Properties of Durable Mullite Bodies Manufactured from Waste Clay-Diatomite

Durable mullite bodies have been fabricated using diatom frustules from diatomite powder as the Si source and Al-nitrate as the Al precursor, resulting in fibrous pore morphology. The hard mullite ceramics prepared by mold pressing without additives showed high compressive strength (up to 133 MPa when sintered at 1500 °C). The diatomite-nitrate samples were sintered at three temperatures (1300, 1400, and 1500 °C) for 2 hours. XRPD analysis of the sintered samples showed that the crystalline mineral phases mainly comprise mullite, cristobalite, and corundum. SEM results indicate the presence of rod-like mullite grains measuring 5 µm in length and 500 nm in diameter (aspect ratio 1:10). XRPD analysis of the samples sintered at 1300 °C demonstrated good thermo-mechanical stability and the formation of new hard phases (mullite, corundum, and cristobalite), making the analyzed diatomaceous earth suitable to produce various types of ceramic, construction, and thermal insulating materials.