Effect of mechanochemical treatment on the crystallization behaviour of diphasic mullite gel

The effect of mechanochemical treatment on the structure and crystallizatio n behaviour of diphasic mullite gel was investigated. The structural differ ences caused by mechanochemical treatment in diphasic gel were characterize d by Al-27 and Si-29 MAS-NMR, XRD, DTA-TG and FT-IR. These investigations s how that the crystallization process in this system is affected by the stru ctural changes caused by grinding. Grinding for 20h changed a diphasic syst em containing discrete octahedral Al-O units (8 ppm) and silica units (-111 ppm) to a more homogeneous system containing tetrahedral, "pentahedral" (3 0 ppm) and octahedral alumina, and a strong Si-29 resonance at -83 ppm (app roximate to 70% of the total Si) associated with aluminosilicate units. The ground gel converts to mullite via the spinel-phase at 1150-1200 degrees C . Mechanochemical treatment thus converts the diphasic type II gel precurso r into a more homogeneous type III gel precursor, as reflected by its therm al behaviour. (C) 1998 Elsevier Science Limited and Techna S.r.l. All right s reserved.