Effect of lithium perchlorate addition on LiNO3–KNO3 nitrate eutectic

Abstract

In our work, thermal properties, phase transitions, and processes of molecular relaxation of nitrate and perchlorate ions in the lithium nitrate–potassium nitrate binary eutectic system doped with lithium perchlorate LiClO₄ were studied by differential scanning calorimetry and Raman spectroscopy. The values of specific electrical conductivity of the LiNO₃–KNO₃ nitrate eutectic and the LiNO₃–KNO₃–LiClO₄ ternary salt system were also obtained. The electrical conductivity was investigated up to melting temperatures and it was found that the addition of lithium perchlorate LiClO₄ to the LiNO₃–KNO₃ binary eutectic leads to an increase in the specific ionic conductivity of the ternary salt system. Lithium perchlorate functions as an active additive that promotes the increase of ion mobility due to competing mechanisms of anion-cation interactions. The value of specific ionic conductivity reaches a maximum in the system when 0.2 mol of lithium perchlorate is added. It has been established that with the increasing addition of lithium perchlorate to the nitrate eutectic, the melting peak of the LiNO₃–KNO₃ eutectic decreases. For the composition with an initial content of 0.5LiClO₄, a phase transition of the LiNO₃–KNO₃ eutectic is not registered. It is obvious that in the system take place an exchange reaction between potassium nitrate and lithium perchlorate with the formation of KClO₄ and LiNO₃. This conclusion is also confirmed by the data of Raman scattering spectra, which show that with increasing addition of LiClO₄, the peak of fully symmetric stretching vibration ν₁(KNO₃) decreases and the peak of ν₁(KClO₄) is observed. The addition of 0.5 mol of LiClO₄ leads to the total disappearance of the peak of ν₁(KNO₃). Interionic interactions in the salt systems, leading to changes in the local symmetry of the NO₃ˉ-ion, are reflected in their transport and thermodynamic properties.