Process for making nanoporous ultrafine alpha-alumina powder

1. A process for the production of nanoporous α-alumina powders which comprises the steps of

providing an inorganic sol comprising at least one alumina precursor and a plurality of α-alumina seed particles;

adding at least one water soluble organic polymer to the inorganic sol to form an organic-inorganic sol;

freeze drying the organic-inorganic sol to form a solid gel; and

firing the solid gel at a temperature capable of combusting the organic polymer and inducing α-alumina formation of a nanoporous α-alumina powder comprising interconnected α-alumina primary particles having an average particle size of less than about 100 nm and a plurality of voids,

wherein the α-alumina primary particles comprise between about 10-50 vol % of the nanoporous α-alumina powders, the volume of the nanoporous α-alumina powders being the total volume of α-alumina primary particles and the volume of void space.

2. The process of claim 1 , wherein the alumina precursor is boehmite.

3. The process of claim 1 , wherein the molecular alumina precursor is selected from aluminum salts comprising one or more anions selected from alkoxides, aryl oxides, carboxylates, halides, sulfate, nitrate, oxalates, and acetoacetonates.

4. The process of claim 1 , wherein the α-alumina seed particles are homogeneously dispersed in the solid gel.

5. The process of claim 1 , wherein the freeze drying step comprises:

freezing the organic-inorganic sol to a temperature of −20° C. or less; and

subliming water from the frozen sol at a temperature of between 20° C. and about 80° C. and a pressure of about 200 Torr or less.

6. The process of claim 1 , wherein the firing is conducted at a temperature of between about 800° C. and about 1000° C.

7. The process of claim 1 , wherein the α-alumina seed particles have an average particle size of less than about 125 nm.

8. The process of claim 1 , wherein the α-alumina primary particles have a size of between about 30 nm and about 70 nm.

9. The process of claim 1 , wherein at least 99% of the particle sizes of the α-alumina primary particles are distributed within a 10 nm range.

10. The process of claim 1 , wherein the interconnected α-alumina primary particles are connected by a neck.

11. The process of claim 10 , wherein the cross-section of the neck is between about 10% and about 90% of the cross-section of the α-alumina primary particles.

12. The process of claim 1 , wherein the water soluble organic polymer is selected from polyols, sugars, polyalkylene oxides, poly(meth)acrylic acid, poly(meth)acrylates, and mixtures thereof.

13. The process of claim 12 , wherein the water soluble organic polymer is polyvinyl alcohol, polyethylene glycol or a mixture thereof.

14. A process for the production of a nanosized α-alumina powder comprising α-alumina particles having an average particle size of less than about 100 nm, the process comprising the steps of:

providing an inorganic sol comprising at least one alumina precursor and a plurality of α-alumina seed particles;

adding at least one water soluble organic polymer to the inorganic sol to form an organic-inorganic sol;

freeze drying the organic-inorganic sol to form a solid gel;

firing the solid gel at a temperature capable of combusting the organic polymer and inducing α-alumina formation of a nanoporous α-alumina powder comprising interconnected α-alumina primary particles having an average particle size of less than about 100 nm and a plurality of voids, wherein the α-alumina primary particles comprise between about 10-50 vol% of the nanoporous α-alumina powders, the volume of the nanoporous α-alumina powders being the total volume of α-alumina primary particles and the volume of void space; and

breaking the nanoporous α-alumina powder to form a nanosized α-alumina powder comprising the α-alumina primary particles of the nanoporous α-alumina powder.

15. The process of claim 14 , wherein the nanoporous α-alumina powder is broken by milling to form the nanosized α-alumina powder.

16. The process of claim 1 , wherein the α-alumina primary particles have a size of between about 20-90 nm.

17. The process of claim 1 , wherein the α-alumina primary particles have a size of between about 25-80 nm.