Synthesis of zinc oxide/silica composite nanoparticles by flame spray pyrolysis

Zinc oxide (ZnO)/silica (SiO2) composite nanoparticles were made by flame spray pyrolysis. The effects of the Zn/Si ratio on particle properties were examined and compared with those of the pure ZnO and SiO2 particles made at the same conditions. Polyhedral aggregates of nano-sized primary particles were obtained in all experiments. The mixed-oxide primary particle size was smaller than that of pure oxides. The primary particles consisted of ZnO nano-crystals and amorphous SiO2, as seen by high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) analysis using the fundamental parameter approach. The XRD size of ZnO was controlled from 1.2 to 11.3 nm by the initial precursor composition and it was consistent with HR-TEM. The composite particles exhibited an excellent thermal stability and little crystalline growth of ZnO (e.g., from 1.9 to 2.2 nm) was observed even after calcination at 600°

Flame-made Ceria Nanoparticles

Flame spray pyrolysis (FSP) has been used to synthesize high-surface-area ceria from cerium acetate in acetic acid solution. With the addition of an iso-octane/2-butanol mixture to that solution, homogeneous CeO2 nanoparticles were obtained. The specific surface area of the powders ranged from 240 to 101 m2/g by controlling the oxygen dispersion and liquid precursor flow rates through the flame. Furthermore, for production rates from 2 to 10 g/h a constant average primary particle size could be obtained at selected process parameters. The ceria showed high crystallinity and primary particles with a stepped surface. The powder exhibited good thermal stability and conserved up to 40% of its initial specific surface area when calcinated for 2 h at 900 °C. This shows the potential of FSP made ceria for high-temperature applications as in three-way catalysts or fuel cell

Simultaneous deposition of Au nanoparticles during flame synthesis of TiO2 and SiO2

Nanostructured gold/titania and gold/silica particles with up to 4 wt% Au were made by a single-step process in a spray flame reactor. Gold(III)-chloride hydrate and titania- or silica-based metalorganic precursors were mixed in a liquid fuel solution, keeping concentrations in the flame and overall combustion enthalpy constant. The powders were characterized by x-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller, and ultraviolet-visible analysis. The titania or silica specific surface area and the crystalline structure of titania were not affected by the presence of gold in the flame. Furthermore the size of the gold deposits was independent of the metal oxide support (TiO2 or SiO2) and its specific surface area (100 and 320 m2/g, respectively). The gold nanoparticles were nonagglomerated, spherical, mostly single crystalline, and well dispersed on the metal oxide support. Depending on the Au weight fraction (1, 2, and 4 wt%) the Au nanoparticles' mass mean diameter was 3, 7, and 15 nm, respectively, on both titania and silica. The particles showed surface plasmon absorption bands in the ultraviolet-visible region, which is typical for nano-sized gold. This absorption band was red shifted in the case of the titania support, while no shift occurred with the silica suppor

Opinion: Eliminating aircraft soot emissions

Soot from aircraft engines deteriorates air quality around airports and can contribute to climate change primarily by influencing cloud processes and contrail formation. Simultaneously, aircraft engines emit carbon dioxide (CO2), nitrogen oxides (NOx), and other pollutants which also negatively affect human health and the environment. While urgent action is needed to reduce all pollutants, strategies to reduce one pollutant may increase another, calling for a need to decrease, for example, the uncertainty associated with soot's contribution to net radiative forcing (RF) in order to design targeted policies that minimize the formation and release of all pollutants. Aircraft soot is characterized by rather small median mobility diameters, dm=8–60 nm, and at high thrust, low (&lt; 25 %) organic carbon to total carbon (OC/TC) ratios, while at low thrust, the OC/TC can be quite high (&gt; 75 %). Computational models could aid in the design of new aircraft combustors to reduce emissions, but current models struggle to capture the soot, dm, and volume fraction, fv, measured experimentally. This may partly be due to the oversimplification of soot's irregular morphology in models and a still poor understanding of soot inception. Nonetheless, combustor design can significantly reduce soot emissions through extensive oxidation or lean, near-premixed combustion. For example, lean, premixed prevaporized combustors significantly reduce emissions at high thrust by allowing injected fuel to fully vaporize before ignition, while low temperatures from very lean jet fuel combustion limit the formation of NOx. Alternative fuels can be used alongside improved combustor technologies to reduce soot emissions. However, current policies and low supply promote the blending of alternative fuels at low ratios (∼ 1 %) for all flights, rather than using high ratios (&gt; 30 %) in a few flights which could meaningfully reduce soot emissions. Here, existing technologies for reducing such emissions through combustor and fuel design will be reviewed to identify strategies that eliminate them.</p

Kaptan Gibson

Jules Verne'in Servet'te yayımlanan Kaptan Gibson adlı romanının ilk ve son tefrikalar

Fluid Particle Accelerations in Fully Developed Turbulence

The motion of fluid particles as they are pushed along erratic trajectories by fluctuating pressure gradients is fundamental to transport and mixing in turbulence. It is essential in cloud formation and atmospheric transport, processes in stirred chemical reactors and combustion systems, and in the industrial production of nanoparticles. The perspective of particle trajectories has been used successfully to describe mixing and transport in turbulence, but issues of fundamental importance remain unresolved. One such issue is the Heisenberg-Yaglom prediction of fluid particle accelerations, based on the 1941 scaling theory of Kolmogorov (K41). Here we report acceleration measurements using a detector adapted from high-energy physics to track particles in a laboratory water flow at Reynolds numbers up to 63,000. We find that universal K41 scaling of the acceleration variance is attained at high Reynolds numbers. Our data show strong intermittency---particles are observed with accelerations of up to 1,500 times the acceleration of gravity (40 times the root mean square value). Finally, we find that accelerations manifest the anisotropy of the large scale flow at all Reynolds numbers studied.Comment: 7 pages, 4 figure