WO2016144729A1 - Plasma-based production of nanoferrite particles - Google Patents

Abstract

The present disclosure relates to spinel ferrite nanoparticles. Also provided are systems and methods of preparation of the ferrite nanoparticles using plasma-based methods. The spinel ferrite nanoparticles are useful in a variety of applications, for example, for use as high- frequency circuit components and as antennas in communication devices such as cellular phones.

Description

PLASMA-BASED PRODUCTION OF NANOFERRITE PARTICLES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority benefit of United States Provisional Patent Application No. 62/129,532, filed March 6, 2015. The entire contents of that application are hereby incorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present disclosure relates to the field of nanotechnology. More specifically, the present invention relates to magnetic nanoparticles for high frequency devices, for example as antennas in mobile phones.

BACKGROUND OF THE INVENTION

[0003] Modern communication devices rely on high-frequency circuit components. Mobile phones, for example, operate in a wide frequency band ranging from several hundreds of MHz to several GHz. The electromagnetic materials used as antennas in mobile phones need to have high electrical resistivity over a wide frequency range in order to minimize induced currents (called eddy currents), and have high magnetic permeability and stability over a wide

temperature range. As mobile phones continue to be designed with ever-increasing

miniaturization and high speed, there is a need for novel materials with superior electromagnetic properties for use as antennas. Many technologically useful magnetic materials, including iron and metallic alloys, display low electrical resistivity. Low electrical resistivity allows induced currents to flow through the material itself, producing heat as wasted energy. At high

frequencies, the amount of heat that is generated by these materials results in poor efficiency.

[0004] Spinel ferrites having the structure MFe₂0₄, where M refers to divalent metal ions, have properties that are favorable for use at high frequencies. In particular, spinel ferrites display high electrical resistivity, permeability, and temperature stability. Furthermore, ferrites are generally a lower cost alternative to magnetic metals and alloys. The preparation of magnetic materials on the nanoscale is an area of great interest because magnetic nanoparticles display electrical conductivity and mechanical strength that differ from particles of larger size.

[0005] Superparamagnetic nanoparticles of spinel ferrites are promising materials for use as high-frequency circuit components. The properties of these materials are very sensitive to the method of preparation. Known methods of producing spinel nanoferrite particles often yields nanoparticles with a large size distribution. Furthermore, many of these methods rely on post- synthesis annealing at various temperatures. The annealing process can affect both the nanoparticle size and the cation distribution. Consequently, the magnetic properties of the spinel nanoferrite particles are also affected, as they depend on the cation distribution within the crystal lattice.

[0006] Accordingly, there is a need for producing spinel ferrite nanoparticles using a method that permits good control of nanoparticle size.

SUMMARY OF THE INVENTION [0007] In some embodiments, the invention provides spinel ferrite nanoparticles of good purity and uniform size, as well as methods of making such nanoparticles, and products prepared from such nanoparticles.

[0008] In one embodiment, the invention provides a nanopowder comprising nickel-zinc ferrite nanoparticles. In one embodiment, the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 50% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 50% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 60% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 60% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 70% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 70% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In one embodiment, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. In any of the preceding embodiments, at least about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about 99% of the nanopowder can comprise nickel-zinc ferrite nanoparticles in spinel form.

[0009] In another embodiment, the invention provides a nanopowder comprising nickel-zinc ferrite nanoparticles. In one embodiment, the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 40 nm. In one embodiment, the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 10 nm. In the preceding embodiment, at least about 50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about 99% of the nanopowder can comprise nickel- zinc ferrite nanoparticles in spinel form.

[0010] In other embodiments, including any of the preceding embodiments, the nickel-zinc ferrite nanoparticles are of the formula NixZn₍i_x₎Fe₂0₄ , where X is between approximately 0.5 and 0.7; or where X is between approximately 0.55 and 0.65; or where X is approximately 0.6.

[0011] In any of the foregoing embodiments, the nickel-zinc ferrite nanoparticles can be produced by plasma synthesis. [0012] In another embodiment, the invention provides a method of making nickel-zinc ferrite nanoparticles, comprising a) feeding one or more starting materials which together comprise nickel, zinc, and iron into a plasma production chamber; b) vaporizing the one or more starting materials to form a vaporized material; c) injecting oxygen gas into the vaporized material; and d) quenching the vaporized material to form the nickel-zinc ferrite nanoparticles. In one embodiment, the one or more starting materials which together comprise nickel, zinc, and iron comprise a nickel-containing material, a zinc-containing material, and an iron-containing material. In one embodiment, the nickel-containing material is NiO. In one embodiment, the zinc-containing material is ZnO. In one embodiment, the iron-containing material is Fe metal. In one embodiment, the nickel-containing material is NiO, the zinc-containing material is ZnO, and the iron-containing material is Fe metal. In one embodiment, the one or more starting materials which together comprise nickel, zinc, and iron, comprise zinc ferrite and nickel ferrite. In one embodiment, the one or more starting materials which together comprise nickel, zinc, and iron comprise about 50 mole % to 60 mole % zinc ferrite, and the remaining mole percent of the starting materials comprises nickel ferrite.

[0013] In another embodiment, the invention provides a composition comprising nickel-zinc ferrite nanoparticles, wherein the nanoparticles are made by a) feeding one or more starting materials which together comprise nickel, zinc, and iron into a plasma production chamber; b) vaporizing the one or more starting materials to form a vaporized material; c) injecting oxygen gas into the vaporized material; and d) quenching the vaporized material to form the nickel-zinc ferrite nanoparticles. In one embodiment, the one or more starting materials which together comprise nickel, zinc, and iron comprise a nickel-containing material, a zinc-containing material, and an iron-containing material. In one embodiment, the nickel-containing material is NiO. In one embodiment, the zinc-containing material is ZnO. In one embodiment, the iron-containing material is Fe metal. In one embodiment, the nickel-containing material is NiO, the zinc- containing material is ZnO, and the iron-containing material is Fe metal. In one embodiment, the one or more starting materials which together comprise nickel, zinc, and iron, comprise zinc ferrite and nickel ferrite. In one embodiment, the one or more starting materials which together comprise nickel, zinc, and iron comprise about 50 mole % to 60 mole % zinc ferrite, and the remaining mole percent of the starting materials comprises nickel ferrite. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic illustration of a system for producing spinel ferrite

nanoparticles in accordance with embodiments of the present disclosure.

[0015] Figure 2 is a flowchart illustrating a method of producing spinel ferrite nanoparticles in accordance with embodiments of the present disclosure.

[0016] Figure 3 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-1.

[0017] Figure 4 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-2.

[0018] Figure 5 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-3.

[0019] Figure 6 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-4.

[0020] Figure 7 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-7.

[0021] Figure 8, panels A), B), and C), are a series of TEM images of nickel-zinc ferrite sample SDC-7 shown at a varying magnification.

[0022] Figure 9 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-5.

[0023] Figure 10 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-8.

[0024] Figure 11 is an X-ray diffraction spectrum of nickel-zinc ferrite sample SDC-6.

DETAILED DESCRIPTION OF THE INVENTION [0025] The procedures described herein provide methods for production of ferrite particles on a nanometer- size scale, with good control over the chemical composition and size distribution of the particles. Also disclosed herein are populations of particles having defined chemical composition and size distribution, including, but not limited to, spinel ferrites and spinel nickel- zinc ferrites.

[0026] The chemical composition of spinel ferrites is MFe₂0₄, where M refers to divalent metal ions. The structure of spinel ferrites is a cubic close-packed arrangement of oxygen atoms, with M²⁺ and Fe³⁺ occupying tetrahedral and octahedral crystallographic sites. The metal cation M²⁺ may refer to a single divalent metal ion or to multiple metal cations. The properties of spinel ferrites are described in detail in Mathew, D. S. et al. Chem. Eng. J. 2007, 129, 51-65. The magnetic moments of the cations in the tetrahedral sites are aligned in parallel to one another, as are the cations in the octahedral sites. However, the magnetic moments of the cations in the tetrahedral site are antiparallel to those in the octahedral sites, resulting in ferrimagnetic ordering of the crystal lattice. The magnetic properties of spinel ferrites are therefore tunable, both by the specific metal cation (M²⁺) and the distribution of cations between the tetrahedral and octahedral sites.

[0027] Magnetic materials are classified as either soft or hard, referring to their ability to be magnetized and demagnetized. Soft magnetic materials are easily magnetized and

demagnetized, whereas hard magnetic materials are not. Accordingly, soft magnetic materials are useful for electromagnets, and hard magnetic materials are useful for permanent magnets. Properties of soft magnetic materials include high saturation magnetization, high permeability, low anisotropy, high Curie temperature, and high electrical resistivity. Spinel ferrites are soft magnetic materials, and their magnetic properties are attributed to the interactions between metal ions occupying particular positions relative to the oxygen atoms in the crystal lattice. In the absence of an applied magnet, the magnetic domains are random and result in a net flux contribution of zero. However, in the presence of an applied magnet, the magnetic domains align in the direction of the magnetizing force and the net flux is large. As the size of particles in magnetic materials is reduced to below 20 nm, superparamagnetism can arise.

Superparamagnetism occurs in nanoparticles when the applied magnetic field can easily shift the magnetic moment of a particle away from the preferred crystallographic axes, permitting each nanoparticle to behave like a paramagnetic atom having a very large magnetic moment. Various spinel ferrite nanoparticles have been prepared that are superparamagnetic and have potential use in high-frequency electronic circuitry.

[0028] Existing methods of preparing spinel ferrite nanoparticles include gas condensation, aerosol reduction, chemical precipitation, sol-gel processing, thermal decomposition or organometallic precursors, continuous hydrothermal processing, and microemulsion methods. The nanoferrite particles produced using many of these methods, however, yields nanoparticles displaying a large size distribution, which ultimately affects the magnetic properties of the nanoparticles.

[0029] Nickel-zinc ferrites, in particular, are used in modern electronics. Nickel-zinc ferrites have the general formula NixZn₍i_x₎Fe₂0₄. The high electrical resistivity of these materials results in low induced currents, or eddy currents, even at high frequencies (10 KHz to hundreds of MHz or to GHz). Other attractive properties of nickel-zinc ferrites include high saturation magnetization, high magnetic permeability, high mechanical strength, good chemical stability, low coercivities, and low dielectric losses. Nano-sized nickel-zinc ferrites are of interest to the electronics industry in order to further reduce energy losses associated with eddy currents, as well as to increase the density of the resulting materials.

[0030] Described are spinel ferrite nanoparticles and methods of making spinel nanoferrite particles using plasma-based technology. The described spinel ferrite nanoparticles may be produced with good control of nanoparticle size.

[0031] In addition, the described nanoferrite particles may display favorable magnetic properties, allowing for their production as antennas for communication devices such as mobile phones. The described nanoferrite particles may exhibit superparamagnetism.

[0032] The described nanoferrite particles described herein may be produced, for example, in a plasma reactor.

[0033] The nanoferrite particles described herein are useful as circuit components in high- frequency communication devices such as mobile phones. These nanoferrite particles are especially useful as antennas in mobile phones.

[0034] Various aspects of the disclosure can be described through the use of flowcharts.

Often, a single instance of an aspect of the present disclosure is shown. As is appreciated by those of ordinary skill in the art, however, the protocols, processes, and procedures described herein can be repeated continuously or as often as necessary to satisfy the needs described herein. In addition, it is contemplated that certain method steps can be performed in alternative sequences to those disclosed in the flowcharts.

[0035] When numerical values are expressed herein using the term "about" or the term

"approximately," it is understood that both the value specified, as well as values reasonably close to the value specified, are included. For example, the description "about 50 °C" or

"approximately 50 °C" includes both the disclosure of 50 °C itself, as well as values close to 50 °C. Thus, the phrases "about X" or "approximately X" include a description of the value X itself. If a range is indicated, such as "approximately 50 °C to 60 °C," it is understood that both the values specified by the endpoints are included, and that values close to each endpoint or both endpoints are included for each endpoint or both endpoints; that is, "approximately 50 °C to 60 °C" is equivalent to reciting both "50 °C to 60 °C" and "approximately 50 °C to approximately 60 °C."

[0036] This disclosure provides several embodiments. It is contemplated that any features from any embodiment can be combined with any features from any other embodiment. In this fashion, hybrid configurations of the disclosed features are within the scope of the present invention.

[0037] It is understood that reference to relative weight percentages (or relative mole percentages) in a composition assumes that the combined total weight percentages (or relative mole percentages) of all components in the composition add up to 100. It is further understood that relative weight percentages (or relative mole percentages) of one or more components may be adjusted upwards or downwards such that the weight percent (or mole percent) of the components in the composition combine to a total of 100, provided that the weight percent (or mole percent) of any particular component does not fall outside the limits of the range specified for that component.

[0038] This disclosure refers to both particles and powders. These two terms are equivalent, except for the caveat that a singular "powder" refers to a collection of particles. The present invention can apply to a wide variety of powders and particles. The terms "nanoparticle" and "nano-sized particle" are generally understood by those of ordinary skill in the art to encompass a particle on the order of nanometers in diameter, typically between about 0.5 nm to 500 nm, about 1 nm to 500 nm, about 1 nm to 100 nm, or about 1 nm to 50 nm. Preferably, the nanoparticles have an average grain size less than 250 nanometers and an aspect ratio between one and one million. In some embodiments, the nanoparticles have an average grain size of about 50 nm or less, about 30 nm or less, or about 20 nm or less. In additional embodiments, the nanoparticles have an average diameter of about 50 nm or less, about 30 nm or less, or about 20 nm or less. The aspect ratio of the particles, defined as the longest dimension of the particle divided by the shortest dimension of the particle, is preferably between one and one hundred, more preferably between one and ten, yet more preferably between one and two. "Grain size" is measured using the ASTM (American Society for Testing and Materials) standard (see ASTM El 12 - 10). When calculating a diameter of a particle, the average of its longest and shortest dimension is taken; thus, the diameter of an ovoid particle with long axis 20 nm and short axis 10 nm would be 15 nm. The average diameter of a population of particles is the average of diameters of the individual particles, and can be measured by various techniques known to those of skill in the art, such as transmission electron microscopy (TEM).

[0039] This disclosure refers to both ferrite nanoparticles and nanoferrite particles. These two terms are equivalent.

[0040] In additional embodiments, the nanoparticles have a grain size of about 50 nm or less, about 40 nm or less, about 30 nm or less, about 20 nm or less, about 10 nm or less or about 5 nm or less. In additional embodiments, the nanoparticles have a diameter of about 50 nm or less, about 40 nm or less, about 30 nm or less, about 20 nm or less, about 10 nm or less or about 5 nm or less.

[0041] The terms "micro-particle," "micro-sized particle," "micron-particle," and "micron- sized particle" are generally understood to encompass a particle on the order of micrometers in diameter, typically between about 0.5 μιη to 1000 μιη, about 1 μιη to 1000 μιη, about 1 μιη to 100 μηι, or about 1 μιη to 50 μιη. Spinel Ferrite Nanoparticles

[0042] Spinel ferrite nanoparticles may include nickel-zinc ferrite nanoparticles. Other spinel ferrite nanoparticles may include zinc ferrites, manganese-zinc ferrites, cobalt ferrites, and nickel-copper ferrites. Described below is the preparation of nickel-zinc ferrite nanoparticles. However, one skilled in the art would understand that the preparation of other spinel ferrite nanoparticles (such as zinc ferrites, manganese-zinc ferrites, cobalt ferrites, and nickel-copper ferrites) may be prepared using the methods described herein.

[0043] The spinel ferrite nanoparticles may be embedded within a resin or matrix.

Alternatively, the spinel ferrite nanoparticles may be mixed with a resin or matrix. In some embodiments, the resin is polymerized resorcinol. Polymerized resorcinol may be produced by reaction of resorcinol and formaldehyde.

[0044] The spinel ferrite nanoparticles and resin may be machined into different shapes for subsequent use. For example, the nanoparticles and resin may be shaped into cylinders or discs.

Production of Spinel Ferrite Nanoparticles

[0045] The spinel ferrite nanoparticles are produced by plasma-based methods. These particles have advantageous properties as compared to spinel nanoferrite particles prepared by other methods. For example, spinel ferrite nanoparticles produced by the plasma-based methods described herein may show good size control, for example a narrow size distribution, better purity (i.e., lower percentages of impurities), or a higher percentage of the desired spinel form of the materials, as compared to non-plasma methods of making spinel particles.

[0046] The spinel ferrite nanoparticles may be formed by plasma reactor methods. These methods include feeding metals into a plasma gun, where the materials are vaporized. Systems equipped with a plasma production chamber, a reaction chamber, and a quench chamber such as those disclosed in U.S. Patent Publication No. 2008/0277270 and U.S. Patent No. 8,663,571 may be utilized. Plasma guns such as those disclosed in U.S. Patent Publication No. 2011/0143041 can be used, and techniques such as those disclosed in U.S. Patent No. 5,989,648, U.S. Patent

No. 6,689,192, U.S. Patent No. 6,755,886, and U.S. Patent Publication No. 2005/0233380 can be used to generate plasma. The highly turbulent quench chamber disclosed in U.S. Patent Publication No. 2008/0277267 is particularly useful for rapid quenching of plasma. The high- throughput plasma synthesis system disclosed in United States Patent Appl. No. 14/207,087 and International Patent Appl. No. PCT/US2014/024933 is also useful for production of spinel ferrite nanoparticles. The contents of all of the foregoing applications are incorporated by reference herein in their entirety.

[0047] A working gas, such as argon, is supplied to the plasma gun for the generation of plasma. In some embodiments, the working gas is a mixture of argon and hydrogen in a ratio of about 30: 1 to about 3: 1. In some embodiments, the working gas is a mixture of argon and hydrogen in a ratio of about 20: 1. In some embodiments, the working gas is a mixture of argon and hydrogen in a ratio of about 12: 1. In some embodiments, the working gas is a mixture of argon and hydrogen in a ratio of about 8: 1. In some embodiments, the working gas is a mixture of argon and hydrogen in a ratio of about 5: 1 or about 6: 1.

[0048] Metal oxides (such as NiO and ZnO) and solid metals (such as Fe), generally in the form of metal particles of about 15 to 25 microns diameter, are introduced as a fluidized powder in working gas. Alternatively, micron-sized nickel ferrite and zinc ferrite, typically in the form of particles of about 15 to 25 microns diameter, are introduced as a fluidized powder in working gas. Other methods of introducing the materials into the reactor can also be used, such as in a liquid slurry. [0049] For preparation of nickel-zinc ferrite nanoparticles, a composition of NiO, ZnO, and Fe metal may be fed into the plasma gun. Examples of ranges of materials that can be used for the preparation of nickel-zinc ferrite nanoparticles are from about 10 mole % of combined NiO and ZnO and about 90 mole % of Fe metal, to about 70 mole % of combined NiO and ZnO and about 30 mole % of Fe metal. In some embodiments, about 20 mole % of combined NiO and ZnO and about 80 mole % of Fe metal is used. In other embodiments, about 25 mole % of combined NiO and ZnO and about 75 mole % of Fe metal is used. In still other embodiments, about 30 mole % of combined NiO and ZnO and about 70 mole % of Fe metal is used. In other embodiments, about 35 mole % of combined NiO and ZnO and about 65 mole % of Fe metal is used. In other embodiments, about 40 mole % of combined NiO and ZnO and about 60 mole % of Fe metal is used. In other embodiments, about 45 mole % of combined NiO and ZnO and about 55 mole % of Fe metal is used. In other embodiments, a composition contains about 50 mole % of combined NiO and ZnO and about 50 mole % of Fe metal.

[0050] In some embodiments, examples of ranges of materials that can be used for the preparation of nickel-zinc ferrite nanoparticles are from about 10 mole % of combined NiO and ZnO and about 90 mole % of Fe metal, to about 70 mole % of combined NiO and ZnO and about 30 mole % of Fe metal; or from about 20 mole % of combined NiO and ZnO and about 80 mole % of Fe metal, to about 70 mole % of combined NiO and ZnO and about 30 mole % of Fe metal; or from about 30 mole % of combined NiO and ZnO and about 70 mole % of Fe metal, to about 70 mole % of combined NiO and ZnO and about 30 mole % of Fe metal; or from about 40 mole % of combined NiO and ZnO and about 60 mole % of Fe metal, to about 70 mole % of combined NiO and ZnO and about 30 mole % of Fe metal; or from about 45 mole % of combined NiO and ZnO and about 55 mole % of Fe metal, to about 70 mole % of combined NiO and ZnO and about 30 mole % of Fe metal; or from about 40 mole % of combined NiO and ZnO and about 60 mole % of Fe metal, to about 60 mole % of combined NiO and ZnO and about 40 mole % of Fe metal; or from about 45 mole % of combined NiO and ZnO and about 55 mole % of Fe metal, to about 55 mole % of combined NiO and ZnO and about 45 mole % of Fe metal. In any of the foregoing embodiments, the composition of the combined NiO and ZnO material can range from about 5 mole % NiO and 95 mole % ZnO to about 95 mole % NiO and 5 mole % ZnO, or from about 10 mole % NiO and 90 mole % ZnO to about 90 mole % NiO and 10 mole % ZnO, or from about 20 mole % NiO and 80 mole % ZnO to about 80 mole % NiO and 20 mole % ZnO, or from about 30 mole % NiO and 70 mole % ZnO to about 70 mole % NiO and 30 mole % ZnO, or from about 40 mole % NiO and 60 mole % ZnO to about 60 mole % NiO and 40 mole % ZnO, or from about 40 mole % NiO and 60 mole % ZnO to about 50 mole % NiO and 50 mole % ZnO, or from about 50 mole % NiO and 50 mole % ZnO to about 60 mole % NiO and 40 mole % ZnO, or from about 45 mole % NiO and 55 mole % ZnO to about 55 mole % NiO and 45 mole % ZnO, or from about 60 mole % NiO and 40 mole % ZnO to about 50 mole % NiO and 50 mole % ZnO.

[0051] In some embodiments, the percentages of materials fed into the plasma gun are as indicated in each row of Table 1. The percentages given are in mole percent, and represent both approximate proportions and exact proportions (thus, for example, "1-14%" in the table represents both "about 1% to about 14%" and "1% to 14%"). The total of the percentages of NiO, ZnO, and Fe actually used adds up to 100 mole % across a row; the mole percent of any one component in a given row can be adjusted up or down such that the total mole percent adds up to 100, provided that the mole percent of any particular component does not fall outside the limits of the range specified for that component.

Table 1

[0052] Nickel-zinc ferrite nanoparticles may be prepared using a composition of about 10 mole % micron- sized zinc ferrite to about 90 mole % micron- sized zinc ferrite as the material supply to the plasma gun, with the remaining mole percent comprising micron-sized nickel ferrite (for example, using 55 mole % zinc ferrite will result in use of 45 mole % nickel ferrite). In some embodiments, the composition contains about 20 mole % micron-sized zinc ferrite to about 80 mole % micron-sized zinc ferrite, with the remaining mole percent comprising micron-sized nickel ferrite. In some embodiments, the composition contains about 30 mole % micron-sized zinc ferrite to about 70 mole % micron-sized zinc ferrite, with the remaining mole percent comprising micron-sized nickel ferrite. In some embodiments, the composition contains about 40 mole % micron- sized zinc ferrite to about 60 mole % micron- sized zinc ferrite, with the remaining mole percent comprising micron-sized nickel ferrite. In some embodiments, the composition contains about 50 mole % micron-sized zinc ferrite to about 60 mole % micron- sized zinc ferrite, with the remaining mole percent comprising micron-sized nickel ferrite. In some embodiments, the composition contains about 50 mole % micron-sized zinc ferrite and about 50 mole % micron-sized nickel ferrite. In some embodiments, the composition contains about 55 mole % micron-sized zinc ferrite and about 45 mole % micron-sized nickel ferrite. In some embodiments, the composition contains about 60 mole % micron-sized zinc ferrite and about 40 mole % micron- sized nickel ferrite.

[0053] Nickel-zinc ferrite nanoparticles may be prepared using a composition of micron-sized zinc ferrite, micron-sized nickel ferrite, NiO, and ZnO as the material supply to the plasma gun. In some embodiments, the composition contains from about 30 mole % to about 70 mole % micron-sized zinc ferrite, from about 30 mole % to about 70 mole % micron-sized nickel ferrite, from about 0.1 mole % to about 10 mole % NiO, and from about 0.1 mole % to about 10 mole % ZnO; the sum of the mole percentages of the individual components totals 100%. In some embodiments, the composition contains from about 35 mole % to about 60 mole % micron-sized zinc ferrite, from about 40 mole % to about 65 mole % micron- sized nickel ferrite, from about 0.5 mole % to about 5 mole % NiO, and from about 0.5 mole % to about 5 mole % ZnO; the sum of the mole percentages of the individual components totals 100%. In some embodiments, the composition contains from about 40 mole % to about 50 mole % micron-sized zinc ferrite, from about 50 mole % to about 60 mole % micron- sized nickel ferrite, from about 1 mole % to about 2 mole % NiO, and from about 1 mole % to about 2 mole % ZnO; the sum of the mole percentages of the individual components totals 100%.

[0054] The nickel-zinc ferrite nanoparticles may contain from about 2.5 weight % of nickel, about 25 weight % of zinc, and about 47 weight % of iron to about 22 weight % of nickel, about 3 weight % of zinc, and about 47 weight % of iron. In some embodiments, the nickel-zinc ferrite nanoparticles may contain from about 5 weight % of nickel, about 20 weight % of zinc, and about 47 weight % of iron to about 20 weight % of nickel, about 5 weight % of zinc, and about 47 weight % of iron. In some embodiments, the nickel-zinc ferrite nanoparticles may contain from about 10 weight % of nickel, about 15 weight % of zinc, and about 47 weight % of iron to about 18 weight % of nickel, about 7.5 weight % of zinc, and about 47 weight % of iron. In some embodiments, the nickel-zinc ferrite nanoparticles may contain about 15 weight % of nickel, about 11 weight % of zinc, and about 47 weight % of iron.

[0055] The nickel-zinc ferrite nanoparticles may be comprised of the formula: Ni_xZn(i_x)Fe₂0₄ where X is between about 0.1 and about 0.9. In some embodiments, X is between about 0.2 and about 0.8. In some embodiments, X is between about 0.3 and about 0.7. In some embodiments, X is between about 0.4 and about 0.7. In some embodiments, X is between about 0.5 and about 0.7. In some embodiments, X is between about 0.55 and about 0.65. In some embodiments, X is about 0.6.

[0056] The nickel-zinc ferrite nanoparticles may be in a composition further containing NiO (bunsenite), ZnO (zincite), a-Fe, a-Fe₂0₃, and/or FeO (wuestite). In some embodiments, the composition may contain from about 10% nickel-zinc ferrite nanoparticles to about 90% nickel- zinc ferrite nanoparticles. In some embodiments, the composition may contain from about 20% nickel-zinc ferrite nanoparticles to about 85% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain from about 30% nickel-zinc ferrite nanoparticles to about 80% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain from about 35% nickel-zinc ferrite nanoparticles to about 75% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 35% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 40% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 45% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 50% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 55% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 60% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 65% nickel-zinc ferrite nanoparticles. In some embodiments, the composition may contain about, or at least about, 70% nickel-zinc ferrite nanoparticles. In some

embodiments, the composition may contain about, or at least about, 75% nickel-zinc ferrite nanoparticles. [0057] The nickel-zinc ferrite nanoparticles may be in a composition further containing magnetic particles. In some embodiments, the magnetic particles may be comprised of iron. In some embodiments, the magnetic particles may be comprised of nickel. In some embodiments, the magnetic particles may be comprised of a combination of iron and nickel.

[0058] The nickel-zinc ferrite nanoparticles may be in a composition further containing nonmagnetic particles. In some embodiments, the non-magnetic particles may be comprised of iron (that is, one or more non-magnetic compounds containing iron). In some embodiments, the nonmagnetic particles may be comprised of nickel (that is, one or more non-magnetic compounds containing nickel). In some embodiments, the non-magnetic particles may be comprised of zinc (that is, one or more non-magnetic compounds containing zinc). In some embodiments, the nonmagnetic particles may be comprised of a combination of iron and nickel (that is, one or more non-magnetic compounds containing iron and nickel). In some embodiments, the non-magnetic particles may be comprised of a combination of iron and zinc (that is, one or more non-magnetic compounds containing iron and zinc). In some embodiments, the non-magnetic particles may be comprised of a combination of nickel and zinc (that is, one or more non-magnetic compounds containing nickel and zinc). In some embodiments, the non-magnetic particles may be comprised of a combination of iron, nickel, and zinc (that is, one or more non-magnetic compounds containing iron, nickel, and zinc). In some embodiments, the non-magnetic particles may comprise any two or more of the immediately previous non-magnetic compounds.

[0059] The nickel-zinc ferrite nanoparticles may be embedded within a resin. Alternatively, the nickel-zinc ferrite nanoparticles may be mixed with a resin. The resin may comprise polymerized resorcinol. The polymerized resorcinol may be prepared by reaction of resorcinol and formaldehyde. Other resins which can be used include, but are not limited to, acrylate or urethane resins with low curing temperatures (below about 60°C), such as methyl methacrylate. Resins should have a low pre-cure viscosity in order to prevent bubbles from being trapped in the resin.

[0060] In a plasma reactor, any solid or liquid materials are rapidly vaporized or turned into plasma. The kinetic energy of the heated material, which can reach temperatures of 20,000 to 30,000 Kelvin, ensures extremely thorough mixture of all components.

[0061] The heated material of the plasma stream may be treated with 0₂ gas. Oxygen gas may be injected into the heated material. In some embodiments, oxygen gas is injected into the heated material at flow rates of about 2 liters per minute to about 10 liters per minute. In some embodiments, oxygen gas is injected into the heated material at flow rates of about 3 liters per minute to about 9 liters per minute. In some embodiments, oxygen gas is injected into the heated material at flow rates of about 4 liters per minute to about 8 liters per minute. In some embodiments, oxygen gas is injected into the heated material at flow rates of about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10 liters per minute. The heated material of the plasma stream may be treated with 0₂ gas by injecting the oxygen gas into the shield gas of the plasma reactor where the shield gas contacts the plasma; the shield gas is typically used at a rate of about 2,400 liters per minute.

[0062] The oxygen gas may be injected into the plasma stream after the starting material or starting materials have vaporized completely, but before the heated material cools sufficiently to cause condensation and/or crystallization.

[0063] The oxygen gas may be introduced in a single stream or jet, or in a multiplicity of streams or jets. In some embodiments, the oxygen gas is introduced in a single stream. In some embodiments, the oxygen gas is introduced in multiple streams. In some embodiments, the oxygen gas is introduced in about 2 to about 12 streams. In some embodiments, the oxygen gas is introduced in about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, or about 12 streams.

[0064] The heated material of the plasma stream is then rapidly quenched, using methods such as the turbulent quench chamber disclosed in U.S. Publication No. 2008/0277267. Argon quench gas at high flow rates, such as 2400 to 2600 liters per minute, may be injected into the heated material. The material may be further cooled in a cool-down tube, and collected and analyzed to ensure proper size ranges of material.

[0065] The plasma production method described above can be used to produce highly uniform nickel-zinc ferrite nanoparticles. In some embodiments, the nickel-zinc ferrite nanoparticles have an average diameter or average grain size between approximately 0.3 nm and

approximately 10 nm, preferably between approximately 1 nm to approximately 5 nm, that is, approximately 3 nm + 2 nm. In some embodiments, the nickel-zinc ferrite nanoparticles have an average diameter of approximately 20 nm or less, or approximately 15 nm or less, or between approximately 0.3 nm and approximately 20 nm, or between approximately 1 nm and approximately 20 nm, or between approximately 5 nm and approximately 20 nm. In some embodiments, the nickel-zinc ferrite nanoparticles have an average diameter of between approximately 10 nm and approximately 20 nm, that is, approximately 15 nm + 5 nm, or between approximately 10 nm and approximately 15 nm, that is, approximately 12.5 nm + 2.5 nm.

[0066] In some embodiments, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 20 nm. In some embodiments, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 20 nm. In some embodiments, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 20 nm. In some embodiments, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 20 nm.

[0067] In some embodiments, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 40 nm. In some embodiments, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 40 nm. In some embodiments, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 40 nm. In some embodiments, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 40 nm.

[0068] In some embodiments, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 10 nm. In some embodiments, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 10 nm. In some embodiments, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 10 nm. In some embodiments, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 0.3 nm and approximately 10 nm.

[0069] In some embodiments, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 1 nm to approximately 5 nm, that is,

approximately 3 nm + 2 nm. In some embodiments, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 1 nm to approximately 5 nm, that is, approximately 3 nm + 2 nm. In some embodiments, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 1 nm to approximately 5 nm, that is, approximately 3 nm + 2 nm. In some embodiments, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter or grain size between approximately 1 nm to approximately 5 nm, that is, approximately 3 nm + 2 nm.

[0070] In some embodiments, at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter of approximately 40 nm or less, or approximately 20 nm or less, or approximately 15 nm or less, or between approximately 10 nm and approximately 20 nm, that is, approximately 15 nm + 5 nm, or between approximately 10 nm and approximately 15 nm, that is, approximately 12.5 nm + 2.5 nm. In some embodiments, at least about 90% of the nickel-zinc ferrite nanoparticles have a diameter of approximately 40 nm or less, or approximately 20 nm or less, or approximately 15 nm or less, or between approximately 10 nm and approximately 20 nm, that is, approximately 15 nm + 5 nm, or between approximately 10 nm and approximately 15 nm, that is, approximately 12.5 nm + 2.5 nm. In some embodiments, at least about 95% of the nickel-zinc ferrite nanoparticles have a diameter of approximately 40 nm or less, or approximately 20 nm or less, or approximately 15 nm or less, or between approximately 10 nm and approximately 20 nm, that is, approximately 15 nm + 5 nm, or between approximately 10 nm and approximately 15 nm, that is, approximately 12.5 nm + 2.5 nm. In some embodiments, at least about 99% of the nickel-zinc ferrite nanoparticles have a diameter of approximately 40 nm or less, or

approximately 20 nm or less, or approximately 15 nm or less, or between approximately 10 nm and approximately 20 nm, that is, approximately 15 nm + 5 nm, or between approximately 10 nm and approximately 15 nm, that is, approximately 12.5 nm + 2.5 nm.

[0071] During the production of the nanoparticles, undesired materials, such as nickel oxide, zinc oxide, iron oxide, or other side products may form. In any of the embodiments above, the desired spinel nickel-zinc ferrite nanoparticles make up at least about 40% of the nanopowder, at least about 45% of the nanopowder, at least about 50% of the nanopowder, at least about 55% of the nanopowder, at least about 60% of the nanopowder, at least about 65% of the nanopowder, at least about 70% of the nanopowder, at least about 75% of the nanopowder, at least about 80% of the nanopowder, at least about 85% of the nanopowder, or at least about 90% of the nanopowder, or at least about 95% of the nanopowder, or at least about 99% of the nanopowder. [0072] The spinel ferrite nanoparticles produced using the methods described herein may be characterized using standard techniques such as inductively coupled plasma (ICP), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), magnetic permeability, DC resistivity, and dielectric measurements.

[0073] Desirable properties of the spinel ferrite nanoparticles, and of components formed from the spinel ferrite nanoparticles, include a high Q-factor, particularly at radio frequencies; a low change in permeability with change in temperature; a low change in permeability with changes in stress (such as compressive stress, tensile stress, or shear stress). Systems and Methods for Preparation of Spinel Ferrite Nanoparticles

[0074] A typical nanoparticle production system can generate nanoparticles by feeding starting material(s) into a plasma stream, thereby vaporizing the material to form a vaporized reactive mixture, followed by quenching of the vaporized reactive mixture to form precipitate

nanoparticles. The yield of spinel ferrite nanoparticles may be increased by injecting oxygen gas into the vaporized reactive mixture prior to the formation of precipitate nanoparticles.

[0075] Figure 1 shows a system for producing ferrite nanoparticles that is in accordance with some embodiments. The particle production system 100 comprises a plasma production unit 120 that has a plasma production chamber 125. Working gas flows from working gas supply device 110. The microparticle starting materials for use in the production of nanoparticles are stored within the material supply device 130, and are fed into the plasma production chamber 125. The plasma stream vaporizes the starting materials within the plasma production chamber 125, thereby forming a vaporized reactive mixture. The vaporized reactive mixture flows to the reaction chamber 140. The oxygen gas supply device 150 is configured to supply oxygen gas to the reaction chamber 140, such that oxygen gas flows from the oxygen gas supply device 150 into oxygen gas mixing region 145 of the reaction chamber 140. In the oxygen gas mixing region 145 of the reaction chamber 140, the ferrite nanoparticle starting materials are still in vapor phase and have not yet cooled sufficiently to condense and/or crystallize, that is, the reactive mixture has not cooled sufficiently to form precipitate nanoparticles. A quench chamber 160 is coupled to the reaction chamber 140 through an ejection port 170 at the end of the reaction chamber 140. The ejection port 170 is configured to supply the reactive mixture stream from the reaction chamber 140 into the quench chamber 160. In an alternate embodiment, the reaction chamber where the oxygen gas is injected is simply the initial region of the quench chamber; that is, reaction chamber 140 is not a separate chamber, but rather an initial region of quench chamber 160, and no ejection port 170 is present. The quench chamber 160 is configured to receive a conditioning fluid (such as argon, for example, cold gaseous argon or liquid argon) into the quench region 165, which is formed within the quench chamber 160 between the ejection port and the cooled mixture outlet/cooling conduit 180. The conditioning fluid may mix with and cool the reactive mixture stream from the reaction chamber 140. Within the quench region 165, nanoparticles may precipitate from the reactive mixture stream. A cooling conduit 180 receives the particle and gas mixture from the quench region 165. The particle and gas mixture may enter the cooling conduit 180 by application of vacuum. The cooling conduit 180 may be equipped with an active cooling system. The collection device 190 is configured to receive the cooled mixture via the cooling conduit 180; the nanoparticles are collected in the collection device 190.

[0076] The plasma production unit 120 is configured to produce a plasma stream within the plasma production chamber 125. The plasma production chamber 125 may contain a plasma gun. The plasma gun may include a male electrode and a female electrode. A working gas may flow from working gas supply device 110 into the plasma production chamber 125. Application of energy to the working gas in the plasma production chamber 125 may produce the plasma stream.

[0077] Figure 2 illustrates a method 200 for producing spinel ferrite nanoparticles in accordance with some embodiments. At Step 201, a plasma stream is produced within a plasma production chamber. At Step 202, the microparticle starting materials for the ferrite

nanoparticles are fed into the plasma stream to yield a reactive mixture stream contained in a reaction chamber that is coupled to the plasma production chamber. At Step 203, while the reactive mixture stream is still vaporized (prior to nanoparticle precipitation), oxygen gas is injected into the reaction chamber and is applied to the vaporized reactive mixture stream. At Step 204, the mixture stream is rapidly quenched within the quench region to form precipitate nanoparticles. At Step 205, the quenched mixture stream flows to a collection device. Finally, at Step 206, the condensed nanoparticles are separated from the mixture stream. General Procedures for Preparation of Spinel Ferrite Nanoparticles

[0078] Using the systems and methods described above, spinel ferrite nanoparticles can be produced. The powder starting materials may be introduced into the plasma production unit at a feed rate of about 1 to about 1.5 grams per minute using a working gas composed of Ar and H₂ in a ratio of about 85: 15. The current of the plasma may be about 900 amperes, corresponding to about 50-60 kilowatts of power. The addition of oxygen gas into the reaction chamber may increase the amount of spinel ferrite nanoparticles that is produced.

[0079] Oxygen gas may be introduced into the reaction chamber by use of a single stream or jet, or by use of multiple streams or jets. The introduction of oxygen gas into the reaction chamber may occur while the starting materials of the ferrite nanoparticles are still in vapor phase, prior to condensation and/or crystallization. The oxygen gas may be introduced into the reaction chamber at a flow rate of about 2 to about 10 liters per minute. Upon injection of 0₂ into the reaction chamber, the total flow rate of gas may be about 2400 liters per minute, of which oxygen comprises only a small fraction, while the conditioning fluid/quench fluid (typically argon) comprises the vast majority of the gas flow.

General Procedures for Incorporating Spinel Ferrite Nanoparticles into Resin

[0080] The spinel ferrite nanoparticles may be incorporated into a resin such as polymerized resorcinol using the procedure described below. The plasma-generated ferrite nanoparticles, in the form of a dry powder, may be combined in a solvent (for example, ethanol) with a dispersant (such as Disperbyk-145, BYK-Gardner GmbH, Germany). The resulting dispersion can then be sonicated in a stirring bath, followed by removal of large particles (for example, by

centrifugation). Resins or resin precursors may then be added to the clarified solution. The solution may be dried (at elevated temperatures, such as from about 50 °C to about 100 °C, or from about 55 °C to about 80 °C, or from about 60 °C to about 70 °C). The final material is a solid containing the ferrite nanoparticles suspended in an organic resin.

[0081] The nanoparticle/resin mixture can be machined into different shapes. For example, cylinders or discs may be formed. The nanoparticle/resin mixture may be used for various applications, such as in high-frequency circuitry. Antennas

[0082] In some embodiments, the invention provides for antennas, which can comprise any of the spinel ferrite nanoparticles described herein. The antennas are useful in a variety of applications, such as in mobile phones.

[0083] Antennas comprised of any of the spinel ferrite nanoparticles described herein, such as solid antennas, shaped antennas, or slot antennas, are contemplated. (A slot antenna consists of a metal surface, usually a flat plate, from which a hole or slot is cut out.) The antenna can be integrated with a printed circuit board (PCB). The antenna dimensions are determined by the PCB, which are fixed by the size of the communication device, for example a mobile phone. The antenna can comprise spinel ferrite nanoparticles, or the surface of an antenna can be coated with spinel ferrite nanoparticles. For a slot antenna, a hole or slot is cut into a surface formed from spinel ferrite nanoparticles, and upon application of a driving frequency, the slot radiates electromagnetic waves. Also contemplated are patch antennas such as the Planar Inverted-F antenna (PIFA), as well as other microstrip antennas. Alternatively, the ferrite nanoparticles may also be applied directly to a PCB.

[0084] Antenna performance is typically evaluated by resonance bandwidth, return loss, radiation efficiency, and radiation pattern of the antenna at various frequencies.

Exemplary embodiments

[0085] The invention is further described by the following embodiments. The features of each of the embodiments are combinable with any of the other embodiments where appropriate and practical.

[0086] Embodiment 1. A nanopowder comprising nickel-zinc ferrite nanoparticles, wherein the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 10 nm.

[0087] Embodiment 2. A nanopowder comprising nickel-zinc ferrite nanoparticles, wherein at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm.

[0088] Embodiment 3. The nanopowder of embodiment 1, wherein at least about 50% of the nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 10 nm. [0089] Embodiment 4. The nanopowder of embodiment 2, wherein the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 10 nm.

[0090] Embodiment 5. The nanopowder of embodiment 1 or embodiment 2, wherein at least 50% of the nanopowder comprises nickel-zinc ferrite nanoparticles in spinel form.

[0091] Embodiment 6. The nanopowder of any one of embodiments 1-5, comprising nickel- zinc ferrite nanoparticles of the formula:

Ni_xZn₍i_x₎Fe₂0₄

where X is between approximately 0.5 and 0.7.

[0092] Embodiment 7. The nanopowder of any one of embodiments 1-6, wherein the nickel- zinc ferrite nanoparticles are produced by plasma synthesis.

[0093] Embodiment 8. A nanopowder comprising nickel-zinc ferrite nanoparticles of the formula:

Ni_xZn₍i_x)Fe₂0₄

where X is between approximately 0.5 and 0.7.

[0094] Embodiment 9. The nanopowder of embodiment 8, where X is between approximately 0.55 and 0.65.

[0095] Embodiment 10. The nanopowder of embodiment 8, where X is approximately 0.6.

[0096] Embodiment 11. The nanopowder of any one of embodiments 8-10, wherein the nickel-zinc ferrite nanoparticles are produced by plasma synthesis.

[0097] Embodiment 12. A method of making nickel-zinc ferrite nanoparticles, comprising:

[0098] a) feeding one or more starting materials which together comprise nickel, zinc, and iron into a plasma production chamber;

[0099] b) vaporizing the one or more starting materials to form a vaporized material;

[0100] c) injecting oxygen gas into the vaporized material; and

[0101] d) quenching the vaporized material to form the nickel-zinc ferrite nanoparticles.

[0102] Embodiment 13. The method of embodiment 12, wherein step c) of injecting oxygen gas is performed after at least about 95% of the one or more starting materials have vaporized, and prior to condensation or crystallization of more than about 5% of the vaporized material. [0103] Embodiment 14. The method of embodiment 12, wherein the one or more starting materials which together comprise nickel, zinc, and iron comprise a nickel-containing material, a zinc-containing material, and an iron-containing material.

[0104] Embodiment 15. The method of embodiment 14, wherein the nickel-containing material is NiO, the zinc-containing material is ZnO, and the iron-containing material is Fe metal.

[0105] Embodiment 16. The method of embodiment 12, wherein the one or more starting materials which together comprise nickel, zinc, and iron comprise zinc ferrite and nickel ferrite.

[0106] Embodiment 17. The method of embodiment 16, wherein the one or more starting materials which together comprise nickel, zinc, and iron comprise about 50 mole % to 60 mole % zinc ferrite, and the remaining mole percent of the starting materials comprises nickel ferrite.

[0107] Embodiment 18. A composition comprising nickel-zinc ferrite nanoparticles, wherein the nanoparticles are made by:

[0108] a) feeding one or more starting materials which together comprise nickel, zinc, and iron into a plasma production chamber;

[0109] b) vaporizing the one or more starting materials to form a vaporized material;

[0110] c) injecting oxygen gas into the vaporized material; and

[0111] d) quenching the vaporized material to form the nickel-zinc ferrite nanoparticles.

EXAMPLES

[0112] As discussed above, spinel nickel-zinc ferrite nanoparticles provide examples of the nanoferrite particles that can be prepared using the methods disclosed herein.

General Procedure for Incorporation of Ferrite Nanoparticles into Polymerized Resorcinol

[0113] The spinel ferrite nanoparticles are combined with the dispersant (Disperbyk-145, BYK-Gardner GmbH, Germany) in ethanol; the dispersant was added in an amount of 9% by weight of the dispersion in ethanol. The final solid concentration of the resulting suspension is 10-12%. The dispersion is then sonicated for 6-8 hours in a stirring bath. Large particles are removed from the resulting mixture by centrifugation. Next, resorcinol is dissolved in the decanted solution, followed by the addition of formaldehyde (37% in water). The molar ratio of resorcinol to formaldehyde used was 1 to 0.8, and the total amount of combined resorcinol- formaldehyde added was 120% by weight of the ethanol dispersion. The solution is then cured by drying at 60-70 °C for 1-2 weeks. The final material is a solid containing approximately 8% ferrite nanoparticles suspended in polymerized resorcinol. The nanoparticle-resin mixture was machined into cylinders measuring 1 cm x 6 cm, and discs measuring 3 cm in diameter and 0.5 cm thick.

Example 1: Preparation of Nickel-Zinc Ferrite Nanoparticles using NiO, ZnO, and Fe Metal

[0114] Nickel-zinc ferrite nanoparticles were prepared using the methods described herein using NiO, ZnO, and Fe metal as starting materials. The ratio of NiO:ZnO:Fe was varied in order to optimize the amount of nanoferrite particles that formed. Argon quench gas was used in an amount of about 2400 to 2500 liters per minute for each sample prepared. The heated material was injected with oxygen gas using the flow rates and number of jets indicated for each sample. ICP analysis of the nanoparticle preparations are provided in Table 2, and the composition of the samples is summarized in Table 3. a) 1.4NiO:ZnO:3.9Fe (Sample: SDC-1)

[0115] Nickel-zinc ferrite nanoparticles were prepared using a starting material composition of 22.05% NiO, 16.02% ZnO, and 61.92% Fe metal. This corresponds to a NiO:ZnO:Fe ratio of 1.4: 1:3.9. Oxygen was injected at about 7 LPM (liters per minute) 0₂, configured with 2 points of injection at the exit of the plasma. XRD analysis (Figure 3) indicated that the nanoferrite particles comprised 35% of the total material that formed. b) 1.4NiO:ZnO:3.2Fe (Sample: SDC-2)

[0116] Nickel-zinc ferrite nanoparticles were prepared using a starting material composition of 24.85% NiO, 18.05% ZnO, and 57.11% Fe metal. This corresponds to a NiO:ZnO:Fe ratio of 1.4: 1:3.2. Oxygen was injected at about 7 LPM 0₂, configured with 2 points of injection at the exit of the plasma. XRD analysis (Figure 4) indicated that the nanoferrite particles comprised 65% of the total material that formed. c) 1.4NiO:ZnO:2.6Fe (Sample: SDC-3)

[0117] Nickel-zinc ferrite nanoparticles were prepared using a starting material composition of 27.74% NiO, 20.15% ZnO, and 52.11% Fe metal. This corresponds to a NiO:ZnO:Fe ratio of 1.4: 1:2.6. Oxygen was injected at about 7 LPM 0₂, configured with 2 points of injection at the exit of the plasma. XRD analysis (Figure 5) indicated that the nanoferrite particles comprised 35% of the total material that formed.

Example 2: Preparation of Nickel-Zinc Ferrite Nanoparticles using NiFe₂C>4 and ZnFe₂C>4

[0118] Nickel-zinc ferrite nanoparticles were prepared using the methods described herein using nickel ferrite (NiFe₂0₄) and zinc ferrite (ZnFe₂0₄) as starting materials. The ratio of NiFe₂0₄ and ZnFe₂0₄ was varied in order to optimize the amount of nanoferrite particles that formed. The heated material was injected with oxygen gas using the flow rates and number of jets indicated for each sample. ICP analysis of the nanoparticle preparations are provided in Table 2, and the composition of the samples is summarized in Table 3. a) 1.5NiFe₂0₄:ZnFe₂0₄ (Sample: SDC-4)

[0119] Nickel-zinc ferrite nanoparticles were prepared using a starting material composition of 59.32% NiFe₂0₄ and 40.68% ZnFe₂0₄. This corresponds to a NiFe₂0₄:ZnFe₂0₄ ratio of 1.5: 1. Oxygen was injected at about 10 LPM 0₂, configured with 2 points of injection at the exit of the plasma. XRD analysis (Figure 6) indicated that the nanoferrite particles comprised 60% of the total material that formed. b) 1.3NiFe₂0₄:ZnFe₂0₄ (Samples: SDC-6 and SDC-7)

[0120] Nickel-zinc ferrite nanoparticles were prepared in duplicate using a starting material composition of 56.00% NiFe₂0₄ and 44.00% ZnFe₂0₄. This corresponds to a NiFe₂0₄:ZnFe₂0₄ ratio of 1.3: 1. Oxygen was injected at about 3 LPM 0₂, configured with 6 points of injection at 1 inch downstream of the exit of the plasma. XRD analysis (Figure 11 and Figure 7) indicated that the nanoferrite particles comprised 75% of the total material that formed. TEM images of these ferrite nanoparticles are shown in Figure 8. c) 1.2NiFe₂0₄:ZnFe₂0₄ (Sample: SDC-8) [0121] Nickel-zinc ferrite nanoparticles were prepared using a starting material composition of 55.00% NiFe₂0₄ and 45.00% ZnFe₂0₄. This corresponds to a NiFe₂0₄:ZnFe₂0₄ ratio of 1.2: 1. Oxygen was injected at about 3 LPM 0₂, configured with 6 points of injection at 1 inch downstream of the exit of the plasma. XRD analysis (Figure 10) indicated that the nanoferrite particles comprised approximately 60-70% of the total material that formed.

Example 3: Preparation of Nickel-Zinc Ferrite Nanoparticles using NiO, ZnO, NiFe₂0₄ and ZnFe₂0₄

a) 1.4NiO:ZnO:52NiFe₂0₄:ZnFe₂0₄ (Sample: SDC-5)

[0122] Nickel-zinc ferrite nanoparticles were prepared using a starting material composition of 1.53% NiO, 1.11% ZnO, 57.75% NiFe₂0₄ and 39.60% ZnFe₂0₄. This corresponds to a

NiO:ZnO:NiFe₂0₄:ZnFe₂0₄ ratio of 1.4: 1:52:35.7. Oxygen was injected into the heated material at about 21 LPM 0₂, configured with 2 points of injection at the exit of the plasma. XRD analysis (Figure 9) indicated that the nanoferrite particles comprised 55% of the total material that formed.

[0123] ICP analysis of the nanoparticle preparations are provided in Table 2, and the composition of the samples is summarized in Table 3.

Table 2. ICP Analysis of Nickel-Zinc Ferrites

Table 3: X-ray Diffraction Analysis of Nickel-Zinc Ferrites

[0124] The disclosures of all publications, patents, patent applications, and published patent applications referred to herein by an identifying citation are hereby incorporated herein by reference in their entirety.

[0125] The present invention has been described in terms of specific embodiments

incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be readily apparent to one skilled in the art that other various modifications can be made in the embodiments chosen for illustration without departing from the spirit and scope of the invention. Therefore, the description and examples should not be construed as limiting the scope of the invention.

Claims

CLAIMS What is claimed is:

1. A nanopowder comprising nickel-zinc ferrite nanoparticles, wherein the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 40 nm.

2. A nanopowder comprising nickel-zinc ferrite nanoparticles, wherein at least about 80% of the nickel-zinc ferrite nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm.

3. The nanopowder of claim 1, wherein at least about 50% of the nanoparticles have a diameter or grain size of between approximately 0.3 nm and approximately 40 nm.

4. The nanopowder of claim 2, wherein the nanoparticles have an average diameter or average grain size of between approximately 0.3 nm and approximately 40 nm.

5. The nanopowder of claim 1 or claim 2, wherein at least 50% of the nanopowder comprises nickel-zinc ferrite nanoparticles in spinel form.

6. The nanopowder of any one of claims 1-5, comprising nickel-zinc ferrite nanoparticles of the formula:

Ni_xZn₍i_x₎Fe₂0₄ where X is between approximately 0.5 and 0.7.

7. The nanopowder of any one of claims 1-6, wherein the nickel-zinc ferrite nanoparticles are produced by plasma synthesis.

8. A nanopowder comprising nickel-zinc ferrite nanoparticles of the formula: Ni_xZn(i_x)Fe₂0₄ where X is between approximately 0.5 and 0.7.

9. The nanopowder of claim 8, where X is between approximately 0.55 and 0.65.

10. The nanopowder of claim 8, where X is approximately 0.6.

11. The nanopowder of any one of claims 8-10, wherein the nickel-zinc ferrite nanoparticles are produced by plasma synthesis.

12. A method of making nickel-zinc ferrite nanoparticles, comprising:

a) feeding one or more starting materials which together comprise nickel, zinc, and iron into a plasma production chamber;

b) vaporizing the one or more starting materials to form a vaporized material;

c) injecting oxygen gas into the vaporized material; and

d) quenching the vaporized material to form the nickel-zinc ferrite nanoparticles.

13. The method of claim 12, wherein step c) of injecting oxygen gas is performed after at least about 95% of the one or more starting materials have vaporized, and prior to condensation or crystallization of more than about 5% of the vaporized material.

14. The method of claim 12, wherein the one or more starting materials which together comprise nickel, zinc, and iron comprise a nickel-containing material, a zinc-containing material, and an iron-containing material.

15. The method of claim 14, wherein the nickel-containing material is NiO, the zinc-containing material is ZnO, and the iron-containing material is Fe metal.

16. The method of claim 12, wherein the one or more starting materials which together comprise nickel, zinc, and iron comprise zinc ferrite and nickel ferrite.

17. The method of claim 16, wherein the one or more starting materials which together comprise nickel, zinc, and iron comprise about 50 mole % to 60 mole % zinc ferrite, and the remaining mole percent of the starting materials comprises nickel ferrite.

18. A composition comprising nickel-zinc ferrite nanoparticles, wherein the nanoparticles are made by:

a) feeding one or more starting materials which together comprise nickel, zinc, and iron into a plasma production chamber;

b) vaporizing the one or more starting materials to form a vaporized material;

c) injecting oxygen gas into the vaporized material; and

d) quenching the vaporized material to form the nickel-zinc ferrite nanoparticles.