Nitrided valve metals and processes for making the same
View Patent ↗Nitrided valve metals are described, such as nitrided tantalum and nitrided niobium. The nitrided valve metals preferably have improved flow properties, higher Scott Densities, and/or improved pore size distribution which leads to improved physical properties of the valve metal and improved electrical properties once the valve metal is formed into a capacitor anode. Processes for preparing a nitrided valve metal are further described and involve nitriding the valve metal at a sufficient temperature and pressure during a heat treatment that is prior to the deoxidation step. Capacitor anodes and other products incorporating the valve metals of the present invention are further described.
1. A process of preparing a nitrided valve metal comprising nitriding a valve metal powder at a sufficient temperature and pressure during a heat treatment that is prior to a deoxidation step, wherein said nitriding occurs at a temperature of from about 200° C. to about 600° C.
2. The process of claim 1 , wherein said nitriding begins at average valve metal temperature of about 200° C. to about 350° C.
3. The process of claim 1 , wherein said nitriding occurs prior to a sintering phase of the heat treatment of the valve metal.
4. The process of claim 1 , wherein said nitriding occurs after a sintering phase of the heat treatment of the valve metal.
5. The process of claim 1 , wherein said nitriding is accomplished with nitrogen gas.
6. The process of claim 1 , wherein said nitriding is accomplished with at least one nitrogen-generating compound.
7. The process of claim 1 , wherein said nitriding results in said valve metal having a nitrogen content of from about 1,500 ppm to about 4,000 ppm.
8. The process of claim 1 , wherein said heat treatment comprises heating the valve metal to a temperature of from about 1250° C. to about 1500° C. for a period of time of from about 10 minutes to about 2 hours, wherein said valve metal is tantalum.
9. The process of claim 1 , wherein said nitriding occurs at a temperature of from about 250° C. to about 600° C.
10. The process of claim 1 , wherein prior to said nitriding, said valve metal is hydrogen degassed.
11. The process of claim 1 , wherein said nitrided valve metal, after nitriding, is subjected to at least one passivation step, at least one deoxidation step, and at least one sintering step.
12. The process of claim 1 , wherein said valve metal is tantalum.
13. The process of claim 1 , wherein said valve metal is niobium.
14. The process of claim 2 , wherein the average valve metal temperature is increased at a rate of less than 10° C. per minute until nitriding is complete.