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).