Niobium powders having a particle shape

1. A valve metal powder having a particle shape factor mean value f, as determined by SEM image analysis, of 0.65≦f≦1, said powder has an average agglomerate particle size D50 value, as determined with a MasterSizer in accordance with ASTM B 822, of 40 to 200 μm and wherein the valve metal powder is niobium.

2. The valve metal powder according to claim 1 , wherein the particle shape factor mean value f, as determined by SEM image analysis, is 0.70≦f≦0.95.

3. The valve metal powder according to claim 1 , wherein the powder has a particle shape factor mean value f, as determined by SEM image analysis, of 0.65≦f≦1.

4. The valve metal powder according to claim 1 , wherein said powder has an average agglomerate particle size D50 value, as determined with a MasterSizer in accordance with ASTM B 822, of 60 to 120 μm.

5. The valve metal powder according to claim 1 , wherein the particle shape factor mean value f has a standard deviation less than or equal to 0.10.

6. The valve metal powder according to claim 1 , wherein the powder has a magnesium content of less than 20 ppm.

7. The valve metal powder according to claim 1 , wherein the powder has a primary particle size d of between 0.1 and 2 μm and a half-width of 0.3 times the mean value.

8. The valve metal powder according to claim 1 , wherein the powder flows freely through a Hall flow funnel, ASTM B 212 or B 417, having a funnel opening diameter of 2/10 inch.

9. The valve metal powder according to claim 1 , the powder having sodium and potassium contamination levels of less than 20 ppm.

10. The valve metal powder according to claim 1 , the powder comprising agglomerates having an average particle size of no more than 2.0 μm (FSSS).

11. The valve metal powder according to claim 1 , wherein the powder, after sintering at a temperature of 1100 to 1300° C. for 10 minutes and subsequent forming at a voltage of 16 to 30 volts, has a specific capacity of 80,000 to 300,000 μFV/g.

12. The valve metal powder according to claim 11 , wherein the powder, after sintering at a temperature of 1100 to 1300° C. for 10 minutes and subsequent forming at a voltage of 16 to 30 volts, has a leakage current of less than 1.6 nA/μFV.

13. The valve metal powder according to claim 1 , wherein the powder, after sintering at a temperature of 1100 to 1300° C. for 10 minutes and subsequent forming at a voltage of 16 to 30 volts, has a leakage current of less than 1.6 nA/μFV.

14. The valve metal powder according to claim 1 , having a BET specific surface area of 1.5 to 20 m 2 /g.

15. The valve metal powder according to claim 1 , having a nitrogen content of 50 to 20,000 ppm.

16. A capacitor comprising a valve metal powder according to claim 1 .