36 research outputs found
High temperature heat treatment of B precursor and P.I.T. process optimization to increase Jc performances of MgB2-based conductor
Promising results reported in our previous works led us to think that
production of B powder plays a crucial role in MgB2 synthesis. A new method for
boron preparation has been developed in our laboratory. This particular process
is based on magnesiothermic reaction (Moissan process) with the addition of an
initial step that gives boron powder with nano-metric grain size. In this paper
we report our efforts regarding optimization of PIT method for these nanometric
powders and the resolution of problems previously highlighted such as the
difficulty in powder packaging and the high friction phenomena occurring during
cold working. This increases cracking during the tape and wire manufacturing
leading to its failure. Packaging problems are related to the amorphous nature
of boron synthesized in our laboratory, so a crystallization treatment was
applied to improve crystallinity of B powder. To prevent excessive friction
phenomena we synthesized non-stoichiometric MgB2 and using magnesium as
lubricant. Our goal is the Jc improvement, but a global physical-chemical
characterization was also made to analyze the improvement given by our
treatments: this characterization includes X-ray diffraction, resistivity vs.
temperature measurement, SEM image, besides magnetic and transport Jc
measurements.Comment: 15 pages, 11 figure
Validation of a Simulation Methodology for Thermoplastic and Thermosetting Composite Materials Considering the Effect of Forming Process on the Structural Performance
This research work investigated the influence of the press molding manufacturing process on the mechanical properties, both for thermoplastic and thermosetting fiber reinforced composite materials. The particular geometry of the case study, called Double Dome, was considered in order to verify the behavior of the Thermoplastic and Thermosetting prepreg in terms of shell thickness variation and fibers shear angle evolution during the thermoforming process. The thermoforming simulation was performed using LS-DYNA Finite Element Analysis (FEA) code, and the results were transferred by Envyo, a dedicated mapping tool, into a LS-DYNA virtual model for the structural simulation. A series of Double Dome specimens was produced with industrial equipment, and a bending experimental test was been carried on. Finally, a numerical-experimental correlation was performed, highlighting a significant forecast of the mechanical properties for the considered component
Magnetic properties of spin diluted iron pnictides from muSR and NMR in LaFe1-xRuxAsO
The effect of isoelectronic substitutions on the microscopic properties of
LaFe1-xRuxAsO, for 0< x< 0.8, has been investigated by means of muSR and 139La
NMR. It was found that Ru substitution causes a progressive reduction of the
N\`eel temperature (T_N) and of the magnetic order parameter without leading to
the onset of superconductivity. The temperature dependence of 139La nuclear
spin-lattice relaxation rate 1/T_1 can be suitably described within a two-band
model. One band giving rise to the spin density wave ground-state, while the
other one is characterized by weakly correlated electrons. Fe for Ru
substitution yields to a progressive decrease of the density of states at the
Fermi level close to the one derived from band structure calculations. The
reduction of T_N with doping follows the predictions of the J_1-J_2 model on a
square lattice, which appears to be an effective framework to describe the
magnetic properties of the spin density wave ground-state.Comment: 6 pages, 8 figure
Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)
We investigate the effect of external pressure on magnetic order in undoped
LnFeAsO (Ln = La, Ce, Pr, La) by using muon-spin relaxation measurements and
ab-initio calculations. Both magnetic transition temperature and Fe
magnetic moment decrease with external pressure. The effect is observed to be
lanthanide dependent with the strongest response for Ln = La and the weakest
for Ln = Sm. The trend is qualitatively in agreement with our DFT calculations.
The same calculations allow us to assign a value of 0.68(2) to the Fe
moment, obtained from an accurate determination of the muon sites. Our data
further show that the magnetic lanthanide order transitions do not follow the
simple trend of Fe, possibly as a consequence of the different -electron
overlap.Comment: 16 pages, 11 figure
Implementation of the ERAS (Enhanced Recovery After Surgery) protocol for colorectal cancer surgery in the Piemonte Region with an Audit and Feedback approach: study protocol for a stepped wedge cluster randomised trial: a study of the EASY-NET project
The phase diagram of the Sr-Si system
The phase diagram of the Sr\u2013Si system has been investigated across almost the whole composition range (0\u201375 at.% Si) using differential thermal analysis (DTA), metallographic analysis, X-ray diffraction and electron microscopy. Four intermediate phases exist: Sr2Si (PbCl2-type), Sr5Si3 (Cr5B3-type), SrSi (CrB-type) and the dimorphic SrSi2 compound. The low-temperature form alpha-SrSi2 is cubic, SrSi2-type, and the
high-temperature form beta-SrSi2 is tetragonal with the alpha-ThSi2 structure-type. For this last phase a solid solubility range, from about 62.0 to 66.7 at.% Si, has also been found. Four eutectics occur in the system: at about 3 at.% Si and 745 \u25e6C, 44 at.% Si and 1110 \u25e6C, 61 at.% Si and 1055 \u25e6C, 74 at.% Si and 1045 \u25e6C