JP5074787B2 - Manufacturing method of ceramic powder - Google Patents

Description

  The present invention relates to a method for producing a ceramic powder, and more particularly to a method for producing a ceramic with a reaction that generates a large amount of heat.

  In recent years, high-quality ceramic powders have been demanded in the electric and semiconductor fields. High-quality ceramic powders are manufactured by oxidizing, nitriding, and carbonizing high-purity metal powder with a high-purity gas body.

  In this production method, a large amount of heat is often generated during the reaction of the metal powder with the high-purity gas body (reactive gas), and the reaction temperature (temperature when the reaction actually proceeds) becomes excessively high. It was.

  Usually, the ceramic material (AB) obtained from the metal (A) and the reactive gas body (B) is more stable than the metal (A) in terms of heat and energy. However, in order for the metal (A) and the reactive gas body (B) to react, FIG. 7 (Noda Inayoshi, edited by “Inorganic Materials Chemistry-I”, Corona, 1977, P125, 3-2 “solid phase reaction” As shown in ")", it has to go through an active complex having a high energy level once. When this level is exceeded, a rapid reaction occurs at an accelerated rate, and the reaction product and tray become high temperature due to the reaction heat. In order to prevent high temperature, it has become a subject to prevent this rapid reaction.

  In addition, high-performance ceramic powders are required to have a fine crystalline size. Usually, the crystalline size depends on the reaction temperature and becomes finer as it is produced at a lower temperature. Moreover, when the reaction temperature at the time of manufacture becomes low temperature, the crushability of the aggregate of ceramic powder will improve.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the manufacturing method of the ceramic powder whose crystal grain diameter is fine and is excellent in crushability.

  In order to solve the above-mentioned problems, the present inventor has conducted extensive studies on a method for synthesizing ceramic powder by effectively removing reaction heat and reacting at a low temperature, and has obtained the following knowledge to make the present invention. It came.

That is, in a method for producing a ceramic powder in which a metal powder is held in a reactive gas atmosphere containing a reactive gas capable of reacting with the metal powder and heated to start the reaction, the temperature in the reaction chamber containing the metal powder is increased. While the temperature is below the activation temperature, the reactive gas is switched to an inert gas atmosphere with respect to the metal powder, and the temperature is further increased. When the temperature in the reaction chamber sufficiently exceeded the activation temperature, the heating was stopped and held, and a decrease in the furnace temperature was awaited. It was found that even when the furnace temperature was lowered by 300 ° C. or more, the reaction was started again and the reaction product (AB) was obtained by changing the atmosphere to the reactive gas body (B).
In the production method of the present invention, a reactor having a muffle that partitions the reaction chamber, a furnace shell that has an upper furnace shell and a lower furnace shell that are openable and closable, and that houses the muffle inside is provided. Used, regardless of the position of the muffle in the axial direction, the furnace shell is opened at the same opening to radiate the heat of the reaction chamber to the outside.
Further, it has been found that it is useful to make the heat in the reaction chamber radiated to the outside by, for example, opening the furnace (furnace shell) half and cooling the furnace body with air.

Usually, heat removal from a heat generating material is often performed using heat conduction between objects. However, it is well known that radiant heat transfer is more dominant than heat conduction at temperatures above 700 ° C. In the case of heat conduction, the amount of heat transfer is proportional to the power of the difference between the temperature of the generated object (T ₁ ) and the temperature of the absorbing object (T ₂ ). The amount of heat transfer is proportional to “(T ₁ ) ⁴ − (T ₂ ) ⁴ ” (unit of temperature is absolute temperature). For this reason, in the present invention, the heat in the reaction chamber can be radiated to the outside (outside of the reaction chamber). Therefore, in the subsequent steps, the temperature in the reaction chamber is radiated even if the reaction chamber becomes hot due to an exothermic reaction. , It is possible to suppress the temperature in the reaction chamber from becoming excessively high.

  In the method for producing a ceramic powder according to the present invention, the metal powder and the reactive gas react with each other in a state where heat generated in the reaction chamber can be radiated to the outside of the reaction chamber, thereby generating reaction heat. And reaction heat is radiated | emitted to the exterior of a reaction chamber, and the temperature (reaction temperature) in a reaction chamber falls. Due to this heat dissipation, the ceramic formation reaction proceeds at a low temperature. That is, the production method of the present invention exhibits the effect of producing a fine crystalline ceramic powder because the reaction proceeds at a low temperature.

  The method for producing a ceramic powder of the present invention is a production method in which a metal powder is held in a reactive gas atmosphere containing a reactive gas capable of reacting with the metal powder, and the reaction is started by heating and raising the temperature.

  Desirable embodiments of the production method of the present invention are shown below.

  The metal powder used is a fine powder of high purity, desirably 100 mesh or less, and the reactor used is desirably a tight furnace that can be maintained at 0.1 KPa or less when evacuated.

The inert gas to be used may be any gas that does not react with the metal powder, and argon (Ar) and nitrogen (N ₂ ) are recommended for oxidation and carbonization reactions, and argon (Ar) is recommended for nitriding reactions. .

  Desirable forms such as temperature rise and reaction will be described.

  Metal powder and, if necessary, additives are placed in a tray and charged into the furnace. Once the vacuum is replaced, the temperature is raised in an atmosphere of reactive gas.

  Subsequently, in a state where the temperature in the reaction chamber is equal to or lower than the activation temperature, the gas atmosphere is made inert from the reactive gas to the metal powder, and the temperature is further increased. The activation temperature is different from the so-called reaction start temperature, and is a temperature equal to or slightly lower than the reaction start temperature. The activation temperature varies greatly depending on the type of reactive gas used, but is usually about 600 to 2000 ° C.

  When the temperature in the reaction chamber sufficiently exceeds the activation temperature, heating is stopped and held, waits for the furnace temperature to drop, and when the furnace temperature has dropped sufficiently, the atmosphere is set to reactive gas again to complete the reaction. . In addition, it is desirable that the furnace (furnace shell) be opened halfway and the furnace body be cooled with air so that the heat in the reaction chamber can be radiated to the outside.

The degree of opening of the furnace shell may be about 1/10 to 1/2, and opening it too much will only cause thermal damage to the surroundings. A fan or turbo blower is recommended for air cooling. Next, the relationship between the temperature difference inside and outside the furnace and the amount of heat removal will be described .

  The cylindrical muffle of the reactor is made of stainless steel (for example, SUS304) or heat-resistant steel (25Cr, 20Ni steel, etc.), and the reactant is placed in a graphite container across the space without contact with the muffle. Assuming that

Radiant heat energy reactants in this case (1) of the muffle (2) to interact with a space (heat removal amount); Q ₁₂ is given by the following equation.

Where σ is the Stefan Boltzmann constant, A ₁ and A ₂ are the respective surface areas, ε ₁ and ε ₂ are the respective emissivities, and T ₁ and T ₂ are the respective absolute temperatures.

Next, the heat removal amount in two cases is calculated. Here, F (t) = T ₁ ⁴ −T ₂ ⁴ is set.

(Case 1)
This case is generally a common case, and is a case where T ₁ = 1500 ° C. and T ₂ = 1300 ° C. The difference between T ₁ and _{T 2} a is 200 ° C..

F (t) = (1773) ⁴ − (1573) ⁴ = 3.76 × 10 ¹²
(Case 2)
This case is a case using the manufacturing method of the present invention, where T ₁ = 1300 ° C., 1200 ° C., 1100 ° C., and T ₂ is 600 ° C. lower than T ₁ .

T ₁ = 1300 ° C. In ^{F (t) = 5.22 × 10} 12, T 1 = At 1200 ℃ F (t) = 4.13 × 10 12, T 1 = 1100 ℃ in F (t) = 3.19 × 10 ¹²

Even in the case where the reaction temperature (T ₁ ) is 1300 to 1100 ° C., which is 200 to 400 ° C. lower than the case 1 as in the case 2, the energy equal to or higher than the conventional radiant energy at 1500 ° C. It can be seen that heat can be removed.

For reference, the amount of heat removed per unit area when ε ₁ and ε ₂ are 0.9 and 0.6, T ₁ is 1200 ° C. (T ₂ = 600 ° C.), and A ₁ / A ₂ is 2/3, respectively. (Q ₁₂ ) is
Q ₁₂ = σ × 1 × 4.13 × 10 ¹² ÷ 1.55
= 12.8 × 10 ⁴ Kcal / m ²
It becomes.

In this case, although the reaction temperature (T ₁ ) is lower by 300 ° C., the heat removal amount is about 10% higher than the case where the reaction temperature (T ₁ ) is 1500 ° C. (conventional case). That is, it can be seen that the amount of energy that can be dissipated does not decrease even when the reaction temperature for the production of ceramics is lower than that in the prior art. As a result, by opening the furnace shell, the heat of the muffle is allowed to cool by radiant heat transfer so that the reaction heat can be dissipated through the muffle and the reaction temperature can be lowered.

  The production method of the present invention is a production method in which a metal powder reacts with a reactive gas to produce a ceramic powder, and the specific types of the metal powder and the reactive gas are not limited and are conventionally known materials. Can be used.

  In the production method of the present invention, ceramics can be produced by causing a reaction such as nitriding, carbonizing, and oxidizing a metal powder such as aluminum, silicon, boron, and titanium.

  As the reactive gas in the carbonization reaction, it is preferable to use methane gas. Methane gas is almost decomposed into carbon and hydrogen at 800 ° C. or higher and exhibits an excellent carbonization effect. Further, ethane gas, butane gas and the like and gases obtained by modifying them, such as RX gas, are known as high-performance carbonization gases, and these gases may be used. Moreover, nitrogen gas and ammonia gas can be mention | raise | lifted as reactive gas in nitriding reaction.

  Hereinafter, the present invention will be described using examples.

  As an example of the present invention, a nitriding furnace was prepared, and aluminum nitride powder was produced using this reactor.

(Nitriding furnace)
The nitriding furnace 1 according to the present embodiment includes a substantially cylindrical furnace shell 10, a heat-resistant muffle 14 having rib reinforcement inside the furnace shell 10, and an outer peripheral surface of the heat-resistant muffle 14 in the furnace shell 10. And an electric furnace having a heater (not shown). The structure of the nitriding furnace 1 of the present embodiment is shown in FIGS. FIG. 1 is a cross-sectional view showing the configuration of the nitriding furnace 1, and FIG. 2 is a cross-sectional view taken along the line II in FIG. 1.

  The furnace shell 10 is formed in a bottomed cylindrical shape whose axial direction extends along the horizontal direction. The heat resistant muffle 14 is disposed inside the furnace shell 10.

  The furnace shell 10 includes an upper furnace shell 11, a lower furnace shell 12, and a connection portion 13 that connects the upper furnace shell 11 and the lower furnace shell 12 in an openable / closable state. The upper furnace shell 11 and the lower furnace shell 12 both have a substantially boat-like shape, and are closed with a combination of openings. The contact surfaces of the openings of the upper furnace shell 11 and the lower furnace shell 12 were provided along the central axis of the heat-resistant muffle 14.

  The heat-resistant muffle 14 has a tight furnace structure that can be maintained at 0.1 KPa or less when evacuated by a vacuum pump (not shown). The heat-resistant muffle 14 has a substantially cylindrical shape with both ends closed with an inner diameter of 165 mm made of a heat-resistant metal. The heat-resistant muffle 14 is formed such that one end portion side of a substantially cylindrical shape can be opened and closed, and the raw material powder is disposed inside from the end portion.

The heat-resistant muffle 14 has the sample stage 2 installed therein. The sample stage 2 is a member for arranging the raw material (aluminum powder) to be nitrided in the heat-resistant muffle 14. The sample stage 2 is a ladder-shaped (substantially square-shaped) member (outer dimension: 70 × 100 ) formed by combining and joining seamless pipes (made of SUS304) having an outer diameter of 9 mm (FIG. 3). The sample stage 2 is formed in a state in which the end portion 200 of the pipe 20 extending in the width direction protrudes from the pipe extending in the longitudinal direction, and is arranged in the heat-resistant muffle 14 in a point contact with the eight portions of the end portion 200. Yes. That is, the heat transfer between the raw material arranged through the sample stage 2 and the heat-resistant muffle 14 is substantially achieved only by radiant heat transfer.

  The heat-resistant muffle 14 is placed in the lower furnace shell 12 with the furnace shell 10 opened, and is assembled by closing the upper furnace shell 11.

  The nitriding furnace 1 is provided with a gas introduction pipe 15 and a gas discharge pipe 16 connected to a gas supply device and a gas discharge device (both not shown), and supplies nitrogen gas and argon gas into the heat-resistant muffle 14. Thus, the atmosphere in the heat-resistant muffle 14 can be adjusted.

  The gas supply device has a nitrogen gas cylinder and an argon gas cylinder connected to the gas introduction pipe 15. The gas introduction pipe 15 has a mass flow meter for measuring the flow rates of nitrogen gas and argon gas flowing from the nitrogen gas cylinder and the argon gas cylinder. With this mass flow meter, the supply gas flow rate can be appropriately selected in the range of 2 to 50 L / min from the gas supply device into the heat-resistant muffle 14.

  The gas discharge device includes a gas discharge pipe 16 and a discharge valve that adjusts the amount of gas that is provided in the gas discharge pipe 16 and passes through the discharge pipe 16.

  The nitriding furnace 1 is provided with a pressure gauge (not shown) for measuring the gas pressure in the heat-resistant muffle 14.

  Further, the nitriding furnace 1 is provided with a thermocouple 17. The thermocouple 17 passes through the upper furnace shell 11 and is inserted into the furnace shell 10. The thermocouple 17 is provided in a state where the temperature measuring portion at the tip thereof is in contact with the heat-resistant muffle 14, and measures the temperature of the outer peripheral surface of the heat-resistant muffle 14. In this embodiment, a plurality of thermocouples (not shown) are provided in addition to the thermocouple 17.

  The nitriding furnace 1 further includes an air supply device, an air discharge device, a pressure gauge, a thermocouple 17, and a valve.

  In this embodiment, the aluminum powder nitrided in the nitriding furnace 1 is stored in the heat-resistant muffle 14 while being accommodated in the reaction tray 3. The reaction tray 3 is a member formed in a box shape having an outer shape of 110 × 360 × 60 mm made of graphite.

Example 1
First, 250 g of high-purity aluminum powder (99.997% or more) having an average particle diameter of 20 μm and 400 g of aluminum nitride powder (manufactured by Toyo Aluminum Co., Ltd.) having an average particle diameter of 1.6 μm are weighed and mixed uniformly. Then, the mixed powder is filled in the reaction tray 3. At this time, in order to measure the temperature of the workpiece (mixed powder in the tray 3), a thermocouple with an insulator was simultaneously inserted into the mixed powder.

  The reaction tray 3 filled with the mixed powder was placed inside the heat-resistant muffle 14. And it heated up slowly, evacuating for 1 hour using a vacuum pump.

  When the temperature in the furnace (temperature measured by the thermocouple 17) reached 450 ° C. due to the temperature increase, nitrogen gas was introduced into the heat-resistant muffle 14 from the gas supply device. Thereby, the inside of the heat-resistant muffle 14 became a nitrogen gas atmosphere.

  When the temperature was further increased and the temperature reached 580 ° C., the gas supplied from the gas supply device was switched to argon gas. Thereby, the inside of the heat-resistant muffle 14 became an argon gas atmosphere. Since the activation temperature of aluminum powder and nitrogen gas seems to be 600 to 650 ° C., it was heated in an inert gas atmosphere from a temperature slightly lower than this activation temperature.

  When the temperature reached 700 ° C., the gas introduced into the heat-resistant muffle 14 was switched from argon gas to nitrogen gas. The introduction amount (flow rate) of nitrogen gas was 4 L / min. At this time, the power switch of the heater for heating was turned off. In addition, the furnace shell 10 was opened, and the inside of the furnace shell 10 was blown with a fan. The furnace shell 10 was held in a state where the contact surfaces of the upper furnace shell 11 and the lower furnace shell 12 made an angle of 12 ° (opening: 2/15). The state where the furnace shell 10 is opened is shown in FIG.

  FIG. 5 shows the temperature change of the workpiece before and after the introduction of nitrogen gas at 700 ° C. was taken as the zero point of the reaction start.

  Ten minutes after the start of the reaction, the temperature of the outer wall of the heat-resistant muffle 14 is 350 ° C. or lower. On the other hand, after the workpiece temperature has decreased to 630 ° C., the temperature gradually increases.

  20 minutes after the start of the reaction, argon gas was added at 0.8 L / min to nitrogen gas (4 L / min) in the atmosphere (mixed gas of nitrogen gas and argon gas was introduced).

  47 minutes after the start of the reaction, a decrease in the work temperature was confirmed, and the argon gas was cut. Thereby, the inside of the muffle path 14 again became a nitrogen gas atmosphere.

  After 60 minutes from the start of the reaction, the workpiece temperature reached 450 ° C., so the reaction was judged to be complete.

  From the above temperature course, the synthesis of aluminum nitride was started at 630 ° C., passed through the maximum temperature; 930 ° C., and finally, it was judged that the synthesis reaction was completed at 880 ° C.

Here, the calorific value of 250 g of pure aluminum was 700 Kcal, and the surface area of the reaction tray 3 was 1120 cm ^2. Therefore, the amount of heat removal calculated using Equation 1 was 0.625 Kcal / cm ² . This amount of heat removal is an average value in a reaction time of 40 minutes.

(Example 2)
First, 450 g of pure aluminum powder and 400 g of aluminum nitride powder similar to those used in Example 1 are weighed and mixed uniformly. Then, the mixed powder is filled in the reaction tray 3. At this time, in order to measure the temperature of the workpiece (mixed powder in the tray 3), a thermocouple with an insulator was simultaneously inserted into the mixed powder.

  The reaction tray 3 filled with the mixed powder was placed inside the heat-resistant muffle 14. And it heated up slowly, evacuating for 1 hour using a vacuum pump.

  When the temperature in the furnace (temperature measured by the thermocouple 17) reached 450 ° C. due to the temperature increase, nitrogen gas was introduced into the heat-resistant muffle 14 from the gas supply device. Thereby, the inside of the heat-resistant muffle 14 became a nitrogen gas atmosphere.

  When the temperature was further increased and the temperature reached 580 ° C., the gas supplied from the gas supply device was switched to argon gas. Thereby, the inside of the heat-resistant muffle 14 became an argon gas atmosphere. Since the activation temperature of aluminum powder and nitrogen gas seems to be 600 to 650 ° C., it was heated in an inert gas atmosphere from a temperature slightly lower than this activation temperature.

  When the temperature reached 700 ° C., the gas introduced into the heat-resistant muffle 14 was switched from argon gas to a mixed gas of nitrogen gas and argon gas. The mixed gas was a mixed gas of nitrogen gas introduced at 2 L / min and argon gas introduced at 2 L / min. At this time, the power switch of the heater for heating was turned off. In addition, the furnace shell 10 was opened, and the inside of the furnace shell 10 was blown with a fan. The furnace shell 10 was held in a state where the contact surfaces of the upper furnace shell 11 and the lower furnace shell 12 made an angle of 12 ° (opening: 2/15).

  Then, when nitrogen gas was introduced at 700 ° C., the reaction started (0 minutes), and the temperature change of the workpiece and the heat-resistant muffle 14 was shown in FIG.

  Ten minutes after the start of the reaction, the temperature of the outer wall of the heat-resistant muffle 14 is 350 ° C. or lower.

  On the other hand, after the work temperature has dropped to 480 ° C. 20 minutes after the start of the reaction, the temperature gradually rises. 20 minutes after the start of the reaction, argon gas was further added at 1 L / min to the mixed gas (4 L / min) in the atmosphere (argon gas was introduced at 3 L / min).

  70 minutes after the start of the reaction, a decrease in the workpiece temperature was confirmed, and the argon gas was cut (only nitrogen gas was introduced at 2 L / min).

  After 80 minutes from the start of the reaction, the workpiece temperature reached 450 ° C., so the reaction was judged to be complete.

  From the above temperature course, the synthesis of aluminum nitride was started at 480 ° C., passed through the maximum temperature; 815 ° C., and finally, it was judged that the synthesis reaction was completed at 670 ° C.

  Here, since the calorific value of 450 g of pure aluminum is 1260 Kcal and the surface area of the reaction tray 3 is 1120 cm 2, the heat removal amount calculated using Equation 1 is 1.125 Kcal / cm 2. This amount of heat removal is an average value in a reaction time of 50 minutes.

(Evaluation)
When the aluminum nitride powder produced in each of the above examples was analyzed, it was found that all had a nitriding rate of almost 100%.

  Moreover, when the aluminum nitride powder of each Example was observed, it was confirmed that the particle diameter was approximately 1 μm or less. The particle diameter of the aluminum nitride powder of each example is approximately 1 μm or less, which indicates that the powder is a fine powder that has been difficult to manufacture by the conventional aluminum nitride manufacturing method. In addition, although the secondary particle which the primary particle condensed could be observed, it was able to be easily made into the fine aluminum nitride powder by performing the crushing process. The fine particle size of the aluminum nitride powder in each example is such that the reaction temperature decreases due to the furnace shell 10 being opened during the nitriding reaction and the heat of the heat-resistant muffle 14 being dissipated (in Example 1, 930 ° C. or less, Example 2). 815 ° C. or lower).

  From the above, the aluminum nitride powder of each example manufactured by the manufacturing method of the present invention is an aluminum nitride particle having a nitriding rate of almost 100% and a fine particle size of 1 μm or less. I understood.

  That is, it can be seen that by using the production method of the present invention, a high-quality ceramic powder having a fine crystal grain size and excellent crushability could be produced.

It is the figure which showed the structure of the nitriding furnace of the Example. It is the figure which showed the structure of the nitriding furnace of the Example. It is the figure which showed the structure of the sample stand used for the nitriding furnace of an Example. It is the figure which showed the structure of the nitriding furnace of the Example. 2 is a graph showing the temperature at the time of production of aluminum nitride in Example 1. 6 is a graph showing the temperature at the time of production of aluminum nitride in Example 2. It is the graph which showed the free energy of reaction.

Explanation of symbols

1: Nitriding furnace 10: Furnace shell 11: Upper furnace shell 12: Lower furnace shell 13: Connection part 14: Heat-resistant muffle 15: Gas introduction pipe 16: Gas discharge pipe 17: Thermocouple 2: Sample stage 3: Reaction tray

Claims (3)

In a method for producing a ceramic powder in which a metal powder is held in a reactive gas atmosphere containing a reactive gas capable of reacting with the metal powder, and the reaction is started by heating and heating,
In a state where the temperature in the reaction chamber containing the metal powder is lower than the activation temperature, the reactive gas is switched to an inert gas atmosphere with respect to the metal powder, and the temperature is further increased.
The heating is stopped when the temperature in the reaction chamber exceeds the activation temperature, and the reaction chamber is set as the reactive gas atmosphere in a state where the heat in the reaction chamber can be radiated to the outside.
Using a muffle which divides the reaction chamber, openably it provided having an upper furnace shell and the lower furnace shell, a furnace shell for accommodating the muffle inside, the reactor having,
What is claimed is: 1. A method for producing ceramic powder, comprising: opening the furnace shell at the same opening to radiate heat from the reaction chamber to the outside regardless of the position of the muffle in the axial direction. A muffle disposed in a state in which the reaction chamber is partitioned and its axial direction extends in a horizontal direction;
The upper furnace shell and the lower furnace shell having a substantially boat shape in which the abutment surfaces are formed along the axial direction and the muffle is coaxial in a closed state can be relatively swung by a connecting portion. A furnace shell formed to be openable and closable in a state, and containing the muffle inside,
Using a reactor having
The method for producing ceramic powder according to claim 1, wherein when the furnace shell is opened, the air is blown into the interior by a blower so that the high temperature of the reaction chamber can be radiated to the outside.   The method for producing a ceramic powder according to claim 1, wherein a temperature difference between the inside and outside of the reaction chamber is 300 ° C. or more.

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