Synthesis of AlPO4-5 powder by microwave heating: Influence of starting gel pH and reaction time

Extremely pure AlPO4-5 powder was synthesized using a microwave heating met hod. The yield as well as the size distribution of the AlPO4-5 crystals dep ended on the pH value of the starting gel. On reducing the pH value from 7. 0 to 4.0, the average size of the product crystal was found to increase, th e size distribution became wider, and the yield increased. The pH value of the supernatant liquid after the synthesis was always ca. 7.5, independent of the pH values of the starting gels. During the first step of crystalliza tion, disk-like crystals are formed, and they grow in the c-axis direction resulting in the formation of a hexagonal rod-like shape. The channels of t he crystals are completely open, and, therefore, the crystals obtained are suitable for use as a host to stabilize guest materials. (C) 1999 Elsevier Science B.V. All rights reserved.