Enhanced methods of crystallization: The crossover synthesis from gel to melt flow - A case study on sodalites

A new crystallization pathway composed of a combination of gel synthesis and crystallization in a melt flow is demonstrated using the sodalite system as a case study. The specific characteristics of this enhanced method of crystallization persists in a controlled heating of a pressed pellet of a mixture of selected solids, containing a “water donator” as well as a “fluxing agent”. The reaction of zeolite 13 X (“water donator and Si[sbnd]Al-source”) NaOH granulate (“fluxing agent”) and a template salt like NaCl (or others) is shown to yield suitable products already after a few hours of heating the mix-pellet under open conditions. In a first synthesis series experiments were performed to investigate the details of the reaction mechanism. Beside a study of the role of the hydrate water, the NaOH granulate and certain template salts, even the total decomposition of the zeolite 13 X framework structure could be demonstrated under the conditions of the crossover from gel to flux growth. According to the results it could be claryfied that the mechanism consists of alkaline aluminosilicate gel formation and crystallization in the early period but shifts into crystal growth in NaOH melt at elevated temperature. In a second series examples of tailored sodalites and the characterization of these products will show the effectiveness of the new method. From SEM invertigations could be further derived that the crystal size and morphology depends on T_max. the holding period at T_max. and nano- or micro-crystalline sodalites can be obseved.