Anodes containing spherical powder and capacitors
Anodes made from powder, such as tantalum powder, that is highly spherical is described. Methods to make the anodes are further described.
1. A capacitor anode comprising a powder that is pressed and sintered, wherein said powder comprises a spherical powder that is a metal or metal sub-oxide or both, said spherical powder comprising
a. a spherical shape wherein the powder has an average aspect ratio of from 1.0 to 1.4;
b. a purity of at least 99.5 wt %;
c. an average particle size of from about 0.5 micron to about 250 microns;
d. an apparent density from about 1.5 g/cc to about 15.5 g/cc;
e. a true density that is within +−3% of the metal or metal sub-oxide; and
f. a Hall flow rate of 40 sec or less.
2. The capacitor anode of claim 1 , wherein said spherical metal powder is plasma heat-treated or gas atomized.
3. The capacitor anode of claim 1 , wherein said metal powder has an oxygen level of from 50 ppm to 15,000 ppm.
4. The capacitor anode of claim 1 , wherein said metal powder has an oxygen level of 600 ppm to 10,000 ppm.
5. The capacitor anode of claim 1 , wherein said average aspect ratio is from 1.0 to 1.25.
6. The capacitor anode of claim 1 , wherein said average aspect ratio is from 1.0 to 1.1.
7. The capacitor anode of claim 1 , wherein said purity is at least 99.99 wt %.
8. The capacitor anode of claim 1 , wherein said average particle size is from about 0.5 micron to about 10 microns.
9. The capacitor anode of claim 1 , wherein said average particle size is from about 5 microns to about 25 microns.
10. The capacitor anode of claim 1 , wherein said average particle size is from about 15 microns to about 45 microns.
11. The capacitor anode of claim 1 , wherein said average particle size is from about 35 microns to about 75 microns.
12. The capacitor anode of claim 1 , wherein said average particle size is from about 55 microns to about 150 microns.
13. The capacitor anode of claim 1 , wherein said average particle size is from about 105 microns to about 250 microns.
14. The capacitor anode of claim 1 , wherein said powder has at least one of the following properties:
a. a D10 size of from about 5 microns to 25 microns; or
b. a D90 size of from about 20 microns to 80 microns.
15. The capacitor anode of claim 1 , wherein said powder is selected from niobium, tantalum, conductive niobium sub-oxide, or any combination thereof.
16. The capacitor anode of claim 1 , wherein said powder further comprises non-spherical powder comprising a metal or conductive metal sub-oxide or both.
17. The capacitor anode of claim 16 , wherein said non-spherical powder comprises angular powder, flake powder, nodular powder.
18. The capacitor anode of claim 16 , wherein said powder comprises from 1% to 99% by weight of said spherical powder and from 1% to 99% by weight of said non-spherical powder.
19. The capacitor anode of claim 16 , wherein said powder comprises from 25% to 75% by weight of said spherical powder and from 25% to 75% by weight of said non-spherical powder.
20. The capacitor anode of claim 16 , wherein said powder comprises from 50% to 99% by weight of said spherical powder and from 1% to 50% by weight of said non-spherical powder.
21. The capacitor anode of claim 16 , wherein said powder comprises from 75% to 99% by weight of said spherical powder and from 1% to 25% by weight of said non-spherical powder.
22. The capacitor anode of claim 1 , wherein said spherical powder comprises at least two different size fractions based on average particle size.
23. The capacitor anode of claim 1 , wherein said spherical powder comprises a first size fraction having an average particle size from about 10 microns to about 25 microns, and a second size fraction of from about 26 microns to about 45 microns.
24. The capacitor anode of claim 1 , wherein the capacitor anode has a capacitance (CV) of from 1000 μF-V/g to 100,000 μF-V/g, and a leakage current of 6 nA/μFV or less.
25. An electrolytic capacitor comprising the capacitor anode of claim 1 .
26. A method to make to the capacitor anode of claim 1 , said method comprising:
a. plasma heat-treating a starting powder to at least partially melt at least an outer surface of said starting powder in an inert atmosphere to obtain a heat-treated powder, wherein said starting powder is a metal or conductive metal sub-oxide or both,
b. cooling said heat-treated powder in an inert atmosphere to obtain said spherical powder,
c. pressing said spherical powder to form a pressed body;
d. sintering said pressed body one or more times to form a sintered body; and
e. anodizing the sintered body in an electrolyte to form a dielectric oxide film on the sintered body to form said capacitor anode.
27. The method of claim 26 , wherein said starting powder is sodium-reduced tantalum powder.
28. The method of claim 26 , wherein said starting powder is a basic lot tantalum powder.
29. The method of claim 26 , wherein said starting powder has a first particle size distribution, and said powder has a second particle size distribution, and said first particle size distribution and said second particle size distribution are within 10% of each other.
30. The method of claim 26 , wherein prior to step a, the starting powder is formed by sintering a first powder to obtain a sintered powder, and then e-beam melting of said sintered powder to obtain an ingot, and then reducing said ingot to said starting powder.
31. A metal or metal sub-oxide powder comprising
a. a spherical shape wherein the powder has an average aspect ratio of from 1.0 to 1.4;
b. a purity of at least 99.5 wt % based on total weight of said powder, excluding gas impurities;
c. an average particle size of from about 0.5 micron to about 250 microns;
d. an apparent density from about 1.5 g/cc to about 15.5 g/cc;
e. a true density that is within +−3% of the metal or metal sub-oxide; and
f. a Hall flow rate of 40 sec or less.
32. A sintered pellet comprising a metal powder that is shaped in the form of a pellet and sintered, wherein said metal powder comprises the metal powder of claim 31 .