In this study, the effect of different amounts of silica fume additive on the bonding strength of sodium silicate binder, over time, was studied. It has been concluded that silica fume can improve the bonding strength and humidity resistance of sodium silicate bonded sand. The microscopic morphology of the adhesive film was examined by scanning electron microscopy, and the functional group changes of the polymerised adhesive were analysed by Fourier-transform infrared (FT-IR) spectroscopy. In addition, the hardening mechanism, between the sodium silicate binder and silica fume on the sand surface, and the hydration reaction mechanism, after polymerisation, were investigated using first-principles calculations in the CASTEP program based on density functional theory (DFT). It was found that silica fume enhances the binding energy of the binder by enhancing the degree of polymerisation, while subsequent hydration of the hardened binder is a spontaneous reaction. After the sodium silicate binder hardens, the water molecules are adsorbed by unpolymerised –OH and Na⁺; these water molecules destroy the -Si-O-Si bonds to depolymerise the sodium silicate bonded network. This research provides important theoretical support for improving or even eliminating the hygroscopic properties of sodium-silicate-bonded sand during casting.

在这项研究中，随着时间的推移，研究了不同数量的硅粉添加剂对硅酸钠粘合剂粘结强度的影响。已经得出结论，硅粉可以改善硅酸钠粘结砂的粘结强度和耐湿性。通过扫描电子显微镜检查粘合剂膜的微观形态，并通过傅立叶变换红外（FT-IR）光谱分析聚合的粘合剂的官能团变化。此外，使用CASTEP程序中基于密度泛函理论（DFT）的第一原理计算方法，研究了砂表面上的硅酸钠粘合剂和硅粉之间的硬化机理以及聚合后的水合反应机理。发现硅粉通过增强聚合度来增强粘合剂的结合能，而随后硬化的粘合剂的水合是自发反应。硅酸钠粘合剂硬化后，水分子被未聚合的-OH和Na吸附⁺ ; 这些水分子破坏了-Si-O-Si键，从而解聚了硅酸钠键网络。该研究为改善甚至消除铸造过程中钠硅酸盐粘结砂的吸湿性提供了重要的理论支持。