Effect of Carbon Dioxide Temperature on Adhesion of Na 2 SiO 3 Binder to Silica Sand Surface: Comparison of Experimental Data with Molecular Dynamics Simulations

The effects of different CO 2 gas blowing temperatures on the strength and gel structure of sodium silicate binder system were studied. Through the experimental study, it is found that the increase in blowing gas temperature has a significant effect on the bond strength of CO 2 -hardened Na 2 SiO 3 sodium glass sand mold. The blowing gas temperature of CO 2 is closely related to the diffusion coefficient of CO 2 at different temperatures. By thermogravimetric analysis of the sample weight change from room temperature to 80 °C combined with SEM results, the primary reason for the increase in tensile strength of sand mold was the acceleration of binder gel rate due to the increase in temperature. Through SEM observation, it was found that the adhesive gel obtained at appropriate temperature was denser and the bond bridge was stronger. The above results show that the increase in tensile strength of sand mold is due to the formation of more uniform, non-lamellar crystals by silicic acid gel at the appropriate temperature, and the acceleration of water loss in the hardening process of sand mold, which enhances the strength of the binder. But too high temperature will lead to violent reaction, dendritic crystal to lamellar crystal transformation, and tensile strength gradually decreased. Finally, based on molecular dynamics simulation, it was found that the diffusion coefficient of CO 2 in sodium silicate binder system was greatly affected by different blowing temperature, which confirmed the effect of temperature on gel quality. This study provides an important theoretical basis for improving the casting process of CO 2 -hardened Na 2 SiO 3 sand.