New composite enhances solar towers

Jon Lawson

A research group, consisting of scientists from Central Metallurgical R&D Institute (Cairo) and National University of Science and Technology MISIS (Moscow) have developed a composite material that can extend the durability of solar towers - stations that collect thermal energy of the sun - from 2-3 to 5 years.

Photovoltaic power stations (PV systems) are becoming more and more popular, as they allow to collect and recycle thermal energy of the sun on an industrial scale. Solar towers are a high construction with a water tank and turbine system inside. The tower is surrounded by heliostats - big rotating mirrors 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°C. This temperature heats the neighbouring water tank, and the steam spins the turbines of the station.

Traditionally, for the receivers SiC (silicon carbide) is used; it is porous, highly dense, durable and resistant to oxidation. However, SiC has some disadvantages - for instance, it is sensitive to aggressive environments of liquid sodium.

A promising addition to SiC is AlN (aluminium 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.

Scientists from CMRDI together with scientists from NUST MISIS have developed porous composites based on SiC/AlN, containing up to 40% of AlN. 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.

Due to good thermochemical and thermomechanical properties, SIC/AlN composites are also promising for use in other high-temperature fields, such as metallurgy and aerospace engineering. The research continues.

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