Microwave assisted hydrothermal conversion of Ba-exchanged zeolite A into metastable paracelsian

A microwave assisted crystallization of paracelsian, a metastable phase for which no synthetic occurrence is at present reported, was obtained. A sample of thoroughly Ba-exchanged zeolite A was prepared and reacted in alkaline media and hydrothermal conditions under the action of microwaves (frequency 2.45 GHz, irradiation power 1000 W). The alkaline environment was created by using aqueous solutions of LiOH and tetraethylammonium hydroxide. Treatment temperature, reaction time and weight solid/liquid ratio ranged between 150 and 230 °C, 40 and 120 min, 1/5 and 1/40, respectively. The pressure was autogeneous. The action of microwaves appears to strongly enhance the ability of hydrothermal systems to produce highly metastable phases, an important observation.