Corrosion Of Alloy Materials In Molten Chloride Salts Containing Aluminum Corrosion Inhibitor

The development and utilization of sustainable energy is an important way to solve the energy crisis and environmental problems,and the combination of solar thermal power generation technology and thermal energy storage can generate a large amount of electricity without interruption.Molten chloride salt is the most promising thermal medium energy storage and heat transfer fluid in solar thermal power generation technology due to its abundant reserves,low cost,high operating temperature（>800℃）and large specific heat capacity.However,molten chloride salts are extremely corrosive at high temperatures.Therefore,it is of great significance to study the purification scheme of molten salt to prevent hightemperature corrosion of structural materials.In this paper,the effect of adding 0 wt.%,1 wt.%,2 wt.%,10 wt.%Al corrosion inhibitor on the corrosion behavior of HT700 alloy and 316 stainless steel in NaCl/KCl/MgCl₂（24.5/20.5/55wt.%）molten salt was studied by hightemperature electrochemical method at 800℃.The corrosion morphology and phase composition of alloys were determined by scanning electron microscope and X-ray diffractometer with energy spectrometer,and the corrosion mechanism of alloys in chloride molten salt was analyzed;The corrosion electrochemical behavior of alloys in chloride molten salt containing Al corrosion inhibitor was studied by electrochemical impedance spectrum and potentiodynamic polarization curve,the sustained release mechanism and corrosion control process of Al powder in chloride molten salt were elucidated,the main results were as follows:（1）The corrosion resistance of HT700 alloy and 316 stainless steel in NaCl/KCl/MgCl₂ decreases with the increase of corrosion time at 800℃,but the corrosion resistance of HT700 alloy with higher Ni content is better than that of 316 stainless steel.（2）Adding Al powder can reduce the corrosion rate of the two alloys in chloride molten salt.With the increase of Al powder content,the corrosion current density and corrosion layer thickness of the two alloys decreased.Al corrosion inhibitor has better corrosion inhibition effect on 316 stainless steel.（3）When the two alloys are corroded in chloride molten salt containing Al powder inhibitor,the content of Al₂O₃ in the corrosion products increases,which can effectively reduce the corrosion rate of the alloys;Al powder corrosion inhibitor can inhibit the diffusion rate of Cr in HT700 alloy,and Cr will be dissolved and diffused with the growth and dissolution of Al₂O₃ layer.When the Al content is 2 wt.%,the Al rich phase begins to form on the alloy surface.When the Al content is 10 wt.%,the Al rich phase transformation is continuous.When the amount of 10 wt.%Al corrosion inhibitor is added,a diffusion layer（composed of Al-,Ni-,Fe-and Cr-）is formed inside the HT700 alloy,and its depth increases over time:11.04 μm（100 h）,185.8 μ（200 h）,145.66 μm（300 h）,166.02 μm（400 h）.The protective layer formed from the outside to the inside of 316 stainless steel at high temperature is Al-Ni-Fe-Cr,Al-Fe-Cr,Ni-Fe,Al-Fe-Cr,Cr₂O₃,Al-Ni-Fe-Cr,and its depth changes with time:24.24 μm（100 h）、45.3 μm（200 h）、363.1 μm（300 h）、139.5 μm（400 h）.（4）The corrosion of the two alloys in molten chloride without corrosion inhibitor is mainly controlled by the diffusion of active elements in the alloy into the molten salt.With the extension of corrosion time,R_p decreases and the corrosion resistance decreases.Al₂O₃ layer and Alrich layer formed on the alloy surface after adding Alpowder can inhibit the diffusion of active elements in the alloy;Both materials have electric double-layer capacitance:one is oxide layer and the other is al rich alloy layer.R_p increases and corrosion resistance increases.