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In the framework of joining processes of ultrahigh temperature ceramics (UHTCs), sessile drop experiments were performed in the Ni-B/ZrB2 system in the range 1110° ≤ T ≤ 1200 °C. They show that, at temperatures between 1110 and 1150 °C, isothermal solid-liquid transitions occur in a sequence; while in fact at T ≥ 1200 °C, the drop melts without any further phase transition, at lower temperatures, complete melting is followed by a solidification stage and final remelting. This complex behavior, which can be very relevant when utilizing Ni-B alloys for brazing processes (e.g., by the transient liquid phase bonding technique), is successfully interpreted on the basis of the complete B-Ni-Zr phase diagram newly computed by CALPHAD: Isothermal sections, calculated between 1110 and 1150 °C, show that the composition of the drop enters, crosses, and leaves the primary solidification region of the Zr2Ni21B6 ternary compound. The use of thermodynamic modeling for the explanation of experimental data sets a link between wetting and joining experiments and phase diagrams assessment. [ABSTRACT FROM AUTHOR]

This article reviews studies undertaken on diamond cutting tools, with particular regard to the characteristics and performance of diamond/metal interfaces. The affinity of carbon to metals, as well as the wettability of diamond by molten metals, and the advantage of using coated diamonds under certain cutting conditions, are described. The choice of the appropriate metallic matrix in the field of both impregnated and brazed diamond tools is discussed in terms of the diamond/alloy interface, mechanical properties of the segment, diamond wear speed, and desired cutting performance. The effect of several principal elements and elements added in minor amounts to the metallic matrix is critically evaluated. Relevant open questions, related to the optimization of cutting tools performance, are outlined, with special attention directed toward the need for advanced fundamental studies on the functional link between work of adhesion and work of fracture. [ABSTRACT FROM AUTHOR]

In this work, a systematic study of the wetting behavior of two Ni-based and one Co-based superalloys, used, in particular, for the fabrication of turbine blades, is presented with reference to different ceramic substrates: sapphire, polycrystalline alumina, zirconia, and mullite. Wettability tests have been performed by means of the “sessile drop” method at 1500 °C; the characterization of the interfaces between the molten drop and the substrates has been performed by SEM/EDS analysis in order to check the final characteristics of the solidified interfaces. The results are discussed in terms of chemical interactions in relation to the processing parameters and as a function of the surface and interfacial, morphological and energetic properties of the systems. [ABSTRACT FROM AUTHOR]

The possibility to exploit the peculiar characteristics of transition elements diboride ceramics—a class of promising materials for high temperature and highly aggressive applications—often depends to a great extent on the ability to join the ceramic parts one to the other or to special metallic alloys. Therefore, the knowledge of wettability, interfacial tensions and interfacial reactions is mandatory to optimise the joining processes. Data on the wettability and the interfacial features of different metal–ceramic systems, particularly of (Ti,Zr,Hf)B2 in contact with liquid non-reactive metals Cu, Ag, Au and their alloys, are reported and critically discussed, beginning with the pioneering work made in European eastern countries in the 70s up to the most recent published and new data. Moreover, interfacial energetics at the atomistic level is being increasingly investigated by means of sophisticated modelling techniques such as pseudopotential-based Density Functional Theory (DFT). These approaches will be presented, referred to non-oxide metal–ceramic systems. Given the complexity of ab initio calculations, the study is limited to the ideal work of separation, i.e. with plastic and diffusional degrees of freedom suppressed. Nevertheless, it is shown that the results on the specific transition borides-molten metal systems can be used to interpret the wetting behaviour and the adsorption/reaction interfacial phenomena involved. [ABSTRACT FROM AUTHOR]

The possibility to exploit commercially the peculiar characteristics of refractory metallic and ceramic materials and in particular of Zirconium diboride ceramics-a class of promising materials for high temperature applications-often depends to a great extent on the ability to join different ceramics one to the other or to special metallic alloys. As the behaviour of a metal-ceramic joint is ruled by the chemical and the physical properties of the interface, the knowledge of wettability, interfacial tensions and interfacial reactions is mandatory to understand what happens at the liquid metal-ceramic interface during joining processes.In the framework of an extensive study aimed at evaluating the wettability and the interfacial characteristics of different metal-ceramic systems, the behaviour of ZrB2 in contact with liquid Ag and its alloys (Cu, Ti, Zr, Hf) has been studied. ZrB2 pure, with different sintering aids or “alloyed” with other ceramic materials (SiC, Si3N4), have been used. The wetting and spreading experiments have been performed by the sessile drop technique under controlled atmospheres. The wetting and spreading characteristics and the interfacial reactions are discussed as a function of time, compositions of the ceramic and of the alloy involved. The interfacial morphologies, analysed by SEM and EDS, show the presence of regular interfaces and adsorption layers and of different bulk phases which are interpreted in terms of the relevant phase-diagrams. [ABSTRACT FROM AUTHOR]

Within the context of the design of high-temperature brazing process for C and SiC-based composites, a basic study is presented here about the wetting and interfacial reactivity of Co-Ta alloys in contact with graphite or SiC. Wetting results are presented for the first time showing that Co-Ta alloys wet C or SiC fairly or excellently depending on the relative amount of Ta. The final interfacial microchemistry and microstructures are the result of the interplay between the typical interfacial phenomena of the pure elements. Specifically, depending on the alloy composition, dissolution of the ceramic phase by Co or formation of a continuous interfacial layer of TaC that prevents dissolution prevails. The discussion about the interfacial reactivity between liquid Co-Ta alloys and graphite or SiC, as well as the interpretation of solidification phenomena and the formation of interfacial phases, is supported by making reference to new multi-component phase diagrams calculated by CALPHAD method. [ABSTRACT FROM AUTHOR]

A composite joining technique, using a Ni–56Si filler alloy and Mo as interlayers, was used to join SiC to SiC and to Kovar. The wetting of the Ni–Si alloy on SiC ceramic was studied in a vacuum at 1,350 °C by the sessile drop technique as a function of time; the non-reactive wetting characteristics in the Ni–Si/SiC system were confirmed, with an equilibrium contact angle of about 23°. SiC/SiC joints were fabricated by two processes using a Ni–Si/Mo/Ni–Si structure as the interlayer. SiC/Kovar joints were produced by means of a multilayer structure: molybdenum, which is used as the interlayer, was joined to Kovar on one side by means of transient liquid phase bonding and to SiC on the other side, using a Ni–Si coating as a filler alloy. The resulting joints were analyzed and discussed in terms of joint morphology and microstructure, joint strength, and fracture behavior. Two interfacial layers form at the Kovar/Mo and the Mo/Ni–Si interfaces due to dissolution and interdiffusion phenomena between the metallic elements, without there being any observable reactions with the SiC component. The type of joining process and the experimental conditions used play a key role in determining the joint microstructure and composition, the joint strength and its fracture behavior. [ABSTRACT FROM AUTHOR]

Wetting of molten Ni–56 at.% Si alloy on different substrates (SiC ceramic, Ni- and Co-based superalloys, Kovar, and Mo) are performed under different experimental conditions by the sessile drop technique. Temperature, atmosphere, and substrate composition play the key roles in determining the wettability, the spreading characteristics, and the interfacial morphology of the final interfaces. The non-reactive wetting characteristics in Ni–Si/SiC system are confirmed, with a spreading rate increasing with temperature increasing. In the Ni–Si/metal systems the spreading process is determined by the competition between spreading along the substrate surface and the interfacial interactions. Excellent wettability and fast spreading are found in the Ni–Si/Co-based superalloy, Ni–Si/Kovar, and Ni–Si/Mo systems at both the temperatures (1100 and 1200 °C). These results can be used as a reference guide for joining SiC to these metallic components, or to itself, using the Ni–Si alloy as filler metal. [ABSTRACT FROM AUTHOR]

The relative stability of different realizations of the Ag(111)/Alumina interfaces with varying oxygen partial pressures is investigated by means of ab initio density functional theory (DFT) simulations. Previous theoretical studies of similar systems always involve oversimplified geometries like stoichiometric Al-terminated, Al-rich, or O-terminated alumina interfaces. Such framework cannot explain the experimental behavior observed at intermediate oxygen partial pressure. Our approach, instead, suggests that the oxygen at the interface can play an important role at intermediate concentrations, leading to a more realistic interpretation of the experimental data. [ABSTRACT FROM AUTHOR]

The distribution of two main Boron neutron capture therapy (BNCT) agents, borocaptate sodium (BSH) and borono-phenylalanine (BPA), in C6 rat glioma cells has been investigated by means of radiowave dielectric spectroscopy measurements. Significant differences between cells treated with the two different boron carriers were found in the magnitude of passive electrical cell parameters. This technique offers a new procedure for the measurement of boron compounds interactions with different biological environments at cellular level and is suggested to have the potentiality for becoming an attractive tool for biodistribution studies of BNCT compounds in biological tissues. [Copyright &y& Elsevier]

Abstract: One of the main limitations for BNCT effectiveness is the insufficient intake of 10B nuclei within tumour cells. This work was aimed at investigating the use of l-DOPA as enhancer for boronophenylalanine (BPA) uptake in the C6 glioma model. The investigation was first performed in vitro, and then extended in vivo to the animal model. BPA accumulation in C6 glioma cells was assessed, using radiowave dielectric spectroscopy (RDS), with and without l-DOPA preloading. C6 glioma cells were also implanted in the brain of 25 rats, randomly assigned to two experimental branches: (1) intra-carotid BPA infusion; (2) intra-carotid BPA infusion after pre-treatment with l-DOPA, administrated 24h before BPA infusion. All animals were sacrificed, and assessment of BPA concentrations in tumour tissue, normal brain, and blood samples was performed using high performance liquid chromatography (HPLC). l-DOPA preloading induced a massive increase of BPA concentration either in vitro on C6 glioma cells or in vivo in the animal model tumour. Moreover, no significant difference was found in the normal brain and blood samples between the two animal groups. This study suggests the potential use of l-DOPA as enhancer for BPA accumulation in malignant gliomas eligible for BNCT. [Copyright &y& Elsevier]