Effects of Reynolds and Froude dimensionless numbers on geometry of silica powders: simultaneous optimization using overall evaluation criteria technique

Abstract

Specific surface area, mean pore diameter, and pore volume are among the most important geometrical properties, which can be controlled by the sol-gel mixing parameters during the silica synthesis. In this paper, these geometrical parameters were simultaneously optimized by overall evaluation criteria (OEC) technique in the Taguchi method. The optimum conditions were obtained at Reynolds dimensionless number (Re) of 250,000, Froude dimensionless number (Fr) of 0.034, acid dripping time (θ) of 60 min and acid normality (N) of 8, which resulted in BET specific surface area, BJH pore diameter and pore volume of 473.12 m2g−1, 5.21 nm, and 0.861 m3g−1, respectively. Analysis of variance demonstrated that only Re had a significant effect on the OEC values with 76.3% of contribution. The samples were characterized by SEM, BET–BJH analyses. Morphological observations confirmed the considerable effects of N, Re, and Fr on geometrical properties such as particle shapes, N2 adsorption–desorption isotherms and pore size distribution.