Aluminum Nitride to extend durability of solar towers

Scientists from Central Metallurgical R&D Institute (CMRDI, Cairo) and National University of Science and Technology (NUST MISIS, Moscow) have developed a composite material that can extend the durability of solar towers from 2 to 3 to 5 years. A solar tower with water tank and turbine system inside is surrounded by heliostats that capture the sunlight and concentrate it in one point on the tower as a giant light beam. The beam reaches the receiver (heat-absorbing element), which, in its turn, heats liquid sodium up to 600 degrees Celsius. This temperature heats the neighboring water tank, and the steam spins the turbines of the station.
Traditionally, for the receivers SiC (silicon carbide) is used. However, SiC is sensitive to aggressive environment of liquid sodium. According to the research team, »a promising addition to SiC is AlN (aluminum nitride), which has high thermal conductivity, low thermal expansion coefficient and high heat resistance.« Now SiC/AlN composites are used mainly in electronics, but can potentially be used in different spheres, including solar energy.
The scientists have developed porous composites based on SiC/AlN, containing up to 40 percent of AlN. In the process of the work, the optimal compositions of additives and sintering regimes of new composites were selected, which significantly exceed the traditional ones due to the formation of a solid solution at the grain boundaries of silicon carbide. Along with high thermal conductivity and heat resistance, such composites have a low coefficient of thermal expansion, which significantly improves their performance. According to Emad Ewais, head of the Egyptian research team, »the further prospects lay is testing of the composite in the solar furnace to evaluate its efficiency.«

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