JPH04132700A - Continuous production of zinc oxide whisker - Google Patents

Abstract

PURPOSE:To continuously and stably obtain the subject whisker of a large tetrapod-like shape for a long time with using a raw material such as Zn ingot by providing a specific construction in a heating furnace, continuously supplying Zn gas and subjecting to oxidation reaction. CONSTITUTION:Inside of a heating furnace 1 is vertically divided into a non- oxidative atmosphere 15 and an oxidative atmosphere 16 and Zn gas is continuously supplied from a Zn gas supplying port 13 installed in the non-oxidative atmosphere 15, then introduced into the oxidative atmosphere 16 to be subjected to oxidation reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for continuously producing zinc oxide in the form of tetrapods.

BACKGROUND OF THE INVENTION Zinc oxide whiskers have a wide range of uses, such as reinforcing materials for various materials, vibration damping materials, and electronic component materials that take advantage of their electrical conductivity and radio wave absorbing properties.

As a method for producing this zinc oxide Wisno 1, the following methods are known or proposed.

(1) In JP-A-50-6597, zinc and a zinc alloy made of a metal with a boiling point higher than zinc or a mixture thereof are heated in an oxygen-containing atmosphere to form an alumina sintered body and a mullite sintered body. It has been shown that zinc oxide can be formed on the underlying material such as the body.

(2) In Japanese Patent Publication No. 60-5529, a zinc raw material is placed in an inner cylinder provided inside an outer cylinder, and an inert gas such as nitrogen gas or argon gas is flowed into the inner cylinder to remove the zinc raw material. After heating to generate zinc vapor, this vapor is injected into the oxygen-containing atmosphere inside the outer cylinder using the above-mentioned inert gas as a carrier gas to oxidize and burn it, and then cooling air is blown in to heat the generated zinc oxide at 480°. C, / sec
It is disclosed that rapid cooling is performed at a cooling rate higher than that.

In addition, regarding this method, the Journal of the Chemical Society of Japan (1984゜V
o l 6. In P2S5), zinc vapor is introduced into the combustion chamber together with a carrier gas (the nozzle structure is triple-layered, and argon gas is flowed twice around the central zinc vapor nozzle to block oxygen from the nozzle tip). It has been shown that

(3) In Japanese Patent Application No. 0i10743, zinc powder having an oxide film is continuously supplied into a fluidized bed furnace, and the zinc powder is heated while being fluidized with an inert gas to generate zinc vapor. A method has been proposed in which oxygen gas or oxygen-containing gas is continuously supplied to a portion of the fluidized bed furnace containing zinc vapor to cause the zinc vapor to undergo an oxidation reaction.

Problems to be Solved by the Invention However, the method (1) above is unsuitable for continuous production because it requires a base material to generate whiskers.

Furthermore, the method (2) above has the problem of clogging of the zinc vapor nozzle. In other words, the nozzle that spews out zinc vapor along with the carrier gas is in contact with an oxygen-containing atmosphere, so oxygen is completely cut off, and if the oxidation reaction continues for a long time, hard deposits of zinc oxide will form around the nozzle. death,
This is a phenomenon that blocks the vent. Regarding this problem, as mentioned above, there is an idea to improve the flow of inert gas around the nozzle, but this method cannot be expected to be sufficiently effective in large-scale industrial equipment where the diameter of the nozzle is large. In addition, in order to obtain whiskers with large dimensions, it is necessary to slow down the ejection speed of zinc vapor, but the slower the ejection speed, the more pronounced the above phenomenon becomes.For this reason, this method It was not possible to produce a whisker.

Furthermore, in the method (3) above, there is a problem that the zinc raw material must be once powdered, and that precise flow control of the powder in the fluidized bed furnace is required.

As described above, the conventional methods each have their own problems, and it is difficult to stabilize large tetrabod-shaped zinc oxide whiskers with an average length of several tens of micrometers or more using a simple raw material such as a zinc ingot. A manufacturing method that allows continuous production has not yet been found.

The present invention solves the above-mentioned conventional problems, and aims to provide a manufacturing method that can stably and continuously produce large tetrabod-shaped zinc oxide whiskers having an average length of several tens of μm or more from a zinc ingot. purpose.

Means for Solving the Problems In order to achieve the above object, the present invention vertically separates the inside of a heating furnace into a non-oxidizing atmosphere and an oxidizing atmosphere, and a zinc vapor supply port is provided in the non-oxidizing atmosphere. The purpose is to continuously supply zinc vapor from the zinc vapor supply port, introduce the zinc vapor into the above-mentioned oxidizing atmosphere, cause the zinc vapor to undergo an oxidation reaction, and produce tetrabod-shaped zinc oxide whiskers. A carrier gas is used to introduce the zinc vapor into an oxidizing atmosphere.

In the present invention, gases for creating a non-oxidizing atmosphere include so-called inert gases such as helium, neon, argon, nitrogen, and carbon dioxide, as well as oxygen-free combustion exhaust gas produced by burning propane, charcoal, and the like.

The method of the present invention is further divided into two methods depending on the density of the gas, that is, whether the density of the gas is higher or lower than that of oxygen.

Helium is used as a gas to create a non-oxidizing atmosphere.

When using a gas with a lower density than oxygen, such as neon or nitrogen, create a non-oxidizing atmosphere above the heating furnace and an oxidizing atmosphere below the heating furnace, and close the gas outlet to the oxidizing atmosphere. It is installed at the bottom to allow the generated zinc oxide whiskers to fall and be collected. The heating furnace shall have a closed structure except for the gas outlet.

In addition, when using a gas with a higher density than oxygen, such as argon, carbon dioxide, or combustion exhaust gas, as the gas for creating a non-oxidizing atmosphere, a non-oxidizing atmosphere is created in the lower part of the heating furnace.
An oxidizing atmosphere is formed above the inside of the heating furnace, and a gas outlet is provided above the oxidizing atmosphere to create an upward gas flow, and the generated zinc oxide whiskers are guided to a predetermined location by the gas flow and collected. do it like this. In this case as well, the heating furnace has a closed structure except for the gas outlet.

On the other hand, as the oxidizing gas, an oxygen-containing gas such as oxygen gas or air is used, and these gases are continuously supplied into the furnace from a predetermined position in the heating furnace to maintain a predetermined oxygen concentration.

As the carrier gas for transporting the zinc vapor, the gas that forms the non-oxidizing atmosphere described above is used. Therefore, the carrier gas primarily contributes to the transport of zinc vapor, but also to the formation of a non-oxidizing atmosphere.

Effect: According to the above-described means, zinc vapor is transported by the carrier gas from the zinc vapor supply port provided in the non-oxidizing atmosphere of the heating furnace to the oxidizing atmosphere, and zinc oxide whiskers are generated by an oxidation reaction.

If the gas forming the non-oxidizing atmosphere is a gas with a lower density than oxygen, such as helium, neon, or nitrogen, the non-oxidizing atmosphere gas will gather above the oxidizing atmosphere gas in the heating furnace, and the exhaust port will be located at the bottom. Because of this, the gas flow in the furnace is directed downward, and the non-oxidizing atmosphere and the oxidizing atmosphere are kept separated. If the gas forming the non-oxidizing atmosphere is a gas with a higher density than oxygen, such as argon, carbon dioxide, or combustion exhaust gas, the non-oxidizing atmosphere gas will collect below the oxidizing atmosphere gas in the heating furnace, and the gas will be exhausted. Since the outlet is located at the top, the gas flow in the furnace is directed upward, and the non-oxidizing atmosphere and the oxidizing atmosphere are kept separated.

In this way, since the zinc vapor supply port is always located in a non-oxidizing atmosphere and isolated from oxidizing gases, regardless of the jetting velocity of zinc vapor at the zinc vapor supply port,
Since zinc oxide is not deposited around the zinc vapor spout and the speed of the zinc vapor can be arbitrarily selected, large tetrapod-shaped zinc oxide whiskers with an average length of several tens of micrometers can be stabilized. can be produced continuously.

Example Examples thereof will be described below with reference to the drawings.

FIG. 1 shows the structure of a first embodiment of the zinc oxide whisker production apparatus, in which the density of the gas forming the non-oxidizing atmosphere is lower than that of oxygen.

In Fig. 1, 1 is a heating furnace main body, 2 is a metal zinc evaporation chamber provided at the upper part of the heating furnace main body 1, 3 is an oxidizing gas inlet, 4 is a carrier gas inlet, and 5 is a non-oxidizing gas inlet. 6 is a metal zinc inlet, 7 is a gas outlet, 8 is a whisker collection port, 9 is a heater that heats the heating furnace main body 1 and the zinc evaporation chamber 2, 10 is metal zinc, 11 is metal zinc 1o
12a, 12b, 12c are oxygen concentration meters that measure the oxygen concentration inside the heating furnace main body, 13 is a zinc vapor supply port, 14 is the generated zinc oxide whisker, 15 is a non-oxidizing atmosphere area, and 16 is an oxidizing It is a sexual atmosphere area.

In the apparatus having the configuration shown in FIG.
Then, heat the metal zinc evaporation chamber 2 to a temperature of 880°C or higher, preferably 920°C.
Heat to ~980°C. Next, a carrier gas is supplied from the carrier gas inlet 4 and a non-oxidizing gas is supplied from the non-oxidizing gas inlet 5 to create a non-oxidizing atmosphere above the interior of the metal zinc evaporation chamber 2 and the heating furnace main body 1. . The non-oxidizing gas supplied from the non-oxidizing gas inlet 5 may also serve as the carrier gas supplied from the carrier gas inlet 4.

At the same time, oxidizing gas is supplied from oxidizing gas inlet 3,
The lower half of the interior of the heating furnace body 1 is made into an oxidizing atmosphere. The state of the atmosphere inside the heating furnace main body 1 is determined by the oxygen concentration meters 12a, 1.
2b, 12C, the oxygen concentration meter 12a shows a value near 0% oxygen concentration or a value of = (minus), indicating that the oxygen concentration meter 12a is in a non-oxidizing atmosphere. If b and 12c show values of oxygen concentration + (plus), it indicates that the atmosphere in the heating furnace 1 has been separated. In this case, - (minus) indicates a reducing atmosphere. Therefore, the boundary between the non-oxidizing atmosphere region 15 and the oxidizing atmosphere region 16 is located between the oxygen concentration meters 12a and 121]. At this time, all the zinc vapor supply ports 13 exist in a non-oxidizing atmosphere and are isolated from an oxidizing atmosphere. Note that the position of the boundary between the two atmospheric regions is moved depending on the flow rate of the non-oxidizing gas or the carrier gas.

After adjusting the atmosphere in this way, a zinc ingot is introduced from the metal zinc inlet 6 and melted in the crucible 11 to generate zinc vapor and gas. 1, and as soon as it enters the oxidizing atmosphere 16, an oxygen reaction is started and whiskers] 4 are generated, fall while growing, and are collected from the whisker collection port 8 by a whisker collection device (not shown). Be it.

On the other hand, the continuously supplied non-oxidizing gas and oxidizing gas are continuously discharged from the gas exhaust lower, except for oxygen consumed in the oxidation reaction.

In this example, helium is used for the hourly gas,
The carrier gas also served as a non-oxidizing atmosphere forming gas. Air was used as the oxidizing gas. The temperature inside the heating furnace body 1 is 9
The temperature of the metal zinc evaporation chamber 2 was 9300C.

The flow rate of carrier gas is 3e/min, and the flow rate of air is 20e/min.
The value of the oxygen concentration meter 12a indicating the separation state of the atmosphere is 0.0 at the preliminary adjustment stage.
5%, 12F) is -1-1,3,1%, ], 2c is 1-17%, and during the oxidation reaction, 12a is 1.
05%, 12b +0.5%, and 12c 10.7%.

FIG. 3 shows an electron micrograph of zinc oxide whiskers obtained in the experiment. The length of the tetrabod-shaped zinc oxide tube 1 from the core to the tip is 30 to 100 μm.

FIG. 2 shows a second embodiment of the present invention, that is, an embodiment of a zinc oxide whisker manufacturing apparatus in which the density of the gas forming the non-oxidizing atmosphere is higher than that of oxygen.

In FIG. 2, the same parts as in FIG. 1 are designated by the same numbers, detailed explanations are omitted, and differences will be explained.

In FIG. 2, since a gas heavier than oxygen is used as the gas forming the non-oxidizing atmosphere, a non-oxidizing atmosphere region 15 is formed in the lower part, an oxidizing atmosphere region 16 is formed in the upper part, and the zinc evaporation chamber 2. Carrier gas inlet 4. Non-oxidizing gas inlet 5. Addition of metallic zinc] 6. The main difference from Example 1 is that the crucible 11 is located at the bottom of the heating furnace body 1, and the whisker collection port 8, which also serves as a gas discharge port, is located at the top of the heating furnace body 1. The procedure for operating this apparatus and producing zinc oxide whiskers is the same as in Example 1. Oxygen concentration meter 1
2a, 12b, ]-2c is upside down from Example 1, but the boundary between the oxidizing atmosphere region 16 and the non-oxidizing atmosphere 15 is the same as the oxygen concentration meters 12a and 12b.
Or it is formed between 12a and 12c.

In the apparatus of the second example, carbon dioxide gas was used as the carrier gas, and Yaria gas was also used as the non-oxidizing atmosphere forming gas, and the other conditions were the same as in Example 1. As a result, electronics w1 in FIG. As the mirror shows, a zinc oxide whisker with a length of 15-130 μm from the core to the tip was (q).

Furthermore, with the apparatus of the second embodiment, the carrier gas is propane fuel exhaust gas, the non-oxidizing atmosphere is propane combustion exhaust gas, which is the same as the carrier gas, and air is used as the oxidizing gas to produce zinc oxide. Manufactured whiskers.

Propane gas was combusted at a mixing ratio of 5 to 7% air to create flue gas.

The temperature of the heating furnace was the same as in Example 1, the carrier gas flow rate was 3 e/min, and the air was continuously supplied at a flow rate of 20 e/min. The value of the oxygen concentration meter, which indicates the state of separation of the atmosphere in the heating furnace, is determined when the oxygen concentration meter 12a is -
4.2%, 12b shows +9.5%, 12c shows 12.8%, and during the oxidation reaction, 12a shows -4.5%, 12
b was -0.45% and 12c was +0.11%.

An electron micrograph of zinc oxide whiskers obtained by this method is shown in FIG.

In addition, in order to confirm the long-term stability of the zinc vapor supply port 13, continuous operation for 8 hours was performed using all the methods described in the above examples. No deposits were present, and it was confirmed that oxygen was sufficiently blocked.

Effects of the Invention As is clear from the explanation in Section 2, according to the present invention, by using a raw material that has not been preprocessed, such as a zinc ingot, the average length from the core to the tip is several tens of μm. It is possible to provide a method for stably and continuously producing large tetrabod-shaped zinc oxide whiskers for a long period of time, and productivity can be significantly increased.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing the configuration of the apparatus of the first embodiment used in the continuous production method of zinc oxide whiskers of the present invention, and FIG. 2 is a schematic vertical cross-sectional view showing the configuration of the apparatus of another example. Figures 3 to 5 are electron micrographs of zinc oxide whiskers produced by the method of the present invention. ■... Heating furnace body, 2... Metal zinc evaporation chamber, 7... Gas exhaust port, 8... Wisno 1 collection port, 11... ... Crucible, 13...
... Zinc vapor supply port, 14 ... Zinc oxide whisker, ]5 ... Non-oxidizing atmosphere area, 16 ...
... Oxidizing atmosphere area. Name of agent: Patent attorney Haruaki Ogata and two others Procedural amendment Shima Ko February 20, 1991 S.

Claims (3)

[Claims] (1) Separate the inside of the heating furnace vertically into a non-oxidizing atmosphere and an oxidizing atmosphere, and continuously supply zinc vapor from a zinc vapor supply port provided in the non-oxidizing atmosphere to the oxidizing atmosphere. 1. A method for continuously producing zinc oxide whiskers, characterized by conducting an oxidation reaction. (2) Using a gas with a lower density than oxygen in the non-oxidizing atmosphere to form a non-oxidizing atmosphere above and a non-oxidizing atmosphere below, and providing a gas outlet at the bottom of the oxidizing atmosphere. 2. The method for continuously producing zinc oxide whiskers according to claim 1, wherein the zinc oxide whiskers are collected by falling. (3) Using a gas with a higher density than oxygen in the non-oxidizing atmosphere to form a non-oxidizing atmosphere downward and an oxidizing atmosphere upward, a gas outlet is provided above the oxidizing atmosphere to direct the upward gas. 2. The method for continuously producing zinc oxide whiskers according to claim 1, wherein the generated zinc oxide whiskers are guided to a predetermined location and collected by the gas flow.