The disclosure relates to magnetic nanoparticles and techniques for forming magnetic nanoparticles.
Iron oxide nanoparticles (IONPs) have been widely used for magnetic diagnosis and treatment such as magnetic resonance imaging (MRI), magnetic particle imaging (MPI), gene/drug delivery, magnetic hyperthermia therapy, magnetic separation, and magnetic biosensors. The research interest in pursuing inexpensive, high magnetic moment, low biotoxicity, colloidal stable, and environmentally friendly magnetic nanoparticles (MNPs) is growing rapidly in view of the increasing demands of high sensitivity magnetic diagnosis and low dose treatments. To this end, γ′-Fe4N is one promising candidate, because 1) both iron and nitrogen are inexpensive, low biotoxicity, and environment friendly; and 2) the saturation magnetization of γ′-Fe4N is around two times higher than that of IONPs. Minnealloy α″-Fe16NxZ2-x or α′-Fe8NxZ1-x) is another promising candidate, because of its giant saturation magnetization and ultralow magnetic anisotropy constant.
In some examples, the disclosure describes a method that includes wet ball milling a plurality of iron nitride nanoparticles in the presence of a surface active agent to modify a surface of the plurality of iron nitride nanoparticles and form a plurality of surface-modified iron nitride nanoparticles.
In some examples, the disclosure describes a suspension that includes a solvent and a plurality of surface-modified iron nitride nanoparticles suspended in the solvent.
The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description, drawings, and claims.
Iron nitride (such as γ′-Fe4N, α′-Fe8N, α″-Fe16NxZ2-x, or α′-Fe8NxZ1-x, wherein Z comprises at least one of C, B, or O) is one promising candidate for a material in magnetic nanoparticles, as 1) both iron and nitrogen are inexpensive, low biotoxicity, and environment friendly, and 2) the saturation magnetization of γ′-Fe4N is around two times higher than that of IONPs. A comparison of bulk magnetic materials is shown below in Table 1.
In view of saturation magnetizations, iron nitride nanoparticles (γ′-Fe4N, α′-Fe8N, α″-Fe8N2-xZx and α′-Fe8N1-xZx nanoparticles, where Z includes at least one of C, B, or O) and FeCo nanoparticles show higher saturation magnetizations over iron oxide. However, FeCo cannot be directly used in biomedical applications because of the concerns of oxidation and corrosion. Thus, using FeCo requires a core-shell structure nanoparticle, with the high saturation FeCo magnetization material as the core and protective biocompatible nonmagnetic materials as the shell to prevent oxidation as well as improve biocompatibility. This reduces the overall saturation magnetization of the core-shell nanoparticles.
The preparation of colloidally stable, uniformly sized, and sub-100-nm γ′-Fe4N nanoparticles for biomedical applications is challenging. A gas nitriding method has been used to mass production γ′-Fe4N nanoparticles. In the gas nitriding method, IONPs may be used as a precursor and a hydrogen reduction step is carried out to remove oxygen and obtain reduced Fe nanoparticles. Next, a mixture of ammonia and hydrogen gas is used to nitride the Fe nanoparticles at a temperature between about 400° C. and about 600° C. Single-phase γ′-Fe4N nanoparticles have been reported using this method. Although the high temperature gas nitriding approach can realize massive production of high-magnetic-moment γ′-Fe4N nanoparticles, due to the relatively high processing temperature, some nanoparticles are sintered together, leading to a larger and wider size distribution of the resulting material. The sintered, larger nanoparticles show remanent magnetization (i.e., are not superparamagnetic, showing magnetizations at zero external field). This type of nanoparticles will agglomerate and may block the blood vessels for in vivo applications (such as hyperthermia therapy) and will cause non-uniform magnetic signals for in vitro bioassays. Such material may be less useful, as nanoparticles that are sub-100-nm and with a narrow size distribution are required for most biomedical applications. Further, gas nitriding produces dry γ′-Fe4N nanoparticles, in which weak forces such as electrostatics, van der Walls forces, and capillary effects may reduce stability of colloidal solutions of the γ′-Fe4N nanoparticles. Although there have been many reports of the stabilization of IONPs with different functional groups in various solution conditions, direct surface chemical modification of γ′-Fe4N nanoparticles has not been reported. This disclosure describes example, synthesis and surface functionalization strategies for obtaining stable, substantially monodispersed, sub-100-nm, narrow-size-distributed γ′-Fe4N nanoparticle colloidal suspensions.
This disclosure describes synthesis methods for γ′-Fe4N nanoparticles through a gas nitriding approach. These γ′-Fe4N nanoparticles are then surface functionalized using wet ball milling and a surface-active media such as a commercially available nanoparticle surfactant, oleic acid (OA), or tetramethylammonium hydroxide solution (TMAOH). The surface-active nanoparticles then may be separated using a centrifugation process to collect the uniformly sized, sub-100-nm γ′-Fe4N nanoparticles from the supernatants. The morphologies and hydrodynamic sizes of processed γ′-Fe4N nanoparticles, as well as the surface chemical groups on nanoparticles were characterized by the standard transmission electron microscope (TEM), nanoparticle tracking analyzer (NTA), and Fourier-transform infrared spectroscopy (FTIR). The colloidal stability of processed γ′-Fe4N nanoparticle suspensions was evaluated by a zeta potential analyzer (ZPA) and through a 21-day period observation period.
In examples in which a plurality of iron nitride nanoparticles are formed using a gas phase nitriding process (12), the gas phase nitriding process may include placing a plurality of precursor nanoparticles in a furnace. The precursor nanoparticles may include iron oxide (e.g., γ-Fe2O3) nanoparticles, iron (e.g., elemental Fe) nanoparticles, or other iron-containing nanoparticles (e.g., iron carbide, iron boride, or the like). The furnace may include any suitable furnace, including a tube furnace.
In some examples in which the precursor nanoparticles include iron oxide, the gas phase nitriding process may include reducing the plurality of iron oxide nanoparticles to form a plurality of iron nanoparticles. In examples in which the precursor nanoparticles do not include iron oxide (e.g., examples in which the precursor nanoparticles include elemental iron, iron carbide, or iron boride), the reducing step may be omitted. The precursor nanoparticles may be reduced by introducing a reducing gas into the furnace. The reducing gas may include, for example, hydrogen gas, alone or mixed with another gas. In some examples, the reducing step may occur at a temperature of between about 350° C. and about 450° C. and a time between about 2 hours and about 5 hours.
Once the optional reduction step is complete, the resulting nanoparticles may include iron, iron carbide, iron boride, or the like. The nanoparticles then may be nitride. The nitriding may be performed by exposing the nanoparticles to elemental nitrogen or a nitrogen-containing compound, such as ammonia, urea, diatomic nitrogen, ammonium nitride, an amide, hydrazine, or the like. The nitriding may be performed at a temperature of between about 350° C. and about 450° C. (such as about 400° C.) and a time between about 2 hours and about 3 hours.
In some examples, during the nitriding step additional elements may be introduced to the nanoparticles. For example, at least one of carbon, boron, phosphorus, silicon, or oxygen may be introduces to the nanoparticles. Such elements may result in the formation of Fe4N, Fe4NxZ1-x, α″-Fe16N2-xZx and/or α′-Fe8N1-xZx, where Z includes at least one of C, B, P, Si, or O. Sources of carbon may include carbon monoxide, carbon dioxide, methane, graphite, urea, or the like. Some compounds may be used as a source of both carbon and nitrogen, such as urea.
The nitriding may form nanoparticles including iron nitride. The iron nitride may include at least one of γ′-Fe4N, γ′-Fe4NxZ1-x, α′-Fe8N, α″-Fe16NxZ2-x, or α′-Fe8NxZ1-x, wherein Z comprises at least one of C, B, P, Si, or O. In some examples, the nanoparticles may include a mixture of iron nitride phases, may include iron nitride and one or more iron phases, or the like.
Regardless of whether the iron nitride is formed (12) or purchase, the technique of
The wet ball milling may be performed for between about 1 hour and about 10 hours at an rpm of between about 100 rpm and about 1000 rpm. The wet ball milling may help break up any sintered or agglomerated nanoparticle clumps while the surface modification reaction is proceeding.
The technique of
The technique of
In some examples, the surface-modified iron nitride nanoparticles may be consolidated into a bulk material, such as a soft magnet material. As one example, the surface-modified iron nitride nanoparticles may be dried and compacted into a dense bulk material having grain sizes that correspond to an average diameter of the surface-modified iron nitride nanoparticles. As another example, the surface-modified iron nitride nanoparticles may be dried and dispersed in a binder to form a composite material. The consolidated surface-modified iron nitride nanoparticles may have an irregular shape due to the forces exerted on the iron nitride nanoparticles during wet ball milling, and may be reflected by a high hydrodynamic size, surface area to volume ratio, or other measure of irregularity of a shape or surface.
Iron nitride nanoparticles produced using the techniques described herein may be used in a variety of applications in which high uniformity, high magnetic saturation, and/or low coercivity may be desired. In some examples, iron nitride nanoparticles may be used in biomedical applications including, but not limited to, magnetic resonance imaging (MRI), magnetic particle imaging (MPI), gene/drug delivery, magnetic hyperthermia therapy, magnetic separation, magnetic biosensors, and the like. As one example, a suspension of iron nitride nanoparticles surface functionalized through wet milling and subsequently centrifuged may have a relatively low size (e.g., an average diameter of less than about 20 nm) and high size uniformity (e.g., a 90% size distribution around a single peak) of the iron nitride nanoparticles. As another example, iron nitride nanoparticles formed by wet milling may have an irregular shape that produces a wide distribution of hydrodynamic sizes, resulting in increased transverse relaxivity. As a result, an MRI contrast agent that includes irregularly shaped iron nitride nanoparticles may have increased contrast.
In some examples, iron nitride nanoparticles may be used in soft magnet applications including, but not limited to, inductors, transformers, generators, motors, and the like. For example, iron nitride nanoparticles may be processed into a material having a high saturation magnetization (e.g., >180 emu/g) and low coercivity. Iron nitride nanoparticles having a sub-100 nm average diameter may be compacted or composited, alone or with a binder, to form a dense soft magnetic material. This soft magnetic material may have a relatively small grain size (e.g., <100 nm) corresponding to the small average diameter of the iron nitride nanoparticles, resulting in relatively low coercivity. The soft magnetic material may be incorporated into power electronics and other high temperature, high magnetic field devices.
The γ-Fe2O3 nanoparticle powder was purchased from MTI Corporation. Commercial nanoparticle surfactant (in water dispersion) was purchased from US Research Nanomaterials, Inc. This surfactant product is a mixture of following substances: Nonylphenol (C15H24O, CAS#: 25154-52-3), Polyoxyalkylene amine derivative (CAS#: 68511-96-6), polyethylene glycol (C14H22O(C2H4O)n, n=9-10, CAS#: 9002-93-1), Polyvinylpyrrolidone ((C6H9NO)n, CAS#: 9003-39-8), Butyl ethanoate (C6H12O2, CAS#: 123-86-4), Ethylene glycol monobutyl ether (C6H14O2, CAS#: 111-76-2). Oleic acid (C18H34O2, CAS#: 112-80-1) was purchased from Thermo Fisher Scientific. Tetramethylammonium hydroxide solution (N(CH3)4OH, CAS#: 75-59-225, wt. % in water) was purchased from Sigma Aldrich.
γ-Fe2O3 nanoparticles (nominal diameter of about 20 nm) were used to prepare γ′-Fe4N by a gas nitriding approach. The γ-Fe2O3 nanoparticles were put in a tube furnace with a diameter of 1 inch, as shown in
The nitriding was performed for between 2 hours and 3 hours. Active nitrogen reacts with the reduced Fe to form γ′-Fe4N, which is shown in the schematic drawing in
Four γ′-Fe4N nanoparticle suspensions were prepared through a wet ball milling and centrifugation process.
Despite the high yield in the synthesis of γ′-Fe4N nanoparticles by means of the gas nitriding approach, due the high temperatures in the gas nitriding process, the sintered masses of nanoparticles with large sizes are not favored for biomedical applications. Thus, a centrifugation step was carried out to maintain the sub-100 nm γ′-Fe4N nanoparticles and discard larger nanoparticles. There is a trade-off between obtaining the uniformly sized, sub-100 nm nanoparticles and reducing the loss rate of raw materials (i.e., the nanoparticle powder after the wet ball milling step). Two centrifugal speeds, 2,000 rpm and 11,000 rpm, were used to determine the effect of centrifugal speeds on yield and particle size distribution. More nanoparticles were retained, and the particle size distribution was wider when sample was centrifuged at 2,000 rpm. On the other hand, centrifugation at 11,000 rpm resulted in a narrower size distribution, but the number of nanoparticles recovered was lower.
After the wet ball milling process, the turbid suspensions for each sample were allotted into three 1.5 mL vials. The first vial was centrifuged at 2,000 rpm for 30 min, and a 500 μL of supernatant was drawn from the vial. The surface-functionalized γ′-Fe4N nanoparticles from the supernatant of each sample was separated using a permanent magnet, then washed three times by either water (for nanoparticles from samples A, B, and D) or ethanol (for nanoparticles from sample C). Finally, the surface-functionalized γ′-Fe4N nanoparticles from the supernatant of each sample were re-dispersed in water or ethanol solvent to the desired volumes for different characterization purposes. These γ′-Fe4N nanoparticle suspensions were labeled as X@2k (X=A, B, C, and D), as shown in
Similarly, the second vial of each sample was centrifuged at 11,000 rpm for 30 min, and 500 μL of supernatant was drawn from the vial. After magnetic separation and wash out (as described above), the surface-functionalized γ′-Fe4N nanoparticles from the supernatant of each sample were re-dispersed in water or ethanol solvent. These γ′-Fe4N nanoparticle suspensions were labeled as X@11k (X=A, B, C, and D), as shown in
The third vial of each sample was centrifugated at 2,000 rpm for 30 min, and a 1 mL of supernatant was drawn from the vial. These supernatants were labeled as X@supernatant (X=A, B, C, and D) and sealed in transparent glass bottles for a 21-day colloidal stability observation, as shown in
Nanoparticles samples, γ-Fe2O3 and γ′-Fe4N were stored in a N2 glove box to avoid oxidation. All the nanoparticle samples for magnetic characterization were prepared in the N2 glove box. Certain amounts of nanoparticles were weighed and sealed in parafilms to prevent further oxidation after the samples were taken out of the N2 glove box. Hysteresis loops were measured by a Physical Properties Measurement System (PPMS, Quantum Design Inc.) to obtain the magnetic properties of these nanoparticles such as the saturation (Ms) and coercivity (Hc).
The static magnetic hysteresis loops of γ-Fe2O3 (the precursor) and the synthesized γ′-Fe4N nanoparticles are shown in
The high Hc and large remanence of γ′-Fe4N are caused by the sintering during the high temperature gas nitriding process. These sintered γ′-Fe4N particles with wider size distributions and larger sizes (as shown below in
γ-Fe2O3 and γ′-Fe4N nanoparticle samples for X-ray diffraction (XRD) patterns were also prepared in the N2 glove box. Selected amounts of nanoparticles were put on a piece of glass substrate and an epoxy was used to seal the nanoparticles to prevent oxidation after the samples were taken out of the glove box. When the epoxy dried and solidified, these samples were used to for the XRD measurements. The XRD patterns were characterized using a Bruker D8 Discover 2D equipped with a Co radiation source operated at 45 kV and 40 mA. For a convenient comparison, the XRD patterns were converted into a Cu radiation source using MDI Jade software.
The XRD patterns of the precursor γ-Fe2O3 and synthesized γ′-Fe4N nanoparticles are shown in
The morphologies of γ′-Fe4N nanoparticle cores were characterized by a transmission electron microscope (TEM, FEI Tecnai T12). Briefly, 10 μL of X@2k and X@11k (X=A, B, C, and D) nanoparticle colloidal suspensions were dropped on TEM grids and air dried at room temperature before TEM imaging.
The hydrodynamic sizes of these surface functionalized γ′-Fe4N nanoparticles were measured using a nanoparticle tracking analyzer (NTA, Nanosight LM-10). 1.5 mL of samples X@2k and X@11k (X=A, B, C and D) were used for the hydrodynamic size measurements on the NTA. The NTA used a 400 nm (near UV) laser to track the motion of γ′-Fe4N nanoparticles suspended in solvents (i.e., water for samples A, B, D and ethanol for sample C) then calculated the size distributions for nanoparticles between 10 nm and 1 μm.
Initially, it should be noted that the TEM morphology imaging was used to observe the magnetic cores of synthesized γ′-Fe4N nanoparticles, thus, the sizes read from TEM images are different from the hydrodynamic sizes read from NTA.
It can be clearly seen that γ′-Fe4N nanoparticles that are wet ball milled in water (samples A@2k and A@11k) and in oleic acid (OA) (samples C@2k and C@11k) are forming large clusters. This indicates that: 1) wet ball milling in water and OA cannot effectively separate γ′-Fe4N nanoparticles; 2) these γ′-Fe4N nanoparticles are not superparamagnetic and thus, forming clusters due to non-zero remanence; and 3) these γ′-Fe4N nanoparticles processed with water and OA will not be colloidally stable and may form sediments in solvents.
On the other hand, the γ′-Fe4N nanoparticles that are wet ball milled in commercial surfactant product and TMAOH are monodispersed. Samples B@2k, B@11k, D@2k, and D@11k show monodispersed and small size γ′-Fe4N nanoparticles. This indicates that 1) centrifuging at 2,000 rpm for 30 min is sufficient to extract uniform-sized, monodispersed, and sub-100-nm γ′-Fe4N nanoparticles; and 2) these nanoparticles are not forming clusters and will be colloidally stable. Furthermore, many γ′-Fe4N nanoparticles with sizes below 20 nm are observed, while the theoretical size limit for γ′-Fe4N nanoparticles to be superparamagnetic is 19 nm.
The magnetic core size distributions of γ′-Fe4N nanoparticles from samples X@11k were obtained from the TEM images and plotted in
The NTA was used to measure the hydrodynamic size of the γ′-Fe4N nanoparticles after different surface modification processes.
The hydrodynamic size distributions and percentile size distributions of samples X@11k (X=A, B, C, and D) are provided in
From
The colloidal stabilities of surface functionalized γ′-Fe4N nanoparticles by different surface-active media were appraised through a 21-day observation period on samples X@supernatant (X=A, B, C, and D). As shown in
A zeta potential analyzer (ZPA, Stabino) was used to measure the particle charge distribution or the zeta potential of the surface functionalized γ′-Fe4N nanoparticles from solvents (water or ethanol). 5 mL of samples X@2k (X=A, B, C, and D) are prepared, sonicated for 30 min before the zeta potential measurements.
The zeta potentials of surface functionalized γ′-Fe4N nanoparticles in solvent are −29.13 mV, −26.27 mV, −0.55 mV, and −29.99 mV, respectively for A, B, C, and D. This indicates that γ′-Fe4N nanoparticles processed by commercial surfactants, water, and TMAOH are relatively stable due to a large electrokinetic potential (or electrostatic repulsion), while, on the other hand, γ′-Fe4N nanoparticles treated by OA will rapidly coagulate.
Although zeta potential results indicate γ′-Fe4N nanoparticles treated by commercial surfactants, water, and TMAOH should be colloidally stable and that γ′-Fe4N nanoparticles treated by OA should not be colloidally stable, the TEM images and NTA results show that only the γ′-Fe4N nanoparticles that are treated by commercial surfactants and TMAOH are uniformly sized and monodispersed, while nanoparticles treated by water are not. This is because, although γ′-Fe4N nanoparticles treated by water show a large electrokinetic potential (or electrostatic repulsion), there is no surface chemical groups functionalized on these nanoparticles, and the non-zero remanences of these nanoparticles cause clustering.
The chemical groups functionalized on γ′-Fe4N nanoparticle surfaces were characterized by a FTIR spectrometer (Fourier-transform infrared spectroscopy, Thermo Scientific Nicolet iS50 FTIR) on the main detector MCT-A (7000-600 cm−1), with KBr beam splitter and a resolution of 2 cm−1. A total of 32 scans were taken on each sample. Samples X@pellet (X=A, B, C, and D) were evenly spread and dried on a barium fluoride (BaF2) window (diameter 25.4 mm, thickness 2 mm, purchased from EKSMA Optics, UAB) for FTIR transmittance spectrum collection. In addition, the FTIR transmittance spectrum of the commercial surfactant product, OA, and TMAOH are also collected for direct comparisons. These liquid samples were sealed between two BaF2 windows before FTIR characterizations.
The IR transmittance spectrums are given in
The FTIR transmittance spectrum of A@pellet in
In
The transmittance spectrum of C@pellet is shown in
The transmittance spectrum of D@pellet is shown in
During the wet ball milling process, different surfactants were added, and the milling speed was low (350 rpm). The decomposition temperature of γ′-Fe4N is above 600° C. based on the Fe—N phase diagram. The surfactants, except water, can also help protect nanoparticles from oxidation during the milling process. Thus, the produced nanoparticles should still conserve the original phase and have the similar magnetic properties. To demonstrate that the nanoparticles after wet ball milling with the four surface-active media (A: water, B: 5 vol/vol % commercial nanoparticle surfactant in water, C: 25 vol/vol % OA in ethanol, D: 25 wt % TMAOH in water) are still γ′-Fe4N, a new batch of γ′-Fe4N nanoparticles were synthesized and X@pellet samples (X=A, B, C, and D) were prepared as described above. The crystal structure characterizations on the newly synthesized γ′-Fe4N nanoparticle powder and X@pellet samples are shown in
A method includes wet ball milling a plurality of iron nitride nanoparticles in the presence of a surface active agent to modify a surface of the plurality of iron nitride nanoparticles and form a plurality of surface-modified iron nitride nanoparticles.
The method of example 1, wherein the plurality of iron nitride nanoparticles comprise at least one of γ′-Fe4N, α′-Fe8N, α″-Fe16NxZ2-x, or α′-Fe8NxZ1-x, wherein Z comprises at least one of C, B, P, Si, or O.
The method of any of examples 1 and 2, further includes centrifuging the plurality of surface-modified iron nitride nanoparticles to separate a set of surface-modified iron nitride nanoparticles having a selected size profile from the plurality of surface-modified iron nitride nanoparticles.
The method of any of examples 1 through 3, further includes forming the plurality of iron nitride nanoparticles from a plurality of iron oxide nanoparticles using a gas phase nitriding process.
The method of example 4, wherein the plurality of iron oxide nanoparticles comprise a plurality of γ-Fe2O3 nanoparticles.
The method of any of examples 4 and 5, wherein the gas phase nitriding process comprises: reducing, in a furnace, the plurality of iron oxide nanoparticles to form a plurality of iron nanoparticles; and nitriding the plurality of iron particles to form the plurality of iron nitride nanoparticles.
The method of example 6, wherein nitriding the plurality of iron particles to form the plurality of iron nitride nanoparticles further comprises forming the plurality of iron nitride nanoparticles comprising at least one of Fe4N, Fe4NxZ1-x, α″-Fe16NxZ2-x or α′-Fe8NxZ1-x, where Z includes at least one of C, B, P, Si, or O based on introduction of at least one of carbon, boron, silicon, phosphorus, or oxygen to the furnace.
The method of any of examples 1 through 7, wherein wet ball milling the plurality of iron nitride nanoparticles in the presence of a surface active agent comprises wet ball milling the plurality of iron nitride nanoparticles in the presence of a source of at least one of: polyvinylpyrrolidone, a polyoxyalkylene amine derivative, polyethylene glycol, ethylene glycol monobutyl ether, nonylphenol, or tetramethylammonium hydroxide.
The method of any of examples 1 through 8, wherein wet ball milling the plurality of iron nitride nanoparticles in the presence of a surface active agent comprises wet ball milling for a period of between about 1 hour and about 10 hours at an rpm of between about 100 rpm and about 1000 rpm.
The method of any of examples 3 through 9, wherein centrifuging the plurality of surface-modified iron nitride nanoparticles comprises centrifuging the plurality of surface-modified iron nitride nanoparticles at an rpm and for a time selected to obtain a set of surface-modified iron nitride nanoparticles having an average diameter of less than about 100 nm.
The method of example 10, wherein centrifuging the plurality of surface-modified iron nitride nanoparticles comprises centrifuging the plurality of surface-modified iron nitride nanoparticles at a revolutions per minute (RPM) and for a time selected to obtain a set of surface-modified iron nitride nanoparticles having an average diameter of less than about 50 nm.
The method of any of examples 3 through 11, wherein centrifuging the plurality of surface-modified iron nitride nanoparticles comprises centrifuging the plurality of surface-modified iron nitride nanoparticles at an rpm and for a time selected to obtain a set of surface-modified iron nitride nanoparticles having unimodal size distribution.
The method of any of examples 3 through 12, wherein centrifuging the plurality of surface-modified iron nitride nanoparticles comprises centrifuging the plurality of surface-modified iron nitride nanoparticles at a revolutions per minute (RPM) between about 1,000 RPM and about 50,000 RPM.
The method of example 13, wherein centrifuging the plurality of surface-modified iron nitride nanoparticles comprises centrifuging the plurality of surface-modified iron nitride nanoparticles at an rpm of about 2,000 RPM or about 11,000 RPM.
A suspension includes a solvent; and a plurality of surface-modified iron nitride nanoparticles suspended in the solvent.
The suspension of example 15, wherein the plurality of surface-modified iron nitride nanoparticles have an average diameter of less than 100 nm.
The suspension of example 16, wherein the plurality of surface-modified iron nitride nanoparticles have an average diameter of less than 50 nm.
The suspension of any of examples 15 through 17, wherein the plurality of surface-modified iron nitride nanoparticles have a substantially unimodal size distribution.
The suspension of any of examples 15 through 18, wherein the plurality of surface-modified iron nitride nanoparticles are surface-modified by at least one of polyvinylpyrrolidone, a polyoxyalkylene amine derivative, polyethylene glycol, ethylene glycol monobutyl ether, nonylphenol, or tetramethylammonium hydroxide.
The suspension of any of examples 15 through 19, wherein the plurality of surface-modified iron nitride nanoparticles comprise at least one of γ′-Fe4N, γ′-Fe4NxZ1-x, α′-Fe8N, α″-Fe16NxZ2-x, or α′-Fe8NxZ1-x, wherein Z comprises at least one of C, B, P, Si, or O.
A soft magnetic material includes a plurality of consolidated surface-modified iron nitride nanoparticles, wherein the plurality of consolidated surface-modified iron nitride nanoparticles have an average diameter less than about 100 nm.
The soft magnetic material of example 21, wherein the plurality of consolidated surface-modified iron nitride nanoparticles are dispersed in a binder.
The soft magnetic material of example 21 or 22, wherein the plurality of consolidated surface-modified iron nitride nanoparticles have a substantially irregular shape.
The soft magnetic material of any of examples 21 through 23, wherein the plurality of consolidated surface-modified iron nitride nanoparticles have a coercivity less than about 200 Oe.
The soft magnetic material of any of examples 21 through 24, wherein the plurality of consolidated surface-modified iron nitride nanoparticles are surface-modified by at least one of polyvinylpyrrolidone, a polyoxyalkylene amine derivative, polyethylene glycol, ethylene glycol monobutyl ether, nonylphenol, or tetramethylammonium hydroxide.
The soft magnetic material of any of examples 21 through 25, wherein the plurality of consolidated surface-modified iron nitride nanoparticles comprise at least one of γ′-Fe4N, γ′-Fe4NxZ1-x, α′-Fe8N, α″-Fe16NxZ2-x, or α′-Fe8NxZ1-x, wherein Z comprises at least one of C, B, P, Si, or O.
Various examples have been described. These and other examples are within the scope of the following claims.
This application claims the benefit of U.S. Provisional Patent Application No. 63/201,246, filed Apr. 20, 2021, the entire contents of which is incorporated herein by reference.
Number | Date | Country | |
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63201246 | Apr 2021 | US |