Controlled crystallization and characterization of cordierite glass-ceramics for magnetic memory disk substrate

Glass-ceramics containing cordierite (2MgO-2Al₂O₃-5SiO₂) as a crystal phase based on the glasses in the system MgO-Al₂O₃-SiO₂ were investigated for the application to magnetic disk substrate for higher storage capacity. Parent glasses were prepared with CeO₂ addition as a flux and were crystallized by a controlled 2-step heat treatment The maximum nucleation and crystal growth rates were 2.4 × 10⁹/mm³ · hr at 800 °C and 0.3 m/hr at 915°C respectively. Only - cordierite was precipitated after heat-treatment. After nucleation at 800 °C for 5 hours prior to crystallization at 915 °C for 1 hour, the resulting crystal volume fraction and crystal size were 17.6% and 0.3 m, respectively. Heat-treated specimens through the above condition showed the optimum properties for magnetic memory disk substrates as follows.; Bending strength of 192 MPa, Vickers hardness of 642.1 kg/mm², thermal expansion coefficient of 39 × 10^–7/K and surface roughness of 27 Å.