Heat capacity and enthalpy of cesium iodide from 300 to 830 K

The enthalpy and the heat capacity of CsI have been determined from 300 to 830 K by the drop calorimetry. The calorimeter was operated at 323 K and 520 K for normal and inverse drop procedure, repsectively. Heat-capacity measurements were also made with use of a differential scanning calorimeter (DSC) from 300 to 520 K in order to confirm the results. The present results of heat capacity agree well and merge smoothly at 300 K with the published low-temperature values. The heat capacity-temperature curve was found to show a slight upward deviation above 400 K from the linear temperature dependence, which was analyzed to be caused by vacancy formation. By taking this into account, a heat-capacity equation for CsI was derived, which was applicable over the whole temperature range investigated. The thermal functions of CsI were calculated by using this equation from 298 to 899 K (melting point). (orig.)