Diphasic yttrium-aluminum garnet (YAG) sols were gelled across TEM grids to make films. The films were heat-treated up to 300 hours between 800°C to 1150°C. Microstructure and phase evolution were observed by TEM. YAG fraction and grain size, matrix phases and grain size, nuclei/area, and film thickness were measured. Yttrium-aluminum monoclinic and transition alumina appeared at 800°C. YAG nucleated between 800°C and 950°C. Above 850°C nudeation was site-saturated. Final nuclei density averaged 0.3/μm3. Between 850°C and 1000°C YAG growth had ∼t1/2 dependence and Q ∼ 280 kJ/mole. Below 850°C nudeation was continuous and growth had ∼t0.85 dependence. Above 1000°C YAG growth had ∼t1/4 dependence and the matrix grains coarsened with ∼t1/4 dependence. Unreacted areas were more abundant in thinner films because the nuclei/area and reaction rate decreased. YAG growth was often accompanied by formation of 20 – 100 nm subgrains. Above 1100°C there was some readion to YAG by a different process.

Mn-Co-Ni-O thin films of metal atomic ratio 3.0 : 1.9 : 1.0 were prepared on glass substrates from methanol solutions of the corresponding metal β-diketonates by dip-coating. As-prepared films were heated at 900°C for 1 h mostly after being calcined at 450°C for 5 min. The film thickness increased with increasing concentration of the solution as well as the number of lifting times. However, the effect was not apparent with the sample prepared without calcination. The prepared films were observed to crystallize into a complicated spinel phase by the heating process at 900°C for 1 h. The surface of the dense film composed of particles of about 0.2 μm diameter, was almost even. The thermal and aging responses of electric resistance showed the film to be a good material as a thermistor.

Microporous thin films composed either of zeolite crystals embedded in sol-gel derived glass or of a molecular coupling layer, zeolite crystals and a porous silica overlayer, were formed on the gold electrodes of Quartz Crystal Microbalances (QCM). The microporosity of the thin films was characterized by in situ nitrogen and vapor sorption isotherms. Both preparation methods result in thin films with substantial microporosity. Selective adsorption based on molecular size exclusion from the microporous films could be achieved.

The sol-gel method is one of the most appropriate technologies for the preparation of functional thin oxide coatings. However, few studies on the structure near the interface between sol-gel coatings and substrates have been reported. In this study, the structures of thin TiO2 gel coatings were investigated by XPS in order to elucidate the interaction between the coatings and the glass substrates. TiO2 gel coatings were prepared from Ti-alkoxide by hydrolysis and dip-coating on silica glass plates. Thickness and refractive index measurements were made by ellipsometry. Changes in Ols spectra for the coatings were observed at locations near the interface. Dynamic microhardness measurements for the coatings and the coated glasses were made. These results suggest the formation of a Ti-O-Si bond at the interface.

Laser substrate heating is discussed as an alternative for the densification of sol -gel thin films. Homogeneous films of n(550 nm) = 2.30 could be obtained, keeping the bulk substrate temperature below 80 °C.

Well crystallized polycrystalline perovskite-type oxide thin and/or thick films were prepared at sufficiently low temperatures by newly developed “hydrothermal electrochemical techniques” where metals were electrochemically oxidized and reacted with some components in hydrothermal solutions. BaTiO3 films 70 to 300 nm thick were formed in Ba(OH)2 solution at 100–200°C under saturation vapor pressure on the Ti substrate and Ti deposited glass substrates. The electrical current enhanced to thicken their films. SrTiO3, BaFeO3 and LiNbO3 films were also prepared.

The physical, optical, and chemical characteristics of electrophoretically- and dip-coated sol-gel ceramic films are compared. The results indicate that electrophoresis may allow a higher level of control over the chemistry and structure of ceramic coatings than dip-coating techniques. For example, controlled-thickness sol-gel coatings can be prepared by adjusting the deposition time or voltage. Additionally, electrophoretic coatings prepared in a four-component alumino-borosilicate sol display interesting optical characteristics. For example, the ellipsometrically-measured refractive indices of electrophoretic coatings are higher than the refractive indices of dip-coated films cast from identical sols, and they are also higher than any of the individual sol components. This result suggests that there are physical and/or chemical differences between films prepared by dip-coating and electrophoresis.

Corrosion resistant Sol-Gel ZrO2, coatings deposited by dip coating technique on 316 L stainless steel sheets have been fabricated utilizing sonocatalysed precursors sols prepared from zirconium alkoxide Zr(OC3H7)4, isopropanol, glacial acetic acid and water. Their composition varied between 0,025 to 0,9 mol/1 ZrO2. The coatings have been characterized by X-ray diffraction, IR optical reflection, ellipsometry and scanning electron microscopy. When densified under a slow heat treatment thin coatings exhibit outstanding corrosion resistance as no weight change has been observed after 24 h chemical attack in H2SO4 aqueous solution at 81°C and 10 h oxidation treatment in air at 800°C. Thick films as well as films densified under rapid heat treatments tend to crack and are less corrosion resistant.

Stabilized Zirconia thin films were deposited by R. F. Magnetron Sputtering onto iron substrates. Deposition parameters such as gas pressure and R. F. voltage were optimized to obtain homogeneous and well adherent protective coatings. The morphology and structure of films before and after thermal treatments were investigated by Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Thermogravimetrical Analysis (TGA).

Auger Electron Spectroscopy (AES) depth profiling techniques were used to obtain the chemical distribution of the elements in order to study the influence of two important parameters on the adhesion of the ceramic: the presence of a thin layer of native metal oxide and the residual surface roughness after polishing.

The effectiveness of coatings to protect the metal substrate against high temperature oxidation in air was evaluated by thermogravimetrical analysis at 773K. The protective action of the ceramic film was well demonstrated.

This paper presents an experimental study of the air plasma spraying (APS) of alumina-titania powder using argon-hydrogen working gases. This powder system is being used in the fabrication of heater tubes that emulate nuclear fuel tubes for use in thermal-hydraulic testing. Experiments were conducted using a Taguchi fractional-factorial design parametric study. Operating parameters were varied around the typical spray parameters in a systematic design of experiments in order to display the range of plasma processing conditions and their effect on the resultant coatings. The coatings were characterized by hardness and electrical tests, surface profilometry, image analysis, optical metallography, and x-ray diffraction. Coating qualities are discussed with respect to dielectric strength, hardness, porosity, surface roughness, deposition efficiency, and microstructure. Attempts are made to correlate the features of the coatings with the changes in operating parameters.

The separation properties of a microporous silica membrane, prepared be e-beam evaporation of quarz onto a mesoporous support membrane is reported.

The beneficial effects of the support constraint on the improved thermal stability of supported titania membranes were studied by following the anatase to rutile phase transformation in supported and unsupported titania membranes. This was studied using Raman spectroscopy and XRD. Supported membranes showed a higher transformation temperature, about 150°C higher, (slower rate of transformation) compared to the unsupported ones. Unsupported membranes showed a slight thickness dependence on the phase transformation temperature, but less significant compared to the difference in phase transformation behaviour between supported and unsupported membranes of similar thicknesses.

Mesoporous alumina membranes were modified with microporous silica. The polymeric silica sols consist of very weakly branched polymeric molecules with a fractal dimension of 1.3 and Guinier radius of ≈ 2.0 nm. The resulting top layer material is microporous with a porosity of 40% and a layer thickness of 60 nm. Gas transport is activated with an activation energy of 11 kJ/mol for hydrogen and molecular sieve like separation factors have been obtained. From the mechanism of gas transport the conclusion can be drawn that the pores are of molecular dimensions (0.7 – 1 nm diameter).

Imogolite is a structurally microporous tubular clay comprising one-dimensional pore channels that are 0.8 – 1.2 nm in diameter, depending on composition. The microporous structure of natural and synthetic imogolite has been investigated by nitrogen adsorption as a function of outgassing temperature. A significant increase in adsorption at low relative pressure (P/P0 ∼ 10-6) after 275°C outgassing reflects a high concentration and narrow distribution of 0.8 – 0.9 nm diameter pores (i.e., the imogolite tubes) and supports the potential use of imogolite in inorganic membrane applications.

Sol-gel routes were developed to prepare densified PZT fibers. The effects of the degree of hydrolysis and the addition of an organic polymer to the precursor sol on fiber forming ability were investigated. Results on the crystalline and microstructural development of gels and fibers are presented. The effects of the incorporation of excess PbO and sintering atmosphere are also discussed, particularly in relation to densification.

The response of wet gels to applied stresses is discussed, with emphasis on the role of flow of the pore liquid. Even when the network of the gel is purely elastic, the gel exhibits time-dependent behavior that resembles viscoelasticity, which results from fluid flow. The permeability of the gel can be determined from measurement of this time-dependence. Fluid flow also influences the thermal expansion behavior of gels, and can cause severe stresses to develop during supercritical drying, if the autoclave is heated too rapidly.

Variations in gel aging times and temperatures are shown to affect the optical properties of a gel-derived GRIN lens. These properties include the variation of the total index change as well as the shape of the index profile. However, these optical properties do not appear to correlate with the amount of modifier removed during the leaching step. Also, regardless of aging, gels appear identical with respect to calcining response and composition of pore liquid.

The refractive index and porosity of silicate films formed by dip-coating were tailored by varying the aging time of a two-step acid- and base-catalyzed sol to control the size and structure of the polymeric species prior to coating. 29Si NMR showed that there was a 2% increase in the total number of bridging oxygens with sol age, consistent with a cluster-cluster growth mechanism. However, several percent monomer remained regardless of aging. Dip-coated films were characterized by ellipsometry before and after heating to moderate temperatures at three rates. Sol aging prior to film deposition leads to greater film porosity, consistent with the concept of aggregation of fractal clusters, but only after a heat treatment to remove the organic species associated with incompletely hydrolyzed monomers from the pores.

Surface modification of silica via silylation is often undertaken to change surface chemistry and hence, adsorption characteristics but little attention is paid to its use for pore morphology modification, the subject of this work. Modification of two silica samples was conducted by trimethylsilylation. The degree of silylation/ surface coverage was monitored by TGA and elemental analysis. Pore structure was studied by nitrogen adsorption and condensation, and small angle x-ray scattering (SAXS). Previously, we demonstrated that surface area, surface texture, pore size distribution, and total pore volume are indeed changed in a controlled fashion due to silylation of mesoporous silicas. Generally, the mean pore size is smaller, the pore size distribution is narrower, and the pore surface is smoother after silylation. However, questions remain concerning the effect of small-scale surface roughness and the fractional surface coverage on the effective pore size. This study concentrates on the silylation of smaller pore material (r < 40 Å). Significant pore size distribution narrowing and smoothing of the pore surface with increasing surface coverage was noted.

Two-step acid/base (B2) and acid/acid (A2) catalyzed silica gels have been aged in ethanol or water baths followed by various aprotic solvents with a range of surface tensions. The physical and chemical structures of xerogels dried from these aprotic solvents were studied by a series of techniques (nitrogen adsorption, elemental analysis, TGA, SAXS)and compared to the corresponding structures of low temperature (CO2) and high temperature (ethanol) aerogels. The aprotic solvents help to isolate the effects of pore fluid surface tension during drying since they do not react with the gel surface. B2 xerogels showed a linear decrease in surface area with increasing surface tension. Pore volume and pore size followed a similar trend. Micropore analysis on A2 xerogels showed an increase in micropore volume and surface area with increase in surface tension, whereas total surface area and pore volume showed an opposite trend. Thus, by varying surface tension and aging, one is able to independently control surface area, pore volume, and pore size.