Patent Application

App. No. 11/576,320

Abstract

Claims (29)

1 . A method of producing a refractory metal powder comprising:

(A) providing a metal powder containing magnesium tantalate or magnesium niobate; and

(B) heating the powder in an inert atmosphere in the presence of a reducing agent to a temperature sufficient to remove magnesium tantalate or magnesium niobate from the powder (reduction step) and/or heating the powder under vacuum to a temperature sufficient to remove magnesium tantalate or magnesium niobate from the powder (heating under vacuum step), the reduction step and heating under vacuum step can be performed in any order.

2 . The method according to claim 1 , wherein the metal powder is free-flowing.

3 . The method according to claim 1 , wherein the reducing agent in step (B) is selected from the group consisting of magnesium, aluminum, calcium, and combinations thereof.

4 . The method according to claim 1 , wherein the temperature in (B) is a temperature at which the magnesium tantalate or magnesium niobate is unstable.

5 . The method according to claim 1 , wherein step (B) is only the heating under vacuum step.

6 . The method according to claim 1 , wherein step (B) is only the reduction step.

7 . The method according to claim 1 , wherein the reduction step in (B) is conducted in the presence of an inert gas.

8 . The method according to claim 7 , wherein the inert gas is selected from neon and argon.

9 . The method according to claim 1 , wherein the temperature in the reduction step in (B) is from 800° C. to 1,300° C.

10 . The method according to claim 1 , wherein the temperature in the heating under vacuum step in (B) is from 1,100° C. to 1,400° C.

11 . The method according to claim 1 , wherein the heating under vacuum step in (B) is carried out by heating the powder to 800° C. to 1,000° C. for from 1 to 6 hours.

12 . The method according to claim 1 , wherein the reduction step in (B) is carried out by heating the powder under vacuum at 1,100° C. to 1,400° C. for from 15 minutes to 6 hours.

13 . The method according to claim 1 , wherein step (B) is carried out by

i) heating the metal powder under vacuum at 1,100° C. to 1,400° C. for from 15 minutes to 6 hours, and

ii) heating the powder in the presence of a reducing agent at 800° C. to 1,300° C. for from 1 to 6 hours.

14 . The method according to claim 1 , wherein step (B) is carried out by

i) heating the powder in the presence of a reducing agent at 800° C. to 1,300° C. for from 1 to 6 hours; and

ii) heating the metal powder under vacuum at 1,100° C. to 1,400° C. for from 15 minutes to 6 hours.

15 . The method according to claim 13 , wherein the heating step (ii) is conducted in the presence of an inert gas.

16 . The method according to claim 15 , wherein the inert gas is selected from neon and argon.

17 . The method according to claim 14 , wherein the heating step (i) is conducted in the presence of an inert gas.

18 . The method according to claim 17 , wherein the inert gas is selected from neon and argon.

19 . The method according to claim 1 , wherein the magnesium tantalate and/or magnesium niobate in (A) are present at from 0.02 wt. % to 7 wt. % based on the weight of the metal powder.

20 . The method according to claim 1 , wherein after step (B), the magnesium tantalate and/or magnesium niobate are present at less than 500 ppm.

21 . A refractory metal powder prepared according to the method of claim 20 .

22 . The method according to claim 1 , further comprising forming the refractory metal powder into pellets at an appropriate sintering temperature.

23 . The method according to claim 22 , further comprising forming the sintered pellets into electrolytic capacitors.

Assignments (11)