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  • sol-gel  (51)
  • Springer  (51)
  • American Meteorological Society
  • Oxford University Press
  • 2020-2024
  • 1995-1999  (51)
  • 1990-1994
  • 1998  (51)
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  • Springer  (51)
  • American Meteorological Society
  • Oxford University Press
  • Wiley-Blackwell  (3)
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  • 2020-2024
  • 1995-1999  (51)
  • 1990-1994
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  • 1
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    Springer
    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 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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  • 3
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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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  • 4
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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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  • 5
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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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  • 6
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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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  • 7
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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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  • 8
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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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  • 9
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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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  • 10
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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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  • 11
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 12
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 13
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 14
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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)
    Source: Springer Online Journal Archives 1860-2000
    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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  • 15
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 16
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 17
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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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    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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  • 18
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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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    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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  • 19
    ISSN: 1573-4846
    Keywords: porous layers ; chemical sensing ; sol-gel ; optical fiber
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    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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  • 20
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 21
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 22
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 23
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 24
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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
    Source: Springer Online Journal Archives 1860-2000
    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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  • 25
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    Journal of materials synthesis and processing 6 (1998), S. 1-7 
    ISSN: 1573-4870
    Keywords: Alumina ; sol-gel ; structure ; thermal evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The thermal evolution of an alumina gel synthesized by hydrolysis of aluminium alkoxide (sol-gel technique) was studied by thermal analysis (DTA and TGA), X-ray diffraction, FTIR and NMR spectroscopies, and specific surface area measurements. Between 400 and 900°C, γ- and δ-aluminas were formed showing aluminium vacancies preferentially located in tetrahedral sites. The atomic rearrangements produced during α-alumina formation are oriented to the progressive elimination of tetrahedral aluminium in the ultimate phase. The evolution of the specific surface area during heating is explained by changes in structure and microstructure.
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  • 26
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    Journal of sol gel science and technology 13 (1998), S. 1027-1031 
    ISSN: 1573-4846
    Keywords: alumina-silica ; methanol conversion ; pore design ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Amorphous alumina-silicas were prepared from a tetra-alkoxysilane and anhydrous aluminum trichloride or an aluminum alkoxide by a sol-gel process using 2-methyl-2,4-pentanediol, pinacol, 1,2-propanediol, 2,3-butanediol or ethylene glycol as the solvent or complexing agent, and the effect of diols and alkoxy groups on the physical and chemical properties of the alumina-silicas was examined. When the diol or the alkoxy group was bulky, the alumina-silicas had relatively larger micropores, a larger pore volume and higher surface areas. In the conversion of methanol catalyzed by the alumina-silicas, the bulkier diols and alkoxides gave catalysts that produced dimethyl ether in higher yield and hydrocarbons in lower yield. Thus, when ethylene glycol was used as the diol, the best catalyst for the production of hydrocarbons, especially the production of olefins such as ethylene, propylene and butene, was obtained. Furthermore, in comparison with alumina-silica prepared by a traditional kneading process, it was found that the sol-gel alumina-silica could efficiently convert methanol to dimethyl ether and hydrocarbons, but the material prepared by kneading had a very low conversion of methanol to other compounds.
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  • 27
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    Journal of sol gel science and technology 13 (1998), S. 961-967 
    ISSN: 1573-4846
    Keywords: sol-gel ; thin film ; SnO2 : Sb ; transparent conducting coatings ; laser densification ; electrical properties ; morphology
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sb doped sol-gel SnO2 single layers (thickness ≈100 nm) were prepared from alcoholic solution and deposited via a dip coating process on fused silica substrates. The coatings have been sintered at a typical rate of 10–15 cm2/s by CO2 laser irradiation. The laser spot was scanned in one direction at a speed of 15,000 cm/s and the sample was moved in a perpendicular one at a speed up to 250 mm/s. The temperature of the topmost 10 μm layer was monitored by a fast pyrometer (μs resolution). The following properties of the coatings have been determined: the electrical resistivity ρ, the carrier density n, and mobility μ, the structure, the thickness, the mesoscopic and micromorphology and the density. The sintering by CO2 laser radiation is mainly a thermal driven process. At T ≈500°C it allows to obtain coatings with a smaller resistivity (6.8×10−3 Ωcm) than those produced by conventional furnace firing (ρel≈2.9×10−2 Ωcm). The results are discussed in terms of particle size and packing density.
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  • 28
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    Journal of sol gel science and technology 13 (1998), S. 915-921 
    ISSN: 1573-4846
    Keywords: vanadium dioxide ; thermochromism ; sol-gel ; optical switching
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Vanadium dioxide thin films have been deposited from vanadium alkoxides VO(OR)3. An amorphous film is formed that transforms into crystalline VO2 upon heating at 500°C under a reducing atmosphere. Optically transparent VO2 thin films are then obtained that exhibit both electrical and optical switching around 70°C. The switching temperature together with the shape of the hysteresis loop can be modified by doping VO2 films with foreign cations. Doped MxVO2 (M = W6+, Nb5+, Ti4+, Cr3+ or Al3+) thin films have been prepared under the same conditions by mixing the vanadium alkoxide and a metal salt in an alcoholic solution. The switching temperature decreases when the film is doped with high-valent cations (W6+) and increases with low-valent cations (Al3+, Cr3+). The transition temperature first decreases and then increases when TiIV is added to the VO2 film while the width of the hysteresis loop is significantly reduced.
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  • 29
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    Journal of sol gel science and technology 13 (1998), S. 547-551 
    ISSN: 1573-4846
    Keywords: sol-gel ; fast ; micro-optics ; patterning ; replication
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The fast sol-gel method enables facile preparation of siloxane-based glassy matrices, in which polymerization is completed within minutes and volume changes 〈5% take place upon curing. Single-face and two-face replication of micro-optical arrays have been obtained, as well as crack-free elements 〉10 mm thick. Minimizing shrinkage and enabling relaxation of the drying sol-gel are key factors in the elimination of cracking. These features and the resulting optical quality of the glass make this method technologically and economically attractive for replication-produced micro-lenses and micro-optical arrays.
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  • 30
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    Journal of sol gel science and technology 13 (1998), S. 1043-1047 
    ISSN: 1573-4846
    Keywords: magnesium oxide ; sol-gel ; magnesia acidity ; pyridine adsorption
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Traditionally, magnesium oxide has been considered a typical basic catalyst, catalyst carrier and/or adsorbent. In this study MgO was prepared using Mg-ethoxide dissolved in ethanol and hydrolyzed with various aqueous inorganic acids and bases. We have found that it is possible to induce Brønsted and Lewis acid sites depending on the method of preparation and, more specifically, on the type of inorganic acids used in the hydrolysis stage. In the FTIR spectra of adsorbed pyridine on MgO obtained using aqueous HCl (pH = 3), the bands corresponding to Lewis (1603, 1496 and 1444 cm−1) and Brønsted (1550 cm−1) acid sites are observed. The fact that upon vacuum and high temperature treatment, i.e., at 773 K, the above mentioned bands are clearly distinguishable indicated that the acid sites are very strong. On the other hand, the MgO materials obtained using aqueous acetic acid as a hydrolysis catalyst (pH = 5), and that without any catalyst (pH = 7) showed only Lewis acid sites which decreased markedly upon higher temperature treatment. When aqueous NH4OH (pH = 9) was used as the hydrolysis catalyst, the MgO obtained showed only Lewis acid sites. In all cases the number of Lewis acid sites was greater than that of Brønsted sites.
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  • 31
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    Journal of sol gel science and technology 13 (1998), S. 213-217 
    ISSN: 1573-4846
    Keywords: bismuth oxide ; bismuth silicate ; thin film ; sol-gel ; surface techniques
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Bi2O3 thin films were prepared by dipping silica slides in ethanolic solutions of tris(2,2′-6,6′-tetramethylheptane-3, 5-dionato)bismuth(III) [Bi(dpm)3] [1] and heating in air at temperatures ≤500°C. Bi4(SiO4)3 homogeneous thin films were obtained from the reaction of the bismuth oxide coating with the silica glass substrate at temperatures higher than 700°C. For heat treatments at temperatures between 600°C and 700°C, Bi2SiO5 coatings were obtained. The composition and microstructure evolution of the films were determined by Secondary Ion-Mass Spectrometry (SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Glancing Angle X-Ray Diffraction (GA-XRD). The synthesis procedure was reproducible and allowed the control of the Bi2O3 phase composition. Moreover, the thin film annealing parameters were correlated with the formation of bismuth silicates, among which Bi4(SiO4)3 (BSO) is very appealing for the production of fast light-output scintillators [2].
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  • 32
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    Journal of sol gel science and technology 13 (1998), S. 461-466 
    ISSN: 1573-4846
    Keywords: sol-gel ; ORMOSILs ; X-ray diffraction (XRD)
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    Topics: Chemistry and Pharmacology
    Notes: Abstract ORMOSILs have been prepared in the series TMOSx·MTMS(100 − x) (where TMOS is tetramethoxysilane; MTMS is methyltrimethoxysilane; x is mol% silane with respect to total silane for 0 ≤ x ≤ 100) by means of acid catalyzed, sol-gel processing. After drying at 60°C, small bulk samples were obtained of excellent optical clarity. Powder X-ray diffraction (XRD) patterns, in the range of 5 to 60°2Θ, were compared with that of fused silica. All the prepared samples were amorphous. Fused silica exhibits one broad peak, d2 centered at d-spacing 4.12 Å. For the TMOS100 silica xerogel, the analogous broad peak had shifted slightly, to be centered at 3.88 Å; and remained in about the same position as x was decreased for the series TMOSx·MTMS(100 − x). In addition, a second, broad peak, d1, was observed for the ORMOSIL series centered at the d-spacing 8.7 Å for MTMS100 (i.e., x = 0) and increasing smoothly as x was increased, reaching 11.3 Å for x = 70, and 〉11.3 Å for x 〉 70. The intensity of d1 was found to have trebled, relative to the intensity of d2, on increasing the organic character of the matrix from TMOS70·MTMS30 to MTMS100. The d2 peak appearing at about 4 Å for both fused silica and the ORMOSILs is assumed to be associated with the spacing between silicon atoms connected by means of an oxygen bridge. The Si–O–Si angle for silica xerogels is known to depend upon the nature of the sol-gel processing and is bigger than that of fused silica. The d1 peak may be associated with the spacing between silicons attached to methyl groups and indicative of channels of methyl groups in the structure. Alternatively, the d1 peak may have its origin in a preferred, discrete structural unit in the matrix for instance cubane based on a octameric silicon arrangement.
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  • 33
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    Journal of sol gel science and technology 13 (1998), S. 763-767 
    ISSN: 1573-4846
    Keywords: sol-gel ; coatings ; corrosion ; morphology ; atomic force microscopy
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Atomic force microscopy (AFM) was used to study the performance of ≈80 nm thick Al2O3-TiO2-SiO2 sol-gel coatings on glass substrates following corrosion in 1 M NaOH solutions at 60°C. The as-prepared coatings were homogeneous on a nanoscale and displayed the “glass pattern” before corrosion. Layers with different compositions behaved differently during the corrosion process. Thus, TiO2 or TiO2-dominated layers had tetragonal-like crystals on their surfaces after corrosion, possibly of anatase composition. On the other hand, layers with a molar ratio Al2O3 : SiO2 near 1 : 2 displayed a pseudo-hexagonal morphology, possibly with a nepheline (Na2O · Al2O3 · 2SiO2) composition. Layers of 5Al2O3-40TiO2-55SiO 2 were corroded is a stepwise fashion and had no special surface morphology.
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  • 34
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    Journal of sol gel science and technology 13 (1998), S. 523-527 
    ISSN: 1573-4846
    Keywords: nanocomposite ; sol-gel ; photopolymerization ; channel waveguides
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The development and characterization of channel waveguides using wet-process, low temperature sol-gel chemistry is described. Two structures have been developed. The first one is a one-layer structure, composed of a sol-gel solution which is a mixture of photopolymerizable organosilicate and organozirconate precursors. The other is a multilayer structure with a buffer under the guide and a protective coating. The layers are deposited by the dipping technique. The devices are obtained by UV light exposure of the coating through a predefined mask (channel waveguides). The refractive index increase is sufficient enough to allow the use of waveguides in the 1.55 μm telecommunication window. These waveguides are thick enough to reduce the coupling losses with an optical fiber below 0.5 dB. Also, because of our sandwich structure, the propagation losses are less than 0.1 dB.
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  • 35
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    Journal of sol gel science and technology 13 (1998), S. 541-545 
    ISSN: 1573-4846
    Keywords: spectral hole burning ; Sm2+-doped glass ; sol-gel ; fluorescence line narrowing
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Sm2+-doped glasses in the system of Al2O3-SiO2 were prepared by sol-gel processing of metal alkoxides and reacting with H2 gas at 800°C. The hole burning properties of these glasses were investigated. The holes were burned in the 7F0 → 5D0 line of the Sm2+ ions using a DCM dye laser at 77 K. The hole depth increased with increasing the laser irradiation time, reaching up to ∼15% of the total intensity within a few hundred seconds. The hole width was 3 cm−1 full width at half maximum. Fluorescence line narrowing spectra of the 5D0 → 7 F1 transition were analyzed to study the local structure surrounding the Sm2+ ion. It is concluded that the Sm2+ ions are closely coordinated with nine oxygens of the AlO6 group in aluminosilicate glasses and that the addition of Al3+ ions into glass induces an increase in the coordination number of the Sm2+.
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  • 36
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    Journal of sol gel science and technology 13 (1998), S. 869-870 
    ISSN: 1573-4846
    Keywords: sol-gel ; lead lanthanum titanate ; thin film ; optical waveguide ; optical propagation loss
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    Topics: Chemistry and Pharmacology
    Notes: Abstract The preparation and the optical characteristics of highly oriented PLT thin films are investigated. PLT films fabricated on MgO(100) and c-plane sapphire substrates have highly grown in (100) and (111) orientations, respectively. PLT films with high La content have a near cubic structure and weak anisotropy of refractive indices. The optical propagation losses of PLT films decrease as the La content of the films increases due to a complex interaction of surface roughness reduction and a reduction in the anisotropy refractive index. However, optical scattering in thicker sol-gel PLT thin film waveguides occurs by the internal scattering mechanism from the defects and the interfaces rather than by the surface scattering mechanism.
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  • 37
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    Journal of sol gel science and technology 13 (1998), S. 933-936 
    ISSN: 1573-4846
    Keywords: proton conductor ; phosphate glass ; sol-gel ; water containing glass
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Fast proton-conducting P2O5-ZrO2-SiO2 glasses were prepared by sol-gel processing of metal alkoxides. Glasses heated to 150 to 400°C exhibited room temperature conductivities of ∼10−4 S/cm, larger by ∼2 order of magnitude than that of as-prepared gel, ∼3 × 10−7 S/cm at 30°C. The conductivity increased quadratically with the increasing product of proton and molecular water concentration. These high conductivities were regarded as fast proton transfer accelerated by molecular water bonded with the hydroxyl groups.
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  • 38
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    Journal of sol gel science and technology 13 (1998), S. 991-994 
    ISSN: 1573-4846
    Keywords: sol-gel ; indium oxide ; ITO ; crystallization ; ultraviolet laser
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Modification of sol-gel derived indium oxide thin films using ultraviolet lasers was investigated. Irradiation by an ArF excimer (6.4 eV) and the fourth harmonic generation of a Nd : YAG laser (4.7 eV) was found to be effective in crystallization with a loss of hydroxyl groups and a decrease in the sheet resistance of the sol-gel films. Transparent crystalline indium oxide films were successfully obtained by 6.4 eV laser irradiation at fluences below 20 mJ/(cm2·shot), whereas degradation of the films was induced by a relatively high-fluence beam.
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  • 39
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    Journal of sol gel science and technology 13 (1998), S. 1011-1016 
    ISSN: 1573-4846
    Keywords: microspheres ; sol-gel ; titania ; Synroc ; spray-drying
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Porous titanate precursor microspheres (20–60 μm in diameter), with a high sorption capacity for radioactive wastes from nuclear reprocessing plants, have been produced on a 50 kg scale by spray-drying precursor sols. Well-dispersed, stable sols were produced by hydrolyzing acetic acid modified tetraisopropyltitanate and peptizing the titania hydrolysate with acidic zirconia sol. The resulting TiO2 /ZrO2 sols were routinely concentrated to 900 g dm−3 (oxide basis) and exhibited excellent stability. These sols were subsequently mixed with dispersible alumina powder and partially aggregated by adding calcium and barium nitrate salts. The resulting sols were spray-dried to produce microspheres with controlled porosity and morphology. The properties of the spray-dried powder were very dependent upon the chemical properties of the precursor sol. In particular, hollow spheres were produced from well-dispersed sols, whereas solid spheres could be produced from partially-aggregated sols.
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  • 40
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    Journal of sol gel science and technology 13 (1998), S. 623-628 
    ISSN: 1573-4846
    Keywords: sol-gel ; ormosil ; nanosized CdSe particles ; quantum dots ; optical nonlinearity ; solid-state NMR ; near-infrared spectroscopy ; visible spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Nanosized phenyl-capped CdSe particles (quantum dots) were isolated, after preparation inside reversed micelles present in AOT/H2 O/heptane, and then successfully redispersed in amine-functionalized ormosils derived from 3-aminopropyl(trimethoxy)silane (i.e., SA). Doped ormosils were formed into films of a few μm thickness or small bulk samples. Host ormosils were structurally characterized by means of absorption spectroscopy, in the near- and mid-infrared ranges, and by 29Si and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Doped ormosils were prepared and investigated via visible spectroscopy. The size of CdSe particles dispersed into the amino-ormosil hosts was calculated using the Effective Mass Model.
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  • 41
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    Keywords: sol-gel ; rare-earth doping ; optical fibers
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Optical cores of preforms for drawing optical fibers doped with Er3+ and Yb3+ were fabricated by the sol-gel method with the aim of increasing the thickness of glass layers coated in a single coating cycle and to determine the relation between the preparation conditions and optical properties of the fibers. Al2O3-P2O5-SiO2 and TiO2-P2O5-SiO2 glasses have been studied as matrices for entrapping the rare-earth elements. Input sols have been prepared from silicon and titanium alkoxides, AlCl3, ErCl3, YbCl3, POCl3, water and a modifier under acidic catalysis of HCl. The sols were coated on the inner wall of a silica substrate tube and the gel layers were sintered at high temperatures up to 2000°C after which the tube was collapsed into the preform. Continuous and homogenous glass films with the maximum thickness of about 8 μm were fabricated. The influence of high-temperature heat treatment of the layers on their composition and optical attenuation was observed. The amplified stimulated emission of Er3+ around 1.55 μm was measured under the excitation of the fibers by an Nd : YAG laser at 1.064 μm.
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  • 42
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    Journal of sol gel science and technology 13 (1998), S. 651-655 
    ISSN: 1573-4846
    Keywords: metallic tetrasulphophthalocyanines ; aggregation ; monolithic gel ; sol-gel
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Metallic phthalocyanines exhibit, among many useful properties, the ability to protect sensors against short, intense optical pulses deleterious to efficient sensor operation. It is possible by means of low temperature sol-gel techniques to obtain porous monolithic materials encapsulating metallic ions, and all sorts of complex organic molecules. We report here the study of water-soluble metallic tetrasulphophthalocyanines (MTSPc) encapsulated in silica obtained by the sol-gel technique. These materials are transparent and stable and exhibit interesting optical properties. Absorption in the visible region of the spectrum reveals aggregation of the MTSPc species to form dimers which modify the optical absorption of excited states and the resulting optical properties. We investigate the relative importance of the various physicochemical parameters affecting dimer formation (dye concentration, pH, presence of species such as dimethylformamide, pyridine, etc.) in order to control and inhibit dimer formation. Two species are chosen as examples of the general behavior: CuTSPc, which shows a strong tendency to dimerize in water and in mixtures of solvents, and (OH)AlTSPc, which does not form dimers in aqueous solutions because of its hindering OH axial group. The experiments performed show that addition of dimethylformamide or pyridine does not inhibit aggregation in CuTSPc, simultaneously causing the blue color to disappear from the prepared gels. In the case of (OH)AlTSPc addition of relatively high concentrations of pyridine brings about the formation of non-monomeric species.
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  • 43
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    Journal of sol gel science and technology 13 (1998), S. 799-803 
    ISSN: 1573-4846
    Keywords: sol-gel ; thermal stability ; Al2O3 ; TiO2 ; membranes
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    Topics: Chemistry and Pharmacology
    Notes: Abstract A sol-gel route has been used to produce a nanoporous membrane for the separation of “greenhouse” gases from power plants at elevated temperatures (700–900 K). The membrane has a controlled pore size distribution and is multiphasic, in order to prevent grain growth and pore coarsening. The alumina/titania diphasic ceramic was obtained from alkoxide precursors with additional magnesium or lanthanum doping to stabilize low temperature phases and to provide possible chemisorption of CO2. It was found that both Mg and La stabilized the γ-alumina phase to higher temperature by as much as 200 K, although Mg is less effective.
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  • 44
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    Journal of fluorescence 8 (1998), S. 199-205 
    ISSN: 1573-4994
    Keywords: Ammonia optode ; sol-gel ; fluorescence energy transfer
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    Topics: Physics
    Notes: Abstract We report on the effect of organomodified sol-gel materials on fluorosensors for ammonia. The fluorosensors are based on ion pairs composed of an inert fluorophore and a pH-sensitive absorber dye and are embedded in sol-gel glass. Upon exposure to ammonia, deprotonation of the pH-sensitive dye bromophenolblue occurrs, and consequently, energy is transferred from the fluorophore rhodamine B or tetramethylrhodamine ethyl ester to the absorber. The response of the fluorosensors using different ratios of precursors, such as tetramethoxysilane and phenyltrimethoxysilane, is investigated. Detection limits for sol-gel layers composed of 50% tetramethoxysilane and 50% phenyltrimethoxysilane are as low as 0.1 mg/L of aqueous ammonia. Response times are of the order of 3 to 6 min for forward response. The reversibility of the sensor is related to the composition of the organically modified sol-gel glasses and is fastest for sensor layers composed of pure phenyltrimethoxysilane. Conditioning, regeneration, and storage of the layers are shown to be of vital importance for the performance of the sensor layers.
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  • 45
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    Journal of porous materials 5 (1998), S. 59-63 
    ISSN: 1573-4854
    Keywords: sol-gel ; silica ; microwave ; humidity ; porous material
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Silica gel has been prepared by the hydrolysis of TEOS under three different pH conditions. These gels have been subjected to drying in an air oven, under humidity, and also by exposure to microwaves, followed by further calcination at 500°C under slow heating schedule (3°C/min). Silica samples thus obtained are characterised by B.E.T. specific surface area and pore volume data. The thermal decomposition behaviour of the precursor gels are also reported. The adsorption isotherms of these samples indicate different behaviour related to the method of synthesis. Increase in pH of hydrolysis of the TEOS from 3 to 8 results in increase in specific surface area in tune with the earlier reports. However more significant observation is the variation in pore size distribution as evidenced from adsorption isotherms related to method of drying. Silica gels prepared at pH 3 show Type I behaviour irrespective of the method of drying. However gel prepared at pH 6 shows Type II behaviour when dried under microwave with specific surface area as high as 635 m2/g and pore volume 0.9733 cc/g. The precursor gels prepared at still higher pH exhibit Type IV behaviour when subjected to microwave drying. The pH conditions of synthesis of precursor gels along with drying techniques appear to affect not only the surface areas and porosities but also the resultant adsorption isotherms, in sol-gel silica.
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  • 46
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    Journal of porous materials 5 (1998), S. 103-110 
    ISSN: 1573-4854
    Keywords: silica ; sol-gel ; phase separation ; solvent exchange ; surfactant
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The principle of designing double-pore structure in alkoxy-derived silica is described with the experimental system containing polyoxyethylene nonylphenylether. The formation of macropores is consistently explained in terms of the concurrence of a phase separation and a sol-gel transition in the polymerizing silica-surfactant-solvent system. The composition-morphology relationship exhibited a substantial variation depending on the length of oxyethylene units in the surfactant molecule. The mesopore volume obtained after basic solvent exchange and a heat-treatment suggested that the surfactant with shorter oxyethylene chain tends to be incorporated more in the gel phase to give higher mesopore volume. The small-angle X-ray scattering measurement of the gelling and aging system supported this hypothesis indicating micelle formation in the system containing a surfactant with shorter oxyethylene chain.
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  • 47
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    Keywords: sol-gel ; bioceramics ; aggregation ; rheology ; structure
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Potentially bioactive sol-gel derived CaO-P2O5-SiO2 systems are studied and the influence of aggregation mechanism on the gel structure is discussed. A rheological measuring technique is used to monitor the aggregation process and the results are related to heterogeneity of the obtained gel structure. The results indicate that heterogeneity is produced in the sol-gel transition when calcium nitrate and phosphoric acid are used as precursors of CaO and P2O5. This destroys the correlation between bioactivity and the calcium and phosphorus content of the gel derived glasses.
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  • 48
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    Journal of sol gel science and technology 13 (1998), S. 229-232 
    ISSN: 1573-4846
    Keywords: microstructure ; high-Tc Bi-based superconductor ; electron microscopy ; sol-gel ; preparation ; amorphization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Microstructures of high-Tc Bi-based superconductors in a disk form and a tape form sheathed by Ag are examined by SEM and TEM. The disk specimens were prepared by the sol-gel method and are compact with few cavities. Bi-2212 or Bi-2223 grains grow with short heating times leading to rapid increases in magnetization. However, magnetization drops with further heating due to the formation of 2201 areas in the 2212 matrix or 2212 areas in the 2223 matrix together with the amorphization within the matrix. In the tape specimens prepared by conventional powder processing methods, thin plate-like grains grow large with some cavities among them. The Jc increases together with the grain growth and then drops slowly as the amorphization of the grains occurs.
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  • 49
    ISSN: 1573-4846
    Keywords: Turkish Blue pigment ; solid solution ; solid impregnation ; sol-gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In this communication, zircon containing vanadium samples which gradually turn greenish have been prepared by controlling the composition (fluoride addition) and the method of preparation (sol-gel, ceramic and solid impregnation) in order to investigate how to affect the shape and size of the vanadium particles, and their location, clustering and distribution. The level of green color, and consequently the amount of V5+ in the sample, could be associated with the development of an Si-O-Si network in the zircon lattice, bonding with the highly reactive zirconium precursors.
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    Journal of sol gel science and technology 13 (1998), S. 495-497 
    ISSN: 1573-4846
    Keywords: sol-gel ; hybrids ; vanadium ; poly(ethylene glycol)
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    Topics: Chemistry and Pharmacology
    Notes: Abstract Synthesis and characterization of hybrid organic-inorganic nanocomposites based on reaction of vanadium i-propoxide with an organically functionalized poly(ethylene glycol) having di-carbonyl groups is reported. The bulk gels were characterized by thermal analyses (DSC, TGA and TMA) and FT-IR spectroscopy. The results revealed that the gels consist of vanadium-oxygen-vanadium groupings which are cross-linked with the functionalized polymer through the di-carbonyl groups. Gels doped with lithium salt show significant electrical conductivity.
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  • 51
    ISSN: 1573-4854
    Keywords: sol-gel ; silica ; particle size ; xerogels ; surface area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The acid catalyzed hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the absence of alcohol was studied using cylindrical internal reflectance Fourier transform infrared (CIR-FTIR) spectroscopy at four temperatures. Special attention was given to the low-frequency band around 940 cm-1 and its evolution corresponding to the changing silicic acid concentration. This method compared well with other published methods for studying condensation kinetics. Three different conditions for gelation were used to determine temperature and humidity effects on resultant gels. In addition, effect of reaction temperature on gel porosity and surface area was studied. Sols that were gelled at high humidity (84–96% R.H.) and room temperature, 22–24°C, had a much higher surface area and porosity than those gelled at low humidity (5–50% R.H.) and room temperature, 22–24°C, whereas sols gelled at high humidity (79–98% R.H.) and low temperature, 7–8°C, had an intermediate surface area and porosity. Temperature of hydrolysis and condensation reactions did not have a significant effect on surface area. It is proposed that differences in surface area and porosity are mainly caused by the rate of solvent evaporation. Rapid evaporation of solvent and quick gelation of the low humidity samples results in a close-packed microporous xerogel. This is in contrast to the slow gelation and increased available time for condensation in the higher humidity samples, resulting in a more open structure.
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