Densities of liquid lanthanoid sesquioxides measured with the electrostatic levitation furnace in the ISS

The densities of several liquid lanthanoid sesquioxides (Ln₂O₃, Ln = Er, Ho, Tb, Gd) were measured over the temperature range from 2700 K (the approximate melting point of these materials) to 3200 K. These measurements were performed using the Electrostatic Levitation Furnace onboard the International Space Station (ISS-ELF). Based on the Coulomb force between the charged samples and surrounding electrodes and employing a rapid feedback control process, specimens were stably levitated and subsequently melted by high power lasers. The molten oxides exhibited spherical morphologies and their volumes were readily calculated from magnified images. Subsequent weighing of the samples on Earth allowed the densities of the oxides to be determined. The densities of Er₂O₃, Ho₂O₃, Tb₂O₃, and Gd₂O₃ at their melting temperatures (T_m) were found to be 8170, 8035, 7451, and 7268 kg/m³, respectively, and these density values were shown to exhibit a linear correlation with temperature. The molar volumes of these oxides at their T_m values were calculated and compared with those of other sesquioxides (Al₂O₃, Ga₂O₃, and B₂O₃). The molar volumes of the nonglass-forming sesquioxides (Er₂O₃, Ho₂O₃, Tb₂O₃, Gd₂O₃, Al₂O₃, and Ga₂O₃) showed linear correlations with the cubes of their cation radii, whereas those of the glass-forming oxide (B₂O₃, As₂O₃, and Sb₂O₃) showed different correlations.