JP6720053B2 - Method for manufacturing silicon nitride sintered body - Google Patents
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- JP6720053B2 JP6720053B2 JP2016216124A JP2016216124A JP6720053B2 JP 6720053 B2 JP6720053 B2 JP 6720053B2 JP 2016216124 A JP2016216124 A JP 2016216124A JP 2016216124 A JP2016216124 A JP 2016216124A JP 6720053 B2 JP6720053 B2 JP 6720053B2
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- 229910052581 Si3N4 Inorganic materials 0.000 title claims description 118
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims description 118
- 238000004519 manufacturing process Methods 0.000 title claims description 44
- 238000000034 method Methods 0.000 title claims description 43
- 239000000843 powder Substances 0.000 claims description 193
- 238000001354 calcination Methods 0.000 claims description 152
- 238000005245 sintering Methods 0.000 claims description 73
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 70
- 238000002156 mixing Methods 0.000 claims description 52
- 239000011812 mixed powder Substances 0.000 claims description 40
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- 229910052799 carbon Inorganic materials 0.000 claims description 30
- 238000010438 heat treatment Methods 0.000 claims description 30
- 239000000203 mixture Substances 0.000 claims description 30
- 238000000465 moulding Methods 0.000 claims description 28
- 238000010304 firing Methods 0.000 claims description 25
- 239000012298 atmosphere Substances 0.000 claims description 21
- 230000001590 oxidative effect Effects 0.000 claims description 21
- 238000004364 calculation method Methods 0.000 claims description 12
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims description 2
- 239000000395 magnesium oxide Substances 0.000 description 24
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 24
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- 239000000919 ceramic Substances 0.000 description 4
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 4
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- 238000005121 nitriding Methods 0.000 description 4
- 229910052684 Cerium Inorganic materials 0.000 description 3
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 3
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
- 229910052788 barium Inorganic materials 0.000 description 2
- ZFMQKOWCDKKBIF-UHFFFAOYSA-N bis(3,5-difluorophenyl)phosphane Chemical compound FC1=CC(F)=CC(PC=2C=C(F)C=C(F)C=2)=C1 ZFMQKOWCDKKBIF-UHFFFAOYSA-N 0.000 description 2
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- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
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- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 description 1
- UFQXGXDIJMBKTC-UHFFFAOYSA-N oxostrontium Chemical group [Sr]=O UFQXGXDIJMBKTC-UHFFFAOYSA-N 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
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- GCLGEJMYGQKIIW-UHFFFAOYSA-H sodium hexametaphosphate Chemical compound [Na]OP1(=O)OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])O1 GCLGEJMYGQKIIW-UHFFFAOYSA-H 0.000 description 1
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Description
本発明は、窒化ケイ素焼結体の製造方法に関する。 The present invention relates to a method for manufacturing a silicon nitride sintered body.
近年、電子機器や半導体デバイスの高密度化、高出力化に伴い、パワーモジュールの発熱密度が増加している。パワーモジュールの温度上昇は、素子の動作不良を引き起こしたり、絶縁回路基板の割れを引き起こしたりする要因となる。そのため、絶縁回路基板には、比較的に熱伝導率が高い材料であるアルミナや窒化アルミニウムなどのセラミック基板が用いられてきた。しかしながら、アルミナや窒化アルミニウムには、機械的強度が低いという欠点が存在する。それ故、熱応力が強くかかる厚銅をセラミック基板へ直接接合することが出来ず、パワーモジュールの構造に制約を与えてきた。具体的には、銅やアルミニウムなどの放熱板を絶縁回路基板に対して、はんだ接合する必要が生じることから、パワーモジュールが大型化することが問題として挙げられる。そこで、絶縁回路基板として注目されているのが窒化ケイ素（Ｓｉ３Ｎ４）材料である。窒化ケイ素焼結体は、アルミナや窒化アルミニウム焼結体と比較して強度や破壊靭性が２倍程高いことから、絶縁回路基板へ直接厚銅を接合することが可能となり、モジュールの小型化に貢献する。他方、窒化ケイ素の熱伝導率は窒化アルミニウムの半分程度であり、熱伝導率を向上させることが必須である。 2. Description of the Related Art In recent years, the heat generation density of power modules has been increasing with the increasing density and output of electronic devices and semiconductor devices. The rise in the temperature of the power module causes a malfunction of the element or a crack of the insulating circuit board. Therefore, a ceramic substrate such as alumina or aluminum nitride, which is a material having a relatively high thermal conductivity, has been used as the insulating circuit substrate. However, alumina and aluminum nitride have the drawback of low mechanical strength. Therefore, it is not possible to directly bond thick copper, which is strongly subjected to thermal stress, to a ceramic substrate, which has restricted the structure of the power module. Specifically, since it is necessary to solder-bond a heat dissipation plate made of copper or aluminum to the insulated circuit board, the power module becomes large in size. Therefore, a silicon nitride (Si 3 N 4 ) material is attracting attention as an insulating circuit board. Silicon nitride sinter has twice as high strength and fracture toughness as alumina and aluminum nitride sinter, so it is possible to bond thick copper directly to the insulating circuit board, which contributes to module miniaturization. To contribute. On the other hand, the thermal conductivity of silicon nitride is about half that of aluminum nitride, and it is essential to improve the thermal conductivity.
例えば、特許文献１は、機械的特性に優れているとともに、高い熱伝導性を持つ窒化ケイ素質焼結体の製造方法を開示する。該製造方法では、Ａｌ含有量が０．１重量％以下の窒化ケイ素粉末に、Ｍｇ，Ｃａ，Ｓｒ，Ｂａ，Ｙ，Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｓｍ，Ｇｄ，Ｄｙ，Ｈｏ，Ｅｒ，Ｙｂのうちから選ばれる１種または２種以上の元素の酸化物焼結助剤を１重量％以上１５重量％以下の範囲内で添加して成形した後、１気圧以上５００気圧以下の窒素ガス圧下で、１７００℃以上２３００℃以下の温度で焼成する。該製造方法によって得られた窒化ケイ素質焼結体は、８５重量％以上９９重量％以下のβ型窒化ケイ素粒と残部が酸化物または酸窒化物の粒界相とから構成される。また、粒界相中にＭｇ，Ｃａ，Ｓｒ，Ｂａ，Ｙ，Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｓｍ，Ｇｄ，Ｄｙ，Ｈｏ，Ｅｒ，Ｙｂのうちから選ばれる１種または２種以上の金属元素を０．５重量％以上１０重量％以下含有する。そして、粒界相中のＡｌ原子含有量が１重量％以下であり、気孔率が５％以下でかつ焼結体の微構造についてβ型窒化ケイ素粒のうち短軸径５μｍ以上を持つものの割合が１０体積％以上６０体積％以下である。すなわち、特許文献１には、焼結助剤を添加することにより、該窒化ケイ素質焼結体が優れた機械的特性と高い熱伝導率を合わせ持つことが記載されている。 For example, Patent Document 1 discloses a method for producing a silicon nitride sintered body having excellent mechanical properties and high thermal conductivity. In the manufacturing method, the content of Al in the silicon nitride powder is 0.1 wt% or less, Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb. 1% or more and 15% by weight or less of an oxide sintering aid of one or more elements selected from the above, and after molding, under a nitrogen gas pressure of 1 atm to 500 atm. Then, firing is performed at a temperature of 1700° C. or higher and 2300° C. or lower. The silicon nitride sintered body obtained by the manufacturing method is composed of 85% by weight or more and 99% by weight or less of β-type silicon nitride particles and the balance being a grain boundary phase of oxide or oxynitride. Further, in the grain boundary phase, one or more metal elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb. 0.5 wt% or more and 10 wt% or less. The proportion of Al atoms in the grain boundary phase is 1 wt% or less, the porosity is 5% or less, and the microstructure of the sintered body is β-type silicon nitride grains having a minor axis diameter of 5 μm or more. Is 10% by volume or more and 60% by volume or less. That is, Patent Document 1 describes that the silicon nitride sintered body has excellent mechanical properties and high thermal conductivity by adding a sintering aid.
すなわち、高熱伝導性の窒化ケイ素焼結体を得るためには焼結助剤として希土類化合物や酸化マグネシウムを加え、それらの混合比や添加量によって熱伝導率や機械的強度を向上できることが知られている。しかしながら、混合比や添加量の変更による熱伝導率や強度の改善では不十分であり、且つ、限度がある。そして、窒化ケイ素焼結体の機械的特性及び熱伝導率のより一層の向上が求められている。 That is, it is known that in order to obtain a silicon nitride sintered body with high thermal conductivity, a rare earth compound or magnesium oxide is added as a sintering aid, and the thermal conductivity and mechanical strength can be improved by the mixing ratio and the addition amount thereof. ing. However, improvement of the thermal conductivity and strength by changing the mixing ratio and the addition amount is not sufficient, and there is a limit. Further, the mechanical properties and thermal conductivity of the silicon nitride sintered body are required to be further improved.
本発明は、上記課題を解決するために、その製造工程に着目してなされたものであり、その目的は、機械的強度及び熱伝導率の改善を可能とする窒化ケイ素焼結体の製造方法を提供することにある。 In order to solve the above problems, the present invention has been made by paying attention to the manufacturing process thereof, and an object thereof is a method for manufacturing a silicon nitride sintered body capable of improving mechanical strength and thermal conductivity. To provide.
本発明の一実施形態の窒化ケイ素焼結体の製造方法は、
所定の組成比の窒化ケイ素粉末及び焼結助剤粉末に対して、所定量の炭素粉末を混合して混合粉末を得る混合工程と、
前記混合粉末を焼成させないように、非酸化性雰囲気中で前記混合粉末を１２００℃以上の第１仮焼温度で加熱して第１仮焼粉末を得る第１仮焼工程と、
前記第１仮焼粉末から炭素を除去するように、酸化性雰囲気中で９００℃以下の第２仮焼温度で前記第１仮焼粉末を加熱して第２仮焼粉末を得る第２仮焼工程と、
前記第２仮焼粉末を所定の形状に成形して成形体を得る成形工程と、
非酸化性雰囲気中で前記成形体を焼成して、窒化ケイ素焼結体を得る焼成工程と、を含むことを特徴とする。
A method for manufacturing a silicon nitride sintered body according to an embodiment of the present invention,
With respect to the silicon nitride powder and the sintering aid powder having a predetermined composition ratio, a mixing step of mixing a predetermined amount of carbon powder to obtain a mixed powder,
A first calcination step of heating the mixed powder in a non-oxidizing atmosphere at a first calcination temperature of 1200° C. or higher to obtain a first calcinated powder so as not to bake the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder at a second calcination temperature of 900° C. or lower in an oxidizing atmosphere so as to remove carbon from the first calcination powder. Process,
A molding step of molding the second calcined powder into a predetermined shape to obtain a molded body;
And a firing step of firing the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body.
すなわち、所定の配合比の窒化ケイ素粉末及び焼結助剤粉末とともに炭素粉末を含有する混合粉末を仮焼することによって、炭素が窒化ケイ素や助剤酸化物に含まれる酸素と反応し、結果として、酸素含有量が少ない窒化ケイ素及び助剤酸化物の第２仮焼粉末を得ることができる。このような、酸素含有量が少ない第２仮焼粉末を成形して焼成することにより、焼結体内部で物理的な欠陥（クラック、歪み、空隙等）が生じにくくなることが考えられる。その結果、当該製造方法を経ることによって、相対的に高い機械的強度及び熱伝導率を有する窒化ケイ素焼結体を製造することができる。 That is, by calcining a mixed powder containing a carbon powder together with a silicon nitride powder and a sintering aid powder of a predetermined mixing ratio, carbon reacts with oxygen contained in silicon nitride and the aid oxide, resulting in A second calcined powder of silicon nitride and an auxiliary oxide having a low oxygen content can be obtained. It is conceivable that physical defects (cracks, strains, voids, etc.) are less likely to occur inside the sintered body by molding and firing such a second calcined powder having a low oxygen content. As a result, through the manufacturing method, it is possible to manufacture a silicon nitride sintered body having relatively high mechanical strength and thermal conductivity.
本発明のさらなる実施形態によれば、前記第２仮焼工程と前記成形工程との間に、追加の焼結助剤粉末を前記第２仮焼粉末に添加する添加工程をさらに含んでもよい。 According to a further embodiment of the present invention, between the second calcination step and the molding step, an addition step of adding an additional sintering aid powder to the second calcination powder may be further included.
本発明のさらなる実施形態によれば、前記添加工程の前に、前記追加の焼結助剤粉末の添加量を決定すべく、前記第１仮焼工程及び前記第２仮焼工程における熱処理によって揮発した焼結助剤の量を算定する算定工程を含んでもよい。すなわち、追加の焼結助剤粉末の添加量は、第１仮焼工程及び第２仮焼工程における加熱によって揮発した焼結助剤の量に基づいて定められる。そして、算定結果に基づいて、適量の焼結助剤を添加することによって、窒化ケイ素及び焼結助剤間の組成ずれを抑えることができる。 According to a further embodiment of the present invention, prior to the adding step, volatilization is performed by heat treatment in the first calcination step and the second calcination step to determine an addition amount of the additional sintering aid powder. A calculation step for calculating the amount of the sintering aid prepared may be included. That is, the addition amount of the additional sintering aid powder is determined based on the amount of the sintering aid volatilized by the heating in the first calcination step and the second calcination step. Then, based on the calculation result, by adding an appropriate amount of the sintering aid, it is possible to suppress the composition deviation between the silicon nitride and the sintering aid.
本発明のさらなる実施形態によれば、前記混合工程は、前記第１仮焼工程及び前記第２仮焼工程における加熱によって揮発する焼結助剤の量を算定し、所定の組成比の窒化ケイ素粉末及び焼結助剤粉末に対して、揮発する焼結助剤と略同量の焼結助剤粉末を付加してもよい。すなわち、予め適量の焼結助剤を付加することによって、所望の組成の窒化ケイ素焼結体を得ることができる。 According to a further embodiment of the present invention, in the mixing step, the amount of the sintering aid volatilized by heating in the first calcination step and the second calcination step is calculated, and silicon nitride having a predetermined composition ratio is calculated. You may add a sintering aid powder of substantially the same amount as the volatilizing sintering aid to the powder and the sintering aid powder. That is, a silicon nitride sintered body having a desired composition can be obtained by adding an appropriate amount of a sintering aid in advance.
本発明のさらなる実施形態によれば、前記焼結助剤粉末は、ＭｇＯ、希土類酸化物、又はこれらの組み合わせからなってもよい。より好ましくは、焼結助剤粉末は、少なくともＭｇＯを含み、前記第１仮焼粉末から、ＭｇＳｉＮ２が析出されてもよい。さらに好ましくは、焼結助剤粉末は、ＭｇＯ及びＹ２Ｏ３を含んでいる。また、前記炭素粉末は、前記窒化ケイ素粉末及び前記焼結助剤粉末の合計１００重量部に対して、（炭素換算で）２．５重量部以上であってもよい。さらに、前記第２仮焼粉末の酸素量が０．７重量％以下であってもよい。 According to a further embodiment of the invention, the sintering aid powder may consist of MgO, rare earth oxides, or a combination thereof. More preferably, the sintering aid powder contains at least MgO, and MgSiN 2 may be precipitated from the first calcined powder. More preferably, the sintering aid powder contains MgO and Y 2 O 3 . Further, the carbon powder may be 2.5 parts by weight or more (in terms of carbon) based on 100 parts by weight of the total of the silicon nitride powder and the sintering aid powder. Further, the oxygen content of the second calcined powder may be 0.7% by weight or less.
本発明の別実施形態の窒化ケイ素焼結体の製造方法は、
窒化ケイ素粉末に対して所定量の炭素粉末を混合して混合粉末を得る混合工程と、
前記混合粉末を焼成させないように、非酸化性雰囲気中で前記混合粉末を１２００℃以上の第１仮焼温度で加熱して第１仮焼粉末を得る第１仮焼工程と、
前記第１仮焼粉末から炭素を除去するように、酸化性雰囲気中で９００℃以下の第２仮焼温度で前記第１仮焼粉末を加熱して第２仮焼粉末を得る第２仮焼工程と、
前記第２仮焼粉末を所定の形状に成形して成形体を得る成形工程と、
非酸化性雰囲気中で前記成形体を焼成して、窒化ケイ素焼結体を得る焼成工程と、を含むことを特徴とする。
A method for manufacturing a silicon nitride sintered body according to another embodiment of the present invention,
A mixing step of mixing a predetermined amount of carbon powder with silicon nitride powder to obtain a mixed powder;
A first calcination step of heating the mixed powder in a non-oxidizing atmosphere at a first calcination temperature of 1200° C. or higher to obtain a first calcinated powder so as not to bake the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder at a second calcination temperature of 900° C. or lower in an oxidizing atmosphere so as to remove carbon from the first calcination powder. Process,
A molding step of molding the second calcined powder into a predetermined shape to obtain a molded body;
And a firing step of firing the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body.
すなわち、所定の配合比の窒化ケイ素粉末及び焼結助剤粉末とともに炭素粉末を含有する混合粉末を仮焼することによって、炭素が窒化ケイ素や助剤酸化物に含まれる酸素と反応し、結果として、酸素含有量が少ない窒化ケイ素及び助剤酸化物の第２仮焼粉末を得ることができる。このような、酸素含有量が少ない第２仮焼粉末を成形して焼成することにより、焼結体内部で物理的な欠陥（クラック、歪み、空隙等）が生じにくくなることが考えられる。その結果、当該製造方法を経ることによって、相対的に高い機械的強度及び熱伝導率を有する窒化ケイ素焼結体を製造することができる。 That is, by calcining a mixed powder containing a carbon powder together with a silicon nitride powder and a sintering aid powder of a predetermined mixing ratio, carbon reacts with oxygen contained in silicon nitride and the aid oxide, resulting in A second calcined powder of silicon nitride and an auxiliary oxide having a low oxygen content can be obtained. It is conceivable that physical defects (cracks, strains, voids, etc.) are less likely to occur inside the sintered body by molding and firing such a second calcined powder having a low oxygen content. As a result, through the manufacturing method, it is possible to manufacture a silicon nitride sintered body having relatively high mechanical strength and thermal conductivity.
本発明のさらなる実施形態によれば、前記第２仮焼工程と前記成形工程との間で、前記第２仮焼粉末に対して所定量の焼結助剤粉末を添加する添加工程をさらに含んでもよい。 According to a further embodiment of the present invention, the method further comprises an addition step of adding a predetermined amount of sintering aid powder to the second calcination powder between the second calcination step and the molding step. But it's okay.
本発明のさらなる実施形態によれば、前記炭素粉末は、前記窒化ケイ素粉末１００重量部に対して、（炭素換算で）２．５重量部以上であってもよい。また、前記第２仮焼粉末の酸素量が０．７重量％以下であってもよい。さらに、第１仮焼温度は、１３００℃〜１４５０℃であることが好ましい。 According to a further embodiment of the present invention, the carbon powder may be 2.5 parts by weight or more (in terms of carbon) based on 100 parts by weight of the silicon nitride powder. The oxygen content of the second calcined powder may be 0.7% by weight or less. Further, the first calcination temperature is preferably 1300°C to 1450°C.
本発明の窒化ケイ素焼結体の製造方法によって、窒化ケイ素焼結体の機械的強度及び熱伝導率を向上させることができる。 By the method for producing a silicon nitride sintered body of the present invention, the mechanical strength and thermal conductivity of the silicon nitride sintered body can be improved.
本発明の窒化ケイ素焼結体の製造方法について、以下の実施形態に基づいて具体的に説明する。 The method for producing a silicon nitride sintered body of the present invention will be specifically described based on the following embodiments.
［第１実施形態］
本発明の第１実施形態に係る窒化ケイ素焼結体の製造方法は、図１に示すように、所定の配合比の窒化ケイ素（Ｓｉ３Ｎ４）粉末及び焼結助剤粉末（又は窒化ケイ素粉末単体）に対して、所定量の炭素粉末を混合して混合粉末を得る混合工程と、混合粉末を焼成又は溶解させないように、非酸化性雰囲気中で混合粉末を１２００℃以上の第１仮焼温度で加熱して第１仮焼粉末を得る第１仮焼工程と、第１仮焼粉末から炭素を除去するとともに第１仮焼粉末を焼成又は溶解させないように、酸化性雰囲気中で９００℃以下の第２仮焼温度で第１仮焼粉末を加熱して第２仮焼粉末を得る第２仮焼工程と、第２仮焼粉末を所定の形状に成形して成形体を得る成形工程と、非酸化性雰囲気中で成形体を（高圧下で）焼成して、窒化ケイ素焼結体を得る焼成工程と、を含む。以下、各工程について詳細に説明する。
[First Embodiment]
The method for manufacturing a silicon nitride sintered body according to the first embodiment of the present invention is, as shown in FIG. 1, a silicon nitride (Si 3 N 4 ) powder and a sintering aid powder (or silicon nitride) having a predetermined mixing ratio. (A single powder), a mixing step of mixing a predetermined amount of carbon powder to obtain a mixed powder, and a first tentative temperature of the mixed powder of 1200° C. or higher in a non-oxidizing atmosphere so as not to burn or dissolve the mixed powder. A first calcination step of heating at a calcination temperature to obtain a first calcination powder, and 900 in an oxidizing atmosphere so as to remove carbon from the first calcination powder and not to burn or melt the first calcination powder. A second calcination step of heating the first calcination powder at a second calcination temperature of ℃ or less to obtain a second calcination powder, and molding to obtain a compact by molding the second calcination powder into a predetermined shape And a firing step of firing the molded body (under high pressure) in a non-oxidizing atmosphere to obtain a silicon nitride sintered body. Hereinafter, each step will be described in detail.
（１）混合工程
混合工程では、窒化ケイ素（Ｓｉ３Ｎ４）粉末、焼結助剤粉末及び炭素粉末を混合して、混合粉末を得る。なお、焼結助剤粉末を省略して、窒化ケイ素粉末及び炭素粉末のみを混合して混合粉末を得てもよい。混合工程において、原料粉末である窒化ケイ素粉末及び炭素粉末を容器に適量混ぜ入れて、羽根のついた撹拌機で均一に撹拌させる。次いで、撹拌した原料粉末を振動ミルに移して、焼結助剤を加えて混合することにより、混合粉末を得られる。この段階では、溶剤等を入れることのない乾式混合が選択される。
(1) Mixing Step In the mixing step, the silicon nitride (Si 3 N 4 ) powder, the sintering aid powder and the carbon powder are mixed to obtain a mixed powder. Note that the sintering aid powder may be omitted and only the silicon nitride powder and the carbon powder may be mixed to obtain a mixed powder. In the mixing step, raw material powders of silicon nitride powder and carbon powder are mixed in an appropriate amount and uniformly stirred by a stirrer with a blade. Next, the agitated raw material powder is transferred to a vibration mill, and a sintering aid is added and mixed to obtain a mixed powder. At this stage, dry mixing without solvent is selected.
窒化ケイ素粉末は、直接窒化法やイミド熱分解法等によって製造された高純度であり、且つ、酸素含有量が少ない窒化ケイ素粉末であることが好ましい。 The silicon nitride powder is preferably a high-purity silicon nitride powder produced by a direct nitriding method, an imide thermal decomposition method, or the like and having a low oxygen content.
焼結助剤粉末は、酸化ストロンチウム（ＳｒＯ）、酸化バリウム（ＢａＯ）、酸化マグネシウム（ＭｇＯ）、希土類元素（Ｙ，Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ，Ｓｍ，Ｇｄ，Ｄｙ，Ｈｏ，Ｅｒ，Ｙｂ）の酸化物又はこれらの組み合わせ等から選択され得る。好ましくは、焼結助剤粉末は、酸化マグネシウムＭｇＯ、酸化イットリウム（Ｙ２Ｏ３）又はこれらの組み合わせから選択される。 The sintering aid powder is strontium oxide (SrO), barium oxide (BaO), magnesium oxide (MgO), rare earth elements (Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb). Oxide or a combination thereof. Preferably, the sintering aid powder is selected from magnesium oxide MgO, yttrium oxide (Y 2 O 3 ) or combinations thereof.
炭素粉末として、ファーネスブラックやアセチレンブラックのような炭素が主体となる微粒子を使用することができる。特に、混合物への不純物混入が少ないことから、アセチレンブラックを使用することが好ましい。炭素粉末の配合量は、窒化ケイ素粉末及び焼結助剤粉末の合計を１００重量部とすると、炭素換算で２．５重量部以上であることが好ましい。炭素粉末の配合量が２．５重量部未満であると、後述する第１仮焼工程において、酸素量の低減が効果的に行われないからである。また、炭素粉末の配合量は、２０重量部以下であることが好ましい。特に、炭素粉末の配合量が２０重量部を超えると、第２仮焼工程（脱炭処理）において、炭素粉末を除去することが困難となり（又は、長時間の熱処理を要するため工程上望ましくない）、且つ、特性に影響する量の炭素粉末が残留する可能性が高くなるからである。 As the carbon powder, carbon-based fine particles such as furnace black and acetylene black can be used. In particular, it is preferable to use acetylene black, because impurities are less mixed in the mixture. The blending amount of the carbon powder is preferably 2.5 parts by weight or more in terms of carbon when the total amount of the silicon nitride powder and the sintering aid powder is 100 parts by weight. This is because if the blending amount of the carbon powder is less than 2.5 parts by weight, the oxygen amount cannot be effectively reduced in the first calcination step described later. Further, the blending amount of the carbon powder is preferably 20 parts by weight or less. In particular, if the blending amount of carbon powder exceeds 20 parts by weight, it becomes difficult to remove the carbon powder in the second calcination step (decarburization treatment) (or heat treatment for a long time is required, which is not desirable in the process. ), and there is a high possibility that an amount of carbon powder that affects the characteristics will remain.
なお、混合工程において、次の仮焼工程で揮発する焼結助剤の量を予め算定（予測）し、所定の配合比の窒化ケイ素粉末及び焼結助剤粉末に対して、揮発する焼結助剤と略同量の焼結助剤粉末を付加してもよい。つまり、図１に示すように、本製造方法は、混合工程の前に、揮発量を見越した算定工程を任意に含んでもよい。このような算定（予測）は、過去の実験データに基づいて可能である。換言すると、過去の分析結果等を用いて、所望の組成比に対して、焼結助剤の量を増加させて配合することにより、揮発による組成ずれを抑えることができる。 In addition, in the mixing step, the amount of the sintering aid volatilized in the next calcination step is calculated (predicted) in advance, and the volatilization sintering is performed with respect to the silicon nitride powder and the sintering aid powder having a predetermined mixing ratio. You may add a sintering aid powder of about the same amount as an aid. That is, as shown in FIG. 1, the present manufacturing method may optionally include a calculation step in consideration of the volatilization amount before the mixing step. Such calculation (prediction) is possible based on past experimental data. In other words, by using the past analysis results and the like, the composition shift due to volatilization can be suppressed by increasing the amount of the sintering additive and mixing it with the desired composition ratio.
（２）第１仮焼工程
第１仮焼工程では、混合工程で得られた混合粉末を仮焼して、第１仮焼粉末を得る。まず、工程（１）で準備した混合粉末をカーボン製のさや（容器）に対してさや詰めを行う。使用するさやは熱処理時の温度で変形することなく、また、炭素粉末によって還元されないような材質を使用することができる。熱伝導率、熱膨張率、混合物へのコンタミネーションなどを考慮すると、使用するさやの材質はカーボン製が望ましい。
(2) First Calcination Step In the first calcination step, the mixed powder obtained in the mixing step is calcinated to obtain a first calcination powder. First, the mixed powder prepared in the step (1) is pod packed in a carbon pod (container). As the sheath to be used, a material which does not deform at the temperature during heat treatment and which is not reduced by the carbon powder can be used. Considering the thermal conductivity, thermal expansion coefficient, contamination to the mixture, etc., the sheath material used is preferably made of carbon.
混合物をさや詰めした後、発熱体としてカーボンを使用した電気炉内で、例えば窒素ガスを含む非酸化性（不活性）雰囲気下において第１仮焼温度で加熱処理を行う。熱処理時間（第１仮焼時間）は、１２時間程度が好ましいが、第１仮焼温度等に応じて適宜定められる。第１仮焼温度は、１２００℃以上であり、粉末の酸素量や結晶相によって適宜変更することができる。該第１仮焼温度が１２００℃よりも低いと、炭素粉末と原料粉末内の酸素との反応が効果的に進行せず、混合粉末の酸素量の低下が小さくなる。また、第１仮焼温度の上限は、混合粉末が焼成、溶解又は変質されないように定められる。つまり、粉末の形態が維持されるように加熱処理がなされる。特に、第１仮焼温度は、限定されないが、１３００〜１４５０℃であることが好ましい。すなわち、後述するとおり、第１仮焼温度が１３００℃以上であると、仮焼粉末の酸素含有量の低減が明確に確認できる。他方、第１仮焼温度が１４５０℃よりも高くなると（例えば、１４９０℃）、針状の形状をしているβ‐Ｓｉ３Ｎ４の割合が上昇して成形性が悪くなり、且つ、粉体中に粗大粒子が生成され、成形体の密度が低くなることが知見として得られている（Ｘ線回折測定による）。 After the mixture is stuffed, heat treatment is performed at a first calcination temperature in an electric furnace using carbon as a heating element in a non-oxidizing (inert) atmosphere containing nitrogen gas, for example. The heat treatment time (first calcination time) is preferably about 12 hours, but is appropriately determined according to the first calcination temperature and the like. The first calcination temperature is 1200° C. or higher and can be appropriately changed depending on the amount of oxygen in the powder and the crystal phase. When the first calcination temperature is lower than 1200° C., the reaction between the carbon powder and the oxygen in the raw material powder does not proceed effectively, and the decrease in the amount of oxygen in the mixed powder becomes small. Further, the upper limit of the first calcination temperature is set so that the mixed powder is not fired, melted, or altered. That is, the heat treatment is performed so that the powder form is maintained. In particular, the first calcination temperature is not limited but is preferably 1300 to 1450°C. That is, as will be described later, when the first calcination temperature is 1300° C. or higher, the reduction of the oxygen content of the calcination powder can be clearly confirmed. On the other hand, when the first calcination temperature is higher than 1450° C. (for example, 1490° C.), the proportion of β-Si 3 N 4 having a needle-like shape is increased to deteriorate the formability, and It is known as knowledge that coarse particles are generated in the body and the density of the molded body becomes low (by X-ray diffraction measurement).
（３）第２仮焼工程
第２仮焼工程では、第１仮焼工程で生成された炭素元素を含む第１仮焼粉末を、例えば酸素ガスや空気等を含む酸化性雰囲気下で第２仮焼温度で加熱することによって残留炭素を除去して、第２仮焼粉末を得る。換言すれば、この第２仮焼工程の目的は、第１仮焼工程で消費しなかった残留炭素を脱炭処理することにある。第２仮焼温度は、第１仮焼粉末が焼成されず、且つ、仮焼後の窒化ケイ素粉末が再酸化されないように９００℃以下に定められる。そして、粉末の形態が維持されるように加熱処理がなされる。第２仮焼温度の下限は、残留炭素の除去を可能とすべく、５００℃以上であることが好ましい。また、第２仮焼温度の下限は、炭素の酸化反応を促進し、熱処理時間を短縮すべく、６００℃以上であることがより好ましい。
(3) Second Calcination Step In the second calcination step, the first calcination powder containing the carbon element produced in the first calcination step is subjected to the second calcination step in an oxidizing atmosphere containing oxygen gas, air, or the like. Residual carbon is removed by heating at the calcination temperature to obtain a second calcination powder. In other words, the purpose of this second calcination step is to decarburize the residual carbon not consumed in the first calcination step. The second calcination temperature is set to 900° C. or lower so that the first calcination powder is not fired and the silicon nitride powder after calcination is not reoxidized. Then, heat treatment is performed so that the powder form is maintained. The lower limit of the second calcination temperature is preferably 500° C. or higher so that residual carbon can be removed. Further, the lower limit of the second calcination temperature is more preferably 600° C. or higher in order to promote the oxidation reaction of carbon and shorten the heat treatment time.
第２仮焼工程は、第１仮焼粉末から炭素が有意に脱炭されるまで行われる。すなわち、熱処理時間（第２仮焼時間）や酸素ガス濃度の条件は、脱炭後粉末の炭素量を測定することで適宜変更され得る。なお、脱炭後の炭素量は、炭素粉末混合前と同等（すなわち、略０）であれば最もよいが、第２仮焼粉末全体の０．１５重量％以下であれば焼結体の特性に影響を及ぼさないことが分かっている。それ故、脱炭後の炭素量が０．１５重量％以下となる条件で、第２仮焼工程が行われることが好ましい。 The second calcination step is performed until carbon is significantly decarburized from the first calcination powder. That is, the conditions of the heat treatment time (second calcination time) and the oxygen gas concentration can be appropriately changed by measuring the carbon content of the decarburized powder. The amount of carbon after decarburization is best if it is equal to that before mixing with the carbon powder (that is, approximately 0), but if it is 0.15% by weight or less of the entire second calcination powder, the characteristics of the sintered body Is known to have no effect on. Therefore, the second calcination step is preferably performed under the condition that the carbon content after decarburization is 0.15% by weight or less.
後述する実施例（表１参照）に示したとおり、第２仮焼工程を経ることで得られた第２仮焼粉末は、仮焼前の混合粉末と比べて、酸素含有量の低下傾向がみられる。すなわち、第１仮焼工程において、炭素が混合粉末内の酸素と酸化反応して、炭酸ガス等を生成することによって、窒化ケイ素粉末及び／又は焼結助剤粉末に含まれる酸素が消費されることが考察される。そして、第２仮焼工程において、脱炭処理がなされて残留炭素が除去されることで、結果として、酸素量が低減された窒化ケイ素焼結体前駆物質として焼成前の原料粉末を得ることができる。なお、第２仮焼粉末は、例示的に図３に示されるＸ線回折パターンを有する。 As shown in Examples (see Table 1) described later, the second calcination powder obtained by passing through the second calcination step has a lower tendency of oxygen content than the mixed powder before calcination. Seen. That is, in the first calcination step, carbon is oxidized with oxygen in the mixed powder to generate carbon dioxide gas and the like, whereby oxygen contained in the silicon nitride powder and/or the sintering aid powder is consumed. It is considered. Then, in the second calcination step, decarburization treatment is performed to remove residual carbon, and as a result, a raw material powder before firing can be obtained as a silicon nitride sintered body precursor with a reduced amount of oxygen. it can. The second calcined powder has an X-ray diffraction pattern exemplarily shown in FIG.
（４）成形工程
第２仮焼工程で得られた第２仮焼粉末を使用して、通常のセラミックスの成形方法である金型プレス法やシート成形法により成形体を得る。まず、第２仮焼粉末をバインダー、溶剤等とともにボールミルに投入し、スラリー化する。成形に用いるスラリーの調整方法としては、生産性や混合時の酸素量増加を抑制するために、有機溶媒を用いた湿式混合が望ましい。具体的な一例として、第２仮焼粉末に分散剤、トルエン、エタノールを混合した有機溶媒とを添加し、通常行われる混合粉砕方法によって調整される。そして、ボールミル、ビーズミル、振動ミルなどの方法によって、仮焼粉末の均一混合や粒度調整を行う。混合粉砕方法に用いるミルやメディアの材質としては、ウレタンやナイロンなどの樹脂製や、窒化ケイ素や酸化ジルコニウムなどのセラミック製を使用することができるが、スラリーへの不純物混入を防ぐため、材質としては樹脂や窒化ケイ素を使用することが好ましい。なお、分散剤や有機溶媒の添加量は、その種類や原料の比表面積によって調整する必要がある。窒化ケイ素を原料とする場合は、分散剤としてアミン系やリン系の界面活性剤が好適に用いられる。分散剤の添加量は粉体の比表面積によって適宜変更する必要があるが、０．２〜３重量％の範囲であれば良好な分散性が得られる。
(4) Molding step Using the second calcined powder obtained in the second calcining step, a molded body is obtained by a die pressing method or a sheet molding method which are ordinary ceramics molding methods. First, the second calcined powder is put into a ball mill together with a binder, a solvent and the like to form a slurry. As a method for adjusting the slurry used for molding, wet mixing using an organic solvent is desirable in order to suppress productivity and an increase in the amount of oxygen during mixing. As a specific example, the second calcination powder is added with a dispersant, an organic solvent in which toluene and ethanol are mixed, and the mixture is adjusted by a commonly used mixing and pulverizing method. Then, the calcined powder is uniformly mixed and the particle size is adjusted by a method such as a ball mill, a bead mill and a vibration mill. As the material of the mill or media used in the mixing and pulverizing method, resins such as urethane and nylon, and ceramics such as silicon nitride and zirconium oxide can be used. It is preferable to use resin or silicon nitride. The addition amount of the dispersant or the organic solvent needs to be adjusted depending on the type and the specific surface area of the raw material. When silicon nitride is used as a raw material, an amine-based or phosphorus-based surfactant is preferably used as the dispersant. The amount of the dispersant added needs to be appropriately changed depending on the specific surface area of the powder, but good dispersibility can be obtained in the range of 0.2 to 3% by weight.
調整後のスラリーは、真空中で脱泡及び粘度調整され、ドクターブレード法によって所定の厚さのグリーンシートが得られる。グリーンシートの厚さは、必要な焼結体の厚さにより適宜変更することが可能であるが、通常０．１〜１．３ｍｍ程度の範囲である。成形後のグリーンシートが金型プレスや切断機により所望の形状に加工されて、成形体が得られる。 The adjusted slurry is defoamed and the viscosity is adjusted in a vacuum, and a green sheet having a predetermined thickness is obtained by the doctor blade method. The thickness of the green sheet can be appropriately changed depending on the required thickness of the sintered body, but is usually in the range of about 0.1 to 1.3 mm. The green sheet after molding is processed into a desired shape by a die press or a cutting machine to obtain a molded body.
（５）焼成工程
成形工程で得られた成形体を高温で所定時間、焼成することにより、本製造方法の最終目的物である窒化ケイ素焼結体を得る。焼成処理は、焼成炉において、非酸化性（窒素）雰囲気中で、約１７５０〜２０００℃の温度範囲で行われる。また、Ｓｉ３Ｎ４や焼結助剤（例えば、ＭｇＯ）の揮発を防ぐため、５気圧以上の圧力下で加圧焼成を行うことが好ましい。そして、本製造方法において、成形工程の前に脱酸素を目的とした仮焼工程を行っているため、焼成時に酸素が抜けることによる構造的欠陥（格子欠陥、歪み等）が生じにくい。
(5) Firing step By firing the molded body obtained in the molding step at a high temperature for a predetermined time, a silicon nitride sintered body which is the final object of the present manufacturing method is obtained. The firing treatment is performed in a firing furnace in a non-oxidizing (nitrogen) atmosphere in a temperature range of about 1750 to 2000°C. Moreover, in order to prevent volatilization of Si 3 N 4 and a sintering aid (for example, MgO), it is preferable to perform pressure firing under a pressure of 5 atm or more. Further, in the present manufacturing method, since the calcination step for the purpose of deoxidation is performed before the molding step, structural defects (lattice defect, strain, etc.) due to the escape of oxygen during firing are less likely to occur.
上記説明した混合工程から焼成工程を経ることによって、本製造方法（特に第１及び第２仮焼工程）を経ないで製造されたものと比べて、高い機械的強度及び熱伝導率を有する窒化ケイ素焼結体を得ることができる。 Nitriding, which has higher mechanical strength and higher thermal conductivity than those manufactured without the present manufacturing method (particularly the first and second calcination steps), by passing through the firing step from the mixing step described above A silicon sintered body can be obtained.
［第２実施形態］
本発明の第２実施形態に係る窒化ケイ素焼結体の製造方法は、図２に示すように、所定の配合比の窒化ケイ素粉末及び焼結助剤粉末（又は窒化ケイ素粉末単体）に対して、所定量の炭素粉末を混合して混合粉末を得る混合工程と、混合粉末を焼成又は溶解させないように、非酸化性雰囲気中で混合粉末を１２００℃以上の第１仮焼温度で加熱して第１仮焼粉末を得る第１仮焼工程と、第１仮焼粉末から炭素を除去するとともに第１仮焼粉末を焼成又は溶解させないように、酸化性雰囲気中で９００℃以下の第２仮焼温度で第１仮焼粉末を加熱して第２仮焼粉末を得る第２仮焼工程と、第２仮焼粉末に対して追加の焼結助剤粉末を添加する添加工程と、第２仮焼粉末を所定の形状に成形して成形体を得る成形工程と、非酸化性雰囲気中で成形体を加圧焼成して、窒化ケイ素焼結体を得る焼成工程と、を含む。また、該製造方法は、好ましくは、添加工程の前に、追加の焼結助剤粉末の添加量を決定すべく、第１仮焼工程及び第２仮焼工程における熱処理によって揮発した焼結助剤の量を算定する算定工程を含む。
[Second Embodiment]
As shown in FIG. 2, the method for manufacturing a silicon nitride sintered body according to the second embodiment of the present invention is applied to a silicon nitride powder and a sintering aid powder (or silicon nitride powder alone) having a predetermined mixing ratio. , A mixing step of mixing a predetermined amount of carbon powder to obtain a mixed powder, and heating the mixed powder in a non-oxidizing atmosphere at a first calcination temperature of 1200° C. or higher so as not to burn or melt the mixed powder. A first calcination step of obtaining a first calcination powder and a second calcination at 900° C. or lower in an oxidizing atmosphere so as to remove carbon from the first calcination powder and not to burn or melt the first calcination powder. A second calcination step of heating the first calcination powder at a calcination temperature to obtain a second calcination powder, an addition step of adding an additional sintering aid powder to the second calcination powder, and a second It includes a molding step of molding the calcined powder into a predetermined shape to obtain a molded body, and a sintering step of pressure-calcining the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body. Further, the manufacturing method is preferably such that, before the adding step, the sintering aid volatilized by the heat treatments in the first calcination step and the second calcination step is determined in order to determine the addition amount of the additional sintering aid powder. Includes a calculation process to calculate the amount of drug.
すなわち、第２実施形態の製造方法は、第１実施形態と比べて、第２仮焼工程と成形工程との間に、第２仮焼粉末に対して追加の焼結助剤粉末を添加する添加工程、及び、選択的に該添加量を算定する算定工程を追加したものであり、他の工程は共通している。以下、添加工程及び算定工程について説明する。 That is, in the manufacturing method of the second embodiment, as compared with the first embodiment, an additional sintering aid powder is added to the second calcination powder between the second calcination step and the forming step. The addition process and the calculation process for selectively calculating the addition amount are added, and the other processes are common. Hereinafter, the addition process and the calculation process will be described.
（６）添加工程
添加工程では、主に窒化ケイ素及び焼結助剤（又は窒化ケイ素単体）を主成分とする第２仮焼粉末に対して、適量の焼結助剤を添加して、焼成後の窒化ケイ素焼結体の組成を調整することができる。例えば、混合工程では、窒化ケイ素粉末及び炭素粉末のみを混合して混合粉末を作製し、焼成前の段階で所望の窒化ケイ素焼結体の組成に合わせるように、適量の焼結助剤粉末が添加されてもよい。また、加熱で窒化ケイ素や焼結助剤の成分が揮発することによる組成ずれを抑えるべく、以下の算定工程に基づいて、焼結助剤を添加してもよい。
(6) Addition Step In the addition step, an appropriate amount of a sintering aid is added to the second calcination powder mainly containing silicon nitride and a sintering aid (or silicon nitride simple substance) as a main component, followed by firing. The composition of the subsequent silicon nitride sintered body can be adjusted. For example, in the mixing step, only a silicon nitride powder and a carbon powder are mixed to prepare a mixed powder, and an appropriate amount of sintering aid powder is added so as to match the desired composition of the silicon nitride sintered body before firing. It may be added. Further, in order to suppress the composition deviation due to the volatilization of the components of silicon nitride and the sintering aid by heating, the sintering aid may be added based on the following calculation process.
（７）算定工程
第１及び第２仮焼工程において、窒化ケイ素粉末、焼結助剤粉末及び炭素粉末の混合粉末に第１及び第２仮焼工程を施すことで、窒化ケイ素や焼結助剤成分の成分が揮発し、組成ずれを起こすことが考えられる。算定工程では、仮焼前後の粉末を分析（例えば、蛍光Ｘ線分析）し、原料の低減量（揮発量）を測定及び算定する。そして、算定工程で得られた結果に基づいて、添加工程において、揮発した焼結助剤成分を補充するように、適量の追加の焼結助剤粉末を第２仮焼粉末に添加することにより、組成ずれを抑えることができる。
(7) Calculation Step In the first and second calcination steps, the mixed powder of the silicon nitride powder, the sintering aid powder and the carbon powder is subjected to the first and second calcination steps to obtain silicon nitride and a sintering aid. It is conceivable that the components of the agent component volatilize and cause a composition shift. In the calculation step, the powder before and after calcination is analyzed (for example, fluorescent X-ray analysis) to measure and calculate the reduction amount (volatilization amount) of the raw material. Then, based on the result obtained in the calculation step, by adding an appropriate amount of additional sintering additive powder to the second calcination powder in the adding step so as to supplement the volatilized sintering additive component. Thus, compositional deviation can be suppressed.
以下、本発明を実施例及び比較例に基づいて、さらに具体的に説明するが、本発明は下記の実施例によって限定解釈されるものではない。 Hereinafter, the present invention will be described more specifically based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.
［実施例１〜５］
実施例１〜５に係る窒化ケイ素焼結体は以下の条件及び手順によって生成された。実施例１〜５は、窒化ケイ素粉末、焼結助剤粉末及び炭素粉末の配合組成、仮焼温度及び／又は脱炭温度が互いに相違する。また、実施例１〜５において、図２に示すように、混合工程で、窒化ケイ素粉末と炭素粉末の混合粉末が作製され、添加工程で焼結助剤粉末が添加される。具体的には以下のとおりである。
[Examples 1 to 5]
The silicon nitride sintered bodies according to Examples 1 to 5 were produced under the following conditions and procedures. Examples 1 to 5 differ from each other in the compounding composition of the silicon nitride powder, the sintering aid powder and the carbon powder, the calcination temperature and/or the decarburization temperature. Further, in Examples 1 to 5, as shown in FIG. 2, a mixed powder of silicon nitride powder and carbon powder is produced in the mixing step, and a sintering aid powder is added in the adding step. Specifically, it is as follows.
（１）窒化ケイ素粉末に対して炭素粉末（アセチレンブラック）を所定量添加し、振動ミルで窒化ケイ素粉末と炭素粉末の混合粉末を得た。窒化ケイ素粉末は、直接窒化法によって製造された高純度の窒化ケイ素粉末が用いられた。窒化ケイ素粉末は、平均粒子径（Ｄ５０）が約１．０μｍであり、酸素含有量が約０．８重量％である。 (1) A predetermined amount of carbon powder (acetylene black) was added to silicon nitride powder, and a mixed powder of silicon nitride powder and carbon powder was obtained with a vibration mill. As the silicon nitride powder, a high-purity silicon nitride powder produced by a direct nitriding method was used. The silicon nitride powder has an average particle diameter (D50) of about 1.0 μm and an oxygen content of about 0.8% by weight.
（２）混合粉末をカーボン製のさやに詰め、混合粉末を１気圧の窒素雰囲気の下、第１仮焼温度で１２時間、第１仮焼処理を行って第１仮焼粉末を得た。なお、第１仮焼温度を１６００℃以上とした場合、第１仮焼粉末において、ＳｉＣのＸ線回折ピークが発見されたため、所望の窒化ケイ素焼結体が得られなかった。 (2) The mixed powder was packed in a carbon sheath, and the mixed powder was subjected to a first calcination treatment at a first calcination temperature for 12 hours under a nitrogen atmosphere of 1 atm to obtain a first calcinated powder. When the first calcination temperature was set to 1600° C. or higher, an X-ray diffraction peak of SiC was found in the first calcination powder, so that the desired silicon nitride sintered body could not be obtained.
（３）第１仮焼粉末をドライエアー中、第２仮焼温度で１２時間、第２仮焼処理を行って、第２仮焼粉末を得た。この仮焼粉末の炭素量が０．９重量％以下になるまで熱処理を行った。これら仮焼処理は、連続炉にて行われた。 (3) The second calcination powder was obtained by subjecting the first calcination powder to the second calcination treatment in dry air at the second calcination temperature for 12 hours. The heat treatment was performed until the carbon content of the calcined powder became 0.9% by weight or less. These calcination processes were performed in a continuous furnace.
（４）次に、各粉末の配合組成比に合わせて、第２仮焼粉末に対して焼結助剤粉末であるＭｇＯ及びＹ２Ｏ３を適量添加し、これらを混合した。 (4) Next, in accordance with the composition ratio of each powder, suitable amounts of sintering aid powders MgO and Y 2 O 3 were added to the second calcined powder, and these were mixed.
（５）次いで、以下の条件で、成形工程が行われた。１００重量部の第２仮焼粉末及び焼結助剤粉末の混合体に対して、界面活性型分散剤を０．３重量部と、トルエンとエタノールの混合溶媒を５０重量部添加して、窒化ケイ素玉石を用いて粉砕混合を行った。その後、バインダーとしてポリビニルブチラールを１０重量部と、可塑剤としてアジピン酸ジオクチルを５重量部と、トルエンとエタノールの混合溶媒を２０重量部を加え、バインダーが完全に溶解・混合されるまで、ボールミルによって攪拌混合した後、スラリーを作製した。スラリーを真空中で脱泡、粘度調整を行い、ドクターブレード法によってグリーンシートを得た。得られたグリーンシートを金型プレス加工により所定の形状に型抜きし、５００℃でバインダーなどの有機成分を除去した。 (5) Next, the molding step was performed under the following conditions. To 100 parts by weight of the mixture of the second calcination powder and the sintering aid powder, 0.3 parts by weight of the surface active dispersant and 50 parts by weight of a mixed solvent of toluene and ethanol were added, and nitriding was performed. Grinding and mixing was performed using silicon boulders. Then, 10 parts by weight of polyvinyl butyral as a binder, 5 parts by weight of dioctyl adipate as a plasticizer, and 20 parts by weight of a mixed solvent of toluene and ethanol were added, and a ball mill was used until the binder was completely dissolved and mixed. After mixing with stirring, a slurry was prepared. The slurry was defoamed in a vacuum, the viscosity was adjusted, and a green sheet was obtained by the doctor blade method. The obtained green sheet was die-pressed into a predetermined shape, and organic components such as a binder were removed at 500°C.
（６）そして、焼成工程の条件を、９気圧の窒素雰囲気中、１８６０℃で４時間として、成形体の焼成を行って、板厚０．３５ｍｍの窒化ケイ素焼結基板を得た。 (6) Then, the firing process was performed under the conditions of a nitrogen atmosphere of 9 atm at 1860° C. for 4 hours to perform firing of the molded body to obtain a silicon nitride sintered substrate having a thickness of 0.35 mm.
比較例１，２に係る窒化ケイ素焼結体は以下の条件及び手順によって生成された。なお、比較例１，２は、焼結助剤の配合組成が互いに異なる。 The silicon nitride sintered bodies according to Comparative Examples 1 and 2 were produced under the following conditions and procedures. Comparative Examples 1 and 2 differ from each other in the mixing composition of the sintering aid.
（１）窒化ケイ素粉末に対して適量の焼結助剤粉末（ＭｇＯ及びＹ２Ｏ３）を添加し、これらを混合させた。 (1) An appropriate amount of sintering aid powder (MgO and Y 2 O 3 ) was added to the silicon nitride powder, and these were mixed.
（２）次いで、以下の条件で、成形工程が行われた。１００重量部の窒化ケイ素粉末及び焼結助剤粉末の混合体に対して、界面活性型分散剤を０．３重量部と、トルエンとエタノールの混合溶媒を５０重量部添加して、窒化ケイ素玉石を用いて粉砕混合を行った。その後、バインダーとしてポリビニルブチラールを１０重量％と、可塑剤としてアジピン酸ジオクチルを５重量部と、トルエンとエタノールの混合溶媒を２０重量部を加え、バインダーが完全に溶解・混合されるまで、ボールミルによって攪拌混合した後、スラリーを作製した。スラリーを真空中で脱泡、粘度調整を行い、ドクターブレード法によってグリーンシートを得た。得られたグリーンシートを金型プレス加工により所定の形状に型抜きし、５００℃でバインダーなどの有機成分を除去した。 (2) Next, the molding process was performed under the following conditions. To 100 parts by weight of a mixture of silicon nitride powder and sintering aid powder, 0.3 parts by weight of a surface active dispersant and 50 parts by weight of a mixed solvent of toluene and ethanol were added to obtain a silicon nitride cobblestone. Was used for pulverization and mixing. Then, 10% by weight of polyvinyl butyral as a binder, 5 parts by weight of dioctyl adipate as a plasticizer, and 20 parts by weight of a mixed solvent of toluene and ethanol were added, and a ball mill was used until the binder was completely dissolved and mixed. After mixing with stirring, a slurry was prepared. The slurry was defoamed in a vacuum, the viscosity was adjusted, and a green sheet was obtained by the doctor blade method. The obtained green sheet was die-pressed into a predetermined shape, and organic components such as a binder were removed at 500°C.
（３）そして、焼成工程の条件を、９気圧の窒素雰囲気中、１８６０℃で４時間として、成形体の焼成を行って、板厚０．３５ｍｍの窒化ケイ素焼結基板を得た。 (3) Then, the firing step was performed in a nitrogen atmosphere of 9 atm at 1860° C. for 4 hours to perform firing of the molded body to obtain a silicon nitride sintered substrate having a thickness of 0.35 mm.
実施例１〜５に係る第２仮焼粉末の特性として、仮焼粉末の酸素含有量（重量％）、平均粒径Ｄ５０（μｍ）、比表面積（ｍ２／ｇ）が測定された。また、実施例１〜５及び比較例１，２に係る窒化ケイ素焼結体の特性として、相対密度（％）、熱伝導率（Ｗ／ｍＫ）、機械的強度（ＭＰａ）が測定された。各種測定は、以下の条件の下で行われた。 As the characteristics of the second calcined powder according to Examples 1 to 5, the oxygen content (% by weight) of the calcined powder, the average particle diameter D50 (μm), and the specific surface area (m 2 /g) were measured. Further, as the characteristics of the silicon nitride sintered bodies according to Examples 1 to 5 and Comparative Examples 1 and 2, relative density (%), thermal conductivity (W/mK), and mechanical strength (MPa) were measured. Various measurements were performed under the following conditions.
・平均粒径Ｄ５０
株式会社島津製作所のレーザ回折式粒度分布測定装置ＳＡＬＤ‐２０００を使用して測定を行った。分散剤として、ヘキサメタリン酸ナトリウムを使用し、屈折率は２．４とした。
・Average particle size D50
The measurement was performed using a laser diffraction particle size distribution analyzer SALD-2000 manufactured by Shimadzu Corporation. Sodium hexametaphosphate was used as a dispersant, and the refractive index was set to 2.4.
・酸素含有量
株式会社堀場製作所のＥＭＧＡ−９２０を使用して、不活性ガス融解−非分散型赤外線吸収法により測定を行った。
-Oxygen content Using EMGA-920 manufactured by HORIBA, Ltd., measurement was performed by an inert gas melting-non-dispersion infrared absorption method.
・相対密度
窒化ケイ素の密度を３．１８ｇ／ｃｍ３、Ｙ２Ｏ３の密度を５．０ｇ／ｃｍ３、ＭｇＯの密度を３．６ｇ／ｃｍ３として、原料配合比から求めた理論密度に対する焼結体の密度から計算した。焼結体の密度は純水を使用したアルキメデス法により測定した。
· The density of the relative density silicon nitride as 3.18g / cm 3, Y 2 O density of 3 to 5.0 g / cm 3, MgO density 3.6 g / cm 3, and with respect to the theoretical density determined from the raw material mixing ratio It was calculated from the density of the sintered body. The density of the sintered body was measured by the Archimedes method using pure water.
・熱伝導率
アドバンス理工株式会社のＴＣ−７０００を使用して、レーザーフラッシュ法により熱拡散率αの測定を行った。窒化ケイ素の比熱Ｃを０．６８Ｊ／（ｇ・Ｋ）、アルキメデス法によって求めた密度ρを使用して、熱伝導率λは下式に従って計算した。
λ＝α×Ｃ×ρ
-Thermal conductivity The thermal diffusivity α was measured by the laser flash method using TC-7000 manufactured by Advance Riko Co., Ltd. Using the specific heat C of silicon nitride of 0.68 J/(g·K) and the density ρ obtained by the Archimedes method, the thermal conductivity λ was calculated according to the following equation.
λ=α×C×ρ
・機械的強度
機械的強度（曲げ強度）の測定方法には、３点曲げ試験が採用された。評価用の窒化ケイ素焼結体は、６３ｍｍ×２０ｍｍ×０．３２ｍｍｔの試験片を用いた。測定装置は、株式会社島津製作所製の型式ＡＧ−ＩＳであり、その測定条件を測定数２０ｐｃｓ、クロスヘッドスピード０．５ｍｍ／分、支点間距離３０ｍｍとし、その平均値を求めた。
-Mechanical strength A three-point bending test was adopted as the method for measuring mechanical strength (bending strength). As the silicon nitride sintered body for evaluation, a test piece of 63 mm×20 mm×0.32 mmt was used. The measuring device was a model AG-IS manufactured by Shimadzu Corporation, and the measurement conditions were 20 pcs of measurement, a cross head speed of 0.5 mm/min, and a distance between
実施例１〜５及び参考例１，２の条件及び各種測定結果を表１に示した。なお、各粉末の配合組成として、Ｓｉ３Ｎ４粉末、ＭｇＯ粉末及びＹ２Ｏ３粉末の合計１００重量部に対して炭素粉末の重量部が示されている。 Table 1 shows conditions and various measurement results of Examples 1 to 5 and Reference Examples 1 and 2. As the composition of each powder, the weight part of carbon powder is shown to the total 100 weight parts of Si 3 N 4 powder, MgO powder and Y 2 O 3 powder.
表１によれば、実施例１乃至４のいずれにおいても、仮焼工程によって生成された第２仮焼粉末の酸素含有量が０．７重量％以下であり、元の原料粉末の酸素含有量０．８％から有意に低減していることが分かる。他方、実施例１の第１仮焼温度を１２００度とした実施例５では、第２仮焼粉末の酸素含有量が０．８重量％であり、酸素含有量の低減を明確に確認できなかった。そして、焼結体特性に関して、配合組成比が同じである実施例１と比較例１とを比較すると、実施例１の窒化ケイ素焼結体の熱伝導率及び機械的強度は、比較例１よりも大きい。次に、焼結体特性に関して、配合組成比が同じである実施例２，３，４と比較例２とを比較する。実施例２，３，４の窒化ケイ素焼結体の熱伝導率は、比較例２以上であり、機械的強度は、比較例２よりも有意に大きい。そして、実施例２，３を比較すると、仮焼温度を１４００℃から１４５０℃に変更されることで、機械的強度の上昇が見られた。また、実施例３，４を比較すると、炭素の配合量を増加させることにより、機械的強度のさらなる上昇が見られた。さらに、実施例５と比較例１とを比較すると、酸素含有量の低減を確認できなかったものの、実施例５の窒化ケイ素焼結体の熱伝導率及び機械的強度が比較例１から改善したことが見て取れる。つまり、測定誤差等の要因により、酸素量の低減が数値上現れなかったが、１２００℃の第１仮焼温度でも、同様に焼結体特性の改善が見られた。すなわち、表１によれば、本発明の製造工程において、炭素粉末を少なくとも２．５重量部以上添加した上で、炭素混合粉末の仮焼工程を経ることで、窒化ケイ素焼結体の特性が改善されることが分かった。 According to Table 1, in any of Examples 1 to 4, the oxygen content of the second calcined powder generated by the calcining step was 0.7% by weight or less, and the oxygen content of the original raw material powder was It can be seen that it is significantly reduced from 0.8%. On the other hand, in Example 5 in which the first calcination temperature of Example 1 was 1200° C., the oxygen content of the second calcination powder was 0.8% by weight, and reduction of the oxygen content could not be clearly confirmed. It was Regarding the characteristics of the sintered body, comparing Example 1 and Comparative Example 1 having the same composition ratio, the thermal conductivity and mechanical strength of the silicon nitride sintered body of Example 1 are Is also big. Next, regarding the characteristics of the sintered body, Examples 2, 3 and 4 and Comparative Example 2 having the same composition ratio are compared. The thermal conductivity of the silicon nitride sintered bodies of Examples 2, 3 and 4 is equal to or higher than Comparative Example 2, and the mechanical strength is significantly higher than that of Comparative Example 2. When Examples 2 and 3 were compared, it was found that the mechanical strength was increased by changing the calcination temperature from 1400°C to 1450°C. Further, comparing Examples 3 and 4, it was found that the mechanical strength was further increased by increasing the blending amount of carbon. Further, comparing Example 5 with Comparative Example 1, although no reduction in oxygen content could be confirmed, the thermal conductivity and mechanical strength of the silicon nitride sintered body of Example 5 were improved from Comparative Example 1. You can see that. In other words, due to factors such as measurement error, the reduction of the oxygen content did not appear numerically, but even at the first calcination temperature of 1200° C., similar improvement in the characteristics of the sintered body was observed. That is, according to Table 1, in the manufacturing process of the present invention, at least 2.5 parts by weight or more of the carbon powder is added, and the calcination process of the carbon mixed powder is performed to obtain the characteristics of the silicon nitride sintered body. It turned out to be improved.
［実施例６〜１１］
実施例６〜１１に係る窒化ケイ素焼結体は、実施例１〜５と基本的に同様の手順及び条件で生成された。ただし、実施例６〜８では、混合工程においてＳｉ３Ｎ４粉末、ＭｇＯ粉末、Ｙ２Ｏ３粉末及びＣ粉末の混合粉末が作製された。そして、ＭｇＯが仮焼工程で揮発し易いことから、全体の組成ずれを抑えるべく、図２に示すように、第２仮焼粉末に対するＭｇＯの添加工程が行われた。特には、仮焼前後の粉末に対して蛍光Ｘ線分析を行って、それらの解析結果を比較することにより、仮焼で揮発したＭｇＯの量を算出した。そして、揮発した分だけＭｇＯを第２仮焼粉末に補充及び添加することで、原料間の配合比のずれを抑えた。
[Examples 6 to 11]
The silicon nitride sintered bodies according to Examples 6 to 11 were produced by basically the same procedure and conditions as in Examples 1 to 5. However, in Examples 6 to 8, a mixed powder of Si 3 N 4 powder, MgO powder, Y 2 O 3 powder and C powder was produced in the mixing step. Then, since MgO easily volatilizes in the calcination step, an addition step of MgO to the second calcination powder was performed as shown in FIG. 2 in order to suppress the compositional deviation of the whole. In particular, fluorescent X-ray analysis was performed on the powders before and after calcination, and the analysis results were compared to calculate the amount of MgO volatilized during calcination. Then, by replenishing and adding MgO to the second calcined powder in an amount corresponding to the volatilized amount, the deviation of the compounding ratio between the raw materials was suppressed.
他方、実施例９〜１１では、図２に示すように、混合工程において、Ｓｉ３Ｎ４粉末、ＭｇＯ粉末及びＣ粉末の混合粉末が作製され、添加工程において、第２仮焼粉末にＹ２Ｏ３粉末とともに揮発したＭｇＯが添加される。特には、仮焼前後の粉末に対して蛍光Ｘ線分析を行って、それらの解析結果を比較することにより、仮焼で揮発したＭｇＯの量を算出した。そして、揮発した分だけＭｇＯを第２仮焼粉末に補充及び添加することで、原料間の配合比のずれを抑えた。 On the other hand, in Examples 9 to 11, as shown in FIG. 2, a mixed powder of Si 3 N 4 powder, MgO powder and C powder was produced in the mixing step, and Y 2 was added to the second calcined powder in the addition step. Volatile MgO is added together with the O 3 powder. In particular, fluorescent X-ray analysis was performed on the powders before and after calcination, and the analysis results were compared to calculate the amount of MgO volatilized during calcination. Then, by replenishing and adding MgO to the second calcined powder in an amount corresponding to the volatilized amount, the deviation of the compounding ratio between the raw materials was suppressed.
実施例６〜１１に係る第２仮焼粉末の特性として、ＭｇＳｉＮ２の析出量が測定された。また、実施例６〜１１及び比較例２に係る窒化ケイ素焼結体の特性として、実施例１〜５と同様の条件の下、相対密度（％）、熱伝導率（Ｗ／ｍＫ）及び機械的強度（ＭＰａ）が測定された。ＭｇＳｉＮ２の析出量測定は、以下の条件の下で行われた。 As the characteristics of the second calcined powders according to Examples 6 to 11, the amount of MgSiN 2 deposited was measured. Further, as the characteristics of the silicon nitride sintered bodies according to Examples 6 to 11 and Comparative Example 2, under the same conditions as in Examples 1 to 5, relative density (%), thermal conductivity (W/mK), and mechanical properties. The mechanical strength (MPa) was measured. The precipitation amount measurement of MgSiN 2 was performed under the following conditions.
・ＭｇＳｉＮ２の析出量測定
株式会社リガクのＵｌｔｉｍａ ＩＶを使用して、粉末Ｘ線回折法による結晶相の同定を行った。ＭｇＳｉＮ２の結晶相の構成比はＲＩＲ（Ｒｅｆｅｒｅｎｃｅ Ｉｎｔｅｎｓｉｔｙ Ｒａｔｉｏ）法による定量分析を行って算出した。図３は、Ｘ線回折パターンの具体例であり、実施例９で得られた仮焼粉末のＸ線回折パターンである。
-Measurement of MgSiN 2 precipitation amount Ultima IV manufactured by Rigaku Corporation was used to identify a crystal phase by a powder X-ray diffraction method. The composition ratio of the crystal phase of MgSiN 2 was calculated by performing a quantitative analysis by the RIR (Reference Intensity Ratio) method. FIG. 3 is a specific example of the X-ray diffraction pattern, which is the X-ray diffraction pattern of the calcined powder obtained in Example 9.
実施例６〜１１及び参考例２の条件及び各種測定結果を表２に示した。なお、各粉末の配合組成として、Ｓｉ３Ｎ４粉末、ＭｇＯ粉末及びＹ２Ｏ３粉末の合計１００重量部に対して炭素粉末の重量部が示されている。なお、配合組成比は、揮発した原料が添加工程で調整された後の値である。 Table 2 shows conditions and various measurement results of Examples 6 to 11 and Reference Example 2. As the composition of each powder, the weight part of carbon powder is shown to the total 100 weight parts of Si 3 N 4 powder, MgO powder and Y 2 O 3 powder. The blending composition ratio is a value after the volatilized raw material is adjusted in the adding step.
表２によれば、焼結体特性に関して、配合組成比が同じである実施例６乃至１１と比較例２とを比較すると、実施例６乃至１１の窒化ケイ素焼結体の熱伝導率及び機械的強度は、比較例２よりも大きい。特に、実施例６乃至１１の窒化ケイ素焼結体は、熱伝導性において大幅に改善されていることが分かる。すなわち、実施例６乃至１１では、実施例１乃至５と比べて、少なくともＭｇＯ粉末を含む混合粉末が仮焼処理されることによって、焼結助剤中の酸素量が仮焼によって有意に低減されたことが考えられる。 According to Table 2, when the characteristics of the sintered body are compared between Examples 6 to 11 and Comparative Example 2 having the same composition ratio, thermal conductivity and mechanical properties of the silicon nitride sintered bodies of Examples 6 to 11 are compared. Strength is higher than that of Comparative Example 2. In particular, it can be seen that the silicon nitride sintered bodies of Examples 6 to 11 are greatly improved in thermal conductivity. That is, in Examples 6 to 11, as compared with Examples 1 to 5, the mixed powder containing at least the MgO powder was calcined, so that the amount of oxygen in the sintering aid was significantly reduced by calcination. It is possible that
すなわち、本実施形態（実施例１〜１１）の窒化ケイ素焼結体の製造方法は、混合工程において炭素粉末を含有した混合粉末に対して第１及び第２仮焼工程を施すことを特徴とする。したがって、本発明によって、上記製造工程を導入しない同組成の窒化ケイ素焼結体と比べて、相対的な機械的強度及び熱伝導率の改善が実現された。 That is, the method for manufacturing a silicon nitride sintered body of the present embodiment (Examples 1 to 11) is characterized in that the mixed powder containing the carbon powder in the mixing step is subjected to the first and second calcination steps. To do. Therefore, according to the present invention, relative mechanical strength and thermal conductivity are improved as compared with a silicon nitride sintered body of the same composition which does not introduce the above manufacturing process.
なお、上記実施例の製造方法は、一例にすぎず、本発明の技術的思想が他種類の焼結助剤や異なる配合組成による原料粉末からなる窒化ケイ素焼結体の製造についても適用可能であることはいうまでもない。すなわち、上記実施例以外の組成の窒化ケイ素焼結体の製造方法に関しても、本発明による恩恵を受けることが可能であり、本発明の技術範囲内であれば、任意に置換、省略及び／又は追加可能である。 The manufacturing method of the above embodiment is only an example, and the technical idea of the present invention can be applied to the manufacturing of a silicon nitride sintered body made of a raw material powder with another type of sintering aid or a different composition. Needless to say. That is, the method of manufacturing a silicon nitride sintered body having a composition other than the above-described examples can also benefit from the present invention, and within the technical scope of the present invention, arbitrary substitution, omission and/or Can be added.
本発明は上述した実施例に限定されるものではなく、本発明の技術的範囲に属する限りにおいて種々の態様で実施しうるものである。
The present invention is not limited to the above-mentioned embodiments, but can be carried out in various modes within the technical scope of the present invention.
Claims (12)
前記混合粉末を焼成させないように、非酸化性雰囲気中で前記混合粉末を１２００℃以上の第１仮焼温度で加熱して第１仮焼粉末を得る第１仮焼工程と、
前記第１仮焼粉末から炭素を除去するように、酸化性雰囲気中で９００℃以下の第２仮焼温度で前記第１仮焼粉末を加熱して第２仮焼粉末を得る第２仮焼工程と、
前記第２仮焼粉末を所定の形状に成形して成形体を得る成形工程と、
非酸化性雰囲気中で前記成形体を焼成して、窒化ケイ素焼結体を得る焼成工程と、
を含むことを特徴とする窒化ケイ素焼結体の製造方法。 A mixing step of obtaining a mixed powder by mixing a predetermined amount of carbon powder with respect to the silicon nitride powder and the sintering aid powder having a predetermined mixing ratio.
A first calcination step of heating the mixed powder in a non-oxidizing atmosphere at a first calcination temperature of 1200° C. or higher to obtain a first calcinated powder so as not to bake the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder at a second calcination temperature of 900° C. or lower in an oxidizing atmosphere so as to remove carbon from the first calcination powder. Process,
A molding step of molding the second calcined powder into a predetermined shape to obtain a molded body;
A step of firing the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body,
A method for producing a silicon nitride sintered body, comprising:
前記第１又は第２仮焼粉末から、ＭｇＳｉＮ２が析出されることを特徴とする請求項１から５のいずれか一項に記載の窒化ケイ素焼結体の製造方法。 The sintering aid powder contains at least MgO,
Wherein the first or the second calcined powder, method for producing a silicon nitride sintered body according to claim 1, any one of 5, characterized in that MgSiN 2 is deposited.
前記混合粉末を焼成させないように、非酸化性雰囲気中で前記混合粉末を１２００℃以上の第１仮焼温度で加熱して第１仮焼粉末を得る第１仮焼工程と、
前記第１仮焼粉末から炭素を除去するように、酸化性雰囲気中で９００℃以下の第２仮焼温度で前記第１仮焼粉末を加熱して第２仮焼粉末を得る第２仮焼工程と、
前記第２仮焼粉末を所定の形状に成形して成形体を得る成形工程と、
非酸化性雰囲気中で前記成形体を焼成して、窒化ケイ素焼結体を得る焼成工程と、
を含むことを特徴とする窒化ケイ素焼結体の製造方法。 A mixing step of mixing a predetermined amount of carbon powder with silicon nitride powder to obtain a mixed powder;
A first calcination step of heating the mixed powder in a non-oxidizing atmosphere at a first calcination temperature of 1200° C. or higher to obtain a first calcinated powder so as not to bake the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder at a second calcination temperature of 900° C. or lower in an oxidizing atmosphere so as to remove carbon from the first calcination powder. Process,
A molding step of molding the second calcined powder into a predetermined shape to obtain a molded body;
A step of firing the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body,
A method for producing a silicon nitride sintered body, comprising:
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