Hydrothermal/autoclave synthesis of AlPO-5: a prototype space/time study of crystallisation gradients

TEDDI (tomographic energy dispersive diffraction imaging) has been used for in situ time-resolved studies of hydrothermal synthesis of Ge doped AlPO-5. The data for three different levels of Ge doping into AlPO-5 system are presented. Two pathways are observed, the simplest being a direct formation of ALPO-5 accompanied by simultaneous GeO2 dissolution in the bulk gel, plus a variation in which ALPO-5 acts as an intermediate in the formation of ALPO-18, a related framework structure. The TEDDI approach is able to show that these synthesis pathways and kinetics vary significantly with depth inside the synthesis vessel and possible explanations for this are discussed.