JP4037969B2 - Graphite products using boron carbide-coated silicon carbide-carbon composites - Google Patents
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
- C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
- C04B41/52—Multiple coating or impregnating multiple coating or impregnating with the same composition or with compositions only differing in the concentration of the constituents, is classified as single coating or impregnation
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Description
【０００１】
【発明の属する技術分野】
本発明は、高温酸化雰囲気化で使用される窒化ホウ素を被覆した炭化ケイ素ー炭素複合材を用いたホットプレス用黒鉛ダイス、連続鋳造用ダイス、金属溶解用ルツボ、セラミックス焼結用ルツボ等の黒鉛製品に関する。
【０００２】
【従来の技術】
炭素材料は、高温での優れた特性のため、ホットプレス用黒鉛ダイス、連続鋳造用ダイス、金属溶解用ルツボ、セラミックス焼結用ルツボ等の耐熱用材料として広く利用されている。
【０００３】
しかしながら、炭素材は高温酸化雰囲気中で酸化消耗しやすいという欠点を持っており、また、還元雰囲気下でも、前記各種用途に利用されている際に、その被処理物と反応したり、炭素自身から発生するガスにより、被処理物に悪影響を及ぼす場合などがあり、炭素材の酸化防止のため従来から色々と工夫がなされてきた。
【０００４】
本発明者らは、こうした炭素材の欠点を補うために、炭素基材表面に、ケイ素粉末と炭化ホウ素（Ｂ4 Ｃ）粉末と熱可塑性樹脂からなるスラリーを塗布し、熱処理することにより炭素基材の表面に炭化ケイ素ー炭素複合層を深めに形成し、さらにその表面に炭化ホウ素ー炭化ケイ素ー炭素複合層（Ｂ4 ＣーＳｉＣーＣ複合層）が形成してなる、耐酸化性に優れた炭素製品の作製方法を開発し、出願した（特開平７─１４４９８２号）。
【０００５】
先の出願の発明によるＢ4 ＣーＳｉＣーＣ複合層は、酸化雰囲気で使用した場合、最外表層部のＢ4 ＣーＳｉＣーＣ複合層のＢ4 Ｃ、ＳｉＣの一部がホウケイ酸ガラス層を形成し、このホウケイ酸ガラスが酸化保護膜の働きをし、耐酸化性の向上に寄与していた。
【０００６】
【発明が解決しようとする課題】
ところが、金属溶解用ルツボや、セラミックス焼結用ルツボ、連続鋳造用ダイス等の、金属やセラミックス等の被処理物と接触する面にこのＢ4 ＣーＳｉＣーＣ複合層を形成した場合、最外表層部に形成されるこのホウケイ酸ガラスが容易に被処理物である金属と反応してしまい、被処理物が冷却後にルツボやダイスの内面に固着してしまうという問題が発生した。
【０００７】
【課題を解決するための手段】
本発明者らは、この問題を解決すべく、先願である特開平７─１４４９８２号の技術の改良に取り組み、鋭意研究を重ね、形成されたＢ4 ＣーＳｉＣーＣ複合層の上に窒化ホウ素（ＢＮ）を含む層を被覆することが有効であることを見出し本発明を完成させるにいたった。
【０００８】
すなわち、本発明の請求項１に記載の発明は、黒鉛基材の表層部に炭化ケイ素−炭素複合層が形成してなり、該炭化ケイ素−炭素複合材の表面に炭化ホウ素−炭化ケイ素−炭素複合層が形成してなり、さらにその表面に窒化ホウ素とガラス状炭素との複合層が被覆されてなることを特徴とする窒化ホウ素を被覆した炭化ケイ素−炭素複合材を用いた黒鉛製品である。
【０００９】
請求項２に記載の発明は、前記炭化ケイ素−炭素複合層は、黒鉛基材表面から深さ方向に１ｍｍ以上の厚みで均一に形成されてなり、その表面に厚さ１０〜１５μｍの耐酸化性を有した炭化ホウ素−炭化ケイ素−炭素複合層が形成されてなり、さらにその上に３〜２０μｍの厚みの窒化ホウ素とガラス状炭素との複合層が被覆されてなることを特徴とする請求項１に記載の窒化ホウ素を被覆した炭化ケイ素−炭素複合材を用いた黒鉛製品である。
【００１１】
本発明による黒鉛製品は、最表層部を緻密で滑らかな表面のＢＮーＣ複合層により被覆されてなり、第２層目にはＢ4 ＣーＳｉＣーＣ複合層、第３層目には深さ方向に略均一な厚みでＳｉＣーＣ複合層が形成されている。この第２層であるＢ4 ＣーＳｉＣーＣ複合層は粗い表面であるため、最表層部のＢＮーＣ複合層はアンカー効果の作用を受けて、強固に付着している。この最表層のＢＮーＣ複合層の炭素は、樹脂が熱処理後に、ガラス状炭素に変化したものである。これにより、緻密な皮膜が表面を覆うことになり、黒鉛基材からのガスの発生を抑制できる。また、表面はガラス状炭素の特性である潤滑性を有した非常に滑らかな面となり、窒化ホウ素自身の持つ潤滑性と併せ、非常に優れた潤滑性を有する表面となっている。
【００１２】
最表層部のＢＮーＣ複合層は３〜２０μｍの厚みで形成されている。ガラス状炭素の特性を生かし、滑らかな表面にするためには少なくとも３μｍ以上の厚みが必要であり、２０μｍ以上形成すると、剥離する恐れが出てくる。そのため、最表層部のＢＮーＣ複合層の厚みは３〜２０μｍの範囲、望ましくは５〜１０μｍがよい。また、第２層目のＢ4 ＣーＳｉＣーＣ複合層は、耐酸化性を付与させるためにも少なくとも１０μｍ以上必要である。この耐酸化性はこの層に含まれるＢ4 ＣとＳｉＣから形成されるホウケイ酸ガラスが表面を覆うことにより向上していると推測されるが、この層が１５μｍ以上の場合、このホウケイ酸ガラスも厚く形成され、この層の上に形成されるＢＮーＣ複合層の、この層への付着力が弱くなり、最表層部の剥離の恐れもでてくる。第３層目は、黒鉛基材の気孔を埋めるとともに、第１層、第２層目が酸化等の原因で無くなった場合に、黒鉛基材の急激な酸化を防止するためにも、少なくとも１ｍｍ以上の厚みが必要である。
【００１３】
最表層部はガラス状炭素の有する特性により、非常に滑らかな表面となっており、熱処理後に摩擦面などの研摩、機械加工が不要となる。これによって、ホットプレス用黒鉛基材等として優れた特性を示す。また、金属溶解用ルツボやセラミックス焼結用ルツボ内面に、このＢＮーＣ複合層を形成させることにより、被処理物とルツボとの反応が防止できることになる。また、ＢＮーＣ複合層膜が第２層にアンカー効果の作用を受けて強固に付着しているため、処理後に再塗膜する必要がなく、仮に酸化等により一部が除去された場合でも、このＢＮーＣ複合層膜の下部に形成されてなるＢ4 ＣーＳｉＣーＣ複合層と、ＳｉＣーＣ複合層が、酸化性の元素の黒鉛基材への侵入を抑制する効果を発揮する。
【００１４】
このＢＮーＣ複合層が形成されていない場合で、例えば、ホットプレス用ダイスの場合、その処理時にダイスとポンチが固着し、処理後ダイスからポンチの取り除きや、製品の取り出しができないなどの問題が発生する場合がある。金属溶解用ルツボの場合や、セラミックス焼結用ルツボの場合、被処理物がルツボに固着してしまい、一度の処理でルツボを交換しなくてはいけなくなり、ルツボの短命化の原因となってしまう。また、Ｂ4 ＣーＳｉＣーＣ複合層、ＳｉＣーＣ複合層が無い場合は、最表層のＢＮーＣ複合層が熱履歴を受けると容易に剥離してしまう。
【００１５】
本発明に使用する黒鉛基材は特に限定されるものではなく、例えば高密度等方性黒鉛材等が挙げられ、これらのうち水銀圧入法で測定した平均細孔半径が１μｍ以上である黒鉛基材を製品形状に加工したものを使用する事が望ましい。
【００１６】
平均細孔半径が１μｍよりも小さい黒鉛基材を使用すると、ＳｉとＢ4 Ｃを混合したスラリーを基材に塗布する時に、基材の微小細孔にまでスラリーが浸透しにくくなり、層の剥離が生じ易くなるためあまり望ましくない。なお、黒鉛基材の平均細孔半径の上限については、特に制限はなく、炭素繊維強化炭素複合材料等の平均細孔半径が大きい炭素基材は、炭素基材内部奥深くまでスラリーが浸透するため、熱処理後にほぼ全体が複合化したものになる。
【００１７】
まず、平均粒径１０〜５０μｍの金属Ｓｉ粉末、平均粒径４〜５０μｍのＢ4 Ｃ粉末、熱可塑性樹脂及びその樹脂の溶媒からなるスラリーを準備する。ここで使用する熱可塑性樹脂は造膜性が高く、かつ残炭率が低い樹脂を使用し、例えばポリアミドイミド、ポリビニルアルコール、ポリアミド樹脂の内より選ばれたものが特に好ましい。中でもポリアミドが更に望ましく、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキサイド、Ｎメチル─２─ピロリドン等の溶媒に溶解させて使用する。
【００１８】
しかしながら、樹脂として残炭率の高い樹脂、例えばフルフリルアルコール、フェノール樹脂等の熱硬化性樹脂を使用すると、後の工程で高温熱処理を行ったときに炭素基材の表面に樹脂の炭化物、Ｓｉ及びＢ4 Ｃとの反応生成物が固着して、これらを容易に除去できなくなることがあるため好ましくない。
【００１９】
Ｓｉ粉末とＢ4 Ｃ粉末を混合する際の混合割合は、Ｓｉ粉末８０〜９７重量％に対してＢ4 Ｃ粉末３〜２０重量％が望ましい。Ｂ4 Ｃ粉末が３重量％未満では、Ｂ4 Ｃ粉末の混合による効果が少ないからである。具体的には、Ｂ4 Ｃ粉末を混合することにより、Ｓｉの炭素材に対する触媒効果が向上するが、３重量％未満では、この触媒効果があまり向上せず、高温熱処理後も溶融Ｓｉが炭素基材中の気孔に完全に浸透せず、冷却後黒鉛基材表面に金属Ｓｉとして固着した状態で残ってしまう。逆に３重量％以上含有させた場合は、溶融Ｓｉが気孔中に深くまで浸透し、黒鉛基材との反応が進み、ＳｉＣ化され、深さ方向に均一なＳｉＣ層が形成されやすくなるという効果が得られるからである。
【００２０】
上記のように調製されたスラリーをはけ塗り、へら塗り等の適宜な手段で表面全体、又は必要な部分に塗布する。また、スラリー中に浸漬しても良い。この時に塗布する厚みについては、任意の厚みとすることができるが黒鉛基材表面から１〜２ｍｍ程度が望ましい。１００μｍ未満では複合層の形成が浅くなるのであまり好ましくない。この後、約８０℃〜２００℃で１〜２時間程度乾燥することにより、溶媒を揮散させ、樹脂を完全に硬化させる。こうして得られた材料を、１０Ｔｏｒｒ以下の真空で高温熱処理する。処理温度は約１６００〜１８００℃で１〜２時間保持する。加熱手段は特に限定されるものではなく、適当な手段で行えばよい。この操作によって、Ｓｉ成分は溶融し、樹脂の炭化層を通って炭素基材の細孔中に侵入し、炭素と反応してＳｉＣ化する。
【００２１】
前記の一連の処理を得て、スラリーが塗布された部分に相当する基材の表層部がＢ4 ＣーＳｉＣーＣ複合層、ＳｉＣーＣ複合層に転化した緻密な層を得ることができる。
【００２２】
前記のようにして得られたＢ4 ＣーＳｉＣーＣ複合層、ＳｉＣーＣ複合層の上に、ＢＮ粉末、熱可塑性樹脂と溶剤を混合した混合液をスプレーや刷毛などの適宜な方法で塗布する。使用する樹脂は前記Ｂ4 ＣーＳｉＣーＣ複合層、ＳｉＣーＣ複合層を形成させるに使用した樹脂と同様、造膜性が高く残炭率が低い樹脂、例えば、ポリアミドイミド、ポリビニルアルコール、ポリアミド樹脂の内より選ばれたものが特に好ましい。中でもポリアミドが更に望ましく、ジメチルアセトアミド、ジメチルホルムアミド、ジメチルスルホキサイド、Ｎメチル─２─ピロリドン等の溶媒に溶解させて使用する。その後、乾燥機で８０℃〜２００℃で樹脂を硬化させる。次に真空雰囲気下で、１２００℃以上まで徐々に昇温し熱処理を行う。この処理により、樹脂は炭素化され、ガラス状炭素となり、緻密なＢＮーＣ複合層が形成される。また、第２層のＢ4 ＣーＳｉＣーＣ複合層の表面が粗いため、アンカー効果が作用し、強固に付着する。形成されたＢＮーＣ複合層の表面は非常に滑らかな表面となる。これにより、ホットプレス用ダイスや、連続鋳造用ダイスや、金属溶解用ルツボや、セラミックス焼結用ルツボ等に適用できる。
【００２３】
以下に実施例により本発明を説明する。
（実施例１）
炭素基材として、嵩密度１．９５ｇ／ｃｍ3 、平均細孔半径が０．３μm 、曲げ強度が６９０ｋｇｆ／ｃｍ2 の等方性黒鉛（東洋炭素( 株）製) を、内径１００ｍｍ、深さ９０ｍｍのルツボに加工した。また、バインダーとしてのポリビニールアルコール（日本合成産業（株）製）８％溶液を分散媒とした。Ｓｉ粉末（和光純薬工業製、平均粒度４０μｍ）と、Ｂ4 Ｃ粉末（共立窯業社製、平均粒径３０μｍ）を重量比で８０：２０の比率に混合し、分散媒中に混合分散させてスラリーとした。
【００２４】
このスラリーを、ルツボ内面全体に刷毛で厚みが約２ｍｍになるよう塗布し、乾燥機の中で２００℃、１時間で溶媒を蒸発させ、さらに３Ｔｏｒｒの窒素ガス雰囲気下、真空加熱炉において１８００℃まで４時間で昇温し、３０分間保持した後、冷却して取り出した。この一連の処理を行うことにより、黒鉛基材の表面層にＢ4 ＣーＳｉＣーＣ複合層、ＳｉＣーＣ複合層が形成される。
【００２５】
このＢ4 ＣーＳｉＣーＣ複合層の表面に樹脂（カーボンコート剤、ＡＣ−５０１５（日清紡製））と、ＢＮ粉末（平均粒径１〜５μｍ）を重量比で５０：５０の比率で混合し、スプレーで塗布した。塗布厚みは約５μｍである。塗布後、乾燥機で８０℃から２００℃で樹脂を硬化させ、２Ｔｏｒｒの真空雰囲気下で１８００℃まで５時間で昇温し、２時間保持して樹脂を炭化させ、ＢＮーＣ複合層を形成させた。このルツボに、鋳塊を入れ、１６００℃に加熱し、鋳鉄の溶解試験を行った。
【００２６】
（比較例１）
実施例１と同質の黒鉛基材を同形状に加工し、実施例１と同様な手順でルツボ内面にＢ4 ＣーＳｉＣーＣ複合層、ＳｉＣーＣ複合層を形成させ、実施例１と同様に、鋳塊を入れ、溶解試験を行った。
【００２７】
（比較例２）
実施例１と同質の黒鉛基材を、同形状のルツボに加工後、実施例１同様に、鋳塊を入れ、溶解試験を行った。
【００２８】
実施例１は３５回の溶解試験にもかかわらず、鋳鉄の固着がほとんど無く、また、ルツボの割れ、鋳鉄による腐食等のルツボの交換原因となる問題点の発生が確認されなかった。
【００２９】
比較例１は１０回の試験時点で、鋳鉄による腐食は確認されなかったが、鋳鉄の固着が確認された。また、黒鉛基材のみの比較例２では１〜２回の試験時点で、鋳鉄による腐食、及び鋳鉄の固着が確認された。
【００３０】
【発明の効果】
本発明は以上のように構成されており、容易に且つ安価に、黒鉛基材表面の任意の場所に、炭化ケイ素−炭素複合層、窒化ホウ素−炭素複合層を形成させることが可能であり、潤滑性、耐摩耗性、耐酸化性に優れた滑らかな被覆面を形成でき、最終機械加工を省略する事が可能となる。また、ホットプレス用ダイスや、金属溶解用やセラミックス焼結用ルツボ、連続鋳造用ダイス等の各種黒鉛製品の寿命の延命効果が得られる。さらに、この最表層のＢＮーＣ複合層の炭素は、樹脂が熱処理後に、ガラス状炭素に変化したものであり、これにより、緻密な皮膜が表面を覆うことになり、黒鉛基材からのガスの発生を抑制できる。そして、表面はガラス状炭素の特性である潤滑性を有した非常に滑らかな面となり、窒化ホウ素自身の持つ潤滑性と併せ、非常に優れた潤滑性を有する表面となっている。 [0001]
BACKGROUND OF THE INVENTION
The present invention relates to graphite for hot pressing, die for continuous casting, crucible for melting metal, crucible for sintering ceramics, etc., using a boron carbide-coated silicon carbide-carbon composite material used in a high-temperature oxidizing atmosphere. Regarding products.
[0002]
[Prior art]
Carbon materials are widely used as heat-resistant materials such as graphite dies for hot pressing, dies for continuous casting, crucibles for melting metals, and crucibles for sintering ceramics because of their excellent properties at high temperatures.
[0003]
However, the carbon material has a drawback that it is easily oxidized and consumed in a high-temperature oxidizing atmosphere, and also reacts with the material to be treated when used in the various applications even under a reducing atmosphere, or the carbon itself. In some cases, various gases have been devised in order to prevent the carbon material from being oxidized.
[0004]
In order to compensate for the drawbacks of such carbon materials, the inventors apply a slurry comprising silicon powder, boron carbide (B 4 C) powder, and a thermoplastic resin on the surface of the carbon substrate, and heat-treat the carbon base. A silicon carbide-carbon composite layer is formed deeper on the surface of the material, and a boron carbide-silicon carbide-carbon composite layer (B 4 C-SiC-C composite layer) is further formed on the surface. A method for producing an excellent carbon product was developed and filed (Japanese Patent Laid-Open No. 7-144982).
[0005]
Above B 4 C over SiC over C composite layer according to the invention of application, when used in an oxidizing atmosphere, B 4 C in the outermost surface layer portion of the B 4 C over SiC over C composite layer, a portion of the SiC borosilicate A glass layer was formed, and this borosilicate glass served as an oxidation protective film, contributing to the improvement of oxidation resistance.
[0006]
[Problems to be solved by the invention]
However, when this B 4 C-SiC-C composite layer is formed on the surface that comes into contact with the workpiece such as metal or ceramics, such as a crucible for melting metal, a crucible for sintering ceramics, a die for continuous casting, etc. This borosilicate glass formed on the outer surface layer easily reacts with the metal that is the object to be processed, and the object to be processed adheres to the inner surface of the crucible or die after cooling.
[0007]
[Means for Solving the Problems]
In order to solve this problem, the present inventors have worked on improving the technology of Japanese Patent Application Laid-Open No. 7-144882, which is a prior application, and conducted extensive research, on the formed B 4 C—SiC—C composite layer. It has been found that it is effective to coat a layer containing boron nitride (BN), and the present invention has been completed.
[0008]
That is, according to the first aspect of the present invention, a silicon carbide-carbon composite layer is formed on the surface portion of a graphite substrate, and boron carbide-silicon carbide-carbon is formed on the surface of the silicon carbide-carbon composite material. A graphite product using a silicon carbide-carbon composite material coated with boron nitride, characterized in that a composite layer is formed, and further a composite layer of boron nitride and glassy carbon is coated on the surface thereof. .
[0009]
According to a second aspect of the present invention, the silicon carbide-carbon composite layer is uniformly formed with a thickness of 1 mm or more in the depth direction from the surface of the graphite substrate, and the surface thereof has an oxidation resistance of 10 to 15 μm. A boron carbide-silicon carbide-carbon composite layer having properties is formed, and a composite layer of boron nitride and glassy carbon having a thickness of 3 to 20 μm is further coated thereon. A graphite product using the silicon carbide-carbon composite material coated with boron nitride according to Item 1.
[0011]
In the graphite product according to the present invention, the outermost layer portion is covered with a BN-C composite layer having a dense and smooth surface. The second layer is a B 4 C-SiC-C composite layer, and the third layer is The SiC-C composite layer is formed with a substantially uniform thickness in the depth direction. Since the B 4 C—SiC—C composite layer, which is the second layer, has a rough surface, the BN—C composite layer at the outermost layer portion is firmly adhered to each other due to the action of the anchor effect. The carbon of the outermost BN-C composite layer is one in which the resin is changed to glassy carbon after heat treatment. Thereby, the dense film covers the surface, and the generation of gas from the graphite base material can be suppressed. Further, the surface is a very smooth surface having the lubricity that is a characteristic of glassy carbon, and the surface has a very excellent lubricity together with the lubricity of boron nitride itself.
[0012]
The outermost BN-C composite layer is formed with a thickness of 3 to 20 μm. In order to take advantage of the characteristics of glassy carbon and make a smooth surface, a thickness of at least 3 μm or more is required. Therefore, the thickness of the BN-C composite layer at the outermost layer is in the range of 3 to 20 μm, preferably 5 to 10 μm. Further, the second layer of B 4 C over SiC over C composite layer is required to be at least 10μm or more in order to impart oxidation resistance. This oxidation resistance is presumed to be improved by covering the surface with the borosilicate glass formed from B 4 C and SiC contained in this layer, but when this layer is 15 μm or more, this borosilicate glass The BN-C composite layer formed on this layer has a weak adhesion to this layer, and the outermost layer part may be peeled off. The third layer fills the pores of the graphite base material and also prevents the graphite base material from abruptly oxidizing when the first layer and the second layer disappear due to oxidation or the like. The above thickness is necessary.
[0013]
The outermost layer portion has a very smooth surface due to the properties of glassy carbon, so that polishing and machining such as a friction surface are not required after heat treatment. As a result, it exhibits excellent properties as a graphite substrate for hot pressing. Further, by forming the BN-C composite layer on the inner surface of the crucible for melting metal or the crucible for sintering ceramics, the reaction between the workpiece and the crucible can be prevented. In addition, since the BN-C composite layer film is firmly attached to the second layer due to the action of the anchor effect, there is no need to recoat the film after processing, even if a part is removed by oxidation or the like. The B 4 C-SiC-C composite layer formed under the BN-C composite layer film and the SiC-C composite layer exhibit the effect of suppressing the intrusion of the oxidizing element into the graphite substrate. To do.
[0014]
When this BN-C composite layer is not formed, for example, in the case of a hot press die, the die and the punch are fixed during the processing, and the punch cannot be removed from the die after the processing or the product cannot be taken out. May occur. In the case of a crucible for melting metal or a crucible for sintering ceramics, the object to be treated is fixed to the crucible, and the crucible must be replaced in a single process, which shortens the life of the crucible. End up. Further, when there is no B 4 C—SiC—C composite layer or SiC—C composite layer, the outermost BN—C composite layer is easily peeled off when subjected to a thermal history.
[0015]
The graphite base material used in the present invention is not particularly limited, and examples thereof include a high density isotropic graphite material, and among these, a graphite base having an average pore radius of 1 μm or more measured by a mercury intrusion method. It is desirable to use a material processed into a product shape.
[0016]
When a graphite base material having an average pore radius smaller than 1 μm is used, when the slurry in which Si and B 4 C are mixed is applied to the base material, it becomes difficult for the slurry to penetrate into the micropores of the base material. It is less desirable because it tends to cause peeling. In addition, there is no restriction | limiting in particular about the upper limit of the average pore radius of a graphite base material, since a carbon base material with a large average pore radius, such as a carbon fiber reinforced carbon composite material, permeates deep inside the carbon base material. After heat treatment, the whole becomes a composite.
[0017]
First, a slurry comprising a metal Si powder having an average particle size of 10 to 50 μm, a B 4 C powder having an average particle size of 4 to 50 μm, a thermoplastic resin, and a solvent for the resin is prepared. As the thermoplastic resin used here, a resin having a high film forming property and a low residual carbon ratio is used. For example, a resin selected from polyamide imide, polyvinyl alcohol, and polyamide resin is particularly preferable. Of these, polyamide is more preferable, and it is used after being dissolved in a solvent such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methyl-2-pyrrolidone.
[0018]
However, if a resin having a high residual carbon ratio, for example, a thermosetting resin such as furfuryl alcohol or phenol resin is used as the resin, the resin carbide or Si on the surface of the carbon substrate when high-temperature heat treatment is performed in a later step. And the reaction product with B 4 C is not preferable because it may be fixed and cannot be easily removed.
[0019]
The mixing ratio when mixing the Si powder and the B 4 C powder is preferably 3 to 20% by weight of the B 4 C powder with respect to 80 to 97% by weight of the Si powder. This is because if the B 4 C powder is less than 3% by weight, the effect of mixing the B 4 C powder is small. Specifically, by mixing B 4 C powder, the catalytic effect of Si on the carbon material is improved. However, if it is less than 3% by weight, this catalytic effect is not improved so much, and even after high-temperature heat treatment, the molten Si is carbon. It does not completely penetrate into the pores in the substrate, and remains in a state of being fixed as metal Si on the surface of the graphite substrate after cooling. On the other hand, when 3% by weight or more is contained, molten Si penetrates deeply into the pores, the reaction with the graphite substrate proceeds, SiC is formed, and a uniform SiC layer is easily formed in the depth direction. This is because an effect can be obtained.
[0020]
The slurry prepared as described above is applied to the entire surface or a necessary portion by an appropriate means such as brushing or spatula coating. Moreover, you may immerse in a slurry. The thickness applied at this time may be any thickness, but is preferably about 1 to 2 mm from the surface of the graphite substrate. If the thickness is less than 100 μm, formation of the composite layer becomes shallow, which is not preferable. Thereafter, by drying for about 1 to 2 hours at about 80 ° C. to 200 DEG ° C., the solvent was stripped and allowed to fully cure the resin. The material thus obtained is heat-treated at a high temperature in a vacuum of 10 Torr or less. The processing temperature is maintained at about 1600-1800 ° C. for 1-2 hours. The heating means is not particularly limited and may be performed by an appropriate means. By this operation, the Si component melts, penetrates into the pores of the carbon base material through the carbonized layer of the resin, and reacts with carbon to form SiC.
[0021]
By obtaining the above-described series of treatments, it is possible to obtain a dense layer in which the surface layer portion of the substrate corresponding to the portion where the slurry is applied is converted into a B 4 C—SiC—C composite layer or a SiC—C composite layer. .
[0022]
On the B 4 C—SiC—C composite layer and SiC—C composite layer obtained as described above, a mixed liquid obtained by mixing BN powder, a thermoplastic resin and a solvent is applied by an appropriate method such as spraying or brushing. Apply. The resin used is the same as the resin used for forming the B 4 C—SiC—C composite layer and the SiC—C composite layer, such as a resin having a high film forming property and a low residual carbon ratio, such as polyamide imide, polyvinyl alcohol, Those selected from polyamide resins are particularly preferred. Of these, polyamide is more preferable, and it is used after being dissolved in a solvent such as dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-methyl-2-pyrrolidone. Thereafter, to cure the tree fat at 80 ° C. to 200 DEG ° C. in a dryer. Next, heat treatment is performed by gradually raising the temperature to 1200 ° C. or higher in a vacuum atmosphere. By this treatment, the resin is carbonized to become glassy carbon, and a dense BN—C composite layer is formed. Further, since the surface of the B 4 C—SiC—C composite layer of the second layer is rough, the anchor effect acts and adheres firmly. The surface of the formed BN-C composite layer becomes a very smooth surface. Accordingly, the present invention can be applied to hot pressing dies, continuous casting dies, metal melting crucibles, ceramic sintering crucibles, and the like.
[0023]
The following examples illustrate the invention.
Example 1
As a carbon substrate, isotropic graphite (manufactured by Toyo Tanso Co., Ltd.) having a bulk density of 1.95 g / cm 3 , an average pore radius of 0.3 μm and a bending strength of 690 kgf / cm 2 , an inner diameter of 100 mm, a depth Processed into a 90 mm crucible. Moreover, 8% solution of polyvinyl alcohol (manufactured by Nippon Synthetic Sangyo Co., Ltd.) as a binder was used as a dispersion medium. Si powder (manufactured by Wako Pure Chemical Industries, average particle size 40 μm) and B 4 C powder (manufactured by Kyoritsu Ceramics Co., Ltd., average particle size 30 μm) are mixed at a weight ratio of 80:20 and mixed and dispersed in a dispersion medium. To make a slurry.
[0024]
This slurry was applied to the entire inner surface of the crucible with a brush to a thickness of about 2 mm, the solvent was evaporated in a dryer at 200 ° C. for 1 hour, and further 1800 ° C. in a vacuum heating furnace under a nitrogen gas atmosphere of 3 Torr. The temperature was raised to 4 hours and held for 30 minutes, and then cooled and taken out. By performing this series of treatments, a B 4 C—SiC—C composite layer and a SiC—C composite layer are formed on the surface layer of the graphite substrate.
[0025]
A resin (carbon coating agent, AC-5015 (manufactured by Nisshinbo)) and BN powder (average particle size of 1 to 5 μm) are mixed at a weight ratio of 50:50 on the surface of the B 4 C—SiC—C composite layer. And applied by spray. The coating thickness is about 5 μm. After coating, the resin is cured at 200 ° C. from 80 ° C. in a dryer, the temperature was raised at 5 hours 1800 ° C. in a vacuum atmosphere of 2 Torr, and held for 2 hours the resin was carbonized, forming BN over C composite layer I let you. An ingot was put into this crucible and heated to 1600 ° C. to perform a cast iron dissolution test.
[0026]
(Comparative Example 1)
A graphite substrate of the same quality as in Example 1 was processed into the same shape, and a B 4 C—SiC—C composite layer and a SiC—C composite layer were formed on the inner surface of the crucible in the same procedure as in Example 1. Similarly, an ingot was put and a dissolution test was performed.
[0027]
(Comparative Example 2)
A graphite base material having the same quality as that of Example 1 was processed into a crucible having the same shape, and an ingot was placed in the same manner as in Example 1 to conduct a dissolution test.
[0028]
In Example 1, despite the 35 melting tests, there was almost no adhesion of cast iron, and no occurrence of problems causing crucible replacement such as crucible cracking or corrosion by cast iron was confirmed.
[0029]
In Comparative Example 1, corrosion due to cast iron was not confirmed at the time of 10 tests, but adhesion of cast iron was confirmed. Moreover, in the comparative example 2 only with a graphite base material, the corrosion by cast iron and the adhering of cast iron were confirmed in the test time of 1 to 2 times.
[0030]
【The invention's effect】
The present invention is configured as described above, and it is possible to easily and inexpensively form a silicon carbide-carbon composite layer and a boron nitride-carbon composite layer at an arbitrary location on the surface of the graphite substrate. A smooth coated surface excellent in lubricity, wear resistance, and oxidation resistance can be formed, and final machining can be omitted. Further, the life extension effect of various graphite products such as hot pressing dies, metal melting and ceramic sintering crucibles, and continuous casting dies can be obtained. Furthermore, the carbon of the outermost BN-C composite layer is a resin that has been changed to glassy carbon after the heat treatment. As a result, a dense film covers the surface, and the gas from the graphite substrate Can be suppressed. And the surface becomes a very smooth surface having the lubricity which is a characteristic of glassy carbon, and the surface has a very excellent lubricity together with the lubricity of boron nitride itself.
Claims (2)
該炭化ケイ素−炭素複合材の表面に炭化ホウ素−炭化ケイ素−炭素複合層が形成してなり、
さらにその表面に窒化ホウ素とガラス状炭素との複合層が被覆されてなることを特徴とする窒化ホウ素を被覆した炭化ケイ素−炭素複合材を用いた黒鉛製品。A silicon carbide-carbon composite layer is formed on the surface layer portion of the graphite substrate,
A boron carbide-silicon carbide-carbon composite layer is formed on the surface of the silicon carbide-carbon composite,
Further, a graphite product using a silicon carbide-carbon composite material coated with boron nitride, characterized in that a composite layer of boron nitride and glassy carbon is coated on the surface thereof.
その表面に厚さ１０〜１５μｍの耐酸化性を有した炭化ホウ素−炭化ケイ素−炭素複合層が形成されてなり、
さらにその上に３〜２０μｍの厚みの窒化ホウ素とガラス状炭素との複合層が被覆されてなることを特徴とする請求項１に記載の窒化ホウ素を被覆した炭化ケイ素−炭素複合材を用いた黒鉛製品。The silicon carbide-carbon composite layer is uniformly formed with a thickness of 1 mm or more in the depth direction from the surface of the graphite substrate,
A boron carbide-silicon carbide-carbon composite layer having an oxidation resistance of 10 to 15 μm in thickness is formed on the surface,
The boron nitride-coated silicon carbide-carbon composite material according to claim 1, wherein a composite layer of boron nitride and glassy carbon having a thickness of 3 to 20 µm is further coated thereon. Graphite products.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP32218398A JP4037969B2 (en) | 1998-06-09 | 1998-11-12 | Graphite products using boron carbide-coated silicon carbide-carbon composites |
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| JP10-160102 | 1998-06-09 | ||
| JP16010298 | 1998-06-09 | ||
| JP32218398A JP4037969B2 (en) | 1998-06-09 | 1998-11-12 | Graphite products using boron carbide-coated silicon carbide-carbon composites |
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| JP4037969B2 true JP4037969B2 (en) | 2008-01-23 |
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| JP5121521B2 (en) * | 2008-03-20 | 2013-01-16 | 三菱電機株式会社 | Ceramic-coated graphite and method for producing the same |
| CN112661536A (en) * | 2020-12-24 | 2021-04-16 | 江苏集芯半导体硅材料研究院有限公司 | Has SiC-ZrC-B4Heater for monocrystalline silicon furnace with C-BN composite coating and preparation method thereof |
| CN114538928B (en) * | 2022-04-25 | 2022-07-12 | 长沙中瓷新材料科技有限公司 | Graphite carbon-based sagger |
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| WO2020031879A1 (en) * | 2018-08-07 | 2020-02-13 | 新光機器株式会社 | Welding torch shield nozzle |
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