DE2461741A1 - METHOD FOR MANUFACTURING A Sintered CERAMIC PRODUCT - Google Patents

Description

COHAUSZ ft FLORACK

D-4 DÜS S BLDORB ¹ . SCHUMANNSTB. Θ7

PATENT LAWYERS:
Dipl.-Ing.-W. COHAUSZ Dipl.-Ing. W. FLORACK Dipl.-Ing. R. KNAUF · Dr.-lng., Dipl.-Wirtsch.-lng. A. GERBER ■ Dipl.-Ing. HB COHAUS2

Joseph. Lucas Limited

Well Street

GB-Birmingham 23rd December 1974

Method of making a gridded ceramic

product

The invention relates to a method for producing a sintered one Ceramic product.

A method according to the invention is characterized in that aluminum nitride and silicon oxide at a temperature of between

ο °
1200 C and 2000 O is brought to Heaktion, in such a way that a single-phase silicon-aluminum oxyntride ceramic material is formed, the reaction mixture containing not more than 60 wt .- ^ of the aluminum nitride at the temperature and also containing first and second metal oxides, in which it is not silica, said metal oxides being designed to introduce a combination of magnesia and alumina alone into the mixture and further designed to react with a portion of the silica to form a silicate glass combine, which has a liguidus temperature below that which the silicate glass, which is formed from silicon oxide with one or the other of the metal oxides alone, the resulting silicate glass aids in the densification of the ceramic material.

Preferably the ceramic material contains an excess of more than 95 weights - a combination which satisfies the following formula:

^Si 6-z ^A1 z * 8- ° _Z - where ζ is greater than zero and less than or equal to 5.

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A method according to another feature of the invention is characterized in that at a temperature of between 1200 C and 2000 0 a mixture is sintered which contains between 15 and 45 wt .- ^ a silicon oxide, between 0.05 and 50% by weight of aluminum oxide and between 40 and 60% by weight Contains aluminum nitride in such proportions that at the temperature a ceramic material is produced that contains at least 95% by weight of a compound contains that of the formula

^Si 6-z ^A1 z - ^N 8-z ⁰ Z

is sufficient, where ζ is greater than Full and less than or equal to 5, where the gepisch also contains at least two metal oxides, other than silicon oxide, which are intended to be used during heating these react with part of the silicon oxide which is present in the mixture in such a way that a silicate glass is formed which has a liquidus temperature who has the silicate that is made from silicon oxide with one or the other of the metal oxides alone, the Glass supports compression of the ceramic material.

The mixture preferably contains silicon nitride at the temperature, and the relative proportions of silicon nitride, aluminum oxide, aluminum nitride and silicon oxide in the mixture are such that a substance capable of cation is formed at the temperature which is at least 95% by weight of the mixture and in which the atomic ratio of silicon t aluminum: nitrogen: oxygen is 6-z: zt8-z: z, where ζ is greater than zero and and less than or equal to 4, the components of the reactive substance reacting with one another in such a way that the ceramic material is created.

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

Alternatively, if the mixture does not contain silicon nitride, the relative ones are Proportions of aluminum oxide, aluminum nitride and silicon oxide in the mixture in such a way that a reactive material at the temperature which forms at least 95% by weight of the mixture and in which the

6 0 9 8 2 7 / 0'7 2 6

Atomic ratio of silicon: aluminum: nitrogen oxygen 6-z: z: 8-z: z is, where ζ is greater than 4 and the like. is less than or equal to 5, wherewith the components of the reactive substance react together to form the ceramic material.

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

The liquidus temperature is preferably that of silicon with the metal oxides The silicate formed together is at least 100 ° C below that of the silicate that is formed when the silicon is alone with each metal oxide is combined.

Preferably the heating step is accompanied by pressure. *

When the metal oxides are each pressing aids for the ceramic material, is preferably their total amount in the mixture is less than the amount needed when each metal oxide is present alone.

Alternatively, the heating is carried out without applying pressure.

Appropriately, at least one of the ingredients in the Mixture at the stated temperature are present in the starting materials that are used to produce the mixture, as a Substance introduced for the required component or for ' provide the necessary ingredients at the temperature.

Appropriately, at least one of the metal oxides is in the mixture Introduced as a metal compound, referring to the required oxide may decompose during heating.

Alternatively, before the reaction to produce the silicate glass, at least one of the metal oxides in the mixture in combination with a portion of the silicon oxide is present as a metal silicate.

The metal oxides are preferably selected from the group consisting of

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Magnesium oxide, aluminum oxide, a manganese oxide, lithium oxide, tfeitandioxid, a boron oxide and ferric oxide.

For comparison purposes, a control experiment was first carried out, in the case of silicon nitride, aluminum nitride and silicon oxide in powder form were mixed in the required proportions to produce a ceramic material which was essentially entirely composed of one compound, which satisfied the following general formula:

^Si 6-z ^A1 z * 8-z ° z

Here ζ was equal to 1.

The silicon nitride powder used consisted of $ 89 of the alpha phase material and had an average particle size of 3 microns. Bas aluminum nitride powder was the one that by the Koch-Light of the Ty penbezeichnung '8006h' is supplied and in the delivered state, a mean particle size of 11.5 microns hatete, however, prior to use in a colloid mill to an average particle size of -7 microns has been reduced in size. Furthermore, the silicon powder used was that supplied by Hopkin and Wilfeliame Limited as pure precipitated silicon oxide. It was known, however, that the silicon nitride powder contained silicon oxide as a coating over the particles of silicon nitride and that the aluminum nitride further contained aluminum oxide as an impurity. As can be readily understood, both impurities caused the subsequent reaction to produce the silicon-aluminitra-oxyixftride ceramic material because they add silicon, aluminum and oxygen to the reaction. Therefore, prior to mixing the starting materials described above, the impurity levels in the silicon nitride and aluminum nitride were determined by non-heutreon activation analysis, and these impurities were then taken into account to arrive at the required composition for the mixture. Using the respective starting materials given above, it was found that the silicon oxide content of the silicon nitride powder was 4% by weight and that the aluminum oxide content of the aluminum nitride was 5% by weight. From these results, it was calculated that in order to obtain the required

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To obtain ceramic material, the required composition for the starting mixture was 78.48% by weight of the silicon nitride powder, 14 »6 % by weight of the aluminum nitride powder and 6.76% by weight of the silicon oxide powder alone, because taking into account the impurities in the Silicon nitride and, in the aluminum nitride, this mixture provided silicon, aluminum, nitrogen and oxygen in the required proportions, next

6-z: Z; 8-z t ζ

Here ζ was equal to 1.

To the above mixture was added a first metal oxide in the form of magnesium oxide powder, which of course is a known hot-pressing aid for silicon nitride ceramic materials. The magnesia powder was that supplied by Hopkins and Williams Limited under the designation "light" and the amount of magnesia added was such that it constituted 1 % by weight of the total mix. The Gesamtzu composition of the starting mixture so betraug 74 »6 wt -. $ Silicon nitride, 13.72 wt .- # aluminum nitride, 9.8 wt .- $ £ silica, 0.88 wt fo alumina and 1 wt -. $ Magnesium oxide.

After the magnesium oxide powder had been introduced, the starting mixture was introduced into a colloid mill and mixed in isopropyl alcohol until the mean particle size of the mixture was 3 mArons. The mixture was then dried and then it was sieved to remove any powder agglometates. A contamination determination was then made on the Gemisoh which showed that milling, drying and sieving had not changed the contamination levels of the starting materials. The Gemisoh was then placed in the mold space of a graphite mold on a graphite stamp, which closed one open end of the mold space. A graphite stamp was then placed on the powder batch, all graphite surfaces that were in contact with the powder had previously been spray-coated with boron nitride to a depth of the order of 0.25 mm. The tool was then placed in a press, where the temperature and pressure were increased at the same time, for a period of 30 minutes.

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grooves, to 1800 C and a pressure of 1.5 tons / sq.in. The mixture was then held at this temperature and pressure for one hour, and under these conditions it consisted entirely of magnesium oxide together with a reactive composition in which the atomic ratio of silicon {aluminum: nitrogen: oxygen in the The ratios given above were, of course, the ratios required in the ceramic material being manufactured. "The components of the reactive composition thus reacted together to form the required ceramic material, the hot pressing being assisted by the magnesium oxide additive. During cooling the hot-pressed product was taken out of the mold and subjected to X-ray analysis, which showed that the ceramic phase of the product consisted entirely of a compound having a z-vert of 1 in the above formula, and the product was found to have a density of 3.16 g / om ^ , whereby it should be noted that that during hot pressing the mixture had reached 90% of this final density when the temperature had reached about 150 ° C. The final product was also found to have a room temperature modulus of rupture of 60,000 psi and a W _e ibull modulus of 8.0.

In a first example according to the invention, the starting mixture of the control experiment was used again, except that in this example the magnesium oxide content was reduced from 1% by weight to 0.5% by weight and also ate a second metal oxide in the form of 0 , 5 wt .- & manganese oxide (Μη, Ο,) was introduced into the mixture. The manganese oxide used was supplied by Hopkin and Williams Limited, and in this example the procedure was repeated after the control experiment. Upon removal from the mold, the solid product was found to have an average rupture modulus at room temperature of 82,000 psi, a Weibull modulus of 10, and a density of 3 »23 g / cm3. Further, by following the movement of the graphite die during the hot pressing process, it was found that the sample had reached 90% of its bond density by the time the temperature reached about 1450 ° C, which was of course a lower temperature than the control experiment.

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In the method according to the first example, the manganese oxide and the magnesium oxide with each other, with a part of the silicon oxide in the

mixture was present to produce e.g. in magnesium-manganese-silicate glass to let whose liquidus temperature was below that of the silicate, this occurs when magnesium oxide is used alone. So during the hot pressing, the magnesium manganese silicate provided one less viscous liquid glass than that from the magnesium silicate of the control experiment was delivered at the same temperature. Consequently the magnesium manganese silicate glass made it easier to compress of the material being hot-pressed, resulting in a bath product with improved consistency, strength and clarity.

In a second example of the invention, the process of the first example was repeated, but in this case the magnesium oxide and the magngan oxide were increased in their content in the starting mixture to 1 wt .- ^ of the total mixture, while the silicon nitride content was increased by 1 wt .- ^ was reduced. The impurities on the silicon and. Aluminum nitrides were taken into account, the starting mixture consisted of 73.6 wt .- # silicon nitride, 13.7 wt .- # aluminum nitride, 9.8 wt .- # silicon, 0.68 wt .- # aluminum oxide, 1 wt .- $ magnesium oxide and 1 wt% manganese oxide. The final product had an average rupture modulus at tree temperature of 95,000 psi, Weibull modulus of 8.4, and bath density of 3.24 « ⁰ C reached.

In a third embodiment of the invention, the method of the first example repeated again, in this case the manganese oxide content was but increased to 1% by weight of the total mixture without the magnesium oxide content has been increased '. Furthermore, the silicon nitride content reduced by 0.5 wt .- ^ to compensate for the increase of the magnesia content to create so that the overall composition of the starting mixture now 74 »1 wt .- ^ silicon nitride, 13.72 wt .- ^ Aluminum nitride, 9.8 wt .- $ silicon oxide, 0.88 wt .- # aluminum oxide, 0.5 wt% magnesium oxide and 1 wt% manganese oxide. Bas end product had an average modulus of rupture at room temperature of 100,000 psi

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and a Weibull modulus of 9> 0 and a density of 3.20 g / cm. Again it was found that during hot pressing, the material reached 90% of its end thickness at a temperature of about 1450 ° C.

In a fourth example of the invention, the magnesium oxide was des third example decreased by 0.25 wt .- $, and the silicon nitride content was increased by an equal amount. The procedure of the control experiment was repeated to give a final product with an average modulus of rupture of 105,000 psi at room temperature, a Weibull modulus of 12 and a density of 5.21 g / cm. Again it was found that during hot pressing the material was 90 $ of its final density reached at about 1450 ° G.

Better results should therefore be achieved in the method according to the fourth example have been reached, well the relative proportions of magnesium oxide and the manganese oxide were such that a magnesium manganese silicate with a very low liquidus temperature, possibly in the Magnitude of 1200 C. Some magnesium and / or manganese should also be in the silicon-aluminum oxynitride lattice.

In a fifth example of the invention, the procedure of the first example was repeated, but in this case the magnesium oxide content was reduced to 0.05% by weight and the manganese oxide content to 0.2% by weight, while the silicon nitride content was reduced in proportion has been increased in the amounts of oxide additives. The total composition of the starting material of the fifth example was thus 75.6 wt .- $ silicon oxide, 15.72 wt .- $ aluminum nitride, 9.8 wt .- $ silicon, 0.88 wt .- $ aluminum oxide, 0.05 wt .- $. - $ Magnesium Oxide and 0.2 wt .- & $ Manganese Oxide. The end product resulting from this mixture had an average Bruoh modulus at room temperature of 55 psi, a Weibull modulus of 7.0 and a density of 2.78. It was also found that $ 90 to its final density achieved at a temperature of about 1500 ⁰ O during the hot-pressing the material. Further, when the product was subjected to a smell test at 1225 C with an applied load of 5 tsi, it was found to undergo a creep of $ 0.105 in 100 hours.

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In a sixth example of the invention, the mixture that was hot-pressed again contained the first and second metal oxides used in the first example in the same amounts by weight. In this example, however, different batches of silicon nitride and aluminum nitride were worked as powders, and the relative proportions of the raw materials were changed. The "mixture now consisted of 85 wt .- ^ silicon nitride, 10 wt .- ^ aluminum nitride, 6 wt. -Fo silicon oxide and 0.5 wt .- $ each of magnesium and manganese oxide. The mixing and hot-pressing process of the control experiment were each repeated, and on removal from the mold it was found that the end product had an average viscosity modulus at room temperature of 102,000 ρ si, a Weibull modulus of 10 and a density of 3.2 J gm / cm. In honor of the hot pressing, it was found that the sample had also reached 905ε of its bond density,. reached as the temperature is about 145 ° C ^0.

In the case of the starting mixture of the sixth example, the analysis showed that the silicon content of the silicon nitride powder was 2.6% by weight and that the aluminum oxide content of the aluminum nitride powder was 4.25% by weight. Using these numbers, it can easily be calculated that at the hot pressing temperature this starting mixture gives a reactive composition consisting of silicon, aluminum, nitrogen and oxygen in the atomic ratio of 6-zxz * 8-ziz, where ζ is on the order of 0.8 which, however, only made up about 90 vol. 56 of the total mixture. As expected, therefore, the sintered product of the sixth example contained about 5% by weight of a galase phase in addition to a silicon-aluminum oxyntride ceramic material which obeyed the formula SIc ₂ A ₀ 3 ^N 7 2 ⁰ O 8, with some proportions . Weight losses were also observed.

In a modification of the sixth example, the same procedure was used repeated with three separate starting mixtures containing different amounts of the magnesium and manganese oxide powder, wherein the silicon nitride content of the mixtures is adjusted where necessary that was to compensate for the changes in the quantities of the existing Metal oxide was created. The results of this change are given in the following table:

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Composition by weight of the starting mixture

Properties of the hot-pressed product

Si » Aiii SiO ₂ MgO MnO Medium Fractional Weibull density , 5 mdoul module 5.24 82 , 75 10 6th 1 1 110,000 psi 8.4 5.20 82 10 6th 0.5 1 110,000 psi 7.2 5.21 82 10 6th 0.25 i 114,000 psi 20.8

From the table above it can be seen that, as in the fourth example the best results are obtained when the mixture contains 0.25% by weight of magnesium oxide and 1% by weight of manganese oxide.

In a seventh example of the invention, the starting materials of the control experiment were used again, but lithium oxide was used as the second metal oxide in place of the manganese oxide used in the previous examples. The lithium oxide was introduced into the starting mixture as lithium silicate which was supplied by Koch-Light Laboratories Limited as lithium silicate 99.5 $ 525 mesh. The treatment was conducted as in the previous examples, and the relative proportions of the starting materials such that when the Heißpreßtemperatür the total composition of the mixture 71.6 wt .- $ 'silicon, 15.72 wt. -Fo aluminum nitride, 0.88 wt. -. ^ aluminum oxide, 0.125 wt -fo magnesium oxide, 0.125 wt .- ^ lithium oxide and 9.8 wt .- ^ silicon oxide wherein a part of the latter was obviously contributed by the lithium silicate as well as by the Siliziumiitrid, was. The relative proportions of lithium oxide and magnesium oxide in this mixture were selected from the lithium oxide / magnesium oxide / silicon oxide / temperature diagram, which showed that when silicon oxide reacted with these proportions of lithium oxide and magnesium oxide, a silicate was formed which had a lower liquidus temperature than the magnesium silicate of the Control experiment. Subsequent treatment of the mixture followed the procedure of the control experiment, and the resulting product had a density of 5.21 g / cm, an average modulus of rupture at room temperature.

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temperature of 80,000 psi and a Weibull module of 12.

In a modification of the seventh example, the same procedure was repeated, in this case the total composition of the starting mixture was 75.1% by weight silicon nitride, 13.72% by weight aluminum nitride, 9.8% by weight silicon oxide, 0, 88 wt .- $ alumina, 0.25 wt <fi magnesium oxide and 0.25 wt .- ^ lithium oxide. The final product had a density of 3.17, an average modulus of rupture of 100,400 psi at room temperature, and a Weibull modulus of 14 "6. The product was also found to be $ 90" during hot pressing. Final density reached at a temperature of about 135O ⁰ C.

In a further modification of the seventh example, the previously used lithium silicate was added to the starting materials of the sixth example instead of manganese oxide, so that the total composition of the mixture was 83.5% by weight silicon nitride, 10% by weight aluminum nitride, 0.125% by weight . - <$> magnesium oxide, 0.125 wt. Lithium oxide and 6 wt. & $ Silicon oxide, part of the latter being naturally contributed by the lithium silicate a density of 3 » ² ^ g / om, an average modulus of rupture of 99 * 000 psi at room temperature and a Weibull modulus of I3.

In an eighth example according to the invention, the starting mixture of the control experiment was used again, except that in this example the magnesium oxide content was reduced from 1% by weight to 0.5% by weight and that, in addition, 0.5% by weight of titanium dioxide was introduced into the mixture. The control experiment procedure was then repeated and, upon removal from the mold, the final product was found to have an average room temperature brew modulus of 90,000 psi, a Weibull modulus of 12.6 and a density of 3.19 g / cm . By following the movement of the graphite stamp during the hot pressing process, it was also found that the sample reached 905ε of its final density after the temperature had reached about 135O ⁰ C, which was of course a lower temperature than in the control experiment. Further, when the product is subjected to a creep test at 1225 ° C at an

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practiced load of 5 t.si. was subjected to, it was found that the product underwent a $ 0.10 creep in 20 hours.

In the same way as that in the method according to the first example metal oxides used, the magnesium oxide and titanium dioxide of the seventh example reacted with part of the in the starting mixture existing silicon oxide to a magnesium-titanium particlate glass to be formed, the liquidus temperature of which was below that of the silicate that is formed when magnesium oxide is used alone in the control experiment is used. During the hot pressing, the magnesium-titanium silicate was produced thus a less viscous liquid than that which the magnesium silicate of the control experiments at the same temperature. The magnesium titanium silicate thus made a simpler sealing possible of the material that has been hot-pressed, resulting in an end product of improved consistency, strength and density.

In a new example of the invention, the goal of the previous example was repeated, but in this case the amounts of magnesium oxide and titanium dioxide in the starting material were both increased to -1% by weight of the total mixture, while the silicon nitride content was decreased by 1% by weight became. Thus Bas Ausgangsgemisoh contained 75 "6 wt ~ # silicon nitride, 15.72 wt -.% Aluminum nitride, 9.8 wt .- ^ silica, 0.88 weight-56 alumina, 1 wt -fi magnesium oxide and 1 wt .- ^. Titanium dioxide. The final product had an average rupture modulus at room temperature of 7,000 psi, a Weibull modulus of 8, and a final density of 3t. Further, it was found that during hot pressing the material reached 90% of its side density at a temperature of about 1550 ° C.

Although only two metal oxides were added to the starting material in each of the preceding examples in order to produce the required silicon-aluminum oxynitride, it is understood that more than two metal oxides can be used. In a tenth example of the invention, the procedure according to the preceding examples was repeated, with a starting mixture consisting of 10 wt .- ^ aluminum nitride, 6 wt .- ^ silicon oxide, 85.7 wt .- # silicon nitride, 0.1 wt - $ magnesium oxide, 0.1 wt .- $ lithium oxide and 0.1 wt .- ^ boron oxide (B ₂ O,)

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was standing. In this mixture, the magnesium oxide and lithium oxide formed a first and a second metal oxide, respectively, and these were introduced in equal proportions by weight as in the seventh example, because they then reacted with part of the silicon oxide which was present to form a low-melting glass to let. the effect of adding the third metal oxide, that is the boron oxide, was that which was lowered the melting point of the glass. the eingesetz- in this example, 'te boron oxide was OaIo! ne of Orthoborsäure at 800 ⁰ G generated, the resulting oxide was then ground and mixed with the other starting materials in a colloid mill, using this mixture it was found that the ceramic phase of the hot-pressed product consisted essentially entirely of a compound having a value of the order of 0.8 in the preceding 1-order The product was also found to have an average Bruoh modulus at tree tempera ture of 90,000 psi, a Wiebull module of 10. Further, when the sintered product was subjected to a creep test at 1227 ° 0 and with an applied load of 5 tsi, it was found to undergo creep of $ 0.05 in 100 hours. ,

In a modification of the tenth example, the procedure was repeated, but with 0.1 Gew.r $ a fourth metal oxide in the form of aluminum oxide, which was added to the starting mixture, the Siliziumnitridgehalt of the mixture to 0.1 wt -.% Was reduced to compensate for the alumina addition. It was found that the addition of the alumina also aided in densification of the ceramic material during sintering.

Yes

In an eleventh EXAMPLE three metal oxides were re i ⁿ the initial mixture introduced, which in this case consists of 11 wt .- ^ aluminum nitride, 6 wt .- $ silicon oxide, 80.75 wt .- $ silicon nitride, 0 * 25 wt .- $ of magnesium oxide , 1 wt .- $ manganese oxide (Mn, Q ₄ ) and 1 wt .- $ ferric oxide consisted. The hot pressing of the control experiment was repeated and, as in the previous example, the ceramic phase of the resulting product consisted essentially entirely of a compound having a ζ value of about 0.8 in the formula above. The product was also found to have a mean rupture modulus of 1105000 psi at room temperature and a Weibull modulus of 20.

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It is to be understood that each of the foregoing examples is excerpted from pressure could have been done during sintering. In a twelfth example of the invention, a sample of the starting mixture was thus used from the previous example placed in a rubber bag and isostatic at tree temperature and at a pressure of 20,000 t.s.i pressed using a hydraulic enclosure, ttm to create a preform which had a density of 1.5 g / cm3. This preform was then coated with a mixture consisting of equal parts by weight of boron nitride and silicon oxide, and it became buried in a boron nitride powder bed contained in a graphite pot was. The whole was then heated for one hour at 1700 ° 0, and the temperature was then increased to 1800 0 and held at this value for a further hour. The sintered product had one mean breaking modulus at room temperature of 45,000 ps.i., a Weibull modulus of 12 and a density of 2.55 g / cm *.

In each of the above examples, the ceramic phase of the sintered product consisted entirely or predominantly of a compound which satisfied the above formula and had a z value equal to or less than one. It is understood jedooh that the method described can also be used to ceramic materials »manufacture, the values up to 5 have i ⁿ d.er above formula. In a thirteenth example, a ceramic material with a z-value equal to 4 in the above formula was thus produced by sintering a starting mixture consisting of 38 wt .- ^ aluminum nitride, 22.5 wt .- $ silicon oxide, 22.5 wt .-% - aluminum oxide, 16% by weight & $ silicon nitride and 1% by weight lithium oxide. In this mixture, some of the aluminum oxide formed one of the glass-forming metal oxides, while the best reacted at the elevated temperature of the sintering process to produce the required ceramic material. Furthermore, the lithium oxide was added to the starting materials in the form of lithium silicate as in the seventh example, so that "part of the silicon oxide in the starting mixture was applied by the lithium silicate" If the starting mixture was hot-pressed according to the method of the control experiment, the resulting sintered product had an average modulus of rupture at room temperature of 45 «000 psi, while when the mixture without the application of pressure after.

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was sintered using the method of the twelfth example *, the sintered Product has an average modulus of rupture at skin temperature of 55 * 000 psi and had a Weibull modulus of 8.

Although · in the preceding examples, the mixtures that heated have been »to create the desired ceramic product, Have contained silicon nitride, the described Yefrfahren can also be carried out with mixtures consisting solely of silicon oxide, aluminum oxide, aluminum nitride and two or more metal oxides. However, if silicon nitride is not present in the starting mixture, it is been found to be in the reactive substance when heated arises, the atomic ratio of silicon: aluminum »silicont Oxygen can be equal to 6-ztzi8-z: z, but the ζ value always increases as 4 is »The ceramic material obtained from such a material so always has a z-value that is more than 4 in the 4's above Formula is «. , ■

It is understood that in the examples described, one or more the metal oxides can be introduced into the starting mixtures as metal compounds that relate to the required oxides when subsequent Can decompose when heated. As in the seventh example, the metal oxides can be used in combination with part of the silicon oxide be introduced as metal silicates. Furthermore, this can be in the mixture required alumina at hot press temperature in raw materials can be introduced as aluminum hydroxide, while the silicon oxide can be introduced as ethyl silicate. Accordingly, as Raw materials silicon oxynitride (for supplying silicon oxide and silicon nitride at the hot pressing temperature) and aluminum oxynitride (for the delivery of aluminum nitride and silicon oxide at the hot pressing temperature) be used.

When carrying out the method described above, it is preferred at least one of the metal oxides that react to form the silicate glass with low melting point, able to produce in the Crystal lattice of the resulting silicon-aluminum oxynitod ceramic material to penetrate. In this way, the glass not only melts

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rend of boiling, the compaction of the raw materials and do to support the production of the required compacted ceramic product, but also when the temperature is on the for the production of the ceramic material required increases the composition of the glass changed due to the fact that a part of at least one of the metal oxides gets into the ceramic lattice. This change in the glass composition is believed to be accompanied by an increase in the melting point of the glass, so that the high temperature properties of the densified ceramic product can be improved. In this regard, it is to be understood that all are disclosed above Metal oxides are able to get into the lattice of the resulting ceramic materials.

In each of the starting mixtures of the preceding examples, the total amount of metal oxides that react to form the low melting point silicate glass is on the order of 2 parts by weight of the mixture and less. It will be understood, however, that larger amounts of the metal oxides can be used with benefit, especially when sintering is done without the application of pressure to aid densification. In this regard, the metal oxide content is normally adjusted so that, taking into account weight loss during sintering, the amount of silicate glass in the sintered product does not exceed 5% by weight of the product. This is of course not an absolute limit, because higher glass contents can be tolerated, especially if the product is to be used at low temperatures and in situations where its creep resistance is not important (e.g. as a corrosion-resistant material).

It is natural in performing the methods described above possible that one or more of the starting materials contain as impurities metal oxides which react with silicon oxide to create a silicate glass with a low melting point. It is therefore necessary to include such impurities in the calculation the amounts of metal oxide added to the starting materials.

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It is further understood that a sintering of the starting materials "at or above 1,200 ⁰ G must be carried out in the implementation of the method, because below this temperature little or no reaction occurs to give rise to the required ceramic material. However, the sintering temperature door adarf not exceed 2DOO ⁰ C because above this temperature for at least some substances show a marked tendency to separate. The optimal temperature is therefore
between 1500 ° 0 and 1800 ⁰ O, because this leads to a reasonable reaction rate without leading to large weight losses. Bs understands
however, even if the sintering temperature is within the optimum range, some weight loss is inevitable, such as lithium oxide in the seventh, tenth and thirteenth examples, and these must be taken into account when calculating the composition of the raw material.

Expectations

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Claims (24)

J2 f in languages 1. Yerfaiiren for the manufacture of a sintered ceramic product, characterized in that aluminum nitride and silicon oxide are reacted at a temperature of between 1200 ° C and 2000 ° C, such that a single-phase silicon-aluminum oxynitride ceramic material arises, the reaction mixture at the temperature containing no more than 60 wt .- ^ of the aluminum nitride and also contains first and second metal oxides, which are not is silicon oxide, the metal oxides mentioned are provided in such a way that they contain a combination of magnesium oxide and aluminum oxide in the mixture introduce alone, and are further provided so that during the reaction they are with a portion of the .Silikumids to form a Combine silicate glasses that have a liquidus temperature below that which has the silicate glass made from silicon oxide with one or the other of the metal oxides alone, the resulting silicate glass supports the compaction of the ceramic material. 2. The method according to claim 1, characterized in that that the ceramic material has more than 95 wt .- ^ of a compound that contains the formula ^Si 6-z ^A1 z ^N 8-z ° z fulfilled, in which ζ is greater than zero and less than or equal to 5. 3. A method for producing a sintered ceramic product, characterized in that ^{a mixture is sintered at a temperature between 1200 0} C and 2000 C, daas between 15 and 45 wt. -'Fo silicon oxide, between 0.05 and 50 wt .- ^ Aluminum oxide, and between 40 and 60% by weight of aluminum nitride in such relative proportions that a ceramic material is formed at the temperature,. which contains at least 95% by weight of a compound which the lOrmel ^Si 6-z ^A1 z ^N 8-z ° _z fulfilled, in which ζ is greater than Hull or less than or equal to 5, wherein the mixture also contains at least two metal oxides, in which 28 465 5098 2 7/0725 if it is not silicon oxide and is intended to that during the heating they are mixed with some of that present in the mixture Silica react to form a silicate glass, which has a liquidus temperature below that of the silicate, that of silicon oxide with one or the other of the metal oxides alone is formed, with the glass supports the compaction of the ceramic material. 4. The method according to claim 3 »characterized in that the mixture also contains silicon nitride at the temperature and the relative proportions of silicon nitride, aluminum oxide, aluminum nitride and silicon oxide in the mixture are such that a reactive substance is formed at the temperature, which is at least 95 wt . -fo of the mixture and in which the atomic ratio of silicon: aluminum: nitrogen: oxygen is 6-z: z: 8-z: z, in which ζ is greater than zero and less than or equal to -4, the components of reactive substance react with each other to form the ceramic material. · 5 · The method according to claim 4 »characterized in that that at least a portion of the silicon oxide in the mixture is present at the temperature as an impurity, which is the silicon nitride contains. 6. The method according to claim 3, characterized in that that the mixture does not contain silicon nitride and that the relative proportions of aluminum oxide, aluminum nitride and silicon oxide in the mixture are such that at the temperature a reactive substance forms which constitutes at least 95% by weight of the mixture, wherein the atomic ratio of silicon: aluminum / nitrogen »oxygen 6-z: z: 8-z: z, where ζ is greater than 4 and less than or equal to 5, the components of the reactive substance forming of the ceramic material react with each other. 7. Method according to one of Claims 3 to 6, characterized in that that at least a portion of the alumina ■ is present in the mixture at the temperature as an impurity, 509827/0725 -3. - XO which contains the aluminum nitride. 8. The method according to any one of claims 1 "to 71, characterized in that the liquidus temperature of the silicate formed from silicon oxide with the metal oxides together is at least 10Q ⁰ G below that of the silicate formed from silicon oxide with each metal oxide alone. 9. The method according to any one of claims 1 to 8, characterized in that that the heating is accompanied by pressurization. 10. The method according to claim 9 »characterized in that that the metal oxides are each pressing aids for the ceramic material and their total amount in the mixture is less than the amount, which is needed when each metal oxide is present alone. 11. The method according to any one of claims 1 to 8, characterized that the heating is carried out without pressure, 12. The method according to any one of claims 1 to 11, characterized in that that at least one of the ingredients present in the mixture at the temperature is included in the starting materials for the preparation of the Gemisohes is introduced as a compound appropriate for the required ingredient or ingredients at the temperature. 1Y. Method according to one of Claims 1 to 12, characterized in that that at least one of the metal oxides is introduced into the mixture as metal compounds which are based on the required Oxides are decomposable during heating. 14. Method according to one of claims 1 to 12, characterized in that that before the reaction to produce the silicate glass, at least one of the metal oxides in the mixture in combination with part of the silica present as a metal silicate .. 509827/0725 _ ₄ . 15. The method according to any one of claims 1 to I4 »characterized in that that the metal oxides are selected from the group consisting of magnesium oxide, aluminum oxide ', a manganese oxide, lithium oxide, There is titanium dioxide, a boron oxide and ferric oxide. 16. The method according to claim 15 »characterized in that that the metal oxides contain magnesium oxide and trimanganese tetraoxide. 17. The method according to claim 16, characterized in that that the magnesium oxide and the manganese oxide are present in the mixture in a weight ratio y of the order of 1: 4 each. 18. The method according to claim .16 or I7 »characterized that the metal oxides also contain ferric oxide. 19. The method according to claim 15 »characterized in that that the metal oxides comprise magnesium oxide and lithium oxide which are present in the mixture in substantially equal proportions by weight are. 20. The method according to claim 19 »characterized in that that the metal oxides also include an oxide of boron. 21. The method according to claim 20, characterized in that that the metal oxides further comprise aluminum oxide. 22. The method according to claim 15, characterized in: - net that the metal oxides are magnesium oxide and titanium dioxide and in are present in the mixture in substantially equal parts by weight. 25. The method according to claim 15 »characterized in that that the metal oxides are lithium oxide and aluminum oxide. 24. The method according to any one of claims 1 "to 23, characterized in that that the amount of the metal oxides present in the mixture at the temperature is such that the silicate 509827/0725 _ ₅ _ glass forms up to 5% by weight of the sintered product. 509827/0725