Synthesis of SiO2-Al2O3 Aerogel Powder via Low-Temperature Alkaline Fusion Activation of Potassium Feldspar

This study proposes a process combining alkali-activated potassium feldspar, acid leaching, and sol–gel coupling with supercritical drying to prepare high-performance silica–alumina composite aerogel. The optimal parameters for potassium feldspar alkali-melt activation are a calcination temperature of 350 °C, mass ratio of potassium feldspar to sodium hydroxide of 1:1.2, and calcination time of 120 min, achieving an acid-leaching efficiency of 97.3% for the activated potassium feldspar. The acid leachate, using propylene oxide as a gelling promoter, was processed through aging, solvent exchange, and supercritical drying to yield SiO2-Al2O3 aerogel with typical three-dimensional nanoporous network structure. EDS spectroscopy revealed that the spatial distributions of aluminum and silicon elements were highly coincident and uniformly dispersed. XPS and FTIR further confirmed the formation of Si-O-Al bonds, indicating that aluminum atoms were successfully incorporated into the silico-aluminate tetrahedral network, constructing silicon–aluminum composite framework. The SiO2-Al2O3 aerogel exhibits specific surface area of 660.841 m2/g and a pore volume of 1.321 cm3/g. Its mass loss within the 0–1000 °C range is only 9.55%, far lower than the 28% mass loss of pure aluminum oxide aerogel, indicating that the silicon–aluminum composite structure effectively suppresses high-temperature phase transitions and framework collapse.