Passivation of tantalum and other metal powders using oxygen
View Patent ↗A method to passivate a metal or metal oxide or metal suboxide powder, especially a valve metal powder such as tantalum or niobium and the passivated powders formed therefrom are described. The method includes passivating a starting powder with a gas having at least 25 wt. % oxygen present. Passivation is preferably achieved without performing any evacuation steps. Capacitors made from the passivated powders are also described.
1. A method to passivate a powder comprising passivating said powder with a gas having at least 25 wt. % oxygen present to form a passivated powder, wherein said powder is tantalum powder, niobium powder, or niobium suboxide powder, and wherein said powder has a BET surface area of from 0.2 to 40 m 2 /g, and a capacitance capability of from 10,000 to 400,000 CV/g.
2. The method of claim 1 , wherein said powder is a nitrided metal powder.
3. The method of claim 1 , wherein said powder is tantalum.
4. The method of claim 1 , wherein said powder is niobium or a niobium suboxide.
5. The method of claim 1 , wherein said gas has at least 75 wt. % oxygen present.
6. The method of claim 1 , wherein said gas has from about 99 to about 100 wt. % oxygen present.
7. The method of claim 1 , wherein said gas has no inert gases present.
8. The method of claim 1 , wherein said gas has less than 5 wt. % inert gases present.
9. The method of claim 1 , wherein said gas has less than about 25 wt. % nitrogen.
10. The method of claim 1 , wherein said passivation is at a temperature of from about 20 to about 90° C.
11. The method of claim 1 , wherein said passivation forms an oxide layer having a thickness of from about 20 to about 200 Angstrom.
12. The method of claim 1 , wherein said passivation is achieved without any evacuation cycles.
13. The method of claim 1 , wherein said powder is niobium powder.
14. The method of claim 1 , wherein said powder has a primary particle size from about 0.05 to about 5 microns.
15. The method of claim 14 , wherein said powder is granules with a granule size of from about 10 to 1,000 microns.
16. The method of claim 1 , wherein said powder has a D10, D50, and D90 distribution and said D10 and said D90 are within 300% of said D50.
17. The method of claim 1 , wherein said powder has a bi-modal or multi-modal distribution.
18. The method of claim 1 , wherein said powder has a pore size of from about 0.01 to about 1,000 microns.
19. The method of claim 1 , wherein said powder is tantalum and has a Scott density of from about 15 to about 40 g/in 3 .
20. The method of claim 1 , wherein said powder is niobium or niobium suboxide and has a Scott density of from about 10 to about 30 g/in 3 .
21. The method of claim 1 , wherein said BET surface area is from 1.5 to 10 m 2 /g.