Shock synthesis of nanocrystalline Si was accomplished for the first time using thermal spray in which Si powder is injected into a high-energy flame where the particles melt and accelerate to impact on the substrate. A stream of molten Si particles impacted onto Si wafers of two orientations (100) and (111). The shock wave generated by the sudden impact of the droplets propagated through the underlying Si layer, which experienced a phase transition to a high-pressure form of Si due to propagation of the shock wave. The metastable high-pressure form of Si then transformed to metastable Si-IX, Si-IV (hexagonal diamond-Si), R-8, and BC-8 phases as evidenced by transmission electron microscopy and x-ray diffraction studies. Back-transformed metastable Si grains, with a size range from 2 to 5 nm, were found to be dispersed within Si-I (cubic diamond-Si). The metastable phases formed mostly in deposits on the (100) substrate compared to those of the (111) substrate orientations. This behavior can be correlated with the anisotropic nature of the pressure-induced transformations of Si-I.

Applying the scaling relationships developed recently for conical indentation in elastic–plastic solids with work-hardening, we examine the question of whether stress–strain relationships of such solids can be uniquely determined by matching the calculated loading and unloading curves with that measured experimentally. We show that there can be multiple stress–strain curves for a given set of loading and unloading curves. Consequently, stress–strain relationships may not be uniquely determined from loading and unloading curves alone using a conical or pyramidal indenter.

Superconducting films of the Bi–Sr–Ca–Cu–O family of oxides were prepared by electrodeposition of the constituent metals followed by an oxidative thermal treatment. The influence of water, stirring of the electrolyte, cleaning of the substrate, and deposition time on the quality of the films were studied. Before the thermal treatment, the electrodeposited films consisted of a mixture of different metals and carbonates of the constituent elements. The oxidation of the metallic phases and the decomposition of the carbonates occurred in the ranges 260–280 °C and 400–470 °C, respectively. The final oxides were obtained after an oxidative thermal treatment at 800 °C. Lower temperatures were not sufficient for the preparation of the superconducting oxide films. The prepared Bi-2201 films consisted of a mixture of two phases with different strontium, bismuth, and oxygen contents. The Bi-2212 films were composed of platelike particles with a preference to orientate along the (001) direction. These films showed critical temperatures up to 92 K and critical current densities up to 15,000 A/cm2 (at 77 K and zero field) when the films were pressed before the thermal treatment.

Powdered samples of oxygen-deficient YBa2Cu3Oy were annealed in various atmospheres at 880 and 300 °C to study the relations of structural anomaly, phase transition, and oxygen content. It was found that the structural anomaly in the c axis is reversible during oxygenation and deoxygenation. The change of the c axis arose from the electrical repulsion among Ba and Cu cations as oxygen was removed or refilled. The anomaly in the c axis occurred when the oxygen was further removed or refilled to a critical value, at which structural relaxation and electrical repulsion changed greatly. The phase transition is attributed to the anomalous change in the c axis, and the mechanism is proposed and discussed in this paper.

The enthalpy of formation of Y2Ba4Cu7O14.864 at room temperature has been determined by using high-temperature reaction calorimetry. The standard enthalpy of formation of the 247 phase is ΔH°f = −5463 ± 18 kJ mol−1. Phase relationships among the superconductors, namely, the 123, 124, and 247, are assessed. It is intrinsic that impurity phases, such as Y2Cu2O5, BaCuO2, CuO, etc., coexist with the superconductors at equilibrium. Equilibria among the superconductor phases in the Y2O3–BaO–Cu–O system have been determined. The results show that, at the 124 bulk composition, the 247 phase coexists with the excess CuO in a narrow area of pO2 ∼ T space confined by the stability fields of the 124 phase and a mixture of the 123 + CuO. The standard free energies of carbonation and hydration of the 247 phase are also determined, which are −629 ± 13 kJ mol−1 and −873 ± 45 kJ mol−1, respectively. Like the 123 and 124 phases, the 247 phase is thermodynamically unstable for corrosion by water vapor and carbon dioxide in ambient atmosphere.

We investigated the growth of high-quality homoepitaxial diamond on the (111) face in a microwave-assisted plasma chemical-vapor-deposition system incorporating an individual substrate heating/cooling device. The grown diamond films were characterized by scanning electron microscopy, reflection high-energy electron diffraction, atomic force microscopy, confocal micro-Raman spectroscopy, and secondary ion mass spectrometry. The (111) diamond films show a tendency to incorporate a significant amount of hydrogen during chemical-vapor-deposition growth. Hydrogen incorporation degrades the crystal quality and surface smoothness. The amount of incorporated hydrogen decreases with the decrease in deposition temperature. We have shown that the crystal quality and surface smoothness of homoepitaxial diamond strongly depend on the substrate temperature. Independent control of the substrate temperature and incident microwave power is essential for high-quality diamond homoepitaxy.

Thin Si0.8Ge0.2 layers epitaxially grown on (100) Si substrates were oxidized at temperatures from 150 to 450 °C under vacuum ultraviolet (VUV) radiation emitted by an excimer lamp working with Xe (λ = 172 nm). The structure and composition of the grown dielectric layers were investigated by Rutherford backscattering spectrometry, nuclear reactions analysis, ellipsometry, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy. These investigations have shown that, during the VUV-assisted oxidation process, Ge atoms were initially rejected from the grown SiO2 layer even at temperatures as low as those employed here. After a certain quantity of Ge accumulated at the interface, nanocrystalline Ge regions were directly excised from the remaining SiGe layer becoming embedded within the advancing SiO2 layer. The layers containing these nanocrystalline Ge particles exhibited the same visible photoluminescence spectra as those recorded from layers already known to contain nanocrystalline Ge or GeO2 particles, porous Ge, or nanocrystalline Ge particles exhibiting a different crystalline structure. This seems to indicate that the shell region of the nanocrystalline particle, and not its crystalline core, is the source of the photoluminescence.

Microstructures in the reaction interface between molten Al and dense mullite have been studied by transmission electron microscopy to provide insight into mechanisms for forming ceramic–metal composites by reactive metal penetration. The reactions, which have the overall stoichiometry 3Al6Si2O13 + (8 + x)Al → 13Al2O3 + xAl + 6Si, were carried out at temperatures of 900, 1100, and 1200 °C for 5 and 60 min and 1400 °C for 15 min. Observed phases generally were those given in the above reaction; their proportions and interfacial microstructures, however, were strongly dependent on the reaction temperature. Using previously measured reaction kinetics data, the observed temperature dependence of the interfacial microstructure has been modeled as three sequential steps, each of which is rate limiting in a different temperature range.

This paper presents the results of a systematic investigation of structure and formation of the interface between gold and trimethylcyclohexane polycarbonate, particularly concerning interface evolvement during gold evaporation and the influence of evaporation rate, substrate temperature, and subsequent annealing. The means of investigation were cross-sectional transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. Extensive metal diffusion into the polymer and cluster formation near the interface were observed at deposition rates of the order of one monolayer per minute and below. The penetration depth is strongly temperature dependent. At high evaporation rates metal aggregation at the surface prevents cluster formation inside the polymer. No diffusion into the polymer was observed from metal films deposited at room temperature after extensive annealing at elevated temperatures.

A new material system for applications involving thermal shock is proposed. The system consists of thin layers of ceramics and thinner metallic interlayers. In this study, a ceramic/metal laminate was constructed from Coor's ADS96R thin plates alternating with thinner Wesgo Cusil Active Braze Alloy interlayer foils and joined in active brazing. The maximum brazing temperature was 845 °C. Square laminated plates were quenched in room-temperature distilled water, where a very large heat transfer coefficient exists, and therefore, severe conditions of thermal shock occur. The laminated plates, initially at temperatures of 600 and 800 °C, were quenched at their bottom surface only in a specially designed apparatus. The temperatures at the top and the bottom surfaces of the specimens were measured by means of two thermocouples during quenching. The basic features of this architecture are described. The dominant behavior was the absence of interaction between the biaxial cracking mechanisms in a ceramic layer with those in an adjacent ceramic layer, and localization of the damage to those layers that experienced sufficient tensile stresses. The result was a dramatic increase of the residual strength after thermal shock. In addition, R-curve behavior upon mechanical loading caused by plastic deformation of the metallic interlayer was observed.

Oxidation of sputter-deposited nanocrystalline Mo–Si–N (MoSi2.2N2.5) coatings in oxygen–water vapor atmosphere has been studied in the temperature range 400–850 °C. In addition, the oxidation properties of nanolayered Mo–Si–N/SiC coatings at 700 °C were studied and compared to those of single-layer coatings of both components. No pest disintegration was observed in Mo–Si–N up to 200 h of oxidation. A preexponential rate constant of (3.7 ± 0.5) × 109 (1015 atoms/cm2)2/h and activation energy 1.03 ± 0.02 eV were determined from an Arrhenius plot for parabolic oxygen buildup on Mo–Si–N. Up to 20% less oxygen was detected in the oxidized nanolayered coatings compared to either of the components as a single layer, indicating an improvement in oxidation resistance.

The activation energy for crystallization of β-spodumene in TiO2 added Li2O–Al2O3–4SiO2 (LAS) precursor powders by a sol-gel process was studied by using isothermal and nonisothermal methods. Nonisothermal kinetics for the LAS precursor powder system were investigated using differential thermal analysis (DTA) and quantitative x-ray diffraction (XRD) analysis. The rate of crystallization of LAS precursor powders decreased as the TiO2 content increased. For samples with addition of 0, 5.0, and 10.0 wt% TiO2, the activation energies for crystallization by DTA evaluation were 165.06, 194.46, and 205.38 kJ/mol, respectively. According to the quantitative XRD method, the values computed by the Johnson–Mehl–Avrami equation were 162.54, 189.42, and 196.14 kJ/mol, respectively. The values obtained by isothermal and nonisothermal kinetic methods from DTA and XRD analyses were in good agreement. The growth morphology parameters were 0.59, 0.70, and 0.76, respectively, for the LAS precursor powder with TiO2 addition of 0, 5.0, and 10.0 wt%, showing a rodlike growth. In the LAS precursor powder system, TiO2 did not act as the nucleative agent.

The microwave dielectric properties of Ca[(Li1/3Nb2/3)1−xMx]O3−δ (M = Sn, Ti, 0 ≤ x ≤ 0.5) ceramics were investigated. In general, the ceramics prepared were multiphase materials. However, single-phase specimens having orthorhombic perovskite structure similar to CaTiO3 could be obtained in the vicinity of Sn = 0.2 to 0.3, and Ti = 0.2. As Sn concentration increased, the dielectric constant (εr) decreased and the quality factor (Q) significantly increased within the limited Sn concentration. As Ti concentration increased, the dielectric constant (εr) increased, the quality factor (Q) decreased, and the temperature coefficient of resonant frequency (τf) changed from a negative to positive value. The temperature coefficient of resonant frequency of 0 ppm/°C was realized at Ti = 0.2. The Q · fo value and εr for this composition were found to be 26100 GHz and 38.6, respectively.

Low-temperature synthesis of hexaluminate phases for fiber–matrix interphases in ceramic–matrix composites is necessary to minimize processing temperatures to prevent fiber-strength degradation. Citrate-gel-derived lanthanum hexaluminate was synthesized using divalent transition-metal cations to stabilize the magnetoplumbite structure. Pure, undoped LaAl11O18 was obtained in 1 h only at temperatures >1500 °C after the formation and subsequent consumption of the intermediate perovskite, LaAlO3, which first appeared at ∼1150 °C. Powders of LaMAl11O19, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn, were prepared at much lower temperatures. Highly crystalline, phase-pure powders of LaMnAl11O19 and LaCuAl11O19 were obtained at 1000 °C in 1 h directly from the amorphous powder without the formation of the intermediate perovskite. All other compositions could be obtained at 1100 °C in 1 h except for the nominal LaNiAl11O19, which formed primarily LaAlO3, NiAl2O4, and Al2O3. Powders containing dopants all had similar grain sizes and morphologies at 1200 and 1500 °C; the grain size of powders with dopants was significantly greater than that of pure LaAl11O18 powder. The introduction of a second charge-compensating quadrivalent dopant for excess divalent cation did not greatly influence synthesis or grain growth below the eutectic temperature but did seem to enhance the [0001] texture of films on single-crystal yttrium-aluminum garnet substrates compared with singly doped films.

A detailed study of the sintering behavior of titanium carbide (TiC) powder synthesized by the self-propagating high-temperature synthesis (SHS) route was carried out with varying percentages of nickel. With an increase in the nickel content, porosity was found to increase along with Ni2.67Ti1.33 secondary phase at grain boundary. A 90–92% dense sintered body of TiC was produced from SHS-produced powder at 1800 °C with 10 wt% nickel.

Supported and unsupported γ-alumina membranes and alumina–titania composite membranes were prepared using the sol-gel method. In the course of preparation, effects of acid concentration, type of acid, alkoxide, and binder on the particle size of the sols and pore size of the membranes were investigated by thermogravimetry and differential thermal analysis, N2 physisorption, and light scattering. It was observed that the particle sizes of all the sols had only a small affect on the pore sizes of the membranes. Qualities of the membranes were improved by addition of polyvinyl alcohol as binder to the boehmite precursor. This resulted in less critical but more controllable drying and calcining procedures. Composite membranes with different pore sizes from 3.2 to 4.8 nm and surface areas retained above 100 m2/g could be regulated by different alumina-to-titania ratios.

The stabilization stage in the processing of carbon–silicon alloy (CSA) precursor fibers is investigated in this study. The critical stabilization parameters are identified and shown to control the mechanical properties of fibers both at the stabilization stage and, after further pyrolysis and controlled oxidation, to produce oxidation-resistant fibers. The attainment of infusibility in the stabilized fibers, necessary for the production of CSA fibers, determines the lowest stabilization degree, whereas the highest stabilization degree can be identified from the relationship between stabilization temperature and tensile properties of CSA fibers, thus enabling the optimum stabilization conditions to be determined. The CSA fibers produced by proper control of stabilization conditions significantly enhance mechanical properties, which are more than double those of CSA fibers obtained previously. Fourier transform infrared spectroscopy and nuclear magnetic resonance studies show that at stabilization temperatures above the optimum there is significant formation of silica in the stabilized fibers. This leads to a higher modulus but lower tensile strength and elongation.

Polycrystalline Y2O3/ZrO2 superlattice thin films were deposited using opposedcathode reactive magnetron sputtering. Pulsed direct-current power was used to eliminate arcing on the metallic targets. Radio-frequency power was applied to the substrates to achieve ion bombardment of the growing film. In order to reproducibly deposit at high rates in Ar–O2 mixtures, the Y target voltage was used to indirectly feedback-control the O2 partial pressure. Deposition rates as high as ∼70% of the pure metal rates were achieved, typically 3.5 μm/h. Superlattices with periods ranging from 2.6 to 95 nm were deposited. Y2O3 layer thicknesses were either 75% or 50% of the superlattice period. X-ray diffraction and transmission electron microscopy studies showed well-defined superlattice layers. The ZrO2 layers exhibited the high-temperature cubic-fluorite structure, which was epitaxially stabilized by the cubic Y2O3 layers, for thicknesses ≤7 nm. The equilibrium monoclinic structure was observed for thicker ZrO2 layers. Nanoindentation hardnesses ranged from 11.1 to 14.5 GPa with little dependence on period. The hardness results are discussed in terms of current superlattice hardening theories.

Among the oxides, Cr2O3 exhibits the highest hardness value and a low coefficient of friction. These properties make chromium oxide an excellent coating material for tribological applications. Cr2O3 thin films were deposited by radio-frequency reactive magnetron sputtering at substrate temperature in the range 363–593 K. The hardness and elastic modulus of the films were measured by two complementary nanoindentation techniques to investigate the influences of the substrate temperature and the oxygen content in the sputtering gas. While the continuous stiffness data method provides information throughout the whole film thickness, nanoindentation combined with scanning force microscopy of the residual imprints allows visualization of pileup, cracking, and delamination from the substrate. Hardness values up to 32 GPa were obtained for substrate temperatures exceeding 500 K and oxygen contents between 15% and 25% of the total gas pressure. The films, obtained with these deposition conditions, showed good adhesion to silicon substrates.

The physical insight into the Meyer hardness is given on the basis of the experimental results for indentation load P versus indentation depth h relations and of a simple model for elastoplastic contact deformation. The quadratic relationships of P = k1h2 for loading and P = k2(h − hr)2 for unloading with the residual depth of impression hr are essential in the elastoplastic indentation processes and mechanisms. The indentation-induced residual strain energy stored in unloaded impression is properly taken into account. The Meyer hardness is an elastic and plastic parameter that depends not only on the plasticity but also on the elasticity of material indented and significantly depends on the geometry of indenter used. The Meyer hardness is given in terms of the energy consumed to create a residual indentation impression, leading to the concepts of “work of indentation” and “ductility index.”