Raman Spectra Study On Structure Of KNO₃-NaNO₂-NaNO₃Molten Salts System

Molten KNO3-NaNO2-NaNO3mixture is widely applied in the heat storge and tranfer industry for its good physicochemical properities. The physicochemical properities of molten salts are associated with ionic structure. Therefore, it is of actual meaning of the study on molten structure of KNO3-NaNO2-NaNO3system. Furthermore, knowledge on the structure of the system is helpful to improve the theory of molten salts.In the present study, structure of KNO3, NaNO3, NaNO2single sample, NaNO3-NaNO2, KNO3-NaNO2, KNO3-NaNO3binary system, and KNO3-NaN02-NaNO3ternary system was researched based on the high temperature Raman spectra measuring platform of NEU. Relationship between structural properities and relative contents of ion complex in the melts and temperature and weighed-in composition was studied. Converting law of the ion complex was explored and thermal stability of the melt system was investigated.The experimental results has shown that the characteristic peak of KNO3, NaN03and NaN02showed red shift in the Raman spectra calculated when the length of N-O bond increased.The characteristic peak of NO3-and/or NO2-showed red shift in the Raman spectra for all of the sigle, binary and ternary melts. Meanwhile, the width of the characteristic peak increased with the temperature. For KNO3-NaNO3binary system, there is a good linear relation between the Raman shift of vi characteristic peak of NO3-and the molar fraction of NaNO3.The relative contents of the complex in the molten salts system researched was unchanged after30min of holding time. For NaNO3-NaNO2and KNO3-NaNO2binary systems, there was a balance between NO3-and NO2-in the melts. The mole fraction incremental of NO3-showed linear relation with molar fraction of NaNO2. The empirical equations of mole fraction incremental of NO3and molar fraction of NaNO2for the two binary systems were obtained. For the same NaNO2mole fraction, NaNO3-NaNO2binary system showed the more stability than KNO3-NaNO2binary system.For KNO3-NaNO2-NaNO3ternary system, the melt sample contained more NaNO3showed better thermal stability. The empirical equations of mole fraction incremental of NO3-and molar fraction of NaNO3were obtained. When the molar of NaNO2was20%-90%, the molar of NO3-in ternary melts was increased, and when the molar fraction of NaNO2increased and the molar fraction of NaN03increased, the changing value of molar fraction of NO3-increased. Meanwhile, when the molar of NaNO2was10%, the molar of NO3-in ternary melts was decreased, and when the weighted-in molar fraction of NaNO2decreased and the molar fraction of NaNO3increased, the changing value of molar fraction of NO3-increased.