The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.

The primary aim of this present work was to investigate the solubility, microstructure, thermal stability, AlN polytypes, and interfacial reactions in the SiC-AlN system. Alpha SiC particles of different sizes were incorporated into AlN and hot pressed at 2050 °C for 1 to 3 h. XRD, OM, STEM, WDS, and SAD patterns were utilized in analyzing phases, morphology, and distribution of elements. The surface area of SiC particles was found to have substantial effects on the formation of solid solution. Multilayered polytypes, which are usually associated with stacking faults, grew and impeded one another. Additionally, the number of planes between subsequent stacking increased with the increase of either hot-pressing temperature or time. Affinity of oxygen to AlN probably played an essential role in the formation of polytypes and stacking faults.

Stoichiometric β-SiC powders have been successfully prepared by solid state reaction of elemental silicon and carbon powders via the mechanical alloying process. The mechanical alloying process was performed in a high-energy ball mill under argon gas flow at room temperature. The solid-state reacted alloy powders have been characterized as a function of the milling time by means of x-ray diffraction, infrared absorption, scanning and transmission electron microscopy, and chemical analysis. Complete fcc-SiC (β-phase) alloy powders were obtained after 1080 ks of continuous milling. The lattice parameter (a0) of the formed β-SiC was calculated to be 0.4357 nm. No free silicon and/or carbon crystals were observed. The existence of transverse optical (TO) and longitudinal optical (LO)-like phonon modes is observed for the end-product alloy powders. Mechanically alloyed β-SiC powders are stable at elevated temperatures (1773 K) and did not transform to any other phases. The end-product β-SiC alloy powders possess excellent morphological properties, such as homogeneous shape (spherical morphology) with fine and smooth surface relief and uniform size (less than 0.5 μm in diameter). The fabricated β-SiC alloy powders have fine cell-like structure with nanoscale dimensions of about 7 nm.

Epitaxial thin films (4–1000 Å) of Ti contacts have been deposited via UHV electron beam evaporation at room temperature on monocrystalline, n-type, alpha (6H)-SiC(0001). The interfacial chemistry and microstructure, and the electrical properties, were investigated at room temperature and after annealing at 700 °C up to 60 min. High resolution TEM analyses revealed the formation during annealing of reaction zones consisting of Ti5Si3 and TiC. The corresponding electrical properties exhibited considerable stability except after an initial 20 min anneal. Current-voltage (I-V) measurements showed that the Ti contacts were rectifying with low ideality factors (n < 1.09) and typical leakage currents of 5 × 10−7 A/cm2 at −10 V. The Schottky barrier heights calculated from x-ray photoelectron spectroscopy and I-V and V-V measurements were between 0.79 and 0.88 eV for the as-deposited contacts and between 0.86 and 1.04 eV for the annealed contacts.

A mixed alkoxide liquid precursor was used to form epitaxial PbTiO3 thin films by spin-coating on cubic (001) SrTiO3 substrates. The films were heat-treated at temperatures between 380 °C/1 h and 800 °C/1 h. X-ray diffraction, atomic force microscopy, scanning and transmission electron microscopy were used to characterize the microstructure of the films and to evaluate the epitaxial phenomena. At ∼400 °C/1 h, a polycrystalline, metastable Pb-Ti fluorite crystallizes from the pyrolyzed amorphous precursor. At slightly higher temperatures (∼420 °C/1 h), the thermodynamically stable phase with the perovskite structure epitaxially nucleates at the film/substrate interface. A small number of epitaxial grains grow through the film toward the surface and consume the nanocrystalline fluorite grains. Coarsening of the perovskite grains leads to a reduction in mosaic spread during further heating. Pores, which concurrently coarsen with grain growth, produce a pitted surface as they disappear from within the film. At 800 °C/1 ha dense epitaxial PbTiO3 film with a smooth surface is observed. Parameters governing the formation of a- and c-domains are discussed as well as the small tilts of the domain axes away from the substrate normal.

Self-assembled monolayers (SAMs) bearing sulfonate (-SO3H) surface functional groups, on single-crystal Si wafers, were used as substrates for the deposition of TiO2 thin films from aqueous solutions. Polycrystalline TiO2 thin films over 50 nm thick formed in 2 h by hydrolysis of TiCl4 in aqueous HCI solutions at 80 °C. The films were pore-free, showed excellent adherence and uniformity, and consisted of anatase crystallites 2–4 nm in diameter. Annealing at temperatures up to 600 °C caused coarsening of the anatase grains, but no loss of adherence or structural integrity.

Crystalline, uniform, adherent, ultrathin films of TiO2 were deposited onto OH-functionalized organic self-assembled monolayers (SAMs) on single-crystalline Si at low-temperature (<100 °C) from anhydrous ethanolic solutions of titanium isopropoxide. The films were identified as TiO2 by x-ray photoelectron spectroscopy, electron diffraction, and energy-dispersive x-ray microanalysis. Transmission electron microscopy showed the films to be uniform in thickness (2 ± 0.5 nm) and continuous. On bare Si, in contrast, there was no evidence of TiO2 deposition under identical conditions. Unlike the anatase films deposited on SAMs from aqueous solutions (described in the preceding paper), the electron diffraction patterns of the films deposited from alkoxide solutions suggest that they were the rutile phase. It is suggested that the functionalized SAMs enable the anchoring of the Ti alkoxide and initiate the formation of an adherent oxide film, and that they are sufficiently uniform that the resulting film is continuous and uniform in thickness.

Sol-gel Sr2Nb2O7 thin films were deposited on Si(100) and Pt-coated Si substrates for the first time by spin-coating. The Sr2Nb2O7 precursor solution was prepared from strontium metal dissolved in 2-methoxyethanol, acetylacetone, and niobium ethoxide. The formation of phase pure Sr2Nb2O7 occurred via an intermediate perovskite phase of composition close to Sr0.82NbO3. Crack-free Sr2Nb2O7 films of ∼0.4 μm thickness were deposited on these substrates using a single-coating followed by heat treatment at 850 °C for 12 h. SEM microstructure and thin film XRD results indicated the deposition of a grain-oriented film on the Pt-coated Si substrate. The room temperature dielectric constant and the loss values of the film measured at 10 kHz are 45 and 0.045, respectively.

The structure and electrical properties of multi-ion beam reactive sputter (MIBERS) deposited barium strontium titanate (BST) films were characterized in terms of Ba/Sr ratio, substrate temperature, annealing temperature and time, film thickness, doping concentration, and secondary low-energy oxygen ion bombardment. Films deposited onto unheated substrates, followed by annealing at 700 °C showed lower dielectric constant (<200), compared to a dielectric constant of about 560 for those deposited at elevated temperatures, probably due to reduced voids. Two types of microstructures (type I and type II) were observed depending on the incipient phase of the as-grown films, which also led to two types of time domain dielectric response, Curie-von Schweidler and Debye type, respectively. The current-voltage (I-V) characteristics of type II films doped with high donor concentration showed a bulk space-charge-limited conduction (SCLC) with discrete shallow traps embedded in a trap-distributed background at high electric fields. The I-V characteristics of bombarded films deposited at higher substrate temperatures showed promising results of lower leakage currents and trap densities.

The synthesis of β-sialon has been carried out by heat treatment in nitrogen flow of Spanish coals or mineral graphite, both with a high content of mineral matter. The results were compared with those obtained with conventional clay/carbon mixtures. The coals and, especially, the mineral graphite produced a very high yield of β-sialon, with a faster reaction rate than the clay/carbon mixtures due to the more intimate contact among the reactants, with the additional advantage of forming much a lower proportion of vitreous phases. On the other hand, the results show that in the particular case of graphite, the use of high temperatures (even above 1450 °C) does not lead to changes in the crystalline phases of the product, allowing the synthesis to be carried out over a wider temperature range than that used for clay/carbon mixtures. The mechanical properties of the sintered artifacts obtained with the sialon synthesized from natural graphite are superior to those prepared from clay/carbon mixtures and comparable (or even superior) to commercial artifacts manufactured from much more expensive precursors.

This paper presents neutron and ion radiation effects in the Nicalon SiC polymer precursor fiber. It is shown that the serious structural degradation of this fiber and its composites (e.g., CVD SiC/Nicalon) previously reported for the standard grade of Nicalon is primarily due to the presence of the silicon oxycarbide phase. Results supporting this interpretation include microstructural analysis as well as post irradiation mechanical property measurements. Preliminary results of the effects of irradiation on low-oxygen Nicalon fibers are presented. The reduced oxygen content fibers exhibit radiation-induced density, strength, and Weibull's and Young's moduli changes typical of monolithic ceramic materials. This contrasts sharply with the poor irradiation behavior of the standard Nicalon fiber and suggests that improved radiation resistance can be expected in SiC/SiC composites fabricated with low oxygen Nicalon fibers.

Materials with nanocrystalline features are expected to have improved or unique properties when compared to those of conventional materials. Methods for the practical and economical production of nanoparticles in large quantities are not presently available. A method based on combustion synthesis for preparing nanocrystalline powders was investigated in this work. Yttria-doped zirconia powders with an average crystallite size of 10 nm were synthesized. The characteristics of the powder (e.g., surface area and phase content) were found to depend strongly on the fuel content in the starting mixture and on the ignition temperature used in the process. The method is expected to be suitable for commercial fabrication of nanocrystalline multicomponent oxide ceramic powders.

Nanocrystalline powder with an average crystallite size of 8–12 nm, which was produced by a combustion synthesis process, was used to prepare dense, nanocrystalline articles. Green compacts of high green density were prepared by dry pressing and densified by a fast-firing process. During fast-firing, the dwell temperature significantly affected the final grain size and final density. On the other hand, the ranges of heating rates and dwell times that were used had a much less significant effect on the final density and final grain size. It was determined, however, that a high final density (>99% ρth) and a very fine final average grain size (<200 nm) can be simultaneously achieved under three different firing conditions. The high densification rates are, in part, a result of the minimal coarsening that the particles undergo when the sample is taken rapidly through the temperature regime in which surface diffusion predominates to the temperature regime in which the densification mechanisms of grain boundary and lattice diffusion predominate.

Nanocrystalline zirconia doped with 0–10 mol % Y2O3 has been prepared by a combustion synthesis process, followed by a rapid densification process. The concentration of Y2O3 in the as-reacted zirconia appeared to have a significant influence on the reduction of the crystallite size, in the combustion temperature range studied (450 °C–550 °C), as well as on the stabilization of the tetragonal and/or cubic phases. The green compacts were densified by a fast-firing process. During fast-firing, the dwell temperature significantly affected the final average grain size and the final density of the article. On the other hand, the ranges of heating rates and dwell times that were used in this study were shown to have a much less significant effect on the article's final density and final average grain size. The yttria content had the largest influence on the final density and final average grain size. The densification took place much more rapidly in the 4 mol % Y2O3-ZrO2 samples than in the 10 mol % Y2O3-ZrO2 samples. In particular, the difference in densification rates between the samples with different Y2O3 content was attributed to the influence and magnitude of the associated grain-growth process. It was determined, however, that a high final density (>99% ρth) and a very fine final average grain size (<200 nm) could be simultaneously achieved with each of three different heating rates for the 4 mol% Y2O3-ZrO2 articles.

A SHS process has been established for synthesis of AlN powder under low nitrogen pressures. Al and NaN3 powders were used as the metal and nitrogen sources, respectively. The compact of the mixture of the reactants was wrapped up with aluminum foil and then wrapped up with an igniting agent (i.e., Ti + C). The synthesis reaction was triggered by the combustion of the igniting agent. The wrappings were found necessary in achieving high product conversions under low nitrogen pressures (<1 MPa). The product conversion was also affected by the reactant composition and the nitrogen pressure. High conversions were obtained when the mass ratio of Al to NaN3 was 1/2 or lower and the nitrogen pressure was 0.5 MPa or higher. The AlN powders as synthesized were observed to have two major types of morphology, i.e., granular particles with 0.5–3 μm in diameter and fibers with aspect ratios of 10–800.

The absorption of hydrogen and carbon monoxide at room temperature by palladium and 5% ruthenium-palladium foils was studied using thermal desorption spectroscopy. It was found that hydrogen readily diffused in the palladium and desorbed as one broad peak at about 650 K. Plots of the In (rate) versus inverse absolute temperature indicate that the desorption order is n = 1.25 and the activation energy is about 8.5 Kcal/mol. Carbon monoxide is adsorbed, as two different states, on the surface of the foil and complete coverage is quickly reached below 100 L. Hydrogen also diffuses in 5% ruthenium-palladium foil but to a lesser degree. Two hydrogen desorption peaks are observed in the Ru-Pd alloy. The desorption traces can be fitted with two peaks and the desorption orders are n = 2 for the first peak and n = 1.25 for the second peak. Activation energies of 10.7 and 5.6 Kcal/mol are obtained for the first and second hydrogen peaks, respectively. The first hydrogen desorption peak is regarded as hydrogen desorbing from the surface sites while the second peak is regarded as hydrogen diffusing from below the surface. Activation energies for bulk diffusion were obtained from hydrogen uptake measurements using a sensitive microbalance. These energies corresponded to 4.4 Kcal/mol for Pd foil and 4.9 Kcal/mol for the Ru-Pd alloy. Discussion about the relation between these results with prior studies of hydrogen adsorption on Pd single crystal is included. The appearance of a fractional order for hydrogen desorption is also discussed.