AbstractThe densities of the KF–KCl–KI melts with KF/KCl molar ratios of 0.8 and 2 are measured as a function of the KI content by hydrostatic weighing. The measurements were performed in an inert atmosphere using structural materials resistant against the melts. The densities of the 45 mol % KF–55 mol % KCl–KI and 66.6 mol % KF–33.4 mol % KCl–KI melts with KI contents of from 0 to 100% were measured in a temperature range of 973–1073 K. KI additions to the KF–KCl melt were found to increase the density. The temperature dependences of the densities of the melts are described by linear functions. KI is found to increase the coefficient of temperature dependence of the density. Data on the densities of the KF–KCl–KI melts are used to calculate the molar volumes. Dependences of variations in the molar volume on the temperature and the melt composition are given. The molar volumes of the melts are shown to be close to those calculated by the additivity rule, which indicates that the initial salts are mixed without marked chemical interaction.