JP3681780B2 - Porous conductive silicon carbide sintered body, its production method and use - Google Patents
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Description
【０００１】
【産業上の利用分野】
本発明は、ディーゼルエンジン等から排出される可燃性微粒子の捕集用に用いられる多孔質導電性炭化珪素焼結体に関するもので、更に詳しくは補集した可燃性微粒子を、通電発熱により均一にしかも効率的に焼却し、再生可能な導電性ディーゼルパティキュレートフィルターに関する。
【０００２】
【従来の技術】
ディーゼルエンジン等から排出される可燃性微粒子を補集するフィルターは、低熱膨張性のコーディエライトセラミックが使用されているが、一定量の微粒子を捕集すると圧力損失が増大するため、定期的に焼却し再生する必要がある。フィルターの再生は、バーナの燃焼ガスを噴射しその燃焼熱で焼却する方法やニクロム線ヒータあるいは発熱金属層を組み合わせて加熱し焼却する方法がとられている。しかし、これらの方法は外部からフィルターを加熱するため、可燃性微粒子の燃焼に伴い局所的な発熱と大きな温度勾配によってフィルターの溶損や熱応力割れが発生する問題がある。
【０００３】
このため補集した可燃性微粒子を均一に焼却し、コンパクトで現状の装置を大きく変更することなく取り付けられる自己発熱型フィルターが検討されている。この方法で使用されるフィルターは、主に炭化珪素、珪化モリブデン、炭化チタニウムあるいはランタンクロマイトを主成分とした導電性セラミックス（特開昭 58-119317, 特開平 2-42112）を用いる技術が開示されている。
【０００４】
しかしながら、ランタンクロマイトのような導電性の酸化物系セラミックスは、耐熱性が低く熱膨張率が高いため熱応力割れが発生する問題がある。一方、珪化モリブデン、炭化チタニウム等の導電性の非酸化物系セラミックスはフィルター機能を付与するために気孔率、気孔径を大きくすると容易に酸化し導電性が失われる問題がある。また、炭化珪素セラミックは、基本的に絶縁体であるため、所望の導電性を得るためには Ti, Zr のような周期律表IVa 族元素あるいはV,NbのようなＶa 族元素の炭化物、窒化物、ホウ化物を添加し、焼結体中に連続的な導電相を形成させることによって導電性を付与する必要がある。しかし、これら導電性物質は多量の添加が必要で、この多量添加によって大気中など酸素を含む雰囲気で容易に酸化を受け導電性が失われる問題がある。
【本発明が解決しようとする課題】
【０００５】
本発明は以上の状況に鑑がみなされたものであり、導電性付与物質を添加することなく導電性を向上し優れた耐酸化性を付与させるとともに、フィルターとして最適な気孔径及び気孔率を有する多孔質導電性炭化珪素焼結体、及びその製造方法並びにこの焼結体で構成された導電性ディーゼルパティキュレートフィルターの提供を目的とする。
【０００６】
【課題を解決するための手段】
すなわち、本発明の多孔質導電性炭化珪素焼結体は、平均粒子径 5 〜 50 μ m 、粒度分布の累積粒度 10% 径 (D10) と 50% 径 (D50) の粒径比（ D10/D50) が 0.2 以上の炭化珪素粉末 20 〜 80 重量 % とカーボンに対する金属珪素のモル比（金属珪素／カーボン）が 1.0 〜 2.0 である金属珪素粉末と炭素物質の混合粉末 80 〜 20 重量 % とを配合し成形体とした後、該成形体を１）高くても 400 ℃の温度から 1100 ℃〜 1800 ℃の任意の温度までをＮ 2 分圧が 0.2 atm 以上の非酸化性雰囲気中で 600 ℃／ hr 以下の昇温速度で加熱した後、（２）Ｎ 2 分圧が 0.2 atm 未満の非酸化性雰囲気中で 600 ℃／ hr 以下の昇温速度で 1500 ℃以上でかつ（１）の最高温度以上の温度に加熱することによって製造されるα型炭化珪素と粒界結合部とからなる焼結体であって、該α型炭化珪素の含有量が 20 〜 80 体積％であり、該粒界結合部主相がβ型炭化珪素で構成されていることを特徴とする
【０００７】
そして、本発明の製造方法は、平均粒子径 5〜 50 μm 、粒度分布の累積粒度10% 径(D10) と50% 径(D50) の粒径比（D10/D50)が 0.2以上の炭化珪素粉末20〜80重量% とカーボンに対する金属珪素のモル比（金属珪素／カーボン）が 1.0〜 2.0である金属珪素と炭素物質の混合粉末 80 〜 20 重量% とを配合し成形体とした後、該成形体を窒素ガスを含む雰囲気中で加熱し窒化した後、炭化することを特徴とするものである。この際、前記、成形体を窒化し窒化珪素を生成させた後、炭化することによって、反応生成したβ型炭化珪素がα型炭化珪素の粒界相主相を構成することにより、導電性物質を添加することなく導電性を向上させることができるとともに、粒界結合力を高め粒界相が緻密化し耐酸化性を向上させることができる。
【０００８】
より好ましい製造方法は、上記の成形体を窒素ガスを含む雰囲気中で加熱し窒化した後、炭化する工程が次の（１）及び（２）の工程からなることを特徴とするものである。
（１）高くても 400℃の温度から 1100 ℃〜 1800 ℃の任意の温度までをＮ2 分圧が 0.2 atm以上の非酸化性雰囲気中で 600℃／hr以下の昇温速度で加熱した後、（２）Ｎ2 分圧が 0.2 atm 未満の非酸化性雰囲気中で 600℃／hr以下の昇温速度で 1500 ℃以上でかつ（１）の最高温度以上の温度に加熱する。
【０００９】
さらに、出発原料であるα型炭化珪素粉末の粒径及び配合量を適宜、設定することによって、所望の気孔径及び気孔率を有する多孔質導電性炭化珪素焼結体を製造することができる。
【００１０】
以下、さらに詳しく本発明について説明する。
【００１１】
本発明の多孔質導電性炭化珪素焼結体は、例えば金属珪素粉末、炭素質物質及びα型炭化珪素粉末から成る混合原料を窒化し、生成した窒化珪素をさらに炭化することによって得られる。原料中の金属珪素を窒化し、さらに炭化することによって、粒界部に不純物導電相を形成し容易に 10 Ω・ cm以下の比抵抗を有する焼結体となる。また、金属珪素粉末を用いないでも、あらかじめ窒化されて形成された窒化珪素を配合してもよい。このようにして得られた炭化珪素焼結体は、α型炭化珪素とこれを結合する粒界部からなる炭化珪素焼結体であって、α型炭化珪素の含有量 20 〜 80 体積％であって、粒界部の主相がβ型炭化珪素で構成されていることによって、粒界相は通常の炭化珪素の粉末焼結体と比べると緻密化しているため、比抵抗が小さく優れた耐酸化性を有する。また、比抵抗は10Ω・ cm以下で、10Ω・ cmより高いと導電性ディーゼルパティキュレートフィルターとして通電加熱を行う場合、通常、搭載される 24 V のバッテリー容量では捕集したパティキュレートを焼却できる温度まで加熱させることが難しくなる。
【００１２】
本発明の焼結体のα型炭化珪素の含有量は20〜80体積％の範囲であるが、20体積％未満では機械的強度が低下し、80体積％を越えると粒界相を構成するβ型炭化珪素の量が少ないため比抵抗が高く耐酸化性が低下する。粒界相の比抵抗と耐酸化性の変化は次の理由による。すなわち、粒界相を構成するβ型炭化珪素は、窒化珪素を経由して生成されたものであり、多量の窒素固溶量を確保することができ低い比抵抗を備えるため、粒界相を構成するβ型炭化珪素の量が少ないと比抵抗が高くなり、また粒界結合部の緻密性が低下するため容易に粒界酸化が進行し耐酸化性が低下するためである。
【００１３】
一方、本発明の多孔質導電性炭化珪素焼結体の気孔特性は、平均気孔径 5〜40μm の範囲で、5 μm より小さいと、可燃性微粒子の目詰まりが顕著になり短時間に圧力損失が大きくなる。また、気孔径が 40 μm を越えると、捕集効率が低下しフィルター機能が低下する。さらに、気孔率は40％以上、好ましくは50〜80％の範囲で、40％より低いと圧力損失が高く、80％を越えると機械的強度が低下する。
【００１４】
上記、多孔質導電性炭化珪素焼結体を得るための製造方法として、出発原料となるα型炭化珪素粉末の平均粒径及び粒度分布が重要で、焼結体の気孔特性に影響する。すなわち、出発原料となるα型炭化珪素の平均粒径は 5〜 50 μｍで、その粒度分布の累積粒度10％径と50％径の粒径比（D10/D50)が 0.2以上必要である。すなわち、平均粒径が 5μm より小さい場合、または、粒度分布の（D10/D50)がの粒径比が 0.2未満の場合、焼結体の気孔径が小さくなる。一方、平均粒径が 50 μm を越えると焼結体の機械的強度が低下する。金属珪素粉末は、通常の工業用金属珪素で十分で、平均粒径は成形性及び炭素質物質との反応性の点から 100μm 以下が好ましい。また、炭素質物質としてはカーボンブラック、アセチレンブラック等の微粒子固体カーボン粉末の他、フェノール、フラン、ポリイミド等の熱分解し炭素となる有機系樹脂等も使用することができる。
【００１５】
これら出発原料の配合は、α型炭化珪素粉末20〜80重量％と金属珪素粉末と炭素質物質の混合粉80〜20重量％とする。この時の金属珪素粉末と炭素質物質の配合比は、カーボンに対する金属珪素のモル比が 1.0〜2.0 の範囲にする。このモル比が 1.0より小さいと焼結体中にカーボンが残存し、反応生成したβSiC の焼結を阻害する。一方、2.0 より多いと残存する金属珪素が多く機械的強度及び耐酸化性が低下する。
【００１６】
これら原料粉末の混合方法としては、乾式、湿式混合等均一に混合できる方法であれば何れの混合方法でも適用することが可能である。また、混合原料の成形は、メチルセルロース、ポリビニルアルコール等の有機バインダーを添加し、プレス成形、押出成形、射出成形あるいはスラリーを調整し所望の形状の容器に注入固化する方法で成形することができる。
【００１７】
次に、得られた成形体の焼成方法は、まず（１）高くても 400℃の温度から 1100 ℃〜 1800 ℃の任意の温度までをＮ2 分圧が 0.2 atm以上の非酸化性雰囲気中で 600℃／hr以下の昇温速度で加熱する。成形体はバインダーの種類に応じて必要に応じて脱脂するが、脱脂は酸化雰囲気中で行う方が好ましい場合もあり、少なくとも 400℃以上の温度ではＮ2 分圧が 0.2 atm以上の非酸化性雰囲気中で加熱する必要があるが、 400℃未満の温度では必ずしも非酸化性雰囲気中である必要はない。Ｎ2 分圧が0.2atm未満では金属珪素の窒化が不十分で、炭化して得られる焼結体の比抵抗が高くなる。同様に、昇温速度が 600℃/hr を越えると窒化が不十分で比抵抗が高くなる。また、窒化反応の温度が1100℃未満では窒化反応が起こらず、1800℃を越えると生成した窒化珪素の炭化珪素への転化が起こり、このような条件で得られた焼結体は気孔径が小さく、耐酸化性が低下する。
【００１８】
次いで、窒化珪素の生成した成形体を（２）Ｎ2 分圧が 0.2atm 未満の非酸化性雰囲気中で 600℃／hr以下の昇温速度で 1500 ℃以上でかつ（１）の最高温度以上の温度に加熱する。好ましくは 1800 ℃以上、より好ましくは 1900 ℃以上がよい。Ｎ2 分圧が 0.2atm 未満の非酸化性雰囲気としては、真空、又は窒素とアルゴン、一酸化炭素、アンモニア、メタン、水素等との混合ガスの雰囲気も可能である。この工程の温度が1500℃あるいは（１）の工程の最高温度よりも低い温度では炭化が不十分で窒化珪素が残存し比抵抗が高くなる。
【００１９】
本発明の導電性炭化珪素焼結体の用途としては、気孔率が 40%以上、平均気孔径が 5〜40μm 、室温比抵抗が 10 Ω・ cm以下の多孔質導電性炭化珪素焼結体であることから、ディーゼルエンジンから排出される可燃性微粒子を捕集し燃焼することのできるヒーター性能を付加した導電性フィルターとして最適である。一方、これらの特性はダクトヒーター、大型ドライヤーの熱源に使用される熱風発生機用ヒーターとしても、発熱面積を大きくし熱効率を高める点から適している。さらに、通常の暖房機器、調理機器、乾燥機器、焼成炉等に使用されるヒーターとしても充分に使用することが可能である。
【００２０】
【実施例】
以下、実施例、比較例を挙げてさらに具体的に本発明を説明する。
【００２１】
（実施例１〜７及び比較例１〜１０）
出発原料として表１記載の粒径（平均粒径、粒度分布粒径比）の炭化珪素粉末と、工業用金属珪素粉末及びカーボンブラックの混合粉末を表１に示す割合で配合した原料 100重量部に対して、さらに水20重量部、バインダーとしてメチルセルロース 8.0重量部を添加し、ヘンシェル混合機で10分間混合し、次いでニーダ式混練機を用いて30分混練した。得られた混練物は高圧真空押出成形機を用いて、外径寸法□50mm、セル寸法 2.5mm、リブ圧 0.5mmのハニカムを成形圧力 60kg/cm2 で押出成形した。得られた成形体は、乾燥後、窒素雰囲気中、450 ℃× 1hrの脱脂を行った後、表２に示す窒化反応欄の焼成条件で窒化後、炭化反応欄の焼成条件で炭化させた。
【００２２】
得られた焼結体について以下の特性を測定し表３に示した。
(1) 気孔率：アルキメデス法。
(2) 平均気孔径: 水銀圧入法。
(3) 炭化珪素結晶相の同定：Ｘ線回折を行い以下の式により算出した。
α型炭化珪素含有量（体積％）＝１００−｛β型炭化珪素含有量（体積％）｝
但し、β型炭化珪素含有量（体積％）＝１００／（１＋ａ＋ｂ）
ａ＝ 4.571Ｉa ／(100− 2.721Ｉa − 0.665Ｉb)
ｂ＝ 2.531Ｉb ／(100− 2.721Ｉa − 0.665Ｉb)
ここで、Ｉa は CuKα 2θが 34.3 °におけるピーク強度、Ｉb は 34.9 °におけるピーク強度であり、 CuKα 2θ=36.5 °におけるピーク強度を 100とした場合の相対値である。
(4) 室温比抵抗：ハニカム構造体を□10×50mm Lに切断し、銀電極を形成し４端子法で測定した
(5) 耐酸化性：大気中、温度1000℃×100 時間処理後の比抵抗を測定した。
(6) 機械的強度：ハニカム構造体を□10×10mm Lに切断し、押出方向における圧縮強度を測定した。
【００２３】
【表１】
【表２】
【表３】
表１〜３から明らかなように、実施例１〜７で得られた導電性多孔質炭化珪素焼結体は、好適な気孔率及び平均気孔径を有し、室温比抵抗が低く優れた導電性を示すとともに、すぐれた圧縮強度、耐酸化性を示した。これらの焼結体の導電性ディーゼルパーティキュレートフィルターとしての特性、すなわち補集効率、補集された微粒子の加熱除去性能の評価結果は良好であり、ディーゼルパーティキュレートフィルターとして優れた特性を有するものであった。
【００２７】
【発明の効果】
本発明の導電性炭化珪素焼結体の製造方法によれば、導電性付与材を添加することなく、導電性、耐酸化性に優れ、フィルターとして最適な気孔率及び気孔径を有する多孔質導電性炭化珪素焼結体が提供される。また、本発明の多孔質導電性炭化珪素焼結体の用途は、特に、ディーゼルエンジンから排出される微粒子を捕集し燃焼焼却するヒーター性能を有する導電性ディーゼルパティキュレートフィルターとして、さらに、発熱面積が大きく熱効率を高められる観点から、ダクトヒーター、大型ドライヤーの熱源に使用される熱風発生機用ヒーターとして、また、暖房機器、調理機器、乾燥機器、焼成炉等に使用されるヒーターとしても適している。[0001]
[Industrial application fields]
The present invention relates to a porous conductive silicon carbide sintered body used for collecting combustible fine particles discharged from a diesel engine or the like. More specifically, the collected combustible fine particles are uniformly distributed by energization heat generation. Moreover, the present invention relates to a conductive diesel particulate filter that can be efficiently incinerated and regenerated.
[0002]
[Prior art]
Low thermal expansion cordierite ceramic is used as a filter to collect combustible particulates discharged from diesel engines, etc., but when a certain amount of particulates is collected, pressure loss increases. It is necessary to incinerate and regenerate. The regeneration of the filter includes a method of injecting burner combustion gas and incinerating with the combustion heat, or a method of heating and incineration in combination with a nichrome wire heater or a heat generating metal layer. However, since these methods heat the filter from the outside, there is a problem in that the filter is damaged and thermal stress cracking occurs due to local heat generation and a large temperature gradient accompanying combustion of combustible fine particles.
[0003]
For this reason, self-heating type filters that can be installed without burning the collected combustible fine particles uniformly and without changing the current apparatus are being studied. As a filter used in this method, a technique using conductive ceramics (JP 58-119317, JP 2-42112) mainly composed of silicon carbide, molybdenum silicide, titanium carbide or lanthanum chromite is disclosed. ing.
[0004]
However, conductive oxide ceramics such as lanthanum chromite have a problem that thermal stress cracking occurs because of low heat resistance and high coefficient of thermal expansion. On the other hand, conductive non-oxide ceramics such as molybdenum silicide and titanium carbide have a problem that they are easily oxidized and lose conductivity when the porosity and pore diameter are increased in order to provide a filter function. Furthermore, silicon carbide ceramics are basically the insulator, in order to obtain the desired conductivity of Ti, of the periodic table IV a-group element or V, such as Zr, the V a group element such as Nb It is necessary to add conductivity by adding carbide, nitride, boride and forming a continuous conductive phase in the sintered body. However, these conductive substances need to be added in a large amount, and there is a problem that the conductivity is easily lost due to oxidation in an atmosphere containing oxygen such as in the air.
[Problems to be solved by the present invention]
[0005]
The present invention has been considered in the above situation, and without adding a conductivity-imparting substance, improves conductivity and imparts excellent oxidation resistance, and has an optimum pore diameter and porosity as a filter. It is an object of the present invention to provide a porous conductive silicon carbide sintered body, a method for producing the same, and a conductive diesel particulate filter composed of the sintered body.
[0006]
[Means for Solving the Problems]
That is, the porous conductive silicon carbide sintered body of the present invention has an average particle diameter of 5 ~ 50 μ m, the particle size distribution of the particle size ratio of cumulative particle size 10% diameter (D10) and 50% diameter (D50) (D10 / D50) is 20 to 80 % by weight of silicon carbide powder of 0.2 or more, and a mixed powder of metal silicon powder and carbon substance having a molar ratio of metal silicon to carbon (metal silicon / carbon) of 1.0 to 2.0 is 80 to 20 % by weight. After blending into a molded body, the molded body 1) is at most 600 ° C. from a temperature of 400 ° C. to any temperature between 1100 ° C. and 1800 ° C. in a non-oxidizing atmosphere with a N 2 partial pressure of 0.2 atm or more. (2) After heating at a rate of temperature rise of less than / hr , (2) In a non-oxidizing atmosphere with N 2 partial pressure less than 0.2 atm , at a rate of temperature rise of less than 600 ° C / hr and higher than 1500 ° C and the highest of (1) a sintered body made of α-type silicon carbide is produced and the intergranular coupling portion by heating to a temperature above the temperature, the content of the α-type silicon carbide is 20 to 80 vol% der Characterized in that the particulate field coupling portion main phase is composed of β-type silicon carbide [0007]
The production method of the present invention has an average particle diameter. 5 to 50 [mu] m, the particle size ratio (D 10 / D 50) of the cumulative particle size of 10% the diameter of the particle size distribution (D 10) and 50% diameter (D 50) of 0.2 A molded body comprising 20 to 80% by weight of the above silicon carbide powder and 80 to 20% by weight of a mixed powder of metal silicon and carbon having a molar ratio of metal silicon to carbon (metal silicon / carbon) of 1.0 to 2.0. Then, the molded body is heated in an atmosphere containing nitrogen gas, nitrided, and then carbonized. At this time, after the formed body is nitrided to form silicon nitride and then carbonized, the reaction-generated β-type silicon carbide constitutes the grain boundary phase main phase of the α-type silicon carbide. The conductivity can be improved without adding, and the grain boundary bonding force can be increased and the grain boundary phase can be densified to improve the oxidation resistance.
[0008]
A more preferable production method is characterized in that the step of carbonizing the molded body after heating and nitriding in an atmosphere containing nitrogen gas comprises the following steps (1) and (2).
(1) After heating from a temperature of 400 ° C to an arbitrary temperature of 1100 ° C to 1800 ° C at a temperature rise rate of 600 ° C / hr or less in a non-oxidizing atmosphere with an N 2 partial pressure of 0.2 atm or higher (2) In a non-oxidizing atmosphere with an N 2 partial pressure of less than 0.2 atm, heat to a temperature not lower than 1500 ° C. and a temperature not lower than the maximum temperature in (1) at a temperature rising rate of 600 ° C./hr or lower.
[0009]
Furthermore, a porous conductive silicon carbide sintered body having a desired pore diameter and porosity can be manufactured by appropriately setting the particle size and blending amount of the α-type silicon carbide powder as a starting material.
[0010]
Hereinafter, the present invention will be described in more detail.
[0011]
The porous conductive silicon carbide sintered body of the present invention can be obtained, for example, by nitriding a mixed raw material composed of metal silicon powder, carbonaceous material and α-type silicon carbide powder, and further carbonizing the generated silicon nitride. By nitriding and carbonizing the metal silicon in the raw material, an impurity conductive phase is formed at the grain boundary part, and a sintered body having a specific resistance of 10 Ω · cm or less can be easily formed. Further, silicon nitride formed by nitriding in advance may be blended without using metal silicon powder. The silicon carbide sintered body thus obtained is a silicon carbide sintered body composed of α-type silicon carbide and a grain boundary portion that bonds the α-type silicon carbide, and the α-type silicon carbide content is 20 to 80% by volume. In addition, since the grain boundary part is composed of β-type silicon carbide, the grain boundary phase is densified compared to a normal silicon carbide powder sintered body. Has oxidation resistance. In addition, when the specific resistance is 10 Ω · cm or less and higher than 10 Ω · cm, when conducting heating as a conductive diesel particulate filter, the temperature at which the collected particulates can normally be incinerated with the installed 24 V battery capacity. It is difficult to heat up.
[0012]
The content of α-type silicon carbide in the sintered body of the present invention is in the range of 20 to 80% by volume. However, if it is less than 20% by volume, the mechanical strength decreases, and if it exceeds 80% by volume, a grain boundary phase is formed. Since the amount of β-type silicon carbide is small, the specific resistance is high and the oxidation resistance is lowered. The changes in the specific resistance and oxidation resistance of the grain boundary phase are as follows. That is, β-type silicon carbide constituting the grain boundary phase is produced via silicon nitride, and since a large amount of nitrogen solid solution can be secured and a low specific resistance is provided, the grain boundary phase is reduced. This is because when the amount of β-type silicon carbide to be formed is small, the specific resistance is increased, and the density of the grain boundary bonding portion is lowered, so that the grain boundary oxidation easily proceeds and the oxidation resistance is lowered.
[0013]
On the other hand, the pore characteristics of the porous conductive silicon carbide sintered body of the present invention are in the range of average pore diameter of 5 to 40 μm, and if it is smaller than 5 μm, clogging of combustible fine particles becomes conspicuous and pressure loss occurs in a short time. Becomes larger. Also, if the pore diameter exceeds 40 μm, the collection efficiency decreases and the filter function decreases. Further, the porosity is in the range of 40% or more, preferably 50 to 80%. When the porosity is lower than 40%, the pressure loss is high, and when it exceeds 80%, the mechanical strength is lowered.
[0014]
As a production method for obtaining the above porous conductive silicon carbide sintered body, the average particle size and the particle size distribution of the α-type silicon carbide powder as a starting material are important and affect the pore characteristics of the sintered body. That is, the average particle size of α-type silicon carbide as a starting material is 5 to 50 μm, and the particle size ratio of the cumulative particle size distribution of 10% diameter to 50% diameter (D 10 / D 50 ) must be 0.2 or more. is there. That is, when the average particle size is smaller than 5 μm, or when the particle size ratio (D 10 / D 50 ) of the particle size distribution is less than 0.2, the pore size of the sintered body becomes small. On the other hand, when the average particle size exceeds 50 μm, the mechanical strength of the sintered body decreases. As the metal silicon powder, ordinary industrial metal silicon is sufficient, and the average particle size is preferably 100 μm or less from the viewpoint of formability and reactivity with the carbonaceous material. Further, as the carbonaceous material, in addition to fine solid carbon powders such as carbon black and acetylene black, organic resins such as phenol, furan, polyimide and the like which are thermally decomposed to become carbon can be used.
[0015]
The blending of these starting materials is 20 to 80% by weight of α-type silicon carbide powder and 80 to 20% by weight of mixed powder of metal silicon powder and carbonaceous material. The compounding ratio of the metal silicon powder and the carbonaceous material at this time is such that the molar ratio of metal silicon to carbon is in the range of 1.0 to 2.0. If this molar ratio is less than 1.0, carbon remains in the sintered body and inhibits the sintering of the reaction-generated βSiC. On the other hand, if it exceeds 2.0, the remaining metallic silicon is large and the mechanical strength and oxidation resistance are lowered.
[0016]
As a mixing method of these raw material powders, any mixing method can be applied as long as it is a method capable of uniformly mixing such as dry type and wet mixing. The mixed raw material can be molded by adding an organic binder such as methyl cellulose and polyvinyl alcohol, press molding, extrusion molding, injection molding, or by adjusting the slurry and injecting and solidifying into a container having a desired shape.
[0017]
Next, a firing method of the obtained molded body is first (1) high optional up to temperature N 2 partial pressure of even 1100 ° C. ~ 1800 ° C. the temperature of 400 ° C. and is in a non-oxidizing atmosphere above 0.2 atm At 600 ° C / hr or less. The molded body is degreased as necessary depending on the type of the binder, but it may be preferable to perform the degreasing in an oxidizing atmosphere. At a temperature of at least 400 ° C., the N 2 partial pressure is 0.2 atm or more. Although it is necessary to heat in an atmosphere, it is not always necessary to be in a non-oxidizing atmosphere at a temperature below 400 ° C. When the N 2 partial pressure is less than 0.2 atm, nitriding of metal silicon is insufficient, and the specific resistance of the sintered body obtained by carbonization increases. Similarly, when the temperature rising rate exceeds 600 ° C./hr, nitriding is insufficient and the specific resistance increases. Further, when the temperature of the nitriding reaction is less than 1100 ° C., the nitriding reaction does not occur, and when it exceeds 1800 ° C., the generated silicon nitride is converted into silicon carbide, and the sintered body obtained under such conditions has a pore size. It is small and the oxidation resistance is lowered.
[0018]
Next, the formed body formed of silicon nitride is (2) in a non-oxidizing atmosphere with a N 2 partial pressure of less than 0.2 atm, at a heating rate of 600 ° C./hr or less, at 1500 ° C. or higher and above (1) the maximum temperature. Heat to the temperature of. Preferably it is 1800 ° C or higher, more preferably 1900 ° C or higher. The non-oxidizing atmosphere having a N 2 partial pressure of less than 0.2 atm can be a vacuum or a mixed gas atmosphere of nitrogen and argon, carbon monoxide, ammonia, methane, hydrogen, and the like. If the temperature in this step is 1500 ° C. or lower than the maximum temperature in step (1), carbonization is insufficient and silicon nitride remains and the specific resistance increases.
[0019]
The use of the conductive silicon carbide sintered body of the present invention is a porous conductive silicon carbide sintered body having a porosity of 40% or more, an average pore diameter of 5 to 40 μm, and a room temperature resistivity of 10 Ω · cm or less. Therefore, it is optimal as a conductive filter to which a heater performance capable of collecting and combusting combustible fine particles discharged from a diesel engine is added. On the other hand, these characteristics are also suitable as a heater for a hot air generator used as a heat source for a duct heater or a large dryer from the viewpoint of increasing the heat generation area and increasing the thermal efficiency. Furthermore, it can be sufficiently used as a heater used in ordinary heating equipment, cooking equipment, drying equipment, baking furnaces and the like.
[0020]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples.
[0021]
(Examples 1-7 and Comparative Examples 1-10)
100 parts by weight of a raw material in which silicon carbide powder having a particle size (average particle size, particle size distribution particle size ratio) shown in Table 1 and a mixed powder of industrial metal silicon powder and carbon black are blended as shown in Table 1 as a starting material Further, 20 parts by weight of water and 8.0 parts by weight of methylcellulose as a binder were further added, mixed for 10 minutes with a Henschel mixer, and then kneaded for 30 minutes using a kneader-type kneader. The obtained kneaded product was extruded using a high pressure vacuum extrusion molding machine at a molding pressure of 60 kg / cm 2 with a honeycomb having an outer diameter of □ 50 mm, a cell size of 2.5 mm, and a rib pressure of 0.5 mm. The obtained molded body was dried, degreased at 450 ° C. for 1 hour in a nitrogen atmosphere, nitrided under the calcination conditions in the nitriding reaction column shown in Table 2, and then carbonized under the calcination conditions in the carbonization reaction column.
[0022]
The obtained sintered body was measured for the following characteristics and shown in Table 3.
(1) Porosity: Archimedes method.
(2) Average pore size: Mercury intrusion method.
(3) Identification of silicon carbide crystal phase: X-ray diffraction was performed and calculated by the following formula.
α-type silicon carbide content (volume%) = 100− {β-type silicon carbide content (volume%)}
However, β-type silicon carbide content (volume%) = 100 / (1 + a + b)
a = 4.571 Ia / (100-2.721 Ia-0.665 Ib)
b = 2.531 Ib / (100-2.721 Ia-0.665 Ib)
Here, Ia is the peak intensity at CuKα 2θ of 34.3 °, Ib is the peak intensity at 34.9 °, and is a relative value when the peak intensity at CuKα2θ = 36.5 ° is 100.
(4) Specific resistance at room temperature: The honeycomb structure was cut into □ 10 × 50mm L, a silver electrode was formed, and measured by the 4-terminal method.
(5) Oxidation resistance: The specific resistance after treatment in the atmosphere at a temperature of 1000 ° C. for 100 hours was measured.
(6) Mechanical strength: The honeycomb structure was cut into □ 10 × 10 mm L, and the compressive strength in the extrusion direction was measured.
[0023]
[Table 1]
[Table 2]
[Table 3]
As is apparent from Tables 1 to 3, the conductive porous silicon carbide sintered bodies obtained in Examples 1 to 7 have a suitable porosity and average pore diameter, and have a low room temperature specific resistance and excellent conductivity. As well as excellent compressive strength and oxidation resistance. The evaluation results of these sintered compacts as conductive diesel particulate filters, that is, the collection efficiency and the heat removal performance of the collected fine particles are good, and they have excellent characteristics as diesel particulate filters. there were.
[0027]
【The invention's effect】
According to the method for producing a conductive silicon carbide sintered body of the present invention, a porous conductive material having excellent conductivity and oxidation resistance and having an optimum porosity and pore diameter as a filter without adding a conductivity-imparting material. A silicon carbide sintered body is provided. In addition, the use of the porous conductive silicon carbide sintered body of the present invention is particularly applicable as a conductive diesel particulate filter having heater performance for collecting and burning incinerated fine particles discharged from a diesel engine. From the viewpoint of greatly increasing heat efficiency, it is suitable as a heater for hot air generators used as a heat source for duct heaters and large dryers, and as a heater used for heating equipment, cooking equipment, drying equipment, baking furnaces, etc. Yes.
Claims (3)
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP02038195A JP3681780B2 (en) | 1995-02-08 | 1995-02-08 | Porous conductive silicon carbide sintered body, its production method and use |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP02038195A JP3681780B2 (en) | 1995-02-08 | 1995-02-08 | Porous conductive silicon carbide sintered body, its production method and use |
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| Publication Number | Publication Date |
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| JPH08217565A JPH08217565A (en) | 1996-08-27 |
| JP3681780B2 true JP3681780B2 (en) | 2005-08-10 |
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Families Citing this family (15)
| Publication number | Priority date | Publication date | Assignee | Title |
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| WO2001023069A1 (en) | 1999-09-29 | 2001-04-05 | Ibiden Co., Ltd. | Honeycomb filter and ceramic filter assembly |
| JP4307781B2 (en) * | 2001-03-30 | 2009-08-05 | 日本碍子株式会社 | Silicon carbide based porous material and method for producing the same |
| EP1767508B1 (en) | 2005-02-04 | 2010-02-24 | Ibiden Co., Ltd. | Ceramic honeycomb structure |
| WO2006082938A1 (en) * | 2005-02-04 | 2006-08-10 | Ibiden Co., Ltd. | Ceramic honeycomb structure and method for manufacture thereof |
| FR2910468B1 (en) * | 2006-12-21 | 2009-02-06 | Saint Gobain Ct Recherches | PROCESS FOR OBTAINING A POROUS STRUCTURE BASED ON SILICON CARBIDE |
| JP5076192B2 (en) | 2007-01-12 | 2012-11-21 | 国立大学法人 岡山大学 | Catalyst and method for purifying nitrogen oxides in diesel engine exhaust gas using unburned carbon |
| JP2009012005A (en) * | 2008-08-11 | 2009-01-22 | Ibiden Co Ltd | Honeycomb filter and filter aggregate |
| JP2009019634A (en) * | 2008-08-11 | 2009-01-29 | Ibiden Co Ltd | Exhaust emission control device |
| JP5643575B2 (en) * | 2010-08-27 | 2014-12-17 | 東京窯業株式会社 | Method for producing silicon carbide porous body |
| JP5630333B2 (en) * | 2011-03-08 | 2014-11-26 | 信越化学工業株式会社 | Sinterable silicon carbide powder and sintered silicon carbide ceramics |
| JP2016067995A (en) * | 2014-09-29 | 2016-05-09 | イビデン株式会社 | Honeycomb filter and manufacturing method for the same |
| JP6291446B2 (en) * | 2015-03-26 | 2018-03-14 | 東京窯業株式会社 | Method for producing conductive silicon carbide sintered body |
| JP6387128B2 (en) * | 2016-03-25 | 2018-09-05 | 東京窯業株式会社 | Method for producing conductive silicon carbide sintered body and conductive silicon carbide sintered body |
| JP7153684B2 (en) * | 2020-03-25 | 2022-10-14 | 日本碍子株式会社 | Manufacturing method of honeycomb structure containing silicon carbide |
| JP2023135116A (en) * | 2022-03-15 | 2023-09-28 | 日本碍子株式会社 | Composite sintered body, honeycomb structure, electric heating catalyst, and manufacturing method of composite sintered body |
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