Synthesis and characterization of kalsilite powder using a fast sol-gel method

Nitrate replaced alkoxide and alcohol solvent omitted, a TEOS-KNO₃-Al(NO₃)₃-H₂O system turned into gel in 5~12 min with pH adjusted by aqua ammonia. Dried gel treated at 862℃, pure and homogeneous kalsilite powder was prepared with an average particle size of 8μm. The TEOS hydrolysis reaction was catalyzed by H⁺ released from aluminum nitrate hydrolysis firstly, and then promoted again by OH^- with the addition of aqua ammonia. The gelation time was shortened greatly owing to the catalysis mode of acid first and alkali second. A penta-coordination Al was detected by ²⁷Al NMR analyzing the dried aluminosilicate gel.