5,360 research outputs found
Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue
Here we report on a novel chemical route to synthesize homogenous cobalt
doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The
influence of the synthesis temperature, autoclave dwell time and metal doping
on the structural and microstructural as well as on the optical properties of
the synthesized titanate nanotubes is studied and discussed. The optical band
gaps of the CoTNT samples are red shifted in comparison with the values
determined for the undoped samples, such red shifts bringing the absorption
edge of the CoTNT samples into the visible region. CoTNT materials also
demonstrate particular high adsorption ability for methylene blue, the amount
of the adsorbed dye being higher than the one predictable for a monolayer
formation. This suggests the possibility of intercalation of the dye molecule
between the TiO6 layers of the TNT structure. It is also shown that the
methylene blue sensitized Co-doped nanostructures are highly stable under UV
radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure
The Variable Polarity Plasma Arc Welding Process: Its Application to the Space Shuttle External Tank
This report describes progress in the implementation of the Variable Polarity Plasma Arc Welding (VPPAW) process at the External Tank (ET) assembly facility. Design allowable data has been developed for thicknesses up to 1.00 in. More than 24,000 in. of welding on liquid oxygen and liquid hydrogen cylinders has been made without an internal defect
The variable polarity plasma arc welding process: Its application to the Space Shuttle external tank
The technical history of the variable polarity plasma arc (VPPA) welding process being introduced as a partial replacement for the gas shielded tungsten arc process in assembly welding of the space shuttle external tank is described. Interim results of the weld strength qualification studies, and plans for further work on the implementation of the VPPA process are included
Synthesis of sub-5 nm Co-doped SnO nanoparticles and their structural, microstructural, optical and photocatalytic properties
A swift chemical route to synthesize Co-doped SnO nanopowders is
described. Pure and highly stable SnCoO (0 x
0.15) crystalline nanoparticles were synthesized, with mean grain sizes <
5 nm and the dopant element homogeneously distributed in substitutional sites
of the SnO matrix. The UV-visible diffuse reflectance spectra of the
SnCoO samples reveal red shifts, the optical bandgap
energies decreasing with increasing Co concentration. The Urbach energies of
the samples were calculated and correlated with their bandgap energies. The
photocatalytic activity of the SnCoO samples was
investigated for the 4-hydroxylbenzoic acid (4-HBA) degradation process. A
complete photodegradation of a 10 ppm 4-HBA solution was achieved using 0.02%
(w/w) of SnCoO nanoparticles in 60 min of
irradiation.Comment: 29 pages, 2 tables, 10 figure
Blue and green upconversion in Er(3+)-doped fluoroindate glasses
The upconversion properties of Er3+ in fluoroindate bulk glasses (composition: 40InF3-20ZnF2-16BaF2-(20-x)SrF2-2GaF3-2NaF-xErF3 with x=1,2,3 and 4 mole %) are investigated, following F-4(9/2) excitation with a red krypton laser. A strong green and a weaker blue luminescence is observed at room temperature corresponding to emissions from the thermally coupled S-4(3/2) and H-2(11/2) bands and the H-2(9/2) level respectively. Resonant energy transfer processes involving two excited erbium ions and a two-step absorption process are proposed to explain the upconversion phenomena. The emission intensities depend on the excitation power as P(exc)n with 1.5 less-than-or-equal-to n less-than-or-equal-to 1.7 for the green and 1.6 less-than-or-equal-to n less-than-or-equal-to 1.9 for the blue emission. The decay times and the relative intensities of the luminescences are also studied as a function of Er3+ concentration
Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders
Oxide based diluted magnetic semiconductor (DMS) materials have been a
subject of increasing interest due to reports of room temperature
ferromagnetism in several systems and their potential use in the development of
spintronic devices. However, concerns on the stability of the magnetic
properties of different DMS systems have been raised. Their magnetic moment is
often unstable, vanishing with a characteristic decay time of weeks or months,
which precludes the development of real applications. This paper reports on the
ferromagnetic properties of two-year-aged Ti1-xCoxO2-{\delta} reduced anatase
nanopowders with different Co contents (0.03<x<0.10). Aged samples retain
rather high values of magnetization, remanence and coercivity which provide
strong evidence for a quite preserved long-range ferromagnetic order. In what
concern Co segregation, some degree of metastability of the diluted Co doped
anatase structure could be inferred in the case of the sample with the higher
Co content.Comment: 15 pages, 5 figure
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