JPH0454612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high purity aluminum nitride fine powder. In particular, the present invention is a method for producing high-purity aluminum nitride fine powder whose sintered body exhibits properties such as high thermal conductivity, high light transmittance, and high corrosion resistance.

Conventionally, the following two methods are known as methods for producing fine aluminum nitride powder. The first method is a method called a direct nitriding method in which metal aluminum powder is nitrogenated at high temperature in a nitrogen or ammonia atmosphere, and the resulting nitride is crushed to obtain aluminum nitride powder. The second method is a method called an alumina reduction method in which alumina and carbon powder are fired in a nitrogen or ammonia atmosphere, and the resulting nitride is heated in an oxygen-containing atmosphere to remove unreacted carbon. The former direct nitriding method has the disadvantage that the resulting aluminum nitride powder is not uniform because the pulverization step cannot be avoided.
The latter method is also superior to the direct nitriding method in that it provides aluminum nitride powder with relatively uniform particle size.
Furthermore, JP-A-59-50008 reports that aluminum nitride powder that imparts translucency to the sintered body can be obtained by an alumina reduction method.

The present invention provides a method for producing high-purity aluminum nitride fine powder whose properties such as thermal conductivity and translucency can be further improved by selecting a specific production method.

That is, the present invention hydrolyzes a hydrolyzable organoaluminum compound by contacting it with water or a water-containing organic solvent, converts the hydrolyzate into alumina simultaneously with or after the hydrolysis, and converts the alumina to carbon. Mix fine carbon powder in a liquid dispersion medium at a weight ratio of 1:0.36 to 1:2,
The mixture was heated in an atmosphere of nitrogen or ammonia to
This is a method for producing high-purity aluminum nitride fine powder, which involves firing at a temperature of 1800°C, and then heating the obtained fine powder at a temperature of 600 to 900°C in an oxygen-containing atmosphere to remove unreacted carbon.

The hydrolyzable organoaluminum compound used in the present invention is not particularly limited, and may be any known organoaluminum compound, such as an alkyl aluminum such as trimethylaluminum, triethylaluminum, or diethylmonohaluminum; in particular, aluminum propoxide, aluminum ptoxide, aluminum monohaloaluminum, etc. Aluminum alkoxides such as ptoxydiisopropoxide can be suitably used. In particular, aluminum alkoxide is industrially most suitable because not only operations such as hydrolysis reaction and dispersion treatment described below can be easily carried out, but also the properties of the obtained aluminum nitride powder are particularly improved. The above-mentioned hydrolyzable organoaluminum compound may be reacted directly with water, but is generally used after being dissolved or dispersed in an organic solvent. The organic solvent can be used without particular limitation as long as it dissolves or disperses the organoaluminum compound, but usually hydrocarbons such as petroleum ether, hexane, benzene, toluene, etc.; aliphatic solvents such as methanol, ethanol, propanol, isopropanol, etc. Alcohols, etc.; chlorinated solvents such as carbon tetrachloride, etc. are suitable.
In particular, the above alcohols undergo the hydrolysis reaction described below.
This is preferable because operations such as carbon dispersion treatment can be carried out easily. In addition, the concentration of the organic solvent in which the organoaluminum compound is dissolved or dispersed varies depending on the type of organoaluminum compound, the type of organic solvent, the hydrolysis conditions described below, etc., and cannot be absolutely determined, but in general, the concentration of the aluminum compound is lower. is preferred. However, if the concentration of the aluminum compound is too low, the amount of solvent used will increase significantly, and if the concentration is too high, it will be difficult to control the reaction and it will be inconvenient to handle. Therefore, it is usually necessary to take these into account and decide accordingly, but in general, the concentration of the organoaluminum compound is 50% by weight or less,
Most preferably, it is used at concentrations ranging from 5 to 40% by weight.

The organoaluminum compound is mixed with water or a water-containing organic solvent to perform hydrolysis. The organic solvents mentioned above can be used without particular limitation, but alcoholic solutions are most preferred. When using the above-mentioned hydroalcoholic solution, the above-mentioned aliphatic alcohols are preferably used as the alcohol. In addition, the amount of water contained in the alcohol solution may be sufficient as long as it is sufficient to hydrolyze the organoaluminum compound.
It may be determined in advance and used depending on the hydrolysis conditions, other conditions, etc. Further, if necessary, a hydrolysis accelerator such as an alkaline compound such as ammonia or amine, or a mineral acid such as nitric acid, hydrochloric acid, or sulfuric acid may be used to promote hydrolysis.

In general, the hydrolysis reaction is faster as the temperature increases, so it is preferable to carry out the hydrolysis while being heated, for example, the temperature may be selected from 25° C. to the boiling point of the mixed solvent.
Furthermore, it is often preferable to carry out the hydrolysis reaction while stirring the mixed solvent, and in particular, moderate stirring is often effective in making the particle size uniform. Furthermore, the particle size of the particles obtained by hydrolysis is also affected by the concentration of the organoaluminum compound, the type of solvent, etc., so these conditions must be determined in advance in the laboratory according to the required particle size. It is preferable to do so.

The hydrolyzate of an organoaluminum compound obtained by the above method inevitably contains impurities in aluminum nitride obtained by a known method such as a direct nitriding method or an alumina reduction method due to the raw material. It has significantly less impurities compared to other products. Further, the particle size is 0.5 μm or less, and it is also possible to obtain particles with extremely uniform particle size, in which particles with a particle size of 1 μm or less account for at least 90% by volume of the total. Such properties have a great effect on improving the sinterability when obtaining an aluminum nitride sintered body, and on improving the properties of the sintered body, such as thermal conductivity and translucency.

In the present invention, it is an essential step to mix the hydrolyzate and carbon simultaneously with or subsequent to the hydrolysis. In this case, the mixing ratio of carbon is calculated by converting the hydrolyzate into alumina, and the weight ratio of alumina to carbon is 1:0.36 to 1:
2, preferably from the range of 1:0.4 to 1:1. If the amount of carbon used is less than the above range, the reduction reaction described below will not proceed sufficiently, and if it is too large, it will take more time than necessary to remove unreacted carbon, which is not preferable.

As a means of mixing the above-mentioned carbon with the hydrolyzate of the organoaluminum compound as uniformly as possible, carbon powder is present in the hydrolysis reaction system of the organoaluminum compound so that the carbon co-precipitates at the same time as the hydrolyzate precipitates. It is preferable to do so. In this case, the organic solvent of the hydrolysis reaction system, alcohol, water, or a mixed solution thereof can be used as is as the liquid dispersion medium. When mixing the hydrolyzate and carbon after the hydrolysis reaction, the required amount of carbon is added to the reaction system after the hydrolysis reaction is completed, or the hydrolyzate is prepared separately after being filtered. The two may be mixed in a liquid dispersion medium. The liquid dispersion medium in the latter embodiment is not particularly limited, and any known liquid dispersion medium such as water, hydrocarbon, aliphatic alcohol, or a mixture thereof can be used.

In the present invention, it is extremely important that the hydrolysis reaction of the organoaluminum compound and the mixing of the hydrolyzate and carbon are both carried out in liquid form. In particular, carrying out the latter mixing form in liquid form not only allows the aluminum component and carbon component to be mixed extremely homogeneously, which not only greatly affects the reactivity of aluminum nitride, but also minimizes the contamination of impurities in aluminum nitride. Gives an advantage that can be retained. Furthermore, by using the above-mentioned mixing in liquid form, that is, the wet mixing method, it is possible to prevent the raw material particles from agglomerating and becoming coarse, so that the aluminum nitride powder obtained by the nitrogenization described later is itself fine particles. Since the particles are uniform, there is no need to crush the resulting aluminum nitride, and it can be sintered as it is. The advantage of being able to omit this pulverization step plays a valuable role industrially. For example, in the present invention, impurities mixed in during grinding can be completely prevented, and since the surface of aluminum nitride is oxidized and the oxygen content increases during grinding, it is possible to completely prevent impurities in aluminum nitride. The amount will also be extremely small.

When carrying out the wet mixing in the present invention,
It is preferable to carry out the process in an apparatus made of a material that can avoid contamination with impurity components that remain even after aluminum nitride is fired. In general, the wet mixing can be carried out at normal temperature and pressure, and is not adversely affected by temperature and pressure. As long as the mixing device is selected from a material that does not produce residual impurity components even after firing, any known device can be used.
means can be adopted. For example, it is common to use a mill with built-in spheres or rods as a mixing device, but the inner walls of the mill, the materials of the spheres or rods, etc. remain in the resulting aluminum nitride even after firing. In order to avoid contamination with impurity components, it is preferable to use aluminum nitride itself or high purity alumina of 99.9% by weight or more. Furthermore, all surfaces of the mixing device that come into contact with the raw materials may be made of plastic or coated with plastic. The plastics are not particularly limited, and include, for example, polyethylene, polypropylene,
Nylon, polyester, polyurethane, etc. can be used. In this case, since the plastic may contain various metal components as stabilizers, it should be checked before use.

The fine carbon powder used as a raw material in the present invention preferably has a purity of ash content of at most 0.2% by weight, preferably at most 0.1% by weight. Furthermore, since the average particle size of the carbon affects the particle size of the aluminum nitride obtained, it is preferable to use the carbon as fine particles with an average particle size of 1 μm or less. Carbon black, graphitized carbon black, etc. can be used as the carbon, but carbon black is generally most preferred.

The wet-mixed raw materials are filtered and/or dried or dehydrated by heating if necessary, and then calcined at a temperature of 1400 to 1800°C in an atmosphere of nitrogen or ammonia. If the calcination temperature is lower than the above temperature, the reduction and nitrogenation reaction will not proceed industrially sufficiently, which is not preferable. Furthermore, if the firing temperature is higher than the above temperature, a portion of the aluminum nitride obtained will sinter, causing agglomeration between particles, making it difficult to obtain aluminum nitride having the desired particle size, which is not preferable.

According to the present invention, the nitride fine particles obtained by firing are then heat-treated at a temperature of 600 to 900°C in an oxygen-containing atmosphere to oxidize and remove unreacted carbon contained in the nitride fine particles. It is subjected to a process of If the oxidation temperature is lower than the lower limit, it will take a long time to remove unreacted carbon, which is industrially disadvantageous; if the temperature exceeds the upper limit, the surface of the aluminum nitride will be oxidized, resulting in aluminum nitride. The oxygen content increases,
This is not preferable because it causes deterioration of various properties.

The aluminum nitride thus obtained has an extremely low impurity content compared to conventional aluminum nitride, and can significantly improve various physical properties of the aluminum nitride sintered body, such as thermal conductivity and translucency. For example, the AlN content in aluminum nitride obtained by the present invention is 97% by weight or more, the combined oxygen content is 1.5% by weight or less, and the content of metal components other than aluminum is 0.1% by weight as metals.
The content is preferably 0.05% by weight or less.

Further, the aluminum nitride fine powder obtained in the present invention has an average particle size of 2 μm or less. If the average particle diameter is larger than this, there is a greater tendency for sinterability to decrease. The aluminum nitride fine powder of the present invention preferably has an average particle size of 2 μm or less and contains particles with a particle size of 3 μm or less in a proportion of 80% by volume or less.

The aluminum nitride of the present invention is, as mentioned above, of very high purity, eg, the combined oxygen content is preferably at most 1.0% by weight. Conventionally, the combined oxygen content is 2
Considering the state of the art, it was believed that fine aluminum nitride powder with less than 2% by weight does not have sufficient sinterability, and that a combined oxygen content of at least 2% by weight is required to obtain good sinterability. It is true that the high-density aluminum nitride fine powder of the present invention exhibits excellent sinterability.

According to the present invention, a high-purity and high-density aluminum nitride sintered body is provided from the high-purity aluminum nitride fine powder of the present invention. Such a sintered body of aluminum nitride forms the high-purity aluminum nitride fine powder of the present invention, and the obtained compact is heated to
It is manufactured by sintering in an inert atmosphere at a temperature of 2100°C to form a sintered aluminum nitride body.

The aluminum nitride sintered body can also be produced by a method in which sintering is performed in the presence of a sintering aid. The above-mentioned sintering aid is not particularly limited, and known ones can be used. A typical sintering aid that is generally suitably employed is at least one metal selected from the group consisting of alkaline earth metals, lanthanum group metals, and ythtrium, or its oxide, and is generally 0.01 to 5 It is preferable to add % by weight.
The above-mentioned sintering aid is added in the process of producing the aluminum nitride powder of the present invention, such as the hydrolysis process of the organoaluminum compound, the carbon addition process, etc., and the sintering aid is contained in the obtained aluminum nitride powder. It is also possible to make a product with

By sintering the aluminum nitride powder containing the sintering aid at a temperature of 1600 to 2100°C in an inert atmosphere, the above-mentioned excellent aluminum nitride sintered body is obtained.

Further, the sintering method is not particularly limited, and any known sintering method can be employed. For example, the hot press sintering method is carried out under pressure of 20 to 400 kg/ ^cm2 , the gas pressure sintering method is carried out under nitrogen gas pressure of about 1 to 10 atmospheres, or the sintering method is carried out under substantially no pressure. A pressureless sintering method can be employed if necessary.

The aluminum nitride sintered body thus obtained has a density of 3.1 g/cm ³ or more, preferably 3.2 g/cm 3 or more.
It becomes an excellent high-density sintered body of cm ³ or more. In addition, the sintered body has excellent thermal conductivity, for example, 100w/m・
K, preferably 110w/m·K or more.
Furthermore, the translucency of the sintered body can be adjusted, for example, by setting the sintered body to a thickness of 0.5 mm.
The light transmittance of the material processed and polished to mm is 35% or more for a wavelength of 6 μm.

The sintered body thus obtained is used, for example, as a highly heat conductive ceramic as a heat dissipation plate, a heat exchanger material, a substrate for stereo or video amplifiers, an IC substrate, etc. In addition, its excellent translucency can be used to create window materials for lamp arc tubes, sensors that use ultraviolet to infrared rays, radar window materials that utilize radio wave transparency, and special windows that require translucency at high temperatures. It can be used as a material.

Furthermore, the aluminum nitride powder of the present invention is suitably used as a raw material for sialon-based materials, and α-
Sialon, β-Sialon, AlN A sialon compound with high purity and excellent properties that could not be achieved by using conventional AlN as a raw material for polytypes can be obtained.

In addition, since the aluminum nitride powder of the present invention is a uniform fine powder with good dispersibility, it is effective as an additive to various ceramics such as silicon carbide, or as a powder for composites with polymers such as silicone rubber. It has an effect.

The present invention will be explained in detail below with reference to Examples. The various analytical methods and analytical devices used in the following Examples and Comparative Examples are as follows.

Carbon analysis: Metal carbon analyzer (manufactured by Horiba)
EMIA-3200) Oxygen analysis: Metal oxygen analyzer (Horiba, Ltd. EMGA-1300) Nitrogen analysis: Melting separation neutralization titration method X-ray diffraction device: JEOL JRX-12VB Scanning electron microscope: JEOL JSM -T200 Average particle size and particle size distribution measuring device: Horiba CAPA-500 Thermal conductivity measuring device: Rigaku Laser method thermal constant measuring device PS-7 Light transmittance measuring device: Hitachi Self-recording spectrophotometer 330 type red External spectrophotometer 260-30 type In addition, the light transmittance of the sintered body was calculated using the following formula.

I/IO=(1-R) ₂ e ^-ut ...(1) Here, Io is the intensity of incident light, I is the intensity of transmitted light,
R is the reflectance, t is the thickness of the sintered body, and u is the absorption coefficient. R is determined by the refractive index of the sintered body, and if the refractive index is n, R is expressed by the following equation when measured in air.

R=(1-n) ² /(1+n) ² ...(2) u in formula (1) is an index expressing the translucency of the sintered body, and the value of u shown in the examples below is The value is (1)
Calculated according to the formula.

Example 1 Aluminum triisoproboxide (Al(o-
While stirring a solution of 200 g of isoC ₃ H ₇ ) ₃ ) dissolved in isopropanol in step 1, distilled water in step 2 was added and a hydrolysis reaction was carried out for 1 hour to obtain a white precipitate. The solution temperature during the reaction was 90℃.
was held at After filtering the resulting precipitate, 20 g of the powder obtained by drying under reduced pressure at 80°C and 10 g of carbon black with an ash content of 0.08% by weight and an average particle size of 0.45 um were placed in a nylon pot and coated with nylon. Using a ball, ethanol was uniformly mixed in a ball mill using a liquid dispersion medium. After drying the resulting mixture, it was placed in a flat plate made of high-purity graphite and heated at 1600°C while continuously supplying nitrogen gas at a rate of 3/min into an electric furnace.
The mixture was heated at a temperature of 6 hours. The resulting reaction mixture was heated in air at a temperature of 750° C. for 4 hours to oxidize and remove unreacted carbon.

As a result of X-ray diffraction analysis, the obtained white powder was found to be single phase AlN. The average particle diameter of the powder was 1.20 um, and particles of 3 um or less accounted for 95% by volume. When observed using a scanning electron microscope, this powder was found to be uniform particles with an average size of about 0.7 um.
In addition, as a result of analysis of this powder, impurities such as Cr,
Contains trace amounts of metals such as Si, Ni, and Fe, as well as oxygen.
It was an extremely high purity aluminum nitride powder containing 1.0% by weight and 0.05% by weight of C.

Aluminum nitride powder thus obtained
1.0 grams was placed in a graphite die coated with BN (boron nitride) with a diameter of 20 mm, and heated at a pressure of 100 kg/cm ³ in nitrogen gas at 1 atmosphere using a high-frequency induction heating furnace.
Hot pressing was carried out at a temperature of 2000°C for 2 hours. The obtained sintered body was a slightly yellowish, dense, translucent body. The density of this sintered body is 3.26g/ ^cm3 , and according to X-ray diffraction analysis, it is single phase.
It was AlN. Also, the thermal conductivity of this sintered body is
The light transmittance of this sintered body, which was processed and polished to a thickness of 0.5 mm, was 35% for a wavelength of 6 um. In addition, the three-point bending strength of a 2.8 x 3 x 35 mm prismatic sample cut from a disk with a diameter of 40 mm and a thickness of about 3 mm hot-pressed under the same conditions as above was measured at a crosshead speed of 0.5 mm/min and a span of 30 mm.
mm, measured at 1200℃, average 48.5Kg/
It was warm in ^mm2 .

Example 2 Ca was added to aluminum nitride powder (10 g) obtained in the same manner as Example 1 to give a concentration of 0.2 wt% as CaO.
(NO ₃ ) _{2.4H 2} O was added to ethanol as a liquid medium and mixed using a polyethylene pestle in a polyethylene milk needle. After drying this mixture, it was hot pressed under the same conditions as in Example 1 to obtain a sintered body with a diameter of 20 mm. The density of this sintered body was 3.27 g/cm ³ , and according to X-ray diffraction analysis, it was single-phase AlN.
The thermal conductivity of this sintered body was 95 w/m·K.
Furthermore, when this sintered body was processed and polished to a thickness of 0.5 mm, the light transmittance was 42% for light with a wavelength of 6 um.

Comparative Example 1 Instead of the aluminum nitride powder used in Example 2, a commercially available aluminum nitride powder manufactured by nitriding metal aluminum (average particle size of 2.5 um, proportion of particles of 3 um or less was 50 %
The oxygen content is 2.5% by weight and the cationic impurity is 0.35%.
Sintering was carried out in the same manner as in Example 2, except that % by weight) was used. As a result, the density of the obtained sintered body was
The thermal conductivity was 3.22 g/cm ³ and 28 w/m·K. Further, the sintered body was black and had almost no translucency.

Example 3 200g of aluminum triisopropoxide 1
The ash content is dissolved in isopropanol.
50g of carbon black with an average particle diameter of 0.45um at 0.08% by weight was dispersed, and while stirring, distilled water from step 2 was added and a hydrolysis reaction was carried out for 1 hour to form aluminum hydrate and carbon black. A mixture slurry was obtained. Note that the solution temperature during the reaction was maintained at 90°C.

For subsequent operations, change the firing atmosphere to _N2 gas.
Aluminum nitride powder was obtained in the same manner as in Example 1 except that NH ₃ gas was used. The thermal conductivity of the sintered body obtained by sintering the powder under the same conditions as Example 2 and
Transmittance of 5.5um light is 108w/m・K, 46% respectively
It was hot.

Example 4 A solution of 250 g of aluminum butoxide dissolved in 1 part of butanol was dissolved with hydrochloric acid while stirring.
A white precipitate was obtained by adding distilled water 2 adjusted to pH 2 and carrying out a hydrolysis reaction at room temperature for 2 hours.

From the precipitate, aluminum nitride powder having the same properties as in Example 1 was obtained in the same manner as in Example 1. The powder was sintered under the same conditions as in Example 2, and the thermal conductivity and 5.5 um light transmittance were 112 w/m·K and 48%, respectively.

Claims (1)

[Claims] 1. A hydrolyzable organoaluminum compound is brought into contact with water or a water-containing organic solvent to perform hydrolysis, and the hydrolyzate is converted into alumina simultaneously with or after the hydrolysis and converted into alumina. Fine carbon powder is mixed in a liquid dispersion medium so that the weight ratio of carbon is 1:0.36 to 1:2, and the mixture is fired at a temperature of 1400 to 1800°C in an atmosphere of nitrogen or ammonia. A method for producing high-purity aluminum nitride powder, which comprises heating fine powder at a temperature of 600 to 900°C in an oxygen-containing atmosphere to remove unreacted carbon. 2 Claim 1 wherein the hydrolyzable organoaluminum compound is an aluminum alkoxide
Manufacturing method described. 3. The manufacturing method according to claim 1, wherein the organic solvent is alcohol. 4. The manufacturing method according to claim 1, wherein the liquid dispersion medium is alcohol.