Preparation and characterization of foamed ceramics from coal bottom ash for construction insulation materials

Abstract

Foamed ceramic is a novel lightweight wall material combining high strength, low density, and excellent thermal insulation. This study used coal bottom ash (CBA) to fabricate microporous foamed ceramics by the high-temperature foaming method. The CBA content and heating rate effects on the bulk density, compressive strength, pore structure, and phase components of foamed ceramics were systematically investigated. The results demonstrate that using CBA in foamed ceramics can effectively improve the green body foaming capacity. With the increased CBA content, the bulk density of foamed ceramics dropped, while the average pore size and shape factor increased, jointly reducing the compressive strength. Meanwhile, the quartz phase content decreased, and the mullite phase appeared gradually. The transition of the main crystalline phase from MgAl₂O₄ to Mg_0.7Fe_0.23Al_1.97O₄ with the increased CBA content gave rise to a change in the color of the foamed ceramic. The elevation in the heating rate can improve the foaming ability of the green body, contributing to increased porosity. However, the rapid heating rate of 10 °C/min results in an uneven pore size distribution in the foamed ceramics containing more than 70 wt % CBA. It increases the temperature difference in the sample, promoting a stratified distribution of pore size in samples with a CBA content of less than 30 wt %.