JP4530238B2 - Method for producing titanium oxide powder containing anatase-type titanium oxide single crystal - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、光触媒、光学材料等に利用しうる大粒径で高純度のアナターゼ型酸化チタン単結晶の製造方法に関するものである。
【０００２】
【従来の技術】
酸化チタン微粒子は、白色顔料として古くから利用されており、近年はコンデンサ、サーミスタの構成材料またチタン酸バリウムの原料等電子材料に用いられる焼結材料に広く利用されている。また、酸化チタンの単結晶は可視光付近の波長領域において大きな屈折率を示すため、可視光領域では殆ど光吸収は起こらない。このことから、最近化粧料、医薬あるいは塗料等の紫外線遮蔽が要求されるような材料にも広く使用されている。さらに、酸化チタンにそのバンドギャップ以上のエネルギーを持つ光を照射することによって酸化チタンが励起されて、伝導帯に電子また価電帯に正孔が生じるが、この電子による還元力また正孔による酸化力を利用した光触媒反応の用途開発が盛んに行われている。この酸化チタン光触媒の用途は非常に多岐に渡っており、水の分解による水素の発生、排ガス処理、空気清浄、防臭、殺菌、抗菌、水処理、照明機器等の汚れ防止等、数多くの用途開発が行われている。
【０００３】
上記のような酸化チタンの用途のうち、近年光触媒用としての酸化チタンが特に注目されており、ルチル型、アナターゼ型およびブルッカイト型の結晶構造のうち微粒子のアナターゼ型酸化チタン単結晶がその光触媒活性の高さから、主に光触媒材料として用いられている。
【０００４】
一方、酸化チタンの単結晶は、最近アイソレータの偏光子や検光子の光学材料や、大口径の単結晶は薄膜形成用基材として使用されている。従来その製法は、ベルヌーイ法、浮遊帯域溶融法（ＦＺ法）或いはＥＦＧ（Ｅdge-defined Ｆilm Ｇrowth ）法などの溶融成長法によって製造されていた。これらの方法は、酸化チタンの粉末をルツボ内で１８００℃以上の酸化チタンの融点以上に加熱し溶解させるため、得られる酸化チタン単結晶はすべてルチル型であった。
【０００５】
また、アナターゼ型酸化チタン単結晶については、種々文献等にその製法あるいは物性が紹介されている。例えば、「水熱法により結晶化した単分散酸化チタン微粒子の成形性及び焼結性」日本セラミックス協会学術論文誌（ＶＯＬ．１０３，ＮＯ．６ＰＡＧＥ．５５２‐５５６ 1995 ）には、アルコキシチタンを水熱加水分解し、アナターゼ型酸化チタンを生成させ、その後結晶を成長させアナターゼ型単結晶を調製している。また、「Ｕｌｔｒａｆｉｎｅ Ｔｉｔａｎｉａ ｂｙ Ｆｌａｍｅ ＳｐｒａｙＰｙｒｏｌｙｓｉｓｏｆ ａ Ｔｉｔａｎａｔｒａｎｅ Ｃｏｍｐｌｅｘ．」Ｊ. Ｅｕｒ. Ｃｅｒａｍ. Ｓｏｃ. （ＶＯＬ．１８，ＮＯ．４ＰＡＧＥ．２８７‐２９７ 1998 ）では、キレート金属アルコキシドを火炎噴射熱分解によって、アナターゼ型単結晶を製造している。
【０００６】
一方、従来酸化チタンの製法のうち気相酸化法と呼ばれる方法として、四塩化チタンを気相中で酸素と接触させ酸化させる方法、あるいは燃焼して水を生成する水素ガス等の可燃性ガスと酸素を燃焼バーナーに供給し火炎を形成し、この中に四塩化チタンを導入する所謂火炎加水分解法などがある。特開平６−３４０４２３号公報には、四塩化チタン、水素及び酸素の混合ガスを気相において燃焼させて四塩化チタンの加水分解により酸化チタンを製造する火炎加水分解方法において、該混合ガス中の四塩化チタン、水素及び酸素を特定のモル比で反応させる方法が開示されている。また、特開平８−２１７６５４号公報には、チタン化合物を火炎加水分解法において、水素含有ガス中にチタン化合物を、二酸化チタン換算で５０〜３００ g/m3 供給し、３００〜１５００℃の温度で火炎加水分解した平均粒径０．０４〜０．１５μm の結晶質の紫外線遮蔽化粧料用酸化チタン微微粒子が開示されている。
【０００７】
【発明が解決しようとする課題】
上記従来技術で得られるアナターゼ型酸化チタン単結晶は、その粒径がいずれも数ｎｍ〜数１０ｎｍと超微粒子であり、実際にはこれらの一次粒子が凝集した二次粒子であった。そのため、光触媒として用いたときの分散性が悪く、さらにその取り扱いが非常に困難であった。
【０００８】
一方、従来の四塩化チタンを気相で酸化し酸化チタンを製造する方法は、低コストで高純度の酸化チタンが得られ、また比較的高温で反応を行うためルチル型酸化チタンを得るには有利であり、さらにアナターゼ型酸化チタンも得られるが、結晶を成長させ大粒径の単結晶を得ることはできなかった。
【０００９】
従って、本発明の目的は、大粒径で、高純度のアナターゼ型酸化チタン単結晶の製造方法であって、工業的にかつ低コストで製造可能とする方法を提供することにある。
【００１０】
【課題を解決するための手段】
かかる実情において、本発明者は、低コストで製造可能な酸化チタンの製造方法について鋭意検討を重ねた結果、特定条件の四塩化チタンの気相反応法によれば、大粒径で高純度であり、光触媒などに好適なアナターゼ型酸化チタン単結晶を製造しうる方法を見出し本発明を完成するに至った。
【００１１】
すなわち本発明は、四塩化チタンの気相反応において、標準状態と仮定したときのガスの体積を、四塩化チタンガス１ｌに対し、酸素１〜３０ｌの割合で接触させ、７００〜８５０℃で酸化反応を行い酸化チタン粒子を生成させ、次いで、該酸化チタン粒子を３００℃以上７００℃未満且つ前記酸化反応の反応温度よりも低い温度で、１２０分以上加熱処理することを特徴とするアナターゼ型酸化チタン単結晶を含む酸化チタン粉末の製造方法を提供するものである。
【００１２】
【発明の実施の形態】
以下、本発明をさらに詳しく説明する。
【００１３】
本発明のアナターゼ型酸化チタン単結晶の製造方法は、原料として四塩化チタンおよび酸素の２成分を接触させ、四塩化チタンを気相において酸化反応させ、酸化チタン粒子を先ず生成させる。これらの原料の他、水素、水蒸気あるいは燃焼して水を生成するプロパン等の可燃性ガスも併用し得る。
【００１４】
上記各成分を接触し反応させる際の上記各成分の反応部への供給量比としては、標準状態と仮定したときのガスの体積が、四塩化チタン１ｌ（ガス）に対し、酸素が通常１〜３０ｌ、好ましくは２〜２０ｌ、特に好ましくは４〜１０ｌである。さらに本発明では必要に応じて水素あるいは水蒸気を上記成分以外に供給することも可能であり、その際の水素又は水蒸気の供給量比は、標準状態と仮定したとき、水素ガスが四塩化チタン１ｌ（ガス）に対し通常０．１〜１０ｌ、好ましくは０．１〜５ｌであり、水蒸気が通常０．０５〜１．０ｌ、好ましくは０．１〜０．５ｌである。
【００１５】
上記各原料ガスの供給量は、反応スケールあるいは各ガスを供給するノズル径等により異なるので適宜設定するが、反応部での各ガス、特に四塩化チタンガスの供給速度は反応部の燃焼炎が乱流域になるように設定することが望ましい。
【００１６】
本発明は、上記の四塩化チタンガス及び酸素、また必要に応じて水素または水蒸気を反応炉に供給し、気相で接触させ反応させる。これら各成分の供給方法としては、種々の方法が採用し得るが、具体的には、以下の方法が好ましい；
１）四塩化チタンガスと、酸素ガスの供給管をそれぞれ独立に設置し、かつ両者を隣接させ独立に反応炉に供給する方法、
２）四塩化チタンガスと、酸素ガス及び水素ガスの混合ガスの供給管をそれぞれ独立に設置し、かつ両者を隣接させ独立に反応炉に供給する方法、
３）四塩化チタンガスと、酸素ガス及び水蒸気の混合ガスの供給管をそれぞれ独立に設置し、かつ両者を隣接させ独立に反応炉に供給する方法。
【００１７】
先ず、上記各成分を反応炉内に導入し、所定温度の下四塩化チタンを酸化反応させアナターゼ型酸化チタン粒子を生成させる。本発明においてアナターゼ型酸化チタンを気相酸化反応で形成するためには、酸化チタンが生成する温度以上でありかつ酸化チタンの結晶構造がルチル型に転移する温度より低い温度で反応を行う必要がある。上記酸化反応の反応温度は、７００〜８５０℃、好ましくは７５０〜８５０℃、特に好ましくは７５０〜８３０℃である。
【００１８】
次いで、生成したアナターゼ型酸化チタン粒子に加熱処理を施しその結晶を成長させる。加熱処理の温度は、３００℃以上８５０℃未満、好ましくは３００〜８００℃、特に好ましくは５００〜７５０℃、さらに好ましくは５００℃以上７００℃未満で、且つ酸化反応の反応温度よりも低い温度である。該加熱処理の温度と酸化反応の反応温度との差としては、通常５０℃以上、好ましくは１００℃以上、特に好ましくは２００℃以上、さらに好ましくは３００℃以上である。このように加熱処理の温度を酸化反応の反応温度に対して低い温度とすることにより、生成した１次粒子の２次凝集やルチル型結晶への転移を防ぎ、アナターゼ型酸化チタン単結晶を成長させて大粒径にするため好ましい。また、加熱処理の時間としては、得られるアナターゼ型酸化チタン単結晶の粒径により異なるが、０．１μｍ以上のものを得る場合は通常３０分以上、１．０μｍ以上のものを得る場合は通常６０分以上である。ここで、加熱処理とは、前記酸化反応が終了して系内の温度が前記加熱処理の温度まで低下したときから始まる工程をいう。
【００１９】
なお、従来のルチル型あるいはアナターゼ型の凝集粒子を得る方法では、酸化チタン粒子を生成させた後、生成粒子の成長及び凝集を防ぐために、少なくとも酸化チタン粒子が焼成せず且つ２次凝集しない温度以下、具体的には３００℃未満まで冷却を行っていた。これに対し、本発明では反応後の生成粒子の少なくとも酸化チタン粒子が焼成せず且つ２次凝集しない温度以下までの冷却を行わず、生成粒子に所定の加熱処理を施して結晶を成長させるため、大粒径のアナターゼ型酸化チタン単結晶を得ることが可能である。
【００２０】
得られたアナターゼ型酸化チタン単結晶は、冷却し、その後必要に応じて分級、あるいは篩分を行う。アナターゼ型酸化チタン単結晶の冷却方法としては、通常、上記加熱処理の後工程に冷却工程を設けることにより、生成アナターゼ型酸化チタン単結晶を冷却する方法が挙げられる。具体的には反応部のあとに冷却ジャケットを具備した冷却部を設ける。
【００２１】
上記各成分のうち特に四塩化チタンガスおよび酸素は、窒素等の不活性ガスで希釈して反応部に供給してもよい。その際の、四塩化チタンの希釈率は、標準状態と仮定したとき、四塩化チタンガス１ｌに対し、不活性ガスが通常０．１〜１０ｌ、好ましくは０．３〜１ｌである。また酸素の希釈率は、標準状態と仮定したとき、酸素ガス１ｌに対し、不活性ガスが通常０．１〜１０ｌ、好ましくは０．３〜１ｌである。
【００２２】
各成分あるいは混合ガスの供給管をそれぞれ独立に設置し、かつ両者を隣接させる手段としては、種々の方法を採用し得るが、その供給管を内管と外管とが同軸的に配された多重管とすることが好ましい。すなわち、多重管の供給管を用いて上記の各成分あるいは混合ガスを供給すること、特に、最も内側の管から四塩化チタンガス、その外側の管から酸素ガスを供給させることにより、反応が均一となり、粒子性状の良好なアナターゼ型酸化チタン単結晶が生成される。
【００２３】
本発明のアナターゼ型酸化チタン単結晶の製造方法において用いられる反応炉としては、例えば多重管等の各成分の供給管が上部に設けられた、縦型反応炉が好ましい。
【００２４】
また、反応炉内に供給される各成分あるいは混合ガスは、反応炉内に供給する前に予熱し供給することが好ましい。この予熱は後述する反応炉内での反応の温度範囲で行うことが望ましい。
【００２５】
以下本発明のアナターゼ型酸化チタン単結晶の具体的な製法の一例を示す。
【００２６】
先ず、液状の四塩化チタンを予め加熱し、気化させ、必要に応じて窒素ガスで希釈し反応炉に導入し、同時に、酸素ガス及び／又は水蒸気を必要に応じて窒素ガスで希釈して反応炉に導入し、酸化反応を行う。酸化反応の反応温度は７００〜８５０℃、好ましくは７５０〜８３０℃である。本発明では、大粒径かつ高純度で、光触媒などに好適なアナターゼ型酸化チタン単結晶を得るために、比較的低温で酸化反応を行う。
【００２７】
上記の酸化反応によりアナターゼ型酸化チタン粒子を生成させ、その後該酸化チタン微粒子を冷却せず、所定の加熱処理を施すことにより結晶粒子を成長させる。その後得られたアナターゼ型酸化チタン単結晶を冷却する。冷却手段としては、通常冷却ジャケットを具備した冷却槽等が用いられ、同時に空気あるいは窒素ガス等の不活性ガスを生成したアナターゼ型酸化チタン単結晶と接触させて冷却する。
【００２８】
その後生成したアナターゼ型酸化チタン単結晶を捕集し、アナターゼ型酸化チタン単結晶中に残留する塩素ガスを、真空加熱、空気あるいは窒素ガス雰囲気中での加熱あるいはスチーム処理等の加熱処理あるいはアルコールとの接触処理により除去してアナターゼ型酸化チタン単結晶を得ることができる。
【００２９】
以上のようにして得られたアナターゼ型酸化チタン単結晶は、粒径０．１μｍ以上と大粒径であり、好ましくは０．５μｍ以上、特に好ましくは１．０〜１０μｍである。ここで粒径は、電子顕微鏡（ＳＥＭ）により測定したものである。
【００３０】
また、本発明で得られるアナターゼ型酸化チタン単結晶を含む酸化チタン粉末は、ルチル化率が通常５０％以下、好ましくは３０％以下、特に好ましくは２０％以下であり、アナターゼリッチの結晶構造を有する。ここで、ルチル化率は、ASTM D3720-84 の方法に従いＸ線回折測定を行い、ルチル型結晶酸化チタンの最強回折線（面指数１１０）のピーク面積（Ｉｒ）と、アナターゼ型結晶酸化チタンの最強回折線（面指数１０１）のピーク面積（Ｉａ）を求め、次式（１）により算出されるものである。
ルチル化率（重量％）＝１００−１００／（１＋１．２×Ｉｒ／Ｉａ） (1)
【００３１】
なお、ピーク面積（Ｉｒ）及びピーク面積（Ｉａ）は、Ｘ線回折スペクトルの該当回折線におけるベースラインから突出した部分の面積をいう。その算出方法は公知の方法で行えばよく、例えば、コンピュータ計算、近似三角形化などの手法により求められる。
【００３２】
本発明で得られたアナターゼ型酸化チタン単結晶は、比表面積が通常８ｍ2 ／ｇ以下、好ましくは５ｍ2 ／ｇ以下、特に好ましくは０．５〜３ｍ2 ／ｇである。
【００３３】
本発明で得られるアナターゼ型酸化チタン単結晶は、Ｆｅ、Ａｌ、ＳｉおよびＮａの含有量が通常各々１００ppm 未満、好ましくは２０ppm 未満、さらに好ましくは１０ppm 未満であり、かつＣｌの含有量が通常１０００ppm 未満、好ましくは２００ppm 未満、さらに好ましくは１００ppm 未満である。本発明で得られるアナターゼ型酸化チタン単結晶は、四塩化チタンを気相酸化反応させる気相法によって製造されるため、液相法で得られる酸化チタンのような不純物元素が混入したり残留することがない。このため、本発明で得られるアナターゼ型酸化チタン単結晶は、酸化チタン以外の他成分を殆ど含有していない高純度のアナターゼ型酸化チタン単結晶であるので、光触媒に利用した際、酸化チタン本来の特性が変化せず優れた効果を得ることができる。
【００３４】
本発明の方法により製造されるアナターゼ型酸化チタン単結晶は、光触媒などの用途に有効である。
【００３５】
【実施例】
次に、実施例を挙げて本発明を更に具体的に説明するが、これは単に例示であって、本発明を制限するものではない。また、実施例及び比較例において、酸化チタン微粒子の粒径（ＳＥＭ径）、比表面積、Ｘ線回折測定方法および不純物の含有量は以下の方法により測定した。また、単結晶の特定および評価は以下の方法で行った。
１）平均粒径：電子顕微鏡（ＳＥＭ）により微粒子を観察し、インターセプト法により測定した（解析数２００個）。
２）Ｘ線回折測定条件：以下の条件で測定した。
３）比表面積：BET 法により測定した。
４）不純物の定量：酸化チタン中のＦｅ，Ａｌ，ＳｉおよびＮａ成分は原子吸光法により測定した。酸化チタン中のＣｌ成分は吸光光度法により測定した。
５）単結晶の特定および評価：電界放射型透過電子顕微鏡（日立製作所ＨＦ-2000 ）により、その電子回折パターンを解析し、結晶型および結晶性の同定を行った。
【００３６】
実施例１
四塩化チタンを気相中で酸素と接触させ酸化させる気相法によりアナターゼ型酸化チタン単結晶を調製した。
まず、内径４００mmの多重管バーナーを上部に具備した気相反応管において、多重管バーナーに、約８３０℃に予熱し気化させた四塩化チタンを供給し、一方別の供給ノズルより８３０℃に予熱した酸素ガスを供給し、気相反応管内で約８３０℃にて酸化反応させ、酸化チタン微粒子を生成させた。このとき四塩化チタンは標準状態として８１０ｍｌ／分、酸素ガスは１１００ｌ／分でそれぞれ供給した。その後、冷却せず生成したアナターゼ型酸化チタン粒子を３５０〜４００℃で１２０分間保持する加熱処理を行った。
このようにして得られた酸化チタン粒子は、アナターゼ型であり、また結晶粒界のない単結晶であった。粒径、ルチル化率、比表面積、及び不純物の含量を表１に示す。また、得られたアナターゼ型酸化チタン単結晶のＳＥＭ写真を図１に示す。
【００３７】
実施例２
反応温度を８００℃にした以外は実施例１と同様に酸化チタン粒子を調製した。単結晶の同定および評価を行ったところ、単結晶であった。得られた酸化チタン粒子の粒径、ルチル化率、比表面積、及び不純物の含量を表１に示す。
【００３８】
【表１】
比較例１
反応温度を１０００℃にした以外は実施例１と同様に酸化チタン粒子を調製した。得られた酸化チタン粒子の粒径、ルチル化率、比表面積、及び不純物の含量を表１に示す。単結晶の同定および評価を行ったところ、単結晶ではなかった。また、得られた酸化チタン単粒子のＳＥＭ写真を図２に示す。
【００４０】
比較例２
反応後生成した酸化チタン粒子を冷却した以外は実施例１と同様に酸化チタン粒子を調製した。得られた酸化チタン粒子の粒径、ルチル化率、比表面積、及び不純物の含量を表１に示す。単結晶の同定および評価を行ったところ、単結晶ではなかった。
【００４１】
【発明の効果】
以上説明したように、本発明で得られるアナターゼ型酸化チタン単結晶は、従来のものとは異なり、その粒径が大きくかつ不純物成分の少ない高純度のアナターゼ型酸化チタン単結晶であり、光触媒などの材料としての用途に有効である。
【図面の簡単な説明】
【図１】実施例１で調製された酸化チタン単結晶のＳＥＭ写真である。
【図２】比較例１で調製された酸化チタン粒子のＳＥＭ写真である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a large particle size and high purity anatase-type titanium oxide single crystal that can be used for a photocatalyst, an optical material, and the like.
[0002]
[Prior art]
Titanium oxide fine particles have been used for a long time as white pigments, and in recent years, they have been widely used as sintering materials used for electronic materials such as capacitors and thermistors and barium titanate materials. In addition, since a single crystal of titanium oxide exhibits a large refractive index in the wavelength region near visible light, light absorption hardly occurs in the visible light region. For this reason, it has been widely used for materials that require UV shielding such as cosmetics, medicines, and paints. Furthermore, by irradiating titanium oxide with light having energy greater than its band gap, the titanium oxide is excited, generating electrons in the conduction band and holes in the valence band. Development of applications for photocatalytic reactions using oxidizing power has been actively conducted. This titanium oxide photocatalyst has a wide variety of uses. Development of many applications such as generation of hydrogen by decomposition of water, exhaust gas treatment, air purification, deodorization, sterilization, antibacterial, water treatment, and prevention of contamination of lighting equipment, etc. Has been done.
[0003]
Among the applications of titanium oxide as described above, titanium oxide as a photocatalyst has attracted particular attention in recent years. Of the rutile, anatase, and brookite crystal structures, fine-grained anatase-type titanium oxide single crystals have photocatalytic activity. Therefore, it is mainly used as a photocatalytic material.
[0004]
On the other hand, titanium oxide single crystals have recently been used as optical materials for polarizers and analyzers of isolators, and large-diameter single crystals as thin film forming substrates. Conventionally, the manufacturing method has been manufactured by a melt growth method such as the Bernoulli method, the floating zone melting method (FZ method), or the EFG (Edge-defined Film Growth) method. In these methods, since the titanium oxide powder is heated and dissolved in the crucible to a melting point of titanium oxide of 1800 ° C. or higher, all of the obtained titanium oxide single crystals were of the rutile type.
[0005]
In addition, regarding the anatase-type titanium oxide single crystal, its production method or physical properties are introduced in various literatures. For example, “Moldability and Sinterability of Monodispersed Titanium Oxide Fine Crystallized by Hydrothermal Method”, Journal of the Ceramic Society of Japan (VOL. 103, No. 6 PAGE. 552-556 1995), Anatase type single crystal is prepared by thermal hydrolysis to produce anatase type titanium oxide and then growing the crystal. In addition, “Ultrafine Titania by Flame Spray Pyrolysis is a Titanate Complex.” J. Eur. Ceram. Soc. (VOL.18, NO.4PAGE.287-297 1998) Manufactures crystals.
[0006]
On the other hand, as a method called a vapor phase oxidation method among conventional titanium oxide production methods, a method in which titanium tetrachloride is brought into contact with oxygen in the gas phase and oxidized, or a combustible gas such as hydrogen gas which is burned to generate water is used. There is a so-called flame hydrolysis method in which oxygen is supplied to a combustion burner to form a flame and titanium tetrachloride is introduced therein. JP-A-6-340423 discloses a flame hydrolysis method in which a mixed gas of titanium tetrachloride, hydrogen and oxygen is burned in the gas phase to produce titanium oxide by hydrolysis of titanium tetrachloride. A method of reacting titanium tetrachloride, hydrogen and oxygen in a specific molar ratio is disclosed. JP-A-8-217654 discloses that a titanium compound is supplied to a hydrogen-containing gas in a flame hydrolysis method by supplying 50 to 300 g / m 3 in terms of titanium dioxide, and a temperature of 300 to 1500 ° C. The titanium oxide fine particles for crystalline UV-shielding cosmetics having an average particle size of 0.04 to 0.15 μm hydrolyzed with flame are disclosed.
[0007]
[Problems to be solved by the invention]
The anatase-type titanium oxide single crystals obtained by the above-described conventional technique are ultrafine particles having a particle size of several nanometers to several tens of nanometers, and are actually secondary particles in which these primary particles are aggregated. For this reason, the dispersibility when used as a photocatalyst is poor and the handling thereof is very difficult.
[0008]
On the other hand, the conventional method of producing titanium oxide by oxidizing titanium tetrachloride in the gas phase provides high-purity titanium oxide at a low cost, and also provides a reaction at a relatively high temperature to obtain rutile-type titanium oxide. Further, anatase-type titanium oxide can be obtained, but it has not been possible to obtain a single crystal having a large particle size by growing the crystal.
[0009]
Accordingly, an object of the present invention is to provide a method for producing a large particle size, high purity anatase-type titanium oxide single crystal, which can be produced industrially and at low cost.
[0010]
[Means for Solving the Problems]
Under such circumstances, the present inventors have made extensive studies on a method for producing titanium oxide that can be produced at low cost. As a result, according to the gas phase reaction method of titanium tetrachloride under specific conditions, the present inventors have a large particle size and high purity. The inventors have found a method capable of producing an anatase-type titanium oxide single crystal suitable for a photocatalyst and the like, and have completed the present invention.
[0011]
That is, according to the present invention, in the gas phase reaction of titanium tetrachloride, the volume of the gas as assumed in the standard state is brought into contact with 1 liter of titanium tetrachloride gas at a ratio of 1 to 30 liters of oxygen and oxidized at 700 to 850 ° C. Anatase-type oxidation characterized by reacting to produce titanium oxide particles, and then heat-treating the titanium oxide particles at a temperature of 300 ° C. or higher and lower than 700 ° C. and lower than the reaction temperature of the oxidation reaction for 120 minutes or more. A method for producing a titanium oxide powder containing a titanium single crystal is provided.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
[0013]
In the method for producing anatase-type titanium oxide single crystal of the present invention, two components of titanium tetrachloride and oxygen are brought into contact as raw materials, and titanium tetrachloride is oxidized in a gas phase to first produce titanium oxide particles. In addition to these raw materials, hydrogen, water vapor, or a combustible gas such as propane that burns to produce water can be used in combination.
[0014]
The ratio of the amount of each component to be supplied to the reaction section when the components are brought into contact with each other is such that the volume of gas when assuming a standard state is usually 1% of oxygen per 1 l (gas) of titanium tetrachloride. ˜30 l, preferably 2 to 20 l, particularly preferably 4 to 10 l. Furthermore, in the present invention, it is possible to supply hydrogen or water vapor in addition to the above components as necessary. When the supply ratio of hydrogen or water vapor is assumed to be a standard state, hydrogen gas is 1 l of titanium tetrachloride. (Gas) is usually 0.1 to 10 l, preferably 0.1 to 5 l, and water vapor is usually 0.05 to 1.0 l, preferably 0.1 to 0.5 l.
[0015]
The supply amount of each raw material gas varies depending on the reaction scale or the nozzle diameter for supplying each gas, etc., and is set as appropriate. It is desirable to set it to be a turbulent region.
[0016]
In the present invention, the above-described titanium tetrachloride gas and oxygen, and optionally hydrogen or water vapor are supplied to a reaction furnace and brought into contact with each other in the gas phase for reaction. As a method for supplying these components, various methods can be adopted, and specifically, the following methods are preferable;
1) A method in which titanium tetrachloride gas and oxygen gas supply pipes are independently installed, and both are adjacent to each other and supplied to the reactor independently.
2) A method in which supply pipes for titanium tetrachloride gas and mixed gas of oxygen gas and hydrogen gas are installed independently, and both are adjacent to each other and supplied to the reactor independently,
3) A method in which titanium tetrachloride gas and a mixed gas supply pipe of oxygen gas and water vapor are installed independently, and both are adjacent to each other and supplied independently to the reactor.
[0017]
First, each of the above components is introduced into a reaction furnace, and titanium tetrachloride is oxidized at a predetermined temperature to produce anatase-type titanium oxide particles. In order to form anatase-type titanium oxide by a gas phase oxidation reaction in the present invention, it is necessary to perform the reaction at a temperature that is higher than the temperature at which titanium oxide is formed and lower than the temperature at which the crystal structure of titanium oxide transitions to the rutile type. is there. The reaction temperature of the oxidation reaction is 700 to 850 ° C, preferably 750 to 850 ° C, particularly preferably 750 to 830 ° C.
[0018]
Next, the produced anatase-type titanium oxide particles are subjected to a heat treatment to grow crystals. The temperature of the heat treatment is 300 ° C. or higher and lower than 850 ° C., preferably 300 to 800 ° C., particularly preferably 500 to 750 ° C., more preferably 500 ° C. or higher and lower than 700 ° C., and lower than the reaction temperature of the oxidation reaction. is there. The difference between the temperature of the heat treatment and the reaction temperature of the oxidation reaction is usually 50 ° C. or higher, preferably 100 ° C. or higher, particularly preferably 200 ° C. or higher, more preferably 300 ° C. or higher. By setting the temperature of the heat treatment to a temperature lower than the reaction temperature of the oxidation reaction in this way, the generated primary particles are prevented from secondary aggregation and transition to rutile crystals, and anatase-type titanium oxide single crystals are grown. This is preferable because the particle size is increased. In addition, the heat treatment time varies depending on the particle size of the obtained anatase-type titanium oxide single crystal, but when obtaining a 0.1 μm or more, usually 30 minutes or more, and usually obtaining a 1.0 μm or more 60 minutes or more. Here, the heat treatment refers to a step that starts when the oxidation reaction ends and the temperature in the system decreases to the temperature of the heat treatment.
[0019]
In the conventional method for obtaining the rutile-type or anatase-type agglomerated particles, a temperature at which at least the titanium oxide particles are not calcined and secondarily agglomerated in order to prevent growth and agglomeration of the produced particles after the titanium oxide particles are produced. Hereinafter, specifically, cooling was performed to less than 300 ° C. On the other hand, in the present invention, at least the titanium oxide particles of the produced particles after the reaction are not fired and are not cooled to a temperature that does not cause secondary aggregation, and the produced particles are subjected to a predetermined heat treatment to grow crystals. It is possible to obtain a large-diameter anatase-type titanium oxide single crystal.
[0020]
The obtained anatase-type titanium oxide single crystal is cooled and then classified or sieved as necessary. As a method for cooling the anatase-type titanium oxide single crystal, a method of cooling the produced anatase-type titanium oxide single crystal is usually provided by providing a cooling step after the heat treatment. Specifically, a cooling part equipped with a cooling jacket is provided after the reaction part.
[0021]
Of the above components, particularly titanium tetrachloride gas and oxygen may be diluted with an inert gas such as nitrogen and supplied to the reaction section. In this case, when the dilution rate of titanium tetrachloride is assumed to be a standard state, the inert gas is usually 0.1 to 10 l, preferably 0.3 to 1 l, with respect to 1 l of titanium tetrachloride gas. The oxygen dilution rate is usually 0.1 to 10 l, preferably 0.3 to 1 l of inert gas with respect to 1 l of oxygen gas, assuming a standard state.
[0022]
Various methods can be adopted as means for installing each component or mixed gas supply pipe independently and adjoining both, but the supply pipe is coaxially arranged between the inner pipe and the outer pipe. A multiple tube is preferable. That is, by supplying the above-mentioned components or mixed gas using a multi-tube supply pipe, in particular, by supplying titanium tetrachloride gas from the innermost pipe and oxygen gas from the outer pipe, the reaction is uniform. Thus, an anatase-type titanium oxide single crystal having good particle properties is produced.
[0023]
As the reaction furnace used in the method for producing anatase-type titanium oxide single crystal of the present invention, for example, a vertical reaction furnace in which a supply pipe for each component such as a multiple pipe is provided at the top is preferable.
[0024]
In addition, each component or mixed gas supplied into the reaction furnace is preferably preheated and supplied before being supplied into the reaction furnace. This preheating is desirably performed within the temperature range of the reaction in the reaction furnace described later.
[0025]
Hereinafter, an example of a specific method for producing the anatase-type titanium oxide single crystal of the present invention will be shown.
[0026]
First, liquid titanium tetrachloride is preheated and vaporized, diluted with nitrogen gas as necessary and introduced into the reactor, and at the same time, oxygen gas and / or water vapor is diluted with nitrogen gas as necessary to react. It is introduced into the furnace and an oxidation reaction is performed. The reaction temperature of the oxidation reaction is 700 to 850 ° C, preferably 750 to 830 ° C. In the present invention, an oxidation reaction is performed at a relatively low temperature in order to obtain anatase-type titanium oxide single crystal having a large particle size and high purity and suitable for a photocatalyst or the like.
[0027]
Crystalline particles are grown by generating anatase-type titanium oxide particles by the above oxidation reaction, and then subjecting the titanium oxide fine particles to a predetermined heat treatment without cooling. Thereafter, the obtained anatase-type titanium oxide single crystal is cooled. As a cooling means, a cooling tank equipped with a cooling jacket is usually used, and at the same time, it is cooled by bringing it into contact with an anatase-type titanium oxide single crystal that has generated an inert gas such as air or nitrogen gas.
[0028]
Thereafter, the produced anatase-type titanium oxide single crystal is collected, and the chlorine gas remaining in the anatase-type titanium oxide single crystal is subjected to heat treatment such as vacuum heating, air or nitrogen gas atmosphere, steam treatment, or alcohol. The anatase-type titanium oxide single crystal can be obtained by removing by the contact treatment.
[0029]
The anatase-type titanium oxide single crystal obtained as described above has a large particle size of 0.1 μm or more, preferably 0.5 μm or more, particularly preferably 1.0 to 10 μm. Here, the particle size is measured by an electron microscope (SEM).
[0030]
Further, the titanium oxide powder containing the anatase-type titanium oxide single crystal obtained in the present invention has a rutile ratio of usually 50% or less, preferably 30% or less, particularly preferably 20% or less, and has an anatase-rich crystal structure. Have. Here, the rutile ratio is measured by X-ray diffraction according to the method of ASTM D3720-84, the peak area (Ir) of the strongest diffraction line (surface index 110) of rutile type crystalline titanium oxide, and the anatase type crystalline titanium oxide. The peak area (Ia) of the strongest diffraction line (surface index 101) is obtained and calculated by the following formula (1).
Rutile conversion rate (% by weight) = 100-100 / (1 + 1.2 × Ir / Ia) (1)
[0031]
The peak area (Ir) and the peak area (Ia) refer to the area of the portion protruding from the base line in the corresponding diffraction line of the X-ray diffraction spectrum. The calculation method may be performed by a known method, for example, by a method such as computer calculation or approximate triangulation.
[0032]
The anatase-type titanium oxide single crystal obtained in the present invention has a specific surface area of usually 8 m 2 / g or less, preferably 5 m 2 / g or less, particularly preferably 0.5 to 3 m 2 / g.
[0033]
The anatase-type titanium oxide single crystal obtained by the present invention usually has an Fe, Al, Si and Na content of less than 100 ppm, preferably less than 20 ppm, more preferably less than 10 ppm, and a Cl content of usually 1000 ppm. Less than, preferably less than 200 ppm, more preferably less than 100 ppm. Since the anatase-type titanium oxide single crystal obtained by the present invention is produced by a gas phase method in which titanium tetrachloride is subjected to a gas phase oxidation reaction, an impurity element such as titanium oxide obtained by a liquid phase method is mixed in or remains. There is nothing. Therefore, the anatase-type titanium oxide single crystal obtained in the present invention is a high-purity anatase-type titanium oxide single crystal containing almost no other components other than titanium oxide. The characteristic of this is not changed, and an excellent effect can be obtained.
[0034]
The anatase-type titanium oxide single crystal produced by the method of the present invention is effective for uses such as a photocatalyst.
[0035]
【Example】
EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention. In Examples and Comparative Examples, the particle diameter (SEM diameter), specific surface area, X-ray diffraction measurement method and impurity content of titanium oxide fine particles were measured by the following methods. The identification and evaluation of single crystals were performed by the following methods.
1) Average particle diameter: Fine particles were observed with an electron microscope (SEM) and measured by the intercept method (200 analyzes).
2) X-ray diffraction measurement conditions: Measurement was performed under the following conditions.
3) Specific surface area: measured by the BET method.
4) Determination of impurities: Fe, Al, Si and Na components in titanium oxide were measured by atomic absorption method. The Cl component in titanium oxide was measured by absorptiometry.
5) Identification and evaluation of single crystal: The electron diffraction pattern was analyzed with a field emission transmission electron microscope (Hitachi, Ltd. HF-2000) to identify the crystal type and crystallinity.
[0036]
Example 1
Anatase-type titanium oxide single crystals were prepared by a gas phase method in which titanium tetrachloride was contacted with oxygen in the gas phase and oxidized.
First, in a gas phase reaction tube equipped with a multi-tube burner with an inner diameter of 400 mm at the top, titanium tetrachloride preheated and vaporized to about 830 ° C. is supplied to the multi-tube burner, and preheated to 830 ° C. from another supply nozzle. The supplied oxygen gas was supplied, and an oxidation reaction was performed at about 830 ° C. in a gas phase reaction tube to generate titanium oxide fine particles. At this time, titanium tetrachloride was supplied at a standard state of 810 ml / min, and oxygen gas was supplied at 1100 l / min. Then, the heat processing which hold | maintain the anatase type titanium oxide particle produced | generated without cooling at 350-400 degreeC for 120 minutes was performed.
The titanium oxide particles thus obtained were anatase type and were single crystals without crystal grain boundaries. Table 1 shows the particle size, rutile ratio, specific surface area, and impurity content. Moreover, the SEM photograph of the obtained anatase type titanium oxide single crystal is shown in FIG.
[0037]
Example 2
Titanium oxide particles were prepared in the same manner as in Example 1 except that the reaction temperature was 800 ° C. When the single crystal was identified and evaluated, it was a single crystal. Table 1 shows the particle diameter, rutile ratio, specific surface area, and impurity content of the obtained titanium oxide particles.
[0038]
[Table 1]
Comparative Example 1
Titanium oxide particles were prepared in the same manner as in Example 1 except that the reaction temperature was 1000 ° C. Table 1 shows the particle diameter, rutile ratio, specific surface area, and impurity content of the obtained titanium oxide particles. When the single crystal was identified and evaluated, it was not a single crystal. Moreover, the SEM photograph of the obtained titanium oxide single particle is shown in FIG.
[0040]
Comparative Example 2
Titanium oxide particles were prepared in the same manner as in Example 1 except that the titanium oxide particles produced after the reaction were cooled. Table 1 shows the particle diameter, rutile ratio, specific surface area, and impurity content of the obtained titanium oxide particles. When the single crystal was identified and evaluated, it was not a single crystal.
[0041]
【The invention's effect】
As described above, the anatase-type titanium oxide single crystal obtained in the present invention is a high-purity anatase-type titanium oxide single crystal having a large particle size and a small amount of impurity components, unlike a conventional one, such as a photocatalyst. It is effective for use as a material.
[Brief description of the drawings]
1 is an SEM photograph of a titanium oxide single crystal prepared in Example 1. FIG.
2 is a SEM photograph of titanium oxide particles prepared in Comparative Example 1. FIG.
Claims (2)
四塩化チタンガス１ｌに対し、酸素１〜３０ｌの割合で接触させ、７００〜８５０℃で酸化反応を行い酸化チタン粒子を生成させ、
次いで、該酸化チタン粒子を３００℃以上７００℃未満且つ前記酸化反応の反応温度よりも低い温度で、１２０分以上加熱処理する
ことを特徴とするアナターゼ型酸化チタン単結晶を含む酸化チタン粉末の製造方法。In the gas phase reaction of titanium tetrachloride, the volume of the gas, assuming the standard state,
1 l of titanium tetrachloride gas is contacted at a rate of 1 to 30 l of oxygen, and an oxidation reaction is performed at 700 to 850 ° C. to generate titanium oxide particles.
Next, the titanium oxide particles are subjected to a heat treatment at a temperature of 300 ° C. or higher and lower than 700 ° C. and lower than the reaction temperature of the oxidation reaction for 120 minutes or more, thereby producing a titanium oxide powder containing anatase-type titanium oxide single crystals. Method.
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| EP1728765A4 (en) * | 2004-03-26 | 2011-03-30 | Toho Titanium Co Ltd | Anatase-type titanium oxide powder and method for producing same |
| JP4754197B2 (en) * | 2004-08-10 | 2011-08-24 | 株式会社フジクラ | Titanium oxide particles, production method thereof and use thereof |
| JP4517080B2 (en) * | 2005-10-14 | 2010-08-04 | 独立行政法人産業技術総合研究所 | Single crystal anatase TiO2 and method for producing the same |
| EP2351710A4 (en) * | 2008-09-05 | 2013-05-01 | Sumitomo Electric Industries | Ceramic powder, dielectric composite material containing said ceramic powder, and dielectric antenna |
| JP5376893B2 (en) | 2008-10-15 | 2013-12-25 | 昭和電工株式会社 | Method and apparatus for producing metal oxide particles |
| JP5259767B2 (en) * | 2011-04-01 | 2013-08-07 | 株式会社フジクラ | Method for evaluating crystallinity of titanium oxide particles, and method for measuring surface defect density of titanium oxide particles |
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| JPH05112801A (en) * | 1991-10-21 | 1993-05-07 | Osaka Titanium Co Ltd | Superfine-particle titanium oxide powder and ultraviolet shielding cosmetic material using the powder |
| JPH07316536A (en) * | 1994-05-26 | 1995-12-05 | Nippon Aerojiru Kk | Ultraviolet light screening titanium dioxide powder and its production |
| DE19604948A1 (en) * | 1996-02-10 | 1997-08-14 | Telefunken Microelectron | Control arrangement for an automatic electrohydraulically controlled transmission |
| JP3417291B2 (en) * | 1998-03-31 | 2003-06-16 | 日本アエロジル株式会社 | Method for producing external additive for electrophotographic toner |
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