We have used a hydrogel templating technique followed by the subsequent evaporation of water present to fabricate porous cement and porous PDMS composites, and we have analyzed their sound absorption properties. All experiments were carried out with hydrogel slurries of broad bead size distributions. Porous PDMS and cement composites were produced with porosities of up to 80% and 70%, respectively. Scanning electron microscope analysis shows fibrous domains within the voids created by the hydrogel in the cement samples and open pore network in the PDMS composites of initial hydrogel content higher than 70 vol%. Sound absorption was improved with respect to control nonporous samples in all composites with porosities higher than 60 vol%, where an open pore structure was formed. The porous PDMS and porous cement produced by this method show better sound absorption at 200–400 Hz and 1200–1800 Hz frequency ranges when compared with the sound absorption in the intermediate frequencies range between 400 and 1000 Hz.

The intermetallic materials digold bismuthide, gold diantimonide, and gold ditelluride were chemically synthesized with a bottom-up wet chemical approach, which has not been achieved before. These gold-based materials display a nano- to microparticle grain size and a well-defined composition-based structure. True intermetallic nanoparticle-based materials have traditionally proven challenging to obtain via wet chemical approaches, making the materials created here significant from a fundamental synthesis standpoint. The knowledge gained by developing reliable synthesis approaches toward intermetallic nanoparticles may be used to develop new materials and enhance the understanding of how to refine the characteristics and enhanced properties of emerging nanoparticle semiconductor materials in advanced applications such as for thermoelectrics.

High rate of charge carrier recombination is a critical factor limiting the photocatalytic activity of g-C3N4. In this contribution, we demonstrate that this issue can be alleviated by constructing a plasmonic photocatalyst with tailored plasmonic-metal nanostructures, i.e., core–shell-typed Ag@SiO2 nanoparticles. Compared with pure g-C3N4, the photocatalytic hydrogen production activity was enhanced by 63% for Ag@SiO2/g-C3N4. As analysis from the photoluminescence results, the enhancement could be attributed to that plasmonic nanostructures favored the separation of electron–hole pairs in the semiconductor due to localized surface plasmons resonance effect. It was found that the silica shell between the Ag nanoparticles and g-C3N4 was essential for the better photocatalytic activity of Ag@SiO2/g-C3N4 than that of Ag/g-C3N4 by limiting the energy-loss Förster energy transfer process.

Heat transfer coefficients of porous copper samples with single- and double-layer structures, fabricated by the lost carbonate sintering process, were measured under forced convection conditions using water as the coolant. Compared with the empty channel, introducing a porous copper sample enhanced the heat transfer coefficient 5–8 times. The porous copper samples with double layers of porosities of 60% and 80% often had lower heat transfer coefficients than their single layer counterparts with the same overall porosities because the coolant flowed predominantly through the high-porosity layer. For the same double-layer structure, the order of the double layer had a large effect on the heat transfer coefficient. Placing the high-porosity layer next to the heat source was more efficient than the other way around. The predictions of a segment model developed for the heat transfer coefficient of multilayer structures agreed well with the experimental results.

Tetrahedrite-structure compounds, of general composition Cu12−xZnxSb4S13, are an earth-abundant alternative to PbTe for thermoelectric power generation applications in the intermediate high-temperature range (300–400°C). Tetrahedrites can be synthesized in the laboratory using a multi-step process involving long annealing times. However, this compound also exists in natural mineral form, and, in fact, is one of the most abundant copper-bearing minerals in the world. We show here that by simply mixing natural mineral tetrahedrite with pure elements through high-energy ball milling without any further heat treatment, we can successfully obtain material with figure of merit near unity at 723 K.

The relationship between morphology and crystallography of an entangled lathy ferrite during directional solidification in Fe–Cr–Ni alloy has been investigated. During solidification, morphology of the lathy ferrite depends on the orientation relationship between the lathy ferrite and austenite. When the plane in the austenite substrate is ${(1\bar 11)_{\rm{\gamma }}}$, “Y-shaped” lathy ferrite grows in an entangled cluster and the orientation relationship between the lathy ferrite and austenite is the Nishiyama–Wassermann relationship. Lathy ferrite is preferentially elongated along ${\langle 211\rangle _{\rm{\gamma }}}$ and ${\langle 011\rangle _{\rm{\gamma }}}$ directions on ${(1\bar 11)_{\rm{\gamma }}}$ plane due to lower misfit. The included angle among the “Y-shaped” lathy ferrite is about 120° because the angle between each pair of ${[21\bar 1]_{\rm{\gamma }}}$, ${[\bar 112]_{\rm{\gamma }}}$, and ${[\bar 1\bar 2\bar 1]_{\rm{\gamma }}}$ crystal directions is equal to 120°. Formation mechanism of the perpendicular lathy ferrite has also been analyzed according to the relationship between ${\langle 211\rangle _{\rm{\gamma }}}$ and ${\langle 011\rangle _{\rm{\gamma }}}$ on ${(1\bar 11)_{\rm{\gamma }}}$ plane. This indicates that required crystal morphology of the lathy ferrite in the solidified microstructure can be obtained by controlling the crystal plane of austenite.

This paper describes the use of self-patterning anodic aluminum oxide (AAO) layers to enable localized metal contacts and to achieve passivation for the rear surface of silicon solar cells. There are no commercially available technologies that are capable of patterning localized contacts on silicon solar cells with low cost, high-throughput, and robust processing, especially when closely spaced small-area openings are required. In the approach described, nanoporous AAO layers were formed by anodizing aluminum over intervening dielectrics on textured silicon wafers. When the anodized test structures were fired in a belt furnace, localized contacts formed at peaks and valleys of the alkaline-textured silicon surface. Furthermore, the anodization contributed ∼35 mV increment in the implied Voc of the test structures. Low contact resistivity was demonstrated and the proposed contacting mechanism for this innovative localization suggested that the contact percentage can be controlled by varying the anodization duration and/or the surface morphology.

Metal matrix composites manufactured by the powder metallurgy route often exhibit different tensile strength due to particle geometrical reasons. The tensile strength tendency was studied in 2024 Al/30% SiCp composites as a function of relative particle size (RPS) ratio between the matrix and reinforcement particles. Dry blended composite powders, with different RPS ratios, were hot-pressed in vacuum, their microstructures were observed, and their tensile properties were measured. It was found that a decrease in RPS ratio resulted in a decrease in tensile strength, as a result of improved distribution of the SiCp. Despite their low density and heterogeneous distribution, 3-μm SiCp-reinforced composites had maximum tensile strength. The main reasons were due to the few fracture for small SiCp and the strengthening of the matrix microstructure from small particle effects. Solution treatment plus aging of the composites with the RPS ratio of 10:3 resulted in a significant improvement (42%) in strength due to the smaller diffusion path length for the alloying element.

Microcalorimetry was used to study the adsorption of water molecules on the surface of ZnAl2O4 nanoparticles ranging from the anhydrous to the fully hydrated states. Water adsorption of ZnAl2O4 showed similar behavior to the isostructural γ-Al2O3 and revealed possible existence of hydrophobic sites on the surfaces. At the lowest measured coverage (0.49 H2O per nm2), the enthalpy of adsorption is −155.46 kJ/mol. This value decays with increasing coverage and at around 13 H2O per nm2, the heat of adsorption levels at −44 kJ/mol, suggesting further adsorbed water has liquid-like features. The anhydrous surface energy for ZnAl2O4 was calculated to be 1.36 ± 0.08 J/m2 using water adsorption microcalorimetry data. High-temperature oxide melt solution calorimetry was also used to assess the surface energy, which was 1.29 ± 0.33 J/m2. Surface energies at different hydration states are reported and showed decrease with increasing coverage, suggesting that low humidity conditions allow higher driving forces for coarsening.

Understanding the interaction of group V impurities with intrinsic defects in ZnO is important for developing p-type material. We have studied N-doped ZnO thin films and N-doped bulk ZnO crystals, with positron annihilation spectroscopy, in contrast to earlier studies that have concentrated on N-implanted ZnO crystals. We show that the introduction of N impurities into ZnO, irrespective of whether it is done during the growth of thin films or bulk crystals or through implantation and subsequent thermal treatments, leads to the formation of stable vacancy clusters and negative ion-type defects. Interestingly, the stability of these vacancy clusters is found almost exclusively for N introduction, whereas single Zn vacancy defects or easily removable vacancy clusters are more typically found for ZnO doped with other impurities.

Li-stabilized Na-β″/β-Al2O3(Na1.61Li0.29Al10.70O17) nanorods were prepared by a soft chemistry process using a 1-alkyl-3-methylimidazolium bromide ([CXmim]Br, X = 4, 12, 16) ionic liquid as a template. Pure Na-β″/β-Al2O3 rods were obtained by heating at 1100 °C with [C16mim]Br as the template, resulting in nanorods of approximately 50 nm in diameter and 200–300 nm in length. It is demonstrated that alkyl chain length is the main factor determining the aspect ratio of the nanorods. The specific surface area of the powder is 81.3 m2/g, which is more than one order of magnitude higher than that of the powder prepared by a conventional solid state reaction process. The formation mechanism of the nanorods is proposed.

This paper investigates the critical loading condition that causes the emission of dislocations in silicon subjected to nanoindentation. A theoretical model is established, which follows the deformation process that with increasing the indentation load, a phase transformation takes place, followed by partial dislocations emitting from the interface between the phase-transformed zone and the originally crystalline silicon when the indentation load reaches a critical value. In the model, the emission process represents the generation of a dipole of Shockley partial dislocations. One partial dislocation of the dipole, located at the interface, is considered immobile, whereas the other partial dislocation moves into the bulk of silicon. The effects of the indenter geometry and of the location of dislocation nucleation on the critical indentation load are discussed. The model predicts that a sharp indenter leads to a relatively smaller critical indentation load. The model prediction is verified by an indentation experiment.

Large surface area, homogenous, and adhesive TiO2 coatings on stainless steel substrates were prepared by electrophoretic deposition (EPD) of colloidal dispersions of TiO2 nanoparticles in water and ethanol. Several chemical additives were used to optimize the deposition process. The best results were obtained for dispersions in water containing a mixture of Tiron and Pluronic® F127, which gave homogeneous layers, showing excellent adhesion and a large BET surface area, close to 200 m2/g. Ethanol dispersions also gave much adhesive coatings when poly(acrylic acid) was used as an additive. Nevertheless, their thickness was lower, and their surface area was less than 100 m2/g. We have shown that water splitting, occurring in the aqueous sol during the EPD, led to deposited masses lower than those expected from the Hamaker law. However, the electrolysis of water and also the small cracks in the coatings had no detrimental effects on adhesion.

This work attempts to optimize past research results on lead zirconate titanate (PZT) using the fabrication processes at the U.S. Army Research Laboratory so as to achieve a high degree of {001} texture and improved piezoelectric properties. A comparative study was performed between Ti/Pt and TiO2/Pt bottom electrodes. The results indicate that the use of a highly oriented {100} rutile phase TiO2 led to highly textured {111} Pt which in turn improved both the PTO and PZT orientations. PZT (52/48) and (45/55) thin films with and without PTO seed layers were deposited and examined via x-ray diffraction (XRD) methods as a function of annealing temperature. The seed layer provides significant improvement in the {100} orientation generally, and in the {001} subset of planes specifically, while suppressing the {111} orientation of the PZT. Improvements in the Lotgering factor (f) were observed from an existing Ti/Pt/PZT process (f = 0.66) to samples using the PTO seed layer deposited onto the improved Pt electrodes, TiO2/Pt/PTO/PZT (f = 0.96).

Visible light emitting ZnO quantum dots (QDs) were synthesized by a modified sol–gel method and in situ coated with the amino acid cysteine to modify their surface chemistry and govern the crystal growth process. Surface chelation by a hydrophilic thiol such as cysteine offered a fine control over the particle size and modulated the optical emission and its stability by reducing the density of surfacial oxygen deficiencies and also induced the formation of hierarchical nanostructures in the solution. TEM and XRD results confirmed the formation of mono-dispersed and spherical ZnO QDs in the size range 2.5–3.8 nm. The modulation of band gap energies was manifested in the visible emission of cysteine modified QDs, which was found to be remarkably stable for cell labeling applications, when compared to the photoluminescence of conventional ZnO QDs.