Innovative thermal and acoustic insulation foam by using recycled ceramic shell and expandable styrofoam (EPS) wastes

Ceramic foams were produced using ceramic shell (mullite source), an industrial solid waste from the precision casting process, and expandable styrofoams, EPS (d₅₀ < 1 mm) as pore former, envisaging thermal and acoustic insulation applications. Physical, chemical, structural properties of the selected raw materials (wastes) were characterized. The influence of the amount and morphology of the EPS powder beads on the microstructure, thermal conductivity, acoustic absorption and compressive strength of ceramic shell foams were evaluated. Batches containing well mixed ceramic shell powder (d₅₀ < 2 µm), EPS beads, in different proportions (from 10 to 70 vol%), were added as pore forming agent, and BonderPlus® (Na₂SiO₃ solution) were uniaxially pressed at 20 MPa, dried and fired in controlled conditions. The experimental results showed that homogeneous microstructures of elongated and interconnected pores with sizes between 115 and 1200 µm can be obtained. These connections exhibit a significant impact on the thermal/sound absorption properties, as a consequence of the interaction between air molecules within the pores through the passage of the thermal/sound wave. Ceramic shell foams (containing 70 vol% of EPS powder beads) featured porosities up to 77%, thermal conductivity of 0.061 W/mK, sound absorption coefficient of ∼0.9 (3 kHz), and excellent compressive strength ∼5.4 MPa. In addition, the use of ceramic shells wastes for the manufacture of acoustic and thermal insulators with suitable microstructural characteristics is a great sustainable opportunity, since with the use of this refractory waste, is possible to avoid the release to the atmosphere of about 3.1 kg of CO₂ per kg of manufactured material.