In order to develop new precursors for the preparation of titanium nitride, a Ti alkoxide-nitrogen containing polyol condensation product was prepared and heat-treated. A stoichiometric mixture of titanium tetra-isopropoxide (Ti(OC3H7)4) and triethanolamine (N(CHM2H4OH)3) was heated at ca. 200°C under reduced pressure. The distilled liquid was isopropyl alcohol and its amount indicated that the transesterification reaction proceeded almost quantitatively.

The condensation product was a transparent glassy solid on cooling to room temperature. Thermal treatment of the condensation product at 1600°C in a nitrogen flow yielded titanium nitride (TiN1-x-yCxOy) as the main phase with a small amount of Ti3O5. The thermal treatment for a longer time reduced the amount of the oxide. The heat treatment of the product in an Ar flow also yielded nitrogen containing ceramics, which indicated the effectiveness of nitrogen in the condensation product during the conversion.

Current techniques of advanced ceramic component fabrication are based on pressureless green body consolidation technology in which voids often remain in the final microstructure. Much of this residual porosity is created when the organic binder used to consolidate the ceramic powder burns off on sintering. A new concept in the field of ceramic processing is the use of an organometallic binder material which will pyrolyze on sintering and convert into a predetermined ceramic. Silicon nitride (Si3N4) is a ceramic material in great demand for elevated temperature applications because of its excellent high temperature properties. At the present time, silicon nitride cannot be successfully processed without the use of costly pressure sintering (e.g., hot pressing), or the addition of a glassy phase, which degrades the high temperature properties.

Various preceramic polymers to be used as binders for cold pressing operations have been synthesized and studied. It has been demonstrated that these polymers may be dissolved in an appropriate organic solvent and mixed with a powder. Removal of the solvent yields homogeneous mixtures which may be consolidated into highly dense (> 66% of theoretical) green bodies. The ceramic yields of these polymers have also been determined.

Dried monolithic gels of compositions XNa2O-(1-X)SiO2 (with X from 0 mol% to 7 mol%) were obtained by acid catalyzed sol-gel processing using tetramethylorthosilicate and NaNO3. Optically clear monoliths in the range of 20 to 90 mm diameter by 3 to 20 mm thickness were routinely produced by controlling the processing schedule. Complete drying in air without cracking was achieved at 180°C from 10–14 days. The bulk density and optical properties of the gels, characterized by UV/VIS/NIR transmission, IR reflection and index of refraction, showed a compositional dependence on Na2O similar to melt glasses of the same Na2O content. However, the true density and microhardness decreased with Na2O content in contrast to melt glasses.

A method for producing large TiO2-SiO2 gel-glass monoliths using the sol-gel method has been developed. The gel-glasses are prepared by a pre-hydrolysis method using tetramethylorthosilicate and titanium isopropoxide as precursors. The microhardness, specific surface area and pore radius of the gel-glasses do not change significantly below 600°C. Above 600°C, these properties increase rapidly with densification temperature. At lower TiO2concentration, the glasses obtained by heating to 900°C for 15 hours were not crystallized, while for 15 wt % TiO2 glass, anatase precipitated.

Glass-ceramic composites were successfully fabricated by incorporating amorphous lithium aluminosi Iicate (LAS) particulates into a silica gel matrix. LAS volumes in the composites were varied from 50 to 75%, and all composites were easily cast, dried and fired without segregation or cracking. Elevated temperature processing resulted in crystallization of the LAS into a P-spodumene solid solution phase as well as densification of the gel-derived glass matrix. An inverse relationship was found between densification efficiency and LAS volume percent.

High-purity, transparent monolithic spinel (MgAl2O4) was synthesized via the hydrolytic thermal decomposition of mixed alkoxide organo-metallic precursors. Several factors, such as the metal alkoxide concentration in various solvents, the water to solvent ratio, and the reaction temperatures affect the hydrolysis of the mixed alkoxides. These factors also influence the transparency of the resulting sols and gels. The degree of transparency of the sols and gels is also influenced by such factors as pH and drying control chemical additives. Variations in the processing conditions during drying, aging, and sintering of the gels produced ceramic materials with high degree of transparency.

Synthesized zirconia ceramics are prepared through the coprecipita-tion process. Application of the wet chemical approach is aimed at the achievement of highly sintered ceramics at lower temperature. The thermal evolution of the synthesized CeO2-ZrO2 powder is investigated with the aid of DTA and TGA measurement. The exothermic peaks on the DTA thermogram are futher identified by the IR analysis. The effect of CeO on the occurrence of the peaks is probed. For other rare-earth oxiae doped ceramics, such as Nd2O3. and Dy2O3. containing zirconia, the bulk and grain boundary resistances are evaluated by the impedance spectroscopy. The dependence of the associated activation energy in the rare-earth oxide doped zirconia is discussed with respect to the variation of the ionic radius of the rare earth constituent.

High porous alumina fiber structures appear promising for hot gas filtration in particular for diesel particulate traps. For this purpose, however, a method is required for manufacturing of stable shapes resistant to the blow-out by the gas flow. The sol-gel-process was expected to be the best suited method for fiber bonding to provide the required stability.

The main tasks of the development-work were a uniform isotropie fiber-distribution, the adaptation of the sol-gel-process to the application, and the deliberate synthesis of the gel-derived alumina bonding phase.

The appropriate fibrous structure was obtained by a repeated filtration of sol/fiber suspensions. The properties of the ceramic binder were adapted by concentrating the sol and/or adding aluminas or aluminium hydroxides.

Testing of prototypes with optimized structures has shown, however, that the stability of the structure decreased after thermal load. The thermal fatigue of x-A12O3 is assumed to be responsible for this failure.

Continuous ZrO2 precursor fibers were produced by dry spinning an aqueous zirconium acetate solution containing a soluble yttrium salt and a high molecular weight (MW = 5 × 106) polymer (PEO) to control rheology. A ZrO2-Y2O3 binary composition containing 3 mole % Y2O3 was chosen to control grain growth and to produce tetragonal ZrO2 subsequent to pyrolysis and heat treatment. Fine grained (< 0.3 μm), poly crystalline Zr(Y)O2fibers with diameters between 2 to 12 μm were produced by pyrolysis and heat treatment up to 1400 °C. Fiber tensile strength was measured as a function of processing variables. The objective was to relate flaw populations encountered during strength measurements to processing variables with the goal of controlling and increasing fiber strength.

Fluorite-related structures of mixed uranium oxides (Uy,M1-y)O2−x, where M = Ce, Sc, Y, have been studied using High Resolution Electron Microscopy (HREM). Ordered domains have, been observed directly in crystallites of urania-ceria solid solution. Preliminary investigations of urania-yttria also show evidence for the presence of ordered domains. A possible model for the structure of these regions is suggested.

Luminescent oxide gels were prepared by hydrolysis of silicon alkoxides in solutions containing the luminescent hexanuclear molybdenum cluster Mo6Cl12. The resulting gel exhibited emission and lifetime behavior characteristic of Mo6Cl12 thereby indicating that the excited-state properties of the metal cluster species are not significantly perturbed by the gel environment.

Front-surface metal mirrors were coated with a variety of sol-gel derived glass films for preliminary evaluation as protective coatings for silver. Optical measurements (hemispherical, diffuse and specular reflectance) were used to characterize changes in the mirror resulting from the application of the sol, subsequent processing, or environmental testing. The abrasion resistance of the films was determined on sol-gel coated silicon wafers per ASTM procedures. The mirrors were exposed to outdoor environments in Albuquerque, N.M., as well as accelerated testing in H2SO4, with periodic monitoring of optical properties. A two layer coating scheme, consisting of a thin primary protective layer of sputter deposited SiO2 followed by a thicker sol-gel overcoat, was also evaluated.

The planarizing ability of sol-gel films was investigated on several as-rolled stainless steel substrates. The smoothing effect afforded by the films was evaluated, using optical techniques, following deposition of silver over the planarized substrates. The specular reflectance of various substrates, initially ranging from 0.36 to 0.90, could be improved to final reflectance values of -0.93 with sol-gel processing. This process is being used to prepare prototype foil mirrors for evaluation in the next generation of solar concentrators.

Superconducting YBa2Cu3O7-δ, ceramic pieces and fibers were prepared through a sol-gel route from ametal acetate aqueous solution of controlled pH. Concentrating the starting solution by evaporating the solvent provided a transparent viscous sol, from which gel fibers could be drawn. Further concentrating of the viscous solution led to formation of gel pieces. Conversion of gel fibers and pieces to superconductors were investigated in terms of precipitating crystalline species and electrical conductivities.

The structural evolution of YBa2Cu3O6+x precursor sol was investigated using 13C NMR and quasielastic light scattering. A polydisperse colloidal suspension of yttrium, barium and copper alkoxides was characterized as hydrolysis and complexation reactions occurred. Light scattering data showed that the average particle size of a copper(II) alkoxide suspension decreased by a factor of 5 (1100 nm to 220nm) with the addition of the yttrium and barium alkoxides over a period of 24 hours. The acquired particle size data correlated well with 13C NMR spectra, which showed initial peak broadening and the copper complexing to the yttrium and barium as a function of hydrolysis time.

Solution chemistry routes have been used to prepare single-phased superconducting ceramics of YBaSrCu3O6.9 (1113). Resistivity measurements on air annealed samples showed a superconducting onset temperature of 85 K with zero resistance at 78 K which improves to 81 K upon oxygen annealing. Magnetization data show ca. 78% flux exclusion at 5 K for 1113. X-ray diffraction experiments revealed that an orthorhombic to tetragonal transition occurs near 590°C when 1113 was heated in air. This work has demonstrated that such techniques can be utilized to prepare solid solution material with properties similar to those observed in YBa2Cu3Ox (123).

Positronium annihilation has been used to measure pore diameters in silica sol-gels. The results have been compared to those obtained from the BET technique. Pore development in the presence of chemical additives and during the thermal treatment has been studied. A model relating positronium lifetime to the pore size has been proposed.

Low field NMR spin-lattice relaxation measurements of pore fluid were used to study pore structure during aging and drying of two silica gels. The NMR method provides in situ information concerning pore size, size distribution and surface area which is impossible to obtain by other techniques. Surface areas measured for a sol-gel sample aged in a potassium hydroxide solution were compared to similar measurements made on an ethanol aged sample during drying. Surface area and pore size distributions of the corresponding final dried gels were measured by both NMR and nitrogen adsorption/condensation. The measurements for a given sample were in good agreement. The surface area of samples before drying were much higher than after drying and the base-aged sample had a higher initial surface area than the ethanol-aged sample although after drying, this trend was reversed.

The reaction between ammonia and aluminum hydride (AIH3) was investigated as a possible synthetic route to aluminum nitride (AIN), using tetrahydromran (THF) as the solvent. When an excess of ammonia was employed, a white powder was obtained which was converted to AIN by calcination. However, when a stoichiometric amount of ammonia was used, a soluble intermediate was obtained. This intermediate polymerized slowly at room temperature via a condensation reaction involving the elimination of hydrogen to give a gel that could be converted to AIN.

Vanadium dioxide thin films have been grown from vanadium tetrakis (t-butoxide) by the sol-gel process. A new method for the synthesis of the vanadium precursor was developed. Films were deposited by dipcoating glass slides from an isopropanol solution, followed by post-deposition annealing of the films at 600 °C under nitrogen. The properties of these films, to a high degree, were a function of the preparation conditions. These gel-derived VO2 films undergo a reversible semiconductor-to-metal phase transition near 72 °C, exhibiting characteristic resistive and spectral switching comparable with near stoichiometric VO2 films prepared on non-crystalline substrates by other techniques. Paralleling the investigation of pure VO2, films were doped with hexavalent transition metal oxides to demonstrate lowering of the transition temperature.