High strength polycrystalline ceramic spheres
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.
1. A method comprising propping open fractures in a subterranean formation with hollow, porous spheres of alumina or aluminate wherein the void volume is approximately 90% of the sphere volume and wherein the spheres have a hardness of at least 750 kg/mm 2 on the Vickers hardness scale.
2. The method of claim 1 wherein the spheres have a hardness of at least 1800 kg/mm 2 on the Vickers hardness scale.
3. The method of claim 1 wherein the spheres range from 1-80 microns in diameter.
4. The method of claim 2 wherein the spheres range from 1-80 microns in diameter.
5. The method of claim 1 wherein all or a portion of the spheres are contained within a polymer matrix composite.
6. The method of claim 5 wherein the composite is a reaction product of a resin and a hardener.
7. The method of claim 5 wherein the composite is an epoxy resin.
8. The method of claim 5 wherein the composite has a hardness greater than the hardness of the spheres.
9. The method of claim 5 wherein the spheres are surface functionalized.
10. The method of claim 1 wherein all or a portion of the spheres further comprise metal oxide.
11. The method of claim 5 wherein all or a portion of the spheres further comprise metal oxide.
12. The method of claim 1 wherein the spheres have a thickness of about 1 micron.
13. The method of claim 1 wherein the spheres are multilayered.
14. The method of claim 1 further comprising flowing fluid from the formation through the pores of the spheres.
15. A wellbore fracture proppant comprising hollow, porous spheres of alumina or aluminate wherein the void volume is approximately 90% of the sphere volume and wherein the spheres have a hardness of at least 750 kg/mm 2 on the Vickers hardness scale.
16. The proppant of claim 15 wherein the spheres have a hardness of at least 1800 kg/mm 2 on the Vickers hardness scale.
17. The proppant of claim 15 wherein the spheres range from 1-80 microns in diameter.