JP3734170B2 - Ultrafine metal particles and production method thereof - Google Patents

Description

【００８４】
【表２】

【００８５】
【表３】

【００８６】
（実施例３）
Ｎｉを含有するＦｅの酸化物の粉末５ｇと、ほう素粉５ｇをＶ型混合機に投入して混合した。この混合粉末をアルミナ製ボートに適量充填し、炉の中に配置し、流量が２（ｌ／ｍｉｎ）の窒素ガス気流中で、室温から３℃／ｍｉｎの速度で昇温した後、１１００℃で２時間保持して室温まで炉冷した。熱処理後の粉末について観察したところ、窒化ほう素で表面を被覆した金属粒子を得た。組成分析したところ、金属粒子はＮｉを含有するＦｅであることがわかった。
【００８７】
(実施例４)
金属粒子とＢＮまたはＣ分離操作について説明する。図４は、ＢＮ被覆金属粒子およびＢＮ微小体の製造工程図を示すものである。被覆金属粒子を製造する場合、製造工程は図４のＳ１→Ｓ２→Ｓ３→Ｓ４となる。Ｓ２では原料の粉末を入れた窒化ほう素製ルツボ４２を管状炉４３中で熱処理した。Ｓ２で得られた熱処理粉末は被覆金属粒子と微小体の混合粉末４１であるため、被覆金属粒子はＳ３、Ｓ４の分離精製の工程を経て回収された。Ｓ３工程では、熱処理粉末をアセトンやエタノールなどの有機溶媒で代表される媒体４５中に分散させたものを洗浄槽４４で攪拌させ、被覆金属粒子を自然沈降させた。攪拌の手段として洗浄槽４４に超音波を印加すべく超音波洗浄装置４６を用いた。なお、超音波印加に代えて、ガラス棒による手動攪拌やペンシルミキサーなどの攪拌機を攪拌の手段として使用したところ、十分に攪拌することができた。
【００８８】
Ｓ４工程では、上澄み液４７を取り除いて沈殿物を乾燥させることにより被覆金属粒子４８が回収された。同時に上澄み液を乾燥させるとＢＮ微小体が回収された。上記工程ではＢＮ被覆金属粒子とＢＮ微小体を同時に得ることが出来た。特にＢＮ微小体のみを製造する場合、製造工程は図４のＳ１→Ｓ２→Ｓ５→Ｓ６としてもよい。Ｓ５工程は、塩酸や硫酸などの酸性溶液によって熱処理粉末中の金属粒子を溶解させる工程である。酸性溶液中に熱処理粉末を浸漬させた後、沈殿物を回収した。Ｓ６工程は、沈殿物を水洗した後、乾燥させる工程である。Ｓ５で得られた沈殿物に純水を適量注ぎ、ガラス棒などで攪拌した後、再び沈殿させて上澄み液を除去後、乾燥させることによりＢＮ微小体が得られた。酸性溶液の完全除去のために、Ｓ６工程は数回繰り返すことが好ましい。なお上記製造工程は炭素で被覆された金属粒子および炭素微小体を製造する工程にも適用することができた。
【００８９】
図５は、電子顕微鏡（ＴＥＭ）で観察した本発明に係る粒子構造の顕微鏡写真であり、ＢＮ被覆したＦｅ粒子を示している。図６は、図５の構造を模式的に説明するための概略図である。図６に示すように、Ｆｅ粒子１は周囲をＢＮ膜２で被覆されている。ＢＮ被膜の様子をさらに拡大した写真を図７に示す。
【００９０】
図７は、電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真であり、ＢＮ被覆したＦｅ粒子を示している。図８は、図７の構造を模式的に説明するための概略図である。図７に示すように、Ｆｅ粒子１の表面に被覆されたＢＮ膜には、積層された結晶格子の縞模様が認められる。格子面３の部分は、格子面がＦｅ粒子１の表面に沿って、複数の格子面がほぼ並行に積層されている。格子面４や格子面５の部分は、格子面同士が平行でない箇所を有するが、Ｆｅ粒子１の表面を十分に被覆していることがわかる。
【００９１】
（実施例５）
平均粒径０．０３μｍのα−Ｆｅ₂Ｏ₃粉（ａ粉末）５ｇと平均粒径２０μｍの炭素粉（ｂ粉末）５ｇとをＶ型混合機に投入して１０分間混合した。この混合粉末５１を窒化ほう素製ルツボ５２に適量充填し、管状炉５３内に前記ルツボ５２を設置して流量２ｌ／ｍｉｎの窒素ガス気流中で、室温から３℃／ｍｉｎの速度で昇温した後、１０００℃で２時間保持して室温まで３℃／ｍｉｎの速度で炉冷した。管状炉の構造は図１７の概略図に示す。熱処理前後の各粉末についてＸ線回折測定（Ｃｕ，Ｋα線）を行なったところ、図９（熱処理前）および図１０（熱処理後）に示すような回折パターンが得られた。上記熱処理を施した粉末からは主にグラファイトの（００２）ピークとα−Ｆｅの（１１０）ピークを検出した。さらに上記熱処理後の粉末の磁気特性をＶＳＭ（試料振動型磁力計）にて測定した結果を表４に示す。飽和磁化は比較例４の値の１００倍程度であり、Ｘ線回折測定の結果と合わせてＦｅ₂Ｏ₃がＦｅに還元されていることがわかる。上記熱処理後の粉末をＰＣＴ試験機（プレッシャークッカーテスト試験機）にて湿度１００％、１２０℃、１気圧で２４時間曝した後、粉末の含有酸素量を金属中酸素・窒素・水素分析装置（堀場製ＥＭＧＡ−１３００）にて分析した。酸素量の分析結果を表５に示した。ＰＣＴ試験後も酸素量の増分がなく、Ｆｅ粉表面がグラファイト膜で被覆されていることを裏付ける。なお、上記金属中酸素・窒素・水素の分析は、黒鉛ルツボに試料粉末０．５ｇを充填し、ルツボを２０００〜３０００℃へ急速加熱することにより試料中のＯ，Ｎ，Ｈを熱分解し、ガスクロマトグラフと熱伝導度検出器により、発生したＣＯ_２，Ｎ_２，Ｈ_２Ｏガスを検出することによってＯ，Ｎ，Ｈの含有量を分析する方法である。
【００９２】
（比較例３）
熱処理温度を５００℃とした以外は実施例５と同様にして混合粉末を熱処理してＸ線回折、ＶＳＭ測定、ＰＣＴ試験を行なった。Ｘ線回折パターンは熱処理前後で変化がみられず、反応が進行していない。飽和磁化の値も殆ど変化していない。
【００９３】
（比較例４）
平均粒径０．０２μｍのＦｅ粉（真空冶金株式会社製超微粒子）を実施例５と同条件で耐食試験を行なった。飽和磁化は純鉄の値（約２６０×１０^−６ｗｂ・ｍ／ｋｇ）の３０％程度まで低下している。
【００９４】
【表４】

【００９５】
【表５】

【００９６】
図１１は、ＴＥＭ（透過型電子顕微鏡）で観察した実施例５に係る金属超微粒子の構造の顕微鏡写真である。ＴＥＭ観察するにあたり、必要とされる試料調整以外、粒子への損傷や変異などを与える加工は一切施していない。図１２は、図１１の構造を模式的に説明する概略図であり、若干拡大している。金属超微粒子１１は、α−Ｆｅの粒子１２の表面が全て所定の厚さのグラファイト薄膜２０で被覆された粒子である。この被覆はα−Ｆｅの粒子１２の表面を保護しており、効果的に酸化防止している。グラファイト薄膜２０の外側に散在する凸部２１，２１ｂは、グラファイトの異層が成長したものか、異物が付着したもののいずれかと推定される。α−Ｆｅの粒子１１自体の明暗のパターン１３ａ，１３ｂ，１３ｃは、α−Ｆｅの粒子１１の形状（略球形）に起因する干渉パターン（２点鎖線で表示）である。α−Ｆｅの粒子の両端では、グラファイト薄膜の境界１４が若干不明瞭に撮影されているため、点線で表示した。これは略球形の形状により全てに焦点を合わせることが難しいためであり、実際の形状が不明瞭になっている訳ではない。１点鎖線で輪郭を表示した領域は、金属超微粒子１１をＴＥＭ観察のサンプルホルダーに固定させるためのコロジオン膜１５である。符号１６の線と符号は、その３本線の長さが２０ｎｍに相当するスケールである。図１１を撮影した際のスケールをコピーして図１２に付け加えた。
【００９７】
図１３は、ＴＥＭ（透過型電子顕微鏡）で観察した本発明に係る粒子構造の顕微鏡写真であり、図１１の左下半分近傍を拡大してグラファイト薄膜２０の様子を説明するものである。図１３の構造を図１４の概略図で模式的に説明する。グラファイト薄膜２０は、グラファイトの結晶構造を主として構成されている。例えば、格子縞２０ａ，２０ｂ，２０ｃは、グラファイトの層状格子面を表しており、格子縞の間隔がほぼ等間隔であり、α−Ｆｅの粒子１２の表面に対してほぼ平行に配列している。
【００９８】
ただし、α−Ｆｅの粒子は球状であって、その表面には多少の凹凸があることから、グラファイト薄膜の一部には、格子縞２０ｆのようにα−Ｆｅの粒子１２の表面に対して傾斜している箇所もある。格子縞２０ｆは他の格子縞２０ｅを派生し、さらに、格子縞２０ｄとなっている。線の図示を省略したが、格子縞２０ｄはα−Ｆｅの粒子１２の表面に対してほぼ平行に配列している。このように、グラファイト薄膜には、層状格子面の配列の向きが変化したり、配列の状態が不鮮明になる箇所（梨地模様に見える箇所）が存在するが、隣接する結晶構造同士で整合を取ったり、α−Ｆｅの粒子１２の表面に対して結晶構造の面が平行になるように成長するために、ほぼ均一なグラファイト薄膜の被覆が構成されている。
【００９９】
図１４のグラファイト薄膜２０において、格子縞の一部を実線や点線で模式的に図示している。図示を省略しているが、空白の部分にも結晶構造は存在する。また、α−Ｆｅの粒子１２の表面とグラファイト薄膜２０の間には、中間層２５があると推定されるが、その詳細は図１５及び図１６にて説明する。
【０１００】
図１５は、ＴＥＭ（透過型電子顕微鏡）で観察した本発明に係る粒子の構造の顕微鏡写真であり、図１３のグラファイト薄膜２０近傍をさらに拡大した写真である。図１６は、図１５の構造を模式的に説明する概略図であり、若干拡大している。α−Ｆｅの粒子１２では、矢印ａの向きに沿って格子縞２４が見られ、α−Ｆｅの特有の結晶面を示している。Ｆｅ原子の並びが数珠つなぎになっている様子を克明に模写することは難しいので、点線で表示した。α−Ｆｅの粒子１２の表面近傍では、前記の矢印ａに沿った格子縞が崩れているが、その配列の端が平坦な面を構成しており、グラファイトの結晶が徐々に成長していく起点（グラファイトの成長層）となっている。以下、これらの領域を中間層２５と称する。中間層２５を経てグラファイト薄膜２０は成長し、形成される。
【０１０１】
図１６に示すように、α−Ｆｅの粒子１２の表面が比較的滑らかな球面（平坦面）であれば、グラファイトの層状格子面２２は矢印ｄに沿った面となり、規則的に平行に配列しながら成長するため、緻密で非常に薄い被覆を構成する。ここで、緻密とは規則的な格子面が積層している部分を有することを指す。矢印ｄに垂直な方向に、層状格子の面が、１５〜１７層積層して非常に薄く被膜を構成していた。中間層２５の厚さは、グラファイトの層状格子面２２の間隔で言うと、１〜２層に見える。成長し始めたグラファイトの結晶面も中間層に含めると、中間層１５の厚さは、グラファイトの層状格子面２２の間隔でいうと、２〜４層程度である。
【０１０２】
転位した箇所２３は、結晶成長にズレが生じ、結晶構造が不連続化した部分と推定される。層状格子が成長して積層構造となるときに、格子の欠陥に起因して、ある部分の成長が１層分遅れたとする。ある部分の成長が再開されたとき、ある部分のｎ−１層目の格子面と隣接する部分のｎ層目の格子面が結合して１つの面（転位した面）を構成することがある。転位した面の発生率は高くなく、被膜全体でみると均一で緻密な薄膜といえる。なお、グラファイト薄膜２０の表面には凸部２１ｂが存在するが、図１５の写真では鮮明には撮影されなかったため、その箇所を点線で表示した。
【０１０３】
（参考例２）
平均粒径０．０３μｍのヘマタイト（Ｆｅ_２Ｏ_３）粉末３ｇと平均粒径２６μｍのほう素粉末７ｇをＶ型混合機に投入して１０分間混合した。この混合粉末１２１を窒化ほう素製の坩堝１２２に充填して管状電気炉１２３に設置し、流量２（ｌ／ｍｉｎ）の窒素ガス気流中で、室温から３（℃／ｍｉｎ）の速度で昇温した後、１１００℃で２時間保持して室温まで炉冷した。熱処理前の混合粉末は赤黒色であったが、熱処理後の粉末は灰白色に変色していた。熱処理後の粉末についてＸ線回折測定（Ｃｕ，Ｋα線）を行なったところ、図１８に示すような回折パターンが得られ、上記熱処理を施した粉末からは六方晶の窒化ほう素（ｈ−ＢＮ）と菱面体の窒化ほう素（ｒ−ＢＮ）、およびα−Ｆｅの回折ピークを検出した。窒化ほう素とＦｅを分離するため、アセトン５００ｃｃ（０．５×１０^−３ｍ^３）の中に上記粉末５ｇを投入して５分間超音波洗浄を施し、上澄み液と沈殿物を分離した。上澄み液１２７をドラフト内で更に２４時間放置してアセトンを乾燥させ、窒化ほう素粉末１２８（重量６ｇ）を回収した。
【０１０４】
この窒化ほう素粉末を透過型電子顕微鏡（ＴＥＭ）にて観察したところ、図１９の写真に示すようなワイヤ状の組織が観察された。格子像を解析すると、この窒化ほう素ワイヤは菱面体構造であった。流量の単位は（ｌ／ｍｉｎ）≒約１６．７×１０^−６（ｍ^３／ｓ）に相当する。参考例２の製造工程は、粉末混合工程（Ｓ１１）、雰囲気中熱処理工程（Ｓ１２）、粉末を分散させた媒体への超音波印加工程（Ｓ１３）、窒化ほう素微小体の分離・乾燥工程（Ｓ１４）を有し、図２２の工程フローと概略図に対応する。同図中、符号１２４は洗浄槽、符号１２６は超音洗浄機、符号１２５は熱処理後の粉末を分散させた溶媒（アセトン）に相当する。なお、生成した粒子を分散させるべく超音波を印加できるのであれば、洗浄機に限らず使用することができる。
【０１０５】
図２０は、図１９の写真の構造を模写した概略図であり、ワイヤ状の窒化ほう素微小体を示す。この窒化ほう素微小体１０１は、内部に空洞１０２を有するチューブ１０３が多数個連結して、長い屈曲したチューブ状を構成している。一方の端はチューブ１０３の構造で終端されている。他方の端は、チューブ１０３であるｒ−ＢＮ組織と、ｈ−ＢＮ的な部位１１２ｂが混在した組織を経て、ｈ−ＢＮ組織１１２で終端されている。図２０中、点線で表示した曲線は、電子顕微鏡のサンプルホルダーに窒化ほう素微小体１０１を固定するためのコロジオン膜の外延を表している。図２０の方形の囲いの右外の線と文字は、線の長さが２００ｎｍの寸法に対応することを示す。
【０１０６】
図２１は、図２０中の窒化ほう素チューブのみを抜粋・拡大した概略図である。チューブの先端近傍１１１は、チューブの途中の部分と重なって見えており、明瞭ではない為に先端が閉鎖されているかは定かでない。この先端近傍から、空洞１０２とそれを囲うチューブ１０３の構造が続いており、途中、チューブ間の節１０４と考えられる部位や、チューブの厚さが厚いか斜めに観察する為に厚く見える箇所と考えられるコブ１０５が存在する。連続するチューブの向きは、例えば屈曲部１１０で大きく屈曲しているように見える。チューブの厚さは必ずしも一様に見えておらず、コブ１０５や節だけでなく、複雑な線や脈理に見える構造を伴いながら空洞１０２を形づくっている。チューブ構造は先端近傍１１１から節１０４ｂまで明瞭に観察され、チューブの直径は０．１２〜０．２０μｍ（１２０〜２００ｎｍ）である。この辺りは結晶組織が複雑であるため、ｒ−ＢＮとｈ−ＢＮが混在しているか、混相となっていると推測される。異相の混在は、チューブの屈曲と関係すると考えられる。明瞭にパイプ状に見えるチューブ１０３の結晶構造を拡大観察すると、原子の並びが３層周期を繰り返すｒ−ＢＮとなっており、その周期の繰り返し方向は、チューブの直径方向を向いている。
【０１０７】
（参考例３）
平均粒径０．０３μｍのα−Ｆｅ₂Ｏ₃粉（ａ粉末）５ｇと平均粒径２０μｍの炭素粉（ｂ粉末）５ｇとをＶ型混合機に投入して１０分間混合した。この混合粉末２５１を窒化ほう素製ルツボ２５２に適量充填し、管状炉２５３にて流量２ｌ／ｍｉｎの窒素ガス気流中で、室温から３℃／ｍｉｎの速度で昇温した後、１０００℃で２時間保持して室温まで３℃／ｍｉｎの速度で炉冷した。流量の単位は（ｌ／ｍｉｎ）≒約１６．７×１０^−６（ｍ^３／ｓ）に相当する。
【０１０８】
熱処理前後の各粉末についてＸ線回折測定（Ｃｕ，Ｋα線）を行なったところ、図２３（熱処理前）および図２４（熱処理後）に示すような回折パターンが得られた。上記熱処理を施した粉末からは主にグラファイトの（００２）ピークとα−Ｆｅの（１１０）ピークを検出した。図２４にて、○印はグラファイトの結晶構造に対応するピークであり、■印はα−Ｆｅの結晶構造に対応するピークであり、横軸は回折角度の２θ（°）、縦軸は回折Ｘ線の強度（ｃｐｓ）である。グラファイトの最大強度のピークは半値幅が約０．２°となっており、熱処理後の粉末の結晶性はよい。さらに、図２３と図２４に対応した熱処理前後の粉末について磁気特性をＶＳＭ（試料振動型磁力計）にて測定した所、飽和磁化は前者で１．３０×１０^−６Ｗｂ・ｍ/ｋｇ、後者で１３１×１０^−６Ｗｂ・ｍ/ｋｇであった。以上より、Ｆｅ_２Ｏ_３がＦｅに還元されていることがわかる。
【０１０９】
上記熱処理後の粉末をＴＥＭ（透過型電子顕微鏡）観察した所、図２５に示すようなチューブ状の微小体が確認された。図２５は電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。ＥＤＸ（エネルギー分散型Ｘ線検出器）による組成分析の結果、微小体の先端の黒色粒子はＦｅであり、チューブはＣ（炭素）であることが判明した。
【０１１０】
図２６は、図２５の写真の構造に対応する概略図である。炭素微小体２０１は、Ｆｅ粒子２０２をベースにして炭素のチューブ２０３が曲線状に成長した構造である。チューブ２０３の内部には複数の節２０４が存在し、対向する節とチューブの壁２０３ｂに囲われた領域は空洞２０５を構成する。チューブ２０３の他端は閉じられており、先端部２０６となっている。この炭素微小体２０１において、チューブの成長方向が曲がっていることは、チューブの壁の厚さや節の間隔が均一ではないことと関係すると考えられる。特に、チューブの壁２０３ｃ，２０３ｅの箇所はチューブの厚さが薄い。
【０１１１】
もう一つの炭素微小体２０７は、Ｆｅ粒子２０８をベースにして炭素のチューブ２０９が曲線状に成長するとともに、先端に他のＦｅ粒子２１３を包含する構造である。チューブ２０９の内部には複数の節２１０が存在し、対向する節とチューブの壁に囲われた領域は空洞２１１を構成する。Ｆｅ粒子２１３の近傍にあるＦｅ粒子２２０はチューブの壁２２０等により隔てられているように見える。この炭素微小体２０７にて、Ｆｅ粒子２１３はチューブの成長当初から付いていたものか、チューブが成長した過程で取り込んだものかは定かでない。なお、Ｆｅ粒子２０８やチューブの壁２１２は、炭素微小体２０１と重複して見えているだけで、接続はされていない。さらに、他のＦｅ粒子２１４は単独で存在している。同図中、直線若しくは屈曲した一点鎖線は原料の炭素２１５，２１６の輪郭を表している。曲線状の一点鎖線は炭素微小体等を電子顕微鏡のサンプルホルダーに固定するためのコロジオン膜２１７，２１８の輪郭を表している。符号２１９は、図２６の寸法を判りやすくするために記入したスケール表示であり、元の図２５にそのような構造がある訳ではない。スケール表示の３本線の長さは１００ｎｍに相当する。
【０１１２】
図２５の写真に基づいて、各々の炭素微小体の外径Ｒｏと内径Ｒｉの比を測定した。任意の箇所について測定し、（Ｒｉ／Ｒｏ）＝０．６７、０．７５、０．４０、０．６９、０．５７、０．６３、０．７５、０．４４というようなデータを得た。参考例３の条件を変えて炭素微小体を製造すると、平均外径や平均内径も変えることができた。これらの条件変更を考慮すると、（Ｒｉ／Ｒｏ）の上限を０．８とすることができる。
【０１１３】
図２７は、電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。図２５において、Ｆｅ粒子２０２とチューブ２０３の接合箇所の近傍を拡大したものである。図２８は、図２７の写真の構造に対応する概略図である。なお、図２８は、説明し易くするために、図２７の結晶組織の主要な部分のみを実線や点線に代えて表現した。従って、点線でハッチングした領域の周囲が空白であったとしても、その部分は記載を省略しているだけである。
【０１１４】
図２８によると、Ｆｅ粒子２０２では、ほとんどの領域で特定の結晶面に沿った表面を有するように見える組織となった。以下、Ｆｅ主相２２０，２２１と称する。Ｆｅ主相２２０の左側には、配列の面の向きが異なる相２２５や、梨地模様に見える異相２２６などが観察された。なお、平行に配置した点線でＦｅ主相２２０等を表現したが、点間隔や線間隔は必ずしも図２７と一致するものではない。線の配列の向き等を判り易く説明するために描いたものである。
【０１１５】
図２８中の炭素のチューブについて説明する。仮想的な境界線２２７およびＦｅ主相２２１から先にはチューブ２０３が生成されている。筒状のチューブの壁の中が節２３６、２３９で仕切られた構造であることが判る。節２３６とＦｅ粒子２０２とチューブの壁で囲われた領域、または節２３６，２３９とチューブの壁で囲われた領域は空洞となった。
【０１１６】
チューブの壁は、結晶の配列がグラファイト構造的な相を主として構成されている。以下、グラファイトとそれに類似の組織を併せてグラファイト相と称する。グラファイト相は、結晶の配列が特定の面に沿って積層したように見えるという点で、Ｆｅよりも明瞭である。チューブの壁の成長方向に対してグラファイト相２３０，２３１，２３２，２３３，２３７，２３８，２４０の面は、平行若しくは略平行と言える。これらに対して、節２３６，２３９ではグラファイト層の面は、チューブの壁の成長方向に対して直交若しくは略直交と言える。節２３６の左側の付け根では、グラファイト層の向きが下向きの層２３４と上向きの層２３５にＹ字状に分かれており、樹木の幹と枝の如き組織を呈している。節２３９の付け根はチューブの壁にほぼ直交しており、節の組織は少なくとも２通りあると考えられる。グラファイト相２４２は架橋もしくは節と考えているが、他の構造体のグラファイト相２４２が紛れこんでいるため、断定はできない。
なお、グラファイト層の原子配列の積層の様子は、グラファイト層２３５，２３８や節２３６，２３９に表現したように間隔が狭い。全ての層を同様に図示すると複雑になるため、他の部分では層の数を減らして図示した。また、一層一層が明瞭に判る場合には線で図示したが、途切れ途切れで続いているように見える場合には、点線で表示した。
【０１１７】
上記熱処理後の粉末５ｇをアセトン５００ｃｃの中に投入して５分間超音波洗浄を施し、上澄み液と沈殿物を分離した。上澄み液２５７をドラフト内で更に２４時間放置してアセトンを乾燥させ、炭素微小体の粉末２５８を得た。粉末２５８は粗大遷移金属粒子等を除くことにより、炭素微小体の割合を向上させたものである。
【０１１８】
参考例３の製造工程は、粉末混合工程、雰囲気中熱処理工程、粉末を投入した媒体への超音波印加（分散工程）、粗大遷移金属粒子などの分離および乾燥工程を有し、図２９の工程フローと概略図に対応する。同図中、符号２５４は洗浄槽であり、符号２５５は熱処理後の粉末を分散させた溶媒（アセトン）であり、符号２５６は超音波洗浄装置に相当する。なお、生成した各粒子を溶媒中に分散させるべく超音波を印加できるものであれば、洗浄装置に限らず使用することができる。
【０１１９】
【発明の効果】
以上説明したように、本発明の金属超微粒子およびその製造方法を用いることにより、安全且つ簡便で工業的利用に適した被膜を金属粒子表面に付与した金属超微粒子を得ることができる。
【図面の簡単な説明】
【図１】 熱処理前の混合粉末のＸ線回折パターンを示すグラフである。
【図２】 熱処理後の混合粉末のＸ線回折パターンを示すグラフである。
【図３】 Ｆｅ_２Ｏ_３とＢが反応することにより、窒化ほう素被覆Ｆｅ粒子等が生成する反応過程を説明する概略図である。
【図４】 窒化ほう素被覆金属粒子および窒化ほう素微小体の製造工程図である。
【図５】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図６】 図５の構造を模式的に説明するための概略図である。
【図７】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図８】 図７の構造を模式的に説明するための概略図である。
【図９】 熱処理前の混合粉末のＸ線回折パターンを示すグラフである。
【図１０】 熱処理後の混合粉末のＸ線回折パターンを示すグラフである。
【図１１】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図１２】 図３の構造を模式的に説明するための概略図である。
【図１３】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図１４】 図５の構造を模式的に説明するための概略図である。
【図１５】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図１６】 図７の構造を模式的に説明するための概略図である。
【図１７】 実施例１の製造工程で用いる管状炉の概略図である。
【図１８】 本発明の粉末のＸ線回折パターンを示すグラフである。
【図１９】 電子顕微鏡で観察した本発明に係る粒子構造の写真である。
【図２０】 図１９の写真の構造に対応する概略図である。
【図２１】 図２０の一部を拡大した概略図である。
【図２２】 参考例２の製造工程を説明するフロー及び概略図である。
【図２３】 熱処理前の混合粉末のＸ線回折パターンを示すグラフである。
【図２４】 熱処理後の混合粉末のＸ線回折パターンを示すグラフである。
【図２５】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図２６】 図２５の写真の構造に対応する概略図である。
【図２７】 電子顕微鏡で観察した本発明に係る粒子構造の顕微鏡写真である。
【図２８】 図２７の写真の構造に対応する概略図である。
【図２９】 参考例３の製造工程を説明する工程フロー及び概略図である。
【符号の説明】
１ Ｆｅ粒子、 ２ ＢＮ被膜、 ３ 格子面、 ４ 格子面、
５ 格子面、
１１ 金属超微粒子、 １２ α−Ｆｅの粒子、
１３ａ １３ｂ １３ｃ パターン、
１４ グラファイト薄膜の境界、 １５ コロジオン膜、
１６ スケール、 ２０ グラファイト薄膜、
２０ａ ２０ｂ ２０ｃ 格子縞、
２０ｅ 格子縞、 ２０ｄ 格子縞、 ２０ｆ 格子縞、
２１ ２１ｂ 凸部、
２２ 層状格子面、
２３ 転位した箇所、 ２４ 格子縞、
２５ 中間層、 ２７ グラファイトの成長層、
４１ 混合粉末、 ４２ 窒化ほう素製ルツボ、 ４３ 管状炉、
４４ 洗浄槽、 ４５ 媒体、 ４６ 超音波洗浄装置、
４７ 上澄み液、 ４８ 被覆金属粒子、
５１ 混合粉末、 ５２ 窒化ほう素製ルツボ、 ５３ 管状炉、
１０１ 窒化ほう素微小体、 １０２ 空洞、 １０３ チューブ、
１０４ １０４ｂ 節、
１０５ コブ、 １１０ 屈曲部、 １１１ 先端近傍、
１１２ ｈ−ＢＮ組織、 １１２ｂ ｈ−ＢＮ的な部位、
１１３ コロジオン膜、 １２１ 混合粉末、 １２２ 坩堝、
１２３ 管状電気炉、 １２７ 上澄み液、 １２８ 窒化ほう素粉末、
２０１ 炭素微小体、 ２０２ Ｆｅ粒子、 ２０３ チューブ、
２０３ｂ チューブの壁、
２０３ｃ ２０３ｅ チューブの壁、
２０４ 節、 ２０５ 空洞、 ２０６ 先端部、
２０７ 炭素微小体、 ２０８ Ｆｅ粒子、 ２０９ チューブ、 ２１０ 節、
２１１ 空洞、 ２１２ チューブの壁、 ２１３ Ｆｅ粒子、
２１４ Ｆｅ粒子、
２１５ ２１６ 原料の炭素、
２１７ ２１８ コロジオン膜、
２１９ スケール表示、 ２２０ Ｆｅ粒子、
２２０ ２２１ Ｆｅ主相、
２２４ ２２７ 仮想的な境界線、
２２５ 配列の面の向きが異なる相、 ２２６ 梨地模様に見える異相、
２３０ ２３１ ２３２ ２３３ ２３７ ２３８ ２４０ グラファイト相、
２３４ ２３５ グラファイト相、
２３６ ２３９ 節、
２４１ グラファイト相、 ２４２ 他の構造体のグラファイト相、
２５１ 混合粉末、 ２５２ 窒化ホウ素製ルツボ、 ２５３ 管状炉、
２５４ 洗浄槽、 ２５５ 熱処理後の粉末を分散させた溶媒、
２５６ 超音波洗浄装置、 ２５７ 上澄み液、 ２５８ 炭素微小体の粉末[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a metal particle used as a raw material for a magnetic recording medium such as a magnetic tape and a magnetic recording disk, and an electronic device (soft magnetic shape body such as a yoke) such as a radio wave absorber, an inductor, and a printed board, and a method for manufacturing the same. Furthermore, the present invention relates to a micro object that is a by-product when forming metal particles and a method for manufacturing the same.
[0002]
[Prior art]
  As electronic devices become smaller and lighter, the raw materials that make up electronic devices themselves are also required to be nanosized. At the same time, device performance must be improved. For example, for the purpose of improving the magnetic recording density, it is required to simultaneously increase the nanosize and the magnetization of the magnetic particles applied to the magnetic tape.
[0003]
  Conventionally, ferrite powder has been mainly used for magnetic recording media, but there is a problem that the magnetization is small and the signal strength is low. In order to obtain sufficient output characteristics, metal magnetic particles represented by Fe and Co are suitable. For example, if the particle diameter is reduced to 1 μm or less for high recording density, the metal particles are resistant to oxidation. Since it is active, the oxidation reaction proceeds vigorously in the atmosphere, and a part or all of the metal is transformed into an oxide and the magnetization is lowered. In order to improve the handling of fine metal particles, a method of coating the surface of magnetic particles containing Fe and Co with a ferrite layer (for example, Patent Document 1), a method of coating an Fe powder surface with graphite (for example, Patent Document 2) ) Etc. have been proposed.
[0004]
  In the metal particles having a particle size of 1 μm or less as in the above example, in order not to impair the function as a metal, a coating is applied to the particle surface so that the particles are not directly exposed to the atmosphere (oxygen). It is essential. However, the method of covering the surface with a metal oxide as in Patent Document 1 oxidizes and degrades the metal to some extent.
  Further, when the metal particles are coated with graphite as in Patent Document 2, in order to coat, the metal must be heat-treated at an extremely high temperature of 1600 ° C. to 2800 ° C. in order to create a state in which the metal melts carbon. Don't be. Metal carbonization and graphite CO₂There is a concern about conversion. As a coating method that overcomes these problems, there is a method of coating metal particles with boron nitride (BN) (for example, Non-Patent Document 1). BN is a material used for “crucibles”, has a high melting point of 3000 ° C. and excellent thermal stability, and has low reactivity with metals. It also has an insulating property. The production method for applying a BN film to metal particles is as follows: (1) a mixed powder of metal and B is heated by arc discharge in a nitrogen atmosphere, or (2) a mixed powder of metal and B is mixed in a mixed atmosphere of hydrogen and ammonia. There are methods such as heating, or (3) heat-treating a mixture of metal nitrate, urea and boric acid in a hydrogen atmosphere.
[0005]
[Patent Document 1]
        JP 2000-30920 A (pages 9-11, FIG. 2)
[Patent Document 2]
        JP-A-9-143502 (pages 3-4, FIG. 5)
[Non-Patent Document 1]
        “International Journal of Inorganic Materials 3 2001”, 2001, p. 597
[0006]
[Problems to be solved by the invention]
  In the BN coating method, since the manufacturing methods (1) and (2) use metal particles as a raw material, there is a risk of ignition due to a rapid oxidation reaction, particularly when handling ultrafine particles having a particle size of 1 μm or less. In the production method (3), toxic gas (NO_x) Occurs. In addition, the method using arc discharge in the production method (1) is not suitable for industrial use because not only the processing amount is low and the productivity is low, but also the reaction temperature is high around 2000 ° C. Moreover, since the hydrogen gas used by manufacturing method (2) and (3) has a danger of explosion, it is not preferable to utilize industrially. In addition, the coated metal particles obtained by the conventional technique have a problem that the saturation magnetization is deteriorated by modifying a part of the metal particles.
[0007]
[Means for Solving the Problems]
  The inventors have completed the present invention as a result of earnestly examining ultrafine metal particles in which a coating suitable for industrial use is coated on the surface of the metal particles and a method for producing the same in a safe and simple manner in order to solve the above problems. It came to do.
[0008]
  [1] The ultrafine metal particles of the present inventionA powder obtained by mixing a powder containing metal oxide and boron is heat-treated in an atmosphere containing nitrogen,Metal particles obtained by reducing metal oxide, and the surfaces of the metal particles are coated with boron nitride, and the average particle size is 1 μm or less. Desirably, the average particle size is in the range of 0.001 to 1 μm. More desirably, the average particle diameter is 0.01 μm to 0.1 μm. When the particle size is 0.1 μm or less, the effect of preventing oxidation by coating the surface with boron nitride is particularly remarkable. Further, for example, ultrafine metal particles having an average particle diameter of 0.2 to 0.5 μm and excellent in oxidation resistance can be obtained.
[0009]
  The sample is observed with an electron microscope and the average particle size is measured. For example, an electron micrograph of a sample is taken. Measure the average particle size by measuring the particle size of ultrafine metal particles in an arbitrary area in the photograph, or draw a line segment of an arbitrary length in the photograph, and the length of the part that crosses the particle of the line segment From the sum L and the number N of particles crossed by the line segment, the average particle diameter is determined as L / N. However, an average value of at least 50 particles is obtained. Further, the particle diameter of Fe after the heat treatment can be calculated from the (110) peak of Fe of X-ray diffraction measurement using analysis software “Jade5” manufactured by Rigaku.
[0010]
  In the present invention, it is desirable that all of the fine particles are coated with boron nitride (or carbon), but not all of the particles are necessarily coated. Further, it is desirable that the surface of the ultrafine particles is covered with boron nitride (or carbon), but it is not necessary to be composed only of particles whose surface is completely covered with boron nitride (or carbon). In addition, description of the numerical range in this-application specification and a claim is what described "the particle size is 0.001-1 micrometer", for example, "the particle size is the range of 0.001 micrometer or more and 1 micrometer or less. It is used as an equivalent to the expression “in”.
[0011]
  [2] In the above [1], the metal oxide is an oxide containing a transition metal. Examples thereof include Fe particles coated with boron nitride, Ni particles coated with boron nitride, FeNiCo particles coated with boron nitride, NiFe particles coated with boron nitride, and the like.The metal particles are preferably selected from Fe and alloys containing the same..
[0012]
  [3] In the ultrafine metal particles according to [1] or [2], the boron nitride mainly has a crystal structure of h-BN.
[0013]
  [4] The ultrafine metal particles according to any one of [1] to [3], wherein the boron nitride is a film having a thickness of 100 nm or less. Here, the film thickness corresponds to the distance between the surface of the particle to be coated and the surface of the thin film to be coated. More preferably, the film thickness can be 20 nm or less.
[0014]
  [5] The ultrafine metal particles according to any one of [1] to [4], wherein the boron nitride has two or more crystal lattice planes or stacked planes. More preferably, the film has four or more crystal lattice planes or stacked planes. Here, it is desirable that boron nitride is mainly composed of hexagonal crystals, and the lattice plane or the laminated plane of the crystal is a hexagonal c-plane (that is, (002) plane). It is desirable that the lattice plane or the laminate plane of the crystal is formed along the plane of the metal particles.
  [6] In the above [5], an intermediate phase may be provided in the particles or boron nitride.
[0015]
  [7] In any one of the above [1] to [6], the main component of the metal ultraparticle is a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is the magnetic metal element.Material specificThe saturation magnetization is 10% or more and less than 100%.
  Regarding the above [7], when the nuclei of the metal ultrafine particles are composed of magnetic particles, the coated boron nitride film can be made extremely thin, 30 nm or less. Therefore, in the ultrafine metal particles, the volume ratio occupied by the magnetic particles can be increased, and the decrease in saturation magnetization of the ultrafine metal particles can be suppressed as compared with the prior art. A particle composed of a transition metal or an alloy containing a transition metal is coated with a boron nitride film when the saturation magnetization specific to the material that is the main component responsible for the magnetism of the particle is used as a reference (ie, 100%). The saturation magnetization of the ultrafine metal particles may have a magnitude of 10% or more with respect to the reference.
[0016]
  [8] In any one of the above [1] to [7], after heat treatment under conditions of humidity 100%, temperature 120 ° C., 1 atm, 24 hours with respect to oxygen content (mass%) before heat treatment The oxygen mass increment is 50% or less. Even if the surface of the metal ultrafine particles is not completely covered with the boron nitride film, that is, even if the coating is locally thin, it can be used. However, since it is difficult to prevent the progress of oxidation when stored for a long period of time, it is desirable to completely cover the surface of the ultrafine particles with a boron nitride film.
[0017]
  In the present specification and claims, mass%, that is, mass percentage (mass%) represents a composition ratio by the mass of a substance. That is, it expresses how much each elemental component is contained with respect to the unit mass of the ultrafine metal particles.
  The method for measuring the mass% for each composition is, for example, pyrolyzing oxygen in the sample by rapidly heating the sample powder to 2000 to 3000 ° C., and generating oxygen gas by a gas chromatograph and a thermal conductivity detector. Alternatively, the oxygen content is analyzed by detecting a gas containing oxygen. Since the ultrafine metal particles according to the present invention are particularly excellent in oxidation resistance, an increase in oxygen mass after treatment is suppressed with respect to the oxygen content before treatment even when the above-described humidification / heating treatment is performed. .
[0018]
  The magnetic particles may contain impurities and unavoidable impurities (elements originally contained in the raw material) included in the mixing of the raw materials to such an extent that the magnetic properties are not extremely deteriorated.
  In addition, in the X-ray diffraction pattern of a particle composed of a metal or an alloy, at least one of the peak having the highest intensity (Intensity (cps)) and the second highest peak (excluding the coating) ). More preferably, the oxide peak of the elements constituting the particles (excluding BN) is sufficiently smaller than the third highest peak or not detected at all.
[0019]
  [9] In the method for producing ultrafine metal particles of the present invention, a powder obtained by mixing a powder containing a metal oxide and a powder containing boron is heat-treated in an atmosphere containing nitrogen to thereby form boron nitride. It is characterized by producing coated metal particles. It is desirable that the metal oxide contains a transition metal (more preferably, it is composed of a transition metal oxide). The generated metal particles coated with boron nitride preferably have an average particle size of 1 μm or less. The “atmosphere containing nitrogen” corresponds to an atmosphere selected from a mixed gas of nitrogen gas, inert gas such as argon, and nitrogen gas.
[0020]
  More preferably, in the production method of [9] above, a powder obtained by mixing particles containing iron oxide and boron is heat-treated in an atmosphere containing nitrogen to convert the iron oxide into at least one of iron and an iron boron compound. It is reduced to seeds to produce boron oxide, which finally produces at least one particle of iron or iron nitride, the surface of which is coated with boron nitride. And
[0021]
  The method for producing ultrafine metal particles according to the above [9] is characterized in that the step of reducing the metal oxide particles and the step of coating the surfaces of the metal particles with a boron nitride film are performed in one heat treatment step. The production method of the present invention is superior to the production method of a comparative example that will be described later in that it hardly contains oxygen. In the manufacturing method of the comparative example, after producing ultrafine metal particles, an inert atmosphere containing oxygen at a low concentration is gradually supplied to the ultrafine metal particles in order to avoid spontaneous ignition and combustion (oxidation). This is a method for producing ultrafine particles in which a thin oxide film is formed on the surface.
[0022]
  [10] In the above [9], the heat treatment is performed at a temperature of 800 to 1700 ° C.
[0023]
  [11] Other ultrafine metal particles of the present invention includeA powder obtained by mixing a powder containing metal oxide and carbon is heat-treated in an atmosphere containing nitrogen, andMetal particles obtained by reducing metal oxide, and the surface of the metal particlesMainly composed of graphiteCovered with carbon,The layered lattice plane of the graphite crystal is formed along the plane of the metal particles,The average particle size is 1 μm or less. Desirably, the average particle size is in the range of 0.001 to 1 μm. More desirably, the average particle diameter is 0.01 μm to 0.1 μm. When the particle size is 0.1 μm or less, the effect of preventing oxidation by coating the surface with carbon is particularly remarkable. Further, for example, ultrafine metal particles having excellent oxidation resistance such as an average particle size of 0.2 to 0.5 μm can be obtained.
[0024]
  [12] In the above [11], the metal oxide is an oxide containing a transition metal. The metal particles are preferably selected from Fe, Ni, Co, and an alloy containing at least one of them. Examples thereof include Fe particles coated with carbon, Ni particles coated with carbon, FeNiCo particles coated with carbon, NiFe particles coated with carbon, and the like.
  [13] In the ultrafine metal particles of [11] or [12], the carbon may have a crystal structure of graphite and amorphous, and may be mainly composed of graphite.
[0025]
  [14] The ultrafine metal particles according to any one of [11] to [13], wherein the carbon has a thickness of 100 nm or less. More preferably, the film thickness can be 20 nm or less.
[0026]
  [15] The ultrafine metal particles according to any one of [11] to [14], wherein the carbon has two or more crystal lattice planes or stacked planes. More preferably, the film has four or more crystal lattice planes or stacked planes. Here, it is preferable that carbon is mainly composed of graphite, and the lattice plane or the lamination plane of the crystal is a graphite lamination plane. It is desirable that the lattice plane or the laminate plane of the crystal is formed along the plane of the metal particles.
  [16] In the above [15], an intermediate phase may be provided in the particles or carbon.
[0027]
  Since the carbon constituting the coating is mainly graphite whose lattice planes are arranged in layers, it has a plurality of layered lattice planes in which six-membered rings are connected. That is, a plurality of crystal lattice planes are provided. The lattice plane of the layered lattice may have a laminated structure with respect to the surface of the particle. Since the interface between the particle and the coating has an intermediate layer, a region where transition metal and carbon are mixed, or a crystal matching region of both, forming the layered lattice plane in at least two layers suppresses oxidation of the particle This is desirable. The plane of the layered lattice (lattice surface) can be formed, for example, within a range of 4 to 20 layers. The intermediate phase refers to a portion or boundary region of an intermediate structure between the crystal structure of the metal particles and the crystal structure of the coating. The thickness of the intermediate phase is about 1 to 5 layers of the lattice spacing of graphite or the graphite layer. When the intermediate phase is thin, it is considered that the crystal lattice mismatch between the particles and the carbon film is relaxed and eliminated at a short distance, and the entire surface of the particles can be uniformly coated with the carbon film.
[0028]
  [17] In any one of the above [11] to [16], the metal superFineThe main component of the particles is a magnetic metal element, and the saturation magnetization of the ultrafine metal particles is the magnetic metal element.Material specificThe saturation magnetization is 10% or more and less than 100%. Regarding the above [17], when the core of the ultrafine metal particles is composed of magnetic particles, the coating carbon film can be made extremely thin with a film thickness of 30 nm or less. Therefore, the volume fraction occupied by the magnetic particles can be increased in the ultrafine metal particles. Compared with the prior art, it is possible to suppress a decrease in saturation magnetization of the ultrafine metal particles. In a particle composed of a transition metal or an alloy containing a transition metal, when the saturation magnetization peculiar to the material of the main component responsible for magnetism is used as a reference (that is, 100%), the metal ultrafine particles in which the particle is coated with a carbon film The saturation magnetization of may have a magnitude of 10% or more with respect to the reference.
[0029]
  [18] In any one of the above [11] to [17], after heat treatment under conditions of humidity 100%, temperature 120 ° C., 1 atm, 24 hours with respect to the oxygen content (mass%) before heat treatment The oxygen mass increment is 50% or less. Even if the surface of the ultrafine metal particles is not completely covered with the carbon film, that is, even if the coating is locally thin, it can be used. However, since it is difficult to prevent the progress of oxidation when stored for a long period of time, it is desirable to completely cover the surface of the ultrafine particles with a carbon film.
[0030]
  The magnetic particles may contain impurities or unavoidable impurities (elements originally contained in the raw material) contained in the raw materials to such an extent that the magnetic properties are not extremely deteriorated.
  In the X-ray diffraction pattern of a particle composed of a metal or an alloy, the peak having the first to second highest intensity (Intensity (cps)) corresponds to the main element of the particle or the peak of graphite. It is desirable to be. More preferably, the peak of the oxide of the elements constituting the particles (excluding carbon) is sufficiently smaller than the third highest peak appearing in the X-ray diffraction pattern or not detected at all.
[0031]
  [19] In the method for producing ultrafine metal particles of the present invention, a powder obtained by mixing a powder containing a metal oxide and a powder containing carbon is heat-treated in an inert atmosphere to coat the surface with carbon. It is characterized by producing metal particles. It is desirable that the metal oxide contains a transition metal (more preferably, it is composed of a transition metal oxide). It is desirable that the produced metal particles coated with carbon have an average particle size of 1 μm or less.
[0032]
  In the production method of [19], more preferably, a powder obtained by mixing particles containing iron oxide and particles containing carbon is heat-treated in an inert atmosphere to reduce the iron oxide to at least one of iron or iron carbide. Then, by producing a carbon oxide, at least one kind of particles of iron or iron carbide, the surface of which is coated with carbon, is produced.
[0033]
  The method for producing ultrafine metal particles according to the above [19] is characterized in that the step of reducing the metal oxide particles and the step of coating the surfaces of the metal particles with a carbon film are performed in one heat treatment step. The production method of the present invention is superior to the production method of a comparative example that will be described later in that it hardly contains oxygen. In the manufacturing method of the comparative example, after producing metal ultrafine particles, in order to avoid spontaneous ignition and combustion (oxidation), oxygen is gradually converted into metal ultrafine particles in an inert atmosphere containing a low concentration of oxygen. And a thin oxide film is formed on the surface.
[0034]
  [20] In the above [19], the heat treatment is performed at a temperature of 600 to 1600 ° C.
[0035]
  [21] According to the method of manufacturing a microbody of the present invention, a boron nitride microparticle is obtained by heat-treating a powder obtained by mixing a powder containing a metal oxide and a powder containing boron in an atmosphere containing nitrogen. It is characterized by producing a body. Here, the micro object corresponds to a micro object obtained as a by-product when the ultrafine metal particles according to any one of [1] to [10] are produced.
[0036]
  [22] According to another method for producing a microscopic object of the present invention, a powder containing boron and metal oxide particles is heat-treated in an atmosphere containing nitrogen to thereby form metal particles or boron nitride. It is characterized in that a product having at least one microbody is obtained. The metal particles may be coated with boron nitride. As the atmosphere containing nitrogen, for example, nitrogen gas, a mixed gas obtained by mixing nitrogen gas with a rare gas such as argon gas, or the like can be used.
[0037]
  [23] In the above [21] or [22], the heat treatment is performed at a temperature of 800 to 1700 ° C.
[0038]
  The production method according to any one of [21] to [23] is very excellent in mass productivity. The required thermal energy is small compared to the conventional manufacturing method. In addition, high vacuum is not required, and precise pressure control of the atmosphere is unnecessary. Since an inert gas is used, the heat treatment furnace is not damaged, and there is no problem that impurities are mixed into the micro object due to the damage. Furthermore, there is no explosive or toxic danger. The oxide powder used as a raw material is easy to produce and handle even if it is a nanometer-sized particle. Another advantage is that the raw material is hardly ignited or burned, and the problem that the raw material loss or shape due to the ignition or the like is out of design or the process interruption is difficult to occur.
[0039]
  [24] A powder having boron nitride microparticles and metal particles is produced by the method for manufacturing a microparticle according to any one of [21] to [23], and at least a part of the metal particles is formed from the powder. It is characterized by removing. It is desirable to remove all the metal particles to make a powder containing only boron nitride microparticles. That is, a process of removing the metal particles or the fine particles containing the metal particles after the heat treatment is performed. For example, when the metal particles reduced during the heat treatment are further grown to become coarse metal particles, it is desirable to remove them.
  This process is a step of increasing the proportion and purity of boron nitride in the fine powder. For example, this micro object is dispersed in a medium (liquid), and the specific gravity difference between the metal-based particles and the boron nitride micro object (or the specific gravity difference between the metal-containing micro object and the metal-free micro object) is used. A method of separating and reducing metal particles and the like by a method such as natural sedimentation after centrifugation and centrifugation (separation method 1) can be used. Alternatively, a method (wet method or dry method) in which a magnetic field is applied to metal particles to be attracted and separated from fine particles of boron nitride that are not attracted (wet method or dry method) can be used. Moreover, the method of reducing the quantity of a metal particle can be used by chemically dissolving and removing a metal particle with solutions, such as an acid (separation method 3). Separation method 3 may be mixed with undissolved residues and impurities, but is effective in reducing metal particles. When the surfaces of the metal particles are all covered and a solution such as an acid does not penetrate, it is desirable to perform the separation method 1 or the separation method 2 in order to increase the purity of the powdered microparticles. It should be noted that even if the fine powder contains a metal powder, it is not necessarily a problem. The microscopic body has a small size and powder handling is not easy. For example, a powder containing a transition metal fine particle powder as a carrier has an advantage that it is easier to handle than a powder consisting of only a fine body.
[0040]
  [25] Another minute body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere containing nitrogen, and is mainly composed of boron nitride, and has a wire shape or a cylindrical shape. It is characterized by. Boron nitride is preferably rhombohedral. This fine body is obtained as a by-product when the metal ultrafine particles according to the above [1] to [10] are produced.
  Another micro body of the present invention is a micro body in which nitrogen and boron are combined by reducing a metal oxide in an inert gas atmosphere containing nitrogen, and is mainly composed of boron nitride. It is wire-shaped or cylindrical. By performing a heat treatment in an inert atmosphere containing nitrogen using a metal oxide as a mediator or promoter, boron and nitrogen are combined to form a boron nitride microparticle. As the metal oxide, for example, a metal or alloy oxide can be used. In particular, it is desirable to use a transition metal or an alloy containing at least one transition metal. More preferably, a magnetic metal oxide is used. For example, the metal or alloy can be selected from Fe, Ni, Co, and an alloy containing at least one of them.
[0041]
  “Micro body” means, for example, a nanotube, a nanowire, a three-dimensional atomic structure, a nanoparticle, a structure having dimensional characteristics on the order of nanometers (nm), an aggregate or a powder including at least one of them ( Or a fine substance such as powder). The micro body having a cylindrical shape is more preferably a nanotube. “Wire shape or cylindrical shape” means, for example, a wire shape, a rod shape, a tube shape, a tubular shape, a hollow or solid shape, a combination of any of these, a small piece (plate shape) It is used as a term including a long shape formed by adding pieces, scale pieces or block pieces).
[0042]
  [26] In the above [25], the micro body has an average diameter of 0.5 μm or less. The average diameter is desirably 0.01 to 0.5 μm, and more desirably 0.05 to 0.5 μm. More specifically, for example, the diameter may be 0.1 to 0.3 μm.
  In addition, if a fine powder having an average particle diameter in the range of 0.001 to 1 μm is used as the metal oxide as a raw material, a fine body having a diameter in the range of 0.001 to 1 μm can be obtained. More preferably, a metal body having a mean particle diameter of 0.001 to 0.05 μm is used to obtain a minute body having a diameter of 0.001 to 0.05 μm. By using a raw material having a small average particle size and a sharp particle size distribution, a microparticle having a small average diameter can be obtained.
[0043]
  The diameter corresponds to, for example, the outer diameter when a cross section (cross section in a direction perpendicular to the longitudinal direction) of a wire-like or cylindrical part is seen for one minute body. When the cross section is not circular, the maximum value is regarded as the diameter. When the micro object has a diameter that gradually changes along the longitudinal direction, an intermediate value between the maximum diameter and the minimum diameter when viewed in the longitudinal direction may be expressed as the diameter of the micro object. If there is a location that deviates significantly from the wire or cylindrical shape, the location is ignored and the diameter is evaluated only at the wire or cylindrical portion.
[0044]
  With an average diameter, for example, an electron micrograph is taken using a powder having a wire-like or cylindrical fine body as a sample. The average value is obtained by measuring the diameter of each micro object within an arbitrary area in the photograph. That is, for N micro objects (N ≧ 50), the diameter is measured and expressed as average diameter = (sum of measured diameters) / N. Instead of a photograph, an image may be acquired and the diameter may be measured using a personal computer and image processing software.
[0045]
  [27] Another minute body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere, and the ratio of the outer diameter Ro to the inner diameter Ri is (Ri / Ro) ≦ 0.8. It is a cylindrical boron nitride micro body provided with a part. When the ratio of Ri / Ro is close to 1, the wall thickness is reduced, so that the weight of the micro object is reduced, and as a result, the specific surface area is increased. The boron nitride microbody according to the present invention has a portion where the ratio of (Ri / Ro) is close to 1, but there is also a portion where the inner diameter is small. For example, the inner diameter may be reduced at the end of the cylindrical shape or at the location where the cylindrical shape is bent, but this is practically acceptable.
  This boron nitride micro body can be formed in multiple layers of boron nitride atomic layers constituting the wall of the tube, and can also be generated to increase the number of nodes and bridges. Therefore, it is also possible to manufacture a micro object with a small (Ri / Ro) by increasing the thickness of the wall of the wire or cylindrical micro object. Ri is an inner diameter (corresponding to the diameter of the cavity) when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction, and does not include a cross section of a node. Ro corresponds to the outer diameter when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction.
[0046]
  [28] Another micro body of the present invention is a mixture of a rhombohedral phase boron nitride micro body and a hexagonal phase boron nitride micro body.
  Regarding the crystal structure, rhombohedral boron nitride is also expressed as r-BN. Hexagonal boron nitride (Hexagonal Boron Nitride) is also represented as h-BN.
  [29] Another micro body of the present invention is boron nitride having a rhombohedral phase and a hexagonal phase.
[0047]
  [30] Another minute body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere, and is mainly composed of boron nitride, and is cylindrical and has nodes or bridges inside. It is characterized by having.
  Here, the “node” corresponds to a member that can divide the inside of a cylindrical (or tubular) microscopic object into a plurality of cavities or be divided into a plurality of compartments. “Bridge” corresponds to a member that connects arbitrary portions of the inner wall of a cylindrical microscopic object. It is considered possible to construct a node by gathering more bridges. The surface of the node is close to the tube wall or the cylindrical wall, rather than being arranged parallel to each other, rather than being arranged orthogonally. When there are a plurality of nodes, the interval between the nodes is set to 0.5 d or more, for example. Here, d corresponds to the diameter d of the cylindrical portion between the nodes. In addition, even if the micro body is provided with a plurality of nodes, the outer diameter and the wall thickness are not always unilaterally decreased, but can be increased rather, and a long micro body can be obtained. it can.
[0048]
  [31] Another minute body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere, and includes metal particles, a boron nitride film covering the metal particles, and a wire shape or a cylindrical shape. It is characterized by comprising boron nitride.
  The wire-shaped or cylindrical portion is not limited to one growth direction, and may have a plurality of growth directions. The wire-like or cylindrical boron nitride may be grown directly from the boron nitride film, or may be grown directly from metal particles obtained by reducing the metal oxide. The metal particles may be arranged at either the tip or the center of the boron nitride microparticle. As a state of arrangement, one metal particle is provided with one boron nitride micro body (or a structure in which bonding, connection, bonding, connection, and connection) is provided, or one metal particle is provided with a plurality of boron nitrides. A structure provided with elementary micro-objects can be mentioned. As another arrangement state, there is a structure (or a structure such as covering, fitting, embedding, inclusion, winding, holding, carrying, etc.) in which metal particles are encapsulated in a carbon microparticle. The arrangement state of the metal particles can be changed by changing conditions such as raw materials and heat treatment in the manufacturing method.
  The metal particles are preferably composed of a transition metal or an alloy containing at least one transition metal. More preferably, the metal particles are made of a magnetic metal. For example, the metal particles have a composition selected from Fe, Ni, Co, and an alloy containing at least one of them.
[0049]
  [32] According to another method of manufacturing a micro object of the present invention, a carbon micro object is obtained by heat-treating a powder containing a metal oxide-containing powder and a carbon-containing powder in an inert atmosphere. It is characterized by producing. More desirably, the fine powder of carbon is produced by heat-treating a powder obtained by mixing a powder composed of an oxide of a transition metal and a carbon powder in an inert atmosphere. This method for producing a micro object relates to a micro object that can be obtained as a by-product when producing the ultrafine metal particles according to the above [11] to [20] and a method for producing the micro object.
[0050]
  [33] According to another method of manufacturing a microparticle of the present invention, a metal particle or a carbon microparticle is produced by heat-treating a powder containing carbon and metal oxide particles in an inert atmosphere. It is characterized in that a product having at least one is obtained. The metal particles may be coated with carbon.
[0051]
  [34] In the above [32] or [33], the heat treatment is performed at a temperature of 600 to 1600 ° C.
[0052]
  The production method according to any one of the above [32] to [34] is very excellent in mass productivity. The required thermal energy is small compared to the conventional manufacturing method. In addition, high vacuum is not required, and pressure control of the atmosphere is not easily restricted by mass production. Since an inert gas is used, the heat treatment furnace is not damaged, and there is no problem that impurities are mixed into the micro object due to the damage. The oxide powder used as a raw material is easy to produce and handle even if it is a nanometer-sized particle. Another advantage is that the raw material is hardly ignited or burned, and the problem that the raw material loss or shape due to the ignition or the like is out of design or the process interruption is difficult to occur.
[0053]
  [35] A powder having carbon microparticles and metal particles is produced by the method for manufacturing a microparticle according to any one of [32] to [34], and at least a part of the metal particles is removed from the powder. It is characterized by that. It is desirable to remove all of the metal particles to make a powder of only carbon fines. That is, a process of removing the metal particles or the fine particles containing the metal particles after the heat treatment is performed. For example, when the metal particles reduced during the heat treatment are further grown to become coarse metal particles, it is desirable to remove them. As this removal process, the same process as in the above [24] can be used.
[0054]
  [36] Another minute body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere, is composed of carbon in a graphite phase, and is characterized by a wire shape or a cylindrical shape. To do. By performing a heat treatment in an inert atmosphere using a metal oxide as a mediator or accelerator, carbon is decomposed and reconstructed to obtain carbon microparticles. This fine body can be obtained as a by-product when the metal ultrafine particles according to the above [11] to [20] are produced.
  The micro body of the present invention is a micro body in which the shape of carbon particles is reconstructed by reducing a metal oxide in an inert gas atmosphere, and is mainly composed of carbon and has a wire-like or cylindrical shape. It is characterized by having. More specifically, particulate carbon is decomposed and reconstructed using a reduction reaction that takes oxygen away from the metal oxide and an inert gas, thereby generating a carbon micro-particle. As the metal oxide, for example, a metal or alloy oxide can be used. In particular, it is desirable to use a transition metal or an alloy containing at least one transition metal. More preferably, a magnetic metal oxide is used. For example, the metal or alloy can be selected from Fe, Ni, Co, and an alloy containing at least one of them.
[0055]
  [37] In the above [36], the minute body has an average diameter of 0.5 μm or less. The average diameter is desirably 0.01 to 0.5 μm, and more desirably 0.05 to 0.5 μm. More specifically, for example, the diameter may be 0.1 to 0.3 μm. In addition, if a fine powder having an average particle diameter in the range of 0.001 to 1 μm is used as the raw material metal oxide, a fine body having an average diameter in the range of 0.001 to 1 μm can be obtained. More preferably, a metal body having an average particle diameter of 0.001 to 0.05 μm is used to obtain a minute body having an average diameter of 0.001 to 0.05 μm. By using a raw material having a small average particle size and a sharp particle size distribution, a microparticle having a small average diameter can be obtained.
[0056]
  [38] Another minute body of the present invention is formed by reducing a metal oxide in an inert gas atmosphere, and is a cylindrical carbon minute body having a ratio of an outer diameter Ro to an inner diameter Ri of ( (Ri / Ro) ≦ 0.8.
  When the ratio of (Ri / Ro) is close to 1, the wall thickness is reduced, so that the weight of the micro object is reduced, and as a result, the specific surface area is increased. The carbon microbody according to the present invention has a portion where the ratio of (Ri / Ro) is close to 1, but there is also a portion where the inner diameter is small. For example, the inner diameter may be small at the end of the cylindrical shape or where the cylindrical shape is bent, but this is practically acceptable.
  This carbon micro-object can be formed to have multiple layers of graphite atomic layers constituting the wall of the tube, and can also be generated to increase the number of nodes and bridges. Therefore, it is also possible to manufacture a carbon micro object with a small (Ri / Ro) by increasing the wall thickness of the wire or cylindrical carbon micro object. Ri is an inner diameter (corresponding to the diameter of the cavity) when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction, and does not include a cross section of a node. Ro corresponds to the outer diameter when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction.
[0057]
  [39] Another minute body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere, and is mainly composed of carbon in a graphite phase, and is cylindrical and has nodes or bridges inside. It is characterized by having.
  Here, the definition of “clause” is the same as described in [30] above.
[0058]
  [40] Another fine body of the present invention is produced by reducing a metal oxide in an inert gas atmosphere, and includes metal particles, a carbon film covering the metal particles, and wire-like or cylindrical carbon. It is characterized by providing.
  The metal particles are preferably composed of a transition metal or an alloy containing at least one transition metal. More preferably, the metal particles are made of a magnetic metal. For example, the metal particles have a composition selected from Fe, Ni, Co, and an alloy containing at least one of them.
[0059]
DETAILED DESCRIPTION OF THE INVENTION
  An embodiment of the present invention according to any one of the above [1] to [10] will be described. In the present invention according to the above [1] to [10], the metal powder raw material of the transition metal, especially Fe, Co, Ni, etc., plays the role of a boron nitride (BN) formation catalyst, It was noted that when the metal powder and boron (B) were heated at around 2000 ° C., boron nitride was formed with the metal particles as nuclei. Furthermore, when the starting material is not a metal but an oxide of a transition metal typified by Fe, Co, and Ni, the oxide is reduced at 800 ° C. to 1700 ° C. and boron nitride is formed at the same time. It has been found that novel ultrafine metal particles encapsulated in a boron nitride coating (BN coating) are produced.
[0060]
  The metal oxide which is the starting material of the present invention according to the above [1] to [10], the concept of the raw material of boron, the reason for limiting the numerical value, and the like will be described. The metal constituting the oxide according to the present invention (hereinafter referred to as M) is preferably a transition metal or an alloy thereof (particularly a magnetic material). More preferably, Fe, Co, Ni, Cr, Mn, Mo, Pd, Ir, or an alloy containing them is suitable. Fe, Co, Ni, Cr, Mn, Mo, Pd, and Ir have the standard enthalpy of formation of MB bond (B is boron) as H_M-B, Standard production enthalpy of MN bond (N is nitrogen) is H_MN, H_M-B<H_MN
Therefore, borides are easier to form than nitrides. As a result, boron-containing metal powder is formed in the initial stage of the heat treatment. When nitrogen is in a gaseous state and uniformly exists around the metal powder, boron and nitrogen contained in the metal powder are finally included. And the surface of the metal particles can be easily uniformly coated with boron nitride. Metal oxide (M_aO_b) May have been conventionally shown in a phase diagram, for example, in the case of Fe, Fe₂O₃, Fe₃O₄FeO.
[0061]
  Further, boron is suitable as a raw material powder to be a boron supply source, but a metal containing boron may be used. For the metal (M) containing boron, the standard enthalpy of formation of MB bond is H_M-B, Standard production enthalpy of MN bond is H_MN,
  H_M-B> H_MN
That in which the relationship is established is preferable, and examples thereof include Sc, Ti, V, Y, Zr, Nb, La, Hf, and Ta.
[0062]
  (Reaction process)
  Fe₂O₃A reaction process in which BN-coated Fe particles, a BN tube, or a BN wire is generated by the reaction between B and B will be described. FIG. 3 schematically shows the reaction process. FIG. 3 (1.) shows the state of the raw material. FIG. 3 (2.) shows the state of the initial stage of the reaction. That is, B is Fe₂O₃B combined with oxygen₂O₃And reduced Fe particles are present in the vicinity of B. B₂O₃Is in a liquid phase or gas phase. Further, the progress of the reaction is shown in FIG. At this stage, B reacts with Fe to form an Fe—B compound. As shown in the figure, the structure of the powder includes complete Fe—B compound grains, incomplete B diffusion into Fe, or grains having Fe as the core and Fe—B compound in the vicinity of the surface. . When the reaction further proceeds, as shown in FIG. 3 (4), B in the Fe—B compound reacts with N atoms in the atmosphere, and BN nuclei are generated all over the particle surface. When these BN nuclei grow, B diffuses from the inside of the particle to the surface. As a result, only Fe remains inside the particles, and BN-coated Fe particles are generated. Further, when B is excessively present, BN is not limited to covering Fe but extends in a tube shape or a wire shape. FIG. 3 (5.) is a schematic diagram of BN-coated Fe particles and a BN tube.
[0063]
  The average particle diameter of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. If the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and it is not easy to obtain uniform metal particles. The average particle size of the boron powder (b powder) is preferably 0.01 to 100 μm, more preferably 1 to 50 μm. Boron powder with an average particle size of less than 0.01 μm is expensive and impractical. On the other hand, if the average particle diameter exceeds 100 μm, the dispersion of the powder b in the mixed powder is biased, and finally it becomes difficult to uniformly coat the metal particles. The mixing ratio of the a powder and the b powder is preferably in the range of 25 to 95% by weight of the b powder. If the mass ratio of the b powder is less than 25%, the reduction of the metal oxide becomes insufficient due to the lack of boron. If the blending ratio of boron powder exceeds 95%, the volume ratio of the metal to be reduced becomes extremely small, which is not practical.
[0064]
  For the mixing of the a powder and the b powder, a V-type mixer, a pulverizer (for example, a device that combines pulverization and mixing as in the case of a raikai machine), a mortar or the like is used. The mixed powder is heat-treated under a predetermined condition by filling a predetermined amount in a heat-resistant crucible such as alumina or boron nitride. The atmosphere during the heat treatment is preferably a nitrogen gas atmosphere, an ammonia gas atmosphere or a mixed gas atmosphere containing them. The mixed gas may be mixed with an inert gas such as argon or helium. A gas containing oxygen such as air is not suitable because it hinders the reduction reaction. The heat treatment temperature is preferably 800 ° C to 1700 ° C, more preferably 1000 ° C to 1400 ° C. If it is less than 1000 degreeC, the time required for reaction to complete will become long. If it is less than 800 degreeC, reaction itself does not advance. When the temperature exceeds 1400 ° C. in a non-oxygen atmosphere, there is a concern that oxygen may be released due to the decomposition of the oxide ceramic used as the furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. When the temperature exceeds 1700 ° C., it is indispensable to use a heat-resistant member not only for the crucible but also for the equipment itself, which increases the manufacturing cost and is not suitable for industrialization.
[0065]
  Next, an embodiment of the present invention according to any one of [11] to [20] will be described. In the present invention related to the above [11] to [20], transition metal oxides typified by Fe, Co, and Ni are selected and heated as the raw material for the metal powder of the transition metal. It has been found that the oxide is reduced at ℃ and carbon mainly composed of graphite is formed on the surface of the metal particles. Moreover, the structure by which a metal particle is included in a carbon film was also discovered. It is considered that transition metals, especially Fe, Co, and Ni, which are constituent elements of the starting material, play a role of a catalyst for forming a graphite layer.
[0066]
  Carbon powder such as graphite, carbon black, and natural graphite is suitable as a raw material powder to be a carbon supply source, but may be a compound containing carbon. That is, it may be a carbon containing carbon, activated carbon, coke, fatty acid, polymer such as polyvinyl alcohol, BC compound, or metal. Therefore, in the means for solving the claims and the problems, “carbon powder” is used as a term encompassing both carbon powder and a compound containing carbon. However, carbon powder may be used to increase the carbon purity of the coating.
[0067]
  The average particle diameter of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. If the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particle, and it is not easy to obtain uniform metal particles. The average particle size of the carbon powder (b powder) is preferably 0.01 to 100 μm, more preferably 0.1 to 50 μm. Carbon powder having an average particle size of less than 0.1 μm is expensive and impractical. On the other hand, when the average particle size exceeds 100 μm, the dispersion of the powder b in the mixed powder is biased, and the metal particles cannot be uniformly coated finally. The mixing ratio of the a powder and the b powder is preferably in the range of 25 to 95% by weight of the b powder. If the weight ratio of the powder b is less than 25%, the reduction reaction does not proceed sufficiently due to insufficient carbon. On the other hand, if the blending ratio of the powder b exceeds 95%, the volume ratio of the metal to be reduced becomes extremely small, which is not practical. An average particle diameter of 0.001 to 1 μm, more desirably 0.01 μm to 0.1 μm, is used in applying the ultrafine metal particles of the present invention to magnetic recording media, magnetic shields, electronic devices, and the like. desirable.
[0068]
  For the mixing of the a powder and the b powder, a V-type mixer, a pulverizer (for example, a device that combines pulverization and mixing as in the case of a raikai machine), a mortar or the like is used. The mixed powder is heat-treated under predetermined conditions by filling a predetermined amount of transition metal oxide and carbon compound in a heat-resistant crucible such as alumina, boron nitride, and graphite. The atmosphere during the heat treatment is not limited as long as it is an inert gas, but a mixed atmosphere with nitrogen gas or an inert gas such as argon gas containing nitrogen as a main component can be used. The heat treatment temperature is preferably 600 ° C to 1600 ° C, more preferably 900 ° C to 1400 ° C. If it is less than 900 degreeC, the time required until reaction is completed will become long. If the temperature is lower than 600 ° C., the reaction itself does not proceed. Further, when the temperature exceeds 1400 ° C. in a non-oxygen atmosphere, there is a concern that oxygen may be released due to decomposition of oxide ceramics used as a furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. When the temperature exceeds 1600 ° C., it is indispensable to use a heat-resistant member not only for the crucible but also for the equipment itself, which increases the manufacturing cost and is not suitable for industrialization.
[0069]
  Next, embodiments of the invention relating to the above [21] to [31] will be described.
  According to the present invention according to the above [21] to [31], when the transition metal oxide (a powder) and the boron powder (b powder) are heated at a temperature of 800 to 1700 ° C. in a nitrogen atmosphere, the metal oxidation is performed. The product serves as a catalyst for forming boron nitride microparticles, and a wire-shaped boron nitride microparticle powder having an average diameter of 0.5 μm or less can be produced. Compared with the prior art, boron nitride micro bodies can be manufactured at a low temperature.
[0070]
  a transition metal or an alloy thereof (particularly magnetic material) is preferable as the metal constituting the oxide of the powder, more preferably Fe, Co, Ni, Cr, Mn, Mo, Pd, Ir or an alloy containing them is suitable. Yes. Metal oxide (M_aO_b) May have been conventionally shown in a phase diagram. For example, when M is Fe, Fe₂O₃, Fe₃O₄FeO. The metal oxide is reduced in the process of forming boron nitride, and finally becomes metal particles.
[0071]
  In addition to the boron powder, the b powder may be a metal powder containing boron. As the metal (M) containing boron, the standard enthalpy of formation of MB bond (B is boron) is H._M-B, Standard production enthalpy of MN bond (N is nitrogen) is H_MN,
  H_M-B> H_MN
Those satisfying the relationship are preferable. Specific examples include Sc, Ti, V, Y, Zr, Nb, La, Hf, and Ta.
[0072]
  The average particle diameter of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. On the other hand, if the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and it does not function sufficiently as a catalyst. The average particle size of the boron powder (b powder) is preferably 0.01 to 100 μm. Boron powder with an average particle size of less than 0.01 μm is expensive and impractical. On the other hand, if the average particle size exceeds 100 μm, the dispersion of the powder b in the mixed powder becomes uneven, and it becomes difficult to finally coat the metal particles uniformly. The mixing ratio of the a powder and the b powder is preferably in the range of 25 to 95% by weight of the b powder. When the weight ratio of the powder b is less than 25%, boron is insufficient and boron nitride is not sufficiently formed. On the other hand, when the blending ratio of the powder b exceeds 95%, the powder a is decreased, the catalytic function is lowered, and boron nitride is not sufficiently formed.
[0073]
  A V-type mixer or a mortar is used for mixing the powder a and powder b. The mixed powder is heat-treated under predetermined conditions by filling a predetermined amount in a heat-resistant crucible such as alumina or boron nitride. The atmosphere during the heat treatment is preferably a nitrogen gas atmosphere or a mixed gas atmosphere containing nitrogen gas. The mixed gas may be mixed with an inert gas such as Ar or He. Gases containing oxygen such as air are not suitable. The heat treatment temperature is preferably 800 ° C to 1700 ° C, more preferably 1000 ° C to 1400 ° C. If it is less than 1000 degreeC, the time required for reaction to complete will become long. If it is less than 800 degreeC, reaction itself does not advance. When the temperature exceeds 1400 ° C. in an inert gas atmosphere, there is a concern that oxygen may be released due to decomposition of the oxide ceramic used as the furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. . When the temperature exceeds 1700 ° C., it is indispensable to use a heat-resistant member not only for the crucible but also for the equipment itself, which increases the manufacturing cost and is not suitable for industrialization.
[0074]
  When the crystal structure of the boron nitride powder obtained by the above method is identified by X-ray diffraction measurement, hexagonal boron nitride (h-BN) and rhombohedral boron nitride (r-BN) as shown in FIG. These two peaks can be detected. Note that FIG. 18 is described later.Reference example 2The powder obtained in 1 was measured. Further, when the powder structure was observed by TEM observation, it was confirmed that wire-like boron nitride was formed as shown in FIG. 19, and it was identified as h-BN from observation of the lattice image.
[0075]
  Next, embodiments of the invention related to the above [32] to [40] will be described. According to the present invention according to the above [32] to [40], when the transition metal oxide (a powder) and the carbon powder (b powder) are heated at a temperature of 600 to 1600 ° C. in an inert gas atmosphere, the metal The oxide serves as a catalyst for the formation of carbon fine bodies, and a wire-shaped carbon fine body powder having an average diameter of 0.5 μm or less can be produced.
[0076]
  As the metal constituting the oxide of a powder, a transition metal or an alloy thereof (particularly a magnetic material) is preferable. Metal oxide (M_aO_b) May have been conventionally shown in a phase diagram. For example, when M is Fe, Fe₂O₃, Fe₃O₄FeO. The metal oxide is reduced in the process of carbon formation, and finally becomes metal particles.
[0077]
  Further, as the powder b, carbon powder such as graphite, carbon black, and natural graphite is suitable, but a compound containing carbon may be used. That is, it may be coal, activated carbon, coke, fatty acid, polymer such as polyvinyl alcohol, BC compound, or metal carbide.
[0078]
  The average particle diameter of the metal oxide powder (a powder) is preferably 0.001 to 1 μm. Powders having an average particle size of less than 0.001 μm are difficult to produce and are not practical. On the other hand, if the average particle size exceeds 1 μm, oxygen cannot be sufficiently reduced to the center of the particles, and it does not function sufficiently as a catalyst. The average particle size of the carbon powder (b powder) is preferably 0.01 to 100 μm. Carbon powder having an average particle size of less than 0.01 μm is expensive and impractical. The mixing ratio of the a powder and the b powder is preferably in the range of 25 to 95% by weight of the b powder. When the weight ratio of the b powder is less than 25%, carbon is insufficient. On the other hand, when the blending ratio of the powder b exceeds 95%, the powder a is reduced and the catalytic function is lowered.
[0079]
  A V-type mixer or a mortar is used for mixing the powder a and powder b. The mixed powder is heat-treated under predetermined conditions by filling a predetermined amount in a heat-resistant crucible such as alumina or boron nitride. The atmosphere during the heat treatment is preferably an inert gas atmosphere. Gases containing oxygen such as air are not suitable. The heat treatment temperature is preferably 600 ° C to 1600 ° C, more preferably 900 ° C to 1400 ° C. If it is less than 900 degreeC, the time required until reaction is completed will become long. Below 600 ° C, the reaction itself does not proceed. When the temperature exceeds 1400 ° C. in an inert gas atmosphere, there is a concern that oxygen may be released due to decomposition of the oxide ceramic used as the furnace member, and at the same time, for example, an alumina crucible may be damaged in a short period of time. . If the temperature exceeds 1600 ° C., it is indispensable to use a heat-resistant member not only for the crucible but also for the equipment itself, which increases the manufacturing cost and is not suitable for industrialization.
【Example】
[0080]
  Hereinafter, the present invention will be described by way of examples. However, the present invention is not necessarily limited by these examples.
  Example 1
  Α-Fe with an average particle size of 0.6 μm₂O₃5 g of powder (a powder) and 5 g of boron powder (b powder) with an average particle size of 30 μm were weighed, and each powder was put into a V-type mixer so that the blending ratio of b powder was 50% by mass. And mixed for 10 minutes. An appropriate amount of this mixed powder is filled in an alumina boat, placed in a furnace, heated in a nitrogen gas stream having a flow rate of 2 (l / min) at a rate of 3 ° C / min from room temperature, And kept in the furnace for 2 hours. The mixed powder before the heat treatment was reddish black, but the powder after the heat treatment was turned grayish white. When X-ray diffraction measurement (Cu, Kα ray) was performed on each powder before and after heat treatment, diffraction patterns as shown in FIG. 1 (before heat treatment) and FIG. 2 (after heat treatment) were obtained. From the heat-treated powder, the (002) peak of hexagonal boron nitride (h-BN) and the (110) peak of α-Fe were mainly detected. The particle diameter of Fe calculated from the (110) peak of Fe using Rigaku analysis software “Jade 5” was 89 nm. Table 1 summarizes the particle sizes of each phase and Fe detected from the X-ray diffraction pattern. Further, Table 2 shows the results of measuring the magnetic characteristics of the off-white powder by VSM. The saturation magnetization is 20 times or more the value of Comparative Example 2 described later, and together with the result of X-ray diffraction measurement, Fe₂O₃It can be seen that is reduced to Fe. Further, only the powder sucked up from the grayish white powder with a permanent magnet was subjected to a corrosion resistance test for 24 hours at a humidity of 100% and 120 ° C. using a PCT tester, and then subjected to oxygen analysis by an ashing method. The obtained results are shown in Table 3.
[0081]
  (Example 2)
  Fe₂O₃Fe instead of powder₃O₄An off-white powder was prepared in the same manner as in Example 1 except that powder (average particle size: 0.5 μm) was used, and X-ray diffraction, VSM measurement, and PCT test were performed.
[0082]
  (Reference Example 1)
  The mixed powder was heat-treated and subjected to X-ray diffraction and VSM measurement in the same manner as in Example 1 except that the mixing ratio of boron powder (b powder) was 20% by mass.
  (Comparative Example 1)
  The mixed powder was heat-treated in the same manner as in Example 1 except that the heat treatment temperature was 500 ° C., and X-ray diffraction and VSM measurement were performed.
  (Comparative Example 2)
  A corrosion resistance test was performed on Fe powder having an average particle size of 20 nm (ultrafine particles manufactured by Vacuum Metallurgical Co., Ltd.) under the same conditions as in Example 1. The results are shown in Table 3.
[0083]
[Table 1]

[0084]
[Table 2]

[0085]
[Table 3]

[0086]
  (Example 3)
  5 g of Fe oxide powder containing Ni and 5 g of boron powder were put into a V-type mixer and mixed. An appropriate amount of this mixed powder is filled in an alumina boat, placed in a furnace, heated in a nitrogen gas stream having a flow rate of 2 (l / min) at a rate of 3 ° C / min from room temperature, And kept in the furnace for 2 hours. Observation of the powder after the heat treatment gave metal particles whose surface was coated with boron nitride. The composition analysis revealed that the metal particles were Fe containing Ni.
[0087]
  Example 4
  The metal particle and BN or C separation operation will be described. FIG. 4 shows a production process diagram of BN-coated metal particles and BN microparticles. When the coated metal particles are manufactured, the manufacturing process is S1-> S2-> S3-> S4 in FIG. In S 2, the boron nitride crucible 42 containing the raw material powder was heat-treated in the tubular furnace 43. Since the heat-treated powder obtained in S2 is a mixed powder 41 of coated metal particles and fine bodies, the coated metal particles were recovered through the separation and purification steps of S3 and S4. In step S3, the heat-treated powder dispersed in a medium 45 typified by an organic solvent such as acetone or ethanol was stirred in the washing tank 44, and the coated metal particles were naturally precipitated. An ultrasonic cleaning device 46 was used to apply ultrasonic waves to the cleaning tank 44 as a stirring means. In place of applying ultrasonic waves, manual stirring with a glass rod or a stirrer such as a pencil mixer was used as a stirring means, and sufficient stirring was achieved.
[0088]
  In step S4, the coated metal particles 48 were recovered by removing the supernatant liquid 47 and drying the precipitate. At the same time, when the supernatant was dried, BN microparticles were recovered. In the above process, BN-coated metal particles and BN microparticles could be obtained simultaneously. In particular, when only the BN micro object is manufactured, the manufacturing process may be S1-> S2-> S5-> S6 in FIG. Step S5 is a step of dissolving the metal particles in the heat-treated powder with an acidic solution such as hydrochloric acid or sulfuric acid. After the heat treatment powder was immersed in the acidic solution, the precipitate was collected. In step S6, the precipitate is washed with water and then dried. An appropriate amount of pure water was poured into the precipitate obtained in S5, and the mixture was stirred with a glass rod or the like, and then precipitated again to remove the supernatant, followed by drying to obtain BN microparticles. In order to completely remove the acidic solution, the step S6 is preferably repeated several times. The above production process could be applied to a process of producing metal particles and carbon microparticles coated with carbon.
[0089]
  FIG. 5 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope (TEM), showing BN-coated Fe particles. FIG. 6 is a schematic diagram for schematically explaining the structure of FIG. As shown in FIG. 6, the Fe particles 1 are covered with a BN film 2. The photograph which expanded further the mode of the BN film is shown in FIG.
[0090]
  FIG. 7 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope, showing BN-coated Fe particles. FIG. 8 is a schematic diagram for schematically explaining the structure of FIG. As shown in FIG. 7, the BN film coated on the surface of the Fe particles 1 has a stripe pattern of stacked crystal lattices. In the portion of the lattice plane 3, a plurality of lattice planes are stacked substantially in parallel with the lattice plane along the surface of the Fe particle 1. It can be seen that the portions of the lattice plane 4 and the lattice plane 5 have portions where the lattice planes are not parallel to each other, but sufficiently cover the surface of the Fe particles 1.
[0091]
  (Example 5)
  Α-Fe with an average particle size of 0.03 μm₂O_Three5 g of powder (a powder) and 5 g of carbon powder (b powder) having an average particle diameter of 20 μm were put into a V-type mixer and mixed for 10 minutes. An appropriate amount of this mixed powder 51 is filled in a boron nitride crucible 52, the crucible 52 is placed in a tubular furnace 53, and the temperature is increased from room temperature to 3 ° C./min in a nitrogen gas flow with a flow rate of 2 l / min. Then, it was kept at 1000 ° C. for 2 hours and cooled to the room temperature at a rate of 3 ° C./min. The structure of the tubular furnace is shown schematically in FIG. When X-ray diffraction measurement (Cu, Kα ray) was performed on each powder before and after heat treatment, diffraction patterns as shown in FIG. 9 (before heat treatment) and FIG. 10 (after heat treatment) were obtained. From the heat-treated powder, the (002) peak of graphite and the (110) peak of α-Fe were mainly detected. Further, Table 4 shows the results of measuring the magnetic characteristics of the powder after the heat treatment with a VSM (sample vibration magnetometer). The saturation magnetization is about 100 times the value of Comparative Example 4, and together with the result of X-ray diffraction measurement, Fe magnetization₂O_ThreeIt can be seen that is reduced to Fe. After the heat-treated powder is exposed to a PCT tester (pressure cooker test tester) at 100% humidity, 120 ° C. and 1 atm for 24 hours, the oxygen content of the powder is analyzed for oxygen / nitrogen / hydrogen analyzer in metal ( HORIBA EMGA-1300). The analysis results of the oxygen amount are shown in Table 5. Even after the PCT test, there is no increase in oxygen content, confirming that the Fe powder surface is coated with a graphite film. The analysis of oxygen, nitrogen, and hydrogen in the metal described above was performed by pyrolyzing O, N, and H in the sample by filling a graphite crucible with 0.5 g of the sample powder and rapidly heating the crucible to 2000 to 3000 ° C. , CO generated by gas chromatograph and thermal conductivity detector₂, N₂, H₂In this method, the content of O, N, and H is analyzed by detecting O gas.
[0092]
  (Comparative Example 3)
  The mixed powder was heat treated in the same manner as in Example 5 except that the heat treatment temperature was 500 ° C., and X-ray diffraction, VSM measurement, and PCT test were performed. The X-ray diffraction pattern does not change before and after the heat treatment, and the reaction does not proceed. The value of saturation magnetization is hardly changed.
[0093]
  (Comparative Example 4)
  A corrosion resistance test was performed on Fe powder (ultrafine particles manufactured by Vacuum Metallurgical Co., Ltd.) having an average particle size of 0.02 μm under the same conditions as in Example 5. The saturation magnetization is that of pure iron (about 260 × 10^-6wb · m / kg) to about 30%.
[0094]
[Table 4]

[0095]
[Table 5]

[0096]
  FIG. 11 is a photomicrograph of the structure of ultrafine metal particles according to Example 5 observed with a TEM (transmission electron microscope). In TEM observation, no processing that gives damage or mutation to particles other than the necessary sample preparation is performed. FIG. 12 is a schematic diagram schematically illustrating the structure of FIG. 11 and is slightly enlarged. The ultrafine metal particles 11 are particles in which the surfaces of α-Fe particles 12 are all coated with a graphite thin film 20 having a predetermined thickness. This coating protects the surface of the α-Fe particles 12 and effectively prevents oxidation. The projections 21 and 21b scattered on the outside of the graphite thin film 20 are presumed to be either those in which a different layer of graphite has grown or those to which foreign matter has adhered. The light-dark patterns 13a, 13b, and 13c of the α-Fe particles 11 themselves are interference patterns (indicated by two-dot chain lines) due to the shape (substantially spherical) of the α-Fe particles 11. At both ends of the α-Fe particles, the boundary 14 of the graphite thin film is photographed slightly indistinctly, so that it is indicated by a dotted line. This is because it is difficult to focus on everything due to the substantially spherical shape, and the actual shape is not unclear. A region whose outline is indicated by a one-dot chain line is a collodion film 15 for fixing the metal ultrafine particles 11 to a sample holder for TEM observation. A line and a reference numeral 16 are scales corresponding to a length of the three lines of 20 nm. The scale at the time of photographing FIG. 11 was copied and added to FIG.
[0097]
  FIG. 13 is a photomicrograph of the particle structure according to the present invention observed with a TEM (transmission electron microscope), and illustrates the appearance of the graphite thin film 20 by enlarging the vicinity of the lower left half of FIG. The structure of FIG. 13 will be schematically described with reference to the schematic diagram of FIG. The graphite thin film 20 is mainly composed of a graphite crystal structure. For example, the lattice fringes 20 a, 20 b, and 20 c represent a layered lattice plane of graphite, and the lattice fringes are substantially equally spaced and are arranged substantially parallel to the surface of the α-Fe particles 12.
[0098]
  However, since the α-Fe particles are spherical and have some irregularities on the surface thereof, a part of the graphite thin film is inclined with respect to the surface of the α-Fe particles 12 like the lattice stripes 20f. There are also places that do. The lattice fringes 20f are derived from the other lattice fringes 20e, and further become the lattice fringes 20d. Although the illustration of the lines is omitted, the lattice fringes 20d are arranged substantially parallel to the surface of the α-Fe particles 12. As described above, the graphite thin film has a portion where the arrangement direction of the layered lattice plane is changed or the arrangement state is unclear (a portion that looks like a satin pattern), but the adjacent crystal structures are matched. In order to grow such that the plane of the crystal structure is parallel to the surface of the α-Fe particles 12, a substantially uniform graphite thin film coating is formed.
[0099]
  In the graphite thin film 20 of FIG. 14, a part of lattice fringes is schematically illustrated by a solid line or a dotted line. Although not shown, a crystal structure also exists in the blank portion. Further, it is estimated that there is an intermediate layer 25 between the surface of the α-Fe particles 12 and the graphite thin film 20, and the details will be described with reference to FIGS. 15 and 16.
[0100]
  FIG. 15 is a micrograph of the structure of the particles according to the present invention observed with a TEM (transmission electron microscope), and is a photograph further enlarging the vicinity of the graphite thin film 20 of FIG. FIG. 16 is a schematic diagram schematically illustrating the structure of FIG. 15 and is slightly enlarged. In the α-Fe particles 12, lattice fringes 24 are seen along the direction of arrow a, indicating a peculiar crystal plane of α-Fe. Since it is difficult to reproduce the state in which the arrangement of Fe atoms is connected in a rosary manner, it is displayed with a dotted line. In the vicinity of the surface of the α-Fe particles 12, the lattice stripes along the arrow a are broken, but the end of the array forms a flat surface, and the starting point for the gradual growth of graphite crystals. (Graphite growth layer). Hereinafter, these regions are referred to as an intermediate layer 25. The graphite thin film 20 grows and is formed through the intermediate layer 25.
[0101]
  As shown in FIG. 16, if the surface of the α-Fe particles 12 is a relatively smooth spherical surface (flat surface), the layered lattice surface 22 of graphite becomes a surface along the arrow d and is regularly arranged in parallel. As it grows, it forms a dense and very thin coating. Here, the term “dense” refers to having a portion in which regular lattice planes are stacked. In the direction perpendicular to the arrow d, 15 to 17 layers of the surface of the layered lattice were laminated to form a very thin film. The thickness of the intermediate layer 25 appears to be one or two layers in terms of the interval between the graphite layered lattice planes 22. When the crystal plane of graphite that has begun to grow is included in the intermediate layer, the thickness of the intermediate layer 15 is about 2 to 4 layers in terms of the interval between the layered lattice planes 22 of graphite.
[0102]
  The dislocation portion 23 is presumed to be a portion where the crystal growth is shifted and the crystal structure is discontinuous. It is assumed that when a layered lattice grows to have a laminated structure, growth of a certain part is delayed by one layer due to lattice defects. When the growth of a certain part is resumed, the lattice plane of the n−1th layer of a certain part and the lattice plane of the nth layer of the adjacent part may be combined to form one surface (dislocation surface). . The occurrence rate of dislocation surfaces is not high, and it can be said that the entire coating film is a uniform and dense thin film. In addition, although the convex part 21b exists in the surface of the graphite thin film 20, since it was not image | photographed clearly by the photograph of FIG. 15, the location was displayed with the dotted line.
[0103]
  (Reference example 2)
  Hematite with an average particle size of 0.03 μm (Fe₂O₃) 3 g of powder and 7 g of boron powder having an average particle size of 26 μm were put into a V-type mixer and mixed for 10 minutes. This mixed powder 121 is filled in a boron nitride crucible 122 and installed in a tubular electric furnace 123, and the temperature is increased from room temperature to 3 (° C./min) in a nitrogen gas stream at a flow rate of 2 (l / min). After warming, it was kept at 1100 ° C. for 2 hours and cooled to room temperature. The mixed powder before the heat treatment was reddish black, but the powder after the heat treatment was turned grayish white. X-ray diffraction measurement (Cu, Kα ray) was performed on the powder after heat treatment.18A diffraction pattern as shown in FIG. 5 is obtained, and from the heat-treated powder, diffraction peaks of hexagonal boron nitride (h-BN), rhombohedral boron nitride (r-BN), and α-Fe are obtained. Detected. To separate boron nitride and Fe, 500 cc of acetone (0.5 × 10^-3m³5 g of the above powder was put in, and ultrasonic cleaning was performed for 5 minutes to separate the supernatant and the precipitate. The supernatant liquid 127 was left in the fume hood for an additional 24 hours to dry the acetone and collect boron nitride powder 128 (weight 6 g).
[0104]
  When this boron nitride powder was observed with a transmission electron microscope (TEM), a wire-like structure as shown in the photograph of FIG. 19 was observed. When the lattice image was analyzed, the boron nitride wire had a rhombohedral structure. The unit of flow rate is (l / min) ≈about 16.7 × 10^-6(M³/ S).Reference example 2The manufacturing process includes a powder mixing step (S11), a heat treatment step in atmosphere (S12), an ultrasonic application step (S13) to the medium in which the powder is dispersed, and a boron nitride microparticle separation / drying step (S14). And corresponds to the process flow and schematic diagram of FIG. In the figure, reference numeral 124 denotes a cleaning tank, reference numeral 126 denotes an ultrasonic cleaner, and reference numeral 125 denotes a solvent (acetone) in which the powder after heat treatment is dispersed. In addition, if an ultrasonic wave can be applied in order to disperse | distribute the produced | generated particle | grains, it can use not only in a washing machine.
[0105]
  FIG. 20 is a schematic view showing the structure of the photograph shown in FIG. 19 and shows a wire-like boron nitride micro body. The boron nitride micro-body 101 is formed into a long bent tube shape by connecting a plurality of tubes 103 each having a cavity 102 therein. One end is terminated with the structure of the tube 103. The other end is terminated with the h-BN tissue 112 through the tissue in which the tube 103 is mixed with the r-BN tissue and the h-BN-like portion 112b. In FIG. 20, the curve indicated by the dotted line represents the outer extension of the collodion film for fixing the boron nitride micro-object 101 to the sample holder of the electron microscope. The lines and letters on the right outside of the square enclosure in FIG. 20 indicate that the line length corresponds to a dimension of 200 nm.
[0106]
  FIG. 21 is a schematic diagram showing only the boron nitride tube in FIG. 20 extracted and enlarged. The vicinity of the tip 111 of the tube is seen to overlap with the middle part of the tube, and it is not clear, so it is not clear whether the tip is closed. From the vicinity of the tip, the structure of the cavity 102 and the tube 103 surrounding the cavity 102 continues, and a part considered to be a node 104 between the tubes and a part that appears thick to observe whether the tube is thick or diagonally. There is a possible bump 105. The direction of the continuous tube appears to be largely bent at the bent portion 110, for example. The thickness of the tube does not always appear uniform, and the cavity 102 is formed not only with the bump 105 and the nodes but also with a structure that looks like a complex line or striae. The tube structure is clearly observed from the vicinity of the tip 111 to the node 104b, and the diameter of the tube is 0.12 to 0.20 μm (120 to 200 nm). Since the crystal structure is complex around this area, it is presumed that r-BN and h-BN are mixed or mixed. It is considered that mixing of different phases is related to the bending of the tube. When the crystal structure of the tube 103 that clearly looks like a pipe is magnified and observed, the arrangement of atoms is r-BN that repeats a three-layer cycle, and the repetition direction of the cycle faces the diameter direction of the tube.
[0107]
  (Reference example 3)
  Α-Fe with an average particle size of 0.03 μm₂O_Three5 g of powder (a powder) and 5 g of carbon powder (b powder) having an average particle diameter of 20 μm were put into a V-type mixer and mixed for 10 minutes. An appropriate amount of this mixed powder 251 is filled in a boron nitride crucible 252 and heated in a tubular furnace 253 at a rate of 3 ° C./min from room temperature in a nitrogen gas flow with a flow rate of 2 l / min. The furnace was cooled to the room temperature at a rate of 3 ° C./min with the time kept. The unit of flow rate is (l / min) ≈about 16.7 × 10^-6(M³/ S).
[0108]
  When X-ray diffraction measurement (Cu, Kα ray) was performed on each powder before and after heat treatment, diffraction patterns as shown in FIG. 23 (before heat treatment) and FIG. 24 (after heat treatment) were obtained. From the heat-treated powder, the (002) peak of graphite and the (110) peak of α-Fe were mainly detected. In FIG. 24, ◯ is a peak corresponding to the crystal structure of graphite, ■ is a peak corresponding to the crystal structure of α-Fe, the horizontal axis is 2θ (°) of the diffraction angle, and the vertical axis is diffraction. X-ray intensity (cps). The peak of maximum intensity of graphite has a half width of about 0.2 °, and the crystallinity of the powder after heat treatment is good. Further, when the magnetic properties of the powder before and after the heat treatment corresponding to FIGS. 23 and 24 were measured with a VSM (sample vibration magnetometer), the saturation magnetization was 1.30 × 1010 in the former.^-6Wb · m / kg, 131 × 10 for the latter^-6Wb · m / kg. From the above, Fe₂O₃It can be seen that is reduced to Fe.
[0109]
  When the powder after the heat treatment was observed with a TEM (transmission electron microscope), a tube-shaped fine body as shown in FIG. 25 was confirmed. FIG. 25 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope. As a result of composition analysis using EDX (energy dispersive X-ray detector), it was found that the black particles at the tip of the microscopic body were Fe and the tube was C (carbon).
[0110]
  FIG. 26 is a schematic diagram corresponding to the structure of the photograph of FIG. The carbon microparticle 201 has a structure in which a carbon tube 203 grows in a curved shape based on Fe particles 202. There are a plurality of nodes 204 inside the tube 203, and a region surrounded by the opposite node and the wall 203 b of the tube constitutes a cavity 205. The other end of the tube 203 is closed and forms a distal end portion 206. In this carbon micro object 201, it is considered that the fact that the growth direction of the tube is bent is related to the fact that the thickness of the wall of the tube and the interval between nodes are not uniform. In particular, the tube walls 203c and 203e have a thin tube thickness.
[0111]
  Another carbon microbody 207 has a structure in which a carbon tube 209 grows in a curved shape based on Fe particles 208 and includes other Fe particles 213 at the tip. A plurality of nodes 210 exist inside the tube 209, and a region surrounded by the opposite node and the wall of the tube forms a cavity 211. The Fe particles 220 in the vicinity of the Fe particles 213 appear to be separated by the tube wall 220 and the like. In this carbon micro-body 207, it is not certain whether the Fe particles 213 are attached from the beginning of the tube growth or are taken in during the growth of the tube. Note that the Fe particles 208 and the tube wall 212 only appear to overlap with the carbon microparticles 201 and are not connected. Further, the other Fe particles 214 exist alone. In the figure, a straight line or a curved one-dot chain line represents the outline of carbon 215, 216 as a raw material. The curved dashed-dotted line represents the outline of the collodion films 217 and 218 for fixing the carbon microparticles or the like to the sample holder of the electron microscope. Reference numeral 219 is a scale display entered to make the dimensions of FIG. 26 easier to understand, and the original FIG. 25 does not have such a structure. The length of the three lines on the scale display corresponds to 100 nm.
[0112]
  Based on the photograph of FIG. 25, the ratio of the outer diameter Ro and the inner diameter Ri of each carbon microbody was measured. Measure at any point and get data like (Ri / Ro) = 0.67, 0.75, 0.40, 0.69, 0.57, 0.63, 0.75, 0.44 It was.Reference example 3When the carbon microparticles were manufactured under the above conditions, the average outer diameter and average inner diameter could be changed. Considering these condition changes, the upper limit of (Ri / Ro) can be set to 0.8.
[0113]
  FIG. 27 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope. In FIG. 25, the vicinity of the joint portion between the Fe particles 202 and the tube 203 is enlarged. FIG. 28 is a schematic diagram corresponding to the structure of the photograph in FIG. In FIG. 28, only the main part of the crystal structure of FIG. 27 is represented by a solid line or a dotted line for easy explanation. Therefore, even if the periphery of the area hatched with a dotted line is blank, the description is omitted.
[0114]
  According to FIG. 28, the Fe particle 202 has a structure that appears to have a surface along a specific crystal plane in most regions. Hereinafter, they are referred to as Fe main phases 220 and 221. On the left side of the Fe main phase 220, a phase 225 having a different orientation of the array surface, a different phase 226 that looks like a satin pattern, and the like were observed. Although the Fe main phase 220 and the like are represented by dotted lines arranged in parallel, the point spacing and the line spacing do not necessarily match those in FIG. This is drawn for easy understanding of the orientation of the line array.
[0115]
  The carbon tube in FIG. 28 will be described. A tube 203 is generated ahead of the virtual boundary line 227 and the Fe main phase 221. It can be seen that the wall of the tubular tube has a structure partitioned by nodes 236 and 239. A region surrounded by the nodes 236 and the Fe particles 202 and the wall of the tube, or a region surrounded by the walls of the nodes 236 and 239 and the tube, was a cavity.
[0116]
  The wall of the tube is mainly composed of a graphite structural phase in the crystal arrangement. Hereinafter, graphite and a similar structure are collectively referred to as a graphite phase. The graphite phase is clearer than Fe in that the crystal arrangement appears to be stacked along a particular plane. It can be said that the surfaces of the graphite phases 230, 231, 232, 233, 237, 238, and 240 are parallel or substantially parallel to the growth direction of the tube wall. On the other hand, at the nodes 236 and 239, the surface of the graphite layer can be said to be orthogonal or substantially orthogonal to the growth direction of the tube wall. At the base of the left side of the node 236, the graphite layer is divided into a downward layer 234 and an upward layer 235 in a Y-shape, and exhibits a structure such as a tree trunk and branches. The root of the node 239 is substantially perpendicular to the wall of the tube, and it is considered that there are at least two types of node tissue. The graphite phase 242 is considered to be a bridge or a node, but cannot be determined because the graphite phase 242 of another structure is mixed.
  It should be noted that the atomic layers of the graphite layer are stacked with a narrow interval as expressed in the graphite layers 235 and 238 and the nodes 236 and 239. Since it is complicated to illustrate all the layers in the same manner, the number of layers is reduced in other portions. In addition, when a layer can be clearly understood, a line is shown, but when it seems to be continuous, it is indicated by a dotted line.
[0117]
  5 g of the powder after the heat treatment was put into 500 cc of acetone and subjected to ultrasonic cleaning for 5 minutes to separate the supernatant and the precipitate. The supernatant liquid 257 was allowed to stand in the fume hood for an additional 24 hours to dry the acetone and obtain carbon fine powder 258. The powder 258 is obtained by improving the ratio of carbon fine bodies by removing coarse transition metal particles and the like.
[0118]
  Reference example 3The manufacturing process includes a powder mixing process, a heat treatment process in the atmosphere, application of ultrasonic waves to the medium charged with powder (dispersion process), separation and drying processes of coarse transition metal particles, etc. Corresponds to the figure. In the figure, reference numeral 254 denotes a cleaning tank, reference numeral 255 denotes a solvent (acetone) in which the powder after heat treatment is dispersed, and reference numeral 256 corresponds to an ultrasonic cleaning apparatus. In addition, as long as it can apply an ultrasonic wave to disperse | distribute each produced | generated particle | grain in a solvent, it can use not only in a washing | cleaning apparatus.
[0119]
【The invention's effect】
  As described above, by using the ultrafine metal particles of the present invention and the method for producing the same, ultrafine metal particles provided with a coating that is safe, simple and suitable for industrial use can be obtained.
[Brief description of the drawings]
FIG. 1 is a graph showing an X-ray diffraction pattern of a mixed powder before heat treatment.
FIG. 2 is a graph showing an X-ray diffraction pattern of a mixed powder after heat treatment.
FIG. 3 Fe₂O₃It is the schematic explaining the reaction process which boron nitride covering Fe particle | grains etc. produce | generate by reacting with B.
FIG. 4 is a manufacturing process diagram of boron nitride-coated metal particles and boron nitride microparticles.
FIG. 5 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope.
6 is a schematic diagram for schematically explaining the structure of FIG. 5; FIG.
FIG. 7 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 8 is a schematic diagram for schematically explaining the structure of FIG. 7;
FIG. 9 is a graph showing an X-ray diffraction pattern of a mixed powder before heat treatment.
FIG. 10 is a graph showing an X-ray diffraction pattern of a mixed powder after heat treatment.
FIG. 11 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope.
12 is a schematic diagram for schematically explaining the structure of FIG. 3; FIG.
FIG. 13 is a micrograph of the particle structure according to the present invention observed with an electron microscope.
FIG. 14 is a schematic diagram for schematically explaining the structure of FIG. 5;
FIG. 15 is a micrograph of a particle structure according to the present invention observed with an electron microscope.
FIG. 16 is a schematic diagram for schematically explaining the structure of FIG. 7;
17 is a schematic view of a tubular furnace used in the manufacturing process of Example 1. FIG.
FIG. 18 is a graph showing an X-ray diffraction pattern of the powder of the present invention.
FIG. 19 is a photograph of the particle structure according to the present invention observed with an electron microscope.
20 is a schematic view corresponding to the structure of the photograph in FIG.
FIG. 21 is a schematic view enlarging a part of FIG. 20;
FIG. 22Reference example 2It is the flow and schematic diagram explaining the manufacturing process of.
FIG. 23 is a graph showing an X-ray diffraction pattern of a mixed powder before heat treatment.
FIG. 24 is a graph showing an X-ray diffraction pattern of a mixed powder after heat treatment.
FIG. 25 is a photomicrograph of the particle structure according to the present invention observed with an electron microscope.
26 is a schematic view corresponding to the structure of the photograph in FIG. 25. FIG.
FIG. 27 is a micrograph of a particle structure according to the present invention observed with an electron microscope.
28 is a schematic view corresponding to the structure of the photograph in FIG. 27. FIG.
FIG. 29Reference example 3It is a process flow and a schematic diagram explaining a manufacturing process.
[Explanation of symbols]
  1 Fe particle, 2 BN coating, 3 lattice plane, 4 lattice plane,
  5 lattice planes,
  11 ultrafine metal particles, 12 α-Fe particles,
  13a 13b 13c pattern,
  14 Boundary of graphite thin film, 15 Collodion film,
  16 scale, 20 graphite thin film,
  20a 20b 20c plaid,
  20e plaid, 20d plaid, 20f plaid,
  21 21b Convex part,
  22 layered lattice plane,
  23 dislocations, 24 checkers,
  25 Intermediate layer, 27 Graphite growth layer,
  41 mixed powder, 42 boron nitride crucible, 43 tubular furnace,
  44 cleaning tank, 45 medium, 46 ultrasonic cleaning device,
  47 supernatant, 48 coated metal particles,
  51 mixed powder, 52 boron nitride crucible, 53 tubular furnace,
  101 boron nitride micro, 102 cavity, 103 tube,
  104 104b,
  105 Cobb, 110 Bend, 111 Near tip,
  112 h-BN tissue, 112b h-BN-like site,
  113 collodion membrane, 121 mixed powder, 122 crucible,
  123 tubular electric furnace, 127 supernatant, 128 boron nitride powder,
  201 carbon microparticles, 202 Fe particles, 203 tubes,
  203b the wall of the tube,
  203c 203e the wall of the tube,
  204, 205 cavity, 206 tip,
  207 carbon microparticles, 208 Fe particles, 209 tube, section 210,
  211 cavities, 212 tube walls, 213 Fe particles,
  214 Fe particles,
  215 216 raw material carbon,
  217 218 collodion membrane,
  219 scale display, 220 Fe particles,
  220 221 Fe main phase,
  224 227 virtual border,
  225 Phases with different orientation of the surface of the array, 226 Different phases that look like satin patterns,
  230 231 232 233 237 238 240 graphite phase,
  234 235 graphite phase,
  236, 239,
  241 Graphite phase, 242 Graphite phase of other structures,
  251 mixed powder, 252 boron nitride crucible, 253 tubular furnace,
  254 cleaning tank, 255 solvent in which the powder after heat treatment is dispersed,
  256 Ultrasonic cleaning device, 257 Supernatant liquid, 258 Powder of carbon microparticles

Claims (15)

Metal particles obtained by heat-treating a powder obtained by mixing a metal oxide and boron-containing powder in an atmosphere containing nitrogen and reducing the metal oxide, and the surface of the metal particles is nitrided An ultrafine metal particle which is coated with boron and has an average particle size of 1 μm or less. The metal ultrafine particles according to claim 1, wherein the metal of the metal particles is Fe or an alloy containing Fe .   3. The ultrafine metal particles according to claim 1, wherein the surface of the metal particles is mainly composed of boron nitride having an h-BN crystal structure.   The ultrafine metal particles according to any one of claims 1 to 3, wherein the boron nitride has a thickness of 100 nm or less.   The metal ultrafine particles according to any one of claims 1 to 4, wherein the boron nitride has two or more crystal lattice planes or stacked planes. The metal ultraparticle is mainly composed of a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is 10% or more and less than 100% of the saturation magnetization specific to the material of the magnetic metal element. The metal ultrafine particles according to any one of claims 1 to 5.   The oxygen mass increment after heat treatment under conditions of humidity 100%, temperature 120 ° C, 1 atm, 24 hours with respect to the oxygen content (mass%) before heat treatment is 50% or less. Metal ultrafine particles according to any one of 1 to 6. A metal particle obtained by heat-treating a powder obtained by mixing a metal oxide and carbon-containing powder in an atmosphere containing nitrogen and reducing the metal oxide, and the surface of the metal particle is mainly graphite. An ultrafine metal particle, characterized in that it is coated with carbon, and the layered lattice plane of the graphite crystal is formed along the plane of the metal particle, and the average particle size is 1 μm or less. 9. The ultrafine metal particles according to claim 8, wherein the layered lattice plane of the graphite crystal is 4 to 20 layers. The metal ultraparticle is mainly composed of a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is 10% or more and less than 100% of the saturation magnetization specific to the material of the magnetic metal element. The metal ultrafine particles according to claim 8 or 9. The oxygen mass increment after heat treatment under conditions of humidity 100%, temperature 120 ° C, 1 atm, 24 hours with respect to the oxygen content (mass%) before heat treatment is 50% or less. The ultrafine metal particles according to any one of 8 to 10. A metal characterized by producing metal particles coated with boron nitride by heat-treating a powder containing a metal oxide-containing powder and a boron-containing powder in an atmosphere containing nitrogen. A method for producing ultrafine particles. The method for producing ultrafine metal particles according to claim 12, wherein the heat treatment is performed at a temperature of 800 to 1700 ° C. A metal particle coated with carbon is produced by heat-treating a powder containing a metal oxide-containing powder and carbon-containing powder in an atmosphere containing nitrogen. Production method. The method for producing ultrafine metal particles according to claim 14, wherein the heat treatment is performed at a temperature of 600 to 1600 ° C.

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