Metallic magnetic material with controlled curie temperature and processes for preparing the same

Abstract

The invention relates to a metallic magnetic material with biocompatible elements (Ti, Ta or Mn), with glassy quasi-amorphous structure and controlled Curie temperature, and the processes for preparing the same. The hereby material has its composition expressed in atomic percent: Fe=59 . . . 67%, Nb=0.1 . . . 1%, B=20%, biocompatible material (Ti, Ta or Mn)=12 . . . 20%), Curie temperature within the interval 0 . . . 70 C., saturation magnetic induction of 0.05 . . . 1.1 T and strong magnetic response when introduced in a high frequency magnetic field. The processes used to obtain this material directly under the form of ribbons, glass-coated micro/nanowires or nano/micropowders consist in rapid quenching of the mixtures with previously mentioned compositions under extremely rigorous controlled conditions, in high vacuum of minimum 10.sup.4 mbars or in controlled helium or argon atmosphere in order to avoid oxidation.

Claims

1. FeNbB-based metallic magnetic material for use in magnetic sensors based on magnetic permeability variation and for hyperthermia applications, having the composition Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20, where M is a biocompatible material chosen from Ti, Ta and Mn, and x=12 to 20 at %, with glassy quasi-amorphous structure, obtained under the form of ribbons, micro/nanowires and micro/nanopowders, the concentration of the biocompatible material being chosen such that the magnetic transition temperature Tc ranges between 0 C. and 70 C., the saturation magnetic induction is between 0.05 and 1.1 T, and the relative magnetic permeability is 3500-4000, and presenting a significant variation of over 90% of the magnetic permeability/susceptibility in the proximity of the magnetic transition temperature.

2. A process to obtain FeNbB-based metallic magnetic material with biocompatible elements, according to claim 1, under the form of metallic ribbons with a thickness of 10-40 m, width of 0.2-5 mm and specific quasi-amorphous glassy structure, comprising: a first step of obtaining a metallic alloy from pure components within a vacuum chamber; a second step of extracting pieces of 3-4 g each, from the metallic alloy; a third step of introducing the pieces extracted in the second step in the amorphizing crucible ended with a piece of boron nitride, which has at its end a rectangular nozzle with a width of 0.5-0.8 mm and a length of 1-3 mm, depending on the desired size of the ribbon to be produced, which is placed inside an induction coil consisting of 5 turns of copper pipe, supplied by a frequency power generator, in a vacuum of a minimum 104 mbar or in He or Ar atmosphere, through the application of an Ar overpressure of 0.15-0.22 bars and melting the alloy pieces previously extracted; and a fourth step of ejecting the molten alloy on a copper disc with a diameter of 36 cm, rotating with a peripheral speed of 30-35 m/s, at a distance of 0.5 mm from the lower margin of the boron nitride nozzle, in order to provide a uniform flow of the molten alloy.

3. A process to obtain FeNbB-based metallic magnetic material with biocompatible elements, according to claim 1, under the form of glass-coated micro/nanowires with metallic core diameters of 80-950 nm and glass coating thickness of 5-6.5 m, with specific quasi-amorphous glassy structure, comprising: a first step of obtaining a metallic alloy from pure components within a vacuum chamber; a second step of extracting pieces of 3-4 g each, from the metallic alloy; a third step of heating to melting the alloy in a Duran glass pipe with a diameter of 12 mm and glass wall thickness of 1 mm, sealed at a bottom and connected at its upper part to a vacuum system with a 60-70 mm H.sub.2O vacuum in the glass tube, placed inside an induction coil supplied by a frequency power generator, in order to produce glass softening; and a fourth step of drawing the molten alloy from the third step at a speed of 2500-3000 m/min. on a collecting bobbin, resulting in the production of a glass-coated metallic nano/microwire.

4. The process to obtain FeNbB-based metallic magnetic material with biocompatible elements under the form of nano/micropowders with dimensions comprised between 5 nm and 80-100 m, comprising the process to obtain the ribbons according to claim 2, and further comprising: a fifth step of treating of the ribbons in a vacuum of 10.sup.5 mbar at temperatures of 300-400 C. to diminish the ribbon hardness; a sixth step of mechanical milling of the ribbons obtained in the fifth step, resulting in the fragmentation of the treated ribbons in pieces of 3-5 mm each by introducing into two hardened stainless steel milling vials of a planetary ball mill together with the balls, in a mass ratio balls:material=50:1, the milling being performed in a liquid medium in which the oleic acid and heptane represent 15-20 vol. % and 2-5 vol. %, respectively, from the quantity of milled material, at a rotation speed of the milling vials of 550 rpm, with a two-way rotation, for 1-120 hours; a seventh step of washing the powders from the sixth step at least five times with heptane in an ultrasound bath to remove the oleic acid traces; and an eighth step of drying the powders from the seventh step in vacuum oven for 2 h at the temperature of 70 C., and the powders have the same quasi-amorphous structure as that existing in the ribbons obtained and magnetic properties.

5. FeNbB-based metallic magnetic material for use in magnetic sensors based on magnetic permeability variation and for hyperthermia applications, having the composition Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20, where M is a biocompatible material chosen from Ti, Ta and Mn, and x=12 to 20 at %, with glassy quasi-amorphous structure, obtained under the form of ribbons and micro/nanopowders, the concentration of the biocompatible material being chosen such that the magnetic transition temperature Tc ranges between 0 C. and 70 C., the saturation magnetic induction is between 0.05 and 1.1 T, and the relative magnetic permeability is 3500-4000, and presenting a significant variation of over 90% of the magnetic permeability/susceptibility in the proximity of the magnetic transition temperature, under the form of metallic ribbons with a thickness of 10-40 m, width of 0.2-5 mm and specific quasi-amorphous glassy structure, obtained by a process comprising: a first step of obtaining a metallic alloy from pure components within a vacuum chamber; a second step of extracting pieces of 3-4 g each, from the metallic alloy; a third step of introducing the pieces extracted in the second step in the amorphizing crucible ended with a piece of boron nitride, which has at its end a rectangular nozzle with the width of 0.5-0.8 mm and the length of 1-3 mm, depending on a wanted size of the ribbon to be produced, which is placed inside an induction coil consisting of 5 turns of copper pipe, supplied by a medium frequency power generator, in a vacuum of minimum 10.sup.4 mbar or in He or Ar atmosphere, through the application of an Ar overpressure of 0.15-0.22 bars, melting the alloy pieces previously extracted; a fourth step of ejecting the molten alloy on a copper disc with the diameter of 36 cm, rotating with a peripheral speed of 30-35 m/s, at a distance of 0.5 mm from the lower margin of the boron nitride nozzle, in order to provide a uniform flow of the molten alloy; and under the form of nano/micropowders with dimensions comprised between 5 nm and 80-100 m, by the process further comprising: a fifth step of treatment of the ribbons obtained in the fourth step in a vacuum of 10.sup.5 mbar at temperatures of 300-400 C. to diminish their hardness; a sixth step of mechanical milling the ribbons, resulting the fragmentation of treated ribbons in pieces of 3-5 mm each by introduction in two hardened stainless steel milling vials of a planetary ball mill together with the balls, in a mass ratio balls:material=50:1, the milling being performed in a liquid medium in which oleic acid and heptane represent 15-20 vol. % and 2-5 vol. %, respectively, from the quantity of milled material, at a rotation speed of the milling vials of 550 rpm, with a two-way rotation, for 1-120 hours, obtaining powders having the sizes between 5 nm and 80-100 m; a seventh step of washing the powders at least five times with heptane in an ultrasound bath to remove some traces of the oleic acid; and an eighth step of drying the powders in vacuum oven for 2 h at a temperature of 70 C., and the powders having the same quasi-amorphous structure as that existing in the ribbons.

6. The process to obtain FeNbB-based metallic magnetic material with biocompatible elements according to claim 4, wherein the ribbons obtain magnetic properties.

Description

(1) Three examples are given in the following related to FIGS. 1 . . . 7, which represent:

(2) FIG. 1, X-ray diffraction patterns obtained for as-quenched ribbons with nominal compositions Fe.sub.79.9-xTi.sub.xNb.sub.0.3B.sub.20, where x=12 . . . 20 at. %;

(3) FIG. 2, Magnetic hysteresis loops for as-quenched ribbons with nominal compositions Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20, where x=12 . . . 20 at. %;

(4) FIG. 3, Curie temperature variation vs. Ti content for as-quenched ribbons with nominal composition Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20, where x=12 . . . 20 at. %;

(5) FIG. 4, SEM images of a glass-coated wire with the inner metallic diameter of 90 nm and glass coating thickness of 5.5 m, with nominal composition Fe.sub.64.7-xMn.sub.15Nb.sub.0.3B.sub.20;

(6) FIG. 5, Magnetic hysteresis loops for as-quenched glass-coated nanowires with nominal compositions Fe.sub.79.7-xMn.sub.xNb.sub.0.3B.sub.20, where x=12 and 16 at. %, with the inner metallic diameter of 90 nm and glass coating thickness t.sub.g=5.5 m;

(7) FIG. 6, Variation of the real part of the magnetic susceptibility with temperature for as-quenched glass coated nanowires with nominal compositions Fe.sub.79.7-xMn.sub.xNb.sub.0.3B.sub.20, where x=12 . . . 20 at. %, with the inner metallic diameter .sub.m=90 nm and glass coating thickness t.sub.g=5.5 m;

(8) FIG. 7, Equilibrium temperature vs. time for nanopowders of Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20, Fe.sub.79.7-xTa.sub.xNb.sub.0.3B.sub.20 and Fe.sub.79.7-xMn.sub.xNb.sub.0.3B.sub.20 respectively, where x=12 . . . 17 at. %, with sizes between 20 . . . 100 nm, obtained by milling ribbons with the same composition in oleic acid, in an alternative magnetic field, H=350 mT, and the frequency, f=153 kHz.

EXAMPLE 1

(9) Procedure hereby consists in the preparation of an alloy of pure components, with nominal composition Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20, by inductive melting in a quartz tube sealed at the bottom, placed in a vacuum chamber. From the molten alloy one then extract, by means of a special system consisting of several quartz tubes, pieces of alloy of 3 . . . 4 g each to provide a good homogeneity of the alloy and an adequate shape for its subsequent use for producing metallic ribbons by rapid quenching from the melt. The alloy piece of 3 . . . 4 g is then introduced in a quartz tube ended at its bottom with a boron nitride part, which has at its end a rectangular nozzle with the length of 0.5 mm and width of 3 mm. This crucible is placed in front of a copper disc with the diameter of 36 cm, rotating with a peripheral speed of 30 m/s, at a distance of 0.5 mm, in order to provide a uniform flow of the molten alloy. The crucible is introduced in an induction coil consisting of 5 turns of copper pipe, supplied by a medium frequency power generator, which provides re-melting of the piece of alloy previously extracted from the molten alloy. When the alloy is melted and heated at 120050 C., an overpressure of argon gas of 0.15 bar is introduced at the upper part of the crucible, which forces the liquid alloy to be ejected on the rotating disc, thus resulting in the formation of a metallic melt-spun ribbon with the thickness of 15 . . . 20 m and widths of 0.4 . . . 0.5 mm. In order to avoid the oxidation of the molten alloy, the copper disccrucible system is placed inside a vacuum chamber (at least 10.sup.4 mbar), after which argon or helium is introduced, the ribbon being obtained in a controlled atmosphere.

(10) The melt-spun ribbons obtained hereby present a quasi-amorphous structure, as in FIG. 1, consisting in atoms agglomerations (clusters) with the size of 2 . . . 6 nm, specific to the glassy metals materials, irrespective of the Ti content. This specific microstructure confers the FeNbB metallic material a ferromagnetic behavior with the following characteristics: saturation magnetic induction, .sub.oM.sub.s of 0.05 . . . 0.07 T, depending on the Ti content, as in FIG. 2; coercive field H.sub.c of 100 . . . 300 Oe, depending on Ti content, as in FIG. 2; Curie temperature, T.sub.C of 30 . . . 78 C., depending on Ti content, as in FIG. 3.

(11) The Curie temperature T.sub.C of 20 . . . 70 C. of interest for the FeNbTiB ribbons, according to the invention, are obtained for concentrations of Ti from 18 to 16 at. %, as in FIG. 3, for which the values of the saturation magnetic induction also range between 0.2 and 0.45 T, according to magnetic hysteresis loops from FIG. 2. These ribbons with glassy-type quasi-amorphous structure can be used directly in magnetic field sensors to determine other physical parameters which depend on the magnetic field, sensors whose operation is blocked at a certain temperature, according to the invention.

EXAMPLE 2

(12) The process hereby consists in the preparation of glass-coated nano/microwires with nominal composition Fe.sub.79.7-xMn.sub.xNb.sub.0.3B.sub.20, where x=12 . . . 20 at. %. The basic alloy is prepared from pure elements through magnetic induction in a quartz tube sealed at the bottom, placed inside a vacuum chamber. Pieces of 34 g are extracted from this alloy according to the description from Example 1, then introduced in a Duran glass pipe with the diameter of 12 mm and wall thickness of 1 mm, sealed at its bottom and connected at its upper part to a vacuum system, placed inside an induction coil supplied by a medium frequency power generator. The alloy inductively heated up to the melting temperature T.sub.melt=1100 C.50 C. produces glass softening and is initially drawn manually to initiate the process, and then automatically with a controlled speed of 3000150 m/min., on a collecting bobbin located in air, thus resulting a glass-coated metallic wire with the metallic inner diameter of about 90 nm and glass coating thickness of 5.5 m, as in FIG. 4. In order to avoid the oxidation of the melted alloy and to draw the metallic wire into the glass, a vacuum of 60 . . . 70 mm H.sub.2O in ensured.

(13) The glass coated nanowires with nominal composition Fe.sub.79.7-xMn.sub.xNb.sub.0.3B.sub.20, where x=12 . . . 20 at. %, obtained hereby, preserve the quasi-amorphous structure as in the case of ribbons presented in the Example 1; they present a magnetic saturation induction of 1 . . . 1.1 T depending on the Mn content, as in FIG. 5, and relative magnetic permeability of 3500 . . . 4000. Their magnetic transition temperature T.sub.C significantly changes with the Mn content for the glass-coated nanowires, from 70 C. to over 70 C., as in FIG. 6, thus covering the temperature interval of 20 . . . 70 C., according to the invention. These glass-coated nanowires hereby can be used in the realization of magnetic field sensors within a well-established operation range, such as the sensors which can get blocked at temperatures lower or equal with the transition temperature, T.sub.C. This kind of nanowires can be also used in the process of cancer cell destruction through hyperthermia, by automatically maintaining the temperature at a value equal to T.sub.C.

EXAMPLE 3

(14) Process hereby consists in obtaining a metallic magnetic material of FeNbB type with biocompatible (Ti, Ta, Mn) elements under the form of micro/nanopowders through milling in a liquid medium, from the ribbons obtained through rapid quenching from the melt as in Example 1. The obtained powders must preserve the quasi-amorphous structure existing in the obtained ribbons as in Example 1, in order to have the magnetic transition temperature (T.sub.C) within the interval 20 . . . 70 C., according to the invention. That is why the milling process that implies dissipation of energies and local high temperatures induced by the friction process must be controlled very strictly. According to the invention, the FeNbB ribbons with biocompatible elements (Ti, Ta, Mn) are subjected to a preliminary thermal treatment at a temperature of 400 C., in a vacuum of 10.sup.5 mbar, in order to diminish the hardness and to increase the brittleness. The annealed ribbons are cut in pieces of 3-5 mm and introduced in two vials of hardened stainless steel, together with the balls made of the same material at a mass ratio balls:milling material=50:1, oleic acid 18 vol. % and heptane 2.7 vol. %. The two planetary two-ways ball mills are rotating with a speed of 550 rpm. The Fe.sub.79.7-xTi.sub.xNb.sub.0.3B.sub.20 powders (where x=12 . . . 20 at. %), with average size of 20 . . . 60 nm, are obtained by milling the ribbons for 3 hours, while for the powders of Fe.sub.79.7-xTa.sub.xNb.sub.0.3B.sub.20, with x=12 . . . 20 at % a milling time of 13 hours is necessary to obtain similar dimensions. In the case of Fe.sub.79.7-xMn.sub.xNb.sub.0.3B.sub.20, where x=12-20 at. %, the milling time was 26 h, and the average powder dimensions range between 40 . . . 100 nm, depending on the Mn content. The powders obtained in this way are washed at least 5 times with heptane to remove the traces of oleic acid in ultrasound bath, each washing operation lasting at least 5 minutes. For their use in hyperthermia, the powders are additionally washed in a solution of NaOH 10% in ultrasound bath for at least 5 minutes, the operation being repeated 5 times. Powders are then dried for 2 h in a vacuum oven at 70 C. The tests for plotting the variation in time of the temperature of thermal equilibrium presented in FIG. 7 were carried out in an experimental set-up especially designed for hyperthermia, in the presence of an alternative magnetic field with H=350 mT and the frequency f=153 kHz. An amount of 10 mg powder is introduced in a double-walled glass vessel voided inside for a better thermal isolation, with a volume V=0.13 ml of H.sub.2O, the mixture being induction heated by means of a high frequency generator. By controlling the Ti, Ta or Mn content, one can obtain equilibrium temperatures useful for hyperthermia (between 40 C. and 47-48 C.), like in FIG. 7(c), which is maintained irrespective of the heat duration and the value of the induction coil heating power. In this way one can realize, according to the invention, the self-control of the heating temperature in the case of hyperthermia, according to the necessities of the cancer cells destruction process.

REFERENCES

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