JPH04265208A - Aluminum nitride powder for sintered material and its production - Google Patents

Abstract

PURPOSE:To produce an AlN powder for sintering easy to sinter, capable of being uniformly sintered and having high heat conductivity from the alumina of ordinary purity. CONSTITUTION:Ca<2+> ion is deposited in the aluminum hydroxide stage to obtain transition alumina uniformly impregnated with the Ca ion, and the alumina is nitrided while reducing the consumption of carbon and controlling an increase in the nitriding reaction temp. Consequently, an AlN powder contg. 0.010-0.030wt.% of a Ca compd. as the Ca element, 0.6-1.1wt.% oxygen, <=400ppm of inevitable cationic impurities such as Fe and Si as the metal element and <=300ppm carbon and having 1-5mum average particle diameter and 1.50-1.90g/cm<3> bulk density when pressed at 500kg/cm<2> is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an easily sinterable and highly thermally conductive aluminum nitride powder for use as a sintering raw material, and a method for producing the same.

0002

2. Description of the Related Art Aluminum nitride (hereinafter referred to as "AlN") sintered bodies used as materials for electronic devices and the like must be uniformly sintered, dense, and highly thermally conductive. In order to obtain raw materials for dense sintered bodies, Japanese Patent Application Laid-Open No. 50-23441
In this issue, 0.1 to 1% of cheap CaO was used instead of rare earth elements.
An example of adding 0% by weight of CaO is disclosed, and an example of adding 0.1 to 6% by weight of CaO is disclosed in JP-A-58-55377, and an example of adding 0.1 to 6% by weight of CaO is disclosed in JP-A-2-160610.
A method is disclosed in which ~2% by weight is added during alumina reduction. However, although the addition of Ca component according to these inventions can impart easy sinterability to AlN powder, on the other hand, the high concentration causes uneven sintering in the obtained sintered body and deteriorates the properties of the sintered body. There is a risk of causing Also, JP-A-59-5
No. 0008 shows an example in which the obtained AlN powder contains 0.015% by weight of Ca element, but it also contains 1000 ppm of carbon, which has poor sinterability and thermal conductivity. It is presumed that this is the case.

0003

[Problems to be Solved by the Invention] The inventors have discovered that even if ordinary purity alumina is used instead of high purity alumina as a raw material, it will have high purity, be easily sintered, will not cause uneven sintering, and will have high thermal conductivity. In order to advance research on obtaining AlN powder and achieve the above objectives, it was necessary to add an appropriate amount of Ca, minimize the amount of carbon, and keep the pressed bulk density of the obtained AlN powder within a predetermined range. They discovered that it was necessary to do so and completed the present invention.

0004

[Means for Solving the Problems] According to the present invention, the calcium compound contains 0.010 to 0.030% by weight in terms of Ca element, the oxygen content is 0.6 to 1.1% by weight, and Fe. Unavoidable cation impurities such as Si as a metal element are 400 ppm or less, carbon content is 300 ppm or less, average particle size is 1 to 5 μm, and the pressurized bulk density at 500 kg/cm2 is 1.50 to 1.90 g/cm3. Aluminum nitride powder for sintering raw material, characterized by the above-mentioned A
The optimal method for producing IN powder is to use transition alumina that does not substantially contain α-alumina, but has been immersed in a calcium salt solution to contain 0.008 to 0.025% by weight in terms of Ca element, and also uses carbon. This is achieved by allowing the nitriding reaction to proceed under reduced pressure purification treatment under conditions where the amount is regulated to a small amount.

The composition of the aluminum nitride powder for sintering according to the present invention is all internal, but it is necessary to satisfy the following conditions. 1) The content of calcium compounds as Ca element is 0.
It is necessary that the content is 0.010 to 0.030% by weight, and 0.0
If it is less than 10% by weight, low temperature sinterability is insufficient, and 0.030
If it exceeds % by weight, uneven distribution of Ca will occur and uneven sintering will likely occur. Note that this Ca compound is presumed to be contained in the form of calcium oxide, calcium aluminate, or the like. 2) Unavoidable cation impurities such as Fe and Si are 0.04
If it is 0% by weight or less and exceeds 0.040% by weight, AlN
This is not preferable because it becomes difficult to ensure the sinterability of the powder and to suppress a decrease in the thermal conductivity of the sintered body. 3) Oxygen content is in the range of 0.6-1.1% by weight, 0
．． If it is less than 6% by weight, sinterability is poor and the sintering temperature becomes high.
If it exceeds 1.1% by weight, the thermal conductivity of the sintered body will decrease. 4) The carbon content of AlN must be 300 ppm or less.
It is necessary to ensure good sinterability of the powder, and if coloring is undesirable, it is better to use as little as possible. That is, in the case of AlN powder obtained by the alumina reduction method, carbon remains if the decarburization treatment is insufficient. A
When sintering the AIN powder, if the carbon content exceeds 300 ppm, the oxygen in the AIN powder is consumed, so liquid phase sintering does not occur properly and sintering becomes incomplete. Moreover, since it colors the sintered body, it is unsuitable for some uses.

Next, as for other characteristic values that the present aluminum nitride powder should have, it is necessary to satisfy the following conditions. 1) If the average particle size range is 1 to 5 μm, and less than 1 μm, Al
The amount of oxygen adsorbed by the N powder increases, reducing the thermal conductivity of the sintered body, and if it exceeds 5 μm, the sinterability deteriorates and the sintering temperature increases. 2) Pressure bulk density (500 kg/cm2) is 1.50 to 1
．． 90 g/cm3, and if it is less than 1.50 g/cm3, the green density during molding will be low, the sintering temperature will be high, and 1.
．． If it exceeds 90 g/cm3, the green density during molding becomes too large, making degreasing difficult, making sintering unevenness more likely, and sintering warpage, sintering cracks, etc. more likely to occur.

[0007] Below, a method for producing aluminum nitride for sintering having the above composition and characteristic values will be explained. A. Raw material 1) Alumina: 99.9% purity by weight, containing virtually no α-alumina
or more, wherein a) the soda content is 0.90% by weight or less as Na2O, Al;
Na2O vaporized and removed from alumina during the purification process in the N powder production process will contaminate the inner wall of the processing furnace in a short time. Therefore, it is preferable to use a content not exceeding 0.90% by weight in view of the work cycle. b) Unavoidable metal impurities are 400p alone as oxides
pm or less, and 1,000 ppm or less in total.If this upper limit is exceeded, purification and removal requires high-temperature and long-term reduced-pressure heat treatment, which is not economical. Moreover, the obtained sintered body also becomes colored, which is undesirable depending on the application. c) The calcium content of the impregnated coating is 0.008 to 0.025% by weight as Ca element.The above range improves the low-temperature sinterability of the AlN powder produced and prevents uneven sintering in the sintered body. This is the range necessary to ensure that. Here, "impregnated and coated" refers to a state in which CaO does not exist separately or independently from transition alumina, but instead exists integrally in transition alumina particles in an impregnated or coated manner. d) Particle size: 0.2 to 5 μm When the particle size exceeds 5 μm, the particle size of the AlN produced becomes large and the sinterability deteriorates. On the other hand, for those less than 0.2 μm,
Not desirable from a cost standpoint. e) BET specific surface area 30m2/g or more 30m2/g
If it is less than
time) gets worse. An example of the method for producing the above transition alumina is shown below. Bayer method gypsite type fine aluminum hydroxide (purity 99% by weight)
Calcium hydrogen carbonate,
After immersion treatment (including cleaning means) in a 50 to 500 mg/l aqueous solution of a calcium salt selected from calcium chloride, calcium nitrate, and calcium acetate,
After raising the temperature at a rate of approximately 500 hr,
CaO-impregnated transition alumina can be obtained by firing at 0 to 800°C. Note that a method of immersing transition alumina in the same aqueous solution as described above and then drying it may also be used, although it is inferior in terms of cost. 2) The carbon black should have a purity of 99.7% or more, an ash content of 0.3% by weight or less, and a particle size of 0.3 μm or less, and if it exceeds 0.3 μm, the surface coating effect on alumina will be insufficient. Alumina: Carbon = 1:0.36-0.45 (weight ratio)
If it is less than 0.36, there is a risk that nitriding will be insufficient;
．． If it exceeds 45, the decarburization process will take a long time, the oxygen concentration in AlN will increase, and the fuel cost will also increase. 3) Organic polymer compounds Organic polymer compounds are those that are carbonized at 1000°C or lower as a solid phase without passing through a liquid phase or through a gas phase, and have a particle size of 10 μm or less, such as phenol. Formaldehyde resin, polyphenylene, polyvinylidene chloride, cellulose, etc. are preferably used. The amount added is 0.1 based on the total amount of alumina and carbon black.
~5% by weight, and if it is less than 0.1% by weight, the atomization effect of the generated AlN powder will be insufficient, while if it exceeds 5% by weight, the amount of carbon remaining in the AlN powder after decarburization will decrease. There are too many and it is inappropriate. 4) Organic grinding aids Any commonly used organic grinding aids may be used, such as propylene glycol, higher fatty acids such as palmitic acid, stearic acid, oleic acid, Mg, Ca, and Ba salts of higher fatty acids, and the amount added is 0. If the amount is 5 to 3% by weight, and if it is less than 0.5% by weight, the effect of use is insufficient, and if it exceeds 3% by weight, the pulverization efficiency will not be improved although the cost will increase.

B. Method for producing AlN powder AlN of the present invention
After mixing the above-mentioned raw materials in a predetermined amount, the powder is prepared using the following methods 1) to 4).
Manufactured using the following process sequence. 1) Dry grinding/mixing As the grinding/mixing machine, a ball mill, a rotary ball mill, an attritor, etc. are used. By pulverization and mixing, the light bulk density is adjusted to a range of 0.3 to 0.6 g/cm3. 0.
If it exceeds 6 g/cm3, the ventilation of N2 gas necessary for the reaction will become poor and the reaction efficiency will decrease. 2) Nitriding reaction After the mixed reaction raw materials are placed in a tray and placed in a nitriding reactor, the following heating and nitriding reactions are performed in sequence in a nitrogen atmosphere. 2-1) Preheating: Heating from room temperature to a maximum of 1100°C at an appropriate temperature increase rate. 2-2) Vacuum purification treatment: 3 at a temperature of 800 to 1100°C
By heating under reduced pressure of 0 torr or less, the temperature is raised to near the starting temperature of the nitriding reaction while vaporizing and separating impurities such as Na2O, Fe2O3, SiO2, MgO, etc. in the transition alumina. At this time, only the Ca component, which is advantageous for sintering, can remain. Preferably 10 to 20 torr
Treat for minutes to 5 hours. 2-3) Prioritized nitriding treatment: Next, after creating a nitrogen atmosphere of 1 atm, the temperature is raised to a maximum of 1600°C at 20°C/hr.
Hereinafter, by preferentially nitriding only the surface of the transition alumina grains at a heating rate of preferably 10 to 17°C/hr, the crystal growth of Al2O3 grains is suppressed, and the resulting roughness of the AlN grains is suppressed. Suppresses granulation. 2-4) Full-scale nitriding treatment: Next, treatment is performed at 1500 to 1700° C. for 10 to 70 hours in a similar nitrogen atmosphere to complete the nitriding reaction. 3) Desired Crushing Treatment By crushing in the presence of residual carbon after the nitriding reaction, it is possible to crush the AlN powder while appropriately preventing an increase in oxygen content. 4) Decarburization treatment In a dry air circulation heating furnace, at 500 to 600°C for 5 to 10 minutes.
Remaining carbon is removed by time treatment.

C. Manufacturing process of AlN sintered body Add 100 parts by weight of AlN powder, 1 to 5 parts by weight of sintering aid, 7 to 15 parts by weight of binder for molding, and 50 to 70 parts by weight of solvent in the case of molding by doctor blade method. Adjust the viscosity of the mixture to 100-200 points. As the above-mentioned sintering aid, oxides of rare earth elements (
Y2O3, etc.), alkaline earth metal oxides (e.g. CaO
, BaO, SrO), and for example 1 to 5 parts of Y2O and 1 to 3 parts of CaO are added depending on the desired sintering conditions. As a molding binder, polyvinyl butyral,
Paraffin, stearic acid, etc. are used, and as the solvent, butanol, methyl ethyl ketone, toluene, ethanol, etc. alone or in a mixture thereof are used. When molding the above materials by, for example, a doctor blade method, the mixture is wet mixed with ball mill wet pulverization in a nylon pot for 20 to 48 hours, and then stirred under reduced pressure. It is treated for 10 minutes to 5 hours at a pressure of 0.1 atm or less to defoam and adjust the viscosity. Next, it is formed into a sheet by a doctor blade method, dried, and then cut into a desired size. Then 400-600℃ in air and 700-800℃ in N2 gas.
A degreasing treatment is performed at ℃ to volatilize the solvent and obtain a dry green molded body. It goes without saying that conventional molding processes such as mold pressing and isostatic pressing can also be applied. Next, pressureless sintering is performed in a sintering reactor to obtain an AlN sintered body. The conditions for pressureless sintering are a 1 atm atmosphere of N2 gas (flow rate of 1 to 10
l/min) at a sintering temperature of 1800°C or less (1700°C
~1800°C), and the sintering time was 2 to 10 hours. In addition,
Of course, a common hot press sintering method may also be used.

0010

[Function] [1] AlN powder manufacturing method 1) At the transition alumina stage, when Ca content is supported by the impregnated coating, the Ca content is uniformly dispersed in the grains, and during each heating process during the nitriding reaction. As other cationic impurities are volatilized and separated, Ca content is diffused and concentrated on the surface side of the Al2O3 particles, so in the generated AlN powder, Ca content is concentrated on the surface side rather than the center of the particle. It is thought that this improves wettability with the sintering aid and facilitates sintering. 2) By dry grinding and mixing, the surface of the alumina particles is uniformly covered with carbon particles when the light bulk density is set within a predetermined range. , a uniform nitriding reaction occurs even with a small amount of carbon. Moreover, the effect of suppressing the grain growth of the generated AlN grains is also expressed at the same time. 3) In "reduced pressure heat treatment", the heating temperature is 800 to 1100 degrees Celsius, which is about 200 degrees Celsius lower than the conventionally proposed conditions.
By processing under moderately reduced pressure, unnecessary impurities such as Na2O, Fe2O3, SiO2, etc. can be removed, while Ca content, which is effective for sintering, can remain. 4) In the process of raising the temperature to the nitriding reaction temperature, by going through a stage in which the temperature raising rate is regulated, it is possible to suppress the particle growth of Al2O3 grains while allowing the preferential nitriding reaction on the surface of the grains, thus reducing the AlN produced. It is possible to prevent grain coarsening and generation of residual α-alumina. [2] AlN powder The AlN powder obtained by the above-mentioned manufacturing method has Ca content uniformly diffused and concentrated on the surface side of the grains, so it is difficult to sinter even though the absolute value of the content is small. It is presumed that the compatibility with the auxiliary agent is good and the pressurized bulk density is within a predetermined range, which together improve the sinterability.

[0011]

[Examples] The present invention will be specifically explained below with reference to Examples and Comparative Examples. (1) Preparation of transition alumina Bayer process gypsite type fine-grained aluminum hydroxide [A
] (Example 1) and [B] (Example 2) were used.
[A] [B]
Purity as Al2O3 99.5% by weight 99.6% by weight Na2O
0.40 〃
0.15 MgO
0.001 〃
0.001 〃 Fe2O3
0.020 〃 0.0
18 〃 SiO2
0.015 〃 0.019
〃CaO
0.013 〃 0.025 〃
Average particle size 0.
5 μm 2 μm The above aluminum hydroxide, calcium hydrogen carbonate, CaCO
The Ca concentration to be impregnated and coated was adjusted by appropriately immersing the sample in an aqueous solution containing 300 to 1000 ppm in terms of Ca concentration. Next, the aluminum hydroxide treated above was calcined in a rotary kiln at 700°C for 5 hours in an air atmosphere to give α-
Transition alumina containing no alumina was obtained. Next, carbon black (manufactured by Nippon Steel Chemical Co., Ltd., trade name Niteron #20)
0), phenol formaldehyde resin powder (manufactured by Asahi Yokuzai Kogyo Co., Ltd., trade name: AV Light) and propylene glycol were blended in predetermined amounts and dry mixed and pulverized to a predetermined light bulk density.

[0012] The above-mentioned mixed raw materials are stored in a thin layer in a tray, and the tray is arranged in a tiered manner in a nitriding reactor.
The temperature was raised to 250° C./hr while flowing N2 gas to 950° C., and while the temperature was maintained at 950° C., the pressure was reduced to 15 torr in a N2 gas atmosphere and held for 15 minutes. Then,
Return to 1 atm N2 gas atmosphere and heat at 50℃ to 1100℃
After raising the temperature at a rate of 17°C/hr, the temperature was raised to 1500°C at a rate of 17°C/hr to perform preferential nitriding treatment. Furthermore, 16
The temperature was maintained at 00°C for 40 hours to complete the nitriding reaction. Next, in the case of Example 2, a separate crushing treatment was performed for 30 minutes in a ball mill after cooling to room temperature. Further, the reaction mixture was transferred into a stainless steel dish, placed in an electric furnace, and decarburized at 600° C. for 6 hours under a stream of dry air. Table 1 shows the raw material composition, chemical analysis values, and characteristic values of the obtained AlN powder.

[0013]

[Table 1]

As a comparative example, AlN powders having different raw material composition ranges from the present invention were prepared and treated under the same conditions as in the above examples, and in cases where they were different, under the conditions shown in Table 2. Table 2 shows the raw material composition, chemical analysis values, and characteristic values of the obtained AlN powder.

[0015]

[Table 2]

The method for measuring the chemical analysis values and physical property values shown in Tables 1 and 2 above will be explained. (1) Na, Ca, Fe, Si, and Mg are determined by fluorescent X-ray analysis (
Based on System 3070 manufactured by Rika Denki Kogyo Co., Ltd. (2) Carbon is detected using combustion infrared detection method (Horiba EMIA-
110). (3) The BET specific surface area was measured with an automatic specific surface area measuring device (Monosorb MS15 type manufactured by Counterchrome Co., Ltd.). (4) The average particle size was measured using a Sedigraph (5000ET, manufactured by Shimadzu-Micromeritics). (5) The amount of α-alumina was determined by X-ray diffraction. (6) Oxygen content was determined by activation analysis method (activation analyzer model NAT-200 manufactured by Toshiba). (7) Pressure bulk density is 40 mm x 20 mm mold, AlN
This was determined by adding 15 g of powder, pressurizing it to 500 kg/cm2, and measuring the size and weight of the compact.

(2) Example (characteristic evaluation of obtained AlN powder)
AlN powder: obtained in the previous section (1)
100 parts by weight Sintering aid: Yttria

2 parts by weight Molding binder: polyvinyl butyral 10 parts by weight Solvent: butanol
After wet-mixing 60 parts by weight or more in a nylon pot for 24 hours, the mixture was defoamed while stirring under reduced pressure, and a test piece of 50 mm square and 1 mm thick was formed by the doctor blade method. 50 of this
Degreased in a drying oven at 0°C, heated to sintering temperature in a sintering reactor at a rate of 450°C/hr under N2 gas atmosphere, and sintered at that sintering temperature for 2 hours. The sintering temperature at which the density of the body becomes 99% or more of the theoretical density was determined. The results are shown in Table 3 below.

[0018]

[Table 3]

[0019]

Effects of the Invention: (1) As the aluminum nitride powder itself for sintering, high thermal conductivity is obtained when made into a sintered body, and (1) the filling property is improved despite the small Ca concentration. The freezing temperature can be lowered. This makes it possible to reduce the amount of sintering aid used and reduce sintering costs. 2) By lowering the carbon content, it is possible to stabilize the sintering properties, such as preventing uneven sintering, and prevent coloring.

(2) Method for producing aluminum nitride powder for sintering: 1) AlN powder of high purity can be obtained from an alumina source of ordinary purity. 2) By setting the reduced pressure treatment temperature to 800 to 1100° C., Ca, which is a useful component, can remain while removing harmful impurities such as Si, Fe, Na, and other cationic impurities. 3) By reducing the amount of atomizing agent and carbon,
While increasing the atomization effect, the amount of carbon in the product AlN powder can be stably reduced, and since decarburization becomes easy, the oxygen content can also be regulated to a low level. 4) By slowing down the rate of temperature increase after 1100° C. during the nitriding reaction, it is possible to prevent the generation of residual α-alumina caused by coarsening of the AlN powder and coarsening of the Al2O3 grains.

Claims (2)

[Claims] [Claim 1] Calcium compound as Ca element 0
．． 010-0.030% by weight, oxygen content 0.6-1
．． 1% by weight, unavoidable cationic impurities such as Fe and Si as metal elements are 400ppm or less, carbon content is 300ppm or less, average particle size is 1 to 5μm, 50
Pressure bulk density at 0kg/cm2 is 1.50-1.90g
An aluminum nitride powder for use as a sintering raw material, characterized in that: /cm3. Claim 2: a) Purity of 99.0% by weight or more that does not substantially contain α-alumina, soda content is 0.90% by weight or less as Na2O, and unavoidable metal impurities are 400 ppm alone as oxides. Below, total 1000ppm
Below, the impregnated CaO is 0.00 as Ca element.
8 to 0.025% by weight, and the particle size is 0.2 to 5μ
b) Carbon black with an average particle size of 0.3 μm or less and an ash content of 0.3% by weight or less is added to transition alumina with a BET specific surface area of 30 m2/g or more. , alumina: carbon = 1:0.36
At a weight ratio of ~0.45, (1) an organic compound that is carbonized as an atomizing agent for the produced AlN without passing through a liquid phase or through a gas phase at temperatures below 1000°C is combined with alumina and carbon black; After adding 1 to 5% by weight of the total amount and (1) 0.5 to 3% of an organic grinding aid to the alumina, c) The above mixture has a light bulk density of 0.3 to 0.6 g/cm.
d) Then, in a nitrogen gas atmosphere in a nitriding reactor, the temperature was raised appropriately from room temperature to a maximum of 1100°C, and
Vacuum purification treatment under reduced pressure of 30 torr or less in a temperature range of ~1100°C, followed by 20°C up to a maximum of 1600°C.
After performing a preferential nitriding reaction on the alumina surface at a heating rate of /hr or less,
) A method for producing aluminum nitride powder for sintering raw material, which comprises subjecting it to decarburization in an oxidizing atmosphere after crushing if desired.