Effect of Silica Fume on Humidity Resistance of Sodium Silicate Binder for Core-making Process

In this study, an inorganic sand core that exhibited high tensile strength was fabricated by sodium silicate, silica sand, as well as silica fume. The effects of the silica fume on the properties of the sand core were studied. According to the optimal hardening process of sand core material, the mold was first heated to 175 °C and the compressed air purging continuously for 30 s at 150 °C. According to the results, silica fume is capable of enhancing the hardening speed, tensile strength and humidity resistance of sand core. The results of SEM analysis suggested that the humidity resistance of the sand core after the addition of silica fume was noticeably enhanced, and the quality of bonding bridge was better than that without silica fume at the identical environment humidity. The results of TG/DTG test suggested that the mass loss rate of the bonded material was the fastest at 175 °C, and the mass loss tended to be stable after 600 °C. The results of infrared spectrum analysis revealed that the types of Si–O–Si characteristic peak increased when containing silica fume, which suggested that silica fume can promote the polymerization of sodium silicate.