JPH05294753A - Production of ferrite porous body - Google Patents

Abstract

PURPOSE:To uniformly distribute uniform spherical pores having <=10mum diameter and to facilitate the control of pore diameter and porosity. CONSTITUTION:A sublimable material which is readily soluble in an org. solvent but slightly soluble in water., e.g. camphor is perfectly dissolved in the org. solvent and the resulting soln. is jetted into water from pores to deposit fine particles of the sublimable material. The fine particles are added in the wet state to ferrite powder and they are mixed, compacted and fired. The soln. is preferably jetted into about >=10 times as much water as the soln. and about <=0.5% surfactant is preferably added to the water before jetting. The density of the resulting ferrite porous body is reduced in accordance with the increase of the amt. of camphor added.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention provides a ferrite porous body in which a myriad of uniform spherical pores having a diameter of 10 μm or less are uniformly distributed by adding fine particles of a sublimable substance such as camphor. The present invention relates to a manufacturing method. The ferrite porous body obtained by this technique is useful, for example, as a ferrite electromagnetic wave absorber.

[0002]

2. Description of the Related Art Various methods for producing a porous sintered body using ceramic powder have already been proposed. As one of the methods, there is a method in which particles of a substance that decomposes and burns and scatters during firing are added to ceramic powder in advance and mixed, and the mixture is molded and fired. During the firing, these particles are decomposed and burned to be gasified and scattered to form pores in the sintered body. As the particles of the decomposable / combustible substance, various organic substances (for example, stearic acid), synthetic resin powders, or rice husks are used.

[0003]

In the case of a ferrite porous body used as a radio wave absorber or the like, it is an important requirement that it exhibits desired magnetic properties. Decomposition during the firing process
If the combustible substance is not completely decomposed and remains in a small amount, it causes deterioration of magnetic properties. However, it is difficult to completely remove conventional decomposable / combustible substances, and heat or gas generated during decomposition / combustion causes blisters or cracks in the compact (sintered body) or prevents sintering. I was afraid. Therefore, it was difficult to apply it to applications such as ferrite that requires electromagnetic characteristics.

From this point of view, it is desirable to use a substance that volatilizes smoothly in the initial stage of the firing step or in the step before the firing step. Therefore, the use of camphor powder, which is easily volatilized, can be considered. This is because camphor is very easy to sublime, and sublimation gas has low toxicity and has little effect on the human body. However, it is difficult to finely crush camphor by the usual method. Generally, commercially available ground camphor has a particle size of several tens to one hundred and several tens of μm,
The particle size is widely distributed and the shape is irregular. Therefore, even if the above-mentioned ground camphor product is added to the ferrite powder, the pore diameter is widely distributed to several tens to hundreds of tens of μm, and the pores having fine and uniform particle diameter are uniformly distributed. Is impossible.

An object of the present invention is to provide a method for producing a ferrite porous body in which uniform spherical pores having a diameter of 10 μm or less can be uniformly distributed and the pore diameter and porosity can be easily controlled. That is.

[0006]

According to the present invention, a sublimable substance that is easily dissolved in an organic solvent but is difficult to be dissolved in water is completely dissolved in the organic solvent, and the solution is jetted into the water through the pores. In this method, fine particles of the sublimable substance are precipitated, the obtained fine particles are added to the ferrite powder, mixed, and fired after molding.

For example, camphor is preferable as the sublimable substance, and in this case, alcohol (methyl alcohol or ethyl alcohol) can be used as the organic solvent. It is preferable that the camphor fine particles precipitated in water are filtered and added to the ferrite powder in a wet state in order to prevent aggregation. When jetting the camphor solution into water, it is preferable to jet into the water about 10 times or more the amount of the solution,
It is also preferable to add a surfactant to water in an amount of about 0.5% or less in advance.

The sublimable substance used in the present invention is easily dissolved in an organic solvent but hardly dissolved in water, and has a low toxicity of sublimation gas. From that point, in addition to camphor, naphthalene, paradiculebenzene and the like may be used.

The sublimable substance is completely dissolved in the organic solvent. Of course, the concentration of the solution should be within the solubility limit of the sublimable substance. This solution is ejected from the pores into water in an amount twice or more that amount. The fine particles thus deposited are mixed with the ferrite powder, shaped, and fired. There is no particular limitation on the material of the ferrite powder used. The addition ratio of the fine particles of the sublimable substance to the ferrite powder is appropriately adjusted according to the required porosity of the ferrite porous body. By increasing the addition ratio, it is possible to make the pores continuous. Since the size of pores and the distribution of pore diameters are determined by the fine particles of the sublimable substance to be added, they can be controlled by preparing the fine particles. The ferrite powder and the sublimable fine particles may be mixed by dry mixing or by wet mixing in which a small amount (10% by weight or less) of water is added to facilitate mixing. Alternatively, a large amount of water may be added to form a slurry and mixed.

For the molding of the mixture, any conventional method can be adopted. In addition to press molding and extrusion molding using a mold, injection of slurry into a gypsum mold may be used. A small amount of a binder such as PVA (polyvinyl alcohol) may be added in order to increase the strength of the molded product, but camphor itself does not need to be added particularly because PVA or the like itself functions as a binder. ..

When camphor is used, it is very easy to sublime, so it is advisable to carry out a decamou process of heating to about 130 ° C. in advance. At this time, since the present invention is sublimation rather than thermal decomposition, it is possible to collect and reuse camphor by collecting sublimation gas, cooling it, and passing it through water. After the decamping treatment, the porous compact may be fired based on the firing data of the ferrite powder used.

[0012]

When a solution of a sublimable substance is jetted into water, the sublimable substance is sparingly soluble in water. Therefore, when it is jetted into water, its solubility limit is exceeded, so that precipitation immediately occurs. The particle size of the fine particles of the sublimable substance to be precipitated can be controlled by selecting the diameter of the fine holes to be ejected and the ejection speed. The smaller the pore size and the higher the ejection velocity, the smaller the particle size of the fine particles. As a result, fine particles having a much smaller particle diameter (10 μm or less) and a uniform particle diameter can be obtained as compared with those on the market. Moreover, the shape of the fine particles becomes close to a sphere. If an appropriate amount of surfactant is added to water in advance, the dispersibility of fine particles to be precipitated will be further improved.

When an appropriate amount of fine particles of the sublimable substance is added to the ferrite powder, mixed, shaped and sintered, the sublimable substance is volatilized in the initial stage of the firing process or in the preheating process before firing, resulting in a molded body. Voids corresponding to the shape of the fine particles are formed in the portion where the sublimable substance was present. For example, camphor has a melting point of 178 ° C and a boiling point of 204 ° C, but when the mixture with ferrite powder is actually heated, 130 ° C
Sublimate almost completely. For this reason, the removal of camphor is much easier than other conventionally used organic substances (such as stearic acid), and since it is sublimated rather than decomposed, its recovery and reuse are possible.

In the present invention, the fine particles of the sublimable substance have a spherical shape with a diameter of 10 μm or less and can be uniformly mixed, so that the pores in the sintered ferrite also have a diameter corresponding to that. Uniform spherical pores of 10 μm or less are formed,
A ferrite porous body in which the innumerable holes are uniformly distributed can be obtained.

[0015]

Example Commercially available ground camphor (C ₁₀ H ₁₆ O) pulverized product (having a particle size widely distributed in the range of several tens to several hundreds of tens μm) is completely dissolved in industrial alcohol. Of course, the concentration of the solution is below the solubility limit of camphor. This solution was ejected from a thin injection needle 10 having an injection needle shape (inner diameter of about 0.5 mm) as shown in FIG. 2 into water in an amount 10 times or more the amount of solution. As a result, camphor fine particles were deposited. Then, the fine particles dispersed in water were filtered and separated. The resulting fine particles of camphor have a particle size of 10 μm.
It was close to a sphere at about m.

A mixture sample was prepared by adding the camphor fine particles to the ferrite powder in the range of 10 to 40% by weight. At the time of addition, a state in which the camphor fine particles remained wet (a state in which the filter body was drained to such an extent that water droplets did not drop) was used. When completely dried,
This is because the aggregation of fine particles has occurred. To the above mixture sample, 10% by weight of water was further added and wet-mixed. This mixture was allowed to stand at room temperature for about 30 minutes, and then it was molded into a cylindrical shape using a mold. And it baked at 1245 degreeC for 30 minutes in an electric furnace. FIG. 1 shows the relationship between the amount of camphor added and the density in the fired ferrite. The density of the sintered ferrite decreases as the amount of camphor added increases. This shows that the porosity can be controlled by the amount of camphor added. The addition amount of 0% by weight is the case of a sample that was similarly molded and baked without adding camphor. When the ferrite porous body was observed with an electron microscope, the pore diameter was uniform at about 10 μm, and the pores were uniformly distributed throughout. Moreover, the shape of the pores was also uniform and was close to a sphere.

For comparison, a commercially available crushed camphor product was added to the ferrite powder as it was, mixed and molded and fired in the same manner as in the above-mentioned method. It was distributed over a wide range of hundreds of tens of μm and had an irregular shape. Further, when the addition amount was small, the distribution of pores became non-uniform.

[0018]

As described above, according to the present invention, a substance that easily sublimes such as camphor is once dissolved and re-precipitated.
Fine particles of a sublimable substance having a uniform particle diameter are obtained, and the particles are spherical and the particle diameter can be controlled. The fine particles can be uniformly dispersed in ferrite. Therefore, uniform spherical pores with a diameter of 10 μm or less can be obtained. A ferrite porous material having a uniform distribution can be easily manufactured. In the present invention, the pore diameter can be easily controlled by selecting the pores, the pore diameters can be made uniform, and the porosity can be easily controlled by the addition amount. There is an effect that can be easily realized.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of camphor added and the ferrite density.

FIG. 2 is a sectional view showing an example of a nozzle for ejecting a solution.

[Explanation of symbols]

 10 Jet nozzle

Claims (3)

[Claims] 1. A sublimable substance which is easily dissolved in an organic solvent but is hardly dissolved in water is completely dissolved in an organic solvent, and the solution is jetted into water from pores to form fine particles of the sublimable substance. A method for producing a ferrite porous body, in which fine particles obtained by precipitation are added to ferrite powder, mixed, and fired after molding. 2. The method according to claim 1, wherein the sublimable substance is camphor, the organic solvent is alcohol, and the camphor fine particles precipitated in water are filtered and added to the ferrite powder in a wet state. 3. The method according to claim 1, wherein the solution is jetted into water containing 0.5% or less of a surfactant.