A Monte Carlo Simulation of the Development of Surface Roughness and Its Effect on the Dissolution Kinetics of SiO2 Aerogels

The development of surface roughness during dissolution of spherical particles is studied by the Monte Carlo method. The simulation results are used to analyze the dissolution kinetics of silicon dioxide aerogels in an aqueous solution of alkali (NaOH). The suggested model is shown to be suitable for describing the experimental dissolution curves obtained for aerogels with a small diameter of primary particles (3.5 and 2.9 nm). For aerogels with larger particles, a good agreement with the experiment can be achieved under the additional assumption that only part (p < 1) of the particle surface is originally active in dissolution; the best agreement is reached at p ≈ 0.5. In the kinetic regime of dissolution, the dissolution rate may be more than three times higher (owing to the formation of rough surfaces of primary particles with relatively large diameters, 40 atoms or more) than the rate calculated for the same parameters within the framework of the modified Delmon model, which does not make allowance for the development of roughness. Relatively small particles (with the diameter of less than 15 atoms) are dissolved before a significant roughness can be developed; therefore, the kinetic curves obtained for both models have virtually identical shapes in this case. The formation of roughness has an especially large effect on the dissolution of intermediate-size particles, whose dissolution time has the same order of magnitude as the time required for establishment of the steady-state roughness.