A model is developed to analyze the microstructure evolution in a continuously solidified hypermonotectic alloy. The model takes into account the common actions of the nucleation and diffusional growth/shrinkage of the minority phase droplets, the spatial phase segregation, and the convections of the melt. The microstructure formation in a continuously solidified hypermonotectic alloy is calculated. The numerical results demonstrate that the convections have great effect on the microstructure formation. The convective flow against the solidification direction causes an increase in the nucleation rate while the convective flow along the solidification direction causes a decrease in the nucleation rate of the minority phase droplets. The convections lead to a more nonuniform distribution of the minority phase droplets in the melt. It causes an increase in the size of the largest minority phase droplets and is against the obtaining of the hypermonotectic alloys with a well-dispersed microstructure.

Welded joints of P92 steel subjected to creep testing at 650 °C and 70 MPa were investigated. Type IV cracking was observed in the fine-grained heat-affected zone (FGHAZ) of the welded joints by optical microscopy. It was found that with varying creep times, the number of creep voids increased at an accelerating rate and the maximum number of voids was formed in the FGHAZ. Scanning electron microscopy observations revealed that precipitates were formed in the interior of creep voids, suggesting that the nucleation of the creep voids is related to the precipitates. These creep voids then connected with each other, isolated the grain from the matrix, and formed zigzag microcracks, leading to type IV cracking. New coarse carbides—the Laves phase and Cr7C3—were precipitated during creep. These carbides can deteriorate the creep strength and stimulate the nucleation of creep voids in the FGHAZ.

We report on the enhanced dielectric constant and electrical resistivity of the Co-ferrite (CoO.Fe2O3) by partially substituting Fe with La. Structural characteristics of La-doped Co ferrite namely CoO.Fe1.925La0.075O3 indicate the cubic inverse spinel phase with a small amount of LaFeO3 additional phase. The lattice parameter obtained is 8.401 Å (±0.001 Å), which is higher than that reported for Co ferrite (8.387 Å, ±0.001 Å). The dielectric constant and electrical resistivity of CoO.Fe1.925La0.075O3 are higher compared with pure Co ferrite. The dielectric constant dispersion of CoO.Fe1.925La0.075O3 in the frequency range of 100 Hz to 1 MHz fits to the modified Debye’s function with more than one ion contributing to the relaxation. Temperature-dependent electrical resistivity curves exhibit two distinct regions indicative of two different types of conduction mechanisms. Analysis of the data indicates that the small polaron and variable-range hopping mechanisms are operative in the 220 to 300 K and 160 to 220 K temperature regions, respectively.

In this study, we synthesized ZnO nanowires using Au catalytic particles formed on a ZnO seed layer. We modulated the microstructure of the ZnO seed layer by changing the sputtering power to investigate how the underlying ZnO film microstructure affects the distribution of ZnO nanowires. Examining the samples after each of the three key steps of the growth process (ZnO seed layer deposition, Au catalytic particle formation, and nanowire growth) using various characterization methods such as scanning electron microscopy, transmission electron microscopy, and x-ray diffraction helped us illuminate the profound impacts of the grain size of the seed layer on the nanowire density.

Over a long period (>10 years), the prediction of iron/mild steel corrosion in concrete requires the use of a mechanistic approach. For that purpose, a key point of the mechanisms involved is the localization of the oxygen reduction sites within the thick corrosion layers, which may greatly influence the nature of the rate-limiting step. In this context, iron rebars (originally covered with concrete) were sampled from a 50-year-old historical building and submitted to isotopic tracers methods (18O) combined with structural Raman microspectroscopy analyses on transverse sections. By this method, the authors demonstrate that the oxygen reduction sites are strongly impacted by the presence of a conductive phase (magnetite) in contact with the metallic substrate.

By measuring the ion concentration in a pressure-induced infiltration experiment on a hydrophobic Zeolite Socony Mobil-5, it is found that the nanopore wall has a strong ion repelling effect. When the initial ion concentration is relatively low, only water molecules can enter the nanopores. Once the initial ion concentration is relatively high, ions can infiltrate into the nanopores, but the effective ion concentration of the confined liquid is much lower.

We report a novel approach to realize the formation of well-distributed nanodispersions in n-type filled skutterudite through the manipulation of metastable void fillers by a designed sophisticated process of materials synthesis. Metastable Ga filling in CoSb3 is proved to happen at high temperature. The subsequent controlled annealing procedure drives Ga out of the crystal voids and finally leads to the homogeneous dispersion of GaSb nanodots with an average size of 11 nm in CoSb3 matrix. The grain size of nanodispersions can be manipulated by the controlled cooling procedure. The well-distributed nanodispersions are observed to enhance Seebeck coefficients and reduce lattice thermal conductivity at low temperature. Therefore, the thermoelectric performance of nanocomposite is improved in the whole temperature range. The highest figure of merit (ZT) is obtained to be 1.45 at 850 K, and an average ZT of 0.99 in 300−850 K is achieved for Yb0.26Co4Sb12/0.2GaSb nanocomposite.

Soldering to Cu interconnect pads with Sn-containing alloys usually leads to the formation of a layered Cu3Sn/Cu6Sn5 structure on the pad/solder interface. Frequently, microscopic voids within Cu3Sn have been observed to develop during extended thermal aging. This phenomenon, commonly referred to as Kirkendall voiding, has been the subject of a number of studies and speculations but so far the root cause has remained unidentified. In the present work, 103 different Cu samples, consisting of 101 commercially electroplated Cu and two high-purity wrought Cu samples, were surveyed for voiding propensity. A high temperature anneal of the Cu samples before soldering was seen to significantly reduce the voiding level in subsequent thermal aging. For several void-prone Cu foils, the anneal led to significant pore formation inside the Cu. In the mean time, Cu grain growth in the void-prone foils showed impeded grain boundary mobility. Such behaviors suggested that the root cause for voiding is organic impurities incorporated in the Cu during electroplating, rather than the Kirkendall effect.

Cadmium selenide (CdSe) belongs to a class of important II–VI semiconductors widely used in optical, sensor, and laser materials and quantum-dot light-emitting diodes. Here we present the first direct calorimetric measurement of the surface energy of wurtzite CdSe. CdSe nanoparticles with particle size between 20 and 60 nm were prepared by a hydrothermal method without additives to control morphology, and the surface energy was derived from the drop solution enthalpies in molten sodium molybdate and from water adsorption calorimetry. The surface energy of the hydrated surface is 1.31 ± 0.26 J/m2, whereas that of the anhydrous surface is 1.65 ± 0.27 J/m2. These values are significantly lower than those for ZnO and many other oxides.

The heterocomponent films of polypyridine ruthenium(II) complexes and methyl viologen derivatives, and polypyridine ruthenium(II) complexes and alkyl chain derivatives have been successfully obtained using a layer-by-layer fabrication method. We determined their photocurrent generation properties and noted that the photocurrent generation strongly depended on the inner layer. A higher photocurrent generation in the donor–acceptor film was obtained than in a single-component film of the chromophore.

We study the one-pot facile hydrothermal growth of ultralong silver–carbon (Ag–C) nanocables with Ag nanowires as the cores and carbon as the sheaths through the mediation of H2SO4 and without using an organic surfactant. In the investigation, Ag–C nanostructures were systematically and extensively examined as a function of both temperature and H2SO4 concentration to locate the optimal conditions for preparing ultralong, robust, and uniform Ag–C coaxial nanocables at T = 180 °C and 0.5 M H2SO4. The characterization clearly demonstrated a simple, efficient, and surfactant-free synthesis of Ag–C nanocables. In the hydrothermal process, glycerol acts as both reducing agent and carbon source, while H2SO4 mediates the directional growth of the silver nanowire core and assists the deposition of carbon. Moreover, the nanocables manifest unusual ferromagnetism at room temperature and a plausible mechanism of forming Ag–C nanocables was proposed as a result of the chain-like hydrogen sulfate compounds owing to the H2SO4 mediation.

A rich research history exists for crystalline growth by vapor–liquid–solid (VLS) methods, but not for amorphous growth. Yet VLS growth in the absence of crystallographic influences provides an ideal laboratory for exploring surface energy effects, including the role of line tension. We discuss the growth of amorphous silica nanowires from indium droplets by a modified VLS method. Multiple strands issue from each droplet, each strand having <1% (i.e., < 5 nm) of the radius of the droplet. We analyze the surface forces for this system, including line tension, and combine data in a novel way to estimate the surface energy of silica, the interfacial energy of liquid indium on silica, and the line tension at the three-phase boundary. The results suggest that the growth of these silica strands would be impossible without the presence of a negative line tension that also serves to stabilize the strand radii against perturbation.

A comprehensive investigation has been made of the solidification of nitrogen-atomized Al86Ni6Y4.5Co2La1.5, using focused ion beam, transmission electron microscopy, and other analytical means. Face-centered cubic Al2Y was identified to be the leading crystalline phase rather than crystalline Al. A new orthorhombic-structured phase was identified in partially or fully crystallized powder particles. Apart from oxygen, nitrogen was also found to be associated with the leading crystalline phase Al2Y in which nitrogen exists as substitutional Nx−. These findings facilitate the basis for understanding the unique aspects of the Al86Ni6Y4.5Co2La1.5 bulk metallic glass, including its powder preparation by gas atomization.

Electromigration behavior and fast circuit failure with respect to crystallographic orientation of Sn grains were examined. The test vehicle was Cu/Sn–3.0 wt% Ag–0.5 wt% Cu/Cu ball joints, and the applied current density was 15 kA/cm2 at 160 °C. The experimental results indicate that most of the solder bumps show different microstructural changes with respect to the crystallographic orientation of Sn grains. Fast failure of the bump occurred due to the dissolution of the Cu circuit on the cathode side caused by the fast interstitial diffusion of Cu atoms along the c-axis of the Sn grains when the c-axis was parallel to the electron flow. Slight microstructural changes were observed when the c-axis was perpendicular to the electron flow. In addition, Cu6Sn5 intermetallic compound (IMC) was formed along the direction of the c-axis of the Sn grains instead of the direction of electron flow in all solder ball joints.

We report a detailed study of the structural, chemical, electrical, and magnetic properties of undoped ZnO thin films grown under different conditions and the films that were annealed in various environments and irradiated with an ultraviolet laser. Samples prepared in low oxygen pressure or subsequently annealed in vacuum have always been strongly magnetic. Oxygen-annealed films displayed a sequential transition from the ferromagnetic to the diamagnetic state as a function of the annealing temperature. Reversible switching of room temperature ferromagnetism and n-type conductivity have been demonstrated either by annealing in different environments or by a novel laser irradiation treatment. Enhancements in both the electrical conductivity and magnetic moment have been controlled precisely with laser pulses, without altering the crystal structure. Electron paramagnetic resonance data were found to be in good agreement with the magnetization and conductivity measurements. Our secondary ion mass spectrometer and electron energy loss spectrometer studies conclusively rule out the presence of any external ferromagnetic impurities.