Iron nitride powder with anisotropic shape

Abstract

Techniques are disclosed for milling an iron-containing raw material in the presence of a nitrogen source to generate anisotropically shaped particles that include iron nitride and have an aspect ratio of at least 1.4. Techniques for nitridizing an anisotropic particle including iron, and annealing an anisotropic particle including iron nitride to form at least one α″-Fe16N2 phase domain within the anisotropic particle including iron nitride also are disclosed. In addition, techniques for aligning and joining anisotropic particles to form a bulk material including iron nitride, such as a bulk permanent magnet including at least one α″-Fe16N2 phase domain, are described. Milling apparatuses utilizing elongated bars, an electric field, and a magnetic field also are disclosed.

What is claimed is: 
     
         1 . An apparatus comprising:
 a plurality of elongated bars, wherein at least some of elongated bars of the plurality of elongated bars have a width between about 5 millimeters (mm) and about 50 mm;   a bin configured to house the plurality of elongated bars;   at least one support structure configured to support the bin; and   a means for rotating the bin about an axis of the bin.   
     
     
         2 . The apparatus of  claim 1 , further comprising a means for vibrating the bin. 
     
     
         3 . The apparatus of  claim 1 , further comprising a means for rotatably coupling the support structure and the bin. 
     
     
         4 . The apparatus of  claim 1 , wherein the bin is configured to rotate at a speed greater than 250 revolutions per minute (rpm). 
     
     
         5 . The apparatus of  claim 1 , wherein the means for rotating the bin comprises a motor mechanically coupled to the bin. 
     
     
         6 . The apparatus of  claim 1 , wherein each elongated bar of the plurality of elongated bars has a length along a horizontal axis of the elongated bar that is longer than a diameter of the bin. 
     
     
         7 . An apparatus comprising:
 a plurality of milling media;   a bin configured to house the plurality of milling media;   a generator comprising at least one of a spark discharge mode or a glow discharge mode, wherein the generator is configured to generate an electric field within the bin;   a first wire comprising a first end and a second end, wherein the first end of the first wire is affixed to at least one milling medium and the second end of the first wire is electrically coupled to a first terminal of the generator;   a second wire comprising a first end and a second end, wherein the first end of the second wire is electrically coupled to the bin and a ground and the second end of the second wire is electrically coupled to a second terminal of the generator;   at least one support structure configured to support the bin; and   a means for rotating the bin about an axis of the bin.   
     
     
         8 . The apparatus of  claim 7 , further comprising a means for vibrating the bin. 
     
     
         9 . The apparatus of  claim 7 , further comprising a means for rotatably coupling the support structure and the bin. 
     
     
         10 . An apparatus comprising:
 a plurality of milling media;   a bin configured to house the plurality of milling media;   a means for generating a magnetic field within the bin;   at least one support structure configured to support the bin; and   a means for rotating the bin about an axis of the bin.   
     
     
         11 . The apparatus of  claim 10 , further comprising a means for vibrating the bin. 
     
     
         12 . The apparatus of  claim 10 , further comprising a means for rotatably coupling the support structure and the bin. 
     
     
         13 . A method comprising:
 nitridizing an anisotropic particle including iron to form an anisotropic particle including iron nitride; and   annealing the anisotropic particle including iron nitride to form at least one α″-Fe 16 N 2  phase domain within the anisotropic particle including iron nitride,   wherein the anisotropic particle including iron nitride has an aspect ratio of at least 1.4,   wherein the aspect ratio for the anisotropic particle including iron nitride comprises the ratio of the length of a longest dimension to the length of a shortest dimension of the anisotropic particle including iron nitride, and   wherein the longest dimension and the shortest dimension are substantially orthogonal.   
     
     
         14 . The method of  claim 13 , further comprising, prior to nitridizing the anisotropic particle including iron, reducing an anisotropic iron precursor to form the anisotropic particle including iron. 
     
     
         15 . The method of  claim 13 , wherein the anisotropic iron precursor comprises an anisotropic particle including iron oxide. 
     
     
         16 . The method of  claim 13 , wherein reducing the anisotropic iron precursor comprises exposing the iron precursor to hydrogen gas to form the anisotropic particle including iron. 
     
     
         17 . The method of  claim 13 , wherein annealing the anisotropic particle including iron nitride comprises heating the anisotropic particle including iron nitride at a temperature between about 100° C. and about 250° C. for between about 20 hours and about 200 hours. 
     
     
         18 . The method of  claim 13 , wherein the anisotropic particle including iron includes a plurality of anisotropic particles including iron, wherein the plurality of anisotropic particles including iron are nitridized to form a plurality of anisotropic particles including iron nitride, and wherein the plurality of anisotropic particles including iron nitride are annealed to form at least one α″-Fe 16 N 2  phase domain within at least some of the anisotropic particles including iron nitride of the plurality of anisotropic particles including iron nitride. 
     
     
         19 . A workpiece comprising the anisotropic particles made by the method of  claim 13   
     
     
         20 . The workpiece of  claim 19 , wherein the workpiece is a film or wire. 
     
     
         21 . The workpiece of  claim 19 , wherein the workpiece is a wire, rod, bar, conduit, hollow conduit, film, sheet, or fiber.