Effects of mechanical grinding on the physicochemical properties of silica aerogels

Abstract

Mechanical grinding is a facile method to get silica aerogels (SAs) with various particle sizes. However, the relationship between the grinding parameters and physicochemical properties is still unclear. In this study, we concentrated on the effects of grinding time and grinding speed on the physical and chemical properties of silica aerogels. The results reveal that the physicochemical properties of silica aerogels are more sensitive to the grinding speed rather than the grinding time. When the grinding speed is over 200 rpm, large particles of silica aerogels are crushed into smaller particles with obviously decreasing particle sizes and the silica skeletons of silica aerogels have collapsed. The reduction of particle sizes and the collapse of skeleton lead to an increase in both the tap density and thermal conductivity. Therein, the thermal conductivity is positively proportional to the density. Furthermore, the grinded silica aerogels powders still possess the contact angles over 135°, indicating the good hydrophobicity. All these demonstrate that the mechanical grinding has evident effects on the microstructure, density, thermal conductivity and particle sizes, which further impact the performance of silica aerogels during the practical applications. Given the expanding applications of SAs across various industries, the study serves as a valuable reference for optimizing the mechanical post-treatment of SAs, facilitating the achievement of desired particle sizes. Ultimately, this research holds great potential in diversifying the application fields of SAs in their powdered form.

Water Removal Enables High-Efficacy Synthesis of 5-Ethoxymethylfurfural and Ethyl Levulinate as Biofuel Candidates from High-Concentration Fructose

“…The water-adsorption capacities of the broken and unbroken silica gels after the fifth run were tested separately. The results shown in Figure f reveal that the water-adsorption capacities of the fresh and unbroken silica gels were comparable (0.32 g/g), whereas it decreased to 0.25 g/g for the broken gel because of the collapse of the internal pore structure and reduction in the specific surface area . Therefore, the decrease in the product yield in the successive reactions was ascribed to the breaking of the dewatering reagent.…”

“…The results shown in Figure 5f reveal that the wateradsorption capacities of the fresh and unbroken silica gels were comparable (0.32 g/g), whereas it decreased to 0.25 g/g for the broken gel because of the collapse of the internal pore structure and reduction in the specific surface area. 47 Therefore, the decrease in the product yield in the successive reactions was ascribed to the breaking of the dewatering reagent. Meanwhile, the Fourier-transform infrared (FTIR) spectra of the fresh and spent silica gel suggested that no humins were adsorbed on the silica gel during the fructose-to-EMF/EL conversion (Figure S2), which excluded the possibility of humin adsorption on the dewatering reagent for lowering the recyclability of the catalytic system.…”