz and a field amplitude of 50 V/μm a remanent polarization of about 40 μC/cm2 and coercivity of about 8 V/μm was obtained. The films were stable against dielectric breakdown up to 70V/μm.
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  • 32
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    Journal of sol gel science and technology 13 (1998), S. 27-30 
    ISSN: 1573-4846
    Keywords: sol-gel ; structure control ; X-ray scattering ; polyviologen ; lyotropism
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Two polyviologens synthesized by the Menshutkin reaction were incorporated into silica networks using the sol-gel method. The effects of the incorporated polymers on the structure of the resulting organic-inorganic hybrid materials were investigated using X-ray scattering (small and wide angle). This provided evidence that the polyviologens in a lyotropic liquid crystalline state were causing the silica network to become more dense and less branched than sol-gel glasses synthesized without added polyviologen. Additional evidence for the templating effect of these polymers was obtained using FTIR spectroscopy and N2 adsorption-desorption isotherms.
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  • 33
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    Journal of sol gel science and technology 13 (1998), S. 109-112 
    ISSN: 1573-4846
    Keywords: inorganic oxide ; sol-gel ; non-hydrolytic ; catalyst ; calcination
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Inorganic oxides have been synthesized successfully under mild reaction conditions using a solvent-free non-hydrolytic sol-gel process based on the condensation reaction of “metal” chlorides with oxygen donors such as alkoxides, aldehydes and ethers. Iron(III) chloride was found to be an effective catalyst for the reactions. The order of reactivity of the halides was generally titanium 〉 aluminium 〉 silicon, but in some cases reaction was halted by premature gelation of intermediate species. Silica, alumina and titania were all prepared and characterized by various methods. Calcination studies on the silicas showed these materials to be amorphous up to at least 700°C, but devitrification occurred at 1000°C. Crystallization was studied by X-ray powder diffraction.
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  • 34
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    Journal of sol gel science and technology 13 (1998), S. 95-98 
    ISSN: 1573-4846
    Keywords: sol-gel ; composite ; matrices ; fluorescence ; probing
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    Notes: Abstract Transparent composite SiO2/organic matrices have been made by the sol-gel method using tetramethoxysilane and either cetyltrimethylammoniumbromide (CTAB) or a polyethylene glycol oligomer (PEG-200) or a cationic polyelectrolyte. We have investigated conditions under which transparent xerogel matrices are possible and we have characterized them mainly by time-resolved fluorescence probing using stretched exponentials. CTAB creates a hydrophobic and PEG-200 a hydrophilic subphase in the matrix. An important property of these composite matrices is that they allow molecular diffusion contrary to matrices made in the absence of surfactants or polymers.
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  • 35
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    Journal of sol gel science and technology 13 (1998), S. 559-563 
    ISSN: 1573-4846
    Keywords: sol-gel ; hybrid ; nanocomposite ; optical nonlinearity
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    Notes: Abstract In this paper the nonlinear refractive index, optical limiting effect, photoinduced and electroinduced second harmonic generation of dye-doped hybrid and nanoparticle-doped composite materials prepared by the sol-gel process have been reported. The origin of these nonlinear optical effects has been discussed.
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  • 36
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    Keywords: porous layers ; chemical sensing ; sol-gel ; optical fiber
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    Notes: Abstract Polysiloxane porous layers doped with TiO- and phenyl-groups were fabricated by the sol-gel method. Starting sols were prepared from alkoxides using catalysis by HCl or HF. Stable SiO-TiO-sols were obtained by using HF. Porous gel layers with thicknesses of 0.3–1.1 μm were coated on fiber surfaces or silicon wafers. Layers with the refractive index of 1.38–1.48 were prepared. The fractional porosity of the layers was estimated to be 0.1–0.35. The interactions of the layers with vapor or liquid chlorinated hydrocarbons, alcohols or aromatic hydrocarbons have been studied in immersing experiments by measuring the output light intensity from the fibers. The observed changes of the output intensity could be correlated to changes of the refractive index of the layer caused by the penetration of the tested chemicals into the layer pores.
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  • 37
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    Journal of sol gel science and technology 13 (1998), S. 535-539 
    ISSN: 1573-4846
    Keywords: optical waveguide amplifiers ; erbium ; sol-gel ; GeO2-SiO2
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    Topics: Chemistry and Pharmacology
    Notes: Abstract GeO2-SiO2 sol-gel planar waveguides doped with Er were deposited by spinning on silica substrates. P2 O5 or Al2O3 were used as co-dopants to improve erbium dissolution in the GeO2-SiO2 matrix. Multilayer amorphous films were obtained at 600 or 700°C. Er ions in the planar waveguide pumped at 980 nm showed fluorescence features around 1530 nm. Narrow fluorescence spectra (∼20 nm) and long lifetimes (∼6 ms) were found in P2O5 co-doped samples, whereas Al2O3 co-doping gave wider spectra (∼50 nm) with slightly lower lifetimes (∼5 ms). The quenching concentration in the Al2O3 co-doped samples was 0.9 mol% Er. Heat treatments in CCl4 improve the active properties and the addition of Yb enhances the pump absorption efficiency.
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  • 38
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    Journal of sol gel science and technology 13 (1998), S. 439-443 
    ISSN: 1573-4846
    Keywords: photoluminescence ; sol-gel ; polysiloxane gel ; conjugated polymer
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Photoluminescence of a polysiloxane gel film incorporating a partially conjugated copolymer polyether-polyphenylenevinylene (PEPPV) has been studied and compared with results obtained from bulk and vacuum evaporated films of the same starting material. The evaporation clearly affects the distribution of lengths of the conjugated parts, yet the incorporation in the gel matrix induces only slight changes in the spectroscopic properties of the polymer.
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  • 39
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    Journal of sol gel science and technology 13 (1998), S. 529-533 
    ISSN: 1573-4846
    Keywords: sol-gel ; aluminosilicate thin films ; waveguides ; erbium doping
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Er3+ doped-aluminosilicate thin films were prepared on silica and silica/Si substrates by the sol-gel process and dip-coating. The sol-gel aluminosilicate planar waveguides were prepared from silicon and aluminium alkoxides. Their structural characterization has been carried out by Raman spectroscopy, Atomic Force and Scanning Electron Microscopies. The results indicated that these films present an amorphous structure until an annealing temperature of 900°C, while at temperatures higher than 1000°C, crystallization occurs. An estimate of microcrystallite sizes using Raman spectroscopy is given, which agrees with data from scanning electron microscopy. The optical properties have been investigated by Fluorescence spectroscopy in the visible region.
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  • 40
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    Journal of sol gel science and technology 13 (1998), S. 673-678 
    ISSN: 1573-4846
    Keywords: electrochromism ; sol-gel ; tungsten oxide ; peroxotungstic acid ; nanocrystalline
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Stable tungsten oxide coating sols suitable for electrochromic applications were prepared by a modified peroxotungstic acid route. Layers up to 250 nm thickness could be deposited on ITO-coated and/or FTO-coated glass substrates in a single dip-coating process. Optoelectrochemical measurements were employed to determine the variation of the electrochromic properties (change in optical density (ΔOD) and switching times) of WO3-layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of heat treatment. High resolution transmission electron microscopy (HR-TEM) has shown that the optimized layers possess a partially crystalline morphology with nanocrystalline regions 2–3 nm in size.
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  • 41
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    Journal of sol gel science and technology 13 (1998), S. 1023-1026 
    ISSN: 1573-4846
    Keywords: PZT fibers ; piezoelectric fibers ; sol-gel ; fibers
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A fiber forming PZT gel containing 58.5 wt% PZT was synthesized by using zirconium-n-propylate, titanium-iso-propylate, lead acetate and butoxyethanol. Unseeded PZT gels and gels containing 0.5 wt% PZT perovskite seeds (Ø = 200–300 nm) could be extruded through a monofilament nozzle (Ø = 100 μm) at pressures between 50 and 150 bar, whereas PZT gels, containing 1 and 2 wt% PZT particles, were pressed through the nozzle at higher pressures (200–300 bar). The microstructure of unseeded and seeded (0.5, 1, 2 wt% PZT) PZT fibers was characterized by SEM. Unseeded fibers had three different shells at 450°C: an external dense shell (approx. 200 nm thick), a middle shell consisting of a porous structure (1.5μm thick) and the center of the fiber, characterized by a matrix containing globular particles. At 700°C, a 200–250 nm thick and dense external shell and a porous fiber interior were be observed. 2 wt% of PZT seeds was necessary to densify the fiber completely. The seeds were located in the center of each PZT perovskite rosette.
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  • 42
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    Journal of sol gel science and technology 7 (1996), S. 77-79 
    ISSN: 1573-4846
    Keywords: sol-gel ; immobilization ; entrapment ; bacteria ; atrazine ; biodegradation ; herbicide
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel entrapment was evaluated as a method for immobilization of an atrazine degrading Pseudomonas. It was found that the bacterium lost much of its atrazine degrading activity upon immobilization. However, partial activity could have been restored by amendment of nutrients. Bacteria immobilized using a prehydrolysis technique for the preparation of the sol-gel, retained better activity in comparison to bacteria immobilized using a composite calcium alginate/sol-gel procedure. Further study is underway to improve the activity of sol-gel entrapped bacteria.
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  • 43
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    Keywords: iron oxide ; structural control ; complexing agent ; thin film ; sol-gel
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    Notes: Abstract The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α -Fe2O3 with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one mole of iron nitrate and the calcination temperatures were below 400° C, γ -Fe2O3 with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α -Fe2O3 appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in thin films. Thus, a transparent magnetic film composed of γ -Fe2O3 could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz and calcining the gel film at 350° C.
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  • 44
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    Journal of sol gel science and technology 8 (1997), S. 83-88 
    ISSN: 1573-4846
    Keywords: sol-gel ; gelation modelling ; TiO2 gels ; simulation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract We present here an experimental and numerical study of the chemical and aggregative mechanisms for titanium alkoxide in a reverse micellar medium. NMR experiments were done to study the first step of the sol-gel process: hydrolysis of titanium isopropoxide. Light and X-ray scattering experiments were then conducted to characterize the clustering of aggregates and aggregation kinetics. Fractal dimension, measured by U.S.A.X.S., varies with the hydrolysis ratio and the hydration of the surfactant. This evolution was explained by polydispersity of the hydrolysis which depends on the surfactant concentration. This hypothesis was tested through a numerical simulation of irreversible aggregation using a chemically limited aggregation model. The hydrolyzed sites are distributed among the monomers by a random procedure governed by a polydispersity parameter p , varying from 0 to 1. The total number of hydrolyzed sites is governed by a parameter q belonging to the interval [0, 1]. The p -q evolution of the fractal dimension coincides rather well with the experimental data in all the region of the two dimensional phase space.
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  • 45
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    Journal of sol gel science and technology 8 (1997), S. 107-110 
    ISSN: 1573-4846
    Keywords: sol-gel ; zinc aluminate ; spinel structure ; catalyst support
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    Topics: Chemistry and Pharmacology
    Notes: Abstract ZnAl2O4 was prepared by hydrolyzing a mixture of aluminum alkoxide with zinc nitrate dissolved in hexylene glycol and calcining at 800°C. The results are compared with those obtained by wet mixing and coprecipitation. The sol-gel method produces solids whose surface areas and pore volumes are 100% larger and with a more homogeneous pore size distribution.
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  • 46
    ISSN: 1573-4846
    Keywords: mullite ; organic ligand ; hydrolytic polymerization ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of mullite by the sol-gel method using organic polydentate ligands and the effect of the raw materials and organic polydentate ligands on the formation of mullite were investigated. Two series of samples were prepared using tetraethoxyorthosilicate (TEOS) and aluminum nitrate nonahydrate, or dibutoxyethylacetoacetatoaluminum (Al(OBu)2(AcAcEt)) as the silica and alumina sources, respectively, and using ethylene glycol (EG), 1,3-propanediol (PD), 1,3-butanediol (BD), 2-methyl-2, 4-pentanediol (MPD), diethlene glycol monoethyl ether (DEME) and ethoxyethanol as the ligands. When the alumina source was aluminum nitrate nonahydrate, mullite was apt to appear in the order of EG 〉 PD 〉 MPD. When Al(OBu)2(AcAcEt) was the alumina source, the tendency toward the appearance of mullite crystalline phase was EG 〉 BD 〉 DEME 〉 MPD. Between the two alumina sources, aluminum nitrate nonahydrate gave mullite much easier than Al(OBu)2(AcAcEt). These relationships were discussed from the viewpoints of the coordination ability of the ligands and the miscibility between the silica and alumina.
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  • 47
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    Journal of sol gel science and technology 9 (1997), S. 279-283 
    ISSN: 1573-4846
    Keywords: AgTCNQ ; photochromism ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Preparation and photochromic behavior of ormosil containing encapsulated AgTCNQ molecules were studied in this paper. The ormosil resulted from hydrolysis and polycondensation of glycidoxypropyltrimethoxysilane, dimethyldimethoxysilane and methyltrimethoxysilane. The time to add AgNO3 water solution into the resultant sol was a key factor to synthesize AgTCNQ molecules inside ormosil matrix. AgTCNQ molecules encapsulated in the ormosil showed different photochromic behavior compared with pure AgTCNQ film: normal photochromic reaction can be realized, while reverse photochromic reaction can not. The “cage” model was used to explain this phenomenon.
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  • 48
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    Journal of sol gel science and technology 9 (1997), S. 239-249 
    ISSN: 1573-4846
    Keywords: sol-gel ; alumina-gel ; multicomponent ; mullite ; phase transformation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The capacity of the sol-gel process of producing highly pure, homogeneous alumina-silica based materials had been demonstrated in the last few years. However, a full understanding on the mechanisms associated to sol formation and sol to gel transition has not yet been achieved and is required for the development of a new generation of nano-structurally tailored materials that will significantly enhance the technological importance of the sol-gel process. In this work, tetraethyl orthosilicate (TEOS) and aluminum isopropoxide were used to prepare materials within the entire silica-alumina system. Process parameters, such as gelation time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis and water/alkoxide ratio. The obtained gels were dried at 105°C and subsequently heat treated at 500 and 1100°C for 3 hours. X-ray diffraction and infrared spectroscopy were used to characterize the materials and phase transformations. Structural information obtained from phase characterization and phase transformations was correlated to the effects of the process variables on sol formation and gelation, providing insights related to the mechanisms involved. The influence of temperature of aluminum isopropoxide hydrolysis on peptization and gelation of the mixtures was noted. The different behavior of mixtures hydrolyzed at low and high temperatures was suggested to be caused by different mechanisms of surface charge formation on the structurally different aluminum hydroxides. Monophasic and diphasic mullite xerogels were produced by changing temperature of aluminum isopropoxide hydrolysis, and led to formation of mullite and Al−Si spinel phases respectively, when treated at 1100°C.
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  • 49
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    Journal of sol gel science and technology 7 (1996), S. 69-76 
    ISSN: 1573-4846
    Keywords: sol-gel ; bioactive ; protein ; adsorption
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Recent theories suggest that the local adsorption of biologically active peptide growth factors onto the surface of an implant may contribute to the unique osteogenic nature of silica-containing bioactive ceramics. A sol-gel derived glass is used as a model of the in-vivo reaction product of 45S5 bioactive glass at relatively short times (〈48 hrs.) to investigate protein adsorption/desorption behavior. The adsorption kinetics of three heme-class proteins (cytochrome c, myoglobin, and hemoglobin) are measured spectroscopically. The rate of adsorption is shown to increase with average pore size, which is determined by the silica content of the gel. Adsorption rate decreases as protein size is increased and as solution pH is decreased. Biological function of an adsorbed peroxidase enzyme on pre-reacted Bioglass® is shown to be retained. Desorption during physiologic conditions is shown to be linear with time and pH dependant, while independent of gel bioactivity.
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  • 50
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    Journal of sol gel science and technology 7 (1996), S. 81-85 
    ISSN: 1573-4846
    Keywords: sol-gel ; functionalized films ; grafting of antibodies ; biological activity
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    Topics: Chemistry and Pharmacology
    Notes: Abstract In this work we investigated the biological properties of sol-gel films in aqueous medium. Functionalized silica films were prepared by the sol-gel process, from organically modified silicon alkoxides with amino or thiol groups. Covalent binding of proteins with different orientations according to the hydrophilic or hydrophobic character of the surface was studied. This binding occurred via a covalent coupling agent providing a very stable linkage. No denaturation was detected and a good detection of the antigen was observed. Immunoassays have demonstrated the biological activity of grafted antibodies.
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  • 51
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    Journal of sol gel science and technology 7 (1996), S. 109-116 
    ISSN: 1573-4846
    Keywords: ferritin ; sol-gel ; magnetism
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A significant recent development in sol-gel science has been the encapsulation of biomolecules such as proteins and enzymes in optically transparent silica glasses. This paper reports on the encapsulation of an iron (Fe) storage protein, ferritin, to develop a magnetic silica glass. Native ferritin, which has a nanometer-sized microcrystalline Fe oxide core, was encapsulated in optically transparent silica glasses using the sol-gel process. Fe could be released from ferritin but could not be reconstituted into apoferritin when the protein was trapped in the pores of the glass. Transmission electron microscopy of ferritin-doped aged silica gels indicated that crystallinity of the Fe oxide core was retained upon sol-gel encapsulation. Magnetic measurements on ferritin-doped silica gels indicated the material to be paramagnetic, but not superparamagnetic.
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  • 52
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    Journal of sol gel science and technology 7 (1996), S. 123-128 
    ISSN: 1573-4846
    Keywords: sol-gel ; biosensor ; electrode ; glucose oxidase
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Several types of amperometric biosensors comprised of immobilized glucose oxidase in chemically-modified ceramic-carbon matrices are compared. The electrodes are comprised of several building blocks each performing a specific function. Glucose oxidase is used to catalyze the bio-oxidation of glucose; carbon powder imparts conductivity and favorable electrochemical characteristics; the Ormosil network provides rigidity and porosity; and the organic modification of the Ormosil imparts controlled surface polarity. Additionally, hydrophilic chemical modifiers are incorporated in order to control the size of the wetted, electroactive layer; high dispersion of inert metal catalysts is used to enhance hydrogen peroxide oxidation and redox mediators may be co-immobilized when oxygen independent response is desirable. The electrodes can be prepared either in the form of thick supported film, useful for disposable electrodes or as bulk-modified, disk shape electrodes, which can be used as renewable surface electrodes.
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  • 53
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    Journal of sol gel science and technology 7 (1996), S. 129-133 
    ISSN: 1573-4846
    Keywords: itaconic acid ; biosynthesis ; Aspergillus terreus ; fungi ; aconitate decarboxylase ; E.C. 4.1.1.6 ; enzyme immobilization ; silicate ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A new technique of investigation of labile metabolic pathways using immobilization of the pathway in sol-gel derived silicate matrices was demonstrated. The biosynthetic pathway of itaconic acid in Aspergillus terreus is believed to proceed through decarboxylation of cis-aconitate catalyzed by an unstable enzyme aconitate decarboxylase, E.C. 4.1.1.6. Stabilization of this pathway in sol-gel derived silicate matrix enabled the elucidation of the correct sequence of biosynthetic steps. The decarboxylation of cis-aconitate does not lead directly to itaconate, but rather to citraconate. The latter is then isomerized to itaconate by a previously unknown enzyme.
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    Journal of sol gel science and technology 7 (1996), S. 151-161 
    ISSN: 1573-4846
    Keywords: ormosils ; organic-inorganic hybrids ; sol-gel ; modified silica network
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Many organically modified silicates (ormosils) can be prepared by the sol-gel method with very different mechanical properties by varying the ratio of polydimethylsiloxane (PDMS) to tetraethoxysilane (TEOS) contents and processing conditions. With a low PDMS concentration, the ormosils are harder, stiffer and stronger than those with higher concentration of PDMS. Even harder ormosils are possible when ultrasonic irradiation is used during synthesis. As the PDMS concentration is increased, the ormosils take on a more flexible nature, and over a critical concentration actually become rubbery. These new rubbery materials can contain as much as 75% inorganic components, and have more stable mechanical properties than commercial rubbers at elevated temperatures. Effects of PDMS addition to the network structure and mechanical properties of the ormosils were investigated.
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  • 55
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    Journal of sol gel science and technology 7 (1996), S. 135-143 
    ISSN: 1573-4846
    Keywords: antibody ; atrazine ; immunoassay ; entrapment ; sol-gel ; ELISA ; pesticide residue ; chromatography
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    Topics: Chemistry and Pharmacology
    Notes: Abstract We report the successful doping of a sol-gel matrix with an antibody, retaining its ability to bind free antigen from an aqueous solution. The particular system described is monoclonal anti-atrazine mouse antibody which was entrapped in SiO2 sol-gel matrices, prepared from tetramethoxysilane by several methods. Atrazine was selected as a model compound for this study, within the framework of the development of immunochemical-based methods for monitoring pesticide residues and other organo-synthetic environmental contaminants. Nanogram quantities of atrazine were applied on SiO2 sol-gel columns doped with this antibody, and the amount of eluted antigen was determined by Enzyme Linked ImmunoSorbent Assay (ELISA). Under appropriate sol-gel-forming conditions, high amounts of atrazine were bound to the sol-gels, ranging between 60% and 91% of the amount applied to the column. The combination of the properties of the sol-gel matrix (e.g., stability, inertness, high porosity, high surface area and optical clarity), together with the selectivity and sensitivity of the antibodies, enable extension of this feasibility study to development of a novel group of immunosensors which could be used for purification, concentration and monitoring of a variety of residues from different sources.
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  • 56
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    Journal of sol gel science and technology 8 (1997), S. 365-369 
    ISSN: 1573-4846
    Keywords: sol-gel ; SiO2 ; TiO2 ; ultraviolet ; densification
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural changes in SiO2 and TiO2 gel films were investigated using ultraviolet (UV) and vacuum ultraviolet (VUV) irradiations. A significant compaction with dehydration of SiO2 gel films was induced by irradiation of photons in the range of 9–18 eV. The refractive index and the shrinkage of the irradiated SiO2 gel films were comparable to those obtained by sintering at 1000°C. Densification of TiO2 gel films was also observed with irradiation of 5–14 eV photons. However, effects of the irradiation on TiO2 gel were smaller that those on SiO2 gel. The structural changes in the gel films are attributed to electronic excitations which are induced by irradiation with photons having higher energies than the bandgap of the oxides. The photo-induced effects are presumed to depend on the optical properties and structure of the gels.
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  • 57
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    Journal of sol gel science and technology 9 (1997), S. 239-249 
    ISSN: 1573-4846
    Keywords: sol-gel ; alumina-gel ; multicomponent ; mullite ; phase transformation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The capacity of the sol-gel process of producing highly pure, homogeneous alumina-silica based materials had been demonstrated in the last few years. However, a full understanding on the mechanisms associated to sol formation and sol to gel transition has not yet been achieved and is required for the development of a new generation of nano-structurally tailored materials that will significantly enhance the technological importance of the sol-gel process. In this work, tetraethyl orthosilicate (TEOS) and aluminum isopropoxide were used to prepare materials within the entire silica-alumina system. Process parameters, such as gelation time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis and water/alkoxide ratio. The obtained gels were dried at 105°C and subsequently heat treated at 500 and 1100°C for 3 hours. X-ray diffraction and infrared spectroscopy were used to characterize the materials and phase transformations. Structural information obtained from phase characterization and phase transformations was correlated to the effects of the process variables on sol formation and gelation, providing insights related to the mechanisms involved. The influence of temperature of aluminum isopropoxide hydrolysis on peptization and gelation of the mixtures was noted. The different behavior of mixtures hydrolyzed at low and high temperatures was suggested to be caused by different mechanisms of surface charge formation on the structurally different aluminum hydroxides. Monophasic and diphasic mullite xerogels were produced by changing temperature of aluminum isopropoxide hydrolysis, and led to formation of mullite and Al-Si spinel phases respectively, when treated at 1100°C.
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  • 58
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    Journal of sol gel science and technology 8 (1997), S. 381-384 
    ISSN: 1573-4846
    Keywords: barium osumilite ; sol-gel ; alkoxide ; crystallisation ; microstructure
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The crystallisation sequence of stoichiometric barium osumilite prepared by partial-alkoxide (PAR) and all-alkoxide routes (AAR) and the microstructure of the fully crystallised glass ceramic were examined. Comparing the crystallisation behaviours of the gel-glasses obtained revealed that the first phase to crystallise was mullite in PAR but hexacelsian in AAR. Barium osumilite crystals grew randomly and more homogeneously in PAR while in AAR larger barium osumilite crystals grew in clusters. Cordierite formed as a secondary phase in both routes and it crystallised on and between the osumilite lamellae. Mullite and hexacelsian also persisted up to the stage when full crystallisation had taken place.
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  • 59
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    Journal of sol gel science and technology 8 (1997), S. 409-413 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; crystallization ; anatase ; rutile
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The aim of this work was to investigate the crystallization behavior of thin films of SiO2-TiO2 made by the sol-gel process as function of the TiO2 content and the temperature and time of heat treatment. Precursor solutions were prepared by hydrolysis of TEOS (tetraethoxysilane) and TPOT (titanium tetraisopropoxide). Multilayer films were spun on single crystal silicon wafers. The compositions studied were (on a molar percentage basis) 20TiO2-80SiO2, 30TiO2-70SiO2, 40TiO2-60SiO2 and pure TiO2. The films were heat treated at different temperatures between 300°C and 1200°C, for different periods of time (30 s–90 h). The crystallization kinetics were followed by micro-Raman spectrometry. Grazing incidence X-ray diffraction showed that the films crystallized into one or both of two crystalline phases of TiO2: anatase and rutile (for pure TiO2 only). The volume fractions of the crystalline phase varied from very low values (〈1%), up to 100%, for a TiO2 sample heat treated at 800°C for 8 hours. The results show that the volume fraction of crystalline phase is strongly influenced by the heat treatment temperature and also, to a smaller extent, by the heat treatment time. The most important parameter, however, is the composition of the films: the higher their TiO2 concentration, the lower is the crystallization temperature and the larger is the crystallized fraction.
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    Journal of sol gel science and technology 8 (1997), S. 425-430 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; lead titanate ; microstructure
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    Notes: Abstract A sol-gel route is developed for the synthesis of samarium modified lead titanate precursor solutions. The solutions are used for the deposition of thin films. After thermal treatment of the films, two crystalline phases are observed by X-ray diffraction analysis: an undesirable pyrochlore phase and a ferroelectric perovskite. These two phases are clearly distinguished in the film microstructure, showing a fined grained fraction of pyrochlore and a-axis oriented rosette grains of perovskite. The development of these phases as well as the evolution of the perovskite/pyrochlore ratio in the films is related to the chemistry of the synthesized solutions and the thermal treatment used for crystallization.
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  • 61
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    Keywords: sol-gel ; silsesquioxanes ; hybrid organic-inorganic materials ; silicas ; pore structure ; Si–C bond cleavage ; alkynyl silanes
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Hybrid organic-inorganic materials containing labile organic fragments with various structural features have been prepared. The mild cleavage of Si–C bonds allowed removal of the organic moities. It led to silica which pore structure varied according to the nature of the organic component eliminated.
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    Journal of sol gel science and technology 8 (1997), S. 615-618 
    ISSN: 1573-4846
    Keywords: sol-gel ; magnetic nanocomposite ; iron oxide ; Mössbauer spectroscopy ; Kerr effect
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Magnetic nanocomposites γ-Fe2O3/silica were prepared by a one-step sol-gel method. The sol was prepared by TEOS (tetraethyl orthosilicate) acid hydrolysis in the presence of an iron salt soluble in methanol. After gelation and drying, the transparent samples were characterized after treatment at different temperatures. The particle size, observed by HR TEM, was in the range of 2–10 nm and depended on Fe-concentration and heating temperature. Magnetic measurements showed either a ferromagnetic or a superparamagnetic behaviour and could be explained by the particle size. The dependence of the magnetic behaviour on the particle size was also studied by Mössbauer spectroscopy. The samples in which the Fe2O3 particle size was approximately 10 nm showed magnetic splitting (sextet) at room temperature, while smaller particles (2–3 nm) showed this splitting only at the temperature of liquid helium. The optomagnetic properties of the samples were also measured (Kerr effect).
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    Journal of sol gel science and technology 8 (1997), S. 663-666 
    ISSN: 1573-4846
    Keywords: sol-gel ; immunoassays ; antigen ; antibody
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Porous silica gels, synthesized via the acid hydrolysis and basic condensation of TMOS, have been used for the encapsulation of antigens. The pores of the matrix are large enough to allow the diffusion of antibodies through the gel. Antigen-antibody specific fixation occurs within the sol-gel matrix. It can be detected via the so-called enzyme linked immunosorbent assays (ELISA). Antigen-antibody associations occurring in the gel are optically detected via the reaction of a peroxidase conjugate with ortho-phenylenediamine leading to the formation of a yellow coloration. Immunoassays have been performed using the hydatid cyst fluid as the source of antigens and sera from human patients as the source of antibodies. Specific fixation appears to be as good in the sol-gel matrix as in antigen solutions.
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    Journal of sol gel science and technology 8 (1997), S. 681-684 
    ISSN: 1573-4846
    Keywords: sol-gel ; acetates ; Bi-based superconductors
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    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.
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    Journal of sol gel science and technology 8 (1997), S. 721-723 
    ISSN: 1573-4846
    Keywords: sol-gel ; lead titanate ; ferroelectric ; electroactive material ; composites
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    Notes: Abstract Powders of (Pb0.8Ca0.2)(Ti0.99Mn0.01)O3 have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality was found to be 1.053 ± 0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient of 17.4 μC/m2K and a pyroelectric figure of merit (FOMp = p/ɛ) of 0.51 μ C/m2K.
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    Journal of sol gel science and technology 8 (1997), S. 729-734 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; titanate perovskites
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A description is made of a wet chemical method for obtaining ferroelectric thin films. The processing is based on a twofold synthetic scheme: the synthesis of a titanate gel from a sol-gel process and the rehydration of this gel during the incorporation into the system of other ions as water-soluble salts. The versatility of this route has made possible preparation of modified lead titanate precursor solutions. Alkaline earth ions or lanthanides such as Ca2+ or Sm3+, have been used as modifier elements. Physico-chemical properties of the solutions are studied as well as the reaction mechanisms that make possible the rehydration of the titanate gel. The solutions obtained are used for the deposition and crystallization of titanate based thin films. Crystallinity, microstructure and polarization-electrid field characteristics of the films are shown.
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    Journal of sol gel science and technology 8 (1997), S. 735-742 
    ISSN: 1573-4846
    Keywords: sol-gel ; Nb2O5 ; film ; photoconductivity ; photoelectrochemistry ; semiconductor ; solar cell
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb2O5 coatings have been determined. The coatings are n-type semiconductor with indirect allowed transition and present an overall low quantum efficiency (φ 〈 4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb2O5 coatings can be made of 10–20 nm size nanoparticles.
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    Journal of sol gel science and technology 8 (1997), S. 759-763 
    ISSN: 1573-4846
    Keywords: sol-gel ; bismuth titanate ; spin-coating ; thin films ; ferroelectric
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Bi4Ti3O12 thin films were obtained by the sol-gel method. The precursor solution was prepared by allowing the two metallic alkoxides, Bi(OC2H4OCH3)3 and Ti(OC2H4OCH3)4, to react in 2-methoxy-ethanol to form the mixed alkoxide. This stable sol was deposited by spin-coating onto platinized silicon substrates. X-Ray diffraction patterns indicate that the perovskite initial crystallization temperature is 460°C for powder samples and it ranges between 400 and 500°C, for thin films, as a function of the number of coating layers. Dense, smooth and crack free thin films with grain sizes ranging from 20 nm to 500 nm are obtained, depending on the number of coating layers and on the post-deposition temperature annealing.
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  • 69
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    Journal of sol gel science and technology 8 (1997), S. 819-824 
    ISSN: 1573-4846
    Keywords: sol-gel ; diffusion limited cluster-cluster aggregation ; theory of gelation ; fluctuating bond aggregation ; numerical simulations ; aggregation ; chemical gels formation
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The diffusion limited cluster-cluster aggregation (DLCA) model is modified by including cluster deformations during aggregation, with a tuning flexibility parameter F. A three-dimensional computer simulation is presented, which starts from a collection of f-functional monomers randomly distributed in a cubic box with a volumic fraction c (concentration) and which uses the highly efficient bond fluctuation algorithm to describe the cluster deformations. It is shown that, for F ≠ 0, there exists a well defined threshold value of the volumic fraction below which the realization of all intra-aggregate bonding possibilities prevents the formation of a gelling network. For c 〉 c g , a true sol-gel transition occurs at a characteristic time t g , after which an infinite cluster (which is self connected via the boundary conditions) appears. In contrast to DLCA, t g does not increase as the box size increases. The transition at c g is characterized by a divergence of the final clusters size for c〈c g and a divergence of the gel time for c〉c g . Several other numerical results are reported.
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    Journal of sol gel science and technology 8 (1997), S. 895-899 
    ISSN: 1573-4846
    Keywords: luminescence ; pyranine ; sol-gel ; hybrid coatings ; emission anisotropy
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The sensitivity of the pyranine fluorescence to protonation/deprotonation is used to follow modifications in cured sol-gel thin films. The acid concentration in the sol-gel solution is varied for TEOS-based coatings and a series of organically modified silanes Si(OR)3R′ are added to the TEOS solution. The concentration of the organically modified silane is varied as well as the chain length of the alkylgroup (R′). The stationary fluorescence measurements show that the equilibrium between the protonated and the deprotonated form of pyranine changes depending on the type of silica matrix. The deprotonated form is dominant in the cured SiO2 films and the protonation/deprotonation ratio of pyranine is constant for the different acid concentrations used. The protonated form becomes dominant as the concentration of Si(OR)3R′ is increased and as the alkyl chain length (R′) of the organically modified silanes is augmented. Emission anisotropy measurements of pyranine in the same coatings show that the rotational freedom of the molecule changes due to modifications in the cages for the TEOS-based coatings. These modifications are produced by the acid concentration used to prepare the coatings. An increase in the rotational freedom of pyranine is observed in the TEOS-Si(OR)3R′ systems.
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    Journal of sol gel science and technology 8 (1997), S. 927-929 
    ISSN: 1573-4846
    Keywords: organic-inorganic hybrids ; sol-gel ; photochromic performance ; spirooxazine
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Organic-inorganic hybrid materials synthesized via sol-gel processing are excellent solid matrices for photochromic dyes like spirooxazine, and the photochromic performance can be further enhanced by introducing suitable additives. This work describes the effects of additives on the photochromic intensity (Δ A 0), decolouration rate (k) and photostability of spirooxazine in sol-gel derived organic-inorganic hybrid matrices. They include fluoro-alkylsilane (FAS), bisphenol A (BPA) and methyl-imidazole (MI). FAS enhances both Δ A 0 and photostability, but has little effect on k. The higher the content of BPA, the higher the Δ A 0 and the higher the photostability, but the lower the k. The effect of MI on Δ A 0 and k is not so considerable as that of BPA and is a little complicated, while significant improvement in photostability is achieved by the addition of MI at an optimum concentration with the presence of BPA at a higher content.
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    Journal of sol gel science and technology 8 (1997), S. 931-935 
    ISSN: 1573-4846
    Keywords: photochromic ; fiber optic ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively. If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.
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    Journal of sol gel science and technology 8 (1997), S. 979-983 
    ISSN: 1573-4846
    Keywords: fluorescence ; pH ; ruthenium polypyridyl ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Tetraethoxysilane (TEOS) sol-gel monoliths impregnated with three different luminescent [Ru(L)3]2+ complexes (where L = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), or 4,7-diphenyl,1,10-phenanthroline (dpp)) have been prepared. The photoluminescence properties of these complexes were followed as a function of time, as the sol-gel reactions proceeded. Clear differences were observed in the emission energies and the emission lifetimes of the complexes upon gel formation. These differences can be explained by the different extent of electrostatic interaction between the surface of the siloxane polymer and the immobilised complex.
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    Journal of sol gel science and technology 8 (1997), S. 991-997 
    ISSN: 1573-4846
    Keywords: sol-gel ; optical waveguides ; semiconductor-doped glass ; nonlinear optics ; laser writing
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel processes show many promises for the development of low-loss, high-performance glass integrated optical circuits. Special attention is being paid to the preparation of composite glass films, where the properties of organic or inorganic dopant compounds included in the glass matrix are fully exploited. Nonlinear optical glass film waveguides have the potential to become key devices in the future, leading to further technical advances of fiber optic communication systems. This paper briefly reviews current activities in sol-gel glasses for integrated optics, with particular focus on silica-titania and semiconductor-doped films.
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    Journal of sol gel science and technology 8 (1997), S. 999-1005 
    ISSN: 1573-4846
    Keywords: ZrO2 ; sol-gel ; planar waveguide ; Raman scattering
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    Topics: Chemistry and Pharmacology
    Notes: Abstract ZrO2 waveguides are prepared by the sol-gel process from a solution containing zirconium n-propoxide and acetylacetone in propanol-2. Structural characterizations are investigated for different annealing temperatures using suitable techniques including Waveguide Raman Spectroscopy, Electron Microscopy and Atomic Force Microscopy. Films are amorphous at 300°C and the pure ZrO2 tetragonal crystalline phase appears beyond 400°C. Crystallized films present a dense, uniform and polycrystalline structure made up by randomly oriented nanocrystallites, the diameter of which increases from 38 Å at 400°C to 53 Å at 600°C. Waveguides are at least monomode TE0 at 632.8 nm. At this wavelength, optical losses are about 0.8 ± 0.2 dB/cm for amorphous layers and increase up to 2.5 ± 0.4 dB/cm for 600°C heat-treated waveguides.
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    Journal of sol gel science and technology 8 (1997), S. 1013-1016 
    ISSN: 1573-4846
    Keywords: sol-gel ; neodymium and erbium doped planar waveguide ; fluorescence lifetime measurement ; phosphorous and aluminium codoping
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A multilayer sol-gel process has been developed in order to make highly doped rare-earth planar waveguides on silica or silicon substrates. Starting with a small range of constituents, such as SiO2, TiO2, P2O5 and Al2O3, we show that a large variety of gel compositions, with different spectroscopic behaviour, can be made when doped with rare-earths. We have doped the sol-gel films with neodymium and we have optimized their compositions by measuring the neodymium fluorescence lifetime. For a composition with 10 atom% of phosphorous, the lifetime evolution with neodymium concentration was studied and a quenching concentration was found at 1% of neodymium. We have also shown the strong influence of phosphorous or aluminium in the sol composition on the fluorescence lifetime, for a given neodymium concentration. First results on similar planar waveguides, doped with erbium, are also presented. The stability of the fluorescence lifetime over a long period of time is an other important point to be checked for these new materials: the lifetime evolution over a 9 months measurement period is presented.
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    Journal of sol gel science and technology 8 (1997), S. 1053-1061 
    ISSN: 1573-4846
    Keywords: sol-gel ; optical chemical sensor ; waveguide sensor ; fibre optic sensor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The use of the sol-gel process to produce materials for optical chemical sensors and biosensors is attracting considerable interest. This interest derives mainly from the design flexibility of the sol-gel process and the ease of fabrication. In most applications the sol-gel material is used to provide a microporous support matrix in which analyte-sensitive species are entrapped and into which smaller analyte molecules may diffuse. Sensors based on entrapped organic and inorganic dyes, enzymes and other biomolecules have been reported. A range of sensor configurations has been employed, including monoliths, thin films, as well as more elaborate structures. In this paper a selection is presented of recent significant developments in optical chemical sensors which employ sol-gel-derived materials. These developments include the tailoring of sol-gel materials to optimise sensor response, advanced waveguide structures and novel probe-tip sensors. Those issues which remain critical to the eventual deployment of sol-gel sensors are examined. In particular, the problems of leaching, microstructural stability, diffusion-limited response time, and susceptibility to interferents are discussed and some solutions proposed.
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    Journal of sol gel science and technology 8 (1997), S. 1063-1066 
    ISSN: 1573-4846
    Keywords: GDLC ; color display ; liquid crystal ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Liquid crystal microdroplets trapped into silica gel-glasses by sol-gel processes may be used for display applications. Gel-glass dispersed liquid crystals (GDLC) are switched between opaque and transparent states by applying external AC-voltage signals; no polarizers are required. The feasibility of applying these materials to colored displays has been explored. A comparative study of different dyes for GDLC color displays, which were either embedded in the sol-gel matrix or dissolved in the liquid crystal microdroplets is presented.
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    Journal of sol gel science and technology 8 (1997), S. 1067-1070 
    ISSN: 1573-4846
    Keywords: cholinesterase ; sol-gel ; pesticide ; THA ; enzyme activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Biological activity of cholinesterases can be determined by optically monitoring the enzymatic reaction with indophenyl acetate, (N-4′-acetoxyphenyl)-4-quinone imine. At pH 8.0 cholinesterases hydrolyze this yellow dye to yield a blue reaction product. Cholinesterase inhibitors reduce the rate of this hydrolysis. Thus, by monitoring absorbance of the hydrolysis product at its maximum (630 nm) as a function of time, reaction rates of both cholinesterase activity and cholinesterase inhibition may be quantified spectroscopically. Using this technique, we measured the enzymatic activity of butyrylcholinesterase (BuChE) molecules encapsulated in tetramethyl orthosilicate (TMOS) silicate gel-glass prepared by hydrolysis and condensation. This activity is reduced, in a concentration-dependent manner, by the reversible cholinesterase inhibitors 1,5-bis(4-allyldimethyl-ammoniumphenyl) pentan- 3-one dibromide (BADAPP) and 9-amino-1,2,3,4-tetrahydroacridine (THA; tacrine, Cognex). The gel-glasses are rigid and compact, transparent, and porous enough to allow reagents to diffuse in and out.
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  • 80
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    Journal of sol gel science and technology 8 (1997), S. 1121-1125 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; oxygen sensor
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sol-gel-derived silica films were fabricated by dip-coating onto planar and optical fibre substrates. The films were pre-doped with the oxygen-sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], whose fluorescence is quenched in the presence of oxygen. The structure and behaviour of sol-gel films is related to the fabrication parameters. In order to optimise the films for oxygen sensing in gaseous and in aqueous media, the quenching behaviour was monitored as a function of dip-speed and water : precursor ratio. By adjusting the above parameters, film properties can be tailored to optimise oxygen quenching in particular concentration ranges and environments.
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  • 81
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    Journal of sol gel science and technology 8 (1997), S. 29-33 
    ISSN: 1573-4846
    Keywords: ceramic fibers ; spinnability ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural ceramic oxide fibers like α-Al2O3, MgAl2O4 (spinel), Y3Al5O12 (YAG) and eutectic Al2O3−Y3Al5O12 as well as the functional Pb(Zr1−xTix)O3 (PZT) fibers were successfully prepared by sol-gel processing. All precursors are based on metal oxohydroxopropionates. A comparative study of sol-gel routes leading to spinnable sols demonstrates the key role of propionic acid as an excellent agent for controlling hydrolysis and condensation reactions.
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  • 82
    ISSN: 1573-4846
    Keywords: iron oxide ; structural control ; complexing agent ; thin film ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The structure of iron oxide was controlled by regulating the hydrolytic polymerization of aquo iron complexes with organic polydentate ligands such as diols. Iron oxides were prepared by calcining the precursor polymers obtained from iron nitrate nonahydrate and diols. When the diols were 1,2-pentanediol, 1,2-hexanediol and 1,2-octanediol, α-Fe2O3 with corundum structure appeared exclusively or as the main crystalline phase, in spite of the amount of diol used and the calcination temperature. In the case of 1,2-decanediol and 1,2-dodecanediol, when five moles of the diols were used to one mole of iron nitrate and the calcination temperatures were below 400°C, ψ-Fe2O3 with spinel structure appeared as the main phase and, when less than five moles of the diols were used, α-Fe2O3 appeared exclusively or as the main phase, irrespective of the calcination temperature. This tendency was also observed in thin films. Thus, a transparent magnetic film composed of γ-Fe2O3 could be prepared by applying a benzene solution of the iron polymer, obtained with 5 equivalents of 1,2-decanediol, on quartz and calcining the gel film at 350°C.
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  • 83
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    Journal of sol gel science and technology 8 (1997), S. 83-88 
    ISSN: 1573-4846
    Keywords: sol-gel ; gelation modelling ; TiO2 gels ; simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We present here an experimental and numerical study of the chemical and aggregative mechanisms for titanium alkoxide in a reverse micellar medium. NMR experiments were done to study the first step of the sol-gel process: hydrolysis of titanium isopropoxide. Light and X-ray scattering experiments were then conducted to characterize the clustering of aggregates and aggregation kinetics. Fractal dimension, measured by U.S.A.X.S., varies with the hydrolysis ratio and the hydration of the surfactant. This evolution was explained by polydispersity of the hydrolysis which depends on the surfactant concentration. This hypothesis was tested through a numerical simulation of irreversible aggregation using a chemically limited aggregation model. The hydrolyzed sites are distributed among the monomers by a random procedure governed by a polydispersity parameterp, varying from 0 to 1. The total number of hydrolyzed sites is governed by a parameterq belonging to the interval [0, 1]. Thep-q evolution of the fractal dimension coincides rather well with the experimental data in all the region of the two dimensional phase space.
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  • 84
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    Keywords: mullite ; organic ligand ; hydrolytic polymerization ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation of mullite by the sol-gel method using organic polydentate ligands and the effect of the raw materials and organic polydentate ligands on the formation of mullite were investigated. Two series of samples were prepared using tetraethoxyorthosilicate (TEOS) and aluminum nitrate nonahydrate, or dibutoxyethylacetoacetatoaluminum (Al(OBu)2(AcAcEt)) as the silica and alumina sources, respectively, and using ethylene glycol (EG), 1,3-propanediol (PD), 1,3-butanediol (BD), 2-methyl-2, 4-pentanediol (MPD), diethlene glycol monoethyl ether (DEME) and ethoxyethanol as the ligands. When the alumina source was aluminum nitrate nonahydrate, mullite was apt to appear in the order of EG〉PD〉MPD. When Al(OBu)2(AcAcEt) was the alumina source, the tendency toward the appearance of mullite crystalline phase was EG〉BD〉DEME〉MPD. Between the two alumina sources, aluminum nitrate nonahydrate gave mullite much easier than Al(OBu)2(AcAcEt). These relationships were discussed from the viewpoints of the coordination ability of the ligands and the miscibility between the silica and alumina.
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  • 85
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    Journal of sol gel science and technology 8 (1997), S. 365-369 
    ISSN: 1573-4846
    Keywords: sol-gel ; SiO2 ; TiO2 ; ultraviolet ; densification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural changes in SiO2 and TiO2 gel films were investigated using ultraviolet (UV) and vacuum ultraviolet (VUV) irradiations. A significant compaction with dehydration of SiO2 gel films was induced by irradiation of photons in the range of 9–18 eV. The refractive index and the shrinkage of the irradiated SiO2 gel films were comparable to those obtained by sintering at 1000°C. Densification of TiO2 gel films was also observed with irradiation of 5–14 eV photons. However, effects of the irradiation on TiO2 gel were smaller than those on SiO2 gel. The structural changes in the gel films are attributed to electronic excitations which are induced by irradiation with photons having higher energies than the bandgap of the oxides. The photo-induced effects are presumed to depend on the optical properties and structure of the gels.
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  • 86
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    Journal of sol gel science and technology 8 (1997), S. 381-384 
    ISSN: 1573-4846
    Keywords: barium osumilite ; sol-gel ; alkoxide ; crystallisation ; microstructure
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The crystallisation sequence of stoichiometric barium osumilite prepared by partial-alkoxide (PAR) and all-alkoxide routes (AAR) and the microstructure of the fully crystallised glass ceramic were examined. Comparing the crystallisation behaviours of the gel-glasses obtained revealed that the first phase to crystallise was mullite in PAR but hexacelsian in AAR. Barium osumilite crystals grew randomly and more homogeneously in PAR while in AAR larger barium osumilite crystals grew in clusters. Cordierite formed as a secondary phase in both routes and it crystallised on and between the osumilite lamellae. Mullite and hexacelsian also persisted up to the stage when full crystallisation and taken place.
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  • 87
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    Journal of sol gel science and technology 8 (1997), S. 409-413 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; crystallization ; anatase ; rutile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The aim of this work was to investigate the crystallization behavior of thin films of SiO2−TiO2 made by the sol-gel process as function of the TiO2 content and the temperature and time of heat treatment. Precursor solutions were prepared by hydrolysis of TEOS (tetraethoxysilane) and TPOT (titaniums tetraisopropoxide). Multilayer films were spun on single crystal silicon wafers. The compositions studied were (on a molar percentage basis) 20TiO2−80SiO2, 30TiO2−70SiO2, 40TiO2−60SiO2 and pure TiO2. The films were heat treated at different temperatures between 300°C and 1200°C, for different periods of time (30 s-90 h). The crystallization kinetics were followed by micro-Raman spectrometry. Grazing incidence X-ray diffraction showed that the films crystallized into one or both of two crystalline phase of TiO2: anatase and rutile (for pure TiO2 only). The volume fractions of the crystalline phase varied from very low values (〈1%), up to 100%, for a TiO2 sample heat treated at 800°C for 8 hours. The results show that the volume fraction of crystalline phase is strongly influenced by the heat treatment temperature and also, to a smaller extent, by the heat treatment time. The most important parameter, however, is the composition of the films: the higher their TiO2 concentration, the lower is the crystallization temperature and the larger is the crystallized fraction.
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  • 88
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    Journal of sol gel science and technology 8 (1997), S. 23-28 
    ISSN: 1573-4846
    Keywords: hydrolysis pathway ; Ni-Sb-ethoxides ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The hydrolysis-condensation pathways of Ni-Sb-ethoxides in different toluene-ethanol solvents have been studied. The hydrolysis was performed by slow addition of controlled amounts of water, diluted in toluene-ethanol solvents. Characterization of the hydrolysis products was performed with single crystal X-ray determinations, IR-spectroscopy, UV-Vis spectroscopy and TGA. In this way, a number of different Ni-Sb-(oxo)-ethoxides have been isolated and characterized. It was thereby shown that the Ni:Sb ratio of the hetero bimetallic oxo-alkoxides varied much depending on the degree of hydrolysis and that the species formed vary with the solvent used and the speed at which the water is added.
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  • 89
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    Journal of sol gel science and technology 8 (1997), S. 29-33 
    ISSN: 1573-4846
    Keywords: ceramic fibers ; spinnability ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural ceramic oxide fibers like α-Al2O3, MgAl2O4 (spinel), Y3Al5O12 (YAG) and eutectic Al2O3-Y3Al5O12 as well as the functional Pb(Zr1−xTix)O3 (PZT) fibers were successfully prepared by sol-gel processing. All precursors are based on metal oxohydroxopropionates. A comparative study of sol-gel routes leading to spinnable sols demonstrates the key role of propionic acid as an excellent agent for controlling hydrolysis and condensation reactions.
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  • 90
    ISSN: 1573-4846
    Keywords: sol-gel ; silsesquioxanes ; hybrid organic-inorganic materials ; silicas ; pore structure ; Si−C bond cleavage ; alkynyl silanes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Hybrid organic-inorganic materials containing labile organic fragments with various structural features have been prepared. The mild cleavage of Si−C bonds allowed removal of the organic moities. It led to silica which pore structure varied according to the nature of the organic component eliminated.
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  • 91
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    Journal of sol gel science and technology 8 (1997), S. 615-618 
    ISSN: 1573-4846
    Keywords: sol-gel ; magnetic nanocomposite ; iron oxide ; Mössbauer spectroscopy ; Kerr effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Magnetic nanocomposites γ-Fe2O3/silica were prepared by a one-step sol-gel method. The sol was prepared by TEOS (tetraethyl orthosilicate) acid hydrolysis in the presence of an iron salt soluble in methanol. After gelation and drying, the transparent samples were characterized after treatment at different temperatures. The particle size, observed by HR TEM, was in the range of 2–10 nm and depended on Fe-concentration and heating temperature. Magnetic measurements showed either a ferromagnetic or a superparamagnetic behaviour and could be explained by the particle size. The dependence of the magnetic behaviour on the particle size was also studied by Mössbauer spectroscopy. The samples in which the Fe2O3 particle size was approximately 10 nm showed magnetic splitting (sextet) at room temperature, while smaller particles (2–3 nm) showed this splitting only at the temperature of liquid helium. The optomagnetic properties of the samples were also measured (Kerr effect).
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  • 92
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    Journal of sol gel science and technology 8 (1997), S. 663-666 
    ISSN: 1573-4846
    Keywords: sol-gel ; immunoassays ; antigen ; antibody
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Porous silica gels, synthesized via the acid hydrolysis and basic condensation of TMOS, have been used for the encapsulation of antigens. The pores of the matrix are large enough to allow the diffusion of antibodies through the gel. Antigen-antibody specific fixation occurs within the sol-gel matrix. It can be detected via the so-called enzyme linked immunosorbent assays (ELISA). Antigen-antibody associations occurring in the gel are optically detected via the reaction of a peroxidase conjugate with ortho-phenylenediamine leading to the formation of a yellow coloration. Immunoassays have been performed using the hydatid cyst fluid as the source of antigens and sera from human patients as the source of antibodies. Specific fixation appears to be as good in the sol-gel matrix as in antigen solutions.
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  • 93
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    Journal of sol gel science and technology 8 (1997), S. 681-684 
    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.
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    Journal of sol gel science and technology 8 (1997), S. 721-723 
    ISSN: 1573-4846
    Keywords: sol-gel ; lead titanate ; ferroelectric ; electroactive material ; composites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Powders of (Pb0.8Ca0.2)(Ti0.99Mn0.01)O3 have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality was found to be 1.053±0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient of 17.4 μC/m2K and a pyroelectric figure of merit (FOMp=p/ε) of 0.51 μC/m2K.
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    Journal of sol gel science and technology 8 (1997), S. 729-734 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin films ; titanate perovskites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A description is made of a wet chemical method for obtaining ferroelectric thin films. The processing is based on a twofold synthetic scheme: the synthesis of a titanate gel from a sol-gel process and the rehydration of this gel during the incorporation into the system of other ions as water-soluble salts. The versability of this route has made possible preparation of modified elements. Physico-chemical properties of the solutions are studied as well as the reaction mechanisms that make possible the rehydration of the titanate gel. The solutions obtained are used for the deposition and crystallization of titanate based thin films. Crystallinity, microstructure and polarization-electrid field characteristics of the films are shown.
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  • 96
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    Journal of sol gel science and technology 8 (1997), S. 735-742 
    ISSN: 1573-4846
    Keywords: sol-gel ; Nb2O5 ; film ; photoconductivity ; photoelectrochemistry ; semiconductor ; solar cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Structural, optical, electro and photoelectrochemical properties of amorphous and crystalline sol-gel Nb2O5 coatings have been determined. The coatings aren-type semiconductor with indirect allowed transition and present an overall low quantum efficiency (ϕ〈4%) for UV light to electric conversion. The photoconducting behavior of the coatings is discussed within the framework of the Gärtner and Södergren models. Improvement can be foreseen if Nb2O5 coatings can be made of 10–20 nm size nanoparticles.
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  • 97
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    Journal of sol gel science and technology 8 (1997), S. 759-763 
    ISSN: 1573-4846
    Keywords: sol-gel ; bismuth titanate ; spin-coating ; thin films ; ferroelectric
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bi4Ti3O12 thin films were obtained by the sol-gel method. The precursor solution was prepared by allowing the two metallic alkoxides, Bi(OC2H4OCH3)3 and Ti(OC2H4OCH3)4, to react in 2-methoxy-ethanol to form the mixed alkoxide. This stable sol was deposited by spin-coating onto platinized silicon substrates. X-Ray diffraction patterns indicate that the perovskite initial crystallization temperature is 460°C for powder samples and it ranges between 400 and 500°C, for thin films, as a function of the number of coating layers. Dense, smooth and crack free thin films with grain sizes ranging from 20 nm to 500 nm are obtained, depending on the number of coating layers and on the post-deposition temperature annealing.
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  • 98
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    Journal of sol gel science and technology 8 (1997), S. 819-824 
    ISSN: 1573-4846
    Keywords: sol-gel ; diffusion limited cluster-cluster aggregation ; theory of gelation ; fluctuating bond aggregation ; numerical simulations ; aggregation ; chemical gels formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The diffusion limited cluster-cluster aggregation (DLCA) model is modified by including cluster deformations during aggregation, with a tuningflexibility parameterF. A three-dimensional computer simulation is presented, which starts from a collection off-functional monomers randomly distributed in a cubic box with a volumic fractionc (concentration) and which uses the highly efficientbond fluctuation algorithm to describe the cluster deformations. It is shown that, forF≠0, there exists a well defined threshold value of the volumic fraction below which the realization of all intra-aggregate bonding possibilities prevents the formation of a gelling network. Forc〉c g , atrue sol-gel transition occurs at a characteristic timet g , after which an infinite cluster (which is self connected via the boundary conditions) appears. In contrast to DLCA,t g does not increase as the box size increases. The transition atc g is characterized by a divergence of the final clusters size forc〈c g and a divergence of the gel time forc〉c g . Several other numerical results are reported.
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  • 99
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    Journal of sol gel science and technology 8 (1997), S. 895-899 
    ISSN: 1573-4846
    Keywords: luminescence ; pyranine ; sol-gel ; hybrid coatings ; emission anisotropy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The sensitivity of the pyranine fluorescence to protonation/deprotonation is used to follow modifications in cured sol-gel thin films. The acid concentration in the sol-gel solution is varied for TEOS-based coatings and a series of organically modified silanes Si(OR)3R’ are added to the TEOS solution. The concentration of the organically modified silane is varied as well as the chain length of the alkylgroup (R’). The stationary fluorescence measurements show that the equilibrium between the protonated and the deprotonated form of pyranine changes depending on the type of silica matrix. The deprotonated form is dominant in the cured SiO2 films and the protonation/deprotonation ratio of pyranine is constant for the different acid concentrations used. The protonated form becomes dominant as the concentration of Si(OR)3R’ is increased and as the alkyl chain length (R’) of the organically modified silanes is augmented. Emission anisotropy measurements of pyranine in the same coatings show that the rotational freedom of the molecule changes due to modifications in the cages for the TEOS-based coatings. These modifications are produced by the acid concentration used to prepare the coatings. An increase in the rotational freedom of pyranine is observed in the TEOS-Si(OR)3R’ systems.
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  • 100
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    Journal of sol gel science and technology 8 (1997), S. 931-935 
    ISSN: 1573-4846
    Keywords: photochromic ; fiber optic ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Photochromic-doped sol-gel materials have been prepared by adding a spiropyran photochromic dye to a solution of ethoxy silane monomers containing non-reacting ethyl radicals. After polymerization, normal photochromism (i.e., colored material upon UV irradiation) is obtained in the resulting matrix. The sol-gel matrix hinders the organic molecule rotations, thus giving two stable states, which can be reversibly switched by UV and green-blue irradiation respectively. If these materials are attached to optical fibers, the properties of the light throughput may be modified. Simple fiber-optic/photochromic devices made of two optical fibers placed in a V-groove removable connector have been prepared. Once cured, these devices behave as optically addressed variable delay generators. The same devices can be used for preparing simple optical switches and routing systems.
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