Urethane- and thioether (meth)acrylate alkoxysilanes have been used, as sol-gel precursors, for the preparation of a special family of inorganic/organic copolymers (ORMOCER®s). The basic silane type offers the following structural and synthetic possibilities for modifying the properties of the resulting copolymers: variation of the number of alkoxy groups, combination with other, different, sol-gel precursors, variation of the number of attached (meth)acrylate groups (1– 5), and variation within the molecular segment (kind, structure and length) connecting the inorganic with the organic polymer structure. To achieve the additional organic polymer structure in the cured copolymer the use of different radically induced polymerization approaches (UV-, visible light-, thermal-and redox induced) is possible. Taking the incorporation of fillers into account, the Young's modulus of these copolymers is adjustable in a range of 1–17000 MPa, and the thermal expansion coefficient in a range of 17–250·10-6·K-1 (5 - 50 °C). Other advantages are the low shrinkage (1 - 2,8 vol.-%), the high flexural strength (up to 160 MPa), and the high abrasion resistance. This new copolymer type seems to have significant potential for medical applications, especially as dental filling material to replace the currently used controversial amalgam fillings.

Organically modified silica aerogels were prepared by NH4OH-catalyzed hydrolysis and condensation of RSi(OMe)3 / Si(OMe)4 mixtures, followed by supercritical drying of the alcogels with methanol or CO2. Terminal alkyl or aryl groups, bridging groups or functional organic (methacryloxypropyl or glycidoxypropyl) groups were employed for R. By the proper choice of the organic groups, the RSi(OMe)3 / Si(OMe)4 ratio and the drying conditions, hydrophobic aerogels, being insensitive towards moisture, were obtained with no residual Si-OH or Si-OMe groups left. The transparency and porosity of the organically modified aerogels was only slightly diminished relative to unmodified silica aerogels. The elastic constant of the aerogels was significantly influenced by the kind of organic groups. By pyrolysis of the phenyl-substituted aerogels, nanometer-sized carbon structures were generated. They partly coat the primary aerogel particles and provide a very high mass specific extinction in the wavelengths interval critical for thermal radiative transport.

Copolymerization of the cubic octameric silicate anion (Si8O208-) with dimethyldichlorosilane in 2, 2-dimethoxypropane has yielded organic-silica hybrid materials consisting of the S13O20 structure as a building block. The hybrid materials have shown high surface area by calcination in air. The reaction conditions have been optimized to produce the materials with higher specific surface area. As a result, the hybrid materials with BET surface area of 406 m2 g-1 have been obtained.

The multiphase electrodispersion precipitation of zirconia powders has been done in the electric dispersion reactor (EDR). This paper presents the first results obtained where the bench-scale EDR unit was operated in the continuous mode to synthesize 130 ± 2 g of ZrO2 powder in approximately 12 h. An aqueous solution of zirconyl nitrate was dispersed and precipitated in a 2-ethyl-l-hexanol continuous phase containing 0.012 M to 0.12 M ammonia. A gravity settler was used to remove soft agglomerates of the ZrO2 particles from the organic solvent. Electric bed filtration was employed to remove the fines from the solvent, which was then recycled.

The particle-size distribution was varied by changing the electric field strength. At high field strengths (approximately 20 kV/cm), the particle sizes ranged from approximately 0.1 to 5 μm. The dried powder had a consistency of talcum powder. Microwave and conventional heating experiments showed that the powders were sinterable. The BET surface area of the powders ranged from approximately 20 to 90 m2/g.

The isothermal sintering behavior of a colloidal gel with a well-characterized pore structure was studied using a newly commissioned in-situ small-angle neutron scattering furnace. The apparatus enables small-angle scattering measurements to be performed on monolithic samples during heat treatment in an oxidizing, reducing, or neutral environment at temperatures up to 1700°C. In-situ, quantitative measurements of the pore size evolution within a gel possessing a bimodal pore size distribution is discussed. Also reported is the in-situ measurement of the gel's surface area evolution which is an important microstructural parameter in understanding the sintering behavior of highly porous materials.

In order to densify and to improve the physical properties, TiO2 sol-gel films, about 100 nm in thickness, on silica glass or silicon wafer were implanted with Ar+ or B+ ions. The refractive index of the as-dried films increased and the IR absorption band of OH disappeared after Ar+ implantation. Drying and densification of sol-gel films were enhanced by Ar+ implantation. On the other hand, the refractive index and the thickness of the films hardly changed with B+ implantation. However, IR absorption bands of B-O bond were observed after B+ implantation. This suggests that sol-gel films could be chemically modified by ion implantation with reactive ion species.

For more than a decade, the sol-gel process has been used to prepare lithium silicate gels that have potential applications as solid electrolytes in lithium batteries and electrochromic windows. The interest in these Li2O-SiC2 materials is their fast and stable ionic conductivity from room temperature up to 350°C. Typically these materials have been prepared with 15 mole % Li2O in bulk samples, but rarely in thin films. This work was undertaken to prepare chemically stable lithium silicate thin films with up to 30 mole % Li2O. Lithium nitrate was used as the lithium precursor. Solutions were evaluated for gelling time and homogeneity. Thin films were made by dip coating. After heat treatment at 200, 250 and 300°C, films were characterized for surface quality, thickness and microstructure using electron microscopy, x-ray diffraction analysis and profilometry. Transparency was investigated in the visible range (350–800 nm).

This paper describes a novel colloidal route for the preparation of hollow mullite ceramic microspheres with sizes in the range of 10 μm. An emulsion technique was combined with a water extraction sol-gel process, to form an aqueous droplet dispersion and gel the resulting droplets by extracting water with a dehydrating liquid. The liquid-filled gelled microcapsules were then dried and fired to form hollow ceramic microspheres. Important processing variables controlling the microspherc morphology were determined and a formation mechanism was proposed. Due to its potential applications in microelectronic packaging, mullite was selected as the model material for the present work, but the synthesis technique may be used for making other single or multiphase ceramic compositions

The beam-bending method was used to measure the effect of partial drying on the viscoelastic relaxation behavior and permeability of a two-step acid-base catalyzed silica gel. Both the elastic modulus (E) and the permeability (D) showed a power-law dependence on density (ρ): E ～ ρm, m ≈ 3.0; D ～ ρ-n, n ≈ 2.5. The viscosity of the network rose from ～1011 to ～1013 Pa·s, and was strongly dependent on age as well as density of the gel. The viscoelastic relaxation function was well described by the stretched exponential function with an exponent of 0.3–0.5.

Results obtained with small angle neutron and X-ray scattering will be presented of systems with various silica concentrations. Silica gels with low silica concentration exhibit uniform mass fractal behaviour and after prolonged aging, dual mass fractal behaviour. A zeolite (silicalite) synthesis precursor gel with a high silica concentration was also investigated and was found to exhibit surface fractal behaviour. A model is presented, explaining the occurrence of dual fractality after prolonged aging. The change-over from mass fractal behaviour to surface fractal behaviour is explained, supported by scattering spectra calculated from simulated aggregate structures.

The aqueous deposition of calcium oxalate onto colloidal oxides has been studied as a model system for understanding heterogeneous nucleation processes of importance in biomimetic synthesis of ceramic thin films. Calcium oxalate nucleation has been monitored by measuring induction times for nucleation using Constant Composition techniques and by measuring nucleation densities on extended oxide surfaces using an atomic force microscope. Results show that the dependence of calcium oxalate nucleation on solution supersaturation fits the functional form predicted by classical nucleation theories. Anionic surfaces appear to promote nucleation better than cationic surfaces, lowering the effective energy barrier to heterogeneous nucleation.

A simple method of producing very fine, homogeneous BaxSr1-xTiO3 powders was developed in this study by wet-chemically reacting Ti(0H)4-xH2O, Ba(OH)2, and Sr(OH)2 as raw materials under 100°C. Relationships were obtained between particle size, composition, and reaction temperatures, reaction tunes, Sr/Ba ratios, and (Ba+Sr)/Ti ratios of the solution.

Experimental results indicated that the particle size, which was around 40 nm, was both proportional to the reaction temperature as well as independant of the reaction time. In light of the varying reactivities of Ba and Sr towards Ti, reaction time was found to be a primary factor which controls the precise Ba/Sr ratio and (Ba+Sr)/Ti ratio of the titanate powder. A suitable reaction condition was observed to have prevented by-products Ba6Ti17O40 or Ba2Ti04 from being formed.

The titanate powders were compressed and sintered for various temperatures. The compressibility and the sinterability of the powders were obtained. The microstrucure, dielectric constant and dissipation factor of the titanate ceramics ware observed and measured. These values sufficiently correlated with those of the titanate ceramics produced from the powders by the solid-state sintering method.

Hydroxyapatite (Ca5(P04)3(0H)) is an effective material for artificial human bone production. Hydroxyapatite powders were hydrothermally produced in this work by reacting Ca(OH)2 with Na3PO4·12H2O in an autoclave at various temperature and for various times. The particle size of hydroxyapatite was observed to be very fine, uniform, around 50 nm, as well as independent of reaction time.

The hydroxyapatite powders were compacted and sintered at various temperatures for 2 hrs. The density, grain size, and hardness of the hydroxyapatite ceramics were measured and compared with those of the hydroxyapatite ceramics produced by the powders from the commercial source. The hydroxyapatite ceramics from the hydrothermal powders were found to have a higher density, smaller grain size, and higher hardness.

After the hydroxyapatite ceramics were dipped in a simulated biological body liquid for 10 days, the density and hardness of the hydrooxyapatite ceramics from the hydrothermal powders were less deteriorated than those of the hydroxyapatite ceramics from the commercial powder.

VOSO4.3H2O was used as doping agent to prepare GeO2 xerogels, via the sol-gel process. Samples were analyzed by Thermal Gravimetric Analysis (TGA), Differential Thermal Analysis, (DTA), Diffuse reflectance (UV-Vis) spectroscopy and electron spin resonance (ESR). Study of thermally treated samples was done. VO2+ were found in V2O5 at 350 °C. VO2+ ions were incorporated to the GeO2 network after thermal treatment at 700 °C. From the results we propose that VO2+ acts as crystal former in these samples.

Absorption spectra of Cytochrome c Peroxidase (CcP) in phosphate buffer at pH 6.5 were recorded from 700 to 250 nm. The CcP solution was then encapsulated in sol-gel derived glass. The absorption spectra of CcP in xerogels were compared to those in buffer solutions. An increase in absorptivity at the Soret maximum, a decrease between 360 and 380 nm, and a spectral shift of the charge-transfer band from 645 to 620 nm was observed for CcP in gel matrix as compared to those in solution. Those spectral observations indicate a change in the coordination of the iron porphyrin ring in CcP from penta-coordinated in solutions to hexa-coordinated in gels. The oxidant H2O2, reductant Na2S2O4, and inhibitors NaF and KN3 were allowed to diffuse through the porous glass, to react or to complex with the encapsulated CcP in sol-gel glass. The results show that H2O2 and S2O42- lead to a change of oxidation state from Fe(III) to Fe(IV) and to Fe(II), respectively. Moreover, F- results in an enhancement of high-spin CcP, and N3- promotes a spin state change to a low-spin CcP. For CcP in xerogels, the chemical changes caused by inhibitors were found to be reversible when washed with deionized water. The possible applications of CcP immobilized xerogels in chemical and biochemical sensor technologies are discussed.

Sols were prepared in the system TMOS:H2O:SOLV:HC1 with molar ratios of 1:4:3:0.0005 for SOLV = MeOH, EtOH and DMF. The gelation and aging of these sols took place in cuvettes covered by parafilm. The gels were removed from the cuvettes 14 days after gelation. Solvent exchange was carried out in each of the three solvents for a period of 14 days. Starting with fresh solvent, the exchange was repeated three times.

TGA and DTA curves were taken with pieces of the original gels and of gels after the 2nd and 3rd solvent exchange. The TGA curves display a considerable weight loss in the temperature range of solvent evaporation. A small step is observed at higher temperatures if MeOH or EtOH represent the exchange solvent. The DTA curves allow a distinction what mixtures of solvents are present. The effectiveness of the solvent exchange can be evaluated.

On the basis of consideration of the properties of AI, In, Ln, Ti, Zr, Hf, NbO3+, MoO4+, WO4+, MoO22+ MO22+, Fe, Co, Ni alkoxide derivatives the main regularities in poly- and oligomerization properties have been deduced:

1) The molecular complexity increases in time (aging) and on action of alcohols. This process is followed by the increase in the melting and boiling points, decrease in solubility in ROH and weakening of colour. In the mass-spectra - in connection with the temperature of transition into the gas phase - increases the stability of products with lower molecular masses. 2) oligomerization occurs on dissolution in aromatic hydrocarbons or on a short thermal treatment (melting, distillation). The oligomerization products possess lower thermal constants, higher solubility in ROH and more intense colour. Their mass- spectra are containing the fragments of higher masses corresponding to oligomers existing apparently also in the condensed phase.

The mastering of these regularities permits the monitoring of molecular composition and thus physicochemical properties of the samples which are of importance for their technological application.

The presence of oxoalkoxides in the “M(OR)n” samples should be taken into consideration on the preparation of solutions used in the synthesis of powders and films of pure simple and mixed oxides.

Photophysical properties of l-Docosyl-4-(4-hydroxystyryl)pyridiniurn bromide (SB), a merocyanine dye in solution and encapsulated in sol-gel derived glass are investigated at 298 and 77 K. In solution, the absorption spectra of SB display an equilibrium between the quinolinium and benzoid forms. The equilibrium can be shifted to either quinolinium or benzoid form under an acidic or basic condition, respectively. The emission spectra of SB, on the other hand, give not only the quinolinium and benzoid forms but also the quinoid form which emits at 500 nm. The existence of excited state quinoid form of SB is also evident in the excitation spectrum while the emission at 500 nm is monitored. Both in solution and in xerogel, the quinoid form of SB is shown to be photochemically unstable as compared to the benzoid form. It is proposed that the photoexcited quinolinium form of SB is a proton dissociative species which transforms readily to become the quinoid form. The results indicate that photochemistry channels of SB are originated from the quinoid form. Moreover, the benzoid form of SB (photochemically stable) exhibits large hyperpolarizability due to its charge-transfer characteristic, and is a desired molecular form for nonlinear optical (NLO) applications. The material processing techniques for stabilizing the benzoid form of SB in optically transparent sol-gel glasses are illustrated for the first time.

Effects of vibration ball-milling of a powdered mixture of two gels, prepared from mixing ZrO2 andTiO2 sols, on crystallization processes during heating are studied in order to elucidate enhanced mechanochemical reactions with the aid of hydroxyl groups. TiO2 (anatase) and ZrO2 (tetragonal) crystallized at 698 K and 712 K, respectively, when heating non-milled gel mixture at 10 K min1 in air. Few reactions between the two phases were detected below 1023 K. After vibro-milling a powdered gel mixture at room temperature for 3 to 30 h, ZrTiO4 (orthorhombic) crystallized directly from non-crystalline precursors on heating to 1023 K. The fraction of crystallizedZrTi04, determined by Raman spectroscopy, increased linearly with increasing the index of micro-homogeneity for non-heated gels. We suggest that short-range ordering of ZrTiO4 rather than crystallization of individual oxides occurs through the non-thermal atomic movement between different metallic species under mechanical stress.

The fluoroisopropoxide ligand (HFIP) has allowed the synthesis of mixed-metal homoleptic Ba2Y and CuBa alkoxides. However, although these species are all volatile, their poor thermal stability precludes their use as CVD precursors. Their properties have thus been optimized by introduction of 2,2,6,6-tetramethylheptane-3,5-dione (thdH) in the metal coordination sphere. Compounds such as Y2Ba(μ-HFIP)4(thd)4, the first volatile Y-Ba species reported so far, as well as BaCu2(HFIP)4(thd)2 and YCu(HFIP)2(thd)3 have been obtained. These heterometallic ϐdiketonatoalkoxides have been characterized by a variety of techniques including X-ray diffraction, mass spectrometry, vapor pressure measurements and thermogravimetric analysis. Preliminary data on thermal decomposition experiments are given.