Density and Molar Volume of CaO–SiO2–FeO Melts Measured by Electrostatic Levitation Aboard the International Space Station

The densities of CaO–SiO 2 –FeO melts were measured under microgravity conditions using the Electrostatic Levitation Furnace aboard the International Space Station (ISS-ELF). The nominal FeO contents were 20, 60, and 80 mass% (CS20F, CS60F, and CS80F, respectively), with CaO and SiO 2 comprising the balance in a 1:1 mass ratio. Density was calculated from the sample mass and the droplet volume determined using shadow images recorded during cooling. For all compositions, the density decreased approximately linearly with increasing temperature. At a given temperature, the density increased with increasing FeO-equivalent content. The maximum relative expanded uncertainty in the density was 3.46 %, with a coverage factor of k = 2. After the experiments, the recovered samples were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy. Molar volumes were calculated from the measured densities using compositions derived from the measured Ca, Si, and Fe contents, and they were compared with literature data and an additive reference at approximately 1400 °C. The molar volume decreased from CS20F to CS60F and changed only slightly between CS60F and CS80F. The molar volumes of CS20F and CS60F were close to the additive reference, whereas that of CS80F showed a clear positive deviation.