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Publications (188)
Several oxidation protective coatings, both glass-based and ceramic/polymer hybrid coatings, for p- and n-type thermoelectrics were designed at the Politecnico di Torino in recent years, and they were characterised and tested under relevant conditions. The ‘glass-ceramic route’ to obtain a thermo-mechanical compatible and high-temperature resistant...
Sound graphite/graphite joints were obtained using ZrHfNbTa and TiZrHfTa alloys as interlayers using flash Spark Plasma Sintering (SPS) joining and conventional SPS joining. The ZrHfNbTa and TiZrHfTa foils showed a single high entropy phase. The influence of the two different interlayers and heat treatments were investigated. After flash SPS joinin...
Power generation based on thermoelectric (TE) materials is very attractive due to its low environmental impact and waste heat recovery. Thermoelectric materials based on cobalt triantimonide CoSb3 exhibit one of the highest energy conversion efficiencies, revealing thermoelectric figures of merit, ZTs > 1, but undergo oxidation above 380 °C and sub...
A systematic microstructural characterization of alumina joined to Hastelloy C22® by means of a commercial active TiZrCuNi alloy, named BTi-5, as a filler metal is reviewed and discussed. The contact angles of the liquid BTi-5 alloy measured at 900°C for the two materials to be joined are 12° and 47° for alumina and Hastelloy C22® after 5 min, resp...
A new system that exploits optical fiber distributed sensing for the detection of hydrocarbons is presented. The system relies on a custom-designed silica core/thin silicone cladding optical fiber to provide a quick and selective absorption of oil products through the cladding; moreover, it exhibits insensitivity to water. Optical fiber sensor inte...
Silicon carbide fiber reinforced silicon carbide (SiC/SiC) composites have unique properties that make them suitable for demanding applications. These materials have to be joined with other materials or with the same type of material to produce the final component. This work investigates the effectiveness of a fluorine-based plasma process on SiC/S...
Glass-to-metal interfaces play a crucial role in the robustness and the mechanical integrity of solid oxide cells, and it is well known that a sound interface improves the mechanical reliability of the whole stack. The present work focuses on the torsional behaviour of hourglass-shaped Crofer 22 APU stainless steel joined by a glass sealant specifi...
This work deals with the joining of porous Fe22Cr ferritic stainless steel to a dense Crofer22APU plate by using a silica-based, Ba-containing glass-ceramic. The chemical and interfacial stability and the mechanical properties of the joints were evaluated before and after thermal ageing at 700 °C for 500hrs. The sintering behaviour of the glass was...
The high mechanical and chemical properties of SiC make it difficult to texture and modify its surface using such conventional methods as mechanical machining and wet etching. Among possible alternative strategies, Atmospheric Pressure Plasmas (APPs) could be used, cutting cost and time, but much still has to be understood about their feasibility f...
Nowadays adhesive joints are more and more used; therefore, a precise and reliable shear strength measurement of these joints is necessary to design and predict a final components’ performance. This work aimed to assess the shear strength value of adhesively joined ceramics (SiC, Si3N4) and steel in the case of an elasto-plastic (ductile) joining m...
In this study, authors explore the application of modelling and Additive Layer Manufacturing (ALM) for creating and testing materials with interlocking structures aimed to reduce the stress concentration along the edges of a typical lap joint. The effectiveness of this approach is discussed by means of modelling and experimental validation of joint...
A summary and update of the research on the design, process, and testing of glass and glass‐ceramic to metal seals for solid oxide cells (SOC) conducted during the last 13 years at the Politecnico di Torino, Italy, within our research group and with several international collaborations, is presented and discussed. Glass and glass‐ceramic‐based mate...
Solid oxide cells (SOCs) devices are of great interest for effective power generation and for highly efficient conversion of electricity to hydrogen, fuels and chemicals using high temperature electrolysis. Electrochemical energy conversion in SOCs can be achieved only by a reliable integration and joining technology. In this context, glass-based m...
UV-initiated cationic frontal polymerization is exploited as a solvent-free, extremely fast, and low-temperature technique to obtain epoxy-based adhesives. Epoxy formulations are prepared by blending commercial resins at different weight ratios and adding photo and thermal initiators at different percentages. In addition, the influence of other cri...
This work addresses the integration of ceramic matrix composites (CMCs) and an Al alloy to obtain mechanically reliable and in-service durable CMC-Al alloy joints for high-performance road brake discs. Such a braking system is based on the use of CMC discs mounted onto a hub or stub axle by means of a mounting bell, manufactured in aluminium alloy....
A silica-based glass-ceramic, with Y2Ti2O7 as the major crystalline phase, is designed, characterised and tested as an oxidation-protective coating for a titanium suboxide (TiOx) thermoelectric material at temperatures of up to 600 °C. The optimised sinter-crystallization treatment temperatures are found to be 1300 °C and 855 °C for a duration of 3...
Incineration is the most common way to reduce the mass and the volume of municipal solid wastes. One of the most dangerous by-products of the incineration process is fly ash that contains a considerable amount of heavy metals. Therefore, its treatment is crucial to prevent the leaching of heavy metals into the environment. In the present work, two...
The surface texturing of ceramics is generally performed through acid-based etching and machining; however, laser texturing may be considered as a more precise, reproducible and eco-friendly process. Furthermore, laser ablation may be used to produce complex patterns on ceramic surfaces, thus offering new surface engineering opportunities. The stud...
A key aspect of ceramic matrix composites integration is related to a reliable joining technique. An ytterbium disilicate based glass-ceramic material is processed by reactive viscous flow sintering between a barium aluminium borosilicate glass and ytterbium oxide and it is used to join SiC/SiC and C/SiC composites. The joining temperature and the...
Glass Fibre Reinforced Polymer (GRFP) composites are increasingly being used as new materials for civil and petrochemical engineering infrastructures, owing to the combination of relatively high specific strength and stiffness and cost-competitiveness over traditional materials. However, practical concerns remain on the environmental stability of t...
A Mg2Si–Mg2Sn based thermoelectric material (TE), with composition of Mg2Si0·487Sn0·5Sb0.013, produced by ball-milling combined with spark plasma sintering, is successfully coated with a new silica-based glass, which is specifically designed, characterised and tested as an oxidation protective coating for mid-temperature range (up to 500 °C) applic...
The design of interfaces, coupled with suitable joining materials and joining technologies, is a key parameter in component manufacturing and surface pre-treatments are crucial steps for the production of robust and reliable bonds. In this work, plasma pre-treatments on SiC and Si3N4 are studied and discussed. The pre-treated joined samples have sh...
A revision and update about the research activity done in the past 25 years at Politecnico di Torino (Italy) on design and testing of glasses and glass‐ceramics for the joining of Ceramic Matrix Composites (CMCs) will be presented and discussed. The “glass‐ceramic method” to obtain a thermo‐mechanically stable joint starting from a glass will be de...
The aim of this work was to discuss the suitability of the joining process called “RM‐Wrap” (RM = Refractory Metals, ie, Mo, Nb, Ta, Zr) as a pressure‐less and tailorable technique to join several different ceramics such as SiC, alumina, and mullite (3Al2O3.2SiO2). In the RM‐Wrap joining technique the refractory metal foil is used as a wrap contain...
This work aims to evaluate the potential suitability of nonvitrified and vitrified bottom ashes to serve as substitute materials for both OPC and sand in mortars on an industrial scale. Three bottom ashes were selected as OPC substitutes: one was vitrified inside the incinerator plant (W1‐C), one was carbonated under ambient conditions for 3 months...
The interfacial reaction between graphite and a ZrNbHfTa foil was investigated using a spark plasma sintering (SPS) machine. The interlayer was converted during the treatment into a high-entropy carbide by the reaction between the alloy and the graphite substrate. The degree of conversion depended on the processing time and temperature, but could b...
This work has focused on surface engineering coupled with brazing to join SiCf/SiC composites and to improve the joint strength. The surface engineering was carried out through the Selective Thermal Removal (STR) of SiC fibres from a SiCf/SiC composite to obtain “brush-like” surfaces; the modified composites were then joined by means of an AgCuTi b...
Magnesium germanate (MgGeO3) ceramics represent a model system for geological study of the upper earth's mantle and are recently being investigated for applications in which red luminescence properties are required. The mechanical and optical properties of MgGeO3 are greatly influenced by the its polymorphic nature and by the complex series of phas...
Two commercial hybrid coatings, cured at temperatures lower than 300 °C, were successfully used to protect magnesium silicide stannide and zinc-doped tetrahedrite thermoelectrics. The oxidation rate of magnesium silicide at 500 °C in air was substantially reduced after 120 h with the application of the solvent-based coating and a slight increase in...
Optical fiber sensors (OFSs), which rely on evanescent wave sensing for the early detection of the diffusion of water and hydrochloric acid through glass fiber-reinforced polymers (GFRPs), have been developed and tested. Epoxy and GFRP specimens, in which these sensors were embedded, were subjected to tests in artificial sea water and hydrochloric...
Novel Na-containing glass-ceramic sealant with excellent thermo-mechanical properties. • Electrical resistivity monitored @ 800 °C in dual atmosphere. • Volatile Na 2 CrO 4 formation enhanced by 1.3 V applied voltage. • New insights for the use of Na-containing sealants with high applied voltage. A B S T R A C T A new alkali-containing diopside bas...
To provide a reliable integration of components within a solid oxide electrolysis cell stack, it is fundamental to evaluate the mechanical properties of the glass–ceramic sealing materials, as well as the stability of the metal–glass–ceramic interface. In this work, the mechanical behavior of two previously developed glass–ceramic sealants joined t...
Over the past few years, significant progress towards implementation of environmentally sustainable and cost-effective thermoelectric power generation has been made. However, the reliability and high-temperature stability challenges of incorporating thermoelectric materials into modules still represent a key bottleneck. Here, we demonstrate an impl...
The transformation of vitrified waste, such as bottom ash from municipal waste incineration, into cellular
glass-ceramics is convenient, if the additional processing is simple and inexpensive. The present paper
aims at presenting a possible route to achieve this goal, based on the recently proposed mechanical foaming of alkali-activated suspensions...
The RM-wrap (RM = Refractory Metal) is a pressure-less, versatile and tailorable joining process: it consists of wrapping Si foils inside a refractory metal wrap (i.e., Mo, Nb, Ta) in order to prevent molten silicon from leaking outside the joined region and infiltrating the facing materials during the joining process.
RM-wrap (RM = Mo, Nb, Ta) has...
Alumina dispersion-strengthened copper, Glidcop, is used widely in high-heat-load ultra-high-vacuum components for synchrotron light sources (absorbers), accelerator components (beam intercepting devices), and in nuclear power plants. Glidcop has similar thermal and electrical properties to oxygen free electrical (OFE) copper, but has superior mech...
We have investigated the formulations and curing parameters to obtain an epoxy foam to be used as thermal insulator layer for a glass fiber reinforced polymer (GFRP). A relevant decrease (50%) of the apparent density of the foam was achieved by adding up to 5 wt % of foaming agent without affecting the glass‐transition temperature (Tg). The mechani...
This paper reports on an epoxy matrix for glass fibre reinforced polymers equipped with low cost optical fibre sensors for the early detection of water diffusion, with devised applications in the oil and gas industry. Novel evanescent wave optical fibre sensors were designed, fabricated and embedded in epoxy resin samples. The tips of the optical f...
This poster presents a study on the mechanical and thermal properties of an epoxy foam. It is synthesized from a commercial epoxy resin with the addition of a Chemical Foaming Agent. Epoxy foams are of interest in structural applications in junction with more popular Polymer Matrix Composites. The foam can add buoyancy and thermal insulation to com...
This paper presents an innovative testing methodology to evaluate the effect on Glass Fibre Reinforced Polymers (GFRPs) of long-term exposure to a simulated marine environment, typical in offshore Oil & Gas applications. The performance of material samples exposed to seawater at 25, 55, 80 °C was quantified. Gravimetric, Dynamic Mechanical Analysis...
This paper presents a study on the mechanical and thermal properties of an epoxy foam. It is synthesized from a commercial epoxy resin with the addition of a Chemical Foaming Agent. Epoxy foams are of interest in structural applications in junction with more popular Polymer Matrix Composites. The foam can add buoyancy and thermal insulation to comp...
Alumina dispersion-strengthened copper, Glidcop, is used widely in high-heat-load ultra-high-vacuum components for synchrotron light sources (absorbers), accelerator components (beam intercepting devices) and in nuclear power plants. Glidcop has similar thermal and electrical properties to OFE (oxygen free electrical) copper, but has superior mecha...
Poster presented by Katarzyna Placha, associate research scientist in European Thermodynamics Ltd. on the 37th International Conference on Thermoelectrics in Caen, France.
The joining of hypereutectic Al-Si alloy heat pipes to CRFP skins has been studied for radiator panel applications. Three different epoxy adhesives (two thermal conductive adhesives and one high-strength structural one) were used and mechanically characterised before and after thermal cycling. Two adhesives gave the most promising results, in terms...
The aim of this work was to investigate and discuss the microstructure and interface reaction of a calcia-alumina based glass-ceramic (CA) with SiC. CA has been used for several years as a glass-ceramic for pressure-less joining of SiC based components. In the present work, the crystalline phases in the CA glass-ceramic and at the CA/SiC interface...
Two pressureless and reliable procedures for brazing SiC-based materials have been designed. The joining was obtained by the in-situ formation of a Ti3Si(Al)C2 MAX phase using simple Al-Ti interlayers. Wettability studies were conducted using several Al-Ti alloys in contact with SiC at 1500 °C. The interfacial microstructures and thermodynamic anal...
SiC foams sandwiched between two Ceramic Matrix Composite (CMC) skins are of interest for several high temperature applications ranging from aeronautics to energy production.
In this paper, SiC foams were joined to C/SiC composites by the “Mo-wrap” method to obtain sandwich structures. The Mo-wrap method is a recently developed joining technique: i...
IR pulsed laser radiation in air was applied to Si3N4 and Invar to obtain reliable Si3N4/Si3N4 and Si3N4/Invar adhesive bonded components. The laser pre-treatment produced a homogeneous nanostructured oxide layer on the surfaces, which effectively increased the adhesion at the adhesive/adherends interface and led to cohesive failure in the joining...
In this work, three new glass-ceramic compositions are designed and characterised as sealant materials for solid oxide electrolysis cells (SOEC), having operating temperature of 850°C. The crystallization and the sintering behavior of the glasses are investigated by using differential thermal analysis (DTA) and heating stage microscopy (HSM), respe...
Chromium carbide modified C/C and Ti6Al4V were successfully joined using a TiCuZrNi brazing alloy in powder form. The braze/composite interface and the mechanical strength of C/C-Ti6Al4V joints were evaluated. The apparent shear strength of chromium carbide modified C/C joined to Ti6Al4V, measured by single lap test in compression, was 52±6 MPa, wh...
A higher manganese silicide (HMS) thermoelectric, with composition MnSi1.74, densified by spark plasma sintering, was successfully coated with a glass-ceramic, in order to be used at temperatures higher than 500 °C. Compositional changes in both the HMS substrate and the glass-ceramic coating are reviewed and discussed with respect to the electrica...
Evanescent wave optical fibre sensors have been designed, fabricated and tested for the early detection of water diffusion through glass fibre reinforced polymers.
This study is focused on a diopside-based glass-ceramic sealant for solid oxide fuel cells and its compatibility with AISI 441 stainless steel interconnect. The morphological and chemical stability with both bare and Mn. Co spinel coated AISI 441 steel, after 3500 h exposure at 800 °C in air, is reviewed and discussed. Post-mortem samples are morph...
Alumina (Nextel™ 610) fibre reinforced YAG-ZrO2 matrix composites were successfully joined by using different brazing alloys, metallic interlayers and a glass-ceramic. All joints were mechanically stable and free of cracks. Three commercial brazing alloys and a new alloy based on Ti/Cu/Al interlayers were selected to join these composites for appli...
Electrophoretic deposition, thermal co-evaporation and RF magnetron sputtering methods are used for the preparation of Mn-Co based ceramic coatings for solid oxide fuel cell steel interconnects. Both thin and relatively thick coatings (1–15 μm) are prepared and characterised for their potential protective behaviour. Mn-Co coated Crofer22APU samples...
The present study illustrates the effects of processing conditions on phase and microstructure of CaGeO3 ceramics. It is shown that the fabrication of single phase, high density and crack-free CaGeO3 ceramics is particularly challenging using conventional sintering or spark plasma sintering. The main difficulties in achieving single phase are predo...
This poster presents an innovative testing methodology to evaluate the effect on Glass Fibre Reinforced Polymers (GFRPs) of long-term exposure to a simulated marine environment, typical in offshore Oil & Gas applications. The performance of material samples exposed to seawater at 25, 55, 80 °C was quantified. Gravimetric testing and Dynamic Mechani...
Surface engineering based on the Selective Thermal Removal (STR) of SiC fibers from SiCf/SiC composites was used to obtain a brush-like surface in view of joining processes. As observed through 3D confocal microscopy, the thermal treatment led to a selective removal of the surface fibers so that the specific surface increased. Wetting tests were pe...
This study focuses on the design, characterization and testing of a new glass-ceramic sealant for Na-based batteries. The thermo-mechanical properties as well as the sintering behaviour of the new sealant have been characterized by thermal analyses and x-rays diffraction studies. The exothermic peak in the differential thermal analysis plots has be...
The effect of a pulsed laser irradiation (Nd:YVO4, 1064 nm) in air on the surface morphology and chemical composition of silicon carbide and on the adhesion with an epoxy adhesive was investigated. Scanning and transmission electron microscopies, atomic force microscopy, and X-ray photoelectron spectroscopy revealed that the laser treatment reduced...
CoACH (Advanced glasses, Composites and Ceramics for High Growth Industries, www.coach-etn.eu) is a 4 year project coordinated by Politecnico di Torino and supported by the European Commission through the Marie Sklodowska-Curie Action. It provides an innovative and inter-sectorial doctoral training for young researchers in prestigious academic inst...
In this work, a silica-based glass–ceramic coating has been deposited on higher manganese silicide (HMS) thermoelectrics in order to provide oxidation protection at high temperature (up to 600 °C). The coating showed good densification behaviour and an excellent thermomechanical and chemical compatibility with the HMS substrate, suppressing the sil...
CVD-SiC coated and uncoated ceramic matrix composites (C-f/SiC and SiCf/SiC) were joined to their counterparts with a pre-sintered Ti3SiC2 foil using Spark Plasma Sintering. For the first time pre-sintered Ti3SiC2 foil was used as a joining filler. The joining parameters were carefully selected to avoid the decomposition of Ti3SiC2 and the reaction...
C/C composites and Ti6Al4V sheets were joined using a novel Cu/TiCuZrNi composite braze and the effect of Cu foil thickness on the microstructure and mechanical properties of the joints were investigated. A composite joining material, consisting of a TiC particle reinforced brazing alloy formed in situ during the brazing process was obtained. Befor...
A combination of evanescent wave optical sensors (EWOSs) and fibre Bragg gratings (FBGs) were embedded in an epoxy vinyl ester and an epoxy vinyl ester based glass reinforced polymer (GRP) composite to measure fluid ingress that would result in degradation under hostile conditions. Samples were subjected to accelerated aging in the form of single s...