The oxidation behavior of polymer-derived SiAlCN ceramic in a water vapor environment was studied at 1400 °C. The oxidation and corrosion rates of the SiAlCN are much lower than those of SiCN and pure silicon-based ceramics. The material retains about 75% of its original strength after exposure in water vapor for 300 h at 1400 °C. It is believed that the superior resistance of the SiAlCN to water vapor-related oxidation and corrosion is due to the formation of an aluminum-doped silica layer, in which the aluminum has reduced the activity of the silica.

Herein we propose an alternate simpler mechanism for a new phenomenon we reported recently in this journal [Z.M. Sun, S. Gupta, H. Ye, and M.W. Barsoum, J. Mater. Res.20, 2618 (2005)]. The presence of freestanding Ga nanoribbons on Cr2GaC surfaces were found to be the leftover skins of Ga whiskers or spheres that were reabsorbed into the Cr2GaC grain boundaries, most likely as a result of their melting.

ZnO thin films have been grown by metalorganic chemical vapor deposition (MOCVD) and plasma-assisted (PA) MOCVD on c-axis-oriented sapphire (0001) and Si (001) substrates using the novel Zn(2-thenoyltrifluoroacetonate)2·N,N,N′,N′-tetramethylethylendiamine precursor. The structural, morphological, and optical properties of ZnO films have been investigated. The results show that the O2 PA growth results in highly c-axis-oriented hexagonal ZnO thin films also on cubic substrates. PA-MOCVD ZnO films have good optical properties, as inferred by the presence of a sharp and intense exciton in the dielectric function.

Low-energy cluster beam deposition (LECBD) is considered an intriguing technique for obtaining thin layers with well-defined structures at the nano- and mesoscale levels, allowing novel optical, electronic, and magnetic properties. The produced layers are highly porous and extremely reactive due to the high surface to volume ratio and must be characterized with in situ techniques to study their original composition and their evolution once exposed to reactive gases. In this work, we present a general overview and some results on the formation, evolution, and deposition of silicon and carbon cluster beams produced using a laser vaporization source.

The microstructures of Tl2Ba2Ca1Cu2O8 (Tl-2212) films are very strongly influenced by the processing parameters used to synthesize the superconducting phase and also control the microwave surface resistance values that are of key importance in the application of these materials in high-frequency devices. We report here on detailed studies of how the mesotexture of Tl-2212 films develops during synthesis at 820 and 855 °C. Our key observation is that the microstructure, and hence the superconducting properties, are controlled by the mechanism by which stress is relieved in the films and that apparently perfectly epitaxial films do not have the best microwave performance because in these samples the stress is relieved by macroscopic defects rather than local, low-angle grain misorientations.

Carbon nitrogen nanotubes and nanofibers with controlled nitrogen concentration have been prepared by reaction of cyanuric chloride and hexachlorobenzene (HCB) with sodium metal at 250 °C in cyclohexane. Electron microscopy and spectroscopic analysis were used to characterize the products. The total yields of the tubes and fibers decrease as the ratio of cyanuric chloride to HCB increases, and nitrogen content in the products could be controlled by the ratio. The nanostructures depended strongly on the nitrogen content. Lower nitrogen content was favorable for producing linear products.

A novel microwave-assisted combustion method was used to prepare Ni powder. The method involves the combustion reaction of nickel nitrate and urea as a fuel in the microwave field. The initiation of the exothermic peak of the combustion reaction was found to vary as a function of urea content. The microwave-prepared Ni powder was characterized using x-ray diffraction (XRD), scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, thermogravimetric (TG) analysis, differential thermal analysis (DTA), and magnetic measurement. The XRD pattern revealed that the Ni powder crystallizes with the cubic phase when the molar ratio of fuel to nitrate is varied between 5:1 and 6:1. Above or below that molar ratio, NiO phase coexists as an impurity along with the Ni phase. The magnetization value of Ni measured at room temperature is 53.5 Am2/kg, which is close to the value observed for commercial Ni powder (55.0 Am2/kg). The mechanism for the formation of the Ni and NiO phase is discussed based on the infrared, TG, and DTA data. The method shows that highly pure Ni powder can be prepared using urea as a fuel and microwaves as a source of energy via the solution combustion method.

We report a novel phenomenon in which minor element additions (∼1 at.%) can dramatically enhance the glass-forming ability (GFA) of CuZr(Al) metallic alloy, which can be cast into glasses with large cross-section sizes using a conventional casting method. The minor additions cause the liquidus temperature Tl to decrease from 1219 (for Cu50Zr50) to 1139 K [for (Cu50Zr50)92Al7Gd1], and the reduced glass transition temperature Trg (=Tg/Tl) of the alloys increases from 0.550 (for Cu50Zr50) to 0.613 [for (Cu50Zr50)92Al7Gd1]. The mechanism involved in the achievement of the superior GFA is explained by the stronger tendency of short-range ordering in the stronger microalloyed alloys as well as the thermodynamic and kinetic aspects.

Finite element analyses were carried out to simulate the loading, unloading, and reloading processes of indentation tests. It was found that the validity of applying the elastic contact theory to the indentation unloading process is strongly related to the strain hardening and residual stress in impression. It is the combination of strain hardening and residual stress that causes the unloading or reloading curves to show elastic loading in the range from zero to the maximum load whereas the reloading curve on the impression without strain hardening and residual stress shows elastic–plastic loading in the same range. These computations indicate that applying the elastic contact theory to the unloading or reloading processes, the fundamental prerequisite of the instrumented indentation technique, is valid because of the existence of strain hardening and residual stress. The mechanism of this hardening effect is discussed through energy analysis.

Bulk fully nanocrystalline grain structures were successfully obtained in ultralow carbon stainless steel by means of equal channel angular pressing at room temperature. Transmission electron microscopy (TEM) and high-resolution TEM investigations indicated that two types of nanostructures were formed: nanocrystalline strain-induced martensite (body-centered cubic structure) with a mean grain size of 74 nm and nanocrystalline austenite (face-centered cubic structure) with a size of 31 nm characterized by dense deformation twins. The results about the formation of fully nanocrystalline grain structures in stainless steel suggested that a low stacking fault energy is exceptionally profitable for producing nanocrystalline materials by equal channel angular pressing.

High-quality epitaxial InN thin films grown on (0001) sapphire with GaN buffer were characterized using transmission electron microscopy. It was found that the GaN buffer layer exhibits the (0001) Ga polarity and the InN film has In-terminated polarity. At the InN/GaN interface, there exists a high density of misfit dislocation (MD) array. Perfect edge threading dislocations (TDs) with (1/3)〈1120〉 Burgers vectors are predominant defects that penetrate the GaN and InN layers. Pure screw and mixed TDs were also observed. Overall, the TD density decreases during film growth due to annihilation and fusion. The TD density in GaN is as high as ∼1.5 × 1011 cm−2, and it drops rapidly to ∼2.2 × 1010 cm−2 in InN films. Most half-loops in GaN are connected with MD segments at the InN/GaN interface to form loops, while some TD segments threaded the interface. Half-loops were also generated during the initial stages of InN growth.

In this work, a novel substitutional solid solution (W0.8Al0.2)C was synthesized by mechanically activated high-temperature reaction. X-ray diffraction was used for phase identification during the whole reaction process. Environment scanning electronic microscopy–field emission gun and energy dispersive x-ray were used to investigate the microstructure and the quantitative material composition of the specimen. (W0.8Al0.2)C was found to crystallize in the WC-type, and the cell parameters were a = 2.907(1) Å and c = 2.837(1) Å. The hardness of (W0.8Al0.2)C was tested to be 19.3 ± 1 GPa, and the density was 13.19 ± 0.05 g cm−3.

The alternating current electrical conductivity of a gel-derived glass of composition 55Fe2O3⋅45SiO2 (mol%) was measured over a frequency range of 100 Hz to 6 MHz. The gel was subjected to a reduction treatment at 923 K for ½ h and subsequently heated in ordinary atmosphere at a temperature 773 K for ½ h to grow a Fe-core Fe3O4 shell nanostructure with a median diameter of 6.2 nm. This formed a percolative network within the silica gel. Mossbauer spectra confirmed the presence of Fe3O4 in the nanoshell. Electrical measurements were also carried out on these nanocomposites at different frequencies and temperatures. Isothermal electrical modulus data for both reference and treated glass systems were analyzed using both the CK0 and CK1 Kohlrausch-related frequency response models. Reference-glass shape parameter values, estimated by fitting the experimental data to the K0 model at several temperatures, were found to be ∼0.32. Here, the K0 model led to much better fits than the K1 did. However, for the treated core–shell-structured nanocomposite material, both models yielded good fits with consistent but different shape parameter estimates: very close to ½ for the K0 model and ⅓ for the K1 model. In accordance with the structural measurements and with axiomatic topological considerations that predict a shape-parameter value of ⅓ for one-dimensional motion and ½ for two-dimensional motion, it appears that the ∼0.32 value is consistent with one-dimensional motion of charge carriers along the narrow channels of the interconnected iron-rich three-dimensional phase of the reference glass. Further, although the K1-model ⅓ estimates for the treated material also indicate the presence of one-dimensional charge motion at the two-dimensional interface between the two interconnected phases of the reference glass, the ½ K0 estimates for the same material suggest an effective charge-motion dimension of 2. Importantly, comparison of the high-frequency dielectric constant estimates for the K0 reference glass and the K1 treated one clearly leads to the new but physically plausible conclusion that the bulk frequency-independent dielectric constant of about 30 is independent of the treatment.

Sn–In alloys are promising low-melting-point Pb-free solders. Cu and Ni are common substrates in the electronic products. This study examines the interfacial reactions in the Sn–20 at.% In(γ–InSn4)/Cu and Sn–20 at.% In/Ni couples at 160 °C. Only the η–Cu6Sn5 phase layer is formed in the Sn–20 at.% In/Cu couple, and the layer grows thicker with longer reaction time. The reaction path is γ–InSn4/η–Cu6Sn5/Cu. A peculiar phenomenon with the bulging of the couple near the Ni substrate is found in the Sn–20 at.% In/Ni couple. A liquid phase is formed by interfacial reaction in the solid/solid Sn–20 at.% In/Ni couple at 160 °C, and the reaction path is γ–InSn4/liquid/δ–Ni3Sn4 + liquid/(δ–Ni3Sn4)/Ni. Usually Ni has a slower reaction rate with solders; however, the consumption rates of Ni substrate are much higher than those of Cu substrate in this study when they are in contact with the Sn–20 at.% In alloy at 160 °C due to the formation of the liquid phase in the Sn–20 at.% In/Ni couple.

Layered manganese oxide nanocomposite (PQN2MO) with Polyquaternium-2 (PQN2) incorporated between manganese oxide sheets was synthesized through a delamination/reassembling process. The synthesized material was characterized by powder x-ray diffraction (XRD), elemental analysis, thermal analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy observation. XRD analysis showed that the expansion of the interlayer depended on the amount of PQN2 intercalated; the largest expansion was 0.94 nm, corresponding to a layer of PQN2 chains existing in the interlayer at an angle of about 30°. Chemical analysis results indicated that the tetramethylammonium (TMA+) ions in the interlayer were partly replaced by PQN2 polycations by an ion exchange mechanism, resulting in a nanocomposite in which TMA+ ions and PQN2 polycations simultaneously existed in the interlayer. The intercalated PQN2 polycations were selectively extracted, and TMA+ ions were stable enough to remain in the interlayer against the acid treatment. PQN2MO nanocomposite was composed of platelike nanocomposite particles.

Sn, Sn-Sb, Ti, Ce, Zr, Zn, In, In–Sn, and Fe oxides of nanometric size were obtained through the hydrolytic route, starting from molecular precursors in the presence of starch. Gels were treated with α-amylase to produce oxide suspensions and starch degradation. Solid oxide products resulted from reaction with H2O2, washing with H2O, and centrifugation of the suspensions. The nanometric size and morphology of crystallites were assessed by x-ray diffractometry, transmission electron microscopy, and, for SnO2, solid-state nuclear magnetic resonance. Product consolidation at 600 °C did not produce any noticeable increase in dimensions. Thermal analysis coupled with mass spectrometry of evolved gaseous species showed that glucoside residues remain chemically bonded to the nanoparticles, thus explaining the effective stabilization of crystallite dimensions. Aqueous suspensions of nanopowders were mixed with a silicon tetra-ethoxide ethanol solution and subjected to an ordinary sol-gel process. The resulting suspensions were used to obtain stable and homogeneous coatings on glass sheets.

Highly porous films of titania composed of nanoparticle aggregates were synthesized via gas-to-particle conversion and particle-precipitated chemical vapor deposition. The films were annealed in air for 12 h at temperatures ranging from 400 to 1000 °C. Atomic force microscopy was used to determine the Young's modulus and hardness of both the as-synthesized and annealed films. The Young's modulus and hardness of the as-synthesized films were 4.0 ± 0.4 MPa and 0.026 ± 0.003 MPa, respectively. There was no significant change in either modulus or hardness upon annealing until the films were annealed at a temperature of 1000 °C. The Young's modulus and hardness of these films were 56 ± 6 MPa and 0.10 ± 0.01 MPa, respectively. Results from dynamic light scattering measurements of aggregate size and surface area measurements suggest that annealing at 1000 °C leads to increased networking between distinct nanometer-scale titania aggregates, which strengthens the film.

Effects of particle size of Cr2O3 catalyst on the hydrogen absorption/desorption kinetics of Mg + 5 wt% Cr2O3 mixtures have been studied. To explain the effect of particle size of Cr2O3 and also to yield information about the role of Cr2O3 during the sorption process, the kinetics data have been analyzed using Avrami–Erofeev rate equations. The activation energies and diffusion coefficients of these mixtures are in the ranges of 50.6–63.2 kJ/mol and 1.2.10−11 to 8.9.10−10 cm2/s, respectively. The addition of nano-oxides led to an increase of the diffusion coefficient of hydrogen by one order of magnitude.

The improvement of optical reflectance of BaO–ZnO–B2O3–SiO2 (BZBS) glass by the addition of various types of micron-scale crystalline fillers (TiO2, SiO2, ZrO2, Al2O3, MgO, and cordierite) was investigated for application of the materials to barrier ribs of plasma display panels. The fillers were partially dissolved during sintering, yielding an increased local volume of the fillers in the submicron range, filler rearrangement along boundaries of sintered glass frits, and rather irregular and rugged filler shapes differing from the original morphologies. The measured optical reflectance of the various filler added specimens was within the 30–70% range, which was much higher than the predicted values (less than 10%) based on the rule of mixture of the refractive index. Here we report that the high reflectance of the barrier rib glass for plasma display panels is explained by light scattering by the increased submicron portion of the partially dissolved residual fillers, the size of which is similar to the visual spectrum range (0.4–0.7 μm). The order of reflectance improvement among different types of filler-embedded specimens was consistent with that of the degree of dispersion of the residual fillers in the glass matrix.

The debonding behavior of perfluorocyclobutane (PFCB) films on silicon (Si) has been investigated using Vickers indentation as a function of cure temperature and film thickness. PFCB films on Si were processed by spin coating (1–4 μm) and solution casting (20–60 μm). The interfacial shear strength of solution-cast PFCB films was independent of film thickness. The interfacial shear strength increased with cure temperature. The PFCB/Si cured at 225 °C exhibited interfacial shear strength of 123 MPa, and the strength increased to 163 MPa when the cure temperature was raised to 275 °C. The increase in interfacial-shear strength with temperature has been attributed to the increase in the density of bonds between PFCB and Si due to an increase in the density of crosslinks. Spin-coated films exhibited cracking due to the penetration of the indenter into the substrate, and the extent of cracking increased with the load.