Thermoanalytical examination under quasi-isothermal—quasi-isobaric conditions

The infrared absorption, infrared emission, and Fourier transform (FT)-Raman spectra of a series of gibbsites well defined by X-ray diffraction have been obtained Hydroxyl stretching frequencies were found at ~ 3670, 3620, 3524, 3452, 3395, 3375, and ~ 3300 cm-1 Hydroxyl deformation vibrations were observed at 1059, 1023, 969, 938, and 915 cm-1 Hydroxyl stretching bands were observed in the Raman spectra at 3524, 3436, and 3365 cm-1 and correspond well with the three infrared bands These bands are both Raman and infrared active The bands at ~ 3670, 3620, and 3395 cm-1 are infrared active only The hydroxyl stretching frequencies show a pronounced blue shift, while the hydroxyl deformation modes show a pronounced red shift Infrared absorption bands were observed at 3413, 3283, and 3096 cm-1 for the hydroxyl stretching frequencies and at 1024, 969, and 914 cm-1 for the hydroxyl deformation frequencies Low-frequency infrared absorption vibrations were found at ~ 860, 838, 800, 747, 666, ~ 625, 585, 560, 522, 452, and 423 cm-1 and infrared emission bands at 834, 778, 728, 652, 640, 609, 580, 512, and 489 cm-1 The infrared emission low-frequency bands moved to higher frequencies upon thermal treatment The dehydroxylation of gibbsite was followed by the combination of infrared emission spectroscopy and differential thermal analysis over the 200 to 750 C temperature ranges Dehydroxylation is followed by the loss of intensity of the hydroxyl stretching frequencies observed at 3620 and 3351 cm-1 and by the loss of intensity of the hydroxyl deformation modes at 1024 cm-1 Dehydroxylation starts at 220 C and is complete by 350 C Some variation in the gibbsite endotherms was found between the synthetic and natural gibbsite dehydroxylations Spectral changes in the low-frequency bands confirm that dehydroxylation commenced at 220 C

Vibrational Spectroscopy and Dehydroxylation of Aluminum (Oxo)Hydroxides: Gibbsite:

The thermal decomposition mechanism of synthetic Al(OH)3 (gibbsite) was studied in situ by neutron thermodiffractometry in an ambient atmosphere from room temperature to 600°C with 50°C steps. Gibbsite decomposed to yield AlO·(OH) (boehmite) and then poorly crystallized χ-Al2O3. Rietveld analysis was used to refine the cell parameters' variation of gibbsite and its thermal expansion coefficients were obtained: for the a-axis: 15±1 × 10−6 K−1, for b: 10±2 × 10−6 K−1, and for c: 17±2 × 10−6 K−1.

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On the Decomposition of Synthetic Gibbsite Studied by Neutron Thermodiffractometry

Mineralogical characteristics of the superlarge Quaternary bauxite deposits in Jingxi and Debao counties, western Guangxi, China

Study of the thermal preparation and stability of tetrametaphosphates of bivalent metals

Mechanism and kinetics of the dehydration of hydrargillites. Part I

Die Zersetzung des Aluminiumchloridhexahydrats wurde mit Differentialthermoanalyse und Thermogravimetrie in Kombination mit Thermogastitrimetrie unter Anwendung eines Q-Derivatographs untersucht. Es wurde gefunden, das die Reaktion zu Aluminiumoxid uber die Zwischenstufe eines basischen Aluminiumchlorids ablauft. Aus dem Vergleich der unter dynamischen und quasiisothermen Heizbedingungen erhaltenen Ergebnisse folgt, das diese Zwischenstufe nur unter quasiisothermen Bedingungen beobachtbar ist.

D. Petzold

Papers

Mechanism and kinetics of the dehydration of hydrargillites. Part I

Untersuchungen zur Thermischen Zersetzung von Aluminiumchloridhexahydrat unter Dynamischen und Quasiisothermen Bedingungen