IMSE
Institute of Materials Science and EngineeringPublications list
A protective coating for SiC fiber reinforced borosilicate glass-matrix composites based on zinc borosilicate (ZBS) glass-ceramic was developed. The coating was deposited on the composite surfaces by a simple and cost-effective method, based on slurry dipping followed by a densification and crystallisation stage carried out at optimised temperature and holding time. The coatings were shown to be able to withstand temperatures of up to 700 °C without softening and without exhibiting microcracking.
The oxidation resistances of different kinds of SiC-based laminates are compared. The materials under investigation are produced by tape casting of green ceramic sheets, followed by stacking of the sheets in a multilayer structure and laminate consolidation by de-binding and sintering. Three kinds of specimens are tested: multilayer SiC with fully dense layers, multilayer SiC integrating porous layers and multilayer composites made by stacking SiC/Cf composite layers. Two kinds of chopped carbon fibres (polyamide coated and uncoated) are used for the manufacture of the composite sheets.
Research groups: CoatMat
Wear and failure of die casting dies involve a complex interaction between various mechanisms. The most important wear and failure modes are summarized as follows: (i) the so-called washout damages on working die surfaces are attributed to erosion, corrosion and soldering; (ii) thermal fatigue is the most important failure mode in die casting. The sector of surface thin PVD coatings is constantly enhancing in order to meet the increasing demand for improved performances of tooling. Advanced PVD coatings are designed to withstand severe mechanical and thermal stress conditions.
Research groups: CeraMat
Well-dispersed nano-crystalline transition alumina suspensions were mixed with yttrium chloride aqueous solutions, with the aim of producing Al2O3–Y3Al5O12 (YAG) composite powders. DTA analysis allowed to highlight the role of yttrium on the α-phase crystallization path. Systematic XRD and HRTEM analyses were carried out in parallel on powders calcined in a wide temperature range (600–1300 °C) in order to follow phase and microstructural evolution.
Research groups: HTMat
Phase transition temperatures of γ-TiAl alloys were successfully identified by Thermo Mechanical Analysis. The derivative curve of the displacement as a function of temperature exhibits well defined peaks at the temperatures 1100 ≤ Teu ≤ 1200 °C and 1250 ≤ Tα ≤ 1350 °C which correspond to the phase transformations (α2 + γ) ↔ α and (α + γ) ↔ α respectively. The well-known effects of Al and Nb content on transition temperatures were studied for validation.
Research groups: PetroMat
Sintered samples containing Mo, Ni and Mn, were plasma nitrided or nitrocarburized or sulphonitrocarburized with seven different cycles. After characterization the dry wear resistance of the treated samples was evaluated by an Amsler tribometer. The samples with the best wear resistance have a surface layer formed by martensite and retained austenite. A good wear resistance is also observed for the samples with a surface layer formed by a high amount of ε solid solution, or ε solid solution with a great carbon content.
Research groups: PetroMat
Ordered mesoporous carbon (OMC)was used as catalyst (Pt) support in polymer electrolyte membrane fuel cells (PEMFC) with the aim of increasing its effectiveness towards the oxygen reduction reaction (ORR). The mesoporous carbon (CMK3 type) was synthesized as inverse replica of a silica template (SBA-15). Platinization was achieved by impregnation with chloroplatinic acid hexahydrate, H 2PtCl 6, followed by a reduction in H 2 flow at 573K. Samples containing 20wt% in Pt were prepared and characterized by ICP, XRD and HRTEM analysis.
Research groups: CoatMat
Purpose
The accurate selection of materials and the fine tuning of their properties represent a fundamental aspect in the realization of new active systems able to produce actuating forces, such as artificial muscles. In this regard, exciting opportunities for the design of new advanced systems are offered by materials belonging to the emerging class of functional polymers: exploiting their actuation response, specific devices can be realized.
Research groups: CeraMat
In many cases the production of advanced ceramics is still limited in reliability and reproducibility of material performances by inadequate technologies. Above all this is due to the fact that a real control of all the microstructure parameters (chemical composition, phases distribution and composition, surface compositional gradients, grain size, etc.), on which the properties of the ceramic mainly depend, has not been yet achieved.
Multilayered ceramics seem very promising for applications at very high temperatures in an oxidising environment. Actually, they present lower cost and better oxidation resistance than many conventional ceramic composites.
The multilayered SiC oxidation and shock resistance has been investigated on tubular specimens processed by tape casting and pressureless sintering.
The artificial aging characteristics at 177 °C of MgAlZn (AZ80A) alloy and its composite reinforced by B4C particles were compared. The morphology and the different distributions of the hardening precipitate (Mg17Al12) were observed by optical microscopy in these two materials. The aging sequence was studied by differential scanning calorimetry. This technique coupled with X-ray diffraction analyses allowed us to evaluate both the precipitation kinetics and the amount of Mg17Al12 obtained as a function of the aging time.
Research groups: CoatMat
Under various working conditions, rolling elements may suffer from different types of damage behaviour, including fractures in the coatings and bonding interfaces, and plastic deformation in the substrate materials. The present paper reports research into the prediction of the critical load of a metal-rolling system (metal-rolling system) by considering the damage of the coated surface based on a novel FE simulation-procedure developed by the present authors.
Synthetic ferrous alloys containing chromium and/or nickel were prepared and borided at 1173 K with powders containing B4C, KBF4 and SiC for times varying from 20 to 60 h. The surface layers composed of borides of type (Fe, M)B and (Fe, M)2B were characterized by means of X-ray diffraction, microscopic observations, analysis with the microprobe and microhardness measurements. A quantitative study was carried out on the differentiated distribution of chromium and nickel in the phases constituting the borided layer.
Research groups: CeraMat
A method is proposed to quantitatively evaluate the preferred orientation of FeB and Fe2B crystals, constituting the borided layer obtained on iron. The preferred orientation is expressed by an empirically calculated factor σ, which allows a fair fit of calculated with observed peak intensities by X-ray diffraction analysis of the layer (R value ≤0.15). In a further investigation, this coefficient (σ) was used to quantitatively examine the influence of temperature and reagent composition on the degree of orientation of the phases obtained by boronizing pure iron.
As an alternative to previously developed catalytic FeCrAlloy fibre mat burners based on perovskite catalysts, new catalytic burners have been developed based on Pd catalyst on lantana-stabilised Al2O3 and different fibre structures (NIT100A, NIT100S and NIT200S by ACOTECH NV).
Research groups: CeraMat
The composite powders 90 vol.% Al2O3–5 vol.% YAG–5 vol.% ZrO2 were produced by doping commercial alumina powders with zirconium and yttrium chloride aqueous solutions. Both a nanocrystalline transition alumina and a pure α-phase powder were used as starting materials. The obtained materials were characterized by DTA-TG, XRD and dilatometric analyses and compared to the respective biphasic systems developed by the same procedure.
Research groups: CeraMat
Amorphous precursors of LaNbO4 have been prepared by coprecipitation and mechanical alloying. Powder characteristics before and after calcination were studied by thermogravimetric analysis, differential thermal analysis, Fourier transform-infrared spectroscopy and X-ray diffraction, and the crystallographic changes during thermal treatment were documented by high-temperature X-ray diffraction.
Research groups: CeraMat
A modified gel casting procedure based on a natural gelatin for food industry and commercial polyethylene spheres as pore formers was successfully exploited to produce dense and porous ceramic bodies made of yttria stabilized tetragonal zirconia polycrystal (Y-TZP). Vickers and Knoop microhardness, elastic modulus and fracture toughness measurements on dense samples obtained by experimental investigation closely matched results found in the literature for similar materials.
Reactive metal penetration was used to prepare intermetallic–ceramic composites with co-continuous structure, starting from silica glass preforms. Two subsequent metal penetrations were performed: first, the silica was immersed in a liquid Al bath, obtaining an Al(Si)/Al2O3 composite, then Ni was put in contact with the composite at high temperature, bringing to the substitution of Al with a Ni–Al intermetallic. The obtained composites present both phases continuous, and the whole process is a near net-shape one.
Research groups: PetroMat
Rapidly solidified Al100-x-Cux alloys (x=5, 10, 15, 25, 35wt%) were prepared and analyzed. High cooling rate increased the Cu solubility in α-Al matrix. The influence of the cooling rate on Cu solubility extension in Al was experimentally simulated. Thus the pouring was performed in metallic die and by melt spinning-low pressure (MS-LP) technique. Melt processing by liquid quenching was performed using a self-designed melt spinning set-up which combined the cooling technology of a melt jet on the spinning disc with the principle of the mold feeding from low pressure casting technology.
Co-continuous ceramic-metal composites (C4) were prepared by reactive metal penetration of cordierite-based ceramics used as oven refractory. A compositional and physical characterisation of both precursors and composites was carried out to understand how the choice of the starting material affects the reactive metal penetration. Mechanical behaviour was then compared with that of composites obtained from silica glass or fully sintered cordierite ceramics.
Research groups: CeraMat
A sol-gel process produced microsphere of Al2O3 containing 10 wt% ZrO2 by coprecipitating Al and Zr hydroxides from the respective chlorides through the addition of NH4OH. In this paper, gel processing is examined as a function of temperature, pH, and residual Cl- content. The washed gel was peptized at 80°C with HCl and the sol concentrated to an Al3+ ion content of 4 mol/L. The concentrated sol is used to feed a pilot plant for microsphere production. The microspheres calcined at 1200°C are dense, with an average size of 20 μm and a BET surface area of 30 m2/g.
Research groups: CeraMat
Crystalline powders of Li2ZrO3 were prepared by gelling ZrCl4 and CH3COOLi with NH4OH at 50 °C, at different pH values (5, 7 and 8) and for different times (3, 12 and 24 h), then drying and calcining. Compacts from these powders were found sinter to higher densities than a commercial Li2ZrO3; their porosity at 1200°C was close to 3 μm and was suitable for blanket material applications. Tritium release as HTO begins at 300 °C and reaches 73% at 400 °C, a temperature much lower than that required for Li2O.
Research groups: PetroMat
A processing method common to composite ceramics with very different ZrB2/SiC ratios was developed in order to exploit ZrB2–SiC laminates comprising alternate layers with different compositions for thermal protection systems of re-entry vehicles. Ceramic laminates were made using SiC, ZrB2 and composites with a SiC/ZrB2 ratio ranging from 100 vol.-%SiC to 100 vol.-%ZrB2. The preparation was performed by tape casting of a slurry, layer stacking, debinding and pressureless sintering.
Research groups: CeraMat
Research groups: CoatMat
Research groups: CeraMat
Research groups: CoatMat
Processing of a natural hydroxyapatite powder: From powder optimization to porous bodies development
This paper deals with the development of macro-porous components made of a carbonated hydroxyapatite (HAp) nanopowder which was extracted from pig bones. Prior to sintering, the powder was treated at 700 °C for 1 h. During calcination, a partial carbonate decomposition occurred yielding CaO. In order to eliminate this by-product, the calcined HAp was washed in distilled water several times, checking the effect of washings by FT-IR spectroscopy.
Zirconia toughened alumina (ZTA) materials are frequently used in mechanical engineering and biomedical applications due to their enhanced toughness, strength and wear resistance compared to monolithic alumina. In this study, a submicron size alumina powder was modified via wet chemical route: the alumina particles surface was coated with zirconium chloride, to yield 10 vol% zirconia by subsequent thermal treatment. From this powder, several ZTA materials were produced by slip casting, sintered at different temperatures from 1475 to 1575 °C.
The reactive penetration of Al based alloys in massive silica glass and sintered preforms (made of silica, silica plus silicon carbide or silica plus aluminium nitride) was investigated. The reactions occurring during preform sintering and reactive metal penetration were preliminarily studied by Differential Thermal Analysis. Square bars of co-continuous composites were then processed by using this reactive metal penetration (RMP) method.
Research groups: CoatMat
Electrodeposition is well-known as a versatile and economical processing technique to produce metal coatings on conductive substrates. Recently, it has been gaining increasing interest also for the production of tailored composite coatings, containing for instance floropolymers or silicon carbide. A more novel approach concerns the use of carbon nanotubes or even graphene, in the form of graphite nano-platelets.
The preparation of highly pure MgB2 powder is here presented. The two steps preparation method, together with an ad hoc projected reactor, permits us to obtain the desired stoichiometric phase without MgO impurities and other degradation compounds, which depress the superconductive properties. The formation of a liquid phase during the first step of the preparation leads to small grain size particles. New techniques of film preparation (Electrophoretic deposition) have also been approached.
Research groups: CeraMat
The bottom ashes coming from two different municipal solid waste incinerators were vitrified at 1400 _C. The obtained glass, mixed with other wastes coming from metallurgical and mineral industrial wastes, was used as raw material for the production of glass-ceramic tiles. Two different mixtures were used for the tile production: (a) glass from bottom ashes plus corundum-based waste from an aluminum foundry and (b) glass from bottom ashes plus kaolin-based waste from the kaolin ore extraction process.
Research groups: PetroMat
Alloys with a cobalt binder content in the range from 3 to 15 wt.% were studied. The carbides grain size also range between 0.7 and 5 μm. Mechanical properties, such as transverse rupture strength and hardness, were tested. The residual porosity and the micro structure were accurately observed by optical microscopy and the carbide grain size was estimated using an optical image analyser.