Abstract
Due to their high thermal stability and low cost, molten chlorides are promising high-temperature fluids for example for thermal energy storage (TES) and heat transfer fluid (HTF) materials in concentrated solar power (CSP) plants and other applications. However, the commercial application of molten chlorides is strongly limited due to their strong corrosivity against commercial alloys at high temperatures. The work addresses on a fundamental level whether carbon based composite ceramics could be potentially utilized for some corrosion critical components. Liquid silicon infiltration (LSI) based carbon fiber reinforced silicon carbide (called C/C–SiC) composite is immersed in a molten chloride salt (MgCl2/NaCl/KCl 60/20/20 mole%) at 700 °C for 500 h under argon atmosphere. The material properties and microstructure of the C/C–SiC composite with and without exposure in the molten chloride salt have been investigated through mechanical testing and analysis with scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) scanning. The results reveal that the C/C–SiC composite maintains its mechanical properties after exposure in the strongly corrosive molten chloride salt. The oxidizing impurities in the molten salt react only with residual elemental silicon (Si) in the area of the C/C–SiC matrix. In comparison, no indication of reaction between the molten chloride salt and carbon fiber or SiC in the matrix is observed. In conclusion, the investigated C/C–SiC composite has a sound application potential as a structural material for high-temperature TES and HTF with molten chlorides due to its excellent corrosion resistance and favorable mechanical properties at high temperatures.
Highlights
As an emerging renewable energy technology, the global capacity of installed concentrated solar power (CSP) plants has a significant increase from ~0.3 to 4.8 GW from 2005 to 2015, in particular from 2010 to 2015 grew at an average rate of 50% per year.[1]
We focus on carbon fiber reinforced silicon carbide (C/ C–SiC) composite as an alternative structural material for corrosion critical components in chloride molten salt systems
The measured Young’s modulus (E) shows ~9% difference after the exposure, which will be explained with the microstructural analysis results in section “Analysis” of microstructure for corrosion mechanisms
Summary
As an emerging renewable energy technology, the global capacity of installed concentrated solar power (CSP) plants has a significant increase from ~0.3 to 4.8 GW from 2005 to 2015, in particular from 2010 to 2015 grew at an average rate of 50% per year.[1]. Owing to the excellent mechanical properties, fracture toughness and corrosion resistance, carbon fiber reinforced silicon carbide (C/C–SiC) composite is a potentially attractive hightemperature structural material for energy-related applications. It could be potentially used in corrosion critical components, such as pumps and valves for CSP plants and molten salt nuclear power plants.[13,14,15] to our best knowledge, there is a lack of studies on its corrosion resistance of the C/C–SiC composite to strongly corrosive molten chlorides at high temperatures (>600 °C), which contain corrosive impurities (e.g., hydroxide species) due to hydrolysis of the hydrated water in the chloride salts.[9]. The corrosion mechanism of the C/C–SiC composite in the molten chloride salt is discussed based on the microstructural analysis
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