Molten salt de-oxygenation of metal powders
Methods of removing oxygen from a metal are described. In one example, a method ( 100 ) can include forming a mixture ( 110 ) including a metal, a calcium de-oxygenation agent, and a salt. The mixture can be heated ( 120 ) at a de-oxygenation temperature for a period of time to reduce an oxygen content of the metal, thus forming a de-oxygenated metal. The de-oxygenation temperature can be above a melting point of the salt and below a melting point of the calcium de-oxygenation agent. The de-oxygenated metal can then be cooled ( 130 ). The de-oxygenated metal can then be leached with water and acid to remove by-products and obtain a product ( 140 ).
1. A method of removing dissolved oxygen from a metal, comprising:
forming a mixture comprising a metal having a dissolved oxygen content, a calcium de-oxygenation agent, and a salt, wherein the calcium de-oxygenation agent is present in an amount such that a molar ratio of calcium atoms in the calcium de-oxygenation agent to oxygen atoms in the metal is from about 1 to 5;
heating the mixture at a de-oxygenation temperature for a period of time in a controlled atmosphere to reduce the dissolved oxygen content of the metal to form a de-oxygenated metal, wherein the de-oxygenation temperature is above a melting point of the salt and below a melting point of the calcium de-oxygenation agent; and
cooling the de-oxygenated metal.
2. The method of claim 1 , wherein the metal is in a form of powders, milled articles, finished articles, scrap material, turning, cuttings, chips, chunks, or combinations thereof.
3. The method of claim 1 , wherein the metal is in the form of a metal powder and has an average particle diameter from about 1 μm to 10 mm.
4. The method of claim 1 , wherein the metal has an average diameter from about 1 μm to 10 cm.
5. The method of claim 1 , wherein the metal comprises titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, hydrides thereof, alloys thereof, or combinations thereof.
6. The method of claim 1 , wherein the metal comprises titanium.
7. The method of claim 1 , wherein the calcium de-oxygenation agent comprises calcium metal, CaH 2 , or combinations thereof.
8. The method of claim 1 , wherein the controlled atmosphere includes argon and the salt comprises a calcium halide-containing salt.
9. The method of claim 8 , wherein the calcium-containing salt further comprises a secondary halide salt of a metal other than calcium.
10. The method of claim 8 , wherein the calcium-containing salt is a eutectic mixture with a melting point from about 400° C. to about 770° C.
11. The method of claim 1 , wherein the controlled atmosphere comprises hydrogen and the salt includes an alkali metal halide salt, an alkaline earth metal halide salt, a non-alkali halide salt, or combination thereof.
12. The method of claim 11 , wherein the salt is non-calcium halide-containing salt including an alkali halide salt, or alkali halide-alkali halide eutectic salt.
13. The method of claim 12 , wherein the non-calcium halide-containing salt is selected from the group consisting of potassium halide, lithium halide, magnesium halide, sodium halide, and combinations thereof.
14. The method of claim 1 , wherein the de-oxygenation temperature is from about 400° C. to about 850° C.
15. The method of claim 1 , wherein the controlled atmosphere comprises argon, hydrogen, or a combinations thereof.
16. The method of claim 1 , further comprising:
leaching the de-oxygenated metal with water then an acid; and
drying the de-oxygenated metal.
17. The method of claim 16 , wherein the drying occurs in air or by freeze drying in vacuum.
18. The method of claim 1 , wherein the oxygen content of the de-oxygenated metal is less than about 0.1 wt %.
19. A method of removing dissolved oxygen from a metal powder, comprising:
a) mixing a calcium de-oxygenation agent with a metal powder to be deoxygenated according to a specific ratio depending on an amount of dissolved oxygen to be removed to form a powder mixture, wherein the calcium de-oxygenation agent includes solid calcium (Ca), calcium hydride (CaH 2 ), or both, wherein the specific ratio is a molar ratio of calcium atoms in the calcium de-oxygenation agent to oxygen atoms in the metal is from about 1 to 5;
b) blending the powder mixture with a salt to form a blended mixture, wherein the salt has a melting point below a melting point of the calcium de-oxygenation agent;
c) heating the blended mixture to a high temperature for a period of time, in an inert or reducing atmosphere, sufficient to reduce dissolved oxygen content of the metal powder below a predetermined oxygen threshold to form a de-oxygenated metal powder, wherein the high temperature is above a melting point of the salt and below the melting point of the calcium de-oxygenation agent; and
d) cooling the de-oxygenated metal powder.
20. The method of claim 19 , wherein the heating is in an inert atmosphere and the salt comprises calcium halide salt, calcium halide-alkali halide eutectic salt, calcium halide-calcium halide eutectic salt, or a combination thereof, to form a blended mixture.
21. The method of claim 19 , wherein the heating is in a reducing atmosphere and the salt comprises an alkali halide salt, and optionally a non-calcium alkali halide salt.