JPH02225304A - Production of silicon nitride, silicon nitride powder and use of the same powder - Google Patents

Abstract

PURPOSE:To obtain silicon nitride powder producible sintered material having a large strength at high temperature useful for gas turbine, etc., by nitriding metallic silicon powder in nitrogen-containing atmosphere and in the presence of alkali (earth) metallic powder in gaseous state. CONSTITUTION:Metallic silicon is nitrided to obtain powder having following properties; oxygen content: <=0.6wt.%., gamma-phase content: >=80%, average granular diameter: 0.3-0.8mum, strength of the sintered material (used of MgO-Al2O3-Y2O3 three components-system sintering auxiliary) at 1200 deg.C: >=700MPa. Said powder is used as silicon nitride powder for producing high-temperature structural material. Said silicon nitride powder is produced by continuously, intermittently or temporarily supplying halogenated alkali metal or halogenated alkaline earth metal (especially fluoride of Ca, Mg or Li is preferable) to metallic silicon powder in an atmosphere containing nitrogen and/or ammonia at 1150-1450 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing electrified silicon that can produce a sintered body TA with high high-temperature strength, a powder, and its uses. Silicon nitride is used as a high-temperature structural material in gas turbine components,
It is used for nozzles and bearing temples.

[Conventional technology]

Conventionally, methods for producing silicon nitride powder include the +11 metal compound @substituent method, (2) the silica reduction snow conversion method, and (3) the silicon halide method.The powders produced by these methods are , perhaps due to different manufacturing histories, even if the overall impurity evidence, oxygen content, particle size, and specific surface area are similar, the sinterability of the powder and the properties of the sintered body after sintering, such as the bending stiffness, may be significantly different. There is a difference.

In general, the powder produced by method (1) is easy to sinter but has low sieve hot bending strength, and the powder produced by method +21 is sinterable but has a flat Si hot bending strength. However, it is said that the powder produced by method (3) exhibits intermediate performance.

Regarding the amount of oxygen, (because the pulverization process is applied to the powder in method 11, the total oxygen content often exceeds 200%). Therefore, if the total oxygen t is reduced through an acid treatment process, it is still difficult to reduce the amount to 1.01%. - 10,000, (
Even in the powder produced by method 2), since silica powder is used as a raw material, there is a residual amount of silica, and the total oxygen t usually exceeds 2 bundles.

The above powders are currently available in 11 quantities. Naturally, powder baking 11! It goes without saying that the S properties and the properties of the cursed body are influenced by the amount of powder, but there are also various other powder properties such as specific surface area, IF3 quality, particle shape, and particle size (m powder). Currently, there is little understanding of how the powder percentage of each of the above-mentioned manufacturing methods is related to powder customization.

Japanese Patent Publication No. 61-43311 describes the relationship between the aging of silicon snow powder and high temperature bending strength.

[Problem to be solved by the invention]

However, although the invention #-i proposes an fc sintered body that reduces the number of 88 violets in the silicon nitride bed and collapses with high temperature strength, l(
Possibly because the P sintering method is used, #1t% other than walking
The analogy arises from the fact that the description of fine particles, metal impurities, specific surface area, etc. that are unavoidable in the method of crushing the ingot, which is a lump, is not clearly specified, and the special treatment is applied in the manufacturing method of the low-oxygen powder. The cost is high, the sintering method uses IP (as mentioned above, which is not very versatile), and there is a history of high temperatures! ! There is no detailed explanation of the reason for the limitation of the Akatsuki Consolidation Aid, which is related to whether or not J degree has been expressed, and the organization of the G8 body.

An object of the present invention is to provide a method for manufacturing silicon nitride, a powder, and uses thereof that solve the above-mentioned problems.

[Means to solve the problem]

To summarize the non-invention, the invention of ggl of the present invention is an invention related to snowy silicon powder, which is a snowy silicon powder obtained as metal silicon powder as i family, and r1! , the fiber content is less than 16 times, the α phase content is more than 80 mm, the average particle size is (L5 ~ αB μm, and the powder is made of Mg0
The high temperature strength of the sintered body at 1200° C. using a five-component sintering aid of -A40s-Y*Os is 700 MPa or more.

Further, the second invention of the present invention is an invention related to a method for producing electrified silicon, and in the method for producing silicon nitride by nitriding metal silicone powder in an atmosphere containing nitrogen and/or ammonia, an alkali metal At least one type of halide selected from the group consisting of halides and alkaline earth metal halides is supplied in a gaseous state in a delayed, intermittent or -temporal manner as the tW feature.

Furthermore, a third invention of the present invention is an invention relating to a silicon nitride powder composition, which comprises the silicon nitride powder of the first invention, magnesium oxide and/or its precursor, and rare earth element oxidation. ! The percentage indicates that the material consists of 9 binding agents containing l.

A fourth invention of the present invention relates to a silicon nitride sintered body, characterized in that the silicon nitride powder composition of the third invention is sintered in an inert gas atmosphere. .

The inventors have thoroughly studied the above points, and found that by nitriding metal silicon powder under a special ambient gas, the oxygen content, specific Ifl product, average particle size, and fine powder of nitrided silicon powder can be improved. In addition to producing a powder with controlled amount and metal impurities, we also produce a sintering aid that is compatible with quantified silicon powder, and also use sand, which greatly contributes to the development of high-temperature strength of the sintered body. Misfire f! Completed A.

Oxygen in the Xuehua Kui Xue powder Song Dynasty in the unknown is less than A610,
The reason why oxygen is limited to less than α61 is that the α → 1 transition that occurs during sintering is likely to occur from low temperatures, and furthermore ``ttJ8 binder forms a large number of grain boundary phase chambers, so its solubility in silicon nitride increases, and as a result, β
This is because the number of nuclei increases, making it difficult to obtain sufficiently grown β columnar crystals with a high aspect ratio.

The average particle size is very small, especially when using normal pressure
It is generally considered that a smaller size is preferable. The average particle diameter of the present invention is in the range of α3 to α8 μm. If α exceeds 8 μm, the solubility of silicon nitride in the composite oxide produced by the reaction between firing aids such as yttrium oxide, magnesium oxide, aluminum oxide, etc. and oxygen contained in silicon nitride powder will decrease. This is because it will not become sufficiently dense. If it is α5 μm droplet, t18
The solubility of the binder in the grain boundary phase increases, and as a result, the number of β-nuclei increases, and the sintered body that can withstand high temperatures without being sufficiently converted into 'G)'M is produced by pressureless sintering. This is because the result is a gamble.

Note that the average particle diameter used in the present invention refers to the diameter of 50 cm in volume measured with CAPA-700 manufactured by Aiba Seisakusho.

Generally, when the amount of acid:A in silicon nitride powder decreases, the general sintering aid Yッ0! , At, O, in the system, S.

H, /% pumpsha and ni,! (, Jack CS, H,
Haspahira.

K, H, Jack, Proc.

Brlt, Ceram, Soc) Vol. 51, pp. 57-49 (1981)], et al., there is a tendency for sintering to become difficult because sufficient shinsaido cannot be obtained. That is, the phase boundary reaction becomes rate-determining, and a sintering aid such as MgO'k #, which has the effect of accelerating diffusion, is generally added to the sintering agent. In that case, the sinterability is improved, but the problem with the high aspect ratio β columnar crystals as described above remains. In other words, the β columnar crystals having a high 7-spectral ratio have a large influence on the amount of fine powder, as described in Japanese Patent No. 63-277560, m+*. That is, when the amount of fine powder snow increases, the number of β nuclei generated in the liquid phase increases, and the aspect ratio becomes high, resulting in β columnar products, which become female, and as a result, high temperature strength is not developed.

In other words, the amount of fine powder is 脣顛昭t53-277360
As described in the specification No. 8A, when the amount of fine powder of α2 μm or less is defined as fc, it is preferably 7 valleys 1i or less. Mafc
By adding a sintering aid that helps the rate-determining phase boundary reaction and firing, the degree of sintering is sufficiently increased, and β-columnar crystals with a good aspect ratio are crystallized. As a physical characteristic, h #Im 9i degrees (σuoo℃) is 70
0 MPa or more. Such sintering aids include %Ml (O-based, MgO-A4Os-based, ygo
-Rare earth elements are compounds, MgO-Human 1.0. -Rare earth element

The relationship between the high aspect ratio β columnar crystals in the sintered body and high temperature strength as mentioned in IW will be discussed in detail later, but what we have discovered this time is that the high aspect ratio β columnar crystals have a large effect on the development of high temperature strength. This is Jin who is playing a role.

In addition, as mentioned above, the sintering mechanism of silicon nitride is that α-silicon nitride is once dissolved in the liquid phase, and then) MT
Basically, it becomes a sum of I8 and precipitates as β-silicon nitride, so it is desirable that the a-phase content of the silicon nitride powder is high, that is, the α-phase content is at least 8
It is necessary that it be present in an amount of 0% or more. This is because if it is less than 80 cm, the aforementioned β columnar crystals with a high aspect ratio will be difficult to crystallize and will not lead to development of leg temperature strength.

It is preferable that the total fi of metal impurities in the snow-containing silica powder, especially tit of Fe, metal, and Ca, be 500 ppm or less. This is because if it exceeds 500 ppm, the creep tendency at high temperatures will decrease when long M is used repeatedly at high temperatures. Therefore, it is preferable that the amount of metal impurities be as small as possible.

Regarding the specific surface area, when making a shape using each molding method such as press molding, injection molding, slip casting, etc., generally #'i is used for reasons such as handling and viscosity.
Preferably 6 to 14 m”/t. 6-/f
If it is less than this, the particle size becomes coarse, resulting in poor sinterability, which is not preferable. If it exceeds 14 m''/t, the powder itself becomes bulky, making it difficult to handle and increasing the viscosity, which is important for injection moldability, which is not preferable.

Furthermore, if it is less than 6 rn"/1, the particles will become large, the sintering rate will not increase, and the high temperature strength will not be improved, and in order to exceed s 14 m"/f, over-pulverization is required. As a result, the number of fine powder trays increases and %
This is because, as described above, the number of β nuclei increases, resulting in the formation of β columnar crystals with a high aspect ratio, resulting in dullness.

Next, the method for manufacturing silicon nitride explained above will be described.

In the method of producing silicon nitride by t-nitriding metallic silicon powder while introducing an atmospheric gas rich in silicon nitride xi-tgz and/or ammonia according to the present invention, 1
It is produced by continuously, intermittently, or occasionally supplying danganese or two or more kinds thereof in a gaseous state.

Hereinafter, non-invention will be explained in more detail.

The particle size of the metal silicon powder used in the invention is preferably 88 μm. The reason why it is possible to use relatively large silicon metal is that, as will be explained later, not all reactions between silicon metal and the nitrogen source are solid-gas reactions.
After a slight solid-gas reaction on the surface, the gas-air reaction is largely responsible for the progress of nitridation. In other words, in the present invention, even if a part of the surface of metallic silicon is about 88 m thick, if nitridation occurs due to solid-gas reaction, the metallic silicon and α
- This is because the difference in precision of silicon nitride causes a phenomenon of destruction of the metal silicon, resulting in 5 & fine metal silicon. However, 88
μml-, a similar phenomenon occurs, but the surface hardness
The temperature at which the gas reaction occurs increases, and under normal nitriding conditions, a
Female $1 tends to remain, which is not preferable. There is no limit to the lower limit of bones. In other words, the smaller the average particle size of the metal silicon powder used, the more 810 (
G) is easily generated and the gas-gas reaction is promoted, making it easier to produce the desired granulated α-silicon nitride ingot. Furthermore, since the purpose of oxygen in the metal silicon powder is to reduce oxygen as described in detail in the above-mentioned Menghua silicon powder, the RF in the metal silicon powder is as low as possible.
It is desirable that the number of elements is small. In the present invention, α2% or less is sufficient.

As described above, the present invention is an application of the reaction technique disclosed in Japanese Patent Application No. 198987/1987 for producing silicon nitride from metallic silicon powder. In other words, the reaction between metallic silicon powder and nitrogen is not a solid-gas reaction, but rather an O! N via
-NH3 or N1-H, the rate is determined by the gas-gas reaction of the system, and the
The reaction formula t for production was examined one by one. An example of this is shown below, but regarding the form of solid generation by such a gas-gas reaction, see Kato [Akio Kato: Powder Engineering Association P, Vol. 18,
No. 1, pp. 36-45 (1980)), the degree of supersaturation, that is, 10 g kp, is greatly influenced. In other words, 10g k at 1300℃ of the following formula 111
While p is about t6, (21 formula is about 46).

Therefore, it is presumed that the form of silicon nitride produced under both equations is a whisker in equation (0) and a granular form in equation (2).

3SiO(G)φ4NHs(S = 5isN4(8)
+M(h(G) + 6Hz(G) +11581((
)) + 4NH3(G) = 5is)J4(S)
+ 6H2(G) 121 Also, taking CaF2(G) as an example, the reaction equation until the loss of Sl(Li) and the circulation reaction in the microscopic crystal field are expressed by equations (3) to (6). Shown below.

5rs) + name o, (o) →5xo (o)
+31SiO(G)+CaF,
(G)+H, (G)-4Si(G)+Ca0(S)+2
HF(G)(415Si(G)+4NH3(G)→5i
sN4(S)+68! (G) +5
1(Ca 0(S) ” 2 HF (G) →CaF
1 (o) ”H2 ((J) 4% 0H(G) )
161 As is clear from this, it is also possible that the aT syndrome is present in the microcrystalline layer in the halide gas entrained as a gas. fact.

A sufficient granulation effect was observed even with halide gas below this grave.

Therefore, we conducted a search for nine gaseous compounds that have a stronger compatibility with oxygen than SiO(G). As a result, KFIAL, which nitrides metallic silicon powder while introducing an atmospheric gas rich in nitrogen and/or ammonia, produces silicon nitride by intentionally supplying gases of halides of alkali metals and alkaline earth metals. It has been found that the actual shape is not whisker-like but granular. Regarding the concentration of halides of alkali metals and alkaline earth metals, for example, as can be seen from the estimated reaction equation described above, 5i(S) 1
For each mole, it is sufficient that the gas is 1 mob of alkaline earth metal halides, and 2 m01 or more of alkali metal halides. Also, since nitriding is not performed all at once, the value marked with * may be less than that. Regarding the supply method, for example, all the halides of alkali metals and alkaline earth metals are charged into a separate furnace, heated and sublimated, and then heated at a degree t into the furnace in which the metal silica powder is charged.
- Supply with two accompaniments while stipulating.

Alternatively, the halide may be supplied in the vicinity of the metal silicon powder into a furnace in which the metal silicon powder is charged, in such a manner that the metal silicon powder is nitrided and the halide is sublimated. The supply method is not limited to the following. In addition, the introduction format is not limited to the following, but can be introduced separately or in the same mixture.

Furthermore, as for the supply timing, once the bifurcation is being carried out, at a light temperature of 1,150° C. to 1,450° C., it is supplied continuously, intermittently, or occasionally at 1 g. This supply can be accomplished by, for example, opening and closing the introduction piping to the sublimation furnace and the nitriding furnace as described above.

It is understood that this temporal supply is supported by the fact that in the microcrystalline layer, the halide of the gas introduced, for example, is distributed within the system as shown below. In fact, in terms of temperature, even if the halide was introduced up to 1,550°C and the gas supply was then stopped, the form of silicon nitride produced was still the same as expected, even though it was introduced up to 1,450°C. .

Examples of the alkali metals and alkali metal halides mentioned above include Ll, Na, K%ME, Ca, and Sr.

Ba is a fluoride, chloride, and bromide of the element.

Particularly preferred is a fluoride of Ca%Mg%L1. The reason for this is that in the relationship between the standard energy of formation of oxides and humidity, the difference between Si and p oxygen is 8. This is because the in nature is strong, and as a result, the above-mentioned nine-grain formation is further promoted.

In addition, the pre-rubihalide may be used in a single eclipse, or in two eclipses.
There is no problem even if you use something more than oak.

Furthermore, it cannot be added to nitriding furnaces.6 For example, batch furnaces, continuous pusher furnaces, continuous rotary furnaces,
It can be applied to both slow-starting screw furnaces and fluidized bed furnaces.

Granulated silicon nitride and special a 1986-198 explained above
Figures 1 and 2 show specific examples of whisker-shaped silicon nitride as described in FIA specification No. 987, and Figure 3 shows a typical solid-gas reaction obtained by the direct nitriding method of Sl. An example is shown, that is, a form exhibiting a narrow shape. Each figure is double *! This is a 5500x scanning electron microscopy fi (8HM) photograph.

As is clear from this, it can be seen that the particles in FIG. 1 are several orders of magnitude smaller and rounder than the S1 powder used, and it is also worrying that a gas-gas reaction has occurred.

It is clear from Figure 2 that a qi-qi reaction has occurred,
Perhaps due to the insufficient 1141 degree of SiO(G), it has a morphology with many needle crystals. In Figure 3, it can be clearly seen that the 81 powders first interacted with each other, then nitrogen diffused, and nitridation progressed.

As a result, it becomes difficult to produce fine powder when pulverized into such granulated silicon nitride.

This also leads to lower oxygen levels, and it is possible to easily produce a nitrided fiber cable initial bed with a low thickness and a small amount of fine powder, which is the objective of the present invention.

Here, to explain in more detail about the next granular silicon nitride, which was hoped for by the non-inventor, instead of crushing the thin whiskers or acicular crystals while physically bending them, as shown in Figure 2, Since the pulverization proceeds in a manner that loosens the granular crystals as shown in Figure 1, there is less generation of g powder accompanying the pulverization of the ingot, and as a result, oxidation of the electrified silicon is suppressed, resulting in a low-element powder. In other words, the silicon nitride 'X powder is close to an equiaxed powder free of fine particles as obtained by the silicon halide method. Quantitatively, when crushed into coarse/medium crushed materials using a normal coarse crusher and medium crusher, the particle size (L2w) of the coarse/medium crushed materials is
Silicon nitride is such that the ratio IfI ratio shown below is 2 to 5-/f, and the amount of oxidation accumulation is α4% or less.

In addition, as the above-mentioned crusher for evaluating the crushability of silicon nitride, for example, the chemical engineering handbook October 2, 18W55
On the 5th, the food described on pages 1279 to 1283 of Ku'4 Co., Ltd. is used.

That is, coarse crushers such as show crushers and gyratory crushers, medium crushers such as roll crushers, roller mills, and edge runners.

The α-silicon nitride of the present invention having small granular crystals obtained as described above is produced by a conventional method such as a ball mill, a vibration mill, a jet mill, an attritor mill, a pearl mill, etc. after being roughly crushed or medium crushed. Wet and dry grinding to obtain α-silicon nitride powder. With regard to fineness, the above-mentioned average particle size should be carefully considered, and the grinder should be operated and processed under appropriate conditions.

Next, as described above, high temperature 11N using silicon nitride powder
A silicon nitride powder composition suitable for obtaining a silicon nitride sintered body having a strength of 6 will be described.

Shiso is a basic uninvented technology, which is a snow-sealed silicon powder obtained by the ITL aggregation method of metal wires, and moreover, it is made by using a low-8-element silicon nitride raw material using an atmospheric pressure sintering method. , in order to sufficiently increase the degree of sintering and to increase the spectral ratio of β-columnar particles constituting the sintered body.
There are regulations on the combination of powder and sintering aids.

Silicon nitride powder contains impurities, and most of it is oxygen. Furthermore, to explain, this oxygen reacts with the oxidized sintering aid and forms a grain boundary phase. Needless to say, it is preferable that the amount is small. In other words, low #I* is very important for high temperature and high strength. Of course, as mentioned above, impurities in the entire range have a negative effect on high-temperature creep, so it is preferable that they be as small as possible.

Also, what is unique and inventive is that low oxygen plays an important role in nucleation in the α→β transition of silicon nitride. In other words, the bath S degree to the liquid phase composed of the sintering aid with a low oxygen number decreases, and heterogeneous nucleation occurs, resulting in the formation of abnormally high β-columnar crystals with a high aspect ratio. It was also found that this effect is more effective in developing high-temperature high strength than the aforementioned reduction in the amount of grain boundary phase.

Furthermore, the present inventors believe that the less fine powder there is in the raw material silicon nitride, for example, the fine powder below α2 Jim as described in Japanese Patent Application No. 65-277560, the more likely this fine powder will be. Although it is thought that many elements are involved in this process, we have also found that they greatly contribute to the heterogeneous nucleation of the α→β transition described above.

However, in general, when the oxygen content of the raw material silicon nitride powder decreases, normal pressure problems occur, such as Y, O, AlgOB %S.
Even if you add 7 to 10% of a combination of sintering aids such as moz, COO, etc. of 1 or 2 d or more, it is inevitable that a sufficient sintered body cannot be obtained. be.

As explained above, 2f: silicon nitride powder ri of the invention
It has the optimum characteristics for high temperature and high strength. but,
Sintering at normal pressure is very convenient due to the low oxygen content.

Therefore, we believe that this Togeyaki M Isoyori is the rate-determining phase boundary reaction described by Hampshire et al., and as a result of examining 41 compounds that are said to break the rate-determining rate, we found that magnesium oxide and/or its precursors It has been found that the sintered density can be sufficiently improved even at normal pressure by applying 27+111. Precursors include magnesium nitrate, magnesium carbonate, magnesium hydroxide, etc., and it was also found that less than 5% by weight of the silicon nitride IX powder composition is sufficient as the precursor.

Furthermore, as mentioned above, the properties of the grain boundary phase are low in order to develop high-temperature and high strength, and it is obvious that it is preferable that the decomposition temperature is higher than that, and for this purpose, rare earth oxides It is also important to bring out all the crystals of a high-melting-point interfacial phase composed of other sintering aids such as Al2O and/or silicon nitride. Rare earth oxides include Y,
La.

Examples include oxides such as C8, Pr%Nb, and 8m%Eu.

As described above, the silicon nitride composition of the present invention, which is composed of silicon nitride, 1-gnesium oxide or its precursor, and a sintering aid rich in rare earth FJ, is indispensable for high-temperature high strength development. be. It should be noted that the sintering aid in the silicon nitride .

tyc, more specifically, since the silicon snow powder of the present invention is low in oxygen, it can be used in systems that form a liquid phase independently other than the sintering aid described above, or systems that form a liquid phase in a slightly lower temperature range. You may also use a sintering aid.

For example, the former uses zinc oxide, nickel oxide, etc., and the latter uses, for example, Y, O, -*z, o, etc.
The method is to use a sintering aid with a composition rich in AZ and O3, up to the YAG composition. Even if the amount added is low, if the amount of sintering aid violet increases, the glass phase will increase, so 12'f! L! % or less is appropriate.

Next, a silicon nitride sintered body obtained by firing the silicon nitride powder composition described above will be described.

The :ff-like structure of the present invention is that many β columnar crystals with a large aspect ratio are observed at the bottom due to the α→β transition. In other words, the thickness of the β-columnar crystals is heterogeneous, but if you measure the heterogeneity, it is homogeneous in an area of several tens of micrometers. This is because we discovered that letters of address play an important role.

In general, the development of high-temperature strength is mainly studied by strengthening the grain boundary phase, such as by selecting sintering aids that can synthesize high melting point grain boundary phases, and by crystallizing glassy materials. The approach was from the sintering side. Therefore, as a result of repeated experiments with a constant sintering aid using powders with different oxygen concentrations, powders with different specific surface areas, powders with different degrees of crystallinity, etc., we found that the unit It was found that there is a strong correlation between the pot temperature strength against the lid and the high aspect ratio β columnar crystals that make up the sintered body structure. 19, (30μFFI
)X (25 μm) If the average aspect ratio of the β-columnar crystals, which are thought to have a large aspect ratio, in the field of view of the sintered body is 10 or more, the high temperature strength will reach a unit density of 250 MP.
It was found that more than a. In other words, I felt that it was sufficient to sinter the material to a value close to the theoretical density, and that it was quite possible to achieve a strength of 700 MPa or more at 1200°C. This density increase inhibition is caused by the oxygen in the silicon nitride powder, which has been described above, and is a fine powder.

Further, the above-mentioned magnesium oxide in the silicon nitride powder composition helps in inhibiting this increase in density.

As explained above, the silicon nitride sintered body of the present invention has a structure with a sufficiently improved density, and is composed of heterogeneous β columnar crystals, and some of the heterogeneous β columnar crystals are It is a sintered body that has a large aspect ratio and whose microscopically heterogeneous structure is macroscopically homogeneous.

Regarding the method for producing the silicon dioxide six-membered 'P' rectangle of the present invention, the silicon nitride powder composition of the present invention is pulverized and mixed in a dry or F'i wet type, and then, after being molded into a desired shape, an inert gas For example, g6, under argon gas, 1,600-1,80
It is obtained by holding at a temperature of 0° C. for about 5 hours. There are no particular limitations on the type A of the molding method, such as press molding, injection molding, slip casting, etc., pressure, filling powder, etc.

As explained in detail above, #'C1 Fueni BA investigated the characteristics of silicon snow powder, specifically the relationship between oxygen, specific surface area, average particle diameter, amount of fine powder, and metal impurities and high-temperature strength. Recognized the correlation between oxygen cypress and fine powder amount and high @strength development,
In addition, a sintering aid with the above-mentioned characteristics was discovered, and β-columnar crystals with a very high aspect ratio were introduced in the structure of the sintered body, which played an important role in the high-temperature 1171i temperature range. I found out that there is. Moreover, such a powder is not obtained by the halogenated silicon method, but is obtained economically by oxidizing the entire silicon powder under a special 1 yen ambient gas, and then pulverizing it by a conventional method.

〔Example〕

The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these actual hvJs.

In addition, each example shows 7? , the measured values were based on the following method.

(1) t11 cumulative (1/L quantity connection): TC manufactured by LECO
Based on simultaneous analysis of -136 type 07N.

(2) Specific surface area (m''/f): Based on Yuasa Ionics company's Canterthorpe Jr. BET 1 point method.

(3) Particle size (JJm): Aiba Seisakusha NC
According to APA-700.

(41α fraction (%): Based on X-ray diffraction using Geiger 7 Lux RAD-II B type manufactured by Isosha.

(5) Metal impurities (ppm): J15-G-
1322.

(Fe1 person 4Ca) (6) Relative density (%): (7) 3-point bending strength (MPa) ：Shima#made f￥shoshakari O By Archimedes method.

Toge Ruff AG-200OA Depends on the type.

Examples 1 to 7, Comparative Examples 1 to 4 Gold [8i N degree? ? , 9 E1 double oath joint Kinpa Kei Muchusong 100 heavy IT part with α fraction 90 and specific surface area 20 m2
/y of silicon nitride powder 10J 1 part mixed powder Z5 was molded into a nitrided specimen having a bulk specific gravity of 150 x 150 x 20 as shown in Table 1, and filled in an electric furnace.

The nitriding was carried out as shown in the gt table.
001: CaF2 from another electric furnace held at
(G) was heated and nitrided while being entrained in an argon gas so that the temperature became (I BN26 ) j/Hr (25° C.).

For Comparative Examples 1 to 4, heating and nitriding were performed under the conditions shown in Table 1 without introducing F'1CaF2 (G).

When the silicon nitride obtained in Table 1 was observed by SEM, it was found that all of Examples 1 to 9 were granulated, but Comparative Example 1
~4d whisker The shape of the terrain! Just in case it shows IJ4.

As an example, Example 1, Comparative Example 1, Comparative Example 30SEM
The photographs are shown in Fig. 1, Fig. 2, and Fig. 5, respectively.

The obtained nine-nitride Kui: A was crushed to a level below α2 using a coarse crusher/medium frame (show crusher and top grinder), and further, 50 tons of the crushed product under α2 was placed in a ball mill with a capacity of 1 ton.
4φFe ball CL 5t.

100 tons of water was added, and after wet grinding for 2Q hours, acid treatment was performed with hydrochloric acid for 7 hours, followed by 15% filtration, iIL drying, and crushing to produce silicon nitride composite powder for baking M raw material. Regarding the obtained silicon nitride X powder, oxygen, average particle diameter, specific surface area, α2 Ji
The content of Fe+At+C'a below m was measured and shown in Table 2.

Next, this silicon nitride powder was internally milled to obtain an average particle size L S
YICl of JJm and Al of Jim with an average particle size of 1.4
S*
*S, 2X1rs% sM*%m7yo, fiK, 1
．． l, 1-) Lichloroethane was added and wet mixed in a 4#18 ball mill, dried, molded into a 6XIOX60m shape with a molding pressure of 100Y75+1, and then 27
A CIP bottom shape was formed at a molding pressure of 00kJ9/-. These O molded bodies were set in a carbon crucible and fired in an s'N gas atmosphere under the conditions shown in Table 2 to obtain sintered bodies. After the obtained sintered body was ground, its three-point bending strength at homology, normal temperature, and high temperature was measured. The results are shown in Table 2.

Examples 8 to 9 In order to know the influence of Fe%At and Ca on metal impurities, when sintering the silicon nitride powder of Example 1, a pre-prepared Fe-T-Ca alloy powder was used. was opened as shown in Table 3, and a sintered body was produced under the same conditions as in Example 1. The characteristics of the obtained sintered body are shown in the third column.

Examples 10 to 11 This example was carried out to understand the influence of the fineness of silicon nitride. When wet-pulverizing the silicon nitride obtained in Example 1, the wet-pulverizing time was 21 (r (!I
I! Example 1 A nitride composite powder was obtained and a sintered body was produced in the same manner as in Example 1 except that the flow rate was changed to 40 Hr (actual hNu 1 ). The results are shown in Table g4.

Examples 12-17, ratio d? 5 In this first example, the halogen gas source was changed.

Using the same raw materials, nitriding specimens, and filled violet as in Example 1, nitriding was carried out using the nitriding material 1 shown in Table 5. The method of introducing halogen gas was the same as in Example 1. Note that in Example 12, the halogen gas introduction temperature was +,
The temperature was 150°C to 1,350°C. In addition, in Example 17, the method of introducing nitrogen gas was not from a separate furnace, but by molding solid CaF2 next to the nitriding specimen in the same furnace and nitriding while raising the water. In Comparative Example 5, no halogen gas was introduced.

The obtained subgrade silicon was wet-pulverized in the same manner as in Example ←j1 to obtain silicon nitride powder. Obtained peel powder 9! - Properties are shown in Table 5.

The sintered silica powder bed was sintered using a method similar to 1++11 (51), and a sintered body was produced and sold.

The results are shown in Table 5.

β-columnar crystals with an unusually high aspect ratio (Example 1
] Figures 4 and 4 show the grain structures of the β columnar crystals (ratio ff?!15) with a low spectral ratio of 7 spectral ratios of Comparative Se1j, respectively.
W, shown in Figure 5.

Note that FIGS. 4 and 5 are SEM photographs at a magnification of 7500 times.

Figure 4 shows a heterogeneous homogeneous structure with many β-columnar crystals with an aspect ratio of 10 or more, while Figure 5 shows a confined composition with a relatively low aspect ratio (approximately #5). I understand that.

Examples 91118-26, Comparative Examples 6 and 7 This example
The type of sintering aid used is different from 1. Example 18~
In No. 26, a sintered M body was produced in the same manner except that the sintering aid 1 in Table 6 was changed in Refreshing 1.

In Comparative Examples 6 and 7, the silicon nitride Jg powder used in Examples 25 and 26 was used in place of that in Comparative Example 5. The results are shown in Table 1!6.

Examples 27 to 35, Comparative Examples 8 and 9 In this example, the sintering conditions were changed.

A sintered body was produced in the same manner as in Example 1+v1, except that the silicon nitride powder composition of Example 1 was used and sintered under the conditions shown in No. 76. Comparison ψ1j8 and 9 are Example 1
The powder of Comparative Example 5 was used in place of the silicon nitride powder. The results are shown in Table 7.

〔Effect of the invention〕

The silicon nitride powder produced according to the present invention is low in oxygen and M
gO-people! , 0. -When using normal pressure g8 using Y, O, type sintering aid, 1200℃0 high temperature bending strength is 700
It is a powder of MPa or more.

This is a sintered body! -Columnar, 1 & is caused by controlling the powdery bone properties related to its growth and 7'c cohesion.

[Brief explanation of the drawing]

i@Figure 1, Figure 2, and Figure 3 are magnifications of 3 and 5 showing the morphology of the grain structure of the silicon nitride obtained in Example 1 and Comparative Example 1.3.
00x 8EM photographs, Figures 4 and 5 show the M diagram of the grain structure of the silicon nitride sintered body obtained in Example 1 and Comparative Example 5. *True.

Claims (6)

[Claims] 1. Silicon nitride powder obtained from metallic silicon powder as a raw material, which has an oxygen content of 0.6% by weight or less, an α phase content of 80% or more, and an average particle size of 0.3 to 0.8 μm, and The powder was converted into MgO-Al_2O_3-Y_2O_
12 of the sintered body sintered using the three-component sintering aid of 3.
A silicon nitride powder having a high temperature strength of 700 MPa or more at 00°C. 2. The total content of Fe, Al and Ca is 500 ppm
The silicon nitride powder according to claim 1, which is as follows. 3. The silicon nitride powder according to claim 1 or 2, having a specific surface area of 6 to 14 m^2/g. 4. In a method for producing silicon nitride by nitriding metal silicon powder in an atmosphere containing nitrogen and/or ammonia, at least one halide selected from the group consisting of alkali metal halides and alkaline earth metal halides, A method for producing silicon nitride, characterized by supplying silicon nitride continuously, intermittently or temporarily in a gaseous state. 5. A silicon nitride powder composition comprising the silicon nitride powder according to claim 1, 2 or 3, and a sintering aid containing magnesium oxide and/or its precursor, and a rare earth element oxide. 6. A silicon nitride sintered body, which is obtained by sintering the silicon nitride powder composition according to claim 5 in an inert gas atmosphere.