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

Organically modified silica aerogels were prepared byNH4OH-catalyzed hydrolysis and condensation of RSi(OMe)3 / Si(OMe)4 mixtures, followed bysupercritical 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 theproper choice of the organic groups, the RSi(OMe)3 / Si(OMe)4 ratio and the drying conditions, hydrophobicaerogels, being insensitive towards moisture, were obtained with no residualSi-OH or Si-OMe groups left. The transparency and porosity of theorganically modified aerogels was only slightly diminished relative tounmodified silica aerogels. The elastic constant of the aerogels wassignificantly influenced by the kind of organic groups. By pyrolysis of thephenyl-substituted aerogels, nanometer-sized carbon structures weregenerated. They partly coat the primary aerogel particles and provide a veryhigh mass specific extinction in the wavelengths interval critical forthermal radiative transport.

Copolymerization of the cubic octameric silicate anion (Si8O208-) with dimethyldichlorosilane in 2, 2-dimethoxypropane hasyielded organic-silica hybrid materials consisting of the S13O20 structureas a building block. The hybrid materials have shown high surface area bycalcination in air. The reaction conditions have been optimized to producethe materials with higher specific surface area. As a result, the hybridmaterials with BET surface area of 406 m2 g-1 havebeen obtained.

The multiphase electrodispersion precipitation of zirconia powders has beendone in the electric dispersion reactor (EDR). This paper presents the firstresults obtained where the bench-scale EDR unit was operated in thecontinuous mode to synthesize 130 ± 2 g of ZrO2 powder inapproximately 12 h. An aqueous solution of zirconyl nitrate was dispersedand precipitated in a 2-ethyl-l-hexanol continuous phase containing 0.012 M to 0.12 M ammonia. Agravity settler was used to remove soft agglomerates of the ZrO2particles from the organic solvent. Electric bed filtration was employed toremove the fines from the solvent, which was then recycled.

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

The isothermal sintering behavior of a colloidal gel with awell-characterized pore structure was studied using a newly commissionedin-situ small-angle neutron scattering furnace. The apparatus enablessmall-angle scattering measurements to be performed on monolithic samplesduring heat treatment in an oxidizing, reducing, or neutral environment attemperatures up to 1700°C. In-situ, quantitative measurements of the poresize evolution within a gel possessing a bimodal pore size distribution isdiscussed. Also reported is the in-situ measurement of the gel's surfacearea evolution which is an important microstructural parameter inunderstanding the sintering behavior of highly porous materials.

In order to densify and to improve the physical properties, TiO2sol-gel films, about 100 nm in thickness, on silica glass or silicon waferwere implanted with Ar+ or B+ ions. The refractiveindex of the as-dried films increased and the IR absorption band of OHdisappeared after Ar+ implantation. Drying and densification ofsol-gel films were enhanced by Ar+ implantation. On the otherhand, the refractive index and the thickness of the films hardly changedwith B+ implantation. However, IR absorption bands of B-O bondwere observed after B+ implantation. This suggests that sol-gelfilms could be chemically modified by ion implantation with reactive ionspecies.

For more than a decade, the sol-gel process has been used to prepare lithiumsilicate gels that have potential applications as solid electrolytes inlithium batteries and electrochromic windows. The interest in these Li2O-SiC2 materials is their fast and stable ionicconductivity from room temperature up to 350°C. Typically these materialshave been prepared with 15 mole % Li2O in bulk samples, butrarely in thin films. This work was undertaken to prepare chemically stablelithium silicate thin films with up to 30 mole % Li2O. Lithiumnitrate was used as the lithium precursor. Solutions were evaluated forgelling time and homogeneity. Thin films were made by dip coating. Afterheat treatment at 200, 250 and 300°C, films were characterized for surfacequality, thickness and microstructure using electron microscopy, x-raydiffraction analysis and profilometry. Transparency was investigated in thevisible range (350–800 nm).

This paper describes a novel colloidal route for the preparation of hollowmullite ceramic microspheres with sizes in the range of 10 μm. An emulsiontechnique was combined with a water extraction sol-gel process, to form anaqueous droplet dispersion and gel the resulting droplets by extractingwater with a dehydrating liquid. The liquid-filled gelled microcapsules werethen dried and fired to form hollow ceramic microspheres. Importantprocessing variables controlling the microspherc morphology were determinedand a formation mechanism was proposed. Due to its potential applications inmicroelectronic packaging, mullite was selected as the model material forthe present work, but the synthesis technique may be used for making othersingle or multiphase ceramic compositions

The beam-bending method was used to measure the effect of partial drying onthe viscoelastic relaxation behavior and permeability of a two-stepacid-base catalyzed silica gel. Both the elastic modulus(E) and the permeability (D) showed apower-law dependence on density (ρ): E ～ ρm, m ≈ 3.0; D ～ ρ-n, n ≈ 2.5. The viscosity of the network rosefrom ～1011 to ～1013 Pa·s, and was strongly dependenton age as well as density of the gel. The viscoelastic relaxation functionwas well described by the stretched exponential function with an exponent of0.3–0.5.

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

The aqueous deposition of calcium oxalate onto colloidal oxides has beenstudied as a model system for understanding heterogeneous nucleationprocesses of importance in biomimetic synthesis of ceramic thin films.Calcium oxalate nucleation has been monitored by measuring induction timesfor nucleation using Constant Composition techniques and by measuringnucleation densities on extended oxide surfaces using an atomic forcemicroscope. Results show that the dependence of calcium oxalate nucleationon solution supersaturation fits the functional form predicted by classicalnucleation theories. Anionic surfaces appear to promote nucleation betterthan cationic surfaces, lowering the effective energy barrier toheterogeneous nucleation.

A simple method of producing very fine, homogeneous BaxSr1-xTiO3 powders wasdeveloped 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 wereobtained 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 40nm, was both proportional to the reaction temperature as well as independantof the reaction time. In light of the varying reactivities of Ba and Srtowards Ti, reaction time was found to be a primary factor which controlsthe precise Ba/Sr ratio and (Ba+Sr)/Ti ratio of the titanate powder. Asuitable 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. Themicrostrucure, dielectric constant and dissipation factor of the titanateceramics ware observed and measured. These values sufficiently correlatedwith those of the titanate ceramics produced from the powders by thesolid-state sintering method.

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

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

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

VOSO4.3H2O was used as doping agent to prepare GeO2 xerogels, via the sol-gel process. Samples were analyzedby 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 wereincorporated to the GeO2 network after thermal treatment at 700°C. From the results we propose that VO2+ acts as crystal formerin these samples.

Absorption spectra of Cytochrome c Peroxidase (CcP) in phosphate buffer atpH 6.5 were recorded from 700 to 250 nm. The CcP solution was thenencapsulated in sol-gel derived glass. The absorption spectra of CcP inxerogels were compared to those in buffer solutions. An increase inabsorptivity at the Soret maximum, a decrease between 360 and 380 nm, and aspectral shift of the charge-transfer band from 645 to 620 nm was observedfor CcP in gel matrix as compared to those in solution. Those spectralobservations indicate a change in the coordination of the iron porphyrinring 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 reactor to complex with the encapsulated CcP in sol-gel glass. The results showthat H2O2 and S2O42- lead to a change of oxidation state from Fe(III) to Fe(IV) andto Fe(II), respectively. Moreover, F- results in an enhancementof high-spin CcP, and N3- promotes a spin state change to alow-spin CcP. For CcP in xerogels, the chemical changes caused by inhibitorswere found to be reversible when washed with deionized water. The possibleapplications of CcP immobilized xerogels in chemical and biochemical sensortechnologies are discussed.

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

TGA and DTA curves were taken with pieces of the original gels and of gelsafter the 2nd and 3rd solvent exchange. The TGA curves display aconsiderable weight loss in the temperature range of solvent evaporation. Asmall step is observed at higher temperatures if MeOH or EtOH represent theexchange solvent. The DTA curves allow a distinction what mixtures ofsolvents are present. The effectiveness of the solvent exchange can beevaluated.

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 inpoly- and oligomerization properties have been deduced:

1) The molecular complexity increases in time (aging) and on action ofalcohols. This process is followed by the increase in the melting andboiling points, decrease in solubility in ROH and weakening of colour. Inthe mass-spectra - in connection with the temperature of transition into thegas phase - increases the stability of products with lower molecular masses.2) oligomerization occurs on dissolution in aromatic hydrocarbons or on ashort thermal treatment (melting, distillation). The oligomerizationproducts possess lower thermal constants, higher solubility in ROH and moreintense colour. Their mass- spectra are containing the fragments of highermasses corresponding to oligomers existing apparently also in the condensedphase.

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

The presence of oxoalkoxides in the “M(OR)n” samples should be taken intoconsideration on the preparation of solutions used in the synthesis ofpowders 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 derivedglass are investigated at 298 and 77 K. In solution, the absorption spectraof SB display an equilibrium between the quinolinium and benzoid forms. Theequilibrium can be shifted to either quinolinium or benzoid form under anacidic or basic condition, respectively. The emission spectra of SB, on theother hand, give not only the quinolinium and benzoid forms but also thequinoid form which emits at 500 nm. The existence of excited state quinoidform of SB is also evident in the excitation spectrum while the emission at500 nm is monitored. Both in solution and in xerogel, the quinoid form of SBis shown to be photochemically unstable as compared to the benzoid form. Itis proposed that the photoexcited quinolinium form of SB is a protondissociative species which transforms readily to become the quinoid form.The results indicate that photochemistry channels of SB are originated fromthe quinoid form. Moreover, the benzoid form of SB (photochemically stable)exhibits large hyperpolarizability due to its charge-transfercharacteristic, and is a desired molecular form for nonlinear optical (NLO)applications. The material processing techniques for stabilizing the benzoidform of SB in optically transparent sol-gel glasses are illustrated for thefirst time.

Effects of vibration ball-milling of a powdered mixture of two gels,prepared from mixing ZrO2 andTiO2 sols, oncrystallization processes during heating are studied in order to elucidateenhanced mechanochemical reactions with the aid of hydroxyl groups. TiO2 (anatase) and ZrO2 (tetragonal) crystallizedat 698 K and 712 K, respectively, when heating non-milled gel mixture at 10K min1 in air. Few reactions between the two phases were detectedbelow 1023 K. After vibro-milling a powdered gel mixture at room temperaturefor 3 to 30 h, ZrTiO4 (orthorhombic) crystallized directly fromnon-crystalline precursors on heating to 1023 K. The fraction of crystallizedZrTi04, determined by Raman spectroscopy,increased linearly with increasing the index of micro-homogeneity fornon-heated gels. We suggest that short-range ordering of ZrTiO4rather than crystallization of individual oxides occurs through thenon-thermal atomic movement between different metallic species undermechanical stress.

The fluoroisopropoxide ligand (HFIP) has allowed the synthesis ofmixed-metal homoleptic Ba2Y and CuBa alkoxides. However, althoughthese species are all volatile, their poor thermal stability precludes theiruse as CVD precursors. Their properties have thus been optimized byintroduction of 2,2,6,6-tetramethylheptane-3,5-dione (thdH) in the metalcoordination sphere. Compounds such as Y2Ba(μ-HFIP)4(thd)4, the first volatileY-Ba species reported so far, as well as BaCu2(HFIP)4(thd)2 and YCu(HFIP)2(thd)3 have been obtained. Theseheterometallic ϐdiketonatoalkoxides have been characterized by a variety oftechniques including X-ray diffraction, mass spectrometry, vapor pressuremeasurements and thermogravimetric analysis. Preliminary data on thermaldecomposition experiments are given.