Corrosion Behavior Of Ternary Chloride Molten Salt And Construction Of New Chloride Molten Salt Systems

Heat transfer and storage system is an important part of solar thermal power generation and industrial energy saving technology.The properties of heat transfer and storage materials in the heat transfer and storage system directly affect the efficiency and cost of solar thermal power generation system.Molten salt is the ideal heat storage material with the characteristics of large heat capacity,wide use temperature range,low vapor pressure,low viscosity and so on.In particular,chloride molten salt is one of the objectives for countries to develop new high-temperature heat transfer and storage materials with the advantages of non-decomposition,high boiling point,less expensive and earth abundant.However,as a heat transfer and storage fluid,chloride molten salt shows a greater corrosive to the piping/container alloys.It is of great significance to study the corrosive properties of chloride molten salts and develop new high performance chloride heat transfer materials.In this paper,the corrosion properties of stainless steel 316 L,nickel-based alloy Inconel 625,Inconel 600,Hastelloy X,Hastelloy C-276 and Hastelloy B-3 were investigated in a ternary NaCl-CaCl2-MgCl2 eutectic molten salt by gravimetric methods.The effects of temperature and air on corrosion were explored.The long-term corrosive studies of 316 L,Inconel 625,Hastelloy X and Hastelloy B-3 are preferred.The corrosion dynamic curves and corrosion rate curves of the above four alloys in NaCl-CaCl2-MgCl2 molten salt were given under the experimental conditions.The corrosion products and corrosion morphologys of the metals were analyzed by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The relevant corrosion mechanism was analyzed.It provides a reference for the application of NaCl-CaCl2-MgCl2 eutectic molten salt as a heat transfer fluid and the the selection of the corresponding thermal energy storage system equipment.A quinary eutectic chloride molten salt(LiCl-NaCl-KCl-MgCl2-CaCl2)heat transfer and storage material with low melting point was prepared.DSC method was used to determine the low eutectic melting point and composition of the lithium containing quinary eutectic salt mixture.The variation law of thermophysical properties(melting point,latent heat,specific heat,viscosity,density,thermal diffusivity,thermal conductivity and so on)with temperature and thermal stability and dynamic circulation heat storage and discharge characteristics was measured.The corrosion of the molten salt to iron-based AISI 316 L,310S,321 stainless steel and nickel base Inconel 625 alloy was determined,too.Results show that the melting point of the molten salts is 356.5 ?,heat of fusion is 150.9 J?g-1,the average heat capacity of liquid salt at 650 ? is 1.208 J?g-1?K-1,the density is 1.699 g?cm-3,viscosity is 2.56 cp,thermal diffusivity is 0.0104 mm2?s-1,the thermal conductivity is 0.0213 W?m-1?K-1.The quinary salt mixture showed excellent thermal circling stability under the isothermal condition.Meanwhile,in low oxygen partial pressure,the corrosion of the quinary salt mixture to the four alloys is follow the sequence of 310 S,321,316 L,Inconel 625 decrease in turn.NaCl,CaCl2 and MgCl2 and CuCl were chosed to build new ternary chloride molten salt thermal storage materials.The phase diagrams of two ternary chloride molten salt systems were studied(NaCl-CaCl2-CuCl and CaCl2-MgCl2-CuCl).The molten salt phases of the binary system NaCl-CaCl2,NaCl-CuCl,CaCl2-CuCl and MgCl2-CuCl were calculated by using the "hard sphere" ion model.The results are in good agreement with the experimental phase diagram.The phase diagrams of ternary NaCl-CaCl2-CuCl and CaCl2-MgCl2-CuCl molten salt systems were obtained by using the conformal ion solution model(CIS)and the formal solution model.The calculated phase diagram is verified by DSC curve.