JPH02164795A - Production of zinc oxide whisker - Google Patents

Abstract

PURPOSE:To inexpensively obtain the zinc oxide whiskers of a gigantic tetrapod- shape structure excellent in a reinforcing effect by heating the zinc powder obtained by the gas melting-type flame spraying in an oxygen-contg. atmosphere to form zinc oxide. CONSTITUTION:Zinc powder is melted by an oxygen-gaseous fuel combustion flame or the plasma or air, argon, etc., and injected into the air to produce the zinc powder coated with an oxide film. When the oxide film is insufficiently formed, the zinc powder is brayed in the presence of water, aged, and then dried. The zinc powder coated with an oxide film is placed into a heat-resistant vessel, and heated at 700-1300 deg.C in an oxygen-contg. atmosphere to grow the gigantic tetrapod-shape whiskers. Since the obtained whiskers have a three- dimensional structure free of anisotropy, the anisotropy in the mechanical characteristic is not caused when the whiskers are used as a reinforcing material, etc.

Description

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

BACKGROUND OF THE INVENTION At present, zinc oxide used as a general industrial raw material is mostly produced by the so-called French process, and is an aggregate of nodular particles of various particle sizes, particularly shapes.

In addition, a method for forming thin and short acicular crystal particles with high yield (
For example, Japanese Patent Publication No. 60-5529 (Japanese Patent Publication No. 60-5529) is an improved method of the above-mentioned French method, which rapidly cools the heated zinc vapor. Therefore, giant crystals are not formed, and micro-dimensions (length is 0.1 to 1.5 μm).

Acicular crystals having 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. In other words, whiskers, which are monocrystalline in the form of fibers, have much higher mechanical strength than nodule-like substances 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 metal oxides, metal carbides, metal nitrides, etc. are commercially available.

Also, in zinc oxide, there is an example of a whisker with an interdigital length (
(Japanese Unexamined Patent Publication No. 50-5597), but these are simple needle-shaped bodies, and because they use a zinc alloy, they contain impurities in the crystal, require a substrate during growth, and are low-quality. Many of these are merely laboratory studies, such as yield issues, complicated equipment, and long operation times.

Problems to be Solved by the Invention The object of the present invention is to provide a method for producing giant crystals of zinc oxide having dimensions of industrial whisker size or larger. The present invention also provides a method for producing zinc oxide whiskers having a giant tetrabod-like structure.

Means for Solving the Problems The method for manufacturing zinc oxide whiskers according to the present invention involves heat-treating zinc powder obtained by gas-dissolving or plasma-jet zinc metal spraying in an oxygen-containing atmosphere to generate zinc oxide. It is characterized by

In particular, the zinc powder obtained by zinc metal spraying is ejected into the air as molten particles, and an oxide film is formed on the surface thereof. In order to further improve the size and shape of the whiskers, these particles can be crushed and aged in the coexistence of water as described below.

Function The zinc oxide whiskers obtained by the method of the present 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
The length from the base to the tip of the needle-like crystal portion is 3 to 200 μm. In addition, there are some cases where the needle-shaped crystal part is triaxial or biaxial, but these are the result of part of the whisker being broken during growth or later coming into contact with other whiskers, or growth being stopped. .

Also, due to contact during this growth, some complete tetrabods have some other tetrabods attached to them.

Although other shapes, i.e., plate crystals, may be attached to the needles,
According to the manufacturing method of the present invention, tetrabod-like materials are mainly used.

The present inventors have discovered a giant tetrabod-like whisker, which has never been realized before, and has needle-shaped parts that are thin and short as described above, and are dramatically larger than conventional crystals with attached secondary growth parts. As a result of various experimental studies to achieve this, we have confirmed that the zinc raw material used is an extremely important factor. More specifically, it is possible to control the size and shape of microcrystals by selecting the firing atmosphere conditions using molten zinc metal, reduced zinc, metal zinc from zinc compounds, etc. as in the past. It was confirmed that it was impossible to produce giant tetrabod-like whiskers, and that in order to achieve this, it was necessary to use zinc metal powder, unlike conventional methods, and moreover, use zinc powder obtained by the above-mentioned zinc metal spraying. . That is, as mentioned above, the zinc powder obtained by thermal spraying has an oxide film formed on its surface. This film has a high degree of sealing, and compared to powders with partially attached oxides or powders that do not have an oxide film, zinc smoke is produced at a higher temperature.

A high concentration of steam is generated, oxidation occurs, and giant tetrabod-like whiskers appear. Another effect of this oxide film is that the internal zinc metal parts of the zinc powder do not melt or become molten metal, thereby promoting the generation of highly concentrated zinc smoke vapor.

Thirdly, we 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 zinc smoke and steam are kept sealed without being released to a high temperature range. This depends 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 thickness and structure of the oxide film are often achieved during the production of metal powder, and the thermal spray powder used in the present invention is often made of molten zinc powder that is ejected into the air. A somewhat porous beaked film is obtained. The surface of the powder is liquid and smooth, and the film thickness may be uniform. If the film grows too thick, the surface may become brittle and cracks or defects may occur. Next, in order to correct deterioration in sealing performance such as defects or cracks in these films or to increase the film thickness, crushing and aging treatments are performed.

By these treatments, oxides can be selectively deposited on film defects.

Next, the metallic zinc powder used in the present invention will be described in detail.

These particles can have a diameter of 0.1 to 500 .mu.m, with the best result being 1 to 300 .mu.m. This powder can be produced by thermal spraying of zinc as described above. Conventionally, there are gas spraying methods, gas powder methods, gas molten rod methods, and plasma jet methods for thermal spraying zinc. Usually, it is melted using plasma or the like and sprayed onto an adherend in the air. It is also common to form a thermal spray coating under conditions that do not form an oxide film on the surface before adhering to the adherend. However, the zinc powder used in the present invention has an oxide film formed on its surface, similar to powders used in the field that have conventionally been scattered to areas other than adherends, and is It can be obtained by launching the Furthermore, the thickness of the coating can be increased by changing the atmosphere of the thermal spraying part from air to a nitrogen-oxygen mixed gas atmosphere.

That is, when used in the present invention, it is effective if an oxide film is formed, so the zinc powder is sprayed into water, high humidity, and high temperature (however, at a temperature below the melting point of zinc) to produce zinc powder with an oxide film. Including cases.

Furthermore, if the formation of an oxide film is insufficient even after using the above-mentioned oxide film-assisting method, the following preferred method is used.

First, the particles are mechanically treated in the presence of water using a mortar-type crusher, rolls, etc., and mechanical pressure is applied to the particles. Further, if it is kept in water for 24 hours or more, especially 72 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. Although the oxide film can be formed by chemical reaction such as aging without using the mechanochemical reaction described above, the latter method usually takes too much time.

As described above, there are various factors that cause oxide film formation and growth.
To summarize, the following factors are involved: ■ Addition of mechanical pressure, ■ Oxidation reaction in water or under high humidity, ■ Reciprocal effect of ■ and ■ (mechanochemical reaction), ■ Oxygen concentration effect, ■ Temperature effect, etc. Judging from the dimensions of the generated whiskers, especially the length of the needle-like portions, the time given in (2) above has a large influence. However, the effect is great in a short period of time.

The above-mentioned dimensions tend to increase as the crushing time in the coexistence with water increases. It is thought that the oxide film on the powder suppresses the release of zinc from the metallic zinc part inside the powder during firing, and also suppresses the migration of oxygen into the powder. For this reason, sufficient time is given during single crystal growth, and the crystal grows to a large size, and it is thought that giant tetrabod-shaped zinc oxide whiskers, which are far different from those of the normal gas phase method, are developed.

Next, leave it to dry. The purpose of this drying is to remove moisture from the surface of the powder, and to prevent cracking of the crucible due to moisture, which occurs at the beginning of the transition to the high temperature of the firing process.
It is good if it dries to the extent that there is no scattering of powder.

This drying can be carried out in a temperature range from air drying to high temperatures at which the zinc powder does not melt.

Next, the dried powder is placed in a heat-resistant container, usually a crucible made of alumina, and heated to 700-1300°C in an oxygen-containing atmosphere.
Among these, heating at 900 to 110° C. gives good results regardless of the particle size. Even if the crucible is held in a furnace in the above temperature range and the prepared powder is charged and fired, a favorable result is obtained. Baking time is 700~1
900-110 for 120-10 minutes at 300°C
At 0°C, 90 to 10 minutes a1 is appropriate. The heating and baking process may normally be carried out in air, but good results can also be obtained by using a gas in which the mixing ratio of nitrogen and oxygen is adjusted.

Metallic zinc powder can develop a preferable oxide film by controlling the powder manufacturing method and its conditions as described above, and can be further perfected by aging treatment in the coexistence of water.

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

The oxide film formed in this way or these treatments has a special effect on the firing process in which whiskers develop. In other words, the zinc powder has just been produced using a good method that does not undergo oxidation, and there is no formation of an oxide film, or
If the film has an extremely thin and fragile film that cannot be detected at all by the linear diffraction method, it will not be baked uniformly under the above conditions, and even if the temperature, oxygen concentration, etc. A system in which zinc and unburned metallic zinc coexist is formed, and no giant whiskers are formed. On the other hand, in the case of the zinc powder having the preferable grown oxide film, the high-temperature firing progresses uniformly and completely, the metallic zinc part is completely oxidized, and the giant tetrabod-like whiskers grow in extremely high yield. On the other hand, the oxide in the film part forms a layered block of zinc oxide.

In this way, when the zinc powder is completely covered with an oxide film, the tetrabod-like whiskers grow completely,
In terms of shape, there are extremely few secondary growth parts and plate-like crystals, making it huge. Therefore, in a system in which an oxide film is formed during production and further film formation is promoted by the above-mentioned crushing and ripening, whiskers with good shape and size can be obtained. However, as mentioned above, the quality of the film cannot be determined uniquely by the film thickness alone, and in particular, the nine dimensions vary depending on the structure of the film, the volume ratio of the metal part (depending on the particle size), etc. Therefore, even if an oxide film is locally formed, it is possible to obtain tetrabod-like whiskers, but the shape and yield will be quite low.

In addition, during firing production, the volume of the whisker generation system increases rapidly compared to the apparent volume of the processed powder, but in the complete vapor phase method, whiskers do not adhere to the outside of the source area or grow. Basically, most of them are of the volume-increasing type that continuously generate and grow in the raw material installation area.

Example Examples of the present invention will be described below.

Example 1 A pure zinc wire with a purity of 99°99% was thermally sprayed by gas melt spraying. The diameter of the above zinc wire is 1.5 mm, and the zinc wire system is gasified with oxygen-liquefied natural gas combustion flame to achieve a humidity of eo%RH.
launched into the air. The spraying speed was 6 kg/hr. This powder was collected, left in a humidity of 5oRH for 24 hours, dried at 120°C for 3 hours, then placed in an alumina porcelain crucible, and the crucible was placed in an electric furnace previously maintained at 970°C. Then, firing treatment was performed for 26 minutes.

As a result, nodular zinc oxide was produced in the lower layer of the crucible, and a giant tetrabod-shaped zinc oxide whisker aggregate with an apparent bulk specific gravity of 0.11 was produced in the upper layer. The proportion of the whisker aggregates in the produced zinc oxide is 87 wt%
Met.

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. Although some crystals with needle-like crystals have three or two axes, it is thought that some of the basic four-axes were connected to each other and broke during or after growth. A small number of plate crystals were also observed. In any case, according to the above method, more than 90% of the particles are in the form of tetrabods.

FIG. 2 shows an X-ray diffraction pattern of the zinc oxide whiskers.

It showed a total zinc dioxide peak, and electron diffraction results also showed single crystallinity with few dislocation lattice defects. In addition, the content of impurities is low, and as a result of atomic absorption spectrometry, zinc oxide content is 99.9%.
It was 7%.

Example 2 Zinc wire with a purity of 99.91% was thermally sprayed in the same manner as in Example 1, and the powder was collected and left at a temperature of 31° C. and a humidity of 75 SRH for 10 days. This was added to 700g of zinc powder in ion-exchange water soog, and crushed with a mortar-type extractor for 25
The mixture was stirred for a minute. Next, it was left to mature in water at a temperature of 30° C. for 72 hours. The amount of water was kept at about 1 crn from the powder layer and stored in the atmosphere. After being left in the water, it was dried at 150° C. for 1 hour to remove moisture, and then fired in the same manner as in Example 1. The firing temperature was 96C) ℃.
o minutes.

In this way, 81 wt % of zinc oxide whiskers with an apparent bulk specific gravity of 0.13 were obtained. The rest was nodular zinc oxide obtained in the lower layer. An electron micrograph of this whisker is shown in FIG. Among the resulting whiskers, 4-axis tetrabod-like ones were 9
I was in charge 2. The results of X-ray diffraction and electron beam diffraction are shown in Example 1.
Similarly, zinc oxide is 99.96 in nine atomic absorption spectrometry.
%Met.

Example 3 Zinc powder with a purity of 99.6% was used for thermal spraying using a gas powder method. Zinc powder was gasified with an oxygen-liquefied natural gas combustion flame and launched into air with a humidity of RHes%. Spraying speed is 4
I went there in 2/hours. Collect this powder and keep the humidity at 7 for 3 days.
It was left in 04RH.

It was dried at 160'C for 12 hours and fired in the same manner as in Example 1. The firing temperature was 950°C for 40 minutes. Nodular zinc oxide was produced in the lower part of the crucible, and giant tetrabod-shaped zinc oxide whisker aggregates with an apparent bulk specific gravity of 0.12 were produced in the upper part. The ratio of the whisker aggregates in the produced zinc oxide was 81 wt.

An electron micrograph of the obtained zinc oxide whiskers is shown in FIG. The number of four-axis tetrabod-like whiskers thus obtained was 91 inches. The results of X-ray and electron diffraction were the same as in Example 1. Atomic absorption spectrometry showed that zinc oxide was 99.
It was 97%.

Example 4 Thermal spraying was performed using a gas powder method using zinc powder with a purity of 99.2%. The thermal spraying conditions were the same as in Example 3. This powder was collected and left for 12 days at a temperature of 27° C. and a humidity of 76% RH. Add this to 4009 parts of ion exchange water and 600 parts of zinc powder.
g, and stirred for 10 minutes using a mortar-type crusher. Next, this was left to mature in water at a temperature of 30° C. for 79 hours. The amount of water was kept at about 1 crn from the powder layer and stored in the atmosphere. After being left in the water, it was dried at 160° C. for 4 hours to remove moisture, and fired in the same manner as in Example 1. However, the firing temperature was 990°C for 30 minutes.

In this way, 82 wt % of giant zinc oxide whiskers with an apparent bulk specific gravity of 0.11 were obtained. In addition, nodular zinc oxide was obtained in the lower layer of the crucible.

An electron micrograph of this whisker is shown in FIG. The number of four-axis tetrabot-like whiskers was 94. The results of X-ray diffraction and electron beam diffraction were the same as in Example 1. Atomic absorption spectrometry showed that zinc oxide was 99.97%.

Fruitful mountain side 5 Plasma jet thermal spraying was performed using zinc powder with a purity of 99.95%. Zinc powder was gasified with a helium plasma flame and launched into air with a humidity of 67% RH.

The spray rate was 4 to 9/hour. This powder was collected and left in air at a temperature of es%RH for 10 days. 150℃
It was dried for 12 hours and fired in the same manner as in Example 1.

The firing temperature was 960°C for 20 minutes. Nodular zinc oxide is formed in the lower part of the crucible, while the upper part has an apparent bulk specific gravity of 0.
Eleven giant tetrabod-like zinc oxide whisker aggregates were produced. The ratio of the whisker aggregates in the produced zinc oxide was 86%. FIG. 6 shows an electron micrograph of the dissolved zinc oxide whiskers. The results of X-ray and electron diffraction were the same as in Example 1, in which the number of 4-axis tetrabod-shaped whiskers was 92. Atomic absorption spectrometry showed that zinc oxide was 99.97%.

Example 6 Thermal spraying was performed under the same conditions as in Example 5, and powder was recovered. It was left for 1Q at a temperature of 32° C. and a humidity of 71% RH. This powder was added to 600 g of ion-exchanged water at a ratio of 9 parts zinc powder, stirred in a mortar-type tlffi machine for 20 minutes, and left to mature in water at a temperature of 31° C. for 77 hours. The amount of water was kept at a level of about 1 tM from the powder layer and stored in the atmosphere. After being left in this water, it was dried at 150°C for 7 hours. Next, it was fired in the same manner as in Example 1. However, the firing temperature is 986℃ and 35℃.
It was set as 1 minute.

In this way, 80% of giant tetrabod-like whiskers with an apparent bulk specific gravity of 0.09 were obtained. In addition, nodular zinc oxide was obtained in the lower layer of the crucible.

An electron micrograph of this whisker is shown in FIG. The number of four-axis tetrabot-like whiskers was 94.

The results of X-ray diffraction and electron beam diffraction were the same as in Example 1. Electron absorption analysis showed that zinc oxide was 99.99%.

The above embodiments are summarized in a robe.

In the US whisker dimensions, the length refers to the length from the base to the tip of the needle-like resultant portion of the tetrabod-like structure, and the thickness refers to the diameter of the base of the needle-like portion. The numerical values are representative values.

Effects of the Invention According to the production method of the present invention, novel giant tetrabod-shaped zinc oxide whiskers can be obtained. In addition, when the manufacturing method includes preparation of metallic zinc powder, mechanical crushing treatment in the coexistence of water, aging in water, drying, and firing steps, the above-mentioned tetrabod-shaped zinc oxide whiskers can be produced by setting these process conditions. Various sizes are available.

The whiskers obtained by the present invention have a three-dimensional structure with no anisotropy in terms of shape, and are single-crystalline, so they can be used as reinforcing materials for various materials or as electronic materials. Does not cause anisotropy in properties. In addition, it is significantly larger in size than the conventional fine needle-shaped zinc oxide crystals, making it suitable for metals and resins.

It has the advantage of being able to be manufactured at a lower cost than silicon carbide, silicon nitride, etc., which are used for similar purposes, and can be combined with ceramics to strengthen their mechanical strength. It also has an extremely large effect.

[Brief explanation of the drawing]

1 and 3 to 7 are electron micrographs showing the crystal structure of giant zinc oxide whiskers according to the present invention, and FIG. 2 is an X-ray diffraction diagram. Figure 1 Name of agent Patent attorney Shigetaka Awano and one other IO
Example: Shiribonito 10 ←

Claims (3)

[Claims] (1) A method for producing zinc oxide whiskers, which is characterized in that zinc powder obtained by gas-dissolved thermal spraying is heat-treated in an oxygen-containing atmosphere to produce zinc oxide. (2) A method for producing zinc oxide whiskers, which comprises heating zinc powder obtained by plasma jet spraying in an oxygen-containing atmosphere to produce zinc oxide. (3) The method for producing zinc oxide whiskers according to claim 1 or 2, further comprising the step of crushing the zinc powder obtained by the thermal spraying in the coexistence of water, aging it, and then drying the water.