“…The TGA/DTA data of monoliths of group a are presented in Figure a, while typical data of groups b−d are seen in Figure b. The thermogram profiles of all groups could be divided into three main regions: (1) 20−150 °C, (2) 150−600 °C, and (3) 600−1300 °C, that are in general also typical to the thermal behavior of xerogels. − 2 TGA/DTA of alumina aerogel monoliths (a) group a, 0.01 mol of H + /mol of Al and (b) group b, 0.07 mol of H + /mol of Al.…”
Section: Resultsmentioning
confidence: 98%
“…One of the main questions concerning the application of these aerogels is their thermal stability. The structural evolution during heat treatment may be dominated by the effects of phase transformations that often occur along with dehydration. − There are several reports on the thermal treatment of alumina xerogels − that demonstrate that the thermal behavior depends on phase composition and morphological parameters of the starting material (degree of crystallinity, size of crystallites, porosity, etc.). Only a few studies follow the thermal behavior of alumina aerogels. − Mizushima and Hori 14-16 examined the influence of different syn-thesis routes on surface area, phase transition, and morphology properties of alumina aerogels.…”
The phase conversions and morphological changes of alumina aerogel films and monoliths during heat treatment were investigated by TGA/DTA, BET, XRD, and image analysis of SEM micrographs. A preliminary model explaining the structural evolution of the film during heat treatment is proposed.
“…The TGA/DTA data of monoliths of group a are presented in Figure a, while typical data of groups b−d are seen in Figure b. The thermogram profiles of all groups could be divided into three main regions: (1) 20−150 °C, (2) 150−600 °C, and (3) 600−1300 °C, that are in general also typical to the thermal behavior of xerogels. − 2 TGA/DTA of alumina aerogel monoliths (a) group a, 0.01 mol of H + /mol of Al and (b) group b, 0.07 mol of H + /mol of Al.…”
Section: Resultsmentioning
confidence: 98%
“…One of the main questions concerning the application of these aerogels is their thermal stability. The structural evolution during heat treatment may be dominated by the effects of phase transformations that often occur along with dehydration. − There are several reports on the thermal treatment of alumina xerogels − that demonstrate that the thermal behavior depends on phase composition and morphological parameters of the starting material (degree of crystallinity, size of crystallites, porosity, etc.). Only a few studies follow the thermal behavior of alumina aerogels. − Mizushima and Hori 14-16 examined the influence of different syn-thesis routes on surface area, phase transition, and morphology properties of alumina aerogels.…”
The phase conversions and morphological changes of alumina aerogel films and monoliths during heat treatment were investigated by TGA/DTA, BET, XRD, and image analysis of SEM micrographs. A preliminary model explaining the structural evolution of the film during heat treatment is proposed.
“…The transformation of boehmite into -Al O is endothermic and occurs after partial dehydroxylation between 300 and 5503C, while the transformation of transitional aluminas into -Al O is exothermic and requires complete dehydroxylation, which occurs between 800 and 13003C. The transformations of -into -and -alumina proceeds pseudomorphically (11), requiring only small amounts of energy that are hardly detected in DTA experiments. Transformation temperatures strongly depend on boehmite &&cry-stallinity''*boehmite with low &&crystallinity'' traditionally has been named pseudoboehmite, which has been assumed to have water molecules in its crystalline structure (16,17).…”
“…4a), the presence of a-Al 2 O 3 along with the other transitional aluminas is observed. [34][35][36] Besides, as the structural changes involved in the transformations c ? No measurable effect due to the transition transformations from c-Al 2 O 3 to other metastable alumina polymorphs was observed on the TG and DTA curves of Fig.…”
Boehmite synthesized through a sol‐gel route from a nonconventional raw material, as an aluminum waste, was calcined at temperatures between 500 and 1500°C. Quantification of crystalline phases was performed by the Rietveld refinement of the XRD patterns. γ‐Al2O3 is formed at 500°C, and up to 1000°C, is the dominant phase. At temperatures ranging from 1000 to 1400°C, it was observed the appearance of a four‐phase region. The complete transformation into α‐Al2O3 lasts until 12 h at 1400°C or at higher temperatures. The presence of an amorphous phase in calcined samples was confined by direct comparison with a standard of pure α‐Al2O3.
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