Ceramic nanocomposites are attracting growing interest, thanks to new processing methods enabling these materials to go from the research laboratory scale to the commercial level. Today, many different types of nanocomposite structures are proposed in the literature; however, to fully exploit their exceptional properties, a deep understanding of the materials’ behavior across length scales is necessary. In fact, knowing how the nanoscale structure influences the bulk properties enables the design of increasingly performing composite materials.
IMSE
Institute of Materials Science and EngineeringPublications list
Research groups: CeraMat
Carbon free Fe-Ni alloys (12 and 20 wt.% Ni) have been analysed by X-ray diffraction and surface Mössbauer spectroscopy (CXMS and CEMS) after boriding treatment at 1273 K for 20 hours. Some (FexNil-x)2B and FexNil-xB samples, with different values of x, obtained by heating at 1073 K mixtures of elements in powder form, were used as reference. Besides (FexNil-x)2B and FexNil-xB, a third boride phase rich in boron has been detected in the outer borided layers of the alloy specimens. A third phase appears also in the corresponding X-ray patterns.
Research groups: PetroMat
The paper is focused on the processing of aluminum alloy chips using powder metallurgy. Chips obtained from recycled AlSi5Cu2 alloy were ball milled with the addition of silicon carbide powder with an average size of 2um. Mechanical alloying process was employed to obtain homogeneous composite powder. The effect of processing time (0 - 40h) on the homogeneity of the system was evaluated, as well as a detailed study of the microstructure of AlSi5Cu2 aluminum chips and SiC particles during MA was carried out.
Graded structures obtained by coupling different WC grades, also containing cubic carbides type (Ta, Nb)C with Co as binder, were produced by vacuum sintering. Different batches of cylindrical samples were compacted by coupling two different grades and were sintered at 1450°C under vacuum. The hardness properties as well as the shrinkage due to sintering process are function of the employed grades and show gradual change between the single values of each of the coupled grades.
Research groups: PetroMat
The paper deals with the surface hardening of stainless steels trough the application of suitable plasma nitriding cycle to different austenitic and martensitic grades. The cylindrical shaped samples, 18 to 30 mm in diameter and 50 mm long, have been plasma nitrided in an industrial plant, performing the heating in hydrogen based plasma up to 420 °C for 2 h, then the temperature has been elevated at 530 °C in plasma obtained by H2 - N2 (80% and 20% respectively), the cooling has been done in nitrogen based atmosphere.
Research groups: AddiMat
Ceramic matrix composites (CMCs) can be attractive for structural applications, but their machining by conventional methods is expensive and often critical. Complex geometries on advanced ceramics require contactless processes, such as electrodischarge machining or drilling (EDD). These proved to be viable for CMCs with electrical resistivity below a critical value in the range of 1-3 Ω m. The condition is complied with by many CMCs: an example is alumina with titanium carbide.
Research groups: CeraMat
Layered-type perovskite catalysts (A2−xA′xB1−yB′yO4±δ, where A, A′=La, K and B, B′=Cu, V), prepared by the citrates method and characterized by BET, XRD, and catalytic activity analysis, proved to be effective in the simultaneous removal of soot and NOx, the two prevalent pollutants in diesel exhaust gases, but only at temperatures as high as 450–500 °C, seldom reached at the exhaust line location unless next to the engine exit (close-coupled system).
Research groups: PetroMat
Research groups: CeraMat
Thermal spraying processes have many advantages that help improve the performance and extend the life of materials and components. In the present paper the properties and wear behaviour of plain carbon specimenscoated with Ni or Co based alloy powders have been studied for the coating of tools employed in hot working applications, e.g. rolls in a rod mill plant.
Research groups: PetroMat
In the present work reactive powders, mixed to stainless steel ones, have been used to increase the density of sintered parts, through the generation of a liquid phase. High density is connected to porosity decrease and also to transformation from open to close pores: this increases also the corrosion behaviour and the mechanical properties.
Research groups: CeraMat
17th century stuccos located in The Valentino Castle in Turin (Northern Italy) have been studied by means of XRD, TG-DTA, Hg porosimetry and SEM coupled with EDX chemical analysis in order to understand their composition and the degradation causes. The investigated un-degraded samples were made of gypsum, hydrated lime and other carbonates phases on the external surface and up to ca. 20 mm in depth but the compositions were highly heterogeneous.
Research groups: CoatMat
Research groups: CeraMat
This article reports the study of a transition nanometric alumina both as such and after prolonged magnetic stirring in bi-distilled water. Stirring was effective in inducing a significant reduction of starting particles agglomeration and modification of the surface properties of the material. The formation of an Al(OH)3 (gibbsite) phase after magnetic stirring in water was detected by means of XRD on powdered samples. Correspondingly, Infra Red spectrum of magnetically stirred alumina outgassed at 150 °C showed a band at ca.
Research groups: CoatMat
The adhesive bonding technology can be used in combination with other traditional joining methods, such as mechanical fastening techniques (e.g. rivets or bolts) or welding techniques, generating a hybrid joint. Hybrid adhesive joints are designed to exploit the advantages of the different techniques and, if possible, overcome their drawbacks. This study focuses on the interference fitted/adhesive bonded joining technique. This method consists in two cylindrical components coupled together by inserting one into the other, after having placed an adhesive on the mating surfaces.
Wear and failure of die casting dies involve a complex interaction between various mechanisms. A CrAlSiN coating system was deposited on the base material, modulating the chemical composition of the chromium or the aluminium-silicon content. A set of the coated specimens was directly analysed through optical and electronic microscopy, so as to assess the overall quality. Other was subjected to a cyclic immersion program in molten aluminium bath. Coating efficiency was determined through electron microscopy analysis. Thermal fatigue was investigated, quantified.
Metal/ceramic composite materials were produced with core/shell structure by traditional pressing and the influence of the compacting parameters on the material properties has been studied. Different quantities of ceramic have been introduced to coat the base stainless steel powder. The use of a new generation of coated powders gives the opportunity to achieve near net shape massive composite exhibiting a composite microstructure, with a uniform dispersion of ceramic hard particles embedded in the metal matrix.
Research groups: PetroMat
An X37CrMoV5.1KU hot working steel was quenched and tempered, nitrided, overcarburised, overcarburised and nitrided, and nitrocarburised for 18 and 36 h. Wear tests at 50 and 100 kg loads were performed without lubricant on the treated specimens using an A135 Amsler machine in order to determine the most effective treatment. The quenched and tempered specimens showed the worst behaviour and the nitrocarburised specimens the best.
Research groups: PetroMat
Three kinds of turbine blades (made by casting Renè 77, Renè 80 and CMSX-4 nickel based alloys) were submitted to an above pack aluminizing treatment. The suitability of this surface coating for preventing high temperature oxidation and hot salt corrosion was investigated. Oxidation tests were performed in air at 1050°C for 500 and 1000 h; salt corrosion at 950°C was studied by using a NaCl+Na2SO4 mixture. The microstructure of aluminized blades before and after these tests was compared by X-ray diffraction, scanning electron microscopy and electron probe microanalysis.
In this work, the effect of thermal treatment at 380°C and 600°C, under gaseous atmospheres containing some typical components of diesel emissions (SO2 and water), was studied on some promising catalysts for diesel particulate combustion. In particular, the ageing behaviour of two novel catalysts (based on CsVO3+KCl and KVO3+KCl, respectively) and of a more widely studied Cu–K–V–Cl catalyst was investigated.
Research groups: CeraMat
A case history of a severe degradation of concrete foundation plinths and piers of an about-35-year-old building located in Northern Italy is described. Significant amounts of gypsum, near ettringite and/or thaumasite were detected by X-ray diffraction analyses performed on ground concrete samples. Large gypsum crystals were mainly located at the interface between the cement paste and aggregates, as observed by scanning electron microscopy coupled to energy-dispersive spectroscopy microanalysis.
Research groups: PetroMat
To decrease the treatment time and to obtain better properties of the layers, the authors studied a cycle consisting in a pre-oxidation with sulfur dioxide, effected with the purpose of reducing the interconnected porosity, and a nitrocarburizing stage. Steel samples, containing little carbon (0. 01 wt pct) and copper (2 wt pct), with three different density ranges (6. 3 multiplied by (times) 10**3, 6. 7 multiplied by (times) 10**3 and 7. 2 multiplied by (times) 10**3 kg/m**3), were treated in a laboratory furnace with a small flow of SO//2 (1.
Research groups: CeraMat
YAG powder was synthesised by reverse-strike co-precipitation, calcined at 1000 °C and dispersed by either ball-milling with α-alumina (BMA) or zirconia (BMz) spheres or by ultrasonication (US). All the dispersed powders were consolidated by SPS to nearly theoretical density, but only the US powder gave rise to a transparent material (transmittance of about 60% at 600 nm, 1 mm thickness), characterised by an ultra-fine microstructure (average size of 330 nm).
Research groups: CeraMat
(High resolution) TEM and FTIR spectroscopy of in-situ CO adsorption at 300and ∼ 78 K have been used to characterize particle morphology and surface Lewis acidity of three preparations of tetragonal ZrO2 stabilized with Y2O3. Depending on preparation, the starting materials are in the form of individual coin-shaped platelets, or of huge aggregates of small particles. In either case, few low-index crystal planes are most frequently exposed, and the particle edges are irregular.
Research groups: CeraMat
The characterization of three microcystalline Y2O3-stabilized tetragonal zirconia (t-ZrO2) preparations was carried out by BET, XRD, HRTEM, and FTIR spectroscopy, and revealed that morphological and surface features of t-ZrO2 specimens depend, much more than in the case of the monoclinic modification (m-ZrO2), on the preparative history of the material.
Research groups: CeraMat
Two preparations of tetragonal zirconia (t-ZrO2) stabilized with 3 mol% Y2O3 have been characterized, and their features compared with those of a 2 mol% t-ZrO2 preparation and of a monoclinic zirconia (m-ZrO2) preparation. At ambient temperature, CO adsorption occurs only on surface cationic Lewis acid sites located in crystallographically defective configurations. The various t-ZrO2 preparations present several types of such defective sites, depending on the temperature of the sintering stage.
Surface Coating of Oxide Powders: A New Synthesis Method to Process Biomedical Grade Nano-Composites
Composite and nanocomposite ceramics have achieved special interest in recent years when used for biomedical applications. They have demonstrated, in some cases, increased performance, reliability, and stability in vivo, with respect to pure monolithic ceramics. Current research aims at developing new compositions and architectures to further increase their properties. However, the ability to tailor the microstructure requires the careful control of all steps of manufacturing, from the synthesis of composite nanopowders, to their processing and sintering.
The chemical and physical characteristics of ion-nitrided surface layers, obtained on α-β titanium alloys, are examined and correlated both with the working conditions adopted in the ion-nitriding process and with the alloy chemical composition. Besides the influence of the working parameters on the morphology and on the microstructures of the ion-nitrided surface layers, mainly the alloy element distributions both in surface coatings and in the substrate are analysed for five α-β titanium alloys of industrial use, and for titanium c,p.
The investigations were made on alloys OT-4 (Ti-3Al-1. 5 Mn), IMI318 (Ti-6Al-4V) and IMI550 (Ti-4Al-4Mo-2Sn-0. 5Si) of the alpha-beta type. The pressure was fixed at 10 torr and the temperature was made to vary between 800 and 1,000 degree C. A gaseous mixture was chosen, composed of 60 nitrogen and 40 hydrogen vol% and times of 4, 8 and 16 hours were selected for treatment with an ionic discharge. Diffractometric analysis was used for identification of the type of phases present on the hardened surface. It was found that the alloying elements modify the morphology of the surface layer.
Research groups: PetroMat
Research groups: PetroMat
Highly multibranched gold nanostars were obtained by a room-temperature synthesis assisted by deep-eutectic solvents (DES). The concentration of the ascorbate ions and the presence of water in the solution were found to both have a profound influence on branch formation. A growth mechanism of the nanostar is therefore proposed from the analysis of the particle dimensions, the aspect ratio of their protuberances, and the gold crystal size. These spiky nanoparticles would find an application as conductive filler in polymeric piezoresistive composites, based on a tunneling conduction mechanism.
Research groups: CeraMat
Research groups: CeraMat
Powders and pellets of new NASICON compositions have been synthesized using a mixed inorganic-organic sol-gel synthesis, by the preliminary formation of a pre-hydrolized TEOS xerogel. The investigated compositions can be described by the general formula Na3Zr2-(x/4)Si2-xP1+xO12, obtained by keeping the Na concentration constant (= 3) at the optimum value reported for ionic conductivity, with x = 0 (the usual NASICON composition), 0.667, and 1.333. The xerogels were calcined at various temperatures in the range 400-1200°C.
Synthesis of zeolites from thermally activated kaolinite. Some observations on nucleation and growth
Research groups: CeraMat
Depending on the preparation temperature and the origin of the raw material, the products obtained by thermal activation of kaolinite lead, by hydrothermal treatment with sodium hydroxide at 102°C, either to zeolite 4A, or to cubic zeolite P, or to a mixture of cubic and tetragonal zeolite P.
Research groups: PetroMat
Research groups: CeraMat
We studied the voltage and temperature dependency of the dynamic conductance of normal metal–MgB2 junctions obtained either with the point-contact technique (with Au and Pt tips) or by making Ag-paint spots on the surface of MgB2 samples. The fit of the conductance curves with the generalized BTK model gives evidence of pure s-wave gap symmetry. The temperature dependency of the gap, measured in Ag-paint junctions (dirty limit), follows the standard BCS curve with 2Δ/kBTc=3.3.
Titanium metal and some of its alloys of the type Ti-Al-Me (Me=transition metal) were submitted to plasma nitriding. The resulting compound layer was examined by optical microscopy and by XR diffraction in order to establish both its microstructure and texture degree under different nitriding conditions. To this aim a texture evaluation method was employed, which was formerly devised and applied on surface layers obtained by boriding of steels. In these nitrided layers the Ti2N nitride was clearly textured while the TiN did not show an appreciable degree of preferred orientation of crystals.
Research groups: PetroMat
Several hydroxyapatite (HAp) synthesis routes, such as solid state reactions, hydrothermal methods, wet procedures have been widely investigated. At the same time, in the last years many alternative methods to produce HAp, exploiting fish, bovine or pig bones, have been developed; among them the most used are thermal processes as well as subcritical water or alkaline hydrothermal routes. This paper deals with a natural HAp nanopowder extracted from pig bones by a treatment with hot NaOH solution.
Research groups: PetroMat
The paper presents the tensile behavior of sintered steels developed through a new process called gascarbusintering (GCS), consisting of carburizing in gas (CH4) of a set of iron based powder compacts followed by sintering. The influence of compaction pressure and dwell time at the carburizing temperature on the tensile properties of steels processed by GCS is investigated.
The variation in hardness of the phases (Fe, M)B and (Fe, M)2B (M ≡ Cr or Ni), which are the predominant components of the borided layer obtained on iron alloys, was defined and related to increase in chromium, nickel and carbon contents. It was found that chromium increases the hardness both of the borided layer as a whole and of the boride components, even though these values are systematically lower than those measured on pure borides.
This article aims to prepare by injection molding recycled polymeric composites based on PA66 reinforced with short carbon fibers after artificial aging for applications in the automotive field. The aging cycles involves the combined action of UV radiation, moisture, and temperature in order to simulate the common outdoor conditions. The 100% recycled composites are obtained by the regranulation of the aged specimens followed by the remelting and re-injection molding.
Research groups: AddiMat
The performance of structural materials is commonly associated with such design parameters as strength and stiffness relative to their density; a recognized means to further enhance the weight-saving potential of low-density materials is thus to improve on their mechanical attributes. The European Community research project ExoMet that started in mid-2012 targets such high-performance aluminum- and magnesium-based materials by exploring novel grain refining and nanoparticle additions in conjunction with melt treatment by means of external fields (electromagnetic, ultrasonic, and mechanical).
Research groups: PetroMat
Mössbauer spectroscopy of nitrided and carbonitrided iron powders and plates with total interstitial atom contents of between 24 and 33 at% has allowed the variation with composition of the hyperfine magnetic fields of metal atoms with 2 or 3 close interstitial atoms to be determined. Fe atoms with three non-metal nearest neighbours and paramagnetic behaviour have also been detected. Only when the content of non-metal atoms goes beyond 30 at%, do Fe atoms in ε-carbonitrides display higher magnetic fields than in the corresponding ε-nitrides.