JPH02153002A - Heat treating method for flaky metal fine powder - Google Patents

Abstract

PURPOSE:To execute heat treatment at the prescribed temp. without developing aggregation and to enable the desired annealing by heating flaky metal fine powder while forming fluidized bed. CONSTITUTION:The flaky metal fine powder is supplied into a vessel 3 arranged a dispersion plate 1 composed of porous member at the lower part and piled on the dispersion plate 1. Further, non-oxidized gas is supplied from the lower part of the piled powder group through the dispersion plate 1 at the flow rate more than the min. flow rate to make the fluidized bed and the above powder group is made the fluidized bed. All or a part of the fluidized bed generated in this method made a soaking zone of the prescribed annealing temp. with heater 2. Then, it is desirable to uniformize the heating by vibrating the vessel 3 or stirring the inner part thereof. By this method, while preventing the aggregation of the fine powder, strain generated by flattening is sufficiently removed. In the case, the above flaky metal fine powder is flaky soft magnetic alloy fine powder having 0.1-20mum average particle diameter and <=1mum average thickness, the annealing thereof is executed with the above method and this can be made to <=400A/m coercive force.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for heat treatment of flat metal fine powder, and in particular, to flat metal powder having an average particle size of 0.1 to 20 μm and an average thickness of 1 μm or less, and having a soft magnetic property. The present invention relates to an annealing method suitable for fine alloy powder with excellent properties.

[Conventional technology]

In recent years, in the field of magnetic cards related to personal privacy, such as bank cards and credit cards, there has been an increasing need to coat the cart surface with a coating film made of fine powder of high magnetic permeability material for the purpose of magnetic shielding. . Such a coating powder is required to have high magnetic permeability, be a fine powder, and have a flat powder shape. This is not only necessary for ease of application and surface smoothness of the coating film, but also because the shearing force during application causes the flat fine powder to move in the flat direction where the demagnetizing field coefficient is lowest, that is, toward the card substrate. This is essential because high magnetic permeability in the in-plane longitudinal direction can be obtained by arranging them in parallel.

The specific properties of the powder required for this application include an average particle size of 0.1 to 20 μm, an average thickness of 1 μm or less, and a coercive force of 4 in a random aggregation state ignoring the demagnetizing field.
0.008/m or less.

As such powders, Fe-Ni alloys, which have high magnetic permeability and are easily plastically deformed and flattened, and Pe-5i-Al alloys, which are brittle and easily crushed, are being considered. .

As a method for producing the alloy powder, for example, JP-A-63-
No. 35701 and No. 63-35706 propose to obtain flat powder with a thickness of 2 μm or less and a thickness-to-diameter ratio of 1/lo or less by a wet ball mill method. In addition, in the case of Fe-5i-Al alloy, in Japanese Patent Application Laid-Open No. 62-238305, it is made into powder by water atomization so that the crystal grain size is 100 μm or less, and then made into a single crystal by a crusher with high energy density. A method of pulverizing into flake powder having a diameter ratio of 10 or more is shown. However, these flaky powders and flat powders are subjected to extremely large deformations due to pulverization, and therefore are provided with high coercive force due to pulverization distortion. This method is insufficient as a method for producing powder for use.

In addition, as a method for removing crushing distortion, Japanese Patent Application Laid-Open No. 58-59
In No. 268, it is mentioned in the specification that sendust powder, which is obtained from an ingot and made into a flattened form by repeated crushing and grinding processes in multiple stages, is additionally annealed in a hydrogen atmosphere if necessary. However, the coercive force of the powder is not specified, and it does not provide knowledge about a specific annealing method to improve the coercive force, so it is still inappropriate as a powder manufacturing method for magnetic shielding of magnetic cards, etc., which is the subject of this application. It is enough.

The flat fine powder with an average particle size of 0.1 to 20 μm and an average thickness of 1 μm or less, which is the subject of this application, is not only a fine powder but also has undergone severe distortion, and is annealed under the same conditions as normal bulk materials. Then, agglomeration of the powder particles, that is, an annealing phenomenon occurs, and the flat shape obtained by crushing is damaged.
Actual annealing must be performed at a low temperature at which powder agglomeration does not occur, that is, significantly lower than the normal bulk material annealing temperature of around 1100°C, and the coercive force of flat powder is a large value exceeding 400 A/m. .

[Problem that the invention attempts to solve]

The present invention has been made in consideration of the problems of the prior art, and involves agglomerating a large amount of flat soft magnetic alloy fine powder with an average particle size of 0.1 to 20 μm and an average thickness of 1 μm or less. The object of the present invention is to provide an annealing method that can reduce the coercive force to 4008/m or less without causing any damage.

[Means to solve the problem]

That is, the present invention provides a method for heat treatment of flat metal fine powder, which is characterized by heating the flat metal fine powder while forming a fluidized bed when flat metal fine powder is heat-treated, and more specifically, a flat metal fine powder heat treatment method. A method of heat treating gold S fine powder, which includes supplying a non-oxidizing gas from the bottom of the powder deposited in a container at a flow rate higher than the minimum fluidized bed speed to generate a fluidized bed made of fine powder. , is a heat treatment method for flat metal fine powder, characterized in that strain is removed while preventing agglomeration of the fine powder by making all or part of the space between the fluidized beds a soaking zone at a predetermined annealing temperature.

The present invention will be explained below using the drawings.

FIG. 1 is an outline of an apparatus for implementing the above heat treatment method. Powder is supplied and deposited on a dispersion plate 1 made of a porous material placed at the lower part of the container 3, and non-oxidizing gas is supplied from the lower part of the dispersion plate 1. As the fluid velocity of the gas increases, the flow resistance acting on the powder particles becomes equal to the weight of the powder particles at a certain flow velocity. At a flow rate higher than this, the powder particles are dynamically supported (suspended) by the gas, the powder particle layer expands, and the particles move without remaining in a fixed position. The powder bed as a whole is easy to flow and behaves like a single fluid phase, so-called fluidized bed shape B (gas flow fi
). The minimum gas velocity required to maintain fluidization is the minimum fluidization velocity. *Small fluidization rate is based on Wen et al. (C
,'1. Wen et, at: Chem.

Bng, Prog, Symp, Set, 62
．． (1966)). In other words, the minimum fluidization velocity mf for powder with a constant particle size cip is: U,,=C(ρ5−ρv) g dp”/η ・
...(1). Here, C: constant, ρ: true density of powder, ρ: gas density, g: gravitational acceleration, dp: particle diameter, η: gas viscosity.

The fluidized bed obtained by supplying the atmospheric gas at a flow rate above the minimum fluidization speed approximately set in this manner is further classified according to its fluidization state.

A schematic diagram is shown in Figure 2. In other words, a uniform fluidized state in which particles are uniformly dispersed appears at a flow rate directly above Uaf, and as the flow rate increases and exceeds the bubble generation rate Usb, bubbles are generated and a concentrated phase of powder particles occurs. Bubble fluidization state in which air bubbles rise inside ■,
A slagging state when the flow rate is further increased and the slagging rate exceeds 2π; a turbulent fluidization state consisting of a thinner dense phase and small bubbles when the flow rate is further increased; the surface of the fluidized bed disappears and all powder particles It is broadly classified into a high-speed fluidization state (■) in which water is transported by air current. In the present invention, these states (1) to (2) are collectively referred to as a fluidized bed.

According to the classification shown in Figure 2, the fluidization state shown in Figure 1 is
corresponds to the bubble fluidization state.

The dispersion plate 1 shown in Fig. 1 is made of a porous material and has the strength to support powder and the function of allowing gas to pass through.However, in order to prevent uneven flow and obtain a fluidized state, it is necessary to apply pressure at the dispersion plate 1. It is necessary to take large losses.

The necessary pressure loss ΔPd is set by adding the pressure drop ΔPf in the fluidized bed, the pressure difference ΔPr necessary to uniformly disperse gas from the gas supply port to the column to the holes in the distribution plate 1, and the like. Further, from this set value, the aperture ratio m of the dispersion plate 1 is determined, and from m, the hole diameter d is determined.

, , the number of holes N, , , can be set by the following formula (21, +3), respectively. That is, the aperture ratio m is, where: ■ "Nigas flow rate, ρ: gas density, Co: constant (determined by the Re number), m is the hole diameter d61",
Number of holes N or and cross-sectional area of the container S? π mx dor” Nor/S?
...There is the relationship (3).

Although the distribution plate 1 as a perforated plate is set according to such guidelines, the present invention is not limited to its detailed specifications.

Among the fluidized beds shown in FIG. 2, in the bubble fluidized state and in the turbulent fluidized state shown in FIG. 2, a large number of particles are released from the bed surface, and as shown in FIG. A thin layer called a freeboard portion is formed. Powders with large particles and diameters immediately return to the fluidized bed, but small particles reach higher forces. The particle concentration in the freeboard decreases exponentially in the height direction from the fluidized bed surface.
rt Disengaginglleight) or more, it becomes a constant value. Even if the gas outlet is provided at a position higher than the TDH, small-diameter powder whose terminal velocity is smaller than the gas flow velocity flows out of the system and is collected in the tank of the powder collection system 4 at the upper right side of FIG. 1. It is also possible to circulate the powder further into the system from the powder collection system.

In the case of a fluidized bed with a constant height of the fluidized bed, that is, in the case of classifications ■ to ■, This can be done by externally heating the part with a heater 2 to maintain the inside of the tower at a predetermined annealing temperature. Further, even in the slagging state (2) or the high-speed fluidization state (2), heat treatment can be performed if all or part of the tower is used as a soaking zone and the powder is circulated. A more preferable method is to form a turbulent fluidized bed with strong flow and a nearly constant fluidized bed height, and use this time as a soaking zone to circulate the particle layer that flies out of the system, and after processing for a certain period of time. In this method, the gas flow rate is increased to switch to the high-speed fluidization state (2), the circulation system is closed, and the powder is sequentially collected from the collection system. If it is desired to perform slow cooling, it is sufficient to heat the material for a certain period of time using a heater, and then maintain a fluidized state while circulating the material while controlling the temperature and cooling the material in the furnace. In this way, various patterns are possible for controlling the fluidization state in accordance with the annealing cycle, recovery, and circulation.

In addition, when the powder particle size becomes smaller, it is not easy to obtain the fluidized bed of ■ or ■, and it remains in the uniform fluidized state of ■.
In some cases, even the state (2) is not desirable. In this case, the purpose can be achieved by vibrating or stirring the inside of the container.

In other words, a stable fluidized state can be obtained by vibrating the material itself, by vibrating an inner cylinder provided in the main tower, by vibrating the dispersion plate, by introducing a fan and stirring internally, etc. .

The flat soft magnetic alloy fine powder having an average particle size of 0.1 to 20 μm and an average thickness of 1 μm or less, which is particularly targeted by the present invention, is, for example, Fe-8ONi-based PC permalloy, Fe-5ON
i-based PB permalloy, Fe 9.5Si-5,5A
ji-based sendust alloys, etc., and these are ordinary bulk materials that are annealed in a hydrogen atmosphere to remove impurities.
It is often done at around 000°C. As mentioned above, when these flat-shaped fine powders are placed in a container and annealed, they aggregate and cause a sintering phenomenon, which damages the flat shape obtained by pulverization, making it difficult to maintain the flat shape. is 500℃
As a result, the coercive force of the flat powder exceeded 400 A/m.

According to the present invention, generation of a fluidized bed by flat fine powder;
According to the method of heat treating flat fine powder by maintaining the fluidized bed at a predetermined annealing temperature, the average particle size is 0.1 to 20μ.
m, Fe-Ni permalloy with an average thickness of 1 μm or less, e
e Si Aj! Sendust alloys, etc. can be annealed at the heating temperature of 1000°C, which is normally used for the bulk material, and at a high temperature close to this, while maintaining the shape of flat fine powder without agglomerating the powder, improving coercive force. Great effect.

In the present invention, there is no restriction by the annealing atmosphere, and non-oxidizing gases such as hydrogen gas, which is most common, nitrogen gas, Ar gas, ammonia decomposition gas, and various mixed gases can be used. Moreover, although the heat treatment has been explained above specifically as annealing, it goes without saying that the present invention can be applied to heat treatments other than annealing.

〔Example〕

The present invention will be explained below based on examples. The following examples were carried out using the apparatus shown in FIG.

Example 1 An alloy powder containing 79.0% Ni, 4.8% Mo, and the balance being essentially Fe and having an average particle size of 15 μm was obtained by water atomization, and was ground with an attritor to obtain an alloy powder with an average particle size of 14 μm and an average thickness of 0.5 μm. It was made into a flat fine powder of 7 μm. The coercive force of the as-pulverized powder (coercive force in a random aggregation state ignoring the demagnetizing field) was about 300 OA/n+.

This powder was annealed at various temperatures in a turbulent fluidized bed (Fig. 2 ■) using a dry hydrogen stream, and the shape and coercive force of the powder were investigated. The results are shown in Table 1. Even when the temperature was raised to 1000°C, the initial flat fine powder shape was maintained, while the coercive force decreased significantly as the temperature increased, reaching 96^ at 1000°C.
Improved to /111.

For comparison, the powder was placed in a dense A It zOx box and annealed without fluidizing, but at 600°C.
The agglomeration tendency starts at 800℃, forming aggregates of about 25 μI.
Then, it was pre-sintered into a porous shape.

Table 1 Example 2 In the same manner as in Example 1, an alloy powder of 9.6% 5t-5.7% Al-balance substantially Fe with an average particle size of 9 μm was obtained by water atomization, crushed with an attritor, and the average particle diameter was 9 μm. Particle size 2μm,
It was made into a flat fine powder with an average thickness of 0.2 μm. The as-ground coercive force was approximately 720 OA/m.

This powder was made into a bubble fluidized bed by adding a dry hydrogen stream and vibration of the container (vertical amplitude 1 ml, frequency 60112), annealed at various temperatures, and the shape and coercive force of the powder were examined. The results are shown in Table 2.

Even when the temperature is raised to 700°C, the initial flat fine powder shape is maintained, but a tendency to agglomerate is observed from 800°C.
At temperatures above 0°C, the proportion of aggregates with an average diameter of 40 μm was high, making it impossible. However, it can be heated to 700° C., and the coercive force is reduced to 380 A/m, demonstrating a high level of soft magnetism never seen before for flat fine powder.

For comparison, the density A I! The powder was placed in a 03 box and annealed without fluidizing, but at 400°C.
It aggregated into aggregates of about 20 μI, and was pre-sintered into a porous shape at 500°C.

Table 1 The flat fine powder with excellent soft magnetic properties annealed in this way is most suitable as a coating powder for coating a coating film on a magnetic card requiring magnetic shielding. In addition to magnetic cards, it is also useful for coating paints on parts and housings, fillers for composite materials with rubber and plastics, etc.

〔Effect of the invention〕

As described above, according to the present invention, the average particle size is 0.1 to
20. cu++, Fe-Ni alloy with an average wall thickness of 11 Jm or less, Fe-3i-An! It is possible to annealing high magnetic permeability alloy powder such as alloys without agglomeration and at an annealing temperature that is the same as or close to that of bulk materials of ordinary equivalent alloys, while maintaining the initial flat shape. A flat soft magnetic alloy fine powder having porous soft magnetic properties can be obtained, and its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an apparatus for carrying out the present invention, and FIG.
The figure is a classification diagram of fluidized beds for carrying out the present invention. Figure 1 h”Sufu’ 711 people

Claims (5)

[Claims] 1. 1. A method for heat treatment of flat metal fine powder, which comprises heating the flat metal fine powder while forming the fine powder into a fluidized bed. 2. A method of heat treating flat metal fine powder, the method comprising: supplying a non-oxidizing gas from the bottom of the powder group deposited in a container at a flow rate higher than the minimum fluidized bed speed to form a fluidized bed consisting of the powder group. A method for heat treatment of flat metal fine powder, characterized by removing distortion while preventing agglomeration of the fine powder by forming all or part of the space between the fluidized beds into a soaking zone at a predetermined annealing temperature. . 3. 3. The method of heat treating flat metal fine powder according to claim 2, wherein the powder group is deposited on a porous member provided in a lower part of the container. 4. The method for heat treatment of flat metal fine powder according to claim 2 or 3, wherein the flat metal fine powder is flat soft magnetic alloy fine powder having an average particle size of 0.1 to 20 μm and an average thickness of 1 μm or less. 5. 5. The method for annealing flat metal fine powder according to any one of items 2 to 4, wherein the container is vibrated or the inside of the container is stirred.