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 of mechanical strength (apparent shear ~ 25MPa for 100µm thick lap joints). Thermal cycling (10 cycles between −30°C and +90°C) did not significantly affect the mechanical properties of the joints or the failure propagation mode. The use of the thermal conductive adhesive could also guarantee good thermal conductivity of the designed panel.

This paper describes the research done in order to valorise the biomass ash and evaluate its use as supplementary cementitious material (SCM) in the cement industry. The biomass ash samples used in this study were collected from three different power plants. The characterisation of the ashes as SCMs was performed after two different valorisation processes: (i) a vitrification process in order to obtain a new material with high hydraulicity and (ii) an easy de-alkalisation process in order to reduce the alkali content. The results of this work show that biomass ash derived from the combustion of woodchips and straw, properly treated, is characterised by pozzolanic activity and latent hydraulicity that could be exploited for the manufacture of low embodied energy concrete. The ultimate strength of mortars prepared using vitrified biomass ash becomes higher than that of the parent Portland cement after 28 days.

Active solder alloy 92Sn3Ag3Ti was used to join Al2O3 ceramic on cast A356 aluminum alloy substrate using an ultrasonic assisted soldering process. Due to the large discrepancy in thermal shrinkage coefficients between materials, large thermal stresses occur during cooling down to room temperature. Further cooling to -78 degrees C and -196 degrees C was used to inflict additional thermal stress in the samples. Shear strength, image analysis of fractured surfaces and microstructure analysis were performed to study the influence of cooling. Ceramic samples with different surface finish were used to investigate the influence of the contact between ceramic and aluminum alloy substrate on the fracture behavior. Two types of failure were observed, a detachment of the solder alloy from the ceramic surface and a cohesive failure through the solder layer. The results show that cooling the joined sample to -78 degrees C does not significantly affect the bonding strength of the samples. However, samples that were rapidly cooled to -196 degrees C showed reduced shear strengths even when the amount of cohesive failure area was taken into account. Many newly formed cracks in the Sn matrix were observed in the joint after the cooling which were identified as strength-determining defects. (C) 2015 Elsevier Ltd. All rights reserved.

A novel method based on the modification of a commercial brazing alloy was evaluated and used for joining CFC (carbon fiber reinforced carbon composite) to pure copper. This paper deals with the development of a flat and curved joint concept providing a versatile and cheap joining technology, i.e. a single step brazing process by using an innovative brazing alloy deriving from a commercial one. The brazing of CFC to Cu was performed by using a commercial non-active braze. RF-magnetron sputtering and galvanic processes have been used to modify the commercial non-active braze by coating it with Cr, an active element. The aim is to increase its wettability on CFC, instead of using an active braze, having potential embrittlement issues. Optical microscopy and scanning electron microscopy coupled with energy-dispersive spectroscopy were used to evaluate the microstructure and composition of the CFC/Cu joints. In order to evaluate the mechanical strength of the joint, a lap test in compression has been performed. (C) 2013 Elsevier Ltd. All rights reserved.

Spark plasma sintering (SPS) was employed to join monolithic β-SiC with or without titanium as intermediate joining material. Both the localized and rapid heating contributed to the inherent energy saving of electric current assisted joining technique. The effects of uniaxial pressure and surface preparation were analyzed independently with respect to the flexural strength and the morphology of the joints. In particular samples polished down to 1μm and joined at 1900°C for 5min achieved the strength of the as received material. The failure occurred outside the joining interface, confirming the optimum quality of the joint. Pressure in combination with surface preparation was necessary to achieve perfect adhesion and pore free direct joining of SiC. The use of Ti foil as a joining material and pressure allowed joining of unpolished SiC.

CVD–SiC coated C/SiC composites (C/SiC) were joined by spark plasma sintering (SPS) by direct bonding with and without the aid of joining materials. A calcia-alumina based glass–ceramic (CA), a SiC+5wt%B4C mixture and pure Ti foils were used as joining materials in the non-direct bonding processes. Morphological and compositional analyses were performed on each joined sample. The shear strength of joined C/SiC was measured by a single lap test and found comparable to that of C/SiC.

In this paper, we report on the synthesis of pure silica (SiO2) nano- and microwires by a non-catalytic process. The structure, morphology and properties of the products were examined by scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The microstructural analysis shows that the SiO2 wires are high purity silica and are completely amorphous; their diameter ranges from 70 nm to 2 μm. The fiber length varies from 100 μm to several mm. The wire manufacturing process involves reduced temperatures and times (1000 °C, 30 min) compared to other processes, without needing any catalyst and has been carried out on different kinds of substrates (SiC and Si). Successful growth of SiO2 wires on the surface of silicon microcantilevers has been demonstrated; they could be used as an alternatively way to enhance the sensor performances.

Glass-ceramics can be versatile joining materials with tailorable thermal and mechanical properties; they are not affected by oxidation and can be used as pressureless joining materials above their glass softening point. The glassy phase can be minimized by a suitable thermal treatment in order to improve the glass-ceramic creep behaviour. The use of glasses and glass ceramics as sealants in solid oxide fuel cells and as joining materials for SiC-based materials will be discussed.

Fly and bottom ashes are the main by-products arising from the combustion of solid biomass. Since the production of energy from this source is increasing, the processing and disposal of the resulting ashes has become an environmental and economic issue. Such ashes are of interest as a construction material because they are composed of very fine particles similar to fillers normally employed in bituminous and cementitious mixtures. This research investigates the potential use of ash from biomass as filler in bituminous mixtures. The morphological, physical and chemical characteristics of 21 different ashes and two traditional fillers (calcium carbonate and "recovered" plant filler) were evaluated and discussed. Leaching tests, performed in order to quantify the release of pollutants, revealed that five ashes do not comply with the Italian environmental re-use limits. Experimental results show a wide range of values for almost all the investigated properties and a low correlation with biomass type in terms of origin and chemical composition. Furthermore, sieving and milling processes were found to improve the properties of the raw material in terms of grading and sample porosity. The effectiveness of these treatments and the low content of organic matter and harmful fines suggest that most of the biomass ashes investigated may be regarded as potential replacements for natural filler in bituminous mixtures.

The paper presents an extended research work on the re-use of bottom and fly ashes of different origins in substitution of fine aggregates in bituminous mixtures. Bottom ash from a north Italian municipal solid waste incinerator (MSWI), and biomass bottom and fly ashes from twelve different power plants were considered. The MSWI ashes were vitrified at 1450°C. Vitrified MSWI ash and biomass ashes were ground and sieved to different dimensions and used as filler or sand in bituminous mixtures. Physical-mechanical tests included in road materials specifications were carried out on aggregates, mastics and on the whole mixtures. In this last case, ashes were used in partial or total substitution of natural aggregates. The test results demonstrate that vitrified MSWI ash and biomass bottom and fly ashes can be effectively re-used as pavement materials in order to avoid their landfill disposal. Moreover, the vitrification process reduces the ashes absorption potential of binder and the biomass ashes can be re-used in their original state if they are first subjected to sieving selection

The objective of this work is to help in reducing the environmental impact of the building industry through innovative solutions that recover and process valuable raw materials from industrial waste as Supplementary Cementitious Materials (SCMs). With the increasing attention towards the reduction of CO2 emissions, the replacement of the clinker quota with SCMs in cement and concrete production is becoming more and more diffuse: the utilization of industrial by-products allows the development of green-concrete with a reduced environmental impact and lower embodied energy. This research focuses on the potential use of ash from biomass combustion as SCMs in mortars and concrete. The ash was characterised as received and tested after a secondary process that was used to improve its quality. Two processes were conducted: (a) vitrification to improve the hydrauliticy and/or (b) water washing to remove excess alkalies. The results of this work show that some biomass ashes, properly treated, are characterized by pozzolanic activity and latent hydraulicity that could be exploited for the manufacture of low embodied energy concrete

The aim of this work was to develop a new joining/repairing material suitable to be easily applied at temperature not exceeding 300°C, in air atmosphere, on large surfaces of SiCf/SiC composites for aerospace applications. The joining/repairing material proposed here is based on a Carbon Fiber‐reinforced commercial Adhesive (CFA) where silicon carbide particles were added. Mechanical strength of the joined SiC/SiC was tested before and after heat treatment at the maximum working temperature for these SiC/SiC. Flexural strengths higher than 200 MPa and 90 MPa, before and after heat treatment, respectively, were obtained by coupling mechanical and adhesive bonding techniques.

This work describes the design and development of two new silica‐based glass‐ceramic coatings, suitable to be applied as slurries on a foam glass substrate. The coating process was optimized for both compositions, according to their sintering behavior. Scanning electron microscopy ( SEM ) observations and coefficient of thermal expansion ( CTE ) measurements revealed a good thermomechanical compatibility between the foam glass substrate and both coatings. The proposed coatings showed excellent chemical durability: no weight loss was observed after soaking in distilled water at 90°C for 16 days.

A critical issue for a wider use of Ceramic Matrix Composites (CMC) is the development of cheap, user-friendly joining methods to assemble large components into more complex structures, but also to repair damaged parts after mission. Some pressure-less joining techniques and joining materials for CMC will be described: results obtained by using glass ceramics, modification of a commercial adhesive and W/SiC based joining materials will be discussed. Different kinds of joined samples have been manufactured to couple the reliability of a machined joint with bonding properties of the joining materials. The mechanical characterization of the joints will be also discussed. The use of glass-ceramics as joining materials in a neutron environment has been demonstrated up to 820°C, 5 dpa: comparison of bending and shear strength for neutron irradiated and non-irradiated glass-ceramic joined SiC and SiC/SiC indicates that the mechanical strength is unaffected by irradiation at the used irradiation conditions.

This paper reports on the microstructure and properties of two glass–ceramics based on SiO2–Al2O3–MgO (SAMg) and SiO2–Al2O3–Y2O3 (SAY), which have been designed to be used as pressure-less low activation joining materials for SiC/SiC and SiC based components for nuclear applications. Glass–ceramic pellets (SAY and SAMg) were irradiated for approximately 1year in the reactor core of the LVR-15 research reactor at Nuclear Research Institute Rez, Czech Republic, at about 50°C, 6.92×1024n/m2 (E>1MeV, about 1dpa in steel); SiC/SiC composites joined by SAY were irradiated about 1year at High Flux Reactor (HFR), Petten, The Netherlands, 550°C, 9–11×1024n/m2 (E>1MeV, about 1.4–1.8dpa in C), 600°C, 16–22×1024n/m2 (E>1MeV, about 2.6–3.3dpa in C) and 820°C 31–32×1024n/m2(E>1MeV, about 5dpa in C). Optical microscopy with image analysis and scanning electron microscopy (SEM) with X-ray microanalysis (EDS) were used to investigate the glass–ceramics morphology and composition, showing a remarkable similarity before and after neutron irradiation for both glass–ceramics. Comparison of bending strength for irradiated and non-irradiated SAY joined SiC/SiC indicate that the mechanical strength is unaffected by irradiation at these conditions.

Silicon carbide (SiC) samples have been joined by a pressureless slurry based method. The CaO–Al2O3 (CA) glass‐ceramic joining material has been characterized in term of crystalline phases and thermal and mechanical properties. A torsion test based on miniaturized hourglass shaped specimens has been used as pure shear strength test method for joined ceramic samples. Torsion results are compared to those obtained by a single lap offset (SLO) test in compression on the same joined materials. Pure shear strength of 104 ± 25 MPa has been measured by torsion test, whereas single lap offset gave 36 ± 8 MPa.

Future linear accelerators, as CLIC (Compact LInear Collider), are extremely demanding in terms of material properties. Traditionally accelerating structure is made of brazed OFE copper parts. For the high conducting regions submitted to mechanical fatigue, CuZr would represent an improved selection than pure copper while for regions where the highest electric field is applied a refractory metal, i.e. Mo, could result in a better performance. The feasibility of joining such materials, namely CuZr (UNS C15000) and pure Mo has been investigated. The joining method developed and investigated here consists in a vacuum brazing process exploiting a Cu-based brazing filler applied under appropriate vacuum conditions.Apparent shear strength (adapted from ASTM B898) on the joined samples was about 200MPa.

Joining of ceramic matrix composites (CMC) for nuclear applications is considered today an issue for future thermo-nuclear fusion reactors and for new generation fission reactors components. In both cases, in addition to extreme thermo-mechanical loads on the joined components, not completely known service conditions and requirements (including high temperatures, neutron irradiation, harsh chemical environment, and low induced activation) are to be taken into account.Considering that the design of the joined components is continuously reviewed, that one suitable widely accepted mechanical test for joined ceramic matrix components is still unavailable and the influence of neutrons on joining materials is mostly unknown, the required R&D is far from being completed.Materials with the highest potential for these applications are fibre reinforced CMC, mainly carbon fibre reinforced/carbon matrix composites (C/C) and silicon carbide fibre reinforced/silicon carbide matrix composites (SiC/SiC). Joining techniques and characterization tests for these joined CMC will be discussed.