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Effect of Milling Time on the Physical and Mechanical Properties of Celsian-Mullite Composites Synthesized from Coal Fly Ash

Published online by Cambridge University Press:  14 February 2012

Jorge López-Cuevas
Affiliation:
Cinvestav-Saltillo, Carr. Saltillo-Monterrey, km 13.5, Ramos Arizpe, Coahuila, México, 25900
David Long-González
Affiliation:
RHI REFMEX, S.A. de C.V., Carr. Saltillo-Monterrey, Km. 9, Ramos Arizpe, Coahuila, México, 25900
Carlos A. Gutiérrez-Chavarría
Affiliation:
Cinvestav-Saltillo, Carr. Saltillo-Monterrey, km 13.5, Ramos Arizpe, Coahuila, México, 25900
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Abstract

Four Celsian (Ba0.75Sr0.25Al2Si2O8)/Mullite (Al6Si2O13) composites, with potential structural applications at high temperatures, are synthesized from coal fly ash (byproduct of a Mexican coal-burning power plant, constituted mainly by SiO2 and Al2O3). Nominal Celsian/Mullite weight ratios studied are 80/20, 60/40, 40/60 and 20/80. Mullite is synthesized separately at 1600ºC/2h and then mixed with a Celsian precursor mixture previously calcined at 900°C/5h. During this process the Celsian phase is formed by a solid state reaction at 1100-1400ºC/5h. Prior to this, the reacting mixture is milled in a planetary mill during 1 or 2h and then compacted by uniaxial and cold isostatic pressing. The microstructure and phase composition of the synthesized composites are characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS). Their dynamic Young’s modulus is measured by an ultrasonic technique, and their mechanical strength is evaluated from flexural tests carried out at room temperature. The expected phases are obtained in all cases, although with some differences with respect to their expected relative proportions, according to the studied nominal compositions. In general, the longest milling time employed produced samples with the largest degree of crystallinity and density, as well as with the best microstructural characteristics and mechanical properties.

Type
Articles
Copyright
Copyright © Materials Research Society 2012

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