Process for preparing shaped body of alumina

Claim 2

A process for the preparation of a shaped body having at least one dimension less than 100 microns and comprising alumina in either noncrystalline form or in predominantly eta form or both and free of alpha-alumina which includes the steps of: (a) forming into the desired shape of body a composition having a viscosity in the range 0.1 to 5000 poise and comprising a water-soluble aluminum compound decomposable to alumina and selected from the group consisting of the chlorides, sulphates, acetates, formates, propionates, oxalates, phosphates and nitrates of aluminum or mixtures thereof, a water soluble organic polymer having a molecular weight in the range 10 3 to 10 7 and present in an amount by weight less than the aluminum compound, and water; (b) removing at least part of the water from the body so formed; (c) subjecting the body to hydrothermal treatment at a temperature of from 200°-800° C. for 2 minutes to 5 hours to decompose at least partially the aluminum compound to alumina or an alumina hydrate; and (d) calcining the hydrothermally treated body at a temperature of from 600° to 1000° C. for a period of one minute to one hour so as to obtain the alumina in either noncrystalline form or in predominantly eta crystalline form or both and free of alpha-alumina.

Claim 3

A process as claimed in claim 1 wherein the organic polymer comprises less than 10% by weight of the aluminium oxide equivalent of the aluminium compound.

Claim 4

A process as claimed in claim 2 wherein the organic polymer comprises from 0.1% to 8% by weight of the aluminium oxide equivalent of the aluminium compound.

Claim 5

A process as claimed in claim 1 wherein the aluminium compound is aluminium oxychloride, basic aluminium acetate, basic aluminium formate, basic aluminium nitrate, mixtures thereof or mixed compounds thereof.

Claim 6

A process as claimed in claim 1 wherein the organic polymer is a straight-chain polyhydroxylated polymer.

Claim 7

A process as claimed in claim 1 wherein the organic polymer is partially hydrolysed polyvinylacetate or polyvinylalcohol.

Claim 8

A process as claimed in claim 1 wherein the organic polymer is polyvinylpyrrolidone or polyethylene oxide.

Claim 9

A process as claimed in claim 6 wherein the partially hydrolysed polyvinylacetate or polyvinylalcohol has a molecular weight of 75,000 to 125,000.

Claim 10

A process as claimed in claim 7 wherein the polyethylene oxide has a molecular weight of 10 4 to 10 6 .

Claim 11

A process as claimed in claim 1 wherein the hydrothermal treatment is effected at a temperature of 250° C. to 500° C.

Claim 12

A process as claimed in claim 1 wherein the duration of the hydrothermal treatment is from 2 minutes to 30 minutes.

Claim 13

A process as claimed in claim 1 wherein the composition comprises an alkaline earth compound decomposable to an alkaline earth oxide.

Claim 14

A process as claimed in claim 1 wherein the composition comprises an acid oxide or a compound decomposable to an acid oxide.

Claim 15

A process as claimed in claim 1 wherein the composition comprises a catalyst material.

Claim 16

A process as claimed in claim 14 wherein the catalyst material is Pt, Sb, Cu, Al, Pd, Ag, Ru, Bi, Zn, Rh, Ni, Co, Cr, Ti, Fe, V or Mn in elemental or compound form.

Claim 17

A process as claimed in claim 1 wherein a fibre is formed by fibrising the composition.

Claim 18

A process as claimed in claim 16 wherein fibrising is effected by centrifugal spinning, tack-spinning, extrusion through a spinneret or suitable combinations thereof.

Claim 19

A process as claimed in claim 16 wherein fibrising is effected by blowing.

Claim 20

A process as claimed in claim 18 wherein fibrising by blowing comprises extruding the fibrising composition through one or more apertures into at least one gas stream having a component of high velocity in the direction of travel of the extruded composition.

Claim 21

A process as claimed in claim 19 wherein two gas streams converge at or near the point where the composition is extruded from the aperture.

Claim 22

A process as claimed in claim 20 wherein the angle between the converging gas streams is from 30° to 60°.

Claim 23

A process as claimed in claim 19 wherein the gas is more than 60% saturated with the solvent vapour.

Claim 24

A process as claimed in claim 19 wherein the gas is air.

Claim 25

A process as claimed in claim 23 wherein the air is at a relative humidity of greater than 80%.

Claim 26

A process as claimed in claim 16 wherein a catalyst material or a precursor thereof is dissolved in the fibrising composition.

Claim 27

A process as claimed in claim 16 wherein particulate catalyst material or a precursor thereof is dispersed in the fibrising composition.

Claim 28

A process as claimed in claim 16 wherein the fibre is treated with a dispersion or solution of a catalyst material or a precursor thereof in a volatile liquid, and dried.

Claim 29

A process for preventing the formation of alpha-alumina at temperatures below 1000° C. and improving the resistance to physical change of a shaped body when said body is subjected to temperature changes, said body having at least one dimension less than 100 microns and comprising alumina in either noncrystalline form or in predominantly eta form or both and free of alpha-alumina which includes the steps of: (a) forming into the desired shape of body a composition having a viscosity in the range 0.1 to 5000 poise and comprising a water-soluble aluminum compound decomposable to alumina and selected from the group consisting of the chlorides, sulphates, acetates, formates, propionates, oxalates, phosphates and nitrates of aluminum or mixtures thereof, a water soluble organic polymer having a molecular weight in the range 10 3 to 10 7 and present in an amount by weight less than the aluminum compound, and water; (b) removing at least part of the water from the body so formed; (c) subjecting the body to hydrothermal treatment at a temperature of from 200°-800° C. for 2 minutes to 5 hours to decompose at least partially the aluminum compound to alumina or an alumina hydrate; and (d) calcining the hydrothermally treated body at a temperature of from 600° to 1000° C. for a period of one minute to one hour so as to obtain the alumina in either noncrystalline form or in predominantly eta crystalline form or both and free of alpha-alumina.

Claim 30

A process for preventing the formation of alpha-alumina at temperatures below 1000° C. and improving the resistance to physical change of a shaped body when said body is subjected to temperature changes, said body having at least one dimension less than 100 microns and comprising alumina in either noncrystalline form or in predominantly eta form or both and free of alpha-alumina which includes the steps of: (a) forming into the desired shape of body a composition having a viscosity in the range 0.1 to 5000 poise and comprising a water-soluble aluminum compound decomposable to alumina and selected from the group consisting of the chlorides, sulphates, acetates, formates, propionates, oxalates, phosphates and nitrates of aluminum or mixtures thereof, a water soluble organic polymer having a molecular weight in the range 10 3 to 10 7 and present in an amount by weight less than the aluminum compound, and water; (b) removing at least part of the water from the body so formed; (c) subjecting the body to hydrothermal treatment at a temperature of from 200°-800° C. for 2 minutes to 5 hours to decompose at least partially the aluminum compound to alumina or an alumina hydrate; and (d) calcining the hydrothermally treated body at a temperature of from 600° to 1000° C. for a period of one minute to one hour so as to obtain the alumina in either noncrystalline form or in predominantly eta crystalline form or both and free of alpha-alumina.