US 4,732,741 AGranted

Method of making beta"-alumina

AssigneeLilliwyte Societe Anonyme

InventorsJames H. Duncan, Peter Barrow, Arnold Van Zyl, Angus I. Kingon

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Abstract

A method of making beta"-alumina comprises dispersing in a precursor of aluminum oxide a member of the group comprising sodium oxide and its precursors, and dispersing in the precursor of aluminum oxide a spinel stabilizer which is a member of the group comprising spinel-forming oxides and the precursors thereof, to form a mixture. The mixture is then heated to a temperature at which at least some of the precursor of aluminum oxide is converted to beta"-alumina. The precursor of aluminum oxide is one which, when calcined in air by itself, has a calcination product which, when subjected to X-ray diffraction, displays a predetermined X-ray diffraction trace. The X-ray diffraction trace is one whose peak with the highest intensity in the 2 (theta) range of 44.degree.-48.degree. and whose peak with the highest intensity in the 2 (theta) range of 63.degree.-69.degree. respectively have maximum intensities and integrated intensities which comply with equations (I) and (II): A/S is greater than 0.03 (I); and B/S is greater than 0.04 (II).

A method of making beta"-alumina which comprises dispersing in a precursor for aluminium oxide a member of the group comprising sodium oxide and its precursors, and dispersing in the precursor of aluminium oxide a spinel stabilizer which is a member of the group comprising spinel-forming oxides and the precursors thereof, to form a mixture, and then heating the mixture to a temperature at which the precursor of aluminium oxide is converted to beta"-alumina, the precursor of aluminium oxide being one which, when calcined in air by itself, has a calcination product which, when subjected to X-ray diffraction is defined herein, displays an X-ray diffraction trace whose peak with the highest intensity in the 2(theta) range of 44.degree.-48.degree. and whose peak with the highest intensity in the 2(theta) range of 63.degree.-69.degree. respectively have maximum intensities and integrated intensities which comply with equations (I) and (II):

A/S is greater than 0.03 (I);
and
B/S is greater than 0.04 (II),
in which:
##EQU4## in counts per second/2(theta).degree. for the calcination product in the 2(theta) range 44.degree.-48.degree.;
##EQU5## in counts per second/2(theta).degree. for the calcination product in the 2(theta) range 63.degree.-69.degree.;
##EQU6## in counts per second/2(theta).degree. for the 211 peak in a rutile (TiO.sub.2) standard occuring in the 2(theta) range 52.degree.-56.degree.;
maximum intensity=the maximum intensity in counts per second above background displayed by the peak with the highest intensity in the 2(theta) range in question;
and
integrated intensity=the area under the peak, above background, in the 2(theta) range in question, in units of 2(theta).degree..times.counts per second.
A, B and S being mean values for at least five samples having a standard deviation of less than 10% and the rutile standard being the intensity standard rutile of the National Bureau of Standards of the United States Department of Commence accorded standard material No. 674 and having a d-spacing of 1.6874 Angstrom units for the 211 peak in question.

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Abstract

Claims34