三元硝酸熔盐高温劣化的化学热力学计算

CALCULATION OF CHEMICAL THERMODYNAMICS ON DETERIORATION OF TERNARY NITRATE SALTS AT HIGH TEMPERATURE

就太阳能蓄热用三元硝酸熔盐53%KNO_3-7%NaNO_3-40%NaNO_2高温劣化问题进行了化学热力学计算。结果显示:熔盐中NaNO_2含量持续减少是热力学的必然结果。NaNO_2与O_2反应的△_rG~θ在327～727℃范围内从-91.17 kJ·mol^(-1)增大到-21.95kJ·mol^(-1)。NaNO_2分解为NaNO_3(1)、Na_2O(s)和N_2反应的△_rG~θ在327～727℃范围内从-30.73 kJ·mol^(-1)增大到-19.56 kJ·mol^(-1)。两个反应的△_rG~θ在熔盐使用温度范围内皆为负,意味着反应一定可以发生。熔盐可以在450℃下使用是由于反应处于动力学惰性状态。降低NaNO_2分解和氧化反应速度可适当提高熔盐使用温度。

The chemical thermodynamic calculation was carried out for the high temperature deterioration of ternary nitrate salts of 53 % KNO3-7% NaNO3-40% NaNO2 for the storage of solar energy through high temperature. The results show that the constantly decreasing content of sodium nitrite in molten salts is a conclusive consequence of thermodynamics. The △r G^θ of the reaction of NaNO2 with 02 between 327℃ and 727℃ were increased to - 21.95kJ·mol^-1 from - 91.17kJ·mol^- 1 , respectively. The △t G^θ of the decomposed reaction of NaNO2 increased to - 19.56kJ· mol^- 1 from - 30.73kJ·mol^-1 between 327℃ and 727℃. The two reactions would be happened, for both the Ar Go of the two reactions are negatives at the operation temperature range of molten salts. Because the reaction happens in kinetic insert state, molten salts could be used below 450℃. The operation temperature of molten salts could moderately improve by means of reducing the rate of the decomposition and oxidation of NANO2.