Mechanochemical-molten salt synthesis of α-Al2O3 platelets

Billik, Peter; Čaplovičová, Mária; Čaplovič, Ľubomír; Horváth, Branislav

doi:10.1016/j.ceramint.2015.03.095

Cited by 19 publications

(9 citation statements)

References 30 publications

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“…Less often encountered are molten salt syntheses to produce platelets of about 2 µm × 0.1 µm by thermal decomposition of a precursor salt such as polyaluminum chloride, ammonium aluminum carbonate hydroxide, or NaAlO 2 [131][132][133][134]. However, BET surface areas attainable for these dimensions would still be relatively low.…”

Section: Miscellaneous Methodsmentioning

confidence: 99%

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

2020

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This article combines a systematic literature review on the fabrication of macroporous α-Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al2O3 is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al2O3 may be the more stable alumina modification for ABET > 175 m2/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al2O3 amounts to 16–24 m2/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders.

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Section: Miscellaneous Methodsmentioning

confidence: 99%

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

2020

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“…Hydrothermal synthesis has an advantage in morphological diversity to prepare α-Al 2 O 3 nano-needles, nanosheets, and whiskers . Furthermore, α-Al 2 O 3 nanoplatelets can be made using molten salt techniques. , In our work, two-dimensional (2D) α-Al 2 O 3 nanosheets were innovatively and efficiently prepared by an improved molten sugar-blowing method. , The produced α-Al 2 O 3 nanosheets can be down to 30 nm in thickness and up to several hundred micrometers in the radial dimension. We used the 2D α-Al 2 O 3 nanosheets as assembly units and skillfully added silica sols to construct α-Al 2 O 3 nanosheet-based aerogels (ANSAs) to avoid the crystallization-induced pulverization behavior.…”

Section: Introductionmentioning

confidence: 95%

“…33 Furthermore, α-Al 2 O 3 nanoplatelets can be made using molten salt techniques. 34,35 In our work, two-dimensional (2D) α-Al 2 O 3 nanosheets were innovatively and efficiently prepared by an improved molten sugar-blowing method. 36,37 The produced α-Al 2 O 3 nanosheets can be down to 30 nm in thickness and up to several hundred micrometers in the radial dimension.…”

Section: Introductionmentioning

confidence: 99%

Alpha Al₂O₃ Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C

Zhang

Jiao

et al. 2023

ACS Appl. Mater. Interfaces

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Alumina aerogels are desirable for lightweight and highly efficient thermal insulation. However, they are typically constrained by brittleness and structural collapse at high temperatures. The manufacture of alumina aerogels with ultralow thermal conductivity and excellent thermal stability at high temperatures beyond 1300 °C is still challenging. Herein, alumina aerogels with superior ultrahigh-temperature-resistant and thermal insulation were successfully prepared by assembling the α-Al2O3 nanosheets with silica sols as the high-temperature binders. Benefiting from the generation of the mullite-covered alumina biphasic structure, the α-Al2O3 nanosheet-based aerogels (ANSAs) exhibit excellent thermal and chemical stabilities even after calcination at as high as 1600 °C. The ANSAs had a low thermal conductivity (0.029 W·m–1·K–1 at room temperature), structural stability with a measured compressive strength of 0.6 MPa, and good thermal shock resistance. Furthermore, the 2D α-alumina@mullite core–shell sheets were also prepared as assembly units to construct aerogels (AMSAs). This core–shell structure can improve temperature resistance through inter-lattice suppression under continuous energy input at high temperatures. The AMSAs have a linear shrinkage of only 2.7% after calcination at 1600 °C for 30 min, further improving the temperature resistance, making them an ideal super-insulating material for applications at extremely high temperatures.

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“…␣-Al 2 O 3 has been conventionally obtained by producing aluminum hydroxide with a liquid phase method using aluminum salts or minerals and annealing the aluminum hydroxide at temperatures of 1000 • C and higher [8][9][10][11][12]. Several researchers have proposed a sol-gel method, which is another representative liquid phase technique, as a candidate for fabricating ␣-Al 2 O 3 [13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel

Yamamura

Hama

Kobayashi

et al. 2016

Journal of Asian Ceramic Societies

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Please cite this article in press as: K. Yamamura, et al., Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel, J. Asian Ceram. Soc. (2016), http://dx. a b s t r a c tThis paper reports the effect of a hydrothermal process for alumina sol on the crystal structure of alumina gel derived from hydrothermally treated alumina sol to help push forward the development of low temperature synthesis of ␣-Al 2 O 3 . White precipitate of aluminum hydroxide was prepared with a homogeneous precipitation method using aluminum nitrate and urea in aqueous solution. The obtained aluminum hydroxide precipitate was peptized by using acetic acid at room temperature, which resulted in the production of a transparent alumina sol. The alumina sol was treated with a hydrothermal process and transformed into an alumina gel film by drying at room temperature. Crystallization of the alumina gel to ␣-Al 2 O 3 with 900 • C annealing was dominant for a hydrothermal temperature of 100 • C and a hydrothermal time of 60 min, as production of diaspore-like species was promoted with the hydrothermal temperature and time. Excess treatments with hydrothermal processes at higher hydrothermal temperature for longer hydrothermal time prevented the alumina gel from being crystallized to ␣-Al 2 O 3 because the excess hydrothermal treatments promoted production of boehmite.

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Mechanochemical-molten salt synthesis of α-Al2O3 platelets

Cited by 19 publications

References 30 publications

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

Alpha Al₂O₃ Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C

Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel

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Mechanochemical-molten salt synthesis of α-Al2O3 platelets

Cited by 19 publications

References 30 publications

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

Alpha Al2O3 Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C

Effect of hydrothermal process for inorganic alumina sol on crystal structure of alumina gel

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Alpha Al₂O₃ Nanosheet-Based Biphasic Aerogels with High-Temperature Resistance up to 1600 °C