Nanocrystalline alpha alumina and method for making the same

Patent metadata

Field	Value
Publication number	US-10351435-B2
Application number	US-201715730817-A
Country	US
Kind code	B2
Filing date	Oct 12, 2017
Priority date	Oct 21, 2016
Publication date	Jul 16, 2019
Grant date	Jul 16, 2019

Abstract

A process for producing metastable nanocrystalline alpha-alumina (α-Al2O3) having particle sizes smaller than 12 nm. Starting crystallites of α-Al2O3 having a particle size larger than 12 nm, typically on the order of about 50 nm, are ball-milled at low temperatures to produce a nanocrystalline α-Al2O3 powder having a particle size of less than 12 nm, i.e., below the theoretical room temperature thermodynamic size limit at which α-Al2O3 changes phase to γ-Al2O3, wherein the powder remains in the α-Al2O3 phase at all times.

First claim

What is claimed is:

1. A process for producing a metastable alpha alumina (α-Al 2 O 3 ) nanocrystalline powder having a particle size of less than 12 nm, comprising:
placing starting crystallites of α-Al 2 O 3 having a particle size larger than 12 nm into a ball-milling jar containing a ball-milling media; and
ball-milling the α-Al 2 O 3 starting crystallites to produce a metastable ball-milled α-Al 2 O 3 nanocrystalline powder having a particle size of less than about 12 nm;
wherein the ball-milling is performed in a plurality of predetermined time intervals for a predetermined total time, wherein a length of each time interval and the total time of ball-milling prevent the α-Al 2 O 3 from undergoing a phase change to γ-Al 2 O 3 ,
such that the α-Al 2 O 3 starting crystallites and the ball-milled α-Al 2 O 3 nanocrystalline powder remain in the α-Al 2 O 3 phase at all times.

2. The process according to claim 1 , wherein the ball-milling media is WC-Co.

3. The process according to claim 1 , wherein the ball-milling is conducted in a series of 30-minute time intervals.

4. The process according to claim 1 , further comprising washing the ball-milled α-Al 2 O 3 nanopowders with nitric acid and hydrogen peroxide.

Assignees

• Us Gov Sec Navy
• Us Navy

Inventors

• Wollmershauser James A
• Drazin John
• Kazerooni Dana A
• Feigelson Boris N
• Gorzkowski Iii Edward P

Classifications

• C04B35/645

  Pressure sintering · CPC title

• C04B35/62635

  Mixing details · CPC title

• C04B35/62615

  High energy or reactive ball milling · CPC title

• C04B35/6261

  Milling · CPC title

• C01F7/023 Primary

  Grinding, deagglomeration or disintegration · CPC title