One-step microwave preparation of phosphoric acid activated foams from spontaneous combustion coal gangue

Abstract

In this work, the phosphoric acid activated foams from spontaneous combustion coal gangue were successfully fabricated using a simple and fast one-step microwave-assisted method. The physico-mechanical, thermal insulation properties, and microstructure of foam specimens prepared with varying molar concentrations of the activating solution (10–14 M), liquid-to-solid (L/S) ratios (0.425–0.525), microwave power (600–1000 W), microwave irradiation time (7.5–12.5 min), and post-curing temperatures (25–115 °C) were investigated. X-ray microfocus computed tomography (micro CT) and scanning electron microscopy (SEM) results showed that the homogeneous porous structure of the foam specimens was developed at higher H3PO4 concentrations when using 1000 W power of the microwave oven for 10 min. The optimized phosphoric acid-activated foams from spontaneous combustion CG exhibit a thermal conductivity of 0.133 W/mK and an unconfined compressive strength of 10.2 MPa, making them comparable to or better than traditional foam materials derived from CG. The obtained results contribute to further advancing the application of phosphoric acid activated CG foams in the fields of building thermal insulation and other lightweight high-temperature insulating materials. © 2025 The Korean Society of Industrial and Engineering Chemistry