Effect of Milling on the Formation of Nanocrystalline χ‐Al₂O₃ from Gibbsite

Abstract

Gibbsite (FG) with mean particle diameter (d50=13 μm) was milled in an attrition mill for 12 and 24 h using alumina balls as grinding media and calcined at different temperatures in the range of 350°–600°C. The properties of the alumina obtained were determined by X‐ray diffraction, N2 physisorption, thermogravimetric/differential thermal analyses, and transmission electron microscopy. Without milling, the alumina obtained normally contained the mixed phases between γ‐ and χ‐phase alumina. On the other hand, high purity of nanocrystalline χ‐phase alumina (100 wt%) can be produced by calcination of the 24‐h milled FG at 600°C. The isothermal kinetics measurements revealed that the rate constant (k) for phase transformation increased as the particle size of gibbsite decreased and the calculated activation energy for transformation from FG to alumina decreased from 20.6 to 14.7 and 6.8 kJ/mol after milling for 12 and 24 h, respectively. The physical properties of nanocrystalline χ‐alumina obtained by the calcination of milled FG were comparable to those produced by the solvothermal method. The present results offer a simple way to prepare a large amount of pure χ‐phase alumina for particular industrial applications.

Formation of CoAl2O4 Nanoparticles via Low‐Temperature Solid‐State Reaction of Fine Gibbsite and Cobalt Precursor

“…The starting fine gibbsite has an average particle size of 13 μm and is denoted as FG-13 μm. After milling of 100 g of fine gibbsite in an attrition mill for 24 h, the particle size of the fine gibbsite was reduced to 0.6 μm and is denoted as FG-0.6 μm [25]. The solidstate reaction between fine gibbsite and cobalt chloride took place at 450, 550, and 650 • C with a Co : Al molar ratio 1 : 6.…”

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“…Nota-se através da curva de frequência que os materiais apresentam partículas de tamanhos variados compreendidos entre aproximadamente 0,08 e 411 μm, com modas situadas em 0,47, 12,71 e 168,43 μm. De acordo com CHAITREE et al [24] a redução na granulometria das partículas influência direta e significativamente na transformação de fases sofrida pelos hidróxidos de alumínio e ferro, reduzindo a temperatura de degradação e aumentando a perda de massa resultante, o que será acompanhado através da análise térmica.…”

Influência Da Substituição De Cálcio E Bário Em Composições De Perovskitas Tr(1-X) Mxo3 (Tr= Pr, Gd), (M = Ca, Ba) (X= 0,2) Na Atividade Catalítica

“…A mesma relação apresentada na Figura 11 é feita por Chaitree et al (2010), para reações de desidratação da gibbsita e formação de χ-Al 2 O 3 , com pico exotémico em torno de 300ºC e média de perda de massa em 35% até os 600ºC.…”