JP3857352B2 - Hybrid fiber for reinforcing high thermal conductivity FRM and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、高熱伝導性ＦＲＭ強化用ハイブリッド繊維及びその製造方法に関し、詳しくは、シリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーと窒化アルミニウムとが所定に共存されてなり、高熱伝導率を有してＦＲＭの強化用繊維として優れた特性を示す高熱伝導性ＦＲＭ強化用ハイブリッド繊維及びその製造方法に関する。
【０００２】
【従来の技術】
アルミニウム合金等の比較的低融点の軽金属にセラミックス繊維や粒子を添加して強化した複合材料のＦＲＭ（Fiber Reinforced Metals)は、高強度及び耐摩耗性等の優れた機械的特性を有し、その特性が高温まで維持されることから自動車エンジンのピストン等の特に機械的特性が要求される部材用として広く使用されている。例えば、特公平６−３５６２６号、同６−８４５２５号、同６−８４５２６号、同６−８４５２７号及び同６−８０１７９号公報に提案されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、上記公報で提案されるＦＲＭ用のセラミックス繊維等は、主にアルミナやシリカ系の繊維を用いたものであり、熱伝導率がそれほど高くないため、特に、高温下で使用されるＦＲＭでは放熱性が低く、結果的にＦＲＭ自体の温度上昇を招き易いため、温度上昇を防止する必要がある部材や放熱板としては使えない等の用途的制限があった。
本発明は、このような従来のＦＲＭ用強化材の問題点を鑑み、高強度で耐磨耗性にも優れ、更に熱伝導率が高く、高温下での使用部材としての優れた特性を示すＦＲＭ用強化材の開発を目的とする。発明者らは、この目的のために各種セラミックス材料についてそれらの物性等を中心に再検討した。その結果、高熱伝導率を有し半導体素子基板用材料として開発されつつある窒化アルミニウム（ＡｌＮ）を、ＦＲＭ用強化材料として用いることについて検討した。
【０００４】
即ち、例えば、出願人が特願平７−２０６０２７号公報に提案したＡｌＮの繊維または粒子は、γ−Ａｌ2 Ｏ3 を出発原料としているため、得られる短繊維または粒子は比表面積が大きい多孔質体となるため機械的強度が低い。そのため、アルミニウム合金等の軽金属の補強材としての効果が期待できないことが確認された。一方、出願人が特開平２−３００３１９号公報で提案したアルミナ９０％以上の主にα−Ａｌ2 Ｏ3 及びδ−Ａｌ2 Ｏ3 からなるアルミナ繊維を所定に窒化処理して生成するＡｌＮ繊維や、公知のＡｌＮの緻密質のウイスカーは補強効果が期待できることも確認された。しかし、これらＡｌＮ系繊維やウイスカーは高価であり、そのまま機械的な部材のＦＲＭ用として使用することは工業的には好ましくない。また、耐酸化性が高くないため、例えば高圧鋳造前の予熱段階で酸化され結局熱伝導性が低下するおそれもある。そのため、ＡｌＮ系繊維と同等の熱伝導性を有し且つ機械的強度も大きく、更に、耐酸化性にも優れるより安価なＦＲＭ用の補強材について更に検討した。その結果、補強効果の高いセラミック繊維と熱伝導率の高い窒化アルミニウムとをハイブリッド化することにより、優れた機械的特性と熱伝導性とを併せ持ち、且つ、安価な繊維を見出し本発明に到った。
【０００５】
【課題を解決するための手段】
本発明によれば、窒化アルミニウムの繊維または粒子と窒化表面層を有するシリカ−アルミナ系繊維とが均一に混合されてなる高熱伝導性ＦＲＭ強化用ハイブリッド繊維が提供される。
【０００６】
また、本発明は、繊維状または粒子状のγ−アルミナまたはその前駆体及びシリカ−アルミナ系繊維を所定比率で混合して得られる混合物を、炭化水素ガスを３０容量％以下で含有するアンモニアガス雰囲気下、１２００〜１６００℃で加熱処理し、γ−アルミナを窒化アルミニウムとすると共にシリカ−アルミナ系繊維表面を窒化処理することを特徴とする高熱伝導性ＦＲＭ強化用ハイブリッド繊維の製造方法を提供する。
【０００７】
更に、本発明によれば、窒化アルミニウムの繊維または粒子と窒化表面層を有するホウ酸アルミニウムウイスカーとが均一に混合されてなる高熱伝導性ＦＲＭ強化用ハイブリッド繊維が提供される。
【０００８】
また、本発明は、繊維状または粒子状のγ−アルミナまたはその前駆体及びホウ酸アルミニウムウイスカーを所定比率で混合して得られる混合物を、炭化水素ガスを３０容量％以下で含有するアンモニアガス雰囲気下、１２００〜１６００℃で加熱処理し、γ−アルミナを窒化アルミニウムとすると共にホウ酸アルミニウムウイスカー表面を窒化処理することを特徴とする高熱伝導性ＦＲＭ強化用ハイブリッド繊維の製造方法を提供する。
【０００９】
上記の本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維において、シリカ−アルミナ系繊維がｘＳｉＯ2 ・（１−ｘ）Ａｌ2 Ｏ3 で、且つ、０≦ｘ＜１の組成を有することが好ましく、また、上記窒化アルミニウム系繊維が５〜５０重量％含有されることが好ましい。更に、上記高熱伝導性ＦＲＭ強化用ハイブリッド繊維の製造方法において、混合物中にγ−アルミナ繊維またはその前駆体が１０〜７０重量％含有されることが好ましい。
【００１０】
本発明は上記のように構成され、安価なγ−Ａｌ2 Ｏ3 またはその前駆体と高強度で耐酸化性に優れるシリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーを予め所定に混合し、炭化水素含有アンモニア雰囲気下で加熱窒化処理することにより、γ−Ａｌ2 Ｏ3 を熱伝導性のよいＡｌＮとすることができると共に、ＦＲＭのマトリックスであるアルミニウム合金等軽金属合金中のＡｌ等金属単体との反応性が問題とされるシリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーの表面を酸窒化層とすることができ、両者が相乗的に作用してＦＲＭ用としての高熱伝導性で、高強度、且つ非反応性に優れる特性を有するハイブリッド繊維強化材を得ることができる。
【００１１】
【発明の実施の形態】
以下、本発明について詳細に説明する。
本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維は、窒化アルミニウム繊維または粒子（以下、単にＡｌＮ繊維とする）と、表面が窒化処理されて窒化層を有するシリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーとが、局部的に偏ったりすることなく均一に混合分散された状態にあるものである。即ち、各ＡｌＮ繊維と窒化表面層を有するシリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーを単に混合した場合には、その混合状態を完全に均一とすることは困難である。従って、一般的には、下記するように水等の液体中に各混合成分を分散させ攪拌して混合して、均一な混合状態とするものである。但し、機械的装置により、繊維やウイスカーのように複雑に絡み合い易い性状の混合成分を均一な混合状態を形成できるものであれば、そのような混合物も本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維に含まれる。
本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維において、ＡｌＮ繊維が約５〜５０重量％含有されることが好ましい。ＡｌＮ繊維が５重量％未満であると、熱伝導性が低く従来提案の補強材と同様に高温使用の部材用ＦＲＭに適さない。また、５０重量％を超えるとＦＲＭの補強効果が小さくなるためである。
【００１２】
本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維に用いられるＡｌＮ繊維は、γ−Ａｌ2 Ｏ3 繊維または例えば塩基性塩化アルミニウムのように加熱等によりγ−Ａｌ2 Ｏ3 となる繊維状前駆体を原料とするものであり、原料γ−Ａｌ2 Ｏ3 等の繊維形状に依存することになるが、平均直径約２〜１０μｍで、平均長さ約２０〜４００μｍのものが好ましい。また、窒化表面層を有するシリカ−アルミナ系繊維は、平均直径約１〜５μｍで、平均長さ約２０〜４００μｍのものが好ましく、ホウ酸アルミニウムウイスカーは、平均直径約０．１〜１．０μｍ×平均長さ約１０〜５０μｍのものが好ましい。
【００１３】
上記本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維は、下記のような方法で製造することができる。即ち、先ず、繊維状または粒子状のγ−アルミナまたは熱分解等によってγ−アルミナとなるその前駆体と、シリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーを、液体中、通常、水中にそれぞれ分散させて、一般的な攪拌機を用い常法によって攪拌混合し、均一な混合状態、即ちハイブリット化する。上記２種の繊維を均一に混合してハイブリット化した後、所定形状の成形体としてもよく、また成形の際に要すればシリカまたはアルミナのバインダーを添加することができる。上記のようにして繊維状または粒子状のγ−アルミナまたはその前駆体及びシリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーからなるハイブリッド化された繊維またはその成形体は、次いで、ＬＰＧやプロパン等の炭化水素を１〜３０容量％、好ましくは１〜２０容量％、より好ましくは１〜１０容量％、通常５容量％含有するアンモニアガス雰囲気中で１２００℃〜１６００℃、好ましくは１３５０〜１５００℃、より好ましくは１３５０〜１４００℃で加熱処理する。炭化水素含有量が３０容量％を超えると遊離カーボンが析出し、１容量％未満では反応速度が極めて遅くなるためである。また、加熱温度は高いほど処理時間が短縮され好ましいが、１６００℃を超えると生産設備上の制約が大きく工業的実施上好ましくない。また、１２００℃未満では窒化処理速度が遅くなり実用的でない。通常は１４００℃で行われる。加熱処理は、繊維状または粒子状のγ−アルミナまたはその前駆体が完全にＡｌＮに変換され、またシリカ−アルミナ系繊維やホウ酸アルミニウムウイスカーの全表面に約０．１〜１μｍの窒化表面層が形成されるように、各繊維の径及び長さや粒子の大きさ等被処理成分の形態に応じて処理時間を適宜選択して行うことができる。
【００１４】
上記加熱処理により、ハイブリッド化された繊維中に含有されるγ−Ａｌ2 Ｏ3 がＡｌＮに完全に変換され高熱伝導性を有すると同時に、シリカ−アルミナ系繊維やホウ酸アルミニウムウイスカーは表面が窒化され窒化物や酸窒化物を有する窒化表面層が形成されて改質され耐反応性に優れる特性を示す。その結果、優れた補強効果と高い熱伝導率との両特性を併せて保持する強化材を得ることができる。なお、ＡｌＮは、ハイブリッド混合物において、主に熱の伝導体として作用するものであり、繊維状でも粒子状でもよく、その原料のγ−Ａｌ2 Ｏ3 も繊維状、粒子状のいずれでもよいが、好ましくは繊維状がよい。ハイブリッド化し易い、即ち均一な混合状態を得ることが容易であるためである。
【００１５】
本発明のシリカ−アルミナ系繊維またはホウ酸アルミニウムウイスカーは、一般に複合材料の補強材としてよく知られているものを用いることができ、その平均直径及び平均長さ等は、上記したハイブリッド化後に所定の窒化処理した窒化表面層を有する繊維またはウイスカーと同様である。また、繊維状または粒状のＡｌＮの原料のγ−Ａｌ2 Ｏ3 は、繊維状のものは平均直径約３〜５μｍで、平均長さ約５０〜１００μｍのものが好ましく、粒状のものは平均直径約３μｍのものを用いるのが好ましい。
【００１６】
本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維の製造方法は、上記のように窒化処理によりＡｌＮに変換されるγ−Ａｌ2 Ｏ3 の酸化物として予めハイブリッド化して均一な混合状態を形成できることに特に利点がある。即ち、２種以上の繊維や粒子を均一に混合する場合、機械的な混合だけでは充分に均一な混合状態を得ることが困難であり、水等の液体中で撹拌、混合する必要がある。この場合、熱伝導率の向上を図る目的で高熱伝導性のＡｌＮを他のセラミック繊維と混合して使用する場合、ＡｌＮが加水分解され易く水酸化アルミニウムとなるおそれがあり、高熱伝導性が著しく低下することになり熱伝導性特性を付与する目的を満たすことができない。また、窒化表面層を有するホウ酸アルミニウムの場合は、窒化表面層にＡｌＮが存在するため同様な現象が起こり、ＦＲＭ強度の大幅な低下を引き起こすおそれがあった。このため、他の繊維と高熱伝導率を有する繊維状または粒状のＡｌＮとを混合して熱伝導性特性の向上を図る場合には、非水性溶媒のトルエン等の有機溶媒を用いるなどして特殊な技術を要し、作業上複雑な構成を採る必要がある。これに対して、本発明は、原料として酸化物を採用し、その酸化物の形態で水中で撹拌混合することができ作業性が高く、工業上効果的である。また、軽金属合金等と複合化してＦＲＭとする場合に必須のプリフォーム成形時には、液中での撹拌、混合は必ず経由する工程であり、工程を増やすことなくプリフォーム成形と同時にハイブリッド化することができ、工業的実用性が高い。
【００１７】
【実施例】
本発明について実施例に基づき、更に詳細に説明する。但し、本発明は、下記の実施例に制限されるものでない。
実施例１〜３及び比較例１
ＳｉＯ2 ５２％・Ａｌ2 Ｏ3 ４８％の組成をもつシリカ−アルミナ系非晶質繊維と、塩基性塩化アルミニウムを主たる出発原料としたＳｉＯ2 ３％・Ａｌ2 Ｏ3 ９７％の組成をもつγ−Ａｌ2 Ｏ3 繊維を表１に示したように混合比率を変化させ水中で均一な混合状態になるまで約３０分間撹拌・混合した。撹拌、混合後、更にバインダーとして約３重量％のシリカゾルを加え、常法によって４０×４０×１００（ｍｍ）の繊維の体積含有率（Ｖｆ）２０％のプリフォームに成形した。得られたプリフォームをＬＰＧを約５％含有するＮＨ3 ガス中で１４００℃で２時間加熱処理して、プリフォームをを窒化処理した。窒化処理されたプリフォームをＸ線回折により結晶相を測定した。その結果を表１の窒化処理後の繊維の結晶相の欄にＸ線回折による検出強度の強い順に記載して示した。窒化処理されたプリフォームを高圧鋳造法によってアルミニウム−シリコン系合金（ＡＣ８Ａ）と複合化してＦＲＭを製作した。得られたＦＲＭの熱伝導率をレーザーフラッシュ法によって測定した。その結果を表１に示した。
【００１８】
実施例４〜６及び比較例２
シリカ−アルミナ系非晶質繊維の代わりにホウ酸アルミニウム（ＡｌＢＯ3 ）ウイスカーを用いた以外は、実施例１と同様にして表２に示した混合比率でγ−Ａｌ2 Ｏ3 繊維と均一な混合状態とした後、プリフォームを成形して同様に加熱窒化処理した。窒化処理されたプリフォームを同様にＸ線回折により結晶相を測定し、同様に表２の窒化処理後の繊維の結晶相の欄にＸ線回折による検出強度の強い順に記載して示した。窒化処理されたプリフォームを用いＦＲＭを製作し、得られたＦＲＭの熱伝導率を同様に測定した。その結果を表２に示した。
【００１９】
【表１】
【表２】
上記実施例及び比較例より明らかなように、窒化処理後にＸ線回折によりＡｌＮ及びβ−サイアロンまたはθ−アルミナの結晶相が確認され、一方γ−アルミナの結晶相が確認されないことから、加熱窒化処理によりγ−Ａｌ2 Ｏ3 がＡｌＮに変換され、また、シリカ−アルミナ系繊維表面にβ−サイアロンの酸窒化物が形成されていることが分かる。また、γ−アルミナの混合比率が大きくなるに従って、ＡｌＮの結晶相の検出強度が大きくなり、ＦＲＭの熱伝導率が高くなることも分かる。
【００２２】
【発明の効果】
本発明の高熱伝導性ＦＲＭ強化用ハイブリッド繊維は、優れた補強効果と熱伝導率をあわせ持ち、高温で使用される各種部材用のＦＲＭ用として有用である。また、原料に酸化物を用い水中にて均一な混合状態を形成し、その後、高熱伝導率の窒化アルミニウムに変換することができ、耐熱性で高強度のアルミナ質と高熱伝導性の窒化アルミニウムとが均質にハイブリッドすることができ、簡便、且つ安価に高熱伝導性ＦＲＭ強化用ハイブリッド繊維を製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hybrid fiber for reinforcing high thermal conductivity FRM and a method for producing the same, and more specifically, silica-alumina fiber or aluminum borate whisker and aluminum nitride coexist in a predetermined manner and has high thermal conductivity. The present invention relates to a high thermal conductivity FRM reinforcing hybrid fiber exhibiting excellent properties as a FRM reinforcing fiber and a method for producing the same.
[0002]
[Prior art]
FRM (Fiber Reinforced Metals), a composite material reinforced by adding ceramic fibers and particles to a light metal with a relatively low melting point such as an aluminum alloy, has excellent mechanical properties such as high strength and wear resistance. Since the characteristics are maintained up to a high temperature, they are widely used for members that require particularly mechanical characteristics such as pistons for automobile engines. For example, Japanese Patent Publication Nos. 6-35626, 6-84525, 6-84526, 6-84527 and 6-80179 have been proposed.
[0003]
[Problems to be solved by the invention]
However, the ceramic fibers for FRM proposed in the above publication are mainly those using alumina or silica fibers, and their thermal conductivity is not so high, so especially in FRMs used at high temperatures. Since heat dissipation is low, and as a result, the temperature of the FRM itself is likely to rise, there are application restrictions such that it cannot be used as a member or a heat sink that needs to prevent the temperature rise.
In view of the problems of the conventional reinforcing material for FRM, the present invention has high strength, excellent wear resistance, high thermal conductivity, and excellent properties as a member used at high temperatures. The purpose is to develop reinforcing materials for FRM. For this purpose, the inventors reexamined various ceramic materials, focusing on their physical properties. As a result, the use of aluminum nitride (AlN), which has a high thermal conductivity and is being developed as a material for semiconductor element substrates, was investigated as a reinforcing material for FRM.
[0004]
That is, for example, since the fiber or particle of AlN proposed by the applicant in Japanese Patent Application No. 7-206027 uses γ-Al 2 O 3 as a starting material, the obtained short fiber or particle has a large specific surface area. The mechanical strength is low due to the material. Therefore, it was confirmed that the effect as a light metal reinforcing material such as an aluminum alloy cannot be expected. On the other hand, the AlN fiber produced by nitriding the alumina fiber mainly composed of α-Al 2 O 3 and δ-Al 2 O 3 of 90% or more of alumina proposed by the applicant in Japanese Patent Laid-Open No. 2-300319 It was also confirmed that the known AlN dense whiskers can be expected to have a reinforcing effect. However, these AlN fibers and whiskers are expensive, and it is not industrially preferable to use them as they are for FRM of mechanical members. Moreover, since oxidation resistance is not high, there exists a possibility that it may be oxidized in the preheating stage before high pressure casting, for example, and heat conductivity may fall after all. Therefore, further investigation was made on a cheaper reinforcing material for FRM that has the same thermal conductivity as that of the AlN-based fiber, has high mechanical strength, and is excellent in oxidation resistance. As a result, by hybridizing ceramic fibers having a high reinforcing effect and aluminum nitride having a high thermal conductivity, a fiber that has both excellent mechanical properties and thermal conductivity and is inexpensive has been found and the present invention has been achieved. It was.
[0005]
[Means for Solving the Problems]
ADVANTAGE OF THE INVENTION According to this invention, the hybrid fiber for high thermal conductivity FRM reinforcement | strengthening in which the fiber or particle | grains of aluminum nitride and the silica-alumina type fiber which has a nitrided surface layer are mixed uniformly is provided.
[0006]
The present invention also relates to an ammonia gas containing a hydrocarbon gas at 30% by volume or less of a mixture obtained by mixing fibrous or particulate γ-alumina or a precursor thereof and silica-alumina fiber at a predetermined ratio. Provided is a method for producing a hybrid fiber for reinforcing high thermal conductivity FRM, characterized in that heat treatment is performed at 1200 to 1600 ° C. in an atmosphere so that γ-alumina is converted into aluminum nitride and the surface of silica-alumina fiber is nitrided. .
[0007]
Furthermore, according to the present invention, there is provided a hybrid fiber for reinforcing high thermal conductivity FRM in which aluminum nitride fibers or particles and aluminum borate whiskers having a nitrided surface layer are uniformly mixed.
[0008]
Further, the present invention provides an ammonia gas atmosphere containing a hydrocarbon gas at 30% by volume or less of a mixture obtained by mixing fibrous or particulate γ-alumina or a precursor thereof and aluminum borate whisker in a predetermined ratio. A method for producing a hybrid fiber for reinforcing high thermal conductivity FRM, characterized by heat-treating at 1200 to 1600 ° C. to make γ-alumina aluminum nitride and nitriding the aluminum borate whisker surface is provided.
[0009]
In the high thermal conductivity FRM reinforcing hybrid fiber of the present invention, the silica-alumina fiber is preferably xSiO 2. (1-x) Al 2 O 3 and has a composition of 0 ≦ x <1. Moreover, it is preferable that the said aluminum nitride type fiber contains 5 to 50 weight%. Furthermore, in the method for producing a hybrid fiber for reinforcing high thermal conductivity FRM, the mixture preferably contains 10 to 70% by weight of γ-alumina fiber or a precursor thereof.
[0010]
The present invention is configured as described above, and inexpensively γ-Al 2 O 3 or a precursor thereof and silica-alumina fiber or aluminum borate whisker having high strength and excellent oxidation resistance are mixed in advance, By heat-nitriding in an ammonia atmosphere containing γ-Al 2 O 3 , AlN having good thermal conductivity can be obtained, and a simple metal such as Al in a light metal alloy such as an aluminum alloy that is a matrix of FRM. The surface of silica-alumina fiber or aluminum borate whisker where reactivity is a problem can be made into an oxynitride layer, both of which act synergistically to have high thermal conductivity for FRM, high strength, and A hybrid fiber reinforcing material having characteristics excellent in non-reactivity can be obtained.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The high thermal conductivity FRM reinforcing hybrid fiber of the present invention includes an aluminum nitride fiber or particles (hereinafter, simply referred to as AlN fiber), a silica-alumina fiber or an aluminum borate whisker having a nitrided surface and a nitride layer. However, they are in a state of being uniformly mixed and dispersed without being locally biased. That is, when each AlN fiber and a silica-alumina fiber or aluminum borate whisker having a nitrided surface layer are simply mixed, it is difficult to make the mixed state completely uniform. Therefore, in general, as described below, each mixed component is dispersed in a liquid such as water and mixed by stirring to obtain a uniform mixed state. However, as long as a mechanical device can form a uniform mixed state of mixed components that are easily entangled like fibers and whiskers, such a mixture is also a hybrid fiber for reinforcing high thermal conductivity FRM of the present invention. include.
In the high thermal conductivity FRM reinforcing hybrid fiber of the present invention, the AlN fiber is preferably contained in an amount of about 5 to 50% by weight. If the AlN fiber content is less than 5% by weight, the thermal conductivity is low and it is not suitable for the FRM for high-temperature components like the conventionally proposed reinforcing material. Moreover, it is because the reinforcement effect of FRM will become small when it exceeds 50 weight%.
[0012]
The AlN fiber used for the high thermal conductivity FRM reinforcing hybrid fiber of the present invention is a γ-Al 2 O 3 fiber or a fibrous precursor that becomes γ-Al 2 O 3 by heating or the like, such as basic aluminum chloride. The raw material depends on the fiber shape of the raw material γ-Al 2 O 3 or the like, but preferably has an average diameter of about 2 to 10 μm and an average length of about 20 to 400 μm. The silica-alumina fiber having a nitrided surface layer preferably has an average diameter of about 1 to 5 μm and an average length of about 20 to 400 μm, and the aluminum borate whisker has an average diameter of about 0.1 to 1.0 μm. X An average length of about 10 to 50 μm is preferable.
[0013]
The high thermal conductivity FRM reinforcing hybrid fiber of the present invention can be manufactured by the following method. That is, first, fibrous or particulate γ-alumina or a precursor thereof that becomes γ-alumina by pyrolysis or the like and silica-alumina fiber or aluminum borate whisker are dispersed in a liquid, usually in water, respectively. Then, the mixture is agitated and mixed by a conventional method using a general agitator, and is uniformly mixed, that is, hybridized. After the two types of fibers are uniformly mixed and hybridized, a molded body having a predetermined shape may be obtained, and a binder of silica or alumina can be added if necessary for molding. As described above, the hybridized fiber or molded body composed of fibrous or particulate γ-alumina or a precursor thereof and silica-alumina fiber or aluminum borate whisker is then carbonized such as LPG or propane. 1 to 30% by volume of hydrogen, preferably 1 to 20% by volume, more preferably 1 to 10% by volume, usually 1200 to 1600 ° C, preferably 1350 to 1500 ° C in an ammonia gas atmosphere containing 5% by volume Preferably, heat treatment is performed at 1350 to 1400 ° C. This is because when the hydrocarbon content exceeds 30% by volume, free carbon precipitates, and when the hydrocarbon content is less than 1% by volume, the reaction rate becomes extremely slow. Further, the higher the heating temperature, the shorter the treatment time is preferable. However, when the heating temperature exceeds 1600 ° C., the restrictions on the production equipment are large, which is not preferable for industrial implementation. Moreover, if it is less than 1200 degreeC, the nitriding process speed | rate will become slow and is not practical. Usually, it is carried out at 1400 ° C. In the heat treatment, fibrous or particulate γ-alumina or a precursor thereof is completely converted to AlN, and a nitrided surface layer of about 0.1 to 1 μm is formed on the entire surface of silica-alumina fiber or aluminum borate whisker. The treatment time can be appropriately selected according to the form of the component to be treated such as the diameter and length of each fiber and the size of the particles.
[0014]
By the above heat treatment, γ-Al 2 O 3 contained in the hybridized fiber is completely converted to AlN and has high thermal conductivity. At the same time, silica-alumina fiber and aluminum borate whisker are nitrided on the surface. A nitrided surface layer having nitride or oxynitride is formed and modified to exhibit excellent reaction resistance. As a result, it is possible to obtain a reinforcing material that retains both the excellent reinforcing effect and the high thermal conductivity. AlN mainly acts as a heat conductor in the hybrid mixture, and may be fibrous or particulate, and the raw material γ-Al 2 O 3 may be either fibrous or particulate. The fiber shape is preferable. This is because it is easy to hybridize, that is, it is easy to obtain a uniform mixed state.
[0015]
As the silica-alumina fiber or aluminum borate whisker of the present invention, those generally known as a reinforcing material for composite materials can be used, and the average diameter, average length, etc. are predetermined after the above-mentioned hybridization. This is the same as the fiber or whisker having a nitrided surface layer obtained by nitriding. Further, the fibrous or granular AlN raw material γ-Al 2 O 3 is preferably a fibrous one having an average diameter of about 3 to 5 μm and an average length of about 50 to 100 μm, and a granular one having an average diameter. It is preferable to use about 3 μm.
[0016]
The method for producing a hybrid fiber for reinforcing high thermal conductivity FRM according to the present invention can form a uniform mixed state by hybridizing in advance as an oxide of γ-Al 2 O 3 converted to AlN by nitriding as described above. There are particular advantages. That is, when two or more kinds of fibers and particles are uniformly mixed, it is difficult to obtain a sufficiently uniform mixed state only by mechanical mixing, and it is necessary to stir and mix in a liquid such as water. In this case, when AlN having high thermal conductivity is used in combination with other ceramic fibers for the purpose of improving thermal conductivity, AlN may be easily hydrolyzed to become aluminum hydroxide, and the high thermal conductivity is remarkably high. The purpose of imparting thermal conductivity characteristics cannot be satisfied. In the case of aluminum borate having a nitrided surface layer, the same phenomenon occurs because AlN is present in the nitrided surface layer, which may cause a significant decrease in FRM strength. For this reason, when mixing other fibers with fibrous or granular AlN having high thermal conductivity to improve thermal conductivity characteristics, it is special to use an organic solvent such as toluene as a non-aqueous solvent. Requires a complicated technique and requires a complicated construction. In contrast, the present invention employs an oxide as a raw material, can be stirred and mixed in water in the form of the oxide, has high workability, and is industrially effective. In addition, when forming preforms that are indispensable when complexed with light metal alloys or the like to form an FRM, stirring and mixing in the liquid must be performed. Hybridization is performed simultaneously with preform forming without increasing the number of steps. And is highly industrially practical.
[0017]
【Example】
The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples.
Examples 1 to 3 and Comparative Example 1
Silica having the composition SiO 2 52% · Al 2 O 3 48% - with alumina-based amorphous fibers, the composition of SiO 2 3% · Al 2 O 3 97% to a basic aluminum chloride as a main starting material The γ-Al 2 O 3 fibers were stirred and mixed for about 30 minutes until the mixture ratio was changed as shown in Table 1 until the mixture was uniformly mixed in water. After stirring and mixing, about 3% by weight of silica sol was further added as a binder and formed into a preform having a fiber volume content (Vf) of 20% of 40 × 40 × 100 (mm) by a conventional method. The obtained preform was heat-treated in NH 3 gas containing about 5% of LPG at 1400 ° C. for 2 hours to nitride the preform. The crystal phase of the nitrided preform was measured by X-ray diffraction. The results are shown in the column of the crystal phase of the fiber after nitriding treatment in Table 1 in the order of strong detection intensity by X-ray diffraction. The FRM was manufactured by combining the nitrided preform with an aluminum-silicon alloy (AC8A) by high pressure casting. The thermal conductivity of the obtained FRM was measured by a laser flash method. The results are shown in Table 1.
[0018]
Examples 4 to 6 and Comparative Example 2
Except for using an aluminum borate (AlBO 3 ) whisker instead of the silica-alumina-based amorphous fiber, it was uniform with γ-Al 2 O 3 fiber at the mixing ratio shown in Table 2 in the same manner as in Example 1. After being in a mixed state, a preform was formed and similarly heat-nitrided. The crystal phase of the preform subjected to nitriding treatment was measured by X-ray diffraction in the same manner, and similarly described in the column of the crystal phase of the fiber after nitriding treatment in Table 2 in the order of strong detection intensity by X-ray diffraction. An FRM was produced using the nitrided preform, and the thermal conductivity of the obtained FRM was measured in the same manner. The results are shown in Table 2.
[0019]
[Table 1]
[Table 2]
As is clear from the above examples and comparative examples, the crystal phase of AlN and β-sialon or θ-alumina is confirmed by X-ray diffraction after nitriding treatment, while the crystal phase of γ-alumina is not confirmed. It can be seen that γ-Al 2 O 3 is converted to AlN by the treatment, and β-sialon oxynitride is formed on the surface of the silica-alumina fiber. It can also be seen that as the mixing ratio of γ-alumina increases, the detected intensity of the AlN crystal phase increases and the thermal conductivity of the FRM increases.
[0022]
【The invention's effect】
The high thermal conductivity FRM reinforcing hybrid fiber of the present invention has an excellent reinforcing effect and thermal conductivity, and is useful as an FRM for various members used at high temperatures. In addition, an oxide is used as a raw material to form a uniform mixed state in water, which can then be converted into aluminum nitride with high thermal conductivity, and heat resistant and high strength alumina and high thermal conductivity aluminum nitride Can be hybridized homogeneously, and high-conductivity FRM reinforcing hybrid fibers can be produced easily and inexpensively.
Claims (8)
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| Application Number | Priority Date | Filing Date | Title |
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| JP11319996A JP3857352B2 (en) | 1996-04-10 | 1996-04-10 | Hybrid fiber for reinforcing high thermal conductivity FRM and method for producing the same |
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|---|---|---|---|
| JP11319996A JP3857352B2 (en) | 1996-04-10 | 1996-04-10 | Hybrid fiber for reinforcing high thermal conductivity FRM and method for producing the same |
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| Publication Number | Publication Date |
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| JPH09279267A JPH09279267A (en) | 1997-10-28 |
| JP3857352B2 true JP3857352B2 (en) | 2006-12-13 |
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