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Titolo:
Preparation of gamma-alumina membranes from sulphuric electrolyte anodic alumina and its transition to alpha-alumina
Autore:
Ozao, R; Ochiai, M; Yoshida, H; Ichimura, Y; Inada, T;
Indirizzi:
SONY Inst, N Shore Coll, Kanagawa 2438501, Japan SONY Inst Kanagawa Japan 2438501 , N Shore Coll, Kanagawa 2438501, Japan Tokyo Metropolitan Univ, Tokyo 1920397, Japan Tokyo Metropolitan Univ Tokyo Japan 1920397 n Univ, Tokyo 1920397, Japan Seiko Instruments Inc, Mihama Ku, Chiba 2618507, Japan Seiko Instruments Inc Chiba Japan 2618507 ihama Ku, Chiba 2618507, Japan Japan Fine Ceram Ctr, Atsuta Ku, Aichi 4568587, Japan Japan Fine Ceram Ctr Aichi Japan 4568587 Atsuta Ku, Aichi 4568587, Japan
Titolo Testata:
JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY
fascicolo: 3, volume: 64, anno: 2001,
pagine: 923 - 932
SICI:
1388-6150(2001)64:3<923:POGMFS>2.0.ZU;2-W
Fonte:
ISI
Lingua:
ENG
Soggetto:
BOEHMITE;
Keywords:
crystallization; gamma-alumina; nanoporous membrane; phase transition; quasi-crystalline phase; TEM-EDS; TG-DTA;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
13
Recensione:
Indirizzi per estratti:
Indirizzo: Ozao, R SONY Inst, N Shore Coll, Kanagawa 2438501, Japan SONY Inst Kanagawa Japan 2438501 e Coll, Kanagawa 2438501, Japan
Citazione:
R. Ozao et al., "Preparation of gamma-alumina membranes from sulphuric electrolyte anodic alumina and its transition to alpha-alumina", J THERM ANA, 64(3), 2001, pp. 923-932

Abstract

Gamma-alumina membrane was prepared from anodic (amorphous) alumina (AA) obtained in a sulphuric acid electrolyte. The transformation scheme, i.e., the crystallization to form metastable alumina polymorphs and the final transition to alpha -Al2O3 with heating was studied by TG-DTA and X-ray diffraction (XRD) using fixed time (FT) method. When heating at a constant rate, the crystallization occurred at 900 degreesC or higher and the final formation of alpha -Al2O3 occurred at 1250 degreesC or higher, which temperatures were higher than the case of using anodic (amorphous) alumina prepared fromoxalic acid electrolyte. Relative content of S of the products was obtained by transmission electron microscope (TEM)-energy dispersive spectroscopy (EDS). The proposed thermal change of anodic alumina membrane prepared fromsulphuric acid is as follows:1. At temperatures lower than ca 910 degreesC: Formation of a quasi-crystalline phase or a polycrystalline phase (gamma-, delta- and theta -Al2O3);2. 910-960 degreesC: Progressive crystallization by the migration of S toward the surface within the amorphous or the quasi-crystalline phase, forming S-rich region near the surface;3. 960 degreesC: Change of membrane morphology and the quasi-crystalline phase due to the rapid discharge of gaseous SO2;4. 960-1240 degreesC: Crystallization of gamma -Al2O3 accompanying delta -Al2O3; and5. 1240 degreesC: Transition from gamma -Al2O3 (+tr. delta -Al2O3) into the stable alpha -Al2O3. The amorphization which occurs by the exothermic and the subsequent endothermic reaction suggests the incorporation of SO3 groups in the quasi-crystalline structure.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 20/09/20 alle ore 01:04:30