Effect of zirconia as inorganic binder on molds for precision casting

Sand-casting molds suffer from surface defects and low strength. An organic–inorganic binder conversion process, wherein an organic binder is converted to an inorganic binder, has been proposed to increase the application temperature of the sand-casting mold and simplify the manufacturing process for precision casting. However, the usable temperature of the typical SiO₂–Na₂O binder system is limited to approximately 1000°C owing to the low liquefaction temperature of the compound. The resulting glass phase (Na₂SiO₃) exhibits low viscosity, and the casting of large objects results in low strength. Therefore, in this study, we propose a SiO₂–Na₂O–ZrO₂ ternary inorganic binder system; the addition of zirconia (ZrO₂) into sodium silicate (Na₂SiO₃) as an inorganic binder was expected to increase the operating temperature of the mold and improve its mechanical properties. The results confirmed that the addition of ZrO₂ improved the mechanical properties by preventing the formation of Na₂SiO₃. In addition, a higher sintering temperature corresponded to smaller and larger amounts of Na₂SiO₃ and Na₂ZrSiO₅, respectively, and thus a higher strength. Therefore, we expect our developed ternary inorganic binder system to be highly advantageous for producing molds for high-temperature and precision casting.