JPH02172897A - Production of zinc oxide whisker - Google Patents

Abstract

PURPOSE:To obtain an aggregate of zinc oxide macrocrystals having the dimensions of industrial-grade whiskers or above by heating zinc powder having an oxide coat on the surface in an atmosphere contg. oxygen. CONSTITUTION:A vessel with one face open is used and zinc powder having an oxide coat on the surface is put on the bottom of the vessel opposite to the open face. The vessel is set in a preheated furnace, where the zinc powder is heated and oxidized in an atmosphere contg. oxygen to form and deposit whiskers in the vessel. The pref. particle size of the zinc powder is 10-300mum. Each of the obtd. zinc oxide whiskers consists of a central core part and acicular crystal parts extending in different four axial directions from the core part and each of the acicular crystal parts has about 0.7-14mum diameter at the base and about 3-200mum length.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing zinc oxide whisker aggregates having a giant tetrabod-like structure.

BACKGROUND OF THE INVENTION At present, zinc oxide used as a material for boat fishing industry is mostly produced by the so-called French process, and is an aggregate of nodular particles of various sizes, especially shapes. There is also a method of forming thin and short acicular crystal particles with high yield (for example, Japanese Patent Publication No. 60-5629). It is used for cooling, and therefore, giant crystals are not generated, but needle-like crystals with minute dimensions (0.1 to 15 μm in length) are formed.

Acicular crystals of such dimensions are about two orders of magnitude smaller in size than various industrial whiskers currently on the market. Therefore, the reinforcing effect on metals, ceramics, resins, etc., which is a common feature of the whiskers, is not much different from that of the nodular zinc oxide, and no significant whisker-like effects are observed. Whiskers, which are monocrystalline in the form of fibers, have much greater mechanical strength than nodules of the same material, and are attracting attention as reinforcing substances that can be mixed into other substances to obtain high mechanical strength. Currently, industrial whiskers made of two metals, metal oxides, metal carbides, metal nitrides, etc. are commercially available. There is also an example of a long whisker (Japanese Unexamined Patent Application Publication No. 50-6697) for zinc oxide, but this is a simple needle-shaped whisker, and since a zinc alloy is purposely used, impurities are present in the crystal. , require a substrate to be placed at a remote location before starting the growth process, have low yields, require complex equipment and long hours of operation, etc., and are merely laboratory studies. There are many.

Problems to be Solved by the Invention An object of the present invention is to provide a manufacturing method for obtaining an aggregate of gigantic zinc oxide crystals having dimensions comparable to or larger than industrial whiskers.

The present invention also provides a novel method for producing a zinc oxide whisker aggregate having a giant tetrabod-like structure.

Means for Solving the Problems The method for manufacturing zinc oxide whiskers according to the present invention is characterized in that zinc powder having an oxide film on its surface is heat-treated in an atmosphere containing oxygen to generate zinc oxide. Like the improved French method and the method for producing simple needle crystals, etc.
A feature of the conventional vapor phase whisker manufacturing method is that the raw material installation location and the whisker generation and growth locations are separated. However, in the present invention, a container with one side open is used.

The surface corresponding to the opening surface of this container is the bottom surface, and the above-mentioned zinc powder is placed on this bottom surface, and the container is placed in a preheated furnace and heated in an atmosphere containing oxygen such as air.
By performing oxidation treatment.

It is possible to produce a new giant tetrabod-shaped aroused zinc whisker aggregate that is completely different from conventional ones, and the produced whiskers have the characteristic that they are deposited in the upper layer of the container. The container also has the characteristic that a by-product nodular zinc oxide layer is deposited separately from the whisker layer below the whisker deposition layer.

Also, here, it is desirable to sprinkle the zinc powder in a layer on the bottom of the container, and also the method of feeding the raw materials.

It is also possible to heat the container in advance in a furnace and then sprinkle zinc powder on the bottom of the container.

In addition, it is essential that the raw zinc powder has an oxide film formed on its surface, and the formation of the oxide film is often achieved during powder production. The former is somewhat porous but tends to form a thick film, while the latter often results in a dense and thin film.

A preferred method for forming an oxide film on zinc powder or increasing the thickness of the film is to roughly crush zinc powder in the coexistence of water and age it, as described below.

The defeated zinc whiskers obtained by the method of the invention are
Consisting of a central core and needle-like crystal parts extending in four different axial directions from this core, the diameter of the base of the needle-like crystal part is 0.7 to
14 μm, and the length from the base to the tip of the needle-like crystal portion is 3 to 20011 m. In addition, some whiskers with triaxial or biaxial needle-like crystals are mixed in, but these are the result of some of them being broken or growth being stopped due to contact with other whiskers during or after growth. be. Also during this growth contact with other tetrapods makes them part of the complete tetrabod shape.

There are also some pieces with dots attached. Although other shapes, that is, plate-like crystals, may adhere to the needle-like portion, according to the manufacturing method of the present invention, tetrabod-like crystals are the main body.

The present inventor has designed the needle-like portion to be thin and short as described above.

In addition, as a result of various experimental studies to develop a giant tetrabod-like whisker aggregate, which has never been realized before, from a conventional crystalline body with attached secondary growth parts, we found that there is an extremely important factor in the manufacturing method. I confirmed that there is.

More specifically, as in the conventional method, it is not possible to develop the giant tetrabod-like whiskers simply by selecting the firing atmosphere conditions using molten zinc metal from an ingot, 5-reduced zinc, pure metal zinc from a zinc compound, etc. It is impossible,
To achieve this, unlike conventional methods, zinc metal powder,
In particular, it is essential to use zinc powder that has an oxide film on the surface, and by using this powder and using the heating oxidation method using the container described above, whiskers are formed in the upper layer of the container and nodular oxidation is performed in the lower layer. It was confirmed that a new aggregate of giant tetrabod-shaped zinc oxide whiskers appeared in the upper layer by the reaction method of depositing zinc powder.

More specifically, in one of the manufacturing methods of the present invention, the brittle film part of the zinc metal powder having an oxide film on the surface exhibits sealing properties against zinc vapor and smoke from the internal zinc metal part. In other words, a powder with a highly sealed oxide film suppresses the generation of steam and smoke in a low temperature range compared to a powder with a low sealing degree, and in a high temperature range, a high concentration of zinc smoke and steam is generated, followed by an oxidation reaction. 1. The zinc oxide whiskers of the present invention are developed. Another effect of this ophthalmic coating is that the zinc metal parts do not melt or become molten metal, and generate highly concentrated zinc smoke or steam.

That is, this oxide film has the role of controlling the generation of zinc smoke and steam from inside. Thirdly, it was also confirmed that the zinc oxide part of the film plays the role of a substrate for whisker growth. The degree of sealing mentioned above refers to the degree to which vapor and smoke from the zinc metal inside the powder are sealed on the surface. This varies depending on the thickness of the oxide film, its structure, the volume ratio of the metal part to the oxide film part, etc.

In particular, the 1-thickness structure of the oxide film is often achieved during the production of metal powder. That is, the oxidation degree H obtained through molten zinc powder is thick and somewhat porous unless particularly controlled. On the other hand, when the solid material is ground, the film thickness is small and the film is quite dense. The former has better uniformity in film thickness, but the latter has a slightly more complex shape and is in the form of a powder with uneven parts, so the film thickness is often non-uniform. In the former case, if the film grows too thick, the surface becomes fragile, which may cause cracks and defects. Furthermore, in particle systems having such an oxide film, defects are often caused in the film due to dislocation and other factors in addition to the conditions described above.

Next, in order to correct deterioration in sealing performance such as defects and cracks in these films, or to increase the film thickness.

Carefully crushed and aged. It was confirmed that this treatment selectively deposits oxides in the film defect areas.

Furthermore, these zinc powders will be described in detail. These particles can have a diameter of 0.1 to 600 .mu.m, with the best result being 10 to 300 .mu.m. These metal zinc powders are made of zinc wire.

Powder obtained by spraying zinc rods or zinc powder into the air using the gas melt wire method, gas melt rod method, gas powder method, electric (arc) wire method, plasma jet method, etc.

There are powders produced by pulverization of molten metal, ie, granulation method and atomization method. There is also a method of mechanical crushing, in which the raw metal ingot is cut or coarsely crushed using a jaw crusher or gyratory crusher and then re-pulverized. There are mill methods, eddy current mill methods, etc. In order to make the powder even finer, there are powders obtained using a hammer mill, a cutting mill, a micronizer, etc. It is also possible to use zinc powder obtained by electrolysis, physical operation using metal evaporation, coagulation, etc., or chemical operation using chemical reaction. Normally, powders produced by each of the above methods are manufactured with care taken to avoid forming an oxide film on the powder surface, but when used in the present invention, it is effective if an oxide film is formed on the surface. Therefore, it is also possible to produce it in an oxidation-promoting atmosphere, such as in the presence of moisture or a high oxygen concentration (such as in the atmosphere) or high humidity. Also, good powder can be obtained even when produced at high temperature and under high mechanical pressure. In addition, if the formation of an oxide film is insufficient in terms of sealability even if the above zinc powder manufacturing method is adopted, or if a powder manufacturing method that does not form an effective oxide film is adopted, the following preferable method is used. method is adopted.

First, mechanical treatment in the presence of water is performed using a mortar-type crusher, rolls, etc. to apply pressure to the particles.

Furthermore, if it is kept in water for more than 24 hours, especially 76 hours, it will give perfect results regardless of the particle size. Further, it is preferable to keep the aging temperature at 20° C. or higher. The oxide film can be formed by chemical reactions such as aging without using the mechanochemical reactions mentioned above, but the latter usually takes too much time, and as mentioned above, the former is more effective in improving the degree of sealing. .

There are a wide variety of factors that cause the formation, increase, and growth of oxide films, but they can be summarized as follows: (1) application of mechanical pressure, (2) g-oxidation reaction in water or under high humidity, (3), (1)
(2) Reciprocal effect (mechanochemical reaction), (4) M elementary concentration.

(5) Temperature effects etc. are involved. When evaluated from the dimensions of the generated whiskers, especially the length and diameter of the needle-like portions, the time due to the above (3) has a large influence. In other words, the effect is great in a short period of time.

If the crushing and maturing time in the coexistence with water is long, the whisker size will also tend to increase due to the improved sealing degree of the oxide film of the raw material powder.

By improving the degree of sealing, the oxide film on the powder suppresses the release of zinc from the internal metal zinc part at low temperatures, and also suppresses the migration of oxygen into the interior. Therefore, sufficient zinc vapor and smoke concentration are provided during single crystal growth. The crystal size is dramatically larger than that of conventional gas phase methods.

Next, it is left to mature and then dried. This drying only needs to be able to remove water from the powder surface, and it is sufficient if it is dried to the extent that the initial adverse effects of transferring to the high temperature of the next firing process are prevented, that is, there is no cracking of the crucible or scattering of the powder. . For this purpose, air drying or high production temperature ranges in which the zinc powder does not melt can be carried out.

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

It also includes those in which the above-mentioned materials are non-porous and have a dense surface, and those in which the materials are porous. Specifically, cases where these containers are crucibles are also included. Next, the container with the raw material placed at the bottom is introduced into a furnace that maintains a preheated oxygen-containing atmosphere for firing and oxidation. Also, the temperature inside the furnace is 700 to 1300
Heating at a temperature of 900 to 1100° C. gives good results for any particle size.

Further, preferable results can be obtained even if the crucible is kept in a furnace in the above temperature range, and the prepared powder is introduced and fired by scattering. Firing time is 12 at 700-1300℃
For 0 to 10 minutes, at 900 to 1100°C, 90 to 10 minutes is appropriate. The heating and firing may normally be carried out in air, but preferable results can also be obtained by using a gas with an adjusted mixing ratio of nitrogen and oxygen or oxygen gas.

Particularly in the initial stage of the heating oxidation, the heated zinc powder flies up from the core of the container to the opening and falls from near the opening to the bottom. The oxidation reaction and whisker growth proceed while controlling this process, and the whisker aggregate of the present invention is gradually deposited in the upper layer of the container, and the nodular zinc oxide powder is deposited in the lower layer.

In order to achieve the manufacturing method of the present invention as described above, zinc powder having a sealing oxide film is essential as described above. This can be achieved by developing a sealing oxide film through various powder manufacturing methods and controlling the conditions, and can be further perfected by rough crushing and aging treatment in the coexistence of water.

This fact was confirmed by X-ray diffraction and electron microscopy observation.

In addition, the oxide film formed in this way or these treatments has a special effect on the firing process.

In other words, the zinc powder must have just been manufactured using a good method that does not undergo oxidation, and must not have an oxide film formed, or only have an extremely thin and fragile film that cannot be detected at all by X-ray diffraction. During firing under the above conditions, the particles did not rise and fall evenly, resulting in uneven firing, and even after adjusting the temperature and oxygen concentration, nodular zinc oxide of various colors and unburned metallic zinc coexisted. system, but not whiskers.

On the other hand, zinc powder with a grown hermetic oxide film
The high-temperature firing progresses uniformly and completely to grow giant tetrabod-like whiskers with an extremely high yield, and the oxide in the film forms nodular zinc oxide in layers.

In this way, when the zinc powder is completely covered with the edifying film, the tetrabod-like whiskers will grow completely,
In terms of shape, there are fewer secondary growth parts, plate-shaped crystals, etc. For this reason, in a system in which an oxide film is formed during production and the film formation is further promoted through crushing and aging, it is possible to obtain a whisker aggregate with good shape and size. However, the degree of sealing of a film cannot be determined uniquely by the film thickness alone, as mentioned above, and in particular, the size and dimensions are determined by the volume ratio of the metallic part of the film (
(depending on particle size) etc. Therefore, even if an oxide film is locally formed, it is possible to obtain the tetrabod-like whiskers of the present invention, but the shape and yield will be quite low.

In addition, during firing production, the volume of the rice comb production system increases rapidly compared to the apparent volume of the processed powder, but the appearance of whisker adhesion outside the source area, which is normally seen in ordinary vapor phase growth methods, Basically, most of them are of the volume increase type that continuously generate and grow in the raw material installation area, rather than the growth type.

Example Examples of the present invention are shown below.

Example 1 A zinc wire having a purity of 9.99% was thermally sprayed in an oxygen/nitrogen mixed gas atmosphere with a #R elementary concentration of 27 by thermal spraying using an arc discharge method. The temperature of the atmosphere was set at 40°C.

The recovered zinc powder was classified to have a particle size of 160 to 300 μm, dried again at 160° C. for 24 hours, and subjected to firing. This powder 1202 was sprinkled on the bottom of a crucible made of porous alumina porcelain. This alumina crucible is rectangular, 20 m wide, 35 m long, and 16 crn high.
One side of the wide area portion is an opening. The above powder was uniformly sprinkled on the bottom surface corresponding to this opening surface to a thickness of 3 mm. This container was directly introduced into a furnace previously maintained at 960° C. and was subjected to a heat treatment for 36 minutes in an air atmosphere.

As a result, a layer of slightly yellow nodular zinc oxide was formed in the lower layer of the container, and a giant tetrabod-shaped zinc oxide whisker aggregate with an apparent bulk specific gravity of 0.11 was formed in the upper layer. Although a small amount of the whisker layer overflowed outside the container, the main reaction took place inside the container, and the oxidation reaction and whisker generation reaction continued as the high-temperature zinc powder particles at the initial stage of the reaction repeatedly rose to the distance of the opening and then descended. did. At this time, as mentioned above, there may be some overflowing outside the container, but the main reaction was carried out within the container, and most of the products were deposited inside the container.

The ratio of the whisker aggregates in the produced zinc oxide was 88%, and the remaining 12% was nodular zinc oxide. An electron micrograph of the obtained zinc oxide whiskers is shown in FIG.

A tetrabod-like crystal body consisting of a core and needle-shaped crystal parts extending from the core in four different axial directions is clearly recognized. Plate crystals were also observed.

In any case, according to the above method, giant tetrabod-like objects occupy 86 cells or more. FIG. 2 shows an X-ray diffraction pattern of the whisker. All show zinc oxide peaks,
Electron diffraction results also showed single crystallinity with few dislocations and lattice defects. In addition, the content of impurities was low, and as a result of atomic absorption spectrometry, the content of zinc oxide was 99.97%.

Example 2 The same pure zinc wire as in Example 1 was thermally sprayed using the same thermal spraying method, and immediately after
The powder was collected, ion-exchanged water of 501 g/kg of powder was added, stirred for 26 minutes in a mortar-type crusher, and then left to mature in water at 20° C. for 76 hours. Amount of water during storage The sample was stored in the atmosphere with the water level maintained at about 1 m from the powder layer. After standing in the water, the powder is dried at 130° C. for 3 hours to remove moisture from the powder. This powder was then placed in a porous alumina container and sprinkled on the bottom. The container is 40mm wide
cm, length 50 cm, and height 30α, and one side of the wide area is an opening. The powder scattering method was to uniformly spread the above-mentioned zinc powder at a thickness of 3 mm or less. This container was guided as it was into a furnace maintained at 970°C, and
It was fired and oxidized for 0 minutes. The appearance 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, and they were a giant tetrabod-shaped edified zinc whisker aggregate. The percentage was 84%. An electron micrograph of the obtained zinc oxide whiskers is shown in FIG. 4-axis tetrabot-shaped ones account for more than 89 units. The results of X-ray diffraction and electron beam diffraction were the same as in Example 1. Atomic absorption spectrometry shows that zinc oxide is 99.99Wt.
It was above the level of staff.

Example 3 A mechanically milled powder was used. An ingot with a purity of 99.99 cm or higher was cut, coarsely crushed six times with a show crusher, and then finely crushed ten times with a stamp mill. Everything was done in the air. It was obtained by classifying particles having a particle size of 60 to 300 μm. The firing furnace temperature was 970° C., and the firing was carried out in a mixed gas atmosphere of 26% oxygen and nitrogen. The time was 36 minutes. The container is made of silicon carbide, and is a rectangular parallelepiped with a width of 20 α, a length of 40 an, and a height of 20 cm, with one wide surface having an opening. Everything else was the same as in Example 1. 84 wt % of whiskers with an apparent bulk density of 0.1 were obtained, with 16 wt % being nodular zinc oxide. An electron micrograph of this whisker is shown in FIG. The 4-axis tetrabot-shaped one was number 81. X
The results of ray and electron diffraction were the same as in Example 1. Atomic absorption analysis of the whiskers revealed that zinc oxide had a coefficient of 99.97.

Example 4 A powder was obtained by mechanical pulverization in the same manner as in Example 3.

Furthermore, 6002 ion-exchanged water was added to this powder I Kp, stirred for 10 minutes in a mortar-type crusher, and then 2
Leave to mature in water at 6°C for 90 hours. After leaving it in water, 1
The powder was dried at 60° C. for 12 hours to remove moisture. The powder thus prepared was fired in the same manner as in Example 3. The bulk specific gravity of the produced whiskers was 75 wt % in o, 09, and 25 was nodular zinc oxide powder. An electron micrograph of this whisker is shown in FIG. The 4-axis tetrabot-shaped one showed 92 inches. The results of X-ray and electron diffraction were the same as in Example 1. Atomic absorption analysis of the whiskers revealed that zinc oxide was 99.99 wt%. The vessel was used as in Example 3 and a similar reaction configuration was carried out.

Example 6 Spherical zinc powder produced by the volatilization and condensation method was used. Place zinc ingot with purity of 99.97wt% in a porcelain container and heat at 970'C.
The zinc was evaporated and the vapor was condensed in air at room temperature. The particles with an average particle size of 7.6 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 and had the same dimensions as in Example 1.
It was fired in the same manner. However, the firing temperature is 990℃ and 25
I went for a minute. The atmosphere was atmospheric. The behavior of the zinc particles during the reaction was similar to that of Example 1, and the product deposition was also similar.

The resulting whiskers had a bulk specific gravity of 0.09 and 92 wt %. The others were nodular zinc oxide. An electron micrograph of this whisker is shown in FIG. The four-axis tetrabot-like one had a coefficient of 90 or more. In addition, the size of the needle-like portion was smaller than those in Examples up to Example 4. The results of X-ray, electron diffraction, and atomic absorption spectrometry were also the same as in Example 1.

Example 6 The zinc powder used in Example 6 was used. This powder I kg
The mixture was poured into 550-g water and mixed for 6 minutes using a rough crusher. Next, it was left to mature in water at 30'C for 91 hours. then 11
Moisture was removed by drying at 0° C. for 24 hours. The powder thus prepared was oxidized in the same manner as in Example 6 under the same conditions. The generated whiskers had a bulk specific gravity of 0.09 and were obtained in an amount of 84 wt%, and the remainder was nodular zinc oxide. An electron micrograph of the whiskers is shown in FIG. The 4-axis tetrabot-shaped one had a coefficient of 96 or more. As in Example 5, the dimensions of the oblique portion were slightly smaller than those of the others. X-ray, electron diffraction,
The results of atomic absorption spectrometry were also the same as in Example 1.

The above examples are summarized in the following table.

(Hereinafter, blank spaces) Effects of the Invention According to the production method of the present invention, zinc oxide whiskers in the shape of giant tetrabods can be obtained. In addition, the manufacturing method includes particle size selection of zinc powder having an oxide film on the surface as a raw material, adjustment of the sealing property of the oxide film, mechanical iG crushing treatment in water, treatment to improve the sealing degree of the film by aging in water, After drying following the thickening process, whiskers are deposited inside the container during the firing process after the raw material powder is sprinkled on the bottom of the container with an opening on the negative side.If carried out in an atmosphere containing oxygen, the process conditions Various sizes of tetrabod-like zinc oxide whiskers can be obtained by setting .

Since the whiskers obtained in the present invention have a three-dimensional structure without anisotropy, they do not cause anisotropy in mechanical or electrical properties even when used as reinforcing materials for various materials or as electronic materials. In addition, it is much larger in size than the conventional fine acicular crystals of zinc oxide, and can be combined with metals, resins, and ceramics to strengthen their mechanical strength. It has the advantage that it can be produced at a lower cost than silicon, silicon nitride, etc., and has extremely large effects both industrially and economically.

[Brief explanation of the drawing]

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

Claims (1)

[Claims] A container has an opening on one side, and zinc powder having an oxide film on the surface is placed on the bottom surface corresponding to this surface, and is heated and oxidized in an oxygen-containing atmosphere to form whiskers in the same container. A method for producing zinc oxide whiskers, characterized by generating and depositing them.