Crystallization and Spontaneous Phase Transformation of MTN-Type Zeolite with Tetragonal Symmetry

MTN-type zeolite with tetragonal symmetry was hydrothermally synthesized in a reactant system of Na2O–SiO2–NaF–H2O using N-ethyl-hexamethylenetetraammonium bromide as the template. A spontaneous phase transformation of the as-synthesized zeolite at ambient temperature from tetragonal to cubic symmetry was investigated with polarized light microscopy, X-ray powder diffraction, 29Si magic angle spinning nuclear magnetic resonance, and differential scanning calorimetry. The results of the investigations indicate that the as-synthesized tetragonal MTN zeolite is a metastable phase.