JPH11130411A - Production of aluminum nitride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently carry out nitriding at a lower temp. than a conventional method by calcining γ-Al2 O3 or its precursor to control its water content to a specified value or lower to obtain γ-Al2 O3 as an alumina and then heating the alumina in an ammonia gas containing hydrocarbons to nitride. SOLUTION: An alumina is heated and nitrided in a mixture gas of hydrocarbon gas and ammonia gas containing >=0.5 vol.% hydrocarbon gas to produce aluminum nitride. In this method, γ-Al2 O3 as an alumina prepared by calcining γ-Al2 O3 or its precursor to control the water content to <=1 wt.% is used. The heating temp. is specified to 1200 to 1700 deg.C. The calcining temp. is controlled to 600 to 1000 deg.C. The γ-Al2 O3 includes various forms such as fibers, fine particles and flakes. It is preferable to use a basic aluminum chloride as a part or whole of the alumina source for the γ-alumina because the alumina shows good reactivity and formability.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing aluminum nitride, and more particularly to a method for producing aluminum nitride which facilitates nitriding reaction of alumina.

2. Description of the Related Art Aluminum nitride is used as a filler for a resin sealing material of a semiconductor element or as a composite material with another metal. The applicant has already proposed a method for producing aluminum nitride fibers in Japanese Patent Application Laid-Open No. 2-300319. In this method, alumina fibers containing 90% by weight or more of Al ₂ O ₃ and less than 10% by weight of SiO ₂ are heated to 1300 to 1700 ° C. in a mixed gas atmosphere of ammonia and hydrocarbon gas.
To obtain aluminum nitride fibers. However, according to this method, the nitriding reaction was not performed in a temperature range lower than 1300 ° C., and the yield of nitride was low even when the reaction temperature was 1300 ° C. or higher. Therefore, according to this method, operation at higher temperature and longer time is inevitable.
Not only is the cost high, but this method can
It was not easy to obtain near 0% nitride. Accordingly, the inventor of the present invention disclosed in Japanese Patent Application No. 7-206027 a method in which γ-Al ₂ O ₃ or a precursor thereof was mixed in a mixed gas of a carbon dioxide gas and an ammonia gas containing 0.5% by volume or more of a hydrocarbon gas and 1,200%.
A method of manufacturing aluminum nitride by heating at １1700 ° C. was proposed. This using γ-Al ₂ O ₃ having a specific surface area as about 10-fold compared According to this method a α-Al ₂ O ₃ in order to nitriding in a short time easily than the nitriding reaction is conventional This greatly increased the yield. However, as a result of further research, the inventor found that the alumina to be nitrided had a water content of 1% by weight, and
It is intended that was confirmed -al ₂ O ₃ is used when further nitriding reaction proceeds readily. On the other hand, the oxygen content in aluminum nitride greatly affects its thermal conductivity. When the oxygen content exceeds 1% by weight, the thermal conductivity of aluminum nitride rapidly decreases. FIG. 1 shows the relationship between the oxygen content (%) and the thermal conductivity of a sintered body obtained by adding 1% by weight of Y ₂ O ₃ to aluminum nitride (measured by a laser flash method).
It is shown. Therefore, Japanese Patent Publication No. 3-36882 proposes a method for producing an aluminum nitride sintered body having a high thermal conductivity by removing oxygen from a commercially available high oxygen content aluminum nitride. In this method, a high oxygen content aluminum nitride powder is heated at 1600 ° C. or more in a non-oxidizing atmosphere to reduce the oxygen content and sinter.
However, when trying to reduce the oxygen content of aluminum nitride by this method, there was a problem that a long processing time was required. That is, in the heat treatment at 1600 ° C., 2
Processing for 0 hours required 10 hours at 1800 ° C. If you try to do this in a relatively short time, 2000 ℃
The treatment had to be carried out at a high temperature exceeding. However, in a high-temperature treatment exceeding 2,000 ° C., pressure must be applied to prevent sublimation of aluminum nitride, and the apparatus and operation become complicated or complicated, resulting in an increase in cost.

SUMMARY OF THE INVENTION The present invention relates to an alumina provided for a nitriding reaction, which is calcined to reduce the water content.
By using γ-Al ₂ O ₃ in an amount of 1% by weight or less, the nitriding reaction of alumina is facilitated and all of alumina is converted to aluminum nitride. Further, if necessary, this is subjected to a low oxygen treatment to obtain aluminum nitride having a high thermal conductivity.

The present invention relates to a method for producing aluminum nitride by heating and nitriding alumina in a mixed gas of a hydrocarbon gas containing at least 0.5% by volume of hydrocarbon gas and ammonia gas. , Alumina with γ-Al
_{2. A} method of producing aluminum nitride, comprising using γ-Al ₂ O ₃ having a water content of 1% by weight or less by calcining ₂ O ₃ or a precursor thereof, and setting the heating temperature to 1200 to 1700 ° C. Production method (Claim 1), calcination temperature is 600-
2. The method for producing aluminum nitride according to claim 1, wherein the temperature is 1000 ° C., wherein the γ-alumina is selected from the group consisting of fibers, fine particles, and flakes.
3. The method for producing aluminum nitride according to claim 1 or claim 2, wherein the γ-alumina uses basic aluminum chloride for all or a part of the alumina source. Claims 1 to 3 characterized by the following:
4. The method for producing aluminum nitride according to claim 1. Hereinafter, embodiments of these inventions will be described.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, aluminum nitride is manufactured by substantially the same method as that of Japanese Patent Application No. 7-206027 previously proposed by the inventor. That is, γ-Al ₂
O ₃ or its precursor is heated at 1200 to 1700 ° C. in a mixed gas of hydrocarbon gas and ammonia gas containing hydrocarbon gas 0.5% by volume or more is to produce the aluminum nitride. In this specification, γ-Al ₂ O
Precursor ₃ refers to a gelled substance or its calcined substance which is converted to γ-Al ₂ O ₃ when heated to 1000 ° C. to 1100 ° C. γ-Al ₂ O ₃ includes those in various forms such as fibers and fine particle flakes. In the production of aluminum nitride, if γ-Al ₂ O ₃ is used as a raw material, the nitriding reaction temperature can be lowered and the reaction time can be significantly reduced. This is because γ-alumina is mainly dehydrated during its production process, and after dissociation of water, many pores having a diameter of 10 to 100 angstroms remain, whereby the specific surface area becomes extremely large and the production of aluminum nitride is promoted. That's because. The γ-Al ₂ O ₃ used here is obtained by thermally decomposing an organic or inorganic aluminum compound. This includes aluminum alkoxides, aluminum sulfate, aluminum alum, ammonium aluminum carbonate,
Basic aluminum chloride, boehmite and the like. Among these, those using basic aluminum chloride are preferable because of their good reactivity and moldability. An example of basic aluminum chloride showing its thermal decomposition behavior is shown in [Formula 1]. As described above, the basic aluminum chloride is added in a range of 300 to 400.
When heated to ° C., it becomes an alumina hydrate. When this is further heated to 600 to 700 ° C., it becomes γ-Al ₂ O ₃ while releasing H ₂ O and HCl. This is further 1200
When it is heated to a temperature of not less than ° C., it changes to α-Al ₂ O ₃ .
The intermediate product γ-AlAl ₂ O ₃ at this time is H ₂
O and HCl gases are released, and then a large number of pores are formed to have a large specific surface area. Γ-A in this state
The l ₂ O ₃ is then calcined to reduce its moisture content to 1% by weight or less. Starting from a precursor of γ-Al ₂ O ₃ ,
This is heated to obtain γ-Al ₂ having a water content of 1% by weight or less.
O ₃ may be used. In order to reduce the water content of γ-Al ₂ O ₃ to 1% by weight or less, γ-Al ₂ O ₃ or its precursor may be heated at 600 to 1000 ° C. If the calcination temperature is lower than 600 ° C., removal of H ₂ O and HCl is not sufficient. If the calcination temperature exceeds 1000 ° C, θ-Al ₂ O
₃ or α-Al ₂ O ₃ . Next, γ-Al ₂ O ₃ having a water content of 1% by weight or less is placed at 1200 to 1700 ° C. under a mixed gas of a hydrocarbon gas containing a hydrocarbon gas of 0.5% by volume or more and an ammonia gas. To produce aluminum nitride. In this method, alumina gas is reduced and nitrided by ammonia gas to produce aluminum nitride, and at the same time, by-product water vapor is quickly removed by the hydrocarbon gas when aluminum nitride is produced, thereby accelerating the reaction for producing aluminum nitride. Things. γ-Al ₂ O ₃ may be γ-Al ₂ O ₃ during the production reaction of aluminum nitride,
When heated to 1000 to 1100 ° C., γ-Al ₂ O ₃
Can be used. The reason for setting the content of the hydrocarbon in the atmosphere gas at the time of nitriding to 0.5% by volume or more is that if it is less than 0.5% by volume, the partial pressure of the ammonia gas is low and the progress of the reaction is significantly slowed down. . The heating temperature here is 1200 to 1700 ° C. Heating temperature is 120
If the temperature is lower than 0 ° C., the reaction rate is low and the treatment takes a long time, and the nitriding reaction cannot be performed completely. Further, the heating temperature does not need to exceed 1700 ° C., and if the heating temperature is higher than necessary, the manufacturing cost is increased. The precursor of γ-Al ₂ O ₃ is substantially γ-Al at the heating temperature of claim 1.
By converting to Al ₂ O ₃ , the mixture is brought into contact with a mixed gas of a hydrocarbon gas and an ammonia gas and heated to become aluminum nitride. The invention according to claim 3 is characterized in that γ-Al ₂ O ₃ is a fiber,
It is composed of one or more of fine particles and flakes. For example, when the above-mentioned basic aluminum chloride is used, polyvinyl alcohol and colloidal silica are added to the basic aluminum chloride solution, mixed with stirring, and concentrated by an evaporator to obtain a high-concentration solution.
This viscous liquid is put into a centrifugal spinner and rotated. In this case, fibers, fine particles, flakes, or a mixture thereof can be obtained by adjusting the diameter, shape, rotation speed, and viscosity of the spinning solution of the nozzle hole of the spinning device. The above alumina fibers, fine particles and flakes are then
Calcinate at 000 ° C. This calcined material is nitrided at 1200 to 1700 ° C. in the same manner as in claim 1 to obtain aluminum nitride. Claim 4 is the invention according to claims 1 to 3,
Part or all of the alumina source as the raw material is made basic aluminum chloride. Alumina using basic aluminum chloride as an alumina source has good reactivity and moldability and is suitable for producing the aluminum nitride of the present invention. The present invention relates to a γ-type material having a large specific surface area as an alumina raw material at the time of nitriding reaction and having a water content of 1% by weight or less.
By using Al ₂ O ₃ , this γ-Al ₂ O ₃
Are designed to easily react in a mixed gas of a hydrocarbon gas and an ammonia gas, whereby the nitriding reaction is performed at a lower temperature and more sufficiently than before. The aluminum nitride obtained above is, if necessary, then heated at 1600 to 2000 ° C. in an inert gas, an ammonia gas or a gas atmosphere of any one of a mixed gas of ammonia gas and an inert gas. By performing the heat treatment, the content of oxygen can be reduced and aluminum nitride having high thermal conductivity can be obtained.

EXAMPLES (Example 1) Aluminum hydroxide as a raw material was calcined at various temperatures shown in Table 1 and the water content was γ-A as shown in Table 1.
l ₂ O ₃ was adjusted. This γ-Al ₂ O ₃ powder was placed in an ammonia gas atmosphere containing 5% by volume of propane gas.
Heating was performed at 1400 ° C. for 1 hour to perform a nitriding treatment of γ-Al ₂ O ₃ . At this time, the relationship between the moisture content of the raw material γ-Al ₂ O ₃ powder, the presence or absence of α-Al ₂ O _{3 in} the powder after nitriding, and the oxygen content in aluminum nitride was examined. In addition,
The oxygen content was checked with an oxygen analyzer. Table 1 shows the results.

[Table 1] As can be seen from Table 1, when the water content of the raw material γ-Al ₂ O ₃ is 1% by weight or less, no α-Al ₂ O ₃ phase is observed in the product. Further, it can be seen that the smaller the water content in the raw material γ-Al ₂ O ₃ powder, the smaller the oxygen content in the generated AlN. Under the same conditions as above, a nitriding treatment was performed at 1400 ° C. for 10 hours instead of 1400 ° C. for 1 hour. The results are shown in Table 2.

[Table 2] As can be seen from Table 2, even after the long-term treatment for 10 hours, the oxygen content in the generated AlN is slightly improved. (Example 2) γ using basic aluminum chloride as a raw material
-Al ₂ O ₃ (average particle size 0.1 μm)
Calcination was performed at 0 ° C. for 2 hours to reduce the water content to 0.5% by weight. The γ-Al ₂ O ₃ powder was heated at 1400 ° C. for 1 hour in an ammonia gas atmosphere containing 5% by volume of propane gas to perform a γ-Al ₂ O ₃ nitriding treatment. X-ray diffraction of the treated powder confirmed that they were completely aluminum nitride. When the particles were examined with an electron microscope, it was found that the particles had a diameter of 0.1 μm or less. FIG. 2 shows a chart of X-ray diffraction of the obtained aluminum nitride powder. Next, this aluminum nitride is subjected to ammonia treatment at each temperature in the range of 1500 to 2000 ° C. (normal pressure) for 2 hours, and its specific surface area is measured by the BET method (flow-type specific surface area automatic measuring device). Was measured. The result is shown in FIG. As shown in FIG. 3, crystallization progresses as the processing temperature increases, and the specific surface area of aluminum nitride decreases. When the processing temperature reaches 2000 ° C., the specific surface area becomes 0.1 m ² / g, which is close to the limit value of the BET method measurement. In addition, the oxygen content of the sample not subjected to any treatment in an ammonia gas atmosphere and the sample treated at various temperatures in an ammonia gas atmosphere was measured by an oxygen analyzer.

[Table 3] Example 3 To 3200 g of a basic aluminum chloride solution having an Al content of 23.5% by weight in terms of Al ₂ O ₃ , 10
697 g of a polyvinyl alcohol solution having a concentration of 20% by weight and 20%
116 g of colloidal silica having a concentration of% by weight was added and stirred. This solution was concentrated using a rotary evaporator to obtain a gel (a precursor of γ-Al ₂ O ₃ ) having a viscosity of 35 poise at 20 ° C. The viscous liquid was dropped on a rotating disk having a rotation speed of 1000 rpm in a room filled with dry air. The viscous liquid immediately spread on the disk and became small particles by centrifugal force and was blown off to the outside. This was collected and dried at 100 ° C. When the shape of the dried small particles was observed with a microscope, the thickness was about 5 μm, and the width and length were 10 μm.
５０50 μm flakes. This flaky γ
The precursor of -Al ₂ O ₃ was heated in air at 900 ° C for 2 hours and calcined in the same manner as in Example 2 to reduce the water content to 0.5%. This flaky γ-Al ₂ O ₃ is
Heating at 1400 ° C. for 1 hour in a mixed gas atmosphere of propane gas and ammonia gas in the same manner as in Example 2
Al ₂ O ₃ was nitrided. This resulted in aluminum nitride flakes. Next, the aluminum flakes were subjected to an ammonia treatment at a temperature of 1700 ° C. (normal pressure) for 2 hours, and the specific surface area was measured by a BET method to be 2.3 m ² / g. The oxygen content was measured by an oxynitrogen analyzer to be 0.6% by weight. Example 4 and Comparative Example 1 A basic aluminum chloride solution 320 having an Al content of 23.5% by weight in terms of Al ₂ O ₃ .
0 g in 10% by weight polyvinyl alcohol solution 6
97 g and 116 g of colloidal silica having a concentration of 20% by weight were added and stirred. This solution was concentrated with a rotary evaporator, and the viscosity of the solution was changed to a gel (γ-A) having a viscosity of 35 poise at 20 ° C.
l ₂ O ₃ precursor). Next, the spinning machine was rotated at 2000 rpm in a room filled with dry air at 100 ° C., and the fibers were extruded from small holes provided on the outer periphery of the centrifugal spinning machine to spin short fibers. The short fibers were calcined at 900 ° C. for 2 hours to obtain γ-Al ₂ O ₃ short fibers having a water content of 0.5% by weight. This short fiber was subjected to a heat treatment at 1400 ° C. for 1 hour in a mixed gas of propane gas and ammonia gas in which the content of propane gas was variously changed. next,
This short fiber of aluminum nitride was subjected to an ammonia treatment at a temperature of 1800 ° C. (normal pressure) for 2 hours, and its specific surface area was measured by a BET method to be 0.3 m ² / g.
The oxygen content was measured by an oxygen analyzer to be 0.4% by weight. When the crystal phase of the fiber obtained by this was examined by X-ray diffraction, the following Table 4 (No. 3) was obtained.
-No. It was as shown in 5).

[Table 4] Table 4 shows that the mixed gas used for the nitriding treatment contained no propane gas at all (No. 1), and the mixed gas contained less than the value specified in the present invention (N0.
2) is shown as a comparative example. (Example 5 and Comparative Example 2) 5 (Table 4)
The short fibers spun in the same manner as described above were calcined at 900 ° C. for 2 hours to obtain γ-Al ₂ O ₃ fibers having a moisture content of 0.5% by weight. An aluminum nitride fiber was obtained by changing the heat treatment temperature of the fiber under a gas flow of a mixed gas of propane gas and ammonia gas with a propane gas addition rate of 2% by volume. This was further treated at 1700 ° C. for 2 hours under a mixed gas of nitrogen gas and ammonia gas. These results are shown in Table 5 as No. 14-No. 18 is shown.
Table 5 shows comparative examples (Nos. 12 and N) of the present invention.
o. 13) is also shown.

[Table 5] As shown in Table 5, the nitriding treatment of γ-Al ₂ O ₃ was 120
It must be performed at 0 ° C. or higher. In this case, the obtained aluminum nitride fiber also has a low oxygen content, and is a good quality aluminum nitride fiber. Comparative Example (No. 12)
And No. 13) When the treatment temperature is 1000 ° C. and 110 ° C.
In this case, aluminum nitride was not produced, and the oxygen content in the fiber was 43 vol.
% And high. In the case of No. 5 in the above-described Example 5, 14-No. With respect to the aluminum nitride obtained in No. 18 and the products obtained in Comparative Examples (No. 12 and No. 13), the nitriding ratio was measured with a thermobalance. As shown in Table 6, all of the examples of the present invention had a nitriding ratio of 100%.

[Table 6] (Embodiment 6) The short fibers obtained in the same manner as in Table 5 (Table 4) were calcined at 900 ° C. for 2 hours to obtain a water content of 0.5.
5% by weight of γ-Al ₂ O ₃ fiber was obtained. This fiber is treated with methane, ethane, propane and butane gas addition rates of 2
The mixture was heated at 1400 ° C. for 1 hour under a stream of four kinds of mixed gas of a gas of volume% and ammonia gas to obtain aluminum nitride fibers. Further, this is carried out in a nitrogen gas atmosphere.
The treatment was performed at 00 ° C. for 2 hours. The crystal phase of this fiber was examined by X-ray diffraction. These results are shown in Table 7 19
-No. 22.

[Table 7] As shown in Table 7, no difference in the crystal phase was observed depending on the difference in the hydrocarbon gas in the mixed gas. Therefore, the use of the cheapest propane gas is preferred. (Embodiment 7 and Comparative Example 3) 5 (Table 4)
The obtained short fibers were calcined at various temperatures. The calcination temperature was 600 to 1000 ° C. as shown in Table 8. Under a gas flow of a mixed gas of propane gas and ammonia gas containing propane gas containing 2% by volume of calcined short fibers,
Heating was performed at 400 ° C. for 1 hour to obtain an aluminum nitride fiber. This fiber was heat-treated at 1800 ° C. for 2 hours in a nitrogen gas atmosphere. The crystal phase of this fiber was examined by X-ray diffraction. Table 8 shows the results. Further, the oxygen content of these fibers was measured by an oxygen and nitrogen simultaneous analyzer, and the results are shown in Table 8.

[Table 8] As shown in Table 8, no difference was observed in the crystal phase when the calcination temperature was 600 to 1000 ° C. In addition, the comparative example (N
o. 27) The same fibers as in the above example were calcined at 1300 ° C. This is because after calcination, α-Al ₂ O ₃ and θ-
It was a mixture of Al ₂ O ₃ . This was subjected to a nitriding treatment at the same temperature and for the same time as in the above example, and further to a heat treatment at 1800 ° C. for 2 hours. The result obtained was a mixture of α-Al ₂ O ₃ and AlN.
The X-ray charts of the calcined product before nitriding and the product after nitriding are shown in FIG. (Example 8) The Al content was 2 in terms of γ-Al ₂ O _3.
3,200 g of a 3.5% by weight basic aluminum chloride solution
695% by weight polyvinyl alcohol solution 695
g and 200 g of colloidal alumina having a concentration of 18% by weight were added and stirred. The solution was concentrated by a rotary evaporator, and the viscosity of the solution was changed to a gel of 35 poise (γ-Al
₂ O ₃ precursor). This viscous liquid was spun into a short fiber in the same manner as in Example 4, and this was further heated at 900 ° C.
Calcined for 2 hours at γ-Al with a moisture content of 0.5% by weight
₂ O ₃ fibers were used. The fibers were subjected to a heat treatment at 1450 ° C. for 2 hours in a mixed gas of propane gas and ammonia gas containing 2% by volume of propane gas. Further, this was subjected to a heat treatment at 1700 ° C. for 2 hours in a 0.5 gas atmosphere. The crystal phase of the fiber thus obtained is represented by X
When examined by line diffraction, only the AlN phase was observed. This fiber is the same as No. 4 of Example 4. 3-No. It was recognized that the elasticity was slightly lower than that of the fiber obtained in No. 5. In the above case, instead of 200 g of colloidal alumina having a concentration of 18% by weight, colloidal zirconia 100 having a concentration of 10% by weight was used.
g was used. The nitriding temperature of the alumina fiber was set to 1350 ° C instead of the above 1450 ° C. The subsequent heat treatment was performed in the same manner as described above. When the fiber obtained here was subjected to X-ray diffraction, only AlN was observed in the same manner as described above. This fiber is a fiber obtained by using the above-mentioned colloidal alumina, or the fiber of No. 4 of Example 4. 3-No.
It was recognized that the fiber length was slightly shorter than the fiber obtained in No. 5.

As described above, according to the present invention, Al ₂ O
_Since γ-Al ₂ O ₃ or its precursor was used as ₃ ,
Nitriding can be performed at a lower temperature than before,
₂ O ₃ can be nitrided with high efficiency.
Further, when the produced aluminum nitride is treated at a high temperature, it is possible to finally produce good quality aluminum nitride having a low oxygen content and a high thermal conductivity.

[Brief description of the drawings]

FIG. 1 shows 1% by weight of γ-Y ₂ O in aluminum nitride powder
₃ shows the relationship between the oxygen content (%) and the thermal conductivity of a sintered body obtained by adding ₃ to the sintered body.

FIG. 2 shows the X of the aluminum nitride powder obtained by the present invention.
It is a line diffraction chart.

FIG. 3 is a diagram showing a relationship between a heat treatment temperature of aluminum nitride and a specific surface area.

FIG. 4 is an X-ray diffraction chart of a γ-alumina fiber before nitriding used in the embodiment of the present invention and an X-ray diffraction chart of aluminum nitride obtained by nitriding the γ-alumina fiber.

FIG. 5 shows an alumina (α) that cannot be used in the present invention.
FIG. 1 is an X-ray diffraction chart of a mixture of -Al ₂ O ₃ and θ-Al ₂ O ₃ ) and an X-ray diffraction chart of the same alumina obtained by nitriding.

Claims (4)

[Claims] When heating and nitriding alumina in a mixed gas of a hydrocarbon gas containing at least 0.5% by volume of hydrocarbon gas and ammonia gas to produce aluminum nitride, γ-Al ₂ O is added to the alumina. ₃ or calcining the precursor to the moisture content of 1 wt% or less gamma-Al ₂ O
_{3. A} method for producing aluminum nitride, comprising using ₃ and a heating temperature of 1200 to 1700 ° C. 2. The method for producing aluminum nitride according to claim 1, wherein the calcination temperature is 600 to 1000 ° C. 3. The method for producing aluminum nitride according to claim 1, wherein the γ-alumina is at least one of fibers, fine particles, and flakes. 4. The method for producing aluminum nitride according to claim 1, wherein the γ-alumina uses basic aluminum chloride for all or a part of the alumina source.