JPH02175700A - Production of zinc oxide whisker - Google Patents

Abstract

PURPOSE:To separately make ZnO whiskers of small-sized and large-sized tetrapod-like structures on the upper side and the lower side of a partition plate, respectively, in high efficiency and in a short time by sending O2 corresponding to catalyst of zinc vapor accompanying change with time to a crucible at the center of solid-liquid-gas three phase reaction field. CONSTITUTION:A tray 11 comprising a side 10 made of an expand metal having >=20% high opening ratio and a bottom made of a corrosion-resistant stainless steel plate containing no Ni, a member having 0-3% low opening ratio is prepared. Further, a partition plate 12 made of the same member having high opening ratio as the member of rising wall is set at part >=15mm apart above from the bottom and <= the height of the side 10. Them the tray 11 of a high- opening crucible 13 with the partition plate is charged with Zn powder and placed in a muffle furnace 14. Then the Zn powder is heat-treated while introducing a fixed amount of air from the outside to the furnace 14 to give ZnO whiskers of huge crystal having 3-30mum length of needle-like part on the plate 12 and 30-250mum length of needle-like part under the plate 12 and on the bottom. The opening ratio of the plate 12 may have >=20% and does not necessarily require coincidence with that of the side 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing zinc oxide whiskers having a gigantic tetrabod-like structure. The present invention relates to a firing method for producing zinc whiskers.

BACKGROUND OF THE INVENTION Zinc oxide used as a general industrial material is produced by the so-called French method, and is an aggregate of aggregated particles of various particle sizes, especially shapes. There is also a method of forming thin and short acicular crystal particles in high yield (for example, Japanese Patent Publication No. 60-6629), but this is an improved method of the above-mentioned French method, in which metal zinc vapor is rapidly cooled by heating. Therefore, a giant crystal is not generated, but a needle-like crystal with a fine 3 I tone (small size C needle-like length of about 1 to 1.6 microns) is formed. A needle-like crystal of such size is about twice as large in size as the various industrial whiskers currently on the market. Therefore, the reinforcing effect on metals, ceramics, wood, resins, etc., which is a common feature of the whiskers, is at the level of the spacing zinc oxide, and there is no noticeable effect as a whisker.

In other words, whiskers, which are monocrystalline in the form of fibers, have much higher mechanical strength than aggregated materials of the same material, and are used as reinforcing substances to obtain high mechanical strength by mixing them into other materials. This has attracted attention, and today industrial whiskers made of metals, metal oxides, metal carbides, metal nitrides, etc. are commercially available. In addition, there are examples of whiskers with phase-matching lengths in zinc oxide (Japanese Patent Publication No. 60-6697), but these are simple needle-shaped whiskers, and since a zinc alloy is used, impurities are added to the crystal. This is no more than a laboratory study, as it requires a substrate to grow a single crystal, requires complicated equipment, and requires a long time to operate.

In the practical production of zinc oxide, zinc metal is heated in advance at high temperature in a non-oxidizing atmosphere such as nitrogen gas to generate zinc vapor gas - a mixture of this non-oxidizing zinc vapor. Zinc oxide powder is produced by oxidizing the 5-zinc vapor by introducing gas into a high temperature furnace in an oxidizing atmosphere containing separate oxygen. In this case, most of the zinc oxide produced becomes aggregated oxide, so-called zinc white.

Furthermore, as a method for producing zinc oxide whiskers in the form of tetrabod-like giant crystals in which the dimensions of the central core and the acicular portions extending from the core in four different axes directions are 3 to 260 μm, ceramics used in ordinary high-temperature oxidation reactions are used. We investigated a method of placing zinc powder in a crucible and heat-treating it in an oxygen atmosphere to produce giant crystalline zinc oxide whiskers, but a large amount of aggregated zinc oxide was produced in the lower layer of the ceramino crucible. Due to the long firing time, it has not been possible to efficiently produce giant crystalline zinc oxide uska.

Furthermore, in order to obtain a mechanical reinforcing effect for film-like resins, coatings, etc., it is advisable to use tetrabod-like zinc oxide whiskers with a needle-like part length of 3 to 20 μm61\-no, but production using the above-mentioned ceramic crucible is recommended. 3-2 in method
3 to 30 in the range where 50 μm particles are mixed.
We have not yet reached the point of selectively producing only micrometer particles.

Problems to be Solved by the Invention The present invention has a size necessary for an industrial whisker,
And - Zinc oxide whiskers consisting of a tetrabod-like structure can be produced at a VC of 3 to 30 μm in a short period of time with high efficiency.

The present invention provides a manufacturing method for separately manufacturing 30 to 260 μm.

Means for Solving the Problems In the present invention - the crucible has 20 parts as shown in FIG.
Expanded metal with a high aperture ratio of over %.

Wire mesh and punching metal make up 1 side surface and 1 bottom surface.
The plate 11 is made of porcelain, which is a member with a low aperture ratio of ~3%, or a corrosion-resistant stainless steel plate that does not contain nickel, and on which zinc powder having a monoxide film is placed. Furthermore, a partition plate 12 made of the same high aperture ratio member as the rising wall member is provided at least 16 mm above the bottom surface and below the height of one side. Zinc powder having an oxide film is placed in the dish 11 of such a deep aperture crucible 13 with a partition plate, and a Matsufuru furnace 14 as shown in FIG.
Place it inside the furnace and supply a fixed amount of air from outside the furnace? L, 5 heat-treated to obtain giant crystalline zinc oxide whiskers of 3 to 30 μm on one partition plate and 30 to 260 μm on the bottom under the partition plate.

Note that the aperture ratio of the partition plate may be 20% or more, and does not necessarily have to match the side surface.

The nickel-free stainless steel used here is - 18 to 3% chromium. Preferably, the remainder is iron.

Function: In the present invention, zinc powder is used as a material in the first firing step. Here, the particle size of the zinc powder can be from 0.1 to 600 .mu.m, and preferably from 1 to 300 .mu.m gives good results. This is because this is one of the factors that has a very significant effect on the rate of zinc vapor generation during the firing process of the present invention. In other words, when the particle size is extremely small, the evaporation rate of zinc vapor is extremely fast at a constant temperature above the evaporation temperature point of zinc metal and the same amount of metal, making it virtually impossible to control the amount of oxygen in the atmosphere as described below. Therefore, most of the metal vapor is discharged outside the crystal formation system (most commonly outside the kiln).
Even if it remains in the production system, depending on the atmospheric conditions, it may aggregate in a metallic state or become aggregated zinc oxide. In addition, if the particle size is too large, the rate of generation of zinc vapor becomes slow and it becomes difficult to control the amount of oxygen in the atmosphere commensurate with the amount of zinc vapor generated. Radoid whiskers are rarely produced.

In order to more easily control the amount of evaporation of zinc vapor, the present invention uses zinc powder whose surface is previously covered with an oxide film as a material for firing. This is because the increase in the evaporation rate due to the above-mentioned particle size can be moderated by the degree of progress of oxidation. This is because the surface of the zinc metal particles is covered with an oxide film, which has the effect of suppressing vapor diffusion of the zinc metal inside the particles into the atmosphere, increases the heat capacity of the particles as a whole, and increases the evaporation temperature. This is thought to be due to the apparent increase in

By using the powder material as described above, the amount of evaporation of zinc vapor can be controlled, and the atmosphere in one firing furnace, especially the oxygen partial pressure, can be controlled, and the relative ratio of zinc vapor partial pressure and oxygen partial pressure in one furnace can be controlled. Experiments have revealed that the tetrabod-like zinc oxide whiskers of the present invention can be produced by adjusting the stoichiometric ratio of zinc monoxide (ZnO) f within a certain range. Here, in order to form larger whiskers, it is necessary to control the atmosphere of the crystal formation system to a state of considerable zinc vapor excess and oxygen deficiency, while to form smaller whiskers. 5
Contrary to the above, there is a lack of zinc vapor and it is necessary to provide an excess of oxygen.

The present invention is characterized in that zinc metal is fired and oxidized in an atmosphere of 5 or more. Atmosphere inside the reactor 9I\-7 As a means to control the atmosphere, a zone for generating zinc vapor may be set up in advance using a carrier gas (specifically, a non-oxidizing gas such as nitrogen). A so-called gas phase reaction method is usually used in which zinc vapor is transferred to an oxidation reaction zone provided at a later stage and oxidized by an oxygen-containing gas introduced from outside.

In this case, since a carrier gas is essential, it is extremely difficult to achieve a relative ratio of zinc vapor partial pressure and oxygen partial pressure in the range required for the formation of giant whiskers as described above, and it is difficult to achieve an industrial yield. Considering this, it can be said that it is almost impossible.

In the present invention, the atmosphere for forming such giant whiskers is created by mixing zinc powder (solid), zinc vapor (liquid), zinc gas (gas), and oxygen (gas) in the same place. The so-called 5-L-G
Nucleation of zinc monoxide by forming a three-phase reaction field,
Derivation of the crystal habit of tetrabo-nd-like crystals - followed by tetrapo.

Since the huge growth of do-shaped whisker crystals occurs extremely smoothly, Hiko concluded that production with high yields is possible. In other words, the core of the present invention is a place where an extremely high partial pressure of zinc vapor using solid zinc powder as a supply source and a high partial pressure control of oxygen that promotes the completion of whisker formation are continuously formed.

As a specific furnace configuration for forming the above-mentioned atmosphere, as a method for introducing an oxygen-containing atmosphere into the zinc powder vapor field, a normal flow furnace is used. By using a method of temporal control (oxygen partial pressure in the atmosphere and its temporal control corresponding to the amount of zinc vapor generated) and a firing furnace whose wall material is made of porous and breathable material. 5. Due to the evaporation of zinc vapor inside the furnace and the subsequent oxidation reaction, the entire atmosphere is depressurized due to the fixation of oxygen in the atmosphere, and fresh air corresponding to this depressurization is naturally drawn from outside the furnace through the porous walls. There is a method in which materials are introduced into the furnace through a flow of material.In either case, in a ceramic crucible, even if the ratio of zinc vapor partial pressure to oxygen partial pressure is appropriate, the S -The ratio in the crucible, which is the center of the I, G three-phase reaction field, changes with time. In other words, -11.\- Oxygen flow into the ceramic crucible becomes insufficient.

However, in the high aperture ratio crucible of the present invention, oxygen can flow into the crucible easily following changes in the zinc vapor partial pressure. As a result of experiments, the opening ratio of the crucible that allows oxygen to flow easily into the crucible is 20% or more. Opening ratio 60 to fit
% or less. In other words, when it is 60% or more, the portion overflowing from the opening increases.

i! As an experiment to demonstrate the effect of the easy flow of oxygen into the crucible, one tetrapo.7
It was confirmed that hydrogen-shaped zinc oxide whiskers could be produced in high yield, and the easy oxygen distribution effect of the crucible of the present invention was demonstrated.

Furthermore, the above-mentioned upper part of the partition plate may be far away from the source of zinc vapor.Although it is a high aperture ratio member, it is partitioned by the partition plate-and the upper part is exposed to the atmosphere, so the concentration of zinc vapor is low. 3 to 30 on the partition plate due to excess oxygen.
Zinc oxide whiskers in the form of tetrabods of .mu.m are formed - which accumulate on the partition plate. In addition, the lower part of the partition plate is close to the source of zinc vapor, and since there is a partition plate, the concentration of zinc vapor is high and there is a lack of oxygen.
0 μm tetrabod-like zinc oxide can be produced.

Examples Example 1 A crucible shown in Figs. 1 and 2 was used. Side of this crucible 1
0 is width IE50~280 mm, depth 260~36 (Mξ height 130~1801ffff, and partition plate 12 is installed in the center of one side) - each is made of nickel-free corrosion-resistant stainless steel with an aperture ratio of 20~60%. Constructed of extracted band metal made of corrosion-resistant stainless steel with 18.6% chromium in the 5 wood example.

2.4% aluminum and the balance iron. In addition, the bottom surface is made of the same material as above, and the width and depth are smaller by 20mm compared to the side dimensions above, and the height is 1omm.
A box 138-] with an aperture ratio of zero consisting of six sides.

80 to 120 g of zinc powder with an oxide film is uniformly sprinkled on the bottom of this high-opening main crucible, and the internal volume is 200 to 3 o in width.
OIIM-Depth 220~380111111-Height 20
Place it in a Matsufuru furnace of 0-300M and heat it from the outside with 2-41/
Heat treatment was carried out at 900 to 1060°C while supplying 100% air.

The Matsufuru furnace 14 used here has a structure as shown in FIG. This is done to maintain airtightness. 19 is an air supply port, 2
0 is a heater.

After 20 minutes of heat treatment, when the crucible was taken out, 3 to 30 μm of tetrabod-like sulfur oxide was formed on the upper part of the partition plate 12 (part A). 30-260 including several % of 30 μm
Tetrabod-like zinc oxide whiskers of μm size were selectively generated. When the zinc oxide whiskers formed in part A were observed using an electron microscope, it was found that 100% of the product was
%14, \-no was a giant crystalline zinc oxide whisker, and the length of the needle-like part was 3 to 30 μm, with the center being 20 μm.

Furthermore, 96% of the zinc oxide whiskers produced were in the form of tetrabods.

On the other hand, when the zinc oxide whiskers generated in the -B part were similarly observed with an electron microscope, tetrabod-shaped zinc oxide whiskers of 30 to 260 μm containing several % of 3 to 30 μm, which is 80% of the total weight of the product, were obtained. The remainder was yellow zinc in cluster-like particles.

More than 86% of the 80% zinc oxide whiskers were in the form of tetrabods. Electron micrographs (magnification: 200) of parts A and B are shown in FIGS. 6 and 6, respectively.

Example 2 As shown in FIG.
omm, wave-shaped partition plate 12 with a wave width of 40 to 60 mm
'. When zinc powder was put in this crucible and heat treated 5, the peak part (E part) appeared at the upper part CC of the corrugated partition plate.
Almost no zinc oxide whiskers are generated in the Ichitani part CF.
16, -.

generated. The zinc oxide whiskers inevitably formed at the lower part of the corrugated partition plate (part D) take in air from the above-mentioned part E, and the zinc oxide whiskers in part D are more tetrabod-like oxidized than in the previous example, as shown in Figure 7. A product with a high lead whisker ratio was obtained.

In other words, -0 part of the product is 100% giant crystalline zinc oxide whiskers - the length of the needle-like part is 20μ
It was 3 to 30 μm centering on m.

Furthermore, 96% of the generated zinc oxide whiskers were in the shape of tetrabods, which was the same as the zinc oxide whiskers in Part A on the planar partition plate.

However, as shown in FIG. 7, part D was 86% zinc oxide whiskers and 94% thereof could be tetrabod-like zinc oxide whiskers.

Comparative Example 1 A crucible made of a corrosion-resistant stainless steel plate that does not contain nickel and has the same dimensions and the same material as in Fig. 1, and the rising part is the same as the bottom part, was heat-treated in the same manner as above. It is the same as a high aperture ratio crucible without a partition plate, but the bottom is plate-shaped and irregularly shaped zinc oxide ~ The ratio of zinc oxide to the total weight of the product is 67
%, of which the proportion of tetrabod-like zinc oxide whiskers was 76%. The needle-like length of the tetrabod-like zinc oxide whiskers was 3 to 260 μm, and they were generated in a mixed manner.

Comparative Example 2 A high aperture ratio flat partition plate was added to the crucible made of the nickel-free corrosion-resistant stainless steel plate described in Comparative Example 1.

When a corrugated partition plate was attached and subjected to the same heat treatment, the zinc oxide whiskers that formed on the partition plate became tetrabod-like zinc oxide whiskers with a size of 3 to 3 μm on the surface, similar to those in the example, but the zinc oxide whiskers that formed on the partition plate became tetrabod-like zinc oxide whiskers with a diameter of 3 to 3 μm as in the example. There was a lack of oxygen near the top of the plate and under the partition plate, and the production ratio of tetrabod-like zinc oxide whiskers was less than 40%.

Comparative Example 3 Even if the rising portion is a high aperture ratio member, the aperture ratio is 2.
At 0% or less, almost the same as in the ceramic crucible described above, 82% of the total weight of the product becomes 17.
% was tetrabod-like zinc oxide whiskers.

High aperture ratio flat partition plate for 20% aperture ratio crucible.

When a corrugated partition plate was attached and the same heat treatment was performed, the comparison was the same as fl12 - near the top of the partition plate - under the partition plate there is a lack of oxygen. The formation rate of leech-trabod-like zinc oxide whiskers was 48%, which was 5 Practical. Not on point.

Comparative Example 4 When the aperture ratio of the rising member was 60% or more, the giant tetrabod-shaped zinc oxide whiskers that were generated flew out of the crucible regardless of the presence or absence of the partition plate, causing problems in storing the product.

Comparative Example 6 The crucible was made of corrosion-resistant stainless steel with 18.6% chromium, 8.0% nickel, and the balance iron, and was subjected to the same heat treatment as above, but the zinc powder and nickel reacted. Large thermal distortion, metal cracking, and metal corrosion occurred in the crucible material, making it unsuitable for practical use.

The above results are summarized in the following table.

(Hereinafter, blank) 18 〆＼-/ 2 1 ,,-> Effects of the invention As explained in the examples and comparative examples, the effects of the present invention are 5-L
-G Smoothly sends oxygen commensurate with the zinc vapor concentration that changes over time into the crucible, which is the center of the three-phase reaction field,
3-30μm on the top side of the partition plate, 30-260μm on the bottom side
An object of the present invention is to provide a crucible that can selectively produce m tetrabod-like zinc oxide whiskers.

In heat treatment using a crucible, the necessary oxygen could not be delivered, resulting in giant crystalline zinc oxide whiskers that accounted for 80% of the total weight of the product.5The tetrapo-nod shape ratio of total zinc oxide was 87%. Ta.

Sarani, selectively adjust the dimensions of the diagonal part of the tetrabod-shaped zinc oxide Tsunoska using a partition plate for corrosion-resistant stainless steel plate crucibles with open ends, high aperture ratio crucibles with an aperture ratio of 20% or less, and high aperture ratio crucibles with an aperture ratio of 60% or more. The crucible of the present invention was found to be effective in terms of both the production rate of zinc oxide whiskers and the production rate of tetrabod-shaped zinc oxide whiskers.

22 To-7 In addition, - Comparing the heat treatment time of 100 g of zinc powder under the conditions of an external air supply rate of 3 (1/min) and a heating temperature of 960''C - Aluminium crucible odor test
minute, opening host corrosion-resistant stainless steel plate crucible lCj, -
46 minutes for those with partition plates, 36 minutes for those without partitions, and 126 to 20 minutes for those without partition plates with an aperture ratio of 20 to 60%, and tetrabod-like oxidation 27-22 minutes for Example 1 with a partition plate and an aperture ratio of 20-60% that allows the length of the needle-shaped part of the zinc whisker to be selectively created - 26-22 minutes for Example 2
1 minute, which made it possible to generate in a short time with the effect of selectively dividing. Furthermore, we investigated various materials for the high aperture half member and the bottom surface, but it is preferable to use a stainless steel plate that does not contain nickel because it has a low heat capacity. A corrosion-resistant stainless steel plate containing 18 to 20% chromium, 2 to 3% aluminum, and the balance iron, which is 6 to 6 times more than steel, was effective. .

23・＼

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a high aperture ratio crucible with a partition plate used in an example of the present invention, FIG. 2 is a schematic vertical cross-sectional view thereof, and FIG. 3 is a cross-sectional view showing the crucible placed in a Matsufuru furnace. Fourth
Figures 6 and 7 are electron micrographs showing the crystal structure of zinc oxide whiskers. 10...Side, 11...Dish-12,1
2'... Partition plate, 13... Crucible. Name of agent: Patent attorney Shigetaka Awano and 1 other person10
-11 Shikaku I3-11 Rudujopa

Claims (4)

[Claims] (1) The container has one open surface, and the facing side of this surface is from 0 to
It is a member with a low aperture ratio of 3%, and the side wall member is a member with a high aperture ratio of 20% or more, and the distance from the bottom is at least 15m.
A partition plate made of the same high aperture ratio member is provided facing the bottom surface at a distance of at least m or more and below the height of the side surface, and zinc powder having an oxide film is placed on the bottom surface, and heat treated in an atmosphere containing oxygen. A method for producing zinc oxide whiskers, which comprises selectively producing small zinc oxide whiskers on the upper side of a partition plate and large zinc oxide whiskers on the lower side. (2) The method for producing zinc oxide whiskers according to claim 1, wherein the partition plate has a planar shape. (3) The method for manufacturing zinc oxide whiskers according to claim 1, wherein the shape of the partition plate is wavy in a waveform facing the bottom surface. (4) The method for manufacturing zinc oxide whiskers according to claim 1, wherein the bottom surface of the low aperture ratio member is made of porcelain or a corrosion-resistant stainless steel plate that does not contain nickel.