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.

High-melting temperature oxides, carbides and nitrides are superior in hardness and strength to metals, especially in severe conditions. However, the extensive use of such ceramics in structural engineering applications often encountered critical problems due to their lack of damage tolerance and to the limited mechanical reliability. Several ceramic composites and, in particular, laminated structures have been developed in recent years to enhance strength, toughness and to improve flaw tolerance. Significant strength increase and improved mechanical reliability, in terms of Weibull modulus or minimum threshold failure stress, can be achieved by the engineering of the critical surface region in the ceramic component. Such effect can be realized by using a laminated composite structure with tailored sub-surface insertion of layers with different composition. Such laminate is able to develop, upon co-sintering, a spatial variation of residual stress with maximum compression at specific depth from the surface due to the differences in thermal expansion coefficient of the constituting layers. In the present work silicon carbide has been selected as second phase to graduate the thermal expansion coefficient of alumina due to its relatively low specific density that could allow the production of lighter components with improved mechanical performance, also for high temperature applications. Ceramic laminates with strong interfaces composed of Al2O3/SiC composite layers were produced by pressureless sintering or Spark Plasma Sintering (SPS) of green layers stacks prepared by tape casting water-based suspensions. Monolithic composites containing up to 30 vol% silicon carbide were fabricated and thoroughly characterized. Five engineered ceramic laminates with peculiar layers combination that is able to promote the stable growth of surface defects before final failure were also designed and produced. By changing the composition of the stacked laminae and the architecture of the laminate, tailored residual stress profile and T-curve were generated after co-sintering and successive cooling in each multilayer. The results of the mechanical characterization show that the engineered laminates are sensibly stronger than parent monolithic composite ceramic and exhibit surface damage insensitivity, according to the design. Such shielding effect is especially observed when macroscopic cracks are introduced by high load Vickers indentations. Some designed multilayers exhibit reduced strength scatter and higher Weibull modulus, which implies superior mechanical reliability. Fractographic observations on fracture surfaces of the engineered laminates show a graceful crack propagation within the surface layers in residual compressive stress which can be attributed to the stable growth of superficial cracks before final failure as it is predicted by the apparent fracture toughness curve. Such fracture behaviour is considered to be responsible for the peculiar surface damage insensitivity and the improved mechanical performance.

The objective of this work is the investigation of the industrial production process of the Color Masterbatches and of the parameters that influence the pigment dispersion into the polymer matrix. In particular, the project is focused on the production process optimization in order to increase the quality of the final product and to minimize their environmental impact.

Abstract Fuel cells are a very efficient way to transform the chemical energy of a fuel into electrical energy. Among the different kind of fuel cells, the solid oxide based ones (SOFC) are the most promising when cost is considered, since their high operative temperature allows the use of widely available non precious materials as catalysts. The worldwide research activity on SOFC is very active and many aspects are currently under investigation; nevertheless it is generally agreed that the development of suitable low-cost fabrication technologies is presently the key technical challenge which needs to be faced. In the present thesis the two most promising geometries have been developed, i.e. the planar configuration and the microtubular one. Innovative aspects have been considered in both directions. In both cases environmental impact and cost of the processing was minimized by using only water based ceramic powder production technologies. A first aim of this work was to develop a processing technique capable of producing planar anode supported SOFC with thin electrolyte by sequential tape casting method (thus avoiding the lamination step) and co-sintering. In order to do this, different aspects associated with the processing steps, from colloidal suspension stability, to defects related with green forming and sintering have been studied. One of the most critical factors in the co-sintering of ceramic multilayers is the stress generated because of different thermal expansion coefficients and sintering kinetics of the constituting layers. Such stresses, when not controlled, can lead to the formation of several types of defects, such as flaws, delaminations, retarded densification and warping. In order to understand and to solve the problems of defect formation and curvature development, a set up for monitoring in situ the sintering process has been built. The effect of different parameters (such as green composition, type and amount of doping elements, powder granulometry etc.) on the sintering kinetics of the layers constituting the cells has been studied. The different sintering kinetics were related to the developed defects and curvature. Such analysis led to the fabrication of defect free cells which were successfully electrochemically characterised. In order to being able to quantify the stresses which are developed and to predict the curvature behaviour of a bi-layer upon sintering, the knowledge of the very high temperature mechanical parameters of the materials is needed. A technique for measuring the uniaxial viscosity of thin tape cast layers upon sintering was therefore developed and is described in a section of this thesis. Whereas planar SOFC seem to be the preferred choice for future stationary application, micro tubular ones may be much more attractive for portable applications. The first advantage of the micro tubular SOFC design, is the potential very high volumetric power density, being it inversely proportional to the electrolyte diameter. The other advantages are resulting from low thermal mass: (i) high thermal shock resistance, and (ii) rapid turn on/off capability. However, miniaturization issues are arising when the diameter is decreased to less than 1 mm, mainly due to difficulties associated with the application of an internal current collector. The novel approach, which is described in the present thesis, consists in fabricating the cell in the form of a fiber around a metallic wire. The support for the cell fabrication consists of a thin nickel wire, on to which the porous anode layer, the electrode and the cathode, are deposited in succession. This nickel support acts as the current collector as well, and this opens totally new possibilities for downscaling tubular cells. Abstract Le celle a combustibile rappresentano una via efficiente per la conversione diretta dell’energia chimica di un combustibile in energia elettrica. Tra le diverse tipologie di celle, quelle agli ossidi solidi (SOFC), sono le più promettenti in termini di costo, perché l’elevata temperatura operativa consente l’utilizzo di materiali largamente disponibili e non preziosi come catalizzatori. L’attività di ricerca sulle SOFC è fiorente, e diversi aspetti sono investigati attualmente; ciononostante, è generalmente riconosciuto che lo sviluppo di tecnologie di fabbricazione economiche per la produzione di celle rappresenta la sfida tecnica che deve essere affrontata più urgentemente. In questa tesi sono state sviluppate le due geometrie più promettenti: quella planare e quella micro-tubolare. Sono stati considerati aspetti innovativi per entrambe. L’impatto ambientale ed il costo dei processi sono stati minimizzati grazie all’utilizzo di tecnologie delle polveri ceramiche a base acquea. Un primo scopo di questo lavoro è stato quello di sviluppare una tecnologia di processo in grado di produrre celle planari supportate da anodo con elettrolita sottile, tramite colaggio su nastro sequenziale (evitando quindi la fase della laminazione) e co-sinterizzazione. A tal fine sono stati studiati i diversi aspetti delle fasi del processo, dalla stabilità delle sospensioni colloidali, ai difetti associati alla formatura del verde ed alla sinterizzazione. Uno dei fattori più critici nella co-sinterizzazione di multistrati ceramici sono gli sforzi generati dai diversi coefficienti di espansione termica e cinetiche di sinterizzazione dei singoli strati. Tali sforzi, se non controllati, possono portare alla formazione di diversi tipologie di difettosità, come cricche, delaminazioni, densificazione ritardata e curvature. Al fine di comprendere e risolvere il problema della formazione dei difetti e dello sviluppo della curvatura, è stato costruito un apparato atto al controllo visivo del processo di sinterizzazione. È stato quindi studiato l’effetto di diversi parametri (come composizione del verde, tipo e concentrazione di elementi dopanti, granulometria delle polveri, ecc.) sulla cinetica di sinterizzazione degli strati che costituiscono la cella. Le diverse cinetiche di sinterizzazione sono state messe in relazione ai difetti ed alla curvatura riscontrata sul prodotto finale. Al fine di quantificare gli sforzi sviluppati e predire la velocità di curvatura di un bi-strato durante la sinterizzazione, è necessario conoscere i parametri meccanici del materiale alle altissime temperature. A tal fine è stata sviluppata una tecnica di misura per la viscosità uniassiale di film sottili ottenuti per colaggio su nastro. Mentre le celle planari appaiono la scelta preferenziale per la generazione stazionaria, quelle micro-tubolari sono di interesse per applicazioni portatili. Il primo vantaggio della geometria micro-tubolare, è l’altissima densità di potenza volumetrica teorica, che è inversamente proporzionale al diametro dell’elettrolita. Gli altri vantaggi, che derivano dalla bassa massa termica, sono l’elevata resistenza allo shock termico e la possibilità di sopportare cicli rapidi di accensione/spegnimento. Ciononostante, la riduzione del diametro delle celle a meno di 1 millimetro è problematica, principalmente per le difficoltà associate all’applicazione di un collettore di corrente interno. L’approccio innovativo descritto in questa tesi consiste nella fabbricazione della cella in forma di fibra attorno ad un filo metallico. Il supporto per la fabbricazione della cella consiste in un filo sottile di nichel, sul quale vengono depositati in successione l’anodo poroso, l’elettrolita ed il catodo. Il supporto di nichel espleta anche la funzione di collettore di corrente, aprendo nuove possibilità per la miniaturizzazione di celle tubulari.