Ceramic materials with chemical compositions of CaO–X mole % TiO2, where X ranges from 3 to 40, have been prepared for the evaluation of microstructures, mechanical properties, thermal shock resistance, resistance to hydration in air, and resistance to corrosion in molten salt saturated with calcium. When the TiO2 content is less than 40.3 mole %, the CaO forms two-phase microstructures consisting of CaO and Ca3Ti2O7, and the composition CaO−40.3 mole % TiO2 corresponds to the (single-phase) compound Ca3Ti2O7. The data on mechanical properties suggest that the single-phase material has better flexural strength and fracture toughness than do the two-phase materials. It is also demonstrated that the stabilizing effect of TiO2 on CaO imparts resistance to atmospheric hydration. Both scanning electron microscopy and energy-dispersive x-ray analysis of the specimens exposed to molten CaCl2−20 mole % CaF2 saturated with calcium at 900 °C show that corrosion resistance increases with an increase in TiO2 content, but that corrosion does occur in all materials. On the basis of experimental observations and thermodynamic considerations, the degradation of Ca3Ti2O7 is shown to be associated with the reduction of Ca3Ti2O7 by calcium to form CaO and metallic titanium followed by the dissolution of the reaction product CaO in the molten salt.

The equilibrium states of internal penny cracks at interfaces in thin-sheet bodies are investigated. Consideration is given to cracks held open by a center-loading force from an entrapped particle in combination with a uniform pressure from a fixed mass of entrapped gas. A fracture mechanics analysis indicates that under these conditions the cracks are stable, but are amenable to growth from an enhancement in net pressure (increase in internal pressure or decrease in external pressure) or effective particle size. Essential details of the theory are confirmed by experiments on lenticular cracks at healed interfaces in muscovite mica. The results are pertinent to flaw responses in brittle ceramic systems where structural integrity is an issue.

The Li2O–B2O3–H2O system has been studied under hydrothermal conditions. Li4B7O12Cl, Li2B4O7, Li3B5O8(OH)2, Li2HBO3, and LiH2B5O9 are the phases crystallizing in this system at 250 °C and P < 100 bars. The growth of these phases has been discussed in brief. Also, the growth morphology of these phases has been studied with reference to the growth parameters.

Silicon-based ceramic whiskers, such as silicon carbide and silicon nitride, were produced in a plasma arc reactor. Silicon monoxide gas was generated by reacting briquettes of silica and carbon according to the following reaction: SiO2(s or l) + C(s) = SiO(g) + CO(g). The effects of operating variables on the production of silicon monoxide are discussed. The silicon monoxide gas was then back-reacted with carbon monoxide to produce silicon carbide whiskers according to the following reaction: SiO(g) + 3CO(g) = SiC(s) + 2CO2(g). In the presence of nitrogen, the product contained some silicon nitride and silicon oxynitride whiskers. The effects of gas composition and flow rate, crucible mass, and alkali additions on the amount and morphology of the whiskers were determined. It is concluded that the whiskers grew by a vapor-liquid-solid mechanism.

Magnetic Resonance Imaging (MRI) is applied to porous ceramic materials to study structural properties. In ceramics, processing differences create inhomogeneous binder distribution in the materials which can cause the formation of regions with differing densities and voids. These defects can be observed with MRI using solvent permeation. Fractional porosity obtained by using image intensity measurements and weight gain due to solvent permeation can be correlated. Dark regions in the image are due to defects such as closed voids, pockets of binder, or agglomerates. Defects such as voids or agglomerates usually have different magnetic susceptibilities. This difference causes artifacts in the image. By exploiting the increase in signal loss using a gradient-echo sequence, apparent enhancement of voids in ceramics is achieved.

A novel and attractive method for preparing multicomponent electronic ceramics and ceramic-metal composites is the oxidation of solid metallic precursors (SMP). This metallurgical processing route consists of the following steps: (i) preparation of a solid metallic precursor containing the proper ratio of elements for the final ceramic or ceramic-metal composite, (ii) compaction and forming of the metallic precursor into a desired shape, and (iii) oxidation to produce a monolithic ceramic or ceramic-metal composite. While the SMP method has been used to prepare wires and tapes containing a variety of superconducting oxides, this method has not been widely used to synthesize other electronic ceramics. In this paper, the synthesis of dielectric BaTiO3/noble metal laminates from solid metallic precursors is discussed. Ba–Ti precursor powders have been produced by solid-state mechanical alloying. The precursor powder was sealed inside noble metal tubes and rolled to form thin Ba–Ti/noble metal laminates. Exposure of the Ba–Ti core in such tapes to temperatures ≥ 300 °C in pure oxygen resulted in rapid oxidation. Post-oxidation annealing at elevated temperatures (≥900 °C) yielded dielectric BaTiO3/Ag or BaTiO3/Pd laminates.

A maximum Al3+-substitution has been demonstrated to be 45 mole% of (M + Al) in the brucite layer of hydrotalcites. The chemical composition of the highly substituted hydrotalcites can be typically represented by [M0.55Al0.45(OH)2] [(CO3)0.225 · 0.50H2O] where M = Mg, Ni, Zn, and Co. It showed the small lattice parameters of a0 3.05–2.98 A in the hexagonal lattice, which corroborates Al3+-substitution in the brucite layer. The simultaneous thermal analyses (TG and DTA) and mass spectrometry (MS) study have been performed. The highly Al3+-substituted hydrotalcites also showed quite different isotherms for the CO2 adsorption. These materials adsorbed CO2 gas by removing water within the interlayer and showed the selectivity for CO2 adsorption: Cu–Al ∼Zn—Al < Co—Al < Mg—Al < Ni—Al. The Mg—Al and Co—Al hydrotalcite-like compounds showed a doubled amount of CO2 by removing carbonate ions within the interlayer.

The effect of water of hydrolysis on nucleation, crystallization, and microstructural development of sol-gel derived single phase LiNbO3 thin films has been studied using transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction (XRD), and differential scanning calorimetry (DSC). A precursor solution of double ethoxides of lithium and niobium in ethanol was used for the preparation of sol. DSC results indicated that adding water to the solution for hydrolysis of the double ethoxides lowered the crystallization temperature from 500 °C (no water) to 390 °C (2 moles water per mole ethoxide). The amount of water had no effect on the short-range order in amorphous LiNbO3 gels but rendered significant microstructural variations for the crystallized films. AFM studies indicated that surface roughness of dip-coated films increased with increasing water of hydrolysis. Films on glass, heat-treated for 1 h at 400 °C, were polycrystalline and randomly oriented. Those made with a low water-to-ethoxide ratio had smaller grains and smaller pores than films prepared from sols with higher water-to-ethoxide ratios. Annealing films with a low water concentration for longer times or at higher temperatures resulted in grain growth. Higher temperatures (600 °C) resulted in grain faceting along close-packed planes. Films deposited on c-cut sapphire made with a 1:1 ethoxide-to-water ratio and heat-treated at 400 °C were epitactic with the c-axis perpendicular to the film-substrate interface. Films with higher concentrations of water of hydrolysis on sapphire had a preferred orientation but were polycrystalline. It is postulated that a high amount of water increases the concentration of amorphous LiNbO3 building blocks in the sol through hydrolysis, which subsequently promotes crystallization during heat treatment.

This paper presents a novel approach that demonstrates the usefulness of electrorheological fibril formation to form 1-3 connected ceramic-polymer composites. These fillers include ferroelectric, polar, metal, semiconductor, and superconductor crystallite powders. Patterned distributions of ceramic fillers within the polymer matrix can be induced by electric fields applied between patterned electrodes.

The contact radii arising from surface forces were determined for cross-linked polystyrene particles having radii between 1.5 and 10 μm in contact with SiO2/silicon substrates using scanning electron microscopy. It was observed that the contact radius varied approximately as the particle radius to the 0.42 ± 0.13 power. These results are consistent with the theories that assume plastic response of the materials, such as that proposed by Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984)] but are inconsistent with the predictions of models which assume only elastic response, such as that of Johnson, Kendall, and Roberts [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Soc. London A 324, 301 (1971)]. The thermodynamic work of adhesion, calculated from the experimental results, was found to be 0.32 J/m2, which is significantly smaller than that reported previously on a similar system.

MoS2 thin films are sputter-deposited in different conditions in order to obtain well-defined microstructures. They are submitted to ball-on-disk wear tests at moderate loads (0.7 GPa). Cross sections of wear tracks are observed by transmission electron microscopy (TEM). Sliding induces the formation and the wear of a lubricating buffer layer between the film and the sliding ball. This buffer layer shows strong crystal reorientation, suggesting the presence of intergranular motion. Initially amorphous films crystallize during the sliding test. The film's intrinsic failure mechanisms appear to be more determinant for the sliding lifetime than the properties of the interface.

A modified sedimentation process was used in the production of a functionally gradient material (FGM), NiAl/Al2O3. A simple finite element model was used to guide our design and fabrication efforts by estimating residual stress states as a function of composite structure. This approach could lead to tailored designs that enhance or avoid specific residual stress states. Thermal cycling tests were factored into the model to predict time dependent or steady-state internal temperature and stress profiles. Four-point bend tests were conducted to establish the mechanical load-displacement behavior of a single interlayer FGM at room temperature, 800 and 1000 K. Room temperature bend strength of the FGM was 3–4 times that of the base NiAl. At elevated temperatures, composite fracture occurred in a gradual, noncatastrophic mode involving NiAl retardation of a succession of cracks originating in the alumina face.

Two coprecipitation methods were used to synthesize powder precursors of doped lanthanum chromite (La, Ca)(Cr, Co)O3. The effects of synthesis method and calcination temperature on the composition, sintered density, and microstructure of pressed compacts of (La, Ca)(Cr, Co)O3 were studied by differential thermal analysis/thermogravimetric analysis, x-ray diffraction, scanning electron microscopy, and density measurement. The cation ratios in the precipitated solids were, with few exceptions, within experimental error of the desired compositions for all four components. Powders obtained by both techniques could be sintered to densities exceeding 93% at 1400 °C. The highest densities were obtained with calcining temperatures from 450 to 700 °C. The sintered microstructures exhibited uniform grain sizes averaging 3–5 μm. The Cr(vi) compounds, CaCrO4 and La2CrO6, were observed in all of the calcined powders. The possible role of these phases on chromite densification is discussed.

Ignition criteria for gasless self-propagating combustion synthesis have been investigated through an ignition temperature analysis. The calculations were based on the dimensionless energy and mass continuity equations where the dimensionless parameters associated with the rate of local heat generation (β), activation energy (γ), the rate of surface heat loss by convection (ω), the rate of surface heat loss by radiation (δ), and the rate of reaction (λ) were incorporated. The relative significance of each of these parameters on the ignition of the self-propagating combustion reaction was evaluated to be γ > β > δ > ω. The ignition region, transition region, and nonignition region were identified for selected conditions. The correlations between ignition behavior and the material properties, the thermodynamic and kinetic properties, as well as the experimental conditions were discussed. The calculations indicated that only those systems with δH/Cp > 1.5 × 103 (K) will give rise to a self-propagating combustion reaction without external energy input. Thus, this value can be used as an approximate guide for the existence of self-sustaining combustion. The calculations provide a sound basis toward interpreting experimental observations and developing a fundamental understanding of the process.

Synthesizing oxide ceramic powders by application of a microwave plasma is a great advantage. There are two ways the microwave plasma can be used: The first is as a source of heat for the pyrolysis of solutions and the second is to excite gas reactions to obtain nanosized powders. Both applications are superior to standard methods. A microwave cavity well suited for these experiments and its operating characteristics are described. Using a microwave plasma as a source of heat for pyrolytic decomposition of nitrates in aqueous solutions leads to a fine-grained product with particle sizes from 100 to 1000 nm. Crystallite sizes in those particles are in most cases less than 10 nm. This is demonstrated with zirconia-based ceramics, such as ZrO2−3 mol % Y2O3−20 mol % Al2O3. Depending on the conditions during pyrolysis, it is possible to obtain a product in which alumina is either dissolved in zirconia or the onset of the phase separation is observed. The energy efficiency of this process is better than 80%. If the reactants are gaseous, e.g., ZrCl4, it is possible to produce powders with mean particle sizes of about 4 nm. In the case of zirconia, these particles are monocrystalline with a cubic structure. This structure is not in equilibrium under the experimental conditions.

A perturbation method is used to confirm that the elastic contact stiffness associated with a flat-ended punch indenting a layered medium is insensitive to the cross-section shape of the punch as long as the shape does not differ too much from a circle. This result supports the practice of modeling nonaxisymmetric indenters such as Vickers or Berkovich indenters as an axisymmetric flat-ended cylindrical punch.

Lanthanum sulfide (La2S3) exists in three different allotropic forms in the crystalline state. The low-temperature orthorhombic phase (α) transforms to the intermediate tetragonal phase (β) which further undergoes transformation to the high-temperature cubic phase (γ). The intermediate tetragonal phase (β) is an oxysulfide with possible use as a phosphor, and the cubic phase (γ) of La2S3 shows potential for application as a far IR (8–14 μm) window material. We report metal-organic synthesis routes for the preparation of the β- and γ-phases of La2S3 by processing modifications and choice of precursor chemistry. The alkoxide-derived precursors and the transformed sulfide powders were characterized for morphology, microstructure, and thermal stability. Phase evolution studies were also conducted, and the results are discussed in the context of formation of the β- and γ-phases. Results of densification, microstructure, and infrared transmission characteristics are also presented.

Room temperature, high energy ball milling was applied to various transition aluminas (γ, K, χ), producing thermodynamically stable α-alumina–a phenomenon that could otherwise be achieved only by high temperature (1100–1200 °C) heat treatment. The transformation proceeds in two steps. The first one consists of rapid microstructural rearrangements with continuously increasing α-transformation rate. In the second step (1–2 h from the start), only relatively small changes in morphology are observed with a constant α-transformation rate. The rate is influenced only by the milling intensity. The presence or the absence of oxygen in the milling atmosphere has a large influence on the final surface area of α-alumina.

Spherical silica particles, dispersed in ethanol/water solutions, were first coated with titania by hydrolysis of added titanium isopropoxide. The coating thickness could be readily adjusted by the ratio of titanium alkoxide concentration to the amount of silica. The coated cores prepared as above were then treated with ammonia in a temperature-programmed reaction to produce a shell of titanium nitride. After nitridation, the powders of the high specific surface area showed electrical conductivity, which depended on the thickness of the coatings.

LiNbO3 single crystals were implanted at room temperature with Eu+ ions at 70 keV with fluence ranging from 0.5 to 5 × 1016 ions · cm−2. The damage in the implanted layer has been investigated by Channeling Rutherford Backscattering (RBS-C), and the oxidation states of the cations have been determined by x-ray photoelectron spectroscopy (XPS). Following implantation, a fully amorphized layer of 60 nm is generated, even for the lowest fluence employed. Subsequent annealing in air, in the range 800–1250 K, was applied to restore tentatively the crystallinity and promote the substitutional incorporation of Eu in the crystal. Only a partial recrystallization of the damaged layer was observed. For as-implanted samples, XPS spectra clearly reveal europium in Eu2+ and Eu3+ states, and the Nb5+ ions are driven to lower charge states.