Surface area, crystal morphology and characterization of transition alumina powders from a new gibbsite precursor

• Autor(a) principal: Vieira Coelho,Antonio Carlos
• Data de Publicação: 2007
• Outros Autores: Souza Santos,Helena de, Kiyohara,Pedro Kuniiko, Marcos,Kelly Nanci Pinto, Souza Santos,Pérsio de
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Materials research (São Carlos. Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392007000200015
• topic: gibbsite; transition aluminas; active aluminas; alpha-alumina

A new procedure was used to prepare a microcrystalline powder constituted by thin euhedral hexagonal gibbsite plates, 0.2 to 0.6 µm in diameter and 32 nm thick. The powder, fired between 200 and 1000 °C, produced chi and kappa transition aluminas. Alpha-alumina is formed from 1000 °C and recrystallized up to 1500 °C. At 1000 °C, kappa- and alpha-alumina coexisted, but kappa-alumina could only be characterized by SAED. The details of the internal organization of the transition alumina pseudomorphs were clearly observable in TEM due to the great thinness of the I-gibbsite plates. The specific surface area varied from pristine I-gibbsite (24.9 m².g-1) to chi- and kappa transition aluminas (25.4 m².g-1) at 1000 °C to alpha-alumina (4.0 m².g-1) at 1500 °C. The maximum value of specific surface area is 347 m².g-1 in chi-alumina powder at 300 °C, a difference from Bayer gibbsite, in which the chi-alumina highest surface area is 370 m².g-1 at 400 °C.