Modern design and manufacturing methodologies for magnesium (Mg) sheet panels require formability data for use in computer-aided design and computer-aided engineering tools. To meet this need, forming-limit diagrams (FLDs) for AZ31B and ZEK100 wrought Mg alloy sheets were developed at elevated temperatures for strain rates of 10−3 and 10−2 s−1. The elevated temperatures investigated range from 250 to 450 °C for AZ31B and 300 to 450 °C for ZEK100. The FLDs were generated using data from uniaxial tension, biaxial bulge, and plane-strain bulge tests, all carried out until specimen rupture. The unique aspect of this study is that data from materials with consistent processing histories were produced using consistent testing techniques across all test conditions. The ZEK100 alloy reaches greater major true strains at rupture, by up to 60%, than the AZ31B alloy for all strain paths at all temperatures and strain rates examined. Formability limits decrease only slightly with a decrease in temperature, less than 30% decrease for AZ31B and less than 35% decrease for ZEK100 as the temperature decreases from 450 to 300 °C. This suggests that forming processes at 250-300 °C are potentially viable for manufacturing complex Mg components.
Freezing of protein solutions perturbs protein conformation, potentially leading to aggregate formation during long-term storage in the frozen state. Macroscopic protein concentration profiles in small cylindrical vessels were determined for a monoclonal antibody frozen in a trehalose-based formulation for various freezing protocols. Slow cooling rates led to concentration differences between outer edges of the tank and the center, up to twice the initial concentration. Fast cooling rates resulted in much smaller differences in protein distribution, likely due to the formation of dendritic ice, which traps solutes in micropockets, limiting their transport by convection and diffusion. Analysis of protein stability after more than 6 months storage at either 10 degrees C or 20 degrees C [above glass transition temperature (Tg)] or 80 degrees C (below Tg) revealed that aggregation correlated with the cooling rate. Slow-cooled vessels stored above Tg exhibited increased aggregation with time. In contrast, fast-cooled vessels and those stored below Tg showed small to no increase in aggregation at any position. Rapid entrapment of protein in a solute matrix by fast freezing results in improved stability even when stored above Tg. (c) 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:11941208, 2013
Stable dispersions of graphene oxide nanoplatelets were formed in water at pH 2-10 even with 5 wt% NaCl. For these conditions, oil-in-water emulsions stabilized with graphene oxide nanoplatelets remained partially stable for 1 year. The droplet sizes were as small as similar to 1 mu m with a low nanoplatelet concentration of 0.2 wt%. The emulsions were stable even for nanoplatelet concentrations down to 0.001 wt%. The stabilities of the emulsions even at high salinity may be attributed to the high anion density at the graphene oxide nanoplatelet edges which protrude into the water phase. Furthermore, the graphene oxide nanoplatelets are shown to adsorb on the surfaces of the oil droplets. The conceptual picture of graphene oxide nanoplatelets adsorbed to a greater extent on the water side of the oil/water interface, along with the high density of anions on their edges, cause the oil/water interface to curve about the oil phase, resulting in oil-in-water emulsion droplets. The dispersion stability with a very small amount of graphene oxide-based stabilizer, offers an intriguing opportunity for applications including CO2 sequestration and enhanced oil recovery in deep subsurface formations, which generally contain high-salinity brines. (C) 2013 Elsevier Inc. All rights reserved.
A homologous series of Au coated iron oxide nanoparticles with hydrodynamic diameters smaller than 60 nm was synthesized with very low Au-to-iron mass ratios, as low as 0.15. The hydrodynamic diameter was determined by dynamic light scattering and the composition by atomic absorption spectroscopy and energy dispersive x-ray spectroscopy. Unusually low Au precursor supersaturation levels were utilized to nucleate and grow Au coatings on iron oxide relative to the formation of pure Au nanoparticles. This approach produced unusually thin coatings by lowering autocatalytic growth of Au on Au, as shown by transmission electron microscopy. Nearly all of the nanoparticles were attracted by a magnet, indicating a minimal number of pure Au particles. The coatings were sufficiently thin to shift the surface plasmon resonance to the near infrared with large extinction coefficients, despite the small particle hydrodynamic diameters observed from dynamic light scattering to be less than 60 nm.
Perovskites are of great interest as replacements for precious metals and oxides used in bifunctional air electrodes involving the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, we report the synthesis and activity of a phase-pure nanocrystal perovskite catalyst that is highly active for the OER and ORR. The OER mass activity of LaNiO3, synthesized by the calcination of a rapidly dried nanoparticle dispersion and supported on nitrogen-doped carbon, is demonstrated to be nearly 3-fold that of 6 nm IrO2 and exhibits no hysteresis during oxygen evolution. Moreover, strong OER/ORR bifimctionality is shown by the low total overpotential (1.02 V) between the reactions, on par or better than that of noble metal catalysts such as Pt (1.16 V) and Ir (0.92 V). These results are examined in the context of surface hydroxylation, and a new OER cycle is proposed that unifies theory and the unique surface properties of LaNiO3.
Perovskite catalysts are of great interest as replacements for precious metals and oxides used in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Perovskite electrocatalysts have been shown to have greater specific activities than precious metals and their oxides, but high mass activities have not yet been realized due to vague or incomplete mechanistic understanding of catalysts active sites coupled with inadequate synthesis techniques which often result in unwanted phase impurities and micron-scale materials. Herein, we demonstrated precise control over the synthesis of essentially phase pure perovskite nanocrystals with mass activities exceeding that of IrO2 and possessing comparable or greater bifunctional character than leading precious metals such as Ir and Pt. The robust aqueous synthesis of ABO3 perovskites such as LaCoO3, LaMnO3, LaNixFe1-xO3 and Ba0.5Sr0.5Co0.8Fe0.2O3-δ will be demonstrated, and the resulting electrocatalytic activities of these materials will be presented. We will examine these results in the context of proposed perovskite activity descriptors, surface hydroxylation, oxygen vacancies and mechanistic pathways for the OER and ORR. Catalytic activity is determined using electroanalytical techniques such as rotating disk electrochemistry and cyclic voltammetry in conjunction with materials characterization enabled by dynamic light scattering, electron microscopy, nitrogen sorption, X-ray photoelectron spectroscopy and X-ray diffraction. It is demonstrated that these highly active perovskite catalysts are an emerging replacement for the precious metals used not just for the OER and ORR, but also for the chlor-alkali and oxygen depolarized cathode industries as well.
In the face of increasing energy demands, geologic CO2 sequestration (GCS) is a promising option to mitigate the adverse effects of climate change. To ensure the environmental sustainability of this option, we must understand the rates and mechanisms of key geochemical reactions and their impacts on GCS performance, the multiphase reactive transport of CO2, and the management of environmental risks. Strong interdisciplinary collaborations are required to minimize environmental impacts and optimize the performance of GCS operations.