Mechanism of Zeolite A Synthesis

Abstract

Experiments utilizing several different characterization techniques as a function of time, including chemical analyses,Raman spectra, x-ray diffraction, sorption and particle size measurements, have been performed to determine the mechanistic pathway in 4A synthesis.The evidence supports a mechanism involving formation and subsequent dissolution of an amorphous aluminosilicate intermediate, with solution transport from the gel to the growth surface of the crystallite.

In situ ultrasonic monitoring of zeolite A crystallization from coal fly ash

“…This disruption of the US-attenuation trend can also be supported by Cundy and Cox's [29] concept of the formation of the 'pseudosteady-state intermediate' which they had referred to as 'secondary amorphous phase' occurring via solution transport mechanism during the process of evolution of order. The existence of primary (visible gel) and secondary amorphous phases had also been proposed by Angell and Flank [30]. During the nucleation period, between 120 and 150 min (see Fig.…”

“…The overall decrease in the ratio of the amount of amorphous material to the number of crystals of zeolite A shown in Fig. 8 is indicative and confirms the auto-catalytic process which suggest that the 'rate of gel dissolution must increase with the rate of consumption of growth species by increasing cumulative crystal surface area' [29,30,45].…”

“…During the initial mixing of Si and Al source materials, the immediately formed product has been reported to be mostly non-equilibrated amorphous aluminosilicate gel [29,30]. This primary amorphous phase undergoes changes due to stirring and heating which in effect causes changes in reaction fluid properties such as viscosity and density.…”

Vibrational spectra and dissociation of aqueous Na2SiO3 solutions

“…However, such studies are surprisingly rare in the literature, which is partly due to the far less developed molecular spectroscopic identification of dissolved silicate structures than that of solid silicates. There are several Raman [12][13][14][15][16][17][18][19][20][21][22][23] and IR [17,[21][22][23][24][25][26][27][28] publications which focus specifically on aqueous silicate solutions and one can also find such spectra in some zeolite synthesis related papers [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. However, only a small group from these authors has assigned certain vibrational bands to specific molecular structures like monomers or siloxane chains, rings, etc.…”

Ordered Porous Nanomaterials: The Merit of Small

“…From those studies, the role of the solution phase in the zeolite formation mechanism became increasingly important, as evidenced by several different experiments. In this respect, Angell and Flank [46] reached some conclusions different from those reported by McNicol and coworkers [47,48] after using Raman spectroscopy, XRD, and particle size analyses. The former study was later supported by the reports by Culfaz and Sand [49] and Kacirek and Lechert [50] which concluded that the rate-determining step was the linking of silicate species to the surface of the crystal.…”