KR880002226B1 - Method for preparing fine aluminum nitride powder - Google Patents

Abstract

This powder has an average particle diameter (APD) of max 2 microns, and contains by wt. 94%-57% min. AlN; 3-1.5% max combined oxygen; and 0.3-1.5 max metallic compounds forming impurities. The AlN powder is dispersed and mixed in a liquid together with carbon with an APD of max 1 micron and an ash content of max 0.2%. The mixture is heated at 1400-1700 deg.C in N2 or NH3 in order to obtain a powder, which is reheated at 600-900 deg.C to remove residual C and to obtain a fine, highly punified AlN powder.

Description

High purity aluminum nitride powder and its manufacturing method

1: shows the light transmittance relationship of the sintered compact of this invention according to the wavelength of light.

2 is a sample photograph of the sintered body of the present invention.

3 is a scanning electron micrograph of a mechanically cleaved surface of a specimen of the inventive hot rock sintered body.

FIG. 4: Scanning electron micrograph taken after the mechanically divided surface of the thermocompression sintered compact of the present invention as shown in FIG. 3 is treated with an aqueous phosphate solution. FIG.

5 is a scanning electron micrograph of the mechanically cleaved surface of the specimen of the pressureless sintered compact of the present invention.

6 is a scanning electron micrograph of a mechanically cleaved surface of another specimen of the pressureless sintered compact of the present invention.

7 is a scanning electron micrograph taken after the mechanically cleaved surface of the pressureless sintered body of the present invention as shown in FIG. 6 is treated with an aqueous phosphate solution.

The present invention relates to a high purity fine aluminum nitride powder, compositions thereof, and sintered bodies thereof, and methods for producing them.

Sintered aluminum nitride has attracted continued interest as several high temperature materials because of its excellent properties such as high thermal conductivity, corrosion resistance and strength. Since the aluminum nitride powder for sintered aluminum nitride inevitably contains various impurities, its sinterability is insufficient, and it is difficult to obtain a high purity sintered compact and a compact sintered compact having excellent properties inherent to aluminum nitride.

The following two methods are already known as methods for preparing aluminum nitride powder. The first method is a so-called direct nitriding method characterized by nitriding metal aluminum powder under nitrogen or ammonia gas atmosphere at high temperature, and then pulverizing the produced nitride. The second method is a so-called alumina reduction method characterized by combusting alumina and carbon powder under nitrogen or ammonia gas, and then grinding the produced nitride.

First, since the metal aluminum is used as the starting material in the direct nitriding method, it is naturally necessary to grind the metal aluminum to increase the nitriding rate. Moreover, in order to increase the sinterability of the resulting nitride, the step of grinding the nitride to a particle size of several microns or less is required. In the direct nitriding method, it is unavoidable to include a metal or a metal compound as impurities resulting from a grinding mechanism such as a bowl mill used in the grinding step. Moreover, in the direct nitriding method, aluminum nitride powder containing inevitable metallic aluminum as an impurity is produced, and therefore it is very difficult to produce aluminum nitride containing several weight% or less of impurities including impurities generated in the grinding step. Aluminum nitride powder produced by the direct nitriding method is difficult to produce aluminum nitride powder having a sufficiently small and uniform particle size in the grinding step of the direct nitriding method and also cannot prevent oxidation of the surface of the aluminum nitride powder during grinding. Silver usually contains 2 to 5% by weight or more of oxygen.

The second alumina reduction method is believed to be superior to the direct nitriding method in that it provides aluminum nitride powder with a relatively uniform particle size. However, the grinding step can not be omitted to obtain particles having a size of several microns or less. Moreover, unreacted alumina cannot be extremely reduced. Thus, like the direct nitriding method, the second method also has the disadvantage of providing a low purity aluminum nitride powder. The aluminum nitride powders produced by these methods do not have sufficient purity and are generally black to grey. Therefore, sintered bodies made from these powders usually have no light transmittance at all.

It is therefore an object of the present invention to provide fine aluminum nitride powders having high purity.

It is a further object of the present invention to provide a high purity aluminum nitride fine powder composed of fine particles having an average particle diameter of 2 microns or less and having impurities such as a low content metal compound and a low content of bound oxygen.

It is another object of the present invention to provide a fine aluminum nitride nitride powder having excellent sinterability and providing a high purity and high density aluminum nitride sintered body.

Another object of the present invention is to provide an industrially advantageous method for producing the high purity aluminum nitride of the present invention.

Another object of the present invention is to provide a high-purity aluminum nitride fine powder production process according to the so-called alumina reduction method, which can provide fine aluminum nitride powder having an average particle diameter of 2 microns or less without performing the step of grinding the prepared nitride. To provide.

It is another object of the present invention to provide a dense aluminum nitride composition containing the high purity aluminum nitride and the sintering aid of the present invention, and a method for producing the same.

Still another object of the present invention is to provide a high water and high density aluminum nitride sintered body.

It is still another object of the present invention to provide a high purity and high density aluminum nitride sintered body having a low content of metal compound (impurity) and bound oxygen and having a density of 90% or more of the theoretical value.

Another object of the present invention is to provide a high purity and high density aluminum nitride sintered body having light transmittance.

Still another object of the present invention is to provide a method for producing a high purity and high density aluminum nitride sintered body from a high purity aluminum nitride powder of the present invention or the aluminum nitride composition of the present invention.

Other objects and advantages of the present invention will become apparent from the following description.

According to the present invention, the above objects and advantages have an average particle diameter of 2 microns or less, and a metal compound of less than 0.5% (metal) as 94% by weight of aluminum nitride (AIN), 3% by weight of bound oxygen and impurities Achieved preferentially by containing fine aluminum nitride powder.

In accordance with the present invention, fine aluminum nitride powders having an average particle diameter of 2 microns or less are present in the form of spherical particles or secondary nodules thereof.

According to the invention, the aluminum nitride fine powder can be prepared according to the following method. (1) Alumina fine powder having an average particle diameter of 2 microns or less has an alumina fine powder of 1: 0.36 to 1: 1 in a carbon fine powder and a liquid dispersion medium having a recontent of 0.2% or less and an average particle diameter of 1 micron or less. Mix well by weight ratio of carbon fine powder, (2) optionally dry the prepared mixture, and then burn at a temperature of 1,400 to 1.700 ° C. under a nitrogen or ammonia atmosphere, and (3) the resulting fine powder is 600 to 900 ° C. temperature. By heating at to remove unreacted carbon with an average particle diameter of 2 microns or less and containing at least 94% by weight of aluminum nitride, up to 3% by weight of bound oxygen and as a impurities up to 0.5% by weight (calculated as metal) To prepare a fine aluminum nitride powder.

By this method, the step of pulverizing the aluminum nitride obtained by burning the raw material can be omitted. Therefore, impurities resulting from the grinding step are not contained in the final aluminum nitride, and oxidation of the aluminum nitride surface caused during grinding can be prevented by known methods. Therefore, the gain from omitting the aluminum nitride grinding step is very large. In order to omit the grinding step and obtain aluminum nitride with good properties, it is important to use a so-called wet mixing method in which the mixing of the alumina powder and the carbon powder is carried out in the liquid dispersion medium in the above step (1). The wet mixing method not only allows the materials to be mixed evenly but also prevents the particulate starting material from clumping and coarsening. Fine and uniformly sized aluminum nitride particles are prepared by burning the prepared even mixture. In addition, according to the method of the present invention, since it is possible to completely prevent the inclusion of impurities in the grinding step and also to prevent the oxidation of the aluminum nitride surface, it is more excellent in the known method, which provides a sintered body having high purity and light transmittance. A fine aluminum nitride powder having sinterability can be obtained. There is no particular limitation on the liquid dispersion medium used in the wet mixing step, and any known medium for wet mixing may be used. In general, water, hydrocarbons, aliphatic alcohols, and mixtures thereof are widely used in industrial operation. Examples of hydrocarbons are ligroin, petroleum ether, hexane, benzene, and toluene, and examples of aliphatic alcohols are methanol, ethanol and isopropanol.

The wet mixing is preferably carried out in an apparatus made of a material which does not cause the inclusion of impurities in the burned aluminum nitride. Generally wet mixing can be carried out at room temperature and under atmospheric pressure and is not adversely affected by temperature and pressure. Any known mixing apparatus can be used as long as it does not cause impurities remaining in the product after combustion. Generally, mills containing spherical or rod-like materials are used as the mixing device. In order to prevent the inclusion of impurities remaining in the burned aluminum nitride, it is preferable that the inner wall of the mill and the spherical or rod-shaped material consist of aluminum nitride itself or high purity alumina having a purity of at least 99.9% by weight. The mixing device surface in contact with the starting material is made of plastic or coated with it. There is no particular limitation on the plastic used for this purpose, for example polyethylene, polypropylene, polyamide, polyester and polyurethane are used. Many metallic stabilizers are used in plastics, so check them before use. Furthermore, it is important to use alumina and carbon having the properties specified below in order to omit the grinding step and obtain a high purity aluminum nitride fine powder having an average particle of 2 microns or less and good sinterability. The fine alumina powder should have an average particle diameter of 2 microns or less and a purity of at least 99.0% by weight, preferably at least 99.8% by weight. The fine carbon powder should have a content of up to 0.2% by weight, preferably up to 0.1% by weight. Since the average particle diameter of carbon affects the particle diameter of the aluminum nitride to be obtained, the carbon must be in a fine powder state having a size of micron or smaller, that is, an average particle diameter of 1 micron or less. Carbon black and graphitized carbon black are used but generally carbon black is preferred.

The ratio of alumina to carbon varies depending on the purity of the alumina and carbon, particle size, etc. and should be determined by preliminary testing. Alumina and carbon are usually wet mixed in a weight ratio of 1: 0.36 to 1: 1, preferably 1: 0.4 to 1: 1. The mixture is dried if necessary and burned at 1400-1700 ° C. under a nitrogen atmosphere. When the combustion temperature is below the aforementioned threshold, the reductive nitriding reaction does not proceed industrially satisfactorily. When the combustion temperature is above the above-mentioned upper limit, the aluminum nitride produced is partially sintered to form agglomerated particles. Therefore, it becomes difficult to obtain aluminum nitride having a desirable particle diameter.

According to the present invention, the aluminum nitride fine particles obtained by burning are heated to a temperature of 600 to 900 ° C. under an atmosphere containing oxygen to oxidize and remove unreacted carbon.

As a result, the present invention provides a high purity aluminum nitride fine powder having an aluminum nitride content of 94% or more, a combined oxygen content of 3% by weight or less, and an impurity content of 0.5% by weight or less (metal).

According to the present invention, the high purity aluminum nitride fine powder has an aluminum nitride content of 94% or more. Preferred aluminum nitride fine powder having an aluminum nitride content of at least 97% by weight provides a sintered compact having particularly good light transmittance.

The fine aluminum nitride powder of the present invention has a combined oxygen content of 3% by weight or less and an impurity content of 0.5% by weight or less (metal). Bound oxygen is believed to exist in the form of aluminum oxide or in the form of bonding to metals contained as impurities.

The combined oxygen content and the impurity content greatly influence the sinterability of aluminum nitride and the light transmittance of the manufactured sintered body. Preferred defective oxygen content is 1.5% by weight or less, and impurity content is 0.3% by weight or less (metal).

The metal compound as an impurity is formed from impurities contained in alumina and carbon, which are raw materials for producing aluminum nitride, or from solvents, mixing mechanisms, piping, and the like during the manufacturing process. They are compounds of carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper zinc and titanium.

The content of the metal compound present in the fine powder of aluminum nitride is preferably at most 0.1% by weight (metal).

Among the impurities, aluminum oxide produced by oxidation of unreacted alumina and carbon and aluminum nitride surfaces does not significantly deteriorate the properties of the aluminum nitride of the present invention. For example, when cationic impurities such as alumina, carbon and silica are contained in an amount of 0.3 to 0.5% by weight, it does not adversely affect the sinterability of aluminum nitride under atmospheric pressure. On the other hand, iron, chromium, nickel, cobalt, copper, and titanium impurities adversely affect the light transmittance of the aluminum nitride sintered body, and therefore, it should be prevented to contain these components to the maximum. In order for the sintered aluminum nitride to have sufficient light transmittance, it is preferable that the total iron, chromium, nickel, cobalt, copper and titanium content of the fine powder of aluminum nitride of the present invention is 0.1% by weight or less.

The aluminum nitride fine powder of the present invention has an average particle diameter of 2 microns or less. If its average diameter exceeds the limit, its sinterability is greatly reduced. Preferred aluminum nitride fine powders have an average particle diameter of 2 microns or less and contain at least 70% by volume of particles having a particle diameter of 3 microns or less.

The aluminum nitride of the present invention is very pure as described above, and its combined oxygen content is preferably 1.5% by weight or less. Previously, it was believed that aluminum nitride fine powder having a combined oxygen content of 2 wt% or less did not have sufficient sinterability, and a combined oxygen content of 2 wt% or more was necessary to obtain excellent sinterability. In view of the above, it is unexpected that the fine aluminum nitride powder having a high density has excellent sinterability.

According to the present invention, an aluminum nitride sintered body having high purity and high density can be obtained from high purity aluminum nitride fine powder. The sintered compact molds the aluminum nitride fine powder of the present invention, and sinters the molded material at a temperature of 1700 to 2100 ° C. under an inert atmosphere to have a density of 2.9 g / cm 3 or more and 94 wt% or more of aluminum nitride, 1.5 wt% or less. It can be produced by obtaining an aluminum nitride sintered body containing bonded oxygen and up to 0.5% by weight of a metal compound (impurity).

Furthermore, according to the present invention, aluminum nitride sintered bodies having high density and high purity can also be produced by carrying out the sintering step of the above-described method in the presence of a sintering aid. The process comprises at least 90% by weight of aluminum nitride, at most 4.5% by weight of bound oxygen, and from 0.02 to 5.0% by weight of the highest valence oxide of at least one metal element selected from alkaline earth metals, lanthanide metals and yttrium or compounds thereof Aluminum nitride fine powder containing not more than 0.5% by weight of a metal of a different metal compound (impurity), and 90% by weight or more of aluminum nitride by sintering the prepared material at a temperature of 1600 to 2100 ° C. under an inert atmosphere. Oxide, 0.02 to 5.0% by weight of up to 3.5% by weight of combined coral content and a density of 3.0 g / cm 3 or more and having a highest valence of 0.02 to 5.0% by weight of at least one metal selected from alkaline earth metals, lanthanide metals and yttrium or compounds thereof % And 0.5 weight% or less of metal of a metal compound (impurity) different from the compound of the said metal It is carried out by preparing an aluminum nitride sintered body.

In the above two methods for producing the aluminum nitride sintered body of the present invention having high purity and high density, sintering is performed by heating the resultant molded raw material at high temperature under an inert atmosphere. In any of the above methods, the sintering is hot pressure sintering or pressureless sintering. In thermo-pressure sintering, the strength of the pressure mold is the limit pressure, and a pressure of usually 350 kg / cm 2 or less is used. Industrially, a pressure of 20 kg / cm 2 or more, preferably 50 to 300 kg / cm 2, is used. Pressureless sintering is actually performed in the absence of pressure without applying any mechanical pressure to the molded article. When pressureless sintering is performed, the raw molded article to be pressureless sintered is produced under a pressure of 200 kg / cm 2 or more, preferably 500 to 2000 kg / cm 2. Sintering is carried out in an inert atmosphere, in particular in a non-oxidizing atmosphere, for example a nitrogen atmosphere.

In the first method without using a sintering aid, the sintering temperature is 1700 to 2100 ° C, preferably 1800 to 2000 ° C. In the second method using a sintering aid, the sintering can be carried out at lower temperatures, ie 1600 to 2100 ° C, preferably 1650 to 2000 ° C.

Therefore, according to the present invention, a high purity and high density aluminum nitride sintered body having an impurity content of 0.5% by weight or less (metal) and a density of 3.0 g / cm 3 or more (about 92% of theory) is provided.

Therefore, the high purity and high density aluminum nitride sintered body provided by the present invention is first of at least 2.9 g / cm 3, preferably 3.0 g / cm 3 (corresponding to about 92% of theory), more preferably 3.16 g / cm 3 (about the theoretical value). At least 94% by weight, preferably at least 97% by weight of aluminum nitride, at most 1.5% by weight, preferably at most 0.75% by weight of bound oxygen, and at most 0.5% by weight, preferably 0.3 An aluminum nitride fine powder containing a metal in a metal compound (impurity) of not more than% by weight. Secondly, from a starting medium containing sintering aid, a density of at least 3.0 g / cm 3, preferably at least 3.16 g / cm 3 and at least 90% by weight, preferably at least 93% by weight of aluminum nitride, at most 3.5% by weight, Preferably up to 2.5% by weight of bound oxygen, and from 0.02 to 5% by weight of oxides having the highest valence of at least one metal element selected from yttrium or a compound thereof derived from alkaline earth metal, lanthanide metal and sintering aid An aluminum nitride powder containing from 3.0% by weight to 0.5% by weight or less, preferably 0.3% by weight or less of metal of a metal compound (impurity) different from the compound of the metal can be obtained.

Impurities of the sintered compact of the present invention are compounds of metals such as carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper and zinc derived from impurities in the aluminum nitride fine powder of the present invention.

The sintered body of the present invention in a particularly preferred form contains a total amount of impurity metals of 0.1% by weight or less when the impurities are iron, chromium, nickel, cobalt, copper, zinc and titanium.

The sintered compact of this invention is characteristic in that the state of the mechanically divided surface thereof is very different from the cracked surface state of a known sintered compact.

The mechanically cleaved surface of the high density aluminum nitride sintered body of the present invention is formed of closely packed microcrystalline particles which are distinguished from each other in obvious form.

(μ m)이 0.5

내지 1.5

인 결정 입자로 구성되어 있다. 그의 분열된 표면중 70%이상의 결정 입자가 0.5

내지 1.5

범위의 입자 크기를 가지며, 분열 표면상에 비교적 균일한 크기의 입자를 갖는 질화알루미늄 소결체가 과거에는 알려지지 않았었다.The shape of the microcrystalline particles in the cleaved surface is polygonal. More than 70% of the microcrystalline particles have an average particle diameter at the cleaved surface separated by the apparent morphology.

0.5 μm

To 1.5

It consists of phosphorus crystal grains. 0.5% or more of the crystal grains in its split surface

To 1.5

Aluminum nitride sintered bodies having a particle size in a range and having particles of relatively uniform size on the cleavage surface have not been known in the past.

내지 1.5

, 즉 3.5 마이크론 내지 10.4 마이크론의 평균 입자 직경을 갖는 입자의 비율은 83%이다. 기계적으로 분열된 표면에 있어서 본 발명 소결체의 외관상 또 다른 특징은 각 입자의 분열 표면에 나타나는 결정 표면이 비교적 매끈한 편편한 표면을 형성하는 점이다. 이는 본 발명의 소결체가 불순물 또는 기체상(氣體相)의 함유로 인해 형성되는 이상(異相)(대기 분열 표면상의 원형 함몰로서 나타난다)을 거의 함유하지 않음을 나타낸다.For example, the sintered body of the present invention showing the micrograph of FIG. 3 has an average particle diameter (D) of 6.9 microns and is 0.5

To 1.5

That is, the proportion of particles having an average particle diameter of 3.5 microns to 10.4 microns is 83%. Another aspect of the mechanically divided surface of the sintered body of the present invention is that the crystal surface appearing on the split surface of each particle forms a relatively smooth flat surface. This indicates that the sintered compact of the present invention hardly contains any abnormality (appeared as circular depressions on the atmospheric cleavage surface) formed due to the inclusion of impurities or gas phase.

Another feature of the sintered body of the present invention is observed in the treated cleaved surface obtained by treating the mechanically cleaved surface with an aqueous phosphate solution to investigate the structure of the sintered body or the state of existence of the second phase. To explain, the sintered body of the present invention continues to have polygonal crystal grains even after treatment with 35% phosphate aqueous solution for 20 minutes at 62.5 ± 2.5 ° C. as the most representative treatment conditions. Intensive treatment conditions resulted in the same treated cleaved surface even when the hot press sintered body of the present invention was treated with 50% aqueous phosphate solution for 30 minutes at this temperature. On the other hand, it can be seen that the sintered body of the present invention obtained by pressureless sintering removed part of the grain boundary surface of the crystal grains when treated under the above treatment conditions, which is considered to be a result of dissolution. In more detail, most of the crystal grains have respective shapes, but some of the crystal grains have a slightly deformed form that was not observed before treatment.

The above-described properties of the sintered body of the present invention which are not affected by the aqueous solution of phosphate solution are easily dissolved when the known aluminum nitride sintered body is treated with the aqueous solution of phosphate, so that the second phase mainly composed of oxide is easily dissolved, so that the crystal grains are different from the crystalline particles before treatment. It is very characteristic in that it has a very different round shape. Moreover, it is surprising that the sintered bodies of the invention produced by pressureless sintering have excellent resistance to aqueous phosphate solution as described above in that there have been few reports of successful aluminum nitride annealing in the past.

In the X-ray diffraction method of the sintered body of the present invention, six clear diffraction lines resulting from hexagonal aluminum nitride crystals are obtained at a diffraction angle (2θ) between 30 ° and 70 °, that is, 33.3 ° ± 0.5 °, 36.2 ° ± 0.5 °, and 38.1 °. It is shown at diffraction angles of ± 0.5 °, 49.8 ° ± 0.5 °, 59.6 ° ± 0.5 °, and 66.3 ° ± 0.5 °. These diffraction angles correspond to Brack's interplanetary distances (d, Å), 2.69 ± 0.04 Å, 2.48 ± 0.03 Å, 2.36 ± 0.03 Å, 1.83 ± 0.02 Å, 1.55 ± 0.01 Å and 1.41 ± 0.01 Å, respectively.

Due to the large amount of sintering aid (such as CaCO ₃ or Y ₂ O ₃ ) added to increase the sinterability and the high oxygen content of the starting aluminum nitride, known aluminum nitride sintered bodies are for example has a diffraction line attributed to _{CaO.Al 2 O 3, CaO.2Al 2 O} 3 or 3Y ₂ O ₃ .5Al ₂ O ₃ crystals is reported. However, the present invention can provide a high purity and high density aluminum nitride sintered body which does not exhibit diffraction lines of the above-described crystals derived from the sintering aid even when such sintering aid is used during the sintering process.

The mixture containing the aluminum nitride fine powder, or the sintering aid which can be used in the above-mentioned second sintering method using the sintering aid, is selected according to the present invention from the first high purity aluminum nitride powder of the present invention selected from alkaline earth metal, lanthanide metal and yttrium. By uniformly mixing with at least one compound of metal, but mixing at a rate such that the amount of metal compound heavy metal oxide is from 0.02% to 5.0% by weight relative to the total weight of the resulting composition; Secondly, (1) a fine alumina powder having an average particle diameter of 2 microns or less, a carbon fine powder having an ash content of 0.2 wt% or less and an average particle diameter of 1 micron or less, and a compound of a metal selected from alkaline earth metals, lanthanide metals and yttrium In a liquid medium in which the weight ratio of fine alumina powder to fine carbon powder is 1: 0.36 to 1: 1, and the metal oxide having the highest valency of the metal compound is 0.02 to 5.0% by weight, and is uniformly mixed. The mixture is optionally dried and then burned at a temperature of 1400 to 1700 ° C. under a nitrogen or ammonia atmosphere, and (3) the mixture is then heated at a temperature of 600 to 900 ° C. under an oxygen containing atmosphere to remove unreacted carbon. do.

The first method can be carried out by mixing the fine aluminum nitride powder of the present invention with a sintering aid using a mixing device of the type illustrated above to mix alumina and carbon. The second method uses the same mixing apparatus to mix alumina, carbon, and sintering aid [step (1)], and then steps (2) and () in the same manner as described above for preparing the aluminum nitride fine powder of the present invention. By performing 3). The second method is very effective in many cases because despite the high combustion temperatures of 1400-1700 ° C., the sintering aid is surprisingly little consumed.

The sintering aid used in the process is a compound of at least one metal selected from alkali metals, lanthanide metals and yttrium. It is already known that these metal oxides are effective sintering aids for aluminum nitride. However, the research results of the present inventors show the function of these metal compounds not only as a sintering aid but also as a light transmittance enhancer for improving the light transmittance of the aluminum nitride sintered compact associated with the high purity of the fine aluminum nitride powder of the present invention.

Alkaline earth metals include beryllium, magnesium, calcium, strontium and barium. Of these, calcium, strontium and barium are particularly excellent as light transmittance enhancers.

Examples of lanthanide metals include lanthanum, cerium, praseium, neodymium, promethium, samarium, europium, gadlinium, terbium, dystrosium, holmium, erbium, thulium, ytterbium and ruthenium. Of these, lanthanum, neodymium and cerium are preferred.

The sintering aid or light transmittance enhancer is used in an amount of 0.02 to 5.0% by weight, preferably 0.03 to 3.0% by weight.

Therefore, in accordance with the present invention at least 90% by weight, preferably at least 93% by weight of aluminum nitride, at most 4.5% by weight, preferably at most 3.0% by weight of bound oxygen, and alkaline earth metals, lanthanide metals and yttrium or compounds thereof 0.02 to 5.0 wt%, preferably 0.03 to 3.0 wt%, oxide having the highest valence of at least one metal element selected, and 0.5 wt% or less, preferably 0.3 wt% of a metal compound (impurity) different from the compound of the above-described metal A uniform composition of fine aluminum nitride powder containing up to% is provided. In this composition, the impurity is a compound of a metal such as carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper or zinc derived from impurities present in the aluminum nitride fine powder of the present invention.

When the metal of the metal compound as an impurity is iron, chromium, nickel, cobalt, copper, zinc and titanium, the content of these impurities is preferably 0.1% by weight or less as the total amount of these metals.

As described above in detail, the present invention provides an aluminum nitride fine powder having high purity and an average particle diameter of 2 microns or less, and an aluminum nitride sintered body having high purity and high density.

The aluminum nitride sintered body according to the present invention is utilized, for example, as a high thermal conductivity in a heat generating plate, a material for a heat exchanger, a substrate of a stereo system or a video amplifier, and a substrate of an IC. It can be used as a light emitting tube of lamps and window materials for sensors utilizing ultraviolet and infrared light utilizing its excellent light transmission. It may also be used as a window material for radar utilizing its electromagnetic wave transmission and as a special window material requiring light transmission at high temperatures.

The fine aluminum nitride powder of the present invention is suitably used as a raw material for sialon-type materials, and when used as a raw material for alpha-sialon, beta-sialon and AIN poly type, high purity and excellent properties that cannot be obtained with a known AIN powder. It provides a sialon compound having. Moreover, the present invention provides a product having improved light transmittance when the aluminum nitride fine powder is used as a raw material for beta-sialon, Al ₂ O ₃ -AIN spinel and silicon oxynitride glass.

Since the aluminum nitride fine powder of the present invention is uniform and has excellent dispersibility, it can also be used as a powder for making a composite from polymers such as silicone rubber or addition aids in various ceramics such as silicon carbide.

The following examples illustrate the invention in more detail.

The following various analytical methods and instruments are used in the examples.

Cation analysis

IPC emission spectrometer (ICP-AES, manufactured by Dainsei Kosha Co., Ltd.).

Carbon analysis

Carbon analyzer (EMIA-3200, product made by Horiba Seisakusho) in metal.

Oxygen analysis

Oxygen analyzer (EMGA-1300, product made by Horiba Seisakusho) in metal.

Nitrogen analysis

Neutralization titration of ammonia generated by alkali melt decomposition.

X-ray diffractometer

X-ray diffractometer (JRX-12VB, available from Nippon Densh).

Scanning electron microscope

(JSM-T200, product of Nippon Densh).

Specific surface area

BET method (metal surface area measuring instrument SA-100, a Shivata chemical machine company make).

Instrument for measuring average particle size and particle size distribution

Centrifugal automatic particle analyzer (CAPA-500, product made by Horiba Seisakusho).

Thermal conductivity measuring instrument

Thermal constant measurement analyzer by laser (ps-7, product of Ragakudenki Co., Ltd.).

Line transmission measuring instrument

Hatachi 200-10 UV-VIS spectrophotometer (type 330) and Hitachi 260-30 infrared spectrophotometer (type 260-30).

Yaw strength tester

Instron test apparatus (model 1123).

The light transmittance of the aluminum nitride sintered compact is calculated by the following formula.

=(1-R)²e^-ut………………………………………………… (1)

= (1-R) ² e ^-ut ... … … … … … … … … … … … … … … … … … … (One)

Wherein I _O is the intensity of the incident light, I is the intensity of the transmitted light, t is the thickness of the sintered body and μ is the extinction coefficient.

R is determined by the refractive index of the sintered compact. This writing rate is n, and R is given by the following equation when measured in air.

…………………………………………………………… (2)R =

… … … … … … … … … … … … … … … … … … … … … … … (2)

Μ in Formula (1) is the magnitude | size of the light transmittance of a sintered compact, In the following example, the value of μ is calculated according to Formula (1).

)Average diameter on a mechanically cleaved surface (

)

The aluminum nitride sintered sample is mechanically cleaved, and the cleaved surface is photographed through a 2000 times scanning electron microscope.

)를 구할 수 있다.The equivalent diameter (d) of each crystal grain observed in a 7 cm x 10 cm size photograph is measured. By measuring the longest length (d _max ) and the shortest length (d _min ) of the crystal grains, respectively, and calculating their arithmetic mean, the diameter (

) Can be obtained.

)를 구할 수 있다.From the n d value of the n crystal grains, the average particle diameter (

) Can be obtained.

Example 1

The proportion of particles having a particle diameter of 3 microns or less is 95% by weight, the purity is 99.99% (Table 1 shows the analysis of impurities) and 20g of alumina and ash having an average particle diameter of 0.52 microns is 0.08% by weight and average A 10 g carbon black block having a particle diameter of 0.45 microns is mixed uniformly in a ball mill consisting of a nylon pot and a nylon coating ball using ethanol as the dispersion medium.

The resulting mixture is dried and placed in a flat tray made of high purity graphite and heated for 6 hours at 1600 ° C. in an electric furnace while continuing to supply nitrogen gas at a rate of 3 l / min to the furnace. The reaction mixture obtained is heated at 750 ° C. for 4 hours in air to remove unreacted carbon by oxidation.

X-ray diffraction analysis of the resulting white powder shows single phase AIN without diffraction peaks of alumina. The resulting powder has an average particle diameter of 1.31 microns and a proportion of particles having a particle diameter of 3 microns or less is 90% by volume. Observation with a precision electron microscope reveals that the powder consists of uniform particles with an average particle diameter of 0.7 microns. The specific surface area of this powder is 4.0 m <2> / g.

The analytical value of this powder is shown in Table 2.

TABLE 1

Analysis value of Al ₂ O ₃ powder

Al ₂ O ₃ content: 99.99%

Element Content (ppm) Element Content (ppm)

Mg <5 Fe 22

Cr <10 Cu <5

Si 30 Ca <20

Zn <5 Ni 15

Ti <5

Table 2: Analytical Value of AIN Powder

AIN content: 97.8%

Element content element content

Mg <5 (ppm) Ti <5 (")

Cr 21 (") Co <5 (")

Si 125 (") Al 64.8 (wt%)

Zn 9 (") N 33.4 (")

Fe 0 (") O 1.1 (")

Cu <5 (") C 0.11 (")

Mu 5 (")

Ni 27 (")

Example 2

The aluminum nitride powder (1.0 g) obtained in the same manner as in Example 1 was placed in a 20 mm diameter BN-coated graphite die and subjected to a high vibration induction furnace at 2000 ° C. under a pressure of 100 kg / cm 2 in 1 atmosphere of nitrogen gas for 2 hours. During high temperature compression.

The resulting sintered body is light yellow, dense and translucent. The density of this sintered compact is 3.26 g / cm <3>. X-ray diffraction analysis shows single phase AIN. The analytical value of the sintered compact is shown in Table 3. This sintered compact has a thermal conductivity of 75 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the light transmittance for light having a wavelength of 6 μm was 16% (absorption coefficient μ = 34 cm ⁻¹ ).

Under the above conditions, a disk having a diameter of 40 mm and a thickness of about 3 mm obtained by high temperature compression is cut into a rectangular bar shape having a size of 3.8 x 3 x 35 mm. The three-point bending strength of this sample is measured at a piston rod speed of 0.5 mm / min and a 30 mm interval at a temperature of 1200 ° C. The average measurement is 41.5 kg / mm 2.

TABLE 3

Analytical Value of Sintered AIN

AIN content: 98.1%

Element content element content

Mg <5 (ppm) Ni 30 (")

Cr 15 (") Ti <5 (")

Si 110 (") Co <5 (")

Zn 16 (") Al 65.0 (wt%)

Fe 18 (") N 33.5 (")

Cu <5 (") O 0.6 (")

Mn 5 (") C 0.13 (")

Example 3

Aluminum nitride powder (10 g) obtained in the same manner as in Example 1 was mixed with 0.2% by weight of Ca (NO ₃ ) ₂ 4H ₂ O as CaO using ethanol as a liquid medium in polyethylene mortar using a rod made of polyethylene do. The mixture is dried and hot pressed under the same conditions as in Example 2 to form a sintered body having a diameter of 20 mm. This sintered compact has a density of 3.28 g / cm 3 and is found to be single-phase AIN by X-ray diffraction analysis. This sintered body had an AIN content of 97.8% by weight, an oxygen content of 0.7% by weight and a thermal conductivity of 79 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the light transmittance to light having a wavelength of 6 μm was 33% (absorption coefficient μ = 19 cm ⁻¹ ).

The mixed AIN powder was sintered in the same manner as in Example 2, and its three-point bending strength was measured. Average 45.1 kg / mm 2 at 1200 ° C.

Example 4

Aluminum nitride powder (10 g) obtained in the same manner as in Example 1 was mixed with various additives described in Table 4. The resulting mixtures were hot pressed in the same manner as in Example 3 to obtain sintered bodies.

The results are shown in Table 4.

TABLE 4

Example 5

About 1 g of aluminum nitride powder obtained in the same manner as in Example 1 was uniaxially compressed in a die having a diameter of 20 mm and subjected to dynamic pressure compression under 1000 kg / cm 2 collapse to prepare a molded article having a density of 1.56 g / cm 3. The molded article is placed in a boron nitride crucible and heated in a high-frequency induction furnace using a smoking heat controller for 3 hours at 1900 ° C. in one atmosphere of nitrogen gas. The sintered body obtained by pressureless sintering is off white and has a density of 2.93 g / cm 3. X-ray diffraction analysis shows single phase AIN. Analysis of the sintered body has an AIN content of 98.3% by weight and an oxygen content of 0.4% by weight.

The thermal conductivity is 48 W / m-k.

Example 6

10 g of aluminum nitride powder obtained by the same method as in Example 1 is uniformly mixed with ethanol as a dispersion medium with 3.0 wt% of Ca (NO ₃ ) ₂ 4H ₂ O as CaO. The mixture is dried and molded and sintered in the same manner as in Example 5. Before sintering, the density of the molded article is 1.73 g / cm 3. The sintered compact was yellow translucent body and had a density of 3.23 g / cm 3. The sintered body had an AIN content of 96.0 weight%, an oxygen content of 1.5 weight% and a thermal conductivity of 64 W / mk. The light transmittance for light having a wavelength of 6 μm when cut to 0.5 mm thickness is 28% (μ = 23 cm ⁻¹ ).

Example 7

10 g of aluminum nitride powder obtained by the same method as in Example 1 was mixed with the various additives shown in Table 5 in the same manner as in Example 6. The mixture was pressureless sintered in the same apparatus under the same sintering conditions as in Example 5.

The results are shown in Table 5.

TABLE 5

Example 8

Alumina (20 g) and carbon (8 g) as used in Example 1 are uniformly mixed in water as a dispersion medium in a ball mill consisting of nylon lots and balls. The mixture is dried and placed in a flat tray made of high purity graphite, and heated at 1550 ° C. for 6 hours in the furnace while continuously supplying nitrogen gas to the furnace at a rate of 3 l / min. The reaction mixture is heated at 800 ° C. in air for 4 hours to remove unreacted carbon. The resulting powder has an AIN content of 95.8% by weight and an oxygen content of 2.1% by weight. The amount of cationic impurities in the AIN powder is about the same as shown in Table 2 of Example 1. The resulting powder has an average particle diameter of 1.22 microns and contains 92 volume% of particles having a particle diameter of 3 microns or less.

Example 9

1 g of AIN powder obtained by the same method as in Example 8 is hot pressed in the same apparatus under the same conditions as used in Example 2. The resulting sintered body is light yellow semipermeable and has a density of 3.25 g / cm 3, an AIN content of 96.8 weight% and an oxygen content of 1.3 weight%. The sintered body has a thermal conductivity of 52 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the light transmittance for light having a wavelength of 6 μm was 11% (μ−41 cm ⁻¹ ). When the bending strength of the sintered compact was measured on the conditions same as Example 2, it is an average of 35.5 kg / mm <2> at 1200 degreeC.

Example 10

10 g of AIN powder obtained in the same manner as in Example 8 are mixed with 0.5% by weight of Y (NO ₃ ) .6H ₂ O as Y ₂ O ₃ in ethanol as a liquid medium. The mixture (1 g) is dried and hot pressed for 2 hours at 1400 ° C. and 200 kg / cm 2 in vacuo using the same apparatus as used in Example 2. The resulting sintered body is translucent and has a density of 3.27 g / cm 3, an AIN content of 96.5 weight%, an oxygen content of 1.5 weight% and a thermal conductivity of 56 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the light transmittance having a 6 μm wavelength was 20% (μ = 29 cm ⁻¹ )

Example 11

10 g of the AIN powder obtained in the same manner as in Example 8 was uniformly mixed with 4.0% by weight of Ca (NO ₃ ) ₂ 4H ₂ O as CaO in ethanol as a liquid dispersion medium. The mixture (1 g) is dried and pressureless sintered under the same conditions in the same apparatus as used in Example 5. The resulting sintered body was yellow translucent and had a density of 3.20 g / cm 3, an AIN content of 94.2 wt%, an oxygen content of 2.5 wt% and a thermal conductivity of 42 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the permeability to light having a wavelength of 6 μm was 10% (μ = 43 cm ⁻¹ ).

Example 12

20 g of alumina having a purity of 99.3% and an average particle diameter of 0.58 microns and 16 g of carbon black having a content of 0.15% by weight and an average particle diameter of 0.44 microns are uniformly mixed in hexane as a dispersion medium using a nylon pot and a ball. The mixture is dried and placed in a flat tray made of high purity graphite and heated for 6 hours in a furnace at 1650 ° C. with a continuous supply of ammonia gas to the furnace at a rate of 1 l / min. The resulting reaction mixture is heated in 750 ° C. for 6 hours to oxidize unreacted carbon. The resulting powder has an average particle diameter of 1.42 microns and the proportion of particles having a particle diameter of 3 microns or less is 84% by volume.

The results of analyzing the powders are shown in Table 6.

TABLE 6

Analytical Value of AIN Powder

AIN content: 96.9% by weight

Element content element content

Mg 48 (ppm) Ni 120 (ppm)

Cr 110 (ppm) Ti 25 (ppm)

Si 2500 (ppm) Co 5 (ppm)

Zn 20 (ppm) Al 64.9 (% by weight)

Fe 370 (ppm) N 33.1 (wt%)

Cu <5 (ppm) O 1.3 (% by weight)

Mn 40 (ppm) C 0.13 (% by weight)

Example 13

1 g of the AIN powder obtained in the same manner as in Example 12 is subjected to high temperature compression under the same sintering conditions and apparatus as in Example 2. The resulting sintered body is gray translucent and has a density of 3.16 g / cm 3, an AIN content of 97.9 weight%, an oxygen content of 0.8 weight% and a thermal conductivity of 50 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the light transmittance to light having a wavelength of 6 μm was 6% (μ = 53 cm ⁻¹ ).

Example 14

10 g of the AIN powder obtained in the same manner as in Example 12 is uniformly mixed with 0.2% by weight of Ba (NO ₃ ) ₂ as BaO in ethanol as a liquid medium. The mixed powder (1 g) is dried and compressed under high pressure under the same sintering conditions and apparatus as in Example 2. The resulting sintered body is gray translucent and has a density of 3.27 g / cm 3, an AIN content of 97.9 weight%, an oxygen content of 0.9 weight% and a thermal conductivity of 55 W / mk. When cut to 0.5 mm thickness, the light transmittance for light with a 6 μm wavelength is 8% (μ = 48 cm ⁻¹ ).

Example 15

Alumina (130g, purity 99.99% by weight) and carbon black (65g, 0.08% by weight) and 1.0 g of calcium carbonate having an average particle diameter of 3 microns were coated with pot and polyurethane resin as in Example 1. In a ball mill constructed, it is mixed uniformly in ethanol as a dispersion medium. The mixture is dried, reacted and oxidized under the same conditions as in Example 1 to prepare AIN powder. The resulting powder has an average particle diameter of 1.44 microns and contains 86 volume% of particles having a particle diameter of 3 microns or less. The analytical value of the powder is shown in Table 7.

TABLE 7

Analytical Value of AIN Powder

AIN content: 96.9% by weight

Element content element content

Ca 920 (ppm) Ni 27 (ppm)

Mg <5 (ppm) Ti <5 (ppm)

Cr 170 (ppm) Co <5 (ppm)

Si 86 (ppm) Al 63.0 (wt%)

Zn 12 (ppm) N 33.1 (% by weight)

Fe 25 (ppm) O 1.5 (% by weight)

Cu <5 (ppm) C 0.15 (% by weight)

Mn 4 (ppm)

Example 16

1 g of the AIN powder obtained by the same method as in Example 15 is subjected to high temperature compression under the same conditions as in Example 2 and in the same apparatus. The resulting sintered compact is dense and translucent and has a density of 3.2 g / cm 3, an AIN content of 98.1%, an oxygen content of 0.7% and a thermal conductivity of 60 W / mk. When the sintered body was cut to a thickness of 0.5 mm, the light transmittance of light to light having a wavelength of 6 μm was 28% (μ = 23 cm ⁻¹ ).

Example 17

Alumina (130g: purity 99.99% by weight) and carbon black (65g: 0.08% by weight) as used in Example 1 were prepared in ethanol as a dispersion medium in a ball mill consisting of balls coated with pot and polyurethane resin. Mix uniformly with 0.52 g of Y ₂ O _{3 with an} average particle diameter of 1 micron. The mixture is dried, reacted and oxidized under the same conditions as in Example 1 to obtain AIN powder. This powder has an average particle diameter of 1.50 microns and contains 83 volume% of particles having a particle diameter of 3 microns or less. The analytical value of this powder is shown in Table 8.

TABLE 8

Analytical Value of AIN Powder

AIN content: 96.9%

Element content element content

Y 3360 (ppm) Ni 7 (ppm)

Mg 6 (ppm) Ti 10 (ppm)

Cr 11 (ppm) Co <5 (ppm)

Si 123 (ppm) Al 64.9 (wt%)

Zn 16 (ppm) N 33.1 (% by weight)

Fe 36 (ppm) O 1.5 (% by weight)

Cu 16 (ppm) C 0.18 (% by weight)

Mn 5 (ppm)

Example 18

1 g of AIN powder obtained in the same manner as in Example 17 was hot pressed under the same conditions in the same apparatus as used in Example 2. The resulting sintered body exhibits a density of 3.28 g / cm 3, a density of 98.1 weight%, an AIN content of 98.1 weight%, an oxygen content of 0.8 weight% and a thermal conductivity of 63 W / mk. When cut to 0.5 mm thick, the transmission for light with a wavelength of 6 μm is 30% (μ = 21 cm ⁻¹ ).

Comparative Example 1

Alumina (100g: purity 99.99% by weight) and carbon black (100g: 0.08% by weight), as used in Example 1, were mixed dry in a ball mill consisting of balls and pots coated with polyurethane resin do. The mixture is reacted and oxidized under the same conditions as in Example 1 to obtain AIN powder. The resulting powder is white in color with an average particle diameter of 1.8 microns and a proportion of particles having a particle diameter of 3 microns or less is 62% by volume. The analytical value of this powder is shown in Table 9.

The powder is hot pressed in the same apparatus as used in Example 2 and under the same sintering conditions. The sintered body is off-white opaque, has a density of 3.12 g / cm 3 and a thermal conductivity of 28 W / m-k. The 3-point bending strength of the sintered compact averaged 20.3 kg / mm 2 at 1200 ° C.

TABLE 9

Analytical Value of AIN Powder

AIN content: 92.0% by weight

Element content element content

Mg 8 (ppm) Mn 5 (ppm)

Cr 15 (ppm) Ni 12 (ppm)

Si 110 (ppm) Til 10 (ppm)

Zn 10 (ppm) Co <5 (ppm)

Fe 40 (ppm) Al 64.4 (wt%)

Cu 15 (ppm) N 31.4 (% by weight)

O 3.8 (% by weight)

C 0.16 (% by weight)

Comparative Example 2

20 g of alumina having a purity of 99.6 wt% and an average particle diameter of 3.6 microns and 10 g of carbon black 10 having a recontent of 0.08 wt% were prepared using ethanol as a dispersion medium in a ball mill consisting of balls and pots coated with nylon. Mix. The mixture is reacted and oxidized to the same conditions in the same apparatus as in Example 1. The resulting powder is white in color, has an AIN content of 96.1% by weight, an oxygen content of 1.9% by weight and an average particle diameter of 3.9 microns, and the proportion of particles having a particle diameter of 3 microns or less is 33% by volume.

The powders are hot pressed in the same apparatus as in Example 2 and in the same sintering conditions. The resulting sintered body is a gray opaque body with a density of 2.98 g / cm 3 and a 3-point bending strength of 24.5 kg / mm 2 on average at 1200 ° C.

Comparative Example 3

Comparative Example 2 and the AIN powder 10g obtained in the same way as CaO in ethanol as the liquid medium of 0.2% by weight Ca (NO ₃₎ is mixed with ₂ .4H ₂ O. The mixed powder (1 g) is dried and subjected to high temperature compression in the same apparatus and under the same conditions as used in Example 2. The sintered body is a gray opaque body, has a density of 3,11 g / cm 3, a thermal conductivity of 35 W / mk and an average 3-point bending strength of 25.6 kg / mm 2 at 1200 ° C.

[Comparative Example 4]

In a ball mill consisting of 20 g of alumina having a purity of 98.5 wt% and an average particle diameter of 1.0 micron and 16 g of carbon black having a recontent of 0.15 wt% and an average particle diameter of 0.44 micron, a pot made of nylon and a nylon coating ball Mix uniformly with ethanol. The mixture was reacted and oxidized under the same conditions as in Example 1 to obtain AIN powder. The resulting powder is off-white and has an average particle diameter of 1.8 microns and the proportion of particles having a particle diameter of 3 microns or less is 75% by volume. The analytical value of the powder is shown in Table 10.

1 g of this powder is hot pressed in the same apparatus and in the same sintering conditions as used in Example 2. The resulting sintered body was an grey-black opaque body, having a density of 3.22 g / cm 3, a thermal conductivity of 33 W / m-k, and an average 3-point bending strength of 27.4 kg / mm 2 at 1200 ° C.

TABLE 10

Analytical Value of AIN Powder

AIN content: 96.4%

Element content element content

Mg 130 (ppm) Ni 310 (ppm)

Cr 260 (ppm) Ti 180 (ppm)

Si 3600 (ppm) Co 60 (ppm)

Zr 50 (ppm) Al 64.6 (wt%)

Fe 2100 (ppm) N 32.9 (wt%)

Cu 10 (ppm) O 1.8 (% by weight)

Mn 50 (ppm) C 0.13 (% by weight)

Example 19

Example 1 and as CaO in the aluminum nitride powder obtained in the same way 10g of 3% by weight Ca (NO ₃₎ and is a ₂ .4H ₂ O. These are mixed and sintered in the same manner as in Example 3. The resulting sintered body had a density of 3.27 g / cm 3, an AIN content of 97.5 weight% and an oxygen content of 1.2 weight%.

A 2 mm-thick sample of the sintered body was produced and thermal conductivity was measured in the same manner as in the above example. In particular, colloidal carbon is spray coated on both surfaces of the sintered body sample and irradiated with a ruby laser. It has a thermal conductivity of 72 W / m-k when measured by the so-called contact method, which measures the rise of the temperature of the back surface of the sample by the thermocouple in close contact with the back surface by silver paste. When a thin film of gold was vacuum deposited on the laser irradiated surface of the sample to prevent the transmission of the laser beam, and the back surface temperature rise of the sample was measured by a so-called non-contact method using an indium antimony detector, its thermal conductivity is 91 W / mk. .

On the other hand, the sintered compact is wound to a thickness of 0.5 mm to prepare a sample. This sample has a linear transmission of 35% for light with a 6 μm wavelength (μ = 18 cm ⁻¹ ). The total light transmission for light with a wavelength of 1 μm is 73% measured using a 60 mm diameter integrating sphere.

The micrograph of the cracked surface of a sintered compact is shown in FIG.

The cracked surface is etched by treatment with 50% aqueous phosphate solution for 30 minutes at a temperature of 62.5 ± 2.5 ° C.

A micrograph of the etched surface is shown in FIG.

Example 20

Example 1 and a method as CaO in the aluminum nitride powder, 10g of 2% by weight Ca (NO ₃₎ obtained in the same and are the ₂ .4H ₂ O. These are mixed well and sintered in the same manner as in Example 6. The characteristic of the produced aluminum nitride sintered compact is shown below. The micrograph of the crack surface of the produced aluminum nitride sintered compact is shown in Table 5.

Density 3.24g / cm3

AIN content 97.0% by weight

O ₂ content 1.3% by weight

Thermal conductivity 73W / m-k (contact method)

95W / m-k (non-contact method)

33% of light transmittance (μ = 19cm ^-1 ) (linear)

68% (total)

Example 21

As CaO but using 0.5% of _{Ca (NO 3) 2 .4H 2} O , and repeats the second embodiment. The resulting aluminum nitride sintered body has the following characteristics.

A micrograph of the cracked surface of the resulting aluminum nitride sintered body is shown in FIG. A micrograph of the cracked surface after treatment with 50% aqueous phosphate solution at 62.5 ± 2.5 ° C. for 30 minutes is shown in FIG.

Density 3.22 g / cm 3

AIN content 97.3% by weight

O ₂ content 1.0% by weight

Thermal conductivity 75W / m-k (contact method)

98W / m-k (non-contact method)

31% of light transmittance (μ = 21cm ^-1 ) (linear)

65% (total)

Claims (12)

An aluminum nitride fine powder having an average particle diameter of 2 microns or less and containing not less than 94% by weight of aluminum nitride, not more than 3% by weight of bound oxygen, and not more than 0.5% by weight (calculated as metal) of the metal compound. The fine powder of aluminum nitride according to claim 1, wherein the content of bound oxygen is 1.5% by weight or less. The fine powder of aluminum nitride according to claim 1, wherein the content of the metal compound as an impurity is 0.3% by weight or less (calculated as a metal). The fine aluminum nitride powder according to claim 1, wherein the metal of the metal compound is carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc, or titanium. The fine powder of aluminum nitride according to claim 1, wherein the metal of the metal compound is iron, chromium, nickel, cobalt, copper, zinc or titanium and the total content of these metal compounds is 0.1% by weight or less (calculated as metal). The fine powder of aluminum nitride according to claim 1, wherein the content of aluminum nitride is 97% by weight or more. The fine powder of aluminum nitride according to claim 1, which contains 70% by volume or more of particles having a particle diameter of 3 microns or less. The fine aluminum nitride powder according to claim 1, which is composed of spherical particles having a mean particle diameter of 2 microns or less, or secondary nodules thereof. (1) A weight ratio of fine alumina powder to carbon fine powder in a liquid dispersion medium containing carbon fine powder having a mean content of 0.2% or less and an average particle diameter of 1 micron or less in alumina fine powder having an average particle diameter of 2 microns or less is 1: 0.36. To 1: 1, evenly mixed, (2) optionally prepared mixture is dried and then burned at a temperature of 1,400 to 1,700 ℃ under nitrogen or ammonia atmosphere, and (3) 600 to 900 ℃ the fine powder prepared A metal compound as an impurity of not less than 94% by weight of aluminum nitride, not more than 3% by weight of bound oxygen and no more than 0.5% by weight (calculated as metal) by heating at a temperature of A method for producing an aluminum nitride fine powder, characterized in that to prepare a fine powder of aluminum nitride containing. 10. The method of claim 9, wherein the fine alumina powder has a purity of at least 99.0% by weight. 10. The process according to claim 9, wherein the weight ratio of fine alumina powder to fine carbon powder is 1: 0.4 to 1: 1. 10. The process of claim 9 wherein the liquid dispersion medium is water, hydrocarbons, aliphatic alcohols or mixtures thereof.

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