DFT Investigation of the Mechanism and Chemical Kinetics for the Gelation of Colloidal Silica

摘要

The mechanism for the gelation reaction of colloidal silica, Si(OH)_4 +Si(OH)_3 (O)~- → Si_2O_8H_5~- + H_2O, by an anionic pathway was investigated using density functional theory(DFT). Using transition state theory, the rate constants were obtained by analyzing the potential energy surface at the reactants, saddle point, and the products. In addition, reaction rate constants were investigated in the presence of ammonium chloride (NH_4Cl) and sodium chloride (NaCl). These salts act as catalysts to induce gelation by destabilizing the double layer of colloidal silica to allow for Van der Waal interactions. Furthermore, it was observed that ammonium chloride plays an important role by initiating a hydride transfer allowing the reaction to proceed from the second transition state to the final product.