Gianluca Fiore

Effect of minor elements addition on glass formation and properties of gold alloys

In this work the effect of 1 % at additions of Ti or In on structural and thermal properties of the Au49Ag5.5Pd2.3Cu26.9Si16.3 [1] alloy is presented. Formation of a glassy phase was confirmed using X-ray diffraction for rods up to 3 mm in diameter. Data on glass transition, Tg, and crystallization, Tx, temperatures as well as on colour and Vickers microhardness are reported.

Genesis of MgCl2-based Ziegler-Natta Catalysts as Probed with Operando Spectroscopy

Ziegler-Natta catalysts for olefin polymerization are intrinsically complex multi-component systems. The genesis of the active sites involves several simultaneous and sequential steps, making the individual steps and interconnections difficult to be unraveled in an unambiguous manner. In this work, we combine X-ray diffraction and spectroscopy to probe each step of the birth and life of a MgCl2 -based Ziegler-Natta catalyst, namely the formation of high surface area MgCl2 by dealcoholation of an alcoholate precursor, the TiCl4 grafting, and the subsequent activation by triethylaluminum as co-catalyst. The so-prepared catalyst was tested towards ethylene polymerization, leading to the production of mainly crystalline high-density polyethylene. The use of operando characterization techniques allowed probing the transient details that are difficult to be dissected in the aftermath, but can radically affect the overall catalytic process.

Tailoring magnetic properties of multicomponent layered structure via current annealing in FePd thin films

Multicomponent layered systems with tailored magnetic properties were fabricated via current annealing from homogeneous Fe67Pd33 thin films, deposited via radio frequency sputtering on Si/SiO2 substrates from composite target. To promote spontaneous nano-structuring and phase separation, selected samples were subjected to current annealing in vacuum, with a controlled oxygen pressure, using various current densities for a fixed time and, as a consequence, different phases and microstructures were obtained. In particular, the formation of magnetite in different amount was observed beside other iron oxides and metallic phases. Microstructures and magnetic properties evolution as a function of annealing current were studied and interpreted with different techniques. Moreover, the temperature profile across the film thickness was modelled and its role in the selective oxidation of iron was analysed. Results show that is possible to topologically control the phases formation across the film thickness and simultaneously tailor the magnetic properties of the system.

Influence of current annealing on the magnetic properties of amorphous and crystalline soft thin films

In this study, the magnetic properties of thin films prepared by sputtering are presented, before and after submission to current annealing [1]. Three compositions of soft magnetic materials are investigated: Co₆₇Fe₄Si_14.5B_14.5, Fe₇₈Si₉B₁₃, Fe_84.3Si₂P₄B₈Cu_0.7. Hysteresis loops and magnetic domain imaging (MOKE, MFM), together with structural techniques (EDX, TEM, XRD), are used to follow the effects of annealing, which include stress relaxation and crystallization .

Bulk Metallic Glasses

Rapid quenching techniques have been successfully applied since long time for the preparation of metallic glasses in ribbon form. Only in the recent years, the research activity addressed towards the synthesis of bulk metallic glasses (BMG), in form of ingots with a few millimetres in thickness. These materials can be obtained by casting techniques only for selected alloy compositions, characterised by a particularly high glass-forming tendency. Bulk amorphous alloys are characterised by a low modulus of elasticity and high yielding stress. The usual idea is that amorphous alloys undergo work softening and that deformation is concentrated in shear bands, which might be subjected to geometrical constraints, resulting in a substantial increase in hardness and wear resistance. The mechanical properties can be further improved by crystallisation. In fact, shear bands movement can be contrasted by incorporating a second phase in the material, which may be produced directly by controlled crystallisation. Soft magnetic properties have been obtained in Fe-based systems and they are strongly related to small variations in the microstructure, ranging from a fully amorphous phase to nanocrystalline phases with different crystal size. The high thermal stability of bulk metallic glasses makes possible the compression and shaping processes in the temperature range between glass transition and crystallisation. Aim of this paper is to present recent results on glass formation and properties of bulk metallic glasses with various compositions. Examples will be reported on Zr, Fe, Mg and Pd-based materials, focussing on mechanical and magnetic properties.