Viscosity and surface tension measurements of RE₂O ₃-MgO-SiO₂ (RE=Y, Gd, Nd and La) melts

The effect of RE₂O₃ (RE=Y, Gd, Nd and La) on the viscosity and the surface tension of 45.2MgO-54.8SiO₂ (mol%) melts have been investigated with rotating crucible viscometer and ring method, respectively. Additionally, structural characterizations of these quenched vitreous samples have been investigated with Infra-Red spectrometer. The viscosities of RE₂O₃-MgO-SiO₂ melts were found to decrease with increasing the content of any rare-earth additions, which suggests that rare-earth oxide behaves as a network modifier of complex silicate anions in high temperature melts. The viscosities decreased in the order of cationic radius of rare-earth; from Y₂O₃, Gd ₂O₃, Nd₂O₃ to La₂O ₃. The surface tension of MgO-SiO₂ binary melts were found to increase with increasing the content of any rare-earth additions. The surface tensions obviously increased in the order of cationic radius of rare-earth, which the change of with rare-earth addition is direct antithesis of that of viscosities. The decrease of the absorption band of RE ₂O₃-MgO-SiO₂ glasses at 1 060 cm^-1 (Si_4nO_9n^2n-) with the attendant increase of the absorption band at 930 cm^-1 (Si₂O₇ ^6-). These variations with rare-earth oxides content means that the degree of polymerization of complex silicate anions become smaller with rare-earth oxide additions. The viscosity of rare-earth containing silicate melts linearly increases with cationic field strength of RE³⁺. The surface tension of rare-earth containing silicate melts linearly decreases with cationic field strength, except Y₂O₃ additives.