Ceramic materials are generally prepared from structurally simple starting materials, with the consequence that structural properties are difficult to control on a molecular level. This difficulty might be addressed by following the approach taken in polymer chemistry in which molecular building blocks are first prepared and then polymerized in a subsequent step. In the present case, the polysilicic acid esters [Si2O](OCH3)6, [Si3O2](OCH3)8, and [Si8O12](OCH3)8 are prepared and then polymerized by hydrolysis/condensation. Silicon-29 solution nuclear magnetic resonance (NMR) spectroscopy is used to estimate the extent to which the molecular frameworks of these monomers are retained during the course of hydrolysis and condensation.

A solid state multinuclear NMR study of the sol-gel process was performed using the molecular building blocks tetramethoxysilane, hexamethoxydisiloxane, octamethoxytrisiloxane and octamethoxyoctasilsesquioxane as precursor monomers. Water content, solvent content, and hydrolysis/condensation processes were monitored using 17O, 13C, and 29Si FT, FTMAS and CPMAS NMR techniques.

Silicon-29 NMR has been used to investigate the initial steps of hydrolysis and condensation of tetramethoxysilane (TMOS), hexamethoxydisiloxane, and octamethoxytrisiloxane in both basic and acidic methanol solutions. Comparisons of the spectra obtained from the various starting solutions and literature reports of mono-, di-, and tri-silicic acids in aqueous solution were used to identify and assign chemical shifts to condensation intermediates in the TMOS system. The observation of cyclic intermediates in the acid catalysis of TMOS in methanol and the chemical shifts of several products of its hydrolysis and condensation are reported.

The effect of various concentrations of formamide with and without acid catalysis on TMOS derived silica sol and gel structures and physical properties is described using a quantitative structural model. The model is based upon 29Si NMR, SAXS, Raman and FTIR spectroscopy, and an acid solubility test. Changes in chemical reactions during drying due to formamide are presented using FTIR, DSC and TGA data.

Reactions which create and destroy Si-O-Si, Si-O-B, and B-O-B bonds occur in leached layers on borosilicate glasses during glass dissolution. Solid state NMR, Raman, and TEM techniques have been used to determine the distribution of species formed in leached layers as a function of solution pH and the mechanisms of glass-water reactions. The chemical principles which govern the reactivity of silicate and borate bonds in leached layers appear to be similar to those which govern the formation of silicate and borate gels via sol-gel techniques.

In situ FTIR, NMR and SAXS were used to investigate the synthesis and molecular structure of xLi2O-(1−x)B2O3 gels derived from tri-n-butyl borate (TBB) and lithium methoxide. In solution the fraction of tetrahedrally coordinated borons (N4) increases linearly with x, and a critical value of N4 must be exceeded in order to form gels. The primary criterion affecting gel formation is the kinetic stability of borate bonds toward molecules which are able to undergo dissociative chemisorption.

Hydrothermal treatment of zirconyl salt solutions produces uniform m-ZrO2 powder on the order of 80 nm. This powder is porous, has a 3-nm crystallite size, and exhibits an unusually high degree of crystallographic alignment within particles. The generation of this powder occurs via a complex process involving nucleation, growth, and controlled agglomeration of primary particles. Particle formation, crystallographic alignment and particulate uniformity are explained in terms of solution reactions and colloidal behavior.

Monodisperse ceramic powders with sizes in the range of 0.1-μm have been prepared by a number of groups. Generally a dilute solution of a metal compound is hydrolysed to produce amorphous, spherical particles which may be crystallized by subsequent heat treatments. Emulsion polymerization can produce similarly monodisperse latices if the polymerization conditions are carefully controlled. This paper discusses models of the precipitation process which are based on crystallization from aqueous solutions but are believed to be more generally applicable. From simulations it is concluded that monodisperse particles are a most unlikely outcome of a batch precipitation process. Surface active compounds could play an important role in controlling particle size. Inhomogenous mixing during the early stages of reaction should also be important.

Monodisperse and spherical titania powders were prepared by the hydrolysis of titanium tetraethoxide in ethanol with hydroxy-propyl cellulose(HPC) present during particle precipitation. The mean particle size decreased as the concentration of tLPC increased. The critical concentration of HPC for the in situ stabilization of titania powder suspensions was determined by a photographic method, and found to be independent of the molecular weight of HPC within the molecular range of 60,000 to 300,000. The amount of HPC adsorbed on the particle surface, determined by a colorimetric method using a UV-visible spectrophotometer, decreased with the increasing molecular weight of HPC. Suspension stability was confirmed by theoretical calculations based on experimental results.

Zincite has been produced by the controlled hydrolysis of an alkylzinc alkoxide (ethylzinc-t-butoxide) resulting in ∼0.2 μm spherical particles with a narrow size distribution consisting of 150 Å crystallites. The surface area is 30 m2/g. Variation of the concentration of the water drastically affects the particle and crystallite sizes. The results of a systematic study of the hydrolysis parameters are reported here.

Yttrium oxide powders were prepared from water-in-oil type emulsions by loading the yttrium ions into the aqueous phase. Emulsions were characterized with respect to droplet size and distribution, emulsion type, and time and temperature stability. Precursor powders were obtained from the emulsions by evaporation of the aqueous phase in a hot oil bath. Powder characteristics, such as size, shape, composition, and sinterability as a function of procedural variables, were determined. The new technique appears to be practical and may be economically feasible.

Double alkoxides of the general formula Mg[Al(OR)4]2 where R is iso-Pr or sec-Bu were prepared by reacting aluminium and magnesium metals together with the alcohol ROH and purified by vacuum distillation. They were characterised by IR, proton and 27Al NMR spectroscopy and MW determination. A magnesium aluminium double alkoxide was also prepared by treating the commercially available aluminium alkoxide ‘Aliso B’ [a mixed aluminium (iso-propoxide)(sec-butoxide)] with magnesium and iso-propanol. Treatment of magnesium aluminium double alkoxides with water and an alkanolamine (preferably triethanolamine) gives a rigid coherent gel. Viscosity measurements and 27Al NMR spectroscopy suggest that the double alkoxide does not break down to its constituents during hydrolysis. The air-dried gel was shown by XRD to convert quantitatively to spinel on firing to 1500°C. The resistance of the double alkoxide moiety to hydrolysis explains the ease of conversion to spinel on firing. The gel has been used to bind alumina and magnesia grain. Gels suitable for binding refractory grain were obtained only when the alkanolamine content corresponded to one alkanolamine group per metal atom. Electron micrographic and XRD studies showed that in fired refractory pieces, the bonding phase was spinel.

Aqueous precipitation in a computer-controlled continuous crystallizer has been applied to the preparation of cordierite, mullite, alumina, and zirconia precursor powders. The particles are dense, spherical, and x-ray amorphous. The powders have a particle size range of 0.2–5 μm and a surface area of 1 – 10 m2/g The properties of the powders and of some green and fired pieces are described.

PZT and PLZT powders were prepared from nitrate and chloride precursors in a continuous constant volume precipitator. After precipitation, the powders were dried by a variety of methods, including: spray-drying, freeze-drying (in liquid nitrogen), and centrifugal freeze-drying. Spraydried powders were found to have a spherical morphology, and to be solid. The particle size was in the micron range. Powders dried by nitrogen freezedrying were characterized by an open morphology of agglomerated platelets. For centrifugally freeze-dried powders, particle size analyses were found to fit a population balance model, giving crystallite, cluster, and agglomerate population densities and growth rates.

Cordierite and cordierite based glass ceramics are promising materials for electronic packaging. Preparations by organic and inorganic precursors along sol-gel processing are reported. Compared with conventional methods, they show a drastic decrease of the sintering temperatures. A process able to giving better than 95% theoretical density ceramic below 1000°C, with good electronic properties is described.

Lithium Aluminum Silicate (LAS) glass-ceramic compositions with and without phosphorous have been synthesized by Sol-Gel techniques. Resulting LAStype powders are herein designated as NZ and NZP. X-Ray analysis, thermogravimetric analysis (TGA), particle size measurements, and thermal dilatometric shrinkage measurements have been performed on these samples. The NZ and NZP powders in calcined form, as well as commercially-available LAS glass-ceramic produce x-ray diffraction pattern very similar to the pattern of Virgilite LixAlxSi3−xO6 (x=0.5–1.0). There is little difference between powders with and without phosphorous in the diffuse reflectance spectra (DRS). Preliminary results show that the material can be easily processed into glass ceramics.

When the polymerization of Si(OCH3)4 is carried out in the presence of surface active agents, prolonged oscillations (over 1000 hrs) at the gel/xerogel transition are observed. The oscillations are of large amplitude, they are slow (several hrs/period), and they exhibit a chaotic behaviour. The probe by which these oscillations are observed is emission from excited state monomeric and excimeric pyrene. It is suggested tentatively that the driving forces for this oscillation are the structural relaxation of the secondary polymeric gel structure and the dispersion of adsorbed pyrene to thermodynamically favored adsorption sites. Relevant models could be those of oscillatory sol/gel phase transitions and of oscillatory polymerization reactions. We are unaware of previous observations of oscillations in sol/gel systems.

High resolution 1H NMR spectroscopy at high magnetic fields is employed to study the reaction kinetics of the Si(OCH3)4:CH3OH:H2O sol-gel system. Both the overall extent of reaction as a function of time and the equilibrium distribution of species are measured. In acid catalyzed solution, condensation is the rate limiting step while in base catalyzed solution, hydrolysis becomes rate limiting. A kinetic model in which the rate of hydrolysis is assumed to be independent of the adjacent functional groups is presented. This model correctly predicts the distribution of product species during the initial stages of the sol-gel reaction.

Powder x-ray diffraction has been the most common method for rapid structural analysis and identification of crystalline ceramic raw materials. However, new structural ceramic raw materials often have linebroadened or featureless XRD patterns due to structural strain or small crystallite size. Characterization of various silicon carbide and silicon nitride powders and ceramic fibers by Si-29 NMR-MAS spectroscopy has revealed structural details and differences in these materials previously indistinguishable by XRD or other routine methods. Unique variables intrinsic to a given ceramic synthesis process are reflected in the NMR-MAS spectra of the resulting products.

Effective control of sol-gel glass processing requires a detailed understanding of the kinetic and mechanistic aspects of the process. We have investigated structural evolution at the molecular level in the tetramethoxysilane (TMOS) hydrolysis reaction by various spectroscopic techniques. Development of structure at the macromolecular level and evolution of particle/network dimensionality have been studied by small-angle x-ray scattering (SAXS) in both hydrogenated and fully deuterated reactions for silica macromolecular structural development.