Influence of aluminium precursor on physico-chemical properties of aluminium hydroxides and oxides
The process of hydrolysis of aqueous aluminium sulfate was carried on in ammonia medium at 100°C and for different time intervals (0, 20, 39 or 59 h). The products thus obtained were calcined at 550, 900 or 1200°C for 2 h with the aim to obtain aluminium oxides. The materials were studied with the following methods: thermal analysis, IR spectroscopy, X-ray diffraction, low-temperature nitrogen adsorption, adsorption–desorption of benzene vapours and scanning electron microscopy.
Freshly precipitated material was an amorphous basic aluminium sulfate which after prolonged refluxing at elevated temperature in a mother liquor underwent a phase transformation into highly crystalline NH4Al13(SO4)2(OH)6 containing tridecameric unit Al13. It was accompanied by a decrease of specific surface area and the formation of a porous structure less accessible for benzene molecules. Regardless of the duration of the hydrolysis process, all products were characterised with poorly developed porous structure and hydrophilic character. Their calcination at the temperature up to 1200°C resulted in the formation of α-Al2O3 via transition forms of γ/η- and δ-Al2O3. The samples of aluminium oxides obtained after calcination at 550 and 900°C had higher values of specific surface area than starting materials due to processes of dehydroxylation and desulfurization. The process of calcination up to 900°C was reflected in developing of not only porous structure but also hydrophobic character of prepared materials. The S BET values calculated for the oxide samples obtained from aged products of hydrolysis at 1200°C were lower than for the analogous sample prepared without the ageing step. It was concluded that prolonged refluxing at elevated temperature of the products of hydrolysis of aluminium sulfate decreased thermal stability of final aluminium oxides.
Keywordsmetastable aluminium oxides thermal decomposition tridecameric Keggin structure
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- 5.Pacewska, B, Kluk-Płoskońska, O, Szychowski, D 2006J. Therm. Anal. Cal.86747Google Scholar
- 6.Pacewska, B, Szychowski, D, Żmijewski, T, et al. 2000Computer program for evaluation of parameters of porous structure of solidsForum Chemiczne 2000WarsawGoogle Scholar
- 9.Sacks, MD, Tseng, T-Y, Lee, SY 1984Ceram. Bull.63301Google Scholar
- 14.Davey, PT, Lukaszewski, GM, Scott, TR 1963Austr. J. Appl. Sci.14137Google Scholar
- 20.Trawczyński, J 1993Przemysł Chemiczny72279Google Scholar
- 22.Blendell, JE, Bowen, HK, Coble, RL 1984Ceram. Bull.63797Google Scholar
- 26.IUPAC Reporting Physisorption Data, Pure Appl. Chem., 57 (1985) 603.Google Scholar
- 27.Pacewska, B, Szychowski, D 2006Przem. Chem.48171Google Scholar
- 29.Nagai, H, Oshima, Y, Hirano, K, Kato, A 1993Br. Ceram. Trans.92113Google Scholar