Quantitative XRD analysis of coal combustion by-products by the Rietveld method. Testing with standard mixtures

Abstract

Quantitative XRD (QXRD) analysis of coal combustion by-products (CCBs) and their hydration products is not straightforward. CCBs typically include large numbers of crystalline phases and substantial amorphous content. Many CCB phases have varying levels of crystalline order and solid solution. When prepared as XRD specimens, a number exhibit strong preferred orientation, and with quite variable linear absorption coefficients, have the potential for microabsorption problems in mixtures. The conventional internal standard QXRD methods have two problems when applied to CCBs: (1) finding representative standards for analyte phases, and (2) finding sufficiently intense, non-overlapped, analytical peaks. The Rietveld QXRD (RQXRD) method, however, appears to be capable of modeling each of the sample, specimen and instrumental problems. This study focuses on establishing a level of confidence in the ability of RQXRD to handle each of the sample and specimen problems characteristic of CCBs utilizing test mixtures having known amounts of crystalline and amorphous phases.