111 research outputs found
Sonochemical Modification of the Superconducting Properties of MgB2
Ultrasonic irradiation of magnesium diboride slurries in decalin produces
material with significant inter-grain fusion. Sonication in the presence of
Fe(CO)5 produces magnetic Fe2O3 nanoparticles embedded in the MgB2 bulk. The
resulting superconductor-ferromagnet composite exhibits considerable
enhancement of the magnetic hysteresis, which implies an increase of vortex
pinning strength due to embedded magnetic nanoparticles
Effects of High Intensity Ultrasound on BSCCO-2212 Superconductor
Slurries of powdered Bi2Sr2CaCu2O8+x superconductor in low volatility alkanes
were treated with intense ultrasound. Significant enhancements of magnetic
irreversibility as well as transport critical current are reported. The effects
are dependent on the concentration of the slurry and are optimal for 1.5% wt.
slurry loading. Electron microscopy shows that ultrasonic treatment leads to a
change in grain morphology and intergrain welding. The observed enhancement of
superconducting properties is consistent with the limitations in critical
currents in BSCCO superconductor being due to intergrain coupling rather than
intragrain pinning strength.Comment: 3 page
Plasma formation and temperature measurement during single-bubble cavitation
Single-bubble sonoluminescence (SBSL) results from the
extreme temperatures and pressures achieved during bubble
compression; calculations have predicted the existence of a
hot, optically opaque plasma core with consequent bremsstrahlung
radiation. Recent controversial reports claim the
observation of neutrons from deuterium–deuterium fusion
during acoustic cavitation. However, there has been previously
no strong experimental evidence for the existence of a
plasma during single- or multi-bubble sonoluminescence. SBSL
typically produces featureless emission spectra that reveal little
about the intra-cavity physical conditions or chemical processes.
Here we report observations of atomic (Ar) emission and extensive
molecular (SO) and ionic (O2 cation) progressions in SBSL spectra
from concentrated aqueous H2SO4 solutions. Both the Ar and SO
emission permit spectroscopic temperature determinations, as
accomplished for multi-bubble sonoluminescence with other
emitters. The emissive excited states observed from both Ar+
and O2 cation are inconsistent with any thermal process. The Ar excited
states involved are extremely high in energy (>13 eV) and cannot
be thermally populated at the measured Ar emission temperatures
(4,000–15,000 K); the ionization energy of O2 is more than
twice its bond dissociation energy, so O2 likewise cannot be
thermally produced. We therefore conclude that these emitting
species must originate from collisions with high-energy electrons,
ions or particles from a hot plasma core
- …