Compositional patterning in two-phase immiscible alloys during severe plastic deformation at elevated temperatures has been investigated. Kinetic Monte Carlo computer simulations were used to test the proposed idea that patterning derives from a dynamic competition between homogenization by forced chemical mixing and phase separation by thermally activated diffusion [P. Bellon and R.S. Averback, Phys. Rev. Lett.74, 1819 (1995) and F. Wu et al., Acta Mater.54, 2605 (2006)]. We utilize the concept of pair diffusion coefficients to compare thermal diffusion with forced chemical mixing and discuss the fundamentally different behavior with respect to pair separation distance in both mechanisms. While the general ideas of this model are verified and are in good quantitative agreement with our simulations, it is found that the dynamic processes of alloys under high-temperature shear are very complex, even in highly idealized systems, making experimental verification of this model very difficult. We illustrate our findings for a model AB alloy with properties similar to Cu–Ag by showing how alloy morphology and solubility depend on shear rate, temperature, and composition.

Among the different porous materials, bulk metallic glass (BMG) foams are of special interest due to their high strength combined with large elastic limit. Large surface areas and, therefore, high reactivity in chemical applications can be achieved by properly adjusting the pore characteristics. Pore size and pore size distribution are the key factors for determining the overall performance of open-cell porous materials used for functional applications, such as filtration or catalysis. As a result, the control of these factors is a necessary requirement for material design and application. In this work, BMG foams are produced by powder metallurgy through the selective dissolution of a fugitive phase. The work is focused on the manufacturing processes needed to properly control pore size and pore size distribution. The results reveal that customized hybrid BMG porous structures can be produced through the controlled milling of the BMG-composite powders.

Mn-doped bismuth oxide bromide microspheres have been prepared by the hydrothermal method. The resultant composite microspheres exhibited higher photocatalytic activity under visible light irradiation, attributing to the improvement of the photo-absorption property and the separation efficiency of photogenerated electrons and holes. The holes and O2•− are the main active species in aqueous solution under visible light irradiation, rather than •OH.

Solid oxide fuel cells (SOFCs) are attractive for clean and efficient electricity generation, but high operating temperatures (Top > 800 °C) limit their widespread usage. Oxygen ion conducting cathode materials (mixed ion-electron conductors, MIECs), such as La1−xSrxCo1−yFeyO3 (LSCF), enable lower Top by reducing cathode polarization losses. Understanding how composition affects oxygen diffusion in LaFeO3 is vitally important for designing high-performance LSCF cathodes. To do this, we employ first-principles density functional theory plus U (DFT+U) calculations to show how lanthanum vacancies in LaFeO3 dramatically change the oxygen diffusion coefficient. Our ab initio results show that A-site substoichiometry is a viable route to increased oxygen diffusion and higher SOFC performance.

Grain refinement strengthening in low carbon ferrite–cementite steel was investigated using the estimated true stress (σ)–true strain (ε) relationship up to the plastic deformation limit, i.e., just before fracture. Static and stepwise tensile tests were performed using ferrite–cementite (FC) steels with ferrite grain sizes in the range 0.5–34 μm, and the σ–ε relationships up to the plastic deformation limit were estimated by using the Bridgman equation. In the nominal stress–strain curves, the lower yield stress and tensile strength increased and the uniform and total elongations decreased with a decrease in the ferrite grain size. It was found from the σ–ε relationships of the FC steels that grain refinement strengthening up to 0.8 μm can improve σ and ε at the plastic deformation limit. From the scanning electron microscopy observations of the cross-sectional planes parallel to the tensile direction for the FC steels, voids were observed at the interface between ferrite and cementite in the case where the thickness of elongated ferrite came close to the size of the dispersed cementite.

The development and characterization of pressure sensing porous nanocomposites are reported here. A thermoplastic polyurethane (TPU) was chosen as an elastomeric matrix, which was reinforced with multiwall carbon nanotubes (MWNTs) by high shear twin screw extrusion mixing. Porosity was introduced to the composites through the phase separation of a single TPU-carbon-dioxide gas solution. Interactions between MWNT and TPU were elucidated through calorimetry, gravimetric decomposition, conductivity measurements, and microstructure imaging. The piezoresistance (pressure–resistance) behavior of the nanocomposites was investigated and found to be dependent on MWNT concentration and nanocomposite microstructure. Mechanisms of piezoresistance in solid and porous nanocomposites are proposed.

Tissue engineering principles suggest the formation of 3D scaffolds based on polymer fibers and adhesive proteins. These scaffolds aim to mimic the native extracellular matrix and thus providing a favorable environment for cell attachment and proliferation. The application of an electric field (EF) can influence the quantity and the spatial orientation/conformation of adsorbed proteins, which could lead to changes in their functions. We study the influence of alternating current (AC) EF on the adsorption of fibronectin onto poly(etherimide) (PEI) electrospun fiber materials in 3D structures and subsequent cell adhesion. The results are compared with 2D PEI material and glass surface. 3D scaffolds adsorbed a lower amount of fibronectin than 2D film or glass. Application of AC EF with a frequency of 1 Hz decreased the adsorption of fibronectin. Cell adhesion on 3D materials was reduced compared with 2D film and glass. The application of EF with frequencies between 1 and 10 Hz improved cell adhesion on both 2D and 3D materials.

An in situ redox reaction was developed to synthesize bundled tungsten oxide (WO3@W18O49) ultrafine nanowires (BUNs) loaded with Ag nanoparticles using weakly reductive W18O49 and oxidative silver nitrate as precursor. However, due to the weak activation between the two reactants, redox just happened on the surface of W18O49, resulting in the formation of W18O49 coated with WO3 (here, we refer this structure to WOx simply), and the bulk phase of the composites retained the same pattern. Ag nanoparticles (<5 nm) with a narrow size distribution were obtained and immobilized onto WOx BUNs without any aggregation. The paper presented a systematic investigation on the Ag-WOx nanocomposite used as a catalyst for the reduction of p-nitrophenol and as an antibacterial agent against Escherichia coli. The remarkably enhanced performance may be ascribed to the moderate interaction of the small Ag-NPs and WOx BUNs with high specific surface area.

We have studied the magnetoresistance (MR) of hydrogen plasma-treated pure ZnO wires of tens of micrometer diameter at different temperatures. A negative MR of 1% at 8 T applied field is measured for all wires at 4 K, independent of the temperature (300 K … 773 K) used during the hydrogen treatment. However, a positive MR develops, the higher the treatment temperature. The MR can be explained with a semiempirical model taking into account local magnetic moments and the s–d exchange interaction. These results together with field anisotropy in the MR indicate the appearance of magnetic order due to the hydrogen treatment in agreement with recently published reports on the influence of hydrogen in bulk ZnO single crystals. Hydrogen doping may provide a way to trigger defect-induced magnetism in small oxide structures.

Electrical fields can be used to heat selectively dislocations and grain boundaries to a much higher temperature compared with the bulk. This selective joule heating, if uncontrolled by limiting the current flow, can lead to melting of grain boundaries and sintering of poly- and nanocrystalline materials close to the theoretical density in a much shorter time due to fast diffusivities of the order of 10−4 to 10−5 cm2/s in the liquid. I refer to this sintering mode as selective-melt sintering, which can occur at lower overall temperatures with much lower energy consumption compared with conventional sintering involving solid-state diffusion.

The effects of stearic acid on the high-energy ball milling of tin powder have been investigated. The mean crystallite sizes, microstrain, and phase transformations were examined using different techniques like x-ray diffraction (XRD), Rietveld refinement method, and differential scanning calorimetry (DSC). After 28 h of milling, the Rietveld analysis showed the stabilization of Sn mean crystallite sizes at around 50 nm. Due to the presence of oxygen in stearic acid, the milling process gradually produced an amorphous Sn oxide phase. The DSC thermogram of the sample milled for 28 h showed two exothermic peaks separated by an endothermic peak. Based on the DSC measurements, two samples were annealed at 240 and 350 °C for 20 min. The annealing at 240 °C confirmed the presence of an amorphous phase which crystallized in nanostructured tetragonal SnO phase. The annealing at 350 °C revealed the nucleation of nanostructured tetragonal SnO2 phase.

Hyperbranched polyurethane/Fe3O4 nanoparticles decorated multiwalled carbon nanotube (Fe3O4-MWCNT) nanocomposites were prepared by the in situ polymerization technique. The presence of Fe3O4 nanoparticles on the surface of the MWCNTs was confirmed by x-ray diffraction and transmission electron microscopic studies. The saturation magnetization value of Fe3O4-MWCNT was 0.23 emu/g. The glycidyl ether of bisphenol-A epoxy cured thermosetting nanocomposites exhibited enhanced tensile strength (6.4–38.5 MPa), scratch hardness (3.0–8.5 kg), and thermal stability (241–292 °C) with the increase of loading of Fe3O4-MWCNT (0–2 wt%). The nanocomposites possess good shape fixity over the repeated cycles of test. The nanocomposites also showed good shape recovery under the application of microwave irradiation. The shape recovery speed was found to be increased with the increase of the content of Fe3O4-MWCNT. Thus, the studied thermosetting nanocomposites have potential to be used as noncontact shape memory materials.

LM13 Al-alloy—cenosphere hybrid foam (HF) was made by foaming LM13 alloy–cenosphere mixture through a stir casting technique using CaCO3 as a foaming agent. In the melt mixture, 35 vol% of cenosphere was used and the foaming temperature was varied (660 and 690 °C). The foam contains microporosities as well as macroporosities and hence these are referred as HFs. The age-hardening characteristics and thereof deformation behavior of these foams have been examined using both microhardness and plateau stress measurements. It is further noted that energy absorption and plateau stress are maximum, and densification strain is minimum under peak-aged condition irrespective of the density of HF. Empirical relations are proposed to predict plateau stress, densification strain, and energy absorption as a function of aging time and relative density.

Natural fiber composites are becoming more attractive for applications as energy absorbers in the automotive industry despite their high moisture absorption characteristics. The main objective of this paper is to study the impact strength and moisture absorption properties of long fiber and short fiber hybrid composites using a kenaf/polyethylene terephthalate fiber reinforced in the polyoxymethylene matrix. The results obtained from the impact test gave 10.8 J/cm for the longer fiber hybrid composites, which is higher compared to 8.0 J/cm obtained for the short fiber hybrid composites due to less fiber pullout from the matrix. A moisture content of 0.92% and percentage water absorption of 6.77% were obtained for the long fiber composite due to poor interfacial adhesion between the fiber and the matrix. A high void content of 0.52% and porosity of 1.21% also accounted for high water and moisture absorption of the long fiber hybrid composite.

Solid oxide fuel cells (SOFCs) offer an efficient energy conversion technology for alleviating current energy problems. High temperature proton-conducting (HTPC) oxides are promising electrolytes for this technology, since their activation energy is lower than that of conventional oxygen-ion conductors, enabling the operating temperature reduction at 600 °C. Among HTPC oxides, doped BaZrO3 materials possess high chemical stability, needed for practical applications. Though, poor sinterability and the resulting large volume of highly resistive grain boundaries hindered their deployment for many years. Nonetheless, the recently demonstrated high proton conductivity of the bulk revived the attention on doped BaZrO3, stimulating research on solving the sintering issues. The proper selection of dopants and sintering aids was demonstrated to be successful for improving the BaZrO3 electrolyte sinterability. We here briefly review the synthesis strategies proposed for preparing BaZrO3-based nanostructured powders for electrolyte and electrodes, with the aim to improve the SOFC performance.

The structure of ultrathin amorphous carbon (a-C) films synthesized by filtered cathodic vacuum arc (FCVA) deposition was investigated by high-resolution transmission electron microscopy, electron energy loss spectroscopy, and x-ray photoelectron spectroscopy. Results of the plasmon excitation energy shift and through-thickness elemental concentration show a multilayered a-C film structure comprising an interface layer consisting of C, Si, and, possibly, SiC, a buffer layer with continuously increasing sp3 fraction, a relatively thicker layer (bulk film) of constant sp3 content, and an ultrathin surface layer rich in sp2 hybridization. A detailed study of the C K-edge spectrum indicates that the buffer layer between the interface layer and the bulk film is due to the partial backscattering of C+ ions interacting with the heavy atoms of the silicon substrate. The results of this study provide insight into the minimum thickness of a-C films deposited by FCVA under optimum substrate bias conditions.

Grain boundary segregation provides a method for stabilization of nanocrystalline metals—an alloying element that will segregate to the boundaries can lower the grain boundary energy, attenuating the driving force for grain growth. The segregation strength relative to the mixing enthalpy of a binary system determines the propensity for segregation stabilization. This relationship has been codified for the design space of positive enthalpy alloys; unfortunately, quantitative values for the grain boundary segregation enthalpy exist in only very few material systems, hampering the prospect of nanocrystalline alloy design. Here we present a Miedema-type model for estimation of grain boundary segregation enthalpy, with which potential nanocrystalline phase-forming alloys can be rapidly screened. Calculations of the necessary enthalpies are made for ∼2500 alloys and used to make predictions about nanocrystalline stability.

Metal oxide optoelectronics is an emerging field that exploits the intriguing properties of the ns orbital-derived isotropic band structure as a replacement for traditional silicon-based electronics in advanced active-matrix information displays. Although the device performance of metal oxide thin film transistors (TFTs) has been substantially improved, the device reliability against external light and gate bias stress remains a critical issue. This paper provides a literature review of light-induced gate bias stress instability in metal oxide TFTs and explain the importance of photo-bias instability in the applications of metal oxide TFTs to optoelectronic device. The rationale of threshold voltage (Vth) instability under the negative bias illumination stress (NBIS) condition is discussed in detail. The charge trapping/injection model, oxygen vacancy photoionization model, and ambient interaction model are described as plausible degradation mechanisms. Finally, the possible approaches to prevent NBIS-induced Vth instability are proposed based on an understanding of the NBIS instability.

A novel surface enhanced Raman scattering (SERS) substrate was produced by combining Ag nanoparticles (AgNPs) and carbon nanocoils (CNCs). Three different methods were developed for loading AgNPs on CNCs, which include (i) direct deposition of AgNPs on CNCs by radio-frequency magnetron sputtering (RFMS) to form an Ag–CNC hybrid, (ii) deposition of a TiO2 film on CNCs by RFMS, followed by photoinduced growth of AgNPs to form an Ag–TiO2–CNC hybrid (called A-substrate), and (iii) deposition of a TiO2 film on CNCs by spin coating and then photoinduced growth of AgNPs to form an Ag–TiO2–CNC hybrid (called B-substrate). Experimental SERS results showed that B-substrates exhibited the highest SERS enhancement with an enhancement factor of over 107 for rhodamine 6G. The as-prepared Ag–TiO2–CNC substrates also showed much higher Raman signal enhancement than ordinary planar SERS substrates in our system. This was mainly due to the unique three-dimensional structure where the large surface area was available for loading more densely packed AgNPs which contribute to abundant Raman hot spots.