KR100771387B1 - Process for producing aluminum nitride and aluminum nitride - Google Patents

Abstract

The present invention provides a method for producing aluminum nitride, which maintains an aluminum powder in a nitrogen atmosphere having a nitrogen gas pressure of 105 to 300 kPa and advances a nitriding reaction at 500 to 1,000 ° C. It relates to a method for producing aluminum nitride, characterized in that the supply into the reaction chamber containing the. In this production method, the reaction inhibiting gas is contained in the nitrogen atmosphere during the progress of the nitriding reaction. Therefore, the progress of the nitriding reaction is controlled to allow the nitriding reaction to proceed at a low temperature. As a result, aluminum nitride powder having a small particle diameter can be produced.

Aluminum nitride, Nitriding reaction, Aluminum powder, Nitrogen gas atmosphere, Nitrogen storing process, Reaction suppression gas

Description

Process for producing aluminum nitride and aluminum nitride

1 is a view showing the configuration of a nitriding furnace used in the embodiment according to the present invention.

2A and 2B are SEM (ie, scanning electron microscope) photographs of the aluminum nitride powder of Example 1 according to the present invention.

3A and 3B are SEM photographs of the aluminum nitride powder of Example 5 according to the present invention.

The present invention relates to a method for producing aluminum nitride.

Aluminum nitride (i.e., AlN) has excellent properties such as heat resistance, thermal conductivity, and electrical conductivity, and its applications are expanding. As an applicable use of aluminum nitride, a high temperature container, an IC board | substrate, etc. are mentioned.

Industrial aluminum nitride is an artificial ceramic that does not exist in its natural state. It is mainly produced using two methods, carbon reduction nitriding of alumina and direct nitriding of aluminum.

(a) Carbon Reduction Nitriding of Alumina

(Ie Al ₂ O ₃ + 3C + N ₂ = 2AlN + 3CO)

The carbon reduction nitriding method of alumina is a manufacturing method for producing aluminum nitride by reducing high purity alumina at high temperature (for example, 1,700 to 1,900 ° C) with graphite and nitrogen gas, and nitriding the reduced aluminum produced with nitrogen. to be.

However, carbon reduction nitriding requires a long time to complete the reaction. Therefore, the manufacturing cost rises, resulting in a problem that the resulting aluminum nitride is higher in price than other ceramics, for example, silicon carbide (i.e., SiC), alumina, and the like.

(b) direct nitriding of aluminum

(I.e. 2Al + N ₂ = 2AlN)

Direct nitriding of aluminum has been used since Briegleb et al. Since this reaction is an exothermic reaction, it has the advantage that aluminum nitride can be easily produced by simply placing pure aluminum in a nitrogen stream.

However, in the direct nitriding method of aluminum, when the surface of aluminum is covered with a nitride film, the supply of nitrogen to aluminum is blocked by the nitride film. When the supply of nitrogen is interrupted, the nitriding reaction of aluminum is stopped. Therefore, the direct nitriding of aluminum has the drawback that it is impossible to obtain aluminum nitride of 100% purity. As a result, industrially, nitriding is performed while heating aluminum at the temperature of 1,000-2,000 degreeC.

In addition, in the direct nitriding of aluminum, in order to increase the reaction yield, the produced aluminum nitride is repeatedly nitrided and pulverized, or further treatment such as addition of AlF ₃ or AlN is performed to complete the reaction. However, since most aluminum nitrides are hard, various steps are required to grind them. As a result, manufacturing cost rises. Therefore, the direct nitriding method of aluminum has the problem that the price of the produced aluminum nitride becomes high.

A method for producing aluminum nitride by direct nitriding using aluminum and aluminum nitride as a raw material is described in US Pat. No. 5,710,382. In the production method described in this US patent, two types of heating methods are described as a method of initiating a nitriding reaction, a method of igniting raw materials with an igniter and a method of simply heating them in a furnace. According to the US patent, the peak temperature in the furnace and the peak temperature of the workpiece in the nitriding reaction are 1,845-2,115 ° C. when the raw material is ignited by an igniter and at a high temperature of 1,400-2,225 ° C. when the raw material is heated together with the furnace. Set it. Note that the reaction initiation temperature of the nitriding reaction heated with the furnace is 1,020 to 1,250 ° C. Therefore, the peak temperature in the furnace and the peak temperature of the workpiece are much higher than the reaction start temperature. This is because the nitriding reaction is exothermic, and the reaction heat of the nitriding reaction advances the nitriding reaction.

Therefore, in the manufacturing method of aluminum nitride by the direct nitriding method, the peak temperature in a furnace and the peak temperature of a workpiece | work become high temperature. Thus, crystal growth and sintering of aluminum nitride occurs. As a result, there exists a problem that the particle diameter of the produced aluminum nitride particle becomes large.

The present invention was developed in view of the above described situation. Accordingly, an object of the present invention is to provide a method for producing aluminum nitride having a small particle diameter.

In order to achieve the above object, the inventors of the present invention have found that aluminum nitride powder having a small particle diameter can be produced by containing a reaction inhibiting gas that suppresses the nitriding reaction in a nitrogen gas atmosphere during the progress of the nitriding reaction.

That is, the method for producing aluminum nitride according to the present invention includes maintaining the aluminum powder in a nitrogen atmosphere having a nitrogen gas pressure of 105 to 300 kPa and performing a nitriding reaction at 500 to 1,000 ° C. to suppress the progress of the nitriding reaction. The reaction inhibiting gas is supplied into the reaction chamber containing the aluminum powder.

In the production method of the aluminum nitride, the reaction suppression gas is contained in the nitrogen gas atmosphere during the progress of the nitriding reaction, and the progress of the nitriding reaction is suppressed. Since the nitriding reaction, which is an exothermic reaction, is suppressed, further nitriding reactions induced by the heat of reaction are suppressed. As a result, the chain nitriding reaction hardly proceeds and the nitriding reaction can be advanced at low temperature. According to the aluminum nitride production method of the present invention, it is possible to proceed the nitriding reaction at a low temperature. Therefore, aluminum nitride powder with a small particle diameter can be manufactured. Further, according to the aluminum nitride production method of the present invention, the temperature of the workpiece can be suppressed from rising by releasing heat generated in the nitriding reaction to the outside of the reaction chamber. Thus, fine aluminum nitride powder can be produced.

The aluminum nitride according to the present invention is obtained by maintaining an aluminum powder in a nitrogen atmosphere having a nitrogen gas pressure of 105 to 300 kPa and carrying out a nitriding reaction at 500 to 1,000 ° C. Is fed into the reaction chamber to receive the reaction.

In the production of the aluminum nitride of the present invention, since the reaction suppression gas is supplied into the reaction chamber when the nitriding reaction proceeds, the progress of the nitriding reaction which is an exothermic reaction is suppressed. Thus, further nitriding reactions induced by the heat of reaction of nitriding reactions are suppressed. That is, in the preparation of the aluminum nitride of the present invention, the nitriding reaction proceeds at low temperature. As a result, the aluminum nitride of the present invention produces an aluminum nitride powder having a small particle diameter. In the production of the aluminum nitride of the present invention, it is possible to suppress the rise of the temperature of the workpiece by releasing heat generated in the nitriding reaction to the outside of the reaction chamber. Therefore, the aluminum nitride of the present invention produces aluminum nitride powder having a fine particle diameter.

Therefore, according to the manufacturing method of aluminum nitride of this invention, reaction suppression gas is supplied to reaction chamber at the time of progress of nitriding reaction. Therefore, the progress of nitriding reaction is suppressed. Since the nitriding reaction, which is an exothermic reaction, is suppressed, further nitriding reactions induced by the heat of reaction are suppressed. In addition, the temperature of the workpiece can be suppressed from rising by releasing heat generated in the nitriding reaction to the outside of the reaction chamber. As a result, the chain nitriding reaction hardly proceeds and the nitriding reaction can be advanced at low temperature. According to the aluminum nitride production method of the present invention, the nitriding reaction can be carried out at a low temperature. Therefore, aluminum nitride powder with a small particle diameter can be manufactured. Moreover, when using aluminum nitride powder with a small particle diameter as a raw material of a base material, the temperature which bakes a base material can be reduced. Therefore, active use of such aluminum nitride powder as a raw material of a substrate having excellent quality can be expected.

A more fully understood and numerous advantages of the invention will be more readily understood with reference to the following detailed description when considered in conjunction with the accompanying drawings and detailed description, which form a part of the description.

By describing the present invention in general, it may be further understood by reference to certain preferred embodiments, which are provided herein for purposes of illustration only and are not intended to limit the scope of the appended claims.

(Method for producing aluminum nitride)

In the method for producing aluminum nitride of the present invention, the aluminum powder is maintained in a nitrogen atmosphere having a nitrogen gas pressure of 105 to 300 kPa, and the nitriding reaction is advanced at 500 to 1,000 ° C.

That is, in the manufacturing method of the aluminum nitride of this invention, nitriding reaction of aluminum is advanced by hold | maintaining aluminum powder in the atmosphere of predetermined | prescribed nitrogen gas pressure and heating temperature. Note that, in general, the size of the primary particle diameter of the ceramic depends on the reaction initiation temperature. However, when there is a temperature rise due to subsequent heat of reaction, the crystal grains are sintered and grown to be coarse. In the manufacturing method of this invention, since further temperature rise from reaction start temperature can be suppressed, the particle diameter of aluminum nitride particle can be determined by reaction temperature of a nitriding reaction. The lower the reaction temperature of the nitriding reaction, the smaller the particle diameter. The reaction temperature largely depends on the type of raw material and the particle diameter. For example, in aluminum alloys containing magnesium, the reaction starts at low temperature, for example 500 ° C. In aluminum alloys containing silicon, the reaction starts at high temperatures. In addition, the smaller the particle diameter of the aluminum powder is, the reaction is initiated at a lower temperature. In pure aluminum powder, nitriding is usually initiated at 550 to 700 ° C. For example, in pure aluminum powder of particles having a diameter of about 100 μm, generally referred to as coarse particles, the nitriding reaction is started at about 750 ° C. if the nitrogen absorption reaction is carried out during the temperature increase.

When the nitrogen gas pressure is maintained at 105 to 300 kPa, a sufficient amount of nitrogen gas for the nitriding reaction can be supplied to the aluminum powder. For example, if the nitrogen gas pressure is less than 105 kPa, there is a risk that air may invade from outside and oxidize the aluminum powder. On the other hand, when the nitrogen pressure exceeds 300 kPa, the reaction efficiency hardly increases in the nitriding reaction, and the cost required for production increases.

In addition, when the temperature of nitriding reaction is less than 500 degreeC, it takes a long time until the start of nitriding reaction. On the other hand, when it exceeds 1,000 degreeC, the particle diameter of the manufactured aluminum nitride particle increases excessively.

In the direct nitriding method of the aluminum powder with nitrogen gas (ie, 2Al + N ₂ = 2AlN), the production free energy of aluminum nitride (i.e., free energy of Gibbs) is always negative. Therefore, for example, even when the temperature is less than 460 ° C, it is considered that aluminum nitride is formed by keeping the aluminum powder at that temperature for a long time. However, when it takes a long time, the cost required for manufacturing rises. In addition, in the nitriding reaction of aluminum powder, the higher the temperature, the faster the reaction rate. Therefore, from an industrial point of view, the nitriding reaction occurs at a slightly high temperature, for example, 500 ° C or higher. As for the temperature of nitriding reaction, it is more preferable that it is 550 degreeC or more.

In more detail, the following facts were confirmed by experiment. When the aluminum powder is held in a nitrogen gas atmosphere at 520 ° C., the nitriding reaction is started after 3 to 30 hours has elapsed, and the reaction is stopped at about 92% of the nitriding rate. The reason why it takes a long time to start the nitriding reaction is because of the oxide film formed on the aluminum surface. In addition, in a normal nitriding reaction at low temperature, it is impossible to reduce aluminum oxide to nitrogen in the initial stage of the reaction. That is, it takes time for nitrogen to gradually invade the interior of aluminum. The nitriding reaction begins rapidly after several hours and ends. Therefore, it is usually difficult to achieve 100% nitriding in nitriding at low temperatures.

In addition, in the direct nitriding of aluminum powder, it is important to lower the oxygen content in the nitrogen gas atmosphere. This is because aluminum is a metal that is very susceptible to oxidation. From this the dew point in the reaction chamber may preferably be -50 ° C or less.

In the manufacturing method of the aluminum nitride of this invention, the reaction suppression gas which suppresses advancing of nitriding reaction is supplied to the reaction chamber which accommodates aluminum powder at the time of advancing nitriding reaction. Since the reaction suppression gas is supplied into the reaction chamber, chain progression of the nitriding reaction of the aluminum powder is suppressed. Therefore, nitriding reaction can be advanced at low temperature.

Specifically, the direct nitriding reaction is a significant exothermic reaction, theoretically producing 2,800 kcal (ie, about 1.172 x 10 ⁴ kJ) heat by nitriding 1 kg of aluminum. In addition, in order to nitride 1 kg of aluminum, it is necessary to use about 420 L of nitrogen gas. Therefore, when nitriding reaction is started in a part of aluminum, the chain nitriding reaction by reaction heat progresses and the temperature of aluminum abruptly rises.

Typically, the temperature rise of aluminum is about 250 to 600 ° C. However, depending on the amount of aluminum and the structure of the reactor, the temperature is 1,000 ° C or higher. As the temperature of aluminum rises, crystal growth of the aluminum nitride particles proceeds and the particles sinter each other. Thus, the resulting aluminum nitride particles are coarse and undesirable.

In the method for producing aluminum nitride of the present invention, the aluminum powder to be nitrided may have an oxide film on its surface. This is because aluminum has a characteristic of reacting with oxygen contained in the atmosphere in the atmosphere to form a stable oxide film on the surface.

The nitriding reaction is preferably carried out after the aluminum powder is held in a nitrogen gas atmosphere at 450 to 600 ° C. for 30 to 120 minutes to carry out a nitrogen occlusion treatment in which nitrogen is occluded in the aluminum powder. By adsorbing nitrogen into the aluminum powder before the nitriding reaction proceeds, the nitrogen which reacts with the aluminum powder in the subsequent nitriding reaction is maintained in the vicinity of the aluminum powder. Therefore, even when a rapid reaction occurs in the nitriding reaction, an insufficient amount of nitrogen required for the nitriding reaction is prevented.

The mechanism by which nitrogen is occluded in aluminum powder is not yet clear. However, it is presumed that nitrogen penetrates into the interior of aluminum from the surface of the aluminum oxide along the interface of defects or particles, and aluminum oxide and nitrogen form a conjugated compound and nitrogen is occluded into the aluminum powder.

In the nitrogen occlusion treatment, the aluminum powder is preferably heated from a temperature of at least 460 ° C to a nitriding temperature of the nitriding reaction at a temperature rising rate of 10 ° C / min or less. When heating aluminum powder at the temperature increase rate of 10 degrees C / min or less, aluminum powder can fully occlude nitrogen. On the other hand, when the temperature increase rate exceeds 10 DEG C / min, aluminum remains in the aluminum nitride produced by insufficient storage of nitrogen by the aluminum powder.

In the nitrogen occlusion treatment, the aluminum powder is preferably heated from a temperature of at least 460 ° C to a nitriding temperature of the nitriding reaction at a temperature rising rate of 1 to 6 ° C / min. When the temperature increase rate is below the lower limit of the range described above, it takes a long time to heat the aluminum powder to the nitriding temperature. Therefore, it is preferable that the temperature increase rate is 1-6 degree-C / min.

In the nitrogen storage process, the aluminum powder is preferably maintained at a temperature of 460 ° C to 600 ° C for a predetermined time. When the aluminum powder is kept at a temperature of 460 ° C. to 600 ° C. for a predetermined time, the aluminum powder may occlude nitrogen in a sufficient amount.

In the nitrogen storage treatment, the predetermined time is preferably 5 to 30 minutes. If the aluminum powder is maintained at the temperature described above for a predetermined period of 5 to 30 minutes, the aluminum powder can occlude a sufficient amount of nitrogen.

After a predetermined time has elapsed in the nitrogen storage process, it is preferable to immediately heat the aluminum powder to the nitriding temperature of the nitriding reaction at a temperature rising rate of 10 ° C / min or more. Maintaining the aluminum powder for a long time at a predetermined temperature and increasing the temperature more slowly is undesirable because they suddenly cause a common nitriding reaction accompanied by the heat of reaction at some point.

The heat generated by the nitriding reaction is released to the outside of the reaction chamber by the furnace wall of the reactor partitioning the reaction chamber, and the nitriding reaction is controlled while controlling the temperature difference between the workpiece temperature and the initiation temperature of the nitriding reaction to 100 ° C or lower. It is preferable to proceed. When the temperature difference between the workpiece temperature and the start temperature of the nitriding reaction is adjusted to 100 ° C. or less, an aluminum nitride powder having a fine particle diameter can be produced. That is, the rise of the temperature of a workpiece | work at the time of progress of a nitriding reaction is suppressed. Thus, the progress of the chain nitriding reaction is suppressed. Therefore, nitriding reaction can be advanced at low temperature. In addition, since the heat generated by the nitriding reaction is released to the outside of the reaction chamber by the furnace wall of the reactor that partitions the reaction chamber, the temperature of the workpiece can be suppressed from rising.

Heat generated by the nitriding reaction can be released to the outside of the reaction chamber in the following manner. For example, the furnace wall of the reactor is formed of a material having excellent thermal conductivity, and the outside temperature of the reactor is controlled to be lower than the inside temperature of the reactor. In this way, heat can be released outside the reaction chamber. In this case, the outside temperature of the reactor can be adjusted to be lower than the inside temperature of the reactor in the following manner. For example, a method of cooling the reactor by reducing the heating capacity of the heater that causes the nitriding reaction and controls the reaction temperature of the nitriding reaction or by supplying air to the outside of the reactor.

In the manufacturing method of the aluminum nitride of this invention, a workpiece means the aluminum powder which nitriding reaction is progressing. That is, this means a state in which aluminum nitride produced by the nitriding reaction is mixed with aluminum where no nitriding reaction occurs.

In the nitriding reaction, when the nitriding reaction of the aluminum powder proceeds, the peak temperature of the workpiece is preferably 900 ° C. or less. Here, the peak temperature means the highest temperature of the workpiece increased by the nitriding reaction. When the peak temperature is suppressed to 900 ° C. or less, aluminum nitride powder having a fine particle diameter can be produced. If the peak temperature exceeds 900 ° C., the resulting aluminum nitride particles are coarse by crystal growth and sintering.

The nitrogen gas atmosphere is preferably maintained by the nitrogen gas conveyed from the nitrogen supply device which continuously supplies the nitrogen gas to the reaction chamber and the nitrogen gas discharged from the discharge device which discharges the nitrogen gas from the reaction chamber. That is, the nitrogen gas pressure of the reaction chamber in which the aluminum powder is accommodated by the nitrogen gas supplied from the nitrogen supply device and the nitrogen gas discharged from the discharge device can be maintained.

Specifically, the nitriding reaction of aluminum powder proceeds rapidly. Therefore, when the nitriding reaction is started, nitrogen in the reaction chamber is consumed, and the nitrogen gas pressure is drastically lowered. Therefore, by maintaining the nitrogen gas pressure in the reaction chamber by using the nitrogen supply device and the discharge device, it is possible to suppress the change of the nitrogen gas pressure in the reaction chamber.

In addition, when measuring the pressures of the nitrogen gas supplied from the nitrogen supply device and the nitrogen gas discharged from the discharge device, the nitrogen gas pressure in the reaction chamber can be measured. In addition, nitrogen occlusion of the aluminum powder in nitrogen occlusion treatment can be computed, and the amount of nitrogen gas fall at the time of the progress of nitriding reaction can be computed.

It is preferable to supply reaction suppression gas to a reaction chamber when the nitrogen gas pressure in a reaction chamber falls. The reaction inhibiting gas is a gas supplied into the reaction chamber when the nitriding reaction is started. By measuring the nitrogen gas pressure, the start of the nitriding reaction can be observed. This is because when the nitriding reaction is started, the nitrogen gas constituting the nitrogen gas atmosphere reacts with the aluminum powder so that the amount of nitrogen gas in the reaction chamber decreases and the nitrogen gas pressure decreases. Therefore, progress of nitriding reaction can be suppressed by supplying reaction suppression gas to a reaction chamber when nitrogen gas pressure falls.

It is preferable to start supply of the reaction suppression gas into the reaction chamber when the nitrogen gas pressure in the reaction chamber is lowered, and to terminate it when the nitrogen gas pressure in the reaction chamber is restored. This is because the recovery of the nitrogen gas pressure occurs when the consumption of nitrogen in the nitriding reaction decreases, and thus the nitriding reaction is terminated.

It is preferable that the reaction suppression gas is supplied to the reaction chamber when the temperature of the workpiece increases. The reaction inhibiting gas is supplied into the reaction chamber when the nitriding reaction is started. On the other hand, the start of nitriding reaction can be observed by measuring the temperature of a workpiece. This is because when the nitriding reaction is initiated, heat of reaction is generated to raise the workpiece temperature.

The reaction inhibiting gas is preferably at least one gas selected from the group consisting of argon gas and ammonia gas. These gases can suppress the progress of the nitriding reaction.

Argon gas is used as a carrier gas of nitrogen gas in the plasma nitridation of alumina. Plasma nitriding is carried out using a mixed gas in which 5-20% by volume of nitrogen gas is mixed with the remainder of the argon gas.

It is not known that argon gas is actually used in the direct nitriding of ordinary aluminum. 1992, Report [Itoh and Enami et al., Tokyo University of Science, Journal of the Ceramic Society of Japan 100 [5] pp. 629-633 (1992) discloses a method for producing aluminum nitride using a surface-oxidized aluminum powder as a raw material. In this report, an example of performing a nitriding experiment with nitrogen gas to which 30 to 70 volume% of argon gas was added is recorded. In this example, aluminum nitride is produced at a reaction temperature of 900 to 1300 ° C. while supplying a predetermined amount of argon gas from the start to the end, and after 2 and 5 hours from the start of the reaction, the nitriding rate and the crushability of the reaction product are Investigate.

According to this report, nitriding reactions occur over all temperature ranges and all argon contents, with a highest nitriding rate of 94%. The researchers interpreted this highest nitrification value as being due to oxidation. In this report, it is also reported that a nitrification rate of 97.5% was obtained using a mixed gas having an argon gas content of 10% by volume. The researchers also reported improved crushability of all reaction products, regardless of argon gas content.

On the other hand, the present inventors investigated how the addition of argon gas to the nitriding reaction in the low temperature region of 600 to 750 ℃. In this investigation, argon gas was supplied from the start to the end of the nitriding reaction at a ratio of 30 vol% or more with respect to 100 vol% of the total mixed gas supplied.

According to the results of the investigation of how the addition of argon gas at low temperature affects the nitriding reaction, when the content of argon gas is 50 vol% or more, no nitriding reaction is started. In addition, the inventors confirmed that the nitriding reaction was stopped when argon gas was supplied at a rate of 50 vol% or more while the nitriding reaction proceeded with pure nitrogen gas only.

In addition, the inventors of the present invention confirmed that the nitriding reaction is proceeding even though the reaction proceeds slowly when argon gas is supplied at a rate of 3 to 20% by volume while performing nitriding reaction with pure nitrogen gas only. According to the report for the study, when using a nitrogen gas mixed with argon gas at a ratio of 30 to 70% by volume, no effect of argon gas was observed at a reaction temperature of 900 to 1,300 ° C, and a nitriding reaction occurred. . On the other hand, in the heating temperature range of 600-750 degreeC by the manufacturing method of aluminum nitride of this invention, nitriding reaction stops or progresses slowly. This difference appears to be a temperature difference, but is thought to be due to the difference in reactivity, i.e., the nitriding reaction occurring in the liquid phase described in the report (on the one hand, according to the present invention the nitriding reaction takes place in the solid phase).

In addition, ammonia gas is added in a small amount to nitrogen gas as a nitriding agent when nitriding aluminum or steel. As in the case of argon gas, the reactivity of ammonia gas was investigated in the temperature range of 600-750 degreeC. However, as a result, the inventors confirmed that the nitriding reaction was stopped. That is, when the nitriding reaction proceeds, the nitriding reaction can be temporarily stopped by supplying ammonia gas into the reaction chamber. The reason why the nitriding reaction is stopped by the supply of ammonia gas is not yet clear. However, since the raw material is a solid in the experimental temperature range, it is presumed that a compound such as AlH ₃ is formed in the solid aluminum powder to prevent the intrusion of nitrogen gas.

Therefore, it is preferable that the reaction inhibiting gas is supplied to the reaction chamber at a ratio of 1 to 50 volume% when the amount of gas in the reaction chamber is 100 volume%.

In the manufacturing method of the aluminum nitride of this invention, it is preferable to stop supplying reaction suppression gas to reaction chamber immediately before completion of nitriding reaction, and to raise reaction temperature to 30-120 degreeC. Not only the supply of the reaction suppression gas is stopped but also the reaction temperature is raised, all of the raw aluminum powder can be nitrided.

The aluminum powder is preferably in a non-compressed assembly state. If the aluminum powder is in an uncompressed integrated state, the resulting aluminum nitride particles are suppressed from sintering together with the adjacent aluminum nitride particles. The change from aluminum to aluminum nitride involves volume expansion. Therefore, when the aluminum powder is in a compacted integrated state, the produced aluminum nitride particles cause sintering and deterioration in pulverization. In addition, when the aluminum powder is in an uncompressed integrated state, nitrogen can be occluded by nitrogen occlusion treatment. That is, if the aluminum powder is in an uncompressed integrated state, each aluminum powder particle may contact with nitrogen gas with sufficient surface area so that the aluminum powder may sufficiently occlude nitrogen therein.

The aluminum powder is preferably divided into a plurality of parts and accommodated in the reaction chamber. When the aluminum powder is divided into a plurality of parts and each part is accommodated in the reaction chamber, the produced aluminum nitride produces particles in which the particle diameter is suppressed from fluctuating. Therefore, nitriding reaction can be suppressed with respect to all the parts of aluminum powder.

Specifically, when the nitriding reaction proceeds in a state where a large amount of aluminum powder is accommodated in an uncompressed manner in the reaction chamber, a temperature difference is generated between the inside of the aluminum powder assembly and the surface layer thereof. Therefore, it becomes difficult to observe and control the nitriding reaction inside the aluminum powder aggregate. Therefore, the diameter of the produced aluminum nitride particles varies greatly. On the other hand, when a small amount of aluminum powder is accommodated in the reaction chamber in a manner that is divided into a plurality of parts, it is easy to observe and control the nitriding reaction inside each part of the aluminum powder aggregate. Therefore, fluctuation in the diameter of the produced aluminum nitride particles is suppressed.

When the aluminum powder is divided into a plurality of portions and each portion is accommodated in the reaction chamber, the larger the number of divided portions is, the better suppressed the variation in the diameter of the produced aluminum nitride particles is.

The method of dividing the aluminum powder into a plurality of parts to be accommodated in the reaction chamber is not particularly limited. For example, several reactor tray which hold | maintains the aluminum powder divided | divided inside, is laminated | stacked, and accommodated in a reaction chamber is mentioned.

The time required for the nitriding reaction to complete after the temperature of the aluminum powder reaches a predetermined reaction temperature is preferably 2 to 10 hours. By adjusting the reaction time in the range of 2 to 10 hours, an aluminum nitride powder having a small particle diameter can be produced. If the time required for the nitriding reaction to complete is less than 2 hours, the progress of the nitriding reaction becomes very fast, and the produced aluminum nitride particles are aggregated. On the other hand, when the time required for the nitriding reaction to finish exceeds 10 hours, it takes a long time to heat the aluminum powder, and the cost required for producing the aluminum nitride powder increases.

It is preferable that reaction suppression gas is supplied in the following manner. For example, when the aluminum nitride powder is heated to a predetermined reaction temperature, the supply of the reaction suppression gas is started, gradually increasing the supply amount of the reaction suppression gas to a predetermined gas partial pressure capable of suppressing the progress of the nitriding reaction, After maintaining the predetermined gas partial pressure for a predetermined time, the gas partial pressure of the reaction suppression gas is gradually reduced, and the supply of the reaction suppression gas is stopped. By controlling the supply amount of the reaction suppression gas to the reaction chamber, the progress of the nitriding reaction can be controlled. After the temperature of the aluminum powder reaches a predetermined nitriding temperature, the nitriding reaction is started. However, in this case, when a large amount of reaction inhibiting gas is present in the reaction chamber, it takes a long time to start the nitriding reaction. Therefore, when the gas partial pressure of the reaction inhibiting gas is made smaller, the nitriding reaction can be started. Thereafter, when the nitriding reaction proceeds, the reaction suppression gas is supplied into the reaction chamber in an amount sufficient to suppress the nitriding reaction that proceeds in series. Then, when the aluminum powder is sufficiently nitrided, the supply of the reaction inhibiting gas gradually decreases to stop. By gradually reducing the supply of the reaction suppressing gas, it is possible to suppress the unnitriding aluminum powder from rapidly progressing the nitriding reaction.

The gas partial pressure of the reaction inhibiting gas is preferably maintained for a time during which the aluminum powder is nitrided at a 1/2 to 3/4 weight ratio. The nitride amount of the aluminum powder can be calculated from the change in weight of the aluminum powder and the change in the partial pressure of nitrogen gas in the reaction chamber.

Further, after the supply of the reaction inhibiting gas is stopped, it is preferable that nitrogen gas is further supplied into the reaction chamber. When the nitrogen gas is further supplied after the supply of the reaction inhibiting gas is stopped, the unnitrided aluminum powder can be nitrided. In this case, since most of the aluminum powder is nitrided, the chain nitriding reaction hardly proceeds, which causes an increase in severe temperature. Therefore, there is no need to suppress the nitriding reaction.

In the manufacturing method of the aluminum nitride of this invention, since reaction suppression gas is supplied when nitriding reaction advances, advancing of nitriding reaction is suppressed. That is, since the progress of nitriding reaction which is exothermic reaction is suppressed, further nitriding reaction by reaction heat is suppressed. As a result, the chain nitriding reaction hardly proceeds and the nitriding reaction can be advanced at low temperature. According to the production method of the present invention, nitriding can be performed at a low temperature. Thus, aluminum nitride powder having a small particle diameter can be produced.

(Aluminum nitride)

The aluminum nitride according to the present invention is a step of maintaining the aluminum powder in a nitrogen atmosphere having a nitrogen gas pressure of 105 to 300 kPa, and carrying out a nitriding reaction at 500 to 1,000 ° C. The step of feeding into the reaction chamber containing the aluminum powder is processed.

That is, during the production of the aluminum nitride of the present invention, the reaction suppression gas is supplied while the nitriding reaction of the aluminum powder is carried out in a nitrogen gas atmosphere, so that the nitriding reaction can be advanced at a low temperature. In general, the size of the primary particle diameter of the ceramic depends on the reaction initiation temperature. In the aluminum nitride of the present invention, the particle diameter of the aluminum nitride particles is determined by the start temperature of the nitriding reaction. In the aluminum nitride of the present invention, since the nitriding reaction proceeds at a low temperature, aluminum nitride powder having a small particle diameter is produced.

Except for the following specific arrangement, the arrangement of the aluminum nitride of the present invention is the same as the method for producing the aluminum nitride of the present invention. Accordingly, the same specific arrangements will not be described in detail herein. The aluminum nitride of the present invention preferably has a particle diameter of 1 m or less and a specific surface area of 2.5 m ² / g or more. When the particle diameter is 1 μm or less and the specific surface area is 2.5 m ² / g or more, the aluminum nitride of the present invention produces an aluminum nitride powder having a small particle diameter.

Example

Hereinafter, the present invention will be described with reference to specific embodiments.

As an example according to the present invention, a nitriding furnace was fabricated and the aluminum powder was nitrided. The structure of the produced nitriding furnace is shown in FIG.

(Nitriding furnace)

The nitriding furnace 1 is an electric furnace including a furnace shell 10, a heat resistant muffle 11, and a heater 12. The heat resistant muffle 11 is retained inside the furnace shell 10 and has a reinforcement rib. The heat resistant muffle 11 also has a furnace wall made of stainless steel (for example, SUS304 in accordance with Japanese Industrial Standards). The wall thickness of the furnace is 6 mm. The inner capacity of the heat resistant muffle 11 is 80L. In the furnace shell 10, a heater 12 is disposed to face the outer circumferential surface of the heat resistant muffle 11.

The heat resistant muffle 11 has an air-tight furnace structure capable of maintaining a pressure of 0.1 kPa when vacuumed by the vacuum pump 14.

The nitriding furnace 1 has a space of about 70 mm between the inner circumferential surface of the furnace shell 10 and the bottom surface of the heat resistant muffle 11. The nitriding furnace 1 is equipped with the air supply apparatus 15 which supplies air to this space, and the air discharge apparatus 16 which discharges air in the space. Note that the air supply device 15 can supply factory air having a pressure of 0.6 MPa in the space between the furnace shell 10 and the heat resistant muffle 11.

In addition, the nitriding furnace 1 is equipped with the gas supply apparatus 2. The gas supply device 2 may supply nitrogen gas and argon gas into the heat resistant muffle 11.

The gas supply device 2 includes a nitrogen gas bomb 21, an argon gas cylinder 25, a conduit 20, valves 22 and 26 and mass flow meters 23 and 27. One end of the conduit 20 is connected to the nitrogen gas cylinder 21 and the argon gas cylinder 25, and the other end thereof is opened to face the furnace wall of the heat resistant muffle 11. Valves 22 and 26 are disposed at respective connections between the conduit 20 and the nitrogen gas cylinder 21 and between the conduit 20 and the argon gas cylinder 25. In the conduit 20, material flow meters 23 and 27 are arranged, which measure the flow rate of the gas passing through the conduit 20. The mass flow meters 23 and 27 are manufactured by YAMATAKE Co., Ltd. Note that the flow rates of the gas supplied from the gas supply device 2 can be properly adjusted in the range of 2 to 50 L / min by the mass flow meters 23 and 27.

In addition, the nitriding furnace 1 includes a discharge device 4 for discharging the gas in the heat-resistant muffle 11 to the outside. The discharge device 4 comprises a conduit 41 and a discharge valve 42. One end of the conduit 41 is opened by the heat resistant muffle 11, and the other end thereof is opened to the outside of the nitriding furnace 1. A discharge valve 42 is disposed in the conduit 41, which regulates the flow rate of the gas passing through the conduit 41.

Further, the nitriding furnace 1 is provided with a pressure gauge 51 for measuring the gas pressure in the heat resistant muffle 11. The pressure gauge 51 is a product of CKD Co., Ltd., and has a measurable range of 0 to 200 kPa and 4 contacts.

In addition, four thermocouples 52 are provided in the nitriding furnace 1. The thermocouples 52 are heat resistant muffle 11 in four positions, namely inside and outside of the bottom furnace wall of the heat resistant muffle 11, in the aluminum powder retained in the upper furnace wall and the heat resistant muffle 11 of the heat resistant muffle 11. Measure the temperature.

The nitriding furnace 1 adds an arithmetic unit 55 to which an air supply device 15, an air discharge device 16, a pressure gauge 51, a thermocouple 52, and valves 22, 26, and 42 are electrically connected. It includes. The computing device 55 calculates environmental variables in the heat resistant muffle 11 from data measured by devices such as the pressure gauge 51 and the thermocouple 52, and the valve 22, in accordance with the deviation from the desired setting condition. It is possible to determine the opening amount of the 26, 42, and to open and close the respective valves 22, 26, 42. In addition, the computing device 55 may operate the air supply device 15 and the air discharge device 16 to maintain the temperature of the heat-resistant muffle 11 at a desired temperature. In addition, the arithmetic unit 55 can display the measurement data on an output device not shown.

In addition, the aluminum powder to be nitrided by the nitriding furnace 1 is accommodated in the heat resistant muffle 11 in a state of being stored in the box-shaped reactor tray 17. The reactor tray 17 is made of graphite and has a volume of 6L. Depending on the amount of aluminum powder, the reactor tray 17 is used by laminating in one to three stages.

(Example 1)

As Example 1, the high-purity aluminum powder whose average particle diameter is 30 micrometers was nitrided using the nitriding furnace 1, and aluminum nitride powder was manufactured. Aluminum powder is a product of TOYO ALUMINIUM Co., Ltd., and its purity was 99.7%.

First, 500 g of aluminum powder and 500 g of aluminum nitride powder, which were raw materials, were sufficiently mixed with a hand mixer. Aluminum nitride powder was a product of Toyo Aluminum Company Limited, and its average particle diameter was 1.6 mu m. The mixing ratio of the raw materials is shown in Table 1 below.

Example Raw material Al powder (g) Al foil (g) AlN Powder (g) One 500 0 500 2 300 200 500 3 700 300 500 4 Top: 500 Bottom: 500 0 0 Top: 500 Bottom: 500 5 Top: 400 Suspension: 400 Bottom: 400 0 0 0 Top: 600 Suspension: 600 Bottom: 600 6 1000 0 1500 7 Top: 1000 Bottom: 1000 0 0 Top: 1500 Bottom: 1500

Subsequently, the raw material mixed powder is stored in the reactor tray 17. The reactor tray 17 is positioned at the center of the heat resistant muffle 11. The reactor tray 17 was used independently in one stage. The raw mixed powder was not compressed when stored in the reactor tray 17.

Thereafter, the valve 22 of the gas supply device 2 and the valve 42 of the discharge device 4 were opened to continuously supply nitrogen gas into the heat resistant muffle 11 at a flow rate of 10 L / min. The pressure in the heat resistant muffle 11 was maintained in the range of 115 to 125 kPa. Therefore, in the heat resistant muffle 11, when temperature rose to 450 degreeC, dew point was -50 degreeC or less. Note that the dew point was observed using a dew point hygrometer 45 which is arranged to detect the inside of the conduit 41 of the discharge device 4.

While supplying nitrogen gas to the heat resistant muffle furnace 11 at a flow rate of 10 L / min, the heater 12 of the nitriding furnace 1 is turned on and the temperature in the heat resistant muffle furnace 11 is raised to 460 ° C. at a temperature increase rate of 7 ° C./min. Let's do it. This temperature was then maintained for 30 minutes.

Then, the temperature in the heat resistant muffle 11 was raised to 630 degreeC at the temperature increase rate of 5 degree-C / min, and the nitriding reaction was advanced under the processing conditions shown in Table 2.

Example Setting condition N ₂ occlusion reaction temperature (℃) N ₂ occlusion reaction time (min) Temperature rise rate (℃ / min) Nitriding Reaction Temperature (℃) One 460 30 5 630 2 460 30 5 First: 640 Second: 750 3 460 30 5 630 4 460 30 5 630 5 460 30 5 640 6 460 30 10 670 7 460 30 10 First: 670 second: 700

The flow rate of nitrogen gas and argon gas, the amount of electricity supplied, the temperature difference between the inside and outside of the furnace wall of the heat-resistant muffle 11 and the workpiece and the furnace wall of the heat-resistant muffle 11 generated from the flow rate and the electricity supply will be described. When the temperature in the heat resistant muffle 11 reaches 630 ° C., the temperature is maintained and the valve 26 of the gas supply device 2 is opened to supply argon gas to the heat resistant muffle 11 at a flow rate of 3 L / min. It was.

During operation, if the rate of nitriding reaction was slowed, the valve 26 was closed to reduce or stop the supply of argon gas, and the valve 22 was also opened to increase the flow rate of nitrogen gas to 13 L / min. In this way, the nitriding reaction was advanced. Note that the rate of nitriding reaction was observed by the temperature measured by the thermocouple 52 and the gas pressure in the heat resistant muffle 11 measured by the pressure gauge 51.

Thereafter, when the nitriding reaction proceeded, the valve 26 was opened to supply the argon gas to the heat resistant muffle 11 again at a flow rate of 1.5 L / min.

When the gas pressure in the heat resistant muffle 11 was recovered, the valve 26 was closed and the valve 22 was opened to increase the flow rate of nitrogen gas to 15 L / min. After holding the aluminum powder for 20 minutes in this state, a decrease in gas pressure and a temperature rise were not observed. In this way, the end of the nitriding reaction was confirmed. The reaction time was exactly 3 hours.

Note that the reaction temperature was controlled by adjusting the amount of electricity supplied to the heater 12 to 36 to 50% during the progress of the nitriding reaction. In addition, the temperature difference between the inside and the outside of the furnace wall of the heat resistant muffle 11 was 20 to 30 ° C.

Finally, the heat resistant muffle 11 was cooled to recover the aluminum nitride powder of the reactor tray 17. The reaction conditions of the nitriding reaction and the operating conditions of the nitriding furnace 1 are shown in Table 3 below. In this way, the aluminum nitride powder of Example 1 was prepared.

Example Conditions of Nitriding Reaction Operating conditions of nitriding furnace Power supplied (%) Gas mix ratio (nitrogen gas (L / min) / argon gas (L / min)) Reaction time (hours) Temperature of workpiece (℃) Temperature difference * (℃) At the start of the reaction Intermediate reaction (1) Medium reaction (2) final One 36-50 10/3 13/0 13 / 1.5 15/0 3.0 610-640 20-30 2 30 ~ 70 (automatically adjusted) 10/3 13/0 13/3 15/0 5.0 730-770 30-70 3 40-50 10/3 13/0 13 / 0.3 ~ 13 / 0.8 15/0 3.5 620-670 15-50 4 30-70 10/3 13/0 13 / 0.3 ~ 13 / 0.8 15/0 3.3 630-670 5 ~ 80 5 30 ~ 70 (automatically adjusted) 10/3 13 / 0.8 ~ 13 / 1.5 13 / 0.3 or 13 / 1.0 15/0 3.7 600-660 20-90 6 10-55 8/2 8/6 8/4 10/0 2.0 677-723 5-50 7 30-76 8/2 8 / 3.6 8 / 3.6 10/0 3.5 670-716 5-40

* "Temperature difference" means the difference between the internal temperature and the external temperature of the heat resistant muffle 11.

(evaluation)

1260 g of the aluminum nitride powder of Example 1 was recovered. Since 500 g of aluminum nitride powder was used as part of the raw material, 760 g of aluminum nitride was formed. This indicates that 500 g of aluminum powder is nitrided at a nitriding rate of 100% to produce aluminum nitride powder.

That is, when aluminum (A1) is reacted with nitrogen (N) to form aluminum nitride, the weight of the product is theoretically 1.52 times the weight of the reactant (ie, (27 + 4) / 27 = 1.52). In preparing the aluminum nitride powder of Example 1, 500 g of aluminum powder was charged. Therefore, multiplying the charge by the factor 1.52 gives 760 g.

In addition, analysis of the aluminum nitride powder of Example 1 found that the nitrogen content was 34.1% by weight and the oxygen content was 0.68% by weight. Thus, from the gravimetric result, it is understood that the nitriding rate of the aluminum nitride powder produced in this manner is almost 100%.

When the specific surface area of the aluminum nitride powder was measured, it showed a high value as 3.1 m <^2> / g. The preparation and analysis results of the aluminum nitride powder of Example 1 are shown in Table 4 below.

Example Manufacture results Analysis Total AlN Amount (g) Amount of AlN produced (g) Nitrogen content (%) Oxygen content (%) Average diameter of primary particles (μm) Specific surface area (m ² / g) Crystalline size (Å) One 1260 760 34.1 0.68 1 or less 3.1 Not measured 2 1260 760 34.0 0.73 1 or less 2.8 Not measured 3 2010 1510 33.7 0.85 1 or less Not measured 1266 and 1103 4 2520 1520 34.1 0.74 1 or less Not measured 1224 and 1234 5 3630 1830 34.0 9.20 1 or less Not measured 1665 and 1779 6 2010 1510 33.9 0.75 1 or less 3.2 Not measured 7 6020 3020 34.2 0.64 1 or less 4.5 Not measured

Moreover, the aluminum nitride powder of Example 1 was photographed by SEM, and the obtained SEM photograph is shown in FIG. Here, FIG. 2A is an SEM photograph magnified 6,000 times, and FIG. 2B is an SEM photograph magnified 4,000 times. Note that the SEM photograph shown in FIG. 2 is a photograph taken after crushing the prepared aluminum nitride powder with mortar. Grinding could be performed easily.

As shown in FIG. 2, it was confirmed that the particle diameter of the aluminum nitride powder of Example 1 was almost 1 micrometer or less. Therefore, it is understood that the aluminum nitride powder of Example 1 is made into a fine powder that is difficult to manufacture by a conventional method for producing aluminum nitride. Note that in FIG. 2, slightly coarse particles are observed. These slightly coarse particles are particles of aluminum nitride powder used as part of the raw material. Also in FIG. 2, large particles are found. These large particles are secondary particles in which primary particles are aggregated. The secondary particles can be easily made into fine aluminum nitride powder by performing grinding.

From the above, it is understood that the aluminum nitride powder of Example 1 is produced at a nitriding rate of almost 100% and includes fine aluminum nitride particles having a particle diameter of 1 m or less.

In Example 1, aluminum nitride primary particles having a particle diameter of 1 μm or less were produced from aluminum powder having an average particle diameter of 30 μm, and it was also confirmed that the surface area was increased. It is known that the reaction from aluminum to aluminum nitride involves 16% volumetric expansion. Thus, Example 1 shows that when the nitriding reaction proceeds at low temperatures, even though no sintering occurs, adjacent particles adhere to each other by volume expansion of aluminum produced from the reaction.

(Example 2)

As Example 2, the aluminum nitride powder was manufactured by nitriding the high purity aluminum powder of 30 micrometers of average particle diameters mixed with the scraped aluminum foil using the nitriding furnace 1. As shown in FIG. Aluminum powder was a product of Toyo Aluminum Company Limited, and the purity was 99.7%.

In Example 2, a plurality of spaces are formed between the particles of the raw aluminum powder to be nitrided by including the fragmented aluminum foil, which is coarser than the particles of the raw aluminum powder having an average particle diameter of 30 mu m. Therefore, this is an embodiment in which the nitriding reaction is performed under the assumption that when the nitriding reaction proceeds in an environment where a plurality of spaces exist, the space suppresses the adhesion of particles even when volume expansion occurs.

The scraped aluminum foil was formed by tearing an aluminum foil having a thickness of 20 to 30 µm. The apparent specific gravity of the scraped aluminum foil was 0.7 to 0.8, and the aluminum purity was 99.7%. The fragmented aluminum foils are different in shape because they are formed by tearing the aluminum foil.

The aluminum nitride powder of Example 2 was prepared in the following manner. First, as shown in Table 1, the raw materials were weighed and thoroughly mixed with a hand mixer. In detail, the aluminum powder raw material contained 300 g of aluminum powder, 200 g of fragmented aluminum foil, and 500 g of aluminum nitride powder whose average particle diameter is 1.6 micrometers.

The aluminum powder raw material is then stored in the reactor tray 17 in the same manner as in Example 1. After nitriding the aluminum powder raw material using the nitriding furnace 1, the nitriding reaction was advanced. Moreover, when the start of nitriding reaction was confirmed, supply of argon gas was started. The operating conditions of the nitriding furnace 1 are shown in Table 3.

In Example 2, it should be noted that since the aluminum powder raw material includes coarse aluminum foil sculpted therein, it was maintained at 640 ° C. for 2 hours and then at 750 ° C. for 1 hour. Heating was carried out separately to completely nitrify the scrapped aluminum foil.

In addition, in Example 2, the electricity supply to the heater 12 was performed automatically using the computing device 55. Moreover, in Example 2, when the nitriding reaction advanced at 750 degreeC, it advanced violently. Thus, argon gas was supplied to the heat resistant muffle 11 for about 15 minutes at a flow rate of 3 L / min. The reaction conditions in the nitriding reaction are also shown in Table 3.

(evaluation)

In Example 2, the amount of aluminum nitride powder recovered was 1260 g and the amount of aluminum nitride powder formed was 760 g. The preparation and analysis results of the aluminum nitride powder of Example 2 are also shown in Table 4. In the recovered aluminum nitride powder, no form remains due to the scraped aluminum foil. The recovered aluminum nitride powder was formed into a brittle dry powder.

Therefore, the aluminum nitride powder of Example 2 contains 760g of formed aluminum nitride. The weight change indicates that 500 g of aluminum powder was nitrided at a nitriding rate of 100%.

The aluminum nitride powder of Example 2 had a nitrogen content of 34.0 wt% and an oxygen content of 0.73 wt%. Since the nitrogen content was a high value of 34.0%, the nitriding rate of the aluminum nitride powder of Example 2 was found to be almost 100%. In addition, when the particle diameter of the aluminum nitride powder of Example 2 was measured, it was 1 micrometer or less similarly to the aluminum nitride powder of Example 1.

In addition, when the specific surface area of the aluminum nitride powder was measured, it showed a high value as 2.8 m <^2> / g. The preparation and analysis results of the aluminum nitride powder of Example 2 are also shown in Table 4.

From the above, it is understood that the aluminum nitride powder of Example 2 is produced at a nitriding rate of almost 100% and includes fine aluminum nitride particles having a particle diameter of 1 m or less.

(Example 3)

As Example 3, the aluminum nitride powder was manufactured by nitriding the high purity aluminum powder of 30 micrometers of average particle diameters mixed with the scraped aluminum foil using the nitriding furnace 1. As shown in FIG. Aluminum powder was a product of Toyo Aluminum Company Limited, and the purity was 99.7%.

In Example 3, it is the same as Example 2 except using 300g of sliced aluminum foil, 700g of high-purity aluminum powder whose average particle diameter is 30 micrometers, and setting reaction temperature of nitriding reaction to 630 degreeC. The aluminum powder raw material was nitrided under the set conditions.

In Example 3, since the aluminum powder to be nitrided was used twice as much as in Example 2, the total calorific value was doubled as in Example 2. Therefore, Example 3 aims to advance the nitriding reaction of the coarse aluminum foil scraped off by the increased heat of reaction.

The composition of the aluminum powder raw material and the detailed reaction conditions of the nitriding reaction are all shown in Tables 1 to 3. Also in Example 3, it should be noted that the aluminum powder raw material was stored in the reaction vessel 17, the nitriding reaction was carried out using the nitriding furnace 1, and the nitriding reaction was advanced. Moreover, when the start of nitriding reaction was confirmed, supply of argon gas was started. The operating conditions of the nitriding furnace 1 are shown in Table 2. In Example 3, the reaction time of the nitriding reaction was 3 hours 30 minutes.

(evaluation)

In Example 3, the recovered aluminum nitride powder was 2,010 g and the formed aluminum nitride powder was 1,510 g. The preparation and analysis results of the aluminum nitride powder of Example 3 are also shown in Table 4. The recovered aluminum nitride powder did not leave any form due to the aluminum foil. The scraped aluminum foil became aluminum nitride particles.

Therefore, 1,510 g of formed aluminum nitride is contained in the aluminum nitride powder of Example 3. The weight change indicates that 1,000 g of aluminum powder was nitrided with a nitriding rate of nearly 100%.

The aluminum nitride powder of Example 3 had a nitrogen content of 33.7 wt% and an oxygen content of 0.85 wt%. Since the nitrogen content was a high value of 33.7%, the nitriding rate of the aluminum nitride powder of Example 3 was found to be almost 100%.

In addition, when the crystallite size of the aluminum nitride powder of Example 3 was computed from the half-value width by X-ray diffraction analysis, it was 1,266 microseconds and 1,103 microseconds in two positions, respectively. Table 4 shows all the results of the analysis of the aluminum nitride powder of Example 3.

From the above, it is understood that the aluminum nitride powder of Example 3 is produced with a nitriding rate of almost 100% and includes fine aluminum nitride particles having a particle diameter of 1 탆 or less.

(Example 4)

As Example 4, an aluminum nitride powder was prepared by nitriding a high purity aluminum powder having an average particle diameter of 30 μm stored at the top and bottom of a reactor tray stacked in three stages using the nitriding furnace 1. Aluminum powder was a product of Toyo Aluminum Company Limited, and its purity was 99.7%.

Specifically, 1,000 g of aluminum powder raw material was sufficiently mixed with 1,000 g of aluminum nitride powder, which is a company product, using a hand mixer. Aluminum nitride powder was manufactured in the following manner. Aluminum nitride powder was prepared in the same manner as in Example 1. The resulting aluminum nitride powder was pulverized and sieved to 500 mesh or less.

1,000 g of each fully mixed raw material mixed powder is dispensed. Each was stored in a separate reactor tray. Two reactor trays containing the dispensed raw powder were stacked with an empty tray in between. The purpose of Example 4 is to carry out the nitriding reaction under the assumption that the heater 12 of the nitriding furnace 1 can individually control the temperatures of the top and bottom of the two reactor trays, ie stacked reactor trays.

The stacked reactor trays were placed in the center of the heat resistant muffle 11 of the nitride furnace 1 shown in FIG. Also in Example 4, after carrying out nitrogen storing process of the raw material mixed powder using the nitriding furnace 1, nitriding reaction was advanced. Moreover, when confirming the start of nitriding reaction, supply of argon gas was started. The reaction conditions of the nitriding reaction are all shown in Table 3.

In the nitriding reaction of Example 4, after 4 minutes of reaching the set reaction temperature, for example, 630 ° C, a slight pressure drop in the heat resistant muffle 11 was detected, for example, 132.9 kPa to 131.0 kPa. Thus, the electricity supply was reduced to 30%. In this case argon gas was supplied at a flow rate of 1.5 L / min. At this time exotherm was observed only at the bottom of the reactor tray. Due to the decrease in the electricity supply, the temperature at the top of the reactor tray was reduced to 580 to 590 ° C. Therefore, 1.5 hours after the start of the reaction, the amount of electricity supplied to the heater 12 increased to 60%. As a result, the nitriding reaction was started when the temperature of the raw material mixed powder at the top of the reactor tray was 640 ° C.

The temperature difference between the inside and the outside of the bottom surface of the heat resistant muffle 11 measured by the thermocouple 52 was 5 to 80 ° C. In Example 4, the reaction time of the nitriding reaction was 3 hours 20 minutes.

(evaluation)

In Example 4, the amount of aluminum nitride powder recovered was 1260 g at the top of the reactor tray, 1260 g at the bottom, and the total amount of aluminum nitride powder formed was 1,520 g, that is, 760 g at the top of the reactor tray and 760 g at the bottom. In addition, the preparation and analysis results of the aluminum nitride powder of Example 4 are shown in Table 4.

Therefore, the aluminum nitride powder of Example 4 contains 1,520g of formed aluminum nitride in total. The weight change indicates that 1,000 g of aluminum powder was nitrided with a nitriding rate of nearly 100%.

According to the weight analysis result of the aluminum nitride powder of Example 4, the nitrogen content was 34.1 weight% and the oxygen content was 0.74 weight%. Since the nitrogen content was a high value of 34.1%, the nitriding rate of the aluminum nitride powder of Example 4 was found to be almost 100%.

In addition, when the crystallite size of the aluminum nitride powder of Example 4 was computed from the half width by X-ray-diffraction analysis, it was 1,224 kPa and 1,234 kPa in two positions, respectively. Table 4 shows all the results of the analysis of the aluminum nitride powder of Example 4.

From the above, it is understood that the aluminum nitride powder of Example 4 is produced at a nitriding rate of almost 100% and includes fine aluminum nitride particles having a particle diameter of 1 m or less. In addition, when the nitriding reaction proceeds, a deviation of the exothermic start occurs between the upper end and the lower end of the reactor tray 17. Therefore, the inventors have found that it is possible to shift the occurrence of nitriding reactions in the same furnace. In Example 4, the aluminum powder raw material was used in a total amount of 1,000 g, that is, the sum of 500 g and 500 g, and absorption of reaction heat was relatively easy. However, it is very advantageous to shift the occurrence of nitriding reactions at each stage of the reactor tray, assuming that the storage amount of the aluminum powder raw material at each stage of the reactor tray is increased. For example, if the heater of the nitriding furnace can control the temperature of each of the top, middle and bottom of the reactor tray, it is possible to shift the occurrence of the nitriding reaction in each reactor tray to Throughput can be increased.

(Example 5)

The aluminum powder was prepared in the same manner as in Example 4 except for storing the aluminum nitride powder of Example 5 using the nitriding furnace 1 and storing it in the middle of the reactor tray stacked in three stages.

In detail, 1,200 g of high-purity aluminum powder having an average particle diameter of 30 µm was sufficiently mixed with 1,800 g of aluminum nitride powder, which is a company product, using a hand mixer. Aluminum powder was a product of Toyo Aluminum Company Limited, and the purity was 99.7%. It should be noted that the aluminum nitride powder, which is its product, was manufactured in the following manner. Aluminum nitride powder was prepared in the same manner as in Example 1. The resulting aluminum nitride powder was pulverized and sieved to 500 mesh or less.

The fully mixed raw material mixed powder is divided into three portions of 1,000 g each. Each portion was stored in a separate reactor tray. Three reactor trays containing the dispensed raw material mixed powder were stacked and housed in a heat resistant muffle (11). Then, the nitriding reaction was advanced. Detailed conditions are shown in Tables 2 and 3.

In Example 5, unlike Example 4, there were workpieces in each of the three reactor trays, and the set reaction temperature was increased to about 10 ° C. Therefore, the start of the nitriding reaction is further delayed at the upper end of the reactor tray, but exotherm occurred in the workpiece stored in all three stages of the reactor tray. The entire heat generated in the three-stage reactor tray was discharged to the outside of the heat-resistant muffle 11 by not only the reactor tray but also the furnace wall of the heat-resistant muffle 11 in which the reactor tray is located. Thus, the temperature difference between the inside and outside of the furnace wall of the heat resistant muffle 11 was maintained for 1.5 hours in the range of 60 to 90 ° C. In detail, the temperature of the workpiece | work in the heat resistant muffle 11 of the nitride furnace 1 was 630-650 degreeC. On the other hand, the external temperature of the heat resistant muffle 11 was 550-590 degreeC.

In the nitriding reaction, the temperature difference between the inside and the outside of the bottom of the heat resistant muffle 11 was 5 to 90 ° C. In Example 5, the reaction time of the nitriding reaction was 3 hours 40 minutes.

(evaluation)

In Example 5, the amount of aluminum nitride powder recovered was 1,210 g at the top of the reactor tray, 1,210 g at the stop, and 1,210 g at the bottom. Therefore, the total amount of aluminum nitride powder recovered was 3630 g. The amount of aluminum nitride powder formed was 610 g at the top of the reactor tray, 610 g at the middle and 610 g at the bottom. Thus, the total amount of aluminum nitride powder formed was 1830 g. There is no difference in the nitriding rate of the aluminum nitride powder produced at the top, middle and bottom of the reactor tray. The preparation and analysis results of the aluminum nitride powder of Example 5 are also shown in Table 4.

In this way, the aluminum nitride powder of Example 5 contained 1830 g of formed aluminum nitride in total. The weight change indicates that 1,200 g of aluminum powder was nitrided with a nitriding rate of nearly 100%.

According to the weight analysis result of the aluminum nitride powder of Example 5, the nitrogen content was 34.0 weight% and the oxygen content was 9.20 weight%. Since the nitrogen content was a high value of 34.0%, the nitriding rate of the aluminum nitride powder of Example 5 was found to be almost 100%.

In addition, when the crystallite size of the aluminum nitride powder of Example 5 was computed from the half width by X-ray-diffraction analysis, it was 1,665 microseconds and 1,779 microseconds in two positions, respectively. Table 4 shows the analysis results of the aluminum nitride powder of Example 5.

In addition, the aluminum nitride powder of Example 5 was photographed by SEM, and the obtained SEM photograph is shown in FIG. 3A is an SEM photograph magnified 2,800 times, and FIG. 3B is an SEM photograph magnified 4,000 times. The SEM photograph shown in FIG. 3 is a photograph taken after crushing the prepared aluminum nitride powder with mortar. Grinding could be performed easily.

As shown in FIG. 3, it was confirmed that the particle diameter of the aluminum nitride powder of Example 5 was almost 1 micrometer or less. Therefore, it is understood that the aluminum nitride powder of Example 5 is made into a fine powder that is difficult to manufacture by a conventional method for producing aluminum nitride.

From the above, it is understood that the aluminum nitride powder of Example 5 prepared at a nearly 100% nitride rate contains fine aluminum nitride particles having a particle diameter of 1 μm or less.

(Example 6)

As Example 6, high-purity aluminum powder having an average particle diameter of 30 µm was nitrided using the nitriding furnace 1 to prepare aluminum nitride powder. Aluminum powder was "AHL 2504 (trade name)" manufactured by Toyo Aluminum Co., Ltd., and the purity was 99.95%.

First, 1,000 g of aluminum powder raw material and 1,500 g of aluminum nitride powder were sufficiently mixed with a "V" type blender. Aluminum nitride powder was "UF (trade name)" which is a product of Toyo Aluminum Co., Ltd., and average particle diameter was 1.6 micrometers. The mixing ratio of the raw materials is also shown in Table 1.

Subsequently, the raw mixed powder was stored in the reactor tray 17. The reactor tray 17 was placed in a heat resistant muffle 11. The reactor tray 17 was used separately in one stage. The raw mixed powder was not compressed when stored in the reactor tray 17.

Thereafter, the valve 22 of the gas supply device 2 and the valve 42 of the discharge device 4 were opened to continuously supply nitrogen gas into the heat resistant muffle 11 at a flow rate of 8 L / min. The pressure in the heat resistant muffle 11 was maintained in the range of 120 to 150 kPa. Therefore, in the heat resistant muffle 11, when temperature rose to 450 degreeC, dew point was -50 degreeC or less. The dew point was observed using a dew point hygrometer (45).

While supplying nitrogen gas into the heat resistant muffle furnace 11 at a flow rate of 8 L / min, the heater 12 of the nitriding furnace 1 is turned on and the temperature in the heat resistant muffle furnace 11 is raised to 460 ° C. at a temperature increase rate of 7 ° C./min. Let it be. This temperature was then maintained for 30 minutes.

Subsequently, the temperature in the heat resistant muffle 11 was raised to 670 degreeC at the temperature increase rate of 4 degree-C / min, and the nitriding reaction was advanced under the processing conditions shown in Table 2.

The flow rate of nitrogen gas and argon gas, the amount of electricity supplied, the temperature difference between the inside and outside of the furnace wall of the heat-resistant muffle 11 and the workpiece and the furnace wall of the heat-resistant muffle 11 generated from the flow rate and the electricity supply will be described. When the temperature in the heat resistant muffle 11 reaches 670 ° C and the nitriding reaction is started, or when the pressure in the heat resistant muffle 11 decreases, the valve 26 of the gas supply device 2 is opened to release 2 to 6 L of argon gas. The heat resistant muffle 11 was supplied at a flow rate of / min.

During operation, if the rate of nitriding reaction was slowed, the valve 26 was closed to reduce or stop the supply of argon gas, and the valve 22 was also opened to increase the flow rate of nitrogen gas to 12 L / min. In this way, the nitriding reaction was advanced.

If the raw material mixed powder is kept in this state for 30 minutes, a decrease in gas pressure and a rise in temperature are not observed. Thus, the inventors confirmed the end of the nitriding reaction. The reaction time was about 2 hours.

The reaction temperature was controlled by adjusting the amount of electricity supplied to the heater 12 to 10 to 55% at the time of progress of the nitriding reaction. Moreover, factory air was supplied to the furnace wall of the heat resistant muffle 11 by the air supply apparatus 15, and the temperature of the furnace wall was maintained at 500-550 degreeC. The temperature of the workpiece | work from the start to the end of nitriding reaction was 675-723 degreeC. Moreover, the temperature difference between the inside and the outside of the furnace wall of the heat resistant muffle 11 was 5-50 degreeC.

Finally, the heat resistant muffle 11 was cooled to recover the aluminum nitride powder of the reactor tray 17. In this way, the aluminum nitride powder of Example 6 was prepared.

(evaluation)

3,010 g of the aluminum nitride powder of Example 6 was recovered. Since 1500 g of aluminum nitride powder was used as part of the raw material, 1,510 g of aluminum nitride was formed. This indicates that 1,000 g of aluminum powder is nitrided at a nitriding rate of almost 100% to produce aluminum nitride powder.

In addition, an analysis of the aluminum nitride powder of Example 6 showed that the nitrogen content was 33.9% by weight and the oxygen content was 0.75% by weight. Therefore, from the gravimetric result, it was understood that the nitriding rate of the aluminum nitride powder produced in this manner was almost 100%.

In addition, when the specific surface area of the aluminum nitride powder is measured, it shows a high value of 3.2 m ² / g. The results of the preparation and analysis of the aluminum nitride powder of Example 6 are also summarized in Table 4.

From the above, it is understood that the aluminum nitride powder of Example 6 prepared at a nearly 100% nitride rate contains fine aluminum nitride particles having a particle diameter of 1 μm or less.

(Example 7)

As Example 7, an aluminum nitride powder was prepared by nitriding a high purity aluminum powder having an average particle diameter of 30 μm stored at the top and bottom of a reactor tray stacked in three stages using the nitriding furnace 1. Aluminum powder was "AHL 2504 (brand name)" of the Toyo Aluminum Company Limited, and its purity was 99.95%.

Specifically, 2,000 g of aluminum powder raw material was sufficiently mixed with 3,000 g of aluminum nitride powder, which is a product of the company, in a "V" type blender. Aluminum nitride powder was manufactured in the following manner. Aluminum nitride powder was prepared in the same manner as in Example 1. The resulting aluminum nitride powder was pulverized and sieved to 500 mesh or less.

2,500 g of the fully mixed raw material mixed powder was each distributed. Each was stored in a separate reactor tray. An empty tray was stacked between two reactor trays in which the dispensed raw powder was stored. The purpose of Example 7 is to carry out the nitriding reaction under the assumption that the heater 12 of the nitriding furnace 1 can individually control the temperatures of the top and bottom of two reactor trays, ie stacked reactor trays.

Thereafter, in Example 7, after the nitrogen occlusion treatment in the same manner as in Example 6, the nitriding reaction was advanced. Moreover, when confirming the start of nitriding reaction, supply of argon gas was started. The reaction conditions of the nitrification reaction of Example 7 are also shown in Table 3.

(evaluation)

In Example 7, aluminum nitride powder was recovered in an amount of 6,020 g. Since 3,000 g of aluminum nitride powder, which is a company product, was used as part of the raw material, 3,020 g of aluminum nitride powder was formed. This indicates that 2,000 g of aluminum powder is nitrided at a nitriding rate of almost 100% to produce aluminum nitride powder.

In addition, an analysis of the aluminum nitride powder of Example 7 showed that the nitrogen content was 34.2% by weight and the oxygen content was 0.64% by weight. Therefore, from the gravimetric result, it was understood that the nitriding rate of the aluminum nitride powder produced in this manner was almost 100%.

In addition, when measuring the specific surface area of the aluminum nitride powder, it shows a high value of 4.5m ² / g. The results of the preparation and analysis of the aluminum nitride powder of Example 7 are also summarized in Table 4.

From the above, it is understood that the aluminum nitride powder of Example 7 prepared at a nearly 100% nitride rate contains fine aluminum nitride particles having a particle diameter of 1 μm or less.

According to Examples 1 to 7, the nitriding reaction can be carried out at a low temperature using the method for producing an aluminum nitride of the present invention, it is possible to produce an aluminum nitride powder containing fine particles having a small particle diameter.

In addition, in Examples 1 to 7 according to the present invention, aluminum nitride powder is produced at a nitriding rate of almost 100%. Thus, when using a reactor tray as described in Examples 1-7, no impurities are mixed in the product. Therefore, by using the reactor tray as described in Examples 1 to 7, the cost required for the production of aluminum nitride powder can be reduced.

While the invention has been fully described, it will be apparent to those skilled in the art that many changes and modifications can be made therein without departing from the spirit and scope of the invention as set forth herein, including the appended claims.

Claims (20)

A method for producing aluminum nitride comprising maintaining an aluminum powder in a nitrogen atmosphere having a nitrogen gas pressure of 105 to 300 kPa and performing a nitriding reaction at 500 to 1,000 ° C. A reaction inhibiting gas, which suppresses the progress of nitriding reaction, which is at least one gas selected from the group consisting of argon gas and ammonia gas, is supplied into a reaction chamber containing aluminum powder. The method of claim 1, wherein the aluminum powder is maintained in a nitrogen gas atmosphere of 450 to 600 ℃ for 30 to 120 minutes to carry out the nitrogen storage process for storing the nitrogen in the aluminum powder after the nitriding reaction, the production of aluminum nitride Way. delete The nitrogen gas atmosphere according to claim 1, wherein the nitrogen gas atmosphere is maintained by nitrogen gas delivered from a nitrogen gas supply device for continuously supplying nitrogen gas to the reaction chamber and nitrogen gas discharged from the discharge device for discharging nitrogen gas from the reaction chamber. Method for producing aluminum nitride. The method for producing aluminum nitride according to claim 1, wherein the reaction inhibiting gas is supplied into the reaction chamber when the nitrogen gas pressure in the reaction chamber is reduced. The method for producing aluminum nitride according to claim 1, wherein the reaction inhibiting gas is supplied into the reaction chamber when the temperature of the workpiece increases. delete The method for producing aluminum nitride according to claim 1, wherein the reaction inhibiting gas is supplied into the reaction chamber at a ratio of 1 to 50 volume% when the amount of gas in the reaction chamber is 100 volume%. delete delete The method for producing aluminum nitride according to claim 1, wherein after supply of the reaction inhibiting gas is stopped, nitrogen gas is further supplied into the reaction chamber. delete delete delete delete delete delete delete delete delete

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