IMSE
Institute of Materials Science and EngineeringPublications list
Performances of metal matrix composites (MMCs) rely strongly on the distribution of particles within the metal matrix but also on the chemical reaction which may occur at the liquid-solid interfaces. This paper presents the chemical reaction between aluminum based particles Al2O3 and Al2O3-AlOOH with magnesium alloys matrixes AZ91 and EL21, respectively, and studies the microstructure of these reinforced composites.
Research groups: CeraMat
In this work, the synthesis of RKKP bioactive glass composition by an aqueous sol-gel method is reported. A complete and systematic characterisation of the produced material was carried out. Characteristic functional groups were detected by Fourier transform infrared (FT-IR) spectroscopy, the thermal behaviour was investigated by simultaneous thermogravimetric and differential thermal analysis (TG-DTA), crystallisation kinetics and phase evolution were followed by X-ray diffraction (XRD) analyses.
Interactions between β-Al2O3 and a sodium aluminosilicate conductive glass, after thermal treatment at 900 °C, have been investigated on screen-printed gas sensors. Due to the high level of glass additions, the starting powder made of β/β″-alumina, underwent strong compositional modifications. SEM and TEM imaging, coupled with chemical analysis, evidenced the formation of nepheline and α-Al2O3 at the interface between β-Al2O3 and the glass.
The effect of Al2O3 (Saffil) short fibers on the response of 2014-Al2O3(f) composite to thermal treatment was investigated. Composite samples were produced by squeeze casting starting from ceramic preforms of Saffil (13% vol. of fibers). Their behaviour was compared to that of 2014 unreinforced alloy fabricated by squeeze casting as well. The best process parameters suitable for solution of alloying elements were assessed by means of differential scanning calorimetry (DSC) and electron microprobe analysis (SEM-EDS).
Research groups: CeraMat
An ultra-fine alumina powder was doped with yttrium or zirconium chloride to produce Al2O3–5 vol.%ZrO2 (AZ-5) and Al2O3–5 vol.%YAG (AY-5) composite powders. Composite samples and pure alumina, used as a reference, were submitted to dilatometric analyses up to 1500–1550 °C at 2, 5 and 10 °C/min for supplying the data required for the modeling of their sintering behaviour. The best fit for the three samples was obtained by applying an Avrami–Erofeev nucleation and growth model (An) and a subsequent power law reaction (AnFn).
Research groups: CeraMat
De-agglomeration of a nanocrystalline transition alumina powder was performed in distilled water at its natural pH under magnetic stirring for 170 h or by ball milling for 3 h. Gibbsite appeared near transition aluminas in the magnetic stirred sample. In addition, a relevant lowering of the α-Al2O3 crystallization temperature was observed in the dispersed materials with respect to the as-received powder. However, the activation energy of the above transformation, determined by the Kissinger method, was in any case about 480–500 kJ/mol and unaffected by the dispersion route.
In this work, different techniques are proposed to realize ammonia (NH3) sensors working at room temperature and a preliminary electrical characterization under water vapor and in NH3 atmospheres is presented.
Experimental evidences are reported on the potential of direct metal laser sintering (DMLS) in manufacturing flat and finned heat sinks with a remarkably enhanced convective heat transfer coefficient, taking advantage of artificial roughness in fully turbulent regime. To the best of our knowledge, this is the first study where artificial roughness by DMLS is investigated in terms of such thermal performances. On rough flat surfaces, we experience a peak of 73 % for the convective heat transfer enhancement (63 % on average) compared to smooth surfaces.
Research groups: CoatMat
In this work, the scratch resistance of laser surface textured TiN coatings is studied to discriminate laser conditions in terms of coating adhesion and integrity in view of future wear tests. Laser surface texturing (LST) is performed on TiN coating ,3 mm thick using a pulsed active fibre laser working in nanosecond pulse regime. Laser process parameters are varied to obtain several patterns with different dimple diameter, depth and pitch, all of which are essential for controlling tribological behaviour.
Many materials have a cellular structure, cork, wood, sponge and trabecular bone are natural cellular solids, while engineered honeycombs and foams are now made from polymers, metals, ceramics and glasses. Materials containing tailored porosity exhibit unique properties and features. Therefore, porous materials find nowadays many applications as end products in several technological processes. Contrary to metallic and polymeric porous structures, pores have been traditionally avoided in ceramic components because of their intrinsic brittle nature.
In view of possible application of multilayer SiC as oxidation resistant and self-passivating component of re-usable thermal protection systems for space re-entry vehicles, this material was tested in a re-entry simulation chamber. A multilayer SiC laminate was processed by tape casting and pressure less sintering. Both the as-processed multilayer SiC and a similar passivated material, with a surface silica layer obtained by high temperature oxidation, were investigated. The microstructure and the mechanical features of these two materials were compared before and after the re-entry test.
Research groups: CeraMat
The preparation and characterization of the properties of mullite ceramic foams suitable for diesel exhaust filtration systems are described. Two foams of different cell sizes, 32 and 61 ppi (pores per inch), were prepared from slurries by the replication process with polyurethane sponges as the templates. The microstructure and the dependence of the porosity and the mechanical properties on the preparation and resulting foam cell size and normalized density are discussed.
Research groups: PetroMat
The investigation of the performance of small single PEMFC was carried out by employing a purposely designed test bench with complete control of the operational parameters. A MEA preparation method was also developed constituting the base for testing new electrocatalytic materials or improved electrode assembling techniques. Beyond determining the polarization curves, other tests have been carried out like electrical resistance measurement by the current interruption method and voltammetric characterization.
Research groups: PetroMat
Recently, the screen printing has experimented a larger diffusion for producing microelectronic devices: resistors, conductors, humidity and gas sensors. Simplicity, versatility and low cost are the most significant reasons for its development and success. It has been applied in several high technology applications, because of its suitability to be printed on different materials; in microelectronics, various functional devices have been realised very competitive, if compared to massive materials.
Research groups: CeraMat
A gas sensor based on a β-alumina thick film was recently developed on a laboratory scale. This sensor can be successfully used for selective detection of CO and NO x, resulting from an appropriate choice of the working temperature of the sensing element. This paper deals with the approach of the industrial transfer of the sensor prototype, mainly concerning the scale-up of the screen-printing procedure from a hand-operated apparatus to an industrial production machine.
Research groups: CeraMat
The aim of this research is to produce self-healing cementitious composites based on the use of cylindrical capsules containing a repairing agent. Cementitious hollow tubes (CHT) having two different internal diameters (of 2 mm and 7.5 mm) were produced by extrusion and used as containers and releasing devices for cement paste/mortar healing agents. Based on the results of preliminary mechanical tests, sodium silicate was selected as the healing agent.
Research groups: PetroMat
Silver particles with spiky nanostructured morphologies have been obtained by two different wet-synthesis approaches. A detailed investigation was carried out into the synthesis parameters to tune the shape of the sample into desert-rose- and succulent-like particles. The first synthetic route was based on the reduction of silver nitrate by iron sulfate in the presence of maleic acid as anisotropic agent, whereas in the second method ascorbic acid was used as the reducing agent and citric acid as the anisotropic agent.
Silicon carbide ceramics obtained by silicon reactive infiltration are nowadays employed within industry in several high temperature applications. Although these ceramics show good thermo-mechanical properties and oxidation resistance, they suffer temperature limitations (1400 °C). At higher temperatures another type of ceramics, commonly known as ultra high temperature ceramics (UHTCs), is under study. These include the transition metal diborides of group IV; one in particular, zirconium diboride, is interesting in certain applications (e.g. aerospace) because of its low relative density.
Synthetic hydroxyapatites incorporating small amounts of Si have shown improved biological performances in terms of enhanced bone apposition, bone in-growth and cell-mediated degradation. This paper reports a systematic investigation on Si-substituted hydroxyapatite (Si 1.40 wt%) nanopowders produced following two different conventional wet methodologies: (a) precipitation of Ca(NO3)2.4H2O and (b) titration of Ca(OH)2. The influence of the synthesis process on composition, thermal behaviour and sinterability of the resulting nanopowders is studied.
Silicon carbide multilayered composites containing short carbon fibres were prepared by tape casting followed by pressureless sintering. The dispersion of fibres into the SiC slurry was studied either by ultrasonics or by mechanical agitation, choosing the best solvent-dispersant couple that was compatible with the requirements of the tape casting technique. The effect of sintering temperature was studied, using carbon and boron as sintering aids, and mechanical properties were measured on composites containing from 5 vol.% to 25 vol.% of short carbon fibres.
Research groups: PetroMat
Electrochemical investigations (polarization curves, polarization resistance measurements), together with weight loss measurements and quantitative chemical analysis of the solutions after immersion of samples were used to evaluate the corrosion behaviour of type 304L and 316L sintered austenitic stainless steels in sulphate and chloride containing solutions. The samples were sintered in nitrogen based atmosphere, at 1120 and 1190°C, and in vacuum at 1200°C and submitted to X-ray diffraction analysis and SEM observation together with EDS microanalysis before and after the corrosion tests.
Research groups: CeraMat
Research groups: CeraMat
85Al2O3-15ZrO2 (wt%) powders were synthesized by gel precipitation starting from AlCl3 · 6H2O and ZrCl4 solutions and dried by two different methods: (i) by spray-drying and (ii) via a sol-gel route by n-octanol in a pilot plant. The particles by process (i) were spherical granules of diameter 15 μm, and those by process (ii) were microspheres of 25 μm. The powders were characterized in terms of morphology, particle size distribution, surface area, weight loss and crystallization behaviour at different temperatures.
Research groups: CeraMat
The sinterability of two different ceramic wastes coming from the hydrometallurgy processing of zinc ores was investigated in view of their low-cost reuse as porous building materials for heat and sound insulation. Their chemical composition, the phase and mass changes during heat treatment were firstly investigated for setting up the thermal cycle for their densification. The materials demonstrated to sinter to high final density without any sintering aid at temperatures close to 1300 °C.
Research groups: CeraMat
The influence of the heating rate on phase transformation and microstructural evolution during sintering of a de-agglomerated nanocrystalline, transition alumina was investigated. A low heating rate treatment allowed to decrease the α-Al2O3 crystallization temperature as well as to displace densification at lower temperatures, also implying a refinement of the fired microstructures.
Research groups: CeraMat
Two mullite powders, different in chemical and morphological characteristics, were compared with respect to their sinterability. For the development of a low-cost sintering step, MgO was added as sintering aid and its content was optimized for both mullites: the enhancement in sintering was imputed to a liquid phase formation. The two mullites presented a strongly different sinterability; the one gave rise to high density sintered bodies while the other, even after a grinding step which made its particle size distribution similar to that of the first, did not reach high final density.
Research groups: CeraMat
The sinterability of two industrial mullite powders, in the presence of MgO as a sintering aid, was investigated. A glassy phase, which was generated during preparation, was present in both powders; this glassy phase had a strong influence on sintering, depending on its content, composition, and spatial distribution. MgO promoted sintering in the presence of a liquid phase, both in the as-received materials and in samples washed with HF, in which most of the pre-existing glassy phase was eliminated.
Research groups: CeraMat
To obtain the best surgical results in orthognathic surgery, treatment planning and evaluation of results should be performed. In these operations it is necessary to provide the physician with powerful tools that can underline the behavior of soft tissue. For this reason, considering the improvements provided by the use of 3D scanners in medical diagnosis, we propose a methodology for analyzing facial morphology working with geometrical features. The methodology has been tested on patients with malocclusion in order to analyze the reliability and efficiency of the provided diagnostic results.
Research groups: CeraMat
Research groups: CeraMat
The preparation of NASICON powders has been achieved by sol-gel methods. The precursor solution was either rapidly hydrolyzed, to get a precipitate, or slowly gelated under exposure to atmospheric humidity. The slow hydrolysis process was studied using nuclear magnetic resonance (NMR) spectroscopy in liquid phase. Two-dimensional experiments indicate the occurrence of ligand exchange reactions in solution. Monodimensional 1H, 13C, 31P, and 23Na NMR spectra were also measured. NMR allowed us to follow the advancement of the reaction and determine the degree of polymerization.
Research groups: CeraMat
In this work, the 45S5 bioactive glass was synthesized through an aqueous sol–gel method. Characteristic functional groups were evidenced by Fourier transform infrared spectroscopy, the thermal behaviour was investigated by thermogravimetric and differential thermal analysis, crystallization kinetics and phase evolution were followed by X-ray diffraction measurements. The sintering behaviour of the sol–gel derived 45S5 was then studied by dilatometry and the microstructural evolution was followed step-by-step, interrupting the thermal cycle at different temperatures.
High surface area MgAl2O4 has been synthesised by a sonochemical method. Two kinds of precursors were used, alkoxides and nitrates/acetates and in both cases nanostructured MgAl2O4 was obtained. The effect of the addition of a surfactant during the sonication, cetyl trimethyl ammonium bromide, was also investigated. In the case of alkoxides precursors the as-made product is a mixture of hydroxides of aluminium and magnesium, while with nitrates/acetates a gel is obtained after sonication, containing the metal hydroxides and ammonium nitrate.
Research groups: PetroMat
The aim of the presented paper is to describe the sintered duplex stainless steels manufactured in sinter-hardening process and their structural and mechanical properties. Duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed base powders by controlled addition of alloying elements powder. Prepared mixes were compacted at 700MPa and sintered in a vacuum furnace with argon backfilling at temperature of 1240°C for 1h.
Research groups: CeraMat
The aim of this work is to study the sensing behavior of Sr-doped hematite for soil water content measurement. The material was prepared by solid state reaction from commercial hematite and strontium carbonate heat treated at 900 °C. X-Ray diffraction, scanning electron microscopy and mercury intrusion porosimetry were used for microstructural characterization of the synthesized powder. Sensors were then prepared by uniaxially pressing and by screen-printing, on an alumina substrate, the prepared powder and subsequent firing in the 800–1,000 °C range.