JPH0748176A - Silicon nitride sintered material and method for producing the same - Google Patents

Abstract

(57) Summary [Objective] To provide a sintered silicon nitride material which exhibits no or relatively little strength loss at elevated temperatures and is easy to manufacture. An oxide sintering aid additive and added carbon or carbon precursor to avoid the formation of surface oxide and silicate phases in the final sintered material and increase its high temperature strength Co-sintering produces a Si ₃ N ₄ material (Si ₃ N ₄ itself or Si ₃ N ₄ and other ceramics such as nitrides, borides, carbides).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a silicon nitride-based sinter material and a process for its manufacture by sintering silicon nitride powder with an oxide sintering aid.

Known single oxides and double oxides
It is known that silicon nitride powders can be sintered by adding oxide sintering aids which are de) and mixed oxides such as magnesium oxide, aluminum oxide, spinel, yttrium oxide or other rare earth oxides. ing. During the sintering process, a liquid silicate phase forms from the surface areas of the Si ₃ N ₄ particles containing sintering aids and oxygen, and the silicate phase cools to give a glassy solid. Depending on its composition and cooling curve, the silicate phase is optionally obtained in partially crystalline form. For this reason Si ₃ N ₄
It was previously thought that a constant oxygen content on the surface of the particles was necessary to produce the silicate phase (G. Woetting, G. Ziegler, Sprechsaal, 120 , 96-99 (198
7)). However, on the other hand, it has a detrimental effect on the high temperature properties of the sintered product because the silicate phase softens at temperatures at which silicon nitride itself is resistant without strength degradation.

It is an object of the present invention to provide a sintered silicon nitride material which does not exhibit this strength reduction at elevated temperatures or exhibits only a relatively small extent and is simple to manufacture.

[0004]

SUMMARY OF THE INVENTION According to the present invention, the above object is based on the fact that the residual oxygen of the whole material is bonded in large amounts in the final sintered material to the extent that it essentially corresponds to the oxygen content of the additive. This is achieved by a novel sintered material which is sintered with an oxide sintering aid additive such that the surface of the nitride powder particles of (1) is substantially free of surface oxygen. Such materials may be reducing agents (preferably carbon or carbon precursors) according to the method of the present invention.
Is added to the compacted material to be sintered.

Surprisingly, carbon or a carbon-containing cokable compound is added to an unsintered green compact without losing the sinterability of silicon nitride. Most surface oxygen can be removed from silicon nitride. The silicon nitride sintered material obtained in this way has a total oxygen content which is essentially solely due to the oxygen added together with the oxide sintering aid.

The surface oxygen, which is essentially present as SiO ₂ , is due to the carbon added at about 1600 ° C. before true sintering in the carbon monoxide form, according to one or more reactions known per se. To be removed.

(I) SiO ₂ + 3C → SiC + 2C (II) 3SiO ₂ + 6C + 2N ₂ → Si ₃ N ₄ + 6CO (III) SiO ₂ + 2SiC + 2N ₂ → Si ₃ N ₄ + 2CO After subtracting oxygen generated from the oxide sintering aid The remaining calculated residual oxygen content corresponds substantially to the oxygen added in silicon nitride, and if common silicon carbide powders are used, it is typically 0.5 of the total sintered product.
It is an amount less than weight%. The binder phase of the silicon nitride sintered material according to the invention consists essentially of added oxide sintering aid, and typically has a silicon content of less than 5% by weight of the sintered product. Yes, it can be measured by microanalytical methods (by SEM / EDX).

The silicon nitride sintered material according to the invention optionally comprises other ceramics, eg nitrides such as TiN, AlN or BN, and / or eg SiC, Ti.
It can be modified by adding carbides such as C or B ₄ C and / or borides such as TiB ₂ .

The oxides and complex oxides mentioned above and their mixtures can be used as oxide sintering aids. A mixture of Al ₂ O ₃ and Y ₂ O ₃ is preferably used, which may be present partially or completely in the form of complex oxides, such as yttrium-aluminum-garnet (YAG). The amount of sintering aid material corresponds to the amount used in known silicon nitride sintering materials. (Si ₃ N ₄ + Y
Particularly good results are obtained by adding about 10% by weight of YAG (relative to the total amount of AG).

Such that the amount of carbon necessary to remove the surface oxygen content is added to the mixture used to produce the green pressure-molded material in the form of elemental carbon or coketable compounds. In the process, the silicon nitride sintered material according to the invention is advantageously produced, the mixture comprising silicon nitride powder, sintering aids and optionally further nitrides, carbides and / or borides, optionally further eg lubricants, solutions. Manufactured from common auxiliaries such as glues or antifoams. Elemental carbon in the form of carbon black is preferably used. The amount of carbon depends on the oxygen content of the silicon nitride powder and is typically about 1-3% by weight of the total pressure molding material.

The production of the mixture and the green pressure-molded material is otherwise known in a manner known per se, for example by wet mixing in a stirred ball mill and the suspension thus obtained. It can be carried out by drying and molding.

Sintering is generally carried out at temperatures of 1750 to 1900 ° C, preferably about 1850 to 1900 ° C. Since Si ₃ N ₄ is having appreciable decomposition pressure at this temperature, sintering is conducted in a nitrogen superatmospheric pressure such as for example, 10 to 100 bar.

[0013]

Detailed Description of the Preferred Embodiments The following non-limiting examples clarify the methods of practicing the invention and illustrate preferred embodiments of the products and methods of the invention.

[0014]

EXAMPLE 1: in a ball mill being agitated, 90 g Si ₃ N ₄ powder (UBE grade SN-E10), 4g of Y
₂ O ₃ powder, 6 g Al ₂ O ₃ powder, 1.5 g carbon black, 3 g lubricant (polyethylene glycol), 2
g peptizer, 2 g amino alcohol and 0.5 g defoamer in deionized water with Si ₃ N ₄ ground balls (diameter 2.5 m
m). The suspension thus obtained was dried in a ceramic crucible at 100 ° C. The dried material was ground in a mortar, sieved to a set size of ≤0.25 mm and compressed using uniaxial force of 50 MPa to give tablets. These tablets were heated in air at 300 ° C. for 4 hours to remove organic components. The green density here was 1.48 g / cm ³ .

The tablets were heated to 1600 ° C. at 10 Kelvin temperature (K) / min, initially at standard pressure, under nitrogen atmosphere, kept at this temperature for 30 minutes, and further 10 K / min.
Heated to 1850 ° C in minutes. When the temperature of 1700 ° C. was reached, the nitrogen pressure was raised to 20 bar. 1850 ° C
After 3 hours in, the nitrogen pressure was raised to a further 100 bar and the pressure was kept at this level for another hour at 1850 ° C. and for 2 hours during cooling. A graphite crucible coated with boron nitride was used as the sintering vessel.

The sintered material had a density of 3.23 g / cm ³ . The weight loss on sintering was 4.8% and the (linear) shrinkage was about 23.6%. Oxygen content is 4.
It was 2% by weight. (Theoretical oxygen content, which is assumed to be due to the sintering aid alone: 3.9% by weight.
The presence of 2 wt% SiO ₂ will give a total oxygen content of 4.9 wt%. Example 2: Using the same process as described in Example 1, but with 67.5 g Si ₃ N ₄ powder and 22.5 g Si.
C powder was used in place of (Lonza (Lonza) UF-25) A mixture of pure Si ₃ N _4. The amount of carbon black was increased to 2g.

The green density was 1.50 g / cm ³ and the sintered density was 3.24 g / cm ³ . Weight loss was 5.2% and shrinkage was about 23.8%.

Example 4 The same process as in Example 3 was used, but the sintering temperature was 1900 ° C. The sinter density was as in Example 3, the weight loss was 5.5% and the shrinkage was 23.9%.

Example 5: The same process as described in Example 1 was used, but with 90 g of Si ₃ N ₄ and SiC.
A 3: 1 ratio of carbothermally prepared composites was used in place of pure Si ₃ N ₄ . The sintering additives Al ₂ O ₃ and Y ₂ O ₃ were each used in amounts of 5 g and the carbon content was increased to 3 g.

The green density was 1.35 g / cm ³ and the sintered density was 3.25 g / cm ³ . Weight loss was 6.8% and shrinkage was 27.4%.

Example 6: The same process as in Example 5 was used, but the temperature was 1900 ° C. The sinter density was as in Example 5, the weight loss was 7.2% and the shrinkage was 27.6%.

Example 7: 90 g of Si ₃ N ₄ powder (UBE grade SN-E1 in a stirred ball mill)
0) 5 g Y ₂ O ₃ powder, 3 g Al ₂ O ₃ powder, 3 g carbon black, 3 g lubricant (PEG), 2 g peptizer, 2 g amino alcohol and 0.5 g defoamer. Was mixed with Si ₃ N ₄ ground spheres (2.5 mm diameter) in deionized water. The suspension thus obtained was dried in a ceramic crucible at 100 ° C. The dried material was crushed in a mortar, sieved to a set size of ≤ 0.25 mm and compressed into tablets using uniaxial force of 100 MPa. The tablets were further compressed isostatically at 250 MPa and heated in air at 300 ° C. for 4 hours to remove organic components. Green density is 1.69 g /
It was cm ³ .

The tablets were heated under a nitrogen atmosphere, initially at standard pressure, to 1600 ° C. at 10 K / min, kept at this temperature for 1 hour, and further heated to 1900 ° C. at 10 K / min. After 2 hours at 1900 ° C, increase the nitrogen pressure to 1
It was raised to 00 bar and kept at 1900 ° C. for a further 30 minutes. The nitrogen pressure was reduced to 30 bar and the tablets were cooled to 1250 ° C at 10K / min.

The sintered material had a density of 3.26 g / cm ³ . The weight loss on sintering was 6.2% and the (linear) shrinkage was about 20.3%.

The main features and aspects of the present invention are as follows.

1. Primarily comprising silicon nitride, M
Sintered substance to which one or more sintering aid additives selected from the group consisting of g, Y, rare earth elements, oxides of Al, mixed oxides and complex oxides of these substances are added. A sintered material characterized in that the calculated residual oxygen content remaining after subtracting the oxygen generated from the oxide sintering additive is less than 0.5% by weight.

2. Primarily comprising silicon nitride, M
One or more sintering aids selected from the group consisting of g, Y, rare earth elements, Al oxides, mixed oxides and complex oxides of these metals are added, and sintering is performed here. A sinter material in which a sinter aid is later present as a second phase in addition to silicon nitride, the second phase having a silicon content of less than 5% by weight.

3. Characterized in that it comprises, in addition to silicon nitride, at least one other sintered ceramic selected from the group consisting of nitrides, carbides and borides.
The sintered material according to 1 or 2 above.

4. A silicon nitride powder and at least one sintering aid selected from the group consisting of Mg, Y, oxides of rare earth elements and Al, mixed oxides and complex oxides of these metals are mixed and unsintered. What is claimed is: 1. A method for producing a silicon nitride-based sintered material to which one or more sintering aids has been added by molding and sintering a pressure-molding material, the method comprising: Carbon or a carbon-containing coketable substance is added to the green pressure-compacting material before sintering to completely or partially remove the oxygen present on the surface of the silicon nitride powder and to sinter at 1750 ... 21
A process characterized in that it is carried out at a temperature of 00 ° C. under a nitrogen pressure of at least 2 bar.

5. The method according to the above 4, characterized in that carbon is added in the form of carbon black.

6. A mixture of Al ₂ O ₃ and Y ₂ O ₃ was used as a sintering aid additive and sintering was carried out between 1850 and 1900.
The method according to any one of 4 and 5 above, which is carried out at a temperature of ° C.

7. 7. Method according to claim 6, characterized in that at least one other ceramic selected from the group consisting of nitrides, carbides and borides is added to silicon nitride.

8. 4 or 5 above, characterized in that at least one other ceramic selected from the group consisting of nitrides, carbides and borides is added to silicon nitride.
Either way.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication point 102 T 35/64 AL (72) Inventor Franciscus Juan Deien Germany 79802 Detzteichhofen YES TESTER SHUTTRASE 5A

Claims (2)

[Claims] 1. M comprising mainly silicon nitride,
Sintered substance to which one or more sintering aid additives selected from the group consisting of g, Y, rare earth elements, oxides of Al, mixed oxides and complex oxides of these substances are added. A sintered material characterized in that the calculated residual oxygen content remaining after subtracting the oxygen generated from the oxide sintering additive is less than 0.5% by weight. 2. Mixing silicon nitride powder and at least one sintering aid selected from the group consisting of oxides of Mg, Y, rare earth elements, Al, mixed oxides and complex oxides of these metals. , A method of producing a sintered material based on silicon nitride to which one or more sintering aids has been added by molding and sintering an unsintered pressure-molding material. A suitable amount of carbon or a coke-forming material containing carbon is added to the green compacted material before sintering to completely or partially remove oxygen present on the surface of the silicon nitride powder, And sintering 1750-21
A process characterized in that it is carried out at a temperature of 00 ° C. under a nitrogen pressure of at least 2 bar.