Claims
- 1. A method of making powder from a metallic melt having a composition including a reactive alloying element, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets, and
- b) contacting a reactive gas and the droplets at a downstream location in the chamber relative to the location of melt atomization where at said downstream location the droplets have cooled to a temperature where they have at least a solidified exterior surface and where the reactive gas reacts with said reactive alloying element to form a reaction product layer whose penetration into the droplets is limited by the presence of said solidified surface to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the reactive alloying element from the melt composition at the droplet core.
- 2. The method of claim 1 wherein in step b, the reactive gas reacts with the reactive alloying element to form an environmentally protective barrier layer on the droplet, said barrier layer comprising a refractory compound of the reactive alloying element.
- 3. The method of claim 1 wherein in step b, the droplets are passed through a zone of the reactive gas disposed in the chamber downstream of the location where the melt is atomized, said droplets cooling to said temperature as they pass from the atomization location to said zone.
- 4. The method of claim 1 including the additional step of forming in the chamber a carbon-bearing layer on the reaction product layer.
- 5. The method of claim 4 wherein a graphite layer is formed on the reaction product layer.
- 6. The method of claim 4 wherein the droplets are contacted at an elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
- 7. The method of claim 1 wherein in step b, the reactive gas and the droplets are contacted when the droplets are solidified from the exterior surface substantially to the droplet core.
- 8. A method of making powder from a rare earth-transition metal alloy melt having a composition selected to provide desired powder magnetic properties, comprising the steps of:
- a) atomizing the rare earth-transition metal alloy melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets, and
- b) contacting a reactive gas and the droplets at a downstream location in the chamber relative to the location of melt atomization where at said downstream location the droplets have cooled to a temperature where they have at least a solidified exterior surface and where the reactive gas reacts with said rare earth element to form a reaction product layer whose penetration into the droplets is limited by the presence of said solidified surface to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the rare earth element from said melt composition at the droplet core.
- 9. The method of claim 8 wherein in step b, the reactive gas reacts with the rare earth to form an environmentally protective barrier layer on the droplet, said barrier layer comprising a refractory compound of the reactive alloying element.
- 10. The method of claim 8 wherein in step b, the droplets are passed through a zone of the reactive gas disposed in the chamber downstream of the location where the melt is atomized, said droplets cooling to said temperature as they pass from the atomization location to said zone.
- 11. The method of claim 8 including the additional step of forming in the chamber carbon-bearing layer on the reaction product layer.
- 12. The method of claim 11 wherein a graphite layer is formed on the reaction product layer.
- 13. The method of claim 11 wherein the droplets are contacted at elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
- 14. The method of claim 8 wherein in step b, the reactive gas and the droplets are contacted when the droplets are solidified from the exterior surface to the droplet core.
- 15. A method of making powder from a rare earth-iron-boron alloy melt having a composition selected to provide desired powder magnetic properties, comprising the steps of:
- a) atomizing the rare earth-iron-boron alloy melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets, and
- b) contacting a reactive gas and the droplets at a downstream location in the chamber relative to the location of melt atomization where at said downstream location the droplets have cooled to a temperature where they have at least a solidified exterior surface and where the reactive gas reacts with at least one of said rare earth and said boron to form a reaction product layer whose penetration into the droplets is limited in surface depth by the presence of said solidified surface to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the rare earth and boron from said melt composition at the droplet core.
- 16. The method of claim 15 wherein in step b, the reactive gas reacts with at least one of said rare earth and boron to form an environmentally protective barrier layer on the droplet, said barrier layer comprising a refractory compound of the reactive alloying element.
- 17. The method of claim 15 wherein in step b, the droplets are passed through a zone of the reactive gas disposed in the chamber downstream of the location where the melt is atomized, said droplets cooling to said temperature as they pass from the atomization location to said zone.
- 18. The method of claim 15 including the additional step of forming in the chamber a carbon-bearing layer on the reaction product layer.
- 19. The method of claim 18 wherein a graphite layer is formed on the reaction product layer.
- 20. The method of claim 18 wherein the droplets are contacted at an elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
- 21. The method of claim 15 wherein in step b, the reactive gas and the droplets are contacted when the droplets are solidified from the exterior surface to the droplet core.
- 22. A method of making powder from a melt having a composition including a reactive alloying element, comprising the steps of:
- a) atomizing the melt into molten droplets in a drop tube using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization allowing for free fall of said droplets downwardly through the tube and cooling of said droplets as they fall, and
- b) establishing a zone of reactive gas in the tube downstream of the atomizing location where the droplet temperature is so reduced from said cooling that said droplets have at least a solidified exterior shell thereon and that the reactive gas reacts with the reactive alloying element as the droplets pass through the zone to form a reaction product layer thereon whose penetration into the droplets is limited in surface depth by the presence of said shell to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the reactive alloying element from said melt composition at the droplet core.
- 23. The method of claim 22 wherein in step b, the reactive gas reacts with the reactive alloying element to form an environmentally protective barrier layer on the droplet, said barrier layer comprising a refractory compound of the reactive alloying element.
- 24. The method of claim 22 wherein the melt is inert gas pressure atomized in step a.
- 25. The method of claim 22 wherein in step b, the droplets are passed through the zone when said droplets are solidified from the exterior surface to the core.
- 26. The method of claim 22 further including contacting the droplets at elevated temperature with a gaseous carbonaceous material in the chamber after formation of the reaction product layer to form a carbon-bearing layer on the reaction product layer.
- 27. The method of claim 26 wherein a graphite layer is formed on the reaction product layer.
- 28. A method of making powder from a metallic melt having a composition including a reactive alloying element, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets, and
- b) forming a reaction product layer not exceeding about 500 Angstroms in thickness on the droplets by reacting the reactive alloying element and a reactive gas at a downstream location in the chamber relative to the location of melt atomization where at the downstream location, the droplets have at least a solidified exterior shell.
- 29. A method of making powder from a rare earth-transition metal alloy melt, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets, and
- b) forming a reaction product layer not exceeding about 500 Angstroms in thickness on the droplets by reacting the rare earth of the alloy and a reactive gas at a downstream location in the chamber relative to the location of melt atomization where at the downstream location, the droplets have at least a solidified exterior shell.
- 30. A method of making powder from a metallic melt having a composition including a reactive alloying element, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas so as to form droplets,
- b) forming a reaction product layer on the droplets by reacting a reactive gas in the chamber and the reactive alloying element, and
- c) forming a carbon-bearing layer on the reaction product layer by contacting a gaseous carbonaceous material in the chamber therewith.
- 31. A method of making powder from a rare earth-transition metal alloy melt, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas that is inert to said melt,
- b) forming a reaction product layer on the droplets by reacting a reactive gas in the chamber and the rare earth, and
- c) forming a carbon-bearing layer on the reaction product layer by contacting a gaseous carbonaceous material in the chamber therewith.
- 32. A method of making powder from a rare earth-iron-boron melt, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas that is inert to said melt,
- b) forming a reaction product layer on the droplets by reacting a reactive gas in the chamber and the rare earth and boron, and
- c) forming a carbon-bearing layer on the reaction product layer by contacting a gaseous carbonaceous material in the chamber therewith.
- 33. A method of making powder from a metallic melt having a composition including a reactive alloying element, comprising the steps of:
- a) atomizing the melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets,
- b) contacting a reactive gas and the droplets at a downstream location in the chamber relative to the location of melt atomization where at said downstream location the droplets have cooled to a temperature where they have at least a solidified exterior surface and where the reactive gas reacts with said reactive alloying element to form a reaction product layer whose penetration into the droplets is limited by the presence of said solidified surface to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the reactive alloying element from the melt composition at the droplet core, and
- c) forming in the chamber a carbon-bearing layer on the reaction product layer.
- 34. The method of claim 33 wherein a graphite layer is formed on the reaction product layer.
- 35. The method of claim 33 wherein the droplets are contacted at an elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
- 36. A method of making powder from a rare earth-transition metal alloy melt having a composition selected to provide desired powder magnetic properties, comprising the steps of:
- a) atomizing the rare earth-transition metal alloy melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets,
- b) contacting a reactive gas and the droplets at a downstream location in the chamber relative to the location of melt atomization where at said downstream location the droplets have cooled to a temperature where they have at least a solidified exterior surface and where the reactive gas reacts with said rare earth element to form a reaction product layer whose penetration into the droplets is limited by the presence of said solidified surface to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the rare earth element from said melt composition at the droplet core, and
- c) forming in the chamber a carbon-bearing layer on the reaction product layer.
- 37. The method of claim 36 wherein a graphite layer is formed on the reaction product layer.
- 38. The method of claim 36 wherein the droplets are contacted at an elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
- 39. A method of making powder from a rare earth-iron-boron alloy melt having a composition selected to provide desired powder magnetic properties, comprising the steps of:
- a) atomizing the rare earth-iron-boron alloy melt in a chamber using an atomizing gas that is inert to said melt so as to avoid reaction therewith during atomization and form molten droplets,
- b) contacting a reactive gas and the droplets at a downstream location in the chamber relative to the location of melt atomization where at said downstream location the droplets have cooled to a temperature where they have at least a solidified exterior surface and where the reactive gas reacts with at least one of said rare earth and said boron to form a reaction product layer whose penetration into the droplets is limited in surface depth by the presence of said solidified surface to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the rare earth and boron from said melt composition at the droplet core, and
- c) forming in the chamber a carbon-bearing layer on the reaction product layer.
- 40. The method of claim 39 wherein a graphite layer is formed on the reaction product layer.
- 41. The method of claim 39 wherein the droplets are contacted at an elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
- 42. A method of making powder from a melt having a composition including a reactive alloying element, comprising the steps of:
- a) atomizing the melt into molten droplets in a drop tube using an atomizing gas that is inert to said melt to avoid reaction therewith during atomization for free fall of said droplets downwardly through the tube and cooling as they fall,
- b) establishing a zone of reactive gas in the tube downstream of the atomizing location where the droplet temperature is so reduced from said cooling that said droplets have at least a solidified exterior shell thereon and that the reactive gas reacts with the reactive alloying element as the droplets pass through the zone to form a reaction product layer thereon whose penetration into the droplets is limited in surface depth by the presence of said shell to not exceed about 500 Angstroms reaction product layer thickness so as to avoid selective removal of the reactive alloying element from said melt composition at the droplet core, and
- c) forming in the chamber a carbon-bearing layer on the reaction product layer.
- 43. The method of claim 42 wherein a graphite layer is formed on the reaction product layer.
- 44. The method of claim 42 wherein the droplets are contacted at an elevated temperature with a gaseous carbonaceous material in the chamber to form said carbon-bearing layer.
Parent Case Info
This is a continuation of application Ser. No. 594,088 filed Oct. 9, 1990, now abandoned.
CONTRACTUAL ORIGIN OF REFERENCE AND GRANT REFERENCE
The United States Government has rights in this invention pursuant to U.S. Department of Commerce Grant ITA 87-02.
US Referenced Citations (5)
Foreign Referenced Citations (1)
Number |
Date |
Country |
63-100108 |
May 1988 |
JPX |
Continuations (1)
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Number |
Date |
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Parent |
594088 |
Oct 1990 |
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