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Kinetic Analysis of the Formation of Low-Carnigieite from Zeolite Na-A [LTA]

Kinetics of isothermal amorphization of zeolite A and recrystallization of the amorphous phase to low-carnegieite at three different temperatures were investigated by powder X-ray diffraction method. Changes in the fractions ZA of zeolite A, Am of the amorphous phase and L-Carn of low- carnegieite during heating of zeolite A at 1078 K (Fig.1) show that amorphization and recrystallization take place simultaneously. Both kinetics of amorphization and recrystallization can be mathematically described by the Johnson–Mehl-Avrami-Kolmogorov (JMAK) kinetic equation, i.e., f(t) =1-exp[-K(T)tn], where f(t) = ZA or L-Carn is the fraction of zeolite A and low- carnegieite, K(T) is the rate constant, t is the time of transformation and n is determined by the mechanisms of nucleation and crystal growth. Plotting [ln(-ln(1-f(t))] vs lnt, the values of K(T) and n as well as the activation energies of amorphization and recrystalization are obtained. The mechanisms of amorphization and recrystallization are discussed in terms of the characteristic numerical values of K(T) and n.

Zeolite NaA; Low-carnegieite; Kinetics; Formation; Amorphization

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