Szcshr123

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If you have any questions, please don't hesitate to contact me on my talk page. Ian (Wiki Ed) (talk) 19:28, 19 January 2016 (UTC)Reply

Zeolite Crystal Growth Mechanism and Observations

History/Background

Zeolite is a widely used solid compound which both oxidized silicon and aluminum are existed in a tetrahedral form. And the silicate and aluminate are used determine the property and appearance of the final zeolite crystal. People produce large amount of zeolite industrially for the using of water purification and softening in daily life. In chemistry, zeolite can be treated as catalysts and sorbents. Zeolite crystal carries negative charges with the presence of alumina tetrahedral. As the result, organic or inorganic cations need to be presented during the formation of the crystal.

Mechanism

In general, the reaction proceeds in batch system with silicate and aluminate solution mixed inside. Then this solution undergoes hydrothermal(HT) treatment at different elevated temperate at different times, which can range from minutes to days. As the result, the raw material after the mixing will give gel or suspension, which is the precursor mixture for zeolite crystal. Then the precursor will go through nucleation stage of zeolite and finally form the crystal structure. Additionally, the crystallization of zeolite needs assistance from “templet”, which are organic ions required to stabilize and synthesis crystal. Specifically, the nucleation stage of crystal formation can be achieved via different mechanisms, including growing from the addition of atoms or molecules and growing from the aggregation of nanoparticles. (reference) Mechanisms also need to be modified under the consideration of different mixing types: gel or colloidal suspension.

In gel, the procedure can be established in four steps: first, formation of the gel and zeolite nuclei: second, exchange between the gel and the solution part; third, aggregation of small crystals around the zeolite nuclei; fourth, crystal growth by propagation. (reference).

While in colloidal suspension, it can also be separated in four different steps: first, amorphous transform to crystalline phase; second, self-assembling building block; third, monomer addition to nucleus; fourth, combination of silicalite mechanisms.

Observations

Latest comment: 8 years ago1 comment1 person in discussion

For growth in gel, irst observable image under high-resolution transmission electron microscopy (HRTEM) was the formation of small spherical objects with diameter of 5 to 10 nm. (Mintova) After the organic template was added, crystallization of zeolite could happen after around 5 minutes forming gel particles with a diameter of 40 to 80 nm. Using dynamic light scattering, these gel-zeolite aggregates can also be confirmed. After the first three days, crystalline zeolite structure could be observed in amorphous gel aggregates, and the size of crystals usually between 5 to 30-unit cell dimensions. After 7 days at room temperature, crystallites could be obtained with diameter of 40 to 80 nm.

File:Crystallites obtained after 7 days at room temperature

Crystallites obtained after 7 days at room temperature

Szcshr123 (talk) 06:24, 22 February 2016 (UTC) ^[1]Reply

^ Cundy, C. S., & Cox, P. A. (2005). The hydrothermal synthesis of zeolites: Precursors, intermediates and reaction mechanism. Microporous and Mesoporous Materials, 82(1-2), 1–78. doi:10.1016/j.micromeso.2005.02.016 Coronas, J. (2010). Present and future synthesis challenges for zeolites. Chemical Engineering Journal, 156(2), 236–242. doi:10.1016/j.cej.2009.11.006 Gabelica, Z., G. Derouane, E., & Blom, N. (1983). Synthesis and characterization of pentasil type zeolites. Applied Catalysis, 5(1), 109–117. doi:10.1016/0166-9834(83)80299-1 Lowe, B. M. (1983). An equilibrium model for the crystallization of high silica zeolites. Zeolites, 3(4), 300–305. doi:10.1016/0144-2449(83)90173-2 Rimer, J. D., Kumar, M., Li, R., Lupulescu, A. I., & Oleksiak, M. D. (2014). Tailoring the physicochemical properties of zeolite catalysts. Catalysis Science & Technology, 4(11), 3762–3771. doi:10.1039/C4CY00858H Mintova, S. "Mechanism Of Zeolite A Nanocrystal Growth From Colloids At Room Temperature". Science 283.5404 (1999): 958-960. Web.

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[1] Cundy, C. S., & Cox, P. A. (2005). The hydrothermal synthesis of zeolites: Precursors, intermediates and reaction mechanism. Microporous and Mesoporous Materials, 82(1-2), 1–78. doi:10.1016/j.micromeso.2005.02.016 Coronas, J. (2010). Present and future synthesis challenges for zeolites. Chemical Engineering Journal, 156(2), 236–242. doi:10.1016/j.cej.2009.11.006 Gabelica, Z., G. Derouane, E., & Blom, N. (1983). Synthesis and characterization of pentasil type zeolites. Applied Catalysis, 5(1), 109–117. doi:10.1016/0166-9834(83)80299-1 Lowe, B. M. (1983). An equilibrium model for the crystallization of high silica zeolites. Zeolites, 3(4), 300–305. doi:10.1016/0144-2449(83)90173-2 Rimer, J. D., Kumar, M., Li, R., Lupulescu, A. I., & Oleksiak, M. D. (2014). Tailoring the physicochemical properties of zeolite catalysts. Catalysis Science & Technology, 4(11), 3762–3771. doi:10.1039/C4CY00858H Mintova, S. "Mechanism Of Zeolite A Nanocrystal Growth From Colloids At Room Temperature". Science 283.5404 (1999): 958-960. Web.

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