MXPA00002246A - Encapsulated nanometer magnetic particles - Google Patents

Abstract

Composite nanorparticles comprising an elemental metal core surrounded by a metal-containing shell material are described wherein the particles have an average diameter of from about 5-500 nm;the core metal is preferably selected from the group consisting of the transition metals and especially Fe, Co and Ni, whereas the shell material is advantageously a metal such as an alkaline earth metal, or a metal salt such as a metal oxide or metal halide. The shell material is preferably more oxophilic than the elemental core material, enabling the core metal to remain purely metallic. These core/shell composite particles can be used to fabricate magnetizable recording media such as tapes and disks.

Description

NANOMETRIC PARTICLES, MAGNETIC ^ ENCAPSULATED BACKGROUND OF THE INVENTION Field of the invention.

The present invention is broadly concerned with composite nanoscale polymetallic particles, as well as magnetic recording media (e.g., flexible tapes and hard disks) and integrated circuits that use nanoscale polymetallic particles. More particularly, the invention pertains to such composite particles and finished products wherein, in preferred forms, the nanoscale composite particles have an average diameter of about 5-500 nm with an elemental metal core surrounded by a layer containing a metallic material.

Description of previous techniques.

The U.S. patents Nos. 4,588,708 and 4,877,647 describe metal catalysts and coatings made by the Soldered Metal Atomic Dispersion (SMAD) process. This method uses metallic vapors (that is atoms) that are produced by heating -pieces of metallic elements in a high crucible.

EEF .: 32909 temperature, to the vaporization point of the metal under vacuum. The metallic vapor condenses on the inner walls of the vacuum vessel which is cooled to very low temperatures. At the same time the vapors of an organic solvent are co-deposited with the metallic vapors in the walls of the container at low temperature, forming a frozen matrix. After co-deposition, the frozen matrix contains metallic atoms, atomic oligomers such as dimers, trimers and small metal clusters. By heating, atomic atoms and oligomers begin to migrate and bond with each other to form metal particles of various sizes depending on the concentration of metal atoms in the solvent, the chemical structure of the solvent, degree of heating, and other parameters. Two important facets of this process are: (1) as the clusters grow they become heavier and less mobile, and (2) as the clusters grow the solvent adheres to the clusters surface and tends to slow down the subsequent growth. Thus, the SMAD process produces metal clusters / particles in solvent medium free of foreign reagents.

It has also been known to use the SMAD process for the manufacture of core / shell composite particles where the particles of the metal element are encapsulated within a shell of metallic material. For example, core-shell particles of Fe-Mg, metastables were described by Klaubunde et al. (Chem Mater, Vol. 6, No. 6, 1994). Additionally, the co-deposition of Fe and Ag has been attempted but the method for obtaining nuclide-coated particles failed, resulting generally in separate Se and Ag particles (Easom et al., Polihedron, V-ol 13 , No. 8,1994). The key-to producing metal core / shell compounds is to choose combinations of metals that are not normally thermodynamically miscible. The SMAD process forces the atoms of the immiscible elements to combine at low temperatures, so that the alloy of composite particles forms. By heating these particles, controlled phase segregation can be achieved where there is a natural tendency for the two elements to separate. Although it can not be predicted which metal will nucleate and form the core, and which will form the shell, experience has shown that the metal with the strongest metal-metal bonds will generally form the core material.

A major driving force after the study of nanoscale ferromagnetic particles is the search for improved magnetic recording materials useful in magnetic recording and the like. In such applications, the ferromagnetic particles should be a single unitary domain possessing two stable opposing magnetic poles along a preferred axis. The commutator field is the minimum magnetic field necessary to switch the magnetic poles in the single domain particles. The size j of the units of change (single domain particles) is important in the operation of the recordable medium. It should be small enough to allow recording of the projected magnetization pattern and provide a high signal-to-noise ratio, which requires the use of small units of change that are partially independent, so that one unit is not strongly affected by the magnetization of the other units. Additionally, a magnetic recording medium must be chemically stable under the conditions of use. For this reason Fe, Co, or Ni metals that are extremely oxophilic in the form of ultrafine particles are not generally useful. Instead, iron oxide, chromium oxide, boron ferrate and expanded cobalt iron oxide are more commonly employed. However, such metal oxides have relatively low magnetization intensities and are therefore not optimal for recordable materials. On the other hand, the elemental iron has a magnetization intensity of 1700 emu / cm3, which is several times that of the oxides. Therefore, elemental iron could be admirably suitable for use in recording media if the oxophilic properties of it could be properly controlled.

SUMMARY OF THE INVENTION.

The present invention overcomes the problems outlined above and provides novel polymetallic (especially dimethalic) composite particles having an average diameter from about 5-500 nm (more preferably from about 10-100 nm and more preferably from about 15-60 nm) with a core of elemental metal surrounded by a cover of metallic content; The material of the core and shell are thermodynamically immiscible and each is evaporable at a temperature of up to about 2000 ° under vacuum. The material of the cover is preferably non-magnetic and selected from the group including In, Nd, and metal salts; In many instances, the metal portion of such salts is different than the core metals. Preferred metallic salts are metal oxides and halides, particularly fluorides.

In preferred forms, the nuclear fraction of the composite particles is present at a level of at least about 30% by weight, more preferably from about 30-90% by weight, and more preferably from about 50-70% by weight- . Correspondingly, the cover material is present at a level of up to -about 70% by weight, more preferably from about 10-70% by weight and more preferably from about 30-50% by weight. The core metals are normally selected from the group that includes the transition metals, and especially Fe, Al, Mg, Cr, Co, Ni, Pd, Au, Cu, and Ag. The cover material can be a elemental metal such as an alkaline earth metal or a metal salt; The metal salts are normally selected from the group that includes the metal oxides, sulfides, and halides, especially the metal fluorides. The compounds are preferably formed by co-condensing the vapors of the elemental metal of the core and the metallic material of the shell, followed by heating the condensate. A conventional SMAD reactor can be used for this purpose. Generally speaking, the core metal and metal cover material are heated to their respective vaporization temperatures in individual crucibles within the SMAD reactor at a vacuum of at least 10 3 Torr.The outer walls of the SMAD reactor are typically cooled to a temperature of approximately -100 ° C and lower.

The magnetic recording medium of the invention is generally flexible tape or hard disk. The tapes include an elongated network of a substrate of synthetic resinous material having a magnetic coating applied to at least one face thereof. The magnetic coating includes a synthetic binder resinous material with magnetizable particles dispersed therein. The particles are of the type described above with an elemental core surrounded by a blanket material containing a metal. The core and shell material are thermodynamically immiscible and each is evaporable at a temperature of up to 2000CC under vacuum. The magnetizable particles have two opposite magnetic poles and stable switchable under the influence of an externally applied magnetic field.

In this context, the core material is preferably selected from the group consisting of Ni, Fe, Cr, Co, while the metallic coating material comprises the non-magnetic elemental metals and metal salts (eg elemental lithium, magnesium , gold and magnesium fluoride) advantageously, the cover material should be more xophilic than the elemental metal of the core so that any trace of oxygen is expelled. On the other hand, the coating material should be inert and essentially impermeable to oxygen and other environmental gases. This would allow the core material to remain purely metallic in use and inhibit the formation of harmful oxides.

In the manufacture of flexible taxable magnetic media, the substrates can be selected from a wide variety of materials such as polyethylene terephthalates, polyethylene naphthalates, aramides and polyimides. These substrates should typically have a thickness of about 1-10 mils. The magnetic coatings applied to the substrates are manufactured by mixing the magnetic particles in synthetic binder resins such as those selected from the group including polystyrenes, vinyl chloride copolymers, vinylidene chloride copolymers, acetate resins, polyvinyl, acrylic and polyacrylate resins, polyurethane elastomers, modified cellulose derivatives, epoxy and phenoxy resins, polyamides and combinations of polyethers with -OH groups with polyester and polyisocyanates. Such magnetic coatings can have from about 1-80% by weight of magnetic particle charge, more preferably from about 3-60% by weight, and more preferably from about 5-30% by weight.

The magnetic rigid discs can be prepared by applying a coating made of a synthetic resin (for example, phenol-formaldehyde, urea-formaldehyde, epoxy, polyvinyl acetate and silicone resins) with the magnetic particles described above to a hard disk (for example made of aluminum or other suitable material); The charge of particles in such coatings is the same as that used in the manufacture of flexible network media.

BRIEF DESCRIPTION OF THE DRAWINGS.

Figure 1 is a powder X-ray diffraction pattern for SMDA particles of Fe-In (Fe molar ratio: In = 1: 1) heat treated at (A) 400 ° C, (B) 600 ° C and (C-) 700 ° C for 2 hours followed by oxidative passivation; Figure 2 is a powder X-ray diffraction pattern of iron crystal size and electron transmission micrograph (TEM) of the global particle size of Fe-In samples (molar ratio of Fe-In = 1: 1); Figure 3 is an Mdssbauer spectrum of the SMAD particles of Fe-In (Fe: In = 1: 1 molar ratio) treated with heat at 400 ° C, followed by oxidative passivation; Figure 4 is a graph illustrating the magnetization saturation values of the SMAD particles of Fe-In (molar ratio Fe: In = 1: 1) against different sizes of Fe crystals for the particles; Figure 5 is an X-ray diffraction pattern of heat treated and passivated SMAD treated Fe-Nd powder particles at (A) 450 ° C, (B) 325 ° C, and (C) 225 ° C; Figure 6 is a plot of the saturation values of magnetization against temperature for SMAD particles of Fe-Nd without fresh and exposed heat treatment; Figure 7 is a graph of the coercivity against temperature for SMAD particles of Fe-Nd without fresh and exposed heat treatment; Figure 8 is a graph of saturation magnetization versus size of Fe crystals for passivated Fe-Nd SMAD particles; Figure 9 is an X-ray diffraction pattern of fresh passivated SMAD particle powders of Fe-MgF2 (molar ratio Fe: MgF2 = l: 2) where the particles were (A) fresh, as prepared, (B) heat treated at 200 ° C and passivated, (C) heat treated at 400 ° C and passivated and (D) heat treated at 600 ° C and passivated; Figure 10 is an X-ray diffraction pattern of different sizes of particulate Fe crystals SMAD of Fe-MgF2 treated with heat in the different particles; Figure 11 is a TEM (150 nm) photo of SMAD particles of Fe-MgF2 treated with heat at 200 ° C for 2 hours; Figure 12 is a TEM (600 nm) photo of SMAD particles of Fe-MgF2 treated with heat at 500 ° C for 2 hours; Figure 13 is a graph of saturation values magnetization versus size of Fe crustals for passivated Fe-MgF2 SMAD particles (Fe volume percent value, 220 emu / g Fe); Figure 14 is a schematic representation illustrating the encapsulation of a Fe metal core within a MgF2 blanket material; Fig. 15 is a J-ray diffraction pattern of fresh passivated SMAD particle powders of fresh C0-MgF2: (A), as prepared; (B) heat treated at 200 ° C and passivated; (C) heat treated at 400 ° C and passivated; and (D) heat treated at 700 ° C and passivated; Figure 16 is a TEM (200 nm) photo of SMAD particles of Co-MgF2 heat treated at 400 ° C for 2 hours; Figure 17 is a TEM (300 nm) photo of SMAD particles of Co-MgF2 heat treated at 600 ° C for 2 hours; Figure 18 is a graph of the size of Co crystals against heat treatment temperature for SMAD particles of Co-MgF2 treated at different temperatures; Figure 19 is a plot of the magnetization saturation values versus the size of Co crystals for passivated Co-MgF2 SMAD particles; Figure 20 is a graph of magnetic coercivity versus size of Co crystals for passivated Co-MgF2 SMAD particles;s a schematic representation illustrating the encapsulation of a Co metal core within a MgF2 blanket material; Figure 22 is an X-ray diffraction pattern of powders of fresh and passivated SMAD particles of Ni-MgF2: (A) fresh, as prepared; (B) heat treated at 200 ° C and passivated; (C) heat treated at 400 ° C and passivated; and (D) heat treated at 700 ° C and passivated; Figure 23 is a TEM (300 nm) photo of SMAD particles of Ni-MgF2 treated with heat at 500 ° C for 2 hours; Figure 24 is a graph of saturation values magnetization versus crystal size of JsT ± for passivated Ni-MgF2 SMAD particles; and Figure 25 is a graph of magnetic coercivity against the size of Ni crystals for passivated Ni-MgF2 SMAD particles.

DETAILED DESCRIPTION OF THE MODALITIES PREFERRED.

The following examples establish preferred methods according to the invention. Understand, however, that these examples are provided by way of illustration and nothing in them should be taken as a limitation on the entire scope of the invention. In these examples, the following preferred methods are used for the preparation and determination of the characteristics of the samples thereof: Methods and materials A. Equipment 1. X-ray powder diffraction: SCINTAG_3000_XRD diffractometer X-ray powder diffraction (XRD) was used to study the chemical composition and structure of powders. For samples with a fresh surface, degassed mineral oil was applied to cover the sample for temporary protection from oxidation by forming a powder / oil paste in a dry box filled with argon. The XRD analysis (which takes about an hour) was carried out immediately after the coating because the protection of the mineral oil was effective for only a few hours. For samples with passivated surfaces, no such precaution was taken.

Diffraction of the powder with X-rays was also used to estimate the crystallite sizes of the core metal of the particles. This was achieved with the help of Scherrer's formula: t = 0.91? / B? os? B Where ? is the wavelength of the X-rays, t is the diameter of the crystallite in A, B is the amplitude of the peak at the average height, and TB is the value of the maximum position in degrees. 2. - surface area BET: Micrometer Flo sorb II 2300 BET The direct information of the BET measurements is the surface area of the particles. Under assumed conditions, such as that the particles were spherical, individually spaced, the average particle size was calculated from the data of the specific surface area, as follows: Given a group of spherical particles N with the total mass M , the average specific area of these particles is: S = (N) (4pR2) / M Where R is the average radius of these particles. Where M equals N (4/3) pRp is the average mass of the particles. A) Yes, S = N (4pR2) / N (4/3) pR3p S = 3 / Rp and R = 3 / Sp, Therefore, the average size BET of the particles is: t = 2r = 6 / Sp 3. - Electron Transmission Microscopy (TEM) Both the global particle size and the size of the crystallite nucleus were estimated from TEM studies. 3-5 mg of each sample were placed in a vial of samples containing toluene, and agitated for 3-5 minutes in a sonicator so that a suspension of the particles formed. A drop of the test suspension was transferred to a carbon coated grid as the sample holder. After evaporation of the solvent, the sample was enrolled for the TEM study. To avoid the sintering of the particles caused by the heat generated by the electron beam, liquid nitrogen was used to cool the sample chamber (-196 ° C). 4. Móssbauer spectroscopy The Mossbauer spectrum was obtained in an Mdssbauer Ranger Scientific Inc. MS-1200 spectrometer. Mdssbauer spectroscopy was used to study the oxidation states and fine structures (for example, size of the metallic core crystal, surface effect / interface over the Mdssbauer parameters of the core metal) of the metallic core species in the samples. Approximately 5-10 mg of the elemental metal of the core were required to obtain the Mdssbauer spectrum of each sample. Thus, the corresponding amount of sample required in each study was estimated based on the mass balance of the sample. Like the XRD study, samples with fresh surfaces were protected with mineral oil before starting the transfer into the sample chamber. The Mdssbauer spectrum was taken at both room temperature (298 K) and liquid nitrogen temperature (77 K).

. SQUID Magnetometry The magnetic properties of the samples were taken from a magnetometer MPMS2 (Magnetic Properties Measurement System) and SQUID (Superconducting Quantum Interference Device) designed by Quantum Design. The range of the equipment field was ± 55,000 Oe, with a sensitivity of 10"8 emu.The fresh samples were protected during measurements in mineral oil in a gel capsule.The magnetization curves of these samples were taken at different temperatures between 10K and 300K up to 55,000 Oe.

B. Method of Dispersion of Solvated Metal Atoms (SMAD) with Metals Unstable.

This method involves the co-deposition of a metallic coating material (for example In or MgF2) with a metal core (such as Fe) as well as the simultaneous deposition at 77 K of an excess of organic diluent (solvent) as they described Klabunde et al., J. Am. Chem. Soc, 98 (1979), Free atoms, Clusters, and Nanoescale Particles, Academic Press (1994), Active metals - Preparation, Characterization, applications, VCH Publ. , 237 (1996), incorporated by reference herein mentioned. Concisely the SMAD apparatus consists of a vacuum vessel provided with a jacket for cooling by liquid nitrogen. The center of the vessel is equipped with independently cooled electric crucibles to vaporize the core metal and the metallic cover material, and with an admission for the solvent. In the operation of the apparatus, the solvent vaporizes at the inlet and then condenses on the inner walls of the vessel together with the vaporized metal atoms of the core and the metal shell. This condensation and cooling generates a frozen matrix of the metallic core atoms and the solvent that are collected in the walls of the container. Upon termination of condensate formation, cooling by liquid nitrogen is discontinued. The container can be heated to stimulate the kinetic growth of the bimetallic particles. The metastable particles are isolated and heat treated to cause phase segregation within the composite core / shell particles. To be successful, the metallic material of the shell must be inert towards the atoms of the core metal and clusters that grow, and be able to protect the encapsulated core metal clusters from oxidation by air.

C. Preparation of Materials Prior to the evaporation of the metallic core material and the cover, the pentane was pre-dried by refluxing over Na / K with benzophenone. Before being deposited in the SMAD reactor, the dry pentane (remained in a Schel-nk tube) was degassed, in a vacuum line with liquid nitrogen. The crucibles used were tungsten baskets obtained from R.D. Mathis Company. The tungsten baskets were coated with water-based alumina cement (Zircar Alumina Cement) obtained from Zircar Products, Inc. Zircar alumina Cement consisted of 70% alumina in a combination of ground fibers and sub-micro particles. Alumina cement is moderately acidic (pH 5) and forms a strong bond by removing the solvent water. Prior to use, the coated crucibles were heated to approximately 100 ° C in air for two hours and then heated to red in vacuum (10 ~ 3 Torr) in increments of about 200 ° C for two hours at each temperature, up to about 1,650 ° C to eliminate volatiles as well as to avoid cracking of the alumina coating.

D. Sample Preparation Although several metals were co-evaporated in the following examples, each of the evaporations was carried out as follows: Prior to evaporation, the crucibles containing the core metal (such as Fe) and the metallic coating material (such as In or MgF2) were heated in increments of approximately 100 ° C for about two hours at each temperature increase around 100-200 ° C below the boiling points of the initial materials. This slow heating process effectively gasifies the initial materials, and minimizes sudden vaporization waves during deposition. After the crucibles were heated, approximately 40-50 ml of pentane was deposited on the walls of the reactor. The evaporation of the core material was initiated after a stable evaporation of the metallic coating material was achieved. Heating of the core metal was carefully controlled by slow increases in the voltage to the crucible to prevent surges of ppression in the reactor. In the complete evaporation process, an evaporation of the metallic coating material and a constant deposition of pentane at a rate of 2-3 ml per minute before and after the evaporation of the core metal is ensured. Approximately one gram of core metal was evaporated in each experiment and about 100 ml of pentane were used. After evaporation, 40-50 ml of additional pentane were deposited to cover the product (approximately 200 ml total of liquid pentane).

After the final coating of pentane, the reactor was separated from the vacuum line. The liquid nitrogen ar vessel was removed to allow the reactor to warm to room temperature. Then the vacuum was reapplied to transfer the pentane to a cold trap and a black powder was obtained. The reactor was separated from the vacuum line again and filled with argon at normal pressure. The lower part of the reactor containing the final product was quickly removed, covered with an aluminum sheet and carefully transferred to a dry box filled with argon.

The heat treatments at various temperatures were applied to the SMAD particles collected to increase the sizes of the crystallites of the core metal within these particles. A certain amount of the sample, usually 70-100 mg, was transferred into a Pyrex glass tube in the dry box filled with argon. The glass tube filled with argon was then sealed on a hydrogen / oxygen flame. It was then heated to the desired temperature for the desired period of time. The sample tube is cut open to the dry box and stored in a sample bottle.

After the bimetal powder sample was treated with heat, careful controlled exposure to the air (oxygen) was required to stabilize the surfaces of these particles against subsequent oxidations (passivation). Thus, a slow oxidation process was used in which a sample bottle containing 50 to 100 mg of the fresh SMAD sample (heat treated or as prepared) was transferred from the dry box to the open air. The lid was slightly open to allow slow diffusion of air into the bottle. After a period of 12 to 24 hours the lid was removed and the sample was found stable against subsequent oxidations. In some cases the color of the sample changed slightly during this process.

EXAMPLE 1 In this example, using the preferred method described above, a sample was prepared using iron as the core and indium material as the metallic coating material. The properties of Fe and In are shown in table 1 as follows: Table 1 Fierro and Indio properties About 2.6 grams of In and 1.3 grams of Fe (Fe: In molar ratio of 1: 1) were co-evaporated in the presence of pentane at 77 K and 10"3 Torr, after evaporation about 3 grams were collected. SMAD reactor dark powder X-ray powder diffraction of the sample as prepared showed a weak signal for the indium, but the crystalline form of the iron could not be detected A second sample of Fe-In with a ratio molar Fe: In of 2: 1 was also studied.The XRD of the sample as prepared from this relationship showed iron and indium, both being closely amorphous.It was desirable to have equal or in excess of the iron to protect the Indian metal from oxidation beyond the formation of closely homogeneous amorphous Fe-In alloys, however, the 1: 1 ratio was chosen for further studies.

The sample of the system with molar ratio Fe: In = l: l was divided into several portions and transferred into glass tubes in an argon atmosphere. After the tubes were sealed, they were heated in a tubular oven at 200 ° C, 300 ° C, 350 ° C, 400 ° C, 600 ° C, or 700 ° C for two hours. The powders were transferred to small flasks, passivated slowly, and analyzed by XRD. In the sample at 200 ° C, a strong In signal was detected while only a weak Fe signal could be observed. Although neither iron oxide or indium oxide were present, a small peak at 2? of 41.5 ° suggested the presence of -a-Fe203. After it was heated to 300 ° C, the sample showed signals for Fe, In a-Fe203 and ln203. For the sample at 350 ° C, a similar pattern was evident. In the samples at 300 ° C and 350 ° C, the signals of the In and the indium oxide signals had approximately the same strength.

In the case of the sample heated to 400 ° C, iron spikes became very pronounced, signals from indium oxide also appeared stronger than samples treated with heat at lower temperatures (Figure 1), and there remained a weak peak for a-Fe203 at approximately 41.5 ° of 2? After these particles were heated to 600 ° C and 700 ° C, no iron oxide signals could be found until after their exposure to air was extended (Figures IB and 1C). In the molar ratio system Fe: In = 2: 1, the XRD results of the heat-treated samples showed similar results.

Since Fe and In were both susceptible to oxidation, in the heat treatment at high temperatures more Fe atoms were taken to the center of the particles and were protected by In atoms that moved to the surface of the particles. During this process, the In reduced to iron oxides as well as protected it from any upstart trace of oxygen that might have been present.

The XRD and TEM provided the overall size and sizes of the Fe crystals of these composite core / shell particles. These sizes are summarized in fig. 2 and in table 2.

Table 2 Global Particle Sizes and Crystallite Sizes of SMAD Fe-In Particles Obtained by TEM and XRD Studies An Mdssbauer at room temperature of the Fe / In particles (2: 1) is shown in Figure 3. After the particles were heated to 400 ° C, the iron in the sample was much better protected and only a small amount It was rusted.

The magnetic properties of these samples were obtained in a SQUID magnetometer. In a Fe / ln / a-Fe203 / In203 mixture, only Fe was strongly magnetic with a saturation saturation value of 220 emu / gram. The α-Fe2Q3 was only slightly magnetic with a saturation saturation value of 0.6 emu / gram, and neither of In or In203 was magnetic. The SQUID could only provide the global magnetization value of the sample, therefore it was necessary to transfer the SQUID data to the magnetization values of the metallic iron. If the samples did not take any oxygen during the passivation process, the chemical composition of these samples should have been very close to that of the initial material. For example, for the Fe: In = l: l system, the chemical composition of the samples should have contained 33% Fe in mass and 67% In in mass. Based on the XRD and the Mdssbauer data, about 50% by mass of the In was in the form of ln203 after the passivation procedure. This resulted in a mass balance of 30% by mass for Fe ° in the molar ratio system Fe: In = l: l. For the molar ratio system Fe: In = 2: l, the mass balance for Fe ° should be 46% by mass. These values were used in the calculation of the saturation values of magnetization per gram of iron (emu / g of Fe) as shown in table 3. Table 3 Magnetization Saturation Values (emu / g of Iron) for the Samples Of Faith: In The coercivity values of the Fe: In samples are shown in Table 4, and Figure 4 shows the values of Ms versus the size of the Fe crystallites.

Table 4 Coercivity values in Oersteds of the Faith: In the samples EXAMPLE 2 In this example the evaporation of iron and Neodymium was carried out using the preferred method described above. The Fe was evaporated by means of a crucible of Tungsten coated with alumina and Nd by means of a crucible of boron nitrate located in a basket of tungsten with a layer of alumina on the outside in the presence of pentane at 77K and 10"3. Torr Several reactions were carried out using a 1: 1 molar ratio system of Fe: Nd. In a typical reaction where approximately 0.56g of Fe (10.0 mmol) and 1.50g of Nd (10.4 mmol) were used, 1 , 6 g of pyrophoric black powder was collected.The elemental analysis of the powder gave 25.1% and 69.3% by weight of Fe and Nd, respectively.

The fresh Fe-Nd pyrophoric powders were heat treated in argon at different temperatures ranging from 250 ° C to 750 ° C for two hours. After the heat treatment, these powders were slowly passive in air allowing metal oxides to form a layer on the surface of these powders. No physical evidence of changes in stabilized powders was observed after they were stored in sample vials for six months. X-ray diffraction of powders from the fresh sample of Fe-Nd SMAD powders showed only a broad peak due to metallic iron. The XRD patterns of the heat-treated samples of the passivated powders showed that the iron began to crystallize at very low temperatures (Fig. 5), but no clear signs of the Nd203 were observed in the heat treatment until reaching 500 ° C. temperature. In addition, no clear signs of iron oxides or metallic Nd were observed after any heat treatment. A weak signal for the Fe-Nd inter-metallic compound Fe2Nd was observed for the samples heated at 500 ° C and above, the average XRD sizes of the a-Fe crystallites, estimated with the Scherrer formula, are in listed in Table 5 together with the BET surface area data and the estimated densities of the sample under the assumption that all the particles had a spherical shape. For comparison, the estimated TEM sizes of these particles are also listed in Table 5.

TABLE 5 Data of the Surface Area of the Samples of Faith: Nd (molar ratio 1: 1) by XRD, TEM, and BET to. Assuming that all the particles would have a spherical shape. b. The estimate was based on the information obtained from the XRD and the Mossbauer studies on Fe, a-Fe203 and Nd203 concentrations.

To determine the valence states of the Fe atoms in these samples, the Mossbauer spectra were taken. When exposed to air, all the Fe atoms of the particles as treated were oxidized to a-Fe203. Samples treated by heat and Passive Fe-Nd showed a gradual increase in the I percentage of metallic iron (as the a-Fe sextet) according to the increase-temperature of the treatment. These changes together with Mossbauer's data on the metallic phase of a-Fe (sextet) are summarized in the Table 6: Table 6 Mossbauer environmental temperature data from Fe-Nd samples The Mossbauer data indicate the presence-of pure a-Fe, while the rest of the signal was attributed to xx-Fe203 and Fe2Nd. Since the signal of a-Fe203 and the Fe2Nd (each as a doublet) overlap each other, Their relative abundances may not be valued. The hyperfine field of Fe-Nd powder was not exposed, fresh (324 KOe) were slightly lower than the standard values (333 KOe). This indicated a close range of electronic interaction between the iron atoms (electronegativity 1.8) and Nd (electronegativity 1.1) this allowed Fe atoms to be removed some density of electrons surrounding Nd atoms. The Mossbauer data showed that when heat-treated samples at very high temperatures such as 450 ° C, less than 70% of the mass of the iron atoms are protected against the promotion of oxidation (like a-Fe) then the powders are stabilized by a passive oxidation of the surface, however, a spectrum Mossbauer from the sample treated with heat at 750 ° C showed a slightly low content of the a-Fe phase because more Fe atoms were formed in Fe2Nd at this high temperature. In addition, extensive sintering of the surface layer led to shrinkage of the protective coating resulting in the exposure of the core of the crystals of Fe to oxygen. Magnetic studies of these Fe-Nd bimetallic particles allowed an examination of the saturated magnetization and coercivity values of these powders. Based on the XRD samples, none of the exposed samples would have metallic Nd as a constituent. In this way, all the Nd was assigned as Nd? 03 in the exposed particles, and all the Fe atoms as metallic Fe when the mass balance of the passivated samples was calculated. This gave an estimated Fe mass balance of 25% for all passive samples with a beginning of molar ratio of 1: 1 Fe / Nd. For fresh, not exposed fresh Fe-Nd bimetallic powders, only metal Fe atoms and Nd metal atoms were considered as the constituents, and for the molar ratio system Fe: Nd = l: l, the theoretical mass balance for the Faith approaches 28%. The comparison between the saturated magnetization values of the unexposed (unheated) Fe-Nd samples as prepared, the exposed Fe-Nd samples (not heated) are illustrated in Fig. 6, and the comparison of their Coercitivities are given in Fig. 7. Fig. 6 demonstrates the saturation magnetization value of the Fe-Nd sample as it was prepared had a strong dependence on temperature. The saturation magnetization value of this sample approximates 162 emu / g of Fe at 10K, and gradually decreases to about 85 emu / g of Fe at 300k. Because this sample was not oxygen, the values of Ms in the sample will be lower compared to those of the Fe mass due to the formation of Fe-Nd alloys on the surface of the iron crystallites. The exposed Fe-Md particles (not heated) had very low values of _M? confirming that most of the iron atoms in that sample were oxidized to a-Fe203 during exposure to air as indicated in the Mossbauer ambient temperature data. The coercivity values of the frescoes and exposed frscas particles will also be totally different. The high coercitivities of the fresh Fe-Nd particles as prepared indicated that this sample contained ferromagnetic metal iron clusters. While the coercivities of the exposed Fe-Nd sample were very low due to a-Fe203 -amorph (Fig. 7) Although no information was found on the magnetic properties of Nd203 in the literature, it was reasonable to believe that the Nd203 I had a very low magnetic moment. Therefore, the contribution of Nd203 in the saturation magnetization values of the passivated Fe-Nd particles was omitted. In addition, a-Fe203 had a saturation magnetization value of 0.6 emu / g compared to the saturation magnetization value of pure Fe of 220 emu / g, so the magnetic moment of these samples came only from metallic Fe . Based on the i >Estimated mass balance of these samples the magnetization values of the Fe-Nd particles were calculated and are illustrated in figure 8 contrary to the sizes of the crystallites of -Fe.

The passivated Fe-Nd particles, especially the sample that did not receive heat treatment, reduced their saturation magnetization values due to oxidation by passivation. However, the formation of Fe-Nd alloys on the surface of the Fe groupings were also taken into consideration. For the samples heated to low temperatures (small crystallites of Fe), the oxidation effect predominated while, for the samples heated to high temperatures, less Fe was oxidized and more Fe formed alloys with Nd. The low Ms value of the samples at 750 ° C (compared to the sample at 600 ° C) was due to the extensive formation of Fe203 in this sample.

The passivated Fe-Nd particles showed very low coercitivities of 12.6-105 Oe at 300k. For a-Fe crystallites with an outer coating of Fe oxide, the coercivity values at ambient temperature can be as high as 1.050 Oe. These -Fe-Nd powders should therefore be considered to be slightly magnetic and consistent materials of Fe ° clusters protected by covers of Fe2Nd and Nd203.

Example 3 The Fe-MgF2 system studied in this example using the preferred method described above had a molar ratio of Fe to MgF? of 1: 2 where 0.80 g of Fe (14.3 mmol) and 1.78 g of MgF2 (28.6 mmol) were co-evaporated and deposited at 77 K with pentane vapor. The evaporation temperature of MgF2 under the normal pressure of the ^ MD reactor (about 10"3 Torr) was 1100 ° C. Approximately 2 grams of the product were collected, Fig. 9 provides the XRD patterns of the samples as shown in FIG. They prepared likewise the heat-treated and passivated Fe-MgF2 powders (molar ratio 1: 2) .In the sample as it was prepared, the MgF2 and Fe signals were both present and the estimated size of the crystallites of Fe was Approximately 9 nm XRD patterns of the heat treated passive samples showed only the Fe and MgF2 signals and the signals for the Fe oxide were not visible. The estimated sizes for Fe crystallites by XRD for each of the heat treatment temperatures are given in table 7. A graphic version of the information provided in this table is given in Fig. 10.

TABLE 7 Sizes of Fe in the Fe-Mgf2 particles by XRD The TEM photos of these particles are shown in Figures 11 and 12. The measured sizes of the particles and the sizes of the a-Fe crystallites are listed in Table 8.

Table 8 TEM Sizes of Fe-MgF Particles? to. Big crystallites of Faith b. Fe small Critalites isolated The TEM photos showed that after they were heated to low temperatures, the Fe-MgF2 particles still had a structure close to a single phase with the Fe crystallites embedded in an MgF2 matrix demonstrating that the Fe crystallites grew very little. When the temperature reached 500 ° C, a severe phase separation occurred. Many of the Fe clusters were added into very large Fe particles (50 to 100 nm), and only a small number of the smaller Fe crystallites remained. In the samples at 500 ° C and 600 ° C, there were actually two groups of crystallites of Fe. One graph included large particles of Fe with a size range of about 100 nm, and the other group contained the Fe crystallites. smaller than 10-15 nm. Large Fe particles accounted for more than 90% of the total mass of Fe in these materials, while small Fe crystallites accounted for less than 10% of the total Fe content. After heat treatment at temperatures of 500 ° C and 600 ° C the MgF2 crystals also grew in large pieces with a size range of a few hundred nm.

The magnetic properties of these Fe-MgF2 particles were studied using a SQUID magnetrometer. Although a small portion of the carbon atoms in these materials was actually oxidized during the passivation process, the values of the magnetization per gram of Fe were calculated without taking into account the mass change caused by the oxidation of Fe atoms because the extent of oxidation was very difficult to estimate, and also because the oxidation of Fe caused only a small change in the mass balances of these materials. The calculated values of the magnetization of these materials are listed in Table 9, and the values of coercivity are given in Table 10. Fig. 13 gives the percentage of the magnetization value per mass (220 emu / g Fe) a 300K against the sizes of crystallites of Fe in these particles.

Table 9 Magnetization Values of Fe-MgF2 Passivated Particles Table 10 Magnetic Coercivity Values of Fe-MgF Particles The magnetization data in Table 9 and the information provided in Figure 13 show that after they were heated to temperatures of 400 ° C and above, more than 85% of the Fe atoms were protected when these particles were exposed to air. A schematic illustration for the formation of the encapsulation of the Fe groupings in an MgF2 matrix using the SMAD method is shown in fig. 14 EXAMPLE 4 In this example, the evaporation of Co and MgF2 followed the preferred method described above. The Co-MgF2 system had a molar ratio of 1: 2 in which 0.80 g of cobalt (13.6 mmol) and 1.69 g of MgF2) were co-evaporated in the presence of pentane at 77K. Co-evaporated at approximately 1300 ° C under the pressure of the SMAD reactor (10"3 Torr) Figure 15 provides the XRD patterns of the fresh powders, as prepared from Co-MgF2 as well as the heat treated samples. The average size of the Co crystallites of the fresh sample as prepared was estimated at around 4.5 nm by the use of the Scherrer formula for the extended XRD All the XRD standards showed metallic cobalt and MgF2, and no clear signs of cobalt oxides could be observed.The sizes estimated by XRD and the estimated TEM sizes of the cobalt crystallites in these samples are listed in Table 11 The TEM photos of these particles are given in Figs 16 and 17 Table 11 Estimated Sizes of Co Crystallites in Co-MgF2 Particles A graphical version of the ratio of the size of the crystallites of Co to the temperature of the heat treatment is given in Fig. 18. From a comparison of table 11 and Fig. 18, it will be appreciated that the size of the Co particles by XRD was generally smaller than the sizes estimated from the TEM photos because, in the XRD patterns of the Co-MgF2 particles, the cobalt line (2? = 44.2 °) by which the size of the crystallites of Co was calculated with the formula of Scherrer, it overlapped partially with the line of MgF2 which was approximately at 39.8 ° of 2 ?. As a result, the sizes of Co calculated by XRD were smaller than they should have been, thus TEM sizes were more accurate. The magnetic properties of these Co-MgF2 particles are listed in Tables 12 and 13 and also shown in Figs. 19 and 20.

Table 12 Co-MgF2 Particle Magnetization Saturation Values Table 13 Magnetic Coercivity Values of Co-MgF2 Particles The cobalt had a mass magnetization value of 162.5 emu / g of Co, so at least 80% of the carbon atoms were protected as soon as these particles were heated to temperatures higher than 500 ° C before they were exposed air as illustrated in table 12 and in Fig. 19. The Co-MgF2 system had a narrower size of Co distribution, therefore, a simplified schematic illustration of the encapsulation of the Co particles in the matrix of MgF2 is given in Fig. 21 EXAMPLE 5 Evaporation of Ni and MgF2 also followed the preferred method as described above. Ni was vaporized at around 1400 ° C under the pressure of the SMAD reactor of approximately 10 ~ 3 Torr. The Ni-MgF2 system had a molar ratio of 1: 2 in which 0.80 g of Ni (13.6 mmol) and 1.69 g of MgF2 (27.2 mmol) were co-evaporated in the presence of pentane at 77K. Fig. 22 provides the XRD patterns of the fresh particles, as prepared and passivated Ni-MgF2. The average size of the Ni crystallites was estimated at 5.8 nm in the fresh sample, as prepared. In all the XRD patterns of the heat treated and passivated samples, only the Ni and MgF2 signals were clearly visible. No signs of nickel oxides were detected. The TEM photos of these particles are given in figs. 23. The sizes estimated by XRD and TEM of the Ni crystallites are listed in Table 14 Table 14 Sizes by TEM and XRD of the Ni Cristalites in the Ni-MgF2 Particles From the comparison above it can be appreciated that the sizes by XRD and TEM correspond to each other. The magnetic properties of these materials are listed in Tables 15 and 16 and Figs. 24 and 25 also illustrate these results.

Table 15 Magnetization Saturation Values of Ni-MgF2 Particles Table 16 Magnetic Coercitivities of Ni-MgF2 Particles EXAMPLE 6 A sample of 0.5 g of polystyrene resin (plastic) was dissolved in 15 mL of toluene in a bucket and 0.3 g of Fe-Mg composite particles were added (overall diameter 50-60 nm, size of iron crystallite) 16 nm) with stirring (37% by weight of composite particles in the charge) followed by 3 minutes of sonication in a conventional cleaning sonicator. Some of the toluene was evaporated at room temperature until the slurry became viscous. The mixture was then poured into a circular mold about 3"in diameter, and the toluene was allowed to evaporate completely leaving a thin, black disc having a thickness of about hundredths of an inch. The resulting disc was rigid if it remained in contact with the mold. However, it could be detached by obtaining a flexible disk and cut into tape lengths.

After magnetization with a manual permanent magnet, the magnetized tape was studied using a Hall probe. A signal of 400-1000 milliGauss was detected. The direction of magnetization was reversed, and again a signal of 400-1000 milliGauss was detected.

For comparison, a commercial magnetic tape was measured, which showed a signal of approximately 500 milliGauss for the magnetization remnant.

In another series of tests, various types of magnets were manufactured by magnetic Fe-Mg particles according to this invention in a polystyrene binder, as described above. The charge of composite particles averaged 5-40% by weight. For example, with a 5% load, 40-80 milligaus read on the Hall probe were obtained.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (35)

1. Claims: A compound, characterized in that it includes a particle having a diameter of about 5-500 ji with a metal of the elemental core surrounded by a metallic content coating material, the core and coating materials being thermodynamically immiscible and each evaporable at a temperature of up to about 2000 ° C under vacuum, characterized in that the coating material is selected from the group consisting of In, Nd and metal salts wherein the metal portion of such salts is different than characterized by core metal.
2. 2. The compound of claim 1, characterized in that the core metal is present at a level of at least about 30% by weight, and characterized in that coating material is present at a level of up to about 70% by weight.
3. 3. - The compound of claim 1, characterized in that the core metal is selected from the group consisting of the transition metals.
4. 4. - compound composite of claim 3, characterized in that the core metal is selected from the group consisting of Al, Mg, Cr, Fe, Co, Ni, Pd, Au, Cu and Ag.
5. The compound of claim 1 , characterized in that the metal salts are selected from the group consisting of the metal oxides and metal halides.
6. 6. The compound of claim 1, characterized in that the compound is formed by co-condensing the vapors of said elemental metal of the core and said metallized coating material, followed by heating the condensate.
7. 7. A compound characterized in that it includes a particle having a diameter from about 5-500 nm with an elemental metal core surrounded by a coating material containing a metal, said core and coating materials are thermodynamically immiscible and each is evaporable to temperatures of up to about 2000 ° C under vacuum, characterized in that the coating material is selected from the group consisting of the salts of metal oxides and metal halides.
8. 8. The compound of claim 7, characterized in that the coating material is magnesium fluoride.
9. 9. The compound of claim 7, characterized in that the core metal is present at a level of up to about 30% by weight, and said coating material is present at a level of up to about 70% by weight
10. 10. The compound of claim 7, characterized in that the core metal is selected from the group consisting of the transition metals.
11. 11. The compound of claim 10, characterized in that the core metal is selected from the group consisting of Al, Mg, Cr, Fe, Co, Ni, Pd, Au, Cu and Ag.
12. 12. The compound of claim 7, characterized in that said compound is formed by c- condensation of the vapors of said elemental metal of the core and said metallic coating material, followed by heating of the condensate.
13. 13. A compound characterized in that it includes a particle having a diameter of about 5-500 nm with a metal of the elemental core surrounded by a coating material containing a metal, characterized in that core and coating materials are thermodynamically immiscible and each evaporable at temperatures up to 2000 ° C under vacuum, characterized in that core material is selected from the group consisting of Al, Mg, Cr, Co, Ni, Pd, Au, Cu and Ag. And the coating material which is selected from the group consisting of metal sulfide salts and metal halide salts.
14. 14. The compound of claim 13, characterized in that the metal halide salts are salts of metal fluorides.
15. 15. A compound characterized in that it includes a particle having a diameter of about 5-500 nm with a metal of the elemental core surrounded by a metallic content coating material, said core and coating materials being thermodynamically immiscible and each evaporable to temperatures of up to 2000 ° C under vacuum, thermodynamically immiscible core and coating materials materials selected from the group consisting of the metal halide salts.
16. 16. The compound of claim 15, characterized in that the core metal is iron and said coating material is magnesium fluoride.
17. 17. Magnetic recording media, characterized in that they include a substrate material having a magnetic coating applied to at least one face thereof, characterized in that magnetic coating including a binder of synthetic resin with magnetizable particles embedded therein, said magnetizable particles including composite particles having an average diameter of about 5-500 nm with a metal of the elemental core surrounded by a metallic content coating material, said core and coating materials being thermodynamically immiscible and each evaporable at a temperature up to around 2000 ° C under vacuum, said magnetizable particles having two stable opposite poles switchable under the influence of an externally applied magnetic field.
18. 18. The means of claim 17, characterized in that the core metal of said particles is present at a level of up to 30% by weight, and characterized in that coating material is present at a level of up to about 70%.
19. 19. The means of claim 17, characterized in that the core metal is selected from the group consisting of the magnetizable transition metals.
20. 20. The means of claim 19, characterized in that the core metal is selected from the group consisting of Ni, Fe, Cr and Co
21. 21. The means of claim 17, characterized in that the metallic coating material is selected from the group consisting of metallic elements and metal salts.
22. 22. The means of claim 21, characterized in that the coating material is selected from the group consisting of elemental lithium, magnesium and gold, and magnesium fluoride.
23. 23. The means of claim 17, characterized in that the compound is formed by the co-condensation of the vapors characterized by elemental metal of the core and said coating material, followed by heating of the condensate.
24. 24. The means of claim 17, characterized in that the media is a magnetic, flexible recordable tape, said substrate material including an elongated network of synthetic resinous material.
25. 25. The means of claim 17, characterized in that the means include a magnetic rigid disk.
26. 26. The means of claim 17, characterized in that the magnetic coating includes from about 1-80% by weight of said magnetizable particles within said synthetic binder resin.
27. 27. a compound characterized in that it includes a particle having a diameter of about 5-500 nm with a metal of the elemental core surrounded by a metallic content coating material which are thermodynamically immiscible and each evaporable at a temperature of up to about 2000 ° C under vacuum, said coating material is selected from the group consisting of In, Nd and metallic salts thereof, characterized in that the composite is formed by co-condensing the vapors of said elemental core metal and said coating material, followed by condensate heating.
28. 28. A magnetic coating adapted for application to a substrate to form a magnetic recordable medium, said coating characterized in that it contains dispersible magnetizable particles within a synthetic binder r-esine, said magnetizable particles including composite particles having an average diameter of about 5 mm. -500 nm with an elemental metal core surrounded by a metallic content coating material, said core and coating materials which are thermodynamically immiscible and each of which is evaporable at a temperature of up to 2000 ° C under vacuum, said magnetizable particles that have two stable opposite magnetic poles commutatable under the influence of an externally applied magnetic field.
29. 29. The coating of claim 28, characterized in that said core metal of said particles is present at a level of up to 30% by weight-, and said coating material is present at a level of up to 70% by weight.
30. 30. The coating of claim 28, characterized in that said core metal is selected from the group consisting of the magnetizable transition metals.
31. 31. The coating of claim 30, characterized in that said core metal is selected from the group consisting of Ni, Fe, Cr and Co.
32. 32. The coating of claim 28, characterized in that said metallic coating material is selected from the group consisting of the elemental metals and metal salts.
33. 33. The coating of claim 32, characterized in that said coating material is selected from the group consisting of elemental lithium, magnesium and gold, and magnesium fluoride.
34. 34. The coating of claim 28, characterized in that said compound is formed by the co-evaporation of the vapors characterized in that the core metal and said metallic coating material, followed by heating of the condensate.
35. 35. The coating of claim 28, comprising from about 1-80% by weight of said magnetizable particles within said synthetic binder resin.