Fabrication of Cu-based metal matrix composites reinforced with carbon nanofillers

The thesis takes inspiration from the worldwide issues related to the shortage of critical raw materials (CRMs) and the need of finding sustainable alternatives to CRMs within fields and sectors strategic to the well-being and economy of industrialized countries. The research activity has been focused on the fabrication of Cu-matrix composites reinforced with carbon nanofillers, nano-graphite and graphene in particular. This class of composites attracts considerable interest as a consequence of the broad spectrum of applications Cu-MCs could find due to their thermal and electric conductivities, self-lubricating properties of graphite, cost-effectiveness and availability. Ball milling (BM) and spark plasma sintering (SPS) have been combined to provide an innovative methodology to fabricate Cu-MCs reinforced with carbon nanofillers enabling the fine dispersion of nanoparticles into the Cu matrix. Specifically, a two-stage cycle involving BM first and, then, SPS has been shown to result in the dispersion of graphite particles in relatively large Cu grains. The iteration of cycles allows the refinement of graphite nanoparticles and their dispersion in Cu powders on the microscopic scale, mostly at grain boundaries, and the subsequent incorporation of nanoparticles into Cu grains due to grain growth mechanisms activated and promoted by high temperatures during SPS. Molecular level mixing has been also tested to obtain Cu-MCs reinforced with graphene starting from liquid solutions of Cu nanoparticles and graphene. In particular, graphene was dispersed during the redox synthesis to obtain Cu nanopowder, subsequently consolidated by SPS. Despite the intrinsic different between the two methods, it has been possible to prepare Cu-MCs with graphite nanoparticles and graphene as dispersoids. Structural and microstructural characterization indicate that dispersoids are finely dispersed into the Cu matrix. Nanoindentation measurements clearly demonstrate the significant enhancement of mechanical properties, thus providing an important clue to the validity of the methodology developed

graphene mediated surface enhanced raman scattering in silica mesoporous nanocomposite films

Highly performing mesoporous nanocomposite films with embedded exfoliated graphene and gold nanoparticles display a significant enhancement of G-SERS properties

Non-monotonic variation of the grain size in Cu nanopowders subjected to ball milling

Ball milling (BM) a Cu nanopowder resulted in an increase of the average grain size from 8 to 52 nm, followed by a gradual decrease to 19 nm. In contrast, the grain size of coarse-grained Cu decreased monotonically from 290 nm to 19 nm. Fitting a model to the kinetic curves indicates that the two processes have similar activated volumes during collisions. It also reveals that particles over 100 nm are formed when nanoparticles are compressed during a collision for the first time.University of Cagliari and performed within the European Community Horizon 2020 Programme, COST Action CA15102 Solutions for Critical Raw Materials under Extreme Conditions (CRM_EXTREME

Synthesis, Structural investigation and luminescence spectroscopy of nanocrystalline Gd3Ga5O12 Doped with lanthanide ions

Gadolinium gallium garnet (GGG) nanocrystalline powder doped with. lanthanide ions (Eu3+ and Er3+) have been obtained using two different methods (coprecipitation and Pechini). The X-ray diffraction results show that single phase cubic GGG nanopowders have been obtained for both preparation methods. The samples prepared by the two procedures show different morphologies, as revealed by scanning electron microscopy images. The Er3+-doped nanopowders obtained with the coprecipitation method show strong luminescence upon 488.0 nm excitation. The emission spectrum is similar to the one of the single crystal and of nanopowders of the same composition prepared by a combustion synthesis. The Er3+-doped GGG nanopowders obtained by the coprecipitation method show efficient upconversion in the green region (around 550 nm) upon excitation in the near IR at a wavelength of 800 nm

Photodegradation of rhodamine 6G dimers in silica sol–gel films

The process of dimerization of rhodamine 6G at high concentrations in solution and when incorporated in a solid state matrix is well known but the dimer response to photodegration is still not well understood. Silica sol–gel films have been doped with rhodamine 6G with a concentration up to 10−1 M to form large amounts of dimers within the matrix. Fluorescence and UV absorption spectra have shown that both not-fluorescent H-dimers and fluorescent J-dimers together with the monomer form of rhodamine 6G are present in the matrix. Upon exposure up to 11 h to UV light a selective photodegradation of the different species has been finally observed. Analysis of the absorption spectra has shown that the H-type dimers are more resistant to photodegradation with respect to the J-type dimers

XRF investigation on skeletal remains from King Peter III of Aragon (1239–1285 A.D.) and Queen Blanche of Anjou (1280–1310 A.D.)

We conducted an X-Ray Fluorescence investigation on bone fragments belonging to King Peter III of Aragon and Queen Blanche of Anjou. The spectroscopic analysis was carried out in selected points of the bone fragments. Several transitional elements normally unexpected in the bone composition have been found at varying level of concentration. The presence of these elements was interpreted in relation to chemical treatments for mummification of bodies as well as to dietary habits, including tools used for cooking and for the consumption of food

Thermal behaviour of clay ceramics obtained by Spark Plasma Sintering: is fractal geometry a new possible road to design porous structures?

Porous clay ceramics represent an important class of construction materials. Their properties are strongly conditioned by microstructure features. In particular, a special attention has to be paid to porosity (pore fraction, pore shape, pore size, pore size distribution and topology distribution). In this work, thermal behaviour of porous ceramics has been studied comparing different modelling procedure. Fractal modelling, proposed in this paper, proves to be most reliable in predicting thermal behaviour of porous ceramics. For this reason, a design procedure for obtaining porous structures with specific thermal properties has been illustrated

Fabrication of Cu-graphite metal matrix composites by ball milling and spark plasma sintering

This work reports on the use of graphite as dispersoid to strengthen Cu. Material processing involved two-stage cycles of ball milling and spark plasma sintering, respectively for the dispersion of graphite nanoparticles into nanostructured Cu and the formation of dense compacts with relatively large Cu grains. The 3 wt% of graphite allows progressive hardening and stiffening of the Cu-graphite composite, showing the potential of graphite as effective dispersoid upon suitable processing

Molecularly imprinted La-doped mesoporous titania films with hydrolytic properties toward organophosphate pesticides

The present work is aimed at developing a titania-based mesoporous film with catalytic properties toward organophosphate pesticides by combining two different approaches: the molecular imprinting and the self-assembly with a supramolecular template. The mesoporosity of the material has been obtained by using a tri-block copolymer (Pluronic F127) as a micellar template while the molecular imprinted cavities have been templated by a complex between La 3+ and bis-4-nitro-phenyl-phosphate. The template removal allowed opening, in one step, both the mesopores and the imprinted cavities with a simultaneous estimation of the active sites. The catalytic activity of the molecularly imprinted and not imprinted films toward the pesticide Paraoxon® has been evaluated by means of UV-Vis spectroscopy titration of the 4-nitro-phenolate released by the Paraoxon® hydrolysis. The analysis of the initial rates of molecularly imprinted and not imprinted films has shown that the presence of a very low number of molecular cavities improves the catalytic properties of the imprinted film when compared to the not imprinted films and the background hydrolysis

Synthesis, structural investigation and luminescence spectroscopy of nanocrystalline Gd₃Ga₅O₁₂ doped with lanthanide ions

Gadolinium gallium garnet (GGG) nanocrystalline powder doped with lanthanide ions (Eu3+ and Er3+) have been obtained using two different methods (coprecipitation and Pechini). The X-ray diffraction results show that single phase cubic GGG nanopowders have been obtained for both preparation methods. The samples prepared by the two procedures show different morphologies, as revealed by scanning electron microscopy images. The Er3+-doped nanopowders obtained with the coprecipitation method show strong luminescence upon 488.0 nm excitation. The emission spectrum is similar to the one of the single crystal and of nanopowders of the same composition prepared by a combustion synthesis. The Er3+-doped GGG nanopowders obtained by the coprecipitation method show efficient upconversion in the green region (around 550 nm) upon excitation in the near IR at a wavelength of 800 nm