NL8400796A - FINE ALUMINUM NITRIDE POWDER, A COMPOSITION AND SINTERED ARTICLE THEREOF, AND METHODS FOR ITS FORMATION. - Google Patents

Description

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Fine aluminum nitride powder, a composition and sintered article thereof, as well as methods for their formation.

This invention relates to a fine powder of high purity aluminum nitride, a composition and a sintered article thereof, as well as methods for forming it.

Sintered aluminum nitride has always attracted attention as. a high-temperature material with excellent properties, such as high thermal conductivity, corrosion resistance and strength. Aluminum nitride powders for sintered aluminum nitride, depending on their production methods, inevitably include various impurities, making it insufficiently sinterable and difficult to obtain compact, sintered articles of high purity possessing the inherent excellent properties of aluminum nitride.

The following two methods have already been used for the preparation of aluminum nitride powders.

The first method is called the direct nitride-forming method-15 and involves nitriding high temperature metallic aluminum powder in a nitrogen atmosphere or ammonia gas and pulverizing the resulting nitride.

The second method is called the alumina reduction method and involves burning alumina and carbon powder in nitrogen or ammonia gas, after which the resulting nitride is pulverized.

Since metallic aluminum is used as the starting material in the first direct nitride forming method, the metallic aluminum must of course be pulverized in order to improve the nitride formation rate. To increase the sinterability of the resulting nitride, it is further necessary to pulverize the nitride to a particle size smaller than several micrometers. Thus, in the direct nitride formation method, it can be said that it is impossible to avoid the inclusion of metals or metal compounds as impurities from a grinding mill, such as a ball mill, used in pulverization. Furthermore, since the direct nitride formation method gives aluminum nitride powder, which inevitably contains unreacted metallic aluminum as an impurity, it is particularly difficult to produce aluminum nitride, which contains less than several percent by weight impurities, including those entering. at the pulverization steps. In the pulverizing step of the direct nitride-forming method, it is difficult to obtain an aluminum nitride powder with a sufficiently small and uniform particle size, while, moreover, due to the inevitable oxidation of the surface of the aluminum nitride powder, the aluminum nitride powder obtained by the direct nitride-forming method is usually 2 -5 wt% or even more oxygen.

The second alumina reduction method is generally considered to be better than the direct nitride formation method, since aluminum nitride powder having a relatively uniform particle size is obtained. However, to obtain a size smaller than several micrometers, a pulverization step must be used.

Furthermore, the content of unreacted alumina cannot be reduced to a very low value. As with the direct nitride formation method, therefore, the second method also has the disadvantage that an aluminum nitride powder of low purity is obtained. Aluminum nitride powders produced by these methods do not have sufficient purity and generally take on a black to gray color. Sintered articles obtained from these powders therefore have no light-transmitting properties.

It is an object of this invention to provide a fine powder of aluminum nitride of high purity.

It is another object of this invention to provide a high purity aluminum nitride fine powder composed of very fine particles having an average particle diameter of not more than 2 microns and having a very low impurity content. such as metallic compounds and a very low content of bound oxygen.

It is yet another object of the invention to provide a high purity fine aluminum nitride powder which is excellent for sintering and provides a high purity, high density sintered aluminum nitride article.

It is yet another object of this invention to provide an industrially advantageous process for producing high purity aluminum nitride.

It is a further object of the invention to provide

Si Λ Λ Λ “ï VV i 3 υ 3 in a process for producing a fine powder of aluminum nitride of high purity by the so-called alumina reduction method / but obtaining a fine powder of aluminum nitride with an average particle diameter, which does not exceed 2 micrometers without having to subject the nitride obtained to a pulverization step.

A further subject of this invention is to provide a compact aluminum nitride composition which is very strong. pure aluminum nitride of this invention as well as a sintering aid and a process for its production.

It is a further object of this invention to provide a high purity, high density sintered aluminum nitride article.

It is a further object of this invention to provide a high purity, high density sintered aluminum nitride article having very low levels of metal compounds such as impurity and bound oxygen, the density of which is at least 90% of theoretical value.

It is another object of the invention to provide a high purity, high density sintered aluminum nitride article having translucent properties.

It is yet a further object of this invention to provide a method for producing a sintered article of very high purity and high density aluminum nitride from the high purity fine aluminum nitride powder of the invention or the aluminum nitride composition of the invention.

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

According to this invention, said objects and advantages are achieved by means of a fine powder of aluminum nitride, which has an average particle diameter of not more than 2 micrometers and which contains at least 94 wt.% Aluminum nitride (AlNj, at most 3 wt.% Bound oxygen and at most 0.5% metal or metal compounds as impurities.

35 The fine powder of aluminum nitride with the average particle diameter of not more than 2 micrometers according to this invention 8400796 4

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it exists in the form of spherical particles or secondary agglomerates thereof.

Fig. 1 shows the dependence of the air permeability of the sintered body of the invention on the wavelength of the light.

Pig. 2 is a photograph of an example of the sintered body according to the invention.

Fig. 3 is a scanning electron micrograph of the mechanically broken surface of an example of a hot press sintered body of the invention.

Fig. 4 is a scanning electron micrograph of the mechanically broken surface of the same hot-press sintered body of the invention of FIG. 3 taken after the broken surface was treated with an aqueous solution of phosphoric acid. FIG. 5 is a scanning electron micrograph of a mechanically broken surface of an example of the pressureless sintered body of the invention.

Fig. 6 is a scanning electron micrograph of a mechanically broken surface of another example of the pressureless sintered body of the invention.

Fig. 7 is a scanning electron micrograph of the mechanically broken surface of the same pressureless sintered body of the invention of FIG. 6 taken after the broken surface was treated with the aqueous solution of phosphoric acid.

According to this invention, the fine aluminum nitride powder can be prepared by a method comprising: (1) thoroughly mixing a fine alumina powder having an average particle diameter of no greater than 2 microns with a fine carbon powder having an ash content of at most 0 2% and an average particle diameter of no greater than 1 micron in a liquid dispersion medium, the weight ratio of the fine alumina powder to the fine carbon powder being 1: 0.36-1: 1; (2) burning the obtained thorough mixture at a temperature of 1400-1700 ° C in an atmosphere of nitrogen or ammonia after optionally drying thereof and (3) subsequently heating the obtained fine powder to a temperature of 600 - 900 ° C to remove the non-converted 7 0 ^ 5 *? v O / 5 y Λ * 5 carbon, forming a fine aluminum nitride powder with an average particle diameter of no greater than 2 microns, containing at least 94% by weight aluminum nitride, at most 3% by weight of bound oxygen and at most 0, 5% by weight, calculated as metal, contains metal compounds as impurities.

According to the above method, an aluminum nitride pulverization step obtained by burning the starting material can be avoided. Thus, no impurities are incorporated into the obtained aluminum nitride via the pulverizing step, while it is also possible to avoid oxidation of the surface of aluminum nitride which occurs in the known pulverizing. Thus, the advantage of being able to omit the aluminum nitride pulverization step is unexpectedly great. For the omission of the pulverization step and for obtaining aluminum nitride with good properties it is important to use the so-called wet mixing method, wherein the mixing of the alumina powder and the carbon powder in the aforementioned stage (1) in a liquid dispersion medium is carried out. According to the wet mixing method, not only can the materials be thoroughly mixed, but surprisingly the tendency of the finely divided starting materials to agglomeration and lump formation can be avoided. Burning of the obtained thorough mixture results in aluminum nitride particles of fine uniform size. Also, according to the method of the invention, the inclusion of impurities in the pulverizing step, etc., can be completely avoided, while also the oxidation of the aluminum nitride surface can be avoided, so that a fine aluminum nitride powder is obtained with better sintering capacity than with conventional sintering power. methods; this gives a sintered object with high purity and translucent properties. The liquid dispersion medium used in the wet mixing step is not particularly critical and any known wet mixing medium can be used. In general, water, hydrocarbons, aliphatic alcohols and mixtures thereof are used for industrial applications. The hydrocarbons include, e.g. ligroin, petroleum ether, hexane, benzene and toluene, while the aliphatic alcohols, e.g. methanol, ethanol and isopropanol.

The above wet mixing is preferably performed in a device made of a material which is not in-Q Λ Λ 'T Λ £

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* »6 Closure of impurities in the burned aluminum nitride.

Generally, the wet mixing can be performed at room temperature and at atmospheric pressure and is not adversely affected by the temperature and pressure. Known mixers can be used as long as they do not form impurities which remain in the product after burning. Generally, a mill containing spherical or rod-like materials is used as a mixer.

The interior wall of the mill and the spherical or rod-shaped materials are made of aluminum nitride itself or of a high purity alumina with a purity of at least 99.9 wt%, to absorb impurities remaining in the burned aluminum nitride , to avoid. The surface of the mixer, which comes into contact with the starting materials, can be made of or coated with plastic. The plastics used for this purpose are not particularly critical, and one can e.g. use polyethylene, polypropylene, polyamides, polyesters and polyurethane. Since various metallic stabilizers are used in plastics, these must be checked beforehand. Furthermore, in order to avoid the pulverizing stage and obtain a highly pure fine powder of aluminum nitride having an average particle size of not more than 2 micrometers and good sintering power, use alumina and carbon with specified properties. The fine alumina powder used must have an average particle diameter of no greater than 2 micrometers and a purity of at least 99.0 wt%, preferably at least 99.8 wt%. The fine carbon powder must have an ash content of at most 0.2% by weight, preferably 0.1% by weight. Since the average particle diameter of the carbon affects the particle diameter of the aluminum nitride obtained, the carbon should be a fine micro-sized powder, i.e., having an average particle diameter of no greater than 1 micron. Carbon black and graphitized carbon can be used, but carbon black is generally preferred.

Since the ratio of alumina and carbon depends on the purity, particle size, etc. of the alumina and the carbon, it should preferably be determined by preliminary tests. Usually, alumina and carbon are mixed wet in a weight ratio of 1: 0.36-1: 1, preferably 1: 0.4-1: 1. The mixture is dried if necessary and fired at a temperature of 1400 -1700 ° C in a nitrogen atmosphere, if necessary. When the burning temperature is below the above-stated limit, the reductive nitride formation reaction does not proceed satisfactorily industrially. If the firing temperature is above the specified upper limit, the aluminum nitride obtained is partially sintered to form agglomerated particles. Thus, it is difficult to obtain aluminum nitride with the desired particle diameter.

According to the invention, the fine particles of aluminum nitride obtained by burning are heated in an oxygen-containing atmosphere to a temperature of 600-900 ° C to oxidize and remove the unreacted carbon. Thus, the invention provides a fine powder of high purity aluminum nitride having an aluminum nitride content of at least 94%, a bound oxygen content of up to 3% by weight and an impurity content of up to 0.5% by weight (as metal).

The high purity fine aluminum nitride powder of this invention has an aluminum nitride content of at least 94%. A preferred powder with at least 97 wt% aluminum nitride gives a sintered article with particularly good light transmission properties.

The fine aluminum nitride powder of the invention has a bound oxygen content of up to 3% by weight and an impurity content of up to 0.5% by weight (as metal). Bound oxygen is believed to be present in a form bound to metals, included as impurities or in the form of aluminum oxide.

The bound oxygen content and the impurity content have a great influence on the sintering capacity of aluminum nitride and the light transmission properties of the obtained sintered article. The bound oxygen content is preferably at most 1.5 wt% and the impurity content is at most 0.3 wt% (as metal).

etal compounds as impurities may come from impurities present in the alumina and carbon as starting materials in the production of aluminum nitride or from solvents, mixers, pipeline, etc., during the preparation. They are compounds of carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc and titanium.

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Preferably, the metal of such metal compounds in the fine aluminum nitride powder is at most 0.1% by weight (as metal). Among these impurities, the unreacted alumina and carbon as well as aluminum oxide formed by oxidation of the surface of aluminum nitride do not have a particularly bad effect on the properties of the aluminum nitride of this invention. The inclusion of cationic impurities such as alumina, carbon and silica in an amount of about 0.3-0.5 wt% has e.g. does not adversely affect the sintering power of aluminum nitride at atmospheric pressure. However, since iron, chromium, nickel, cobalt, copper, and titanium as impurities adversely affect the light transmission properties of the sintered aluminum nitride article, the entrapment of these components should be minimized as much as possible. In order to impart sufficient light transmission properties to the sintered aluminum nitride, the fine aluminum nitride powder of the invention should preferably contain less than 0.1% by weight in total iron, chromium, nickel, cobalt, copper and titanium.

The fine aluminum nitride powder of this invention has an average particle diameter no greater than 2 microns. If the average diameter is greater than this upper limit, the sintering power deteriorates considerably. The fine aluminum nitride powder preferably has an average particle diameter of no greater than 2 microns and contains at least 70% by volume of particles with a particle diameter no greater than 3 microns.

The aluminum nitride of this invention is, as mentioned above, very pure and the bound oxygen content is preferably at most 1.5% by weight. It had previously been believed that a fine aluminum nitride powder with a bound oxygen content of less than 2 wt% does not have sufficient sintering power and that to achieve this a bound oxygen content of at least 2 wt% was necessary. In view of this prior art, it is particularly surprising that the high density fine aluminum nitride powder has excellent sintering ability.

According to the present invention, a high-purity, high-density aluminum nitride sintered article can be obtained from the high-purity fine aluminum nitride powder. The sintered 8400795 9 article can be made by forming the fine aluminum nitride powder of this invention, sintering the formed article at an temperature of 1700 - 2100 ° C in an inert atmosphere to a sintered aluminum nitride article having a density of at least 5 2.9 g / cm3 containing at least 94 wt% aluminum nitride, at most 1.5 wt% bound oxygen and at most 0.5 wt% metal compounds as impurities.

Furthermore, according to this invention, the sintered aluminum nitride article of high density and high purity can also be obtained by performing the sintering step in the above method in the presence of a sintering aid. Such a method can be performed by a fine powder of aluminum nitride containing at least 90 wt% aluminum nitride, at most 4.5 wt% bound oxygen, 0.02-5.0 wt%, as an oxide having the highest atomic valency, of at least one metal element selected from alkali metals, lanthanum group metals and yttrium or a compound thereof and up to 0.5% by weight, as metal, of metallic compounds as impurities other than compounds of the above metals, the sintering the resultant molded article at a temperature of 1600 DEG-2100 DEG C. in an inert atmosphere, thereby forming a sintered aluminum nitride article having an aluminum nitride content of at least 90 wt%, a bound oxygen content of at most 3.5 wt .% and a density of at least 3.0 g / cm3, which is 0.02-5.0 wt% as the oxide having the highest atomic valence of 0.02-5.0 wt% of at least one metal selected 2 5 from alkaline earth metals, lanthanum group metals e n yttrium or a compound thereof and contains not more than 0.5% by weight - as metal of a metallic compound as impurities other than compounds of the above metals.

In the above two methods of manufacturing the high purity, high density aluminum nitride sintered article of this invention, the sintering is performed by heating the resulting molded blank at a high temperature in an inert atmosphere. In either of these methods, the sintering can be either a hot press sintering or a pressureless sintering. In hot sintering, the strength of a printing form forms a boundary pressure, and pressures of no greater than 350 kg / cm 2 are usually selected.

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Pressures of at least 20 kg / cm *, preferably 50-300 kg / cm2, are used in industry. Pressureless sintering is performed virtually in the absence of pressure without applying mechanical pressure to the formed article. When performing pressureless sintering, the raw molded article is manufactured at a pressure of at least 200 kg / cm2, preferably 500-2000 kg / cm2. Sintering is carried out in an inert atmosphere, in particular a non-oxidizing atmosphere, for example in a nitrogen atmosphere.

The sintering temperature is 1700-2100 ° C, preferably 1800-2000 ° C, in the first method where no sintering aid is used. In the second method using a sintering aid, the sintering is carried out at a lower temperature, in particular 1500 - 2100 ° C, preferably 1650 - 2000 ° C.

Thus, according to this invention, there is provided a sintered article of high purity, high density aluminum nitride having an impurity content of up to 0.5 wt%, as metal and a density of at least 3.0 g / cm2 (about 92 % of the theoretical value).

Thus, the high purity, high density aluminum nitride sintered article provided by this invention is first a fine powder of aluminum nitride having a density of at least 2.9 g / cm3, preferably at least .3, 0 g / cm3 (corresponding to about 92% of the theoretical value), most preferably at least 3.16 g / cm3 (corresponding to about 97% of the theoretical value), which is at least 94 wt%, at preferably at least 97 wt% aluminum nitride, at most 1.5 wt%, preferably at most 0.75 wt% bound oxygen and at most -0.5 wt%, preferably 0.3 wt%, as metal of metal compounds as impurity.

Secondly, from a starting material batch containing a sintering aid, an aluminum nitride powder having a density of at least 3.0 g / cm3, preferably at least 3.16 g / cm3, containing at least 90 wt. .%, Bee. preferably at least 93 wt%, aluminum nitride, at most 3.5 wt%, preferably at most 2.5 wt%, bound oxygen, 0.02 - 5 wt%, preferably 0.05 - 3.0 wt%, as an oxide with the highest atomic valency, of at least one 8400796>> 11 metal element selected from the group consisting of alkaline earth metals / lanthanum group metals and yttrium derived from the sintering aid or a compound thereof and at most 0.5 wt%, preferably not more than 0.3 wt%, as metal or metallic compound as impurities, other than compounds of the above metals.

In the sintered article of this invention, the impurities may be metal compounds, such as carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper and zinc, from the impurities in the fine aluminum nitride powder of this invention.

The sintered article of this invention, in its most preferred form, contains at most 0.1 wt% in total, as metal, impurities, when the impurities are iron, chromium, nickel, cobalt, copper, zinc and titanium.

The sintered body of this invention is characterized in that the state of its mechanically broken surface is much different from that of a broken surface of a conventional sintered body.

The mechanically fractured surface of the high density aluminum nitride sintered body of the invention is formed from densely packed fine crystal seeds which differ from each other by clear contours. The clear contours of the fine crystal germs at the fractured surface are polygonal. At least 70% of the fine crystal seeds consist of crystal seeds with an average particle diameter of 25 meters at the fractured surface defined by the clear contours, D (micrometer) from 0.5 5 to 1.5 5. A sintered aluminum nitride body which gives a fractured surface of which at least 70% of the crystal seeds have a particle size in the range of 0.5 to 1.5 D, ie an aluminum nitride sintered body with particles of relatively uniform size at the fractured surface was up to not known so far.

For example, the sintered body of this invention which provides the micrograph of Figure 3 has an average particle diameter (5) of 6.9 microns, with the amounts of particles having an average particle diameter of 0.5 D to 1.5 D, ie, 3.5 microns to 10.4 microns, is 83%. Another property of the appearance of the sintered body of this invention in its mechanically broken surface is that a crystal surface appearing on the broken surface of the individual particles forms a relatively smooth flat surface.

This shows that the sintered body of this invention contains virtually no foreign phase (which usually appears as a circular indentation on the fractured surface) formed by the incorporation of impurities or a gas phase.

Yet another property of the sintered body of this invention is observed in a treated fractured surface obtained by treating a mechanically fractured surface with an aqueous solution of phosphoric acid to examine a texture of the sintered body or its condition of a secondary phase. Even when the sintered body of this invention has been treated under the most typical treatment conditions, ie treated with a 35% aqueous solution of phosphorus at 62.5 ± 2.5 ° C for 20 minutes, it still has specific crystal germs with polygonal contours. When the treatment conditions are made more stringent and the hot pressed sintered body of this invention is treated with 50% aqueous solution of phosphoric acid 20 at the same temperature as above for 30 minutes, it still shows the same treated broken surface as above. However, when the sintered body of the invention obtained by pressureless sintering is subjected to these treatment conditions, it is found that a part has disappeared in the seed interface of the crystal seeds, which appears to be the result of dissolution. More specifically, most crystal germs have an angular contour, but some of the crystal germs have a slightly deformed contour that is not observed before treatment.

The aforementioned behavior of the sintered body of this invention which is resistant to treatment with an aqueous solution of phosphoric acid is very characteristic in view of the fact that when a conventional aluminum nitride sintered body is treated with an aqueous solution of phosphoric acid, a secondary phase consisting mainly of an oxide is easily dissolved and therefore the crystal grains have a round-like contour which is very different from the contour of the crystal seeds before the treatment. In view of the fact that few reports have so far been reported on the successful pressureless sintering of aluminum nitride with 8 4 0 0 7 S δ 13, it is indeed surprising that the sintered body of this invention formed by pressureless sintering has an excellent resistance has an aqueous solution of phosphoric acid as mentioned above.

An X-ray diffraction pattern of the sintered body of this invention shows six clear diffraction lines assigned to hexagonal aluminum nitride crystals with a diffraction angle (2Θ) between 30 and 70 °, ie at diffraction angles of 33.3 ° ± 0.5 °, 36.2 ° ± 0 , 5 °, 38.1 ° ± 0.5 °, 49.8 ° ± 0.5 °, 59.6 ° ± 0.5 ° and 66.3 ° ± 0.5 °. This diffrac-

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10 angle angles correspond to Bragg (d, A) interplanar distances of 3.69 ± 0.04 £, 2.48 ± 0.03 £, 1.36 ± 0.03 £, 1.83 ± 0.02 £, 1.55 ± 0.01 £ and 1.41 ± 0.01 £.

It has been reported that conventional aluminum nitride sintered bodies have diffraction lines assigned, for example, to CaO AljOCaO.ZAl ^ O ^ or 3Y20 ^ -5 ^ 1 ^ 0 ^ crystals in addition to those assigned to the hexagonal aluminum nitride crystals, due to the large amounts of sintering aids (such as CaCO 2 or added for improved sinterability, and the high oxygen content of the starting aluminum nitride. Even when such sintering aids are used in the sintering process, the present invention can provide a sintered body of high purity and high strength aluminum nitride. density that shows substantially no diffraction lines of the said crystals derived from the sintering aids.

The fine aluminum nitride powder or the thorough mixture thereof with a sintering aid used in the aforementioned second sintering method can be obtained according to this invention according to a method, wherein the fine aluminum nitride powder of this. high purity invention is thoroughly mixed with a compound of at least one metal selected from alkaline earth metals, lanthanum-group metals and yttrium in such amounts that the amount of the metal compound is 0.02-5.0 wt% as metal oxide with the highest atomic valence, based on the total weight of the resulting composition, is; as well as by a method comprising (1) thoroughly mixing a fine alumina powder having an average particle diameter not greater than 2 microns, a fine carbon powder having an ash content of at most 0.2% by weight and an average of 8400796 t 14 particle diameter of more than 1 micron and a compound of a metal selected from alkaline earth metals, lanthanum group metals and yttrium in a liquid medium, the weight of the fine alumina powder to the fine carbon powder 1: 0.36-1 : 1 is 5 -.- and the amount of the metal compound is 0.02-5.0 wt% as metal oxide with the highest atomic valence, (2) firing the resulting thorough mixture at a temperature of 1400-1700 ° C in an atmosphere of nitrogen and ammonia, after it has been optionally dried and then (3) subsequently heating the mixture at a temperature of 600-900 ° C in an oxygen-containing atmosphere to remove non- converted carbon.

The first method can be performed by mixing the fine aluminum nitride powder of the invention with a sintering aid using a mixer of the type mentioned above for mixing alumina and carbon. The second process can be carried out by mixing alumina, carbon and the sintering aid with the same mixer (step 1) and then performing steps (2) and (3) in the same manner as in the aforementioned process to form. the fine aluminum nitride powder of the invention. The second method is very effective because in many cases unexpectedly little of the sintering aid is consumed, regardless of the high fire temperature of 1400 - 1700 ° C.

The sinter-25 auxiliary used in the above method is a compound of at least one metal selected from alkaline earth metals, lanthanum group metals and yttrium. These metal oxides for aluminum nitride were already known to be effective sintering aids. Research by the inventors has shown that these metal compounds function not only as a sintering aid, but also as an agent that improves the light transmitting properties and thus improves the air permeability of the sintered aluminum nitride article in conjunction with the high purity of the fine aluminum nitride powder of this invention.

The alkaline earth metals may include beryllium, magnesium, calcium, strontium and barium. Of these, in particular calcium, strontium and barium as metals which improve the light transmission properties 8400798 are important.

Examples of the lanthanum group metals include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium. Of these, lanthanum, neodymium and cerium are preferred.

The sintering aid or the light transmittance improving agent is used in an amount of 0.02-5.0 wt%, preferably 0.03-3.0 wt%.

thus, according to the invention, a thoroughly mixed composition of a fine powder of aluminum nitride is provided, which comprises at least 90% by weight, preferably at least 93% by weight, aluminum nitride, at most 4.5% by weight, preferably highest 3.0 wt% bound oxygen, 0.02-5 wt%, preferably 0.03-3.0 wt% as an oxide having the highest atomic valency of at least one metal element selected from nature-15 alkali metals, lanthanum group metals and yttrium or a compound thereof and contains up to 0.5% by weight, preferably up to 0.3% by weight, of metal compounds as impurities other than compounds of said metals. In this composition, the impurities may be metal compounds, such as carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper or zinc, which are derived from the impurities contained in the fine aluminum nitride powder of the invention. When the metals of the metal compounds such as impurities are iron, chromium, nickel, cobalt, copper, zinc and titanium, the content of these impurities is preferably at most 0.1% by weight, based on the total amount of these metals.

As noted in detail above, the present invention provides a high purity fine aluminum nitride powder having an average particle diameter of no greater than 2 microns as well as a high purity, high density sintered aluminum nitride article.

For example, the sintered aluminum nitride article of this invention is used as a highly thermally conductive ceramic in heat-emitting plates, heat exchanger materials, stereophonic system substrates or video amplifiers, and integrated circuit substrates. Utilizing its excellent translucent properties, it can be used as a window material for sensors using UV light and infrared light and light emitting tubes of lamps. It can also be used as a radar window material using its electric wave transmission properties and as a special window material where translucent properties at high temperatures are desired.

The fine aluminum nitride powder of this invention is particularly suitable as a starting material for Sialon type materials and when used as a starting material for α-sialon, β-sialon 10 and AlN polytypes, high purity sialon compounds having excellent properties are not obtained. conventional AlN powders. When further used as a starting material for β-sialon, Al 2 O 4 AlN spinel and silicon oxynitride glass, it gives products with improved light transmission properties.

Since the fine aluminum nitride powder of this invention is uniform and has good dispersibility, it can also be effectively used as an auxiliary for various ceramics, such as silicon carbide, or as a powder for making a combination with a polymer, such as a silicone rubber.

.20 The following examples more particularly illustrate the present invention.

The following different analysis methods and devices were used in these examples:

Cation analysis 25 XPC emission spectroanalyzer (ICP-AES, from Daini Seikosha Co. Ltd.

Carbon analysis

Carbon analyzer in metal (EMIA 3200, from Horiba Seisakusho Co. r.

Ltd.)

Oxygen Analysis 30 Metal Oxygen Analyzer (EMGA-1300 from Horiba Seisakusho Co.

Ltd.)

Nitrogen analysis

Neutralization titration of ammonia developed by alkali melt decomposition 35 X-ray diffraction device X-ray diffraction meter (JRX-12 VB from Nippon Denshi Co. Ltd.) 84 0 0 7 9 8 17

Scanning electron microscope JSM-T200 (from Nippon Denshi Co. Ltd.)

Specific surface BET method (specific surface measuring device (SA-100 from Shibata 5 Chemical Machinery, Co. Ltd.)

Device for measuring the average particle size and particle size distribution

Centrifugal Automatic Particle Analyzer (CAPA-500 from Horiba Seisakusho Co. Ltd.) 10 Thermal Conductivity Hero Measuring Device Thermal Constant Measuring Analyzer by Laser (PS-7 from Rigaku Denki Co., Ltd.)

Light transmission measuring devices

Hitachi 200-10 µV-VIS spectrophotometer (330 type) and Hitachi 260-15 30 infrared spectrophotometer 260-30 type)

Flexural Strength Meter Instron Measuring Machine (Model 1123)

The light transmittance of an aluminum nitride sintered body was calculated from the following equation.

20 1- (1- R) 2 ”/ Ut ..... U) Σ0 e where:

Iq = intensity of incident light, I = intensity of transmitted light, R = reflection, 25 t = thickness of the sintered object and ju. = absorption coefficient R is determined depending on the refractive index of the sintered object. When the refractive index is n, R is given by the following equation when measured in air.

30 ..... (2) ^ u in equation (1) is a measure of the light transmission properties of the sintered article and the values in the following examples were calculated according to equation (1).

8 400 798 18

Average diameter (D) with a mechanically broken surface

A sample of an aluminum nitride sintered body was mechanically broken, and the broken surface was photographed by a scanning electron microscope at 2,000 times magnification.

The equivalent diameters (d) of the individual crystal seeds observed in a photo with a size of about 7 cm x about 10 cm were measured. The diameter d can be determined by measuring the maximum length (d) and the minimum length (d.) Of each of the crystal seeds crossing its clear contour in the surface of the photograph 10 and calculating the arithmetic mean from the measured maximum and minimum lengths.

From ncl values of yes crystal seeds, the mean particle diameter D can be calculated according to the following equation. n king.

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Example I

20 g Alumina with a purity of 99.99% (Table A gives the analyzed impurity values) and an average particle diameter of 0.52 micrometers, the amount of particles 20 having a particle diameter not exceeding 3 micrometers 95 wt. % and 10 g of carbon black with an ash content of 0.008 wt% and an average particle diameter of 0.45 micrometers, were uniformly mixed in ethanol as a dispersing medium in a ball mill consisting of a nylon tub and nylon-coated balls. The resulting mixture was dried, placed on a high-purity graphite flat tray and heated in an electric oven at 1600 ° C for 6 hours with continuous addition of nitrogen gas into the oven at a rate of 3 1 / minute. The resulting reaction mixture was heated in air at 750 ° C for 4 hours to remove the unreacted carbon by oxidation.

X-ray diffraction analysis of the obtained white powder showed that it is single phase AlN without without diffraction peak of alumina. The powder obtained had an average particle diameter of 1.31 micrometers, the amount of particles with a particle diameter of not more than 3 micrometers being 90% by volume. Examination by a scanning electron microscope showed that this powder consisted of 8 4 (f 0 7 9 5 19 uniform particles with an average particle diameter of 0.7 micrometers. It had a specific surface area of 4.0 m2 / g.

The analysis values of this powder are shown in Table B.

5 TABLE A

Analysis values of Al powder Al ^ content: 99.99%

Element Content (ppm)

Mg <5 10 Cr <10

Si 30

Zn <5

Fe 22

Cu <5 15 Ca <20

Ni 15

Ti 5

TABLE B

Analysis values of AlN powder 20 AlN content: 97.8%

Element Content

Mg <5 (ppm)

Cr 21 (")

Si 125 (") 25 Zn 9 (")

Fe 20 (")

Cu <5 (")

Mn 5 ('*)

Ni 27 (") 30 Ti <5 (")

Co <5 (”)

Al 64.8 (wt% 9 N 33.4 (") O 1.1 (") 35 C 0.11 (") 84 0 0 7 7-¾ 20

Example II

Aluminum nitride powder (1.0 g) obtained in the same manner as in Example I, was placed in a BN-coated graphite die with a diameter of 20 mm and at a temperature of 2000 ° C for 2 hours under a pressure of 100 kg / cm2 in nitrogen gas under 1 atmosphere in a high-frequency induction furnace hot pressed. The sintered article obtained was slightly yellow, dense and semipermeable. The sintered article had a density of 3.26 g / cm3. X-ray diffraction analysis showed that the single phase was AlN. The analytical values of the sintered object are shown in Table C. The sintered article had a thermal conductivity of 75 W / m-K. When polishing this sintered object to a thickness of 0.5 mm, its light transmittance for light with a wavelength of 6 µm was 16% (absorption coefficient ^ u = 34 cm *).

A disk with a diameter of 40 mm and a thickness of about 3 mm obtained by hot pressing under the same conditions as mentioned above was cut to form a rectangle. rod with a size of 3m8 x 3 x 35 mm. The three-point bending strength of this sample was measured at a crosshead speed of 0.5 mm / minute and a temperature of 1200 ° C with a wingspan of 30 mm. This averaged 41.5 kg / mm2.

TABEE C

Analysis values of sintered AlN AlN content: 98.1% Element Content

Mg <5 (ppm)

Cr 15 (")

Si 100 ('")

Zn 16 (") 30 Fe 18 (")

Cu <5 (’’)

Mn 5 (”)

Ni 30 (”)

Ti <5 ("*) 35 Co <5 (")

Al 65.0 (wt.%) 8400796 21 TABLE C (Continued)

Element Content N 33.5 (ppm) O 0.6 (") C 0.13 (")

Example III

Aluminum nitride powder (10 g) obtained in the same manner as in Example 1 was mixed with 0.2 wt% as CaO, Ca (NO 2) using ethanol as a liquid medium in a polyethylene mortar using a polyethylene pestle. The mixture was dried and then hot pressed under the same conditions as in Example XI to form a sintered article of 20 mm diameter. The sintered article had a density of 3.28 g / cm 2 and was found to be single phase AIN by X-ray diffraction analysis. The sintered article had an AlN content of 97.8 wt%, an oxygen content of 0.7 wt%, and a thermal conductivity of 79 W / m-K.

When polishing the sintered object to a thickness of 0.5 mm, it had a light transmittance for light with a wavelength of 6 micrometers of 33% (absorption coefficient yU = 19 cm. Figure 1 shows the dependence of the light transmittance of this sintered object. of the light wavelength while Fig. 2 shows a photograph of the appearance of the sintered object.

The mixed AlN powder was sintered according to the same procedure as in Example II and its three-point flexural strength measured.

This was on average 45.1 kg / mm2 at 1200 ° C.

Example IV

Aluminum nitride powder (10 g) obtained by the same method as in Example I was mixed with each of the various additives in Table D. The resulting mixtures were each hot pressed to sintered articles by the same method as in Example III. The results are shown in Table D, 84007-22

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Example V

About 1 g of aluminum nitride powder obtained by the same method as in Example 1 was uniaxially compressed in a 20 mm diameter die and isotactically compressed under a pressure of 1000 mg / cm 2 to form an article with a density of 1.56 g / cm3. The article was placed in a boron nitride crucible and heated to 1900 ° C in nitrogen gas under 1 atmosphere in a high frequency induction furnace with a graphite heat generator for 3 hours. The article obtained by the pressureless sintering was grayish-white and had a density of 2.93 g / cm3. X-ray diffraction analysis showed that it was single phase AIN. Analysis of the sintered article showed that it had an AlN content of 98.3 wt% and an oxygen content of 0.4 wt%. The thermal conductivity qas 48 W / m-iC. Example VI

10 g of aluminum nitride powder, obtained by the same method as in Example 1, was uniformly mixed with 3.0 wt%, as CaO, Ca (NO ^) 2 * 4 ^ 0 in ethanol as a dispersing medium. The mixture was dried, pressed and sintered in the same manner as in Example V. Before sintering, the pressed article had a density of 1.73 g / 20 cm 3. The sintered body was yellowish and semipermeable and had a density of 3.23 g / cm3. The sintered body had an AlN content of 96.0 wt%, an oxygen content of 1.5 wt%, and a thermal conductivity of 64 w / m-K. When polished to a thickness of 0.5 mm, it had a light transmittance for light with a wavelength of 6 micrometres of 28% (µm = 23 cm).

Example VII

10 g of aluminum nitride powder obtained by the same method as in Example I was mixed with each of the various additives indicated in Table E in the same manner as in Example VI.

The mixtures were each subjected to pressureless sintering in the manner described in Example V. The results are shown in Table E.

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Example VIII

25

The same alumina (20 g) and carbon (8 g) as used in Example I were uniformly mixed in water as a dispersing medium in a ball mill composed of a nylon tub and balls. The mixture was dried, placed on a flat tray made of high-purity graphite, and heated in an oven at 1550 ° C for 6 hours, continuously introducing nitrogen gas at a rate of 3 1 / minute. The reaction mixture was heated in air at 800 ° C for 4 hours to remove unreacted carbon. The resulting powder had an AlN content of 95.8 wt% and an oxygen content of 2.1 wt%. The amount of cationic impurities in the AlN powder was almost equal to that indicated in Table B, Example I. The powder obtained had an average particle diameter of 1.22 micrometers and did not contain 92% by volume of particles with a particle diameter greater than 3 micrometers.

Example IX

1 g of AlN powder obtained by the same method as in Example VIII was hot pressed in the same apparatus and under the same conditions as used in Example II. The sintered article obtained was slightly yellowish and semipermeable and had a density of 3.25 g / cm3, an AlN content of 96.8 wt% and an oxygen content of 1.3 wt%. The sintered article had a thermal conductivity of 52 W / m-K. Upon polishing the sintered object to a thickness of 0.5 mm, it had an air transmittance to light with a wavelength of 6 µm of 11% (µ h = 41 cm 1). The flexural strength of the sintered article, measured under the same conditions as in Example II, at 1200 ° C averaged 35.5 kg / mm 2.

Example X.

10 g of AlN powder, obtained in the same manner as in Example VIII, was mixed with 0.5 wt.% As, Y (NO 2) 3 .beta. In ethanol as liquid medium. The mixture (1 g) was dried and then hot pressed in vacuo at 1400 ° C and 200 kg / cm 2 for 2 hours using the same equipment as used in Example II. The resulting sintered article was semipermeable and had a density of 3.27 g / cm3, an AlN content of 96.5 wt%, an oxygen content of 1.5 wt% and a thermal conductivity of 56 W / m-K. Upon polishing the sintered object to a thickness of 0.5 mm, it had a light transmittance to light with a wavelength of 6 micrometers of 20% (, u = 29 -1.7 cm}.

Example XX

10 g of AlN powder, obtained by the same method as in Example VIII, was uniformly mixed with 4.0% by weight, as CaO,

Ca (NO ^) in ethanol as a liquid dispersing medium. The mixture (1 g) was dried and then subjected to pressureless sintering at the same sintering conditions and in the same apparatus as used in Example V. The sintered body obtained was yellowish and half-.10 permeable and had a density of · 3.20 g / cm 3, an AlN content of 94.2 wt%, an oxygen content of 2.5 wt% and a thermal conductivity of 42 W / mK. On polishing the sintered object to a thickness of 0.5 mm, it had a light transmittance for light with a wavelength of 6 micrometers of 10% (yU = 43 cm ^).

Example XII

20 g of Alumina with a purity of 99.3% and an average particle diameter of 0.58 micrometers, as well as 16 g of carbon black with an ash content of 0.15 wt% and an average particle diameter of 0.45 micrometers were uniformly dispersed in hexane as a dispersant mixed under 20 application of a nylon ball box. The mixture was dried, placed on a flat scale made of high purity graphite and heated in an oven at 1650 ° C for 6 hours, continuously feeding ammonia gas at a rate of 1 1 / minute. The resulting reaction mixture was heated in air at 750 ° C for 6 hours to remove the unreacted carbon by oxidation. The powder obtained had an average particle diameter of 1.42 micrometers, the amount of particles having a particle diameter of not more than 3 micrometers-84% by volume.

The powder was analyzed, the results of which are shown in Table F.

3400798 27. ·

TABLE F

Analv e values of AlN powder AlN content: 96.9 wt%

Element Content

Mg 48 (ppm) 5 Cr 110 (")

Si 2500 (")

Zn 20 (")

Fe "370 (") - Cu <5 n 10 Mn 40 (-)

Ni 120 (")

Ti 25 (»)

Co 5 (”)

Al 64.9 (wt%) 15 N 33.1 (") 0 1.3 (") C 0.16 (")

Example XIII

1 g of AlN powder obtained in the same manner as in Example 20 XIX was hot pressed under the same sintering conditions and in the same apparatus as used in Example II. The sintered article obtained was grayish and semi-transparent and had a density of 3.26 g / cm3, an AlN content of 97.9 wt%, an oxygen content of 0.8 wt%, and a thermal conductivity of 50 W / mK. When polished from a sintered object to a thickness of 0.5 mm, it had a light transmittance for light with a wavelength of 6 micrometers of 6% (.u = 53 cm -1).

Example XIV

10 g of AlN powder obtained by the same method as in Example XII was uniformly mixed with 0.2% by weight, as BaO, of 3a (NO2) ^ in ethanol as a liquid medium. The mixed powder (1 g) was dried and then hot pressed under the same sintering conditions and in the same apparatus as used in Example II. The sintered body obtained was grayish and semi-transparent and had a density of 3.27 g / cm 3, an AlN content of 97.9 wt%, an oxygen content of 84 0 0 7-ii * 28-0.9 wt% and a thermal conductivity of 55 W / mK.

When polished to a thickness of 0.5 mm, it had a light transmittance for light with a wavelength of 6 µm of 8% (µh = 48 cm -1).

Example XV

The same alumina (130 g; purity 99.99 wt%) and carbon black (65 g; ash content 0.08 wt%) as used in Example 1 and 1.0 g calcium carbonate with an average particle diameter of 3 micrometers were uniformly mixed in ethanol as a dispersing medium in a ball mill consisting of a ball box lined with polyurethane resin. The mixture was dried and then reacted and oxidized under the same conditions as in Example 1 to form an AlN powder. The resulting powder had an average particle diameter of 1.44 micrometers and contained 86% by volume of particles with a particle diameter no greater than 3 micrometers. The analysis values of the powder are shown in Table G.

TABLE · G

Analysis values of AlN powder AlN content: 96.9 wt%

Element Content

Ca 920 (ppm) 20 Mg <5 ("j

Cr 17 Γ) • Si 86 (")

Zn 12 (")

Fe 25 (") 25 Cu ^ 5 (")

Mn Λ Γ)

Ni 27 (")

Ti ^ 5 (") CO <5 (") 30 Al 65.0 (wt%) N 33.1 (") O 1.5 (") C 0.15 (")

84 0 0 7 9 S

29

Example XVI

One gram of AlN powder obtained by the same method as in Example XV was hot pressed under the same conditions and in the same apparatus as used in Example II. The sintered article obtained was compact and semi-transparent and had a density of 3.26 g / cm3, an AlN content of 98.1%, an oxygen content of 0.7% and a thermal conductivity of 60 W / mK. When polished, the sintered body to a thickness of 0.5 mm had a light transmittance for light with a wavelength of 6 micrometers of 28% (µh = 23 cm) Example XVII

The same alumina (130 g; purity 99.99 wt%) and carbon black (65 g; ash content 0.08 wt%) as used in Example I were uniformly mixed with 0.52 g ^ 2 ° 3 with an average particle diameter of 1 micron, in ethanol as a dispersion medium in a ball mill, composed of a ball box coated with polyurethane resin. The mixture was dried and then converted under the same conditions as in Example 1 and oxidized to an AlN powder. The powder had an average particle diameter of 1.50 micrometers and contained 83% by volume of particles with a particle diameter of no greater than 3 micrometers. The analysis values of this powder are shown in Table H.

T A B E l H

Analysis values anAlN powder AlN content: 96.9%

Element - Assay Y 3360 (ppm) 25 Mg 6 (")

Cr 11 O

Si 123 0 ')

Zn 16 (")

Pe 36 (") 30 Cu 16 ('*)

Mn 5 (")

Ni 7 (")

Ti 10 (”)

Co <5 (”) 840070a 30 TABLE H (Continued)

Element Content

Al 64.9 (wt%) N 33.1 (") O 1.5 (") 5 C 0.18 (")

Example XVIII

1 g of AlN powder, obtained in the same manner as in Example XVII, was hot pressed under the same conditions and in the same apparatus as used in Example II. The resulting sintered article had a density of 3.28 g / cm3, an AlN content of 98.1 wt%, an oxygen content of 0.8 wt%, and a thermal conductivity of 63 W / m-K. When polished to a thickness of 0.5 mm, it had a transmittance to light with a wavelength of 6 micrometers of 30% (µm = 21 cm *). Comparative Example 1 The same alumina (100 g, purity 99.99 wt.%) And carbon black (100 g; ash content 0.08 wt.%) As used in Example 1 were mixed in a ball mill composed of a tray in the dry state with balls coated with polyurethane resin. The mixture was converted under the same conditions as in Example 1 and oxidized to an AlN powder.

The powder obtained was white and had an average particle diameter of 1.8 micrometers, the amount of particles with a particle diameter not exceeding 3 micrometers being 62% by volume. The analysis values of the powder are shown in Table J.

The powder was hot pressed in the same device and under the same conditions as used in Example II. The sintered article was greyish white and not transparent and had a density of 3.12 g / cm3 at a thermal conductivity of 28 W / m-K-K. The three-point bending test of the sintered body at 1200 ° C gave an average of 20.3 kg / mm2.

8 400 790 30 31

T A Β Ε L J

Analysis values of AlN powder AlN content; 92.0 wt%

Element Content

Mg 8 (ppm) 5 Cr 15 (")

Si 110 (")

Zn '10 (")

Fe 40 Γ)

Cu 15 (") 10 Mn 5 (")

Ni 12 (”)

Ti 10 (w)

Co 5 (")

Al 64.4 (wt%) 15 N 31.4 (") 0 3.8 (") C 0.16 (")

Comparative Example 2 20 g of Alumina with a purity of 99.6 wt.% And an average particle diameter of 3.6 microns and 10 g of carbon black with an ash content of 0.08 wt.% Were mixed in ethanol as a dispersing medium in a ball mill, composed of a box of balls lined with nylon. The mixture was reacted and oxidized as in Example 1. The resulting powder was white and had an AlN content of 26.1 wt%, an oxygen content of 1.9 wt%, and an average particle diameter of 3.9 microns, wherein the amount of particles with a particle diameter no greater than 3 micrometers was 33% by volume.

The powder was hot pressed in the same device and under the same sintering conditions as used in Example II. The resulting sintered article was greyish in color and not transparent and had a density of 2.98 g / cm 3 with a three-point flexural strength at 1200 ° C. Vein averaged 24.9 kg / mm 2.

Comparative Example 3 10 g of AlN powder, obtained in the same manner as in Comparative Example 2, was mixed with 0.2 wt%, as CaO, of CaiNO2) 2 * 4E2 ° 8400796 *% 32 in ethanol as a liquid medium. The mixed powder (1 g) was dried and then hot pressed in the same device and under the same conditions as used in Example II. The sintered article was gray and non-transparent and had a density of 3.11 g / cm3, a thermal conductivity of 35 W / m-K, with a three-point bending strength at 1200 ° C and an average of 25.6 kg / mm2.

Comparative Example 4 20 g of Alumina with a purity of 98.5 wt% and an average particle diameter of 1.0 micron and 16 g of carbon black with an ash content of 0.15 wt% and an average particle diameter of 0.44 micron were uniformly mixed in ethanol in a ball mill, composed of a bucket of nylon and nylon-coated balls. The mixture was reacted and oxidized under the same conditions as in Example 1 to obtain AlN powder. The powder obtained was grayish-white and had a mean particle diameter of 1.8 micrometers, the amount of particles with a particle diameter no greater than 3 micrometers being 75% by volume. The analysis values of the powder are shown in Table K.

1 g of this powder was hot pressed in the same apparatus and under the same sintering conditions as used in Example II. The sintered body obtained was grayish-black and non-transparent and had a density of 3.22 g / cm3, a thermal conductivity of 33 W / m-K and a three-point bending strength at 1200 ° C averaging 27.4 kg / mm2.

TABLE K

Analysis value of AlN powder 25 AlN content: 96.4%

Element Content

Mg 130 (ppm)

Cr 260 (")

Si 3600 (") 30 Zr 50 (")

Fe 2100 (")

Cu 10 (”)

Mn 50 (")

Ni 310 (") 35 Ti 180 (") 8400796> i 33 TABLE K (Continued)

Element Content

Co 60 (ppm)

Al 64/6 (wt.%) N 32/9 (") 5 0 1.8 (") C 0/13 (")

Example XIX

To 10 g of an aluminum nitride powder obtained in the same manner as in Example 1, 3 wt.% Was added as CaO, Ca (NO2) 2 · -H 2 O. These were mixed and sintered in the same manner as in Example III. The sintered body obtained had a density of 3.27 g / cm3, an AlN content of 97.5 wt% and an oxygen content of 1.2 wt%.

A 2 mm thick sample of the sintered body was formed and its thermal conductivity was measured in the same manner as in the aforementioned examples. In particular, colloidal carbon was spray-coated on both surfaces of the sample of a sintered body and irradiated with a ruby laser. It was found to have a thermal conductivity of 72 W / m-k measured by the so-called contact method in which the temperature rise of the back surface of the sample is measured by a thermocouple attached to the back surface by means of a silver paste.

When vacuum depositing a thin gold film on the laser-irradiated surface of the same sample to prevent the penetration of the laser light and when measuring the temperature rise of the back surface of the sample by so-called non-contact method, using an indium- antimony sensor, its thermal conductivity was 91 W / mk.

A sample was further formed by grinding the above-mentioned sintered body to a thickness of 0.5 mm. This sample was found to have a linear transmission to light with a wavelength of 6 µm of 35% (µm = 18 cm *). The total light transmission for light with a wavelength of 1 µm was measured using an integrated sphere with a diameter of 60 mm and was found to be 73%.

? 4 0 0 7 9 1 34

A micrograph of the broken surface of the sintered body is shown in Figure 3.

The fractured surface was etched by treating it with a 50% aqueous solution of phosphoric acid at a temperature of -62.5 ± 2.5 ° C for 30 minutes. A micrograph of the etched surface is shown in Figure 4.

Example XX

To 10 g of an aluminum nitride powder obtained in the same manner as in Example 1, 2 wt.% Was added as CaO, Ca (NO2) 2 ·. These were mixed and sintered in the same manner as in Example VI. The properties of the obtained sintered aluminum nitride body are summarized below. A micrograph of the fractured surface of the obtained sintered aluminum nitride body is shown in Fig. 5.

15 Density 3.24 g / cm1

AlN content 97.0 wt% 02 ~ content 1.3 wt% thermal conductivity 73 W / mk (contact method) 95 W / mk (non-contact method) 20 light transmission 33% (^ h = 19 cm S (linear) 68% (total)

Example XXI

Example II was repeated except that 0.5%, if

CaO of Ca (NO ^) 2-4 ^ 0 was used. The resulting sintered aluminum nitride body had the following properties.

A micrograph of the ordinary surface of the obtained sintered aluminum nitride body is shown in Fig. 6. An icrograph of the same fractured surface taken after it was treated with a 50% aqueous solution of phosphoric acid at 62.5 ± 2.5 ° C for 30 minutes is shown in Figure 7.

Density 3.22 g / cm1

AlN content 97.3 wt% 02 content 1.0 wt% thermal conductivity 75 W / m-k (contact method) 35 98 W / m-K (non-contact method) -1

Light transmission 31% (^ h = 21 cm) (linear) 4 0 0 7 9 5 65% (total)

Claims (52)

3-5 Pain aluminum nitride powder having an average particle diameter of no greater than 2 microns, comprising at least 94 wt% aluminum nitride, at most 3 wt% bound oxygen and at most 0.5 wt%, as metal, of metal compounds as impurities. Powder according to claim 1, characterized in that the bound oxygen content is at most 1.5% by weight. Powder according to claim 1, characterized in that the content of the metal compounds as impurity is at most 0.3% by weight, as metal. Powder according to claim 1, characterized in that the metal of the metal compounds is carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc or titanium. Powder according to claim 1, characterized in that the metal of the metal compounds is iron, chromium, nickel, cobalt, copper, zinc or titanium and the total content of these metal compounds is at most 0.1% by weight, as metal , is. Powder according to claim 1, characterized in that the aluminum nitride content is at least 97% by weight. 7. Powder according to claim 1, characterized in that it contains at least 70% by volume of particles with a particle diameter not larger than 3 micrometers. Powder according to claim 1, characterized in that it is composed of spherical particles with an average particle diameter of greater than 2 micrometers or secondary agglomerates thereof. A process for preparing a fine powder of aluminum nitride, comprising (i) thoroughly mixing a fine powder of alumina with an average particle diameter of not more than 2 micrometers with a fine powder of carbon with an ash content of at most 0.2 % and an average particle diameter of not more than 1 micrometer in a liquid dispersing medium, the weight ratio of the fine aluminum powder to the fine carbon powder being 1: 0.36 - 1: 1, (ii) burning the resulting thorough mixture 84 0 0 7 00 V at a temperature of 1400 - 1700 ° C in an atmosphere of nitrogen and ammonia, after it has been optionally dried and (iii) subsequently heating the obtained fine powder to a temperature of 600 - 900 ° C to remove unconverted carbon to form a fine aluminum nitride powder having an average particle diameter of no more than 2 microns, containing at least 94 wt% aluminum nitride, at most 3 w.% bound oxygen and contains at most 0.5 wt.%, calculated as metal, of metal compounds as impurity. 10. Process according to claim 9, characterized in that the fine aluminum powder gives a purity of at least 99.0% by weight. A method according to claim 9, characterized in that the weight ratio of the fine aluminum powder to the fine carbon powder is 1: 0.4-1: 1. A method according to claim 9, characterized in that the liquid dispersing medium is water, a hydrocarbon, an aliphatic alcohol or a mixture thereof. 13. Thoroughly mixed composition of a fine powder of aluminum nitride, comprising at least 90 wt% aluminum nitride, at most 4.5 wt% bonded oxygen, 0.02-5.0 wt% as an oxide with the highest atoravalence of at least one metal element selected from alkaline earth metals, lanthanum group metals and yttrium or a compound thereof and at most 0.5% by weight, as metal, of metal compounds as impurity other than compounds of said metals. Composition according to claim 13, characterized in that the bound oxygen content is at most 3% by weight. Composition according to claim 13, characterized in that the content of the metal compounds as impurity is at most 0.3% by weight. Composition according to claim 13, characterized in that the metal of the metal compounds as impurity is carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc or titanium. Composition according to claim 13, characterized in that the metal of said metal compounds as impurity is iron, chromium, nickel, cobalt, copper, zinc, or titanium and the total content of these impurities as metal is at most 0.1 wt. .%. 8400798 V. Composition according to claim 13, characterized in that alkaline earth metals are calcium, strontium and barium. A composition according to claim 13, characterized in that the lanthanum group metals are lanthanum, neodymium and cerium. 5-20. Composition according to claim 13, characterized in that the aluminum nitride content is at least 93% by weight. 21. A method of forming a thoroughly mixed composition of a fine aluminum nitride powder comprising (1) thoroughly mixing a fine alumina powder 10 having an average particle diameter of not more than 2 microns, a fine powder of carbon having an ash content of at least highest 0.2 wt% and an average particle diameter of not more than 1 micron and a compound of a metal selected from alkaline earth metals, lanthanum group metals and yttrium in a liquid medium, the weight ratio of the fine alumina powder to the fine carbon powder 1: 0.36-1: 1 and the amount of the compound of the metal is 0.02-5.0 wt%, as the metal oxide with the highest atomic valency based on the resulting composition; (2} then optionally drying the resulting thorough mixture, firing it at a temperature of 1400-1700? C in an atmosphere of nitrogen or ammonia, and (3) then heating the resulting fine powder to a temperature of 600 - 900 ° C in an oxygen-containing atmosphere to remove the unreacted carbon, forming a solid mixed composition comprising at least 90 wt% aluminum nitride, at most 4.5 wt% bonded oxygen, 0.02-5.0 wt%, as an oxide of the highest atomic valency, of at least one metal element selected from the group consisting of alkaline earth metals, lanthanum group metals and yttrium or a compound thereof and at most 0.5 % by weight, calculated as metal, of metal compounds as impurity other than compounds of said metals, A method of forming a thoroughly mixed composition of a fine aluminum nitride powder, comprising thoroughly mixing a fine aluminum nitride powder having an average particle diameter of no greater than 2 microns and containing at least 94 wt% aluminum nitride , at most 3 wt.% bound oxygen and at most 0.5 wt.%, 8400773 as metal, of metal compounds, as impurity comprising a compound of at least one metal selected from alkaline earth metals, lanthanum group metals and yttrium in ratios such that the content of the compound of said metal in the resulting composition is 0.02 -5 5.0 wt%, as the metal oxide having the highest atomic valency, thereby forming a thoroughly mixed composition, which is at least 90 wt % aluminum nitride, up to 4.5 wt% bound oxygen, 0.02-5.0 wt%, as an oxide of the highest atomic valency, of at least one metal element selected from the group consisting of alkaline earth limetals, lanthanum group metals and yttrium or a compound thereof and up to 0.5% by weight, as metal, of metal compounds as impurity other than compounds of said metal. 23. Sintered article of aluminum nitride, which sintered article has a high purity and density of at least 2.0 g / cm 3 and which contains at least 94% by weight aluminum nitride, at most 1.5% by weight of bound oxygen and at most 0 .5 wt.%, If metal, contains metal compounds as impurity. Article according to claim 23, characterized in that the content of bound oxygen is at most 0.75% by weight. Article according to claim 23, characterized in that the content of the metal compound as impurity is at most 0.3% by weight as metal. 26. An article according to claim 23, characterized in that the metal of the metal compounds as impurities is carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc or titanium. 27. Object according to claim 23, characterized in that the metal of the metal compounds as impurities is iron, chromium, nickel, cobalt, copper, zinc or titanium and the total amount of these impurities is at most 0.1% by weight - , like metal. An article according to claim 23, characterized in that the amount of aluminum nitride is at least 97% by weight. Article according to claim 23, characterized in that it has a density of at least 3.16 g / cm3. 30. A method of forming a high purity, high density aluminum nitride sintered article comprising molding a fine powder of aluminum nitride having an average particle diameter of not more than 2 micrometers that is at least Contains 94 wt% aluminum nitride, up to 3.0 wt% bound oxygen and up to 0.5 wt%, calculated as metal, of metal compounds as impurities and sintering the molded article at a temperature of 1700-2100 ° C in an inert atmosphere to form a sintered aluminum nitride body having a density of at least 2.9 g / cm 3, containing at least 94% by weight aluminum nitride, at most 1.5% by weight of bound oxygen and at most 0.5% by weight as metal, of metallic compounds as impurity. A method according to claim 30, characterized in that the sintering is performed using at least 20 kg / cm 3. A method according to claim 30, characterized in that the sintering is carried out in an atmosphere of nitrogen. 33. A method according to claim 30, characterized in that the sintering is carried out substantially in the absence of pressure. A method according to claim 33, characterized in that the sintering is carried out in an atmosphere of nitrogen. A method according to claim 30, characterized in that the sintering is performed in vacuum. 36. High density and purity aluminum nitride sintered article which sintered body has a density of at least 3.0 g / cm3 and at least 90 wt% aluminum nitride, at most 3.5 wt% bound oxygen, 0.02 - 5.0 wt%, as the oxide having the highest atomic valence, of at least one metal element selected from the group consisting of alkaline earth metals, lanthanum group metals and yttrium or a compound thereof and at most 0.5 wt% if metal contains metal compounds as impurity other than said metal compounds. . An article according to claim 36, characterized in that the amount of bound oxygen is at most 2.0% by weight. An article according to claim 36, characterized in that the content of the metal compounds as impurity is at most 0.3% by weight as metal. Sintered article according to claim 36, characterized in that the metal of the metal compounds as impurities is carbon, silicon, manganese, iron, chromium, nickel, cobalt, copper, zinc or titanium. Sintered article according to claim 36, characterized in that the metal of the metal compounds as impurities is iron, chromium, V. v v / V »3 is nickel, cobalt, copper, zinc or titanium and the total content of these impurities is at most 0.1% by weight as metal. An article according to claim 36, characterized in that the content of aluminum nitride is at least 93% by weight. An article according to claim 36, characterized in that it has a density of at least 3.16 g / cm3. A method for forming a sintered article of aluminum nitride of high purity and density, comprising compression molding a fine powder of aluminum nitride, comprising at least 90 wt% aluminum nitride, at most 4.5 wt% bound oxygen 0.02-5.0 wt% as an oxide having the highest atomic valency of at least one metal element selected from the group consisting of alkaline earth metals, lanthanum group metals and yttrium or a compound thereof and at most 0.5 wt% calculated as metal, of metal compounds as impurities other than compounds of said metal, and sintering the molded article at a temperature of 1600-2100 ° C in an inert atmosphere, thereby forming a sintered article with a density of at least 3.0 g / cm3 containing at least 90 wt% aluminum nitride, at most 3.5 wt% bonded oxygen, 0.02-5.0 wt% as an oxide having the highest atomic valency of at least one metal element, ge selected from the group consisting of alkaline earth metals, lanane group metals and yttrium or a compound thereof, and up to 0.5% by weight, as metal, metal compounds as impurity other than compounds of said metal. A method according to claim 43, characterized in that the sintering is carried out at a pressure of at least 20 kg / cm 2. 45. A method according to claim 43, characterized in that the sintering is carried out in an atmosphere of nitrogen. 46. A method according to claim 43, characterized in that the sintering is carried out substantially in the absence of pressure. A method according to claim 46, characterized in that the sintering is carried out in a nitrogen atmosphere. A method according to claim 43, characterized in that the sintering is performed in vacuum. 49. High density aluminum nitride sintered body, a mechanically broken surface of said sintered 8 4 0 0 7 SS * body is formed by densely packed fine crystal seeds distinguished from each other by clear contours, which clear contours of the fine crystal seeds at the fractured surface are polygonal, and at least 70% of said crystal seeds is a particle diameter in the range of 0.5 D to 1.5 D, wherein S in micrometers is the average particle diameter of the fine crystal seeds at said broken surface defined by the clear contours, 50. Sintered body according to claim 49, characterized in that after the fractured surface has been treated with a 35% water solution of phosphoric acid at 62.5 ± 2.5 ° C for 20 minutes, crystal seeds with angular contours at the treated surface. 51. Sintered body according to claim 49, characterized in that it exhibits six clear diffraction lines in its X-ray diffraction pattern assigned to hexagonal aluminum nitride crystals at a diffraction angle (2Θ) between 30 and 70 °, but hardly any other diffraction line. Sintered body according to claims 49 - 51, characterized in that it is formed by pressure sintering. Sintered body according to any one of claims 49 to 20 51, characterized in that it is formed by pressureless sintering. 8400796