Dehydroxylation and the Vibrational Spectroscopy of Aluminum (Oxo)Hydroxides Using Infrared Emission Spectroscopy. Part III: Diaspore

Abstract

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 °C. Dehydroxylation shows that diaspore loses 15% of its weight upon dehydroxylation. The Mn-substituted diaspore shows major endotherms at 620 and 649 °C with a broad endotherm at 539 °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 were 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.

Comparison of Raman spectra in characterizing gibbsite, bayerite, diaspore and boehmite

“…Infrared investigation on diaspore has shown differences in band position. Farmer 14 reported two bands at 2994 and 2915 cm 1 , which are similar to the 2985 and 2910 cm 1 obtained by Van der Marel and Beutelspacher, 1 but differed from the 3365, 3284, 3095 and 2938 cm 1 observed by Frost et al 10 The differences may be due to the variation of the distribution of surface hydroxyl groups in the natural samples. Band overlap occurs in the Raman spectra of diaspore and band component analysis resolves the bands as shown in Table 1 and Fig.…”

“…Raman bands between 2800 and 3700 cm 1 are characteristic of the (OH) stretching modes. 2,3,8,10,14,18 The low-wavenumber region between 200 and 1200 cm 1 consists of υ(OH) and (OH) modes (Table 1) showed infrared absorption bands at 3617, 3520, 3428 and 3380 cm 1 .…”

“…Previous work using FT-Raman spectroscopy has confirmed that the broad bands are attributed to surface hydroxyl groups. 27 Frost et al,8,10 who characterized hydroxyl stretching bands at 3413, 3283, 3096 and 2997 cm 1 , also reported broad bands. Recent work on FT-infrared spectroscopy further confirmed that a shoulder band at 3494 cm 1 and a broad band at 1640 cm 1 were assigned to the stretching and bending modes of adsorbed water in addition to two distinct (OH) stretching modes at 3292 and 3097 cm 1 .…”

“…By combining the Raman and infrared spectra, Kiss et al 17 determined the structure of boehmite. The most recent work of Frost et al 3,8,10 has contributed to the understanding of the molecular structure of these aluminium oxohydroxides using infrared emission and Raman spectroscopic techniques for mineral characterization and phase transformation. In this paper we report the characterization of alumina phases of gibbsite, bayerite, diaspore and boehmite based on Fourier transform (FT) Raman spectroscopy in order to provide information for rapid spectroscopic on-line analysis of the mixed alumina phases of bauxite.…”

¿Nano o micro polvos de alúmina? Una elección antes de la sinterización

“…Homogeneous precipitation provides emulsions formed by nanoparticles that are very stable in time, in fact, it has been verified that once the precipitation step is finished, the suspension keeps stable by at least during six months. The obtained aluminium hydrate could correspond to gibbsite, the reaction takes place at room temperature and according to the data gathered in the published bibliography (16). The H particles are then highly reactive and have a great tendency to agglomerate, even during gel aging.…”