Formation Process of Mullite from NH<sub>4</sub><sup>+</sup>-Exchanged Zeolite A

Abstract

Zeolite A (NH4-A) exchanged with NH4+ was used as a precursor of mullite. NH4-A was dehydrated and deammoniated by heating up to 300°C and it entered an amorphous state. Mullite crystallized directly from the amorphous phase at above 950°C without forming a spinel phase as an intermediate phase. Since the starting material is zeolite A, which has the tetrahedral framework structure with homogeneous arrangement of Si, Al, and O atoms, these experimental results supported the previous hypothesis proposed for the formation process of mullite.