Ionic liquids as diathermic fluids for solar trough collectors' technology: A corrosion study

The AISI 304 and the AISI 1018 steels, frequently used in solar collectors' plants, were studied in contact with some Ionic Liquids suitable as diathermic fluids. Room temperature steels' corrosion behaviours were investigated by electrochemical measurements: Open Circuit Potential curves were recorded to establish the free corrosion potential and potentiodynamic curves were acquired to compare the active/passive tendency of the materials. The corrosion rates, extrapolated from Tafel Plots and by Polarization Resistance measurements, are characterized by low values (<2 mu A cm(-2)) for both the alloys. Immersion tests were performed at 220 degrees C (common working temperature in parabolic trough collectors) starting from 48 h and no appreciable weight-losses for the alloys were observed even after 10 days of immersion. The quantity of the metals dissolved in the ILs was detected via Inductive Coupled Plasma Optical Emission Spectrometry. Finally, the morphology of the corrosion phenomena were investigated by Scanning Electron Microscopy coupled with EDAX analysis.