Method of controlling the oxygen content of a powder
View Patent ↗A method of reducing the oxygen content of a powder is provided. A canister is prepared with a getter, filled with the powder to be densified, sealed and evacuated. The canister is subjected to a hydrogen atmosphere at an elevated temperature whereby hydrogen diffuses into the canister through the walls thereof. The hydrogen forms moisture when reacted with the oxygen of the powder and the moisture in the reacted with the getter in order to remove oxygen from the powder to the getter. The atmosphere outside the canister is then altered to an inert atmosphere or vacuum, whereby hydrogen diffuses out of the canister. A dense body having a controlled amount of oxygen can thereafter be produced by conventional powder metallurgy techniques.
1. A method of producing a metal powder having controlled oxygen content comprising:
introducing a getter into a canister,
introducing a metal powder into the canister, and then evacuating and sealing the canister,
reducing the oxygen content in the metal powder by subjecting the canister to a heat treatment in an environment of gaseous hydrogen providing diffusion through the walls thereof until the hydrogen partial pressure on both sides of the walls of the canister is substantially equilibrated, and
after the oxygen reduction in the metal powder subjecting the canister to an inert atmosphere or a vacuum so as to provide hydrogen diffusion out of the canister through the walls thereof.
2. Method according to claim 1 wherein the metal powder is a stainless steel.
3. Method according to claim 1 wherein the getter is selected from the group consisting of Ti, Zr, Hf, Ta, REM or an alloy or compound based on any of these elements.
4. The method according to claim 3 , wherein the getter is Zr, Ti, or an alloy or compound thereof.
5. Method according to claim 1 wherein the step of subjecting the canister to the heat treatment in the hydrogen environment is performed at a temperature of about 900-1200° C.
6. The method according to claim 5 , wherein the temperature is about 1000-1150° C.
7. Method according to claim 1 wherein the getter is homogeneously distributed along at least one wall of the canister, and wherein said wall has a length that is equal or longer than the other walls of the canister.
8. Method according to claim 7 wherein said wall has an area equal to or bigger than the other walls of the canister.
9. Method according to claim 1 comprising the step of introducing carbon into the metal powder.
10. Method of manufacturing a dense body by powder metallurgy techniques comprising the steps of subjecting a powder to the method according to claim 1 and thereafter densifying the powder.
11. Method according to claim 10 wherein the densifying step comprises a HIP or a CIP process and is performed in the canister.