Anisotropic iron nitride permanent magnet

Abstract

Disclosed herein are a plurality of aligned iron nitride nanoparticles, the iron nitride nanoparticles being α''-Fe 16 N2 phase domains; and α''-α''-Fe for aligned iron nitride nanoparticles. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 A permanent magnet comprising aligned iron nitride nanoparticles in which the integrated intensity ratio of the N2(004) X-ray diffraction peak is at least 7% and the diffraction vector is parallel to the alignment direction, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction that is greater than the squareness measured perpendicular to the alignment direction.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This patent application claims priority to U.S. Provisional Application No. 62 / 979,668, filed February 21, 2020, and U.S. Provisional Application No. 63 / 080,144, filed September 18, 2020, the entire disclosure of each of which is incorporated herein by reference for all purposes.

[0002] Field of the invention The disclosed invention is in the field of iron nitride magnetic materials. [Background technology]

[0003] Permanent magnets can provide high efficiency and reliability for renewable energy technologies. Rare earth permanent magnets are generally hindered by supply constraints and high prices. Novel magnets formed from more abundant and less strategically important elements are desired to replace rare earth magnets, and α''-Fe 16 Materials such as N2 are desirable candidates for such "rare earth free" magnets.

[0004] Permanent nanocomposite magnets can be fabricated from individual nanoparticles by consolidation. A binder can be used to fix the nanoparticles in a matrix. If the nanoparticles have a sufficiently large magnetic anisotropy, external forces can be used to align the nanoparticles before and / or during consolidation. However, electrostatic and electromagnetic forces generally combine to cause the nanoparticles to aggregate, typically porous and relatively large nanoparticle clusters. These aggregates can interfere with the ability of the individual nanoparticles to rotate in response to external aligning forces. Summary of the Invention [Problem to be solved by the invention]

[0005] Thus, there remains a need for rare earth-free anisotropic permanent magnetic materials that overcome the tendency of nanoparticles to agglomerate during processing to fabricate rare earth-free magnets. The disclosed invention addresses these and other important needs. [Means for solving the problem]

[0006] In various examples, the present disclosure describes a permanent magnet comprising a plurality of aligned iron nitride nanoparticles. The aligned iron nitride nanoparticles are α″-Fe 16 The iron nitride nanoparticles may contain N2 phase domains. When the diffraction vector is parallel to the alignment direction, the iron nitride nanoparticles contain at least 7% greater α''-Fe 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The iron nitride nanoparticles may exhibit a squareness measured parallel to the alignment direction that is greater than the squareness measured perpendicular to the alignment direction.

[0007] The present disclosure also describes a dispersion comprising the disclosed iron nitride nanoparticles and a suitable solvent.

[0008] Additionally, the present disclosure describes nanocomposites comprising the disclosed iron nitride nanoparticles and a suitable binder.

[0009] Additionally, this disclosure describes workpieces comprising anisotropic iron nitride nanoparticles made by any of the techniques described in this disclosure. The workpieces can take many forms, such as, for example, wires, rods, tapes, bars, conduits, hollow conduits, films, sheets, or fibers, each of which can have a wide variety of cross-sectional shapes and sizes, and any combination thereof.

[0010] Methods of forming the disclosed iron nitride nanoparticles and methods of forming articles containing same are further described in this disclosure.

[0011] The general description and the following detailed description are exemplary and explanatory only and are not limiting of the invention, as defined in the appended claims. Other aspects of the invention will be apparent to those skilled in the art from the detailed description of the invention as provided in this disclosure. Details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and specification, and from the claims.

[0012] The summary of the invention, as well as the following detailed description, will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the invention, there are shown in the drawings exemplary embodiments of the invention. However, the disclosure is not limited to the particular methods, compositions, and devices disclosed. Additionally, the drawings are not necessarily drawn to scale. [Brief explanation of the drawings]

[0013] [Figure 1] Figure 1 shows the hysteresis loop measured for sample S5, with measurements taken both parallel (solid line) and perpendicular (dashed line) to the aligning field direction.

[0014] [Figure 2] Figure 2 shows the X-ray diffraction pattern measured for sample S5, where the diffraction vector is parallel to the alignment direction.

[0015] [Figure 3] Figure 3 shows the hysteresis loop measured for the comparative sample CS6. Measurements were taken both parallel (solid line) and perpendicular (dashed line) to the aligning field direction. The inset shows the region of the hysteresis loop centered where the descending curve intersects the vertical axis.

[0016] [Figure 4] Figure 4 shows the X-ray diffraction pattern measured for the comparative sample CS6, where the diffraction vector is parallel to the alignment direction.

[0017] [Figure 5] Figure 5 shows the hysteresis loop measured for sample S8. Measurements were performed both parallel (solid line) and perpendicular (dashed line) to the aligning field direction. The inset shows the region of the hysteresis loop centered where the descending curve intersects the vertical axis.

[0018] [Figure 6] Figure 6 shows the X-ray diffraction pattern measured for sample S8, where the diffraction vector is parallel to the alignment direction.

[0019] [Figure 7] Figure 7 shows the hysteresis loop measured for sample S16. Measurements were performed both parallel (solid line) and perpendicular (dashed line) to the aligning field direction. The diamagnetic contribution from the sample holder was subtracted from the hysteresis loop. The inset shows the region of the hysteresis loop centered where the descending curve intersects the vertical axis.

[0020] [Figure 8] Figure 4 shows the X-ray diffraction pattern measured for sample S16, where the diffraction vector is parallel to the alignment direction.

[0021] [Figure 9] FIG. 9 shows an exemplary embodiment according to the present invention.

[0022] [Figure 10] FIG. 10 illustrates deagglomeration of nanoparticles according to an exemplary embodiment.

[0023] [Figure 11] FIG. 11 shows an illustration of aggregated nanoparticles.

[0024] [Figure 12-1] FIG. 12 shows an illustration of aggregated nanoparticles. [Figure 12-2] Continued from Figure 12.

[0025] [Figure 13] FIG. 13 shows the effect of milling on the magnetic properties.

[0026] [Figure 14] FIG. 14 shows the effect of milling on the phase distribution. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present disclosure may be more readily understood by reference to the following detailed description in conjunction with the accompanying drawings and examples, which form a part of this disclosure. It should be understood that the present disclosure is not limited to the specific devices, methods, applications, conditions, or parameters described and / or illustrated herein, and that the terminology used in this disclosure is for the purpose of describing particular examples and is not intended to limit the scope of the claims. When a range of values ​​is expressed, another example includes from one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations by use of the antecedent "about," it will be understood that the particular value forms another example. All ranges are inclusive and combinable. Furthermore, reference to values ​​stated within a range includes each and every value within that range.

[0028] It should be understood that certain features of the present disclosure, which are, for clarity, described in the present disclosure in the context of separate examples, may also be provided in combination in a single example. Conversely, various features of the present disclosure, which are, for simplicity of presentation, described in the context of a single example, may also be provided separately or in any subcombination.

[0029] Similarly, it should be understood that the terminology used in this disclosure is for the purpose of describing particular aspects only and is not intended to be limiting. As used herein and in the claims, the term "comprising" can include "consisting of" and "consisting essentially of" embodiments. Unless otherwise defined, all technical and scientific terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In this specification and in the appended claims, reference will be made to a number of terms, which shall be defined in this disclosure.

[0030] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a thermoplastic polymer component" includes a mixture of two or more thermoplastic polymer components. As used in this disclosure, the term "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0031] Ranges may be expressed in this disclosure as from one value (first value) to another value (second value). When such a range is expressed, the range, in some embodiments, includes either or both of the first and second values. Similarly, when values ​​are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another embodiment. It will further be understood that the endpoints of each range are significant both in relation to the other endpoint, and independently of the other endpoint. Similarly, it should be understood that many values ​​are disclosed in this disclosure, and that each value is also disclosed in this disclosure as "approximately" that particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed. It should be understood that every unit between two specified units is also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

[0032] As used in this disclosure, the terms "about" and "about" mean that the subject quantity or value can be the specified value, approximately the specified value, or approximately the same as the specified value. When used in this disclosure, unless otherwise stated or implied, it should generally be understood to be a variation of ±10% of the indicated nominal value. This term is intended to convey that similar values ​​promote results or effects equivalent to those recited in the claims. That is, it should be understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not exact, and need not be precise, but may be approximate, and / or larger or smaller, as necessary, and may reflect tolerances, conversion factors, rounding, measurement errors, and other factors known to those skilled in the art. In general, amounts, sizes, formulations, parameters, or other quantities or characteristics are "about" or "approximately" regardless of whether they are explicitly stated as such. When "about" is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0033] As used in this disclosure, the term "optional" or "optionally" means that the subsequently described event or circumstance may or may not be present, and the present detailed description is meant to include instances where said event or circumstance is present and instances where it is not. For example, the phrase "optional additional processes" means that the additional processes may or may not be included, and the present detailed description encompasses both methods that include the additional processes and methods that do not include the additional processes.

[0034] Iron nitride nanoparticles can be conveniently produced by the controlled reduction and nitridation of iron oxide nanoparticle precursors. Iron oxide nanoparticle precursors can be manufactured by a variety of means and are typically supplied as dry powders containing aggregated nanoparticle masses. In a low-temperature processing route, iron oxide nanoparticle aggregates can first be reduced to elemental iron by annealing in a hydrogen-containing atmosphere to produce iron nanoparticles. The iron nanoparticles can then be converted to iron nitride by annealing in an ammonia atmosphere. Optionally, a passivation treatment can be applied in which the iron nitride nanoparticles are coated with a thin layer of a stable metal oxide. These process steps produce isotropic aggregates of iron nitride nanoparticles characterized by high saturation magnetization and moderate coercivity. This combination of magnetic properties makes iron nitride nanoparticles useful as components of permanent magnets.

[0035] Aligned nanoparticles and permanent magnets formed therefrom Permanent nanocomposite magnets can be produced from individual nanoparticles by a suitable solidification process. If the nanoparticles have a sufficiently large magnetic anisotropy, external forces can be used to align the nanoparticles before and / or during solidification. However, electrostatic and electromagnetic forces generally combine to cause the nanoparticles to form agglomerates, which are typically porous clusters of nanoparticles that can be hundreds of microns in diameter. Therefore, it is difficult to deagglomerate the nanoparticles to the extent required to give the individual nanoparticles the ability to rotate in response to an externally applied alignment force. Furthermore, the deagglomeration process increases the specific surface area of ​​the nanoparticle aggregate. As a result of this increased surface area, the nanoparticles become more reactive, which in turn makes them more susceptible to oxidation, decomposition, and re-sintering before they align. Therefore, these nanoparticles are not aligned and, when solidified, can form an isotropic nanocomposite permanent magnet.

[0036] Isotropic nanocomposite permanent magnets have low energy product and remanent magnetization, which is due to low squareness. Because these conventional nanoparticle aggregates are isotropic, they cannot be aligned by external forces, resulting in the low remanent magnetization and low squareness described above. The aligned nanocomposite permanent magnets of the present disclosure can overcome the tendency of nanoparticles to form randomly oriented aggregates. Thus, the present disclosure provides anisotropic nanocomposite permanent magnets that exhibit increased squareness.

[0037] According to various embodiments, anisotropic nanocomposite permanent magnets can be formed by aligning the nanoparticles that make up the nanocomposite. The anisotropy of the resulting nanocomposite is thus a volume-weighted average of the anisotropies of each constituent nanoparticle, and the nanocomposite will have a preferred orientation of its magnetization vector. The remanent magnetization of the nanocomposite is the sum of the projections of the magnetization vectors of each nanoparticle onto the preferred orientation vector. Thus, the disclosed nanocomposites can overcome the inherent tendency of magnetic nanoparticles to form aggregates of many randomly oriented nanoparticles.

[0038] In various aspects, the present disclosure provides permanent magnets comprising a plurality of aligned iron nitride nanoparticles. Such permanent magnets offer a high energy product and are characterized by a preferred magnetization direction of each individual nanoparticle or grain that makes up the magnet's microstructure. As a result, the remanence (Mr) of a magnet is a large fraction of the magnet's saturation magnetization (MSat). The ratio of remanence to saturation magnetization (Mr / MSat) is defined as squareness (S). A permanent magnet can be considered anisotropic if the squareness value measured parallel to the alignment direction is greater than the squareness measured perpendicular to the alignment direction. Squareness is therefore increased by the formation of a nanocomposite permanent magnet composed of aligned anisotropic nanoparticles. As a result of this alignment, the nanocomposite has a preferred magnetization direction. The remanence and energy product of the nanocomposite are thereby increased due to the alignment of the magnetic nanoparticles disposed in the composite.

[0039] As provided in the present disclosure, the disclosed aligned nanoparticles are α″-Fe 16 N2 phase domains. 16 N2, α''-Fe 16 N2, α''-Fe 16 N2 phase and α''-Fe 16 The term N2 phase domain refers to the α''-Fe 16In some instances, the anisotropic nanoparticles formed in accordance with the techniques disclosed herein may contain at least one Fe 16 In a further example, such anisotropic particles may include a plurality of iron nitride crystals, at least some (or all) of which are Fe 16 N2 crystal. Fe 16 The disclosed anisotropic iron nitride nanoparticles containing N2 are 16 Compared to conventional isotropic particles containing N2, the particles may have improved magnetic properties, including, for example, at least one of increased squareness, magnetic orientation, or energy product. 16 The disclosed aligned anisotropic particles, including N2, may be desirable for permanent magnet applications.

[0040] The alignment of the disclosed nanoparticles can be detected by observing a greater squareness in the hysteresis loop measured parallel to the aligning field compared to the squareness in the hysteresis loop measured perpendicular to the aligning field. Thus, the nanoparticles of the present disclosure can exhibit favorable alignment when the squareness in the hysteresis loop measured parallel to the aligning field is greater than the squareness in the hysteresis loop measured perpendicular to the aligning field. As an example, iron nitride nanoparticles can exhibit a squareness measured parallel to the alignment direction that is greater than 0.50, greater than 0.75, or greater than 0.9.

[0041] The aligned iron nitride nanoparticles are α''-Fe 16 The alignment can be explained more specifically according to the intensity of specific peaks in the X-ray diffraction pattern, since it contains N2 phase domains. The alignment is along the (004) crystal plane α''-Fe 16 The (004) peak in the X-ray diffraction pattern indicates the preferred orientation of the α''-Fe 16 It corresponds to the c-axis of the unit cell of N2. The c-axis is α''-Fe 16The preferred orientation is the α''-Fe phase, which has the highest intensity in the diffraction pattern when the diffraction vector is parallel to the alignment direction. 16 α''-Fe relative to N2(202) peak 16 It can be determined by measuring the relative intensity of the N2(004) peak.

[0042] The disclosed nanoparticles exhibit such a preferred orientation. More specifically, the disclosed nanoparticles exhibit at least 7% greater α''-Fe for aligned iron nitride nanoparticles when the diffraction vector is parallel to the alignment direction. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The integrated intensity ratio of the N2(004) X-ray diffraction peak is shown. In some cases, the α''-Fe 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The integrated intensity ratio of the N2(004) X-ray diffraction peak is at least greater than 50%. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The integrated intensity ratio of the N2(004) X-ray diffraction peak is at least greater than 100%.

[0043] The anisotropic iron nitride nanoparticles achieved according to the present disclosure can be shaped, for example, as needles, flakes, laminations, wires, thin sheets, or tapes. In a further aspect, the anisotropic iron nitride nanoparticles can be bonded or joined to form bulk materials, such as bulk permanent magnets.

[0044] In some embodiments, these iron nitride particles may be configured as nanocomposites. Such nanocomposites include α''-Fe 16The nanocomposite can include a population of aligned anisotropic nanoparticles comprising N2 and a suitable binder. The nanocomposite can exhibit a squareness measured in a direction parallel to the alignment direction of the anisotropic nanoparticles that is greater than the squareness observed in a direction perpendicular to the alignment direction of the anisotropic nanoparticles. In a further embodiment, the nanocomposite exhibits a squareness of at least 7% greater than the squareness of the α''-Fe nanoparticles when the diffraction vector is parallel to the alignment direction. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 In some cases, the X-ray diffraction pattern exhibits an integrated intensity ratio of the N2(004) X-ray diffraction peak. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The integrated intensity ratio of the N2(004) X-ray diffraction peak is at least greater than 50%. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The integrated intensity ratio of the N2(004) X-ray diffraction peak is at least greater than 100%. The mass fraction of the nanoparticles in the nanocomposite can be in the range of 80% to 95%, 85% to 95%, or 90% to 95%. The volume fraction of the nanoparticles in the nanocomposite can be in the range of 40% to 75%, 50% to 75%, or 60% to 75%.

[0045] In a further aspect, and as further detailed in this disclosure, such anisotropic iron nitride nanoparticles may be formulated into a dispersion using a suitable solvent. The iron nitride nanoparticles may be α″-Fe 16 The iron nitride nanoparticles may contain the α''-FeN2 phase when the diffraction vector is parallel to the alignment direction. 16 α''-Fe versus N2(202) X-ray diffraction peak 16The integrated intensity ratio of the N2(004) X-ray diffraction peak can be aligned to at least 7% greater, and the dispersion exhibits greater squareness measured parallel to the alignment direction than measured perpendicular to the alignment direction. The mass fraction of the nanoparticles relative to the dispersion can be in the range of 80% to 95%, 85% to 95%, or 90% to 95%. The volume fraction of the nanoparticles relative to the dispersion can be in the range of 40% to 75%, 50% to 75%, or 60% to 75%.

[0046] Preparation of aligned nanoparticles and permanent magnets formed therefrom A method for forming an anisotropic permanent magnet can include annealing an iron-containing agglomerated powder in the presence of nitrogen to provide iron nitride nanoparticles. The iron nitride nanoparticles can be produced from iron-based precursor nanoparticles by a gas nitriding process carried out at low temperatures (e.g., below 200°C). This process converts the precursor nanoparticles into α''-Fe 16 Ammonia gas may be introduced to directly convert iron nitride nanoparticles containing the N phase. The low temperature range in which this nitridation process can proceed may require iron-based precursors with high specific surface areas (e.g., nanoparticles or nanoporous foams) due to slow reaction rates.

[0047] The iron-containing agglomerated powder may include, for example, an iron-containing raw material such as iron powder, bulk iron, FeCl3, Fe3O3, or Fe3O4. In some examples, the iron-containing raw material may include substantially pure iron (e.g., iron containing less than about 10 atomic percent (at. %) of dopants or impurities) in bulk or powder form. The dopants or impurities may include, for example, oxygen or iron oxide. The agglomerated powder may refer to an iron-containing material in the form of a discrete collection of particles. While a powder is depicted, the iron-containing raw material can be provided in any suitable form, such as a powder or relatively small particles. In some examples, the average size of the particles in the iron-containing raw material may be from about 50 nanometers (nm) to about 5 micrometers (μm).

[0048] The process of annealing the iron-containing agglomerated powder can be carried out according to a number of methods to reduce the nanoparticles to elemental iron, Fe. As an example, in some instances, annealing anisotropic particles comprising iron nitride can include heating the particles to a temperature of about 120°C to about 250°C, e.g., about 120°C to about 180°C, e.g., about 120°C to 150°C. Annealing can be carried out under nitrogen gas, e.g., ammonia, or the like.

[0049] The annealing process may further include a passivation step. The nanoparticles may be passivated by controlled oxidation, resulting in the formation of a layer of iron oxide on the surface of the nanoparticles. The nanoparticles may also be passivated by coating the nanoparticles with another compound, such as aluminum oxide, silicon oxide, titanium oxide, aluminum nitride, and / or titanium nitride.

[0050] In some examples, the annealing process lasts from about 10 hours to about 200 hours, e.g., from about 10 hours to about 40 hours. In one example, the annealing may be carried out for about 20 hours. In some examples, the annealing process may be carried out under an inert atmosphere, such as argon (Ar) or an Ar / oxygen blend, to reduce or substantially prevent oxidation of the iron. Furthermore, in some embodiments, the temperature is held substantially constant during annealing of the anisotropic particles comprising iron nitride.

[0051] In some instances, at least one α''-Fe is formed by nitriding and annealing an anisotropic iron-containing precursor, rather than being formed using a milling technique. 16 Anisotropic particles containing N2 phase domains can be formed. One exemplary technique involves nitriding anisotropic particles containing, for example, iron to form anisotropic iron nitride nanoparticles.

[0052] The annealed iron nitride nanoparticles can exhibit a particular intrinsic coercivity. By way of example, the iron nitride nanoparticles can exhibit an intrinsic coercivity of about 2,000 oersteds (Oe) to 4,000 Oe. In a further embodiment, the iron nanoparticles have an intrinsic coercivity of 2,500 to 4,000 Oe. In a further embodiment, the iron nanoparticles have an intrinsic coercivity of 3,000 to 4,000 Oe. The intrinsic coercivity can be measured according to many methods known in the art. In one specific example, the intrinsic coercivity can be measured using a vibrating sample magnetometer (VSM).

[0053] To increase squareness, the annealed iron nitride nanoparticles can be dispersed in a suitable fluid for further processing. The mass fraction of the iron nitride nanoparticles in a suitable fluid can be in the range of 80%-95%, 85%-95%, or 90%-95%. The volume fraction of the nanoparticles in a suitable fluid can be in the range of 40%-75%, 50%-75%, or 60%-75%. Suitable fluids include a water-based solvent (aqueous) or an organic solvent (non-aqueous) and one or more suitable additives. The one or more additives can include a dispersant, stabilizer, wetting agent, surfactant, viscosity modifier, corrosion inhibitor, emulsifier, or any combination thereof.

[0054] Thus, in one embodiment, iron nitride nanoparticles can be dispersed in a solution of one or more stabilizers and water. The resulting dispersion can be subjected to a process to deagglomerate the nanoparticles by mechanical agitation, followed by freeze-drying. These mechanical agitation processes can include, but are not limited to, ultrasonication and / or mechanical ball milling. Here, the one or more stabilizers can include steric stabilizers, such as polyethylene glycol. The one or more stabilizers can also be electrostatic stabilizers. Examples of electrostatic stabilizers include sodium citrate, sodium hexametaphosphate, or citric acid. Freeze-drying can be performed in the presence of a magnetic field to further promote alignment of the iron nitride nanoparticles.

[0055] In another embodiment, the annealed iron nitride nanoparticles can be dispersed in an organic solvent for further processing. To this end, the iron nitride nanoparticles can be dispersed in a solution of one or more stabilizers and an organic solvent, followed by ultrasonication and / or mechanical ball milling. The stabilizer that can be added to the organic solvent can include an organic compound. Suitable organic compounds include, but are not limited to, oleic acid, stearic acid, or oleylamine. The organic solvent can include a polar solvent, such as methanol, or a non-polar solvent, such as heptane. A suitable polar solvent is methanol. A suitable non-polar solvent is heptane.

[0056] Sonication can be performed by immersing the transducer of an ultrasonic probe in the nanoparticle / solvent dispersion. Ultrasonic energy can be transmitted through the solvent to the nanoparticle aggregates. Sonication creates cavitation in the solvent, which can occur within and around the nanoparticle aggregates. The collapse of the cavities creates a mechanical agitation effect on the nanoparticles, providing the force necessary to force the nanoparticles to separate (deagglomerate).

[0057] In some instances, milling can be performed using milling balls in a milling apparatus bin, for example, in rolling, stirring, or vibration modes. In some instances, the temperature at which the various components are milled can be controlled to promote the formation of anisotropic iron nitride nanoparticles. For example, techniques according to the present disclosure can include milling an iron-containing raw material with milling media at a predetermined low temperature in the presence of a nitrogen source.

[0058] After processing, excess fluid can be removed and the iron nitride nanoparticles can be dried according to a suitable method, including freeze drying, spray drying, debinding, solvent exchange, or any combination thereof.

[0059] The dried iron nitride nanoparticles can be combined with a suitable binder composition to provide a nanoparticle binder mixture. The suitable binder composition can include a polymeric material, which can be incorporated to further process the iron nitride nanoparticle aggregates. In some embodiments, the polymeric material includes acrylic, acrylate, bismaleimide, ester, urethane, styrene, polyvinyl alcohol, polyvinyl acetate, cellulose acetate, ethyl cellulose, polycarbonate, polyester, syndiotactic polystyrene, or a combination thereof. In one specific example, the iron nitride nanoparticle mixture can be combined with an epoxy composition and further processed. Because smaller aggregates exhibit greater angularity, the resulting iron nitride nanoparticle / epoxy mixture can be centrifuged as a method for separating nanoparticle aggregates, for example, by size.

[0060] In some embodiments, the nanoparticle binder mixture can be aligned in a magnetic field, i.e., in various examples, the nanoparticle binder mixture can be exposed to a magnetic field at a particular magnetic flux density (in Tesla (T)) for a period of time.

[0061] In some examples, the applied magnetic field can be at least 0.2 T (2000 Gauss). The temperature at which the magnetic field is applied can depend, at least in part, on further elemental additions to the iron nitride-based composition and the approach used to initially synthesize the iron nitride-based composition. In some examples, the magnetic field can be at least about 0.2 T, at least about 0.3 T, at least about 1 T, at least about 2 T, at least about 5 T, at least about 6 T, or at least about 8 T. In some examples, the magnetic field is between about 0.2 T and about 1 T. In other examples, the magnetic field is between about 0.3 T and about 1 T. The magnetic field can be applied as a continuous static magnetic field or as a pulsed magnetic field.

[0062] The nanoparticle binder mixture can be cured to form a permanent magnet. In thermosetting binders, the curing process occurs by cross-linking polymer molecules in the starting resin, locking the nanoparticles in place. In thermoplastic binders, curing occurs by cooling the liquid binder below its glass transition temperature.

[0063] Characteristics and Items The anisotropic iron nitride nanoparticles obtained according to the present disclosure may be shaped, for example, as needles, flakes, laminates, wires, thin sheets, or tapes. The shape of the nanoparticles can be determined by the method used to form a given nanoparticle. For example, needles can be formed by nitriding nanorods. Flakes can be formed by nitriding nanoplatelets. Wires can be formed by nitriding nanofilaments.

[0064] In further embodiments, anisotropic iron nitride nanoparticles can be bonded or joined to form bulk materials, such as bulk permanent magnets. In some examples, the workpiece includes a bulk material as described. Iron nitride materials formed by the techniques described in this disclosure can be used as magnetic materials in a variety of applications, including, for example, bulk permanent magnets. Bulk permanent magnets can include a minimum dimension of at least about 0.1 mm. In some examples, bulk materials including iron nitride can be annealed in the presence of an applied magnetic field. In other examples, the iron nitride material need not be a bulk material (it may have a minimum dimension of less than about 0.1 mm), and the iron nitride material can be solidified with other iron nitride materials to form bulk permanent magnets. Examples of techniques that can be used to solidify iron nitride magnetic materials are described in the art.

[0065] In some aspects, as provided in this disclosure, these iron nitride nanoparticles may be configured as nanocomposites or as dispersions.

[0066] In any of the above examples, other techniques for consolidating multiple anisotropic iron nitride nanoparticles may be used, such as pressure, electrical pulses, sparks, externally applied magnetic fields, radio frequency signals, laser heating, infrared heating, etc. Each of these exemplary techniques for joining multiple anisotropic particles comprising iron nitride will vary depending on the temperature used and which Fe 16 The N2 phase domain can also be left substantially unchanged (as a result, Fe 16 Relatively low temperatures may be employed (so as not to convert the N2 phase domains to other types of iron nitrides).

[0067] The present disclosure provides aligned anisotropic iron nitride nanoparticles. As shown in the present disclosure, the iron nitride nanoparticles of permanent magnets exhibit α''-Fe diffracted diffraction when the diffraction vector is parallel to the alignment direction. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 The iron nitride nanoparticles can be aligned such that the integrated intensity ratio of the N2(004) X-ray diffraction peak is at least 7%. Furthermore, the iron nitride nanoparticles can exhibit a squareness measured parallel to the alignment direction that is greater than the squareness measured perpendicular to the alignment direction.

[0068] Permanent magnets containing the disclosed aligned anisotropic iron nitride nanoparticles can exhibit many improved properties, particularly improved squareness. As shown in this disclosure, improved squareness can further improve the performance of permanent magnets. Improved squareness can increase the energy product by increasing the area of ​​the permanent magnet's hysteresis loop. Furthermore, higher squareness can result in a higher density of magnetic flux lines emanating from the poles of the permanent magnet, allowing the permanent magnet to exhibit higher remanence. This results in a higher magnetomotive force (MMF) available in the magnetic circuit.

[0069] Permanent magnets with high squareness can have a linear magnetic flux versus field (B v H) curve in the second quadrant. This property can improve demagnetization resistance in devices with high magnetic loading, such as electric motors and generators. Aligned magnets, such as the disclosed magnets, with improved squareness can also exhibit improved coercivity and further increase energy product. Anisotropic permanent magnets with high squareness have higher economic value than isotropic magnets of the same composition.

[0070] In a further embodiment, the present invention provides a method for determining the saturation magnetization (M sat This provides a method for increasing the coercivity (Hc) of iron nitride nanoparticles without sacrificing the magnetic properties of the iron nitride nanoparticles, thereby creating compositions with higher Hc and, therefore, magnetic materials with higher energy products. sat Towards a higher energy product without reducing Hc-M sat Shifting trade-offs.

[0071] For example, one method uses mechanical milling of nanoparticle precursors. Mechanical milling tailors the magnetic properties of iron nitride nanoparticles derived from agglomerated iron oxide nanoparticles. As a way to reduce the average agglomerate size, mechanical milling can be used to tailor the powder flow and handling characteristics. Without being bound by a particular theory of action, it is believed that mechanical milling can also increase the energy content of the nanoparticles by creating defects such as lattice vacancies and dislocations. Residual strain distributed among connected single nanoparticles can make these nanoparticles more reactive to process gases.

[0072] Furthermore, the milling method as described in this disclosure can promote the formation of a uniform phase composition throughout the nanoparticle aggregates, which includes a high mass fraction of the preferred α″-Fe 16 N2 phase and low mass fractions of harmful α-Fe and ε-Fe 2-3The milling method can result in a composition with a higher coercivity for a given saturation magnetization than can be obtained in iron nitride nanoparticles made without the milling method.

[0073] Aspect 1. A permanent magnet comprising a plurality of aligned iron nitride nanoparticles, wherein the iron nitride nanoparticles are α″-Fe 16 α''-Fe for aligned iron nitride nanoparticles containing N2 phase domains and with the diffraction vector parallel to the alignment direction 16 α''-Fe versus N2(202) X-ray diffraction peak 16 A permanent magnet in which the integrated intensity ratio of the N2(004) X-ray diffraction peak is at least 7% or greater, and the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction that is greater than the squareness measured perpendicular to the alignment direction.

[0074] Embodiment 2. The permanent magnet of embodiment 1, wherein the aligned iron nitride nanoparticles are formed as wires, thin sheets, or tapes, and the wires, thin sheets, or tapes are bonded together to provide the permanent magnet.

[0075] Aspect 3. α''-Fe 16 α''-Fe versus N2(202) X-ray diffraction peak 16 2. The permanent magnet according to embodiment 1, wherein the integrated intensity ratio of the N2 (004) X-ray diffraction peak is at least greater than 50%.

[0076] Aspect 4. α''-Fe 16 α''-Fe versus N2(202) X-ray diffraction peak 16 2. The permanent magnet according to embodiment 1, wherein the integrated intensity ratio of the N2 (004) X-ray diffraction peak is at least greater than 100%.

[0077] Embodiment 5. The permanent magnet of embodiment 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.50.

[0078] Embodiment 6. The permanent magnet of embodiment 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.75.

[0079] Embodiment 7. The permanent magnet of embodiment 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.9.

[0080] Embodiment 8. A dispersion comprising iron nitride nanoparticles, wherein the iron nitride nanoparticles are α″-Fe 16 When the diffraction vector is parallel to the alignment direction, the α''-Fe nanoparticles are 16 α''-Fe versus N2(202) X-ray diffraction peak 16 A dispersion having an integrated intensity ratio of the N2(004) X-ray diffraction peak greater than at least 7%, exhibiting a squareness measured parallel to the alignment direction that is greater than the squareness measured perpendicular to the alignment direction.

[0081] Embodiment 9. The dispersion of embodiment 8, wherein the mass fraction of the nanoparticles relative to the dispersion is in the range of 80% to 95%.

[0082] Embodiment 10. The dispersion of embodiment 8, wherein the mass fraction of the nanoparticles relative to the embodiment is in the range of 85% to 95%.

[0083] Embodiment 11. The dispersion of embodiment 8, wherein the mass fraction of the nanoparticles relative to the dispersion is in the range of 90% to 95%.

[0084] Embodiment 12. The dispersion of embodiment 8, wherein the volume fraction of the nanoparticles in the dispersion is in the range of 40% to 75%.

[0085] Embodiment 13. The dispersion of embodiment 8, wherein the volume fraction of the nanoparticles in the dispersion is in the range of 50% to 75%.

[0086] Embodiment 14. The dispersion of embodiment 8, wherein the volume fraction of the nanoparticles in the dispersion is in the range of 60% to 75%.

[0087] Embodiment 15. The dispersion of embodiment 8, wherein the solvent comprises water and one or more additives.

[0088] Embodiment 16. The dispersion of embodiment 8, wherein the solvent comprises an organic solvent and one or more additives.

[0089] Aspect 17. α''-Fe 16 A nanocomposite comprising a population of aligned anisotropic nanoparticles comprising an N2 phase and a binder, the nanocomposite exhibiting a squareness measured in a direction parallel to the alignment direction of the anisotropic nanoparticles that is greater than the squareness observed in a direction perpendicular to the alignment direction, and exhibiting a diffraction pattern of the highest intensity α''-Fe when the diffraction vector is parallel to the alignment direction. 16 α''-Fe peak with relative intensity exceeding that of the N2(202) peak 16 The nanocomposite exhibits an X-ray diffraction pattern with a N2(004) peak.

[0090] Embodiment 18. The nanocomposite of embodiment 17, wherein the binder comprises a polymeric material.

[0091] Aspect 19. The nanocomposite of Aspect 18, wherein the polymeric material comprises an epoxy-based, acrylic-based, acrylate-based, bismaleimide-based, ester-based, urethane-based, styrene-based, polyvinyl alcohol-based, polyvinyl acetate-based, cellulose acetate-based, ethyl cellulose-based, polycarbonate-based, polyester-based, syndiotactic polystyrene-based polymeric material, or a combination thereof.

[0092] Embodiment 20. The nanocomposite of embodiment 5, wherein the mass fraction of the nanoparticles relative to the nanocomposite is in the range of 80% to 95%.

[0093] Embodiment 21. The nanocomposite of embodiment 5, wherein the mass fraction of the nanoparticles relative to the nanocomposite is in the range of 85% to 95%.

[0094] Embodiment 22. The nanocomposite of embodiment 5, wherein the mass fraction of the nanoparticles in the nanocomposite is in the range of 90% to 95%.

[0095] Embodiment 23. The nanocomposite of embodiment 5, wherein the volume fraction of the nanoparticles in the nanocomposite is in the range of 40% to 75%.

[0096] Embodiment 24. The nanocomposite of embodiment 5, wherein the volume fraction of the nanoparticles in the nanocomposite is in the range of 50% to 75%.

[0097] Embodiment 25. The nanocomposite of embodiment 5, wherein the volume fraction of the nanoparticles in the nanocomposite is in the range of 60% to 75%.

[0098] Embodiment 26. A method of forming an anisotropic permanent magnet, the method comprising: annealing an iron-containing agglomerated powder in the presence of nitrogen to provide iron nitride nanoparticles having an intrinsic coercivity of about 2,000 Oe to 4,000 Oe; dispersing the iron nitride nanoparticles in a fluid; removing excess fluid and drying the iron nitride nanoparticles; combining the iron nitride nanoparticles with a binder composition to provide a nanoparticle binder mixture; aligning the nanoparticle binder mixture in a magnetic field; and curing the nanoparticle binder mixture to form the permanent magnet.

[0099] Embodiment 27. The method of embodiment 26, wherein the iron nanoparticles have an intrinsic coercivity of 2,500 to 4,000 Oe.

[0100] Embodiment 28. The method of embodiment 26, wherein the iron nanoparticles have an intrinsic coercivity of 3,000 Oe to 4,000 Oe.

[0101] Embodiment 29. The method of embodiment 26, wherein the fluid is aqueous.

[0102] Embodiment 30. The method of embodiment 26, wherein dispersing the iron nitride nanoparticles in the fluid comprises: introducing the iron nitride nanoparticles into a mixture of water and one or more additives to provide an aqueous solution; and subjecting the aqueous solution to a process of ultrasonication and / or wet ball milling.

[0103] Aspect 31. The method of Aspect 30, wherein the one or more additives comprise a dispersant, a stabilizer, a wetting agent, a surfactant, a viscosity modifier, a corrosion inhibitor, an emulsifier, or any combination thereof.

[0104] Embodiment 32 The method of embodiment 26, wherein the fluid is non-aqueous.

[0105] Embodiment 33 The method of embodiment 26, wherein drying the iron nitride nanoparticles comprises freeze-drying, spray-drying, debinding, solvent-exchanging, or any combination thereof.

[0106] Embodiment 34. A permanent magnet formed by the method of embodiment 26, wherein the permanent magnet exhibits a squareness measured in a direction parallel to the nanoparticle alignment direction that is greater than the squareness observed in a direction perpendicular to the alignment direction, and wherein the diffraction pattern exhibits the highest intensity α″-Fe 16 The intensity of the α''-Fe peak is larger than that of the N2(202) peak. 16 A permanent magnet showing an X-ray diffraction pattern with the relative intensity of the N2(004) peak.

[0107] Aspect 35. A permanent magnet formed by the method of aspect 26, wherein the α″-Fe for iron nitride nanoparticles is present when the diffraction vector is parallel to the alignment direction. 16 α''-Fe versus N2(202) X-ray diffraction peak 16 A permanent magnet in which the integrated intensity ratio of the N2(004) X-ray diffraction peak is at least 7%. [Example]

[0108] The following examples are presented so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices, and / or methods claimed in this disclosure are made and evaluated, and are intended to be purely illustrative and are not intended to limit the present disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperatures, etc.), but some errors and deviations should be accounted for. Unless otherwise specified, percentages are parts by weight, temperatures are in °C or are at ambient temperature, and pressures are at or near atmospheric pressure. Unless otherwise specified, percentages referring to compositions are in % by weight.

[0109] For example, there are many variations and combinations of component concentrations, desired solvents, solvent mixtures, temperatures, pressures, and other reaction ranges and conditions that can be used to optimize the purity and yield of the products obtained from the described processes, and optimization of such process conditions will require no more than reasonable routine experimentation.

[0110] Example I: Samples 1 to 6 Commercially available nanoparticles of γ-Fe2O3 were obtained as a dried agglomerated powder. The nanoparticle agglomerates were passed through a sieve column, leaving a fraction ranging from 25 μm to 53 μm in size. Seven powder lots, each weighing 2.0 grams, were converted to iron nitride nanoparticles in a rotary tube furnace. Iron nitride nanoparticles were formed by first reducing the nanoparticles to elemental iron (Fe) by annealing in flowing hydrogen gas at approximately 200 standard cubic centimeters per minute (sccm) at approximately 340°C for approximately 17 hours. The Fe nanoparticles were then converted to iron nitride by annealing in flowing ammonia gas at approximately 60 sccm at approximately 145°C for 19 hours. After cooling to room temperature under flowing nitrogen, the iron nitride nanoparticles were passivated by flowing a 1% oxygen / argon mixture over the iron nitride nanoparticles at a flow rate of approximately 2 standard cubic feet per hour (scfh) for approximately 2 hours. The seven lots of iron nitride nanoparticles were combined for further processing. The intrinsic coercivity of the combined nanoparticles was determined to be 1971 Oe. The coercivity was measured using a VSM.

[0111] Approximately 1 gram of passivated iron nitride nanoparticles was introduced into an aqueous solution of stabilizer and water. The mixture was then milled by sonication and / or wet ball milling. After milling, excess solution was removed, and the nanoparticles were either ligated and dried or washed with isopropyl alcohol. Sonication was performed using a 200-watt probe sonicator. Wet ball milling was performed in a planetary ball mill using a stainless steel milling jar and milling media operating at 300 rpm. Table 1 shows the nanoparticle milling conditions, nanoparticle oxide coating, milling solution, and final treatment prior to sample preparation for Samples S1-S5 and Comparative Sample CS6. [Table 1]

[0112] The freeze-dried nanoparticles were mixed with a liquid epoxy composition, allowing the nanoparticles to settle to the bottom of the container. Excess liquid epoxy was removed, and the remaining mixture was remixed with the liquid epoxy and allowed to settle again, forming a gradient of nanoparticle concentration in the epoxy from the top to the bottom of the container. A sample of the nanoparticle / epoxy mixture was taken from the top of the container and placed in a mold positioned between the poles of two permanent magnets. The magnetic field was approximately 5,000 gauss. The nanoparticle-epoxy mixture was allowed to cure overnight in the magnetic field.

[0113] The cured nanoparticle / epoxy composite formed a thin disk with a diameter of approximately 6 mm and a thickness of approximately 1 mm. The orientation of the aligning magnetic field was perpendicular to the plane of the disk.

[0114] Comparative sample CS6 contained iron nitride nanoparticles that were not sonicated, ball milled, or freeze-dried and was made in a similar manner by curing a mixture of nanoparticles in epoxy between the pole pieces of a permanent magnet.

[0115] Figure 1 shows the hysteresis loop measured from sample S5. The loop was measured in the direction parallel and perpendicular to the alignment. The squareness measured in the parallel direction was greater than that in the perpendicular direction (0.53 compared to 0.41). This phenomenon indicates that the nanoparticles in the nanoparticle / epoxy composite are at least partially aligned. The coercivity measured in the parallel direction was 2,376 Oe. The coercivity of the starting material was not recorded.

[0116] The X-ray diffraction pattern of the sample prepared from sample S5 is shown in Figure 2. The XRD spectrum was collected using a D5005 X-ray diffractometer with a Cu radiation source over the 2θ angle range of 25 to 105°. 16 The relative intensity of the N2(004) peak is 16 The integrated intensity of N2(004) is 16 It is calculated by dividing by the integrated intensity of the N2(202) peak. 16 The relative intensity of the N2(004) peak was calculated to be 0.22. 16 The intensity of the (004) peak of N2 relative to the (202) peak is comparable to that of the α''-Fe nanoparticles prepared from the control sample without sonication. 16 The relative intensity of the N2(004) peak was 0.22, which was larger than that of the N2(004) peak (0.11, compared with that of the comparative sample CS6). 16 This shows a preferred orientation of the c-axis of the N2 phase, which is a further indication that the nanoparticles in the nanoparticle / epoxy composite were at least partially aligned.

[0117] The hysteresis loops measured in the parallel and perpendicular directions to the aligning field for comparative sample CS6 are shown in Figure 3. The inset graph shows that the squareness in the parallel direction is slightly smaller than that in the perpendicular direction (0.41 compared to 0.43). This indicates that the nanoparticles in sample CS6 were not oriented by the aligning field. The squareness measured in the perpendicular direction (0.33) was greater than that in the parallel direction (0.43). The coercivity measured in the parallel direction was 1,948 Oe. The coercivity of the starting material was not recorded.

[0118] The X-ray diffraction pattern of the comparative sample CS6 is shown in Figure 4. The diffraction vector was parallel to the aligning magnetic field. The observed peaks were those of α''-Fe 16 The mixture of N2 (diamond) and α-Fe (circle) phases is shown. 16 The relative intensity of the N2(004) peak is 16 The integrated intensity of N2(004) is 16 The intensity was calculated by dividing the integrated intensity of the N2(202) peak by the integrated intensity of the α''-Fe 16 The relative intensity of the N2 (004) peak was calculated to be 0.11. The ratio of the integrated intensity of the (004) peak to the (202) peak is 0.11. This finding indicates a signal from the misaligned nanoparticle / epoxy composite.

[0119] Example II. Samples 7-15 A second series of passivated iron nitride nanoparticles, S7–S15, was prepared. These passivated iron nitride nanoparticles, with a coercive field of 2,521 Oe, were sonicated in a 25% oleic acid / methanol solution for approximately 120 minutes. Sonication was performed using a 200-watt probe sonicator. The sonicated nanoparticles were washed twice with methanol to remove excess oleic acid. The washed nanoparticles were then mixed with epoxy. Table 2 shows the sample preparation method prior to magnetic alignment. Each sample was magnetically aligned by placing it between the pole pieces of two permanent magnets. The alignment field was approximately 5,000 Oe. The samples were allowed to cure overnight. The aligned samples were disk-shaped, approximately 1 mm thick and 6 mm in diameter, with the alignment direction perpendicular to the disk surface. [Table 2]

[0120] Figure 5 shows the hysteresis loops measured in the directions parallel and perpendicular to the aligning magnetic field direction for sample S8. The inset graph shows that the squareness in the parallel direction (0.78) is greater than that in the perpendicular direction (0.40). This indicates that the nanoparticles in Example 8 were partially oriented by the aligning magnetic field. The coercivity measured in the aligning direction was 2,917 Oe, which is significantly larger than that of the starting material.

[0121] Figure 6 shows the X-ray diffraction pattern of Example 8. The diffraction vector was parallel to the aligning magnetic field. The observed peaks were α''-Fe 16 The N2 (diamond) phase and α-Fe (circle) phase are mixed. 16 The relative intensity of the N2(004) peak is 16 The integrated intensity of N2(004) is 16 The calculated intensity was calculated by dividing the integrated intensity of the N2(202) peak by the integrated intensity of the α''-Fe 16 The intensity of the (004) peak of N2 relative to the (202) peak is comparable to that of the α''-Fe nanoparticles prepared from the control sample without sonication. 16The relative intensity of the N2(004) peak was larger than that of the N2(004) peak (0.74 compared to 0.11 for CS6). 16 This shows a preferred orientation of the c-axis of the N2 phase, which is a further indication that the nanoparticles in the nanoparticle / epoxy composite were at least partially aligned.

[0122] Example III: Sample 16 Passivated iron nitride nanoparticles with a coercive force of 2,357 Oe were sonicated in a 10% PEG-400 / water solution for approximately 120 minutes to obtain sample S16. After sonication, the nanoparticles were allowed to settle and excess solution was removed. The nanoparticles were freeze-dried overnight between the pole pieces of two permanent magnets. After freeze-drying, a paste was observed floating between the pole pieces of the permanent magnets. The suspended paste was mixed with epoxy, and a sample of the nanoparticle-epoxy mixture was cured between the pole pieces of two permanent magnets.

[0123] The hysteresis loops measured in the directions parallel and perpendicular to the aligning field for sample S16 are shown in Figure 7. The inset graph shows that the squareness in the parallel direction (0.76) was greater than that in the perpendicular direction (0.41). This indicates that the nanoparticles in S16 were partially oriented by the aligning field. The coercivity measured in the aligned direction was 2.357 Oe, showing a slight decrease compared to the starting material.

[0124] The X-ray diffraction pattern of S16 is shown in Figure 8. The diffraction vector was parallel to the aligning field. The diamagnetic contribution from the sample holder was subtracted from the hysteresis loop. Again, the α''-Fe 16 The relative intensity of the N2(004) peak is 16 The integrated intensity of N2(004) is 16 The intensity was calculated by dividing the integrated intensity of the N2(202) peak by the integrated intensity of the α''-Fe 16 The intensity of the (004) peak (0.55) relative to the (202) peak of N2 is significantly higher than that of the α''-Fe nanoparticles prepared from the control sample without sonication. 16The relative intensity of the N2(004) peak (0.11, CS6) was larger than that of the α''-Fe 16 This shows a preferred orientation of the c-axis of the N2 phase, which is a further indication that the nanoparticles in the nanoparticle / epoxy composite were at least partially aligned.

[0125] Table 3 summarizes the magnetic and crystallographic measurements performed on the nanoparticle / epoxy composite samples of Examples I to III (S1 to S5, CS6, S7 to S16). Squareness was calculated by the following formula: Squareness = Mr / MSat (formula 1) where Mr is the remanent magnetization of the nanoparticle / epoxy sample (measured when the applied field H equals 0 Oersted), and MSat is the saturation magnetization of the composite sample (measured when H = 20,000 Oersted). Mr was measured using a vibrating sample magnetometer (VSM). Squareness was determined from magnetization curves measured parallel and perpendicular to the direction of the aligning field. The difference between parallel and perpendicular squareness is a measure of the magnetic anisotropy of the sample. Br of the nanoparticle is the calculated remanent magnetization of iron nitride nanoparticles (without epoxy) measured parallel to the aligning field. The relative intensity of the (004) X-ray diffraction peak is the remanent magnetization of the α''-Fe 16 The relative intensity of the (004) peak is calculated as the ratio of the (004) X-ray diffraction peak to the (202) X-ray diffraction peak for N2. In these measurements, the diffraction vector was parallel to the alignment direction. The relative intensity of the (004) peak for a randomly oriented sample of iron nitride nanoparticles is 0.07. Therefore, a relative intensity of the (004) peak greater than 0.07 indicates that the crystal lattice of the iron nitride nanoparticles is preferentially oriented parallel to the alignment direction.

[0126] Table 3 also shows magnetic measurements of aligned nanoparticles after they were introduced into epoxy to form bonded permanent magnets. Here, the measure of nanoparticle magnetization is Br. This is the remanence generated once a magnetic field is applied to an epoxy-bonded sample and then removed. Higher Br generally results in better magnets. Br is a function of both saturation magnetization and squareness. Saturation magnetization is calculated by dividing the Br value in the table by the squareness measured in the parallel direction using Equation 1. This calculation yields a range of MSat values ​​from 12.5 to 14 kG, and these values ​​can be used to characterize the saturation magnetization of nanoparticles in bonded permanent magnets. [Table 3]

[0127] In other embodiments, the mechanical milling method promotes the formation of a uniform phase composition throughout the nanoparticle aggregates, resulting in a high mass fraction of the preferred α″-Fe 16 N2 phase and low mass fractions of harmful α-Fe and ε-Fe 2-3 N phase. 16 The combination of an increased amount of N2 phase produces a higher coercivity for a given saturation magnetization compared to conventional iron nitride nanoparticles produced without the milling process. Many processes are described throughout this disclosure. Iron nitride nanoparticles, compositions, and magnetic materials produced using these processes have improved magnetic properties, such as higher coercivity, higher energy product, etc., compared to comparable iron nitride nanoparticles, compositions, and magnetic materials produced without such treatment.

[0128] For example, in one embodiment, the agglomerated iron oxide nanoparticles are mechanically milled prior to the reduction, nitridation, and passivation steps. The iron oxide nanoparticle agglomerates are received as dry agglomerates. The agglomerates are comprised of numerous iron oxide nanoparticles having particle sizes in the range of 1-100 nanometers. The agglomerates have diameters in the range of 1-200 micrometers and porosities in the range of 10-90 volume percent. Within the agglomerates, the nanoparticles are held together by a combination of chemical, electrostatic, magnetic, and / or frictional forces.

[0129] Regarding mechanical milling, any form of mechanical milling is contemplated to deagglomerate the nanoparticles. For example, mechanical milling of iron oxide aggregates can be achieved by any of the following: sonication in a fluid, ball milling in the presence of a fluid, dry ball milling, high-shear mixing in the presence of a fluid, jet milling in a high-velocity gas stream, or some combination thereof. The fluid can be water, an organic solvent, or another fluid capable of transporting nanoparticle aggregates. The fluid may contain a surfactant to facilitate deagglomeration of the nanoparticles. The fluid can be removed after milling by any drying method, such as freeze-drying and / or spray-drying. The agglomerated iron oxide nanoparticles may be sieved before or after the milling process. The temperature of the milling process can be controlled to avoid overheating or sintering of the nanoparticles. For example, the temperature can be controlled by immersing the milling vessel in an ice bath. Alternatively, purpose-designed cryomilling equipment can be used.

[0130] The effect of the milling process is to reduce the average size of the aggregated iron oxide nanoparticles. The aggregate size can be expressed as Dx, which is the diameter below which x% of the cumulative size distribution lies. In many cases, the aggregate size is expressed as D, which is the diameter below which 50% of the cumulative size distribution lies. 50 For example, D 50means that 50% of all particles have a particle size equal to or less than the indicated value. 99 means that 99% of all particles have a particle size less than or equal to the indicated value. Aggregate size distribution can be measured by laser diffraction, dynamic light scattering, optical microscopy and / or electron microscopy.

[0131] The effect of the milling process can also introduce crystalline defects, such as vacancies, dislocations, and strain gradients, within the nanoparticle aggregates, and can also reduce the strength of the interparticle bonds that form due to partial sintering. The strain induced in the aggregates during milling can lead to the formation of micropores in the nanoparticles, which can be useful for subsequent gas reduction and nitridation.

[0132] In another embodiment, the agglomerated iron nanoparticles are mechanically milled after the reduction step is completed and before the nitridation step is performed. The iron nanoparticles can be exposed to reducing species. For example, a hydrogen reduction step can be applied before nitriding the iron nanoparticles, which creates microchannels that enhance nitrogen diffusion. The iron nanoparticles can be exposed to H2 at temperatures between about 200°C and about 500°C for up to about 24 hours. In some examples, the material can be exposed to H2 at temperatures of about 300°C or higher. The flow rate of the hydrogen source during hydrogen reduction can be about 100 standard cubic centimeters per minute (sccm). In some examples, the flow rate of the hydrogen source during hydrogen reduction can be about 400 standard cubic centimeters per minute (sccm) or higher. In other examples, as the size of the reaction vessel and the quantity of particles increase from grams to kilograms, the flow rate of the hydrogen source during hydrogen reduction can be greater than 400 sccm and 10 liters per minute (lpm) or higher. The mechanical milling process can completely or partially eliminate any sintering of the iron nanoparticles that may occur during the reduction step. To avoid reoxidation and / or contamination of the iron nanoparticles prior to nitridation, dry milling methods, such as dry ball milling, are contemplated. Dry ball milling can be performed in an inert atmosphere, such as nitrogen, argon, and / or helium, to prevent oxidation of the iron nanoparticles.

[0133] In another embodiment, the aggregated iron nitride nanoparticles are mechanically milled after nitridation is complete and before any additional coatings and / or passivation layers are applied to the surfaces of the iron nitride nanoparticles. Nitriding the iron nanoparticles can include exposing the iron nanoparticles to atomic nitrogen material, which diffuses into the iron nanoparticles. In some examples, the atomic nitrogen material can be provided as diatomic nitrogen (N), which is then dissociated (cracked) into individual nitrogen atoms. In other examples, the atomic nitrogen can be provided from another atomic nitrogen precursor, such as ammonia (NH). In other examples, the atomic nitrogen can be provided from urea (CO(NH)). The nitrogen can be provided in the gas phase alone (e.g., substantially pure ammonia or diatomic nitrogen gas) or as a mixture with a carrier gas. In some examples, the carrier gas is argon (Ar). In this embodiment, the mechanical milling process can completely or partially eliminate any sintering of the nanoparticles that may occur during the reduction and nitridation steps.

[0134] Coating and / or passivation can stabilize the milled particles and prevent re-agglomeration. Surface oxidation can be reduced by using surface passivation methods. Without being bound by any theory, reducing or substantially preventing oxidation of iron nitride particles can contribute to improving the magnetic properties of annealed iron nitride nanoparticles, such as coercivity and magnetization. In some examples, the iron nitride nanoparticles can be coated. Suitable coatings include carbon and boron. In other examples, the coating can be aluminum oxide, copper metal, or aluminum metal. The coating can be applied using atomic layer deposition. Dry milling methods, such as dry ball milling, are considered to avoid reaction and decomposition of the iron nitride nanoparticles. Dry ball milling can be performed in an inert atmosphere, such as nitrogen, argon, and / or helium, to prevent oxidation of the iron nitride nanoparticles.

[0135] In yet another embodiment, the aggregated iron nitride nanoparticles can be mechanically milled after passivation but before magnetic alignment. Annealing the iron nitride nanoparticles in the presence of an applied magnetic field results in the formation of Fe in the iron nitride nanoparticles. 16 It can enhance the formation of N2 phase domains. 16 The increased volume fraction of N phase domains can improve the magnetic properties of iron nitride-containing core-shell nanoparticles, including, for example, coercivity, magnetization, and magnetic orientation.

[0136] In some embodiments, a mechanical milling process can increase the magnetic anisotropy of aggregated iron nitride nanoparticles by completely or partially deagglomerating them into their individual single-crystal components. Mechanical milling of iron nitride aggregates can be suitably achieved by sonication in a fluid, ball milling in the presence of a fluid, dry ball milling, high-shear mixing in the presence of a fluid, jet milling, or the like, or some combination of these methods. The fluid can be aqueous (e.g., water or a water-containing fluid), non-aqueous (an organic solvent or an organic solvent-containing fluid), or another fluid in which the nanoparticle aggregates are dispersible, as well as combinations thereof. The fluid can have a surfactant, a dispersant, or both added to it to facilitate deagglomeration of the nanoparticles and / or to prevent re-agglomeration of the nanoparticles. The fluid can be removed after milling by any drying method, such as freeze-drying and / or spray-drying. The effect of the milling process is to reduce the average size of the aggregated iron oxide nanoparticles. Mechanical milling can be performed at a milling energy sufficient to deagglomerate the nanoparticles but not high enough to disrupt the passivation layer coating the iron nitride nanoparticles. Agglomerated iron nitride nanoparticles may be sieved before or after the milling process. The milled iron nitride nanoparticles may be subjected to a further passivation and / or coating step to repair damage to the oxide shell sustained during the milling process. As previously mentioned, the iron nitride nanoparticles, compositions, and magnetic materials produced using the above-described processes have improved magnetic properties, such as higher coercivity and higher energy product, compared to corresponding iron nitride nanoparticles, compositions, and magnetic materials produced without such treatment.

[0137] The milling media and containers used during wet and dry ball milling of nanoparticles can themselves be magnetic or non-magnetic. In some situations, the use of magnetic milling media and containers may be preferred, as they can help prevent nanoparticles from accumulating in the crevices of the milling container. In other situations, the use of non-magnetic milling media and containers is considered a way to increase milling efficiency and yield by helping to minimize magnetic agglomeration of nanoparticles.

[0138] In yet another embodiment, the milling step can occur with any combination of steps in the above process. In one example, milling can occur before reduction and after nitridation. In another example, milling can occur before reduction, after nitridation, and after passivation.

[0139] To prepare agglomerated iron oxide nanoparticles as precursors, several process modifications are possible. If iron oxide nanoparticles are produced by chemical means, capping agents can be used to stop nanoparticle growth and prevent aggregation. Alternatively, digestive ripening methods can be used to chemically modify the size distribution of iron oxide nanoparticles. If iron oxide nanoparticles are produced by steam condensation, processing methods can be tailored to promote the formation of spherical nanoparticles with a narrow particle size distribution.

[0140] Generally, higher milling energies are required to generate and / or modify nanoparticles than to deagglomerate nanoparticles. The mechanical milling methods of the present invention generally tend to deagglomerate nanoparticles and beneficially alter nanoparticle behavior during reduction, nitridation, passivation, and / or alignment operations.

[0141] Figure 9 shows four different material processing schemes for producing iron nitride magnets. Scheme #1 shows milling of agglomerated iron oxide nanoparticles before reduction and nitridation. Scheme #2 shows milling of agglomerated nanoparticles after reduction and before nitridation. Scheme #3 shows milling of agglomerated nanoparticles after nitridation and before coating / passivation. Scheme #4 shows milling of agglomerated nanoparticles after coating / passivation and before magnetic alignment.

[0142] Figure 10 illustrates deagglomeration of nanoparticles according to an exemplary embodiment. For example, mechanical milling methods such as sonication and / or ball milling (wet and dry) of gamma iron oxide nanoparticles supplied as dry agglomerates are highly effective in reducing the particle size and size distribution of the agglomerates.

[0143] Figure 11 shows an illustration of agglomerated nanoparticles. Tightly bound aggregates consist of multiple nanoparticles that are physically joined together. Loosely bound aggregates of nanoparticles are characterized as having nanoparticles that are attracted to each other (flocculate) but are not physically joined together. The stabilizer desirably helps prevent flocculation so that the size distribution of the iron oxide nanoparticles is on the order of tens of nanometers in size.

[0144] Figure 12 illustrates the measurement of the size of aggregated, flocculated, and primary (small) nanoparticles using laser diffraction. Sonication breaks up loosely bound aggregates of iron oxide nanoparticles. Sonication in a stabilizer desirably produces primary (small) iron oxide nanoparticles. Measurements: 1. Starting point; 2. Even if particles separate during sonication, they flocculate back to their "equilibrium" state. 3. Sonication breaks up loosely bound aggregates and stabilizers prevent flocculation, where small particles begin to appear.

[0145] Figure 13 shows the range of saturation magnetization and coercivity for several anisotropic iron nitride nanoparticles. The circled data points have the required combination of Msat and Hc, i.e., Msat greater than 190 emu / g and Hc greater than 2,500 Oe.

[0146] FIG. 14 shows the effect of milling on the phase distribution of α″% in the core vs. α-Fe% in the core in iron nitride nanoparticles. Sonicated nanoparticles according to the method described in this disclosure yield iron nitride nanoparticles with greater than 70% alpha″ phase. α-Fe, α″-Fe 16 N2, ε-Fe 2-3 Mössbauer spectroscopy was used to determine the fraction of N and Fe atoms in the superparamagnetic Fe oxide and superparamagnetic Fe nitride phases. "α'' in the core" refers to α''-Fe 16 The "α-Fe in core" is calculated as the Fe atoms in the N2 phase divided by the Fe atoms in all non-oxide phases. The "α-Fe in core" is calculated as the α-Fe divided by the Fe atoms in all non-oxide phases. The Fe atoms are divided by the ε-Fe based on a function derived from the total fraction of atoms in the superparamagnetic phase. 2-3 The iron oxide nanoparticles were distributed in the N and oxide phases. "D50" is the total volume fraction of milled iron oxide nanoparticle aggregates with a diameter of less than 50 microns. The symbols indicate the milling method applied to the iron oxide nanoparticles before nitridation.

[0147] The present disclosure relates to at least the following additional aspects:

[0148] Aspect 36. A method for producing iron nitride nanoparticles, comprising: mechanically milling iron-containing nanoparticles; and aligning the milled iron-containing nanoparticles in the presence of a magnetic field.

[0149] Embodiment 37 The method of embodiment 36, wherein the iron-containing nanoparticles are in the form of agglomerates of iron-containing nanoparticles prior to mechanical milling.

[0150] Embodiment 38 The method of embodiment 36, further comprising performing a step of reducing the iron-containing nanoparticles in the presence of a reducing species.

[0151] Embodiment 39. The method of embodiment 38, wherein the reducing species comprises hydrogen.

[0152] Embodiment 40. The method of embodiment 38, wherein mechanical milling is performed before the reduction step.

[0153] Embodiment 41 The method of embodiment 38, further comprising performing a step of nitriding the iron-containing nanoparticles in the presence of an atomic nitrogen agent to obtain iron nitride nanoparticles.

[0154] Embodiment 42. The method of embodiment 41, wherein mechanical milling is performed after the reduction step and before the nitriding step.

[0155] Aspect 43. The method of aspect 41, further comprising, after the nitriding step, coating the iron-containing nanoparticles with any of carbon and boron, aluminum oxide, copper metal, and aluminum metal, wherein the iron-containing nanoparticles comprise iron nitride nanoparticles.

[0156] Embodiment 44. The method of embodiment 43, wherein mechanical milling is performed after the nitriding step and before the coating step.

[0157] Aspect 45. The method of aspect 36, wherein the mechanical milling is carried out by any of ultrasonic treatment in a fluid, ball milling in the presence of a fluid, dry ball milling, high shear mixing in the presence of a fluid, and jet milling in a high velocity gas stream.

[0158] Embodiment 46 The method of embodiment 36, further comprising the step of immersing the milling vessel in an ice bath after the mechanical milling, wherein the mechanical milling is performed in the milling vessel containing the iron-containing nanoparticles.

[0159] Embodiment 47. The method of embodiment 45, wherein any of the fluids comprises water, an organic substance, or both.

[0160] Embodiment 48 The method of embodiment 45, wherein any of the fluids includes a surfactant to promote deagglomeration of the iron-containing nanoparticles.

[0161] Embodiment 49. The method of embodiment 45, wherein the dry ball milling is carried out in an inert atmosphere comprising any of nitrogen, argon, and helium.

[0162] Embodiment 50. The method of embodiment 43, wherein mechanical milling is performed after the coating step.

[0163] Embodiment 51 The method of embodiment 36, wherein the magnetically annealed iron-containing nanoparticles have a D50 of 25 μm or less.

[0164] Embodiment 52 The method of embodiment 36, wherein the magnetically annealed iron-containing nanoparticles have a D50 of 10 μm or less.

[0165] Embodiment 53 The method of embodiment 36, wherein the magnetically annealed iron-containing nanoparticles have a D50 of 2.5 μm or less.

[0166] Embodiment 54 The method of embodiment 36, wherein the mechanical milling is carried out in the presence of a magnetic medium.

[0167] Embodiment 55. At least one of the iron nitride nanoparticles is α″-Fe 16 37. An aggregate of iron nitride nanoparticles obtained by the method of embodiment 36, comprising N2 phase domains.

[0168] Embodiment 56. A plurality of anisotropic iron nitride nanoparticles, characterized in that they have a saturation magnetization MSat greater than 190 emu / g and a coercivity Hc greater than 2,500 Oe.

[0169] α''-Fe 16 20. The plurality of anisotropic iron nitride nanoparticles of claim 18, wherein the mass percentage of N2 phase is at least 70%.

[0170] Embodiment 57. The plurality of anisotropic iron nitride nanoparticles of embodiment 56, further characterized by having a generally uniform phase composition, including a high mass fraction of α″-Fe. 16 N2 phase and low mass fractions of α-Fe and ε-Fe 2-3 57. The plurality of anisotropic iron nitride nanoparticles of embodiment 56, comprising:

[0171] Aspect 58. α''-Fe 16 58. The plurality of anisotropic iron nitride nanoparticles of embodiment 57, wherein the mass percentage of N2 phase is at least 70%, at least 75%, or at least 80%.

[0172] Embodiment 59. The plurality of anisotropic iron nitride nanoparticles of embodiment 56, wherein the iron nitride nanoparticles are coated with one or more of carbon, boron, aluminum oxide, copper metal, or aluminum metal.

[0173] Aspect 60. A permanent magnet comprising a plurality of iron nitride nanoparticles, characterized in that the permanent magnet has a saturation magnetization MSat in the range of about 12.5 to about 14 kG.

[0174] Embodiment 61. The permanent magnet of embodiment 60, wherein the iron nitride nanoparticles are magnetically aligned and bonded in a matrix.

[0175] Embodiment 62. The permanent magnet of embodiment 60, wherein the nanoparticles are further characterized by having a uniform phase composition throughout, the nanoparticles comprising a high mass fraction of the preferred α″-Fe 16 N2 phase and low mass fractions of α-Fe and ε-Fe 2-3 61. The permanent magnet of embodiment 60, comprising:

[0176] Aspect 63. α''-Fe 16 63. The permanent magnet of embodiment 62, wherein the mass percentage of N2 phase is at least 70%, 75%, 80%.

[0177] Embodiment 64. The permanent magnet of embodiment 60, wherein the iron nitride nanoparticles are coated with one or more of carbon, boron, aluminum oxide, copper metal, or aluminum metal.

[0178] Embodiment 65. The permanent magnet of embodiment 60, wherein at least a portion of the iron nitride nanoparticles are deagglomerated individual primary particles.

[0179] Various examples have been described. These and other examples are within the scope of the following claims.

[0180] When ranges are used in this disclosure for physical properties, such as molecular weight, or chemical properties, such as chemical formula, all combinations and subcombinations of ranges for specific embodiments therein are intended to be included.

[0181] The disclosures of each patent, patent application and publication cited or described herein are hereby incorporated by reference in their entirety.

[0182] Those skilled in the art will understand that many changes and modifications can be made to the preferred embodiments of the present invention and that such changes and modifications can be made without departing from the spirit of the present invention. It is, therefore, intended that the appended claims cover all such equivalent variations as fall within the true spirit and scope of the present invention.

[0183] The foregoing description is intended to be illustrative, not limiting. For example, the above examples (or one or more aspects thereof) can be used in combination with each other. Other aspects may also be utilized by one of ordinary skill in the art, for example, in light of the above description. The Abstract is provided to comply with 37 CFR §1.72(b) to enable the reader to quickly ascertain the content of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Similarly, in the foregoing Detailed Description, various features may be grouped together to streamline the disclosure. This should not be construed as intending that any unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may reside in less than all features of a particular disclosed embodiment. Thus, the following claims are incorporated into the Detailed Description as examples or embodiments, with each claim standing on its own as a separate embodiment, and such embodiments can be combined with each other in various combinations or permutations. The scope of the present disclosure should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. Some of the embodiments of the invention related to the present invention are shown below. [Embodiment 1] 1. A permanent magnet comprising a plurality of aligned iron nitride nanoparticles, The iron nitride nanoparticles are α''-Fe 16 N 2 Contains phase domains; When the diffraction vector is parallel to the alignment direction, α''-Fe 16 N 2 α''-Fe for (202) X-ray diffraction peak 16 N 2 The integrated intensity ratio of the (004) X-ray diffraction peak is at least 7% or more; the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction that is greater than a squareness measured perpendicular to the alignment direction; Permanent magnet. [Embodiment 2] 2. The permanent magnet of embodiment 1, wherein the aligned iron nitride nanoparticles are formed as wires, thin sheets, or tapes, and the wires, thin sheets, or tapes are bonded together to provide the permanent magnet. [Embodiment 3] α''-Fe 16 N2 α''-Fe for (202) X-ray diffraction peak 16 N 2 2. The permanent magnet of embodiment 1, wherein the integrated intensity ratio of the (004) X-ray diffraction peak is at least greater than 50%. [Embodiment 4] α''-Fe 16 N 2 α''-Fe for (202) X-ray diffraction peak 16 N 2 2. The permanent magnet of embodiment 1, wherein the integrated intensity ratio of the (004) X-ray diffraction peak is at least greater than 100%. [Embodiment 5] 2. The permanent magnet of embodiment 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.50. [Embodiment 6] 2. The permanent magnet of embodiment 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.75. [Embodiment 7] 2. The permanent magnet of embodiment 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.9. [Embodiment 8] α''-Fe 16 N 2 1. A nanocomposite comprising a population of aligned anisotropic nanoparticles comprising a phase and a binder, the nanocomposite exhibits a squareness measured in a direction parallel to the alignment direction of the anisotropic nanoparticles that is greater than the squareness observed in a direction perpendicular to the alignment direction of the anisotropic nanoparticles; The nanocomposite exhibits α''-Fe in the diffraction pattern when the diffraction vector is parallel to the alignment direction. 16 N 2 The intensity of the α''-Fe (202) peak is larger than that of the 16 N 2 exhibiting an X-ray diffraction pattern with an intensity of the (004) peak, Nanocomposites. [Embodiment 9] 9. The nanocomposite of embodiment 8, wherein the binder comprises a polymeric material. [Embodiment 10] 10. The nanocomposite of embodiment 9, wherein the polymeric material comprises an epoxy-based, acrylic-based, acrylate-based, bismaleimide-based, ester-based, urethane-based, styrene-based, polyvinyl alcohol-based, polyvinyl acetate-based, cellulose acetate-based, ethyl cellulose-based, polycarbonate-based, polyester-based, syndiotactic polystyrene-based polymeric material, or a combination thereof. [Embodiment 11] 9. The nanocomposite of embodiment 8, wherein the mass fraction of the nanoparticles relative to the nanocomposite is in the range of 80% to 95%. [Embodiment 12] 9. The nanocomposite of embodiment 8, wherein the mass fraction of the nanoparticles relative to the nanocomposite is in the range of 85% to 95%. [Embodiment 13] 9. The nanocomposite of embodiment 8, wherein the mass fraction of the nanoparticles relative to the nanocomposite is in the range of 90% to 95%. [Embodiment 14] 9. The nanocomposite of embodiment 8, wherein the volume fraction of the nanoparticles relative to the nanocomposite is in the range of 40% to 75%. [Embodiment 15] 9. The nanocomposite of embodiment 8, wherein the volume fraction of the nanoparticles relative to the nanocomposite is in the range of 50% to 75%. [Embodiment 16] 9. The nanocomposite of embodiment 8, wherein the volume fraction of the nanoparticles relative to the nanocomposite is in the range of 60% to 75%. [Embodiment 17] A plurality of anisotropic iron nitride nanoparticles characterized by having a saturation magnetization MSat greater than 190 emu / g and a coercivity Hc greater than 2,500 Oe. [Embodiment 18] The plurality of iron nitride nanoparticles are further characterized by having a uniform phase composition throughout, the plurality of iron nitride nanoparticles comprising a high mass fraction of α″-Fe 16 N 2 phase and low mass fractions of α-Fe and ε-Fe 2-3 18. The plurality of anisotropic iron nitride nanoparticles of embodiment 17, comprising a N phase. [Embodiment 19] The α''-Fe 16 N 2 19. The plurality of anisotropic iron nitride nanoparticles of embodiment 18, wherein the mass percentage of the phase is at least 70%. [Embodiment 20] 18. The plurality of anisotropic iron nitride nanoparticles of embodiment 17, wherein the iron nitride nanoparticles are coated with one or more of carbon, boron, aluminum oxide, copper metal, or aluminum metal. [Embodiment 21] A permanent magnet comprising a plurality of iron nitride nanoparticles, the permanent magnet having a saturation magnetization MSat in the range of about 12.5 kG to about 14 kG. [Embodiment 22] 22. The permanent magnet of embodiment 21, wherein the iron nitride nanoparticles are magnetically aligned and bonded in a matrix. [Embodiment 23] The nanoparticles are further characterized by having a uniform phase composition throughout, the nanoparticles comprising a high mass fraction of α''-Fe 16 N 2 phase and a low mass fraction of α-Fe and ε-Fe 2-3 22. The permanent magnet of embodiment 21, comprising: [Embodiment 24] The α''-Fe 16 N 2 24. The permanent magnet of embodiment 23, wherein the mass percentage of the phase is at least 70%. [Embodiment 25] 22. The permanent magnet of embodiment 21, wherein the iron nitride nanoparticles are coated with one or more of carbon, boron, aluminum oxide, copper metal, or aluminum metal. [Embodiment 26] 22. The permanent magnet of embodiment 21, wherein at least a portion of the iron nitride nanoparticles are deagglomerated individual primary particles.

Claims

1. 1. A permanent magnet comprising a plurality of magnetically aligned iron nitride nanoparticles, The iron nitride nanoparticles are α''-Fe １６ N ２ containing a phase domain; When the diffraction vector is parallel to the magnetic alignment direction of the iron nitride nanoparticles, α''-Fe １６ N ２ (202) α''-Fe for X-ray diffraction peak １６ N ２ The integrated intensity ratio of the (004) X-ray diffraction peak is at least 50% or more; the iron nitride nanoparticles exhibit a squareness measured parallel to the magnetic alignment direction of the iron nitride nanoparticles that is greater than a squareness measured perpendicular to the alignment direction. Permanent magnet.

2. 10. The permanent magnet of claim 1, wherein the aligned iron nitride nanoparticles are formed as wires, thin sheets, or tapes, and the wires, thin sheets, or tapes are bonded together to provide the permanent magnet.

3. 10. The permanent magnet of claim 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.

50.

4. 10. The permanent magnet of claim 1, wherein the iron nitride nanoparticles exhibit a squareness measured parallel to the alignment direction of greater than 0.

75.

5. α''-Fe １６ N ２ 1. A nanocomposite comprising a population of magnetically aligned anisotropic nanoparticles comprising a phase and a binder, the nanocomposite exhibits a squareness measured in a direction parallel to the magnetic alignment direction of the anisotropic nanoparticles that is greater than the squareness observed in a direction perpendicular to the magnetic alignment direction of the anisotropic nanoparticles; The nanocomposite is α″-Fe when the diffraction vector is parallel to the alignment direction. １６ N ２ (202) α''-Fe for X-ray diffraction peak １６ N ２ (004) X-ray diffraction pattern in which the integrated intensity ratio of the X-ray diffraction peak is at least 50% or more; Nanocomposites.

6. The nanocomposite of claim 5 , wherein the binder comprises a polymeric material.

7. 7. The nanocomposite of claim 6, wherein the polymeric material comprises an epoxy-based, acrylic-based, acrylate-based, bismaleimide-based, ester-based, urethane-based, styrene-based, polyvinyl alcohol-based, polyvinyl acetate-based, cellulose acetate-based, ethyl cellulose-based, polycarbonate-based, polyester-based, syndiotactic polystyrene-based polymeric material, or a combination thereof.

8. The nanocomposite of claim 5, wherein the mass fraction of the nanoparticles in the nanocomposite is in the range of 80% to 95%.

9. The nanocomposite of claim 5, wherein the mass fraction of the nanoparticles in the nanocomposite is in the range of 85% to 95%.

10. The nanocomposite of claim 5, wherein the mass fraction of the nanoparticles in the nanocomposite is in the range of 90% to 95%.

11. The nanocomposite of claim 5, wherein the volume fraction of the nanoparticles in the nanocomposite is in the range of 40% to 75%.

12. The nanocomposite of claim 5, wherein the volume fraction of the nanoparticles in the nanocomposite is in the range of 50% to 75%.

13. The nanocomposite of claim 5, wherein the volume fraction of the nanoparticles in the nanocomposite is in the range of 60% to 75%.

14. having a saturation magnetization MSat greater than 190 emu / g and a coercivity Hc greater than 2,500 Oe; α''-Fe １６ N ２ (202) α''-Fe for X-ray diffraction peak １６ N ２ A plurality of anisotropic iron nitride nanoparticles characterized by an integrated intensity ratio of (004) X-ray diffraction peaks greater than at least 50%.

15. The plurality of iron nitride nanoparticles are further characterized by having a uniform phase composition throughout, the plurality of iron nitride nanoparticles comprising a high mass fraction of α″-Fe. １６ N ２ phase and a low mass fraction of α-Fe phase and ε-Fe phase ２－３ 15. The plurality of anisotropic iron nitride nanoparticles of claim 14, comprising a N phase.

16. The α″-Fe １６ N ２ 16. The plurality of anisotropic iron nitride nanoparticles of claim 15, wherein the mass percentage of the phase is at least 70%.

17. 15. The plurality of anisotropic iron nitride nanoparticles of claim 14, wherein the iron nitride nanoparticles are coated with one or more of carbon, boron, aluminum oxide, copper metal, or aluminum metal.

18. A permanent magnet comprising a plurality of iron nitride nanoparticles, the permanent magnet having a saturation magnetization MSat in a range of about 12.5 kG to about 14 kG; α''-Fe １６ N ２ (202) α''-Fe for X-ray diffraction peak １６ N ２ A permanent magnet characterized in that the integrated intensity ratio of (004) X-ray diffraction peaks is at least greater than 50%.

19. 20. The permanent magnet of claim 18, wherein the iron nitride nanoparticles are magnetically aligned and bonded in a matrix.

20. The nanoparticles are further characterized by having a uniform phase composition throughout, the nanoparticles comprising a high mass fraction of α''-Fe. １６ N ２ phase and a low mass fraction of α-Fe phase and ε-Fe phase ２－３ 20. The permanent magnet of claim 18, comprising an N phase.

21. The α″-Fe １６ N ２ 21. The permanent magnet of claim 20, wherein the mass percentage of the phase is at least 70%.

22. 19. The permanent magnet of claim 18, wherein the iron nitride nanoparticles are coated with one or more of carbon, boron, aluminum oxide, copper metal, or aluminum metal.

23. 20. The permanent magnet of claim 18, wherein at least a portion of the iron nitride nanoparticles are deagglomerated individual primary particles.

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