BONDING OF CERAMICS: AN ANALYSIS OF THE TORSION HOURGLASS SPECIMEN

There is a recent and growing interest in joining ceramic parts due to their increased use in several fields such as next-generation nuclear plants, aeronautic engine parts and aerospace components. For high temperature applications, glass-ceramics are used as an “adhesive” for ceramic parts, this generates the need for test methods suitable to assess their bond strength. Unfortunately, the various test procedures currently used lead to different results. One recent test is based on torsion of hourglass shaped joined ceramics, originated from a modification of the ASTM F734-95 standard, with the aim of obtaining failure under a pure shear state in the bondline subjected to torsion. However, results obtained from different versions of the hourglass geometry show differences which are still difficult to compare. Moreover, due to the brittle nature of the materials and especially when the adhesive strength is comparable to that of the substrates, the failure is not confined in the bond and propagates also in the substrates. In this case, the results are still of arguable application for design purposes. The aim of this paper is to give an insight on torsion of hourglass-shaped joined ceramics and on the interpretation of the obtained results, by means of detailed analytical and numerical studies of the stress distribution in the specimen, and taking into account the brittle nature of the materials. The main findings are: i) the stress state in the bondline is not singular; ii) a non negligible stress concentration arises out of the bondline

Joining of C/SiC for aerospace applications

To join C/SiC to C/SiC with a new, pressure-less composite joining material and technique, for high performance application

Silver Nanoparticles: Review of Antiviral Properties, Mechanism of Action and Applications

New antiviral drugs and new preventive antiviral strategies are a target of intense scientific interest. Thanks to their peculiar properties, nanomaterials play an important role in this field, and, in particular, among metallic materials, silver nanoparticles were demonstrated to be effective against a wide range of viruses, in addition to having a strong antibacterial effect. Although the mechanism of antiviral action is not completely clarified, silver nanoparticles can directly act on viruses, and on their first steps of interaction with the host cell, depending on several factors, such as size, shape, functionalization and concentration. This review provides an overview of the antiviral properties of silver nanoparticles, along with their demonstrated mechanisms of action and factors mainly influencing their properties. In addition, the fields of potential application are analyzed, demonstrating the versatility of silver nanoparticles, which can be involved in several devices and applications, including biomedical applications, considering both human and animal health, environmental applications, such as air filtration and water treatment, and for food and textile industry purposes. For each application, the study level of the device is indicated, if it is either a laboratory study or a commercial product

Virucidal effect against Coronavirus SARS-CoV-2 of a silver nanocluster/silica composite sputtered coating

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Fracture behavior of concretes containing MSWI vitrified bottom ash

The incorporation of waste materials into concrete allows responding to some of the most significant issues of our society: waste management and climate change. Experimental studies carried out in last decades have shown that municipal solid waste incineration (MSWI) ash, and particularly bottom ash, which constitutes the major solid by-product of incineration process, can be adopted to produce building materials. However, several issues are related to the safety and the environmental impact of MSWI ash utilization for concrete production, mainly linked with the leaching of heavy metals and toxic organic components. To solve these problems, several treatments for MSWI ash can be adopted and, among them, in this work the attention was focused on vitrification technology, which enables to convert the ash in a glassy inert solid material. The aim of the present paper is to study the feasibility of developing a “green concrete” that incorporates vitrified MSWI bottom ash as partial cement replacement, so reducing the cement content and consequently the carbon dioxide emissions as well as the raw materials consumption related to its production. The vitrified MSWI bottom ash, ground at micrometer size, was inserted into the admixtures by considering two percentages of cement substitution (10% and 20% by weight of cement). The flexural behavior of concrete containing vitrified MSWI ash was investigated through three-point bending tests under crack mouth opening displacement control. The crack path evolution was further explored by adopting the Digital Image Correlation technique. By analyzing the obtained results, it can be concluded that the use into concrete of vitrified MSWI bottom ash as cement replacement up to a percentage of 20% by weight of cement, allows reaching comparable flexural resistances with respect to the reference concrete. So, the proposed approach can represent a viable solution for the development of environmental-friendly concretes able to reduce the environmental impact of the concrete industry, which is mostly related to cement production, as known

SiC foam sandwich structures obtained by Mo-wrap joining

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: it consists of wrapping Si foils inside a Mo wrap in order to prevent molten silicon leaking from the joined area and infiltrating SiC foam and C/SiC during the joining process. Compression and thermal shock resistance tests were performed on the C/SiC – SiC foam – C/SiC sandwich obtaining sound results