CA2331707A1

CA2331707A1 - Reduction of nb or ta oxide powder by a gaseous light metal or a hydride thereof

Info

Publication number: CA2331707A1
Application number: CA002331707A
Authority: CA
Inventors: Leonid N. Shekhter; Terrance B. Tripp; Leonid L. Lanin; Karlheinz Reichert; Oliver Thomas; Joachim Vieregge
Original assignee: Individual
Current assignee: Taniobis GmbH
Priority date: 1998-05-06
Filing date: 1999-05-05
Publication date: 2000-11-16
Anticipated expiration: 2019-05-05
Also published as: IL139061A; UA67779C2; IL139061A0; CA2331707C

Abstract

Metal powder Ta and/or Nb, with or without one or metals from the group Ta, Nb, Ti, Mo, W, V, Zr and Hf, is made in a fine powder form by reduction of metal oxide by contact with a gaseous reducing agent, preferably an alkaline earth metal, to near complete reduction, leaching, further deoxidation and agglomeration, the powder so produced being sinterable to capacitor anode form and processable to other usages.

Claims

1. Process for production of metal powders selected from the class consisting of Ta and Nb, and all up thereof, alone or with one or more metals selected from the class consisting of Ti, Mo, W, Hf, V and Zr added thereto or coproduced therewith, comprising the steps of:
(a) providing an oxide or mixed oxides of the metal(s), the oxide itself being in a form that is traversable by gas, (b) generating a gaseous reducing agent at a site outside the oxide mass and passing the gas through the mass at an elevated temperature, (c) the reactants selection, porosity of the oxide, temperature and time of the reduction reaction being selected for substantially complete reduction of the oxide(s) to free the metal portion thereof, the residual oxide of reducing agent formed in the reaction being easily removable, whereby a high surface area powder is formed in a process that essentially avoids use of molten state reducing agent in production of metal or alloy powder.

2. Process for production of metal powders from the class consisting of Ta and/or Nb and all up thereof alone or with one or more of metals selected from the class of Ti, Mo, W, Hf and V and Zr comprising the steps of:

(a) providing an oxide or mixed oxides of the metal(s), the oxide being in a form that is traversible by gas, (b) passing a hydrogen containing gas through the mass at an elevated temperature, (c) the porosity of the oxide, temperature and time of reduction reaction being selected to remove at least 20% of the oxygen contained in the oxide to produce a suboxide, (d) further reducing the suboxide in a second stage with reducing agents selected from the class of reducing metals and hydrides of reducing metals, thereby substantially completely reducing the oxide to free the metal portion thereof.

3. Process in accordance with claim 1 or 2, wherein the reducing agent is selected from the class consisting of Mg, Ca, Al, Li, Ba, Sr and the hydrides thereof.

4. Process in accordance with one of claims 1 to 3, wherein the metal or alloy powder is processed to an agglomerated secondary form.

5. Process according to one of claims 1 to 4, wherein the metal powder is further deoxidized by new exposure to a gaseous reducing agent.

6. Process according to claim 2, characterized in that the reduction in the first stage is carried out at least until the volume of solid matter is reduced by to 50%.

7. Process according to claim 2 or 6, characterized in that the reduction in the first stage is conducted as far as MeO x, wherein Me denotes Ta and/or Nb and x assumes a value of 1 to 2.

8. Process according to one of claims 2, 6 or 7, characterized in that the reduction product from the first stage is maintained at approximately the reduction temperature for a further 60 to 360 minutes.

9. Process according to one of claims 2 or 6 to 8, characterized in that Mg, Ca and/or hydrides thereof are used as reducing agents in the second stage.

10. Process in accordance with one of claims 1 to 9, wherein the metal consists essentially of tantalum and the oxide is tantalum pentoxide.

11. Process in accordance with one of claims 1 to 10, wherein the metal comprises niobium and the oxide comprises niobium pentoxide or a niobium suboxide.

12. Process in accordance with claim 11, wherein the oxide contains tantalum in an amount of up to 50 at.-% based on the total content of metals.

13. Process in accordance with one of claims 1 to 12, wherein the form of the oxide mass traversible by gas provides a void volume of at least 90%.

14. Process in accordance with one of claims 1 to 13, wherein the oxide is provided in the form of agglomerated primary oxide particles with diameters of between 100 to 1000 nm and an average agglomerate size of 10 to 1000 µm (Mastersizer D50).

15. Process in accordance with one of claims 1 to 14, wherein the reducing agent is magnesium.

16. Process according to one of claims 1 to 15, wherein the elevated temperature during passing the gaseous reducing agent through the oxide mass is below 0.5 TM, wherein TM means the melting point of metal powder.

17. Process according to claim 16, wherein the temperature is below 0.4 TM.

18. Process in accordance with one of claims 1 to 17, wherein the primary metal powder is subjected to a further deoxidation treatment to produce a finished powder.

19. Process in accordance with claim 18, wherein one or more finishing deoxidation steps are provided as an extension of the reduction reaction.

20. Process in accordance with claim 19, wherein the finishing deoxidation is a separate treatment.

21. Process in accordance with one of claims 1 to 20, wherein the metal powder is processed to an agglomerated secondary form.

22. Process in accordance with claim 21, wherein a deoxidation step is applied to the agglomerated secondary form of the powder.

23. Process in accordance with one of claims 1 to 22, wherein the metal powder is further formed into a coherent porous mass.

24. Niobium powder in the form of agglomerated primary particles with a particle size of 100 to 1000 nm, wherein the agglomerates have a particle size corresponding to D10 = 3 to 80 µm, D50 = 20 to 250 µm and D90 30 to 400 µm as determined by Mastersizer.

25. Niobium powder according to claim 24, containing up to 40 at.% of Ta alone or with one or more of at least one metal selected from the group of Ti, Mo, W, Hf, V and Zr, based on the total metal content.

26. Niobium powder according to claim 25, containing at least 2 at.-% of the other metal(s).

27. Niobium powder according to claim 25, containing at least 3.5 at.-% of the other metal(s).

28. Niobium powder according to claim 25, containing at least 5 at.-% f the other metal(s).

29. Niobium powder according to claim 25, containing at least 10 at.-% of the other metal(s).

30. Niobium powder according to claims 25 to 29, containing up to 34 at.-% of the other metal(s).

31. Niobium powder according to one of claims 25 to 30, containing tantalum as the other metal.

32. The powder according to one of claims 24 to 31, in the form of agglomerated substantially spherical primary particles of 100 to 1500 nm diameter.

33. The powder according to one of claims 24 to 32, having a product of BET-surface and alloy density of 8 to 250 (m2/g) x (g/cm3).

34. The powder according to one of claims 24 to 33, having a ratio of Scott-density and alloy density of 1.5 to 2.3 (g/inch3/(g/cm3).

35. The powder according to claim 32 having an agglomerate particle size of 20 to 300 µ as determined as D50-value according to Mastersizer.

36. Niobium powder according to one of claims 24 to 35, containing oxygen in amounts of 2500 - 4500 ppm/m2 BET-surface, up to 10,000 ppm nitrogen, up to 150 ppm carbon, and less than a total of 500 ppm impurity metals.

37. Niobium powder according to one of claims 24 to 35, which after sintering at 1100°C and forming at 40 V exhibit a specific capacitor capacitance of 80,000 to 250,000 µFV/g and a specific leakage current density of less than 2 nA/µFV.

38. Niobium powder according to one of claims 24 to 35, which after sintering at 1250°C and forming at 40 V exhibit a specific capacitor capacitance of 30,000 to 80,000~µFV/g and a specific leakage current density of less than 1 nA/µFV .

39. A capacitor anode obtained by sintering of a powder in accordance with one of claims 24 to 38 and anodization.

40. A capacitor containing an anode according to claim 39.

41. The capacitor according to claim 40 as a solid electrolyte capacitor.

42. An alloy powder for use in the manufacture of electrolyte capacitors consisting essentially of niobium and containing up to 40 at.-% of tantalum based on the total content of Nb and Ta.

43. The powder according to claim 42, containing at least 2 at.-% of tantalum.

44. The powder according to claim 43, containing at least 3.5 at. -% of tantalum.

45. The powder according to claim 43, containing at least 5 at.-% of tantalum.

46. The powder according to claim 43, containing at least 10 at.-% of tantalum.

47. The powder according to claim 42, containing from 12 to 34 at.-% of tantalum.

48. The powder according to one of claims 42 to 47 in the form of agglomerated flakes having a product of BET surface area and alloy density of 8 to 45 (m2/g) x (g/cm3).

49. The powder according to one of claims 42 to 47 in the form of agglomerated substantially spherical primary particles having a diameter of 100 to 1500 nm and having a product of BET surface and density of 15 to 60 (m2/g) x (g/cm3).

50. The powder according to claim 7 or 8 having a mean particle size D50-value according to Mastersizer of 20 to 250 µm.

51. The powder according to one of claim 42 to 50, having a Scott density of 1.5 to 3(g/inch3)/(g/cm3).

52. A capacitor anode obtained by sintering of a powder in accordance with one of claim 42 to 51 and anodization.

53. A capacitor comprising an anode according to claim 52.

54. A process for the manufacture of alloy powder according to claim 48, comprising the steps of (a) Hydriding an electron-beam melted alloy ingot containing Nb and up to 40 at.-% Ta based on the total content of Nb and Ta, and (b) Comminuting said hydrided alloy ingot, and (c) Dehydriding the comminuted alloy obtained from step (b), and (d) Forming said comminuted alloy into flakes, and (e) Agglomerating said flakes at a temperature of 800 to 1150°C in the presence of an alkali earth metal as a reducing agent, and (f) Leaching and washing the agglomerated alloy flakes to remove any residual and residual product of the reducing agent.

55. The process according to claim 54, wherein during the agglomeration step the alloy powder is doped with phosphorous and/or nitrogen.

56. A niobium-tantalum alloy powder capable of achieving after sintering and forming a ratio of specific capacitance and powder BET surface of more than 65,000 (µFV/g)/(m2/g) preferably more than 70.000 (µFVg)/(m2/g).