JP2004124248A5 - - 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】
（実施例６）
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１７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。実施例６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】
（実施例７）
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。実施例７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】
実施例７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。さらに、金属超微粒子を製造する際に副生成物に係る微小体とその製造方法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】
実施例６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】
実施例７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 [Document name] statement
Patent application title: Ultrafine metal particles, method for producing the same, method for producing fine particles, and fine particles
[Claim of claim]
    1. Metal particles obtained by reducing metal oxidesYes andThe surface of the metal particle is coated with boron nitride or carbon, and the average particle diameter is 1 μm or less.
    2. The metal ultrafine particles according to claim 1, wherein the metal oxide is an oxide containing a transition metal.
    3. The metal particle according to claim 1, wherein the surface of the metal particle is composed of boron nitride having a crystal structure of h-BN or carbon mainly composed of graphite. Metal ultrafine particles.
    4. The metal ultrafine particles according to any one of claims 1 to 3, wherein said boron nitride or carbon has a film thickness of 100 nm or less.
    5. The metal ultrafine particles according to any one of claims 1 to 4, wherein the boron nitride or carbon has two or more lattice planes or lamination planes of crystals.
    [6] In the metal superparticles, the main component of the particles is a magnetic metal element, and the saturation magnetization of the metal ultrafine particles is 10% or more and less than 100% of the saturation magnetization of the magnetic metal element. The metal ultrafine particle according to any one of Items 1 to 5.
    [7] The oxygen mass increment after heat treatment under the conditions of humidity 100%, temperature 120 ° C., 1 atm, 24 hours with respect to oxygen mass (mass%) before heat treatment is 50% or less. Metal ultrafine particles according to any one of 1 to 6.
    [Claim 8] A metal comprising a metal particle coated with boron nitride by heat treating a powder obtained by mixing a powder containing a metal oxide and a powder containing boron in a nitrogen-containing atmosphere. Method of producing ultrafine particles.
    [9] The method of claim 8, wherein the heat treatment is performed at a temperature of 800 to 1700C.
    10. A metal ultra-fine particle characterized by producing a carbon-coated metal particle by heat treating a powder obtained by mixing a powder containing a metal oxide and a powder containing carbon in an atmosphere containing nitrogen. Production method.
    11. The method of claim 10, wherein the heat treatment is performed at a temperature of 600 to 1,600 ° C.
    [12] A powder is prepared by mixing a powder containing a metal oxide and a powder containing boron, in a nitrogen-containing atmosphere, to produce a boron nitride microbody. Method.
    [13] The method according to claim 12, wherein the heat treatment is performed at a temperature of 800 to 1700C.
    14. A minute body which is formed by reducing metal oxide in an inert gas atmosphere, is mainly composed of boron nitride, and is wire-like or cylindrical.
[15] A microbody which is produced by reducing metal oxide in an inert gas atmosphere, is mainly composed of boron nitride, is cylindrical, and has nodes or crosslinks inside.
    [16] A minute structure characterized by comprising metal particles, a boron nitride film formed by reducing metal oxides in an inert gas atmosphere, and coating the metal particles, and wire-like or cylindrical boron nitride. body.
    [17] What is claimed is: 1. A method for producing a microbody, comprising producing a carbon microbody by heat treating a powder containing a metal oxide and a powder containing carbon in an inert atmosphere.
    [18] The method according to claim 17, wherein the heat treatment is performed at a temperature of 600 to 1600C.
    [19] A minute body which is produced by reducing metal oxide in an inert gas atmosphere, is composed of carbon in a graphite phase, and is wire-like or cylindrical.
    [20] A microbody which is produced by reducing a metal oxide in an inert gas atmosphere, is mainly composed of carbon in a graphite phase, is cylindrical, and has nodes or crosslinks inside.
    21. A minute body comprising metal particles, a carbon film coating the metal particles, and a carbon film formed in a wire shape or a cylindrical shape by reducing metal oxides in an inert gas atmosphere.
Detailed Description of the Invention
      [0001]
    Field of the Invention
  The present invention relates to a metal particle used as a raw material of a magnetic recording medium such as a magnetic tape and a magnetic recording disk, an electronic device such as a radio wave absorber, an inductor, and a printed circuit board (soft magnetic material such as a yoke). Further, the present invention relates to a microparticle which is a by-product in forming metal particles and a method for producing the same.
      [0002]
    [Prior Art]
  With the reduction in size and weight of electronic devices, there is a demand for nano-size of the raw materials themselves that constitute electronic devices. At the same time, high performance of the device must be realized. For example, for the purpose of improving the magnetic recording density, it is simultaneously required to improve the size and magnetization of magnetic particles applied to a magnetic tape.
      [0003]
  Conventionally, ferrite powder has been mainly used for magnetic recording media, but there has been a problem that the magnetization is small and the signal strength is low. Although metallic magnetic particles represented by Fe and Co are suitable for obtaining sufficient output characteristics, for example, when the particle diameter is reduced to 1 μm or less for high recording density, the metal particles are resistant to oxidation. As it is active, the oxidation reaction proceeds violently in the air, and some or all of the metal is transformed into an oxide to lower the magnetization. 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 case of metal particles with a particle size of 1 μm or less as in the above-mentioned example, in order to prevent the particles from being exposed directly to the atmosphere (oxygen), a film is applied to the particle surface in order not to impair the function as a metal. Is essential. However, the method of covering the surface with a metal oxide as in Patent Document 1 causes the metal to be oxidized and degraded to some extent.
  Further, when metal particles are coated with graphite as in Patent Document 2, heat treatment must be performed at an extremely high temperature of 1600 ° C. to 2800 ° C. in order to make the metal melt carbon in order to coat it. It does not. Carbonized metal and graphite CO₂Is a concern. As a coating method that overcomes these problems, coating of metal particles with boron nitride (BN) is mentioned (for example, Non-Patent Document 1). BN is a material used for a "crucible" and has a high melting point of 3000 ° C. and excellent thermal stability, as well as low reactivity with metals. Moreover, it has the characteristic which has insulation. The method of applying the BN film to the metal particles is (1) heating the mixed powder of metal and B by arc discharge in a nitrogen atmosphere, or (2) mixing the mixed powder of metal and B in a mixed atmosphere of hydrogen and ammonia There is a method of 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 to 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 method of producing the BN film, since the production methods (1) and (2) use metal particles as a raw material, there is a danger such as ignition due to a rapid oxidation reaction particularly when handling ultrafine particles with a particle diameter of 1 μm or less. In addition, in the production method (3), since the metal nitrate is thermally decomposed, toxic gas (NO_x) Occurs. In addition, the method utilizing the arc discharge of the production method (1) is not only suitable for industrial use because it has a low treatment amount and low productivity, but also has a high reaction temperature of about 2000 ° C. In addition, hydrogen gas used in the production methods (2) and (3) has a risk of explosion, so it is not preferable to use it industrially. Also, the coated metal particles obtained by the prior art have problems such as deterioration of saturation magnetization caused by modifying a part of the metal particles.
      [0007]
    [Means for Solving the Problems]
  MEANS TO SOLVE THE PROBLEM The inventors completed the present invention as a result of earnestly examining a metal ultrafine particle in which a film suitable for industrial use is coated on the surface of metal particles by a safe and simple method in order to solve the above-mentioned problems. It came to
      [0008]
  [1] The metal ultrafine particles of the present invention are metal particles obtained by reducing metal oxidesYes andThe surface of the metal particles is coated with boron nitride, and has an average particle diameter of 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.In addition, for example, metal ultrafine particles having an average particle diameter of 0.2 to 0.5 μm and excellent in oxidation resistance can also be obtained.
      [0009]
  The sample is observed with an electron microscope to determine the average particle size. For example, take an electron micrograph of the sample. Measure the particle size of the metal ultrafine particles in any area in the photo and calculate the average value, or draw a line segment of any length in the picture, and the length of the segment crossing the particle From the sum of length L and the number N of particles traversed by the line segment, the average particle diameter is determined as L / N. However, an average value of at least 50 or more particles shall be obtained.In addition, the particle size of Fe after the heat treatment can be calculated from the (110) peak of Fe in X-ray diffraction measurement using Rigaku analysis software “Jade 5”.
      [0010]
  In the present invention, it is desirable that all of the fine particles are coated with boron nitride (or carbon), but not all the particles need to be coated. In addition, although it is desirable that the surface of the ultrafine particles be coated with boron nitride (or carbon), it is not necessary that the surface be completely composed of particles coated with boron nitride (or carbon). In the specification and claims of this application, for example, those described as “particle diameter is 0.001 to 1 μm” are “particle diameter is in the range of 0.001 μm or more and 1 μm or less Is used as an equivalent to the expression
      [0011]
  [2] In the above-mentioned [1], the metal oxide is an oxide containing a transition metal. The metal particles are desirably selected from Fe, Ni, Co, and an alloy containing at least one of them. For example, 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 can be mentioned.
      [0012]
  [3] The metal ultrafine particles according to the above [1] or [2], wherein the boron nitride mainly has a crystal structure of h-BN.
      [0013]
  [4] The metal ultrafine particles according to any one of the above [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 metal ultrafine particles according to any one of the above [1] to [4], wherein the boron nitride has two or more layers of crystal lattice planes or lamination planes. More preferably, the film has four or more layers of crystal lattice planes or lamination planes. Here, it is preferable that boron nitride is mainly composed of hexagonal crystals, and the lattice plane or lamination plane of the crystals is a hexagonal c-plane (ie, (002) plane). It is desirable that the lattice plane or lamination plane of the crystal is formed along the plane of the metal particles.
  [6] In the above-mentioned [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 superparticle is a magnetic metal element, and the saturation magnetization of the metal ultrafine particle is the saturation magnetization of the magnetic metal element. 10% or more and less than 100% of
  In regard to the above [7], when the core of the metal ultrafine particles is formed of magnetic particles, the covering boron nitride film can be made extremely thin at 30 nm or less. Therefore, in the metal ultrafine particles, the volume ratio occupied by the magnetic particles can also be increased, and the decrease in the saturation magnetization of the metal ultrafine particles can be suppressed as compared to the prior art. In a particle composed of a transition metal or an alloy containing a transition metal, the particle is coated with a boron nitride film when the saturation magnetization specific to the material of 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 can have a size of 10% or more with respect to the reference.
      [0016]
  [8] In any of the above [1] to [7],After heat treatment under the conditions of humidity 100%, temperature 120 ° C., 1 atm, for 24 hours with respect to the contained oxygen mass (mass%) before heat treatmentThe oxygen mass increment is 50% or less. The surface of the metal ultrafine particles can be used even if it is not completely covered with the boron nitride film, that is, even if the coating is locally thin. However, since it is difficult to prevent the progress of oxidation when stored for a long time, it is desirable to completely coat 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 the composition ratio by mass of a substance. That is, it indicates how much mass each element component is contained with respect to the unit mass of the metal ultrafine particles.
  As a method of measuring the mass% for each composition, for example, oxygen in the sample is thermally decomposed by rapidly heating the sample powder to 2000 to 3000 ° C., and oxygen gas generated by a gas chromatograph and a thermal conductivity detector Alternatively, it is a method of analyzing the content of oxygen by detecting an oxygen-containing gas. Since the metal ultrafine particles according to the present invention are particularly excellent in oxidation resistance, the increase in oxygen mass after treatment is suppressed with respect to the oxygen content before treatment even if the above-mentioned humidification and heating treatment is performed. .
      [0018]
  The magnetic particles may contain impurities or unavoidable impurities (elements originally contained in the raw material) contained in the mixing of the raw materials to an extent that the magnetic properties are not extremely degraded.
  In addition, in the particle composed of a metal or an alloy, at least one of the peak with the highest intensity and the second highest peak in the X-ray diffraction pattern of the particle (a coating is excluded) It corresponds to the peak of. More preferably, the peak of the oxide of the element (excluding BN) constituting the particle is sufficiently smaller than the third highest peak or not detected at all.
      [0019]
  [9] A method of producing metal ultrafine particles according to the present invention comprises treating a powder obtained by mixing a powder containing a metal oxide and a powder containing boron with heat treatment in a nitrogen-containing atmosphere to obtain boron nitride. Coated metal particlesTo makeIt is characterized by The metal oxide preferably contains a transition metal (more preferably, it comprises an oxide of a transition metal). It is desirable that the generated boron nitride-coated metal particles have an average particle size of 1 μm or less. The “nitrogen-containing atmosphere” corresponds to an atmosphere selected from nitrogen gas and a mixed gas of an inert gas such as argon and nitrogen gas.
      [0020]
  More preferably, in the production method of the above [9], a powder obtained by mixing particles containing iron oxide and particles containing boron is heat-treated in an atmosphere containing nitrogen to make iron oxide at least one of iron and iron boron compound. It is characterized by producing particles of at least one kind of iron or iron nitride and finally coated with boron nitride by reducing the species to form boron oxide. I assume.
      [0021]
  The method of producing metal ultrafine particles according to the above [9] is characterized in that the step of reducing metal oxide particles and the step of covering the surface of the metal particles with a boron nitride film are performed in one heat treatment step. The manufacturing method of the present invention is superior to the manufacturing method of the comparative example described later in that it contains almost no oxygen. According to the manufacturing method of the comparative example, after preparing the metal ultrafine particles, an inert atmosphere containing a low concentration of oxygen is gradually supplied to the metal ultrafine particles in order to avoid spontaneous combustion and combustion (oxidizing). This is a method of producing ultrafine particles in which a thin oxide film is formed on the surface.
      [0022]
  [10] In the above-mentioned [9], the heat treatment is800-1700 ° CIt is characterized in that it is carried out at a temperature of
      [0023]
  [11] Another metal ultrafine particle of the present invention is a metal particle obtained by reducing a metal oxideYes andThe surface of the metal particles is coated with carbon, and the average particle diameter 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.In addition, for example, metal ultrafine particles having an average particle diameter of 0.2 to 0.5 μm and excellent in oxidation resistance can also be obtained.
      [0024]
  [12] In the above-mentioned [11], the metal oxide is an oxide containing a transition metal. The metal particles are desirably selected from Fe, Ni, Co, and an alloy containing at least one of them. For example, carbon-coated Fe particles, carbon-coated Ni particlesChildAnd carbon-coated FeNiCo particles, carbon-coated NiFe particles, and the like.
  [13] The metal ultrafine particles according to the above [11] or [12], wherein the carbon is mainly composed of graphite. Furthermore, the carbon may have a crystalline structure of graphite and amorphous, and may be mainly composed of graphite.
      [0025]
  [14] The metal ultrafine particles according to any one of the above [11] to [13], wherein the carbon has a film thickness of 100 nm or less. More preferably, the film thickness can be 20 nm or less.
      [0026]
  [15] The metal ultrafine particles according to any one of the above [11] to [14], wherein the carbon has two or more layers of crystal lattice planes or lamination planes. More preferably, the film has four or more layers of crystal lattice planes or lamination planes. Here, it is preferable that carbon is mainly made of graphite, and the lattice plane or lamination plane of the crystal is a lamination plane of graphite. It is desirable that the lattice plane or lamination plane of the crystal is formed along the plane of the metal particles.
  [16] In the above-mentioned [15], an intermediate phase may be provided in the particles or carbon.
      [0027]
  Since carbon constituting the coating is mainly graphite in which lattice planes are arranged in layers, a plurality of planes of a layered lattice in which six-membered rings are connected are provided. That is, a plurality of crystal lattice planes are provided. The lattice planes of the layered lattice may be laminated to the surface of the particles. Since the interface between the particles and the film has an intermediate layer, a region in which transition metal and carbon are mixed, or a crystal matching region of both, forming at least two layers of planes of the layered lattice suppresses the oxidation of the particles. It is desirable to do. The plane of the layered lattice (lattice plane) can be formed, for example, in the range of 4 to 20 layers. A mesophase refers to a part or boundary region of the intermediate structure between the crystal structure of the metal particle and the crystal structure of the coating. The thickness of the mesophase is about 1 to 5 in the lattice spacing of the graphite or the graphite layer. When the mesophase is thin, it is thought that the crystal lattice mismatch between the particle and the carbon film can be relaxed and eliminated at a short distance, and the entire surface of the particle can be uniformly coated with the carbon film.
      [0028]
  [17] In any one of the above [11] to [16], the metalFineThe particles are characterized in that the main component of the particles is a magnetic metal element, and the saturation magnetization of the metal ultrafine particles is 10% or more and less than 100% of the saturation magnetization of the magnetic metal element. In regard to the above [17], when the core of the metal ultrafine particles is formed of magnetic particles, the covering carbon film can be made extremely thin with a film thickness of 30 nm or less. Therefore, in the metal ultrafine particles, the volume ratio occupied by the magnetic particles can also be increased. Compared to the prior art, it is possible to suppress the decrease in the saturation magnetization of the metal ultrafine particles. In a particle composed of a transition metal or an alloy containing a transition metal, metal ultrafine particles obtained by coating a carbon film on the particle when the saturation magnetization unique to the material of the main component responsible for magnetism is used as a reference (ie 100%) The saturation magnetization of may have a magnitude of 10% or more with respect to the reference.
      [0029]
  [18] In any of the above [11] to [17],After heat treatment under the conditions of humidity 100%, temperature 120 ° C., 1 atm, for 24 hours with respect to the contained oxygen mass (mass%) before heat treatmentThe oxygen mass increment is 50% or less. The surface of the metal ultrafine particles can be used even if it is not completely covered with a carbon film, that is, even if the coating is locally thin. However, since it is difficult to prevent the progress of oxidation when stored for a long time, it is desirable to completely coat 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 mixing of the raw materials to an extent that the magnetic properties are not extremely degraded.
  Also, in the particle composed of metal or alloy, the first to second highest intensity (Intensity (cps)) peak in the X-ray diffraction pattern is a peak corresponding to the main element of the particle or the peak of graphite. It is desirable to have. More preferably, the peak of the oxide of the element (excluding carbon) constituting the particle is characterized in that the intensity appearing in the X-ray diffraction pattern is sufficiently smaller than the third highest peak or not detected at all.
      [0031]
  [19] The method for producing metal ultrafine particles according to the present invention covers the surface with carbon by heat treating a powder obtained by mixing a powder containing metal oxide and a powder containing carbon in an inert atmosphere. Metal particlesTo makeIt is characterized by The metal oxide preferably contains a transition metal (more preferably, it comprises an oxide of a transition metal). It is desirable that the produced carbon-coated metal particles have an average particle size of 1 μm or less.
      [0032]
  More preferably, in the production method of the above [19], a powder obtained by mixing particles containing iron oxide and particles containing carbon is heat-treated in an inert atmosphere to reduce iron oxide to at least one of iron and iron carbide. And producing an oxide of carbon, thereby producing at least one particle of iron or iron carbide, wherein the surface is coated with carbon.
      [0033]
  The method for producing metal ultrafine particles according to the above [19] is characterized in that the step of reducing metal oxide particles and the step of covering the surface of metal particles with a carbon film are performed in one heat treatment step. The manufacturing method of the present invention is superior to the manufacturing method of the comparative example described later in that it contains almost no oxygen. In the manufacturing method of the comparative example, after preparing ultrafine particles of metal, oxygen is gradually added to the ultrafine particles of metal in an inert atmosphere containing a low concentration of oxygen in order to avoid spontaneous ignition and combustion (oxidizing). And to form a thin oxide film on the surface.
      [0034]
  [20] In the above [19], the heat treatment is600 to 1600 ° CIt is characterized in that it is carried out at a temperature of
      [0035]
  [21] The method for producing a microbody of the present invention is a method for producing fine particles of boron nitride by heat treating a powder obtained by mixing a powder containing metal oxide and a powder containing boron in an atmosphere containing nitrogen. It is characterized by producing a body. Here, the microbody corresponds to a microbody obtained as a by-product when producing the metal ultrafine particles according to any one of the above [1] to [10].
      [0036]
  [22] Another method for producing microparticles according to the present invention is a method for producing metal particles or boron nitride particles by heat treating a powder containing particles containing boron and particles containing metal oxides in an atmosphere containing nitrogen. It is characterized in that a product having at least one of the microbodies is obtained. The metal particles may be coated with boron nitride. The nitrogen-containing atmosphere may be, for example, nitrogen gas or a mixed gas of nitrogen gas mixed with a rare gas such as argon gas.
      [0037]
  [23] In the above [21] or [22], the heat treatment is800-1700 ° CIt is characterized in that it is carried out at a temperature of
      [0038]
  The manufacturing method according to any one of the above [21] to [23] is very excellent in mass productivity. The required thermal energy is small compared to conventional manufacturing methods. In addition, high vacuum is not required, and precise pressure control of the atmosphere is unnecessary. Since an inert gas is used, there is no damage to the heat treatment furnace, and there is no problem such as the contamination of impurities into the particles due to the damage. Furthermore there is no danger of explosion or toxicity. The powder of the oxide used as a raw material is easy to prepare and handle even nm-sized particles. It is also merited that ignition and combustion of the raw material are unlikely to occur, and problems such as loss of the raw material due to ignition and the shape becoming out of design and problems of process interruption and the like are unlikely to occur.
      [0039]
  [24] A powder having boron nitride microbodies and metal particles is produced by the method for producing microparticles according to any one of the above [21] to [23], and at least a part of the metal particles is prepared from the powder. It is characterized by removing. It is desirable to remove all the metal particles to make only boron nitride minute powder. That is, after the heat treatment, a process of removing metal particles or microparticles containing metal particles is performed. For example, it is desirable to remove metal particles that have been reduced during heat treatment when they are further grown into coarse metal particles.
  This process is a step of increasing the proportion and purity of boron nitride in the fine powder. For example, this microbody is dispersed in a medium (liquid), and the specific gravity difference between the metal-based particle and the boron nitride microbody (or the specific gravity difference between the microbody containing metal and the microbody without metal) is used. A method of separating and reducing metal particles and the like can be used by a method such as natural sedimentation or centrifugation after stirring (Separating method 1). Alternatively, a method (wet method or dry method) can be used in which a magnetic field is applied to metal particles to be attracted and separated from minute particles of boron nitride alone that are not attracted (wet method or dry method). In addition, a method of reducing the amount of metal particles can be used by chemically dissolving and removing the metal particles in a solution such as acid (Separating method 3). Although the separation method 3 has the possibility of mixing of undissolved residue and impurities, it is effective in reducing metal particles. When the surfaces of the metal particles are all coated and a solution such as acid does not penetrate, it is desirable to carry out separation method 1 or separation method 2 in order to increase the purity of the powdery particles. In addition, even if metal powder is contained in fine powder, it does not necessarily mean that there is a problem. The particles are small in size and the powder is not easy to handle. For example, a powder containing a powder of transition metal fine particles as a carrier has an advantage of being easier to handle than a powder consisting only of microparticles.
      [0040]
  [25] Another microparticle of the present invention is produced by reducing metal oxide in an inert gas atmosphere containing nitrogen, is mainly composed of boron nitride, and is wire or cylindrical It is characterized by The boron nitride is preferably in the rhombohedral phase. This minute body is obtained as a by-product when producing the metal ultrafine particles according to the above [1] to [10].
  Another microparticle of the present invention is a microparticle obtained by combining nitrogen and boron by reducing metal oxides in an atmosphere of inert gas containing nitrogen, and is mainly composed of boron nitride, It is characterized in that it is in the form of a wire or a cylinder. Heat treatment is performed using a metal oxide as a mediator or promoter in an inert atmosphere containing nitrogen to combine boron and nitrogen to form boron nitride microparticles. As the metal oxide, for example, an oxide of a metal or an alloy can be used. In particular, it is desirable to use a transition metal or an alloy containing at least one transition metal. More preferably, oxides of magnetic metals are used. For example, the metal or alloy can be selected from Fe, Ni, Co, and an alloy containing at least one of them.
      [0041]
  The “microbody” is, for example, a nanotube, a nanowire, a steric atomic structure, a nanoparticle, a structure having dimensional characteristics in the nanometer (nm) order, an aggregate or powder containing at least one of them ( Or powder), it is used as a term to refer to a minute thing. The microparticles having a cylindrical shape are more preferably nanotubes. “Wire-like or cylindrical-like” means, for example, linear, rod-like, tube-like, tubular, either hollow or solid thereof, any of them connected in series, small pieces (plate-like It is used as a term including a long shape formed by adding a piece, a bowl-like or block-like piece) and the like.
      [0042]
  [26] In the above-mentioned [25], the micro-particles are characterized by having an average diameter of 0.5 μm or less. Preferably, the average diameter is 0.01 to 0.5 μm, and more preferably, the average diameter is 0.05 to 0.5 μm. More specifically, for example, the diameter can be 0.1 to 0.3 μm.
  In addition, if the fine powder which has an average particle diameter in the range of 0.001-1 micrometer is used as a metal oxide of a raw material, the microparticle in the range of 0.001-1 micrometer of diameters can be obtained. More preferably, a metal oxide having an average particle diameter in the range of 0.001 to 0.05 μm is used to obtain microparticles of 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, it is possible to obtain microparticles having a small average diameter.
      [0043]
  The diameter corresponds to, for example, an outer diameter when a cross section (a cross section in a direction orthogonal to the longitudinal direction) of a wire-like or cylindrical portion is observed for one microbody. When the cross section is not circular, the maximum value is regarded as the diameter. If the microbody has a diameter that changes gradually 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 microbody. If there is a place where the wire-like or cylindrical shape is largely deviated, the place is ignored and the diameter is evaluated only with the wire-like or cylindrical part.
      [0044]
  With the average diameter, for example, a powder having a wire-like or cylindrical fine body is used as a sample to take an electron micrograph. The diameter of each of the particles within an arbitrary area in the photograph is measured to obtain an average value. That is, for N number of microbodies (N ≧ 50), the diameter is measured and expressed as an average diameter = (sum of measured diameters) / N. Instead of a picture, an image may be acquired and the diameter may be measured using a personal computer and image processing software.
      [0045]
  [27] Another microbody of the present invention isIt is formed by reducing metal oxides in an inert gas atmosphere,It has a portion where the ratio of the outer diameter Ro to the inner diameter Ri is (Ri / Ro) ≦ 0.8Cylindrical boron nitride microbodyIt is characterized by When the ratio of Ri / Ro is close to 1, the thickness of the wall is reduced, so that the weight of the minute body is decreased, 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 (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 at the point where the cylindrical shape is bent, but this is not a problem in practical use.
  The boron nitride particles can be formed in multiple layers of atomic layers of boron nitride that make up the wall of the tube, and can also be generated to increase nodes and bridges. Therefore, it is also possible to increase the thickness of the wire-like or cylindrical fine-body wall and produce a small body with a small (Ri / Ro). Note that Ri is an inner diameter (corresponding to the diameter of a cavity) when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction, and does not include the cross section of a node or the like. Ro corresponds to the outer diameter of the tube in a cross section substantially perpendicular to the longitudinal direction.
      [0046]
  [28] Another microparticle of the present invention is characterized in that it is a mixture of a rhombohedral boron nitride microparticle and a hexagonal phase boron nitride microparticle.
  For the crystal structure, rhombohedral Boron Nitride is also referred to as r-BN. The hexagonal phase boron nitride (Hexagonal Boron Nitride) is also referred to as h-BN.
  [29] Another microparticle of the present invention is characterized by being boron nitride having a rhombohedral phase and a hexagonal phase.
      [0047]
  [30] Another microbody of the present invention isIt is formed by reducing metal oxides in an inert gas atmosphere,It is mainly composed of boron nitride and is cylindrical and characterized by having nodes or crosslinks inside.
  Here, the “node” corresponds to a member capable of dividing the inside of a tubular (or tubular) minute body into a plurality of cavities or dividing it into a plurality of sections. "Cross-linking" corresponds to a member that connects arbitrary portions of the inner wall of a cylindrical microbody. It is also considered possible that the bridges are more concentrated to form nodes. The faces of the nodes are in a close relationship with the wall of the tube or the wall of the cylinder, rather than parallel but rather orthogonal. When there are a plurality of clauses, the interval between the clauses is, for example, 0.5 d or more. Here, d corresponds to the diameter d of the cylindrical portion between the nodes and the nodes. In addition, even if the minute body is provided with a plurality of nodes, the outer diameter and the wall thickness do not necessarily decrease gradually on one side, but it is possible to increase rather, and it is possible to obtain a long minute body. it can.
      [0048]
  [31] Another microbody of the present invention isIt is formed by reducing metal oxides in an inert gas atmosphere,It is characterized by comprising metal particles, a boron nitride film covering the metal particles, and wire-like or cylindrical boron nitride.
  The wire-like or cylindrical part may have a plurality of growth directions without being limited to one growth direction. In addition, wire-like or cylindrical boron nitride may be grown directly from a boron nitride film, or may be grown directly from metal particles obtained by reduction of metal oxides. The metal particles may be disposed at either the tip or center of the boron nitride microbody. The state of arrangement is a structure (or junction, connection, connection, connection, connection structure) provided on one boron particle in one metal particle, or a plurality of nitride films in one metal particle. There is a structure provided with elementary microbodies. Another arrangement state is a structure in which metal particles are enclosed in carbon microparticles (or a structure such as covering, fitting, embedding, including, winding, holding, carrying, etc.). The arrangement state of the metal particles can be changed by changing the conditions such as the raw material and the heat treatment according to the manufacturing method.
  It is desirable that the metal particles be composed of a transition metal or an alloy containing at least one of transition metals. More preferably, the metal particles are made of 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] Another method for producing microparticles according to the present invention is a method for producing microparticles of carbon by heat treating a powder obtained by mixing a powder containing a metal oxide and a powder containing carbon in an inert atmosphere. To produce. More desirably, fine particles of carbon are produced by heat treating a powder obtained by mixing a powder composed of a transition metal oxide and a carbon powder in an inert atmosphere. The method of producing the minute body relates to the minute body which can be obtained as a by-product when producing the metal ultrafine particles according to the above [11] to [20], and a method of producing the same.
      [0050]
  [33] Another method of producing microparticles according to the present invention is a method of heat treating a powder containing carbon-containing particles and metal oxide particles in an inert atmosphere to obtain metal particles or carbon microparticles. It is characterized by obtaining a product having at least one. The metal particles may be coated with carbon.
      [0051]
  [34] In the above [32] or [33], the heat treatment is600 to 1600 ° CIt is characterized in that it is carried out at a temperature of
      [0052]
  The manufacturing 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 conventional manufacturing methods. In addition, high vacuum is not required, and pressure control of the atmosphere is unlikely to be a restriction on mass productivity. Since the inert gas is used, there is no damage to the heat treatment furnace, and there is no problem that the impurities get mixed in the minute bodies due to the damage. The powder of the oxide used as a raw material is easy to prepare and handle even nm-sized particles. It is also merited that ignition and combustion of the raw material are unlikely to occur, and problems such as loss of the raw material due to ignition and the shape becoming out of design and problems of process interruption and the like are unlikely to occur.
      [0053]
  [35] A powder having fine carbon particles and metal particles is produced by the method of producing fine particles according to any one of the above [32] to [34], and at least a part of the metal particles is removed from the powder. It is characterized by It is desirable to remove all the metal particles and make a powder of only carbon particles. That is, after the heat treatment, a process of removing metal particles or microparticles containing metal particles is performed. For example, it is desirable to remove metal particles that have been reduced during heat treatment when they are further grown into coarse metal particles. As this removal process, the same process as the above [24] can be used.
      [0054]
  [36] Another microbody of the present invention is characterized in that it is produced by reducing metal oxide in an inert gas atmosphere, is composed of carbon in a graphite phase, and is wire-like or cylindrical. Do. By performing heat treatment in an inert atmosphere using a metal oxide as a mediator or promoter, decomposition / reconstruction of carbon is carried out to obtain carbon microparticles. This microbody can be obtained as a by-product when producing the metal ultrafine particles according to the above [11] to [20].
  The microbody of the present invention is a microbody in which the shape of carbon particles is reconstructed by reducing a metal oxide in an inert gas atmosphere, which is mainly made of carbon, and has a wire-like or cylindrical shape. It is characterized by having. More specifically, particulate carbon is decomposed and restructured to generate carbon microbes by using a reduction reaction for removing oxygen from metal oxides and an inert gas. As the metal oxide, for example, an oxide of a metal or an alloy can be used. In particular, it is desirable to use a transition metal or an alloy containing at least one transition metal. More preferably, oxides of magnetic metals are 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-mentioned [36], the microbodies are characterized in that the average diameter is 0.5 μm or less. Preferably, the average diameter is 0.01 to 0.5 μm, and more preferably, the average diameter is 0.05 to 0.5 μm. More specifically, for example, the diameter can be 0.1 to 0.3 μm. In addition, if the fine powder which has an average particle diameter in the range of 0.001-1 micrometer is used as a metal oxide of a raw material, the microparticle in the range of 0.001-1 micrometer of average diameters can be obtained. More preferably, metal oxides having an average particle diameter in the range of 0.001 to 0.05 μm are used to obtain microparticles with 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, it is possible to obtain microparticles having a small average diameter.
      [0056]
  [38] Another microbody of the present invention isIt is formed by reducing metal oxides in an inert gas atmosphere,A cylindrical carbon micro body, wherein the ratio of the outer diameter Ro to the inner diameter Ri is such that (Ri / Ro) ≦ 0.8 is characterized.
  When the ratio (Ri / Ro) is close to 1, the thickness of the wall is reduced, so that the weight of the minute body 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 (Ri / Ro) is close to 1, but there are also portions where the inner diameter is small. For example, the inner diameter may be small at the end of the cylindrical shape or at the portion where the cylindrical shape is bent, but there is no problem in practical use.
  These carbon microparticles can form atomic layers of graphite constituting the wall of the tube in multiple layers, and can also be generated to increase nodes and crosslinking. Therefore, it is also possible to increase the thickness of the wire-like or cylindrical carbon micro-body wall to produce a carbon micro-body having a small (Ri / Ro). Note that Ri is an inner diameter (corresponding to the diameter of a cavity) when the tube is viewed in a cross section substantially perpendicular to the longitudinal direction, and does not include the cross section of a node or the like. Ro corresponds to the outer diameter of the tube in a cross section substantially perpendicular to the longitudinal direction.
      [0057]
  [39] Another microbody of the present invention isIt is formed by reducing metal oxides in an inert gas atmosphere,It is mainly composed of carbon in the graphite phase, and is cylindrical and characterized by having nodes or crosslinks inside.
  Here, the definition of “section” is the same as the description of the above [30].
      [0058]
  [40] Another microbody of the present invention isIt is formed by reducing metal oxides in an inert gas atmosphere,It is characterized by comprising metal particles, a carbon coating coating the metal particles, and wire-like or cylindrical carbon.
  It is desirable that the metal particles be composed of a transition metal or an alloy containing at least one of transition metals. More preferably, the metal particles are made of 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]
    BEST MODE FOR CARRYING OUT THE INVENTION
  The embodiment of the present invention according to any one of the above [1] to [10] will be described. The present invention according to the above [1] to [10] functions as a catalyst for forming boron nitride (BN) among transition metal powder raw materials, especially Fe, Co, Ni, etc. When the metal powder and the boron (B) were heated at around 2000 ° C., attention was focused on the formation of boron nitride with the metal particles as the core. Furthermore, when the starting material is not a metal but is an oxide of a transition metal represented by Fe, Co, Ni, the oxide is reduced at 800 ° C. to 1700 ° C. and at the same time boron nitride is formed, and metal particles are formed. It has been found that a novel metal ultrafine particle contained in a boron nitride film (BN film) is formed.
      [0060]
  The concept of the raw material of the metal oxide and boron which are the starting materials of the present invention according to the above [1] to [10] and the reason for the numerical limitation will be described. As a metal (hereinafter, referred to as M) constituting the oxide according to the present invention, a transition metal or an alloy thereof (particularly, a magnetic material) is preferable. More preferably, Fe, Co, Ni, Cr, Mn, Mo, Pd, Ir or an alloy containing them is suitable. Fe, Co, Ni, Cr, Mn, Mo, Pd, Ir have a standard formation enthalpy of formation of the MB bond (B is boron) H_M-B, Standard formation enthalpy of M-N bond (N is nitrogen) H_M-NH, when expressed as H_M-B<H_M-N
The following relationship holds, and borides are more likely to form than nitrides. As a result, a metal powder containing boron is formed in the initial stage of the heat treatment, and when nitrogen is gaseous and uniformly present around the metal powder, the boron and the nitrogen finally contained in the metal powder. Is easy to bond to uniformly coat the surface of the metal particles with boron nitride. Metal oxide (M_aO_b) May be those conventionally shown in a phase diagram, for example, in the case of Fe, Fe₂O₃, Fe₃O₄And FeO.
      [0061]
  Further, although boron is suitable as a powder of a raw material to be a boron supply source, it may be a metal containing boron. As the metal containing boron (M), the standard formation enthalpy of formation of the MB bond is H_M-B, H, standard formation enthalpy of the M-N bond_M-NWhen expressed as,
  H_M-B> H_M-N
It is preferable that the relationship is satisfied, and examples include Sc, Ti, V, Y, Zr, Nb, La, Hf, and Ta.
      [0062]
  (Reaction process)
  Fe₂O₃And B react to explain the reaction process in which BN-coated Fe particles, BN tubes or BN wires are produced. FIG. 3 schematically shows the reaction process. FIG. 3 (1.) shows the state of the raw material. FIG. 3 (2.) shows the initial stage of the reaction. That is, B is Fe₂O₃Combined with oxygen in B₂O₃Is formed, and reduced Fe particles are present in the vicinity of B. B₂O₃Is in the liquid or gas phase. Further appearance of the reaction is shown in FIG. 3 (3.). At this stage, B reacts with Fe to form an Fe-B compound. As shown in the structure of the powder, there are particles of complete Fe-B compound, particles of incomplete B diffusion to Fe, or particles of Fe as core and Fe-B compound near 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 inside the particle to the surface. As a result, only Fe remains inside the particles, and BN-coated Fe particles are formed. In addition, when B is present in excess, BN does not stay on coating of Fe but extends in a tube or wire form. FIG. 3 (5.) is a schematic view of BN-coated Fe particles and BN tubes.
      [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 can not be sufficiently reduced to the center of the particle, and it is not easy to obtain uniform metal particles. The average particle diameter of the boron powder (b powder) is preferably 0.01 to 100 μm, and more preferably 1 to 50 μm. Boron powder having an average particle size of less than 0.01 μm is expensive and not practical. In addition, when the average particle size exceeds 100 μm, the dispersion of the b powder in the mixed powder is biased, and it becomes difficult to coat the metal particles uniformly in the end. The mixing ratio of the a powder to the b powder is preferably in the range of 25 to 95% by mass ratio of the b powder. If the mass ratio of the b powder is less than 25%, the reduction of metal oxides becomes insufficient due to the shortage of boron. If the compounding ratio of boron powder exceeds 95%, the volume ratio of the metal to be reduced becomes extremely small and it is not practical.
      [0064]
  For mixing a powder and b powder, a V-type mixer, a crusher (for example, an apparatus which combines grinding and mixing like a lai-kray machine), a mortar or the like is used. 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, 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. Gases containing oxygen, such as air, are not suitable because they interfere with the reduction reaction. The heat treatment temperature is preferably 800 ° C. to 1700 ° C., and more preferably in the range of 1000 ° C. to 1400 ° C. If it is less than 1000 ° C., the time required for the reaction to complete becomes longer. Below 800 ° C., the reaction itself does not proceed. If the temperature exceeds 1400 ° C. in a non-oxygen 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 time. If the temperature exceeds 1700 ° C., the use of a heat-resistant member becomes indispensable not only for the crucible but also for the equipment itself, which increases the production cost and is not suitable for industrialization.
      [0065]
  Below, embodiment of this invention which concerns on either of said [11] thru | or [20] is described. The present invention to which the above [11] to [20] are related selects oxides of transition metals represented by Fe, Co, and Ni as raw materials of metal powders of transition metals, and when heated, it is 600 ° C. to 1600 ° C. It has been found that, at 属 C, oxides are reduced and at the same time, graphite-based carbon is formed on the surface of metal particles. In addition, a configuration in which metal particles are included in a carbon film has also been found. It is considered that transition metals which are constituent elements of the starting material, in particular, Fe, Co and Ni play a role of a catalyst for forming a graphite layer.
      [0066]
  As powder of a raw material used as a carbon supply source, carbon powder such as graphite, carbon black and natural graphite is suitable, but a compound containing carbon may be used. That is, coal, activated carbon, coke, a fatty acid, a polymer such as polyvinyl alcohol, a B-C compound, or a carbide containing a metal may be used. Therefore, in the claims and the means for solving the problems, "carbon powder" is used as a term including both carbon powder and a compound containing carbon. However, in order to increase the carbon purity of the film, it is preferable to use carbon powder.
      [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 can not be sufficiently reduced to the center of the particle, and it is not easy to obtain uniform metal particles. The average particle diameter of the carbon powder (powder b) is preferably 0.01 to 100 μm, and more preferably 0.1 to 50 μm. Carbon powder having an average particle size of less than 0.1 μm is expensive and not practical. In addition, when the average particle size exceeds 100 μm, the dispersion of the b powder in the mixed powder is biased, and finally, the metal particles can not be uniformly coated. The mixing ratio of a powder to b powder is preferably in the range of 25 to 95% by weight of b powder. If the weight ratio of b powder is less than 25%, the reduction reaction does not proceed sufficiently due to the lack of carbon. Further, if the compounding ratio of the powder b exceeds 95%, the volume ratio of the metal to be reduced becomes extremely small, which is not practical. When the average particle diameter is in the range of 0.001 to 1 μm, more preferably 0.01 μm to 0.1 μm, when applying the metal ultrafine particles of the present invention to a magnetic recording medium, a magnetic shield, an electronic device, etc. desirable.
      [0068]
  For mixing a powder and b powder, a V-type mixer, a crusher (for example, an apparatus which combines grinding and mixing like a lai-kray machine), a mortar or the like is used. The mixed powder is heat-treated under predetermined conditions by filling predetermined amounts of a transition metal oxide and a carbon compound in a heat-resistant crucible such as alumina, boron nitride, or graphite. The atmosphere during the heat treatment is not limited as long as it is an inert gas, but a mixed atmosphere with an inert gas such as nitrogen gas or 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 ° C., the time required for the reaction to complete becomes longer. If the temperature is less than 600 ° C, the reaction itself does not proceed. If the temperature exceeds 1400 ° C. in a non-oxygen atmosphere, there is 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 time. If the temperature exceeds 1600 ° C., the use of a heat-resistant member becomes indispensable not only for the crucible but also for the equipment itself, which increases the production 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 oxide of transition metal (a powder) and boron powder (b powder) are heated at a temperature of 800 to 1700 ° C. in a nitrogen atmosphere, the metal oxide is oxidized. The substance plays a role of a catalyst for forming boron nitride microparticles, and wire-shaped boron nitride microparticles can be produced with an average diameter of 0.5 μm or less. Boron nitride microspheres can be produced at lower temperatures compared to the prior art.
      [0070]
  The metal constituting the oxide of the powder a 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. There is. Metal oxide (M_aO_b) May be those conventionally shown in the state diagram, for example, when M is Fe, Fe₂O₃, Fe₃O₄And FeO. The metal oxide is reduced in the process of boron nitride formation to finally become metal particles.
      [0071]
  In addition to boron powder, b powder may be a metal powder containing boron. As the metal containing boron (M), the standard formation enthalpy of formation of the MB bond (B is boron) H_M-B, Standard formation enthalpy of M-N bond (N is nitrogen) H_M-NWhen expressed as,
  H_M-B> H_M-N
It is preferable that the relationship is satisfied. Specifically, Sc, Ti, V, Y, Zr, Nb, La, Hf, Ta can be mentioned.
      [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. If the average particle size exceeds 1 μm, oxygen can not be sufficiently reduced to the center of the particle, and the catalyst does not function sufficiently. The average particle diameter of the boron powder (b powder) is preferably 0.01 to 100 μm. Boron powder having an average particle size of less than 0.01 μm is expensive and not practical. When the average particle size exceeds 100 μm, the dispersion of the b powder in the mixed powder is biased, and it becomes difficult to coat the metal particles uniformly in the end. The mixing ratio of a powder to b powder is preferably in the range of 25 to 95% by weight of b powder. If the weight ratio of the b powder is less than 25%, the boron is insufficient and the formation of boron nitride becomes insufficient. Further, when the compounding ratio of the powder b exceeds 95%, the powder a is reduced, the catalytic function is lowered, and the formation of boron nitride becomes insufficient.
      [0073]
  A V-type mixer, a mortar, etc. are used for mixing of said a powder and b powder. 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 for 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., and more preferably in the range of 1000 ° C. to 1400 ° C. If it is less than 1000 ° C., the time required for the reaction to complete becomes longer. Below 800 ° C., the reaction itself does not proceed. If 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 a 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 1700 ° C., the use of a heat-resistant member becomes indispensable not only for the crucible but also for the equipment itself, which increases the manufacturing cost and is not suitable for industrialization.
      [0074]
  The boron nitride powder obtained by the above method has a crystal structure identified by X-ray diffraction measurement, and as shown in FIG. 18, hexagonal boron nitride (h-BN) and rhombohedral boron nitride (r-BN) Can detect two peaks. In addition, FIG. 18 measures the powder obtained in Example 7 to be described later. 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 the observation of the lattice image.
      [0075]
  Next, embodiments of the invention relating to the above [32] to [40] will be described. According to the present invention according to the above [32] to [40], when the oxide of transition metal (a powder) and carbon powder (b powder) are heated at a temperature of 600 to 1600 ° C. in an inert gas atmosphere, The oxide plays a role of a catalyst of carbon microparticle formation, and wire micro carbon powder having an average diameter of 0.5 μm or less can be produced.
      [0076]
  As a metal which comprises the oxide of a powder, a transition metal or those alloys (especially magnetic material) are preferable. Metal oxide (M_aO_b) May be those conventionally shown in the state diagram, for example, when M is Fe, Fe₂O₃, Fe₃O₄And FeO. The metal oxide is reduced in the process of carbon formation and eventually becomes metal particles.
      [0077]
  As the b powder, carbon powder such as graphite, carbon black and natural graphite is suitable, but a compound containing carbon may be used. That is, coal, activated carbon, coke, a fatty acid, a polymer such as polyvinyl alcohol, a B-C compound, or metal carbide may be used.
      [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. If the average particle size exceeds 1 μm, oxygen can not be sufficiently reduced to the center of the particle, and the catalyst does not function sufficiently. Moreover, as for the average particle diameter of carbon powder (b powder), 0.01-100 micrometers is preferable. Carbon powder having an average particle size of less than 0.01 μm is expensive and not practical. The mixing ratio of a powder to b powder is preferably in the range of 25 to 95% by weight of b powder. If the weight ratio of b powder is less than 25%, carbon will be short. When the blending ratio of the b powder exceeds 95%, the a powder decreases and the catalytic function decreases.
      [0079]
  A V-type mixer, a mortar, etc. are used for mixing of said a powder and b powder. 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 at the time of heat treatment is preferably in 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 ° C., the time required for the reaction to complete becomes longer. Below 600 ° C., the reaction itself does not proceed. If 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 a 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., the use of a heat-resistant member becomes indispensable not only for the crucible but also for the equipment itself, which increases the production cost and is not suitable for industrialization.
      [0080]
    【Example】
  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 μm₂O₃Weigh 5 g of powder (a powder) and 5 g of boron powder (b powder) with an average particle diameter of 30 μm, and put each powder in a V-type mixer so that the blending ratio of b powder becomes 50% by mass. Mix for 10 minutes. An appropriate amount of the mixed powder is packed in an alumina boat, placed in a furnace, and heated at a rate of 3 ° C./min from room temperature in a nitrogen gas flow rate of 2 (l / min); And furnace cooled to room temperature. The mixed powder before the heat treatment was red-black, but the powder after the heat treatment was discolored to grayish white. Each powder before and after heat treatment was subjected to X-ray diffraction measurement (Cu, Kα rays), and 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 size of Fe calculated from the (110) peak of Fe using Rigaku analysis software “Jade 5” was 89 nm. Further, Table 1 summarizes the particle sizes of each phase and Fe detected from the X-ray diffraction pattern. Furthermore, the results of measuring the magnetic properties of this off-white powder with VSM are shown in Table 2. The saturation magnetization is at least 20 times the value of Comparative Example 2 described later, and the Fe is combined with the result of the X-ray diffraction measurement.₂O₃Is reduced to Fe. Further, only the powder sucked from the grayish white powder with a permanent magnet was subjected to a corrosion resistance test at a humidity of 100% and 120 ° C. for 24 hours by a PCT tester, and oxygen analysis was performed by an ashing method. The obtained results are shown in Table 3.
      [0081]
  (Example 2)
  Fe₂O₃Powder instead of Fe₃O₄An off-white powder was produced in the same manner as in Example 1 except that powder (average particle diameter 0.5 μm) was used, and X-ray diffraction, VSM measurement and PCT test were conducted.
      [0082]
  (referenceExample 1)
  The mixed powder was heat-treated and X-ray diffraction and VSM measurements were performed in the same manner as in Example 1 except that the compounding ratio of the boron powder (b powder) was changed to 20% by mass ratio.
  (Comparative example1)
  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 example2)
  The corrosion resistance test was conducted under the same conditions as in Example 1 with respect to Fe powder (ultrafine particles manufactured by Vacuum Metallurgy Co., Ltd.) having an average particle diameter of 20 nm. 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 charged into a V-type mixer and mixed. An appropriate amount of the mixed powder is packed in an alumina boat, placed in a furnace, and heated at a rate of 3 ° C./min from room temperature in a nitrogen gas flow rate of 2 (l / min); And furnace cooled to room temperature. As a result of observation on the powder after heat treatment, metal particles coated on the surface with boron nitride were obtained. Composition analysis revealed that the metal particles were Ni-containing Fe.
      [0087]
  (Example 4)
  The metal particles and the BN or C separation operation will be described. FIG. 4 shows a manufacturing process diagram of BN-coated metal particles and BN microparticles. In the case of producing coated metal particles, the production process is S1 → S2 → S3 → S4 in FIG. In S2, the boron nitride crucible 42 containing the powder of the raw material was heat-treated in the tube furnace 43. Since the heat-treated powder obtained in S2 is a mixed powder 41 of coated metal particles and minute bodies, the coated metal particles were recovered through the steps of separation and purification of S3 and S4. In the step S3, the heat treatment powder dispersed in a medium 45 represented by an organic solvent such as acetone or ethanol is stirred in the washing tank 44 to naturally precipitate the coated metal particles. An ultrasonic cleaning device 46 was used to apply ultrasonic waves to the cleaning tank 44 as a means of agitation. In addition, when it replaced with the ultrasonic wave application and used stirrers, such as a manual stirring by a glass rod, and a pencil mixer, as a means of stirring, it was able to fully stir.
      [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, the supernatant was dried to recover BN microparticles. In the above process, BN-coated metal particles and BN fine particles can be simultaneously obtained. In particular, when only BN microbodies are manufactured, the manufacturing process may be S1 → S2 → S5 → S6 in FIG. The 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 immersing the heat-treated powder in the acidic solution, the precipitate was recovered. The step S6 is a step of washing the precipitate and then drying it. 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, precipitated again, and after removing the supernatant liquid, it was dried to obtain BN microparticles. For complete removal of the acidic solution, it is preferable to repeat the S6 step several times. The above production process can be applied to the process for producing carbon-coated metal particles and carbon microparticles.
      [0089]
  FIG. 5 is a photomicrograph of the particle structure according to the invention as observed by electron microscopy (TEM), showing BN coated Fe particles. FIG. 6 is a schematic view for schematically explaining the structure of FIG. As shown in FIG. 6, the Fe particles 1 are coated with the BN film 2 around the periphery. A further enlarged photograph of the BN coating is shown in FIG.
      [0090]
  FIG. 7 is a photomicrograph of the particle structure according to the invention observed with an electron microscope, showing BN coated Fe particles. FIG. 8 is a schematic view for schematically explaining the structure of FIG. As shown in FIG. 7, in the BN film coated on the surface of the Fe particles 1, a stripe pattern of the laminated crystal lattice is observed. In the portion of the lattice plane 3, a plurality of lattice planes are stacked almost in parallel along the surface of the Fe particle 1. Although the lattice plane 4 and the lattice plane 5 have portions where lattice planes are not parallel to each other, it can be seen that the surface of the Fe particles 1 is sufficiently covered.
      [0091]
  (Example 5)
  Α-Fe with an average particle size of 0.03 μm₂O₃5 g of powder (a powder) and 5 g of carbon powder (b powder) having an average particle diameter of 20 μm were charged into a V-type mixer and mixed for 10 minutes. An appropriate amount of the 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 raised at a rate of 3 ° C./min from room temperature in a nitrogen gas flow of 2 l / min. Then, it was maintained at 1000 ° C. for 2 hours and furnace cooled to room temperature at a rate of 3 ° C./min. The structure of the tubular furnace is shown in the schematic of FIG. Each powder before and after heat treatment was subjected to X-ray diffraction measurement (Cu, Kα rays), and 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. Furthermore, the results of measuring the magnetic properties of the heat-treated powder with a VSM (sample vibration type magnetometer) are shown in Table 4. The saturation magnetization is about 100 times the value of Comparative Example 4, and it is Fe together with the result of the X-ray diffraction measurement.₂O₃Is reduced to Fe. After exposing the powder after the above heat treatment to a PCT tester (pressure cooker test tester) at a humidity of 100% and 120 ° C. and 1 atm for 24 hours, the oxygen content of the powder is analyzed by an oxygen / nitrogen / hydrogen analyzer for metal It analyzed by Horiba EMGA-1300). The analysis results of the oxygen content are shown in Table 5. There is no increment of oxygen content even after the PCT test, which confirms that the Fe powder surface is covered with a graphite film. In the above analysis of oxygen, nitrogen and hydrogen in metal, 0.5 g of sample powder is filled in a graphite crucible and the crucible is rapidly heated to 2000 to 3000 ° C to pyrolyze O, N and H in the sample. CO generated by gas chromatograph and thermal conductivity detector₂, N₂, H₂This is a method of analyzing the contents of O, N and H by detecting O gas.
      [0092]
  (Comparative example3)
  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 tests were performed. The X-ray diffraction pattern did not change before and after heat treatment, and the reaction did not proceed. The value of saturation magnetization also hardly changes.
      [0093]
  (Comparative example4)
  A corrosion resistance test was conducted under the same conditions as in Example 5 with an Fe powder (ultrafine particles manufactured by Vacuum Metallurgical Co., Ltd.) having an average particle diameter of 0.02 μm. The saturation magnetization is the value of pure iron (approximately^-6It has fallen to about 30% of wb · m / kg).
      [0094]
  [Table 4]

      [0095]
  [Table 5]

      [0096]
  FIG. 11 is a micrograph of the structure of the metal ultrafine particle according to Example 5 observed by TEM (transmission electron microscope). At the time of TEM observation, no processing giving damage or mutation to particles is performed except for sample preparation required. FIG. 12 is a schematic view schematically illustrating the structure of FIG. 11 and is slightly enlarged. The metal ultrafine particles 11 are particles in which the surfaces of the particles 12 of α-Fe are all coated with a graphite thin film 20 having a predetermined thickness. This coating protects the surface of the particles 12 of α-Fe and effectively prevents oxidation. The projections 21 and 21b scattered on the outside of the graphite thin film 20 are presumed to be either a growth of a different layer of graphite or a adhesion of foreign matter. The light-dark patterns 13a, 13b, 13c of the α-Fe particles 11 themselves are interference patterns (indicated by a two-dot chain line) due to the shape (substantially spherical shape) of the α-Fe particles 11. At both ends of the particles of α-Fe, the boundary 14 of the graphite thin film is photographed somewhat indistinctly, so it is indicated by dotted lines. This is because it is difficult to focus on all due to the substantially spherical shape, and the actual shape is not unclear. A region outlined 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. The line 16 and the code have a scale in which the length of the three lines corresponds to 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 by a TEM (transmission electron microscope), illustrating the state 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 a schematic view of FIG. The graphite thin film 20 mainly has a crystal structure of graphite. For example, the lattices 20a, 20b, and 20c represent layered lattice planes of graphite, and the lattice spacings are approximately equal, and arranged substantially parallel to the surface of the particles 12 of α-Fe.
      [0098]
  However, since the particles of α-Fe are spherical and there are some irregularities on the surface, some of the graphite thin film is inclined relative to the surface of the particles 12 of α-Fe as in the lattice 20f. There are places where you The plaid 20f is derived from another plaid 20e, and is further a plaid 20d. Although illustration of the line is omitted, the lattice 20d is arranged substantially parallel to the surface of the particle 12 of α-Fe. As described above, in the graphite thin film, there are places where the orientation of the arrangement of the layered lattice planes changes or where the state of the arrangement becomes unclear (places that look like a satin pattern). In order to grow so that the plane of the crystal structure is parallel to the surface of the particles 12 of α-Fe, a substantially uniform graphite thin film coating is formed.
      [0099]
  In the graphite thin film 20 of FIG. 14, a part of the checkered pattern is schematically illustrated by a solid line or a dotted line. Although illustration is omitted, the crystal structure also exists in the blank part. The intermediate layer 25 is presumed to be present between the surface of the particles 12 of α-Fe and the graphite thin film 20, the details of which will be described with reference to FIGS.
      [0100]
  FIG. 15 is a photomicrograph of the structure of the particles according to the present invention observed by 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 view for schematically explaining the structure of FIG. 15 and is somewhat enlarged. In the particle 12 of α-Fe, a lattice 24 is seen along the direction of the arrow a, and indicates a characteristic crystal plane of α-Fe. Since it is difficult to clearly map the arrangement of Fe atoms in a beaded connection, they are shown by dotted lines. In the vicinity of the surface of the particle 12 of α-Fe, the checkered pattern along the arrow a is broken, but the end of the array constitutes a flat surface, and the starting point from which the graphite crystal grows gradually (Growth layer of graphite). Hereinafter, these regions are referred to as an intermediate layer 25. The graphite thin film 20 is grown and formed through the intermediate layer 25.
      [0101]
  As shown in FIG. 16, if the surface of the particle 12 of α-Fe is a relatively smooth spherical surface (flat surface), the layered lattice surface 22 of graphite is a surface along the arrow d and regularly arranged in parallel While growing, to form a dense and very thin coating. Here, "fine" 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 as one or two layers in terms of the spacing of the layered lattice planes 22 of graphite. When the crystal plane of graphite which has started to grow is also included in the intermediate layer, the thickness of the intermediate layer 15 is about 2 to 4 layers in terms of the distance between the layered lattice planes 22 of graphite.
      [0102]
  Dislocations 23 occur in the crystal growth, and are presumed to be portions where the crystal structure is discontinuous. When a layered lattice is grown to form a laminated structure, it is assumed that the growth of a part is delayed by one layer due to lattice defects. When growth of a part is resumed, the lattice plane of the n-1st layer of a part and the lattice plane of the nth layer adjacent to each other may combine to form one face (dislocated face) . The rate of occurrence of dislocation planes is not high, and it can be said that the film as a whole is a uniform and dense thin film as a whole. In addition, although the convex part 21b exists in the surface of the graphite thin film 20,15Was not taken clearly inofThe points are indicated by dotted lines.
      [0103]
  (Example 6)
  Hematite with an average particle size of 0.03 μm (Fe₂O₃3) Powder and 7 g of boron powder with an average particle diameter of 26 μm were charged into a V-type mixer and mixed for 10 minutes. The mixed powder 121 is filled in a crucible 122 made of boron nitride and placed in a tubular electric furnace 123, and the temperature is raised from room temperature at a rate of 3 (° C./min) in a nitrogen gas flow of 2 (l / min). After warming, it was held at 1100 ° C. for 2 hours and furnace cooled to room temperature. The mixed powder before the heat treatment was red-black, but the powder after the heat treatment was discolored to grayish white. The powder after heat treatment was subjected to X-ray diffraction measurement (Cu, K α rays), and a diffraction pattern as shown in FIG. 17 was obtained. From the powder subjected to the above heat treatment, hexagonal boron nitride (h-BN) was obtained. Diffraction peaks of () and rhombohedral boron nitride (r-BN) and α-Fe were detected. In order to separate boron nitride and Fe, acetone 500cc (0.5 × 10^-3m³5 g of the above-mentioned powder was charged into the solution and subjected to ultrasonic cleaning for 5 minutes to separate the supernatant and the precipitate. Supernatant 127 was left in a draft for a further 24 hours to dry acetone, and boron nitride powder 128 (weight: 6 g) was recovered.
      [0104]
  When this boron nitride powder was observed by 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, this boron nitride wire had a rhombohedral structure. The unit of flow rate is (l / min) 約 about 16.7 × 10^-6(M³Corresponds to / s). The manufacturing process of Example 6 includes a powder mixing process (S11), an atmosphere heat treatment process (S12), an ultrasonic wave application process (S13) to a medium in which the powder is dispersed, and a boron nitride microparticle separation and drying process 22 corresponds to the process flow and schematic diagram of FIG. In the figure, reference numeral 124 represents a cleaning tank, reference numeral 126 represents an ultrasonic cleaner, and reference numeral 125 represents a solvent (acetone) in which the powder after heat treatment was dispersed. In addition, if an ultrasonic wave can be applied to disperse the produced particles, it can be used without being limited to the washing machine.
      [0105]
  FIG. 20 is a schematic view copying the structure of the photograph of FIG. 19 and showing wire-like boron nitride microparticles. In this boron nitride microbody 101, a large number of tubes 103 each having a cavity 102 therein are connected to form a long bent tube shape. One end is terminated by the structure of the tube 103. The other end is terminated at the h-BN tissue 112 via the r-BN tissue which is the tube 103 and the tissue in which the h-BN-like site 112 b is mixed. In FIG. 20, a curve indicated by a dotted line represents an extension of a collodion film for fixing boron nitride microparticles 101 to a sample holder of an electron microscope. The lines and letters on the right outside of the rectangular enclosure in FIG. 20 indicate that the line length corresponds to a dimension of 200 nm.
      [0106]
  FIG. 21 is a schematic view extracting and enlarging only the boron nitride tube in FIG. The vicinity of the tip 111 of the tube is seen overlapping with the middle part of the tube, and it is not clear that the tip is closed because it is not clear. From the vicinity of the tip, the structure of the cavity 102 and the tube 103 surrounding it continues, and on the way, a portion considered as a node 104 between the tubes and a portion that looks thick for observing the thickness of the tube thick or diagonally There is a possible bump 105. The orientation of the continuous tube, for example, appears to be significantly bent at the bend 110. The thickness of the tube is not always uniform, and it forms the cavity 102 with not only the bumps 105 and nodes but also a complex line and striae-like structure. The tube structure is clearly observed from near the tip 111 to the nodes 104b, and the diameter of the tube is 0.12 to 0.20 μm (120 to 200 nm). Since the crystal structure is complicated in this area, it is presumed that r-BN and h-BN are mixed or in a mixed phase. The mixing of different phases is considered to be related to the bending of the tube. When the crystal structure of the tube 103 which clearly looks like a pipe is enlarged and observed, the arrangement of atoms is r-BN which repeats a three-layer cycle, and the repetition direction of the cycle is directed to the diameter direction of the tube.
      [0107]
  (Example 7)
  Α-Fe with an average particle size of 0.03 μm₂O₃5 g of powder (a powder) and 5 g of carbon powder (b powder) having an average particle diameter of 20 μm were charged into a V-type mixer and mixed for 10 minutes. The mixed powder 251 is charged in an appropriate amount in a boron nitride crucible 252 and heated from room temperature at a rate of 3 ° C./min in a nitrogen gas stream with a flow rate of 2 l / min in a tubular furnace 253 and then 2 at 1000 ° C. The furnace was cooled to room temperature at a rate of 3 ° C./min. The unit of flow rate is (l / min) 約 about 16.7 × 10^-6(M³Corresponds to / s).
      [0108]
  Each powder before and after heat treatment was subjected to X-ray diffraction measurement (Cu, Kα rays), and 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, ○ represents a peak corresponding to the crystal structure of graphite, ▪ represents a peak corresponding to the crystal structure of α-Fe, the horizontal axis represents the diffraction angle 2θ (°), and the vertical axis represents the diffraction X-ray intensity (cps). The peak of maximum strength of graphite has a half width of about 0.2 °, and the crystallinity of the powder after heat treatment is good. Furthermore, when the magnetic properties of the powder before and after heat treatment corresponding to FIGS. 23 and 24 were measured by VSM (sample vibration type magnetometer), the saturation magnetization was 1.30 × 10 at the former.^-6Wb · m / kg, the latter 131 × 10^-6It was Wb · m / kg. From the above, Fe₂O₃Is reduced to Fe.
      [0109]
  When the powder after the heat treatment was observed with a TEM (transmission electron microscope), a tube-like microbody as shown in FIG. 25 was confirmed. FIG. 25 is a photomicrograph of the particle structure of the present invention observed by an electron microscope. As a result of compositional analysis by EDX (energy dispersive X-ray detector), it was found that the black particles at the tip of the microbody are Fe and the tube is C (carbon).
      [0110]
  FIG. 26 is a schematic diagram corresponding to the structure of the picture of FIG. 25. The carbon microbody 201 has a structure in which a carbon tube 203 grows in a curved shape based on the Fe particle 202. A plurality of nodes 204 exist inside the tube 203, and the area surrounded by the opposite nodes and the tube wall 203b constitutes a cavity 205. The other end of the tube 203 is closed and forms a tip portion 206. In this carbon micro-body 201, the fact that the growth direction of the tube is curved is considered to be related to the fact that the wall thickness of the tube and the distance between the nodes are not uniform. In particular, the portions of the tube walls 203c and 203e are thin.
      [0111]
  Another carbon microbody 207 is a structure in which a carbon tube 209 grows curvilinearly based on the Fe particles 208 and includes other Fe particles 213 at the tip. Inside the tube 209 there are a plurality of nodes 210, the area enclosed by the opposite nodes and the wall of the tube constituting a cavity 211. The Fe particles 220 in the vicinity of the Fe particles 213 appear to be separated by the tube wall 220 or the like. It is not clear whether the Fe particles 213 are attached from the beginning of the growth of the tube or those taken in during the growth of the tube. The Fe particles 208 and the wall 212 of the tube are only seen overlapping with the carbon minute body 201, and are not connected. Furthermore, other Fe particles 214 are present alone. In the figure, a straight or bent dashed-dotted line represents the outline of carbon 215, 216 of the raw material. The curved dashed-dotted lines indicate the contours of the collodion films 217 and 218 for fixing carbon microparticles and the like to the sample holder of the electron microscope. The reference numeral 219 is a scale display written in order to make the dimensions of FIG. 26 easy to understand, and there is no such structure in the original FIG. The length of the three lines in the scale display corresponds to 100 nm.
      [0112]
  Based on the photograph in FIG. 25, the ratio of the outer diameter Ro to the inner diameter Ri of each carbon microbody was measured. Measure for any location and obtain data such as (Ri / Ro) = 0.67, 0.75, 0.40, 0.69, 0.57, 0.63, 0.75, 0.44 The Example7The mean outer diameter and mean inner diameter could also be changed by producing carbon microparticles by changing the conditions of In consideration of 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 of the present invention observed by an electron microscope. In FIG. 25, the vicinity of the junction between the Fe particles 202 and the tube 203 is enlarged. FIG. 28 is a schematic diagram corresponding to the structure of the picture of FIG. Note that FIG. 28 is expressed by replacing only the main part of the crystal structure of FIG. 27 with a solid line or a dotted line for easy explanation. Therefore, even if the periphery of the area hatched with dotted lines is blank, the description is omitted.
      [0114]
  According to FIG. 28, in the Fe particles 202, in most regions, the texture appears to have a surface along a specific crystal plane. Hereinafter, the Fe main phases 220 and 221 are referred to. On the left side of the Fe main phase 220, a phase 225 in which the orientation of the face of the array is different, and a heterophase 226 which appears to be a textured pattern are observed. In addition, although the Fe main phase 220 etc. were expressed by the dotted line arrange | positioned in parallel, point space | interval and line space | interval do not necessarily correspond with FIG. It is drawn in order to explain the direction etc of the arrangement of the line intelligibly.
      [0115]
  The carbon tube in FIG. 28 will be described. The tube 203 is generated ahead of the virtual boundary line 227 and the Fe main phase 221. It can be seen that the inside of the wall of the tubular tube is divided by nodes 236, 239. The area surrounded by the nodes 236 and the Fe particles 202 and the wall of the tube or the area surrounded by the nodes 236 and 239 and the wall of the tube became hollow.
      [0116]
  In the tube wall, the arrangement of crystals is mainly composed of the graphite structural phase. Hereinafter, graphite and a similar structure are collectively referred to as a graphite phase. The graphite phase is clearer than Fe in that the crystallographic arrangement appears to be stacked along a particular plane. The planes of the graphite phases 230, 231, 232, 233, 237, 238 and 240 can be said to be parallel or substantially parallel to the growth direction of the wall of the tube. On the other hand, at the nodes 236 and 239, it can be said that the plane of the graphite layer is orthogonal or nearly orthogonal to the growth direction of the wall of the tube. At the base of the left side of the node 236, the graphite layer is divided in a Y-shape into a downward layer 234 and an upward layer 235, presenting a structure such as a tree trunk and a branch. The root of the node 239 is approximately orthogonal 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 node, but can not be determined because the graphite phase 242 of the other structure is mixed.
  The state of lamination of the atomic arrangement of the graphite layers is narrow as expressed in the graphite layers 235 and 238 and the nodes 236 and 239. The same illustration of all layers is complicated, and the other parts are illustrated with a reduced number of layers. Also, when one layer is clearly seen, it is shown by a line, but when it seems that it is discontinuous and continuous, it is displayed 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. Supernatant 257 was allowed to stand in a draft for an additional 24 hours to dry the acetone and obtain carbon fine powder 258. The powder 258 improves the proportion of carbon microparticles by removing coarse transition metal particles and the like.
      [0118]
  The manufacturing process of Example 7 includes a powder mixing process, a heat treatment process in an atmosphere, ultrasonic wave application (dispersion process) to the medium into which the powder is charged, and separation and drying processes of coarse transition metal particles and the like, and the process of FIG. Corresponds to the flow and schematic. In the figure, reference numeral 254 denotes a cleaning tank, reference numeral 255 denotes a solvent (acetone) in which powder after heat treatment is dispersed, and reference numeral 256 corresponds to an ultrasonic cleaning apparatus. In addition, as long as ultrasonic waves can be applied to disperse the generated particles in a solvent, it can be used without being limited to the washing apparatus.
      [0119]
    【Effect of the invention】
  As described above, by using the metal ultrafine particles of the present invention and the method for producing the same, metal ultrafine particles can be obtained in which a coating that is safe, simple and suitable for industrial use is applied to the surface of metal particles. Furthermore, when manufacturing metal ultrafine particles, it is possible to obtain the minute body related to the by-product and the manufacturing method thereof.
Brief Description of the Drawings
    [Fig. 1]
  It is a graph which shows the X-ray-diffraction pattern of the mixed powder before heat processing.
    [Fig. 2]
  It is a graph which shows the X-ray-diffraction pattern of the mixed powder after heat processing.
    [Fig. 3]
  Fe₂O₃It is the schematic explaining the reaction process which boron nitride covering Fe particle etc. produce | generate by reacting and B. FIG.
    [Fig. 4]
  It is a manufacturing-process figure of a boron nitride coating metal particle and a boron nitride microbody.
    [Fig. 5]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 6]
  It is the schematic for demonstrating the structure of FIG. 5 typically.
    [Fig. 7]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 8]
  It is the schematic for demonstrating the structure of FIG. 7 typically.
    [Fig. 9]
  It is a graph which shows the X-ray-diffraction pattern of the mixed powder before heat processing.
    [Fig. 10]
  It is a graph which shows the X-ray-diffraction pattern of the mixed powder after heat processing.
    [Fig. 11]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 12]
  It is the schematic for demonstrating the structure of FIG. 3 typically.
    [Fig. 13]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 14]
  It is the schematic for demonstrating the structure of FIG. 5 typically.
    [Fig. 15]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 16]
  It is the schematic for demonstrating the structure of FIG. 7 typically.
    [Fig. 17]
  FIG. 2 is a schematic view of a tubular furnace used in the manufacturing process of Example 1;
    [Fig. 18]
  It is a graph which shows the X-ray-diffraction pattern of the powder of this invention.
    [Fig. 19]
  It is a photograph of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 20]
  It is the schematic corresponding to the structure of the photograph of FIG.
    [Fig. 21]
  It is the schematic which expanded a part of FIG.
    [Fig. 22]
  FIG. 16 is a flow and schematic diagram illustrating a manufacturing process of Example 6.
    [Fig. 23]
  It is a graph which shows the X-ray-diffraction pattern of the mixed powder before heat processing.
    [Fig. 24]
  It is a graph which shows the X-ray-diffraction pattern of the mixed powder after heat processing.
    [Fig. 25]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [FIG. 26]
  It is the schematic corresponding to the structure of the photograph of FIG.
    [Fig. 27]
  It is a microscope picture of the particle structure which concerns on this invention observed by the electron microscope.
    [Fig. 28]
  It is the schematic corresponding to the structure of the photograph of FIG.
    [Fig. 29]
  FIG. 24 is a process flow and schematic view illustrating a manufacturing process of Example 7;
[Description of the code]
  1 Fe particle, 2 BN film, 3 lattice plane, 4 lattice plane,
  5 lattice planes,
  11 metal ultrafine particles, particles of 12 α-Fe,
  13a 13b 13c pattern,
  14 Graphite thin film boundaries, 15 collodion films,
  16 scale, 20 graphite thin films,
  20a 20b 20c plaid,
  20e plaid, 20d plaid, 20f plaid,
  21 21b convex part,
  22 layered lattice planes,
  23 shifted points, 24 plaid,
  25 interlayer, 27 graphite growth layer,
  41 mixed powder, 42 boron nitride crucible, 43 tube furnace,
  44 washing tanks, 45 media, 46 ultrasonic cleaning devices,
  47 supernatant, 48 coated metal particles,
  51 mixed powder, 52 boron crucible, 53 tube furnace,
  101 Boron Nitride Microbodies, 102 Cavities, 103 Tubes,
  Sections 104 and 104b,
  105 bumps, 110 bends, 111 near the tip,
  112 h-BN tissue, 112 b h-BN site,
  113 collodion film, 121 mixed powder, 122 坩 堝,
  123 tubular electric furnace, 127 supernatant, 128 boron nitride powder,
  201 carbon particles, 202 Fe particles, 203 tubes,
  203b tube wall,
  203c 203e tube wall,
  Section 204, 205 cavity, 206 tip,
  207 carbon microparticles, 208 Fe particles, 209 tubes, 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 boundaries,
  Phases with different orientations of the faces of the 225 arrays, Heteromorphic phases that look like 226 textured,
  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 tube furnace,
  254 washing tank, 255 solvent that dispersed powder after heat treatment,
  256 ultrasonic cleaners, 257 supernatant, 258 carbon powder