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

Abstract

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.