JP2584035B2 - Method for producing zinc oxide whiskers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a zinc oxide whisker aggregate having a huge tetrapod-like structure.

2. Description of the Related Art At present, zinc oxide used as a general industrial material is often based on the so-called French method, and is an aggregate of gang-like particles having various particle sizes, especially shapes. There is also a method of forming fine and short needle-like crystal grains with a high yield (for example, Japanese Patent Publication No. Sho 60-5529). This method is an improvement of the above-mentioned French method. This is to cool, so that a giant crystal is not formed, and it becomes a needle-like crystal having a minute dimension (length: 0.1 to 15 μm).

Needle-like crystals of such dimensions are approximately two orders of magnitude smaller in size in comparison with various commercially available industrial whiskers.
For this reason, the reinforcing effect on the metal, ceramic, resin, and the like, which is a common feature of the whiskers, is not much different from the level of the gang-like zinc oxide, and no remarkable whisker effect is observed. Whisker, which is a fiber-shaped single crystal, has much higher mechanical strength than the same material of the same material, and is attracting attention as a reinforcing material to obtain high mechanical strength by mixing it with other materials. At present, industrial whiskers of metals, metal oxides, metal carbides, metal nitrides and the like are commercially available. As for zinc oxide, there is an example of a whisker having a length of mm order (Japanese Patent Application Laid-Open No. 50-5597). This is a simple needle-shaped body, and a zinc alloy is used. It is only a laboratory study that contains impurities, requires a substrate to be provided at a position away from the source material during growth, low yield, complicated equipment, long operation time, etc. There are many things.

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a method for obtaining an aggregate of large crystals of zinc oxide having dimensional properties of industrial Wistar grade or larger. The present invention also provides a novel method for producing a zinc oxide whisker aggregate having a giant tetrapod-like structure.

Means for Solving the Problems A method for producing a zinc oxide whisker according to the present invention is characterized in that a zinc powder having an oxide film on its surface is subjected to a heat treatment in an atmosphere containing oxygen to generate zinc oxide. It is a feature of the conventional vapor-phase whisker manufacturing method that the place where the raw material is placed and the whisker generation and growth sites are separated and divided, as in the above-mentioned French method and the method for manufacturing a simple needle crystal. In the present invention, however, a container having an open surface is used. The surface corresponding to the opening surface of this container is defined as a bottom surface, and the zinc powder is placed on the bottom surface, and the container is placed in a preheated furnace and heated and oxidized in an atmosphere containing oxygen such as air. By carrying out the above, a novel giant tetrapod-like zinc oxide whisker polymer which is completely different from the conventional one can be produced, and the produced whiskers are characterized in that they are produced by being deposited on the upper layer in this container. In addition, in the lower part of the whisker deposition layer of the above-mentioned container, a gang-like zinc oxide layer as a by-product is characterized in that it is deposited separately from the whisker layer.

In this case, it is desirable that the zinc powder is sprayed in a layer on the bottom of the container, and the raw material charging method is also possible, in which the container is heated in advance in a furnace and then the zinc powder is sprayed on the container bottom. It is.

In addition, it is essential that the raw material zinc powder has an oxide film formed on the surface, and the formation of the oxide film is often achieved at the time of powder production. Although the former is partially porous, the former tends to be thicker, and the latter often has a denser and thinner film.

Further, as a preferable method for forming an oxide film on the zinc powder or increasing the film thickness, there is a method in which the zinc powder is crushed in the presence of water and matured as described later.

The zinc oxide whisker obtained by the method of the present invention comprises a central nucleus and needle-like crystal parts extending in four different directions from this core, and the diameter of the base of the needle-like crystal part is 0.7 mm.
針 14 μm, and the length from the base to the tip of the needle-like crystal part is 3-200 μm. The needle-shaped crystal part has three axes or two.
Although some of the shafts are also mixed, these are the result of contact with other whiskers during or after growth, a part of which is broken, or the growth stops. In addition, some tetrapods are attached to other parts of the complete tetrapod due to the contact during the growth. According to the manufacturing method of the present invention, a tetrapod-like one is mainly used, although other shapes, that is, plate-like crystals may adhere in a needle state.

The present inventor has developed a giant tetrapod-like whisker aggregate that has a needle size that is extremely thin and short as described above, and that has never been realized before, and is dramatically huge from the conventional crystal having the secondary growth portion attached thereto. As a result of various experimental studies to express this, it was recognized that there was an extremely large factor in the production method.

More specifically, as in the conventional method, the selection of firing atmosphere conditions using molten zinc metal from an ingot, reduced zinc, pure metal zinc from a zinc compound, or the like allows the above giant tetrapod-like whisker to be developed. In order to achieve this, it is essential to use zinc metal powder, especially zinc powder having an oxide film on the surface, and to use the above-mentioned container using this powder. By adopting the heat oxidation method, a new giant tetrapod-like zinc oxide whisker aggregate appears in the upper layer by a reaction method in which whiskers are deposited on the upper layer of the container and gang-like zinc oxide powder is deposited on the lower layer. confirmed.

More specifically, in the production method of the present invention, the oxide film portion of the zinc metal powder having an oxide film on the surface shows sealing properties against zinc vapor and smoke from the internal zinc metal portion. In other words, the powder having an oxide film with a high sealing degree suppresses the generation of steam and smoke in a lower temperature range than that of a powder with a low sealing degree, and the generation of high-concentration zinc smoke and steam at a stretch in a high temperature range, and the following oxidation reaction occurs. Thus, the zinc oxide whiskers of the present invention are expressed. Another effect of the oxide film is to generate high-concentration zinc smoke and vapor without melting and melting the zinc metal parts with each other.

That is, this oxide film has a role of controlling the generation of zinc smoke and vapor from the inside. Thirdly, it was simultaneously confirmed that the zinc oxide portion of the film played a role of a substrate for whisker growth. The above-mentioned degree of sealing refers to the degree of sealing vapor and smoke from zinc metal inside the powder on the surface. This varies depending on the thickness and structure of the oxide film, the volume ratio between the metal portion and the oxide film portion, and the like.

In particular, the thickness and texture of the oxide film are often achieved during the production of metal powder. That is, a thick and somewhat porous oxide film can be obtained from the material obtained through the molten zinc powder unless otherwise controlled. Conversely, in a system pulverized as a solid, the film thickness is small and a very dense one can be obtained. In addition, the uniformity of the film thickness is better in the former case, but in the latter case, since the shape is slightly complicated and the powder form has irregularities, the film thickness is often non-uniform. In the former case, if the film thickness is too large, the surface becomes weak and cracks may occur to cause defects. In addition, in the particle system having such an oxide film, a defect often occurs in the film due to dislocation or other factors other than the above conditions.

Next, in order to repair the deterioration of the sealing properties such as defects and cracks of the film and to increase the film thickness, crushing and aging treatments are performed. This processing selectively confirmed that the above-mentioned defect portion deposited oxide on the film defect portion.

Further, these zinc powders will be described in detail. Those having a particle diameter of 0.1 to 500 μm can be used, and among them,
10-300 μm gives the best results. These metallic zinc powders are powders obtained by spraying zinc wire, zinc rods or zinc powders into the air by a gas melting method, a gas melting method, a gas powder method, an electric (arc) melting method, a plasma jet method or the like. ,
There are powders obtained by powdering molten metal, that is, powders obtained by a granulation method and an atomizing method. Also, there is a method by mechanical pulverization, that is, a method in which a metal ingot is cut or coarsely pulverized by a jaw crusher or a gyratory crusher and further crushed again. There are a mill method and a vortex mill method. Further finer powders include powders obtained using a hammer mill, a cutting mill, a micronizer or the like. It is also possible to use zinc powder obtained by electrolysis, evaporation of metal, physical operation using a coagulant, or chemical operation using a chemical reaction. Normally, powders manufactured by the above-described methods are manufactured so that an oxide film is not formed on the surface of the powder, but when used in the present invention, it is effective if an oxide film is formed on the surface. Therefore, it can be produced in an oxidation-promoting atmosphere such as in the presence of moisture or in a high oxygen concentration (such as in the air) and high humidity. Also, a good powder can be obtained when producing under high temperature and high mechanical pressure. In addition, even if the above-described zinc powder production method is adopted, when an oxide film is insufficiently formed in terms of sealing properties, or when a powder production method in which an oxide film is not formed to an effective degree is employed, the following preferable method is used. A method is adopted.

First, as a mechanical treatment in the coexistence of water, the particles are treated with a mortar-type crusher, roll, or the like, and pressure is applied to the particles. In addition, it can give perfect results in any particle size for more than 24 hours in water, especially 76 hours. Aging temperature is 20 ℃
It is preferable to keep the above. The formation of an oxide film can be formed only by a chemical reaction such as aging without relying on the mechanochemical reaction described above, but the latter usually takes too much time, and the former has a greater effect in improving the sealing degree as described above. .

As described above, the factors of the formation, increase, and growth of the oxide film are various, but when summed up, (1) application of mechanical pressure, (2)
Oxidation reaction in water or under high humidity, (3), (1)
The synergistic effect of (2) (mechanochemical reaction), (4) oxygen concentration, (5) temperature effect, etc. are related. When evaluated from the size of the whisker to be generated, especially the length of the needle-shaped portion, the time according to the above (3) greatly affects. That is, the effect is large in a short time.

If the crushing and aging time in the coexistence with water is long, the whisker size tends to increase due to the improvement in the sealing degree of the oxide film of the raw material powder.

The oxide film on the powder suppresses the release of zinc from the metal zinc portion in the low temperature range and also suppresses the transfer of oxygen to the inside by improving the sealing degree. Therefore, sufficient zinc vapor and smoke density are provided during single crystal growth. The crystal size is significantly different from that of the conventional gas-phase method and is remarkably large.

Next, it is dried after aging. This drying may be achieved as long as the powder surface can be drained, and it is preferable to dry the powder so as to prevent the adverse effects at the beginning of the transition to a high temperature in the next firing step, that is, to such an extent that crucible cracking and powder scattering do not occur. .
For this reason, it can be performed in a temperature range from air drying to a high temperature at which the zinc powder does not melt.

Next, the dried zinc powder is sprayed on the bottom of the heat-resistant container used in the present invention, baked and oxidized. The container is metal,
It is obtained from a material such as carbon or porcelain (alumina) and has an opening surface corresponding to the bottom.

In addition, the above-mentioned materials include those obtained from a nonporous and dense surface and those made of a porous material. Specifically, the case where these containers are crucibles is also included. Next, the container in which the raw material is disposed at the bottom is guided into a furnace holding a preheated atmosphere containing oxygen, followed by firing and oxidation. The furnace temperature is 700 ~ 1300 ℃,
Among them, heating at 900 to 1100 ° C. gives good results at any particle size.

Also, holding the crucible in the furnace in the above temperature range,
Preferable results are also obtained by feeding the adjusted powder, spraying and firing. The firing time is suitably from 120 to 10 minutes at 700 to 1300 ° C, and from 90 to 10 minutes at 900 to 1100 ° C. The heating and sintering may be usually performed in air, but a preferable result is obtained by using a gas or oxygen gas in which the mixture ratio of nitrogen and oxygen is adjusted.

Particularly in the initial stage of the thermal oxidation, the heated zinc powder jumps up from the corresponding portion of the container to the opening, and falls from the vicinity of the opening to the bottom. By repeating this, the oxidation reaction and whisker growth proceed, and the whisker aggregate of the present invention is gradually deposited on the upper layer of the container, and the gang-like zinc oxide powder is deposited on the lower layer.

As described above, in order to achieve the production method of the present invention, a zinc powder having a sealing oxide film as described above is essential.
This can form a sealing oxide film by various powder production methods and the control of the conditions, and can be completed by crushing and aging treatment in the presence of water.

This fact was confirmed by X-ray diffraction and electron microscope observation. In addition, the oxide film formed in this way or these treatments have a special effect on the firing step.

That is, immediately after the zinc powder is manufactured by a good method that does not undergo oxidation, there is no formation of an oxide film, or there is only an extremely thin and weak film that cannot be detected by X-ray diffraction. In the firing under the above conditions, the particles do not rise and fall evenly, resulting in uneven firing,
Even when the temperature and the oxygen concentration are adjusted, a system in which zinc oxide having various colors and unburned metallic zinc coexist is generated, and whiskers are not generated.

On the other hand, in the case of zinc powder with a grown sealing oxide film, high-temperature sintering proceeds uniformly and completely to grow into giant tetrapod-like whiskers with extremely high yield, and the oxide in the film part is in a layered shape Generates as zinc oxide.

When the zinc powder is completely covered with the oxide film as described above, the tetrapod-like whiskers grow completely, and the number of secondary growth portions, plate crystals, and the like is reduced in shape. For this reason, an oxide film is formed at the time of manufacture, and in a system in which the formation of a film is further promoted by crushing and aging, a whisker aggregate having a good shape and size can be obtained. However, the sealing degree of the film cannot be uniquely determined only by the film thickness as described above,
In particular, the size and size vary depending on the volume ratio (depending on the particle size) of the tissue metal part of the film. For this reason, it is possible to obtain the tetrapod-like whisker of the present invention even when an oxide film is locally formed, but the shape and the yield are considerably low.

In addition, during sintering, the whisker generation system rapidly increases in volume compared to the apparent volume of the processed powder, but the appearance of whiskers outside the source part, which is usually observed in normal vapor phase epitaxy, Basically, most are not of the growth type, but are of the volume increasing type which is continuously generated and grown in the material setting portion.

Examples Examples of the present invention will be described below.

Example 1 A zinc wire having a purity of 99.99% was sprayed in an oxygen-nitrogen mixed gas atmosphere having an oxygen concentration of 27% by a spraying method using an arc discharge method. The temperature of the atmosphere was set at 40 ° C.

The zinc powder was recovered, classified into a particle size of 150 to 300 μm, dried again at 150 ° C. for 24 hours, and provided for firing. 120 g of this powder was sprayed on the bottom of a crucible made of porous alumina porcelain as a container. This alumina crucible is rectangular and 20c wide
m, length 35 cm, height 15 cm, one side of the wide area is an opening. The powder was evenly sprayed on the bottom surface corresponding to the opening surface in a thickness of 3 mm. This container was directly introduced into a furnace maintained at 960 ° C. in advance, and subjected to a heat treatment in an air atmosphere for 35 minutes. As a result, a somewhat yellow band-like zinc oxide was formed in a layer in the lower part of the container, and a giant tetrapod-like zinc oxide whisker aggregate having an apparent bulk density of 0.11 was formed in the upper part. The whisker layer slightly overflowed outside the container, but the main reaction took place in the container, and the oxidation whisker generation reaction continued while repeating the development in which the high-temperature zinc powder particles in the initial stage of the reaction rise and fall down to the distance of the opening. did. At this time, there may be some overflow outside the container as described above, but the main body of the reaction is performed in the container,
Most of the product deposited in the vessel.

88% of the above whisker aggregates in the generated zinc oxide
And the remaining 12% was zinc oxide. An electron micrograph of the obtained zinc oxide whiskers is shown in FIG.

A tetrapod-like crystal composed of a nucleus and needle-like crystal parts extending from the nucleus in four different directions is clearly recognized. Plate-like crystals were also observed. In any case, according to the above method, giant tetrapods account for 85% or more. FIG. 2 shows an X-ray diffraction diagram of the whisker.
All show zinc oxide peaks, and the results of electron diffraction
It showed single crystallinity with few transitions and lattice defects. In addition, the content of impurities is small, and as a result of atomic absorption analysis, zinc oxide is 99.97
%Met.

Example 2 The same pure zinc wire as in Example 1 was sprayed by the same thermal spraying method. Immediately after that, the powder was recovered, 550 g of ion-exchanged water was added to 1 kg of the powder, and the mixture was stirred with a mortar-type mortar for 25 minutes. Do
Next, it was left to mature in water at 20 ° C. for 75 hours. The amount of water at the time of standing The water level was kept about 1 cm from the powder layer and stored in air. After leaving in water, drying at 130 ° C for 3 hours
Remove moisture from powder. Next, this powder was placed in a porous alumina container and sprayed on the bottom surface. The container is 40 cm wide, 50 cm long,
The height is 30 cm, and one side of the wide area is an opening.
In the powder spraying method, 200 g of the above zinc powder was uniformly sprayed with a thickness of 3 mm or less. This vessel was directly introduced into a furnace maintained at 970 ° C. in advance, and calcined and oxidized for 30 minutes. The state of the deposit and the behavior of the zinc particles during the reaction were the same as in Example 1. The bulk density of the whiskers in the upper layer was 0.09 giant tetrapod-like zinc oxide whisker aggregates. Ratio is 84
%Met. An electron micrograph of the obtained zinc oxide whiskers is shown in FIG. 89% of 4-axis tetrapods
Account for the above. The results of X-ray diffraction and electron diffraction are shown in Example 1.
Was similar to 99.99wt zinc oxide by atomic absorption spectrometry
% Or more.

Example 3 A powder obtained by mechanical pulverization was used. Metal having a purity of 99.99% or more was cut, coarsely pulverized 5 times with a show crusher, and finely pulverized 10 times with a stamp mill. All performed in air. Particles having a particle diameter of 50 to 300 μm were obtained by classification. The firing temperature was 970 ° C. in a nitrogen mixed gas atmosphere of 25% oxygen. The time was 35 minutes. Container is made of silicon carbide, 20c wide
It is a rectangular parallelepiped of m, 40cm in height and 20cm in height. All other steps were the same as in Example 1. A whisker with an apparent bulk specific gravity of 0.1 was obtained in an amount of 84% by weight, and 16% by weight of the whisker was a reticulated zinc oxide. An electron micrograph of this whisker is shown in FIG. 81% of 4-axis tetrapods
Met. X-ray and electron diffraction results were the same as in Example 1. Atomic absorption spectroscopy of whisker shows 99.97 zinc oxide
%Met.

Example 4 A powder was obtained by mechanical pulverization in the same manner as in Example 3. Further, 500 g of ion-exchanged water is added to 1 kg of the powder, and the mixture is stirred for 10 minutes in a mortar-type grinder, and then left in water at 25 ° C. for 90 hours for aging. After standing in water, the powder was dried at 150 ° C. for 12 hours to remove water from the powder. The powder thus adjusted was fired in the same manner as in Example 3. The resulting whiskers had a bulk specific gravity of 0.09, yielding 75% by weight, and 25% were dandelion-shaped zinc oxide powder. An electron micrograph of this whisker is shown in FIG. Those with four-axis tetrapods showed 92%. X-ray,
The result of electron beam diffraction was the same as in Example 1. Atomic absorption analysis of whiskers indicated that zinc oxide was 99.99% by weight. The vessel was used in the same reaction mode as in Example 3.

Example 5 A spherical zinc powder obtained by a volatilization and condensation method was used. 99.97% by weight of zinc ingot was put in a porcelain container and kept at 970 ° C. to evaporate zinc and condense vaporized components in air at room temperature. The particles having an average particle size of 7.5 μm were obtained by classification. This zinc powder was fired in the same manner as in Example 1. The firing container was made of silicon carbide having the same dimensions as in Example 1, and was fired in the same manner as in Example 1. However, the firing temperature was 990 ° C. for 25 minutes. The atmosphere was air. The behavior of the zinc particles during the reaction is shown in Example 1.
The product deposition was similar.

92% by weight was obtained at a bulk specific gravity of the produced whiskers of 0.09. The others were gang-like zinc oxide. An electron micrograph of this whisker is shown in FIG. 90 for 4-axis tetrapod
% Or more. In addition, the size of the needle-shaped part was smaller than that of Example 4. The results of X-ray, electron diffraction and atomic absorption analysis were the same as in Example 1.

Example 6 The zinc powder used in Example 5 was used. 1 kg of this powder to 5
It was thrown into 50 ml of water and mixed for 5 minutes with a crusher. Then 30 ℃
And aged in water for 91 hours. Thereafter, drying was performed at 110 ° C. for 24 hours to remove water. The powder thus adjusted was oxidized under the same conditions as in Example 5. The resulting whiskers had a bulk specific gravity of 0.09 and were obtained at 84 wt%, with the balance being zinc oxide. An electron micrograph of the whiskers is shown in FIG.
The ratio of the tetraaxial tetrapods was 95% or more. As in the case of Example 5, the size of the needle-like portion was slightly smaller than those of the others. The results of X-ray, electron diffraction and atomic absorption analysis are also shown in Example 1.
Was similar to

 The above examples are summarized in the following table.

Effects of the Invention According to the production method of the present invention, zinc oxide whiskers in a giant tetrapod shape can be obtained. In addition, as a production method, as a raw material, select the particle size of zinc powder having an oxide film on the surface, adjust the sealing property of the oxide film, mechanically crush in water, improve the sealing degree of the film by aging in water, After drying after the thickening process, whiskers are deposited in the container in the baking step after spraying the raw material powder on the bottom of the container with an open surface on one side, and when performed in an atmosphere containing oxygen, the process conditions By setting, various sizes of tetrapod-like zinc oxide whiskers can be obtained.

Since the whisker obtained in the present invention has a three-dimensional structure without anisotropy, it does not cause anisotropy in mechanical and electrical characteristics even when used as a reinforcing material for various materials or when used as an electronic material. It is much larger in size than conventional fine needle crystals of zinc oxide, and can be combined with metals, resins, and ceramics to enhance their mechanical strength. It has the advantage of being inexpensive to produce compared to silicon, silicon nitride, etc., and has an extremely large industrial and economical effect.

[Brief description of the drawings]

1 and 3 to 7 are electron micrographs showing the crystal structure of the zinc oxide whiskers according to the present invention, and FIG. 2 is an X-ray diffraction diagram.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Jun Yagi 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. In-house (72) Inventor Takashige Sato 1006 Kazuma Kadoma, Kazuma, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

(57) [Claims] 1. A container having an opening on one surface, a zinc powder having an oxide film on the surface is disposed on a bottom surface corresponding to the opening, and heated and oxidized in an atmosphere containing oxygen to form a whisker. Whiskers are produced and deposited in the same container.