Surface tension and wettability between silicon nitride of RE ₂O₃-MgO-SiO₂ (RE = Y, Gd, Nd and La) melts

The effect of RE₂O₃ (RE = Y, Gd, Nd, and La) additives on the surface tension of 45.2MgO-54.8SiO₂ (mol%) melts have been investigated using the ring (detachment or maximum pull) method. Furthermore, the wettability of RE₂O₃-MgO-SiO₂ melts between the silicon nitride polycrystalline substrate is determined using the sessile drop method. The surface tension of RE₂O ₃-MgO-SiO₂ melts were found to increase with the content of any rare-earth additions, which suggests that a rare-earth oxide behaves as a network modifier of the complex silicate anions in high temperature melts. The surface tension increased in the order of the cationic radius of rare-earth oxides as follows: Y₂O₃<Gd₂O ₃<Nd₂O₃La₂O₃. The contact angle of RE₂O₃-MgO-SiO₂ melts against the silicon nitride substrate rapidly decreased with the annealing time at 1723 K; after annealing for 50 min, the contact angle remained constant. The contact angle and the penetration depth of melts into the substrate increased in the order of the cationic radius of rare-earth oxides as follows: Y ₂O₃<Gd₂O₃<Nd₂O ₃<La₂O₃.