Three different TiO2-SiO2 gels (Xerogel, Carbogel and Aerogel) are more active acid catalysts than other reference samples used here. As deduced from FTIR, XRD and XANES studies, the structural properties of these gels are quite different to each other, thus revealing the strong influence of the drying treatment. It is found that the degree of Si-O-Ti linking and the surface acidity follows the same trend (X 〉 C 〉 A). We conclude that supercritical drying at 600 K and 190 bars can induce Ti leaching followed by redeposition in the narrower pores of the gel. These effects modify both the textural and surface chemical properties of the resulting material.

Anomalous revolving stacking crystal growth of β-type vanadium oxide hydrate formed by hydrothermal treatment was studied by transmission electron microscopy.

Formation of V4+ upon UV-irradiation in the V2O5 · n H2O was confirmed and the layered structure of this material was discussed on the basis of an ESR analysis of the species produced therefrom in combination with spectral change upon H2O adsorption.

ZrO2 coatings were obtained by the the alkoxide route and deposited onto stainless steel using the dip coating technique. The starting solutions were prepared by mixing zirconium tetrabutoxide, isopropanol, acetylacetone. The water content for the hydrolitic reaction arose from the atmosphere moisture.

Useful information for the structural organization of the zirconia/steel interphase is given by XPS analysis.

It is found that during firing treatment, the main components (Fe, Cr, Ni) of the stainless steel diffuse into the ceramic coating. XPS data allow to describe the chemical composition variation from the bulk substrate to the outer coating surface.

Thermal stability of a novel rubbery ORMOSIL of condensed tetraethoxysilane (TEOS) and polydimethylsiloxane (PDMS) was investigated along with methods by which to improve this stability. Based upon literature review of siloxane systems, modifications of the base ORMOSIL system was made which included substitution of polydimethyldiphenylsiloxane (PDMDPS) for PDMS, adding antioxidant, and adding iron compounds. Relative enhancement was investigated in terms of resilience measurements, and was also analyzed with thermo-gravimetric analysis (TGA) and differential thermal anaysis (DTA).

The carbon retention patterns based on evolution of FT-IR spectra at different calcination temperatures for ZrO2 gels derived from Zr-n-propoxide-acetylacetone-water-isopropanol system are examined in detail. For most captured carbon species, carbon can be depleted at relatively low temperature of about 400°C. However, for lattice-included species, especially those incorporated into lattice during phase transition, a temperature around 900°C is needed to eliminate carbon in the gels. It is found that water treatment alone does not provide new routes for carbon retention in as-prepared ZrO2 gels. When gels are pre-treated with Ni2+ and water, new forms of carbon containing species can be observed. This is attributed to an inter-diffusion of Ni2+ and ZrO2 matrix and the catalytic effect of resultant solid solution NiO-ZrO2 on the retained carbon.

The crystallization behaviors of stoichiometric feldspar gels and glasses before and after seeding have been compared, and the role of epitaxy in their crystallization upon seeding has been studied. The crystallization products were mainly determined by X-ray diffraction (XRD) analysis and epitaxy upon seeding was examined with a scanning electron microscope (SEM), and energy dispersive spectrometry (EDS). It was found that upon isostructural seeding, Na-and K-feldspars crystallized epitaxially from their gels and/or glasses. Little or no seeding effect was found in CaAl2Si2O8 and SrAl2Si2O8 gels and glasses. Isostructural seeding in BaAl2Si2O8 gels increased the formation of Ba-feldspar (monoclinic celsian) epitaxially, whereas without seeding hexacelsian was the crystallization product.

The infrared vibrational modes of sol-gel derived optical silica monoliths depend upon thermal treatments and chemical environments, as shown by Fourier transform infrared spectroscopy (FTIR). A semi-empirical quantum mechanical theory (PM-3 in MOPAC 6.1) is used to analyze the structural changes responsible for the spectral shifts. Optimized structures of 2-member, 3-, 4-, 5- and 6-member rings of SiO2 are calculated. The force constants for the molecular bonds in the rings are obtained and converted to the associated vibrational spectra for the rings. The peak position of the asymmetric transverse optical (AS1TO) mode of the rings shifts from 1070 cm−1 for 2-member rings to 1100 cm−1 for 3-member rings, 1150 cnr1 for 4-member rings, 1140 cm−1 for 5-member and 1120 cm−1 for 6-member rings. The IR data show a 38 cm”1 shift of the AS1TO mode as the gel-silica density changes from 1.1 g/cc to 2.2 g/cc. Thus, the intensification and shift of the AS1TO mode in the gel-silica to higher wave-numbers corresponds to a change in the distribution to larger silicate size rings.

The grain boundary phase of silicon nitride containing additives Y2O3 and Nd2O3 has been studied by means of a newly developed 300kV field emission ATEM. The composition of the two-grain boundary phase of about 1 nm thick is successfully determined. It is then found that the compositions among the grain boundaries are not the same and the additives of Y2O3-Nd2O3 are poor in the two-grain boundary, while they are rich in the triple points.

Compositions from the systems Pb-Mn-B-O and Pb-Mn-Te-0 are used to synthesize glass-ceramics obtained by solid state reactions and from supercooled melts. By casting on a metal plate or by quenching with the aid of twin rollers the melts are cooling. The glass-crystalline materials are obtained after heating glasses from the combination of PbO-MnO-B203 and PbO-MnO-TeO2 with the addition of La203 from 10 to 50 wt.% and the formation of the crystalline phases is determined.

Broadband fluorescence and fluorescence line narrowing (FLN) spectra are presented for Eu3+ ions in Eu2O3-SiO3 and Eu2O3-Al2O3-SiO3 systems prepared by the sol-gel process. Clustering of rare earth ions in silica glass can be a limiting factor in the design and engineering of optical device materials. The addition of Al2O3 is known to help disperse rare earth ions in sol-gel silica. In order to develop a more detailed understanding of how Eu3+ is incorporated in these materials, time-resolved, laser-induced FLN studies at 77 K have been performed using a pulsed dye laser to selectively excite subsets of ions in the inhomogeneously broadened 7F0⇆ 5D0 manifold. Fluorescence spectra are discussed in terms of rare earth ion clustering, energy transfer, and bonding site symmetry. It is concluded that Eu3+ ions cluster in sol-gel silica and that the addition of alumina assists in dispersing Eu3+ ions.

The morphology of titanium dioxide aerogel was studied using a variety of complementary techniques that include: nitrogen adsorption, Small-Angle Neutron Scattering (SANS), scanning and transmission electron microscopies (SEM/TEM) and X-ray diffraction. Since these techniques sense different components of the microstructure, global parametrization should coalesce the results into a uniform framework.

Lattice parameters of some different chromium-doped mullites obtained by a sol-gel route and sintered at 1650° C have been determined from X-Ray Diffraction data as a function of both temperature and Cr contents. Profile refinements on the X-ray diffraction diagrams have been carried out, showing that, at temperatures between 800° and 1535° C, an anisotropic thermal expansion takes place for the a and b lattice parameters of the Cr-doped mullite. We show that this anisotropic expansion is dependent on the temperature increase and the chromium content for the different compositions of the mullite crystals.

Poly(l,4-phenylene)-bridged and poly(1,6-hexylene)-bridged silsesquioxanes (PPS and HPS) were prepared by the sol-gel process. The surface areas and pore diameters of these porous xerogels were obtained by BET and BJH methods, respectively. These porous materials were used as a confinement matrix for the growth of small-sized semiconductor and transition metal clusters. Quantum-sized CdS particles in PPS (approximately 58+12 Â) and HPS (91+16 Â) matrices were prepared by first soaking the xerogel in a CdCl2 solution. Following a washing with water, a Na2S solution was then added. EDAX and electron diffraction techniques were used to identify the CdS particles. The particle sizes of CdS in PPS and HPS were determined by both UV measurements and from TEM images. Small-sized Cr clusters were prepared in dried xerogels by an internal doping method. Mixed Cr/CdS phases were also prepared by internal loading of a chromium metal precursor. Following deposition of CdS the xerogel was heated at 120 °C under high vacuum, resulting in formation of intimately mixed phases of Cr metal and CdS. Changes in morphology, in particular the surface area and pore size distribution were noted. A decrease in surface area and an increase in pore size were observed as a result of Cr metal deposition.

Quantum-size silicon enriched regions were formed in silica porous glasses obtained by three different technologies. Processing in the spark discharge and carbon reduction of silicon dioxide in the solid phase were performed for this purpose. All fabricated specimens have been investigated in relation to their electrical and photoluminescence (PL) properties. A pronounced increase of visible luminescence and single-type changes in the a.c. conductivity were registered in all cases.

Pd colloid containing Ormocers (organically modified ceramics) have been prepared from Pd amino complexes of the type Pd[NH2CH2CH2NH(CH2)3Si(OMe)3]2ac2 by hydrolysis and condensation (sol-gel reaction) of the silane together with Si(OEt)4 and Si(OEt)3(CH2)3OCH2CHCH2O. The amino complex formation is necessary to avoid spontaneous reduction and uncontrolled colloid formations in the liquid phase. This synthesis route leads to Pd colloid containing powders and coatings on glass. By thermal curing (temperatures up to 500 °C) using different atmospheric conditions (N2, Ar, H2/N2) brown to deep black coatings on glass with transmission values from 80 to 0 % can be obtained. The average particle size can be controlled by varying the molar ratio of the used Pd salt (Pd(ac)2) and the aminosilane.

Dynamic oscillatory experiments are used to monitor the gelation of the borosilicate systems prepared through the sol-gel process from metal alkoxides. The rheological experiments show that tan δ = G”/G’ is independent of frequency at the gel point in agreement with the results of others on organic gelling systems. The dynamic moduli at the gel point followed power-law behavior with respect to frequency. The power-law exponent is found to be ∼0.70. The apparent fractal dimension, dp, of the network cluster at the gel point is determined. The dF values for the samples ranged from 2.5 to 3.8 depending on the final structure of the evolved products at the gel point. The large values (dF > 3) exclude a simple geometric interpretation of the results. The effect of processing parameters, such as composition of reactants and temperature, on the resulting microstructures near the gel point is discussed.

Spherical particles of lead titanate, PbTiO3, (PT) were prepared from partially hydrolyzed alkoxide solutions modified with benzoic acid. Modified and aged alkoxide solutions were added dropwise to isopropyl alcohol, forming particles (0.2 to 1.0 μm in diameter). FTIR spectroscopy results demonstrate chelation of the PT alkoxide which prevented the formation of an extended gel network. Diffuse reflectance FTIR (DRIFT) spectra indicate the benzoate ligands are present until 450°C; TGA results show significant weight loss at 450°C. PT particles crystallize into the perovskite phase at =450°C, as determined by DTA and XRD. The relatively low crystallization temperature may be due to the effect of benzoate ligands on amorphous structure and presence of internal surfaces.

Low-hydroxyl organically modified silicates (ORMOSILS) were fabricated by a non-hydrolytic reaction between methyl-modified silicon halides and tertiary butyl alcohol under controlled atmosphere. The gels were characterized by DTA and TGA., FTIR, 1H NMR and 29Si NMR. The solutions were doped with anhydrous Erl3, which was dissolved in the sol prior to gelation. Er3+luminescence in the gels was observed at 570 nm under excitation at 488 nm.

Factors controlling hydrothermal synthetic procedures are not well understood. A good knowledge of the solution chemistry of precursor species is the best reference for the design of rational procedures. Examples of the predictive character of simple models in order to rationalize complex syntheses are discussed in detail.