Chemically Strengthened Low Crystallinity Black Glass-Ceramics with High Liquidus Viscosities

Strong, black materials are needed for electronic device backs and appliance facings. While glass-ceramics have good strength and toughness, their liquidus viscosity is too low to enable economical forming of these devices by the fusion or slot draw methods. Thus, we invented a new class of low crystallinity glass-ceramics with 10–20 nm crystallites in the Fe₂O₃-TiO₂-MgO system. These materials were formed into transparent glasses and then heat treated to make black opaque glass-ceramics containing magnetite, pseudobrookite, and/or ε-Fe₂O₃. The ε-Fe₂O₃ phase exhibited extensive solid solution (ss) between Fe₂O₃ and MgTiO₃. The blackness and opacity of the ε-Fe₂O₃ glass-ceramics peaked at a ceram temperature of 750°C where the Fe²⁺ in the crystallites was maximized, resulting in peak Fe²⁺-Ti⁴⁺ charge transfer absorption. The liquidus viscosity was increased to more than 100 kPa*s by optimizing the base glass composition and minimizing the amount of crystallinity, thereby enabling fusion formability. These fusion formable glass-ceramics had strengths exceeding the best commercially available glasses after ion exchange. This work provides a new class of low crystallinity fusion formable glass-ceramics with high strength.