Fe3+离子对硅酸体系聚合行为的影响

向不含金属离子的硅酸体系中加入Fe3+离子，研究了体系胶凝时间、溶胶粒径、凝胶比表面积、官能团及热稳定性的变化. 结果表明，加入Fe3+降低了体系pH值；初始pH≤2时，Fe3+起促凝作用，初始pH≥3时，Fe3+起缓凝作用. 初始pH=2时，放置24 h溶胶粒径随Fe3+浓度增加而增大，凝胶比表面积逐渐增大，Fe3+浓度为0.03 mol/L时粒径为444 nm，比表面积为1500 m2/g；初始pH=3时，放置24 h溶胶粒径随Fe3+浓度增加呈先增大后减小的趋势，最大粒径达379 nm，而凝胶比表面积逐渐减小，Fe3+浓度为0.03 mol/L时为81 m2/g. Fe3+引起聚硅酸网络结构变形，导致凝胶部分吸收峰强度减弱和移位及凝胶结合水减少和晶化转变峰变弱.

Effect of Fe3+ Ion on Polymerization Behavior of Silicic Acid System

After adding different concentrations of Fe3+ ion to silicic acid without metallic ions, the gelation time, average diameter of colloidal particles, specific surface area of gels, functional groups and thermal stability of the systems were investigated. The results showed that the pH value was decreased by Fe3+ addition. For the system with initial pH≤2, the polymerization reaction was accelerated by Fe3+. For initial pH≥3, the reaction was prevented by Fe3+. For initial pH=2, the diameter of colloidal particles set for 24 h and specific surface area of gels increased with increasing of Fe3+. For 0.03 mol/L Fe3+ addition, the diameter of colloidal particles was 444 nm and the specific surface area of gel particles 1500 m2/g. For initial pH=3, the diameter of colloidal particles increased first and then decreased with increasing of Fe3+, and the specific surface area of gel particles decreased. The largest diameter of colloidal particles was 379 nm. And for 0.03 mol/L Fe3+ addition, the specific surface area of gel particles was 81 m2/g. Due to network deformation of polysilicate induced by Fe3+, the intensity of some infrared peaks of gels weakened, their position shifted, the bound water with gel decreased, and the intensity of crystallization peak weakened.