12 research outputs found
Do mergers and acquisitions create shareholder value in the infrastructure and utility sectors? Analysis of market perceptions
No full textThrough an analysis over a 20-year period from 1997 to 2017 for a global sample of listed infrastructure
companies, 80% of which were utilities, this study shows that target companies’ Cumulative Average Abnormal
Returns (CAARs) are positive and statistically significant, while acquirer firms earn positive but not statistically
significant CAARs. The results obtained must be viewed in light of the restructuring that has distinguished the
last 20 years by strongly modifying the infrastructure environment and facilitating the diffusion of mergers and
acquisitions (M&A). Our results support the financial reasonableness and potential efficiency of M&A transactions
in the infrastructure and public utility sectors, with specific reference to target companies
Aerothermal analysis of an advanced hot structure for hypersonic flight tests
No full textABSTRACTThis paper deals with the aerothemodynamic analysis of an advanced concept of hot structure to be investigated in the Expert flight test programme.Three-dimensional fluid dynamic computations have been carried out at the flight conditions of the reference Expert trajectory to evaluate the aerothermodynamic field and the thermal loads on the winglet. The physical model includes viscous effects, real gas properties, non equilibrium chemical reactions and surface catalytic effects. The unsteady aerothermal analysis has been carried out considering different thermal boundary conditions (adiabatic wall or thermal coupling with the capsule metallic skin).The results are discussed with particular attention to the temperature distributions in the Ultra High Temperature Ceramics (UHTC) and in the structural support.</jats:p
Silicon carbide based plasma sprayed coatings
No full textCoatings containing up to 66 vol.% of silicon carbide were deposited by plasma spray. Potential applications can be found in the protection of CMC (ceramic matrix composite) against wear and high temperature oxidation. It is well known that SiC cannot be deposited by thermal spray because it decomposes before melting. To face this problem, a mixture of SiC and ZrB2 was deposited, since those two compounds form a eutectic phase, at a temperature lower than the one of SiC decomposition. Coating microstructure was characterized by XRD, SEM, and EDS, confirming the presence of SiC in the deposited layer and the formation of the eutectic phase during spraying. Samples of the coatings were exposed in air at high temperature, in the range of 650 degrees C to 1700 degrees C. The oxide scale was investigated by means of XRD, SEM, EDS and WDS. It was constituted by a SiO2 layer, which includes islands of ZrO2. Test results showed the good potential of the material investigated to be used as a protection against the high temperature oxidation. (C) 2012 Elsevier B.V. All rights reserved
Effects of heat treatments on oxidation resistance and mechanical properties of ultra high temperature ceramic coatings
No full textA critical point in the development of future generation space vehicles is the availability of materials able to withstand the extreme temperatures generated during orbital re-entry. UHTC (Ultra High Temperature Ceramics) materials, such as Zirconium diboride based ceramic composites, exhibit outstanding oxidation and thermal shock resistance, high emissivity and very high melting temperature: all these properties make ZrB2 based materials possible candidates in designing thermal protection systems for the hottest structures of re-entry vehicles such as wing leading edges and nose-tip. An innovative, proprietary way to deposit ZrB2 based coatings by plasma spraying has been developed. In the present work, the influence of high temperature exposure on oxidation resistance and mechanical properties has been investigated. Several coatings constituted by different amounts of SiC particles dispersed in a ZrB2 matrix were produced; some samples were tested in as sprayed conditions, other ones were submitted to a high temperature heat treatment before testing. Oxidation resistance was determined by exposing samples in air at 2073 K for 180, 1800 and 2520 s. Oxidation kinetics were analyzed and modelled. Evaluation of flexural strength and elastic modulus by means of four-points bending tests were carried out on samples showing better oxidation behaviour; mechanical tests were performed also on samples exposed at a typical operative temperature (1800 s at 2073 K). Results showed that heat treatment does not affect oxidation resistance, whilst it significantly improves mechanical properties. (C) 2008 Elsevier B.V. All rights reserved
Design and realization of a high temperature ceramic winglet for atmospheric re-entry test on suborbital capsule
No full textZirconium diboride based coatings for thermal protection of re entry vehicles: Effect of MoSi2 addition
No full textThe possibility of improving the performances of new generation re-entry vehicles as well as reducing the mission costs is closely connected to the development of new thermal protection systems: innovative heat shield materials, able to withstand higher temperature during the lift re-entry manoeuvre, would permit to improve reusability and easiness of maintenance as well as to increase the manoeuvrability and the payload of vehicles. UHTC materials, and, among them, Zirconium diboride based materials, exhibit outstanding oxidation and thermal shock resistance, high emissivity and very high melting temperature: all these properties make ZrB2 based materials possible candidates for thermal protection systems of atmospheric re-entry vehicles. The experimental activities described in the present work were focused on ZrB2 based coatings deposited by plasma spray, containing SiC and MoSi2 in different ratios: the work aimed at understanding the role of MoSi2 addition in the oxidation resistance. XRD analysis was carried out on starting powders and plasma sprayed coatings, in order to evaluate the transformations of crystalline phases induced by thermal deposition and to analyse the possible presence of amorphous phase; XPS was also used to study the coatings surface composition and to obtain information about chemical bonds in the materials. Oxidation behaviour was studied carrying out exposure tests up to 1800°C in static air to compare and model the oxidation kinetics of the different compositions: results show the better behaviour of materials containing MoSi2. Microstructure of as sprayed and oxidised samples was observed by means of SEM and analysed by EDS to understand the link between dispersion of Mo containing phases and the improved oxidation resistance. © 2010 Elsevier B.V
Search for Enhancement of Neutron Emission from Neutron-Irradiated, Deuterided, High-Temperature Superconductors in a Very Low Background Environment
No full textPlasma wind tunnel testing of UHTC coated components for hypersonic applications
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