METASTABLE SOLIDIFICATION PROCESS OF LN(3)AL(5)O(12)(LN-DY, Y, LU) GARNETS

The solidification process of liquid Ln(3)Al(5)O(12) (Ln = Dy, Y, Lu) garnets was investigated by differential thermal analysis (DTA) and a critical temperature T-cl was found. Cooling from temperatures below T -cl leads to the crystallization of the single garnet phase. Cooling f rom temperatures above T-cl leads to the solidification of a mixture o f LnAlO(3) perovskite and alpha-Al2O3. For Ln=Y, the results are in ag reement with previously proposed stable and metastable phase diagrams. The variation of T-cl with composition was investigated. Rapid coolin g of liquid yttrium aluminium garnet in contactless conditions was per formed, using an aerodynamic levitation device coupled with a CO2 lase r. The results are consistent with those obtained by DTA. In addition, cooling from temperatures above around 2400 degrees C leads to the cr ystallization of a metastable form of garnet.