The effect of forming method (cold isostatic pressing and slip casting) on particle packing and the consequent effects on densification, phase transformation and microstructural evolution were evaluated during sintering of a transition alumina powder (Nanotek®, particle size of 47nm,delta and gamma phases). It is well known that the transformation of transition alumina towards the stable alpha phase has a critical influence on the sintering behaviour.
IMSE
Institute of Materials Science and EngineeringPublications list
Research groups: CeraMat
With the aim of reducing the overall cost of the process, co-continuous metal–ceramic composites were obtained by reactive metal penetration, starting from very low cost cordierite preforms. It was investigated how the preform porosity influences both the residual porosity left in the composites after infiltration and the mechanical properties.
Research groups: CeraMat
Barium titanate—acrylic hybrids with ceramic contents ranging between 10 and 70 wt% were successfully prepared by means of photopolymerization. These composites presented a homogeneous distribution of the ceramic particles within the organic matrix. In addition, an almost complete acrylic double-bond conversion took place. Basic electrical properties of the composites were investigated by dielectric spectroscopy.
This paper deals with the preparation and characterization of nanocomposite (NC) materials, comparing different technologies for sample fabrication, in view of their possible application as piezoelectric sensors. Those NCs consist on BaTiO3 nanoparticles embedded into a polyvinylidene fluoride matrix, where both the ceramic and the polymeric phases could exhibit ferroelectricity.
Research groups: PetroMat
One of the most favored welding techniques of high strength aluminium alloy is commonly metal arc welding (MAW) process due to its high productivity and relatively low production cost. Apart from other process parameters (e.g. joint design) the filler material has a significant influence on the microstructure of the weld at the joint and consequently on the endurance limit of the end-product. The above considered process was used to weld AA6082 aluminum alloy using two different filler metals, Al4043 and Al5356 respectively.
Research groups: CeraMat
Two different alumina powders were dispersed in low-density polyethylene (LDPE) to evaluate if any role can be ascribed to the crystalline phase, size and morphology of the alumina filler. In particular a submicrometric α-alumina and a nanocrystalline transition (γ/δ) alumina were added to the polymer at 5 wt% concentration, using a Brabender mixing unit. Both the neat inorganic fillers showed a good dispersibility in the polyolefin. The thermal and mechanical properties of the composites obtained were evaluated.
Research groups: PetroMat
The correlation between the evaluation of the mechanical and of the fatigue behaviour of the rheocast, T5 and T6 heat treated SSM A356 aluminium alloy with respect to the microstructures of the component has been investigated. The study has been carried out on a suspension arm injected in a rheocasting 800 tons plant in Stampal S.p.A. The new rheocasting is a process that allows obtaining the alloys in a semisolid state directly from the liquid state, by controlled cooling of the molten alloys.
Research groups: CeraMat
In order to clarify the influence of grinding on anhydrite reactivity to water, the authors have ground natural and synthetic products in different ways and investigated the evolution of microstructure and the rate of the conversion: CaSO4 II → CaSO4·2H2O, as a function of grinding. Different parameters have been used to characterize the anhydrite microstructure; nevertheless, only the specific surface BET and very short-range disorder, defined by the 'disorder coefficient' (Cd), can affect the product reactivity.
Research groups: CeraMat
Al2O3-10 vol.% YAG and Al2O3-10 vol.% ZrO2 bi-phase composites as well as Al2O3-5 vol.% YAG-5 vol.% ZrO2 tri-phase composite were developed by controlled surface modification of an alumina powder with inorganic precursors of the second phases. Green bodies were produced by dry pressing and slip casting and then sintered at 1500 °C. In particular, slip casting led to fully dense, defect-free, and highly homogenous samples, made of a fine dispersion of the second phases into the micronic alumina matrix, as observed by SEM.
Research groups: CeraMat
Research groups: CeraMat
Alumina-zirconia (AZ) composites are attractive structural materials, which combine the high hardness and Young’s modulus of the alumina matrix with additional toughening effects, due to the zirconia dispersion. In this study, AZ composites containing different amounts of zirconia (in the range 5–20 vol %) were prepared by a wet chemical method, consisting on the surface coating of alumina powders by mixing them with zirconium salt aqueous solutions. After spray-drying, powders were calcined at 600 °C for 1 h.
Research groups: PetroMat
Semiconducting oxide gas sensors based on La0.8Sr0.2Fe1−xCuxO3 (x = 0, 0.05, 0.10) (LSF, LSFC05, and LSFC10, respectively) were prepared by screen-printing for humidity detection at room temperature.
The thick-films were heat-treated at 800, 900 and 1000 °C for 1 h and all the compositions proved to be effective in humidity sensing and presented a good reproducibility between several measurements.
Research groups: CeraMat
High-conductivity and high-density samples with new compositions in the NASICON-type electrolyte series, i.e., the Na3Zr2-(x/4)Si2-xP1+xO12 system, with x = 0(A), 0.667(B), and 1.333(C) were synthesized using a mixed inorganic-organic sol-gel process. The sinterability was improved with increasing the x value, but the conductivity decreased. Highly dense samples were obtained by sintering at 1100 °C. The conductivity decreased with decreasing the c lattice parameter of the hexagonal structure.
Research groups: CeraMat
Recent progress in the development of a β-alumina gas sensor for automotive applications is reported. The sensing device consists of two solid electrolytes (namely a thin film of sodium sulfate deposited on β-alumina by appropriate treatment in a gaseous atmosphere), with two electrodes having different catalytic properties, one made of platinum, the other of gold. The β-alumina component was prepared as sintered pellets by pressing and as thick films by screen-printing.
Research groups: AddiMat
Cobalt-base alloys are generally adopted in applications that require wear, corrosion, and heat resistance. In particular, cobalt-chromium-molybdenum (Co-Cr-Mo) alloy is currently being used in the aerospace and medical field. Both applications require product personalization and take advantage by parts manufacturing through additive technologies, such as direct metal laser sintering (DMLS). This technology still has limitations for the manufacture of small cavities, such as holes with diameters below 0.6 mm and high aspect ratio, which require drilling of the additive manufactured part.
Third generation γ-TiAl alloys with a high niobium content, Ti–(47–48)Al–2Cr–8Nb, were processed by electron beam melting (EBM). This near-net-shape additive manufacturing process produces complex parts according to a CAD design. The starting powder is deposited layer by layer on the building table and selectively melted to progressively form the massive part. The EBM parameters such as layer thickness, melting temperature, scanning speed, or building strategy were set up to minimize porosity.
Gas atomized Ti–48Al–2Cr–2Nb powders have been used as precursor material in order to evaluate additive manufacturing for the production of near-net-shape γ-TiAl specimens to be employed in the field of aero-engines. In particular electron beam melting (EBM) is used to realize a selective densification of metal powder by melting it in a layerwise manner following a CAD design. The microstructure, the residual porosity and the chemical composition of the samples have been investigated both immediately after EBM and after heat treatments.
Research groups: CeraMat
Electrospun polyamide-6 membranes containing titanium dioxide (TiO2) photocatalyst were prepared and characterized. By tailoring the electrospinning parameters it was possible to obtain membranes having two different thicknesses, namely 5 and 20 µm, in which TiO2 particles were homogeneously dispersed. As a comparison, hybrid films made with polyamide-6 matrix and TiO2 filler were successfully produced, with inorganic/organic ratios of 10 and 20 wt%.
Research groups: PetroMat
This paper investigates the key factors associated to the realization of a hand exoskeleton to be embedded in an astronaut's EVA glove, in order to overcome the stiffness of the pressurized space suit. An overview regarding the main constraints related to the realization of a hand exoskeleton for EVA suits is provided, as well as a preliminary concept analysis of possible solutions in terms of mechanical structure, actuators and sensors.
Research groups: AddiMat
A new E -plane filtering structure suitable for very high-power telecom satellite applications is presented. The conceived configuration exploits the design flexibility provided by cascading highly integrated step/stub resonators with pseudoelliptic frequency responses. Several design examples of filters and diplexers in Ku-, K-, and Q-band are reported and supported by experimental tests campaigns. The components have been designed with a full-wave 2-D spectral element method. Prototypes have been realized in aluminum clam-shell technology.
The aim of this paper is to illustrate a multidisciplinary approach to selecting, designing, and evaluating sustainable solutions for energy-efficient buildings that are integrated into their neighborhoods at the early design stage. The paper discusses the Strategic Choice Approach (SCA), a tool which supports decision-makers in shaping problems in complex contexts.
Epoxy resins, widely used in conservation, still remain controversial materials. Considering some of the drawbacks that currently limit the application of epoxy consolidants, we present the application of the cationic ring opening polymerization as a novel method to cure the epoxy monomer in the restoration field. The cationic polymerization was carried out through a redox system based on the reduction of the iodonium salt in the presence of ascorbic acid catalyzed by a copper salt. The use of this initiator system for carrying out a suitable consolidant for lime plaster is considered.
Epoxy/BaTiO3 hybrid materials are prepared as good candidates for organic capacitors. The hybrid system is cured by using camphorquinone and a iodonium salt through a free-radical promoted cationic polymerization using a long-wavelength tungsten halogen lamp. The cured films are fully characterized. Morphological characterization shows a well-dispersed inorganic phase within the organic matrix. Electrical characterization demonstrates a linear increase of the dielectric constant with increasing filler content, while low dielectric loss values are obtained.
Research groups: CeraMat
Research groups: CeraMat
The expansion of three solid solutions of the ferrite phase, C6A2F, C4AF and C6AF2, in the presence of CaSO4 · 2H2O, Ca(OH)2 and siliceous powder with water/solid ratio of 0.3, has been compared with that of two reference mortars: the first containing C3A, Ca(OH)2 and CaSO4 · 2H2O, the second C3A doped by 4,5% Fe2O3, Ca(OH)2 and CaSO4 · 2H2O. The expansion of mortars, based on the ferrite phase, has been observed to be a function of Al2O3 contents, and is much weaker than that of mortars based on C3A. For these last ones, the expansion decreases from C3A to doped C3A.
Research groups: CeraMat
In this research, we evaluated the feasibility of wheat straw ash and bentonite (raw and heated at 150°C for 8 hrs) as secondary raw materials in self-compacting paste (SCP). The fresh and hardened properties of SCP formulations including water and superplasticizer demand, flow behavior, compressive and flexural strength development, water absorption, and acid attack resistance were evaluated. Moreover, porosity, microstructural, and mineralogical investigations were also carried out on SCP formulations.
An ablative Thermal Protection System (TPS) is a sacrificial shield able to insulate aerospace vehicles during atmospheric re-entry. In this paper, PPO-based composites were investigated in view of their potential exploitation as innovative ablative TPS. Their ability to degrade undergoing endothermic reactions and yielding a char layer was evaluated by means of thermal analyses and cone calorimeter tests. This first part discusses composites containing layered particles, in particular a cationically modified clay, a hydrotalcite and a sepiolite.
Similarly to the activity described in Part I, the PPO-based composites were studied in view of their pre-screening as potential candidates in innovative ablative shields. In this case equiaxial, oxide and non-oxide powders, precisely magnesium aluminate spinel, aluminum hydroxide (boehmite), δ- and α-alumina, silicon carbide, silicon nitride and molybdenum disilicide, were used as fillers. Nanometric and micrometric α-alumina and silicon carbide powders were exploited to investigate the effect of the particle size. The alumina-based composites presented the most promising behavior.
Fluorine-substituted hydroxyapatites are considered promising materials for bone scaffolding. In this study a systematic investigation on F-half substituted hydroxyapatite (F-HAp, Ca10(PO4)6OHF) obtained by precipitation is reported. Results on composition analysis, thermal behaviour, and sinterability are presented for a comparison with the respective pure hydroxyapatite. Samples were characterised by electron microscopy, induced coupled plasma-atomic emission spectroscopy, thermal analysis, infrared spectroscopy, N2 adsorption measurements, X-ray diffraction and dilatometry.
Silicon carbide multilayer composites containing short carbon fibres (Csf/SiC) were prepared by tape casting and pressureless sintering. C fibres were dispersed in solvents and then mixed with SiC slurry to make green Csf/SiC tape. Triton X-100 was found to be the best one for Toho Tenax HTC124 fibres (with water soluble coating) among BYK-163, BYK-410, BYK-2150, BYK-9076, BYK-9077 and Triton X-100 dispersants. Csf/SiC multilayer composites containing 5 vol.% fibre (mean fibre length of 3, 4.5, and 6 mm) were obtained.
Titanium matrix composites reinforced with continuous fibres are candidate materials for high performance structural components in aerospace applications. The present work has been focussed on the use of a fabrication methodology of composite monotapes alternative to the well known fibre-foil techniques. The same fabrication procedure was also selected to produce composite preforms suitable for secondary consolidation processes, as those based upon diffusion bonding methods, in order to obtain multilayered composites.
Research groups: CoatMat
This paper deals with a study of the failure mode of thin PVD coatings in alternated contact with molten aluminum alloy. CrN and ZrN monolayer coatings deposited through cathodic arc evaporation were used. The coatings morphology was assessed by SEM and their mechanical properties evaluated by nanohardness test performed at room temperature. An experimental test rig which cyclically immerses coated steel samples in molten Al-alloy and in a cooling bath was applied.
Research groups: CeraMat
We report on a simple, fast and low-cost synthesis procedure for the complete covering of zinc oxide (ZnO) 1D nanostructures with a protective shell of titania (TiO2) nanoparticles. ZnO nanowires (NWs) were grown on transparent F-doped Tin Oxide (FTO) conductive layer on glass by seed layer-assisted hydrothermal route in aqueous media, while the titania shell was deposited on the ZnO NWs through an in situ non-acid sol-gel synthesis. The nanowires impregnation time in the titania sol was varied from 3 to 10 min.
Research groups: PetroMat
Sintered components are gaining more and more applications, their success towards the most traditional technologies is due to the possibility of low cost manufacturing of parts having complicated shape coupled with restricted tolerances, to the very high yield of the utilisation (>95 %) of the raw material, as well as to the availability of a large choice of powders with a wide range of chemical composition.
Research groups: CeraMat
Research groups: CeraMat
Here we report how thermal treatments of a surface modified α-alumina powder on which a zirconium oxide precursor was grafted can be tailored so as to obtain an alumina-zirconia composite powder with well-controlled phase distribution and size.
Forging behaviour of 2124 aluminium alloy containing 26 vol.% of SiC particles (average size 3 μm) was investigated by means of room and elevated temperature tensile tests (range of temperature 20–350°C). The results obtained were utilized to define the forging parameters (deformation ratio 3.5:1, strain rate 0.14 s−1, sample temperature during the hot deformation process ranging from 440 to 340°C).
Microstructure of as-fabricated and forged specimens was investigated.
Research groups: CoatMat
Results of studies on impact tested gas and plasma nitrided or nitrocarburized blunt notch die steel samples with varying notch root radii are presented.
Research groups: PetroMat
In this paper evolution from hot forging to thixoforging process is proposed and talked over. A realcase study is presented, namely a steel-made steering piston produced by thixoforging technique is considered and some parameter has been numerically analyzed. The transition between the traditional forging process and the new one involves several transformations and presents difficulties mainly due to the high working temperature.
Research groups: CeraMat
Research groups: CeraMat
An improved gel-casting procedure was successfully exploited to produce porous ceramic bodies having controlled porosity features in terms of mean pore size, total pore volume as well as pore geometry. The gel-casting process in which a natural gelatine for food industry is used as gelling agent was firstly set-up to prepare dense alumina and zirconia components. Then, commercial PE spheres, sieved to select proper dimensional ranges, were added to the starting slurries as pore-forming agent.
Research groups: PetroMat
È descritto un giunto articolare (1) per esoscheletro di una articolazione (A) interposta tra almeno due capi ossei (F1, F2) comprendente almeno una prima forcella (3a) calzata assialmente lungo almeno un primo tale capo osseo (F1), almeno una seconda forcella (3b) calzata assialmente lungo almeno un secondo tale capo osseo (F2) ed almeno un mezzo di articolazione (5) interposto tra tale prima forcella (3a) e tale seconda forcella (3b) ed avente asse di rotazione sostanzialmente coassiale con un asse di rotazione di tale articolazione (A), almeno un componente di snodo (5a; 5b) di tale mezzo d
This review reports about the most used glass matrices (2) and reinforcements (3) for the preparation of glass- and glass-ceramic composites, their preparation methods (4), their properties (5) and the foreseen applications (6) in the field of transports, aerospace and biomedical. In particular, the thermal and mechanical properties of glass- and glass-ceramic matrix composites are compared with those of the most common metals and ceramics. Finally, some comments are reported about the probable development of the research in this field of great technological importance (7).
Research groups: PetroMat
Analysis of the grain growth on the galvanic deposition of aluminium is presented aiming to find an optimized process and corresponding ad-hoc designed experimental set-up which guarantees an enhanced quality of the coated layer. In particular, the effects of some process parameters, i.e. deposition time, current density and the liquid agitation on the coating properties of aluminium have been experimentally investigated.The properties of the deposited layer has been evaluated.
Research groups: CeraMat
Brake discs of (Al-Si-Mg)/SiC composite were produced by gravity casting. To this purpose ingots, containing 50 vol.-% of SiC particles, produced by pressureless metal infiltration at Lanxide Corp., were melted, diluted with an unreinforced alloy (thus achieving a SiC content of 30 vol.-%), and cast in permanents moulds. The possibility of repeating the casting process using recycled material was investigated. Brake discs were fabricated by using 50 or 100% of recycled composite.