The solid-solid phase transition of KHF2 was studied by infrared spectrometry at various temperatures and by differential scanning calorimetry(DSC) also. There are hydrogen bonds between the molecules which play a dominant role to the structure at low temperature state. In the temperature range closely corresponding to the solid-solid phase transition, the frequency of antisymmetric stretching(v3) shifted to a higher wavenumber, and the bending(v2) to lower wavenumber. The enthalpy and the temperature of solid-solid phase transition for KHF2 were measured by DSC method and the latter is consistent with the result of IR which could declare the mechanism of solid-solid phase transition of KHF2. With the breaking of hydrogen bonds between the molecules and the introduction of vibrational and rotational disorder KHF2 exhibited crystalline transition.
By kissinger and Ozawa kinetic methods the activation energies and the reaction orders of the phase transitions in ammonium thiocyanate for heat storage in air were calculated from the DSC curve of phase transition at different heating rates.
