Method of making environmentally stable reactive alloy powders

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.