Pseudomorphic formation of aluminas from fibrillar pseudoboehmite

Santos, Helena de Souza; Santos, Pérsio de Souza

doi:10.1016/0167-577x(92)90216-7

Cited by 41 publications

(21 citation statements)

References 7 publications

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“…The other factor reducing the oxidation resistance is the crystal modification of aluminium oxide which forms during the long-term oxidation. It was proved by XRD that d-Al 2 O 3 is the main oxidation product on FeeAleSi alloys at 800 C. According to the published data, g-Al 2 O 3 forms predominanty at 800 C, being consequently transformed to d-Al 2 O 3 [37] . Due to the changes of the crystal lattice of the oxide during the thermal exposure, porous oxidation product is obtained as displayed in Fig.…”

Section: Time [H]mentioning

confidence: 81%

Oxidation resistance of SHS Fe–Al–Si alloys at 800 °C in air

et al. 2011

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Section: Time [H]mentioning

confidence: 81%

Oxidation resistance of SHS Fe–Al–Si alloys at 800 °C in air

et al. 2011

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“…1, it can be seen that delta-Al203 is produced only from γ-Al203; references 19,23,24 indicate that the transformation is pseudomorphic either from hexagonal laths of boehmite or from fibrillar pseudoboehmite as precursors of γ-Al203.…”

Section: Delta-al203mentioning

confidence: 99%

“…Gelatinous boehmite is a synonymous of pseudoboehmite; it is constituted by a linear polymer of the -(Al00H) -group; by TEM appears as microfibrils, which length is dependent of the degree of polymerization. Long fibrils first produce pseudomorphic gamma-Al203 by thermal dehydroxilation 23 . Either by TEM or SEM, there is no evidence of somatoid or fibrillar pseudomorphs presence; on the other hand, Fig.…”

Section: Eta-al203mentioning

confidence: 99%

Standard transition aluminas. Electron microscopy studies

2000

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The aim of this paper is to present the results of characterization of the particle shapes of six standard transition aluminas samples using transmission and scanning electron microscopies; selected area electron diffraction, in parallel with X-ray powder diffraction were used for confirmation of the different transition aluminas types. The transition aluminas -chi; kappa; gamma; theta; delta; and eta were supplied by ALCOA Central Laboratory. The chi-; kappa-;gamma-and delta-Al203 microcrystals are pseudomorphs from their respective precursors gibbsite and boehmite. However, theta-Al203 microcrystals are not pseudomorphs after the standard delta-Al203 sample. Also, eta-Al203 are not pseudomorphs after bayerite somatoids.

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“…After firing at 700ºC, the fibrils from 244 membranes and beads maintained their macro and microscopical morphology; their XRD pattern is of gamma-alumina, as described by Souza Santos and Souza Santos (16) for firing pseudoboehmite at that temperature. After firing at 700ºC, the crystals of 245 membranes and beads also maintained their macro and microscopical morphology; their XRD pattern is of gamma-alumina, because also the aluminum hydroxiacetate crystals, at 700ºC, also produces that transition alumina, as shown by Kiyohara et al (11).…”

Section: Characterization Of Membranes and Beadsmentioning

confidence: 54%

Comparative study between yeasts immobilized on alumina beads and on membranes prepared by two routes

Kiyohara

Lima

Santos

et al. 2003

Braz. J. Microbiol.

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Alumina channeled beads and rough surface membranes prepared from aqueous sols of fibrillar pseudoboehmite are able to immobilize yeasts for ethanol fermentation of sugar solutions. This paper describes comparative results of assays carried out with yeasts immobilized onto alpha-alumina beads and membranes prepared under two different conditions of processing and firing. The fermentation tests evaluated by the decrease of fermentable sugars, referred as Brix degrees per hour, indicated that the yeasts immobilized on beads had similar performance, probably because their surfaces, even being morphologically different, presented the same value of open porosity. One type of membrane (asymmetrical; precursor: pseudoboehmite; firing temperature 1,150ºC; crystal structure; alpha-alumina) had better performance than the other type (asymmetrical; precursor: fibrillar pseudoboehmite plus aluminum hydroxiacetate mixture; 1,150ºC; alpha-alumina) because the yeast cells entered into their porous interior through the surface slits, were immobilized and their growth was easier than on the external surface.
Esferas de superfície canelada ou estriada e membranas de textura porosa e superfície rugosa preparadas com sóis aquosos de pseudoboemita fibrillar são capazes de imobilizar leveduras para fermentação alcoólica de soluções aquosas açucaradas. Este artigo descreve os resultados de ensaios levados a efeito com leveduras imobilizadas em esferas e membranas de alumina-alfa, preparadas sob duas diferentes condições de processamento e queima. A fermentação alcoólica dos meios foi acompanhada pelo decréscimo do teor de sólidos solúveis em graus Brix por hora e indicou que as leveduras imobilizadas nas esferas obtidas pelas duas rotas apresentaram desempenho similar, provavelmente por causa de suas superfícies que, mesmo morfologicamente diferentes, apresentaram o mesmo valor de porosidade aberta. Um tipo de membrana (assimétrica; pseudoboemita fibrilar como precursor; temperatura de queima de 1.150ºC; estrutura cristalina de alumina-alfa), levou a melhor desempenho do que outro (assimétrico; mistura de pseudoboemita fibrilar e hidroxiacetato de alumínio como precursor; 1.150ºC; alumina-alfa), provavelmente porque as células de leveduras penetraram no seu interior poroso pelas fendas superficiais, imobilizaram-se e cresceram mais facilmente do que na superfície externa

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Pseudomorphic formation of aluminas from fibrillar pseudoboehmite

Cited by 41 publications

References 7 publications

Oxidation resistance of SHS Fe–Al–Si alloys at 800 °C in air

Oxidation resistance of SHS Fe–Al–Si alloys at 800 °C in air

Standard transition aluminas. Electron microscopy studies

Comparative study between yeasts immobilized on alumina beads and on membranes prepared by two routes

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