DE2461740A1 - METHOD FOR MANUFACTURING A CERAMIC MATERIAL - Google Patents

Description

Patent attorney's office d-4 düsseldorf · schumannstr. 97

PATENT LAWYERS:
Dipl.-Ing. W. COHAUSZ Dipl.-Ing. W. FLORACK Dipl.-Ing. R. KNAUF Dr.-Ing., Dipl.-Wirtsch.-Ing. A. GERBER - Dipl.-Ing. HB COHAUSZ

Joseph Lucas Limited

Well Street

GB-Birmingham 23rd December 1974

Method of manufacturing a ceramic material

The invention relates to a method for producing a ceramic material.

Am method according to the invention is again characterized in that at a temperature of 1200 ⁰ C and 2000 ° C a mixture comprising silicon nitride in an amount up to 98 wt .- $ of the mixture along with between 1 and 60 wt .- $ aluminum nitride , between 0.5 and 50 wt .-% silica and between 0.05 and 60 wt .- p alumina is heated, with some, but not all of the silica in the mixture being present as an impurity at the temperature which contains the Siliziumnitirid, wherein the silicon nitride, aluminum nitride, aluminum oxide and silicon oxide give rise to a reactive substance in the Temperaatur that at least 95 wt - ausmcht ° ß> of the mixture and in which the silicon oxide in a molar ratio of 1:. 2 with a part of the Aluminum nitride and the aluminum oxide are present in a molar ratio of 1: 1 with the best of the aluminum nitride, the constituents of the reactive substance to form the required Ke ramikmaterials react with each other.

Preferably, the relative proportions of silicon nitride, aluminum nitride, silicon oxide and aluminum oxide are in such Way provided that in the substance the atomic ratio of silicon: aluminum: nitrogen-oxygen 6-z: z: 8-z: z, where ζ is greater than zero and less than or equal to 5.

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A method according to another embodiment of the invention is thereby characterized in that a mixture at a temperature between 1200 G and heated to 2000 C, in which silicon nitride is not present, but that between 40 and 60 wt. Aluminum nitride, between 15 and 45 wt .- νί silicon oxide and between 0.0 5 and 50 wt .- ;, {aluminum oxide contains, the relative proportions of aluminum nitride, aluminum oxide and silicon oxide being such that at the tempera, door a reactive substance arises, which is at least 95% by weight ';' of Mixture forms and in which the silicon oxide in a molar ratio of 1: 2 with part of the aluminum nitride and the aluminum oxide in a pick ratio of 1: 1 with the Eest of the aluminum nitride are, where the atomic ratio of silicon: aluminum: nitrogen: Oxygen in the substance is 6-z: z: 8-z: z, where ζ is greater than 4 and less than or equal to 5, the constituents of the reactive Substance for the formation of the necessary ceramic material, is with each other react.

Conveniently, at least some of the aluminum oxide is in the mixture present at the temperature as an impurity containing the aluminum nitride.

Appropriately, at least one of the ingredients in the Mixture are present, at »temperature, in the starting materials that were used to prepare the mixture, as a compound introduced which reacts to form the required ingredient or ingredients during heating.

Appropriately, the compound silicon oxynibride, aluminum oxynitride, Ethyl silicate or aluminum hydroxide.

Preferably the mixture is pressurized during heating.

Preferably there is also a molten glass in the mixture at the temperature available.

The molten glass is expediently an aluminum

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Niinosiliklatglas or manganese glass or lithium glass.

Alternatively, "the molten glass is a magnesium glass.

The magnesium glass is expediently produced by a reaction during the heating between magnesium oxide and a glass-forming compound, both of the latter substances being present in the mixture.

It is expedient for the glass-forming compound to be Silicon oxide.

The invention is described in more detail below in connection with the drawings explained. In the drawings are:

] Pig. 1 shows a quaternary phase diagram showing compositions as an example shows in various mixtures of aluminum nitride, silicon oxide, aluminum oxide and silicon nitride, which for the invention Process can be used, and

Pig. 2 "is a graph showing the unit cell dimensions of ceramic materials produced according to the following examples.

Referring to the drawings, in a first example a Ceramic material made from a starting mixture consisting of 78.4-8 Wt .- '/ * silicon nitride powder, 14 »76 wt .-% aluminum nitride powder and 6.76 wt .-; ä silicon oxide powder consist, nd. Contained in this mixture the silicon nitride powder used 89 wt .-;:;? of the alpha phase material and had an average particle size of 3 microns, while the aluminum nitride powder the one from Koch-Light as Type 8006H 11.5 microns mean particle size but crushed to an average of β microns prior to processing became. The silicon oxide powder used was that produced by Hopkin and Williams Limited as pure precipitated silicon oxide was delivered.

Of the starting materials used in the above mixture

6098 13/06 15 sad orsqinal "'"

the silicon nitride powder contained a silicon oxide impurity in it as a layer over the articles of silicon nitride, and the aluminum nitride powder contained an impurity in it of aluminum oxide. It goes without saying that the starting material of the first example contained aluminum oxide in addition to aluminum nitride, silicon oxide and silicon nitride. Because those in silicon nitride and aluminum nitride impurities contained as the starting materials further clearly evident in the subsequent reaction to produce the required Ceramic material, the impurity levels of these raw materials were determined prior to the preparation of the above emix determined by a rapid neutron activation analysis. Then, as will be seen below, these impurities were billed to result in the above composition for the starting mix to come. Using the relevant Starting material which has been described, it was found that the silicon oxide content of the silicon nitride powder was 4 wt .- ^ w and the alumina content of the aluminum nitride were 6 wt%. the The total composition of the mixture was in reality to 75.34 wt .-; i silicon nitride, 1J, 87 wt .- ^ aluminum nitride, 0.89 Wt .-> 'alumina and 9.9 wt .- ^ silicon oxide. ! This composition is indicated by the point A in Pig. 1 reproduced, it being understood that that in the drawing the axes correspond to the pure materials, with no impurities being present.

In order to prepare the above mixture, the required amounts were used of the starting materials-placed in a colloid mill for mixing using isopropyl alcohol as the carrier liquid and continued until the mean particle size of the vegetable was less than 3 microns. The mixture was then dried and then sieved to remove any powder aggregates. A contamination test was then carried out on the mixture to determine whether the treatment had an effect on the contamination level of the starting material, but it was found that the colloid milling or the Drying and sifting hadn't changed.

The mixture was then poured into the mold cavity of a graphite mold on a graph

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phit stamp that locked one end of the mold. A graphite stamp was then placed on the powder batch, with all graphite surfaces, who were in contact with the Palvercharge had previously been exposed to boron nitride spray coated to a depth of the order of 0.25 mm. The whole thing was then placed in a press, where the temperature and pressure were simultaneously raised to 1,800 C for a period of 30 minutes and 1.5 tons / square inch, respectively. The mixture was then kept at this temperature and pressure for one hour, and under these conditions the components of the mixture reacted to produce the desired ceramic material. After cooling, the reaction mixture became taken from the mold, and the crystalline phases in the product were determined by X-ray diffraction using a Unicam spectrometer determined with Cr-K ^ .- monochromatic radiation. The X-ray analysis showed that the reaction product consisted essentially entirely of a single crystal phase ceramic material having the formula

Si. Al Έ _ο 0 6-zz 8-z ζ

where ζ was 1. The ceramic material had also been vie festgestllt, a crystal structure which was based on the beta phase silicon nitride, the a-and c-unit Celle dimensions but in each case 7 * 648 ^ ⁰¹⁰ - contributed be ² »958 Veig-cozy with values of T, 62J, and 2.914 for beta phase silicon nitride (see Fig. 2).

It will be understood that using the mixture according to the above Example and taking into account the impurities in the starting materials at the elevated temperature of the reaction, the mixture consisted entirely of a reactive substance, the 5I »3 Mo1- $ silicon nitride, 0.8 MoI-Jt. Alumina, 32.2 mole-ji> Aluminum nitride and 15 »7 mol-Ja A silicon oxide. In the reactive substance So the silicon oxide was in the required 1: 2 molar ratio with part of the aluminum nitride (31.4MoI-Ji) present, while the Aluminum oxide in the required molar ratio of 1: 1 with the order of aluminum nitride (0.8 mole-fi) was present. In the phase diagram In Fig. 1, the hatched triangular area B describes the boundaries the various possible mixtures of aluminum oxide, aluminum nitride,

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Silicon oxide and silicon nitride which, when heated, turn out to be completely reactive Substance in which the aluminum oxide, the silicon oxide and the aluminum nitride is present in the required molar ratios are. Upon arriving at the stated composition for the mixture of the above example, the amounts of the various starting materials were thus calculated in such a way that, taking into account the impurities, the total composition of the mixture (reproduced through point A) was within the limit values defined by the triangular area B.

Bs can easily be calculated that the result of the mixture according to The reactive substance produced in the above example has an atomic ratio of silicon: aluminum: nitrogen: oxygen of 6-z: z: 8-z: z where ζ was 1. The silicon, aluminum, nitrogen and oxygen were thus present in this reactive substance in the proportions that were required in the resulting ceramic material became. It will be understood, however, that other mixtures can be used which are entirely reactive at the molding temperature Composition consist of the required atomic ratios of Silicon, aluminum, nitrogen and oxygen, with such suitable mixtures on line G in Pig. 1 lie.

In a second embodiment of the invention, a ceramic material should be made that the formula

Si * Al N ₀ 0 6-z ζ 8-z 2

where ζ was 2.1. In the production of this ceramic material, the starting materials of the first example were used again, but mixed together in such proportions that the starting mixture of 30.88 wt. / L aluminum nitride, 50.44 wt .- ^ silicon oxide consisted. Taking into account the impurities in the aluminum nitride and silicon nitride as starting materials, the total composition of the mixture was 29.0% by weight, 1 aluminum nitride, 48 »42% by weight silicon nitride and 2Q7% by weight silicon oxide and 1.85% by weight. ^ Alumina, this composition being represented by point D in FIG. Treatment after the first

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Example was repeated, and at the elevated temperature of the hot + When pressed, the mixture consisted entirely of a reactive substance, the 50 mol -). Aluminum nitride, 24.55 l-: ol-> Giliziunnitride, 24.55 mol /. ' Contained silicon oxide and 1.5 ΪΊο1-; ύ aluminum oxide. So Go can be seen that in the reactive composition the silicon oxide in an Ilol ratio of 1: 2 with part of the Aluijiniuxanitrids (48 »7 KoI- /) was present while the alumina was in a wood ratio of 1: 1 with the remainder of the aluminum nitride (1.3 mol-.) was present. Furthermore, it can easily be calculated that the atomic ratio of silicon: aluminum: nitrogen; oxygen in the reactive substance 6-z: z: 8-z: z, where ζ is 2.1. The silicon, the aluminum, the nitrogen and the oxygen were thus in the reactive Substance present in the proportions that were required for the ceramic material to be produced. Again, other mixtures would have used that can be completely reactive at the hot pressing temperature Substances existed that have the atomic proportions which in this example are required in the ceramic material, whereby the line E in Fig. 1 shows the possible compositions of such mixtures shows. As can be seen from Fig. 2, the ceramic material obtained by the method of the second example had a- and c-cell unit dimensions of 7.674 and 2.962, respectively.

In a third example of the invention, the procedure according to the first Example repeated, but in this case the starting mixture consisted of 43 »9S% by weight: aluminum nitride, 27.65% by weight,; ' Silicon nitride and 28.37 wt. yi siliconoside. Taking into account the Yerreini- " in the starting materials was * the actual composition of the mixture 4 "!» 54 wt .- / j aluminum nitride, 26.54 G-ew.-Yes silicon nitride, 29.48 wt .-) ·! - siliconocide and 2.64 wt .- 4 / ί aluminum oxide, whereby this mixture is represented by point F in FIG. At the increased At the temperature of the hot pressing, the mixture produced a reactive substance consisting of 11.04 mol- ^ i silicon nitride, 58.80 mol- ^ aluminum nitride, 28.64 mol- ^ r silicon oxide and 1.52 mol- ^ i aluminum oxide. As in the previous examples, it can be seen that the Aluminum nitride, silicon oxide and aluminum oxide exactly as required Molar ratios, although when using the

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Mixture according to this embodiment, the atomic ratio of silicon / Aluminum! Nitrogen: the same as oxygen in the reactive substance 6-z: z: 8-z: z where ζ was 3. As expected, responded so that the components of the reactive substance in the increased Teinpearatur of the hot pressing reaction with each other to form a ceramic material to let that satisfied the formula above, where ζ equals 3 was. As shown in Figure 2, the a and c unit cell dimensions of the ceramic material 7 »70 or 2.986.

In a fourth example, the same procedure was followed again, but in this PaH the starting mixture consisted of 4-8 »33 wt .- ^ aluminum nitride, 20.12 percent by weight silicon nitride and 31.55 percent by weight ;; Silicon oxide. Taking into account the impurities in the raw materials The actual composition of the mixture was thus 45 »43 percent by weight; Aluminum nitride, 19.31 wt. Ji! Silicon nitride, 3 ^, 36 wt .-; :: - silicon oxide and 2.90 wt .- alumina, this mixture being represented by the point G in Fig. 1 is reproduced. As can be easily calculated, at the elevated temperature of the hot pressing process, this mixture consisted entirely of a reactive substance in which the silicon oxide was present in a molar ratio of 1: 2 with part of the aluminum nitride, while the alumina was present in a 1: 1 molar ratio with the est of the alurainium nitride. In this reactive substance was also the atomic ratio of silicon: aluminum: nitrogen: oxygen 6-z: z: 8-z: z, where ζ was ^> 3. As expected, it passed the ceramic phase of the product of the hot stress reaction is essentially composed of a single crystal phase ceramic material similar to that of the foregoing Formula in which ζ was 3 »3 sufficed. As shown in Fig. 2, were the a and c unit cell dimensions of the ceramic material 7.703 and 2.991, respectively.

In a fifth example, the starting materials used above were used mixed with aluminum oxide powder, as supplied by the Aluminum Company of America as Type XA16, to form a mixture to let the 60.6 wt .- p silicon nitride, 20.3 wt .- ^ aluminum nitride, Contained 7 * 9% by weight of silicon oxide and 11.2% by weight of aluminum oxide. Considering of impurities in the starting materials

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thus the actual composition of this mixture 58 »" IQ wt .-;. i Siliziuinnitrid, 19> 08 wt -fj aluminum nitride, 10.32 wt · / Silizisamoxid and 12.42 wt .-;. b alumina This mixture is characterized by the point H in Fig. 1. The mixture was prepared and hot-pressed as in the previous examples and consisted entirely of a reactive substance at the hot-pressing temperature which had the required molar ratios of aluminum nitride, silicon oxide and aluminum oxide become that the atomic ratio of silicon: aluminum: nitrogen: oxygen in the reactive substance was 6-z: z: 8-z: z, where ζ was 2. Again, the resulting ceramic material satisfied the above formula in which ζ was equal to 2.

In a modification of the fifth example, a ceramic material, as cf. satisfied the above formula and in which ζ was 2 out of the same Starting materials produced, although in this case the initial mixture was 64/75% by weight of silicon nitride, 15.35% by weight of aluminum nitride, 2.65% by weight of silicon oxide and 17 »25% by weight of aluminum oxide. Under Taking into account the impurities in the starting materials, this composition is shown at I in FIG.

It goes without saying that the process according to the preceding examples can also be carried out with starting mixtures which consist only of silicon oxide, aluminum oxide and aluminum nitride. However, it has been found that when using such mixtures, which naturally lack silicon nitride, hot pressing leads to reactive substances which contain silicon ©, aluminum, nitrogen and oxygen in the necessary proportions to provide the atomic ratio © given above, however, the z-value is always »greater than 4. The ceramic materials that originated from mixtures in which silicon is not present, so always point z values of more than 4 in & ^e £ above formula. The reason for this can be readily seen by referring to the line J in Fig. 1, it being understood that in the mixtures having compositions which fall on this line, the silicon, aluminum, nitrogen, oxygen in the required amounts Atomic ratios are present in order to develop a ceramic material

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hen, ds, s satisfies the above formula, in which ζ is 4. Thus, as can be seen, the line J goes through the aluminum / nitride / silicon oxide axis, which of course corresponds to the situation in which there is no silicon nitride. Furthermore, it goes without saying that with the reduction in the silicon nitride content of mixtures which lie in the hatched area B, the ceramic materials arising from this basic structure have increasing ζ values in the above formula. If a mixture is therefore based on the triangular area fr, llt, which is formed between the All ·!, - Al ^ O ₇ - and SiOo sockets, whereby this area naturally _{corresponds to a content of Si 7} N, of EuIl, produces this Mixture necessarily a ceramic material with a value greater than 4.

In order to illustrate the effect of omitting the silicon nitride, the starting materials of the previous example were used in a sixth example to produce a M mixture consisting of 51 »45 wt .- / aluminum nitride, 19 * 18 wt .-}. Aluminum and 29.37 wt. Silicon oxide existed. Taking into account the impurities in the starting materials thus, the actual composition of the mixture was 48.75 wt -. ^ (62.78 Koi- /) aluminum nitride, 21.73 wt} '. (11.25 mol /) aluminum oxide and 29.52% by weight (25.97 mol /) silicon oxide. The mixture was treated as in the previous examples and hot-pressed at 1850 C, and at this temperature the mixture consisted of more than 95 wt .- / a reactive substance in which the silicon oxide in a molar ratio of 1: 2 with a part of the aluminum nitride and the alumina were present in a 1: 1 molar ratio with that of the aluminum nitride. At the hot preheating temperature, the components of the reactive substance also reacted together to produce a ceramic material which satisfied the above formula and had a z-value of Λ.6 . The a and c unit cell dimensions of the ceramic material were 7 »745 A ^ao and 3.012 A °, respectively.

It is of course understood that the ceramic materials, the values of ζ of more than 4 i & of the above equation also from starting mixtures can be made containing silicon nitride. In a seventh example, a ceramic material with a z-

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value of / j, 6 by hot pressing "at 185O ⁰ C of a starting egg made from 10.19 wt. -, ί aluminum nitride and 15, θδ wt .- ^ silicon nitride, all starting materials again being those used in the fifth example. Taking into account the impurities in the starting materials, the mixture thus consisted of 12.15 col. ?. Silica, 28, 6 HoI-C alumina, 52/6 fetch ;: aluminum nitride, and 'J, 03 mol /' from silicon nitride dieseen figures can be readily calculated that the mixture of more than 895 wt -. ' / ■ a reactive substance at the hot-pressing temperature in which the silicon oxide, the aluminum oxide and the aluminum nitride were in the required molar ratios. The resulting ceramic material had the same a- and c-unit cell dimensions as the material of the previous example.

It should be understood that in each of the above examples, hot pressing the output mixture gave rise to a reactive substance, which not only had the required molar ratios of aluminum nitride, alumina and silica, but also the total volume of the starting mixture. It will be understood, however, that provided that the reactive substance is at least 95% by weight; ';, des Mixture makes up other materials in the mixture at the hot press equipment may be present. The other materials can be in the form of excess amounts of one or more of the starting materials be present, and preferably they are arranged so that a molten Glass is created to help seal the ceramic material that is created during hot pressing. Appropriately the molten glass is an alumino, borosilicate or iron silicate glass or alternatively a magnesium glass, a manganese glass or a lithium glass. In the case of a magnesium glass, the starting mixture is arranged to contain magnesium oxide and a glass-forming agent, the the latter is preferably in the form of silicon oxide.

In each of the preceding examples, the starting mixtures were run through Mixing together the actual ingredients required for the reactive composition. It goes without saying

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however, that one or more of the ingredients present in the reactive Substance needed in the starting materials as a compound could have been introduced during the hot pressing ^ decomposed into the required component or components. For example, aluminum hydroxide could have been the starting materials can be added to allow aluminum oxide to form in the reactive substance, while the addition of ethyl silicate to the output materials for the required silicon oxide for the reactive Substance would have provided. Other suitable additives to the starting materials are silicon oxynitride (for supplying silicon oxide and silicon nitride) and aluminum oxynitride (to supply aluminum oxide and aluminum nitride).

To illustrate the situation in the preceding paragraph, in an eighth example of the invention, a ceramic material with a value of 2 in the above formula was produced by hot pressing for one hour at 170 ° C. of a starting mixture consisting of 8.94 wt. - ^ silicon nitride, 29.36% by weight of aluminum nitride, 1% by weight of silicon oxide and 6o.7% by weight; ·: silicon oxynitride. In this mixture the silicon oxynitride had an average particle size of 2 microns and was supplied by Notöton Compang of America, while the other starting materials were the same as used in the previous example. The silicon oxynitride was found to contain free silicon nitride and also a ^1/1- puddle contamination of silicon oxide, but analysis indicated that these were present in the necessary molar ratios to produce silicon oxynitride. For the purpose of calculating the composition of the starting mixture, it was therefore possible to regard the silicon oxynitiide as the pure material. Furthermore, it can readily be shown that 2 moles of silicon oxynitride are equivalent to 1 mole of silicon nitride and 1 mole of silicon oxide, so that, taking this equivalent into account and also compensating for the impurities in the silicon nitride and in the aluminum nitride, the effective total composition of the starting mixture 51,089 Wt .- yi (26.42 mol-p) silicon nitride, 27.57 wt .- '; · (48> 69 mol- #?) Aluminum nitride, 1.76 wt .- ^ (1.25 mol-? Q aluminum oxide and 19.56 wt .- (25.65 mol £ silicon oxide.

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This mixture consisted of more than
95 wt. -Ji of a reactive substance in which the silicon oxide in
a 1: 2 molar ratio was present with a portion of the aluminum nitride, while the sluninium oxide was present in a 1: 1 molar ratio
the remainder of the aluminum nitride was present.

It goes without saying that when carrying out the method according to the invention sintering of the starting materials at or above 1200 G was carried out must be because under this temperature no or hardly any reaction occurs in order to create the required ceramic material. the However, the sintering temperature should not exceed 2000 0 because at least some of the substances have a pronounced tendency above this temperature

show decomposition. The optimal temperature is usually between

o °
see 1500 0 and 1800 C because that results in a reasonable xteaktionsrate

without causing great weight loss. When ceramic materials however, the aim is to produce the z-values which are in approximate formula 5 above, sintering above this should be optimal The solid solubility of the reacting area should be carried out Improve fabrics. For this reason, hot pressing at 1850 0 in the production of high-grade materials has been used and seventh example carried out.

Furthermore, it goes without saying that heating is used in the above examples is associated with pressurization, but also with heating can be done without pressure.

Expectations

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Claims (1)

Expectations 1. Ve £ process for the production of a ceramic material, characterized in that at »a temperature between 1200 0 and 2000 C a mixture, the silicon nitride in an amount of up to 90 wt .- ¹ ; '· the mixture together with between 1 and 60 wt . - ']'. ■ aluminum nitride, between 0.5 and 50 wt .-,! · Silicon oxide and between 0.05 ^and βΟ wt .- '; ü contains aluminum oxide, is heated, some, but not all of the Silica is present in the mixture at both temperature as an impurity containing the silicon nitride, the silicon nitride, aluminum nitride, aluminum oxide and silicon oxide forming a reactive substance at the temperature which is at least 95% by weight of the mixture and in which the silicon oxide in a molar ratio of 1: 2 with a part of the aluminum nitride and the aluminum oxide in a molar ratio of 1: 1 with the Hest of the aluminum nitride, the constituents of the reactive substance for the bil Reaction of the required Keramilcwaterials with each other. 2. The method according to claim 1, characterized in that that the relative proportions of silicon nitride, alurainium nitride, Silica and alumina are such that in the substance the Atomic ratio of silicon: xU.uminium: nitrogen oxygen 6-z: z: 8-z: z where ζ is greater than Hull and less than or equal to 5. 5 · Process for the production of a ceramic material, characterized in that a mixture is heated at a temperature between 1200 C and 2000 G, in which silicon nitride is not present, but which is between 40 and 60% by weight ·;:! Aluminum nitride, between 15 and 45 wt -fc silicon oxide and from 0.05 to 50 wt. ^1; " Contains aluminum oxide, the relative proportions of aluminum nitride, aluminum oxide and silicon oxide being such that at the temperature a reactive substance is formed which forms at least 95% by weight of the mixture and in which the silicon oxide in a col ratio of 1: 2 with a portion of the aluminum nitride and the aluminum oxide in a molar ratio of 1; 1 with the reads of the aluminum nitride are present, Va / Ti -L- 6098 13/0615 SAD original where the atomic ratio of silicon: aluminum: nitrogen: oxygen in the substance 6-z: z-: 8-z: s cheats, where a is greater than 4 and less is than or equal to 5, the constituents of the reactive substance for the formation: of the necessary training materials react with one another. /; j. Process according to one of Claims 1 to 5, characterized in that at least part of the aluminum oxide in which equipment at the temperature is present as an impurity, which contains the aluminum nitride. 5. Method ne.ch onea of claims 1 to ^, characterized in that at least one of the constituents present in the mixture at the temperature is introduced as a compound _{into the starting materials 9 used to prepare the mixture} which reacts to form the required ingredient or ingredients during heating. 6. The method according to claim 5 »characterized in that that the compound silicon oxynitride, alurainium oxynitride, ethyl silicate or aluminum hydroxide. 7. Method according to one of Claims 1 to 6, characterized in that pressure is applied to the appliance during heating is exercised. 8. The method according to any one of claims 1vis7> characterized in that a molten GaIs is included in the mixture the temperature is also present. 9. The method according to claim S, characterized in that that the molten glass is an alumino, borosilicate or iron silicate glass or manganese glass or a conductive glass. 10. The method according to claim 8, characterized in that that the molten glass is a magnesium glass. 11. The method according to "claim 10, characterized in ge - 809813/0615 ~ ^? ~ BATH ORIGINAL net that the aäSagnesiumglas by reaction during heating between magnesium oxide and a glass-forming compound is formed, both of the latter substances being present in the mixture. 12. The method according to claim 11, characterized net that the glass forming compound is silicon oxide. 609813/0615 Blank page