Stoichiometric β–SiC thin films with a high preferred orientation of (111) planes were successfully deposited on Si(100) substrates at a relatively low temperature of 1050 °C from the mixture of methyltrichlorosilane (CH3SiCl3 or MTS) and H2 in a hot wall LPCVD reactor. No etching of the Si substrate and smooth topography of the deposit were observed at high H2/MTS ratios and/or low deposition pressures. The presences of excess silicon, excess carbon, or incorporated hydrogen atoms in the films were not detected. Poor topography, degradation in preferred orientation, and etching of the Si substrate were observed at high values of deposition pressure, MTS concentration, and temperature. The etching on the Si substrate was due to the out-diffusion of Si atoms from the substrate and the presence of Cl-containing radicals resulting from the decomposition of MTS molecules while transporting to the Si substrates. A deposition mechanism was proposed to model the deposition of SiC in a hot wall reactor by using (1) gas phase decomposition of MTS molecules, (2) adsorption of the intermediates on the surface, and (3) reaction of the adsorbed intermediates to form SiC. The deposition rates were predicted very well for various deposition conditions in a hot wall LPCVD reactor.

Microwave-hydrothermal processing has so far been used only to dissolve inorganic solids for chemical analysis. We report herein the use of microwave-hydrothermal processing to synthesize various ceramic powders in binary and polynary systems. We describe the synthesis of some electroceramic powders such as BaTiO3, SrTiO3, Sr0.5Ba0.5TiO3, PbTiO3, BaZrO3, SrZrO3, Pb(Zr0.52Ti0.48)O3, and pyrochlore phases with the Pb(Mg1/3Nb2/3)O3 and Pb(Zn1/3Nb2/3)O3 compositions by this novel microwave-hydrothermal processing technique.

We report measurements and analysis of fracture-induced photon and electron emissions from several polymeric and inorganic systems on time scales of 10−2 to 103 s following fracture. The dominant mechanism for postfracture emission involves the recombination of mobile free carriers (usually electrons) with immobile recombination centers. The emission decays were modeled as (pseudo)unimolecular and bimolecular recombination on fractal lattices as described by Zumofen, Blumen, and Klafter.1 Although the decay kinetics shows a great deal of variability from material to material, this random walk description of the recombination process provides an excellent description of the emissions over long time scales. This analysis shows a strong correlation between the local structure at the fracture surface and the resulting decays.

The ion-exchange selectivity of divalent transition metal ions on cryptomelane-type manganic acid (CMA) with tunnel structure has been studied using the distribution coefficients (Kd) at a small fractional exchange in nitrate media. All metal ions studied showed linear relationships with a slope of −2 on the log-log plot of Kd vs [HNO3] which clearly indicated that the adsorption process is an “ideal” ion-exchange. The selectivity increased in the following order: Pb ≫ Mn > Co > Cu > Hg > Cd > Zn > Ni. The high selectivity of the manganic acid was successfully utilized in the removal of Co2+ from seawater and tap water.

An infinite cylinder model was used to predict the optical transmission of transparent composites containing unidirectionally aligned glass fibers. The parameters used in the model are the volume content and diameter of the glass fibers, the refractive index of the fiber and matrix, the nonwet fiber content, the thickness of the composite, and the temperature coefficient of the refractive index of the matrix. The transmission calculated from the model agreed well with the measured temperature-dependent transmission of a composite from 20 to 70 °C for thin specimen (<1.0 mm) containing fiber less than 10 vol. %. The model showed that a small amount of nonwet fiber (0.7% of fiber content) could cause a substantial reduction in the maximum transmission. The content of nonwet fibers should be as small as possible for making a highly transparent composite.

Isotherms (at 300 K and 328 K) and isobars (in the range 300 to 400 K) of n-pentane intercalation in CsC24 and CsC36 were established. With CsC24, three plateaus were identified at 0.52, 0.7, and 1.0 n-pentane/24 C, whereas only two plateaus at 0.8 and 0.97 n-pentane/36 C were found with CsC36. The progress of the reaction between n-pentane and CsC24, CsC36, and CsC56 (stage 2 to 4) was monitored by real-time neutron diffraction. The intercalation of n-pentane in CsC24 results in the simultaneous formation of a second stage ternary and a first stage binary “CsC8”, whereas, from the third stage CsC36 or the fourth stage CsC56, only pure second stage or third stage ternary compounds are formed, respectively. Owing to the formation of binary domains rich in alkali metal (CsC8) or to stage lowering produced by the ternarization, the in-plane cesium density is smaller in the ternary layer than in the starting binary. The electrostatic repulsion between the cesium ions, provoked by the sorption of n-pentane, is believed to be at the origin of the increased coverage. During the intercalation or de-intercalation processes, three-dimensional segregation occurs in each grain. A pleated layer model with canted fronts is presented. It accounts for the various phases present within each grain and for the structural transformations caused by pressure variations. At room temperature, the ternary layer seems to be disordered. The order-disorder transition appearing either by decreasing the temperature or by increasing the n-pentane pressure is correlated to a hindered motion of the intercalated molecules.

In this work, we explore the use of the chemical vapor composites (CVC) process to increase the rates of silicon carbide (SiC) growth on graphite substrates. Large SiC seed particles are used that are deposited by gravity-driven sedimentation. The results show that addition of large (dp = 28 μm) SiC seed particles to a gas phase containing hydrogen and methyltrichlorosilane increases the deposition rate of SiC by amounts substantially higher than that expected from the addition of the particle volume alone. Insight into the mechanism of this deposition rate enhancement is obtained through analysis of SEM photographs of deposits. Growth rates and deposit structures are consistent with the trends predicted by the previously developed random-sphere model of simultaneous particle-vapor deposition (RASSPVDN), which is used here to interpret the data.

Aluminum nitride (AlN) ceramic samples exhibit a dramatic photo-darkening when exposed to UV radiation. In this paper, this phenomenon has been investigated utilizing photo-induced absorption measurements, where the transmission of a visible probe beam is monitored before and after exposure to a UV pump beam. Changes in the probe transmission as large 60% have been observed. The results of this study show that the center responsible for the photo-induced absorption process is an aluminum vacancy-oxygen impurity complex which resides in the AlN lattice. An energy level diagram is constructed which is consistent with these experimental findings.

A simple model which is able to account for the distribution of matrix crack spacings as a function of applied stress in unidirectional fiber-reinforced brittle materials has been used to generate stress-strain curves for such materials up to the maximum stress level at which transverse matrix cracking can occur when a tensile stress is applied parallel to the length of the fibers. The results give an insight into how to tackle the experimental problem of determining accurately the level of first-matrix-cracking stress in such materials.

A rapid in situ diffraction technique, synchrotron radiation–energy dispersive diffraction, has been used to obtain direct information on the kinetics of the tetragonal-to-monoclinic transformation temperatures for zirconia synthesized by heating the hydroxide up to temperatures between 900 and 1300 °C. In all cases the monoclinic phase appears only during the cooling stage. The effects of chemical (hydroxide preparation–pH) and heat treatments (top dwell temperature and dwell time) have been investigated. The transformation temperature increases with both top temperature and dwell time. For the lesser heat treatments (generally temperatures <1000 °C) the high-pH material displays the higher transformation temperatures, whereas with greater heat treatments (generally temperatures >1000) the low-pH material displays the higher transformation temperatures. These data do now give reliable indications on how to design a required metastability into the final room temperature product.

The operative and controlling mechanisms of steady-state creep in hot-pressed AlN have been determined both from kinetic data within the temperature and constant compressive stress ranges of 1470 to 1670 K and 100 to 370 MPa, respectively, and from the microstructural results of TEM. No secondary phases were detected in the bulk or at the grain boundaries using Raman spectroscopy and HREM. The stress exponent was ≍1.0 at all temperatures. The activation energies ranged between 558 and 611 kJ/mol. The most prominent microstructural features of the crept samples were elongated grains, strain whorls, and triple-point folds. Dislocations were generated only at the strain whorls in order to relieve the localized stress caused by intraboundary mechanical interaction among the grains. They contributed little to the observed deformation. The controlling mechanism for creep was diffusion-accommodated grain-boundary sliding. This mechanism was accompanied in parallel by relatively small amounts of unaccommodated grain-boundary sliding. Cavitation was not observed.

An experimentally verified model, which quantifies the degradation and diffusion of organic vehicle during pyrolysis of a ceramic molding in the shape of an infinite cylinder, has been modified to accommodate the various effects of porosity development as degradation proceeds. Thus, in the first case, a shrinking radius has been taken into account as organic matter recedes. Secondly, the formation of uniformly distributed porosity is considered as organic vehicle is removed. In each of these instances, the model predicts the critical heating rate and temperature at which boiling occurs in the ceramic body, giving rise to internal defects for various cylinder radii.

The roles of additives (MnO2, SiO2, and CdO) in controlling microstructural development and piezoelectric properties of Pb(Ni1/3Nb2/3)O3– PbTiO3–PbZrO3(PNN–PT–PZ) ceramics were systematically examined. The addition of SiO2 (<1 wt. %) to the pseudoternary PNN–PT-PZ system enhances densification, but suppresses grain growth significantly. On the other hand, the presence of MnO2 expedites the rate of grain growth without increasing the rate of densification appreciably. The observed difference in the grain-growth behavior was discussed in terms of the viscosity of liquid phase formed during sintering and the diffusion-controlled process for the solute-atoms transport. The rapid increase in the mechanical quality factor (Qm) and the decrease in the relative dielectric permittivity (∊r) and d33 for the MnO2-doped specimens indicate the formation of oxygen vacancies by the dissolution of Mn-atoms into the B-sites of perovskite structure. On the contrary, the presence of CdO (2 mol %) remarkably increases ∊r and d33 of PNN–PT–PZ ceramics.

The dielectric constant of tetracyanoquinodimethane (TCNQ) single crystals has been obtained by reflection electron energy loss spectroscopy (REELS) over the 0–60 eV energy range, using primary electron energies ranging from 0.5 to 1.5 keV at an incidence angle of about 40°. A self-consistent method is discussed concerning the evaluation of the surface and bulk contributions to the loss spectra. As a result, for the first time, the Im(−1/∊) function and the dielectric constant of TCNQ have been deduced in such a wide energy range. According to the results obtained by other authors, the low-energy loss spectral profile is characterized by two main structures ascribed to the π → π∗ dipole-allowed transitions located at about 3.5 and 6.5 eV while, at higher energy loss, the π + σ plasmon, centered at about 21.5 eV, dominates the spectrum. The differences among the spectra taken at different primary energies are interpreted as due only to surface effects, more evident in the low-energy-loss spectral region. The results are in good agreement with those obtained by recent transmission-mode (TEELS) experiments.

The temperature variation of the thermal conductivity, the electrical resistivity, and the thermoelectric power of a graphitized polyimide film have been measured in the temperature range 2 < T < 300 K. The effect of the electrochemical intercalation with FeCl4− ions has also been studied. The thermal conductivity measurements confirm the high degree of graphitization that may be obtained with polyimide films. They show how intercalation increases the structural disorder and how the intercalate substantially contributes to the thermal conductivity at low temperatures. The electrical-resistivity and thermoelectric-power measurements reveal that the density of free carriers is about three times lower in stage-2 FeCl4− solvated intercalation compounds obtained by an electrochemical way than in stage-2 FeCl3 compounds obtained by a classical synthesis method.

Nanocrystalline α–Fe, Fe3C, and Fe7C3, particles with narrow size distributions were produced by CO2 laser pyrolysis of vapor mixtures of Fe(CO)5 and C2H4. Details of the synthesis procedure are discussed. Mossbauer spectroscopy and x-ray diffraction were used to identify the structural phases and the former was used also to study the magnetism of the nanoparticles. All the nanoparticles were observed to be ferromagnetic in this size range. If excess C2H4 appears in the reactant gas mixture, several monolayers of pyrolytic carbon were observed to form on the particle surface, as deduced from transmission electron microscopy and Raman scattering studies. Results of thermo-gravimetric analysis/mass spectroscopy studies of this carbon coating indicate it is gasified in hydrogen at temperatures T ∼ 250 °C.

ZrO2 thin films were deposited at 1 atm on Si substrates by oxidation-assisted thermal decomposition of zirconium-trifluoroacetylacetonate in the temperature range of 300–615 °C. Above a deposition temperature of 400 °C, the deposited thin films have a columnar grain structure, where each grain is perpendicular to the substrate surface with a c-axis preferred crystallographic orientation, and have poor electrical characteristics as a dielectric thin film. But the thin film deposited at 350 °C has a fine equiaxed microcrystalline structure and has superior electrical characteristics of a breakdown field of 1 MV/cm and a relative dielectric constant of 27.

Molybdenum disulfide is a technologically important solid phase lubricant for vacuum and aerospace applications. Pulsed laser deposition of MoS2 is a novel method for producing fully dense, stoichiometric thin films and is a promising technique for controlling the crystallographic orientation of the films. Transmission electron microscopy (TEM) of self-supporting thin films and cross-sectional TEM samples was used to study the crystallography and microstructure of pulsed laser deposited films of MoS2. Films deposited at room temperature were found to be amorphous. Films deposited at 300 °C were nanocrystalline and had the basal planes oriented predominately parallel to the substrate within the first 12–15 nm of the substrate with an abrupt upturn into a perpendicular (edge) orientation farther from the substrate. Spherically shaped particles incorporated in the films from the PLD process were found to be single crystalline, randomly oriented, and less than about 0.1 μm in diameter. A few of these particles, observed in cross section, had flattened bottoms, indicating that they were molten when they arrived at the surface of the growing film. Analytical electron microscopy (AEM) was used to study the chemistry of the films. The x-ray microanalysis results showed that the films have the stoichiometry of cleaved single crystal MoS2 standards.

The Li2O–B2O3–H2O system has been studied under hydrothermal conditions (T = 250 °C, P < 100 bars). The phases crystallizing in this system are Li4B7O12Cl, Li2B4O7, Li3B5O8(OH)2, LiH2B5O9, and Li2HBO3. Some of these phases are new ones. Their fields of crystallization are shown in the composition diagram. The growth and characterization of these lithium borates obtained in the system Li2O–B2O3–H2O under lower PT conditions have been discussed in brief.

The hot corrosion of single crystal and polycrystalline aluminas has been investigated in SO2–SO3–O2 environments and in the presence of molten Na2SO4-based deposits at temperatures of 700 and 1000 °C. The effect of microstructure and impurities on the corrosion has been emphasized. Weight changes and wetting angles were determined, and the evolution of the morphology of the exposed substrates and the reaction products was investigated in detail. The corrosion was small under the conditions of this study and generally increased with the impurity content of the polycrystalline aluminas. Based on the experimental results, particularly those obtained by electron microscopy and microanalysis using the SEM/EPMA (scanning electron microscope–electron probe microanalyzer), mechanisms are proposed for the corrosion of polycrystalline aluminas which emphasize the role of the silicate impurities and the synergy of their corrosion with that of the alumina grains. As a result, the alumina grains were dissolved by acidic fluxing under the acidic and the basic experimental conditions.