JP2018070436A - Production method of silicon nitride sintered body - Google Patents
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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 121
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Abstract
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 producing 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。 In recent years, with the increase in density and output of electronic devices and semiconductor devices, the heat generation density of power modules has increased. The rise in temperature of the power module causes malfunction of the element or causes the insulating circuit board to crack. For this reason, ceramic substrates such as alumina and aluminum nitride, which are materials having relatively high thermal conductivity, have been used for the insulating circuit substrate. However, alumina and aluminum nitride have a drawback of low mechanical strength. For this reason, it has been impossible to directly bond thick copper, which is subjected to strong thermal stress, to the ceramic substrate, thus limiting the structure of the power module. Specifically, since it is necessary to solder-join a heat sink such as copper or aluminum to the insulated circuit board, the problem is that the power module is increased in size. Therefore, silicon nitride (Si 3 N 4 ) material is attracting attention as an insulating circuit substrate. The silicon nitride sintered body has about twice the strength and fracture toughness compared to the alumina and aluminum nitride sintered bodies, so it is possible to directly bond thick copper to the insulated circuit board, thereby reducing the size of the module. 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 manufacturing a silicon nitride sintered body having excellent mechanical properties and high thermal conductivity. In the production method, silicon nitride powder having an Al content of 0.1% by weight or less is added to Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Yb. After adding and sintering an oxide sintering aid of one or more elements selected from 1 to 15% by weight, under a nitrogen gas pressure of 1 to 500 atm. And firing at a temperature of 1700 ° C. or higher and 2300 ° C. or lower. The silicon nitride-based sintered body obtained by the manufacturing method is composed of 85 wt% or more and 99 wt% or less of β-type silicon nitride grains and the remainder is an oxide or oxynitride grain boundary phase. One or more metal elements selected from Mg, Ca, Sr, Ba, Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb are included in the grain boundary phase. Is contained in an amount of 0.5 wt% to 10 wt%. And the proportion of those having a minor axis diameter of 5 μm or more among β-type silicon nitride grains having a Al atom content in the grain boundary phase of 1% by weight or less, a porosity of 5% or less, and a microstructure of the sintered body Is 10 volume% or more and 60 volume% or less. That is, Patent Document 1 describes that by adding a sintering aid, the silicon nitride sintered body has both excellent mechanical properties and high thermal conductivity.
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, in order to obtain a silicon nitride sintered body having high thermal conductivity, it is known that a rare earth compound or magnesium oxide can be added as a sintering aid, and the thermal conductivity and mechanical strength can be improved by their mixing ratio and addition amount. ing. However, improvement in thermal conductivity and strength by changing the mixing ratio and addition amount is insufficient and has limitations. And further improvement of the mechanical characteristic and thermal conductivity of a silicon nitride sintered compact is calculated | required.
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-mentioned problems, the present invention has been made paying attention to the manufacturing process, and the object thereof is a method for manufacturing a silicon nitride sintered body capable of improving mechanical strength and thermal conductivity. Is 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 producing a silicon nitride sintered body according to an embodiment of the present invention includes:
A mixing step of mixing a predetermined amount of carbon powder with a silicon nitride powder and a sintering aid powder having a predetermined composition ratio to obtain a mixed powder;
A first calcining step of heating the mixed powder at a first calcining temperature of 1200 ° C. or higher to obtain a first calcined powder so as not to fire the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder in an oxidizing atmosphere at a second calcination temperature of 900 ° C. or less 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 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 carbon powder together with silicon nitride powder and sintering aid powder of a predetermined blending ratio, carbon reacts with oxygen contained in silicon nitride and auxiliary oxide, and as a result A second calcined powder of silicon nitride and auxiliary oxide having a low oxygen content can be obtained. It is considered that by forming and firing such a second calcined powder having a low oxygen content, physical defects (cracks, strains, voids, etc.) are less likely to occur inside the sintered body. As a result, a silicon nitride sintered body having relatively high mechanical strength and thermal conductivity can be manufactured through the manufacturing method.
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, an additional step of adding an additional sintering aid powder to the second calcined powder may be further included between the second calcining step and the molding step.
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 addition step, volatilization is performed by heat treatment in the first calcination step and the second calcination step in order to determine the addition amount of the additional sintering aid powder. A calculation step for calculating the amount of the sintering aid 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 heating in the first calcining step and the second calcining step. And based on a calculation result, the composition shift | offset | difference between a silicon nitride and a sintering aid can be suppressed by adding a proper quantity of 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, the mixing step calculates the amount of sintering aid that volatilizes by heating in the first calcination step and the second calcination step, and has a predetermined composition ratio of silicon nitride. About the same amount of sintering aid powder as the volatilizing sintering aid may be added 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 present invention, the sintering aid powder may consist of MgO, rare earth oxide, or a combination thereof. More preferably, the sintering aid powder includes 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 . The carbon powder may be 2.5 parts by weight or more (in terms of carbon) with respect to 100 parts by weight of the total of the silicon nitride powder and the sintering aid powder. Further, the oxygen amount 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。
The method for producing a silicon nitride sintered body according to another embodiment of the present invention includes:
A mixing step of mixing a predetermined amount of carbon powder with silicon nitride powder to obtain a mixed powder;
A first calcining step of heating the mixed powder at a first calcining temperature of 1200 ° C. or higher to obtain a first calcined powder so as not to fire the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder in an oxidizing atmosphere at a second calcination temperature of 900 ° C. or less 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 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 carbon powder together with silicon nitride powder and sintering aid powder of a predetermined blending ratio, carbon reacts with oxygen contained in silicon nitride and auxiliary oxide, and as a result A second calcined powder of silicon nitride and auxiliary oxide having a low oxygen content can be obtained. It is considered that by forming and firing such a second calcined powder having a low oxygen content, physical defects (cracks, strains, voids, etc.) are less likely to occur inside the sintered body. As a result, a silicon nitride sintered body having relatively high mechanical strength and thermal conductivity can be manufactured through the manufacturing method.
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 includes an addition step of adding a predetermined amount of sintering aid powder to the second calcined powder between the second calcining step and the molding step. But you can.
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) with respect to 100 parts by weight of the silicon nitride powder. Further, the amount of oxygen in the second calcined powder may be 0.7% by weight or less. Furthermore, 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。 With 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 manufacturing method of the silicon nitride sintered compact of this invention is demonstrated concretely based on the following embodiment.
［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]
As shown in FIG. 1, the method for manufacturing a silicon nitride sintered body according to the first embodiment of the present invention includes a silicon nitride (Si 3 N 4 ) powder and a sintering aid powder (or silicon nitride) having a predetermined mixing ratio. A mixing step in which a predetermined amount of carbon powder is mixed with a single powder) to obtain a mixed powder, and the mixed powder is first tempered at 1200 ° C. or higher in a non-oxidizing atmosphere so that the mixed powder is not fired or dissolved. A first calcining step of obtaining a first calcined powder by heating at a calcining temperature, and removing carbon from the first calcined powder and preventing the first calcined powder from being fired or dissolved in an oxidizing atmosphere 900 A second calcining step of obtaining a second calcined powder by heating the first calcined powder at a second calcining temperature of less than or equal to 0 ° C., and molding to obtain a compact by molding the second calcined powder into a predetermined shape Process and firing the compact (under high pressure) in a non-oxidizing atmosphere to obtain a silicon nitride sintered body And a firing step. 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, silicon nitride (Si 3 N 4 ) powder, sintering aid powder and carbon powder are mixed to obtain a mixed powder. Note that the sintering aid powder may be omitted, and a mixed powder may be obtained by mixing only silicon nitride powder and carbon powder. In the mixing step, silicon nitride powder and carbon powder, which are raw material powders, are mixed in appropriate amounts in a container and uniformly stirred with a stirrer equipped with blades. Next, the stirred raw material powder is transferred to a vibration mill, and a mixed powder is obtained by adding a sintering aid and mixing. At this stage, dry mixing without solvent or the like 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 silicon nitride powder having a high purity produced by a direct nitriding method, an imide pyrolysis 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). These oxides or combinations thereof may be selected. Preferably, the sintering aid powder is selected from magnesium oxide MgO, yttrium oxide (Y 2 O 3 ) or a combination 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, fine particles mainly composed of carbon such as furnace black and acetylene black can be used. In particular, it is preferable to use acetylene black because there is little impurity contamination 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 of the silicon nitride powder and the sintering aid powder is 100 parts by weight. This is because, when the blending amount of the carbon powder is less than 2.5 parts by weight, the amount of oxygen is not effectively reduced in the first calcining step described later. Moreover, it is preferable that the compounding quantity of carbon powder is 20 weight part or less. In particular, when the blending amount of the carbon powder exceeds 20 parts by weight, it is difficult to remove the carbon powder in the second calcination process (decarburization process) (or a long-time heat treatment is required, which is undesirable in the process). This is because there is a high possibility that an amount of carbon powder that affects 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 the mixing step, the amount of sintering aid that volatilizes in the next calcination step is calculated (predicted) in advance, and the volatilization sintering is performed on silicon nitride powder and sintering aid powder having a predetermined mixing ratio. You may add the sintering auxiliary agent powder of the same quantity as an auxiliary agent. That is, as shown in FIG. 1, the present manufacturing method may optionally include a calculation step in anticipation of the volatilization amount before the mixing step. Such calculation (prediction) is possible based on past experimental data. In other words, compositional deviation due to volatilization can be suppressed by using past analysis results and the like to increase the amount of the sintering aid relative to 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 step (1) is sheathed against a carbon sheath (container). The sheath used can be made of a material that does not deform at the temperature during the heat treatment and is not reduced by the carbon powder. In consideration of thermal conductivity, thermal expansion coefficient, contamination of 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 filling the mixture, heat treatment is performed at a first calcining temperature in a non-oxidizing (inert) atmosphere containing nitrogen gas, for example, in an electric furnace using carbon as a heating element. 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 calcining 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 calcining temperature is lower than 1200 ° C., the reaction between the carbon powder and oxygen in the raw material powder does not proceed effectively, and the decrease in the oxygen content of the mixed powder is reduced. Further, the upper limit of the first calcining temperature is determined so that the mixed powder is not fired, dissolved or altered. That is, heat treatment is performed so that the powder form is maintained. In particular, the first calcining temperature is not limited, but is preferably 1300 to 1450 ° C. That is, as will be described later, when the first calcining temperature is 1300 ° C. or higher, a reduction in the oxygen content of the calcined powder can be clearly confirmed. On the other hand, when the first calcining temperature is higher than 1450 ° C. (for example, 1490 ° C.), the proportion of β-Si 3 N 4 in the shape of needles increases, the moldability deteriorates, and the powder It has been found as a finding that coarse particles are generated in the body and the density of the compact is reduced (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 generated in the first calcination step is subjected to the second step in an oxidizing atmosphere containing, for example, oxygen gas or air. Residual carbon is removed by heating at the calcining temperature to obtain a second calcined powder. In other words, the purpose of the second calcination step is to decarburize residual carbon that has not been consumed in the first calcination step. The second calcining temperature is set to 900 ° C. or lower so that the first calcined powder is not calcined and the silicon nitride powder after calcining is not reoxidized. And heat processing are made so that the form of powder may be maintained. The lower limit of the second calcining temperature is preferably 500 ° C. or higher so that residual carbon can be removed. Further, the lower limit of the second calcining 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 for the heat treatment time (second calcination time) and the oxygen gas concentration can be changed as appropriate by measuring the carbon content of the powder after decarburization. The amount of carbon after decarburization is best if it is the same as that before carbon powder mixing (that is, approximately 0), but if it is 0.15% by weight or less of the entire second calcined powder, the characteristics of the sintered body Is known to have no effect. Therefore, it is preferable that the second calcination step is performed under the condition that the amount of carbon 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 the examples (see Table 1) to be described later, the second calcined powder obtained through the second calcining step has a tendency to decrease the oxygen content as compared with the mixed powder before calcining. 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, so that oxygen contained in the silicon nitride powder and / or the sintering aid powder is consumed. It is considered. Then, in the second calcining step, decarbonization is performed and residual carbon is removed. 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 shown in FIG. 3 as an example.
（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 press method or a sheet molding method, which is a normal ceramic molding method. 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 increase in the amount of oxygen during mixing. As a specific example, an organic solvent in which a dispersant, toluene, and ethanol are mixed with the second calcined powder is added and adjusted by a commonly performed mixing and grinding method. The calcined powder is uniformly mixed and the particle size is adjusted by a method such as a ball mill, a bead mill, or a vibration mill. As materials for mills and media used in the mixing and grinding method, resins such as urethane and nylon and ceramics such as silicon nitride and zirconium oxide can be used. However, in order to prevent impurities from entering the slurry, It is preferable to use resin or silicon nitride. In addition, it is necessary to adjust the addition amount of a dispersing agent and an organic solvent with the kind and the specific surface area of a raw material. When silicon nitride is used as a raw material, an amine-based or phosphorus-based surfactant is preferably used as a dispersant. The addition amount of the dispersant 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 viscosity-adjusted in a vacuum, and a green sheet having a predetermined thickness is obtained by a 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, and a molded body is obtained.
（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 The sintered body obtained in the forming step is fired at a high temperature for a predetermined time to obtain a silicon nitride sintered body that is the final object of the production method. The baking treatment is performed in a temperature range of about 1750 to 2000 ° C. in a non-oxidizing (nitrogen) atmosphere in a baking furnace. 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. And in this manufacturing method, since the calcination process for the purpose of deoxygenation is performed before the forming process, structural defects (lattice defects, strains, etc.) due to the loss 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 having high mechanical strength and thermal conductivity by passing through the firing step from the mixing step described above, compared with those manufactured without going through the present manufacturing method (particularly the first and second calcining steps). 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 producing a silicon nitride sintered body according to the second embodiment of the present invention is based on silicon nitride powder and 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 at a first calcining temperature of 1200 ° C. or higher in a non-oxidizing atmosphere so that the mixed powder is not fired or dissolved. A first calcining step for obtaining a first calcined powder, and a second calcining at 900 ° C. or lower in an oxidizing atmosphere so as to remove carbon from the first calcined powder and not to fire or dissolve the first calcined powder. A second calcining step of heating the first calcined powder at a calcining temperature to obtain a second calcined powder, an adding step of adding an additional sintering aid powder to the second calcined powder, and a second A molding step for obtaining a molded body by molding the calcined powder into a predetermined shape, and a molded body in a non-oxidizing atmosphere Forms pressure sintering, comprises a firing step to obtain a silicon nitride sintered body. In addition, the production method is preferably such that, prior to the addition step, the sintering aid volatilized by the heat treatment in the first calcining step and the second calcining step so as to determine the amount of additional sintering aid powder added. Includes a calculation process to calculate the amount of agent.
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, an additional sintering aid powder is added to the second calcined powder between the second calcining step and the molding step, as compared with the first embodiment. An addition step and a calculation step for selectively calculating the addition amount are added, and other steps are common. Hereinafter, the addition step and the calculation step 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 sintering aid is added to the second calcined powder mainly composed of silicon nitride and a sintering aid (or silicon nitride alone), followed by firing. The composition of the later silicon nitride sintered body can be adjusted. For example, in the mixing step, a mixed powder is prepared by mixing only silicon nitride powder and carbon powder, and an appropriate amount of sintering aid powder is prepared so as to match the composition of the desired silicon nitride sintered body at the stage before firing. It may be added. Moreover, in order to suppress the composition shift | offset | difference by the component of silicon nitride and a sintering auxiliary agent volatilizing by heating, you may add a sintering auxiliary agent based on the following calculation processes.
（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, silicon nitride and sintering aid are obtained by applying the first and second calcination steps to the mixed powder of silicon nitride powder, sintering aid powder and carbon powder. It is conceivable that the component of the agent component volatilizes and causes a composition shift. In the calculation step, the powder before and after calcination is analyzed (for example, fluorescent X-ray analysis), and the reduction amount (volatilization amount) of the raw material is measured and calculated. Then, based on the result obtained in the calculation step, by adding an appropriate amount of additional sintering aid powder to the second calcined powder so as to supplement the volatilized sintering aid component in the addition step. , Composition 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。 EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limitedly interpreted by the following Example.
［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 according to the following conditions and procedures. Examples 1 to 5 differ from each other in the composition of silicon nitride powder, sintering aid powder and carbon powder, calcining temperature and / or decarburization temperature. Moreover, in Examples 1-5, as shown in FIG. 2, the mixed powder of a silicon nitride powder and carbon powder is produced at a mixing process, and sintering auxiliary powder is added at an addition process. 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 by 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 size (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 calcination powder. When the first calcining temperature was 1600 ° C. or higher, an X-ray diffraction peak of SiC was found in the first calcined powder, and thus a 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 first calcined powder was subjected to a second calcining treatment in dry air at a second calcining temperature for 12 hours to obtain a second calcined powder. 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, suitable amounts of MgO and Y 2 O 3 as sintering aid powders were added to the second calcined powder in accordance with the composition ratio of each 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 process was performed under the following conditions. To the mixture of 100 parts by weight of the second calcined powder and the sintering aid powder, 0.3 part by weight of a surface active dispersant and 50 parts by weight of a mixed solvent of toluene and ethanol are added, followed by nitriding Grinding and mixing was performed using silicon cobblestone. Then, add 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. After stirring and mixing, a slurry was prepared. The slurry was defoamed and adjusted in viscosity in vacuum, and a green sheet was obtained by the doctor blade method. The obtained green sheet was punched into a predetermined shape by die pressing, 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 compact was fired in a firing atmosphere under a nitrogen atmosphere of 9 atm at 1860 ° C. for 4 hours to obtain a silicon nitride sintered substrate having a plate 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. In Comparative Examples 1 and 2, the blending compositions of the sintering aids are different from each other.
（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 a mixture of 100 parts by weight of silicon nitride powder and sintering aid powder, 0.3 part by weight of a surface active dispersant and 50 parts by weight of a mixed solvent of toluene and ethanol are added. Was used for pulverization and mixing. Thereafter, 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. After stirring and mixing, a slurry was prepared. The slurry was defoamed and adjusted in viscosity in vacuum, and a green sheet was obtained by the doctor blade method. The obtained green sheet was punched into a predetermined shape by die pressing, 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 compact was fired for 4 hours in a nitrogen atmosphere of 9 atm at 1860 ° C. in a nitrogen atmosphere of 9 atm to obtain a silicon nitride sintered substrate having a plate 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), the average particle diameter D50 (μm), and the specific surface area (m 2 / g) of the calcined powder 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
Measurement was performed using a laser diffraction particle size distribution analyzer SALD-2000 manufactured by Shimadzu Corporation. As the dispersant, sodium hexametaphosphate was used, and the refractive index was 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 It measured by the inert gas melting-non-dispersion type infrared absorption method using EMGA-920 of Horiba Ltd.
・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 calculated from the density of the sintered compact. 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 (alpha) was measured by laser flash method using TC-7000 of advance Riko Co., Ltd. The thermal conductivity λ was calculated according to the following equation using the specific heat C of silicon nitride of 0.68 J / (g · K) and the density ρ determined by the Archimedes method.
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 a 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 model AG-IS manufactured by Shimadzu Corporation, and the measurement conditions were set to 20 pcs, the crosshead speed was 0.5 mm / min, and the distance between fulcrums was 30 mm, and the average value was obtained.
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。 The conditions and various measurement results of Examples 1 to 5 and Reference Examples 1 and 2 are shown in Table 1. As the composition of the powder, Si 3 N 4 powder, parts by weight of carbon powder are shown for a total of 100 parts by weight of 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 produced by the calcining step is 0.7% by weight or less, and the oxygen content of the original raw material powder It can be seen that there is a significant reduction from 0.8%. On the other hand, in Example 5 in which the first calcining temperature of Example 1 was 1200 degrees, the oxygen content of the second calcined powder was 0.8% by weight, and the reduction of the oxygen content could not be clearly confirmed. It was. And when Example 1 and Comparative Example 1 with the same compounding composition ratio are compared regarding the sintered compact characteristic, the thermal conductivity and mechanical strength of the silicon nitride sintered body of Example 1 are from Comparative Example 1. Is also big. Next, with respect to sintered body characteristics, Examples 2, 3, and 4 having the same blending composition ratio are compared with Comparative Example 2. The thermal conductivity of the silicon nitride sintered bodies of Examples 2, 3, and 4 is equal to or higher than that of Comparative Example 2, and the mechanical strength is significantly higher than that of Comparative Example 2. And when Example 2 and 3 were compared, the raise of mechanical strength was seen by changing calcination temperature from 1400 degreeC to 1450 degreeC. Moreover, when Example 3 and 4 were compared, the further raise of mechanical strength was seen by increasing the compounding quantity of carbon. Furthermore, when Example 5 and Comparative Example 1 were compared, although the reduction in oxygen content could not be confirmed, the thermal conductivity and mechanical strength of the silicon nitride sintered body of Example 5 were improved from Comparative Example 1. I can see that. In other words, the reduction of the oxygen amount did not appear numerically due to factors such as measurement error, but the sintered body characteristics were similarly improved even at the first calcining temperature of 1200 ° C. That is, according to Table 1, in the production process of the present invention, after adding at least 2.5 parts by weight of carbon powder and passing through a calcination process of the carbon mixed powder, the characteristics of the silicon nitride sintered body can be improved. It turns out that it improves.
［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 in the same procedures and conditions as in Examples 1 to 5. However, in Examples 6 to 8, mixed powders of Si 3 N 4 powder, MgO powder, Y 2 O 3 powder and C powder were produced in the mixing step. And since MgO is easy to volatilize in a calcination process, as shown in FIG. 2, the addition process of MgO with respect to the 2nd calcination powder was performed in order to suppress the whole composition shift. In particular, the amount of MgO volatilized by calcination was calculated by performing fluorescent X-ray analysis on the powder before and after calcination and comparing the analysis results. And the shift | offset | difference of the compounding ratio between raw materials was suppressed by replenishing and adding MgO to the 2nd calcined powder for the part which volatilized.
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 is produced in the mixing step, and Y 2 is added to the second calcined powder in the adding step. MgO that has volatilized along with the O 3 powder is added. In particular, the amount of MgO volatilized by calcination was calculated by performing fluorescent X-ray analysis on the powder before and after calcination and comparing the analysis results. And the shift | offset | difference of the compounding ratio between raw materials was suppressed by replenishing and adding MgO to the 2nd calcined powder for the part which volatilized.
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 powder 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, relative density (%), thermal conductivity (W / mK), and machine under the same conditions as in Examples 1 to 5 Strength (MPa) was measured. The amount of precipitated MgSiN 2 was measured 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 precipitation amount of MgSiN 2 Crystalline phase identification by powder X-ray diffraction method was performed using Ultimate IV of Rigaku Corporation. The composition ratio of the crystal phase of MgSiN 2 was calculated by performing quantitative analysis by RIR (Reference Intensity Ratio) method. FIG. 3 is a specific example of the X-ray diffraction pattern, and 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。 The conditions and various measurement results of Examples 6 to 11 and Reference Example 2 are shown in Table 2. As the composition of the powder, Si 3 N 4 powder, parts by weight of carbon powder are shown for a total of 100 parts by weight of MgO powder and Y 2 O 3 powder. In addition, a compounding composition ratio is a value after the volatile raw material was adjusted at the addition process.
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 Examples 6 to 11 and Comparative Example 2 having the same blending composition ratio are compared with respect to sintered body characteristics, the thermal conductivity and mechanical properties of the silicon nitride sintered bodies of Examples 6 to 11 are compared. The mechanical strength is greater 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, compared to Examples 1 to 5, the amount of oxygen in the sintering aid is significantly reduced by calcination by subjecting the mixed powder containing at least MgO powder to calcination treatment. 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 producing a silicon nitride sintered body of the present embodiment (Examples 1 to 11) is characterized in that the first and second calcining steps are performed on the mixed powder containing carbon powder in the mixing step. To do. Therefore, according to the present invention, improvement in relative mechanical strength and thermal conductivity was realized as compared with the silicon nitride sintered body having the same composition without introducing 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。 Note that the manufacturing method of the above embodiment is merely an example, and the technical idea of the present invention is applicable to the manufacture of a silicon nitride sintered body made of other types of sintering aids and raw material powders having different blending compositions. Needless to say. That is, the manufacturing method of the silicon nitride sintered body having a composition other than the above-described examples can also benefit from the present invention, and can be arbitrarily substituted, omitted, and / or within the technical scope of the present invention. It 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-described embodiments, and can be implemented in various modes as long as they belong to 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 mixing a predetermined amount of carbon powder with a silicon nitride powder and a sintering aid powder having a predetermined mixing ratio to obtain a mixed powder;
A first calcining step of heating the mixed powder at a first calcining temperature of 1200 ° C. or higher to obtain a first calcined powder so as not to fire the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder in an oxidizing atmosphere at a second calcination temperature of 900 ° C. or less 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;
Firing the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body;
The manufacturing method of the silicon nitride sintered compact characterized by including this.
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,
The method for producing a silicon nitride sintered body according to any one of claims 1 to 5, wherein MgSiN 2 is precipitated from the first or second calcined powder.
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 calcining step of heating the mixed powder at a first calcining temperature of 1200 ° C. or higher to obtain a first calcined powder so as not to fire the mixed powder;
Second calcination to obtain a second calcination powder by heating the first calcination powder in an oxidizing atmosphere at a second calcination temperature of 900 ° C. or less 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;
Firing the molded body in a non-oxidizing atmosphere to obtain a silicon nitride sintered body;
The manufacturing method of the silicon nitride sintered compact characterized by including this.
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| WO2020179699A1 (en) | 2019-03-01 | 2020-09-10 | デンカ株式会社 | Ceramic green sheet, ceramic substrate, method for producing ceramic green sheet and method for producing ceramic substrate |
| WO2021117829A1 (en) * | 2019-12-11 | 2021-06-17 | 宇部興産株式会社 | Plate-like silicon nitride-based sintered body and method for producing same |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2020179699A1 (en) | 2019-03-01 | 2020-09-10 | デンカ株式会社 | Ceramic green sheet, ceramic substrate, method for producing ceramic green sheet and method for producing ceramic substrate |
| EP4215509A1 (en) | 2019-03-01 | 2023-07-26 | Denka Company Limited | Ceramic green sheet, ceramic substrate, method for producing ceramic green sheet, and method for producing ceramic substrate |
| WO2021117829A1 (en) * | 2019-12-11 | 2021-06-17 | 宇部興産株式会社 | Plate-like silicon nitride-based sintered body and method for producing same |
| JPWO2021117829A1 (en) * | 2019-12-11 | 2021-06-17 | ||
| CN114787105A (en) * | 2019-12-11 | 2022-07-22 | 宇部兴产株式会社 | Plate-like silicon nitride sintered body and method for producing same |
| JP7201103B2 (en) | 2019-12-11 | 2023-01-10 | Ｕｂｅ株式会社 | Plate-like silicon nitride sintered body and manufacturing method thereof |
| CN114787105B (en) * | 2019-12-11 | 2024-03-05 | Ube 株式会社 | Plate-like silicon nitride sintered body and method for producing same |
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