A comparative dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA) study was performed in the investigation of mullite and spinel formation from slowly hydrolyzed single phase gels with Al/Si ratios ranging from 1/1 to 14/1. Both metastable tetragonal mullite and spinel were observed to form at temperatures <1000 °C in the gels with Al/Si ratios <8/1 and mullite transformed to the orthorhombic structure at ∼1250 °C. However, at higher Al/Si ratios, spinel was the only crystalline phase detected at <1000 °C and orthorhombic mullite formed directly at temperatures >1250 °C. As the Al/Si ratio increases, both the tetragonal mullite and spinel formation temperatures decrease while the orthorhombic mullite formation temperature increases. Based on the Al/Si composition where the formation extents of tetragonal mullite and spinel were maximum, their compositions are estimated to be 2Al2O3 · SiO2 and 6A12O3 · SiO2, respectively.

PAN-based activated carbon fibers were saturated by dye adsorption and then were regenerated by thermal treatment in carbon dioxide and in air. The dye adsorption and the regeneration were carried out in several cycles. The changes in fiber physical properties and the capacity of dye adsorption will be discussed. Activated carbon fibers regenerated in air had greater dye adsorption and weaker mechanical properties than those regenerated in carbon dioxide. The preferred orientation changed slightly during air reactivation, but it decreased gradually after carbon dioxide regeneration. The regeneration processes led to a decrease in the weight and degradation of mechanical properties, but the processes increased the capacity of dye adsorption. After the second regeneration, the dye adsorption capacity of activated carbon fibers that were recycled by air regeneration was 15% higher than those that were recycled by carbon dioxide regeneration. But, after the third regeneration, the fibers recycled by air regeneration lost their mechanical properties. For carbon dioxide regeneration, fibers retained satisfactory mechanical properties even after the fourth regeneration. This study indicates that multiple effective applications can be accomplished with carbon dioxide treatment in place of air regeneration. The structural changes of activated carbon fiber during different regenerations are proposed.

α-SiC crystals were implanted with aluminum to a high dose at room temperature or 800 °C. Transmission electron microscopy showed that SiC was amorphized by room temperature implantation but remained crystalline after 800 °C implantation. Crystalline aluminum carbide was formed and aluminum redistribution took place in SiC implanted at 800 °C. Implanted and unimplanted crystals were oxidized in 1 atm flowing oxygen at 1300 °C. Amorphization led to accelerated oxidation of SiC. The oxidation resistance of SiC implanted at 800 °C was comparable with that of pure SiC. The oxidation layers formed on SiC implanted at both temperatures consisted of silica embedded with mullite precipitates. The phase formation during implantation and oxidation is consistent with thermodynamic predictions. The results from our current and earlier studies suggest that there exists an optimum range of implantation temperature, probably above 500 °C but below 800 °C, which preserves the substrate crystallinity and retains the high aluminum dosage, for the enhancement of oxidation resistance of SiC.

Microwave dielectric properties and microstructures of BaPr2Ti4O12 and BaPr2Ti5O14 ceramics which have extremely similar crystal structures, were investigated, including those of the solid solution represented by the formula of Ba6−xPr8+2x/3Ti18O54 ceramics. It is suggested that BaPr2Ti5O14 ceramics are composed of mixed phases, approximately 85.0 vol. % Ba4.05Pr9.3Ti18O54 (x = 1.95), 8.1 vol. % TiO2, and 6.9 vol. % BaTi4O9. The microwave dielectric properties of the Ba6−xPr8+2x/3Ti18O54 system are strongly dependent on the x value, which is interesting for studying the relationship between microstructures and dielectric properties. Far infrared reflection spectra were also measured to study the mixed phases formed in these ceramics in more detail.

High-pressure, high temperature (HPHT) annealing of synthetic type I diamond crystals at 1200–1700 °C and 50–60 kbar was found to induce aggregate-nitrogen dissociation and metal coalescence as well as heal diamond lattice dislocations. For crystals with low levels of metal inclusions, HPHT annealing was observed to increase the average compressive fracture strength of the crystals by apparently strengthening the strongest crystals of the population. Crystals with high metal-content, or otherwise of low quality, are weakened by anncaling. Strengthening is believed to occur by locally stabilizing the diamond lattice by healing lattice dislocations as well as dispersing nitrogen within the lattice. A general model is presented that ties together these results with those of other researchers.

The humidity-sensing electrical properties of heterocontacts between p-type La2CuO4 and n-type ZnO semiconductors, and of the single oxides, as a comparison, were studied. The heterocontacts was prepared by mechanically pressing sintered disks of the two oxides. The electrical characterization of the heterocontacts was carried out using dc and ac measurements at various relative humidity (RH) values, in order to evaluate the sensing mechanisms and the electrical properties of these p-n junctions. Their humidity sensitivity was explained in terms of the variation of the barrier height at the p-n junctions, due to the saturation of the original interface states by physisorbed water, which leads to the release of trapped electrons, resulting in an increase in the forward current. The higher the number of interface states, the higher the RH-sensitivity of the heterocontacts. Electrochemical impedance spectroscopy (EIS) measurements showed, at 90% RH, a distribution of capacitances with different relaxation times, which may be caused by the electrolysis of water molecules at p-n junction sites. For their use as humidity sensors, they showed a response of 4 orders of magnitude in the whole RH range tested, and a fast response time. The response of the heterocontacts was bias-dependent, tunable by externally applied electric field. They also have stand-by capability and a self-cleaning mechanism, which allow them to be described as intelligent materials.

Boron-doped diamond films have been grown by the hot filament chemical vapor deposition process. The feed gas was a mixture of argon, bubbled through a solution of B2O3 in ethanol, and hydrogen. The highest growth rate was 0.7 μm/h. The boron concentration in the films depended on the concentration of B2O3 in the ethanol. The highest boron doping level, as measured by secondary ion mass spectroscopy, was 6300 atomic ppm. Raman spectroscopy and x-ray diffraction both confirmed the presence of crystalline diamond in the films. The frequency of the diamond Raman line decreased with increasing boron concentration. This shift may arise from an interaction of the charged carriers (holes) produced by the boron doping and the Raman-active optic phonon. The oxidation rates of doped and undoped films were measured by thermogravimetric analysis at 700 °C in flowing high purity oxygen. Films with a boron concentration of 6300 ppm oxidized at one-tenth the rate of undoped diamond. A layer of B2O3, detected on the surface of an oxidized B-doped film, is believed to act as a protective barrier that decreases the oxidation rate.

Intercalation of AlCl3 into stage 2 FeCl3-graphite intercalation compound (GIC) using an ordinary two-bulb method has been studied by x-ray diffraction. Stages 2, 3, and 4 ternary AlCl3-FeCl3-GlC's are obtained when the temperatures of the stage 2 FeCl3-GIC were set at T (GIC) = 503, 523, and 553 K, respectively, for the AlCl3 intercalate material at T (AlCl3) = 473 K, that is, the vapor pressure of (AlCl3)2 (g) of the main vapor species to be held at p {(AlCl3)2} = 2.4 × 105 Pa. However, for the temperature of the stage 2 FeCl3-GIC at T (GIC) = 573 K, the (AlCl3)2 (g) vapor is found to promote the decomposition of the stage 2 FeCl3-GIC, resulting in the formation of graphite. The decomposition of the stage 2 FeCl3-GIC is considered to take place because the complex AlFeCl6 (g) in the gas phase, which is formed from both (AlCl3)2 (g) and FeCl3 existing at the edge of the FeCl3-GIC, is thermodynamically more stable than the FeCl3 and AlCl3 intercalates in their GIC at p {(AlCl3)2} = 2.4 × 105 Pa and T (GIC) = 573 K.

Polycrystalline LiTaO3 (LT) thin films have been prepared on (001)Si substrates by the sol-gel method. A Li-Ta double alkoxide prepared from lithium methoxide and tantalum ethoxide precursors was spin coated on Si and heated up to 950 °C. The dependence of the film quality upon the process variables, alkoxide concentration before hydrolysis, the water to double alkoxide ratio, and the final double alkoxide concentration, has been established. Preferential alignment of the (104) LT planes was observed parallel to the (100)Si surface. Most films present resistivities of the order of 30 kΩ · cm and breakdown field in excess of 200 kV/cm.

A Scanning Force Microscope (SFM) is employed to indent and image surfaces with sub-micron resolution. The SFM image shows the area and depth of each indentation as well as its location with respect to nearby topographic surface features. The image also reveals the surface roughness, which can set a lower limit on useful nanoindentation size. A cross section of a nitrided steel surface is measured to illustrate the method. The use of the SFM with separate tip-cantilever structures for indenting and imaging has significant advantages over other nanohardness methods for the study of samples with lateral inhomogeneities.

Measurements of fiber strength utilization (FSU) in unidirectional carbon/carbon (C/C) composites as a function of heat-treatment tempcrature (HTT) have been extended beyond the original group of DuPont pitch-based E-series fibers to include additional pitch- and PAN-based fibers. Fibers and composites were characterized by tensile strength, optical microscopy, SEM, fiber preferred orientation, and a single-fiber composite (SFC) fragmentation test to provide a relative measure of fiber-matrix interfacial shear strength (IFSS). Results show that fracture behavior and FSU are dominated by the degree of fiber-matrix bonding, as inferred from microscopic observations and measurements of IFSS. In the very high modulus pitch-based fibers, the behavior of the F,130 is strikingly different from that of the Amoco and Nippon Oil fibers, in that it retains good bond strength and high FSU even with HT to 2400 °C, in contrast to the other very high modulus pitch-based fibers that are already weakly bonded at the lowest HTT of 1100 °C. All PAN-based fibers and lower modulus pitch fibers are characterized by strong bonding, brittle fracture, and low FSU for the 1100 °C HTT. Subsequent heat treatment of these composites to 2150 and 2400 °C, in most cases, results in significant recovery of FSU, suggesting an optimum IFSS for each composite. It is suggested that the difference in bonding between the pitch-based E-series and P-series may be related to the similarity in fine structure between the E-fibers and high-modulus PAN-based fibers.

We used Monte Carlo simulations to study the kinetics and steady states of B2 and B32 ordering in an equiatomic binary bcc alloy having both thermal and ballistic atom movements. Atom movements occurred by a vacancy mechanism, where first-neighbor atoms exchanged sites with the vacancy. In the thermodynamic case, where this jump probability was set by a Boltzmann factor alone, we found the formation of large amounts of transient B2 (B32) during disorder → B32 (B2) order transformations. The transient order developed in distinct regions, but vanished completely when equilibrium was attained. Ballistic jumps were included as random interchanges of the vacancy with one of its neighboring atoms. Even with small fractions of ballistic jumps, there were large changes in the transient states and steady states of order in the alloy. A kinetic explanation is proposed, in which the presence of ballistic jumps contributed a greater amount of internal energy to the B2 phase than to the B32 phase when there was a strong asymmetry in the second-nearest neighbor pair potentials (VAA2 ↗ VBB2). A two-phase coexistence in the steady state was explained by fluctuations in the local density of ballistic jumps.

A novel method to synthesize “clean” carbon nanotubes with relatively high yield in a hydrogen arc discharge has been developed. The quality and yield of the tubes depend sensitively on the gas pressure in the arc discharge. Sharp, open-ended nanotubes with clear lattice fringes at the edges and empty interiors have been observed. The existence of these frozen-open-ended tubes as part of nanotube-bundles provides evidence for an open-ended growth model for nanotubes. Using time of flight mass spectrometry, it was found that fullerenes, such as C60 and C70, are almost absent from the soot collected in the hydrogen arc discharge. The effect of hydrogen on the formation of fullerenes, both in the laboratory and in space, will be discussed.

Barium-substituted lanthanum manganite (La1−xBaxMnO3) powders have been synthesized by a novel autoignition technique, and the effect of barium content on the autoignition characteristics, stability of the compound, and the powder characteristics have been investigated. X-ray examinations show that the material exists as a single phase having perovskite structure up to 40 at. % substitution of Ba for La, beyond which mixed phases of LaMnO3 and BaMnO3 are formed at least up to the highest limit of substitution (50 at. %) and calcination temperature (1350 °C) investigated. Electrical conductivity and thermal expansion behavior of the material have been studied for plausible use as cathode material in solid oxide fuel cells.

In this study, films consisting of B-N-C-H have been synthesized by low pressure chemical vapor deposition using the liquid precursor triethylamine borane complex (TEAB) both with and without ammonia. When no NH3 is present, the growth rate was observed to follow an Arrhenius behavior in the temperature range of 600 to 800 °C with an apparent activation energy of 11 kcal/mol. A linear dependence of growth rate is observed as a function of square root of flow rate for the TEAB range of 20 to 60 sccm, indicating that the reaction rate is controlled by the adsorption of borane. The addition of NH3 to TEAB had the effect of lowering the deposition temperature down to 300 °C and increasing the apparent activation energy to 22 kcal/mol. Above 650 °C, the carbon concentration of the deposits increased significantly, reflecting the breakup of the amine molecule. X-ray diffraction measurements indicated the films to be in all cases amorphous. Infrared spectra of the films showed absorption peaks representing the vibrational modes of B-N, B-N-B, B-H, and N-H. The index of refraction varied between 1.76 and 2.47, depending on composition of the films. Films deposited with no NH3 above 700 °C were seen to be compressive while films below that temperature were tensile. In the range of 350 to 475 °C, the addition of NH3 to TEAB resulted in films that were mildly tensile, while below 325 °C and above 550 °C, the films were found to be compressive. Both the hardness and Young's modulus of the films decreased with higher temperatures, reflecting the influence of the carbon presence.

A new method for the preparation of well-defined colloidal barium titanate (BaTiO3) crystals by the controlled double-jet precipitation (CDJP) technique is described. The process is extremely fast and requires a low temperature (<100 °C). The reactants, barium and titanium salts, can be used in high concentrations and the yield is quantitative. The stoichiometry of the BaTiO3 particles can be controlled precisely and reproducibly. The effects of the composition of the reactant solutions, flow rates, reaction time, and the addition of polymers on the precipitation process were investigated. The BaTiO3 powders, produced by the CDJP technique, sinter to high density at a temperature as low as 1200 °C and exhibit a relative dielectric constant of 5000 at 20 °C, which is the highest value reported in the literature. The grain sizes of the sintered samples are small and uniform, ranging between 1 and 2 μm.

The electromechanical properties of (Pb1−xLax)(ZryTi1−y)O3 [PLZT x/y/(1 - y)] have been investigated in the compositional range 0 < x < 0.10 for y = 0.65 (rhombohedral PLZT) and 0 < x < 0.18 for y = 0.40 (tetragonal PLZT). Both field-induced strains (∊-E) associated with polarization switching and piezoelectric responses (d33) were studied. Transmission electron microscopy (TEM) and dielectric investigations were also performed. Room temperature TEM investigations revealed common trends in the domain structure with increasing La content for both PLZT x/65/35 and x/40/60, including a micron-sized domain structure, a subdomain tweed-like structure, and a nanopolar domain state. Changes in the field-induced strains and piezoelectric properties were then related to these microstructural trends. The dominant electromechanical coupling mechanism in the micron-sized domain state was found to be piezoelectricity. However, an electrostrictive coupling became apparent with the appearance of the subdomain tweed-like structures, and became stronger in the nanopolar domain state. It is believed that polarization switching can-occur through 70°or 110°domains, the subdomain tweed-like structure, or nanopolar domains depending on La content.

A novel method was proposed for measuring the epitaxial growth rate of diamond by microwave plasma-assisted chemical vapor deposition (MPCVD). Cubo-octahedral crystals were formed on an Si(100) wafer and were used as the substrate in the homoepitaxial growth. Growth rates of the {100} and {111} were simultaneously measured from the change in the top view size of crystals. Thus, the relative growth rate of {100} to {111} was obtained without any limitation of its value. The homoepitaxial growth rate was strongly affected by the type of diamond faces, CH4 concentration in the gas phase, and deposition temperature. The growth rate of {100} was more dependent on CH4 concentration than that of {111}, while the activation energy for the [100] growth was about half that for the [111] growth. These tendencies were in accord with growth mechanisms proposed for each diamond plane. Reaction conditions were optimized based on the relative growth rate of (100) to (111) planes, and a highly oriented (100) diamond film with a quite smooth surface was formed on an Si(100) wafer.

An Ir metal target was reactively rf sputtered in a planar magnetron source to develop iridium oxide deposition conditions. Gas blends of hydrogen, oxygen, and argon were used to provide competitive control over the reduction/oxidation characteristics of the sputter plasma. Optical emission spectroscopy allowed direct observation of hydrogen, oxygen, and iridium atomic peaks and OH molecular bands. Each of the twelve gas flow conditions could be clearly defined as either reducing or oxidizing by plasma emission spectroscopy. A given plasma reduction/oxidation state can be maintained over a wide range of gas flow conditions by coordinated adjustment of hydrogen and oxygen flows. The electrochemical properties of the iridium oxide films change dramatically in the vicinity of the reduction/oxidation plasma transition.

Analytical models are presented for the elastoplastic deformation of multilayered materials subjected to fluctuating temperatures. The layered structure comprises an elastic-perfectly plastic ductile material sandwiched between two elastic brittle materials. With creep, heat transfer, and edge effects excluded, closed-form solutions for different characteristic temperatures for thermal cycling are presented as a function of the layer geometries and the thermomechanical properties of the constituent phases. The evolution of curvature, the generation of thermal residual stresses within each layer, and the onset and spread of plasticity in the ductile layer are also examined. It is theoretically shown that reversals of curvature in the layered solid can occur during monotonic changes in temperature, even when the thermomechanical properties of the layer do not vary significantly with temperature. The predictions of the analytical model are seen to compare favorably with experimental observations of curvatures during thermal cycling in the limiting case of bilayer composite with Al–Al2O3 layers and Al–Si layers and in a Si–Al–SiO2 trilayer system. Case studies of the effects of the relative variations in the geometry, elastic properties, and plastic response of the constituent phases on the overall deformation are examined for two practically significant layered systems: a Si–Al–SiO2 layered solid with extensive applications in the electronics industry and a Cr2O3-coated steel with an interlayer of a Ni–Al alloy which is used in structural applications.