In view of the possible application of SiC-based ceramic laminates as critical components of hydrogen generation plants based on sulfur-iodine or hybrid-sulfur thermochemical cycles, the effect of corrosion on this kind of ceramics has been investigated.
IMSE
Institute of Materials Science and EngineeringPublications list
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: CoatMat
Research groups: PetroMat
The corrosion resistance of tool steels used for pressure die casting in molten aluminum environment was investigated. Steel AISI H13, steel for combustion valves and raging steel without coating, with TiAlN coating applied by PVD process and with a semi permanent coating named Protalcar were used for the study. The experiment was conducted under conditions of continuous contact between the die and molten alloy to simulate the corrosion behaviour. Corrosion resistance in static immersion was evaluated as a reduction of the external surface plunged in molten aluminum.
Research groups: PetroMat
The corrosion resistance and electrochemical behavior of sintered AISI 304L and AISI 316L samples is evaluated in sulfate and chloride containing solutions. It is shown that the sintering atmosphere strongly influences the microstructure of austenitic stainless steels. Samples sintered in nitrogen-based atmosphere show better mechanical properties but lower corrosion resistance than samples sintered in vacuum because of the precipitation of chromium carbides.
Research groups: PetroMat
This paper presents corrosion resistance results in salt fog spray test of duplex stainless steels obtained through powder metallurgy starting from austenitic X2CrNiMo 17-12-2, martensitic X6Cr13 powders by controlled addition of alloying elements in the right quantity to obtain the chemical composition of the structure similar to biphasic one. In the preparations of mixtures the Schaffler's diagram was taken into consideration. The prepared mixtures of powders have been sintered in a vacuum furnace with argon backfilling.
In this work, thermal degradation of commercial polymer mixtures was evaluated as a promising approach to the production of ceramic brake components. Currently, there is a wide interest for the production of cost effective ceramic pads, and carbon based materials are good candidates both in monolithic form and as porous networks to be reinfiltrated with a convenient polymer. The process parameters for obtaining porous glassy carbon, starting from mixtures of commercial polymers, have been evaluated in this work with the goal of producing samples with optimized mechanical properties.
Research groups: CeraMat
There is a tremendous increase in the use of high strength and high performance self-consolidating cementitious composites due to their superior workability and mechanical strengths. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to the low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses) etc.
Research groups: CeraMat
Al2O3–5 vol.% Y3Al5O12 (YAG) composite powders have been prepared by surface doping of α-alumina powders by an yttrium chloride aqueous solution. Two commercial, one submicron-sized, the other ultra-fine, alumina powders were compared as matrix materials. YAG phase was yielded by an in situ reaction promoted by the subsequent thermal treatment of the doped powders.
The unreinforced 6061 alloy and a 6061/SiC composite, at the beginning in the T6 temper, were submitted to thermal cycling (up to 2000 cycles) in the temperature ranges 25-180°C and 25-220°C. The microstructure of these materials was studied by scanning electron microscopy and mercury intrusion porosimetry. Mechanical and thermomechanical properties were also investigated. Tensile strength, hardness, Charpy impact resistance, fracture toughness, density, specimen dimensions and thermal expansion were compared before and after thermal cycling.
Research groups: PetroMat
In the last decade the gold industry has been subject to a high degree of automation and to a high development in terms of technological devices. However what seems to be lacking is the approach oriented towards the engineering of the sector, intended as a synchronised study of the material characteristics, related to the process and to the production techniques.
The thermal stability of a 2D-Nicalon/C/SiC composite was studied through the variation of both mechanical properties and microstructure occurring during heat treating. The composite was processed by infiltration of SiC preforms according to SICFILL® method. The material toughness was enhanced by a carbon interphase put between the fibers and the matrix. In order to improve the thermal stability a CVI layer was deposited on the carbon interphase and the specimen surfaces were CVD covered by an external SiC seal coating about 165 μm thick.
A modified gel-casting process was developed to produce both dense and highly porous (40% volume) yttria tetragonal zirconia polycrystal (Y-TZP) using agar, a natural polysaccharide, as gelling agent. A fugitive phase, made of commercial polyethylene spheres, was added to the ceramic suspension before gelling to produce cellular ceramic structures. The characterization of the microstructural features of both dense and cellular ceramics was carried out by FEG SEM analysis of cross-sections produced by focused ion beam.
Research groups: CeraMat
Dense and cellular yttria-tetragonal zirconia polycrystal (Y-TZP) bodies were produced by using a natural gelatine and two different agars as gelling agents, while commercial polyethylene (PE) spheres were added (125 to 300 μm diameter) as a volatile pore forming agent to create 50-65 vol% spherical macro-pores, uniformly distributed in a micro-porous matrix. The microstructure of all dense and cellular ceramics was characterized by FEG-SEM and Focused Ion Beam (FIB) techniques.
Research groups: AddiMat
Selective laser melting (SLM) process allows fabricating strong, lightweight and complex metallic structures. To successfully produce metallic parts by SLM, additional structures are needed to support overhanging surfaces in order to dissipate process heat and to minimize geometrical distortions induced by internal stresses. However, these structures are often massive and require additional post-processing for their removal. A minimization of support structures would therefore significantly reduce manufacturing and finishing efforts and costs.
Biocompatible and biodegradable scaffolds can provide a convenient support for stem cell differentiation leading to tissue formation. Porous hydroxyapatite (HAp) scaffolds are clinically used for applications such as spinal fusions, bone tumors, fractures, and in the replacement of failed or loose joint prostheses. The incorporation of small amounts of silicon within hydroxyapatite lattice significantly improves HAp solubility and rate of bone apposition, as well as the proliferation of human osteoblasts in vitro.
Research groups: CeraMat
The durability of cordierite honeycomb structure for automotive emissions control is strongly affected by the presence of some pollutants on the trap walls during the high temperature step of filter regeneration. The short-term interaction between cordierite and some single pollutant oxides (Na2O, CaO, ZnO, PbO, Fe2O3, V2O5) has been investigated by differential dilatometry, XRD, IR spectroscopy and SEM. There is evidence that the pollutant ions diffuse into the cordierite lattice.
Research groups: CeraMat
CO2 sensing characteristics were examined in dry condition for Pt, Na2CO3/Na2O-Al2O 3-4SiO2//YSZ/Pt structure. After settled at the working temperature at 460°C, emf was gradually decreased with time and then increased. The drift to decrease the emf observed in the initial period is due to the remove of water in Na2CO3 layer with morphological changes. The diffusion of Na ion in Na2O-Al2O 3-4SiO2 layer to YSZ layer is also one of the reason.
Research groups: CeraMat
Porous ceramic materials are of considerable interest for a variety of chemical and industrial applications in extremely harsh conditions, particularly at very high temperatures for long time periods. A combined gel-casting-fugitive phase process employing agar as a natural gelling agent and polyethylene spheres as pore formers was exploited to produce porous ceramic bodies. Alumina and alumina–zirconia powders were used to prepare samples having a porosity of about 65–70–75 vol%. The composite powder was produced by a surface modification route, i.e.
As a part of our research on new gas sensors, an original potentiometric gas sensor was developed. The gas sensor consists of a solid electrolyte associated with two different electrodes located in the same gas mixture. Owing to the interesting behavior of this sensor to the action of CO and NOx, it was decided to develop this device within the framework of a European contract and to produce it industrially by screen-printing. The sensor is designed for use in automotive applications. We propose to expose the problems encountered during the development phase as well as the chosen solutions.
A screen-printed thick film was developed to be overlapped to a gas sensing device for preserving it from contamination and degradation occurring in hostile environments, and also for improving its selectivity to a single pollutant gas when exposed to a complex atmosphere. This protective layer incorporated Al2O3 doped with Cs or Ba oxides as a catalyst material for eliminating gaseous interfering species, precisely CO2, to improve sensor response to CO.
Research groups: CeraMat
A β-alumina-based gas sensor for automotive exhaust application (hydrocarbon, CO, NO2 detection in 10-1000 ppm concentration range) has been developed by thick film technology (screen-printing) in the frame of a European project. The sensing device consists of a solid electrolyte (β alumina) and of two metallic electrodes having different catalytic properties, the whole system being in contact with the surrounding atmosphere to be analyzed.
Pyrovanadates of potassium and cesium were prepared and tested as catalysts for low-temperature combustion of carbon. Their catalytic activity was investigated by both temperature-programmed oxidation and thermogravimetric analysis and compared with that displayed by the metavanadates of the same elements, previously proposed as promising catalysts for soot combustion in diesel emissions. Pyrovanadates show an intrinsic catalytic activity noticeably higher than that of the corresponding metavanadates.
Research groups: PetroMat
As the robotics is moving its interest from the machine tools for industrial production to biomimetic, even human-like systems, the need for materials that fulfill skin role arises. Skin presents a structure that has multiple roles such as protection and tact. The basic requirements for a skin mimetic material are flexibility and a measurable physical property triggered by the pressure. In this work hybrid piezoelectric materials are prepared and characterized. The flexibility of materials is assured by the polymeric matrices while ceramic oxide fillers grant a piezoelectric response.
Research groups: CoatMat
In this work, a nanocomposite (Cr,Al)xN1−x/Si3N4 coating system was deposited on H11 hot work tool steel, using the Lateral Arc Rotating Cathodes (LARC®) deposition system and modulating the chemical composition of the chromium and aluminium–silicon content. Structural characterizations were performed using scanning electron microscopy, equipped with energy dispersive spectroscopy probe, and applying x-ray diffraction, for the evaluation of phase constitution and crystallite size.
Research groups: CeraMat
This work aimed to determine the degradation causes of the Palace of Public Works located in S. Giovanni square in Turin (Piedmont, Italy). The samples collected from the surface layer were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric coupled with differential thermal analysis (TG-DTA), mercury intrusion porosimetry measurements (MIP) and phenolphthalein test. Metallographic and elemental analyses were also carried out on the steel reinforcing bars.
An experimental study was conducted on lab-scale masonry systems constituted by traditional hand-made bricks coupled with external layers of de-humidifying mortar, damaged by means of salt crystallization. The evolution of damage was followed by means of a non-destructive technique denoted as scaling subtraction method (SSM), which is based on the detection and post-processing of the nonlinear response of the system to prescribed ultrasonic excitations.
This paper concerns the development of catalytic traps for diesel particulate removal from the exhaust gases of light-duty vehicles. The studied traps were realised with ceramic (ZTA and mullite) foam structure, on which two different kinds of catalysts, one based on caesium metavanadates and the other on pyrovanadates, were deposited.
Research groups: CeraMat
Alumina-yttrium aluminum garnet (YAG) 50 vol % nanocomposite powders were prepared by a wet-chemical synthesis and characterized by simultaneous DTA-TG, XRD, and TEM analyses. Amorphous powders were preheated at four different temperatures (namely, 600, 800, 900, and 1215°C) on the basis of the previous characterization, and the influence of this thermal treatment on sintering behavior, final microstructure, and density was investigated.
Calcium phosphate-based materials should show excellent bone-bonding and cell-mediated resorption characteristics at the same time, in order to be employed for bone replacement. In this perspective, pure (HAp) and silicon-substituted hydroxyapatite (Si-HAp, 1.4% wt) porous cylinders were prepared starting from synthesized powders and polyethylene spheres used as porogens, and investigated as supports for osteoblast and osteoclast progenitor differentiation.
Research groups: CeraMat
By using a wet chemical route, pure calcium hexaluminate (CA6) was yielded, significantly lowering the reaction temperature and shortening the synthesis time if compared to usual industrial procedures. owever, dilatometric studies performed on compacts made of the as-prepared powder, just after pre-heating at 450°C, has shown a superposition between sintering shrinkage and expansion related to CA2 formation, an intermediate phase formed during calcination and phase evolution to CA6.
Research groups: PetroMat
The dimensional changes that occur in the steel during heat treating is one of the most difficult problems facing the heat treater. While the influence of the alloy chemical composition, of the heat treatment cycle and of the shape and dimensions of the pieces on the deformations caused by heat treatments on the wrought steels are now a days well known, the presence of the porosity in the sintered steels arouses some inconvenients which influence directly the heat treatment effects.
Research groups: PetroMat
In this paper dimensional stability investigation in two hypoeutectic composition is proposed. Specifically, the study of some samples in AlSi7Mg0,3 and AlSi8,5Cu3,5 alloys is realized and a comparison of the obtained data will be discussed. Starting from dilatometric analysis the dimensional modification of the alloys is monitored. For both materials analysis has been conducted by heating to 500°C at various heating rates and determining the activation energy for the decomposition process of the supersaturated solid solution.
Research groups: AddiMat
Direct metal laser sintering (DMLS) is an additive manufacturing (AM) technology for the fabrication of near netshaped parts directly from computer-aided design (CAD) data by melting together different layers with the help of a laser source. Its application for manufacturing three- dimensional objects represents one of the promising directions to solve challenging industrial problems. This approach permits to extend significantly the freedom of design and manufacture by allowing, for example, to create an object with desired shape and internal structure in a single fabrication step.
Research groups: PetroMat
The crystallographic characteristics and the equilibrium ratios for solid solutions containing 33 and 50 at% boron which belong to the Fe-Ni-B system are described. The study was carried out on samples obtained by diffusion at 1073 K, of mixtures of the elements in powder form. It was possible to confirm the existence of a complete solid solution between the compounds Fe2B and Ni2B.
Results of a Differential Scanning Calorimetry (DSC) investigation on precipitation hardening in solubilized 6061 aluminum alloy and its composites reinforced with SiC whiskers are reported. The exothermic and endothermic effects in DSC traces of these materials (in the solubilized state) have been attributed to phase formation and reversion on the base of the 6061 AA ageing sequence described in previous TEM studies. Apparent activation energies have been calculated according to the Ozawa method in non-isothermal conditions. The ageing sequence in composites is analogous to that of 6061 AA.
Research groups: CeraMat
The chemical interactions between sodium (as sulphite), iron and cerium (as oxides), coming from fuel additives, and two ceramic filters, in the working temperature range of a Diesel soot filter, were considered. The filters were a cordierite monolith filter and a wound-fiber filter, made by continuous Al2O3-B2O3-SiO2 fibers, respectively. Using X-ray diffraction (XRD) and Hg porosimetry analyses, scanning electron microscopy (SEM) observations and microprobe investigations, the extent of chemical etching, the involved reaction mechanisms and porosity changes were investigated.
Research groups: CeraMat
Ceramic (cordierite) honeycomb structures are employed in the automotive industry for trapping and incineration of particulate material from the exhaust gases of diesel-powered cars. The most diffuse pollutants present in the particulates are sodium, lead, iron, calcium, zinc and vanadium: they can react with cordierite during regeneration of the filter.
Metal vanadates of K, Rb, and Cs and their solid solutions were prepared by reaction between carbonates and vanadium(V) oxide, characterized by X-ray diffraction and tested as catalysts for carbon combustion. These vanadates are all orthorhombic but show different lattice parameters depending on the ionic radius of alkali metals. A complete solubility in the solid state was found to exist for the systems KVO3-RbVO3 and RbVO3-CsVO3, while only terminal solid solutions were found in the KVO3-CsVO3 system.
Research groups: PetroMat
In the course of a study whose aim was to obtain the optimum mechanical characteristics of chromium white iron, we decided to make a preliminary evaluation of how additions of boron and chromium affected the hardness and morphology of cementite. The samples were obtained from pure elements by melting in an arc furnace under argon atmosphere. The alloys were submitted to microdurometric, micrographic and diffractometric analysis. The composition of the individual crystals was defined with the use of an energy dispersive spectrometer.
Research groups: CoatMat
In this paper, the surfaces of PET/TiO2 thin film were modified by DC glow discharge plasma as a function of discharge potentials for improving the bioactivity. The hydrophilicity of the plasma-treated PET/TiO2 film was measured by contact angle measurement and the surface energy was estimated by using Fowkes method. The structural and chemical composition of the plasma-treated PET/TiO2 was analysed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).
Research groups: PetroMat
The main aim of the present contribution is to show how different heat treatment conditions influence the microstructure of a Fe - [1.5Cr - 0.2Mo] - 0.6C powder system. In vacuum furnaces, the cooling rate is generally determined by the pressure of the gas (basically N2) introduced into the chamber. Different gas pressures have been applied, from 0 to 6 bars. The average cooling rates were calculated in the range of 1180 °C to 400 °C and were varying from 0.1 to 6 °C/s, according to the gas pressure.
Research groups: PetroMat
For mobile applications, performance of polymer electrolyte membrane fuel cells (PEM-FCs) should be maintained with being exposed to subzero temperatures in winter time. To simulate such a situation, a single cell PEM-FC was operated at 70{degree sign}C, stopped, kept at -10{degree sign}C for 8 h, and heated to 80{degree sign}C for the next operation. The cell was unable to work. The degradation was attributed to freezing of water present inside the MEA, produced during operation, and remained in the PEMFC after the operation.
Research groups: CeraMat
Deagglomeration of a nanocrystalline transition alumina performed using different techniques was first demonstrated to be active in the achievement of a better powder compaction ability under uniaxial pressing and consequently in the development of a highly dense and homogeneous microstructure during pressureless sintering. A major effect, however, was associated to the heating rate chosen during the densification cycle.