LiNbO3 and LiTaO3 are very attractive and useful materials, which have been applied to piezoelectric and electro-optic devices. The authors have synthesized the stoichiometric crystalline fine powders and films of LiNbO3 at temperatures as low as 250°C by the controlled hydrolysis of double alkoxide solutions; and this method was used to prepare Li(Nb, Ta)O3 solid solution films with and without the preferred orientation. Water used during the processing played an important role in the low-temperature crystallization and the elimination of free carbon in the films. The water for the partial hydrolysis affected the properties of alkoxide solutions for dip-coating, and the morphologies of crystalline films. Water in a mixed gas flow with oxygen during calcination accelerated the crystallization of the alkoxy-derived films at low temperatures.

Epitaxial, single-crystal films of ZrO2 (Y2O3) were formed on (100) oriented single crystal substrates of ZrO2 (9.5 mol% Y2O3) using water-based solutions of zirconium acetate and yttrium nitrate as a precursor. Film compostions of ZrO2 (0 - 40 mol% Y2O3) were examined; since the lattice parameter of ZrO2 (Y2O3) increases with yttria content, the lattice mismatch was systematically varied to a maximum of 1.5%. Precursor films were deposited by spin coating, pyrolyzed, and held for 1 hour at 900°C, 1000°C, and 1100°C. X-ray diffraction showed that a strongly oriented film had developed after pyrolysis of the precursor. In addition, all samples, except those treated at 1100°C containing 6 – 15 mol% Y2O3, gave (111) peaks, indicating film polycrystallinity. Electron back-scattering patterns showed that epitaxial single crystals were formed at 1100°C for films containing 3 – 20 mol% Y2O3. Scanning electron microscopy showed that the epitaxial films had a porous structure. These results indicate that the epitaxy is a two-stage process: oriented nucleation upon pyrolysis, followed, for low mismatches, by subsequent consolidation into a single-crystal film above 1000°C.

Since many interesting and novel phenomena arise from non-linear interactions between two or more different materials with opposite properties, e.g., acid vs. base, p-type vs. n-type semiconduction, reducing vs. oxidizing, host vs. guest, conducting vs. insulating, etc., it is very important to design or set, the fields where the non-linear interactions take place. This is a very important aspect of materials design. The most interesting and probably most understandable study field for non-linear interactions is interfaces. Since design of interfaces is called “two-dimensional” design [1], and processing is necessary after design, processing may therefore be called “two-dimensional processing” for novel functions.

A preliminary experiment was conducted to prepare semiconducting strontium titanate-based internal barrier layer capacitors with ferroelectric Pb(Fe, W)O3 forming insulating layers along the grain boundaries. Processing, microstructure and the dielectric properties of this new type of BL capacitors are described. The idea to obtain this type of BL capacitors with a very high dielectric constant may be realized when the ferroelectric materials can uniformly be diffused along the grain boundaries by using a more sophisticated processing of the second firing.

Plasma-assisted chemical vapor deposition uses energetic electrons to decompose reactant gas molecules into more simple and more highly reactant species to achieve deposition of amorphous and crystalline films and coatings at reduced temperatures. The basis of this technique, as well as the deposition conditions and properties of several ceramic films including Al2O3, TiO2, ZnO, AN, BN, TiN, SiC, Si, GaAs, SiC, C (diamond) and GaN, are briefly described. Modifications of the classical immersed method, including remote plasmas, the use of microwave frequencies and electron cyclotron resonance techniques, are also described with material examples.

Questions about the mechanism of diamond film growth by low-pressure, plasma-assisted chemical vapor deposition methods have persisted for some time now. As an attempt to explore one aspect of the problem, we examine the energetics of several adsorbed diamond (111) surfaces. The adsorbates are mixtures of methyl groups and hydrogen atoms. The model for these systems is the molecular orbital hamiltonian of Dewar and coworkers.

From these calculations we find that H adsorbtion is preferred due both to bond energy and steric effects. Thus, nucleation of a cluster of three or more methyl groups, as assumed in earlier work, is energetically very demanding.

As part of an investigation of the dynamics that occur in the plume of a thermal spray torch, an experimental and analytical study of the deposition of yttria-stabilized zirconia has been accomplished. Experiments were conducted using a Taguchi fractional factorial design. Nominal spray parameters were: 900 A, 36 kW, 100 scfh argon primary gas flow, 47 scfh helium secondary gas flow, 11.5 scfh argon powder carrier gas flow, 3.5 lb/h powder feed rate, 3 in. spray distance, and an automated traverse rate of 20 in./s. The coatings were characterized for thickness, hardness, and microstructural features with optical microscopy, scanning electron microscopy, and x-ray diffraction. Attempts are made to correlate the features of the coatings with the changes in operating parameters. Numerical models of the physical processes in the torch column and plume were used to determine the temperature and flow fields. Computer simulations of particle injection (10 to 75 μm zirconia particles) are presented.

The investigation involved the synthesis of Si3N4 surface layers on a Ti substrate by a specially designed organosilazane liquid precursor, (CH3SiHNH)x with x=3 or 4, by pyrolysis with a 10.6 μm. continuous wave CO2 laser. Microstructural examinations revealed that the particles of the nitride layers were spherical in shape with diameters ranging from 50 to 150 nm. Based on the experimental evidence, suggestions are made of possible mechanisms occurring during film deposition.

Nanophase oxides (Al2O3, MgO, ZnO and TiO2), with typical grain sizes in the range 2–20 nm, have been synthesized by the condensation of ultrafine particles in a convective inert gas followed by their collection and in-situ consolidation in vacuum at ambient temperature. These new materials, owing to the reduced scale of their grains along with the enhanced cleanliness of their grain boundaries, are found to have significantly improved properties relative to those of their coarser-grained, conventionally-prepared counterparts. Nanophase rutile (TiO2) with an initial mean grain diameter of 12 nm, for example, has been found to sinter at 400 to 600°C lower temperatures than conventional rutile powders, without the need for compacting or sintering aids, while retaining a small grain size. Additionally, the importance of the extremely clean surfaces obtained with the gas condensation method has been demonstrated by comparing the sintering behavior of powders with and without air exposure prior to consolidation. The research completed on the processing and properties of nanophase ceramics is reviewed, and the potential for engineering advanced ceramics using the nanophase processing method is discussed.

The measurement of temperature in a microwave field is critical to the understanding of many phenomena which occur in materials heated in such an environment. Researchers have employed many techniques [1–4] to measure temperature in an electromagnetic field. This work examined three approaches: the use of a thermocouple, an IR meter, and a d. c. resistance technique.

Ceramic matrix composites can be formed by the directed oxidation of a doped molten aluminum alloy into an inert reinforcement or filler. The resultant ceramic matrix consists of interconnected Al2O3 and partially interconnected metal. The growth kinetics of this Al2O3 /metal ceramic matrix can be altered by numerous parameters. The effect of the growth atmosphere composition and temperature on the composite growth rate is dependent on the alloy dopant utilized. The ceramic matrix formation rate is also dependent on the alloy composition. Likewise, alloy composition has a profound effect on the mechanical properties and microstructure of the composites produced.

The Rapid Omnidirectional Compaction (ROC) technique has been applied successfully to the densification of TZP (3 mole % yttria) ceramics at 1260°C. The combination of high pressure (830 MPa) and temperature results in the plastic deformation of the ceramic particles. The extent of deformation, and consequently, the ROCing temperature, can be determined by using hot hardness of the ceramic material as an approximation of the ceramic's yield stress. The materials ROCed at 1260°C are characterized by a grain size of 0.15 gim, a flexure strength of 1300 MPa, a hardness of 1340 kg/mm2, and a fracture toughness of 5.0 MPa m1/2.

A recently developed technique combining photolithography, ion beam milling, and hot pressing allows the production of submicron-scale controlled-geometry, controlled-crystallography pore structures in controlled misorientation bicrystals, single crystal-polycrystal ensembles, and polycrystal-polycrystal ensembles. Such microdesigned interfacial structures provide a new tool for studying fundamental aspects of microstructural evolution. Current applications of the technique, opportunities for future research, and future extensions and refinements of the technique are described.

Two issues, packing powder/reinforcement systems and constrained densification, are reviewed. It is shown that pressure filtration has the greatest potential for packing powders containing reinforcements and packing powders within reinforcement preforms. High particle packing is achieved with repulsive interparticle potentials, and for a very small particle to reinforcement diameter ratio. It is now clear that individual reinforcements do not constrain the densification of powders. Shrinkage constraint is caused by a network of either nontouching or touching reinforcements. Network shrinkage (and thus composite shrinkage) caused by powder densification leads to the development of a denser interconnected matrix material surrounding lower density regions. Densification of the lower density regions requires the creep deformation of the denser continuum. As detailed elsewhere in this proceedings, grain growth causes this denser continuum to become more resistant to creep, and coarsening within the lower density regions causes desintering and the dissipation of sintering ‘stresses’. These phenomena do not occur during the densification of glass powders and explains the different densification behavior of crystalline powder matrices relative to glass powder matrices.

A Monte Carlo computer simulation that percolates soft-core, pseudographic whiskers in a discrete matrix has been developed, and two- and three-dimensional whisker percolation thresholds were determined for various whisker aspect ratios. The percolation thresholds were found to agree with the predictions of the excluded volume theory of percolation; moreover, the thresholds were found to coincide with the zero-shrinkage whisker fraction in ceramic matrix-ceramic particle composites.

A non-discrete Monte Carlo algorithm is used to model the packing of static rods. The results establish that inter-rod contact results solely from rod motion, not from space-filling effects. As the concentration of static rods is increased, clusters of aligned rods form and grow. The effects of rod motion are inferred through thermodynamic analysis. At sufficiently high rod concentrations, rod motion is expected to cause structural coarsening wherein the rods rearrange into larger but fewer clusters. These results should be considered when modeling the structure and mechanical behavior of whisker- and chopped-fiber-reinforced composites.

Whisker-reinforced ceramics have high potential for structural materials application due to their high fracture toughness and high mechanical strength. In this paper, rheological property and consolidation of the colloidal suspension in the alumina powder-silicon nitride whisker system were studied to control the microstructure and density of the green and hot-pressed composite. A12O3 particles of average diameter 0.15 μm and Si3N4 whisker of average size 0.4 μm × 3.7 μm were electrostatically dispersed in water in pH range 1–11 and consolidated by filtration. A welldispersed state of the composite suspension was achieved at low pH. Decreasing the viscosity while increasing the solid content of the suspension at the same time is the key step in making green compact with higher density and a narrower pore size distribution. These compacts were densified to relative density 98.4–99.4% by hot-pressing at 1500°C at a pressure of 39 MPa in N2 atmosphere.

Inert p articulate inclusions in ceramic powder compacts can obstruct densification behavior significantly. The factors that are the causes of this decrease in the sinterability are reviewed. It is concluded that the origin of the sintering difficulty resides in defects that processes such as die compaction introduce during the initial forming of the composite powder compact. Alternative processing methods are suggested that should minimize the negative effects of the dispersed inclusion phase on densification.

Densification experiments using ZrO2 single-crystal particles in an Al2O3 powder matrix were performed to examine the microstructural changes produced by constrained densification. Observations showed the formation of large, lowdensity regions within a denser material network. Enlargement of pores by desintering of necks between grains was observed during grain coarsening within these low-density regions. This pore opening behavior was also investigated in a model experiment.

Cold isostatic pressed (CIP) and slip cast Si3N4 composite materials containing up to 20 vol.% SiC-whiskers were densif led by pressureless sintering and post-HIPing. The slips were characterized by viscosimetry and showed no influence of whisker loading on the rheology of the highly concentrated aqueous suspensions up to 15 vol.! whiskers. During casting the whiskers were preferentially aligned parallel to the mould surface and the CIPed samples showed a 3-dimensional random whisker distribution. The influence of the whisker length and orientation on the densification behaviour was studied in a high-temperature dilatometer. While the CIPed samples exhibit an isotropic shrinkage behaviour, the slip cast samples showed a strong shrinkage anisotropy with a maximum linear shrinkage of 21% perpendicular and only 7% parallel to the whisker plane for the samples with 20 vol.% whiskers. With increased whisker loading, the sintered densities decreased from 0.99 to 0.88 fractional density. The poor sinterability of the composites was attributed to the sintering stresses around the non-sintering SiC- whiskers and the formation of a whisker network which inhibits further shrinkage in the final stage of sintering. Thermodynamic calculations show the optimum fabrication conditions for SIC-whisker reinforced Si3N4-composites.