engleski

Kinetic Analysis of temperature-induced transformation of zeolite A to low-carnegieite

Kinetics of the isothermal amorphization of zeolite A and recrystallization of the formed amorphous phase to low-carnegieite at three different temperatures were investigated by powder X-ray diffraction method. Changes in the fractions fA of zeolite A, fa of amorphous aluminosilicate and fC of low-carnegieite during heating of zeolite A, show that amorphization and recrystallization take place simultaneously. Kinetic analyzes of single processes (amorphization, recrystallization) as well as solution of the population balance of the entire transformation process (simultaneous transformation of zeolite A into amorphous aluminosilicate and its recrystallization into low-carnegieite) have shown that: (A) the transformation of zeolite 4A takes place by a random, diffusion-limited agglomeration of the short-range-ordered aluminosilicate subunits formed by thermally induced breaking of Si-O-Si and Si-O-AL bonds between different building units of zeolite framework and (B) the crystallization of low-carnegieite occurs by homogeneous nucleation of low-carnegieite inside the matrix of amorphous aluminosilicate and diffusion-controlled, one-dimensional growth of the nuclei, thus forming needle-shaped crystals of low-carnegieite. Keywords: Temperature-induced transformation, Zeolite 4A, amorphous aluminosilicate, low carnegieite, kinetics, mechanism

temperature-induced transformation; zeolite 4A; amorphous aluminosilicate; low carnegieite; kinetics; mechanism

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