Synthesis of hollow silica spheres SBA-16 with large-pore diameter

Hollow silica SBA-16 spheres with cubic ordered mesoporous shells were synthesized by an emulsion-templating method, using Pluronic F127 as a structure-directing agent, tetraethyl orthosilicateas as a silica source and heptane as a cosolvent in the presence of NH₄F. The size of these spheres is in the range of 10 to 30 μm. The shell is about 700 nm thick and consists of large pores, ~ 9 nm in diameter, arranged in a cubic order. After calcination, the spheres maintain their mesoporosity and show a high surface area of 822 m²/g. The formation mechanism of the silica hollow spheres is discussed.     

A new route toward semiconductor nanospintronics: highly Mn-doped GaAs nanowires realized by ion-implantation under dynamic annealing conditions

We report on highly Mn-doped GaAs nanowires (NWs) of high crystalline quality fabricated by ion beam implantation, a technique that allows doping concentrations beyond the equilibrium solubility limit. We studied two approaches for the preparation of Mn-doped GaAs NWs: First, ion implantation at room temperature with subsequent annealing resulted in polycrystalline NWs and phase segregation of MnAs and GaAs. The second approach was ion implantation at elevated temperatures. In this case, the single-crystallinity of the GaAs NWs was maintained, and crystalline, highly Mn-doped GaAs NWs were obtained. The electrical resistance of such NWs dropped with increasing temperature (activation energy about 70 meV). Corresponding magnetoresistance measurements showed a decrease at low temperatures, indicating paramagnetism. Our findings suggest possibilities for future applications where dense arrays of GaMnAs nanowires may be used as a new kind of magnetic material system.     

Axial InP nanowire tandem junction grown on a silicon substrate

Tandem InP nanowire pn-junctions have been grown on a Si substrate using metal-organic vapor phase epitaxy. In situ HCl etching allowed the different subcomponents to be stacked on top of each other in the axial extension of the nanowires without detrimental radial growth. Electro-optical measurements on a single nanowire tandem pn-junction device show an open-circuit voltage of 1.15 V under illumination close to 1 sun, which is an increase of 67% compared to a single pn-junction device.     

Historical trends in mercury sedimentation and mixing in the Strait of Georgia, Canada

Seventeen sediment cores collected in the Strait of Georgia reveal a history of mercury contamination that began in the 1860s and include episodic contamination during World War II and in the late 1960s. Surface sediment mercury concentrations ranged from 60 to 420 ng/g dry weight and the current fluxes to sediments are estimated at 5-181 ng cm(-2) a(-1). In one location in Port Moody Arm, a Hg spill seems to have sufficiently poisoned the sediments to eliminate biomixing for about 20 years. Although the surface concentration of Hg is likely to decrease at all stations in coming years, sites in the industrialized Vancouver Harbor and Port Moody Arm will continue to be sufficiently contaminated to endanger benthic organisms. Variations in sedimentation and mixing rates among sites result in surface sediment Hg concentration patterns that do not reflect accurately the distribution of Hg flux. In particular, the concentration of Hg in sediments near the mouth of the Fraser River is low, despite the high Hg load of that river, because of dilution by other particles. A preliminary Hg budget indicates that most of the Hg enters the Strait of Georgia via the Fraser River (2090 kg a(-1)), and that, while burial in Strait of Georgia sediments is a major sink (1800 kg a(-1)), there may be a significant outflow of Hg through Juan de Fuca Strait (approximately 3400 kg a(-1)).     

Influence of genotype and protein content on the baking quality of hearth bread

The relationships between protein content and quality and the loaf characteristics of hearth breads made from the respective flours were investigated for 20 wheat genotypes, comprising both commercially grown cultivars and advanced breeding lines, grown in 1997 and 1998. In both years the average protein content was increased by increasing the level of nitrogenous fertiliser application, this effect being more pronounced in 1997 than in 1998. Grain samples were milled and evaluated for endosperm hardness, protein content, SDS sedimentation volume, mixing properties and baking quality determined by a hearth bread baking test using optimal mixing and fixed proving time. When producing hearth bread, both the form (height/width) ratio and loaf volume are critical external characteristics. Genotype differences, mainly due to differences in protein quality, were more important for both form ratio and loaf volume than differences in protein content. The dough development time of the Farinograph, operated at high speed (126 rev min^?1), was the best indicator of heart bread baking quality, giving high positive correlations to both the volume (r = 0.89) and form ratio of the loaf (r = 0.90). Climatic differences between the two years, in particular temperature during ripening, also affected the quality parameters studied. Copyright © 2004 Society of Chemical Industry     

Heat treatment of PM parts by Hot Isostatic Pressing

Hot Isostatic Pressing (HIP) is a technology that has been around for 60+ years. By using high temperature and high gas pressure, dry metal and ceramic powders can be consolidated and a volume decrease can be achieved. Later developments include rapid cooling and rapid quenching to enable higher productivity and high-pressure heat treatment. This paper shows the advantages of having HIPing and Heat Treatment combined for Powder metallurgy parts.