Cation exchange and amorphization kinetics in Zeolite: mechanisms and applications

Zeolites are widely used materials with tunable structures applied in catalysis, ceramics, and glasses. Their unique ability to function in both crystalline and amorphous phases offers broad potential for tailored applications. Controlled amorphization of zeolites enables fine-tuning of performance characteristics. In ceramic and glass synthesis, the kinetics of crystallization and amorphization are critical to achieving desired phases or melt-quenched amorphous structures. Zeolite phase transitions—from crystal to amorphous—can be induced mechanically, thermally, or under high pressure. Due to their inherent porosity, zeolites exhibit controlled ion uptake and release, governed by species mobility within the framework and surface. Mechanical amorphization, for example, regulates the release dynamics of Co²⁺ ions from faujasitic zeolites. Depending on the degree of amorphization, a two-step release and re-capture mechanism occurs over a timescale of minutes to days. Thermal stability is vital for zeolite applications. At high temperatures, zeolites undergo complete amorphization followed by recrystallization into secondary phases. This process typically involves a transition from a crystalline structure to a low-density amorphous (LDA) phase, then to a high-density amorphous (HDA) phase. Using isothermal and non-isothermal in situ techniques, we examined thermal amorphization kinetics in faujasitic zeolite X derivatives with varying metal cations. In K-for-Na ion-exchanged samples, a mixed-alkali effect influenced both transition temperatures and reaction timescales between LDA and HDA phases. Additionally, by synthesizing samples with low ion exchange degrees, we isolated the role of alkali, alkaline earth, and transition metals in modulating low-temperature melting kinetics in zeolite X.