JPS616104A - Manufacture of aluminum nitride powder - Google Patents

Abstract

PURPOSE:To manufacture high purity AlN powder by mixing a hydrolyzate of an organoaluminum compound with fine C powder in a liq. dispersion medium in a proper ratio, calcining the mixture in an atmosphere of N2, and removing the unreacted C by burning. CONSTITUTION:The hydrolyzable organoaluminum compound such as aluminum alkoxide is brought into contact with water or an org. solvent contg. water such as alcohol, and it is hydrolyzed optionally under heating. During or after the hydrolysis, the resulting hydrolyzate is mixed with fine C powder in a liq. dispersion medium such as alcohol in (1:0.36)-(1:2) weight ratio of Al2O3:C when expressed in terms of Al2O3. The mixtue is calcined at 1,400-1,800 deg.C in an atmosphere of N2 or NH3, and the unreacted C is removed from the resulting fine powder by heating at 600-900 deg.C in an atmosphere contg. O2 to obtain high purity fine AlN powder giving a sintered body having high heat conductivity, high light transmittance and high corrosion resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for producing high purity aluminum nitride fine powder. In particular, this is a method for producing high-purity aluminum nitride TT powder whose sintered body has high conductivity, high light transmittance, and high corrosion resistance.

Conventionally, the following two methods are known as methods for producing aluminum 9ide UNO fine powder. The first method is a direct nitriding method in which gold-grade aluminum powder is carbonized at high temperature in a nitrogen or ammonia atmosphere, and the resulting nitride is pulverized to obtain aluminum nitride powder.

The second method is an alumina reduction method in which alumina and carbon powder are calcined under pressure in an atmosphere of f-4 or ammonia, and the resulting nitride is heated under pressure in an atmosphere containing oxygen to remove unreacted carbon. This is the way to be exposed. The former direct nitriding method has the disadvantage that the resulting aluminum nitride powder is not uniform because it is not possible to avoid crushing. Furthermore, the latter method is superior to the direct nitriding method in that it can produce aluminum sulfur nitride powder with relatively uniform particle size. Special closure in 1988-1985
It has been reported that aluminum nitride powder, which provides VC translucency, can be obtained by an alumina reduction method.

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

[71] First, the present invention involves contacting a hydrolyzable organoaluminum compound with water or a water-containing organic solvent to hydrolyze it,
Simultaneously with the hydrolysis or subsequent to the hydrolysis, the hydrolyzate is converted into alumina and the weight ratio of alumina to carbon is 1.
Carbon fine powder is mixed in a liquid dispersion medium so that the ratio is 0.36 to 1:2, the mixture is fired in a nitrogen or ammonia atmosphere, and the obtained fine powder is then placed in an oxygen-containing atmosphere. This is a method for producing high-purity aluminum nitride fine powder by heating at a temperature of 600 to 900°C 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 alkylaluminum such as trimethylaluminum, triethylaluminum, diethylmonohaloaluminum; in particular, aluminum propoxide, aluminum butoxide. Aluminum alkoxides such as , aluminopropoxide, and 1,000-butoxydiinopropoxide can be suitably used. In particular, aluminum alkoxide is very suitable from a technical standpoint because it not only facilitates operations such as the hydrolysis reaction and dispersion treatment described below, but also improves the properties of the resulting aluminum nitride powder. . The above-mentioned hydrolyzable organoaluminum compound can be reacted with TKn water, but generally it is dissolved in a specific solvent or the molecules 7'1
．． It is used in various ways. , Do you have a nuclear organic solution specialty? It is a substance that dissolves or disperses aluminum compounds, and can act without particular limitation, but it is usually petroleum ether.

Hydrocarbons such as hexane, benzene, toluene, etc.: methanol, ethanol, propatool.

Aliphatic alcohols such as Impropatol; chlorinated solvents such as carbon tetrachloride are preferred.

In particular, the above-mentioned alcohols are suitable because operations such as hydrolysis reaction and carbon dispersion treatment, which will be described later, can be carried out easily. The concentration of the organic solvent in which the small-sized organoaluminum compound is dissolved or dispersed varies depending on the type of the organoaluminum compound, the polarity of the organic solvent, the hydrolysis φ described below, etc., and cannot be absolutely determined, but in general, the concentration of the aluminum compound is low. is preferable. However, if the concentration b' 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, the concentration of the organoaluminum compound may be determined as appropriate in consideration of these factors, but it is generally most preferable to use the organoaluminum compound at a concentration of 50% by weight or less, preferably in the range of 5 to 40% by weight.

The organic aluminum compound is mixed with a water-containing organic solvent to perform hydrolysis. The organic solution 8 is from the above book /F
! Although it can be used without being limited to FK, it is the most clever alcohol solution. When using the above-mentioned hydroalcoholic solution, the above-mentioned aliphatic alcohols are preferably used as the alcohol. Is the algol liquid contact button included and the water stand made of organic alumina/compound? ``'It's enough to hydrolyze it, 1+!] Varicella conditions, other 8
+1 is determined in advance and used according to ft-kasa1. Ota as needed [S+:I'! '：Hydrolysis of external compounds, amines, salts, salts, F1ρ', etc. You can also use accelerators.

The above hydrolysis is a scale that can be done in one step! 1 The water decomposition reaction is fast, so it can be done in a heated state. Reaction number - v, 1 mixture, Mt to 41 to 41 to 1, C moejo T1, 4!? To change the particle size to J/1-, i should be stirred 12 times. 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 parameters should be determined in advance in the laboratory according to the required particle size. It is preferable to decide on this in advance.

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 than the original. In addition, the particle size is 051Im or less, and particles with a particle size of 1μm or less account for at least 90% by volume of the total.
It is also possible to obtain particles in which the extreme pressure particle diameters occupying the entire range are uniform. Such properties improve the sinterability when obtaining an aluminum nitride sintered body, and improve the properties imparted to the sintered body, such as thermal conductivity,
It has a great influence on improving translucency etc.

In the present invention, it is an essential step to mix the hydrolyzate and carbon simultaneously with the hydrolysis or during the hydrolysis reaction. In this case, the mixing ratio of carbon is such that the weight ratio of alumina to carbon is 1:0.36 to 1:2, preferably 1:0.4 when the hydrolyzate is converted to alumina pressure.
It is preferable to select from the range of ~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 preferred.

As a means of combining the above-mentioned carbon with the hydrolyzate of the organoaluminum compound as uniformly as possible, carbon powder is present in the agitated water decomposition reaction system of the organoaluminum compound, and at the same time as the hydrolyzate is precipitated, carbon is co-precipitated. It is preferable to do so. In this case, as the liquid dispersion medium, the organic solvent of the hydrolysis reaction system, alcohol,
Water or a warm solution of these can be used as is. In addition, 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 added to the side after filtration. Both may be mixed in a prepared liquid dispersion medium.

The liquid dispersion medium used in the latter embodiment is not particularly limited, and any known liquid dispersion medium such as water, hydrocarbons, aliphatic alcohols, or mixtures 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. If the latter mixing form is carried out in liquid form, the aluminum component and carbon component will be mixed extremely homogeneously, which will not only greatly affect the reactivity of aluminum nitride, but also cause the contamination of undesirable substances in aluminum nitride. This gives the advantage of being able to minimize the Moreover, by adopting 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. Therefore, the aluminum nitride powder obtained by nitrification, which will be described later, itself has fine particles. Since the resulting aluminum nitride has uniform properties, it is not necessary to crush the obtained aluminum nitride, and it can be sintered. The advantage of being able to omit this pulverization step plays a valuable role industrially. For example, in the present invention, it is possible to completely prevent impurities from occurring during grinding, and it is possible to completely prevent the surface of aluminum nitride from being oxidized and the oxygen content to increase during grinding, so that impurities in aluminum nitride can be completely prevented. The amount of gentleman's clothing is also extremely small.

When carrying out the wet mixing in the present invention, it is preferable to carry out the wet mixing in an apparatus made of a material that can avoid mixing of impurity components that remain even after aluminum nitride is fired. In general, wet mixing can be carried out at normal temperature and pressure, and is not adversely affected by temperature and pressure.

As long as a small mixing device is selected that does not produce any impurity components remaining even after firing, considering the material, two known devices are employed. For example, it is common to use a mill with built-in spheres or rods as a warming 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 warming device that come into contact with the raw material may be made of plastic or may be 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, plastics may contain various metal components as stabilizers, so be sure to check them before use.

The fine carbon powder used as a raw material in the button of the present invention has an ash content of 0.2%, and a maximum of 0.2%.
It is preferable to use it with a purity of 1% by weight. In addition, since the average particle size of the carbon (1d) affects the particle size of the aluminum nitride obtained, it is preferable to use fine particles with an average particle size of 1 μm or less. Examples of the carbon include carbon black, graphitized carbon black, etc. Carbon black is most preferred for h-1-4.

The wet #1 combined raw materials are filtered and/or dried or dehydrated by heating if necessary, and then fired at a temperature of 1400 to 1800 C in a nitrogen or ammonia atmosphere. 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. This is not preferable because the oxygen content increases, causing deterioration of various properties.

The aluminum nitride obtained in this way has an extremely low content of impurities compared to conventional aluminum nitride, and has various physical properties of the aluminum nitride sintered body, such as thermal conductivity,
Translucency etc. can be significantly improved. For example, the AtN content in aluminum nitride obtained in the present invention is 97% or more, the combined oxygen content is 1.5% by weight or less, and the content of other metal components other than aluminum is 0.1% by weight as a metal.
It is preferably less than 0.05% by weight.

Further, the aluminum nitride powder obtained in the present invention has an average particle diameter of 211 m or less. If the average particle diameter ht is larger than this, there is a greater tendency for sinterability to deteriorate. The aluminum nitride powder of the present invention preferably has an average particle size of 2 μm.
Contains particles with a diameter of 511 m or less in a proportion of 80% or more by volume.

The aluminum nitride of the present invention has a very high purity, hn<the above, for example, the combined oxygen content is preferably at most 1.0% by weight. Conventionally, fine aluminum nitride powders with a combined oxygen content of less than 2% by weight have been found to have sufficient sintering properties, and in order to obtain good sinterability, a combined oxygen content of at least 2% by weight is required. Considering the level of technology that I didn't believe in,
It is truly surprising that the high density aluminum nitride mimic 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 powder of the present invention. Such a sintered body of aluminum nitride is produced by molding the high-purity aluminum nitride imitation powder of the present invention and sintering the resulting molded body in an inert atmosphere at a temperature of 1700 to 2100°C. Manufactured by making the body generate.

The aluminum nitride sintered body can also be manufactured 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. Typical sintering aids that are commonly employed are at least IF selected from the group consisting of alkaline earth metals, lanthanum metals, and metals. It is preferable to add 0.01 to 5% by weight of the metal matrix or oxide of the metal. The above-mentioned sintering aid is added in the steps such as the hydrolysis step of the organic aluminum compound and the addition step of carbon when producing the aluminum nitride powder of the present invention.
It is also possible to produce a product containing a sintering aid in the aluminum chloride powder.

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

The sintering method described above is not particularly limited, and any known sintering method can be employed. For example, the hot-press sintering method is carried out under a pressure of 20 to 400 Kf/Ca, the gas pressure sintering method is sintered under a third base gas pressure of about 1 to 10 atm, or the sintering method is performed under substantially no pressure. Pressureless sintering methods may be employed as needed.

The aluminum nitride sintered body thus obtained has a density of 3. LP/Cl11 or more, preferably 3.2f/
- The result is an excellent high-density sintered body. Further, the sintered body has excellent thermal conductivity, for example, 100 W/m-K, preferably 110 W/m-K or more. Further, the light transmittance of the sintered body is, for example, a sintered body processed and polished to a thickness of 0.5 mm, and the light transmittance is 65% or more for a wavelength of 6 μm.

The sintered body thus obtained can be used, for example, as a highly heat conductive ceramic for heat dissipation plates, heat exchanger materials, and substrates for stereo and video amplifiers.

Used as IC boards, etc. Utilizing its excellent translucency, it can be used as a window material for arc tubes of lamps and sensors that use ultraviolet to infrared rays.It can also be used as a window material for 1/- dars that utilizes radio wave encounterability.9 Translucency at high temperatures is required. It can be used as a special window material.

The aluminum lead nitride powder of the present invention has been successfully used as a raw material for sialon-based materials, including α-8iQlon, β
-8ialon r Provides a sialon compound with high purity and excellent properties that could not be achieved by using conventional AtN as a raw material for AtN polytype.

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 ceramic materials such as silicon carbide, and as a powder for composites with polymers such as silicone rubber. It has a powerful effect.

” The invention will be explained in detail with reference to examples.

The various analytical methods and analytical devices used in the following Examples and Comparative Examples are as follows.

Carbon analysis: Carbon analysis device in gold scraps (manufactured by Yoba Yo Seisakusho, FJ4)
IA-3200) (22 analysis: Oxygen analyzer for gold (Le'y, 254 Works 5J FMGA-150rl) Nitrogen analysis: Melting fraction neutralization titration method X-ray diffraction device: 1 electron JRX -12VB scan Ryu Jianzi Hyeonchang: JEOL JJsN E T2o.

Average particle size and particle size distribution 6! It measuring device: CAPA-500 made by Baeba Seisakusho Heat conduction tower (111 u) Equipment: Rigakuden e1/-ther method heat hole a
Column determination device Ps-7 Light transmission ¥, medium 11 Determination device: Hitachi Seisakusho self-recording spectrophotometer 330 type infrared spectrophotometer 2/>0-30 type Ps, the light transmittance of the sintered body is as follows Calculated using the formula.

Engineering here. R is the intensity of incident light, R is the intensity of transmitted light, R is the reflectance, thickness of the tFi sintered body, and μ is the absorption coefficient. lR
The refractive index of the sintered body is determined by the refractive index, and if n is the refractive index, it is expressed by the following formula with I11 constant in air.

μ in the formula (1) is an index representing the translucency of the sintered body, and μ in the example below is shown in formula (1).
Therefore, it was calculated.

Example 1 Aluminum triynepropoxide (A t-(o-
ISO 03H7), ) 20 Of was dissolved in 1 t of Improper Tool, and while stirring, 2 t of distilled water was added and a hydrolysis reaction was carried out for 1 hour to obtain a white precipitate. Note that the solution temperature during the reaction was maintained at 90°C. After filtering the obtained precipitate, powder material 201 obtained by drying under reduced pressure at 80 ° C. and 10 tons of carbon black with an ash content of 0.08% by weight and an average particle size of 0.4571 m,
Using a nylon pot and a nylon-coated ball, the resulting mixture was heated uniformly in a ball mill using ethanol as a liquid dispersion medium. After drying, the resulting mixture was placed in a high-purity graphite flat plate, and nitrogen gas was fed into an electric furnace at 3 t/min. The mixture was heated at a temperature of 1600° C. for 6 hours while being continuously supplied with water. The resulting reaction mixture was heated in air at a temperature of 750° C. for 4 hours to oxidize and remove unreacted carbon.

The obtained white powder was subjected to xM diffraction analysis (Xraydiff
As a result of reaction analysis6), it was found to be single-phase (single phaSe) AtN. The average particle size of the powder was 1.20 thm, and 31
℃m or less accounted for 95% of the total. When observed using a scanning electron microscope, this powder was found to be uniform particles with an average CJ of about 7 ttm. Analysis of this powder also revealed impurities such as cr + 81 and Nl.

It was an extremely high purity aluminum nitride powder that contained trace amounts of metals such as Fe, as well as 1.0% by weight of oxygen and 0.05 weight percent of C.

1.0 g of the aluminum nitride powder thus obtained was placed in a lead die coated with BN (boron nitride) with a diameter of 20 and heated to 100 g in nitrogen gas at 1 atm using a high frequency induction heating furnace: i/- Hot pressing was carried out at a temperature of 2000°C for 2 hours under a pressure of . The obtained sintered body was a slightly yellowish, dense, semi-transparent body.

The density of this sintered body is 26t/cy4, and X-ray diffraction analysis reveals that it is a single phase.
It was A/-N. Thermal conductivity of the sintered body of the bite is 1
10 W/m-, and the light transmittance of this sintered body processed and polished to a thickness of 0.5 mm is F'! r, 65% for a wavelength of 6 μm. In addition, 6-point bending of a prismatic sample measuring approximately 2.8 x 3 x 65 mm was cut from a circle with a diameter of 401° and a thickness of approximately 5 tP @ hot-pressed under the same conditions as above, and the strength was measured at a crosshead speed of 0.5 min/min. , span 60-
q, as a result of identification under the condition of 1200°C, the average was 48.
It was 5 years/, -1 piece.

Example 12 Aluminum nitride powder (1
0f) 0.2wt% as lccao ("a
(NOx)2.4N20 was added to ethanol as a liquid medium and mixed using a polyethylene pestle in a polyethylene mortar.

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 bars.

The density of this sintered body was 5.27 t/-, and according to X-ray diffraction analysis, it was single-phase AtN.

The thermal conductivity of this sintered body was 95 t/m-. The light transmission of a sintered body of octopus processed and polished to a thickness of 0.5-MIC was 42% for light with a wavelength of 5 zrm.

Example 3 Aluminum triimpropoxide 2002 was dissolved in 1 t of impropat tool at a solution pressure, carbon black 50 having an ash content of 0.08 weight and an average particle size of 0.45 ttm.
f was dispersed, 2 tons of distilled water was added while stirring, and a hydrolysis reaction was carried out for 1 hour to obtain a slurry of a mixture of aluminum hydrate and carbon black. The solution temperature during the reaction was maintained at 90°C.

The subsequent operations were the same as in Example 1 except that NH3 gas was used instead of N2 gas for the firing atmosphere to obtain aluminum nitride powder. The thermal conductivity and the transmittance of light at 5.5 μm of the sintered body obtained by sintering the powder under the same conditions as in Example 2 were 1.
08W/m-K, 46%.

Example 4 Aluminum butoxide °25n? Add 1 L of butanol to the solution with stirring and add no acid. N2
A white precipitate was obtained by adding 2 t of distilled water adjusted to 2 t and carrying out a hydrolysis reaction at room temperature for 2 hours.

Aluminum nitride powder having the same properties as in Example 1 was obtained from the cough precipitate in the same manner as in Example 1. A sintered body obtained by sintering the powder under the same conditions as in Example 2. The conductivity and the light transmission of 5.5/Im are each 112 W/m−
K.

Tokuyama Soda Co., Ltd.

Claims (5)

[Claims] (1) A hydrolyzable organoaluminum compound is brought into contact with water or a water-containing organic solvent to perform hydrolysis, and the weight ratio of alumina to carbon is determined by converting the hydrolyzate into alumina simultaneously with or after the hydrolysis. 1:0.36～
Fine carbon powder is mixed in a liquid dispersion medium at a ratio of 1:2, the mixture is fired in an atmosphere of nitrogen or ammonia, and the resulting fine powder is heated in an atmosphere containing oxygen for 6 hours.
A method for producing high-purity aluminum nitride powder, which comprises heating at a temperature of 00 to 900°C to remove unreacted carbon. (2) The production method according to claim (1), wherein the hydrolyzable organoaluminum compound is an aluminum alkoxide. (3) Claims (1) in which the organic solvent is alcohol
) manufacturing method described. (4) The manufacturing method according to claim (1), wherein the liquid dispersion medium is alcohol. (5) The manufacturing method according to claim (1), wherein the firing is performed at a temperature of 1400 to 1800°C.