Preparation of mullite micro-vessels by a combined treatment of zeolite A

A controlled thermal treatment of zeolite NH(4)A results in the formation of a mixture of mullite and amorphous silica by a chain of pseudomorphic transformation processes: zeolite --> amorphous phase --> (mullite + amorphous SiO2). In contrast to the structural changes, particulate properties (particle shape and size, respectively) do not change or change a little during heating. This implies that the resulting mixture of mullite and amorphous SiO2 does not appear as separate particulate systems, and thus that the transformation processes occur inside single particles (micro-reactors). Base treatment of the final product (mullite + amorphous SiO2) results in the extraction of the amorphous SiO2 from the interior of each particle and formation of mullite micro-vessels. (C) 2003 Elsevier Inc. All rights reserved.