Synthesis and Characterization of the Combustion Product of an Alumina–Succinate Xerogel

Aluminum nitrate was used as the oxidizer and succinic acid C4H6O4 as the fuel to obtain aluminum oxide powders in the γ and α forms. Combustion of xerogels prepared from mixtures (stoichiometric, with 25 and 50% excess fuel) ranged from flaming to smoldering, accompanied by the evolution of yellow nitrogen oxides, which was caused by partial decomposition of aluminum nitrate. The synthesized cxerogel combustion products were studied by thermal analysis, X-ray diffraction, IR spectroscopy, scanning electron microscopy, and low-temperature nitrogen adsorption–desorption. The synthesized powders were amorphous products that crystallized upon annealing. An intense exothermic peak (432°C) on the thermogram was accompanied by a significant mass loss and corresponded to the completion of the combustion process. This temperature practically coincided with the measured combustion temperature (438°C). Heat treatment at 900°C led to the formation of crystalline γ-Al2O3. In the range 1000–1100°C, γ-Al2O3 transformed into the α form. In the IR spectrum after heat treatment (900°C), a band at 539 cm–1 appeared, corresponding to AlVI–O vibrations characteristic of the high-temperature α form. Calcination at 1100°C yielded a well-crystallized single-phase α-Al2O3 with a crystallite size of 38.3 nm. The xerogel combustion products consisted of irregularly grained agglomerates of sharp-edged particles with sizes from ~2 to ~10 μm. Adsorption–desorption isotherms showed that the xerogel combustion products were IV type mesoporous materials with a predominant pore size up to 10 nm, which decreased with increasing fuel content in the mixture. The specific surface area SBET of the powders was high (above 100 m2/g), which makes them potentially suitable for use as adsorbents and catalyst supports, with only minor differences in SBET values for different compositions.