A recent report published by the National Petroleum Council (NPC) in the United States predicted a 50–60% growth in total global demand for energy by 2030. Because oil, gas, and coal will continue to be the primary energy sources during this time, the energy industry will have to continue increasing the supply of these fuels to meet this increasing demand. Achieving this goal will require the exploitation of both conventional and unconventional reservoirs of oil and gas in an environmentally acceptable manner. Such efforts will, in turn, require advancements in materials science, particularly in the development of materials that can withstand high-pressure, high-temperature, and high-stress conditions.

This study investigated the polarity effect of electromigration (EM) on the interfacial intermetallic compounds (IMCs) (γ-Cu5Zn8, Cu6Sn5) formation at the anode and the cathode in a Cu/Sn-9Zn/Cu sandwich with a constant direct current density of 1.0 × 103 A/cm2 at 100 °C. The EM had different polarity effects on the nucleation and growth rates of the interfacial Cu5Zn8 IMC from those of Cu6Sn5 IMC. Upon current stressing, the growth rate of the Cu-Zn intermetallic compound (γ-Cu5Zn8) at the cathode interface was much faster than that at the anode. However, the nucleation and growth of the Cu6Sn5 IMC at the anode interface were enhanced, though retarded at the cathode, under the influence of electric current. The mechanism of EM-induced Cu6Sn5 IMC formation towards the anodic Cu is also discussed.

The high-strain-rate mechanical properties, deformation mechanisms, and fracture characteristics of a bulk metallic glass (BMG)-matrix composite, consisting of an amorphous Zr57Nb5Cu15.4Ni12.6Al10 (LM106) matrix with crystalline tungsten reinforcement particles, were investigated using gas gun anvil-on-rod impact experiments instrumented with velocity interferometry (VISAR) and high-speed digital photography. The time-resolved elastic-plastic wave propagation response obtained through VISAR and the transient deformation states captured with the camera provided information about dynamic strength and deformation modes of the composite. Comparison of experimental measurements with AUTODYN-simulated transient deformation profiles and free surface velocity traces allowed for validation of the pressure-hardening Drucker–Prager model, which was used to describe the deformation response of the composite. The impacted specimens recovered for post-impact microstructural analysis provided further information about the mechanisms of dynamic deformation and fracture characteristics. The overall results from experiments and modeling revealed a strain to failure of ∼45% along the length and ∼7% in area, and the fracture initiation stress was found to decrease with increasing impact velocity because of the negative strain-rate sensitivity of the BMG.

In the coming decades, electricity's share of total global energy is expected to continue to grow, I and more intelligent processes will be introduced into the electric power delivery (transmission and distribution) networks. It is envisioned that the electric power grid will move from an electromechanically controlled system to an electronically controlled network in the next two decades. A key challenge is how to redesign, retrofit, and upgrade the existing electromechanically controlled system into a smart self-healing grid that is driven by a well-designed market approach. Revolutionary developments in both information technology and materials science and engineering promise significant improvements in the security, reliability, efficiency, and cost effectiveness of electric power delivery systems. Focus areas in materials and devices include sensors, smart materials and structures, microfabrication, nanotechnology, advanced materials, and smart devices.

Electron-beam-induced effects in preamorphized Sr2Nd8(SiO4)6O2 were investigated in situ using transmission electron microscopy with 200-keV electrons at temperatures ranging from 380 to 780 K. Within the electron-irradiated area, epitaxial recrystallization was observed from the amorphous/crystalline interface toward the surface, with the rate of recrystallization increasing as temperature increased from 380 to 580 K. Structural contrast features (i.e., O deficient amorphous material), as well as recrystallization, were observed outside of the irradiation area at temperatures from 680 to 780 K. Ionization-induced processes and local nonstoichiometry induced by oxygen migration and desorption are possible mechanisms for the electron-beam- induced recrystallization and for the formation of the structural contrast features, respectively.

The enthalpy of formation of cubic ceria–zirconia solid solutions (c-Ce(1−x)ZrxO2, 0.05 ⩽ x ⩽ 0.75) at 25 °C with respect to monoclinic zirconia (m-ZrO2) and cubic ceria (c-CeO2) has been measured by high-temperature oxide melt solution calorimetry. In contrast to fluorite solid solutions containing trivalent oxides (e.g., yttria–zirconia), mixing in c-Ce1−xZrxO2 shows moderate positive deviation from ideality. Evaluating the data within the framework of a regular solution model, the interaction parameter, Ω, is +51.0 ± 8.0 kJ/mol. The introduction of undersized Zr into CeO2 severely distorts and destabilizes the oxygen sublattice. Destabilization of c-Ce1−xZrxO2 may be relieved by reduction or clustering. A stable ordered compound in the CeO2–ZrO2 system is thermodynamically unlikely.

Biomass remains a key energy source for several billion people living in developing countries, and the production of liquid biofuels for transportation is growing rapidly. However, both traditional biomass energy and crop-based biofuels technologies have negative environmental and social impacts. The overall research challenge for bioenergy is to develop the technologies to produce useful products at low costs while minimizing the use of scarce resources such as arable land and water. This requires substantial advancements in modern biomass power generation and the success of liquid biofuel technologies that permit the use of lignocellulosic feedstocks or possibly algae. With such technologies, biomass resources could meet a significant fraction (over 10%) of global energy demand. Both improved policies and technologies are needed to ensure that bioenergy contributes significantly to economic, social, and environmental goals.

The cleanliness of hydrogen and the efficiency of fuel cells taken together offer an appealing alternative to fossil fuels. Implementing hydrogen-powered fuel cells on a significant scale, however, requires major advances in hydrogen production, storage, and use. Splitting water renewably offers the most plentiful and climate-friendly source of hydrogen and can be achieved through electrolytic, photochemical, or biological means. Whereas presently available hydride compounds cannot easily satisfy the competing requirements for on-board storage of hydrogen for transportation, nanoscience offers promising new approaches to this challenge. Fuel cells offer potentially efficient production of electricity for transportation and grid distribution, if cost and performance challenges of components can be overcome. Hydrogen offers a variety of routes for achieving a transition to a mix of renewable fuels.

This article focuses on the modeling and simulation of thin-film silicon solar cells to obtain increased efficiency. Computer simulations were used to study the performance limits of tandem and triple-junction, silicon-based solar cells. For the analysis, the optical simulator SunShine, which was developed at Ljubljana University, and the optoelectrical simulator ASA, which was developed at Delft University of Technology, were used. After calibration with realistic optical and electrical parameters, we used these simulators to study the scattering properties required, the absorption in nonactive layers, antireflective coatings, and the crucial role of the wavelength-selective intermediate reflector on the performance of the solar cells. Careful current matching was carried out to explore whether a high photocurrent [i.e., more than 15 mA/cm2 for a tandem hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) solar cell and 11 mA/cm2 for a triple-junction a-Si:H/amorphous silicon germanium (a-SiGe:H)/μc-Si:H solar cell] could be obtained. In simulations, the extraction of the charge carriers, the open-circuit voltage, and the fill factor of these solar cells were improved by optimizing the electrical properties of the layers and the interfaces: a p-doped, a-SiC layer with a larger band gap (EG > 2 eV) and buffer layers at p/i interfaces were used. Simulations demonstrated that a-Si:H/μc-Si:H solar cells could be obtained with a conversion efficiency of 15% or higher, and triple-junction a-Si:H/a-SiGe:H/μc-Si:H solar cells with an efficiency of 17%.

The pyrochlore compositions Gd2–yNdyZr2O7 (y = 0.0, 0.1, 0.4, 0.6, 1.0, 1.4, 1.6, and 2.0) were synthesized, and their ionic conductivity was determined (100 Hz–15 MHz, 622–696 K). The direct-current (dc) conductivity (σdc) varies upon Nd substitution at the Gd site, and a peaking effect in σdc was observed around y = 1.0. This indicates that a significant increase in conductivity can be obtained at moderately high temperatures by suitable doping at the Gd site with isovalent rare-earth ions like Nd. The extent of oxygen ion disorder determined from x-ray diffraction was found to decrease with increasing Nd content. The dc conductivity obeys the Arrhenius relation σdcT = σ0 exp(−E/kBT). The activation energy E and the preexponential factor σ0, which is a measure of the concentration of the mobile species, increase while going from the ordered Nd2Zr2O7 to the least ordered Gd2Zr2O7. These two processes presumably lead to the peaking of σdc at an intermediate Nd content. Our results also suggest that the cooperative motion of mobile ions does not contribute much to the increase in activation energy in this compound.

Flywheel energy storage systems use the kinetic energy stored in a rotor; they are often referred to as mechanical batteries. On charging, the fywheel is accelerated, and on power generation, it is slowed. Because the energy stored is proportional to the square of the speed, very high speeds are used, typically 20,000–100,000 revolutions per minute (rpm). To minimize energy loss due to friction, the rotors are spun in a vacuum and use magnetic bearings. The rotors today are typically made of high-strength carbon composites. One of the main limits to fywheels is the strength of the material used for the rotor: the stronger the rotor, the faster it can be spun, and the more energy it can store.

Increasing demand for energy, diminishing stocks of oil and natural gas, and the public's desire to enhance environmental quality, particularly by reducing greenhouse gas emissions, all point to the need for improved materials. For example, generating electricity from the most abundant fossil fuel, coal, efficiently and with no environmental damage, presents notable challenges to develop higher performance materials. Technologies exist to transform one fossil fuel to other uses, such as coal to a gas or liquid. New materials that increase the efficiency of the transformation and lower its cost would provide valuable flexibility. Materials should be evaluated in terms of their entire life-cycle in order to discern which will make the greatest contribution. Because society has many pressing needs, both commercial value and contribution to fundamental materials science should guide priorities in materials research.

Catalysis is the essential technology for chemical transformation, including production of fuels from the fossil resources petroleum, natural gas, and coal. Typical catalysts for these conversions are robust porous solids incorporating metals, metal oxides, and/or metal sulfides. As efforts are stepping up to replace fossil fuels with biomass, new catalysts for the conversion of the components of biomass will be needed. Although the catalysts for biomass conversion might be substantially different from those used in the conversion of fossil feedstocks, the latter catalysts are a starting point in today's research. Major challenges lie ahead in the discovery of efficient biomass conversion catalysts, as well as in the discovery of catalysts for conversion of CO2 and possibly water into liquid fuels.

Aviation accounts for about 3% of the current global energy consumption of 15 terawatts (TW). The global annual growth of energy use in the aviation sector is likely to be around 2.15% and will exceed that in other transportation sectors, although land transport will continue to consume the largest amounts of fuel. Figure 1 displays the historical improvements in energy efficiency in the aviation sector. Fuel use is determined by both operational and technological factors. The former includes the passenger load factor, ground efficiencies, taxi procedures, take-off and landing paths and circuitry (actual distance traveled versus a great-circle distance), and changes in the mixture of old and new aircraft and propulsion systems with time. Technology factors, focusing on materials issues, are described in greater detail herein.

Transmission electron microscopy (TEM) images, selected-area electron-diffraction patterns, high-resolution TEM images, and x-ray energy dispersive spectroscopy line scans for the ZnO/n-Si (001) heterostructures annealed at 900 °C showed that stacking faults and amorphous layers were formed in the lower region of the ZnO films. The stacking faults existing in the lower region of the ZnO columnar grains originated from the formation of zinc vacancy layers caused by the thermal treatment, resulting in the existence of a tensile strain. The formation of the amorphous layer in the ZnO film was attributed to the accumulation of zinc vacancy layers.

In many industrial countries, road transportation accounts for a significant portion of the country's energy consumption. In developing countries, the use of energy for transportation is on the rise. The recent increase in petroleum prices, expanding world economic prosperity, the probable peaking of conventional petroleum production in the coming decades, and concerns about global climate changes require efforts to increase the efficiency of the use of, and develop alternatives for, petroleum-based fuels used in road transportation. The energy efficiency of a vehicle could be improved in several ways: lightweighting the vehicle structure and powertrain using advanced materials and designs, improving the efficiency of the internal combustion engine, reducing tire rolling resistance, and hybridization. Each of these efforts will require improvements in materials and processes.

A post heat treatment of reaction-sintered SiC at 1700 °C in nitrogen atmosphere significantly reduced electrical resistivity. A trace of insulating Si3N4 phase was detected via nitrogen heat treatment in high-resolution transmission electron microscopy observation; however, based on x-ray photoelectron spectroscopy, the evidence of nitrogen doping into SiC lattice has been claimed as the mechanism to the decreased resistivity. The increase of the total volume of SiC was apparent in x-ray diffraction during the nitrogen heat treatment, which was interpreted to stem from the growth of the nitrogen-doped intergranular SiC particles and surface doping of the primary SiC to reduce the contact resistance between the primary SiC particles.

California continues its tradition of leading the United States in environmental stewardship through the California Solar Initiative (CSI), a $3.3 billion program established in January 2006. The goal is to generate 3 GW of electricity by 2017 through photovoltaic methods by installing solar cells on the roofs of existing and new residential and commercial buildings (see Figure 1). CSI will “reduce our output of greenhouse gases by 3 million tons,” California Governor Arnold Schwarzenegger said in a speech given in October 2006. “That is equivalent to taking one million cars off the road.”

We propose a new method for the preparation of the polymer/organoclay nanocomposite, termed the solution and melt mixing (SOAM) method, where the polymer and clays are first blended in solution, and subsequently the mixture is further blended in the melt. We prepared the ternary nanocomposite systems of poly(styrene-co-acrylonitrile) (SAN), poly(vinyl chloride) (PVC) and Cloisite25A clays (C25A) by solution blending as well as by the SOAM method. The C25A content in the nanocomposite was optimized by analyzing the x-ray diffraction (XRD) data of binary mixtures (SAN/C25A and PVC/C25A nanocomposites). The values of the interaction parameter (χab) were calculated by using the molar attraction constants of the specific functional groups derived from Hoy’s table. While PVC and C25A were shown to be highly compatible, SAN and C25A were less compatible. XRD data and transmission electron microscopy observations indicated that the SAN/PVC/C25A nanocomposites had at least partially exfoliated structures. The tensile modulus and the elongation at break of the nanocomposites prepared by the SOAM method were higher than those prepared by simple solution blending.