JPS6081067A - Manufacture of silicon nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a porous silicon nitride sintered body at low cost. Reactive sintered silicon nitride has a small coefficient of thermal expansion,
Excellent thermal shock resistance.

Because it has excellent properties such as good corrosion resistance against molten metal and no loss of strength at high temperatures, it is being used in many fields including high-temperature mechanical parts and refractories for the metal industry. The present inventors have researched a method for manufacturing reactively sintered silicon nitride molded products having a complex shape at low cost, and have found that by adding 10 to 50% clay to the base material in the casting method, the properties of the sintered body are impaired. We have devised the present invention to be able to satisfy the above object without any problems.

That is, the present invention contains 30 to 75% by weight of Si and 10 to 5% by weight of clay.
This method is characterized by molding a mixed powder containing 0% by weight and the balance being Si 3 N4, and firing the molded body in a non-oxidizing nitrogen atmosphere.

The water 5 will be explained in detail below. The present invention (1.81)
It is necessary to limit the amount to 30 to 75 weight. Sl
is nitrided to form a 3i3N<bond, so there is a minimum amount necessary to obtain satisfactory strength, and (1@ is 30tllafn%).

As the Sl suspension increases, Si 3 N4 pounds σ) ff
As l hi increases, the strength of the sintered body increases, but 5iffi
As the amount increases, it becomes difficult to proceed with a uniform nitriding reaction within the molded body. The reason for this is that the nitriding of the first wire involves a significant exothermic reaction, and the reaction proceeds rapidly due to the reaction heat, raising the temperature inside the compact, causing unreacted silicon to melt and block the pores. , inhibiting further nitriding; 1. : It causes large pores and makes the tissue uneven.
Ru.

For this reason, in the case of products with a high 5iffi, it is necessary to pay close attention to the heating rate of the furnace and the nitrogen supply rate, and nitriding requires a long time, making it difficult to produce inexpensive silicon nitride sintered bodies. It is desirable to be able to bake in a short time,
The amount of 3i must be kept below 75% by weight.

Addition of clay in the present invention has four effects. 1st
The effect is that raw material costs can be reduced. This means that the price of clay is 1/1 compared to Si and Si3N4.
This is because it is less than 0 and inexpensive.

The second effect is that the grinding time can be shortened.

In casting molding, it is necessary to have at least 20% of particles of 1μ or less in the base material in order to obtain an excellent molded product, but clay is an aggregate of fine particles of 1μ or less and easily disperses when stirred in water. Therefore, there is no need to pulverize Si 2 and St 3 N4, and the pulverization process can be simplified and shortened.

The third effect of adding clay is that as a result of imparting plasticity to the base material, it facilitates the finishing and drying steps in cast molding and enables the molding of products with complex shapes. Si
-8i When a clay-free base made only of 3N4 is cast and molded, it is important to dry the demolded molded body uniformly; even the slightest uneven drying will cause cracks to occur. The reason for this is that the base material has almost no plasticity; for example, if the amount of moisture loss on the surface of the molded product is even slightly greater than that on the inside, the surface will shrink more than the inside, causing cracking and cranking. Therefore, when using such a base material, the demolded molded body is immediately placed in a saturated humidity atmosphere to prevent surface drying, and the moisture inside the molded body is first homogenized, and then the humidity is gradually lowered to evenly distribute the moisture in the molded body. The essence of this is to lower it. For this reason, there is a drawback that careful attention is required for drying and the drying time is long. Furthermore, since clay-free base materials have low plasticity, they tend to crack when demolded, and there is also the problem that only simple shapes that can be easily demolded can be molded. Also, since the molded product is brittle,
The processing requires great care.

These problems can be solved by adding clay to the Sl Si 3 N4 matrix, the lower limit of which is 10% by weight. As the amount of clay increases, the plasticity of the matrix increases. In such a base material, even if some moisture difference occurs in the molded body during the drying process and stress is generated due to the difference in shrinkage, the stress is alleviated by plastic deformation of the base material, making it difficult for cracks to occur. Therefore, even if the molded product is dried in heated air, no cracks will occur, which not only simplifies the drying process but also shortens the time. Furthermore, since the molded product can withstand deformation to a certain extent, even products with more complicated shapes can be demolded without cracking, and the range of shapes that can be formed by casting can be significantly expanded. However, if the amount of clay increases too much, the amount of fine particles in the base material will increase, resulting in a large mass effect such as a decrease in the fastness of skin attachment and an increase in the occurrence of drying cracks. be.

The fourth effect of adding clay is that it absorbs the heat generated by nitrogenization of 3i in the firing process and suppresses non-uniformity of the fired body structure due to melting of Sl. The dried compact is heated in a non-oxidizing nitrogen-containing atmosphere such as N2 gas or N2 + L2 or NH3 gas at a temperature of 1,150 to 1,800°C to proceed with the nitriding reaction.
The temperature rises to ℃. In this process, clay reacts with Si and S
i3N4, O' phase, X phase, etc. are formed. Although it is unclear what kind of reaction occurs at each temperature, clay
1 not only absorbs the reaction heat as a filler during nitriding, but also absorbs heat when Sf 11 N4, O' phase, and X phase are generated, suppressing the temperature increase caused by 3i nitriding.

The above effects of adding clay are not limited to cast molded products, but can also be applied to extrusion molded products and press molded products.

The influence of clay addition on the properties of the sintered body can be reduced by the presence of 30% or more of St as in the composition of the present invention. This is done during the firing process, where Si becomes clay AI 2 Sf 20
Sf3
This seems to be to generate N4, O' phase, and X phase. When the molded body was fired at 1500°C in N2, the clay-added base showed almost the same porosity and bending strength as the reactive sintered 3i3N4 base, there was no significant difference in thermal shock resistance, and it had excellent properties in terms of durable oxidation resistance. even showed. The reason why such properties are obtained is that the sintered body mainly contains Si3, which is the same as the reaction sintered crystal.
Made of N4 crystal, J3 is St-AI-0.
This is due to the addition of a small amount of the 0' phase and the X phase consisting of -N atoms.

Next, examples will be described in order to better understand the present invention.

Example 1 Commercially available metal silicon (average diameter 6μ, purity 98.5%) and Si
3 Na (60 m esh purity 98.5%) was placed in a ball mill, ethanol was added, and the mixture was heated for 4 hours and 4 hours.
Pulverized with Ql+r to obtain powder with an average diameter of 3μ and 1°5μ.
= After removing ethanol, it was dried in air at 150°C. Si, Si3N4 and clay (Iga Frogme clay)
Mix as shown in Table 1, add water and acrylic soda, and boil for 16 hours! A slurry containing 55% moisture was prepared for itching.

A test piece of 1QX5X401nl11 was cast and its properties investigated, and the molding properties shown in Table 1 were obtained.

The rate of inking decreases as the amount of clay increases, plasticity coefficient, drying Table 1 *** 2 42.3 52,7 5.0 0.95 1.70
0 20.0 It is recognized that the strength increases. The appropriate range of clay amount is 10% or more of clay based on plasticity and 50% or less based on inking speed.

;1; Thickening rate constant = [Thickness of thickening cm) / (Thickening time sec) 4: =
l: Plasticity coefficient: Deformation until fracture due to straw moisture with a base strength of 5K (1/CI) ■Example 2 The sample from Example 1 was placed in an aluminum crucible and fired in a 5-man furnace. After creating an N2 atmosphere inside,
Up to 1150℃, the temperature is raised at 400℃/llr.
The temperature was raised at 100°C/1) from ~1350°C to advance the nitrogenization reaction, and the temperature was further raised to 1500°C at 400°C/11", the current was turned off, and the material was allowed to cool. The properties of the sintered body are as follows. .

Table 2 Porosity, strength, and thermal shock resistance were within the variation range of the reaction sintered base with 0% clay content, and no major difference was observed due to the addition of clay. Furthermore, addition of clay resulted in the formation of O° phase and X phase in addition to α and βSi 3N4.

Example 3 No. 1 of Example 1, 1 base (clay 0%), No.

5 base (40% clay) slurry 120φ height 120mm
The crucible was cast. Since cracks occur when drying with O% Motoya clay, the molded body is immediately removed from the mold.
It was necessary to wrap the molded body in plastic to suppress drying and bring the moisture inside the molded body to 1-1, then wrap it in cloth and dry it indoors so that the moisture inside the molded body was reduced evenly. After draining the mud, the base material was dried at 0°C together with the mold, and the molded body was removed from the mold after shrinking and separated from the mold. Drying was continued at 40°C, and no drying cracks occurred. The drying time was at least 3 days for 10% base material, but for clay 4.
The drying process for the 0% base material could be simplified in one day. In addition, since the 0% clay base is hard and brittle, great care was required when handling the molded product, but the 40% clay base has some flexibility and strength even below the moisture range where it exhibits plasticity, so handling is difficult. It was easy.

As is clear from the results of the above examples, Si -8!
3 By adding clay to the N4 base material, it is possible to reduce the cost of raw materials without impairing the properties of the sintered body. It is possible to simplify the raw material crushing process and the forming and drying process, making it possible to simplify the process of forming and drying silicon nitride. The purpose of manufacturing the body at low cost can be achieved.

Patent applicant: Toto Kiki Co., Ltd. Procedural amendment January 1982/? Mr. Kazuo Wakasugi, Commissioner of the Japanese Patent Office (Mr. Examiner of the Japan Patent Office) 1. Indication of the case Patent Application No. 191204 of 1982 2. Name of the invention Method for manufacturing silicon nitride sintered body 3. Person making the amendment Related to the case Patent applicant name (AO8) ToV @ Kiki Co., Ltd. 4, Agent address 5-14-7 Hakusan, Bunkyo-ku, Tokyo Showa year
Month/Date 6, Full text of the specification to be amended 7, Contents of the amendment as shown in attached document 1, Title of the invention: Process for manufacturing silicon nitride sintered body 2, Scope of claims s: 30-75% by weight, clay 1. A method for producing a silicon nitride sintered body, which comprises molding a mixed powder of 10 to 50% by weight and the balance being Sl 3 N 4 and firing the molded body in a non-oxidizing nitrogen-containing atmosphere.

3. Detailed Description of the Invention The present invention relates to a method for manufacturing a porous silicon nitride sintered body at low cost. Reactive sintered silicon nitride has a small coefficient of thermal expansion,
Excellent thermal shock resistance.

Because it has excellent properties such as good corrosion resistance against molten metal and no loss of strength at high temperatures, it is being used in many fields including high-temperature mechanical parts and refractories for the metal industry. The present inventors have researched a method for inexpensively manufacturing reaction-sintered silicon nitride molded products with complex shapes, and have used the casting method to add 10 to 50% by weight of clay to the base material. The inventors have discovered that the above objects can be achieved without impairing physical properties, leading to the present invention.

That is, the present invention has s+ 30-75% Juichi, clay 10-5%
The method is characterized in that a mixed powder consisting of 0% by weight and the balance of Si 3 N4 is molded, and the molded body is fired in a non-oxidizing nitrogen-containing atmosphere.

The present invention will be explained in detail below. In the present invention, it is necessary to limit the weight of Sil to 30 to 75%. Since Sl is nitrided to form a Si 3 N 4 bond, there is a minimum amount necessary to obtain satisfactory strength, and the value is 30
Weight%.

As 5iffi increases, the number of Si 3 N4 bonds increases and the strength of the sintered body increases, but as 81m increases, it becomes difficult to proceed with a uniform nitriding reaction within the compact. The reason for this is that nitriding silicon is a significantly exothermic reaction, and as the reaction proceeds rapidly due to the reaction heat and the temperature inside the molded body rises, unreacted silicon melts and blocks the pores. This may inhibit further nitridation or cause large pores to occur, making the structure non-uniform.

For this reason, in the case of materials containing a large amount of Sil, it is necessary to pay close attention to the heating rate of the furnace and the supply rate of nitrogen, and the nitriding firing takes a long time. From the standpoint of manufacturing inexpensive silicon nitride sintered bodies, it is desirable to be able to fire in a short time, and
It is necessary to keep the ink content to less than 75% by weight.

Addition of clay in the present invention has four effects. 1st
The effect is that raw material costs can be reduced. This is because the price of clay is less than 1/10 that of Si and Si 3N4.

The second effect is that the grinding time can be shortened.

In casting molding, it is necessary to have at least 20% of particles of 1μ or less in the base material in order to obtain an excellent molded product, but clay is an aggregate of fine particles of 1μ or less and easily disperses when stirred in water. Therefore, it is no longer necessary to pulverize Sl 2 and Si 3N4, and the pulverization process can be simplified and shortened.

The third effect of adding clay is that it imparts plasticity to the base material.
The objective is to facilitate the demolding, finishing, and drying processes in cast molding, and to enable the molding of complex-shaped products. S:
When casting a clay-free base made only of Si a N4, it is important to dry the demolded molded body uniformly, and if even the slightest uneven drying occurs, a crank will occur. The reason for this is that the base material has almost no plasticity; for example, if the amount of moisture loss on the surface of the molded product is even slightly greater than that on the inside, the surface will shrink more than the inside, creating stress and causing cracks. Therefore, for such base materials, the demolded molded body is immediately placed in a saturated humidity atmosphere to prevent the surface from drying out, and after first equalizing the moisture inside the molded body, the humidity is gradually lowered to a low F to evenly distribute the moisture in the molded body. It is necessary to reduce the For this reason, there is a drawback that careful attention is required for drying and the drying time is long. Furthermore, since clay-free base materials have low plasticity, they tend to crack when demolded, and there is also the problem that only simple shapes that can be easily demolded can be molded. Furthermore, since the molded product is fragile, great care must be taken when processing it.

These problems can be solved by adding clay to the St -st 2 N4 substrate, and the lower limit of the amount added is 10
Weight%. As the amount of clay increases, the plasticity of the C matrix increases. In such a base material, even if some moisture difference occurs in the molded body during the drying process and a stress equal to J: is generated due to the difference in shrinkage, the stress is relaxed by plastic deformation of the base material, so cracks are less likely to occur. Therefore, even if the molded body is dried in heated air, no cracks occur, which not only simplifies the drying process but also shortens the time. In addition, since the molded product can withstand a certain degree of deformation, even complex shapes can be removed from the mold without cracking, and the range of shapes that can be cast can be significantly expanded. However, if the amount of clay increases too much, the amount of fine particles in the base material will increase, resulting in a large mass effect such as a decrease in the deposition rate and the occurrence of dry cracks, so the upper limit for the amount of clay is 50% of the song age. .

The fourth effect of adding clay is to absorb the heat generated by nitrogenization of 3i in the firing process, and to suppress non-uniformity of the structure of the fired body due to melting of 3i. The dried compact is heated gradually in a non-oxidizing nitrogen-containing atmosphere such as N2 gas, N2+H2 gas, N2 gas, etc. in the range of 1150 to 1400°C to proceed with the nitriding reaction, and then heated to a maximum of 1°C to complete the reaction.
Raise the temperature to 600°C. In this process, clay reacts with Sl to form Sf 3 N4, O' phase, X phase, etc.

It is unclear what kind of reaction is occurring in each ifl1m, but clay not only absorbs the reaction heat as a filler when 3i nitrides, but also absorbs the S: 3 N4, O' phase,
It also absorbs heat when the X phase is generated, suppressing abnormal temperature rise due to 3i nitriding.

The above effects of adding clay are not limited to cast molded products, but can also be applied to extrusion molded products and press molded products.

The influence of clay addition on the properties of the sintered body can be reduced by the presence of 30% by weight or more of Si, as in the composition of the present invention. This is done during the firing process, where Si becomes clay At 2 Si 20
S(OH)4 is reduced to promote the reaction and Si3N
This seems to be to generate the 4.0' phase and the X phase. When the molded body was fired at 1500°C in N2, the clay-added base showed almost the same porosity and bending strength as the reactive sintered Si3N4 wood, there was no significant difference in thermal shock resistance, and it had excellent oxidation resistance. even showed. The reason why such properties are obtained is that the sintered body mainly consists of Si 3 N 4 crystals, which are the same as the reaction sintered crystals, and in addition, there are small amounts of O' phase and X phase consisting of s; -AI-0-N atoms. It is just a matter of adding an iron.

Next, examples will be described in order to better understand the present invention.

Example 1 Commercially available metal silicon (average diameter 6μ, purity 98.5%) and Si
3 N4 (60+11 esh @98.5% degree)
Place each in a ball mill, add ethanol and boil for 4:1r.
and 401+r grinding to obtain powders with average diameters of 3μ and 1.5μ. After removing ethanol, it was dried in air at 150°C. St, S! 3N4 and clay (Nakabaku Kajime clay) were mixed as shown in Table 1, water and sodium acrylate were added, and the mixture was stirred in a pot for 15 hours to prepare a slurry with a moisture content of 55%. A test piece measuring 1010 x 5 x 40 was cast and its properties investigated, and the molding properties shown in Table 1 were obtained.

It is observed that as the amount of clay increases, the deposition rate decreases, and the plasticity coefficient and dry strength increase. The appropriate range of clay amount is 10% or more of clay based on plasticity and 50% or less based on inking speed.

Table 1 2 42.3 52,7 5,0 0.95 1,70
0 20,03 42.3 47.7 10,0 0
,98 1,50 0.21 24,04 42.3
37.7 20.0 1,00 1.13 0.40
30,25 42.3 17.7 40,0 1,38
0.99. 0.58 42.3 * Thickening rate constant - [Nominal wall thickness C1n) 2/ (Thickening time sea)**
Plasticity coefficient: Amount of deformation until fracture due to moisture in the substrate so that the substrate strength is 5 Kg/cm' Example 2 The sample of Example 1 was placed in an alumina crucible and fired in a Tamman type. After creating a N2 atmosphere inside the furnace by vacuum displacement,
The temperature is raised at a rate of 400°C/hr up to 1150°C, and from 1150°C to
During the period of 1350°C, the temperature was raised at a rate of 100°C/hr to advance the nitrogenization reaction.

Further, Wm was applied at a rate of 400° C./hr to 1500° C., and the current was turned off and the sample was left to cool. The properties of the sintered body are as follows.

Table 2 Crystal phase jAIjL J side, ρ' 4at, ρ' 5 42.3 17.7 30 30.8 12,7
5oObLILi4-6'J porosity, strength, and thermal shock resistance are within the variation range of the reaction sintered base material with 0% clay content.
No major difference was observed due to the addition of clay. In addition, the addition of clay resulted in the formation of O' phase and X phase in addition to α and βSi 3N4.

History example 3 No. 1 of Example 1, 1 base (clay 0%), No.

5 base material (40% clay) slurry 120φ height 120II
A IIm crucible was cast. Since cracks occur when drying with a 0% clay base, the molded body is removed from the mold immediately after removing mud, wrapped in plastic film to prevent drying, and
After equalizing the moisture inside the molded object, it was necessary to wrap it in cloth and slowly dry it indoors so that the moisture inside the molded object would be reduced evenly, but with the 40% clay base, the entire mold was dried at 40°C after removing the mud. However, even after the molded product shrunk and separated from the mold, it was removed from the mold and further dried at 40° C., but no drying cracks occurred. While a 0% clay base required at least 3 days to dry, a 40% clay base required only 1 day, simplifying the drying process. Also, since the 0% clay base is hard and brittle, great care was required when handling the molded body, but the 40% clay base
The base material showed plasticity, had some flexibility even below the moisture range, and was strong, making it easy to handle.

As is clear from the results of the above examples, S! -8!
By adding clay to the 3N4m base, it is possible to reduce raw material costs, simplify the raw material crushing process, and simplify the molding and drying process without impairing the properties of the sintered body. The purpose of manufacturing quality sintered bodies at low cost can be achieved.

Patent applicant: Totokiki Co., Ltd.

Claims (1)

[Claims] Si 30-75% by weight, clay 10-50% by weight, 1i1%,
1. A method for producing a silicon nitride sintered body, which comprises forming a mixed powder whose remainder is 5i3N4J, and firing the compact in a non-oxidizing nitrogen-containing atmosphere.