The Contribution of Molecular Diffusion in Silica Coating and Chemical Reaction in the Overall Rate of Reaction of Aluminum Hydroxide with Fluosilicic Acid

The kinetic of the heterogeneous chemical reaction of aluminum hydroxide and fluosilicic acid was studied. It was found that the diffusion of the reactants through the porous silica coating to the aluminum hydroxide surface and the interfacial chemical reaction between the diffusing reactant and aluminum hydroxide platelets control the overall reaction rate. These two phenomena were studied and their contributions to the overall reaction rate were derived using experimental data. By combining these terms a relation for the overall reaction rate was obtained. The activation energy of the chemical reaction was calculated to be 12 kcal/mol and the activation energy of the diffusion into the silica coating was found as 28 kcal/mol. A numerical procedure was adjusted to determine the variation of the specific surface area of un-reacted core, its average particle size and the specific surface area for mass transfer