High strength polycrystalline ceramic spheres

• US 20040224155A1
• Filed: 02/06/2004
• Published: 11/11/2004
• Est. Priority Date: 02/06/2003
• Status: Active Grant

• Current Assignee: Rice University
• Original Assignee: Rice University
• Inventors: Barron, Andrew R., DeFriend, Kimberly A.
• Granted Patent: US 7,220,454 B2
• Time in Patent Office: Days
• US Class Current: 428/402
• CPC Class Codes: B01D 2323/081 Heating
• CPC Class Codes: B01D 67/0088 Physical treatment with compounds, e.g. swelling, coating or impregnation
• CPC Class Codes: B01D 71/025 Aluminium oxide
• CPC Class Codes: B01J 13/02 Making microcapsules or microballoons for medical preparations A61K9/50
• CPC Class Codes: C04B 14/301 porous or hollow
• CPC Class Codes: C04B 2111/00801 Membranes; Diaphragms
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/78 Grain sizes and shapes, product microstructures, e.g. acicular grains, equiaxed grains, platelet-structures
• CPC Class Codes: C04B 2235/96 Properties of ceramic products, e.g. mechanical properties such as strength, toughness, wear resistance
• CPC Class Codes: C04B 28/24 containing alkyl, ammonium or metal silicates; containing silica sols reaction mixtures resulting in mineral polymers C04B28/006; polymeric reaction products of alkali metal silicates with isocyanates C08G18/3895
• CPC Class Codes: C04B 35/10 based on aluminium oxide
• CPC Class Codes: C04B 35/628 Coating the powders or the macroscopic reinforcing agents
• CPC Class Codes: C04B 35/62813 Alumina or aluminates
• CPC Class Codes: C04B 35/62821 Titanium oxide
• CPC Class Codes: C04B 38/0022 obtained by a chemical conversion or reaction other than those relating to the setting or hardening of cement-like material or to the formation of a sol or a gel, e.g. by carbonising or pyrolysing preformed cellular materials based on polymers, organo-metallic or organo-silicon precursors
• CPC Class Codes: C04B 38/009 Porous or hollow ceramic granular materials, e.g. microballoons C04B18/027, C04B20/002 take precedence
• CPC Class Codes: C04B 38/04 by dissolving-out added substances
• CPC Class Codes: C04B 40/0263 Hardening promoted by a rise in temperature C04B40/024 takes precedence
• CPC Class Codes: C04B 40/0268 Heating up to sintering temperatures C04B41/0072 takes precedence
• CPC Class Codes: C09K 8/80 Compositions for reinforcing fractures, e.g. compositions of proppants used to keep the fractures open
• CPC Class Codes: C09K 8/805 : Coated proppants
• CPC Class Codes: Y10T 428/2982 : Particulate matter [e.g., sphere, flake, etc.]

Abstract

A method for making hollow spheres of alumina or aluminate comprises: coating polymeric beads with an aqueous solution of an alumoxane, drying the beads so as to form an alumoxane coating on the beads; heating the beads to a first temperature that is sufficient to convert the alumoxane coating to an amorphous alumina or aluminate coating and is not sufficient to decompose the polymeric beads; dissolving the polymeric bead in a solvent; removing the dissolved polymer from the amorphous alumina or aluminate coating; and heating the amorphous alumina or aluminate coating to a second temperature that is sufficient to form a hollow ceramic sphere of desired porosity and strength. The hollow spheres can be used as proppants or can be incorporated in porous membranes.

Claims

1. A method for making hollow spheres of alumina or aluminate comprising:

a) coating polymeric beads with an aqueous solution of an alumoxane;

b) drying the beads so as to form an alumoxane coating on the beads;

c) heating the beads to a first temperature, wherein the first temperature is sufficient to convert the alumoxane coating to an amorphous alumina or aluminate coating and is not sufficient to decompose the polymeric beads;

d) dissolving the polymeric bead in a solvent;

e) removing the dissolved polymer from the amorphous alumina or aluminate coating; and

f) heating the amorphous alumina or aluminate coating to a second temperature that is sufficient to form a hollow ceramic sphere of desired porosity and strength.

2. The method of claim 1 wherein the alumoxane comprises acetate-alumoxane.

3. The method of claim 1 wherein the average diameter of the polymeric beads is approximately 3 μ

m.

4. The method of claim 1 wherein the first temperature is between 180°

C. and 230°

C.

5. The method of claim 1 wherein the second temperature is above 600°

C.

6. The method of claim 1, further comprising:

g) covering the ceramic sphere with a solution of a metal-doped alumoxane so as to form a metal-doped alumoxane coating on the ceramic sphere; and

h) heating the coated sphere to a temperature sufficient to convert the metal-doped alumoxane coating to a mixed metal oxide phase.

7. The method of claim 6 wherein the metal-doped alumoxane comprises methoxy(ethoxyethoxy)acetic acid alumoxane.

8. The method of claim 6 wherein the metal-doped alumoxane comprises elements La, Ca, Er, Mg, Ti, or Y.

9. A proppant comprising hollow spheres of alumina or aluminate wherein the spheres are produced by the method of claim 1.

10. A ceramic matrix composite comprising hollow spheres of alumina or aluminate wherein the spheres are produced by the method of claim 1.

11. A polymer matrix composite comprising hollow spheres of alumina or aluminate wherein the spheres are produced by the method of claim 1.

12. A porous membrane comprising hollow spheres of alumina or aluminate wherein the spheres are produced by the method of claim 1.

13. A hollow sphere of alumina or aluminate wherein:

the surface of the sphere is porous;

the hardness of the sphere is at least 750 kg/mm2 on the Vickers hardness scale; and

the diameter of the sphere is approximately 3 μ

m.

14. The sphere according to claim 13 wherein the hardness of the sphere is at least 1,800 kg/mm on the Vickers hardness scale.

15. A method for making a porous membrane, comprising:

a) providing a colloidal suspension comprising hollow spheres of alumina or aluminate;

b) coating a porous refractory support with the colloidal suspension;

c) drying the coated support; and

d) firing the dried coated support to a temperature sufficient to achieve a desired porosity and hardness of the membrane.

16. The method of claim 15 wherein the hollow spheres are produced by:

i) coating polymeric beads with an aqueous solution of an alumoxane;

ii) drying the beads so as to form an alumoxane coating on the beads;

iii) heating the beads to a first temperature that is sufficient to convert the alumoxane coating to an amorphous alumina or aluminate coating and not sufficient to decompose the polymeric beads;

iv) dissolving the polymeric bead in a solvent;

v) removing the dissolved polymer from the amorphous alumina or aluminate coating; and

vi) heating the amorphous alumina or aluminate coating to a second temperature sufficient to form a hollow ceramic sphere of desired porosity and hardness.

17. The method of claim 16 whereby the second temperature is at least 600°

C.

18. A method for making a porous membrane, comprising:

a) providing a colloidal suspension comprising colloidal polymeric beads suspended in an aqueous solution of an alumoxane;

b) coating a porous refractory support with the colloidal suspension;

c) drying the coated support; and

d) firing the dried coated support to a temperature sufficient to achieve a desired porosity and hardness of the membrane.

19. The method of claim 18 whereby the temperature in step d) is at least 600°

C.

20. The method of claim 18, further including the step of chemically removing the polymeric beads from the coated support prior to firing.