Addition of α-Fe2O3 seed particles to alkoxide-derived boehmite sols resulted in a 10-fold increase in isothermal rate constants for the transformation of γ- to α-Al2O3. Changes in porosity and surface area with sintering temperature showed no effect of seeding on coarsening of the transition alumina gels, but the 200-fold decrease in surface area associated with transformation to α-Al2O3 occurred ∼ 100°C lower in seeded gels compared with unseeded materials. As a result of high nucleation frequency and reduced microstructure coarsening, fully transformed seeded alumina retained specific surface areas >22 m2/g and exhibited narrow pore size distributions, permitting development of fully dense, submicrometer α-Al2O3 at ∼ 1200°C.

Transformation, Microstructure Development, and Densification in α‐Fe2O3‐Seeded Boehmite‐Derived Alumina

Growth characteristics of boehmite-derived ultrafine theta and alpha-alumina particles during phase transformation

The paper reports a process for synthesis of γ-alumina from kaolin Kaolin was transformed to meta-kaolin by calcination at 800oC for 2h γ-alumina powder was synthesized through extracting alumina from meta- kaolin via H2SO4 and meta-kaolin reactions and consequently precipitation in ethanol, which led to form the aluminum sulfate The precipitated aluminum sulfate was dried and calcined at 900 oC for 2h, which resulted the formation of γ-alumina The structure of γ-alumina was confirmed by XRD and FTIR and the mean particles size of γ-alumina was determined by SEM to be 05 - 09 µm The study revealed the kaolin could be promising material for preparation of γ-alumina

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Production of γ-Al 2 O 3 from Kaolin

http://www.cmdmc.com.br/redecmdmc/lab/arquivos_publicacoes/1881_Structural%20and%20spectroscopic%20analysis%20of%20Al2O3.pdf

Structural and spectroscopic analysis of γ-Al2O3 to α-Al2O3-CoAl2O4 phase transition

Examination on the existence of the critical and primary crystallite size (dcα ∼ 17 nm and dp = 50−55 nm) phenomena during θ- to α-phase transformation of the nanosized Al2O3 powder was designed an...

Examinations on the Critical and Primary Crystallite Sizes during θ- to α-Phase Transformation of Ultrafine Alumina Powders

Two special types of anhydrous aluminum sulfate with extreme grain shapes were prepared; one, obtained by precipitation from concentrated sulfuric acid solution, is rhombohedral near cubic single-crystal grains and the other, from acetic acid solution, consists of very thin flaky particles. The morphology of sulfate and calcined alumina, the sulfate decomposition, the η-α alumina transformation, and the crystallite growth of α alumina were studied and compared with those processes for reagent-grade sulfate. The morphology of anhydrous sulfate was shown to greatly affect the heat-treatment characteristics of alumina and the sulfate decomposition behavior.

Masao Nanbu

Papers

Decomposition of Two Aluminum Sulfates and Characterization of the Resultant Aluminas

Synergic extraction and atomic absorption spectrometric determination of vanadium in silicates