Manufacturing and applications of metal powders and alloys
The present invention is directed to a method of manufacture of metal or alloy powders that uses liquid phase reduction of a metal halide, or a mixture of metal halides, to produce a metal particle coated in salts produced as a reaction byproduct. The reaction conditions can be chosen to select a range of metal particle sizes, and the salt coating prevents oxidation (or reaction with other atmospheric gases) and permits a range of applications hitherto difficult to achieve using metal powders.
1. A process for the production of metal powder comprising the steps of:
(a) reducing a mixture of at least one metal halide by molten metal reduction of the liquid phase of the metal halide in a reductant selected from an alkali or alkaline earth metal, wherein the metal halide is present as a stoichiometric excess of the molten reductant, thereby forming reaction products comprising molten metal, metal halide, and free metallic reductant;
(b) separating the reaction products formed in step (a); and
(c) forming a metal powder from a reaction product in step (b);
wherein the at least one metal halide mixture comprises a mixture of metal chlorides and the reductant is metallic sodium; and
wherein the process is conducted as a one-pass operation in which the molten metal is reacted with a liquid metal halide and the solids are recovered with only the molten metal being intentionally recirculated.
2. The process of claim 1 , wherein the reductant metallic sodium comprises at least 0.1% free metallic sodium by weight.
3. The process of claim 1 , wherein the reductant metallic sodium comprises at least 1% free metallic sodium by weight.
4. The process of claim 1 , further comprising passivation or removal of excess free metallic sodium.
5. The process of claim 4 , wherein the metal powder comprises a valve metal or a valve metal alloy.
6. The process of claim 5 , wherein the valve metal or valve metal alloy is selected from the group consisting of tantalum, niobium, aluminum, and alloys thereof, and aluminum-silicon alloys.
7. The process of claim 6 , further comprising the step of forming one or more powder metallurgical components from the metal powder.
8. The process of claim 7 , wherein the powder metallurgical components include an anode.
9. The process of claim 7 , wherein the powder metallurgical components include a capacitor.
10. The process of claim 7 , wherein the powder metallurgical components include a metal sheet or wafer.
11. The process of claim 7 , wherein the powder metallurgical components include a sputtering target.
12. A process for the production of metal powder comprising the steps of:
(a) reducing a mixture of at least one metal halide by molten metal reduction of the liquid phase of the metal halide in an alkali or alkaline earth metal;
wherein the at least one metal halide mixture is a mixture of metal chlorides and the reductant is metallic sodium;
wherein the reaction product comprises the at least one metal mixture, a salt coating, and at least 1% free metallic sodium; and
wherein the molten metal is reacted with the liquid metal halide and the solids are recovered with only the molten metal being recirculated;
(b) separating the reaction products including formed in step (a); and
(c) forming a metal powder from a reaction product in step (b).