Bacillus pasteurii was used as synthesis director for the formation of hollow cylinder and helical NiO micro/nanostructure under urea hydrolysis conditions. Bacteria were capable of precipitating nickel product from nickel solution by metabolic processes. An appropriate amount of both water and bacterial solution were required to precipitate the nickel product in good yield. The average crystallite size of NiO was 11.45 nm and lengths of the cylinder and helices were non-uniform (~2–7 µm) and were varied with bacterial body structure template. The present study demonstrates a feasibility of synthesizing bacteria-guided metal oxide crystals for various functional applications.

Electrochemical dissolution by congruent oxidation of Fe Pd in 1 M HCl solution was strongly controlled by crystallographic orientation. Anodic dissolution was characterized over a wide variety of grain surface plane orientations providing a detailed view of the crystallographic nature of oxidative dissolution and surface facet evolution as a function of grain orientation. Near {100}-oriented grains retained low surface roughness after corrosion and low dissolution rates. Grains with orientation within 2° of {111} were also topographically smooth after dissolution and were nearly as corrosion resistant as {100} grains. Overall dissolution depth depended linearly on crystallographic angle within 40° of {100} and within 10° of {111} planes. Post-corrosion surface faceting and dissolution were substantially increased at grain orientations near {110} and were highest between 10° and 20° from the {111} plane normal. Grains at these crystallographic angles roughened during oxidative dissolution by forming complex semi-periodic topographies. These finely spaced arrays of terraces and ledges likely consisted of combinations of more corrosion resistant low-index planes. Therefore, the overall corrosion depth within a grain possessing an initially irrational crystal orientation was determined by the amount of dissolution required to expose new, slowly dissolving surface facets with low-index orientations. Computations of Fe–Pd alloy surface energies and surface atom coordination as a function of crystal orientation are utilized to help support this explanation.

The need for reducing the operating temperature of solid-oxide fuel cells (SOFCs) imposed by cost reduction has pushed significant progress in fundamental understanding of the individual components, as well as materials innovation and device engineering. Proton-conducting oxides have emerged as potential alternative electrolyte materials to oxygen-ion conducting oxides for operation at low and intermediate temperatures. This article describes major recent developments in electrolytes, electrodes, and complete fuel cell performance for SOFCs based on proton-conducting electrolytes. Although the performance of such fuel cells is still relatively modest, significant improvements in the power density output have been made during the last couple of years, and this trend is expected to continue.

Solid-oxide fuel cells (SOFCs) are unique in their ability to directly convert the chemical energy of a wide variety of fuels to electric power with unmatched energy conversion efficiency. The articles in this issue of MRS Bulletin highlight the enormous potential of, and recent progress toward, operating SOFCs at lower temperatures (<650°C). Lower temperatures dramatically increase the number of potential applications for this technology as well as provide the opportunity to incorporate a wider variety of materials in SOFC power generation systems with greater reliability and lower cost. The articles in this issue describe materials development and processing for low-temperature SOFCs, including the enabling of nanotechnology and microelectromechanical systems-based cell designs, the development of highly active electrodes and their three-dimensional microstructural characterization, as well as the use of novel proton-conducting electrolytes, all of which provide new avenues of research. New fabrication methods are also being applied in the development of micro-SOFCs and microtubular SOFCs with higher power densities. Finally, advances in lowering performance degradation rates, a critical commercialization issue, are described.

Solid-oxide fuel cells (SOFCs) are an energy conversion technology with unique potential to have the highest energy conversion efficiency with the least environmental impact, as well as broad fuel flexibility from renewable to conventional fuels. Lowering the SOFC operating temperature will further lower system and operational costs, increase long-term durability, and allow more rapid start-up, providing feasibility for load following and transportation applications. Unfortunately, at reduced temperatures, the thermally activated nature of ionic conduction and electrochemical reactions increase polarization resistances, thus decreasing cell and system performance. However, lower operating temperatures also create the opportunity to employ nanostructured materials with higher surface area-to-volume ratios and greater interphase and interfacial regions, which can greatly enhance electrochemical performance. Here, we review recent progress in the development of various nanostructured electrodes and electrolytes and discuss their effects on the enhancement of the electrocatalytic activity of oxygen reduction and fuel oxidation, as well as oxygen-ion conduction, in order to achieve high-performance low-temperature SOFCs.

In this study, bioactive glass powders were synthesized via an inexpensive hydrothermal chemical route by the use of ultrasonic energy irradiation. Soda lime, calcium nitrate tetrahydrate, and diammonium hydrogen phosphate were used as the precursor materials to synthesize low-sodium bioactive glass materials based on the conventional 45S5 Bioglass®. The morphological properties of the synthesized powders and the microwave-sintered dense compact were investigated. The mechanical properties of the fabricated dense bioactive glasses were characterized and were found to be very good. The ability to form biological apatite under physiological conditions was demonstrated with simulated body fluid (SBF). The material was shown to be highly biocompatible using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay with osteoblast-like MG63 cells. The cell adhesion and proliferation behavior of osteoblast-like MG63 cells were investigated and found to be excellent.

The commercially abundant low purity calcium fluoride powder was directly loaded for spark plasma sintering (SPS). In a vacuum atmosphere with a constant pressure held at 70 MPa the sintering temperature was systematically varied in the range of 500–850 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques were used to characterize the raw powder; and for studying the microstructural properties and in-line transmittance of the finalized ceramics, SEM and Fourier transform infrared spectroscopy (FTIR) were used. Digital images of the 700 °C sintered translucent CaF2 ceramic were taken along with transmittance recordings. The grain growth mechanisms and activation energy values were determined; and the influences of temperature on the relative density, grain size, and optical transmittance were demonstrated. Furthermore, for the first time, a plausible predominant mechanism was proposed for describing the different sintering stages of calcium fluoride ceramics.

To produce the magnetic core of electric motors, nonoriented electrical steels (NOESs) are used with an electrically insulating coating applied to the surface. Residual stress is induced during the coating process, which will alter the hardness and magnetic domain structure of the NOES. In this study, the effect of the coating is examined, specifically, its role in creating a residual stress near the coating/steel interface. This stress was investigated by the nanoindentation technique. With this method, a ∼30 µm deep affected area was observed for NOES along both the rolling and transverse cross section directions, when in the presence of the coating. A biaxial tensile stress of ∼200 MPa was calculated from the measured hardness values in the NOES, which was linked to variations in the magnetic domain structure near the interface. The observed magnetic domain structure was simplified by the reduction of supplemental domain structure near the coating/steel interface.

When properly designed at ultra-low density, hollow metallic microlattices can fully recover from compressive strains in excess of 50%, while dissipating a considerable portion of the elastic strain energy. This article investigates the physical mechanisms responsible for energy loss upon compressive cycling, and attributes the most significant contribution to a unique form of structural damping, whereby elastic local buckling of individual bars releases energy upon loading. Subsequently, a simple mechanical model is presented to capture the relationship between lattice geometry and structural damping. The model is used to optimize the microlattice geometry for maximum damping performance. The conclusions show that hollow metallic microlattices exhibit exceptionally large values of the damping figure of merit, (Young's modulus)1/3(loss coefficient)/(density), but this performance requires very low relative densities (<1%), thus limiting the amount of energy that can be dissipated.