Rapid synthesis of AlPO4-11 and cloverite by microwave-hydrothermal processing

This study focuses on the rapid preparation of AlPO4-11 and cloverite by microwave-hydrothermal (M-H) heating and the comparison of this heating technique with the conventional-hydrothermal (C-H) healing technique in the synthesis of these phases. By M-H heating: pure AlPO4-11 phase was synthesized from boehmite at 70 psi (similar to 150 degrees C) within 2.5 h without pretreatment of the hydrogels. C-H preparation of AlPO4-11, on the other hand, requires an aging step for about a day at 90 degrees C prior to crystallization at 200 degrees C. In the M-H heating system, pure cloverite was crystallized at 30 psi (similar to 120 degrees C) within 2.7 h, whereas C-H heating at 120 degrees C required more than 24 h for its crystallization. Large single crystals of dense GaPO4 phase were crystallized at 70 psi (similar to 150 degrees C) within 2.5 h by M-H treatment. This study shows that the crystallization kinetics of AlPO4-11 and cloverite were enhanced by more than an order of magnitude in the M-H system compared with the C-H system. (C) 1998 Elsevier Science B.V.