Diatomite-based porous ceramics with high apparent porosity: Pore structure modification using calcium carbonate

High apparent porosity ceramics have a wide range of applications in chemical, environmental, and automotive sectors as reactors, absorbers, and cleaning devices due to their large specific surface area and excellent permeability for fluids. In this paper, porous ceramics with high apparent porosity were successfully fabricated from diatomite. Importantly, the pore structure of this ceramic was further modified by calcium carbonate (CaCO₃). The results showed that the pores of the modified ceramic were in the space between the loose particles, and the position originally occupied by the calcium carbonate. An addition of 0–50 wt% CaCO₃ improved the apparent porosity up to 67.53% and enlarged the pore size from ~0.7 to ~26.6 µm due to the decomposition of CaCO₃, generating new pores and further transforming isolated pores to interconnected ones. The crystalline phase composition of the ceramic was found to change from cristobalite to the combination of cristobalite, wollastonite and larnite with the addition of CaCO₃. The results also showed that an addition of more than 40 wt% of CaCO₃ did not give much further increase in the apparent porosity due to the densification process. The modified ceramics were found to have a good mechanical strength; the ceramic with the highest apparent porosity (67.53%) had a compressive strength of 7.33 ± 0.28 MPa.