JPH0453829B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a high-density silicon nitride reaction sintered body. Among silicon nitride Si ₃ N ₄ products, those called reaction sintered bodies are usually made by applying nitrogen gas to a molded body of Si powder or a molded body of (Si + Si ₃ N ₄ ) powder mixture while nitriding it. Manufactured by sintering. This kind of product has thermal shock resistance, hardness,
It has excellent electrical insulation and chemical stability at high temperatures, and has almost no shrinkage during reaction sintering.
Because it has the advantage of achieving high dimensional accuracy,
Widely used in applications such as fireproof materials, wear-resistant materials, corrosion-resistant materials, and insulation materials. The drawback of conventional silicon nitride reaction sintered bodies is that they are mechanically weak, with a bending strength of around 20Kgf/ ^mm2 , or at most 30Kgf/ ^mm2 , which is unsatisfactory as a material for heat-resistant structures. be. This is because even products obtained by completely nitriding silicon are only relatively low-density sintered bodies with a porosity of 20 to 30%. If a reaction sintered body with higher density can be produced, it will be possible to improve various properties such as strength from room temperature to high temperature, making it extremely useful as a material for heat-resistant structures by taking advantage of its characteristic of not losing strength even at high temperatures. Become something. The measures taken so far to increase the density of reaction sintered bodies are to increase the density of Si or (Si+Si ₃ N ₄ ) compacts. Specifically, the first step is to increase the powder compaction pressure, but even if the pressure is as high as practical, the density of the product after nitriding is only 2.39 g/cm ³ (75% of the theoretical density). .
Attempts have been made to adjust the particle size of the powder and blend powders with various particle sizes, but the density of the reaction sintered body was still limited to 2.54 g/cm ³ . In order to obtain a reaction sintered body with even higher density, pre-sintering of the Si molded body, that is, sintering in an inert atmosphere prior to nitriding, is introduced to create a high-density sintered body of the Si molded body. It was proposed that
No. 121613). However, the method disclosed above does not allow Si by pre-sintering.
In order to effectively achieve high density of the compact, it is essential to use extremely fine Si powder with an average particle size of 0.2μ or less. Apart from the problem that such fine powder is not easy to manufacture, the density of the resulting reaction sintered body is still 2.39 g/cm ³
(92% of the theoretical density) was the limit. The present inventor has conducted extensive research with collaborators with the intention of further increasing the density of Si molded bodies using pre-sintering, and has achieved a maximum density of 3.05 g/cm ³ (96% of the theoretical density). We succeeded in obtaining an extremely high-density reaction sintered body, which we have already disclosed (Japanese Unexamined Patent Application Publication No. 1987-1999).
188465 and 57-188466). The method is Si
Adding a certain amount of boron to the powder to improve sinterability or adding certain elements i.e. Fe, Co,
Ni, Cr, Mo, Mn, W, Ti, Zr, Ta, Nb, V,
The gist is to promote nitriding by adding a certain amount of one or more elements selected from Mg, Ca, Cu, Zn, and Sn, or a compound thereof. Subsequent research revealed that nitriding promoters such as Fe have the effect of improving sinterability and are useful over a wide range of addition amounts. Additives such as B and Fe mentioned above are
Of course, they may be used in combination, which is preferred. In any case, in order to obtain a high-density silicon nitride reaction sintered body, it is necessary to use raw material Si powder with good sinterability, and for this purpose, the smaller the particle size of the powder, the better. As a result of a detailed study of the relationship between the Si powder particle size and sinterability, the present inventor found that not only the particle size but also the Si
We found that the origin of the powder, that is, the manufacturing method, has a large effect. That is, the pulverized powder obtained by mechanical breakdown often has poor sinterability;
On the other hand, Si powder obtained by build-up via the gas phase has high sinterability and high It has been found that a dense pre-sintered body can be easily obtained. For the same particle size, Si powder obtained from the gas phase exhibits higher sinterability. Based on this knowledge, the method for producing a high-density silicon nitride reaction sintered body of the present invention proposed here involves using 0.15 to 5.0% by weight of boron or its compound as B, and/or Fe, Co, Ni, Cr, Mo, Mn,
W, Ti, Zr, Ta, Nb, V, Mg, Ca, Cu, Zn
A silicon powder containing 0.05 to 2.0% by weight of one or more elements or compounds thereof (in the case of two or more elements, the total amount) is molded, and the molded body is placed in an inert gas atmosphere. The pre-sintered body is pre-sintered by heating to a temperature above 1100℃ but lower than the melting point of Si, and the obtained pre-sintered body is heated to a temperature of 1100-1500℃ and nitrided by the action of _N2 . The manufacturing method is characterized in that silicon powder obtained from a gas phase is used as the raw material silicon powder. This manufacturing method can be said to have greatly enhanced the effectiveness of the previously proposed substance that promotes sintering or nitriding by selecting the raw material Si powder. One way to obtain Si powder from the gas phase is to heat solid silicon under vacuum to create vapor, which is then condensed. The best way is to generate it from a gaseous compound, for example by thermally decomposing SiH ₄ (normally gaseous).
One method involves reducing SiCl ₄ (which is normally liquid, so it is evaporated under reduced pressure and heat). Obtaining Si powder from other Si compounds is also effective as long as it is produced from the gas phase. No matter which raw material is used, the resulting Si powder usually has a particle size of 0.5μ.
These are the following fine particles. The limits and reasons for the contents of the various substances having the effect of promoting sintering or nitriding are the same as in the invention disclosed above. That is, in order to expect the effect of boron, it is necessary to contain at least 0.15% by weight. However, boron generates boron nitride BN in the nitriding process, and in large amounts this inhibits reaction sintering. Therefore, it must be kept within 5.0% by weight. The content of Fe and other substances is 0.05 to Si powder.
If the amount is less than % by weight, no effect will be obtained. Below this lower limit, the density of the pre-sintered body may become high and the time required to nitridize Si to a high degree becomes impractically long. On the other hand, a content exceeding 2.0% causes significant grain growth and prevents high density during preliminary sintering, so it must be avoided. The preferred range varies depending on the element used, but is usually 0.1 to 0.6% by weight. In the case of boron, the existing form may be metallic boron, an amorphous substance, or a metallic boride, and Fe and others may be in an elemental state or in a compound such as an oxide. , compounds among them are of course preferred. When both are used together, it is preferable to select a compound of boron and these elements because both can be present at once. The sintering accelerator or nitriding accelerator substances are also desirably fine particles with a particle size equal to or smaller than that of the Si powder. The techniques for powder compaction and pre-sintering are the same as previously disclosed. That is, it goes without saying that the raw material powder or powder mixture can be formed by any means such as conventional die forming, isostatic pressing, slip casting, injection molding, and the like. The density of the compact to be pre-sintered is 0.82 g/cm ³ (the theoretical density) to facilitate handling and processing and to ensure sinterability during pre-sintering.
35%) or more. If the density is lower than this, it is difficult to obtain a sintered body having a uniform structure even if the density can be increased by preliminary sintering. As a preliminary sintering method, in addition to free sintering, ordinary methods such as uniaxial pressure sintering (so-called hot press) and hot isostatic pressure sintering can be used. Pre-sintering is performed at a temperature of 1100°C or higher. As a result, at low temperatures, high density cannot be expected even if fine powder is used. The upper temperature limit is
Of course, this is the melting point of Si. The atmosphere is preferably an inert gas such as argon, but may also be a vacuum. The degree of densification at the preliminary sintering stage is expressed by the amount of shrinkage caused by sintering. This does not depend on the density of the compact to be sintered, but in order to provide the high-density reaction sintered product that the present invention aims to achieve, the volumetric shrinkage rate must be at least 10%, and 20%. % or more. The density of the preliminary sintered body varies greatly depending on the particle size of the raw material powder, molding conditions, and sintering conditions, but in terms of the density obtained in the reaction sintered body and the ease of nitriding, it is 1.8 to 2.1 g/cm ³ Preliminary sintering should be performed so that the In the present invention, the nitriding of the Si pre-sintered body can be carried out in the same manner as in the production of conventional silicon nitride reaction sintered bodies. That is, generally under a nitrogen gas atmosphere at atmospheric pressure.
Heat to a temperature of 1100-1500 ° C. The temperature is 1100~
It is also possible to gradually increase the temperature from the low temperature side of 1350℃. In order to adjust the reaction rate, the nitrogen pressure may be selected from a range of reduced pressure (up to about 1/100 atm) to increased pressure (up to 2000 atm). In addition to pure nitrogen gas, hydrogen-mixed nitrogen gas and ammonia can also be used. The time required for nitriding varies greatly depending on the density of the pre-sintered body, average grain size, nitriding temperature, and atmospheric conditions, as well as on the allowable amount of residual Si, but ranges from several hours to about 200 hours. As shown in the examples shown below, according to the method of the present invention, the amount of unnitrided residual Si can be suppressed to 0.5% by weight or less, which is a practically preferable allowable limit, and a high density of up to 94% of the theoretical density can be achieved. A reactive sintered body can be produced. Example 1 Ar gas containing 30% _H2 was flowed at a flow rate of 8/min to form a plasma gas (plasma output was 100A,
32V) was applied to a 99.999% pure Si block to create Si vapor, which was deposited on the surface of a water-cooled stainless steel plate placed nearby. Si powder has a particle size of 0.10~
It was a fine powder of 0.13μ. Additives were added to this Si powder, it was molded, and after preliminary sintering, it was nitrided to obtain a reaction sintered body. Examples 2 and 3 In the same arc plasma as in Example 1, 3/3
SiCl ₄ vapor was supplied using N ₂ at a flow rate of min as a carrier gas, and SiCl ₄ was reduced with H ₂ to produce Si powder.
The obtained material is almost uniform with a particle size of around 0.11μ.
It was fine Si powder. Additives were added, molded, pre-sintered, and then nitrided. Example 4 Using the same plasma device as Examples 1 and 2,
Form an arc plasma using Ar with a particle size of 8/min as the plasma gas, and generate 30% SiH ₄ -70% by volume.
Supply a mixed gas of N ₂ at a flow rate of 2/min.
SiH ₄ was thermally decomposed to create Si powder. Particle size 0.08~
Almost uniform Si fine powder of 0.12μ was obtained. This was also molded with additives added, pre-sintered and then nitrided. Comparative Examples 1 and 2 The 99.999% pure Si ingot used in Example 1 was processed in n-hexane medium using a cemented carbide ball mill.
Wet milling for 96 hours resulted in an average particle size of 0.13μ
was made into Si fine powder. It was shaped, presintered, and nitrided with or without additives. The operating conditions and results of each of the above Examples and Comparative Examples are shown in the table. 【table】

Claims (1)

[Claims] 1 Boron or its compound as B is 0.15 to
5.0% by weight, and/or Fe, Co, Ni,
Cr, Mo, Mn, W, Ti, Zr, Ta, Nb, V,
One or more elements of Mg, Ca, Cu, Zn, and Sn or their compounds are used as the above elements (2
Silicon powder containing 0.05 to 2.0% by weight (if the total amount is more than The obtained preliminary sintered body is
A method for producing a high-density silicon nitride reaction sintered body, which consists of heating to a temperature of 1100 to 1500°C and nitriding by applying _N2 , characterized in that silicon powder obtained from the gas phase is used as the raw material silicon powder. manufacturing method. 2. The manufacturing method according to claim 1, wherein the silicon powder obtained from the gas phase is produced by evaporation and condensation of solid Si. 3. The manufacturing method according to claim 1, wherein the silicon powder obtained from the gas phase is produced by thermal decomposition of SiH ₄ gas or reduction of SiCl ₄ vapor. 4. The manufacturing method according to any one of claims 1 to 3, wherein the pre-sintered body has a volumetric shrinkage rate of 10% or more.