Characterizing crystalline phase transitions in zeolitization of coal fly ash using focused ion beam-scanning electron microscopy

Abstract

Coal fly ash (CFA) accounts for a significant portion of coal ash, which is a by-product of thermal power plants. Herein, CFA collected in Korea was used to synthesize a zeolitic material via fusion and hydrothermal synthesis. The crystallographic characteristics of CFA, alkali-fused CFA, and synthesized zeolitic material from CFA (SZC) were investigated via cross-section analysis using focused ion beam-scanning electron microscopy (FIB-SEM) with energy-dispersive X-ray spectroscopy (EDS), which has not been attempted in previous studies. Cross-section milling and EDS line scan were performed using FIB-SEM to develop the existing analysis methods, focusing on the crystalline phase and chemical composition of the surface of synthetic materials. Following the alkali treatment, the amorphous CFA exhibited a biphase comprising both crystalline and amorphous phases. After the synthesis process, both the surface and the interior exhibited a uniform Na-A zeolite crystalline structure with sharp-edged cubes. Furthermore, the SZC comprised crystals of Na-A zeolite with a uniform structure and a Si/Al molar ratio of approximately 1.4. © 2022