Recycling coal overburden waste to fabricate functionally graded SiC foam with gradient microstructure via one step thermo-foaming process

Abstract

An economical and efficient thermo-foaming method, coupled with an in-situ reaction bonding technique, was employed to produce mullite-bonded functionally graded silicon carbide (SiC) foams with gradient microstructures using coal mine overburden waste (CMW). The foaming process utilized sucrose dehydration with sulphuric acid, allowing for tailored porosity in SiC foams. Mullite bonding material was in situ developed during sintering, facilitated by silica and alumina from CMW, promoting mullite phase formation. Alumina incorporation further enhanced mullitization. The use of CMW as a low-cost precursor for mullite conversion facilitated SiC particle bonding through mullite, reducing sintering temperature and overall production cost. Varied sucrose content and sintering temperature influenced foaming behavior, porosity, microstructural gradient, and mechanical properties. Mullitization process, reaction bonding behavior, and mechanical properties were analyzed based on CMW and alumina content, and sintering temperature. The resulting SiC foams exhibited bulk density and porosity in the range of 0.6–1.2 g/cm3, 60–80 % respectively. This study introduces an eco-friendly approach for repurposing CMW waste and cost reduction in SiC foam manufacturing.