Aluminium alloys are characterized by a low specific weight, which make them highly interesting for structural applications. Mechanical properties are lower than those of steels, so the possibility to obtain an increase by means of the structural refining (either nano- or ultra-fine grained structure) would extend their applications in several fields. Bulk nanocrystalline metals and alloys can be produced by high energy milling of powders and their consolidation by sintering techniques characterized by a low thermal load in order to minimize grain growth. This is an alternative approach to other methods based on severe plastic deformation, with the advantage of obtaining near-net shape parts, within the limits of the Powder Metallurgy (PM) route. Even in the case of the part cannot be obtained directly a preform can be produced by Powder Metallurgy and finished by hot working. In this case, Powder Metallurgy is used to produce preforms with geometry closer to the final one than that attainable by other technologies, reducing production costs and raw material consumption. It is well known that nanostructure (D < 100 nm) of Al alloys can be obtained by high energy milling technique. During milling, the grain size is determined by equilibrium between recovery and formation of defects due to heavy plastic deformation. Face centered cubic (FCC) materials, as Al and alloys, are difficult to reduce by mechanical milling. The opposite occurs with body centred cubic (BCC) and hexagonal close packet (HCP) metals due to relatively defects accumulation and difficult of fast recovery kinetics. A valid alternative is the cryogenic milling, where the powders are milled in slurry formed with liquid nitrogen. Cryomilling takes advantage due to low temperature of the liquid nitrogen that either suppresses or limits recovery and recrystallization and leads to finer grain structure faster. In addition cryogenic milling does not require use of process control agent (PCA) that can contaminate the powder with carbon and oxygen. A very important factor to preserve the nanostructure of a material is its thermal stability that depends on the balance between driving and resisting forces. It is well known that the smaller the grain size, the bigger the tendency to grain growth. In most cases, the thermal stability of a nanostructure depends on the lattice defects stored between and within grains, and on the particles such as nitrides and oxides precipitated at the grain boundaries. It is really important achieve an equilibrium between grain size and thermal stability of the material to avoid grain growth on sintering. Moreover, if the powder particles are very fine, sintering becomes hard because of the oxide layer that surrounds the particles. Bulk nanomaterials can be produced through several PM techniques. Hot isostatic press (HIP), dynamic consolidation, hot extrusion and spark plasma sintering (SPS) are effective to achieve a full dense material. In the frame of the near-net shape technologies, SPS is a novel technology that has large potentiality, because of the lower temperature and shorter time required. In this process a pulse electric current flows directly on the powders and a high heating efficiency is offered. It is known that Al powders are hardly sinterable due to oxide layer on their surface. This layer has to be broken in order to form a solid neck between the particles. SPS has been used to produce nanostructured Al and iron alloys starting from nanostructured powders. A bimodal microstructure can be formed during SPS sintering due to the localized overheating generated by the sparks and low thermal stability of the material. It is well known that a bimodal microstructure reveals an improvement of ductility which is the most critical characteristics of nanostructured metals. In a simplistic view, ultra-fine/nano crystallites are responsible for high strength and micrometric grains provide increased ductility. Additional strategies of ductility improvement provides deformation at low temperatures/high strain rates, which furnishes accumulation of dislocations within nanocrystalline/UFG, resulting in increased strain hardening and enhancement of strain rate sensitivity of the flow stress. Hot workability of metals depends on several parameters. Temperature and strain rate affect the flow stress and the strain rate sensitivity. The former increases on decreasing grain size, until the deformation process is determined by dislocation motion. In FCC materials, particularly in Al and its alloys, refining grains to UFG level promotes an increase in strain rate sensitivity. The hot workability is usually defined as the quantity of deformation that a material can undergo without cracking and reaching desirable deformed microstructures at a given temperature and strain rate. Improving workability means increasing the processing ability and the properties of the materials. Hot workability can be studied by the approach of the power dissipation maps. In this PhD work, the production of nanometric Al 2024 alloy powder by cryomilling, ultra-fine grained/micrometric material consolidated by SPS, and its further deformability at high temperature was studied. The results are presented in three chapters. Chapter 1 reports the methodology to obtain the nanostructured 2024 alloy powder. Many aspects such as the evolution of the microstructure, the role of liquid nitrogen during milling and the thermal stability are studied in order to have an insight on the kinetics (1). The study of the thermal stability of the nanostructured powder is presented, as well. Chapter 2 describes the SPS experiments of the as-atomized and as-milled powders and the characterization of the consolidated material. Chapter 3 reports the hot compression experiments on the atomized and milled samples, and discusses the differences in the deformation behaviour on the basis of the starting microstructure and of its evolution during deformation.

State-of-the-art friction materials for applications in disc brake systems are constituted by composite materials, specifically formulated to ensure proper friction and wear performances, under the sliding contact conditions of braking events. The bases of typical friction compound formulations usually include 10 to 30 different components bonded with a polymeric binder cross-linked in situ. Main requests to be fulfilled during braking are an adequate friction efficiency and enough mechanical resistance to withstand the torque generated by forces acting on the disc brake. Generally, each component confers distinctive properties to the mixture and their primary function can be classified in the following categories: binders confer mechanical strength to friction material guaranteeing pad compactness during use, abrasives increase friction efficiency and improve compound wear resistance, solid lubricants are responsible for stabilizing friction coefficient and contrasting the build-up effect, reinforcements increase mechanical strength improving wear minimization and stabilization. Furthermore, other modifying components such as fillers and functionalizers are involved which are not directly related to friction efficiency, e.g. cheap materials, pigments, etc. Organic brake pads for disc-brake applications are based on phenolic resin binders, generally it requires three main manufacturing steps: raw material blending, where friction compound components are mixed by blenders. Hot-molding, where blended friction mix is pressed against a metallic support at controlled high pressure (>2kN/cm2), temperature (150-200 °C) and pressing time (3-10 minutes). Brake pads post-curing, to complete the hardening of polymeric binder. This last step for phenolic resin is usually performed in a batch convective oven at temperature above 150 °C for 4-12 h, or alternatively using a continuous process, such as IR in-line tunnel ovens where the process time is 10-15 min, the oven heater temperature is between 500 and 700 °C and brake pad superficial temperature is easily above 300 °C. Such kind of formulations and manufacturing process reflects the generally acknowledged state of the art as regards organic friction materials for passenger cars and light trucks. In this panorama the idea of introducing a completely inorganic binder matrix would represent nowadays an extremely appealing topic in the field considering potential improvements of this alternative approach. The complete elimination of the organic binder would reduce emission of phenol-formaldehyde hazardous derivatives generated at high-temperature e.g. volatile organic compounds, highly toxic polyaromatic hydrocarbons etc… Nature and toxicity of the organic compounds released at high temperature was investigated on brake pads manufacturing and compared with preliminary studies recently published. Introducing an inorganic hydraulically bonded matrix in place of the traditional organic-based binders would lead to a substantial reduction of the total embodied energy and water of brake pads considering low-temperature manufacturing process and inorganic binders properties. Primary production embodied energy for phenolic resin is estimated in the range of 75 - 83 MJ/kg (cradle to gate), while primary production water usage (embodied water) is in the range of 94 - 282 l/kg. As a matter of comparison, examples of the embodied energy for inorganic binders typically used for concrete construction are: Portland cements 4.9 MJ/kg, fly ash 9.3 MJ/kg, metakaolin 1.4 MJ/kg, silica fume 0.036 1.4 MJ/kg. The embodied water for these raw materials usually is less than 0.048 l/kg. Well-known properties of such peculiar inorganic materials exploiting the hydraulic activity of binders when exposed to water or alkaline environment. The only energy demanding compound was the alkaline solution (e.g. for sodium hydroxide and sodium silicate the embodied energy is respectively of 22MJ/kg and 16 MJ/kg). New brake pad manufacturing process allowed the substitution of commonly implied highly energy-consuming procedures with low-temperatures steps. Friction material components except binders were blended together with conventional plow-blade blender forming a dry friction-mix, then this dry friction-mix is blended with the inorganic binder and water or alkaline activators in a planetary mixer forming a wet friction-mix. Eventually wet friction mix is cold-pressed onto a metal back-plate without the need for further treatments at high temperature. It immediately emerges the energetic benefit connected to the manufacturing process of this inorganic binder-based brake pads. After brake pad production, the behavior of these inorganic materials was compared to traditional phenolic-based friction materials. Brake pads were tested on a full scale automotive brake dynamometer and on a real vehicle (in terms of performance and particle emission) following custom and international standard procedures. The aim of this work was to produce brake pad prototypes with friction material based on an inorganic hydraulic binder at performance comparable to commercial brake pads with organic-matrix based friction materials. The results obtained so far resulted particularly promising and paved the way to further developments of these novel class of friction materials.

Solid Oxide Fuel Cell (SOFC) is an upcoming technology seen with great expectations for the production of electrical energy with good efficiency and minimal environmental impact. Successful commercialization of SOFCs has however been hindered despite the optimistic promises made by some developers. This slackened commercialization of SOFCs technology is mainly due to the high cost associated with SOFC production and its limited long term stability. The long term stability of conventional Anode Supported-Solid Oxide Fuel Cell (AS-SOFC) with Ni based anode is tested by its limited tolerance towards redox cycling and rapid thermal cycling. The introduction of new generation SOFC, the so called Metal Supported- Solid Oxide Fuel Cell (MS-SOFC) has shown to overcome the drawbacks associated with the conventional AS-SOFC. Thus, MS-SOFC is looked upon as the potential candidate for the rapid commercialization of SOFC technology. In MS-SOFC design, the cell is supported on a porous metal substrate instead of expensive and non-reliable anode as in AS-SOFC. In this design the thickness of the functional layers (anode, cathode and electrolyte) is kept thin as possible (in the order of 10-50m) just necessary for electrochemical activities while the support being provided by the metal substrate. Although MS-SOFC can be fabricated by different routes, co-sintering of metal/anode/electrolyte multilayers in non-oxidizing atmosphere at high temperatures (1300 to 1400oC) is the most promising as far cost efficiency and industrial scale up is concerned. The cathode is usually applied after high temperature processes and sintered in situ during operation in this route. This fabrication approach however has some drawbacks associated with it. This work is basically on the development of materials and optimization of the multilayer design for the production of MS-SOFC by cost-effective co-sintering approach. YSZ (Y2O3 stabilized ZrO2), Ni-YSZ cermet, and ferritic stainless steel are considered for the electrolyte, anode and the support respectively. The anode and electrolyte were modified with the help of suitable dopants and the multilayer design was also altered in order to facilitate the co-sintering, preventing or reducing the generally encountered issues in this fabrication route. Coarsening of Ni in Ni-YSZ anode cermet and over-sintering of anode during high temperature co-sintering is a well-known issue. Ni coarsening reduces the number of triple phase boundaries (TPB) thereby affecting electrochemical performance. The electrical conductivity of the anode also degrades due to Ni coarsening. In current work, the effect of Al doping on Ni-YSZ anode sintering in Metal Supported-Solid Oxide Fuel Cell (MS-SOFC) was studied. It was found that, the addition of Al into the anode accounts for a finer microstructure if compared to undoped Ni-YSZ anode material. The electrical conductivity of the Al-doped anode was also found to increase considerabely and such result may be attributed to the fine microstructure caused by the segragation of Al2O3 formed during the course of sintering on the grain boundaries of both Ni and YSZ, thus inhibiting the sintering. 5wt% Al-doped NiO used for Ni-YSZ anode material gave the finest microstucture and the highest electrical conductivity at room temperature although it showed the lowest bulk density. Overall, Al-doped Ni-YSZ anode material was found to be a suitable material for the anode in MS-SOFC produced by co-sintering. The modification of the reduction kinetic of NiO and the interaction between the anode and steel during the fabrication of Metal Supported Solid Oxide Fuel Cells (MS-SOFC) is also studied in the present work. With the aim to limit NiO reduction under inert atmosphere at high temperature, doping elements such as Al and Ce were considered for NiO powders modification and anode production. In order to simulate the reactions at the metal/anode interface, NiO/YSZ/steel composites were prepared with pure and Al-doped NiO. A sudden volume expansion above 10000C followed by substantial shrinkage above 12000C was observed for the composites when sintered in Ar at 14000C. Such volume expansion can be related to the oxidation of steel due to the RedOx reaction between NiO and steel. Moreover, it was found that the volume expansion, i.e. the steel oxidation, can be minimized to a good extent when Al-doped NiO is used. Hence it is proposed that Al-doped NiO is a promising candidate material to be used for anodes in high temperature sintering of MS-SOFC. Other problems encountered during co-sintering of multilayers for MS-SOFC include delamination, cracking, bending, and interdiffusion of Fe,Cr and Ni between anode and the substrate. In another section of work, green multilayers were produced by tape-casting for the fabrication of MS-SOFC half-cell by co-sintering. The binder loss step during co-sintering was optimized so as to prevent the cracking of the multilayers due to the binder loss events. Intermediate layers (layer between metal support and rest of the layers) composed of metal-ceramic powder composite were also investigated to prevent delamination and to inhibit interdiffusion of the elements.CeO2-steel, YSZ-steel, and LDC(La doped Ceria)-steel powder composites were considered for investigation to use as intermediate layer. Out of the different multilayer design considered for investigation, YSZ/(Al-NiO)-YSZ/LDC-steel/steel multilayer design was found to be a good compromise so as to give a half-cell, with good bonding between the layers, which is camber free, and with moderate interdiffusion of elements between the substrate and the anode. It was however found in all the designs that complete densification of YSZ electrolyte could not be obtained. In order to address the issue of limited densification of YSZ electrolyte during co-sintering, Fe was considered for doping YSZ. A comparative study was done on Fe doped YSZ samples for sintering in air and argon atmosphere, with the aim to analyze the effect of Fe as sintering aid under MS-SOFC fabrication by co-sintering conditions. Samples showed enhanced densification with increasing Fe concentration in both the sintering atmospheres thus concluding that Fe can be used as a sintering aid for YSZ even in argon. The samples sintered in argon atmosphere were however characterized by larger lattice parameter, density and grain size. The increase in lattice parameter can be attributed to the oxygen vacancies generated under low p(O2) in argon atmosphere. The microstructural analysis of the samples showed the presence of small amount of secondary phase, and the concentration of such phase was seen to be higher in the argon sintered samples. Comparison of colors of argon and air sintered samples indicates the reduction and/or precipitation of Fe dopant in samples sintered in argon. Gas tight dense electrolyte could be obtained for MS-SOFC fabricated by co-sintering when Fe doped YSZ is employed for electrolyte, although the performance of the cell was quite poor.

X-ray powder diffraction is a well-established technique to analyse structural and microstructural properties of materials. The possibility to record in-situ powder diffraction data allows studying changes within the structure and microstructure of a sample that occur in dependence on the applied external conditions (e.g. temperature, pressure). In the present thesis, in-situ X-ray powder diffraction was used to study structural and microstructural changes of different samples occurring at elevated temperature or upon UV illumination. Several structural phase transitions were studied using the approach of parametric Rietveld refinement. In parametric Rietveld refinement a set of powder diffraction pattern is refined simultaneously, constraining the evolution of some parameters using mathematical models, so that only the variables of the model need to be refined. In order to model and analyse the behaviour of structural parameters, Landau theory and its corresponding equations were used, owing to the fact that structural parameters (e.g. lattice strain, changes in atomic positions or occupancy) comprise an order parameter as defined in Landau theory. For description of the crystal structure of materials, several different approaches were tested, e.g. atomic coordinates, symmetry modes, rigid body rotations or rigid body symmetry modes. The dependence of preparation conditions on the properties of nanomaterials and their growth kinetics was studied using Whole Powder Pattern Modelling. This method allows modelling X-ray powder diffraction pattern using the microstructure of the sample without the use of arbitrary profile functions. The Fourier transforms of frequently observed effects as crystallite shape and size distribution or density of various defects, like dislocations and stacking faults, are utilised in order to get the resulting diffraction profile. Two different systems with industrial application, CeO2 and Cu2ZnSnS4, which were produced using a sol-gel approach, were investigated.

Gelatine, which is produced by collagen partial hydrolysis, has been largely used in the biomedical field for a wide variety of applications, which are ranging from drug delivery to wound healing. Its spread depends strongly on its biocompatibility: this natural polymer is indeed non-toxic, non-carcinogenic, non-immunogenic, enzymatically degradable and bioresorbable. In the biomedical field gelatine is mostly used as highly concentrated hydrogel (with a melting point above 43 °C - 45 °C) or cross-linked. This work investigated the use of uncross-linked gelatine hydrogels, with a melting temperature in the physiological range, for different biomedical applications. Firstly, it was studied the possibility to produce a solid hydrogel to use as easily removable wound dressing. Once applied to a wound, this patch keeps a moist environment in order to improve the regeneration, while releasing drugs or bioactive factors that it could be preloaded of. Moreover, it can be easily removed, without damages to the wound site and the newly formed tissue, by washing with warm sterile water (37 °C - 39 °C). Secondly, the gelatine material was investigated as substrate for the so-named cell sheet engineering. With our procedure cell sheets can be grown on the gelatine gel and, successively, they can be integrally transferred to a different surface, with gelatine being removed by melting at 37 °C, without any proteolytic enzyme. The gelatine sheet supporting cells, differently from the “Okano” cell sheet method, could be also directly implanted in-vivo without any need for removal, due to the gentle melting of the gelatine sheet after implantation. Thirdly, gelatine gels were used as depot to release pro-angiogenic factors in-vivo. Due to their ability to absorb aqueous solutions and release them while dissolving / degrading, gelatine gels were loaded with Amniotic Fluid Stem Cells Conditioned Medium and used to evaluate the effect of grow factors in a model of ischemic fasciocutaneous flap. Additionally, in order to evaluate the in-vivo degradation rate of gelatine gels loaded with Platelet Rich Plasma, a preliminary test was performed. The results of this test suggested the possibility to employ the gel films as antiadhesive membranes in surgery.

The main objectives of this Ph.D. research work are the development of enhanced nickel matrix nanocomposite coatings and the optimization of the codeposition parameters. Two different nanopowder, i.e. silicon carbide and alumina, were added to a Watts type galvanic bath in order to produce the nanocomposites coatings and ultrasonic vibrations have been considered as an alternative to pitting control agents in order to produce pore-free layers. The powders and the stability of their suspensions have been studied by DLS and ζ-potential measurements. After the study of the relationship between process parameters and embedded ceramic particle amount, the optimized deposition condition have been evaluated and used for the production of the sample for the final properties characterization and to test the use of the ultrasounds. Unique, functional properties of composite coatings are derived not only from the presence of the particles dispersed in the bulk of the metallic matrix but also on the matrix microstructural changes induced by the interaction between particles and electrocrystallization. Therefore the microstructure of all type of coatings have been analyze by SEM on the top-view and on the cross-section, the agglomeration of the powder have been observed by LOM in case of Ni/Al2O3 and by TEM in case of Ni/SiC. It has been demonstrated that the codeposition of the SiC particles induces an important microstructural refinement while the Al2O3 powder is strongly agglomerated and only under ultrasonic vibrations can be dispersed and change the field oriented columnar structure into un-oriented fine grains. Ultrasounds revealed to have positive effect not only in avoiding the porosity but also dispersing the ceramic powder and increasing the codeposition rate. This allowed to produce protective and very refined coatings. All these interactions between ultrasounds, nanopowder and electrocrystallization lead to improved mechanical properties and the enhancement is proportional both to powder content and dispersion degree. Moreover a well dispersed powder induce, an improvement also in the corrosion protection leading to the formation of a more stable and resistant passive oxide. Concluding, Ni/Al2O3 nanopowder codeposition leads to hardening effect, but does not affect the corrosion resistance because the particles agglomeration is not completely avoided even if deposited under ultrasonic vibrations. The SiC particles, on the contrary, can be better dispersed thus leading to improved both mechanical and protective properties.

Protective coatings are often deposited on SOFC interconnectors to avoid poisoning of cathode from chromium species that evaporate from stainless steel interconnects or supports. Co2MnO4 spinel compounds are usually considered as the main constituent of protection barriers. Nevertheless, such ceramic sinters at high temperatures (>1200°C) and this can be problematic for the properties of the stainless steel components. One of the major issues is, in fact, the creation of a compact and impermeable coating at relatively low temperature in order to preserve the metal substrate. In the present research work, Co2MnO4 spinel was synthesized by various methods (solid-state, gel-combustion, co-precipitation and reverse micelle) and the obtained specific surface area, structure and particle size were correlated with thermal behaviour, sintering temperature and achieved density. It was found that regardless the synthesis process the only obtained phase is Co2MnO4. Specific surface area from 0,8 to 65 m2g-1 was obtained, depending on the synthesis method. Sintering aids such as Nb2O5 and LiF were used to obtain dense microstructure at relatively low temperature. Considerable changes in sintering temperature were observed this being even 100-200ºC lower than that necessary for the consolidation of pure spinel though microstructure with only close pores was achieved. A novel sintering method based on Field Assisted Techniques (FAST) that promoted flash-sintering phenomenon was finally applied to Co2MnO4. Small electric field (<7,5 V cm-1) applied to the spinel decreases the sintering temperature down to 600°C. The application of an electric field above 7,5 V cm-1 flash-sintering phenomenon takes place and sintering temperature drops to about 300°C, the sintering time being less than 1 second.

Polymeric anion exchange materials can be key components for forming membranes for use in several electrochemical applications. Polyketones seem particularly promising as materials for making anion exchange membranes (AEMs), not only because the starting monomers, carbon monoxide and ethylene, are relatively inexpensive (pointing to the feasibility of producing polyketone at a more competitive cost than other membranes), but also because the presence of 1,4-dicarbonyl units along the backbone is an important chemical feature for the purposes of chemically modifying these polymers. It allows for post-manufacturing functionalization through the so-called Paal-Knorr reaction, which introduces N-substituted pyrrole units along the polymer backbone. An anion exchange membrane (AEM) was made with a modified polyketone using a solvent casting method, followed by iodomethylation and ion exchange with KOH (PK-PDAPm). Every step in the synthetic process was confirmed by Fourier Transform InfraRed spectroscopy (FTIR). Nuclear Magnetic Resonance (NMR) spectroscopy was also used to characterize the structure of the modified polyketone in detail. The results obtained revealed the formation of a pyrrole ring along the polyketone backbone. Polyamines modified in this way are amenable to structural rearrangements to form N-substituted pyrrole crosslinked with dihydropyridine units. Scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction techniques were also used to study the morphological, thermal, and structural characteristics of the modified polyketone, as well as the membranes derived therefrom. Thermogravimetric analyses demonstrated the thermal stability of the material up to 200oC, with no significant mass loss or degradation. The conductivity of the AEM was studied at temperatures up to 120oC, and the highest value of 9x10-4 S.cm-1 was reached at 120oC for the ionic conductivity of the membrane in iodide form, with values of the same order of magnitude (10-4 S.cm-1) for the membrane in OH form. Polyamine (PA-SiNH2)m, membranes containing silica formed by sol-gel reactions of 3-aminopropyltriethoxysilane (APTES) in hydrolytic conditions were prepared by solution casting, followed by methylation and an ion exchange process, in an effort to improve the properties of the AEM. FTIR and NMR were used to investigate the chemical features of the silica and its interaction with the polyamine polymer. The influence of amino-functionalized silica (Si-NH2) on the properties of the membrane obtained was investigated. The results demonstrated: a significant improvement in thermal stability up to 300oC, and an increase in water uptake and ion exchange capacity by comparison with the AEM (PK-PDAPm) containing no silica. The maximum conductivity obtained for (PA-SiNH2)m-I and (PA-SiNH2)m-OH was 2.4 ×10-4 S cm-1 at 130oC, and 4.8 ×10-4 S cm-1 at 120oC. These details may serve as an initial guide to the use of the above-described AEM in electrochemical applications.

Synchrotron Radiation (SR) is one of the most powerful and versatile tools in the study nanomaterials, supporting a variety of analytical techniques. Among the possible spectroscopies, X-ray Diffraction (XRD) is especially suited to investigate materials at the nanoscale. However, to benefit of the full potential of SR XRD, a complete control of the diffracted signal is necessary, including the optics and general setâ up of the beamline, which contribute to the Instrumental Profile Function (IPF). Exploring and characterizing the optical components for powder diffraction beamlines is the bottom line of the present Thesis, with the purpose of properly calibrating and adjusting all components in order to deliver the beam under the best possible conditions. Main benefits of this novel approach appear in the study of relatively large crystalline domains, toward the upper limit of the nanoscale (â hundreds of nm), a critical range between nano- and micro-crystalline, where the IPF is the main feature appearing in the experimental data. Thanks to this investigation it was possible to develop solutions and tools to improve knowledge and enhance the capability of handling the IPF along the life-cycle of a powder diffraction experiment. This result was achieved by studying and characterizing a new possible reference material for Line Profile Analysis (of size and strain effects), and by developing an original simulation/modelling software, based on rayâ tracing algorithms, capable to predict and analyse the instrumental behaviour of a beamline. As such the results of this work, and in a more general sense the emerging paradigm, will be of interest to many other beamlines currently employed for X-ray spectroscopies.

The present work was focused on the synthesis of three different calcium phosphate powders with possible application as bioceramics, their chemical, structural and thermal characterization, and finally their consolidation into dense compounds by conventional and flash sintering techniques. In the first part, Mg-doped (0 - 2 mol% Mg2+) tricalcium phosphate powders with micrometric size were produced by solid state reaction, and the influence of dopant on their sintering behavior and, specifically, on the β→α phase transition was studied. It was shown that magnesium stabilizes β-phase and ensures, after conventional sintering, much better densification and final mechanical properties. Moreover, annealing treatments on sintered compounds are suitable to convert the retained α- into β-TCP only in presence of Mg. Un-doped β-TCP was additionally subjected to flash sintering, thus obtaining dense microstructure at temperatures lower than 1000°C in just 10 min and avoiding any phase transition. A specific physical model based on of thermal-balance equations was considered to investigate the flash sintering process in detail; it was possible to point out that thermal runaway is the main mechanisms that triggers the process, which could be described also in terms of electric behavior of the material, real sample temperature and flash onset. Moreover, the observed blackening effect and the development of an additional resistance contribution at the electrodes were taken into account and discussed. In the second part of the work, Mg-doped (0 - 5 mol% Mg2+) tricalcium phosphate nanometric (~ 20 nm) powders were synthetized by chemical precipitation, thus obtaining highly-defected CDHA easily convertible into β-TCP at 750°C. Magnesium doping was found to inhibit the first crystallization and to promote β-TCP formation directly. The nanopowders were conventionally sintered to produce dense (~90%) β-TCP with sub-micrometric gran size. Flash sintering was also carried out on the nanopowders, demonstrating that the flash event can occur only after CDHA→β-TCP reaction, since the precursor is too resistive for allowing the electrical current flow. A non-linear electrical behavior was found for the β-phase, associated with the grain growth. Flash sintering was also applied in isothermal mode, producing dense sub-micrometric β-TCP at 900°C in just few seconds. It was also possible to build two maps relating the processing parameters for flash sintering on the basis of thermal model and the material behavior. Finally, hydroxyapatite nanopowders were synthesized by chemical precipitation with different amount of Sr2+ replacing Ca2+ into the apatite structure (0 - 100 mol%). The nanopowders were deeply characterized from a morphological, chemical and structural point of view (SEM, TEM, ICP, XRD, FT-IR, 31P-NMR, 1H-NMR, N2 sorption) finding a relation between the experimental evidences and the amount of Sr.