JP2021038901A - Nitriding reaction furnace - Google Patents

Abstract

To provide a batch-type nitriding reaction furnace capable of uniformly completing a nitriding reaction in a short time, and suppressing deterioration of a heater and a heat insulation material caused by a by-product gas.SOLUTION: A nitriding reaction furnace has a heat insulation casing 1, a reaction chamber 5 surrounded by a shield wall 13 held on a bottom plate 11 with an exhaust port 17, and a heater 3 disposed at an outer side, are disposed in the heat insulation casing 1, trays 19 respectively having an opening at a center portion, accommodating a reaction material and having a cutout on a side wall, are stacked in multiple stages on the bottom plate 11 in the reaction chamber 5, a nitrogen gas supply pipe 21 is penetrated through the openings of the trays, a nitriding reaction occurs by bringing the nitrogen gas supplied from the nitrogen gas supply pipe 21 into contact with the reaction material, and an unreacted nitrogen gas and a by-product gas are passed through the cutouts of the side walls of the trays 19, then passed through a clearance S formed between the trays 19 and the shield wall 13, and discharged from the exhaust port 17 of the bottom plate 11.SELECTED DRAWING: Figure 1

Description

The present invention relates to a nitriding reactor applied to a nitriding reaction at a high temperature.

Various nitrides having excellent heat resistance and also excellent properties such as thermal conductivity and electrical insulation, such as aluminum nitride (AlN) and boron nitride (BN), add nitrogen to the raw material powder of various metals or metal compounds. Manufactured by contacting and reacting at high temperature. Moreover, and excellent silicon nitride mechanical properties such as hardness (Si 3 _{N 4),} even or gallium nitride having a semiconductor characteristic (GaN) and there are indium nitride (InN), it is similarly prepared by nitriding at high temperature ..

As a high-temperature reactor that can be applied to the above-mentioned nitriding reaction at high temperature, a box-shaped container (hereinafter, also referred to as a setter) containing raw materials is loaded in multiple stages in a furnace surrounded by a heat insulating material. There is known a batch type furnace in which a heater is arranged around this reaction vessel (see, for example, Patent Documents 1 to 3).
Such a batch type high temperature reactor has an advantage that a large amount of raw materials can be subjected to a nitriding reaction at one time because box-shaped containers containing raw materials are loaded in multiple stages. In addition, the batch type high temperature reactor has a great advantage over the continuous type high temperature reactor in that the operating conditions can be adjusted for each production batch and a wide variety of products can be produced separately as compared with the continuous type high temperature reactor.

By the way, in the batch type high temperature reactor having the above structure, the gas to be reacted with the raw material or the atmospheric gas is supplied from the peripheral part of the box-shaped container, or the gas supply pipe is passed through the central part of the box-shaped container. Means such as supplying gas from the center of the container are adopted, but there are problems that it takes a long time to complete the reaction or it is difficult for the reaction to be carried out uniformly. In addition, there is a problem that the heater arranged in the furnace and the surrounding heat insulating material deteriorate in a short period of time due to the gas produced as a by-product during the reaction. In particular, when a reducing nitride reaction using a metal oxide as a raw material is carried out using a reducing agent such as carbon powder, volatile substances of the metal oxide and oxidizing gas such as carbon dioxide are by-produced, so that the product is made of carbon. Deterioration of heaters and heat insulating materials is remarkable.

Japanese Unexamined Patent Publication No. 61-282790 Japanese Unexamined Patent Publication No. 61-282785 Japanese Unexamined Patent Publication No. 4-273988

Therefore, an object of the present invention is to provide a batch type nitriding reaction furnace capable of completing the nitriding reaction uniformly in a short time and further suppressing deterioration of the heater and the heat insulating material due to the by-product gas. It is in.

According to the present invention, in a nitriding reaction furnace for performing a nitriding reaction,
The nitriding reactor has a heat insulating casing and has a heat insulating casing.
In the heat insulating casing, a reaction chamber surrounded by a shield wall held by a bottom plate provided with an exhaust port and a heater arranged outside the reaction chamber are provided.
In the reaction chamber, trays having an opening in the center, containing reaction raw materials to be subjected to the nitriding reaction, and having notches on the side walls are loaded in multiple stages on the bottom plate. At the same time, a nitrogen gas supply pipe extending through the opening of the tray is provided.
The nitriding reaction is carried out by bringing the nitrogen gas supplied from the nitrogen gas supply pipe into contact with the reaction raw material contained in the tray, and the unreacted nitrogen gas and the by-product gas are formed on the side wall of the tray. The nitriding reaction is characterized by having a structure in which the gas is discharged from the exhaust port of the bottom plate through the gap formed between the peripheral edge of the tray and the shield wall through the notch. A furnace is provided.

In the nitriding reactor of the present invention, the following aspects are preferably applied.
(1) A preheating chamber is provided in the upper part of the reaction chamber, and nitrogen gas heated in the preheating chamber is supplied to a tray arranged in the reaction chamber through the nitrogen gas supply pipe.
(2) As the reaction raw material, a mixed powder containing oxygen-containing aluminum powder and carbon powder is used.
(3) As the reaction raw material, a mixed powder containing boron oxide powder, carbon powder and an auxiliary agent is used.
(4) A mold release layer made of a nitride plate-shaped molded body or powder is laid inside the tray, and the reaction raw material is arranged in layers on the mold release layer.
(5) Heating by the heater is performed so that the temperature in the reaction chamber is in the range of 1200 to 2200 ° C.
(6) The planar shape of the tray is circular.

In the nitriding reaction furnace of the present invention, nitrogen gas is supplied from the center of each tray containing the reaction raw material to be reacted with nitrogen, and unreacted nitrogen gas and by-produced gas are cut off formed in the tray. The structure is such that the material is discharged to the outside of the tray (the gap formed between the peripheral edge of the tray and the shield wall) through the notch. That is, the gas produced as a by-product of the nitriding reaction is rapidly released to the outside without staying on the reaction raw material contained in the tray. Therefore, the nitriding reaction is not suppressed by the by-produced gas, and the nitrogen gas can be quickly brought into contact with every corner of the reaction raw material contained in the tray. As a result, the nitriding reaction can be sufficiently advanced in a short time, and the nitriding reaction can be uniformly advanced.

Further, in the present invention, the reaction chamber is separated from the heater and the heat insulating casing by the shield wall. That is, the by-produced gas or the like has a structure that does not come into contact with the heater or the heat-insulating casing. Therefore, deterioration of the heater or the heat-insulating casing is effectively suppressed, and the life of the device is extremely long.
In particular, in the furnace structure of the present invention, since the gas flow is from the central portion to the peripheral portion of the tray, nitrogen gas having an extremely small amount of impurities can be supplied to the raw material layer, and the nitriding reaction can be made smoother. Ideal for letting you do it.

Schematic side sectional view of the nitriding reactor of the present invention. A plan sectional view taken along the line AA in the nitriding reactor of FIG. The schematic perspective view which shows the form of the tray which holds the reaction raw material in the nitriding reaction furnace of FIG. The figure which shows the state of the reaction raw material contained in a tray. FIG. 6 is a schematic view showing a flow path of nitrogen gas in the nitriding reactor of FIG. The plan view which shows the form of the preheating plate arranged in the preheating chamber in the nitriding reaction furnace of FIG. FIG. 2 is a schematic side sectional view showing a preferable example of a storage form of a reactive raw material on a tray when boron nitride is produced using the nitriding reaction furnace of the present invention.

With reference to FIGS. 1 and 2, the nitriding reactor of the present invention has a basic structure in which a heater 3 and a reaction chamber 5 are provided inside a heat insulating casing 1.

The heat-insulating casing 1 is made of a material having high heat-insulating properties and is formed in a cylindrical shape. However, since it is usually excellent in heat resistance, it is made of carbon, and is formed by stacking blocks made of carbon fiber, for example. The casing. As the carbon material used for the heat insulating casing, it is preferable to use a fibrous carbon molded body in order to improve the heat insulating performance. Further, for the purpose of improving durability, a C / C composite material sheet or the like may be attached to the inner surface of the furnace as an example of a preferable embodiment.
The fibrous carbon molded body is produced by laminating carbon fibers or impregnating them with a resin. Molding is performed by carbonizing and graphitizing a resin impregnated with a resin that is easily carbonized.

Further, the heater 3 is of a type that is heated by resistance heating, and since it is necessary to heat the reaction chamber 5 to a high temperature in the nitriding reaction, a heater made of carbon, preferably graphite, is used. To. For example, as shown in FIG. 2, they are symmetrically arranged at four locations in the casing 1 so as to surround the reaction chamber 5.

As shown in FIG. 1, the heater 3 is held by a holder 9 attached to the tip of a support rod 7 extending through the heat insulating casing 1 and is held in a reaction chamber 5. It should have a length that exists around the entire height direction of the. Therefore, when the height of the reaction chamber 5 is large, the heater 3 may be divided into upper and lower parts. That is, it can be divided into those arranged around the upper portion of the reaction chamber 5 and those existing around the lower portion of the reaction chamber 5.

Further, although not shown, the output of the heater 3 is controlled based on the temperature data of a thermocouple or a radiation thermometer provided in the heat insulating casing so that the temperature can be controlled. There is.
The inner diameter d of the heat insulating casing 1 may be set to a size such that the temperature inside the reaction chamber 5 is usually heated to a temperature suitable for the nitriding reaction by the heater 3.
Further, although not shown, a frame made of stainless steel or the like can be provided on the outer surface of the heat insulating casing 1 in order to stably hold the casing 1.

In the present invention, the reaction chamber 5 is formed of a bottom plate 11 and a tubular shield wall 13 provided so as to cover the bottom plate 11. That is, the internal space surrounded by the bottom plate 11 and the shield wall 13 is the reaction chamber 5, the heater 3 described above has a structure arranged outside the reaction chamber 5, and the heat insulating casing 1 The inner surface of the reaction chamber 5 is completely separated from the reaction chamber 5.

The bottom plate 11 is placed on a pedestal 15 provided at the bottom of the heat insulating casing 1. An exhaust port 17 is formed in the center of the bottom plate 11, and the reaction chamber 5 is formed from the exhaust port 17 by vacuuming through an exhaust pipe 19 communicating with a hole 15a formed in the pedestal 15. The structure is such that exhaust is performed from the inside.
Further, the shield wall 13 is attached to the cradle 15 so that the bottom plate 11 is completely covered by the shield wall 13. This makes it possible to prevent gas from leaking between the cradle 15 and the shield wall 13.
Such a bottom plate 11 and a shield wall 13 are made of a material having high heat resistance, for example, carbon, preferably graphite or the like.

In the present invention, trays 19 containing reaction raw materials to be subjected to the nitriding reaction are stacked in multiple stages in the reaction chamber 5 surrounded by the bottom plate 11 and the shield wall 13. A gap S serving as a gas flow path is formed between the outer surface of the trays 19 stacked in multiple stages and the inner surface of the shield wall 13.

With reference to FIG. 3A, the tray 19 is composed of a bottom wall 19a and a side wall 19b rising from the peripheral edge of the bottom wall 19a, and the upper ends of the side wall 19b are spaced apart from each other in the circumferential direction. Therefore, a plurality of notches 19c (four in the figure) are formed point-symmetrically. A hollow cylinder 19d is formed upright at the center of the bottom wall 19a. That is, the nitrogen gas supply pipe 21 penetrates the tray 19 loaded in multiple stages through the hollow cylinder 19d and extends to the lowermost tray 19x. The lower end of the nitrogen gas supply pipe 21 is closed, and a large number of small holes 21a (omitted in FIG. 1) are formed in the pipe wall on the inside of each of the stacked trays 19. (See FIG. 4), nitrogen gas is supplied to the inside of each tray 15. The tray 19 has an outer diameter smaller than the inner diameter of the tubular shield wall 13, whereby a gap having an appropriate size is provided between the outer surface of the tray 19 and the inner surface of the shield wall 13. S is formed.

As shown in FIG. 3B, a plurality of legs 19e are formed in the tray 19x located at the bottom of the stacked trays 19, and the above-mentioned gaps are formed. The S is in such a form that it communicates with the space Y formed between the lower surface of the tray 19x and the bottom plate 11.
Instead of forming the foot 19e as described above on the lower surface of the tray 19, an appropriate table is provided on the peripheral edge of the bottom plate 11, and the tray 19x is placed on the table to communicate with the space S. It is also possible to form a space Y.

As shown in FIG. 4, powder of the reaction raw material is laid on the bottom wall 19a of the tray 19. Naturally, the thickness t of the reaction raw material is set to such a size that the reaction raw material does not spill from the notch 19c or the hollow cylinder 19d in the center.

With reference to FIG. 5, with the above structure, the gas flow Z of the nitrogen gas introduced into the nitrogen gas supply pipe 21 is discharged from the small hole 21a formed in the supply pipe 21. The gas flow Z that passes through the tray 19 from the center of each tray 19 and flows into the gap S between the outer surface of the tray 19 and the inner surface of the shield wall 13 through the notch 19c described above, and flows into the gap S. Will flow into the space Y between the lower surface of the lowermost tray 19x and the bottom plate 11, and will be discharged to the outside from the exhaust port 17 formed in the bottom plate 11.

As can be understood from such a gas flow Z of nitrogen gas, nitrogen gas flows from the central portion of each tray 19 to the void S formed by the peripheral edge portion of each tray 19 and the shield wall 13, and at this time. The nitriding reaction is carried out in contact with the reaction raw materials contained in each tray 19, and the gas produced as a by-product of this reaction promptly exists outside the tray 19 together with the unreacted nitrogen gas. It is discharged into the gap S, and is further discharged from the exhaust port 17 through the space Y. That is, the gas produced as a by-product of the nitriding reaction is immediately discharged without staying in the tray 19, and the reaction between the reaction raw material and nitrogen proceeds without being hindered by the by-product gas. It is possible to significantly reduce the production time of the nitride in the above. Moreover, since the gas passing through the tray 19 is quickly discharged without stagnation, the reaction raw material contained in the tray 19 can be uniformly nitrided. For example, the reaction raw material located at the peripheral portion of the tray 19 is also nitrided in the same manner as the reaction raw material located at the central portion.

In the present invention, the shield wall 13 is often formed into a cylindrical shape as shown in FIG. 2 from the viewpoint of allowing the above-mentioned nitrogen gas to flow smoothly in a laminar flow state without being disturbed. Further, the planar shape of the tray 19 is preferably circular. That is, if the corners are present on the shield wall 19 or the tray 19, the nitrogen gas (unreacted nitrogen gas and by-product gas) is disturbed when it hits the corners, and the gas flow tends to stagnate, especially in the vicinity of the corners. This is because the nitriding reaction of the position reaction raw material becomes unstable, and the nitriding reaction may become non-uniform.

_{The inner diameter D 1 of the} tray 19 as described above is not particularly limited, but is usually 200 mm or less, particularly 10 to 10 so that the amount of nitride produced for each tray 19 is in an appropriate range. The range is preferably about 80 mm. Further, the height h of the tray 19 is not particularly limited, but the tray 19 is provided so that the height t of the reaction raw material (powdered) contained in the tray 19 is about 10 to 80 mm. it is preferably set according to the inner diameter D _1. If this height h is too small, the processing amount for each tray 19 will be small, and in order to mass-produce nitrides industrially, the number of stacking stages of the tray 19 must be increased more than necessary, and as a result, the number of stacking stages of the tray 19 must be increased. The shield wall 13 and the casing 1 become excessively large, and the work of stacking the trays 19 containing the reaction raw materials, the work of assembling the shield wall 13, and the work of taking out the tray 19 after the reaction is completed are large. It becomes a thing. Further, if the height h is too large, it may be difficult to nitrid the deep part of the reaction raw material.
Thus, the hollow cylinder the height h ₁ of the height or the notch 19c of 19d which center is formed of the tray 19 does not enter the inside of the reaction raw material is a hollow cylinder 19 which is accommodated in the above-mentioned amount, and The height is set so that it does not spill from the notch 19c.

Further, the width and number of the plurality of notches 19c formed in the tray 19 may be set so that the gas flow Z from the center of the tray 19 to the external void S is even in the circumferential direction. The notch 19 of is arranged so as to be point-symmetrical. Further, the number of notches 19 is four in FIG. 3, but it can be two, three or five or more.

Further, the outer diameter D ₂ of the tray 19 described above can be set to about 50 to 95% of the inner diameter D ₃ of the shield wall 13 so that suction from the exhaust pipe 19 through the exhaust port 17 is efficient and smooth. It is suitable for ensuring a good gas flow.

In the present invention, the tray 19 having the above-described form is formed of a heat-resistant material used for various nitriding reactions, reduction nitriding of oxides, and the like, and for example, carbon, particularly graphite, is preferably used. In addition to this, the tray 19 may be formed of a sintered body of ceramic powder such as alumina, silicon carbide, and boron nitride. It is also a preferred embodiment to prevent deterioration of the carbon tray by placing a plate made of a sintered body or a molded body of ceramic powder such as alumina, silicon carbide, or boron nitride on a tray made of carbon.

The number of loading stages of the tray 19 described above is set so that an industrially sufficient amount of nitride can be obtained in one batch according to the size of the tray and the like, and is usually set to 5 to 40 stages.

In the above-mentioned nitriding reactor of the present invention, it is preferable that a preheating chamber 23 is formed in the upper part of the reaction chamber 5 partitioned by the shield wall 13. That is, the nitrogen introduction pipe 25 penetrates the casing 1 and is connected to the upper part of the preheating chamber 23, while the upper end of the nitrogen gas supply pipe 21 described above is connected to the lower part of the preheating chamber 23. That is, the nitrogen gas flows from the introduction pipe 25 into the preheating chamber 23, is introduced into the nitrogen gas supply pipe 21 from the preheating chamber 23, and as described above, the nitrogen gas is supplied from the supply pipe 21 into the tray 19. That is, since the reaction for nitriding the reaction raw material used in the tray 19 (for example, direct nitriding or reduction nitriding) is performed at an extremely high temperature, the inside of the reaction chamber 15 is heated to a predetermined reaction temperature by the heater 3. Even so, if the temperature of the nitrogen gas supplied into the tray 19 is low, the nitriding reaction may become unstable. Therefore, a preheating chamber 23 is provided above the reaction chamber 5, and the nitrogen gas introduced into the nitrogen supply pipe 21 is passed through the preheating chamber 23 heated to the same temperature as in the reaction chamber 5 to be preheated. Is desirable.

Such a preheating chamber 23 heats the nitrogen gas to a high temperature as much as possible by lengthening the residence time of the nitrogen gas introduced from the nitrogen introduction pipe 25 as much as possible. For example, the heat resistance is similar to that of the shield wall 13. A preheating plate 29 having a gas flow vent is stacked inside a box-shaped frame 27 formed of a material.

The above-mentioned preheating plate 29 is formed of carbon having high thermal conductivity, preferably a sintered body of graphite or boron nitride, but in order to prolong the residence time, the preheating plate 29 has a different position of the gas flow permeation port. , It is preferable to use these in combination.

For example, in FIG. 6A, an opening 31 serving as a gas permeation port is formed in the center, and a central opening preheating plate 29a is shown. The central opening preheating plate 29a is provided with airflow regulating protrusions 33 arranged in a ring shape at regular intervals in the circumferential direction so as to surround the central opening 31.
Further, FIG. 6B shows a peripheral small hole preheating plate 29b in which a large number of small holes 34 serving as gas flow permeation ports are distributed on the peripheral edge.

By alternately stacking the central opening preheating plate 29a and the peripheral small hole preheating plate 29b as described above in the frame body 27 to form the preheating chamber 23, the residence time of nitrogen gas in the preheating chamber 23 is lengthened. can do. That is, the nitrogen gas introduced from the nitrogen introduction pipe 25 into the preheating chamber 23 flows onto the central opening preheating plate 29a through the small holes 34 formed on the peripheral edge of the peripheral small hole preheating plate 29b. The nitrogen gas that has flowed onto the central opening preheating plate 29a passes between the airflow regulation protrusions 33 and flows from the central opening 31 onto the peripheral small hole preheating plate 29b. By making the flow of nitrogen gas zigzag with the periphery-center-periphery-center in this way, the residence time can be lengthened and the nitrogen gas can be heated to a sufficiently high temperature.

In this way, the sufficiently heated nitrogen gas is introduced from the nitrogen gas supply pipe 21 into the reaction chamber 5 maintained at a predetermined reaction temperature, and the nitriding reaction is carried out to bring the nitride onto the tray 19. Obtainable.
After completion of the reaction, the heat insulating casing 1 is opened, the preheating chamber 23 is taken out, then the shield wall 13 is pulled out to take out the tray 19, and the reaction product (nitride) on the tray 19 is recovered.
The recovered nitride is appropriately subjected to processes such as high purification and classification by operations such as oxidation, pickling, washing with water, and drying, and is used as a product.

The above-mentioned nitriding furnace of the present invention is a batch type nitriding reaction, but it has a structure in which the by-produced gas does not come into contact with the inner surface of the heat insulating casing 1 or the heater 3. It is suitable for carrying out a reduction nitriding reaction, and is extremely suitable for producing aluminum nitride (AlN) and hexagonal boron nitride (h-BN) that are stable at normal temperature and pressure, for example, by the reduction nitriding method.

Reduction Nitriding The production of aluminum nitride (AlN) by the reduction nitriding method is carried out as follows. That is, an oxygen-containing aluminum compound such as aluminum oxide (Al ₂ O ₃ ) is used as an aluminum source, and a mixed powder of the oxygen-containing boron compound powder and carbon powder is spread on the tray 19 as a reaction raw material, and the tray is covered. 19 is loaded in the reaction chamber 5 of the above-mentioned nitriding furnace, nitrogen is supplied from the nitrogen gas supply pipe 21, and AlN is obtained on the tray 19 by reduction and nitriding of the oxygen-containing aluminum compound.
The above reaction is represented by the following formula.
Al ₂ O ₃ + 3C + N ₂ → 2AlN + 3CO
The above reaction is generally carried out in the reaction chamber 5 at a temperature of 1200 to 2000 ° C, preferably 1400 to 1800 ° C. If this temperature is too low, reduction nitriding does not proceed sufficiently, and if the temperature in the reaction chamber 5 is higher than necessary, the generated AlN may volatilize and be discharged.

Further, the production of hexagonal boron nitride (h-BN) by the reduction nitriding method is carried out as follows. That is, an oxygen-containing boron compound such as boron oxide (B ₂ O ₃ ) is used as a boron source, and a powder of the oxygen-containing boron compound, a carbon powder, and a mixed powder of an auxiliary agent are spread on the tray 19 as a reaction raw material. The tray 19 is loaded in the reaction chamber 5 of the nitriding furnace described above, nitrogen is supplied from the nitrogen gas supply pipe 21, and h-BN is obtained on the tray 19 by reducing and nitriding the oxygen-containing boron compound.
The above reaction is represented by the following formula.
B ₂ O ₃ + 3C + N ₂ → 2BN + 3CO

The above reaction is generally carried out in the reaction chamber 5 at a temperature of 1200 to 2200 ° C., preferably 1800 to 2100 ° C. If this temperature is too low, reduction nitriding does not proceed sufficiently, and if the temperature in the reaction chamber 5 is higher than necessary, the generated h-BN may volatilize and be discharged.

Further, due to the above reaction, an oxidizing gas such as a volatile metal oxide or carbon dioxide is produced as a by-product, but this CO gas does not come into contact with the heat insulating casing 1 or the heater 3 due to the shield wall 13. As a result, deterioration of the heat insulating casing 1 and the heater 3 can be effectively suppressed, and the life of the device can be maintained for a long time.

Further, the auxiliary agent in the reaction raw material is used to uniformly proceed the above reduction nitriding reaction to the inside of the raw material, and for example, oxygen-containing alkaline earth metal compounds, particularly calcium carbonate and calcium oxide are preferable. Used for. That is, when the reduction nitriding reaction is carried out at a high temperature as described above, such an auxiliary agent is decomposed and gas (for example, carbon dioxide gas) is generated in the process of raising the temperature inside the reaction chamber 5 to a high temperature. As a result, voids are formed inside the reaction raw material at the stage of supplying the nitrogen gas, and the nitrogen gas penetrates deep into the reaction raw material, so that the reduction nitriding reaction can proceed quickly and uniformly. For example, when the present inventors produced the above h-BN using the nitriding furnace shown in the above-mentioned figure, the h-BN powder having a high whiteness (for example, whiteness) was produced over the entire tray 19. W is 90 or more) has been confirmed to have been manufactured. For example, when reduction nitriding proceeds non-uniformly, carbon remains, so that a portion having low whiteness is partially generated. However, in the present invention, reduction nitriding proceeds uniformly and to the inside, so that the whiteness is also overall. It has become high over.
Further, when the _{number of stacking stages of the tray 19 having an inner diameter D 1} of 60 mm is set to 20, and the discharge speed (linear speed) of nitrogen gas from the nitrogen gas supply pipe 21 is set to 0.5 Ncm / s or more, 15 hours. It has also been confirmed that the reduction nitriding reaction was completed within the time.

The mixing for preparing the mixed powder as the reaction raw material is not particularly limited as long as each component is uniformly mixed, and is performed using a mixing device such as a vibration mill, a ball mill, or a drum mixer vibration stirrer. ..

Further, the amount ratio of the boron source and the carbon powder in the reaction raw material is set so that the element ratio (B / C) is in the range of 0.60 to 0.85, particularly 0.65 to 0.80. .. If this element ratio (B / C) is smaller than the above range, a large amount of unreacted carbon will be present in the reaction product, and it may be difficult to obtain the desired h-BN. On the other hand, if it is larger than the above range, the amount of boron compound volatilized without being reduced increases, the yield decreases, and the exhaust line is blocked due to reduction nitriding in the exhaust line. May also occur.
As for the amount ratio of the boron-containing compound and the auxiliary agent, for example, the molar ratio of boron to calcium (B ₂ O ₃ / CaO) in terms of oxide is 4.0 to 6.0, particularly 4.5 to 5. It is preferably in the range of 5. If this molar ratio is smaller than this range, a large amount of calcium-derived impurities will be present on the tray 19, and the yield will decrease. On the other hand, if the molar ratio is larger than the above range, the amount of the boron compound volatilized without being reduced increases, which may not only reduce the yield but also cause the exhaust line to be blocked.

Further, in the present invention, when h-BN is produced using the above-mentioned reaction raw materials, as shown in FIG. 7, the release of boron nitride (h-BN) from a molded product or powder. It is preferable that the mold layer is spread on the bottom wall 19a of the tray 19, and the reaction raw material is spread on this.
That is, when h-BN is produced by reduction nitriding on the tray 19, the produced h-BN powder may adhere to the bottom wall 19a of the tray 19, making it difficult to remove the h-BN from the tray 19. is there. This tendency is particularly large when the tray 19 made of graphite carbon is used. In order to prevent such inconvenience, a boron nitride molded body or powder is spread on the bottom wall 19a of the tray 19 to form a release layer, and the generated boron nitride powder is in direct contact with the bottom wall 19a of the tray 19. By avoiding it, the above-mentioned inconvenience can be effectively prevented.

The hexagonal boron nitride (h-BN) powder generated on the tray 19 as described above is recovered from the tray 19 and pickled to remove unreacted boron oxide, Ca or Ca compound derived from an auxiliary agent, and the like. Then, it is washed with water, classified into a predetermined particle size using a vibrating sieve or the like, collected in a packaging bag, and put on the market.

As described above, according to the nitriding reaction furnace of the present invention, a large amount of nitrides can be produced at one time even though it is a batch type, and the nitriding reaction can proceed quickly and uniformly. Deterioration of the heat insulating casing 1 and the heater 3 can be effectively avoided, the device life is long, and nitrides can be efficiently produced, which is extremely useful industrially.

1: Insulation casing 3: Heater 5: Reaction chamber 11: Bottom plate 13: Shield wall 17: Exhaust port 19: Tray 19c: Notch 21: Nitrogen gas supply pipe 23: Preheating chamber S: Void

Claims (7)

In a nitriding reactor for performing a nitriding reaction
The nitriding reactor has a heat insulating casing and has a heat insulating casing.
In the heat insulating casing, a reaction chamber surrounded by a shield wall held by a bottom plate provided with an exhaust port and a heater arranged outside the reaction chamber are provided.
In the reaction chamber, trays having an opening in the center, containing reaction raw materials to be subjected to the nitriding reaction, and having notches on the side walls are loaded in multiple stages on the bottom plate. At the same time, a nitrogen gas supply pipe extending through the opening of the tray is provided.
The nitriding reaction is carried out by bringing the nitrogen gas supplied from the nitrogen gas supply pipe into contact with the reaction raw material contained in the tray, and the unreacted nitrogen gas and the by-product gas are formed on the side wall of the tray. The nitriding reaction is characterized by having a structure in which the gas is discharged from the exhaust port of the bottom plate through the gap formed between the peripheral edge of the tray and the shield wall through the notch. Furnace. The first aspect of claim 1, wherein a preheating chamber is provided in the upper part of the reaction chamber, and nitrogen gas heated in the preheating chamber is supplied into a tray arranged in the reaction chamber through the nitrogen gas supply pipe. Nitrogen reactor. The nitriding reaction furnace according to claim 1 or 2, wherein a mixed powder containing oxygen-containing aluminum powder and carbon powder is used as the reaction raw material. The nitriding reaction furnace according to claim 1 or 2, wherein a mixed powder containing a boron oxide powder, a carbon powder and an auxiliary agent is used as the reaction raw material. The third or fourth aspect of the present invention, wherein a release layer made of a nitride plate-shaped molded body or powder is laid inside the tray, and the reaction raw material is arranged in a layer on the release layer. Nitriding reactor. The nitriding reactor according to claim 3 to 5, wherein heating is performed by the heater so that the temperature in the reaction chamber is in the range of 1200 to 2200 ° C. The nitriding reactor according to any one of claims 1 to 6, wherein the tray has a circular planar shape.