Dehydroxylation and the vibrational spectroscopy of aluminum (oxo)hydroxides using infrared emission spectroscopy. Part III: Diaspore

Dehydroxylation of diaspore has been followed by a combination of differential thermal analysis (DTA) and infrared emission spectroscopy (IES). The DTA endotherm of diaspore is not simple, and two inflections are observed at 505 and 531 degrees C. Dehydroxylation shows that diaspore loses 15% of its weight upon dehydroxylation. The Mn-substituted diaspore shows major endotherms at 620 and 649 degrees C with a broad endotherm at 539 degrees C. Infrared absorption bands of diaspore were observed at 3365, 3284, and 3095 cm(-1) in the hydroxyl stretching region and at 911, 755, 706, 668, 649, 570, and 544 cm(-1) in the low-frequency region. Infrared emission bands were observed at 3239 and 2958 cm(-1) in the hydroxyl stretching region. Low-frequency infrared emission bands in agreement with the absorption bands mere observed at around 916, 752, 706, 668, 649, 570, and 544 cm(-1). The variation of intensity of the hydroxyl stretching frequencies with temperature follows a pattern similar to that for the DTA curves.