Study of the MNO3–Al2O3 nanocomposites by differential scanning calorimetry

This paper presents the results of a differential scanning calorimetry study of phase transitions in (1 − x)MNO3–xAl2O3 (M = Li, Na, K, Rb) composites. It was found that an additional stable high-temperature ferroelectric phase of potassium nitrate (phase III) is formed in KNO3–Al2O3 nanocomposites. Sharp decrease in enthalpies of phase transitions of salts, including melting enthalpies, was observed in the nitrates doped with Al2O3 nanoparticles. For the first time, the concept of the specific enthalpy of phase transitions of a salt in a composite is introduced, which is normalized to the salt concentration and specific surface area of the oxide and depends only on the nature of the contacting substances. The regularities of the change in the enthalpy of melting of (1 − x)MNO3–xAl2O3 versus the radius of alkali metal cation have been established.