The primary objective of the present research was to provide a fundamental understanding of the processing science necessary to fabricate the Aluminum Nitride (AIN) reinforced Aluminum-Magnesium (AIMg) composites via Reactive Gas (N2) Injection in the AIMg alloy melt. Aluminum nitride (AlN) matrix composites were prepared by a novel approach. It was possible to produce a considerable amount of AIN particles in the AI alloy matrix at a reaction temperature as low as 900 °C utilizing the in-situ nitration reaction process developed in the present study.
IMSE
Institute of Materials Science and EngineeringPublications list
Research groups: CoatMat
Reusable thermal protection systems of reentry vehicles are adopted for temperatures ranging between 1000 and 2000 °C, when gas velocity and density are relatively low; they exploit the low thermal conductivity of their constituent materials. This paper presents a new class of light structural thermal protection systems comprised of a load bearing structure made of a macroporous reticulated SiSiC, filled with compacted short alumina/mullite fibers. Their manufacturing process is very simple and does not require special devices or ambient conditions.
In the field of thermal shielding for aerospace applications Cf/SiC composites are raising great interest, provided that they are protected from oxidation by suitable coatings. Conversely, ultra high temperature ceramics, and in particular HfB2, are among the best oxidation resistant materials known. A coating made of a HfB2/SiC composite (20% weight SiC) was tested as an oxidation protection on a Cf/SiC composite.
Nano-sized particles of ceria with high surface area were processed by solution combustion synthesis (SCS) and their catalytic activity towards combustion of carbonaceous materials was compared with that obtained by simple thermal decomposition of cerium nitrate, exhibiting the same specific surface area.
Co-continuous metal–ceramic composites synthesised by the reactive metal penetration method, starting from silica preforms and a 99.5% pure aluminium alloy, were characterised in high cycle tension–compression fatigue. The tests were performed at ambient temperature, in load control and with R = −1; the fracture surfaces were observed in a scanning electron microscope. The Wöhler curve is rather flat, suggesting that these composites behave similarly to ceramics, and the fatigue limit at 107 cycles is 91 MPa.
Sponge-like nanostructured ZnO layers were successfully employed as photoanodes for the fabrication of highly efficient dye-sensitized solar cells. The sponge-like ZnO layers were obtained by room temperature radio-frequency magnetron sputtering deposition of metallic zinc, followed by thermal oxidation treatment in an ambient atmosphere. The porous films show a 3D branched nanomorphology, with a feature similar to natural coral.
Research groups: CeraMat
Nanotechnology has revolutionized every field of science by opening new horizons in production and manufacturing. In construction materials, especially in cement and concrete, the use of nano/microparticles and fibers has opened new ways from improved mechanical properties to enhanced functionalities. Generally, the production or manufacturing processes of nano/micro-sized particles are energy intensive and expensive.
Research groups: HTMat
The high temperature behaviour of a Ti-6Al-4V/TiCp composite (10% Vol. of TiC) was investigated. A composite produced by Dynamet Technology according to the blended-elemental-cold-hot isostatic pressing (BE-CHIP) method was used. The stress-strain properties of the material were tested at 25, 200, 400, 500, 600 and 800°C. Composite specimens were aged in air at 500 and 700°C or under vacuum at 500, 700 and 1050°C, for periods ranging between 100 and 500 hours.
The thrust and efficiency of turbine engines are directly related to the operating temperature. In order to increase temperature without damaging the metallic parts of the engine, thermal barrier coatings (TBC) made of thick ceramic layers are currently deposited on the surface of high pressure turbine blades and vanes of aero engines. However, in the hostile engine environment, the TBC is subjected to degradation phenomena that limit its reliability and time of life. Thus, the comprehension of the TBC degradation process in this aggressive environment entails the greatest importance.
The oxidation behaviour of a multilayer SiC ceramic was investigated at high temperatures. The ceramic samples were processed by tape casting of a slurry containing α-SiC powders, forming of green tubular components and sintering without pressure. The oxidation resistance of this ceramic material was investigated by temperature programmed oxidation (TPO): the gaseous oxidation products were analysed by mass spectrometry. Thermal gravimetric analyses (TGA) were also performed.
Research groups: PetroMat
The aim of this work was to evaluate the hydro-erosion resistance of HVOF thermal sprayed coatings suitable to coat parts to be applied in the water treatment equipments and implants. Several coating materials such as Inconel 625, Inconel 625+10%vol. Al2O3, Stellite 6, AISI 316 stainless steel and WC-Co were applied on steel or cast iron substrates with different geometries. The derived specimens were tested in a special slurry abrasion/hydro-erosion test rig, that simulates the operating conditions of wet erosive wear.
Research groups: CeraMat
The current study is focused to explore a cost effective material for enhancing the electromagnetic interference shielding effectiveness of cement composites. Agricultural residue in the form of peanut and hazelnut shells having little or no economic value was investigated for the subject purpose. These wastes were pyrolyzed at 850 C under inert atmosphere and ground to sub-micron-size before utilization with cement. Dispersion of sub-micron-carbonized shell was initially observed in water through visual inspection and later in cement matrix using FESEM micrographs of fractured composites.
Research groups: PetroMat
The effect of high temperature sintering and high cooling rate on shifting the microstructural composition to the favourably of martensite-bainite structures and thus effective improvement of mechanical properties of sintered steels based on Astaloy CrL powder with an addition of 1 and 2% Cu or 50% Distaloy AB powder and 0.65% C was investigated. All the systems were processed by both sinter-hardening and conventional sintering.
Research groups: CeraMat
There is growing interest in the use of self-consolidating cementitious systems in construction industry. The present research was conducted to enhance the mechanical performance of cement composites by the utilization of micro-sized inert particles. This paper deals with the synthesis of micro-sized inert carbonized particles from hemp hurds. The synthesized carbonized particles were characterized by field emission scanning electron microscope (FESEM). These particles were further used as additive in self-consolidating cement composites. Total of four different wt% additions (i.e.
In this work we present a systematic study of the effects of high temperature treatments on the macroscopic physical and mechanical properties of millimeters thick layers of self-standing vertically aligned multi wall carbon nanotubes (MWCNTs). Annealing treatments were carried out on pristine MWCNT chunks in argon gas, in the temperature range of 1500-2200 °C. The analysis showed a change in most of the physical properties as an effect of the graphitization process.
Research groups: CeraMat
The structure and physicomechanical properties of mortars with added polymer emulsions were compared with those of a pure mortar after curing for 3, 7 and 28 days. No changes were observed in the crystal growth of the hydrated phases. The emulsions did, however, provoke a shift of the pore distribution curve towards higher mean radius values, although this shift became more and more negligible as curing proceeded. Total porosity was more contained when the additive was present, since its fluidifying effect enabled a lower initial water/cement value to be used.
Research groups: CeraMat
Cement matrix composites have been prepared by adding 0.5% in weight of multi wall carbon nanotubes (MWCNTs) to plain cement paste. In order to study how the chemical–physical properties of the nanotubes can affect the mechanical behavior of the composite, we compared the specimen obtained by mixing the same cement paste with three different kinds of MWCNTs. In particular, as-grown, annealed and carboxyl functionalized MWCNTs have been used.
Thermoplastic poly(phenylene oxide) (PPO)-matrix composites were prepared and characterized in order to evaluate the effect of different ceramic fillers on the thermal and combustion behavior of the matrix. In particular, ceramic particles having three different shapes were exploited as fillers, particles showing a platelet-like, a needle-like or an equiaxial morphology. The composite materials were produced through a melt blending method, which yielded a homogeneous distribution of the ceramic particles in the organic matrix.
Thermal fatigue (TF) is a common problem in many tool steel components. It is caused by thermal cycling in presence of internal constraints. The resulting thermomechanical stresses induce thermal cracking (heat checking). A laboratory test was developed to reproduce TF damage on a laboratory scale, under oxidizing conditions. Two different test configurations were used to induce unidirectional and bidirectional cracking. Nitriding impairs TF resistance of plain steel due to the easier propagation of cracks through the diffusion layer.
Research groups: CeraMat
Sol-gel processed NASICON-type with new compositions in the Na3Zr2-(x/4)Si2-xP1+xO12 system showed an improved sinterability with an increase in the x value. This is attributed to liquid phase sintering. This dense electrolyte system is suitable for the application as gas sensors. The CO2 gas sensors using highly dense x = 0.667 (sample B) and x = 1.333 (sample C) samples show a stable EMF response in dry atmosphere which is very close to the theoretical value.
Research groups: CeraMat
Sol-gel processed NASICON-type with new compositions in the Na3Zr2-(x/4)Si2-xP1+xO12 system showed an improved sinterability with an increase in the x value. This is attributed to liquid phase sintering. This dense electrolyte system is suitable for the application as gas sensors. The CO2 gas sensors using highly dense x = 0.667 (sample B) and x = 1.333 (sample C) samples show a stable EMF response in dry atmosphere which is very close to the theoretical value.
Research groups: CeraMat
This paper compares Al2O3-ZrO2 composites obtained from the same powder precursors dried by two different methods: spray drying and alcohol extraction via sol-gel route. The composite with 15% ZrO2 obtained by sintering microsphere powders produced via a sol-gel method exhibited better mechanical properties.
Research groups: AddiMat
Direct metal laser sintering (DMLS) is an additive manufacturing technique for the fabrication of near net-shaped parts directly from computer-aided design data by melting together different layers with the help of a laser source. This paper presents an investigation of the surface roughness of aluminum samples produced by DMLS. A model based on an L18 orthogonal array of Taguchi design was created to perform experimental planning. Some input parameters, namely laser power, scan speed, and hatching distance were selected for the investigation.
Research groups: PetroMat
Research groups: CeraMat
The durability of cordierite honeycomb structure for automotive emission control is deeply affected by the presence of some pollutants (Na2O, CaO, ZnO, PbO, Fe2O3 and V2O5) on the trap walls during the high-temperature step of filter regeneration. The long-term interaction between cordierite and the single pollutant oxides as well as the interaction between cordierite and some binary pollutant mixtures as a function of temperature have been investigated by differential dilatometry, X-ray diffraction and scanning electron microscopy (SEM).
Research groups: CeraMat
This work deals with the development of a new type of product, a catalytic filter, which could be used for treating flue gases, coupling particulate filtration and catalytic abatement of noxious gases. The first step of this project concerned the coating of the pore walls of a ceramic candle filter (made of α Al2O3) with a high specific surface area phase (i.e. a transition alumina). This layer will act as a catalyst support. The coating was obtained by impregnation of the porous support and subsequent calcination, using three different precursors.
Research groups: CeraMat
A pure coprecipitated 3 mol% Y-TZP powder was subjected to two calcination temperatures, 600° and 1000°C, prior to compaction and sintering. Significant differences in the initial sintering behavior were observed. The lower temperature calcined powder exhibited abnormal grain growth. The resultant mechanical properties mirrored the microstructure with the lower temperature calcined material having lower flexural strength. Hardness measurements of the two sintered bodies revealed significant differences in the two phases of the lower temperature calcined material.
Research groups: CeraMat
Yttrium-aluminium garnet (YAG) powders were synthesized using a reverse-strike precipitation, by adding an aqueous solution of yttrium and aluminium chlorides to dilute ammonia while monitoring the pH to a constant value of 9. After precipitation, the gelly product was washed with dilute ammonia and absolute ethanol for avoiding hard agglomeration during drying. Precipitation and washing procedures were performed at three different temperatures, namely at 5, 25 and 60 °C.
Humidity sensing properties of α-Fe2O3 have been studied after doping with alkali and alkaline earth oxides precursors. Sensors were screen-printed and three different firing temperatures were investigated: 850, 900 and 950 °C. Formation of secondary phases has been investigated by means of 57Fe Mössbauer spectroscopy for K-doped hematite samples and by means of TG–DTA and XRD for all the compositions. Alkali and alkaline earth additions to hematite, except sodium ones, increased the opened porosity as evidenced by mercury porosimetry measurements onto pressed pellets.
Research groups: CoatMat
Hybrid adhesive joining techniques are often used in many industrial sectors to design lightweight structures. A hybrid adhesive joint results from the combination of adhesive bonding with other traditional joining methods such as welding and mechanical fastening, with the aim of combining the advantages of the different techniques and overcoming their drawbacks.
This study focuses on the interference fitted/adhesive bonded joining technique. In this application, two cylindrical components are coupled together by inserting one into the other, after having placed an adhesive between them.
Research groups: PetroMat
Pt3Cu nanoparticles are deposited on multi wall carbon nanotubes (MWCNT) according to three different types of synthesis: a thermal reduction using an aprotic solvent (“thermal method”, TM), a chemical reduction using sodium borohydride (“chemical method”, CM), and an alloy method (“alloy method”, AM). The catalysts are characterized by means of BET, FESEM, EDX, XRD, ICP-MS and XPS analyses. The obtained catalysts display a Pt loading of 19.6–19.8 wt.%, with a Pt/Cu atomic ratio of 2.60–2.80. The electrocatalytic activity towards ORR is assessed by RDE in acid conditions (0.1 M HClO4).
Research groups: CeraMat
Analysis of the process used to hydrate orthorombic anhydrite (CaSO4-II) obtained by the heat treatment of gypsum has shown that its reactivity is closely related to its specific surface. If, however, the BET surface is greater than 6-7 m2/g, reactivity is also dependent on the degree of microstructural disorder. These two parameters in turn are closely dependent on the thermal treatment for synthesis.
Research groups: CeraMat
Titanium aluminide alloys are good candidates for structural applications thanks to their low density and good balance of properties up to relatively high temperatures. However, their application is still limited by significant oxidation. Four γ-TiAl alloys with different content of aluminum and niobium were produced by electron beam melting: Ti-45Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb, Ti-45Al-2Cr-8Nb, and Ti-46Al-2Cr-8Nb.
Research groups: CeraMat
Catalytic traps for diesel particulate removal are multifunctional reactors coupling filtration and catalytic combustion of soot. This paper reviews the most recent developments carried out at Politecnico di Torino concerning two different trap types: zirconia-toughened-alumina foams catalysed with Cs-V catalysts, operating according to a deep filtration mechanism, and cordierite or SiC wall-flow filters catalysed with perovskite catalysts (e.g. LaCr 0.9O3), enabling shallow-bed filtration.
Research groups: CeraMat
Today, cordierite plays a very important role in the reduction of noxious substances emitted from internal combustion engines. Honeycomb structures with parallel channels offer a good solution as supports for catalysts at an acceptable counterpressure. Porous ceramic materials permit an efficient mechanical filtration of carbonaceous particles contained in the exhaust gases of diesel engines, which are forced to flow through the walls.