Sol-gel techniques provide a convenient method of applying barium titanate films on solid substrates at ambient temperature. A significant advantage in using this technique is the capability of maintaining compositional homogeneity while coating large areas of surfaces with complex geometries. Solutions prepared by reacting a titanium alkoxide with barium hydroxide in methanol were used for preparing thin films (1000–3000Å) of barium titanate on silicon and metal substrates. Electrical properties of the films depended both on solution parameters and subsequent heat treatment of the films. Highest field strengths (8−9 × 106 V/cm) were observed in amorphous films prepared from partially hydrolyzed solutions.

Coagulation of HLW feed slurry can result from the interaction between acid metal cations and soluble silicates/silica. Feed slurry viscosity depend on a number of factors: (a) concentration and composition of the waste slurry electrolytes, (b) type and concentration of silica and silicate constituents in the glass former, (c) pH of the slurry feed, and (d) degree and order of mixing of the glass former with the waste sludge. Coagulation can be avoided by mixing to achieve a good dispersal of glass former globules in the waste slurry even when pH and electrolyte content favor it.

The sol-gel method for the preparation of ceramics and glasses has frequently been mentioned as more advantageous as compared to conventional methods. However, there are few known examples of a direct comparison for the same material. In the present work both the processing and resultant properties for ferroelectrics such as BaTiO3, KTaO3, KNbO3 and K(Ta,Nb)O3 made by both methods are directly compared. The uniformity is evaluated by high-angle x-ray diffraction, electron microscopy and EDAX and the dielectric properties are compared. The advantages and disadvantages of the sol-gel method are discussed.

Thermal and hydrolytic decomposition of metal alkoxides, M(OR)n, is employed to obtain ultra-high-purity submicron-size < 50 nm refractory, ferroelectric, and electro-optic oxide powders. The high surface activity associated with these powders makes possible relatively low temperature processing of the powder compacts to near theoretical density with uniform fine-grain-size bodies. Transmission electron microscopy, high-temperature X-ray, and infrared and Raman spectroscopy are used to observe nucleation, growth, crystallite morphology of the synthesized powder, and microstructural features.

Controlled alkoxide hydrolysis reactions for the synthesis of monodispersed oxide powders are described. The chemical and physical properties of representative monodispersed powders of TiO2, doped TiO2, ZrO2, doped ZrO2, SiO2, doped SiO2, and ZrO2-Al2O3 are described. The importance of surface chemistry for control of powder dispersion and packing is discussed and related to the control of sintered microstructures.

Organic-derived precursors can facilitate the preparation of PZT ceramics, particularly in the areas of processing and batch reproducibility. The use of partially alkoxide-derived precursors and completely organic-derived precursors has been studied. Two methods of alkoxide hydrolysis were evaluated for preparing zirconia which included direct hydrolysis in water and hydrolysis of alkoxide-base reaction products in acetone-H2O mixtures. The chemistry of these methods is discussed along with pertinent aqueous surface chemistry of the hydrated zirconia products. This work suggests that alkoxide-derived precursor properties are related to the solution chemistry used in their preparation.

Flame-generated particles can be suspended in a nonpolar solvent, molded, and gelled. The microstructure obtained after solvent evaporation depends on the characteristics of the colloid. Higher solids loadings lead to denser green bodies and narrow pore size distributions. The mean pore size is proportional to the particle size. Sintering occurs at relatively low temperatures, producing amorphous or crystalline bodies of high purity.

As the title of this meeting suggests, a paradigm change is underway in the ceramic community; methods of synthesis and use of ceramic powders are being hurriedly reappraised. The imperative for change was all in place by an important meeting that took place in 1977 [1].

Fine-grained, high surface area MgO, NiO and ZnO powders were synthesized by the evaporative decomposition of solutions (EDS) technique at 1000°C from acetate and nitrate salt solutions. The powder characteristics were similar in all cases; however, aggregated powders were obtained from the nitrate salts and aggregate-free powders were obtained from the acetate solutions when reacted in air. This difference is attributed to the oxidation of the acetate radical and/or its residue and that this process acts to disaggregate the salt droplet/particles that are formed during EDS.

A Sr/Ti bimetallic isopropoxide complex was synthesized by two methods. The complex served as a precursor to the production of homogeneous SrTiO3 powders via alkoxide hydrolysis. Infrared spectra were obtained for Sr(OPri)2, Ti(OPri)4, and the product of the syntheses. In addition, the IR spectra of the solutions of each of the alkoxides were followed as hydrolysis reactions proceeded. Detailed analysis of the spectral features support the existence of a 1:1 Sr/Ti bimetallic alkoxide. The new Sr/Ti compound exhibits characteristic absorption bands at (1017, 993, 972, 961 cm−1), (844, 838, 827 cm−1) and (620, 596, and 572 −1). A band at 819−1 might also be associated with the new Sr/Ti bimetallic alkoxide. The infrared spectra suggest that the isopropoxide ligands in the bimetallic alkoxide are in at least three separate local environments. This information offers insight into possible structures for the complex.

High purity, fine-grain size, SrTiO3 ceramics were fabricated from powders which were chemically derived by the Pechini method. The preparation is based upon a thermally polymerizable water-ethylene glycol-citric acid system in which a wide range of metal alkoxides, carbonates, and metal salts are soluble. The process is a closed system, and lends itself to the preparation of complex oxides which can contain numerous additives and dopants. In this study, Wdoped SrTiO3 powders were prepared with various Sr:Ti ratios, and fine grain internal boundary layer capacitors were fabricated by controlled segregation in sintering. Characteristics of the resin, powder, microstructures, and electrical properties are reported. The advantages and disadvantages of this method of chemical preparation for ceramic materials are noted.

Aluminum germanate, the germanium analog of mullite, 3 AlO2O3 . 2 GeO2, was first prepared by Gelsdorf, Muller-Hesse and Schweite (Ref. 1), who demonstrated that both partial and complete substitution of SiO2 by GeO2 in mullite was possible. They also determined the lattice constants of the solid solutions. The following studies reported some physical properties of aluminum germanate such as density (Ref. 2) optical constants (Ref. 2) crystal structure (Ref. 3) and I. R. absorption (Ref. 4). Phase equilibria in the system AlO2O3−GeO2 were investigated by Miller et al. (Ref. 5) and Perez-y-Jorba (Ref. 6). The ratter author found several compounds of which germanium mullite was the most stable and showed a relatively wide compositional range. Miller et al. observed only 3 Al2O3 . 2 GeO2 with no evidence of solid solutions. The compound was reported to melt incongruently at 1530° C. Recently Yamaguchi et al. (Ref. 7) prepared aluminum germanates of a wide range of stoichiometry from alkyl oxides and found, in addition to germanium mullite, the compound Al2O3−2GeO2 which was stable between 1190° and 1310° C. The authors also report infrared absorption spectra.

The application of surface analysis techniques to the characterization of sol/gel surfaces and thin films is described. Secondary-ion mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS) and sputter-induced photon spectroscopy (SIPS) are used to measure the composition of multicomponent silicate films, the relative water content of alumina films, the nitrogen content of ammonia treated silica films, and the depth profiles for films on black chrome. The determination of chemical structure using XPS and SIMS is also discussed. Finally, a brief introduction to temperature-programmed desorption (TPD) and its potential for studying surface chemical reactions, in situ, is presented.

A high-temperature infrared cell was developed to study the gel-to-glass conversion of sol-gel-derived thin films. FT-IR spectra of matched thin-film borosilicate sol-gel samples were taken as the samples were heated at 100°C intervals to 700°C in either air or ammonia. The gels were converted to oxide and oxynitride glasses, respectively, by these heat treatments. The gel-to-glass conversion could be followed and compared for these two treatments by monitoring changes in the vibrational bands present in the spectra. Comparisons between the infrared spectra of NH3-treated and air-treated films heated above 500°C reveal the appearance of new B-N bonds at the expense of B-O-Si bonds for the NH3-fired films. These spectra also exhibit changes which may indicate the formation of Si-N bonds. Thus, ammonolysis reactions can result in thin-film oxynitride glass formation at relatively low temperatures.

This paper reports a recent advance in the understanding of the structure of microporous optical materials such as aerogel through the interpretation of light scattering data. The Fourier transform of the densitydensity correlation function is used to relate measurements of the angular dependence of scattered light to material structure parameters. The results of the approach fit the unusual dependence of the intensity of scattered light as a function of angle for two polarizations. The fit shows that light scattering from aerogels may be interpreted as having two origins; one from the small scale structure of linked particles that comprise the material, and the second due to weak fluctuations in the average density of the microporous structure over distances significantly larger than the pore size.

Characterisation and control of the structure and properties of particulate solids suspensions is of widespread importance with respect to many operations, such as separation, dispersion and densification in the ceramics and related industries. In this paper we describe techniques which have been used to study the effects of changes in basic parameters, for example solids content, particle size, electrolyte concentration and added polymer on the aggregated suspension morphology and characteristics. Suspension morphology was examined by a number of methods, notably freeze-etch microscopy. The mechanical properties of suspensions such as their compressional modulus and rheological behaviour was also examined.

The pyrolytic conversion of an organosilsesquioxane (Owens-Illinois resin GR650) to SiO2 is characterized by ir spectroscopy, thermogravimetry and evolved gas analysis (line-of-sight mass spectroscopy). Scanning calorimetry, ramping at 10°C/min, on the as-received (room temperature annealed) resin indicates a glass transition temperature of 67°C which decreases to 58°C for an unrelaxed sample. The ir spectra have bands which can be assigned to Si-CH3 and Si-O-Si modes. For 30 minute isothermal anneals at temperatures above 420°C there is a continuous decrease in the bands associated with the Si-CH3 groups such that after 30 minutes at 650°C the ir spectrum has evolved to that for SiO2. Evolved gas analysis indicates that there are four major components evolving. Over the temperature range (ramping at 10°C/min) ∼180 to ∼500°C we observe C2H5OH and H2O, both of which are condensation reaction products from the curing reaction. Methane is a major evolving species over the temperature range ∼500 to ∼800°C and the thermal spectrum is double peaked which we attribute to CH3+ bound to the inside and outside of the polymer cage structures. The final major component detected was H2, over the temperature range ∼600 to ∼1100°C, which was attributed to pyrolysis of the organic components, both trapped and evolving. The features of the weight loss curve can be accounted for by the measured evolving species spectra.

Raman spectra were obtained from fresh and aged silica gels using micro-Raman techniques. Comparison of the spectra from wet and dried gels reveals the stages of reaction in the ethanol-TEOS-water system and the gradual development of the silica structure. The steady disappearance of bands assigned to ethanol and the appearance of bands assigned to silatious species can be traced during the drying process. Increases in either acid concentration or water level increase reaction rates to give gels in a more advanced stage of polymerization. Gels tend to develop fluorescence upon aging for several months. The source of this fluorescent could not be determined, but it's development can be prevented by heating freshly dried gels to about 155°C.

High resolution 1H NMR spectroscopy has been employed to study the dynamics of the sol-gel transition in simple silicates. High magnetic fields (360 MHz) were used to detect and identify the various chemical species present in the Si(OCH2CH3)4:C2H5OH:H2O sol-gel system. Using these techniques, the time evolution of the reactant and product species were monitored. The results of these studies have shown that acid and base catalyzed systems react along very different chemical pathways and that the elementary hydrolysis and condensation reactions occur on widely different time scales.

Sample alumina powder prepared with the procedures described by Yoldas [1,2] was suspended in 10−3 M NaCl and contained in precleaned polypropylene cups with air tight lids. Electrophoretic mobilities of the samples were measured at various pH's using a microelectrophoretic technique. The points of zero charge (PZC) were determined from plots of electrophoretic mobility vs pH of the sample suspensions. The initial values of PZC are 10.6 for γ-A12O3. and 8.3 for αAl-2O3 , The corresponding BET surface areas are 206 m2/g and 3m2/g respectively. Upon aging, the PZC decreased in 2 days and then increased by reaching maximum values of 10.4 for γ-Al2 O3 and 8.8 for α-Al2 O3 in 20 days. Aging of sol-gel derived aluminas and commercial alumina derived by precipitation are compared and differences are discussed.