KR20170060970A - Porous silicon nitride sintered body and method for manufacturing the same - Google Patents
Porous silicon nitride sintered body and method for manufacturing the same Download PDFInfo
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- KR20170060970A KR20170060970A KR1020150165787A KR20150165787A KR20170060970A KR 20170060970 A KR20170060970 A KR 20170060970A KR 1020150165787 A KR1020150165787 A KR 1020150165787A KR 20150165787 A KR20150165787 A KR 20150165787A KR 20170060970 A KR20170060970 A KR 20170060970A
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 116
- 229910021426 porous silicon Inorganic materials 0.000 title claims abstract description 39
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 28
- 238000000034 method Methods 0.000 title claims description 43
- 238000005245 sintering Methods 0.000 claims abstract description 98
- 229910052581 Si3N4 Inorganic materials 0.000 claims abstract description 77
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- 239000002994 raw material Substances 0.000 claims abstract description 48
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- 238000002156 mixing Methods 0.000 claims abstract description 26
- 239000011148 porous material Substances 0.000 claims abstract description 13
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- 229910052710 silicon Inorganic materials 0.000 claims description 8
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- 239000013078 crystal Substances 0.000 claims description 6
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- QIQXTHQIDYTFRH-UHFFFAOYSA-N octadecanoic acid Chemical compound CCCCCCCCCCCCCCCCCC(O)=O QIQXTHQIDYTFRH-UHFFFAOYSA-N 0.000 claims description 3
- OQCDKBAXFALNLD-UHFFFAOYSA-N octadecanoic acid Natural products CCCCCCCC(C)CCCCCCCCC(O)=O OQCDKBAXFALNLD-UHFFFAOYSA-N 0.000 claims description 3
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- -1 lanthanide metals Chemical class 0.000 claims description 2
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- 229910052582 BN Inorganic materials 0.000 description 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 1
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/068—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with silicon
- C01B21/0687—After-treatment, e.g. grinding, purification
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J6/00—Heat treatments such as Calcining; Fusing ; Pyrolysis
- B01J6/001—Calcining
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/40—Electric properties
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Ceramic Products (AREA)
Abstract
The present invention relates to a method for producing a silicon nitride raw material, comprising the steps of: controlling an addition amount of a sintering auxiliary agent for forming pores in a silicon nitride raw material powder; Mixing said silicon nitride raw material powder to enable uniform pore formation of said silicon nitride raw material powder; And sintering the silicon nitride raw material powder in an inert atmosphere, and a porous silicon nitride sintered body produced by the manufacturing method.
Description
The present invention relates to a porous silicon nitride sintered body having controlled pore and bending strength through uniform dispersion of a sintering auxiliary agent and control of addition amount of the sintering auxiliary agent, and a method for manufacturing the same.
Ceramic materials have higher heat resistance and hardness, lower specific gravity and better chemical stability than metals, and are suitable for mechanical structural materials. However, due to the inherent brittleness of the ceramic material, there are many limitations to apply to various fields. Nevertheless, non-oxide ceramic materials such as silicon nitride (Si 3 N 4 ) and silicon carbide (SiC) have been attracting attention as structural ceramics because of their high strength and good thermal shock resistance.
Among these, silicon nitride is in the spotlight because various characteristics are balanced with each other as compared with other ceramic materials, and it is possible to manufacture ceramics having various properties according to the use by changing starting materials, sintering additive and manufacturing process .
Silicon nitride is a naturally occurring compound that is artificially synthesized by a chemical reaction between silicon (Si), a metal, and nitrogen (N), a nonmetal, first reported by Deville and Wohler in 1859.
Silicon nitride ceramics were first applied to refractory materials in 1950 based on their high covalent bonding stability and were applied as protective tubes for thermocouples based on their excellent stability to molten metals. In the 1960s, attempts were made to apply to high-temperature structural materials, and studies to apply to engine parts such as gas turbines and pistons, which require thermal shock resistance, have been vigorously conducted, and the overall understanding of silicon nitride has been rapidly increasing .
As described above, the excellent mechanical properties and thermal shock resistance characteristics of silicon nitride are used as filtration filters, catalyst supports, heat insulating materials, biomaterials, and filters for filtering fine dusts of diesel vehicles through the production of porous silicon nitride sintered bodies as well as high- Is a promising material. The dielectric property can be controlled through the porosity control. In addition to the application of the filter and the like as described above, it is also possible to use it as a radio wave transmission window for protecting a device for transmitting and receiving radio waves operating in a high-speed and high-temperature environment.
The durability is basically provided in a high-speed and high-temperature environment, and at the same time, the signal loss when the microwave band is transmitted through the transmission window must be minimized in order to smoothly transmit and receive signals between the devices. For this purpose, controlling the dielectric properties of the antenna window material is one of the most important design factors.
However, most studies on existing silicon nitride materials have been made to utilize them as structural materials for high strength, high thermal conductivity, and high temperature materials through microstructure densification. In order to improve high strength, high thermal conductivity and high temperature strength, a large amount of sintering aid is used to densify the microstructure by utilizing high temperature and high pressure equipment such as hot pressing and gas pressure sintering Researches have been focused on, and studies on the production of relatively porous silicon nitride materials have been lacking.
Korean Patent Laid-Open No. 10-2015-004512 discloses a technique for producing ceramics as a porous article, which comprises a step of adding a pore-forming agent such as polyacrylonitrile, PMMA (poly methyl methacrylate), carbon black, starch and polystyrene The present invention provides a method for producing a ceramic formed body by adding the powdery ceramic powder to a ceramic body.
XM Li (J. Mater. Sci. Technol. (28 (12), 11551-1156)) is a technique for producing a porous article by a silicon nitride-based ceramics in which a phenolic resin is added as a pore- Treated at a temperature of 1700 ° C or higher to produce a porous ceramic.
Korean Patent Registration No. 10-1372464 discloses a method of preparing a slurry by mixing a silicon powder, a dispersant, a binder and a solvent, and then slurry is freeze-cast using a freeze-casting apparatus and then subjected to sublimation and heat treatment to form porous silicon nitride Ceramic is manufactured.
Korean Patent Registration No. 10-0994376 discloses a method for producing silicon nitride by preliminarily sintering silicon nitride in a nitrogen atmosphere using silicon (Si) and a sintering aid, and sintering the silicon nitride by main sintering to form porous silicon nitride ceramics .
However, the porous silicon nitride ceramics prepared by using the pore-forming agent as described above can not ensure uniform pore distribution due to difficulty in uniform mixing due to the difference in density between the silicon nitride powder and the pore-forming agent when the slurry is dried. In addition, the porous silicon nitride ceramics produced by using the pore-forming agent are difficult to control the coherent process and may not be suitable for the enlargement process. On the other hand, in order to remove the pore-forming agent, it is required to undergo a heat treatment process called a degreasing process, which is disadvantageous in terms of productivity.
In the case of producing porous silicon nitride by using silicon, two-step heat treatment of pre-sintering and main-sintering is required as described above, which also requires a long processing time and is disadvantageous in terms of productivity. Although the porous body itself also requires structural strength, porous silicon nitride ceramics using the silicon described above exhibits a flexural strength of 15 MPa, and mechanical stability can not be guaranteed when used with a filter or the like.
The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide a porous silicon nitride ceramics sintered body having a simple process, a uniform pore distribution, And a method for producing the same.
In order to solve the above problems, a method of producing a porous silicon nitride sintered body according to the present invention comprises the steps of: controlling the amount of the sintering auxiliary added for pore formation in the silicon nitride raw material powder; Mixing said silicon nitride raw material powder to enable uniform pore formation of said silicon nitride raw material powder; And sintering the silicon nitride raw material powder in an inert atmosphere.
According to an embodiment of the present invention, the step of mixing the silicon nitride raw material powder may be performed by mixing the silicon nitride raw material powder and the sintering auxiliary agent to produce a sintered body having uniform physical properties, Mixing; And mixing the mixed sintering aid with the silicon nitride raw material powder and mixing the mixture with a ball mill for 24 hours or more. The method of manufacturing a porous silicon nitride sintered body according to any one of
The dispersing agent of the slurry is at least one of an acrylic resin, a polycarboxylic acid salt and an organic polymer surfactant, and the binder may be at least one of a polyvinylbutyl resin, a polyvinyl alcohol resin, a polyester resin and a stearic resin have.
In the step of molding the mixed raw material, the molding method may be one of a wet molding method, a uniaxial molding method and a cold isostatic pressing method, and the wet molding method may be one of slip casting, pressure slip casting and gel casting.
According to another embodiment of the present invention, in the step of sintering the silicon nitride raw material powder, the heat treatment temperature is in the range of 1700 DEG C to 1800 DEG C, the rate of temperature rise to the maximum temperature is 0.5 DEG C / min or more, / min. < / RTI >
According to another embodiment of the present invention, the sintering assistant comprises one single powder selected from the group consisting of Al, Mg, Si, lanthanide metal (Y, La, Ce, Sm, Er, Yb and Lu) Or two or more mixed powders.
The sintering aid is one of oxides, chlorides, nitrates and nitrates of at least one of Al, Mg, Si, lanthanide metals (Y, La, Ce, Sm, Er, Yb and Lu).
According to another embodiment of the present invention, the content of the sintering auxiliary agent is 1 wt.% Or more and 10 wt.% Or less of the total amount of the silicon nitride raw material powder and the sintering auxiliary agent.
To solve another problem, a porous silicon nitride sintered body is manufactured by the above-described manufacturing methods.
According to one example related to the present invention, at least 90 vol% of the silicon nitride crystal grains are? -Type silicon nitride crystal grains.
According to another embodiment of the present invention, the porosity is 1.8 to 42.7%, the dielectric constant is 3.7 to 7.6, and the flexural strength is 150 MPa or more.
According to the present invention, a porous silicon nitride sintered body capable of adjusting the porosity of the silicon nitride sintered body to 1.8 to 42.7% and the dielectric constant to 3.7 to 7.6 through controlling the addition amount of the sintering auxiliary agent and exhibiting excellent mechanical properties with a flexural strength of not less than 150 MPa And a manufacturing method thereof can be provided.
In addition, unlike conventional porous silicon nitride ceramics manufacturing processes, it is possible to provide a porous silicon nitride sintered body manufacturing method by a first heat treatment process which does not require a degreasing process or a post-sintering process for removing pore formers.
Accordingly, the present invention provides a method of manufacturing a highly reliable silicon nitride ceramics sintered body having controlled mechanical properties and pore contents, and can be easily applied to materials such as a filter for filtration, a catalyst carrier, a heat insulating material, a filter for filtering fine dusts of biomaterials and diesel vehicles .
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a method of manufacturing a porous silicon nitride ceramics sintered body of the present invention.
2 is a photograph of the porous silicon nitride sintered body obtained by the present invention.
FIG. 3 is a graph showing a phase analysis of porous silicon nitride ceramics according to an embodiment of the present invention (A01: addition amount of sintering
FIG. 4 is a photograph of the sintering of the composition according to an embodiment of the present invention at 1750.degree. (a) Additive 1 wt.%, (b) Additive 2 wt.%, (c) Additive 4 wt.%, (d) Additive 8 wt.
FIG. 5 is a graph of a three-point bending strength according to an addition amount of a sintering aid having a composition containing 1 to 10 wt.% Of sintering additive added according to an embodiment of the present invention.
6 is a graph of the three-point flexural strength according to porosity of a composition containing 1 to 10 wt.% Of sintering aid added in accordance with an embodiment of the present invention.
7 is a graph showing dielectric constants in a microwave region of a composition containing 1 to 8 wt.% Of sintering aid added in accordance with an embodiment of the present invention.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like or similar elements are denoted by the same or similar reference numerals, and a duplicate description thereof will be omitted. The suffix "part" for the constituent elements used in the following description is to be given or mixed with consideration only for ease of specification, and does not have a meaning or role that distinguishes itself. In the following description of the embodiments of the present invention, a detailed description of related arts will be omitted when it is determined that the gist of the embodiments disclosed herein may be blurred. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. , ≪ / RTI > equivalents, and alternatives.
Terms including ordinals, such as first, second, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another.
It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, but it should be understood that other elements may be present in between something to do.
The singular expressions include plural expressions unless the context clearly dictates otherwise.
In the present application, the terms "comprises", "having", and the like are used to specify that a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.
1 is a flowchart showing a manufacturing method (S100) of the porous silicon nitride ceramics sintered body of the present invention.
Referring to FIG. 1, a method (S100) for manufacturing a porous silicon nitride sintered body according to the present invention comprises the steps of (S10) controlling an addition amount of a sintering auxiliary agent, (S20) mixing silicon nitride fuel powder and sintering a silicon nitride raw powder S40).
To prepare the porous silicon nitride sintered body, a sintering auxiliary agent is added to the silicon nitride raw material powder.
The step S10 of controlling the addition amount of the sintering auxiliary agent controls the addition amount of the sintering auxiliary agent in a certain amount, which forms pores in the silicon nitride raw material powder.
For example, the sintering aid content may be 1 wt.% Or more and 10 wt.% Or less of the total amount of the silicon nitride raw material powder and the sintering assistant.
In addition, step (S20) of mixing the silicon nitride fuel powder enables uniform pore formation of the silicon nitride raw material powder.
The step S20 of mixing the silicon nitride fuel powder includes a step (S21) of mixing only the sintering auxiliary agent with the ball mill for 24 hours or more, and a step (S24) of mixing the mixed sintering auxiliary agent with the silicon nitride raw material powder and then mixing them with the ball mill for 24 hours or more can do.
In the step (S21) of mixing the sintering auxiliary agent for only 24 hours or more with a ball mill, the silicon nitride raw material powder and the sintering auxiliary agent are mixed to prepare a sintered body having uniform physical properties, (Step S21).
Thereafter, the mixed sintering aids are mixed with the silicon nitride raw material powder and mixed by a ball mill for 24 hours or more (S24).
The dispersant of the slurry may be at least one selected from the group consisting of acrylic resin, polycarboxylic acid salt and organic polymer surface active agent at the time of preparing the slurry in which the silicon nitride raw material powder and the sintering aid are mixed. It can be one.
In the preparation of the slurry for mixing the silicon nitride raw material powder and the sintering auxiliary agent, the binder may be a polyvinyl butyl resin, a polyvinyl alcohol resin, a polyester resin, a stearic acid resin stearic acid resin.
Meanwhile, the step (S40) of sintering the silicon nitride raw material powder is a step (S40) of sintering the silicon nitride raw material powder in an inert atmosphere.
In the step (S40) of sintering the silicon nitride raw material powder, the heat treatment temperature is not lower than 1700 DEG C and not higher than 1800 DEG C, and the rate of temperature rise before reaching the maximum temperature is 0.5 DEG C / min or higher and 2.0 DEG C / min or lower.
The manufacturing method (S100) of the porous silicon nitride sintered body further includes a step (S30) of molding the mixed sintering auxiliary agent and the silicon nitride raw material powder between the step (S20) of mixing the silicon nitride raw material powder and the step (S40) .
In the step (S30) of molding the mixed sintering assistant and the silicon nitride raw material powder, the molding may be performed by one of a wet molding method, a uniaxial molding method and a cold isostatic pressing method.
The wet forming method may be one of slip casting, pressure slip casting and gel casting.
2 is a photograph of the porous silicon nitride sintered body obtained by the present invention.
In the porous silicon nitride sintered body produced by the method for producing a porous silicon nitride sintered body of the present invention, at least 90 vol% of the silicon nitride crystal grains may be? -Type silicon nitride crystal grains.
Also, the porosity of the porous silicon nitride sintered body produced by the production method of the porous silicon nitride sintered body may be 1.8 to 42.7%, the dielectric constant may be 3.7 to 7.6, and the bending strength may be 150 MPa or more.
Hereinafter, a method of manufacturing a porous silicon nitride sintered body and Embodiments 1 and 2 relating to a porous silicon nitride sintered body will be described.
[Example 1: Control of strength and porosity by addition of Y 2 O 3 and SiO 2 system sintering auxiliary]
In this experiment, Y 2 O 3 (HC Stark, purity: 99.99%, average particle diameter: 0.7 μm) and SiO 2 (Evonik, purity: 99.8%, particle size> 0.06 μm) were used as the sintering aid. In order to uniformly mix the sintering agent, the sintering agent was ball milled for 24 hours in a Nalgene bottle with anhydrous ethanol using a silicon nitride ball. The slurry was mixed with a raw material powder of silicon nitride (UBE E10,? Phase content> 95%, average particle diameter: 0.5 μm), and a polyvinyl alcohol binder and an acrylic resin dispersant were added and ball milled for 24 hours. The agitated slurry was dried and granulated at 90 DEG C under a condition of 8000 rpm. Table 1 shows the ratio of the sample name, raw material powder and sintering additive amount.
As shown in Table 1, the addition amount of the sintering auxiliary agent was 1 to 10 wt.% Of the sum of the silicon nitride raw material powder and the sintering auxiliary agent. The powder was charged into a mold and subjected to hydrostatic pressure molding at 120 MPa. The formed body was sintered at 1750 ° C for 4 hours under a nitrogen atmosphere at a heating rate of 1 ° C / min without a separate degreasing step and a preliminary sintering step. The sintered body was packed with a silicon nitride and boron nitride atmosphere powder to maintain a nitrogen atmosphere.
FIG. 3 is a graph showing a phase analysis of porous silicon nitride ceramics according to an embodiment of the present invention. 3 is a result of XRD analysis after sintering of the sintered body. FIG. 4 is a photograph of a sintered composition at 1750 ° C. according to an embodiment of the present invention. FIG. 4 (a) shows the result of the sintering at 1750 ° C. and shows that the
Referring to FIG. 3, it can be seen that the phase-change of the α-phase silicon nitride as the raw material powder to 100% β-phase silicon nitride phase occurred without generation of the secondary phase in the range of 1 to 10 wt.%.
As shown in FIG. 4 (a), it was confirmed that a phase change of about 1 wt.% Was obtained even in the sintering addition, and silicon nitride of β phase having an excellent mechanical strength and a large length ratio was produced. It was confirmed in this example that the porosity can be controlled within the range where the needle-like microstructure is maintained at the addition amount of the sintering aid at least 1 wt.% Or more.
FIG. 4 is a scanning electron microscope (SEM) chart of fracture profiles of the sintered bodies to which 1, 2, 3 and 8 wt.% Sintering aids are added. It can be seen that porosity increases as the amount of sintering aid is decreased from 8 to 1 wt.%. As described above, it can be seen that the aspect ratio of the needle-like shape changes only by the degree of porosity without a large change depending on the amount of the sintering aid added.
FIG. 5 is a graph of a three-point bending strength according to an addition amount of a sintering auxiliary added in an amount of 1 to 10 wt.% In an addition amount of a sintering auxiliary agent according to an embodiment of the present invention. The graph of the three-point flexural strength according to the porosity of the composition in which the addition amount is 1 to 10 wt.%. Meanwhile, FIG. 7 is a graph showing dielectric constants in a microwave region of a composition containing 1 to 8 wt.% Of sintering aid added in accordance with an embodiment of the present invention.
Referring to FIG. 6, it can be seen that porosity increases as the amount of sintering aid added decreases. It can be seen that the three-point flexural strength varies from 150 MPa to 614 MPa as the addition amount of the sintering aid is changed by 1 to 10 wt.%. At this time, the porosity varies from 42.7% to 1.8% as shown in FIG.
As shown in FIG. 7, the dielectric constant varies from 3.7 to 7.6 depending on the sintering additive amount in the microwave region. Therefore, it was confirmed that the sintered body had excellent bending strength (> 150 MPa) and porosity (1.8 to 42.7%) and dielectric constant (3.7 to 7.6) were controlled using Y 2 O 3 and SiO 2 sintering aids, And a method of manufacturing the same.
[Example 2: Verification of uniformity of physical properties of sinter at an addition amount of 2 wt.% Sintering aid]
The sintered body having a diameter of about 200 mm as shown in FIG. 2 was manufactured through the same process as shown in FIG. 1 based on the A02 specific composition of Example 1 at all times in order to verify the uniformity of the sintered body in a small amount of the sintering aid. Silicon nitride is generally densified through particle reorganization and dissolution - diffusion - re - precipitation through liquid phase sintering with sintering assistant.
Example 2 demonstrates that the sintering process proceeds according to the above-described mechanism even in the region where the sintering aid is added in a small amount and that the added amount of the sintering aid can maintain uniform physical properties throughout the entire sintered body. In order to uniformly disperse the sintering aid even at a small amount of the sintering additive, ball milling was performed for 24 hours using anhydrous ethanol and silicon nitride ball only in the sintering preparation of Y 2 O 3 and SiO 2 as in 'Claim 2'. Ten pieces of bending strength test specimens, test pieces for checking porosity and test pieces for dielectric property measurement were taken from each of the above-mentioned 200 mm diameter sintered bodies. The results are shown in Table 2.
As can be seen from the above Table 2, it was confirmed that the bending strength, density, porosity and dielectric constant were uniform throughout the entire sintered body. Through the example 2, it was verified that the technique proposed in this patent shows uniform properties throughout the entire sintered body of 200 mm in diameter even when a small amount of the sintering aid is added. Through the utilization of this technology, it was judged that this technique is applicable to commercialization of porous silicon nitride based sintered body having uniform mechanical properties and porosity, applicable to large size, and controlled in strength and porosity.
The porous silicon nitride sintered
It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.
Claims (11)
Mixing said silicon nitride raw material powder to enable uniform pore formation of said silicon nitride raw material powder; And
And sintering the silicon nitride raw material powder in an inert atmosphere.
Wherein mixing the silicon nitride raw material powder comprises:
Mixing the silicon nitride raw material powder and the sintering auxiliary agent to prepare a sintered body having uniform physical properties at the time of preparing the slurry; And
Mixing the mixed sintering aid with the silicon nitride raw material powder, and mixing the mixture with a ball mill for at least 24 hours,
Further comprising molding the mixed sintering aid and the silicon nitride raw material powder between the step of mixing and the step of sintering the silicon nitride raw material powder.
The dispersant of the slurry may be,
An acrylic resin, a polycarboxylic acid salt, and an organic polymer surfactant,
As the binder,
Wherein the porous silicon nitride sintered body is at least one of polyvinyl butyral resin, polyvinyl butyl resin, polyvinyl alcohol resin, polyester resin and stearic acid resin.
In the step of molding the mixed raw material,
The molding method is one of a wet molding method, a uniaxial molding method and a cold isostatic pressing method,
Wherein the wet forming method is one of slip casting, pressurized slip casting and gel casting.
In the step of sintering the silicon nitride raw material powder,
The heat treatment temperature is 1700 DEG C or higher and 1800 DEG C or lower,
Wherein the rate of temperature rise until reaching the maximum temperature is 0.5 占 폚 / min or more and 2.0 占 폚 / min or less.
Wherein the sintering aid is one single powder selected from the group consisting of Al, Mg, Si and lanthanide metals (Y, La, Ce, Sm, Er, Yb and Lu) A method for producing silicon nitride.
Wherein the sintering aid is one of oxides, chlorides, nitrates and nitrates containing at least one of Al, Mg, Si, lanthanide metal (Y, La, Ce, Sm, Er, Yb and Lu) Of silicon nitride.
Wherein the content of the sintering auxiliary agent is 1 wt.% Or more and 10 wt.% Or less of the total amount of the silicon nitride raw material powder and the sintering auxiliary agent.
A porous silicon nitride sintered body in which at least 90 vol% of silicon nitride crystal grains are? -Type silicon nitride crystal grains.
Wherein the porosity is 1.8 to 42.7%, the dielectric constant is 3.7 to 7.6, and the flexural strength is 150 MPa or more.
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