New Material Could Up Efficiency of Concentrated Solar Power

An anonymous reader shares new work that could allow us to generate electricity using supercritical carbon dioxide. Ars Technica reports: The researchers involved in the new work, a large U.S.-based collaboration, focus on a composite material: tungsten and zirconium carbide. These have extremely high melting points: 3,700K for both materials. Both of them conduct heat extremely well, and neither of them expands or softens much under these conditions, meaning they would hold up better to the mechanical stresses. While the stats are impressive, the amazing part of this is how the material is fabricated. The researchers started with tungsten carbide, a ceramic that can be formed into a porous material simply by pouring it as a powder into a mold and heating it. At this point, the ceramic can be further machined to produce a final shape. Once in its final form, the ceramic was placed in a bath of a molten mixture of copper and zirconium. The molten mixture filled the pores, and the zirconium reacted with the tungsten carbide, replacing the tungsten. The copper in the molten material formed a thin film on the surface of the solid.

The tungsten then filled the pores in the resulting material, allowing it to retain the same shape and size despite the chemical changes. The zircon carbide ends up providing the material with a stiffness even at high temperatures, while the tungsten is flexible enough to keep the whole thing from being brittle. And the whole thing conducted heat better than the metals currently in use. The remaining issue is that, at the conditions involved in solar thermal plants, the copper on the material would react with the carbon dioxide, forming a copper oxide and releasing carbon monoxide. But the researchers determined that adding a small amount of carbon monoxide to the supercritical CO2 would suppress this reaction, something that they confirmed experimentally. Because the material holds up to these conditions so much better than the metals currently in use, it's possible to use much less of it to build a heat exchanger. This is great economically (since you need fewer raw materials), and the small size increases the power density and efficiency of the heat exchanger.

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