JP3616829B2

JP3616829B2 - Carbon-boron carbide sintered body, method for producing the same, and material using the sintered body

Info

Publication number: JP3616829B2
Application number: JP35413492A
Authority: JP
Inventors: 照生松田; 敏明曽我部
Original assignee: Toyo Tanso Co Ltd
Current assignee: Toyo Tanso Co Ltd
Priority date: 1991-12-20
Filing date: 1992-12-14
Publication date: 2005-02-02
Anticipated expiration: 2020-02-02
Also published as: JPH05246761A

Description

【０００１】
【産業上の利用分野】
本発明は、核融合炉内のプラズマ対向材や、機械用の耐酸化性材料として極めて好適な炭素−炭化硼素焼結体の製造方法、その方法で得られた焼結体、およびその焼結体の使用方法に関するものである。
【０００２】
【従来の技術】
現在、一般的に知られている炭素−炭化硼素結合体の製造方法としては、炭素粉および炭化硼素、更に必要に応じて炭化し得る原料を加えて混合、成形、焼成する方法が良く知られており、例えば特開昭６２−１０８７６７号、特開昭６２−２９７２０２号等が挙げられる。
【０００３】
しかし、これ等の方法においては、炭素−炭化硼素系焼結体の製造時の焼結温度は、不思議にも一様に最高点において２０００℃までで抑えることが行われていた。
【０００４】
その理由として考えられることは、２０００℃以上の高温焼成を行った場合、Ｂ_４Ｃの状態が不安定となり、硼素成分の揮散損失が著しくなると言われていた。例えば加藤昭夫、山口喬監修、（株）サイエンスフォーラム発行の「ニューセラミック粉体ハンドブック」第１２章第３節、炭化硼素、窒素硼素の項就中２３６頁にも、「原料としては中心粒径１．５〜５μｍ前後のＢ_４Ｃ粉末を用い、２０００℃前後の温度、１５０〜３００ｋｇ／ｃｍ^２の圧力下でホットプレス成形を行う」ことが記されている。
【０００５】
また、上記の引用出願等においても、最高焼成温度は１５００〜２０００℃までに抑えられていた。これ等は原料であるＢ_４Ｃの変質とＢ成分の蒸散、減耗を考えての配慮であったものと推察されるが、黒鉛結晶化を進めるという硼素の特徴は生かされていない。
【０００６】
ところが、通常一般の人造黒鉛の製造時の最高点での焼成温度が２８００〜３０００℃であるのに対し、このようにＢ_４Ｃ粉を混入した場合の２０００℃焼成では、炭素系原料（Ａ）の黒鉛結晶化反応が充分進まないために、熱伝導率が充分上がらず、製品加工時の機械加工性が悪いという欠点があった。また、このような温度条件はＢ_４Ｃが安定に存在するための条件であり、ほとんどの硼素成分はＢ_４Ｃ粒のままで、多量の炭素成分中に存在するため、硼素成分の炭素材中に於ける分散状態は、微視的には完全均一であるとは言い難かった。即ちＢ成分の偏在性と分散性に問題があった。
【０００７】
【発明が解決しようとする課題】
本発明が解決しようとする課題は、従来のこの種炭素−炭化硼素焼結体の上記各難点を解消することであり、更に詳しくは、炭素材中に於ける硼素成分の分散性が、均一でしかも極めて微細に分散しており、この結果、焼結体全体としては、更に一段と優れた中性子吸収性、耐酸化性、大きな熱伝導性、耐熱衝撃性、機械加工性、高靭性等を有する焼結体、特にショアー硬度の平均値が２０以下と比較的柔軟性を有していて、機械加工性が極めて優れたものであり、且つ引張強度が１０ＭＰａよりも低くならずに１０ＭＰａ以上という実用的に十分満足する引張強度を有する焼結体を開発することである。
【０００８】
【課題を解決するための手段】
本発明者は、上記課題を解決するために、研究を続けた結果、炭素粉、炭化硼素および／または炭化し得るバインダー成分を用いて、炭素−炭化硼素複合焼結体を製造するに際し、炭素粉の一成分として人造黒鉛粉を使用し、また焼成手段及び焼成温度として、特定の手段と温度を採用した。更に詳しくは、焼成手段として仮焼成と本焼成という二段焼成を採用し、且つ焼成温度としては本焼成の温度について、従来の通念であった２０００℃までの焼成という上限を超えて、従来当業者が全く考えてもみなかった２０００℃を超える温度で焼成すると、ショアー硬度の平均値が２０以下という比較的柔らかく、機械加工性が極めて優れたものであり、且つ強度や熱伝導が向上し、且つ硼素の分散性が極めて良好になる、これまでとは全く異なる特性の素材が創製されることを見出した。また、強度の低下についても実用上ほとんど支障のない程度に収まり、場合によっては２０００℃以上のある温度帯では、逆に強度の向上が見られた。
【０００９】
更に２４００℃以上で焼成すると、特にショアー硬度や引張強度、更には加工性が著しく向上することも併せ見出された。
【００１０】
【発明の構成並びに作用】
炭素−炭化硼素焼結体は、炭化硼素粉（Ｂ）と炭素粉（Ａ）、および必要に応じ炭化し得るバインダー成分（Ｃ）を用いる。なおこの際本発明に於いては、炭素粉（Ａ）の一成分として必ず人造黒鉛粉を使用する。これら原料を混合、成形、焼成の工程に通すことによって製造される物である。例えば炭化硼素とコークス粉、人造黒鉛粉等をボールミルで混合し、高温高圧で焼結体を得るホットプレス法や自己焼結性を有する炭素粉末、人造黒鉛粉及び炭化硼素を混合、成形、焼成して焼結体を得る方法等がある。
【００１１】
この際の炭化硼素粉（Ｂ）は特に限定はなく市販の物で良いが、平均粒径１〜５０μｍのものが好ましい。サブミクロンの炭化硼素は非常に高価であり、５０μｍを超えると焼結体中の硼素成分の偏在部が大きくなる傾向がある。
【００１２】
また炭素粉（Ａ）は、コークス粉、炭素繊維粉、人造黒鉛粉、所謂メソフェーズ小球体（メソ相炭素球晶）粉等が用いられる。この際必ず人造黒鉛粉が炭素粉（Ａ）の一成分として使用される。特に好ましくは平均粒径が５０μｍ程度のものである。必要に応じ、使用される炭化し得るバインダー成分（Ｃ）としては、タール、ピッチ類、芳香族多環式有機化合物、合成樹脂、例えばフェノール樹脂、フラン樹脂、イミド樹脂、アミド樹脂等の高分子化合物、特に縮合系合成高分子や、天然高分子等が具体的に挙げられる。
【００１３】
これ等の樹脂、高分子類は、主として炭化硼素粉及び炭素粉の成形時のバインダー的作用を利用して添加されるものであるが、昇温焼成時には炭化して、炭素粉等と混然一体となって最終的には焼結体の一成分として機能するものである。
【００１４】
炭化し得るバインダー成分（Ｃ）は、主として炭素粉（Ａ）の持つ粘着性の有無によって、その使用の有無が決定される。例えば、前記したメソフェーズ小球体（例えば川崎製鉄製「ＫＭＦＣグレード」）を炭素粉（Ａ）として用いた場合には、それが持つ粘着成分によって、自己焼結性があり、この（Ｃ）を用いずとも成形することが出来る。しかし、（Ａ）としてコークス粉を用いた場合には、炭化硼素成分（Ｂ）も自己焼結性が無く、固まらないので、バインダー成分として（Ｃ）を添加する必要がある。
【００１５】
この際の各原料成分（Ａ）、（Ｂ）及び必要に応じ用いられる（Ｃ）成分の配合割合は原則として、熱処理時に発生するガスにより、割れやふくれ等を生じない配合割合であれば良い。通常以下の通りである。
【００１６】
＜炭素粉が粘着性を有する場合、例えばメソフェーズ小球体＞
（Ａ）５０〜９９．９重量％
（Ｂ）０．１〜５０重量％
この場合には黒鉛粉を０〜２０重量％更に添加しても良い。
【００１７】
＜炭素粉が粘着性を有しない場合、例えばコークス粉、黒鉛粉等＞
（Ａ）１０〜５０重量％
（Ｂ）０．１〜５０重量％
（Ｃ）１５〜５０重量％
【００１８】
これ等の各原料を、任意の有効な装置により混合した後、昇温し、またはせずして成形する。成形した原料は圧力を加え、または加えずして一旦６００〜１３００℃前後の温度で、仮焼成（予備焼成とも言う）し、炭化し得る原料（Ｃ）等を炭化、焼結させる。
【００１９】
以上は従来公知の方法によるものであるが、次いで本格的な高温焼成工程（本焼成）を行う。
【００２０】
尚、本発明は、若干既に述べた通り、この高温焼成工程における焼成温度の効果、作用に関する知見に基づいてされたものである。
【００２１】
上記のようにして得られた仮焼結体は、常圧不活性ガス雰囲気で２０００℃より高い温度、通常２０５０℃以上、更に好ましくは２１００〜２８００℃、特に好ましくは２４００〜２６００℃の温度で焼結処理を行うことによって、硼素成分が炭素成分中に極めて均一に分布し、且つ機械加工性が極めて優れ、熱伝導の高い焼結体を得ることが出来る。また、配合時に炭化硼素量を調節することにより、任意の硼素濃度とすることが出来る。更に、必要であれば真空炉で例えば５Ｔｏｒｒ、２０００℃等の条件で脱ガス処理の工程を付け加えることも出来る。
【００２２】
上記のように、本発明方法においては、従来の通念であった２０００℃以下という焼成温度を、逆に２０００℃よりもより高い温度で焼成することにより、意外にも硼素成分の揮散損耗も殆ど抑えられたまま、極めて均一に微分散され、且つ機械加工性や熱伝導率、熱膨張係数等の重要物性が寧々向上するという、従来の炭素−炭化硼素焼結体では決して見られなかった実用上極めて好都合な事実を発見し、本発明を完成するに至ったものである。
【００２３】
このような理由については現在明らかではないが、従来Ｂ_４Ｃの安定存在のための温度限界を超えて加熱することにより、Ｂ_４Ｃからの硼素成分の遊離、炭素部分への転移、拡散、再結合等を繰り返し、硼素成分の損失が殆ど無く、極めて均一に、微分散され、且つ高温焼成のため炭素部分の黒鉛化反応が進められ、熱伝導率も高くなし得る副次的効果も発現したものと推考される。
【００２４】
このような高温焼成のため、原料として用いた［Ｂ_４Ｃ＋Ｃ］の形態から、Ｂが全体に混然分散した固溶体、硼素に一部置換された黒鉛結晶の集合体で、あたかも純黒鉛材であるかの様な素材に変化したものと考えられる。
【００２５】
このように、仮焼成と本焼成という二段処理を採用し、且つ本焼成を従来より高い温度で処理することにより、
（イ）通説に反し硼素成分の大きな揮散損耗を生じることがない（後記表２参照）。
【００２６】
（ロ）硼素成分が極めて均一に、且つ微分散され、固溶体化される効果がある（後記図１参照）。
【００２７】
（ハ）この事実により黒鉛材の耐酸化性能は著しく向上した（後記実施例参照）。
（ニ）ショアー硬度の平均値が２０以下であって比較的柔かく機械加工性に優れ、且つ引張強度が１０ＭＰａより低くなることはなく、１０ＭＰａ以上であって、実用上満足出来る強度を有する焼結体が得られること。
【００２８】
（ホ）更に炭素成分についても、硼素成分の存在による黒鉛化反応の触媒的促進効果と高温処理効果等の相乗作用により、炭素成分の黒鉛化度が向上し、従来の炭素−炭化硼素焼結体の欠点であった熱伝導性能が著しく改善され、純黒鉛材に近い値にまで向上した。
【００２９】
（ヘ）このため原子力関連装置に使用される中性子吸収材、核融合装置内のプラズマ対向材等の諸用途に適用可能となった。
【００３０】
（ト）また、このような高温焼成による副次的効果として、後記表３にも示すように、熱膨張係数が黒鉛材及び他の製法にかかる炭素−炭化硼素複合体に比べ、非常に低いことが挙げられる。
【００３１】
（チ）このことは、先に記した高温処理によって熱伝導率が向上した効果と共に考慮すると、この材料が熱伝導率が高く、且つ熱膨張係数が逆に小さい材料、即ち著しく耐熱衝撃性に優れた特異な性質を持つ材料であることを示唆するものである。
【００３２】
この炭素−炭化硼素複合材が原子力関連設備の内部構造材や保護材等に使用されることを考えると、安全性を考える上で極めて重要な特性である。
【００３３】
【実施例】
以下実施例によって具体的に説明する。
【００３４】
【実施例１】
炭化硼素（平均粒径５μｍ）を１５重量％、メソフェーズ小球体（平均粒径１１μｍ）８０重量％、人造黒鉛粉（平均粒径４μｍ）５重量％の割合となるように各原料を配合し、常温で１時間、乾式混合を行った後、油圧プレス２ｔｏｎ／ｃｍ^２で成形し、３０×３０×３０ｍｍの成形体を得た。成形体をコークス粉末中に詰め、非酸化性雰囲気下で１０００℃まで昇温し、予備焼成品とした。この予備焼成品を抵抗式加熱炉内でコークス粉末中に埋め、不活性雰囲気中で２５００℃迄熱処理して、炭素−炭化硼素焼結体を得た。
【００３５】
【比較例１】
実施例１で得られた予備焼成品を抵抗式加熱炉内でコークス粉末中に埋め、不活性雰囲気中にて２０００℃迄熱処理して、炭素−炭化硼素焼結体を得た。
【００３６】
上記実施例１および比較例１に示す方法で得られた２種の焼結体について、その各々の硼素分布をＸ線マイクロアナライザー（ＸＭＡ）によって測定した。この結果を図１および２に示す。但し、図１は実施例１を、図２は比較例１の測定写真の模擬図である。
【００３７】
比較例１では明らかに炭化硼素と考えられる硼素の集中した部分があるが、実施例１では全体に硼素が均一分布していることが判る。
【００３８】
次に、上記実施例１及び比較例１の焼結体について、その耐酸化性試験を行った。この結果を図３に示す。但し、この試験では、実施例１と比較例１のテストピースを、空気中で８００℃で酸化消耗試験を行ったものである。
【００３９】
この図３から明らかなように、実施例１のほうがはるかに重量減少が少ないことが判る。これは酸化防止膜を作ると考えられている硼素が、より均一に焼結体中に分布しているためと考えられる。
【００４０】
【実施例２〜５、および比較例２】
炭化硼素（平均粒径５μｍ、市販品）を１３重量部（以下単に部という）、メソフェーズ小球体（平均粒径１１μｍ）８３部および人造黒鉛粉（平均粒径４μｍ）４部を混合し、２ｔｏｎ／ｃｍ^２の加圧下で成形、トンネル炉内にて１０００℃で予備焼成した。
【００４１】
上記の予備焼成した試料を５分し、それぞれを抵抗式加熱炉内でコークス粉末中に埋め、アルゴン雰囲気下にて、最高処理温度を２０００℃（比較例２）、２２００℃；２４００℃；２６００℃；２８００℃（順次実施例２、３、４、５）にて焼成した。これ等各焼結体についてＸ線回折を行った。その結果を表１に示す。またその曲げ強さ、熱膨張係数、熱伝導率及びボロン濃度を測定した。この結果を表２に示す。加えて、焼成処理温度と強度及び熱伝導率との関係を図４及び５に示す。
【００４２】
【表１】

【００４３】
【表２】

【００４４】
同表１中で、００２、００４はそれぞれ結晶面を指し、上段（Ａ）は結晶面間隔の絶対値を表す指標値を、下段（Ｂ）は文献「炭素材料実験技術１」に記される純粋な黒鉛結晶の面間隔（６．７０８Å）と上記（Ａ）欄の数値との差、即ち、試料の焼成温度を高めるに従って、硼素成分の存在に拘わらず、その結晶構造が純粋な黒鉛結晶の構造と物性に近づいて行くことを示している。
【００４５】
【実施例６】
炭化硼素（平均粒径５μｍ）を１５重量％、メソフェーズ小球体（平均粒径１１μｍ）８５重量％、人造黒鉛粉（平均粒径４μｍ）５重量％の割合となるように各原料を配合し、常温で１時間、乾式混合を行った後、油圧プレス２ｔｏｎ／ｃｍ^２で成形し、１００×１００×３０ｍｍの成形体を得た。成形体をコークス粉末中に詰め、非酸化性雰囲気下で１０００℃まで昇温し、予備焼成品とした。この予備焼成品を抵抗式加熱炉内でコークス粉末中に埋め、不活性雰囲気中で２４００℃に熱処理して、炭素−炭化硼素焼結体を得た。
【００４６】
【実施例７及び８】
上記実施例６に於いて２４００℃の熱処理に代えて、夫々２６００℃（実施例７）及び２８００℃（実施例８）となし、その他はすべて、実施例６と同様に処理して、焼結体を得た。
【００４７】
【実施例９】
炭化硼素（平均粒径５μｍ）を１５重量％、人造黒鉛粉（平均粒径４μｍ）を４５重量％、石油系ピッチを４０重量％の割合となる様に配合し、２００℃で１時間混捏し、冷却後粉砕した。
粉砕粉を静水圧プレスで成形し、１００×１００×１００（ｍｍ）の成形体を得た。この成形体をコークス粉末中に詰め非酸化性雰囲気下で１０００℃まで昇温し、予備焼成品とした。この予備焼成品を不活性雰囲気下２６００℃にて高温処理を行い、炭素−炭化硼素焼結体を得た。
【００４８】
【比較例３】
東洋炭素（株）製等方性黒鉛材「ＩＧ−１１」
【００４９】
【比較例４〜６】
実施例６に於いて、炭化硼素の配合量を夫々５％（比較例４）、１５％（比較例５）、２０％（比較例６）に代え、且つ、加熱温度２４００℃を最高２０００℃迄に代え、その他は実施例６と同様に処理した。
【００５０】
上記実施例６〜９及び比較例３〜６について、夫々その物性を測定した。この結果を表３に示す。
【００５１】
【表３】

【００５２】
またそれぞれの加工性を測定した。この結果を表４に示す。
【００５３】
【表４】

【００５４】
但し表３及び表４の各物性はそれぞれ以下の方法で測定した。
【００５５】
＜ショアー硬度＞
硬さ試験機ショア式Ｄ型で、立方体又は直方体の試験片を用いて、各面３点、合計１８点の測定のショア硬度の平均値。
【００５６】
＜熱伝導率＞
レーザーフラッシュ法により室温で求めた。
【００５７】
＜熱衝撃強度＞
下記［化１］により測定。
【００５８】
【化１】

【００５９】
但し、
бｆ：引張り強さ（ＭＰａ）
λ ：熱伝導率（Ｗ／ｍ・Ｋ）
ＣＴＥ：熱膨張係数（１０^−６／Ｋ）
Ｅ：弾性係数（ＧＰａ）
【００６０】
＜熱膨張係数＞
室温から４００℃までの平均値。
【００６１】
＜弾性係数＞
引張り試験で求めた引張り歪０〜０．０３％を直線とみなして応力−歪曲線から求める。
【００６２】
＜引張り強度＞
インストロン試験機を用いて測定した。
【００６３】
＜加工性＞
下記の切削条件で加工したときの切削トルク、逃げ面摩耗を測定した。
【００６４】
条件
回転数：１３３０ｒｐｍ
送り：１２０ｍｍ／ｍｉｎ
切り込み径：１ｍｍ
切り込み深さ：１０ｍｍ
切削距離：１００ｍｍ
【００６５】
【図面の簡単な説明】
【００６６】
【図１】
【００６７】
実施例１の炭素−炭化硼素焼結体のＸ線マイクロアナライザーによる写真の模擬図である。
【００６８】
【図２】
【００６９】
比較例１の炭素−炭化硼素焼結体のＸ線マイクロアナライザーによる写真の模擬図である。
【００７０】
【図３】
【００７１】
実施例１及び比較例１の焼結体の酸化消耗試験の結果を示すグラフであり、Ａは実施例１を、Ｂは比較例１を示す。
【００７２】
【図４】
【００７３】
実施例２〜５及び比較例２の焼結体の処理温度と曲げ強さとの関係を示すグラフである。
【００７４】
【図５】
【００７５】
実施例２〜５及び比較例２の焼結体の処理温度と熱伝導率との関係を示すグラフである。[0001]
[Industrial application fields]
The present invention relates to a method for producing a carbon-boron carbide sintered body that is extremely suitable as a plasma facing material in a nuclear fusion reactor and an oxidation resistant material for a machine, a sintered body obtained by the method, and a sintering method thereof. It relates to how to use the body.
[0002]
[Prior art]
At present, as a generally known method for producing a carbon-boron carbide combined body, a method of adding carbon powder and boron carbide and, if necessary, a raw material that can be carbonized, mixing, molding, and firing is well known. Examples thereof include JP-A Nos. 62-108767 and 62-297202.
[0003]
However, in these methods, the sintering temperature during the production of the carbon-boron carbide-based sintered body is strangely uniformly suppressed to 2000 ° C. at the highest point.
[0004]
A possible reason for this is that when high-temperature firing at 2000 ° C. or higher is performed, the state of B ₄ C becomes unstable and the volatilization loss of the boron component becomes significant. For example, in the section of “New Ceramic Powder Handbook”, Chapter 12 Section 3 of the “New Ceramic Powder Handbook” published by Akio Kato and Satoshi Yamaguchi Co., Ltd. The hot press molding is performed using B ₄ C powder of about 1.5 to 5 μm at a temperature of about 2000 ° C. and a pressure of 150 to 300 kg / cm ² .
[0005]
Moreover, also in said cited application etc., the maximum baking temperature was suppressed by 1500-2000 degreeC. These are presumed to be due to consideration of alteration of the raw material B ₄ C, transpiration and depletion of the B component, but the feature of boron that promotes crystallization of graphite is not utilized.
[0006]
However, while the firing temperature at the highest point in the production of general artificial graphite is usually 2800 to 3000 ° C., in the firing at 2000 ° C. when the B ₄ C powder is mixed in this way, the carbon-based raw material (A ) Does not proceed sufficiently, so that the thermal conductivity does not sufficiently increase and the machinability during product processing is poor. Moreover, such temperature conditions is a condition for B _{4 C} is stably present, most of the boron component remains B _{4 C} grains, due to the presence in large quantity of carbon component, the carbon material of the boron component It was difficult to say that the dispersion state inside was completely uniform microscopically. That is, there was a problem in the uneven distribution and dispersibility of the B component.
[0007]
[Problems to be solved by the invention]
The problem to be solved by the present invention is to solve the above-mentioned problems of the conventional carbon-boron carbide sintered body. More specifically, the dispersibility of the boron component in the carbon material is uniform. Moreover, as a result, the sintered body as a whole has further excellent neutron absorption, oxidation resistance, large thermal conductivity, thermal shock resistance, machinability, high toughness, etc. Sintered body, in particular, the average value of Shore hardness is 20 or less, has relatively flexibility, has excellent machinability, and has a tensile strength of 10 MPa or more without being lower than 10 MPa. It is to develop a sintered body having a sufficient tensile strength .
[0008]
[Means for Solving the Problems]
The present inventors, in order to solve the above problems, as a result of continued research, carbon powder, with boron carbide and / or binder components that may be carbonized, a carbon - upon producing boron carbide composite sintered body, carbon Artificial graphite powder was used as one component of the powder , and specific means and temperature were adopted as the firing means and firing temperature. More specifically, a two-stage firing called temporary firing and main firing is adopted as the firing means, and the firing temperature exceeds the upper limit of firing up to 2000 ° C., which is the conventional wisdom, and the conventional firing temperature. When fired at a temperature exceeding 2000 ° C., which the trader never thought of, the average value of Shore hardness was 20 or less, and the machinability was extremely excellent, and the strength and heat conduction were improved. In addition, the present inventors have found that a material having completely different properties from the past, in which the dispersibility of boron is extremely good, is created. In addition, the decrease in strength was within a practically no hindrance, and in some cases, the strength was increased in a temperature range of 2000 ° C. or higher.
[0009]
It has also been found that when calcined at 2400 ° C. or higher, especially the Shore hardness, tensile strength and workability are remarkably improved.
[0010]
Configuration and operation of the invention
The carbon-boron carbide sintered body uses boron carbide powder (B), carbon powder (A), and a binder component (C) that can be carbonized as necessary. In this case, in the present invention, artificial graphite powder is always used as one component of the carbon powder (A). It is a product manufactured by passing these raw materials through the steps of mixing, molding and firing. For example, boron carbide and coke powder, artificial graphite powder, etc. are mixed in a ball mill, hot press method to obtain a sintered body at high temperature and high pressure, self-sintering carbon powder, artificial graphite powder and boron carbide are mixed, molded and fired Thus, there is a method for obtaining a sintered body.
[0011]
The boron carbide powder (B) at this time is not particularly limited and may be a commercially available product, but those having an average particle diameter of 1 to 50 μm are preferred. Submicron boron carbide is very expensive, and when it exceeds 50 μm, the uneven distribution portion of the boron component in the sintered body tends to increase.
[0012]
Further, as the carbon powder (A), coke powder, carbon fiber powder, artificial graphite powder , so-called mesophase microsphere (mesophase carbon spherulite) powder, or the like is used. At this time, artificial graphite powder is always used as one component of the carbon powder (A) . The average particle size is particularly preferably about 50 μm. If necessary, the carbonizable binder component (C) includes tar, pitches, aromatic polycyclic organic compounds, synthetic resins such as polymers such as phenol resins, furan resins, imide resins, and amide resins. Specific examples include compounds, particularly condensed synthetic polymers and natural polymers.
[0013]
These resins and polymers are added mainly by utilizing the binder action during the molding of boron carbide powder and carbon powder, but carbonize during temperature rising firing and are mixed with carbon powder and the like. Together, it finally functions as a component of the sintered body.
[0014]
Whether or not the binder component (C) that can be carbonized is used is mainly determined by the presence or absence of tackiness of the carbon powder (A). For example, when the above-mentioned mesophase microsphere (for example, “KMFC grade” manufactured by Kawasaki Steel) is used as the carbon powder (A), it has self-sintering properties due to the adhesive component of the carbon powder (A). It can be molded. However, when coke powder is used as (A), the boron carbide component (B) also has no self-sintering property and does not harden, so it is necessary to add (C) as a binder component.
[0015]
In this case, the mixing ratio of each raw material component (A), (B) and the component (C) used as necessary may be a mixing ratio that does not cause cracking or blistering due to the gas generated during heat treatment. . Usually:
[0016]
<When carbon powder has adhesiveness, for example, mesophase microsphere>
(A) 50-99.9 wt%
(B) 0.1 to 50% by weight
In this case, 0 to 20% by weight of graphite powder may be further added.
[0017]
<When carbon powder is not sticky, for example, coke powder, graphite powder, etc.>
(A) 10 to 50% by weight
(B) 0.1 to 50% by weight
(C) 15-50% by weight
[0018]
Each of these raw materials is mixed with any effective apparatus, and then molded with or without increasing the temperature. The formed raw material is temporarily calcined (also referred to as pre-firing) at a temperature of about 600 to 1300 ° C. with or without applying pressure, and carbonized raw material (C) or the like is carbonized and sintered.
[0019]
Although the above is based on a conventionally well-known method, a full-scale high-temperature baking process (main baking) is then performed.
[0020]
In addition, this invention is based on the knowledge regarding the effect and effect | action of the calcination temperature in this high temperature calcination process as it has already stated a little.
[0021]
The presintered body obtained as described above is a temperature higher than 2000 ° C., usually 2050 ° C. or higher, more preferably 2100 to 2800 ° C., particularly preferably 2400 to 2600 ° C. in an atmospheric pressure inert gas atmosphere. By performing the sintering treatment, it is possible to obtain a sintered body in which the boron component is very uniformly distributed in the carbon component, the machinability is extremely excellent, and the heat conduction is high. Further, by adjusting the amount of boron carbide at the time of blending, an arbitrary boron concentration can be obtained. Furthermore, if necessary, a degassing process can be added in a vacuum furnace under conditions such as 5 Torr and 2000 ° C.
[0022]
As described above, in the method of the present invention, the calcination temperature of 2000 ° C. or lower, which is a conventional wisdom, is conversely fired at a temperature higher than 2000 ° C. Practical use never seen in conventional carbon-boron carbide sintered bodies that are very uniformly finely dispersed while being suppressed, and that important physical properties such as machinability, thermal conductivity, and thermal expansion coefficient are gradually improved. The present inventors have found a very favorable fact and completed the present invention.
[0023]
Although not currently known about this reason, by heating beyond the temperature limit for stable existence of a conventional B _{4 C,} B 4 free of boron components from _C, metastasis to carbon moiety, diffusion, Repeated recombination, etc., almost no loss of boron component, very evenly and finely dispersed, and carbonization is promoted by high temperature firing, and secondary effects that can increase the thermal conductivity are also exhibited. It is inferred.
[0024]
Due to such high temperature firing, from the form of [B ₄ C + C] used as a raw material, a solid solution in which B is mixed and dispersed, an aggregate of graphite crystals partially substituted with boron, as if pure graphite material It is thought that the material has changed to a certain material.
[0025]
In this way, by adopting a two-stage process of pre-baking and main baking, and processing the main baking at a higher temperature than before ,
(B) Contrary to popular belief, there is no significant volatilization and wear of boron components (see Table 2 below).
[0026]
(B) There is an effect that the boron component is very evenly and finely dispersed to form a solid solution (see FIG. 1 described later).
[0027]
(C) Due to this fact, the oxidation resistance performance of the graphite material was remarkably improved (see Examples below).
(D) Sintering having an average value of Shore hardness of 20 or less, relatively soft and excellent in machinability, tensile strength never lower than 10 MPa, 10 MPa or higher, and practically satisfactory strength The body is obtained.
[0028]
(E) Furthermore, with regard to the carbon component, the degree of graphitization of the carbon component is improved by the synergistic effect of the catalytic effect of the graphitization reaction due to the presence of the boron component and the high temperature treatment effect, and the conventional carbon-boron carbide sintering The heat conduction performance, which was a defect of the body, was remarkably improved and improved to a value close to that of pure graphite material.
[0029]
(F) For this reason, it can be applied to various applications such as neutron absorbers used in nuclear equipment and plasma facing materials in nuclear fusion equipment.
[0030]
(G) Further, as a secondary effect of such high-temperature firing, as shown in Table 3 below, the thermal expansion coefficient is very low as compared with the carbon-boron carbide composite according to the graphite material and other manufacturing methods. Can be mentioned.
[0031]
(H) Considering this together with the effect of improving the thermal conductivity by the high-temperature treatment described above, this material has a high thermal conductivity and, on the contrary, a material having a low thermal expansion coefficient, that is, extremely high thermal shock resistance. This suggests that the material has excellent unique properties.
[0032]
Considering that this carbon-boron carbide composite material is used as an internal structural material or a protective material for nuclear facilities, it is an extremely important characteristic when considering safety.
[0033]
【Example】
Examples will be described in detail below.
[0034]
[Example 1]
Each raw material was blended so that the proportion of boron carbide (average particle size 5 μm) was 15% by weight, mesophase microspheres (average particle size 11 μm) 80% by weight, artificial graphite powder (average particle size 4 μm) 5% by weight, After dry mixing at room temperature for 1 hour, the mixture was molded with a hydraulic press ² ton / cm ² to obtain a molded body of 30 × 30 × 30 mm. The compact was packed in coke powder and heated to 1000 ° C. in a non-oxidizing atmosphere to obtain a pre-fired product. This pre-fired product was embedded in coke powder in a resistance heating furnace and heat-treated up to 2500 ° C. in an inert atmosphere to obtain a carbon-boron carbide sintered body.
[0035]
[Comparative Example 1]
The pre-fired product obtained in Example 1 was embedded in coke powder in a resistance heating furnace and heat-treated up to 2000 ° C. in an inert atmosphere to obtain a carbon-boron carbide sintered body.
[0036]
About two types of sintered compacts obtained by the method shown in Example 1 and Comparative Example 1, the boron distribution of each was measured by an X-ray microanalyzer (XMA). The results are shown in FIGS. However, FIG. 1 is a schematic diagram of a measurement photograph of Example 1, and FIG.
[0037]
In Comparative Example 1, there is a portion where boron, which is clearly considered to be boron carbide, is concentrated, but in Example 1, it can be seen that boron is uniformly distributed throughout.
[0038]
Next, the sintered body of Example 1 and Comparative Example 1 was subjected to an oxidation resistance test. The result is shown in FIG. However, in this test, the test piece of Example 1 and Comparative Example 1 was subjected to an oxidation consumption test at 800 ° C. in air.
[0039]
As is clear from FIG. 3, it can be seen that Example 1 has much less weight loss. This is presumably because boron, which is considered to form an antioxidant film, is more uniformly distributed in the sintered body.
[0040]
Examples 2 to 5 and Comparative Example 2
Boron carbide (average particle size 5 μm, commercially available product) 13 parts by weight (hereinafter simply referred to as “parts”), mesophase spherules (average particle size 11 μm) 83 parts and artificial graphite powder (average particle size 4 μm) 4 parts are mixed, Molding was performed under a pressure of / cm ² , and preliminary firing was performed at 1000 ° C. in a tunnel furnace.
[0041]
The above pre-fired samples were divided into 5 minutes, each was embedded in coke powder in a resistance heating furnace, and the maximum treatment temperature was 2000 ° C. (Comparative Example 2), 2200 ° C .; 2400 ° C .; 2600 in an argon atmosphere. C .: baked at 2800.degree. C. (sequential examples 2, 3, 4, 5). X-ray diffraction was performed on each of these sintered bodies. The results are shown in Table 1. The bending strength, thermal expansion coefficient, thermal conductivity and boron concentration were measured. The results are shown in Table 2. In addition, the relationship between the firing temperature, strength and thermal conductivity is shown in FIGS.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
In Table 1, 002 and 004 indicate crystal planes, the upper (A) indicates an index value indicating the absolute value of the crystal plane interval, and the lower (B) is described in the document “Carbon Material Experimental Technique 1”. The difference between the plane spacing of pure graphite crystals (6.708 mm) and the value in the above column (A), that is, as the calcination temperature of the sample is increased, the crystal structure is pure regardless of the presence of the boron component. It shows that the structure and physical properties are approaching.
[0045]
[Example 6]
Each raw material was blended so that the proportion of boron carbide (average particle size 5 μm) was 15% by weight, mesophase spherules (average particle size 11 μm) 85% by weight, artificial graphite powder (average particle size 4 μm) 5% by weight, After dry mixing at room temperature for 1 hour, it was molded with a hydraulic press ² ton / cm ² to obtain a molded body of 100 × 100 × 30 mm. The compact was packed in coke powder and heated to 1000 ° C. in a non-oxidizing atmosphere to obtain a pre-fired product. This pre-fired product was embedded in coke powder in a resistance heating furnace and heat-treated at 2400 ° C. in an inert atmosphere to obtain a carbon-boron carbide sintered body.
[0046]
Examples 7 and 8
In Example 6 above, instead of the heat treatment at 2400 ° C., 2600 ° C. (Example 7) and 2800 ° C. (Example 8), respectively, all the others were processed in the same manner as in Example 6 and sintered. Got the body.
[0047]
[Example 9]
Boron carbide (average particle size 5 μm) is blended to a ratio of 15% by weight, artificial graphite powder (average particle size 4 μm) to 45% by weight, and petroleum-based pitch to 40% by weight, and mixed at 200 ° C. for 1 hour. After cooling, it was pulverized.
The pulverized powder was molded by an isostatic press to obtain a molded body of 100 × 100 × 100 (mm). This compact was packed in coke powder and heated to 1000 ° C. in a non-oxidizing atmosphere to obtain a pre-fired product. This pre-fired product was subjected to high temperature treatment at 2600 ° C. in an inert atmosphere to obtain a carbon-boron carbide sintered body.
[0048]
[Comparative Example 3]
Isotropic graphite material "IG-11" manufactured by Toyo Tanso Co., Ltd.
[0049]
[Comparative Examples 4-6]
In Example 6, the boron carbide content was changed to 5% (Comparative Example 4), 15% (Comparative Example 5), and 20% (Comparative Example 6), respectively, and the heating temperature of 2400 ° C. was maximum 2000 ° C. The other processes were the same as in Example 6.
[0050]
About the said Examples 6-9 and Comparative Examples 3-6, the physical property was measured, respectively. The results are shown in Table 3.
[0051]
[Table 3]

[0052]
Each processability was measured. The results are shown in Table 4.
[0053]
[Table 4]

[0054]
However, the physical properties in Table 3 and Table 4 were measured by the following methods.
[0055]
<Shore hardness>
An average value of Shore hardness of a total of 18 points measured on 3 points on each surface using a test piece of a cube or a rectangular parallelepiped with a Shore D type hardness tester.
[0056]
<Thermal conductivity>
It calculated | required at room temperature by the laser flash method.
[0057]
<Thermal shock strength>
Measured according to [Chemical Formula 1] below.
[0058]
[Chemical 1]

[0059]
However,
бf: Tensile strength (MPa)
λ: Thermal conductivity (W / m · K)
CTE: Thermal expansion coefficient (10 ⁻⁶ / K)
E: Elastic modulus (GPa)
[0060]
<Coefficient of thermal expansion>
Average value from room temperature to 400 ° C.
[0061]
<Elastic modulus>
A tensile strain of 0 to 0.03% obtained in the tensile test is regarded as a straight line and is obtained from a stress-strain curve.
[0062]
<Tensile strength>
Measurements were made using an Instron testing machine.
[0063]
<Processability>
Cutting torque and flank wear when measured under the following cutting conditions were measured.
[0064]
Condition rotational speed: 1330 rpm
Feeding: 120mm / min
Cutting diameter: 1mm
Cutting depth: 10mm
Cutting distance: 100 mm
[0065]
[Brief description of the drawings]
[0066]
[Figure 1]
[0067]
FIG. 3 is a simulation diagram of a photograph of the carbon-boron carbide sintered body of Example 1 by an X-ray microanalyzer.
[0068]
[Figure 2]
[0069]
FIG. 3 is a simulated view of a photograph of a carbon-boron carbide sintered body of Comparative Example 1 using an X-ray microanalyzer.
[0070]
[Fig. 3]
[0071]
4 is a graph showing the results of an oxidation consumption test of the sintered bodies of Example 1 and Comparative Example 1, wherein A shows Example 1 and B shows Comparative Example 1. FIG.
[0072]
[Fig. 4]
[0073]
It is a graph which shows the relationship between the processing temperature and bending strength of the sintered compact of Examples 2-5 and Comparative Example 2.
[0074]
[Figure 5]
[0075]
It is a graph which shows the relationship between the process temperature of the sintered compact of Examples 2-5 and Comparative Example 2, and thermal conductivity.

Claims

A sintered body of mesophase spherules, artificial graphite powder and boron carbide powder, containing 3 to 35% by weight of boron carbide (calculated as boron), an average value of Shore hardness of 20 or less, and tensile strength A carbon-boron carbide sintered body having a thickness of 10 MPa or more.

A sintered body of carbon powder containing artificial graphite powder, boron carbide powder and a binder component, containing boron carbide in an amount of 3 to 35% by weight (calculated as boron), and having an average Shore hardness of 20 or less A carbon-boron carbide termination product having a tensile strength of 10 MPa or more.

The sintered body according to claim 1 or 2, wherein the tensile breaking strain is 1% or more.

The sintered body according to any one of claims 1 to 3, wherein an anisotropic ratio is 1.05 or less.

5. The thermal conductivity is 35 W / (m · K) or more and the coefficient of thermal expansion (CTE) is 4.0 × 10 ⁻⁶ / K or less (average value between room temperature and 400 ° C.). The sintered body according to any one of the above.

The method for producing a carbon-boron carbide sintered body according to claim 1, wherein a mesophase spherule as a carbon powder is produced by sintering a mixture of carbon powder and boron carbide powder to produce a carbon-boron carbide sintered body. 2. The method for producing a carbon-boron carbide sintered body according to claim 1, wherein the carbon-boron carbide sintered body according to claim 1 is sintered at a temperature higher than 2000 ° C. after using artificial graphite powder and calcining.

3. The method for producing a carbon-boron carbide sintered body according to claim 2, wherein carbon powder, boron carbide powder and a binder component are mixed and sintered to produce a carbon-boron carbide sintered body. The method for producing a carbon-boron carbide sintered body according to claim 2, wherein artificial graphite powder is used as one component, and after preliminary firing, sintering is performed at a temperature higher than 2000 ° C.

The method for producing a sintered body of carbon-boron carbide according to claim 6 or 7, wherein the particle size range of boron carbide powder used as a raw material is 1 to 50 µm.

The method for producing a sintered body of carbon-boron carbide according to claim 7, wherein at least one of an aromatic polycyclic compound, pitch and synthetic resin is used as a binder component used as a raw material.

An oxidation resistant material comprising a carbon-boron carbide sintered body, wherein the so-called carbon-boron carbide sintered body according to claim 1 or 2 is used as an oxidation resistant material.

A neutron absorber comprising a carbon-boron carbide sintered body, wherein the so-called carbon-boron carbide sintered body according to claim 1 or 2 is used as a neutron absorber in a nuclear fission nuclear facility.

A material for fusion comprising a carbon-boron carbide sintered body, wherein the so-called carbon-boron carbide sintered body according to claim 1 or 2 is used as a plasma facing material or a first wall material of a fusion reaction-related facility.