Iron cobalt ternary alloy and silica magnetic core

Abstract

A magnetic core of superparamagnetic core shell nanoparticles having a particle size of less than 200 nm; wherein the core is an iron cobalt ternary alloy and the shell is a silicon oxide is provided. The magnetic core is a monolithic structure of superparamagnetic core grains of an iron cobalt ternary alloy directly bonded by the silicon dioxide shells. A method to prepare the magnetic core which allows maintenance of the superparamagnetic state of the nanoparticles is also provided. The magnetic core has little core loss due to hysteresis or eddy current flow.

Claims

1. A magnetic core, comprising: core shell nanoparticles; wherein the core is an iron cobalt ternary alloy and the shell is a silicon oxide, the third component of the ternary alloy is a transition metal selected from the group consisting of scandium, titanium, vanadium, chromium, manganese, nickel, copper and zinc, the magnetic core is a monolithic structure of superparamagnetic core grains of the iron cobalt ternary alloy having a particle size of 5 to 30 nm directly bonded by the silicon oxide shells, which form a silica matrix, and the magnetic core is superparamagnetic.

2. The magnetic core according to claim 1, wherein a space between individual superparamagnetic nano iron cobalt ternary alloy particles is occupied substantially only by the silicon oxide.

3. The magnetic core according to claim 1, wherein the iron cobalt ternary alloy is an iron cobalt vanadium alloy.

4. The magnetic core according to claim 1, wherein the iron cobalt ternary alloy is an iron cobalt chromium alloy.

5. The magnetic core according to claim 1, wherein the silicon oxide is silicon dioxide.

6. The magnetic core according to claim 5, wherein at least 97% by volume of the space between the iron cobalt ternary alloy grains is occupied by silicon dioxide.

7. An electrical/magnetic conversion device, which comprises the magnetic core according to claim 1.

8. A vehicle part comprising the electrical/magnetic conversion device according to claim 7, wherein the part is selected from the group consisting of a motor, a generator, a transformer, an inductor and an alternator.

9. A method to prepare the monolithic magnetic core of claim 1, comprising: sintering the superparamagnetic core shell particles under heat and pressure under flow of an inert gas to obtain the monolithic structure; wherein the monolithic core is superparamagnetic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a TEM image of nanoparticles prepared in Example 1.

(2) FIG. 2 shows a TEM image of nanoparticles prepared in Example 2.

(3) FIG. 3 shows a generalized relationship of particle size and range of superparamagnetism.

DETAILED DESCRIPTION OF THE INVENTION

(4) Applicant has recognized that to increase magnetic core efficiency as measured in terms of core loss, the magnetic core must demonstrate a reduced measure of magnetic hysteresis as well as lowered eddy current formation. Applicant has surprisingly discovered that by producing superparamagnetic iron cobalt ternary alloy nanoparticles that are encapsulated in silica shells and then compacting and sintering these nanoparticles into a monolithic nanomaterial core, the core obtained has zero (or very low) hysteresis and very low eddy current formation because of the insulating silica shells.

(5) According to the invention, the iron cobalt ternary alloy nanoparticle grains are of or approaching the size of the single particle magnetic domain of the iron cobalt ternary alloy and thus are superparamagnetic. While not being constrained to theory, Applicant believes control of grain size to approximately that of the particle magnetic domain is a factor which contributes to the reduced hysteresis of a magnetic core according to the present invention. Moreover, the presence of insulating silica shells about the core grains is a factor which contributes to the low eddy current formation of a magnetic core according to the present invention.

(6) It is conventionally known that the range of particle size for which single domain particles exhibit superparamagnetism has an upper boundary characteristic of the particle chemical constitution. This phenomenon is shown in FIG. 3 which is reproduced from Nanomaterials An Introduction to Synthesis, Properties and Applications by Dieter Vollath (page 112) Wiley-VCH. According to FIG. 3, above a certain size range, nanoparticles will exhibit a measurement time dependency characteristic of ferromagnetic behavior. To avoid this time dependency nanoparticles of a size within the range of superparamagnetism must be prepared and maintained.

(7) Thus, the first embodiment of the invention is a magnetic core, comprising: core shell nanoparticles having a particle size of less than 200 nm; wherein the core is an iron cobalt ternary alloy and the shell is a silicon oxide and the magnetic core is a monolithic structure of superparamagnetic core grains of an iron cobalt ternary alloy directly bonded by the silicon oxide shells. Preferably the particle size is from 2 to 200 nm and more preferably from 2 to 160 nm and most preferably from 5 to 30 nm. These ranges include all subranges and values there between.

(8) The core according to the present invention is monolithic, having the space between the iron cobalt ternary alloy nanoparticle grains occupied by the silicon oxide. Preferably at least 97% of the space between the grains, preferably 98% and most preferably 100% of the space is silicon oxide and further most preferably the silicon oxide is silicon dioxide. According to the present invention neither any binder nor any resin is contained in the matrix of the monolithic core.

(9) The monolithic core according to the present invention is obtained by a process comprising sintering a powder of superparamagnetic core shell particles having a particle size of less than 200 nm under pressure under flow of an inert gas to obtain a monolithic structure; wherein the core of the core shell particle consists of superparamagnetic iron cobalt ternary alloy and the shell consists of silicon dioxide. Because a magnetic material is only superparamagnetic when the grain size is near or below the magnetic domain size, the nanoparticle core must be maintained as small as possible, or the sample will become ferromagnetic, and express magnetic hysteresis. Therefore, the most mild and gentle sintering conditions that still yield a monolithic sample that is robust enough to be machined into a toroid are desired, because more aggressive sintering conditions will promote unwanted grain growth and potentially, loss of superparamagnetic performance.

(10) Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified. Skilled artisans will recognize the utility of the devices of the present invention as a battery as well as the general utility of the electrolyte system described herein.

EXAMPLES

Example 1

(11) To a reaction flask was added 1050 mL ethanol, 2.056 g NaOH, and 145.102 g tribasic sodium citrate. After the sodium hydroxide had an opportunity to dissolve, 20.967 g iron dichloride tetrahydrate, 23.786 g cobalt dichloride hexahydrate, and 0.695 g vanadium trichloride were dissolved in the reaction mixture.

(12) 24.301 g sodium borohydride were dissolved in 900 mL of ethanol.

(13) The sodium borohydride solution was then added to the reaction. The reaction was allowed to stir for 10 additional minutes after all of the sodium borohydride was added.

(14) The product was then purified using a washing solution of 70% H.sub.2O/30% ethanol (by volume).

(15) The nanoparticles were stirred for 20 minutes to fully disperse them throughout a water/triethylamine solution (1260 mL H.sub.2O and 33 mL triethylamine). 3.3 mL tetraethyl orthosilicate was then dissolved in 780 mL ethanol, and added to the stirring reaction flask. After 20 additional minutes of stirring, the product was again collected using a permanent magnet. This final core/shell product was washed with ethanol.

(16) A TEM image of the nanoparticles is shown in FIG. 1. The image indicates that nanoparticles of less than 150 nm were obtained.

Example 2

(17) To a reaction flask was added 1050 mL ethanol, 1.0 g NaOH, and 11.96 g tetrabutylammonium chloride. After the sodium hydroxide had an opportunity to dissolve, 20.967 g iron dichloride tetrahydrate, 23.786 g cobalt dichloride hexahydrate, and 0.695 g vanadium trichloride were dissolved in the reaction mixture.

(18) 24.301 g sodium borohydride were dissolved in 900 mL of ethanol.

(19) The sodium borohydride solution was then added to the reaction. The reaction was allowed to stir for 10 additional minutes after all of the sodium borohydride was added.

(20) The product was then purified using a washing solution of 70% H.sub.2O/30% ethanol (by volume).

(21) The nanoparticles were stirred for 20 minutes to fully disperse them throughout a water/triethylamine solution (1260 mL H.sub.2O and 33 mL triethylamine). 3.3 mL tetraethyl orthosilicate was then dissolved in 780 mL ethanol, and added to the stirring reaction flask. After 20 additional minutes of stirring, the product was again collected using a permanent magnet. This final core/shell product was washed with ethanol.

(22) A TEM image of the nanoparticles is shown in FIG. 2. The image indicates that clusters of core/shell nanoparticles of less than about 175 nm were obtained. The clusters contained magnetic nanoparticles having cores of less than 30 nm and silica shells of less than 10 nm in thickness.

(23) Toroid and Inductor Fabrication

(24) The product of the hot press sintering is a disc. The size of the disk is dependent upon the size of punch and die set used. As described here but not limiting the dimensions of those stated, discs were produced that were 9 mm in diameter and 2.5 mm thick. The disc was converted to a toroid through conventional machining techniques. The fabricated toroid was hand-wound with copper enameled wire to produce a functional inductor.