Correlations between porosity, thermal conductivity, and mechanical strength in bi-layered ceramics with varying carbon black contents

This paper focuses on the correlations between porosity, thermal conductivity, and mechanical strength in bi-layered ceramics with varying carbon black (CB) contents. Dense/porous bi-layered ceramics were synthesized via a solid-state reaction using feldspar, silica, and kaolinite powders, with CB incorporated into the porous bottom layer at 1–5 wt.% as a pore-forming agent, while the dense top layer remained CB-free. All specimens were fabricated under identical processing conditions, which involved uniaxial pressing at 20 MPa and sintering at 1175 ℃ for 3 h. A non-linear relationship was established between the CB content and the material properties. The optimum composition, 3 wt.% CB, exhibited the highest porosity (9.16%), the lowest thermal conductivity (1.483 W/m·K), and the maximum flexural strength (49.73 MPa), thus representing the best compromise between insulation efficiency and mechanical strength. At lower CB contents (1–2 wt.%), insufficient pore development limited the reduction in thermal conductivity, whereas excessive CB loadings (4–5 wt.%) produced diminished porosity and corresponding decreases in strength. These results highlight that controlled CB burnout during sintering governs pore evolution in a manner that optimizes phonon scattering and stress redistribution. Overall, this study demonstrates that precise control of pore-former content is critical to tailor multifunctional properties in bi-layered ceramics and establishes a design guideline for developing lightweight ceramic systems with superior thermal and structural performances.