Nanosized cordierite–sapphirine–spinel glass-ceramics from natural raw materials

Inexpensive nanosized sintered cordierite glass-ceramic was prepared from quartz sand, kaolin, and magnesite. The addition of nucleation catalysts, such as TiO2, Cr2O3, and admixed TiO2–Cr2O3, was tested in the cordierite base glass. Cordierite, sapphirine, spinel, magnesium aluminium silicate, and cristobalite were developed using the crystallisation process. These glass-ceramics have ultra-fine grain sizes with nanorounded crystals measuring less than 200 nm, particularly in the Cr2O3-containing samples. Due to its different crystalline phases, the new glass-ceramics varied in hardness from 6374 to 8139 MPa and had coefficients of thermal expansion (CTE) from 0.83 to 6.89×10−6 °C−1. In glass-ceramic samples, the spinel and sapphirine imparted high CTE (from 6.89 to 5.31×10−6 °C−1) and hardness values (from 8139 to 7894 MPa), whereas cordierite provided lower CTE (from 0.83 to 2.66×10−6 °C−1) and hardness values (from 7453 to 6374 MPa).