JPH04160102A - Composite material and its production - Google Patents

Abstract

PURPOSE:To obtain high insulating property while maintaining the amt. of insulating material small by forming a thin layer on the surface of metal powder particle in a manner that the thin layer consists of insulating oxide of such metal the oxide of which has lower free formation energy than the metal of the powder particle to obtain a composite powder, and then compacting the powder to specified relative density or higher. CONSTITUTION:When Fe-Si-Al alloy is used, a spherical powder of this alloy is treated at specified temp. in an Ar gas atmosphere containing a proper amt. of O2 gas to form a film on the powder surface. This film formed on the powder consists of an insulating oxide material containing not only Al and O but a considerable amt. of Fe and partly contains iron oxide. This composite powder is subjected to hot press sintering in an Ar gas atmosphere or the like under specified conditions to obtain a molded body having >=95% relative density.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to composite materials used in electronic parts and equipment.

Conventional technology Traditionally, composite materials have been used for electronic parts and devices, such as those with resin as a matrix material and ceramics as a filler, and composite materials with ceramics as a metallic matrix material. . Among these, composite materials in which metal is separated as dispersed particles by an insulator are used, for example, high saturation magnetic flux density metal/insulator systems, which increase electrical resistance and reduce eddy current loss in the high frequency region. The aim was to create a new material with unprecedented properties that had both the properties of an insulator and an insulator.

Problems to be Solved by the Invention However, with conventional metal/insulator composite materials, in order to obtain sufficient insulation properties, it is necessary to increase the amount of the insulator continuous phase that serves as the matrix, and the spacing between metal particles is reduced. was a big one. In such a configuration, for example, if the aforementioned composite magnetic material is used for the magnetic core, the high magnetic flux density of the magnetic metal will be diluted by the insulating material, and the magnetic permeability will also significantly increase due to the magnetic resistance of the insulating material. There was a problem that the value decreased.

Therefore, attempts have been made to coat the surface of metal particles with a thin layer of insulator and then fill it with high density to prevent the inherent properties of the metal from being impaired.
As the proportion of the insulator decreases and as the density increases, direct contact between dispersed particles becomes more likely to occur, resulting in a decrease in insulation properties and the failure to obtain the expected characteristics. Furthermore, even if a sample with a certain degree of high electrical resistance is obtained, heat treatment of this sample results in a decrease in resistance.

The present invention aims to provide a composite material that has both high insulation properties and high density while keeping the content of insulators low, and that does not easily cause a decrease in electrical resistance even when subjected to heat treatment, and a method for manufacturing the same. purpose.

Means for Solving the Problems The present invention provides that the surface of the particulate metal or alloy A has an oxidation layer smaller than that of the metal element having the largest free energy of oxide formation among the components contained in the metal or alloy A. This is a composite material characterized by being substantially covered with an insulating oxide containing a metal B that has the free energy of forming a substance.

In addition, the present invention provides a composite powder by forming a thin layer of an insulating oxide of a metal whose oxide formation free energy is smaller than that of the metal on the surface of a metal in the form of powder particles so as to almost uniformly cover the surface of the metal. This method of manufacturing a composite material is characterized by molding this powder to a relative density of 95% or more under high temperature and high pressure.

Effect of the present invention The surface of the particulate metal or alloy has a lower free energy of oxide formation than the metal element which has the largest free energy of oxide formation among the components contained in the metal or alloy A. Since it is substantially covered with an insulating oxide containing metal B, the oxide film itself serves to provide a wire to the metal surface where the insulation film is damaged and exposed, and by repairing the film, It is thought that it is possible to increase the density of composite materials while maintaining their insulation properties. In addition, the decrease in resistance due to heat treatment is thought to be caused by exposure of the metal surface due to sintering of the film inside the sample and contact with it due to diffusion, etc., but it is also believed that the film has a repairing effect by supplying oxygen. Yes, resistance is less likely to decrease.

Example Examples of the present invention will be described below.

In the present invention, the powder particulate metal is Fe-5i-Al, Fe
-Ni, Fe-5i, Fe-AL No-N
When a magnetic material such as i-Fe is used, a composite magnetic material having a high saturation magnetic flux density even at high frequencies can be obtained. On the other hand, Al
, Si, etc., it becomes a material that has both high thermal conductivity and insulation properties and is useful for IC boards and the like. The present invention will be explained below using these materials as examples.

Example 1 Composition is Fe-84wt%, Si-10wt%, Al-6
wt% of Fe-5i-Al alloy (Sendust alloy) spherical powder (average particle diameter of about 20 μm) was heated at 700°C with 0.
01%02 gas - Remaining A "Gas atmosphere or 20%02
The samples were treated in a gas-remaining Ar gas atmosphere for various times to form oxide films with various thicknesses on the surfaces. The composition of the oxide film was determined by weight increase during heat treatment and Auger spectroscopy/A
Evaluation was made by depth profile obtained by r sputtering. As a result, only Al and 0 were detected in the film heat-treated in an atmospheric gas with an oxygen concentration of 0.01%, regardless of the film thickness.
The oxide film contained no other metal components and was an aluminum oxide film. On the other hand, at an oxygen concentration of 20%, a considerable amount of Fe was present in addition to Al and O in the oxide film, resulting in a film containing a portion of iron oxide.

These powders were molded and heated at 1000℃ and 1000J/c+.
Hot press sintering was performed in a gas atmosphere at a pressure of n2, and a high-density composite with a relative density of about 98% (porosity of about 2%) was produced.

A columnar sample of 2XIX12 mm was cut out from the obtained sintered body, and its electrical resistance (using a tester) and magnetic properties were measured. Further, these samples were heat treated at 950° C. in 1 atm Ar gas for 20 hours, and the resistance was measured again. The results are shown in Table 1.

(Left below) Table 1 (Characteristics of the composite) As is clear from Table 1, the densified powder containing iron oxide, which has been heat-treated at a high oxygen concentration, has an insulating film consisting only of Al and O. When compared with the same oxide film thickness, it is easier to obtain high electrical resistance, and this tendency is even higher when the film thickness is thinner.

As a result, the dependence of the relative magnetic permeability on the measurement frequency is weaker in the sample made from the Fe-containing film-coated powder,
Up to I MHz with a film thickness of about 55-1 On, approximately 1000
It showed a relative magnetic permeability of about On the other hand, in the case of the Al-0 based film, at a film thickness of about 510 nI11, the electrical resistance was not yet sufficiently high, so the magnetic permeability at high frequencies was significantly reduced, which is thought to be due to eddy current loss. Note that there was almost no difference in saturation magnetic flux density between the samples.

Next, each sample was heat-treated, and the results showed that the resistance drop was more remarkable in the sample whose oxide film did not contain Fe components.

Example 2 Si metal powder having an average particle size of about 10 μm was heat treated in air at 1100° C. for 10 hours to form an oxide film on its surface.

On the other hand, Al, Ti isopropoxide and Fe,
A solution of Co acetylacetonate dissolved in ethanol was prepared, and Si powder was added to these solutions, stirred, and then dried.

Further, heat treatment was performed in air at 600°C. This solution treatment/
The heat treatment was repeated several times.

The composition near the surface of these five powders was evaluated by Auger spectroscopy/depth profile by Ar sputtering in the same manner as in Example 1. As a result, the powder heat-treated at 1100°C has a 5i02 film on the surface of about 0.21
It was formed with a thickness of 1 m. On the other hand, Auger spectroscopic analysis of the organometallic solution-treated/heat-treated powder revealed that the main components of the surface layer were the respective metals and O, with a small amount of Sl also present. The thickness of these powders was adjusted to be approximately equal to the film thickness of approximately 0.2 μm in the case of only oxidation treatment by changing the number of times of solution treatment/heat treatment.

These powders and untreated Si powder for comparison
Hot press sintering was carried out at 370°C under a pressure of I 000 kg/cm2 in an atmosphere of A for 5 hours. From the obtained sintered body, a 2XIX 12mm columnar sample was cut out and its specific gravity and electrical resistance (using a tester) were measured. The results are shown in Table 2.

(Margins below) Table 2 (Characteristics of composites) As is clear from Table 2, the relative densities were around 96% for all samples, with the exception of the untreated sample, with little difference observed. On the other hand, the electrical resistance was extremely low at 0.1 Ω or less for the untreated product, whereas it was approximately 100 Ω for the 5i02-only oxide film and the oxide film containing T1 or Al.
However, in the case of an oxide film containing Co, it was 32
In the case of an oxide film containing 0Ω and Fe, it was even higher to 20j'lΩ or more. In this way, when an oxide film containing Fe or Co, which has a smaller free energy of oxide formation than Si, was used, a higher electrical resistance was obtained. Note that the coefficient of thermal expansion and thermal conductivity of these samples were both comparable to those of metal S1, and the materials had high electrical resistance.

Next, among the sample preparation conditions, the sintered density was reduced to about 92% by shortening the hot pressing time, thereby making the electrical resistance of all samples 20 MΩ or higher, and then heated to 1200°C under vacuum conditions. When heat-treated for 10 hours at
In the case of an oxide film containing
No decrease in resistance was observed.

Example 3 Al metal powder having an average particle size of about 201IIll was heat treated in air at 400°C for 2 hours to form an oxide film on its surface. On the other hand, a 0.01 mol% ethanol solution 1001 of Si ethoxide was prepared, Al powder was added to this solution, and while heating and refluxing at 70°C, a 1/3 mixed solution of water/ethanol was added until the amount of water was 0. Drop by drop until it becomes .002 mol,
The mixture was heated under reflux for 3 hours.

After completion, the product was filtered, and the resulting powder was dried at 150°C and then heat treated in air at 400°C for 1 hour. These powders were subjected to Auger spectroscopy/A in the same manner as in Example 1.
Evaluation was made by depth profile obtained by r sputtering. As a result, only Al and O were detected in the powder heat-treated in air, and an aluminum oxide film was formed.

In the latter powder treated with Si ethoxide, the surface film has A
Si was included along with l. 800 of these powders
Hot press sintering was carried out at a pressure of 1000 kg/cwt2 at °C.

From these sintered bodies, 2XIX12 mm columnar samples were cut out, and their specific gravity, electrical resistance (using a tester), and thermal conductivity were measured. As a result, the relative density of both is 97%.
However, in the sample with the aluminum oxide film, the electrical resistance was as low as about 100Ω, whereas in the sample with the film containing silicon oxide, it was 20MΩ or more. Moreover, its thermal conductivity was 180 W/m-deg, a value close to that of metal aluminum.

The inventors conducted similar experiments with various powder compositions, film thicknesses, and film qualities in addition to the above-mentioned examples, but they still chose an insulating film composition containing a component with lower oxide formation energy than the matrix metal particles. As a result, with the same insulator content, it is possible to produce a sample with an electrical resistance that is 1-2 orders of magnitude higher than that of the conventional method, and it also has high stability against heat treatment. As a result, it was possible to synthesize a composite material with excellent properties not previously available.

Even if the surface of the metal powder is completely covered with an insulator, when it is pressurized to form a compact with almost 100% density, the surface area will change and some parts will be missing the insulator film. , it is thought that the metal particles come into direct contact with each other and the electrical resistance decreases. In the method of the present invention, the oxide film itself serves to supply oxygen to the exposed metal surface due to damage to the insulation film, and by repairing the film, the composite material can be densified while maintaining insulation properties. considered to be a thing. In addition, the decrease in resistance due to heat treatment is thought to be caused by exposure of the metal surface due to sintering of the film inside the sample and contact with it due to diffusion, etc., but it is also believed that the film has a repairing effect by supplying oxygen. Therefore, it is considered to be a material that is difficult to reduce resistance.

Therefore, as in the Al/Fe2o3 system, this effect was more pronounced as the difference in free energy of oxide formation between the matrix metal particles and the film-forming metal was larger.

In this way, the inventors analyzed a composite material containing two types of materials that was produced using the conventional method of coating the surface of metal particles with an extremely thin layer of insulator and then molding it into a high density material. As a result, it was found that in the final process of densification, the insulator film is damaged due to the expansion of the surface area accompanying the deformation of the metal particles, which tends to cause dielectric breakdown. However, the present invention has been completed in which dielectric breakdown is less likely to occur, and the obtained composite sintered body is more stable against heat treatment than conventional products.

Effects of the Invention The present invention provides that the surface of particulate metal or alloy A is
The metal or alloy is substantially covered with an insulating oxide containing metal B, which has a smaller free energy of oxide formation than the metal element with the largest free energy of oxide formation among the components contained in the metal. Since the particles of A do not substantially come into contact with each other, it is possible to have both high insulation properties and high density while keeping the content of the insulator low.

Further, the present invention has the advantage that electrical resistance does not easily decrease even when subjected to heat treatment.

In particular, when a magnetic material is used as the metal, the composite material of the present invention becomes a magnetic core material with excellent characteristics.

Agent Patent Attorney Matsu 1) Tadashi Michi

Claims (1)

[Scope of Claims] (1) The surface of the particulate metal or alloy A is an oxide that is smaller than the metal element that has the largest oxide formation free energy among the components contained in the metal or alloy A. A composite material characterized in that it is substantially covered with an insulating oxide containing a metal B having a free energy of formation. (2) The composite material according to claim 1, having a relative density of 95% or more. (3) The composite material according to claim 1 or 2, wherein the metal in the form of powder particles is a magnetic material. (4) The composite material according to claim 1 or 2, wherein the metal in the form of powder particles contains Al. (5) The composite material according to claim 1 or 2, wherein the insulating metal oxide contains Fe. (6) The composite material according to claim 1 or 2, wherein the metal in the form of powder particles contains Al, and the insulating metal oxide contains Fe. (7) Form a thin layer of an insulating oxide of a metal whose oxide formation free energy is smaller than that of the metal on the surface of a powdered metal to form a composite powder, and make this powder into a composite powder. , a method for producing a composite material characterized by molding it to a relative density of 95% or more under high temperature and high pressure.