Experiments

Ultra-refractory ceramic absorbers for thermodynamic solar energy generation at high temperature (firb

Solar thermal technology is a safe, sustainable and cost-effective energy supply. The maximum operating temperatures of solar power plants are usually lower than 800 K because of the rapid degradation of their components. However, the efficiency of solar thermal power plants increases rapidly with increasing working temperatures. Hence, the problem to be solved is the improvement of the receiver stability at high temperatures.
The present proposal lies in this context with FUNDAMENTAL RESEARCH AND DEVELOPMENT OF CERAMIC MATERIALS TO BE EMPLOYED IN THERMAL SOLAR ENERGY PLANTS AS ABSORBERS OPERATING AT TEMPERATURES UP TO 1200 K. The main challenge is the development of materials resisting to damage in air at high temperatures, while keeping good thermal conductivity and favourable radiative properties. Diborides and carbides of zirconium, hafnium and tantalum (ZrB2, ZrC, HfB2, HfC, TaB2,TaC), are referred to as Ultra-High-Temperature-Ceramics (UHTCs) and are considered the best-emerging materials for applications in aerospace and advanced energy systems (turbine blades, combustors, scramjet engines, nuclear fusion reactors). The increasing interest in these materials is due to their unique combination of properties, including the highest melting points of any group of materials, high strength, high thermal and electrical conductivities and chemical stability. Recently it has been found that most of these compounds also have the characteristic of being intrinsic solar selective, but the understanding of the optical properties of these materials is still very scanty, especially at high temperature. Ultra high temperature ceramics (UHTCs) have thus the potential to be suited for application in high temperature solar receivers, once their basic properties have been properly investigated and correlated to bulk and surface characteristics. The main goals of SUPERSOLAR, are the development of several UHTCs materials and the study of their fundamental properties. The investigation is mainly concerned with light absorption and emission both at room and high temperatures and their correlation to material parameters such as compositions, porosity and surface finishing with the thermo-mechanical properties, like mechanical strength at room and high temperature, thermal conductivity, oxidation and thermal shock resistance. The research Units involved in the project are two bodies belonging to the National Research Council (CNR), Institute of Science and Technology for Ceramics (ISTEC) and National Institute of Optics (INO), and the University of Cagliari (UNICA). ISTEC is the only Italian and, as far as we know, European research Institute, that has developed expertise on UHTCs that cover the basic science, the understanding of the material stability at very high temperatures in aggressive environment and the fabrication of components and prototypes with complex shapes and textures. UNICA owes a broad experience in the field of synthesis and sintering of innovative materials, both monoliths and composites, included the UHTC category, by use of innovative technologies. In particular, this group is internationally well known and appreciated in the field of combustion synthesis, Self-propagating High temperature Synthesis (SHS), for powder or porous ceramics production, and in the field of sintering assisted by pulsed current, Spark Plasma Sintering (SPS), for the obtainment of fully dense composites. In this prospect, the SPS furnace available at UNICA, (515S, Sumitomo Coal Mining Co. Ltd, Japan), is the first facility of this type that has been installed in Italy. UNICA and ISTEC have recently started a collaboration focused on the fabrication and characterization of UHTC. INO is an Italian Institute with a large experience in the field both of characterization of optical properties and sunlight exploitation. At the beginning of 2010 INO and ISTEC started a fruitful scientific collaboration focused on the optical characterization of ceramics.

Solar thermal technology is a safe, sustainable and cost-effective energy supply. The maximum operating temperatures of solar power plants are usually lower than 800 K because of the rapid degradation of their components. However, the efficiency of solar thermal power plants increases rapidly with increasing working temperatures. Hence, the problem to be solved is the improvement of the receiver stability at high temperatures.
The present project lies in this context with FUNDAMENTAL RESEARCH AND DEVELOPMENT OF CERAMIC MATERIALS TO BE EMPLOYED IN THERMAL SOLAR ENERGY PLANTS AS ABSORBERS OPERATING AT TEMPERATURES UP TO 1200 K. The main challenge is the development of materials resisting to damage in air at high temperatures, while keeping good thermal conductivity and favourable radiative properties. Diborides and carbides of zirconium, hafnium and tantalum (ZrB2, ZrC, HfB2, HfC, TaB2,TaC), are referred to as Ultra-High-Temperature-Ceramics (UHTCs) and are considered the best-emerging materials for applications in aerospace and advanced energy systems (turbine blades, combustors, scramjet engines, nuclear fusion reactors). The increasing interest in these materials is due to their unique combination of properties, including the highest melting points of any group of materials, high strength, high thermal and electrical conductivities and chemical stability. Recently it has been found that most of these compounds also have the characteristic of being intrinsic solar selective, but the understanding of the optical properties of these materials is still very scanty, especially at high temperature. Ultra high temperature ceramics (UHTCs) have thus the potential to be suited for application in high temperature solar receivers, once their basic properties have been properly investigated and correlated to bulk and surface characteristics. The main goals of SUPERSOLAR, are the development of several UHTCs materials and the study of their fundamental properties. The investigation is mainly concerned with light absorption and emission both at room and high temperatures and their correlation to material parameters such as compositions, porosity and surface finishing with the thermo-mechanical properties, like mechanical strength at room and high temperature, thermal conductivity, oxidation and thermal shock resistance.


Research & Technical staff:
Mercatelli LucaSani Elisa

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