Colloidal suspensions prepared with nonaqueous liquids are important in ceramic processing operations such as tape casting, slip casting, etc. [1,2]. However, investigations of the properties of such suspensions are limited. In the present work, the suspension behavior of Al2O3 and silicate glass powders was studied using two nonaqueous liquids – methanol (MEOH) and methyl isobutyl ketone (MIBK). Rheological, sedimentation, and electrokinetic properties were determined for various mixed liquid ratios. The effect of polyvinyl butyral resin, a polymeric binder, on silicate glass suspension properties was also investigated.

Microstructural development in alumina gels is dominated by a series of phase transformations between the hydrous oxides to transition alumina phases, between transition phases, and transformation to alpha-alumina. These microstructural transformations are illustrated in boehmite AlOOH and bayerite Al(OH)3 gels.

The introduction of organic groups into inorganic networks by the sol-gel process opens the possibility for the preparation of new materials, and typical properties resulting from inorganic as well as from organic components may be combined. Some general aspects and different examples of material developments are reviewed.

The field of ceramic composites is reviewed as an outstanding example of where more sophisticated chemistry can aid ceramic processing. Processes reviewed, mostly from work of the author and colleagues, include use of solution, polymer and high temperature chemistry, e.g. in sol-gel, polymer pyrolysis, solid state, and chemical vapor deposition processes. Future needs and opportunities for chemistry in ceramic processing are also discussed, e.g. coating part or all the matrix or its precursor onto the particulates or fibers of the resultant composite.

Instead of aiming to prepare homogeneous gels and xerogels, this paper reports on work done to prepare deliberately diphasic materials. This has been achieved by three different paths: (1) mixing 2 sols; (2) mixing 1 sol with 1 solution; and (3) post formation diffusion of either one or two solutions.

By the last named process we have made SiO2, mullite and alumina based composites, with silver halides, BaSO4, CdS, etc., as the dispersed phase. The crystal size can be confined to the initial pores by rapid diffusion giving rise to extremely fine second phases in the submicron range. Subsequent reduction of appropriate metallic salts can be used to give finely dispersed metals (e.g. Cu, Ni) in essentially any xerogel matrix. The open porosity makes these metal atoms very accessible.

By the first two processes we have made both single phase and di-phasic gels of the same composition (prototype: mullite) and shown that though they cannot be distinguished by XRD, SEM, and TEM, by DTA and thermal processing, they are radically different. Such di-phasic gels store more metastable energy than any other solids.

Sol/gel derived silica thin films were thermally treated in NH3 for four hours at temperatures up to 1300C. The films were analyzed by ellipsometry, X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). Over 30 mol% nitrogen was incorporated in the film treated at 1300C. Using IR and XPS analyses, -NHx groups were found to be present after low temperature treatments, while nitrogen was incorporated in an oxynitride structure after the higher temperature treatments.

Short ceramic fibers or whiskers may be ideally suited for the fabrication of ceramic-ceramic composites using the sol-gel process. The fibers can be uniformly dispersed in a low viscosity sol and then frozen into the matrix through gelation. Several ceramic composites were prepared by synthesizing an Al2O3 precursor from aluminum sec-butoxide and then dispersing fibers of either zirconia, graphite or SiC. The composites were dried at room temperature and fired up to 1200°C. The fibers reduce the volume shrinkages in comparison to that obtained with pure Al2O3 during processing. Structures with dimensions of several cm2 can be rapidly produced with this method without cracking.

A simple casting technique was used to fabricate composites comprised of long fibers in an alumina matrix. Random fiber preforms were placed in trays and subsequently a liquid alumina sol was added and gelled. Dried sheets approximately 6 cm in diameter and 0.2 cm thick were prepared without cracking. The addition of glycerol to the sol improved drying properties, made the dry gel flexible, and permitted the lamination (plying) of several sheets.

The volatile products from the thermal reaction (414°C) of silane in excess acetylene are hydrogen, ethylene, vinylsilane, ethynylsilane, vinylethynylsilane (possibly divinylsilane) and ethynyl-divinylsilane (1,2). We have reexamined this reaction using a 3 C2 H2/1 SiH4 reaction mixture and have obtained product yield curves for these products versus percent silane loss. We have also found that product curves are unaffected when propylene at pressures equal to that of acetylene is also present. Since only trace quantities of propylsilane are produced in the presence of propylene, we can rule out reactions involving silyl radicals. Thus the SiH4−C2H2 reaction involves silylene and silene intermediates. The products can be explained by a mechanism similar to one proposed by Barton and Burns (3).

The continuing search for new types of high-strength materials, and for performance improvements in existing ceramics, has encouraged several nonconventional approaches to ceramics synthesis. Some of the advantages of polymeric routes have already been demonstrated and include new fabrication procedures leading to continuous fibers, coatings and infiltrated porous structures. At a more fundamental level, polymer pyrolysis can allow control over the microstructure of the final ceramic, with important consequences for both physical and chemical properties (1).