engleski

On the real significance of the "Induction period" of zeolite crystallization

An analysis of the relationships between ln (1/t_i) vs. 1/T, ln (df_z/dt_c) vs. 1/T and lnK vs. 1/T (t_i is the "induction period" of crystallization, f_z is the fraction of zeolite crystallized up to time of crystallization, t_c, K is the rate constant of the crystallization process and T is absolute temperature) was made for zeolite crystallization at different temperatures, simulated by population balance method using appropriate mechanisms of gel dissolution, nucleation and crystal growth. The analysis have shown that the slope, S_1, of the ln (1/t_i) vs. 1/T straight line is the same as the slope, S_2, of the ln (df_z/dt_c) vs. 1/T straight line, i.e., that the activation energy calculated from the slope S_1 corresponds to the activation energy, E_c, of the entire crystallization process, and not to the activation energy, E_n of nucleation. The same relations are valid for any crystallization time (ln K vs. 1/T plots), thus indicating that the processes occurring during the "induction period" are qualitatively the same as the processes that occur during the "growth period".

Induction period of zeolite crystallization; Activation energy of gel dissolution/zeolite nucleation and crystal growth

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