High temperature corrosion behavior and mechanism of steel slag-based glass ceramic in the eutectic carbonates

Abstract

Steel slag-based glass ceramic for thermal energy storage was first fabricated by quenching method, and then their high temperature corrosion behavior in the eutectic carbonates and related mechanism have been investigated using X-ray diffraction，Raman spectroscopy and scanning electron microscope techniques. The results show that holding time has a significant influence on the corrosion layer thickness at 800^oC. As the holding time was extended, the thickness of the corrosion layer with obvious cracks tended to increase. Further EDS analyses disclosed that the divided corrosive layers along the extended directions of the cracks should be similar in both the compositions and microstructure. Based on these observations, the possible corrosion mechanism was discussed after defining phase structure of nonstoichiometric (Fe_0.35Al_0.20Mg_0.44) Ca_0.96(Fe_0.08Si_0.70Al_0.20)₂O_6.12 as a combined system of CaMgSi₂O₆(Di)-CaFe³⁺AlSiO₆(Es)-CaAl₂Si₂O₈(An). Oxygen offered by the molten carbonates salt is regarded to play a critical role in the corrosion process. In an atmosphere rich in oxygen, both Na⁺ and K⁺ ions diffused into the diopside can replace Ca²⁺ and Mg²⁺, etc. resulting in polyhedral structural reorganization for electrical neutrality. On the other hand, the bonding stability of the cation-oxygen bonds in diopside was proved to be weaker than that in single oxides. These two aspects contribute to the continuous dissolution of Ca²⁺ and Mg²⁺, etc. in the molten carbonates salt.