The Internal Structure of a Low-Calcium Fly Ash

Abstract

ABSTRACTA low calcium fly ash, rich in iron oxide, was subjected to shaking in 1% HF for up to 20 hours, and measurements were made at intervals of the following parameters: total weight loss, composition of the dissolved material, x-ray peak intensities of crystalline components and residual glass, and internal structures present within the fly ash spheres as revealed by the progressive dissolution treatments. The same fly ash was subjected to similar but longer-term treatment with simulated cement pore solution (potassium and sodium hydroxide). The compositions of the magnetically separated fraction and the non-magnetic residue were also separately determined. As a result of these studies, it was suggested that: (a) the time at which all of the potassium is dissolved might be used as an indicator of the completion of glass dissolution; (b) the position of the x-ray band for residual (more resistant ) glass shifts to higher 2Θ angle before the glass is completely dissolved; (c) in this fly ash, as determined by chemical analysis, all of the iron is in the magnetically-separable fraction, a feature that permitted estimation of the overall glass composition; and (d) this fly ash contains certain poorly understood components including silica-rich spheres, small spheres yielding EDXA signals only for iron, and “patches” of silica and alumina bearing material not of mullite composition, but all of which are highly resistant to HF dissolution.