The proportion of amorphous or glassy material in a series of fly ashes has been evaluatedby X-ray powder diffraction (XRD) using the Rietveld-based SIROQUANT softwarepackage.Several different sample preparation and processing methods were investigated,including XRD analysis of samples spiked with known masses of synthetic corundum andzinc oxide as well as techniques based on analysing the raw or unspiked fly ash directlyusing the SIROQUANT process.In the latter case,two different poorly crystallisedsilicate mineral patterns,metakaolin and tridymite,were used in the SIROQUANTprocessing of the raw ash XRD data to represent the glassy constituents.The results of thedifferent methods based on XRD of spiked samples were found to be mutually consistent,and also consistent with other published data for an international reference fly ash sample.SIROQUANT analysis of the unspiked fly ashes gave similar results,although differentpoorly crystallised silicate reference patterns seem to be more suited for ashes fromAustralian and North American sources.Calculations based on subtracting the inferred chemistry of the crystalline minerals in thefly ashes from the total fly ash chemistry were also investigated as a basis for estimatingthe overall chemical composition of the glass fraction in the fly ashes.The results indicatethat ashes derived from lower-rank coals have different glass compositions to thosederived from higher-rank (bituminous) materials.These different glass compositions mayalso be related to other ash properties,such as particle density and particle surface area,and have implications for ash disposal and utilisation processes.
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