JP2584033B2 - Manufacturing method of zinc oxide whisker - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a zinc oxide whisker having a huge tetrapod-like structure, and more particularly, to a method for producing a tetrapod-like structure having a needle-like portion having a long length. The present invention relates to a firing method for producing zinc oxide whiskers of several microns or more.

Conventional technology Conventionally, zinc oxide used as a general industrial material is:
This is a so-called French method, which is an aggregate of cluster-like particles having various sizes, particularly shapes. There is also a method of forming thin and short needle-like crystal particles at a high yield (for example, Japanese Patent Publication No. Sho 60-5529), which is an improvement of the above-mentioned French method, in which metal zinc vapor is rapidly cooled by heating. Therefore, a giant crystal is not generated, and a needle-shaped crystal having a minute size (a needle-like length of about 1 to 1.5 μm) is obtained. Needle-like crystals having such dimensions are approximately two orders of magnitude smaller in size than various industrial whiskers currently on the market. For this reason, a common feature of the whisker is metal,
The reinforcing effect on ceramics, resin and the like is at the level of the above-mentioned brittle zinc oxide, and no remarkable effect as a whisker is recognized.

In other words, whiskers that are single crystalline in the form of fibers have much higher mechanical strength than bridging substances of the same substance, and as a reinforcing substance to obtain high mechanical strength by mixing this into other substances. Attention has been paid to metals, metal oxides,
Industrial whiskers such as metal carbides and metal nitrides are commercially available. As for zinc oxide, there is an example of a whisker having a length of mm order (Japanese Patent Publication No. 50-5597). However, these are simple needle-like bodies, and since a zinc alloy is used for the purpose, irregularities are included in the crystal. Or a laboratory study that requires a substrate during the growth of the crystal or requires a long time for complicated equipment and operation.

Furthermore, in the actual production of zinc oxide, zinc vapor as a material is heated in advance in a non-oxidizing atmosphere such as nitrogen gas at a high temperature to generate zinc vapor gas, and this non-oxidizing zinc vapor is mixed. Normally, zinc gas is oxidized to produce zinc oxide crystals by introducing a gas into a high-temperature furnace formed in an oxidizing atmosphere containing oxygen. In this case, most of the zinc oxide produced is used. It is a so-called zinc white with a cluster oxide.

SUMMARY OF THE INVENTION The present invention provides a novel and simple method for producing zinc oxide whiskers having a size required for an industrial whisker and having a tetrapod-like structure. More specifically, the present invention provides a novel whisker manufacturing method relating to a firing step for performing evaporation, nucleation, and crystal growth of metal zinc as a material.

Means for Solving the Problems The present invention is to generate zinc oxide whiskers in the air or on a substrate by heating and oxidizing zinc powder, which is essentially a material, in an atmosphere containing oxygen. Here, the zinc powder used as the material has the structure of the firing furnace and the structure of the firing furnace so that the processes of evaporation by heating, generation of crystal nuclei for generating oxide crystals, and crystal growth to form a tetrapod proceed in the same place. Conditions are given. The zinc powder used here is pure zinc, which is partially oxidized, whose surface is already covered with an oxide film, and metals and nonmetals other than zinc are so-called impurities. It is possible to use those that are mixed to a certain extent.

A feature of the present invention is that zinc evaporation generated by heating is immediately oxidized by oxygen contained in the atmosphere, and at the same time, zinc vapor that can supply enough zinc atoms to grow the resulting crystal into a tetrapod is maintained. It is in the content of the conditions to create the atmosphere required for This condition was found out of the structure of the firing furnace and the repetition of an extremely large number of experiments. One is to use a porous material as the furnace wall material of the firing furnace, and the other is to control and supply a certain range of the amount of zinc vapor and the amount of oxygen in the atmosphere corresponding to the production of tetpod. is there.

The zinc oxide whisker obtained in the present invention is composed of a nucleus at the center of the crystal and needle-like crystal parts extending from the nucleus in four different axial directions. The base of the needle-like crystal part has a diameter of 0.1 to 10 μm. Yes, the length from the base to the tip of the needle-shaped portion is 1 to 300
μm. Also, a small amount of needle-like crystal parts containing triaxial, biaxial, or quadriaxial or more may be mixed during the growth of the crystal or after contact with other whiskers, or some of the whiskers may break apart or grow. Is the result of stopping. In addition, another Tetopod is sintered or adhered to a part of the complete Tetopod shape due to the contact of these growth portions. Further, another shape, that is, a plate-like crystal may grow or adhere to the needle-like portion. According to the production method of the present invention, a tetrapod-shaped product can be mainly produced.

In the present invention, zinc powder is used as the zinc metal used in the firing step. Here, the particle size of the zinc powder is 0.1 to 500 μm
Can be obtained, among which 1 to 300 μm gives good results. This is because it is one of the factors that have a very significant effect on the generation rate of zinc vapor in the firing process of the present invention. That is, when the particle size is extremely small,
The evaporation rate of zinc vapor is extremely fast with the same amount of metal at a constant temperature equal to or higher than the evaporation temperature point of zinc metal, and it becomes virtually impossible to control the amount of oxygen in the atmosphere described below. It is discharged outside the crystal formation system (most commonly outside the firing furnace), or even if it stops inside the formation system, it may aggregate in the metal state depending on the atmospheric conditions, Become. In addition, it becomes a needle-like sintered product (sea urchin shell shape) or a plate shape. On the other hand, 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 corresponding to the amount of generated zinc vapor. Pod-like whiskers hardly form.

In order to more easily control the evaporation amount of the zinc vapor, in the present invention, the surface of the zinc powder used as a material for firing is coated with an oxide film in advance rather than pure zinc powder, or zinc oxide is mixed. Used. This is because the increase in the evaporation rate due to the particle diameter can be reduced by the progress of oxidation. This is because the surface of the zinc metal particles is covered with an oxide film,
Having the effect of suppressing the vapor diffusion of zinc metal inside the particles into the atmosphere, increasing the heat capacity of the particles as a whole,
Or, it is considered due to an apparent increase in the evaporation temperature.

By using the powdered material as described above, while controlling the amount of evaporation of the zinc vapor, and controlling the atmosphere in the firing furnace, particularly the oxygen partial pressure, the relative ratio between the zinc vapor partial pressure and the oxygen partial pressure in the furnace. Experimental results have shown that the tetrapod-like zinc oxide whisker of the present invention can be produced by limiting the stoichiometric ratio to the stoichiometric ratio required for forming zinc oxide (ZnO). Here, in order to form a larger whisker, it is necessary to control the atmosphere of the crystal forming system to a state in which there is a considerable excess of zinc vapor and oxygen deficiency with respect to the stoichiometric value. On the contrary, it is necessary to increase the amount of oxygen due to lack of zinc vapor.

The present invention is characterized in that zinc metal is calcined and oxidized under the above atmosphere. As a means for controlling the atmosphere in the reaction furnace, a zone for generating zinc vapor is separately provided in advance, and zinc vapor is provided at a later stage using a carrier gas (specifically, a non-oxidizing gas such as nitrogen). In general, a so-called gas-phase reaction method is adopted in which the material is transferred to an oxidation reaction zone and oxidized by an oxygen-containing gas introduced from the outside. In this case, since the carrier gas is indispensable, it is extremely difficult to set the relative ratio between the partial pressure of zinc vapor and the partial pressure of oxygen to a region necessary for forming the giant whiskers as described above, and the industrial yield is also high. It is almost impossible if you consider

In the present invention, the atmosphere for forming such a huge whisker is zinc powder (solid), zinc vapor (liquid),
It can be formed by mixing zinc gas (gas) and oxygen (gas) in the same place, and is a so-called SL-
By forming a G three-phase reaction field, nucleation of zinc oxide, extraction of the crystal habit of the tetrapod-like crystal, and subsequent huge growth of the tetrapod-like whisker crystal are performed extremely smoothly. A high structure became possible. In other words, it is the core of the present invention that the extremely dense zinc vapor partial pressure region using the zinc powder solid as a supply source and the dense oxygen partial pressure region that promotes the end of whisker formation are continuously formed.

As a specific furnace configuration for forming the atmosphere as described above, as a method for introducing an oxygen-containing atmosphere into a steam field of zinc powder, using a normal circulation furnace, oxygen partial pressure control of the oxygen-containing atmosphere to be introduced and By using a method of temporal control (oxygen partial pressure in the atmosphere corresponding to the amount of generated zinc vapor and its time control) and a firing furnace in which the wall material of the furnace is made of a porous air-permeable material, Due to the evaporation of zinc vapor inside the furnace and the subsequent oxidation reaction, the reduced pressure in the entire atmosphere accompanying the fixation of oxygen in the atmosphere causes only fresh air equivalent to this reduced pressure to naturally flow through the wall material from outside the furnace. The method introduced into the furnace is the specific content of the present invention.

Atmosphere control in the flow furnace described above is performed by controlling the supply amount of the atmosphere gas (oxygen gas) so that the atmosphere becomes a predetermined atmosphere under the input amount of the zinc powder as the material and the temperature conditions of the reaction field necessary for the evaporative oxidation of zinc. (Partial pressure) is externally controlled. On the other hand, when using a porous furnace wall later, by selecting the permeability of the material of the furnace wall, new oxygen is naturally supplied from outside the wall in accordance with the progress of the steam oxidation reaction of the zinc powder. Therefore, by providing a predetermined atmosphere (oxygen partial pressure) outside the furnace, it is possible to provide an extremely simple and reliable method in which there is no need to manually perform temporal control as the reaction proceeds. Things.

Examples Some examples of the present invention will be described below in detail.

Example 1 A reaction tube made of Colts was installed in a usual siliconit tube furnace, and the reaction tube was sealed at both ends with a rubbed cap and used as a firing furnace for zinc oxide whiskers. Atmosphere gas required for the reaction was supplied from one of the branch pipes and discharged from the branch pipe of the other cap so that the atmosphere in the pipe could be exchanged. Further, a U-shaped pipe serving as a manometer and a water bubbler are connected to the branch pipe on the discharge side via a Teflon tube, and the atmospheric gas in the pipe discharged from the reaction pipe is bubbled through the water to outside the reaction system (furnace). Outside). This bubbler is used not only for confirming that the atmosphere gas is flowing when flowing into the pipe, but also as a water seal on the discharge side when the atmosphere is fixed (still). At this time, the absorption amount (reduction amount) accompanying the reaction of the atmospheric gas components in the reaction tube is also used to give a pressure reduction instruction by the water level of the manometer provided in the preceding stage using the backflow of water in the bubbler.

On the other hand, a boat made of Colts was used as a reaction tube, and zinc powder was weighed and charged into the boat to form a reaction bed.

In the procedure for actually reacting, zinc powder as a material was weighed in advance and put into a boat made of Colts, and this boat was temporarily placed at the end of the reaction tube. At this time, the reaction tube had a sufficient length to reach the outside of the heating zone of the tubular furnace, and the end of the reaction tube where the boat was installed was sufficiently far away from the heating zone of the tubular furnace. Zinc powder has almost no thermal effect due to the heating of the furnace, and even when the heating zone in the furnace is heated to the high temperature required for the reaction, the temperature of the boat is at most 200.
° C or less. In addition, during normal atmospheric circulation, the temperature of the boat was further reduced because the boat was installed at the upstream end of the atmosphere gas flow in the reaction tube.
In this state, both ends of the reaction tube are sealed with caps, the branch pipe of the cap on the side where the boat is installed is connected to a gas mixing bottle via a Teflon tube, and this mixed bottle is connected to a high-pressure cylinder of oxygen and nitrogen, respectively. did. The outlet branch of the cap was connected to a manometer and a water bubbler. Next, in order to synthesize the atmosphere in the reaction tube required for the reaction, the flow rates of the oxygen gas and the nitrogen gas were respectively adjusted and were fed into the reaction tube. The oxygen concentration in the synthesis atmosphere gas was measured by introducing a part of the gas discharged from the water bubbler after flowing out of the reaction tube into an oxygen meter.

The reaction tube is then heated to a temperature sufficient to evaporate the zinc metal (800
(1000 ℃), and after confirming that the heating zone of the reaction tube has reached the equilibrium temperature, insert the push rod from the other branch tube attached to the cap at the end of the reaction tube to heat the boat to the heating zone. I moved all at once. Immediately after, the connection tube on the atmosphere gas inflow side was closed with a pinch cock, and the atmosphere in the reaction tube was fixed (stationary). Here, the zinc metal in the boat inserted into the heating zone in the reaction tube is heated at a stretch above the evaporating temperature, and zinc vapor is rapidly generated and fills the reaction tube, and at the same time, reacts with oxygen in the atmospheric gas by an oxidation reaction. After several minutes, white zinc oxide powder was formed in the boat and the reaction tube. At this time, after the water flows backward from the water bubbler connected outside the furnace on the downstream side to the upstream side, it flows into the U-tube manometer installed and connected in front of it, and after confirming that it has stabilized at the equilibrium position, measurement Then, the reduced pressure in the reaction tube was measured.
The reduced pressure in the reaction tube corresponds to the reduction in the oxygen partial pressure in the atmosphere due to the reaction between the zinc metal and the oxygen in the atmosphere, and the amount of oxygen that has contributed to the reaction can be calculated.

After the zinc oxide powder generated in the reaction tube by the above procedure was taken out from the reaction tube, the appearance was observed with a scanning electron microscope, and when the powder was a tetrapod-shaped powder, the size and distribution of the shape were measured. . At the same time, a small amount of yellow-white powder is formed at the bottom of the boat, but when observed with a scanning electron microscope, it does not take the shape of a tetrapod, but is an aggregate of so-called granular crystals, It turned out to be.

In the production of the tetrapod-like zinc oxide crystal according to the present embodiment, the oxygen concentration in the atmosphere before the reaction in the reaction tube was changed as shown in Table 1 while keeping the amount of zinc powder of the material constant, and the respective concentration conditions were changed. The distribution of the tetrapod-like zinc oxide produced at that time (the amount of the tetrapod-like zinc oxide powder with respect to the amount of zinc metal charged is expressed as a percentage) and the distribution of the size of the tetrapod-like crystal produced are shown in the shape of a tetrapod-like needle. Length (length from the base of the tetrapod to the tip of the needle) from the maximum value to the minimum value, the central value of the entire distribution, and the oxygen concentration in the atmosphere immediately after the end of the reaction. The results are shown in Table 1. Also, typical examples of the large and small tetrapod-like whiskers generated here are shown in FIG. 1 and FIG. 2 by electron micrographs, respectively, and typical examples of granular crystals that do not become tetrapod-like are shown in FIG. 3 by electron micrographs. Indicated.

Example 2 Using the same reaction system as in Example 1, only the reaction procedure was as follows. That is, the zinc metal powder of the material is weighed in advance,
The boat was placed on a board made of Colts, and the boat was placed at the end of the reaction tube. Thereafter, both ends of the reaction tube were sealed with caps, and an atmosphere gas having a predetermined oxygen concentration was passed. After confirming that the oxygen concentration of the atmosphere gas in the reaction tube was stabilized, the reactor was heated, and after the temperature of the heating zone of the reaction tube reached an equilibrium state, the reactor was immediately inserted into the heating zone, and immediately the atmosphere gas was sent. Stopped entering. Thereafter, after a predetermined time, an atmosphere gas having a predetermined oxygen concentration was passed again to continue the reaction. After the reaction was completed, the generated zinc oxide powder was taken out of the reaction tube, and the shape was confirmed.

The oxygen concentration in the flowing atmosphere before the reaction performed here,
Table 2 summarizes the time during which the gas flow was stopped, the oxygen concentration in the flowed atmosphere again, and the shape observation results of the whiskers generated under these conditions.

Example 3 Using the same reaction system as in Example 1, the reaction procedure and reaction conditions were as follows. That is, a zinc metal powder as a material was weighed in advance and put into a boat made of Colts, and this boat was placed at an end of a reaction tube. Thereafter, both ends of the reaction tube were sealed with caps, air was supplied, and the inside of the reaction tube was set to an atmospheric atmosphere. Here, the influence on the formation of whiskers when the flow rate (flow velocity) was changed was examined. As in the case of Example 2, the flow conditions of the atmosphere were a static atmosphere (the flow was stopped) for a certain period of time at the beginning of the reaction, and then the flow was resumed. The test was performed in the case where the test was performed in an atmosphere. The results are summarized in Table 3.

Example 4 A main reaction tube made of a small-diameter heat-resistant inorganic fiber was arranged concentrically with the hollow of a large-diameter Colts reaction tube, and one end of the reaction tube (downstream of the atmosphere gas flow) was closed with a homogeneous material. The end was made to be able to cover with a cap made of the same material. On the other hand, both ends of the outer reaction tube had the same configuration as in Example 1 and connected the same additional equipment. The procedure using this reaction tube is almost the same as that of Example 2, except that the boat made of Colts containing zinc powder as the material removes the cap of the outer reaction tube and also removes the cap of the main reaction tube. Then, it was installed at the end of the main reaction tube. Thereafter, a nitrogen balun gas whose oxygen concentration has been adjusted in advance is passed through the outer reaction tube, and after confirming that the temperature of the heating zone in the main reaction tube has reached equilibrium, the boat is pushed from the outside to the heating zone with a push rod, Immediately, the end of the main reaction tube was capped and sealed to react.

At this time, the oxygen concentration of the atmosphere flowing around the outer periphery of the main reaction tube was changed, and the yield and shape of the whisker formed were examined. These results are summarized in Table 4.

Example 5 A box-shaped heat-resistant steel inner box (muffle) having only a front surface (furnace door side) opened was arranged in a normal box-type electric furnace. A pipe for feeding fresh air (atmospheric gas) from the outside of the furnace is welded to a surface opposite to the opening surface of the muffle, and a steel flange is provided on an opening edge of the opening surface, And stick a heat-resistant seal made of heat-resistant non-woven fabric on the entire circumference of this flange surface,
The door can be closed in close contact with the inner surface of the furnace door. The seal inside the muffle by this seal does not ventilate even with a slight pressure difference between the inside and outside of the muffle, but it is possible to discharge and exhaust the pressurized inside the muffle (pressurized by feeding fresh gas from outside). It has become about. For this reason, in a steady ventilation state, this muffle furnace is considered to be a so-called flow furnace, and the atmosphere can be controlled in the same manner as in Examples 2 and 3. On the other hand, the zinc metal powder as the material is spread on the bottom surface of the corrosion-resistant dish in a uniform thickness, and after the oxygen concentration and the temperature of the atmosphere in the muffle have stabilized, the furnace door is opened and quickly inserted into the muffle. The furnace door was immediately closed to react. When the atmosphere in the muffle was set under the conditions corresponding to those of Examples 2 and 3, the yield and formation distribution of the generated whiskers almost corresponded to those of Examples 2 and 3.

Example 6 A box-type electric furnace whose wall material is made of a porous heat-resistant inorganic fiber material (however, the outer case is made of steel and the porous case has an air space) is used. No steel muffle as used in Example 4 was used therein, and neither a fresh air inlet nor a pipe was provided in the furnace. The reaction procedure using this furnace was exactly the same as in Example 5. The variable of the reaction here is only the charged amount of the material zinc metal powder, and the atmosphere in the furnace depends on natural ventilation through the furnace wall material. As a result of another study, the ventilation through the furnace wall material showed that the zinc metal powder in the furnace was heated and evaporated, and the oxygen in the furnace atmosphere was consumed by the oxidation reaction, thereby reducing the furnace pressure. It has been confirmed that a pressure difference occurs between the inside and outside of the furnace, and the atmosphere outside the furnace flows into the furnace through a porous wall material. Here, the results of the yield and the shape of the whisker formed with respect to the charged amount of the material zinc metal powder are summarized in Table 5. In addition, the charged amount of zinc powder was described as a value with respect to the air volume of the furnace.

Example 7 The same reaction system as that used in Example 1 was used. The procedure was as follows. First, an empty Colts boat containing no material was placed at the center of the heating zone of the reaction tube, and both ends of the reaction tube were capped. And the atmosphere gas was passed through the reaction tube. On the other hand, a branch pipe is provided separately in advance on the upstream side cap, and a straight tube made of Colts penetrates this branch pipe so that it reaches directly above the boat installed in the center of the heating zone of the reaction tube. The end should be long enough to be located far enough outside the reaction tube, and T
The following branch pipe is connected, and the opening in the center line direction of this straight pipe is connected directly to the nitrogen gas cylinder via a flow meter, and the upward opening perpendicular to the center line is connected to the zinc metal powder holding bottle for charging the material. Connected. After confirming that the temperature of the heating zone in the reaction tube has stabilized, flow nitrogen gas into the material supply tube, supply zinc powder from the reservoir bottle to the supply tube in a fixed amount, and place it in the nitrogen gas flow to continuously feed the boat in the reaction tube. It was dropped and supplied to react. At this time, the yield of whiskers to be produced and the shape distribution of tetrapod-like zinc oxide crystals change depending on the oxygen concentration in the atmosphere, the amount of flowing atmosphere, and the material supply rate. The effects of these fluctuation factors were very similar to the results of Example 3, but overall there was a tendency for smaller whiskers to form.

Example 8 Normal heat and corrosion resistant materials (porcelain, Inconel, etc.)
At the both ends of an electric furnace comprising a tunnel type muffle, a nitrogen flow curtain is provided for the purpose of preventing outside air (atmosphere) from flowing into the muffle, and an inlet for an atmosphere component gas for controlling the atmosphere inside the muffle. And the outlet was arranged in an appropriate position. Here, the inlet is connected to a synthetic atmosphere sending device, while the outlet is connected to an exhaust pipe that prevents the back diffusion of the atmosphere. Further, a chain-shaped or belt-shaped conveyor made of a heat-resistant and corrosion-resistant material is provided on the bottom surface of the muffle. This conveyor is driven by a device provided outside the muffle furnace. The procedure for producing zinc oxide whiskers using this tunnel furnace was as follows.

The synthesized atmosphere gas flows into the furnace, and after the atmosphere in the furnace reaches the specified composition, the electric furnace is energized, the muffle is heated, and the temperature of the atmosphere in the furnace is raised to the predetermined temperature. Make sure that you do. Here, a plurality of dish-shaped containers made of a heat-resistant and corrosion-resistant material are prepared, and a predetermined amount of zinc powder is scattered on the bottom surfaces of the containers in a uniform thickness. Lined up. After this,
The conveyor was moved at a determined speed and the rows of containers with previous materials were transported sequentially into the furnace. The driving speed of the conveyor at this time is adjusted so that all of the zinc powder scattered in one material container can remain in the furnace for a time sufficient to be completely converted to zinc oxide. The atmosphere in the furnace was substantially the same as that in Example 3, and the composition was such that the total amount of the material contained in the tunnel furnace corresponded to the material input amount in Example 3. Here, as a matter of course, the amount of zinc powder in the furnace increases until a plurality of vessels are introduced from the vessel initially introduced into the furnace to the entire area of the furnace. Therefore, the composition of the atmosphere gas at this time is changed according to a predetermined program. After the material container once occupies the whole area in the furnace, the material can be continuously transported from the furnace inlet to a new material container in an atmosphere having a uniform composition. In order to carry out the reaction under the conditions of Example 1 or 2, the material containers are transported intermittently. That is, fresh air is exchanged in the furnace immediately before the container is fed into the furnace, and after all the material in the container has been converted into zinc oxide, the atmosphere in the furnace is exhausted together with the discharge of the container from the furnace. This is made possible by making the cycle intermittent. The tetrapod-shaped zinc oxide whiskers produced by this method had a shape and distribution very similar to those of Examples 1, 2, and 3. In this case, the manufacturing conditions (temperature, atmosphere composition, atmosphere circulation speed, conveyor driving speed,
By precisely maintaining the input amount of the material zinc metal, etc.), a large amount of tetrapod-like zinc oxide whiskers can be produced.

Further, the previous muffle is constituted by the porous material used in Examples 4 to 6, and the outside is further provided with a double muffle structure made of a non-porous material so as to cover the muffle. It was also confirmed that a continuous furnace having the same effect as in Examples 4 to 6 was possible. At this time, as in the previous case, when there is no material in the entire furnace, no special atmosphere control is performed, and the amount of fresh air according to the reaction amount of the material in the furnace naturally flows through the muffle wall material. Since it is supplied, there is an advantage that complicated atmosphere control becomes unnecessary.

Effect of the Invention As is clear from the results in Examples 1 to 7, the effect of the present invention is that the oxygen concentration in the atmosphere at the time of the reaction, that is, the amount of oxygen in the atmosphere before the reaction, The distribution of the shape (size) of tetrapod-like whiskers and the yield of formation, despite the other reaction conditions being the same, depending on the amount of oxygen remaining in the atmosphere from which the amount of oxygen being removed is subtracted, or the oxygen concentration Can be changed. This means that whiskers are often used as an additive in composite materials by dispersing them in various matrix materials (for example, ceramics, plastics, rubber, glass, and metals). Depending on the type of material, there is inevitably a desirable geometrical size to exert its combined effect. In this sense, in producing whiskers, being able to freely distribute the size is a very important issue in manufacturing. Met. According to the present invention, larger whiskers (60-400 μ
m, the distribution center is 50 μm or more) before the reaction is started so that the residual oxygen concentration in the atmosphere during the reaction is 10% or less, more preferably 3 to 5% or less. This can be achieved by determining the oxygen concentration in the atmosphere or the atmosphere gas to be circulated from the relationship with the amount of zinc metal powder of the material to be charged. Conversely, smaller whiskers (1 to 100 µm with a distribution center of 50 µm or less)
To produce, the residual oxidation concentration during the reaction is 20% ~ 60%
Further, it is more desirably possible to determine the oxygen concentration in the atmosphere before the start of the reaction or in the flowing atmosphere gas so that the concentration becomes 30 to 50%. On the other hand, according to the reaction in a closed system as in Example 1, the zinc powder of the material charged from the oxygen partial pressure in the system before the start of the reaction and the oxygen partial pressure in the system after the end of the reaction was completely converted to zinc oxide. As a result of calculating the oxygen excess ratio with respect to the amount of oxygen necessary to produce a larger whisker, the oxygen excess ratio must be negative, that is, in an oxygen-deficient state, to generate a larger whisker. The shape can be controlled by increasing the excess oxygen ratio to a positive value, specifically, from 20 to 50%.

In the present invention, it is an object of the present invention to provide a manufacturing method for controlling the shape of a whisker to be generated by controlling the atmosphere in the reaction furnace as described above. As a specific method, how to determine the atmospheric concentration of a batch type (closed type) furnace and a flow type furnace and how to determine the concentration when the concentration is changed with time have been described in Examples.

Another specific manufacturing method according to the present invention is a method using a reactor constituted by a porous and air-permeable furnace wall, and has been specifically described in Examples 4 and 6. Originally, in a reaction furnace, the reaction components (in this case, oxygen) from outside the system fluctuate randomly during the progress of the reaction, as in other embodiments of the present invention, in order to facilitate control of the reaction conditions. In order to avoid this, it is usual to use a closed furnace or an atmosphere circulation furnace controlled by humans. However, here, a furnace composed of air-permeable furnace walls was installed in the atmosphere or in a synthesized atmosphere, and the necessary oxygen was naturally taken in from the atmosphere outside the furnace as the reaction progressed, Is to be completed. This is because the formation reaction of the zinc oxide whisker of the present invention is an oxidation reaction, and as shown in Example 1, the oxidation in the atmosphere in the furnace before the start of the reaction is consumed with the progress of the reaction. As a result, the pressure in the furnace is reduced in pressure, so that the fresh air (containing oxygen) is smoothly introduced through the furnace wall with a pressure difference from the outside of the furnace to compensate for the reduced pressure. At this time, the whisker generated by setting the oxygen concentration in the atmosphere outside the furnace so that the amount of the material charged in the furnace further matches the reaction rate of the oxidation reaction (depending on the furnace temperature). Can also adjust the yield and shape distribution. By using this method, even in the case of a reaction with a high speed that cannot be followed by human atmosphere control, it has an extremely simple configuration, more than the technical effect of being able to follow easily, and is necessary when necessary. This is extremely effective because the amount can be controlled automatically.

In the embodiment, some of the most typical examples have been described. However, the control method and the configuration of the permeable furnace wall and the material thereof are not limited to those in the embodiment, and are not limited to the atmosphere described above. The effect of the present invention is not impaired as long as the condition of the oxygen content is satisfied.

[Brief description of the drawings]

FIG. 1, FIG. 2 and FIG. 3 are electron micrographs showing the crystal structure of zinc oxide obtained under different conditions.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Hideyuki Yoshida 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. Inside the company (72) Inventor Takashige Sato 1006 Kazuma Kadoma, Kadoma City, Osaka Inside Matsushita Electric Industrial Co., Ltd.

Claims (5)

(57) [Claims] A zinc oxide whisker characterized by firing zinc powder in a furnace having a porous furnace wall and introducing fresh air through the furnace wall from outside the furnace wall by decompression due to an oxidation reaction in the furnace. Manufacturing method. 2. A process for producing zinc oxide whiskers, characterized in that a zinc powder is fired in an oven having a non-breathable furnace wall through an atmosphere containing oxygen with oxygen partial pressure and its time controlled. . 3. The method for producing a zinc oxide whisker according to claim 1, wherein the reaction system is an atmosphere flow type reaction system in which oxygen is adjusted and supplied from the outside so that the oxygen concentration in the atmosphere during the oxidation reaction becomes constant. 4. The process for producing zinc oxide whiskers according to claim 1, wherein an atmosphere batch reaction system is used in which the oxygen concentration before the start of the reaction is adjusted so that the residual oxygen concentration after the completion of the oxidation reaction is constant. . 5. The method according to claim 1, wherein the atmosphere is stopped for a period of time from immediately after the start of the oxidation reaction until the residual oxygen concentration in the atmosphere becomes 0%, and then the atmosphere is circulated using an atmosphere step type reaction. A method for producing the zinc oxide whisker described in the above.