Semi-Quantitative X-Ray Diffraction Analysis of Fly Ash by the Reference Intensity Ratio Method
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SEMI-QUANTITATIVE X-RAY DIFFRACTION ANALYSIS OF FLY ASH BY THE REFERENCE INTENSITY RATIO METHOD GREGORY J. McCARTHY and A. THEDCHANAMOORTHY Department of Chemistry, North Dakota State University, Fargo ND 58105 Received 28 November, 1988; refereed ABSTRACT
A protocol for relatively inexpensive and rapid semi-quantitative x-ray diffraction analysis of fly ash mineralogy by the Reference Intensity Ratio (RIR) method is described. RIR's for the common crystalline phases in fly ashes derived from low rank and bituminous coal are given. The method is semi-quantitative for some phases because of unavoidable overlaps of the stronger peaks suitable for quantitation. Use of the protocol is illustrated with the four fly ash Standard Reference Materials supplied by the National Institute of Standards and Technology. Recommendations for implementation of this protocol in other laboratories and for improvements in quantitation of fly ash mineralogy are given. INTRODUCTION In the last volume in this series, qualitative x-ray diffraction (XRD) determination of fly ash mineralogy and the crystal chemistry of the common crystalline phases in fly ash were described [1]. Ongoing research in our laboratory requires knowing the amounts of crystalline phases in a wide variety of fly ashes. Because of the very fine grain size and micrometer-scale inhomogeneity of fly ash, x-ray diffraction is the only candidate for meeting these objectives. The analysis is not routine for two principal reasons: (1) the crystalline phases in fly ash are typically present at only the 1-10 wt% levels in this dominantly glassy material, and (2) the diffractograms are often very complex, with overlapping peaks from as many as a dozen crystalline phases. Our requirements for analytical XRD were that it be relatively inexpensive, simple enough for students to use, and applicable to all classes of fly ashes. A protocol for semi-quantitative XRD by the Reference Intensity Ratio (RIR) method [2-4] was recently developed to meet these requirements [5]. The protocol makes use of routinely available x-ray diffraction equipment and does not require advanced knowledge of computer automation, data reduction or crystal structures. The first step in the protocol is determination of ratios of XRD intensities of a strong peak of each crystalline phase to that of the strongest peak of rutile (TiO2 ), as described in references [1,5-7]. In this paper, a summary of the protocol and the RIR's necessary to analyze fly ash mineralogy using the RIR method are presented. The preparations of standards for each crystalline phase in fly ash, procedures for the determination of RIR's, error analyses applied to precision and accuracy, and limits of detection in fly ashes are detailed in a separate paper [5]. As an example of the use and limitations of this protocol, the mineralogies of the four fly ash Standard Reference Materials available from the National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards), previously described in reference [1], a
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