title: In situ ultrasonic diagnostic of zeolite X crystallization with novel (hierarchical) morphology from coal fly ash.
abstract: In this paper the applicability of an in situ ultrasonic diagnostic technique in understanding the formation process of zeolite X with a novel morphology was demonstrated. The complexity of the starting fly ash feedstock demands independent studies of the formation process for each type of zeolite since it is not known whether the crystallization mechanism will always follow the expected reaction pathway. The hierarchical zeolite X was noted to follow a solution phase-mediated crystallization mechanism which differs from earlier studies of the zeolite A formation process from unaged, clear solution extracted from fused fly ash. The use of the in situ ultrasonic monitoring system provided sufficient data points which enabled closer estimation of the time of transition from the nucleation to the crystal growth step. In order to evaluate the effect of temperature on the resulting in situ attenuation signal, synthesis at three higher temperatures (80, 90 and 94 °C) was investigated. It was shown, by the shift of the US-attenuation signal, that faster crystallization occurred when higher temperatures were applied. The novel hierarchical zeolite X was comprised of intergrown disc-like platelets. It was further observed that there was preferential growth of the disc-shaped platelets of zeolite X crystals in one dimension as the synthesis temperature was increased, allowing tailoring of the hierarchical morphology.
authors.affiliation: Environmental and Nano Science Research Group, Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa. Electronic address: nickmulei1@yahoo.com.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Musyoka
authors.forename: Leslie F
authors.initials: LF
authors.lastname: Petrik
authors.forename: Eric
authors.initials: E
authors.lastname: Hums
authors.forename: Hasan
authors.initials: H
authors.lastname: Baser
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Schwieger
mesh_terms: D060729:Coal Ash / Q000737:chemistry* / Q000528:radiation effects; D003460:Crystallization / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008422:Materials Testing / Q000379:methods*; D014463:Ultrasonography / Q000379:methods*; D017641:Zeolites / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D060729:Coal Ash; D017641:Zeolites
keywords: Fly ash; Hierarchical zeolite X; In situ ultrasonic