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Anelastic properties and solid state reactivity of Fe-Al nanostructured intermetallic compounds
No full textStructural evolution of a stoichiometric silicon oxycarbide from gel to glass to decomposition
No full textSAXS STUDY OF COARSENING MECHANISM OF GP ZONES IN THE Al-Li-Mg SYSTEM.
No full textA study by small angle X-ray scattering is reported. Size distribution functions of GP zones in the growth stage are determined. As a result, an Ostwald ripening mechanism for the coarsening process can be inferred
FORMATION AND CRYSTALLIZATION OF AMORPHOUS NI-TI POWDERS PREPARED BY MECHANICAL ALLOYING
No full textStructural investigation of Pd76B24 glassy alloy. Local order parameters from a semi-empirical mathematical model
No full textThe PCF of Pd76B24 glassy alloy was approximated as a sum of analytical expressions each pertaining to a discrete contribution of distances, a further term accounting for the structureless range. The analysis brought to the light the presence of a large spread of pseudo-square distances near r1√2, characteristic of the octahedral coordination, overshadowed in the experimental behavior. A topological distribution close to the trigonal prism capped with three half octahedral appears a sound structural basis for the amorphous arrangement, in spite of its possible evaluation within the conceptual framework of a dense binary mixture of randomly packed hard spheres
Anelastic properties and solid state reactivity of Fe-Al nanostructured intermetallic compounds
No full textIron and Aluminium elemental powders mixed in the atomic ratio Fe50Al50 and Fe75Al25 have been alloyed using an high energy mill system. The structural transformation of the milled products has been followed using XRD techniques. Samples obtained from cold-consolidation of the milled powders have been used for Elastic Energy Dissipation measurements (IF) and analysed in the temperature range 300-980 K. The XRD spectra corresponding to specimens milled for long times reveal the formation of the FeAl and Fe3Al nanostructured intermetallic compounds. The IF spectra show two relaxational damping peaks P-1,P-2 in the temperature range 600-980 K. The peak evolution for different milling treatments indicates a Zener and a grain-boundary relaxation mechanisms for P-1 and P-2 respectively
MECHANICAL ALLOYING PROCESSES AND REACTIVE MILLING
No full textThe great flexibility of mechanically driven processes in designing functional materials has stimulated wide attention in the different side branches and research fields. Our current interest concerns both the inherent chemical properties of amorphous metal powders-in view of a possible exploitation in heterogeneous catalysis-as well as their chemical behaviors under reactive milling. Chemical effects were found to be responsible for changing the course of Mechanical Alloying processes (MA). Furthermore, deep structural characterizations of the powders under milling have revealed the subtle and sometimes unavoidable influence of gaseous contaminants from the reaction environment. These results were obtained from the use of complementary diffraction techniques and from the neutron diffraction analysis in particular. It is only natural to refer to these chemical aspects in terms of reactive milling and Mechanochemistry. Within this framework we focused on the active role of hydrogen, as a gaseous reagent or released in activated form from metal hydride lattices, to steer the end-products of MA and Mechanical Milling (MM) processes. On this basis, the possibility to run gaseous hydrogenation reactions under milling was also proven. For a better understanding of the underlying mechanism, MA and Mechanochemistry both require the proper definition of the main milling parameters. To this extent, an experimental method is briefly outlined for the direct evaluation of the collision frequency and energetical factors in ball milling processes
X-RAY-DIFFRACTION STUDY OF THE AMORPHIZATION PROCESS BY MECHANICAL ALLOYING OF THE NI-TI SYSTEM
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