INFRARED SPECTROSCOPIC INVESTIGATION IN THE MULLITE FIELD OF COMPOSITION - AL-2,(AL2-2X)O-10-X WITH GREATER-THAN-X-GREATER-THAN-0-CENTER-DOT-25(2XSI2)

The infra-red absorption of 2:1 and 3:2 mullites, and a series of heat -treated mullite starting materials of nominal composition 3Al(2)O(3) . 2SiO(2) prepared by the sol-gel process, are investigated in the spe ctral range 400-1400 cm(-1) using the KBr powder method. it is shown t hat the intensity variation of the absorption band in the spectral ran ge 1100-1200 cm(-1) provides a useful empirical scale for the determin ation of mullite compositions. This absorption feature exhibits the su perposition of three peaks, which are related to vibrations of the mul lite specific tetrahedral units [SiO4], [AlO4] and [AlO-4] with frequ ency maxima at about 1165, 1130 and 1108 cm(-1), respectively.