JP4027249B2 - Low halogen low rutile ultrafine titanium oxide and method for producing the same - Google Patents
Low halogen low rutile ultrafine titanium oxide and method for producing the same Download PDFInfo
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N titanium dioxide Inorganic materials O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims description 301
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 title claims description 221
- 229910052736 halogen Inorganic materials 0.000 title claims description 48
- 150000002367 halogens Chemical class 0.000 title claims description 47
- 238000004519 manufacturing process Methods 0.000 title claims description 47
- 239000007789 gas Substances 0.000 claims description 89
- 238000000034 method Methods 0.000 claims description 82
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 57
- 238000006243 chemical reaction Methods 0.000 claims description 39
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical group Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 claims description 35
- 238000010438 heat treatment Methods 0.000 claims description 32
- 230000001590 oxidative effect Effects 0.000 claims description 30
- -1 titanium halide Chemical class 0.000 claims description 26
- 239000002994 raw material Substances 0.000 claims description 24
- 239000010936 titanium Substances 0.000 claims description 23
- 229910052719 titanium Inorganic materials 0.000 claims description 22
- 239000012808 vapor phase Substances 0.000 claims description 13
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 8
- 229910001882 dioxygen Inorganic materials 0.000 claims description 8
- 239000007791 liquid phase Substances 0.000 claims description 8
- 239000012528 membrane Substances 0.000 claims description 8
- 239000011261 inert gas Substances 0.000 claims description 6
- 239000002002 slurry Substances 0.000 claims description 6
- 238000000108 ultra-filtration Methods 0.000 claims description 5
- 230000008569 process Effects 0.000 claims description 3
- 238000001223 reverse osmosis Methods 0.000 claims description 3
- 239000000460 chlorine Substances 0.000 description 106
- 229910052801 chlorine Inorganic materials 0.000 description 106
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 105
- 239000002245 particle Substances 0.000 description 88
- 238000009826 distribution Methods 0.000 description 30
- 239000011882 ultra-fine particle Substances 0.000 description 24
- 239000000843 powder Substances 0.000 description 16
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 15
- 239000001301 oxygen Substances 0.000 description 15
- 229910052760 oxygen Inorganic materials 0.000 description 15
- 238000006298 dechlorination reaction Methods 0.000 description 12
- 239000012071 phase Substances 0.000 description 12
- 239000011941 photocatalyst Substances 0.000 description 12
- 238000001816 cooling Methods 0.000 description 11
- 239000013078 crystal Substances 0.000 description 11
- 238000003809 water extraction Methods 0.000 description 11
- 230000001186 cumulative effect Effects 0.000 description 10
- 229910052717 sulfur Inorganic materials 0.000 description 10
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 9
- 238000000691 measurement method Methods 0.000 description 8
- 238000004458 analytical method Methods 0.000 description 7
- 229910001873 dinitrogen Inorganic materials 0.000 description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- 238000000149 argon plasma sintering Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 238000007254 oxidation reaction Methods 0.000 description 6
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 6
- 239000004810 polytetrafluoroethylene Substances 0.000 description 6
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 5
- 230000000052 comparative effect Effects 0.000 description 5
- 238000007865 diluting Methods 0.000 description 5
- 230000007704 transition Effects 0.000 description 5
- 238000005695 dehalogenation reaction Methods 0.000 description 4
- 238000010790 dilution Methods 0.000 description 4
- 239000012895 dilution Substances 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 230000003647 oxidation Effects 0.000 description 4
- 230000001699 photocatalysis Effects 0.000 description 4
- 238000005245 sintering Methods 0.000 description 4
- 238000003756 stirring Methods 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 235000010724 Wisteria floribunda Nutrition 0.000 description 3
- 239000000654 additive Substances 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 239000011521 glass Substances 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 3
- 239000011164 primary particle Substances 0.000 description 3
- 238000004904 shortening Methods 0.000 description 3
- 229920002379 silicone rubber Polymers 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 239000002537 cosmetic Substances 0.000 description 2
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- 239000010419 fine particle Substances 0.000 description 2
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- 230000003301 hydrolyzing effect Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
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- 239000000203 mixture Substances 0.000 description 2
- 238000004062 sedimentation Methods 0.000 description 2
- 239000004945 silicone rubber Substances 0.000 description 2
- SQGYOTSLMSWVJD-UHFFFAOYSA-N silver(1+) nitrate Chemical compound [Ag+].[O-]N(=O)=O SQGYOTSLMSWVJD-UHFFFAOYSA-N 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 229910000349 titanium oxysulfate Inorganic materials 0.000 description 2
- KPZGRMZPZLOPBS-UHFFFAOYSA-N 1,3-dichloro-2,2-bis(chloromethyl)propane Chemical compound ClCC(CCl)(CCl)CCl KPZGRMZPZLOPBS-UHFFFAOYSA-N 0.000 description 1
- ZCYVEMRRCGMTRW-UHFFFAOYSA-N 7553-56-2 Chemical compound [I] ZCYVEMRRCGMTRW-UHFFFAOYSA-N 0.000 description 1
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- WKBOTKDWSSQWDR-UHFFFAOYSA-N Bromine atom Chemical compound [Br] WKBOTKDWSSQWDR-UHFFFAOYSA-N 0.000 description 1
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 230000000844 anti-bacterial effect Effects 0.000 description 1
- 239000003125 aqueous solvent Substances 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- GDTBXPJZTBHREO-UHFFFAOYSA-N bromine Substances BrBr GDTBXPJZTBHREO-UHFFFAOYSA-N 0.000 description 1
- 229910052794 bromium Inorganic materials 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 238000005660 chlorination reaction Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000004040 coloring Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
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- 230000000382 dechlorinating effect Effects 0.000 description 1
- 239000002781 deodorant agent Substances 0.000 description 1
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- 239000000835 fiber Substances 0.000 description 1
- 238000010574 gas phase reaction Methods 0.000 description 1
- 238000007429 general method Methods 0.000 description 1
- 230000026030 halogenation Effects 0.000 description 1
- 238000005658 halogenation reaction Methods 0.000 description 1
- 229910052740 iodine Inorganic materials 0.000 description 1
- 239000011630 iodine Substances 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000000386 microscopy Methods 0.000 description 1
- 239000004570 mortar (masonry) Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical class [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 1
- 239000000049 pigment Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 238000003918 potentiometric titration Methods 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
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- 230000009257 reactivity Effects 0.000 description 1
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- 238000011084 recovery Methods 0.000 description 1
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- 230000000717 retained effect Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 229910052707 ruthenium Inorganic materials 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 229910001961 silver nitrate Inorganic materials 0.000 description 1
- GCLGEJMYGQKIIW-UHFFFAOYSA-H sodium hexametaphosphate Chemical compound [Na]OP1(=O)OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])OP(=O)(O[Na])O1 GCLGEJMYGQKIIW-UHFFFAOYSA-H 0.000 description 1
- 235000019982 sodium hexametaphosphate Nutrition 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
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- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 description 1
- 239000004408 titanium dioxide Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
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- Inorganic Compounds Of Heavy Metals (AREA)
- Catalysts (AREA)
- Hybrid Cells (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、光触媒や太陽電池、シリコーンゴムへの添加剤、誘電体用途等に好適な低ルチル型の低塩素超微粒子酸化チタン及びその製造方法に関する。さらに詳しくは、ハロゲンチタンを含むガスを酸化性ガスで高温酸化することにより得られる気相法酸化チタンにおいて、ハロゲン含有量が低く、残存したハロゲンの除去も容易で、かつ、分散性の良い低ルチル型の低ハロゲン超微粒子酸化チタン及びその製造方法に関する。
【０００２】
【従来の技術】
超微粒子酸化チタンは、紫外線遮蔽材やシリコーンゴムヘの添加剤、誘電体原料、化粧料等、多岐の用途に亘って使用されてきた（酸化チタンは日本工業規格（ＪＩＳ）には二酸化チタンと記載されており、一般名として酸化チタンが広く使用されているので本明細書中では酸化チタンと略称する）。また、酸化チタンは光触媒や、太陽電池等としても応用される。
【０００３】
酸化チタンの結晶型にはルチル型、アナターゼ型、ブルッカイト型の３種類が存在するが、このうち、前述の光触媒、太陽電池用途の分野ではルチル型よりも光電気化学活性に優れるアナターゼ型やブルッカイト型が用いられる。
【０００４】
酸化チタンの光触媒作用は抗菌タイル、セルフ・クリーニング建材、消臭繊維など、有機物の分解に利用されており、その機構は次のように説明されている。酸化チタンは紫外線を吸収し、その内部に電子と正孔を発生させる。正孔は酸化チタンの吸着水と反応してヒドロキシラジカルを生成させ、酸化チタン粒子表面に吸着した有機物を炭酸ガスや水に分解する（「光クリーン革命」藤嶋昭、橋本和仁、渡部俊也共著，（株）シーエムシー，143−145頁（１９９７））。すなわち、光触媒作用の強い酸化チタンの条件として、正孔を発生させやすいこと、酸化チタン表面に正孔が到達しやすいこと、が挙げられる。「酸化チタン光触媒のすべて」（橋本和仁、藤嶋昭 編集，（株）シーエムシー，29−30頁（１９９８））には、光触媒作用が高い酸化チタンとして、アナターゼ型酸化チタン、格子欠陥の少ない酸化チタン、粒子が小さく比表面積の大きい酸化チタンが挙げられている。
【０００５】
太陽電池としての応用は、１９９１年にローザンヌ工科大学のグレッツエルらが酸化チタンとルテニウム系色素を組み合わせた色素増感型太陽電池を報告して以来、研究が進められている（Ｍ．Ｇｒａｅｚｅｌ，Ｎａｔｕｒｅ，３５３，７３７，（１９９１））。前記色素増感型太陽電池において、酸化チタンは色素の担持体及びｎ型半導体としての役割を有し、導電性ガラス電極に結着された色素電極として用いられる。色素増感型太陽電池は電解層を色素電極と対極で挟み込んだ構造であり、色素は光を吸収することで電子と正孔を発生する。発生した電子は酸化チタン層を通じて導電性ガラス電極に到達し、外部へと取り出される。一方、発生した正孔は、電解層を通じて対極へと運ばれ、導電性ガラス電極を通じて供給された電子と結合する。色素増感型太陽電池の特性を高める一因として、酸化チタンと色素の結合が容易であることが挙げられる。色素との結合が容易な酸化チタンの結晶型としては、例えば、特開平１０−２５５８６３号公報にはアナターゼが使用されており、また、特開２０００−３４０２６９号公報にはブルッカイトが色素増感型太陽電池に好適であることが記載されている。
【０００６】
酸化チタンは分散性の良いものがその機能を引き出す上で重要である。例えば酸化チタンを光触媒として使用する際、分散性が悪いと隠蔽力が強くなるため、使用できる用途が限定されてしまう。太陽電池の分野においても分散性の悪い酸化チタンは光を透過しにくいため、光吸収に寄与できる酸化チタンが限られ、光電変換効率を悪化させる。一般に、光散乱（隠蔽力）は粒径が可視光波長の１／２程度であるとき最大になり、粒径が小さくなると光散乱も弱まるといわれている（「酸化チタン」清野学著，技報堂（株），ｐ．１２９，（１９９１））。前述の分野で利用される酸化チタンの一次粒子径は数〜数十ｎｍであることが多いため分散性が良好であれば光散乱への影響は小さい。しかし、分散が悪く凝集粒径の大きい酸化チタンは光散乱が強まることになる。
【０００７】
以上の理由から上記分野では、酸化チタンには高分散性が要求され、分散性の良いアナターゼ型あるいはブルッカイト型の超微粒子酸化チタンが使用される。一般に、超微粒子の１次粒子径は、明確にされていないが、通常約０．１μｍ以下の微粒子に対して呼称される。
【０００８】
酸化チタンを光触媒、太陽電池で使用する場合、塩素のように腐食性を有する成分が存在すると基材を腐食させたり、変質させたりするため、酸化チタンの塩素含有量は低く抑える必要がある。また、Ｆｅ、Ａｌ、Ｓｉ、Ｓ等も低く抑えた方が良い。例えば、酸化チタン中のＦｅが多すぎると着色の原因になり、透明性を要求される用途での使用に適さない。酸化チタン粒子内部のＡｌ、Ｓ等の成分が多すぎると格子欠陥を生じてしまい、光触媒、太陽電池としての機能を低下させることも考えられる。
【０００９】
酸化チタンの製造方法は、大別して四塩化チタンや硫酸チタニルを加水分解する液相法と、ハロゲン化チタンを酸素あるいは水蒸気等の酸化性ガスと反応させる気相法とがある。液相法による酸化チタンはアナターゼを主相として得ることはできるが、ゾルあるいはスラリー状態にならざるを得ない。この状態で使用する場合、用途は限定される。粉末として使用するためには乾燥させる必要があり、溶媒に濡れた超微粒子は乾燥が進むに連れて凝集が激しくなる（「超微粒子ハンドブック」斎藤進六監修、フジ・テクノシステム、388頁、（１９９０）。この酸化チタンを光触媒等に供する場合には分散性を高めるため酸化チタンを強く解砕したり粉砕する必要があり、粉砕等の処理に由来する摩耗物の混入や粒度分布の不均一さ等の問題を引き起こすことがある。
【００１０】
一般的に、気相法による酸化チタンは、溶媒を使用しないため液相法に比べて分散性に優れている。
【００１１】
気相法で酸化チタンの超微粒子を得る例は数多くあり、例えば、特開平６−３４０４２３号公報では、四塩化チタンを火炎中にて加水分解し酸化チタンを製造する方法において、酸素、四塩化チタン、水素のモル比を調整して反応させ、ルチル含有率の高い酸化チタンを得る方法が開示されている。特開平７−３１６５３６号公報には四塩化チタンを高温気相中で加水分解させ、反応生成物を急速に冷却することにより、結晶質酸化チタン粉末を製造する方法において、炎温度と原料ガス中のチタン濃度を特定することにより平均一次粒子径が４０ｎｍ以上、１５０ｎｍ以下の結晶質透明酸化チタンを得る方法が開示されている。しかし、何れの場合も微粒子ではあるがルチル含有率の高い酸化チタンしか得られていなく、光触媒用途、太陽電池用途として使用するには適さない。
【００１２】
気相法でアナターゼが主相の酸化チタンを製造する方法は、例えば、特開平３−２５２３１５号公報には気相反応において酸素と水素の混合気体中の水素の比率を変えることでルチルの含有比率を調整する製造方法が開示されており、ルチル含有率が９％の酸化チタンが記載されている。しかし、例示された酸化チタンの粒径は０．５〜０．６μｍであり、一般的に超微粒子といわれる粒径の範囲よりも粗い。
【００１３】
ハロゲン化チタンを原料とする気相法で酸化チタンを製造すると超微粒子は得やすいが、原料由来のハロゲンが酸化チタンに残存するため、加熱あるいは水洗等による脱ハロゲンが必要となることが多い。しかし、超微粒子酸化チタンは低ハロゲン化のための加熱によって粒子同士の焼結が進行し比表面積が低下しやすくなる上、アナターゼ型からルチル型への結晶型の転移が生じてしまうことがある。比表面積の低下、結晶転移を抑制するためには低温あるいは短時間の加熱を行わざるを得ないが、充分に脱ハロゲンできなくなる。超微粒子酸化チタンの低塩素化法は、例えば、特開平１０−２５１０２１号公報に開示されている。この方法は、酸化チタンを円筒形回転式加熱炉中で転動させながら水蒸気と接触させ、塩素含有量を低くする方法である。また、これに記載されている酸化チタンのルチル含有率は１５％と高いものであった。
【００１４】
一方、水洗等による脱ハロゲンでは酸化チタン粒子表面に残存したハロゲンを除去することはできるが、粒子内部のハロゲンは水と接触しにくいため、内部ハロゲンが残存しやすいという問題があった。
【００１５】
これらのように従来の気相法において、ハロゲン含有量の低い低ルチル型の超微粒子酸化チタンは得られていなかった。
【特許文献１】
特開平１０−２５５８６３号公報
【特許文献２】
特開２０００−３４０２６９号公報
【特許文献３】
特開平６−３４０４２３号公報
【特許文献４】
特開平７−３１６５３６号公報
【特許文献５】
特開平１０−２５１０２１号公報
【非特許文献１】
「光クリーン革命」藤嶋昭、橋本和仁、渡部俊也共著，（株）シーエ
ムシー，143−145頁（１９９７）
【非特許文献２】
「酸化チタン光触媒のすべて」（橋本和仁、藤嶋昭 編集，（株）シ
ーエムシー，29−30頁（１９９８））
【非特許文献３】
Ｍ．Ｇｒａｅｚｅｌ，Ｎａｔｕｒｅ，３５３，７３７，（１９９１）
【非特許文献４】
「酸化チタン」清野学著，技報堂（株），ｐ．１２９，（１９９１）
【非特許文献５】
（「超微粒子ハンドブック」斎藤進六監修、フジ・テクノシステム、
388頁、（１９９０）
【００１６】
【発明が解決しようとする課題】
本発明は上記問題点を解決すべくなされたものであり、本発明の課題は、気相法において、分散性に優れ、かつハロゲン含有量の低い低ルチル型の超微粒子酸化チタン及びその製造方法を提供することにある。
【００１７】
【課題を解決するための手段】
本発明者らは、上記課題に鑑み鋭意研究した結果、気相法において分散性に優れ、かつ、ハロゲン含有量の低い低ルチル型の超微粒子酸化チタンを製造し得ることを見出し、上記課題を解決するに至った。
【００１８】
本発明は、ハロゲン化チタンを含有するガス及び酸化性ガス（酸素または水蒸気もしくはこれらを含有する混合ガス）を反応させる気相法において、該原料ガスを加熱温度、加熱時間を制御しながら反応させた後、脱ハロゲンすることにより得られる、ルチル含有率が５％以下の酸化チタンであって、かつ、高いＢＥＴ比表面積及び特定の特性を有する低ルチル型の超微粒子酸化チタン及びその製造方法を提供するものである。
【００１９】
すなわち本発明は、以下の発明を含む。
（１）ハロゲン化チタンを含むガスと酸化性ガスとを反応させることにより酸化チタンを製造する気相法において、反応が、ハロゲン化チタン１モルに対し不活性ガス０．１〜２０モルの割合で混合した原料ガスと、ハロゲン化チタン１モルに対し１〜３０モルの酸化性ガスとで行われ、かつ、ハロゲン化チタンを含むガス及び酸化性ガスをそれぞれ反応器に導入し反応させたとき、該反応器内の温度が８００℃以上１，１００℃未満であり、ハロゲン化チタンを含むガス及び酸化性ガスが、反応器内で８００℃以上１，１００℃未満の温度の滞留時間が０．１秒以下であることを特徴とする酸化チタンの製造方法。
（２）ハロゲン化チタンを含むガス及び酸化性ガスが、それぞれ、６００℃以上、１，１００℃未満に予熱されて反応器に導入される上記（１）に記載の酸化チタンの製造方法。
（３）酸化性ガスが、水蒸気を含む酸素ガスであることを特徴とする上記（１）又は（２）に記載の酸化チタンの製造方法。
（４）酸化性ガスが、酸素ガス１モルに対し、水蒸気０．１モル以上を含む上記（３）に記載の酸化チタンの製造方法。
（５）前記ハロゲン化チタンが四塩化チタンである上記（１）〜（４）のいずれか１項に記載の酸化チタンの製造方法。
（６）上記（１）〜（５）のいずれか１項に記載の製造方法で製造された酸化チタンを乾式でハロゲンを除去することを特徴とする酸化チタンの製造方法。
（７）乾式でハロゲンを除去する方法が、酸化チタンを２００〜５００℃に加熱することにより行う方法である上記（６）に記載の酸化チタンの製造方法。
（８）乾式でハロゲンを除去する方法が、水蒸気を含有するガスを２００〜１０００℃に加熱し、酸化チタンと接触させながら行なう方法である上記（６）に記載の酸化チタンの製造方法。
（９）水蒸気を含有するガスが、水蒸気を０．１容量％以上含む空気である上記（８）に記載の酸化チタンの製造方法。
（１０）水蒸気が、酸化チタンに対し質量比で０．０１以上である上記（８）に記載の酸化チタンの製造方法。
（１１）上記（１）〜（５）のいずれか１項に記載の製造方法で製造された酸化チタンを湿式でハロゲンを除去し、酸化チタンを含むスラリーを得ることを特徴とする酸化チタンの製造方法。
（１２）湿式でハロゲンを除去する方法が、酸化チタンを水に懸濁させ、液相に移行したハロゲンを系外に分離する方法である上記（１１）に記載の酸化チタンの製造方法。
（１３）湿式でハロゲンを除去する方法が、ハロゲンの分離を限外ろ過膜で行う方法である上記（１１）または（１２）に記載の酸化チタンの製造方法。
（１４）湿式でハロゲンを除去する方法が、ハロゲンの分離を逆浸透膜で行う方法である上記（１１）または（１２）に記載の酸化チタンの製造方法。
（１５）湿式でハロゲンを除去する方法が、ハロゲンの分離をフィルタープレスで行う方法である上記（１１）または（１２）に記載の酸化チタンの製造方法。
【００２０】
【発明の実施の形態】
本発明の酸化チタンの原料であるハロゲン化チタンとしては、工業的に入手し易い塩化チタン、特に四塩化チタンが好ましい。従って、以下、本発明をハロゲンが塩素の場合を代表例として説明するが、本発明はハロゲンが臭素またはヨウ素である場合にも適用できる。
本発明の低ルチル型超微粒子酸化チタンは、気相法で四塩化チタンを用いて製造したものであるにもかかわらず、粒子内部に塩素が殆ど存在しない。粒子内部に残存する塩素は経時的に粒子内部から表面まで拡散し基材を腐食、変質させることがあるが、水洗や乾燥等の簡単な脱塩素処理では除去しにくい。そのため、酸化チタン粒子内部に塩素が存在しないことが望ましい。
粒子表面と粒子内部の合計塩素量のうちに占める粒子内部の塩素含有率については、酸化チタンから純水で抽出される塩素（水抽出塩素と称する）と、酸化チタン粒子に含まれる全塩素（全塩素と称する）の比率を指標とし、下式（１）
Ｒ＝ＷＣＬ／ＴＣＬ×１００ ・・・・・・・・・・（１）
（式中、Ｒは表面塩素率（％）を表し、ＷＣＬは酸化チタンに含まれる水抽出塩素の含有量（質量％）を表し、ＴＣＬは酸化チタンに含まれる全塩素の含有量（質量％）を表す。）
で表されるＲの値が高いほど酸化チタン粒子内部の塩素含有率が少ないことを示す。本発明における酸化チタンについて、Ｒは８０％以上であることが好ましく、更に好ましくは９０％以上である。
【００２１】
本発明の四塩化チタンを原料とする気相法によって得られる超微粒子酸化チタンは、ルチル含有率〔ルチル含有率は、Ｘ線回折におけるルチル型結晶に対応するピーク高さ（Ｈｒと略する。）、ブルッカイト型結晶に対応するピーク高さ（Ｈｂと略する。）及びアナターゼ型結晶に対応するピーク高さ（Ｈａと略する。）から算出した比率（＝１００×Ｈｒ／（Ｈｒ＋Ｈａ＋Ｈｂ）をいう。〕が５％以下の超微粒子酸化チタン（以下、低ルチル型の超微粒子酸化チタンと略称することがある。）であり、かつ、脱塩素工程の後のみならず、場合によっては脱塩素工程の前でも、下記一般式（２）：
Ｃ≦６５０×ｅ0.02B ・・・・・・・・・・・・・・・（２）
で表される全塩素含有量を有する。式中、Ｃは全塩素含有量（質量％）を示す。Ｃは、例えば、酸化チタンにフッ酸水溶液を添加しマイクロウェーブで加熱溶解させた液を、硝酸銀による電位差滴定法で測定し、酸化チタン中の塩素の質量を得、これを用いた酸化チタンの質量で除することにより得られる。ＢはＢＥＴ比表面積（ｍ2／ｇ）を表し、その範囲は１０〜２００ｍ2／ｇである。）で表される特性を有することを特徴とする。
【００２２】
すなわち、本発明の低ルチル型の超微粒子酸化チタンは、図１において上記一般式（２）の条件を満足する全塩素含有量の少ない酸化チタンであり、かつ上記式（１）のＲが大きい粒子内部の塩素含有率の小さい酸化チタン粒子である。従来の四塩化チタンを原料とする気相法による超微粒子酸化チタンは、低ルチル型酸化チタンであっても、ＢＥＴ比表面積と全塩素含有量との関係において図１に示したＣ＝６５０×ｅ0.02Bで表される曲線の上部にプロットされる領域の特性を有しているものであり、さらにまた上記の粒子内部の塩素含有率も大きい酸化チタン粒子であった。特に、比表面積の大きい酸化チタンほど、脱塩素されにくく、塩素含有量が指数関数的に増加する傾向がある。
【００２３】
本発明の低ルチル型酸化チタンは、塩素含有量とＢＥＴ比表面積との関係が一般式（２）の特性を満足し、超微粒子であって、通常、ＢＥＴ比表面積の範囲は１０〜２００ｍ2／ｇ、好ましくは４０〜２００ｍ2／ｇ、更に好ましくは４５〜１２０ｍ2／ｇの範囲を有するものである。
【００２４】
また、本発明の低ルチル型の超微粒子酸化チタンは、Ｆｅ、Ａｌ、Ｓｉ、Ｓの含有量が各１００質量ｐｐｍ以下、好ましくは各０．１〜１００質量ｐｐｍ、より好ましくは各０．１〜５０質量ｐｐｍ、更に好ましくは各０．１〜１０質量ｐｐｍである。
これらの不純物濃度を０．１ｐｐｍ未満にするには、酸化チタンを製造する原材料を高純度とし、また設備材質をより耐食性の高いものを使用すること等が必要となる。本発明の酸化チタンが通常用いられる用途では、各不純物を０．１質量ｐｐｍ未満としない方が経済的に有利である。
【００２５】
本発明の低ルチル型酸化チタンは分散性が高いことを特徴とする。本発明においては、分散性の指標としてレーザー回折式粒度分布測定法を採用し粒度分布を測定した。分散性の測定法には、「超微粒子ハンドブック」齋藤進六監修，フジ・テクノシステム，ｐ９３，（１９９０）によると、沈降法、顕微鏡法、光散乱法、直接計数法等があるが、このうち沈降法、直接計数法は測定可能な粒径が数百ｎｍ以上であり、超微粒子の分散性を測定するには不適である。また、顕微鏡法も対象試料のサンプリングや試料の前処理によって測定値が変動することもあり、好ましい測定法とはいえない。これに対し、光散乱法は数ｎｍ〜数μｍの範囲で粒径を測定することができ、超微粒子の測定に適している。粒度分布の測定手順について以下に説明する。
【００２６】
酸化チタン０．０５ｇに純水５０ｍｌ及び１０％ヘキサメタリン酸ソーダ水溶液１００μｌを加えたスラリーに、３分間超音波照射（４６ＫＨｚ、６５Ｗ）する。このスラリーをレーザー回折式粒度分布測定装置（（株）島津製作所製ＳＡＬＤ−２０００Ｊ）にかけて、粒度分布を測定する。このようにして測定された粒度分布における９０％累積質量粒度分布径（以下、Ｄ９０と略記することがある）の値が小さければ、親水性溶媒に対して良好な分散性を示していると判断される。５０％累積質量粒度分布径を分散性の指標とすることも可能であるが、分散性の悪い凝集粒子を検知しにくく好ましくない。本発明の超微粒子酸化チタンは、Ｄ９０が２．５μｍ以下であることが好ましい。
【００２７】
本発明の超微粒子状酸化チタンは、各種組成物の原料、顔料または光触媒効果を利用した粒子成分として含まれ、例えば、化粧料、紫外線遮蔽材、誘電体またはシリコーンゴム、太陽電池等、様々な製品の原料、添加剤として利用できる。
【００２８】
次に製造方法について説明する。
気相法による一般的な酸化チタンの製造方法は公知であり、四塩化チタンを酸素または水蒸気等の酸化性ガスを用いて、約１，０００℃の反応条件下で酸化させると微粒子酸化チタンが得られる。
【００２９】
気相法において超微粒子の酸化チタンを得るためには、粒子の成長時間（成長ゾーン）を短くしなければならない。すなわち、反応後速やかに冷却、希釈等を行い、高温滞留時間を極力短くすることにより、焼結等による粒成長を抑えることができる。高温滞留時間の短縮はアナターゼからルチルへの熱転位を抑制することにも繋がり、アナターゼ含有率の高い粒子を得ることができる。
【００３０】
一般に、四塩化チタンを原料とする気相法で得られる酸化チタンには、通常、０．１〜２質量％の塩素が残存している。アナターゼ型酸化チタン表面には、塩素等が結合可能な点が１３個／ｎｍ2あり（前述の清野学著「酸化チタン」）、この全ての結合点が塩素化している場合、酸化チタン粒子表面に残存する塩素含有量は理論上、下式（３）で表される。
Ｙ＝０．０７７×Ａ ・・・・（３）
（式中、Ｙは酸化チタン粒子表面に残存する塩素含有量（質量％）を示し、Ａは比表面積（ｍ2／ｇ）を示す。）
例えば、１００ｍ2／ｇの比表面積を有する酸化チタン粒子表面に残存する塩素含有量は、前記式（３）によれば、約８質量％となる。
【００３１】
実際は、反応で塩素と酸化性ガスが置換すること、また酸化チタン粒子表面と気相の塩素濃度差によって塩素が平衡移動することにより、酸化チタンの塩素含有量は前記式（３）で得られる値よりも若干低くなる可能性があるが、反応での高温滞留時間の短縮は、四塩化チタンの酸化反応を完結させず、一部が塩素化されたままの酸化チタンを増加させることになると考えられる。また、残存塩素が酸化チタン粒子内部に取り残されると粒子内部の塩素量を増やすことにもなるため、塩素除去に要する加熱処理が高温、長時間化し、比表面積の低下を生じることとなる。従って、従来、気相法によって得られる超微粒子は、アナターゼ含有率は高いものの塩素含有量が高い、あるいは、塩素含有量は低いがアナターゼ含有率が低いというものであった。
【００３２】
本発明では、四塩化チタンを含むガスと酸化性ガスとを反応（高温酸化）することにより酸化チタンを製造する気相法において、６００℃以上１，１００℃未満に加熱した四塩化チタンを含有するガス及び６００℃以上１，１００℃未満に加熱した酸化性ガスをそれぞれ反応管に供給し、反応させて得られた酸化チタンを８００℃以上１，１００℃未満の高温度条件で０．１秒以下の時間、反応管内に滞留させることにより、ＢＥＴ比表面積と塩素含有量との関係において全塩素含有量、特に粒子内部の塩素含有量が低い低ルチル型超微粒子酸化チタンが得られ、これを脱塩素処理することによりさらに全塩素含有量が低くかつ粒子内部の塩素含有量も低い低ルチル型超微粒子酸化チタンが得られることを見出した。
ここで、脱塩素には乾式法と湿式法がある。乾式脱塩素法は、例えば、円筒形回転式加熱炉、熱風循環式加熱炉、流動乾燥炉、撹拌乾燥炉等の加熱装置を用いて酸化チタンを加熱し、塩素を除去する方法がある。尚、本発明は、必ずしもこれら加熱装置に限定されるものではない。また、湿式脱塩素法は、例えば、酸化チタンを純水に懸濁させ、液相に移行した塩素を系外に分離する方法がある。塩素を系外に分離した後、得られた酸化チタンを乾燥しても良い。
【００３３】
四塩化チタン含有ガスあるいは酸化性ガスを導入する反応管内の温度は８００℃以上１，１００℃未満が好ましく、更に好ましくは９００℃以上１，０００℃未満である。反応管内温度を高くすることによって、混合と同時に反応は完結するので均一核発生が増進され、かつ、反応（ＣＶＤ）ゾーンを小さくすることができる。反応管内温度が８００℃より低いと、アナターゼ含有率の高い酸化チタンが得られやすいものの、反応が不充分で酸化チタン粒子内部に塩素が残存する。反応管内温度が１，１００℃以上になるとルチル転移や粒子成長が進行し、低ルチル型、超微粒子が得られない。
【００３４】
一方、原料ガスが反応管に導入され反応が進行すると、本反応が発熱反応である為、反応温度が１，１００℃を越える反応ゾーンが存在する。装置放熱は多少あるものの、急冷を施さないかぎり酸化チタン粒子はどんどん成長し、かつ、結晶型がルチルに転移してしまう。そこで、本発明においては８００℃以上１，１００℃未満の高温滞留時間を０．１秒以下、好ましくは０．００５〜０．１秒、特に好ましくは０．０１〜０．０５秒の範囲にする。高温滞留時間が０．１秒を越えると、ルチルへの転移や粒子の焼結が進行するので好ましくない。高温滞留時間が０．００５秒未満では、四塩化チタンの酸化反応時間も短くなるため、四塩化チタンに比べ十分に過剰な酸素量を用いるなど酸化を行い易い条件下で行う必要がある。酸化が不十分では粒子内部の残存塩素量増加につながる。
【００３５】
急冷の手段としては、例えば、反応混合物に多量の冷却空気や窒素等のガスを導入する方法、あるいは水を噴霧する方法等が採用される。
【００３６】
反応管内の温度を前記８００℃以上１，１００℃未満に制御することで粒子内部の塩素含有量が低い超微粒子を得ることができ、また、高温滞留時間を０．１秒以下に制御することでルチル転移及び粒成長を抑制することができる。
【００３７】
反応管内の温度を前記８００℃以上１，１００℃未満にするためには、原料ガスの加熱温度を６００℃以上１，１００℃以下に調整することが好ましい。加熱された原料ガスは反応管内で反応し発熱するが、原料ガス温度が６００℃未満であると、反応管内の温度は８００℃以上になりにくい。また、原料ガス温度が１，１００℃以上であると装置放熱はあるものの、反応管内の温度は１，１００℃を越えやすくなる。
【００３８】
四塩化チタンを含む原料ガス組成は、四塩化チタンガス１モルに対し、不活性ガス０．１〜２０モルであることが好ましく、さらに好ましくは４〜２０モルである。不活性ガスが前記範囲より少ない場合、反応ゾーンにおける酸化チタン粒子密度が高まり、凝集、焼結しやすくなるため、超微粒子酸化チタンが得られにくい。不活性ガスが前記範囲よりも多い場合、反応性が低下し、酸化チタンとしての回収率が低下する。
【００３９】
四塩化チタンを含む原料ガスと反応させる酸素ガス量は、四塩化チタン１モルに対し１〜３０モルであることが好ましい。さらに好ましくは５〜３０モルである。酸素ガス量を増やすと、核発生数が増加し超微粒子は得られやすくなるが、３０モルを越えても核発生数を増加させる効果はほとんど無い。酸素ガス量が３０モルを越えても酸化チタンの特性に影響は無いが、経済的な観点から上限が設定される。一方、四塩化チタンに対し酸素ガス量が不足すると、酸素欠陥の多い酸化チタンとなり着色してしまう。尚、酸化性ガスには、酸素の他に水蒸気が含まれていても良い。
酸化性ガスは、例えば、酸素、水蒸気を含む酸素、空気、これらの酸化性ガスに不活性ガス（窒素、アルゴンなど）を混合したガスがいずれも使用できるが、反応温度の制御しやすいことから水蒸気を含む酸素が好ましい。
【００４０】
酸化チタンの加熱による脱塩素は、水と酸化チタンとの質量比（＝水蒸気の質量／酸化チタンの質量，以下同様）が０．０１以上になるように酸化チタン粉末に水蒸気を接触させながら加熱温度２００℃以上５００℃以下で行うことが好ましい。更に好ましくは水と酸化チタンの質量比は０．０４以上、加熱温度は２５０℃以上４５０℃以下である。加熱温度が５００℃を越えると酸化チタン粒子の焼結が進み、粒成長が生じる。加熱温度が２００℃を下回ると脱塩素の効率が極端に低下する。脱塩素は、酸化チタン表面の塩素が粒子近傍の水あるいは隣接する粒子の表面水酸基と置換反応することにより進行して行く。酸化チタン粒子表面の塩素が、水と置換された場合には粒成長せずに脱塩素化されるが、隣接する粒子の表面水酸基と置換された場合は脱塩素と同時に粒成長することとなる。特に比表面積の大きい酸化チタンほど隣接する粒子表面水酸基と置換反応する確率が高くなるため、粒成長しやすい。すなわち、粒成長を抑制しつつ脱塩素化を図るためには水と酸化チタンの質量比も重要であり、水と酸化チタンの質量比が０．０１以上であれば粒成長を抑制する効果が認められる。
【００４１】
酸化チタンと接触させる水蒸気は、酸化チタンから分離した塩素を効率良く系外に移動させる役割を有するガスと混合して使用することが好ましい。このようなガスとして、例えば、空気が挙げられる。空気を用いる場合、水蒸気は、空気に０．１容量％以上含まれることが好ましく、更に好ましくは５容量％以上、特に好ましくは１０容量％以上である。水蒸気を含んだ空気は２００℃以上１，０００℃以下に加熱しておくことが好ましい。
【００４２】
本発明による低ルチル型超微粒子酸化チタンは粒子内部に塩素が殆ど存在しないため、湿式で低塩素化することも可能である。湿式脱塩素方法には、例えば、酸化チタンを純水に懸濁させ、液相に移行した塩素を限外ろ過膜、逆浸透膜、フィルタープレス等によって系外に分離する方法が挙げられる。
このようにして製造される本発明のＢＥＴ比表面積とハロゲン含有量との関係において全ハロゲン含有量および粒子内部のハロゲン含有量の低い低ルチル型超微粒子酸化チタンは、好ましくは粒子表面のハロゲンをより完全に脱ハロゲンすることで、ＢＥＴ比表面積との関係において全ハロゲン含有量が極めて低い低ルチル型超微粒子酸化チタンを得ることができる。
従って、本発明の低ルチル型超微粒子酸化チタンは、上記の如く、ルチル含有率が５％以下、ＢＥＴ一点法で測定した比表面積が１０〜２００ｍ2／ｇ、レーザー回折式粒度分析計によって測定される９０％累積質量粒度分布径が２．５μｍ以下の酸化チタン粒子であり、かつ、ＢＥＴ一点法で測定した酸化チタンの比表面積をＢ（ｍ2／ｇ）、酸化チタン粒子内部のハロゲン含有量をＣi（質量ｐｐｍ）としたとき、粒子内部に含まれるハロゲン量が０≦Ｃi≦６５０ｋｅ0.02B（ｋは０．２０）、好ましくは０＜Ｃi≦６５０ｋｅ0.02B（ｋは０．２０）、より好ましくは１０＜Ｃi≦６５０ｋｅ0.02B（ｋは０．１５）で示されることを特徴とする。
【００４３】
【実施例】
以下、実施例及び比較例にて具体的に説明するが、本発明はこれらに何ら限定されるものではない。
【００４４】
実施例１：
１１．８Ｎｍ3／ｈｒ（Ｎは標準状態を意味する。以下同じ。）のガス状四塩化チタンを８Ｎｍ3／ｈｒの窒素ガスで希釈した四塩化チタン希釈ガスを９００℃に予熱し、８Ｎｍ3／ｈｒの酸素と３２Ｎｍ3／ｈｒ水蒸気を混合した酸化性ガスを８００℃に予熱し、これらの原料ガスを石英ガラス製反応器に導入した。８００℃以上１，１００℃未満の高温滞留時間を０．１秒となるように冷却空気を反応管に導入後、ポリテトラフルオロエチレン製バグフィルターにて超微粒子状酸化チタン粉末を捕集した。
【００４５】
得られた酸化チタンを円筒形回転式加熱炉に通し、水と酸化チタンの質量比０．０２、加熱温度４５０℃で脱塩素した。その後、得られた酸化チタンは、ＢＥＴ比表面積が２２ｍ2／ｇ、ルチル含有比率（ルチル含有率ともいう。）が１％、水抽出塩素含有量が９００質量ｐｐｍ、全塩素含有量が１，０００質量ｐｐｍであった。但し、ＢＥＴ比表面積は、島津製作所製比表面積測定装置（機種はフローソーブＩＩ，２３００）で測定し、ルチル含有比率はＸ線回折におけるルチル型結晶に対応するピーク高さ（Ｈｒと略する。）、ブルッカイト型結晶に対応するピーク高さ（Ｈｂと略する。）とアナターゼ型結晶に対応するピーク高さ（Ｈａと略する。）から算出した比率（＝１００×Ｈｒ／（Ｈｒ＋Ｈａ＋Ｈｂ））である。式（１）に水抽出塩素含有量 ９００質量ｐｐｍ、全塩素含有量 １，０００質量ｐｐｍを代入して算出される表面塩素率は８０％よりも高く、全塩素含有量は、式（２）に比表面積２２ｍ2／ｇを代入して算出される値よりも小さな数値を示した。
【００４６】
また、ここで得られた酸化チタン粉末の粒度分布について、レーザー回折式粒度分布測定法で９０％累積質量粒度分布径Ｄ９０を測定した結果、１．１μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ、Ｓｉ、Ｓの分析結果を表１に示す。
【００４７】
実施例２：
５．９Ｎｍ3／ｈｒのガス状四塩化チタンを３０Ｎｍ3／ｈｒの窒素ガスで希釈した四塩化チタン希釈ガスを１，０００℃に予熱し、４Ｎｍ3／ｈｒの酸素と１６Ｎｍ3／ｈｒの水蒸気を混合した酸化性ガスを１，０００℃に予熱し、これらの原料ガスを石英ガラス製反応器に導入した。８００℃以上１，１００℃未満の高温滞留時間を０．０３秒となるように冷却空気を反応管に導入後、ポリテトラフルオロエチレン製バグフィルターにて超微粒子状酸化チタン粉末を捕集した。
【００４８】
得られた酸化チタンを熱風循環加熱炉に入れ、水と酸化チタン質量比０．０４、加熱温度４５０℃で脱塩素した。こうして得られた酸化チタンは、ＢＥＴ比表面積が６５ｍ2／ｇ、ルチル含有率が３％、水抽出塩素含有量が９００質量ｐｐｍ、全塩素含有量が１，１００質量ｐｐｍであった。式（１）に水抽出塩素含有量 ９００質量ｐｐｍ、全塩素含有量 １，１００質量ｐｐｍを代入して算出される表面塩素率は８０％よりも高く、全塩素含有量は、式（２）に比表面積６５ｍ2／ｇを代入して算出される値よりも小さな数値を示した。この粉末のレーザー回折式粒度分布測定法にて測定した粒度分布における９０％累積質量粒度分布径Ｄ９０は１．９μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ、Ｓｉ、Ｓの分析結果を表１に示す。
【００４９】
実施例３：
４．７Ｎｍ3／ｈｒのガス状四塩化チタンを３６Ｎｍ3／ｈｒの窒素ガスで希釈した四塩化チタン希釈ガスを１，０００℃に予熱し、３６Ｎｍ3／ｈｒの空気と２５Ｎｍ3／ｈｒの水蒸気を混合した酸化性ガスを１，０００℃に予熱し、これらの原料ガスを石英ガラス製反応器に導入した。８００℃以上１，１００℃未満の高温滞留時間を０．０２秒となるように冷却空気を反応管に導入後、ポリテトラフルオロエチレン製バグフィルターにて超微粒子状酸化チタン粉末を捕集した。
【００５０】
得られた酸化チタンを熱風循環加熱炉に入れ、水と酸化チタン質量比０．０６、加熱温度３５０℃で脱塩素した。こうして得られた酸化チタンは、ＢＥＴ比表面積が９７ｍ2／ｇ、ルチル含有率が１％、水抽出塩素含有率が１，８００質量ｐｐｍ、全塩素含有率が２，０００質量ｐｐｍであった。式（１）に水抽出塩素含有量 １，８００質量ｐｐｍ、全塩素含有量 ２，０００質量ｐｐｍを代入して算出される表面塩素率は８０％よりも高く、全塩素含有率は、式（２）に比表面積９７ｍ2／ｇを代入して算出される値よりも小さな数値を示した。この粉末のレーザー回折式粒度分布測定法にて測定した粒度分布における９０％累積質量粒度分布径Ｄ９０は２．２μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ、Ｓｉ、Ｓの分析結果を表１に示す。
【００５１】
比較例１：
１１．８Ｎｍ3／ｈｒのガス状四塩化チタンを８Ｎｍ3／ｈｒの窒素ガスで希釈した四塩化チタン希釈ガスを９００℃に予熱し、８Ｎｍ3／ｈｒの酸素と３２Ｎｍ3／ｈｒ水蒸気を混合した酸化性ガスを８００℃に予熱し、これらの原料ガスを石英ガラス製反応器に導入した。８００℃以上１，１００℃未満の高温滞留時間を０．２秒となるように冷却空気を反応管に導入後、ポリテトラフルオロエチレン製バグフィルターにて超微粒子状酸化チタン粉末粉を捕集した。
【００５２】
得られた酸化チタンを円筒形回転式加熱炉に通し、水と酸化チタン質量比０．０２、加熱温度４５０℃で脱塩素した。こうして得られた酸化チタンは、ＢＥＴ比表面積が１９ｍ2／ｇ、ルチル含有比率が１１％、水抽出塩素含有量が３００質量ｐｐｍ、全塩素含有量が３００質量ｐｐｍであった。式（１）に水抽出塩素含有率 ３００質量ｐｐｍ、全塩素含有率 ３００質量ｐｐｍを代入して算出される表面塩素率は８０％よりも高く、全塩素含有率は、式（２）に比表面積１９ｍ2／ｇを代入して算出される値よりも小さな数値を示した。この粉末のレーザー回折式粒度分布測定法にて測定した粒度分布における９０％累積質量粒度分布径Ｄ９０は０．８μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ、Ｓｉ、Ｓの分析結果を表１に示す。
【００５３】
比較例２：
４．７Ｎｍ3／ｈｒのガス状四塩化チタンを３６Ｎｍ3／ｈｒの窒素ガスで希釈した四塩化チタン希釈ガスを８００℃に予熱し、３６Ｎｍ3／ｈｒの空気と２５Ｎｍ3／ｈｒの水蒸気を混合した酸化性ガスを８００℃に予熱し、これらの原料ガスを石英ガラス製反応器に導入した。該反応管温度を７５０℃に制御し、原料ガスを０．０８秒滞留するように冷却空気を反応管に導入後、ポリテトラフルオロエチレン製バグフィルターにて超微粒子状酸化チタン粉末を捕集した。
【００５４】
得られた酸化チタンを熱風循環加熱炉に入れ、水と酸化チタン質量比０．０４、加熱温度３５０℃で脱塩素した。こうして得られた酸化チタンは、ＢＥＴ比表面積が７４ｍ2／ｇ、ルチル含有率が２％、水抽出塩素含有率が２，８００質量ｐｐｍ、全塩素含有率が３，９００質量ｐｐｍであった。式（１）に水抽出塩素含有量 ２，８００質量ｐｐｍ、全塩素含有量 ３，９００質量ｐｐｍを代入して算出される表面塩素率は８０％よりも低く、全塩素含有率は、式（２）に比表面積７４ｍ2／ｇを代入して算出される値よりも大きな数値を示した。この粉末のレーザー回折式粒度分布測定法にて測定した粒度分布における９０％累積質量粒度分布径Ｄ９０は３．６μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ、Ｓｉ、Ｓの分析結果を表１に示す。
【００５５】
比較例３：
５．９Ｎｍ3／ｈｒのガス状四塩化チタンを３０Ｎｍ3／ｈｒの窒素ガスで希釈した四塩化チタン希釈ガスを１，１００℃に予熱し、４Ｎｍ3／ｈｒの酸素と１６Ｎｍ3／ｈｒの水蒸気を混合した酸化性ガスを１，１００℃に予熱し、これらの原料ガスを石英ガラス製反応器に導入した。該反応管温度を１，２００℃に制御し、原料ガスを０．０４秒滞留するように冷却空気を反応管に導入後、ポリテトラフルオロエチレン製バグフィルターにて超微粒子状酸化チタン粉末を捕集した。
【００５６】
得られた酸化チタンを熱風循環加熱炉に入れ、水と酸化チタン質量比０．０６、加熱温度４５０℃で脱塩素した。こうして得られた酸化チタンは、ＢＥＴ比表面積が４４ｍ2／ｇ、ルチル含有率が１２％、水抽出塩素含有量が１，２００質量ｐｐｍ、全塩素含有量が１，３００質量ｐｐｍであった。式（１）に水抽出塩素含有量 １，２００質量ｐｐｍ、全塩素含有量 １，３００質量ｐｐｍを代入して算出される表面塩素率は８０％よりも高く、全塩素含有率は、式（２）に比表面積４４ｍ2／ｇを代入して算出される値よりも小さな数値を示した。この粉末のレーザー回折式粒度分布測定法にて測定した粒度分布における９０％累積質量粒度分布径Ｄ９０は１．２μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ、Ｓｉ、Ｓの分析結果を表１に示す。
比較例４：
市販の硫酸チタニル溶液（関東化学（株）製、試薬１級）を煮沸し、得られた沈殿を純水で洗浄し、含水酸化チタンを得た。この含水酸化チタンの残存硫酸を除去するため、純水を加えスラリーとし、これを攪拌しながらアンモニア水溶液を加えてｐＨ５に調整し、１２時間攪拌した。この後、限外ろ過膜で含水酸化チタン濃度を２０質量％まで濃縮した。濃縮液に再びアンモニア水溶液を加えてｐＨ５に調整し、１２時間攪拌の後、純水を加えながら限外ろ過膜でろ過しチタニアゾルを得た。得られたチタニアゾルを３００℃で２時間乾燥し、液相法による超微粒子酸化チタンを得た。
得られた酸化チタンはＢＥＴ比表面積が２１２ｍ２／ｇ、ルチル含有率１％であった。水抽出塩素含有量、全塩素含有量はともに０質量ｐｐｍであった。この酸化チタンを乳鉢で解砕し、レーザー回折式粒度分布測定法にて粒度分布を測定したところ、９０％累積質量粒度Ｄ９０は２６．１μｍであった。ルチル化率、ＢＥＴ比表面積、全塩素含有量、表面塩素率、Ｄ９０、及び、Ｆｅ、Ａｌ，Ｓｉ，Ｓの分析結果を表１に示す。
【００５７】
【表１】
【発明の効果】
本発明により、同等のＢＥＴ比表面積を有する従来の酸化チタンに比べ、粒子内部のハロゲン含有量が低く、分散性に特に優れた、気相法によるアナターゼ型の超微粒子酸化チタン、これを脱ハロゲンすることによりＢＥＴ比表面積（Ｂ）とハロゲン含有率（Ｃ）との関係が前記式（２）の条件を満足する酸化チタン、レーザー回折式粒度分布測定法で測定されたＤ９０が２．５μｍ以下の酸化チタン、及びこれらの製造方法が提供される。
【００５９】
本発明の酸化チタンは、光触媒用途や太陽電池用途等に好適であり、特に、水系の溶媒に対する分散性が優れるので、水中での光触媒用途に好適に用いることができ、粉体としても解砕工程等が不要もしくは極めて軽微な設備で済み、工業的に非常に大きな実用的価値を有するものである。
【図面の簡単な説明】
【図１】超微粒子状酸化チタンのハロゲン含有率とＢＥＴ比表面積との関係を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a low-rutile low-chlorine ultrafine particle titanium oxide suitable for photocatalysts, solar cells, additives to silicone rubber, dielectric use, and the like, and a method for producing the same. More specifically, in vapor phase titanium oxide obtained by high-temperature oxidation of a gas containing halogen titanium with an oxidizing gas, the halogen content is low, the remaining halogen can be easily removed, and the dispersibility is low. The present invention relates to a rutile type low-halogen ultrafine particle titanium oxide and a method for producing the same.
[0002]
[Prior art]
Ultra-fine particle titanium oxide has been used for a wide variety of applications such as UV shielding materials, additives to silicone rubber, dielectric materials, cosmetics, etc. (Titanium oxide is a combination of titanium dioxide and Japanese Industrial Standards (JIS)). Since titanium oxide is widely used as a general name, it is abbreviated as titanium oxide in this specification). Titanium oxide is also applied as a photocatalyst, a solar cell, and the like.
[0003]
There are three types of crystal forms of titanium oxide: rutile, anatase, and brookite. Of these, anatase and brookite, which have better photoelectrochemical activity than rutile, in the aforementioned photocatalyst and solar cell applications. A mold is used.
[0004]
The photocatalytic action of titanium oxide is used to decompose organic substances such as antibacterial tiles, self-cleaning building materials, and deodorant fibers, and the mechanism thereof is explained as follows. Titanium oxide absorbs ultraviolet rays and generates electrons and holes therein. Holes react with the adsorbed water of titanium oxide to generate hydroxy radicals, and decompose organic substances adsorbed on the surface of the titanium oxide particles into carbon dioxide gas and water ("Hikari Clean Revolution" Akira Fujishima, Kazuhito Hashimoto, Toshiya Watanabe, (CMC Co., pp. 143-145 (1997)). That is, conditions for titanium oxide having a strong photocatalytic action include that holes are likely to be generated and holes are likely to reach the surface of titanium oxide. “All about titanium oxide photocatalyst” (Kazuhito Hashimoto, Akira Fujishima, CMC Co., Ltd., 29-30 (1998)) describes anatase-type titanium oxide, which has high photocatalytic activity, and has few lattice defects. Titanium and titanium oxide with small particles and large specific surface area are mentioned.
[0005]
The application as a solar cell has been studied since Gretzell et al. Of Lausanne Institute of Technology reported a dye-sensitized solar cell combining titanium oxide and a ruthenium-based dye in 1991 (M. Graezel, Nature). , 353, 737, (1991)). In the dye-sensitized solar cell, titanium oxide has a role as a dye carrier and an n-type semiconductor, and is used as a dye electrode bound to a conductive glass electrode. The dye-sensitized solar cell has a structure in which an electrolytic layer is sandwiched between a dye electrode and a counter electrode, and the dye generates electrons and holes by absorbing light. The generated electrons reach the conductive glass electrode through the titanium oxide layer and are extracted to the outside. On the other hand, the generated holes are transported to the counter electrode through the electrolytic layer, and are combined with electrons supplied through the conductive glass electrode. One factor that improves the characteristics of the dye-sensitized solar cell is that the titanium oxide and the dye can be easily combined. As a crystal form of titanium oxide that can be easily bonded to a dye, for example, anatase is used in JP-A-10-255863, and brookite is a dye-sensitized type in JP-A 2000-340269. It is described that it is suitable for solar cells.
[0006]
Titanium oxide having good dispersibility is important for extracting its function. For example, when titanium oxide is used as a photocatalyst, if the dispersibility is poor, the concealing power becomes strong, so that the usable applications are limited. Also in the field of solar cells, titanium oxide with poor dispersibility is difficult to transmit light, so titanium oxide that can contribute to light absorption is limited, and photoelectric conversion efficiency is deteriorated. In general, light scattering (hiding power) is maximized when the particle size is about ½ of the visible light wavelength, and light scattering is said to be weaker when the particle size becomes smaller (“Titanium oxide” written by Manabu Seino, Gihodo (Co.), p.129, (1991)). Since the primary particle diameter of titanium oxide used in the above-mentioned field is often several to several tens of nm, if the dispersibility is good, the influence on light scattering is small. However, titanium oxide with poor dispersion and large aggregate particle size will increase light scattering.
[0007]
For the above reasons, in the above field, titanium oxide is required to have high dispersibility, and anatase type or brookite type ultrafine titanium oxide having good dispersibility is used. In general, the primary particle diameter of ultrafine particles is not clarified, but is usually referred to fine particles of about 0.1 μm or less.
[0008]
When titanium oxide is used in a photocatalyst or a solar cell, if a corrosive component such as chlorine is present, the base material is corroded or altered, so that the chlorine content of titanium oxide needs to be kept low. Also, it is better to keep Fe, Al, Si, S, etc. low. For example, if there is too much Fe in titanium oxide, it causes coloring and is not suitable for use in applications requiring transparency. If there are too many components such as Al and S inside the titanium oxide particles, lattice defects may occur, and the functions as a photocatalyst and a solar cell may be reduced.
[0009]
Titanium oxide production methods are roughly classified into a liquid phase method in which titanium tetrachloride and titanyl sulfate are hydrolyzed, and a gas phase method in which titanium halide is reacted with an oxidizing gas such as oxygen or water vapor. Titanium oxide obtained by the liquid phase method can obtain anatase as a main phase, but must be in a sol or slurry state. When used in this state, the application is limited. In order to use it as a powder, it is necessary to dry it, and the ultrafine particles wetted by the solvent become more agglomerated as the drying progresses ("Ultrafine Particles Handbook" supervised by Shinroku Saito, Fuji Techno System, page 388, ( 1990) When this titanium oxide is used for a photocatalyst or the like, it is necessary to strongly disintegrate or grind the titanium oxide in order to enhance dispersibility. May cause problems.
[0010]
In general, titanium oxide produced by a vapor phase method is superior in dispersibility compared to a liquid phase method because a solvent is not used.
[0011]
There are many examples of obtaining ultrafine particles of titanium oxide by a gas phase method. For example, in JP-A-6-340423, in a method for producing titanium oxide by hydrolyzing titanium tetrachloride in a flame, oxygen, tetrachloride A method for obtaining a titanium oxide having a high rutile content by adjusting the molar ratio of titanium and hydrogen is disclosed. JP-A-7-316536 discloses a method for producing crystalline titanium oxide powder by hydrolyzing titanium tetrachloride in a high temperature gas phase and rapidly cooling the reaction product. A method for obtaining a crystalline transparent titanium oxide having an average primary particle size of 40 nm or more and 150 nm or less by specifying the titanium concentration is disclosed. However, in any case, only titanium oxide having fine particles but high rutile content is obtained, and is not suitable for use as a photocatalyst or solar cell.
[0012]
For example, Japanese Patent Application Laid-Open No. 3-252315 discloses a method for producing titanium oxide whose main phase is anatase by a gas phase method, by changing the ratio of hydrogen in a mixed gas of oxygen and hydrogen in a gas phase reaction. A production method for adjusting the ratio is disclosed, and titanium oxide having a rutile content of 9% is described. However, the particle size of the exemplified titanium oxide is 0.5 to 0.6 μm, which is coarser than the particle size range generally referred to as ultrafine particles.
[0013]
When titanium oxide is produced by a vapor phase method using titanium halide as a raw material, ultrafine particles can be easily obtained, but since halogen derived from the raw material remains in titanium oxide, dehalogenation by heating or washing with water is often required. However, ultrafine titanium oxide is subject to the sintering of particles by heating for low halogenation, and the specific surface area tends to decrease, and the crystal form transition from anatase type to rutile type may occur. . In order to suppress the decrease in the specific surface area and the crystal transition, it is necessary to perform heating at a low temperature or for a short time, but it is not possible to sufficiently dehalogenate. A method for reducing the chlorination of ultrafine titanium oxide is disclosed, for example, in JP-A-10-251102. In this method, titanium oxide is brought into contact with water vapor while rolling in a cylindrical rotary heating furnace to reduce the chlorine content. Moreover, the rutile content of the titanium oxide described therein was as high as 15%.
[0014]
On the other hand, halogen remaining on the surface of the titanium oxide particles can be removed by dehalogenation by washing with water or the like, but there is a problem that the internal halogen tends to remain because the halogen inside the particles is difficult to contact with water.
[0015]
As described above, in the conventional vapor phase method, a low rutile type ultrafine particle titanium oxide having a low halogen content has not been obtained.
[Patent Document 1]
Japanese Patent Laid-Open No. 10-255863 [Patent Document 2]
JP 2000-340269 A [Patent Document 3]
JP-A-6-340423 [Patent Document 4]
Japanese Patent Laid-Open No. 7-316536 [Patent Document 5]
Japanese Patent Laid-Open No. 10-2521021 [Non-Patent Document 1]
"Light Clean Revolution" Akira Fujishima, Kazuhito Hashimoto, Toshiya Watanabe, CMC Co., pp.143-145 (1997)
[Non-Patent Document 2]
"All about titanium oxide photocatalysts" (Kazuhito Hashimoto, Akira Fujishima, CMC, 29-30 (1998))
[Non-Patent Document 3]
M.M. Graezel, Nature, 353, 737, (1991)
[Non-Patent Document 4]
“Titanium oxide” written by Manabu Seino, Gihodo Co., Ltd., p. 129, (1991)
[Non-Patent Document 5]
("Ultrafine particle handbook" supervised by Shinroku Saito, Fuji Techno System,
388 pages, (1990)
[0016]
[Problems to be solved by the invention]
The present invention has been made to solve the above problems, and an object of the present invention is to provide a low rutile type ultrafine titanium oxide having excellent dispersibility and low halogen content in a gas phase method, and a method for producing the same. Is to provide.
[0017]
[Means for Solving the Problems]
As a result of diligent research in view of the above problems, the present inventors have found that it is possible to produce a low rutile ultrafine titanium oxide having excellent dispersibility in a gas phase method and having a low halogen content, and the above problems are solved. It came to solve.
[0018]
In the gas phase method in which a gas containing titanium halide and an oxidizing gas (oxygen, water vapor, or a mixed gas containing them) are reacted, the raw material gas is reacted while controlling the heating temperature and the heating time. After that, there is obtained a low rutile ultrafine titanium oxide having a high BET specific surface area and specific characteristics, which is obtained by dehalogenation and having a rutile content of 5% or less, and a method for producing the same. It is to provide.
[0019]
That is, the present invention includes the following inventions.
(1) In a gas phase method for producing titanium oxide by reacting a gas containing titanium halide with an oxidizing gas, the reaction is performed at a ratio of 0.1 to 20 moles of inert gas with respect to 1 mole of titanium halide. When the raw material gas mixed in step 1 and 1 to 30 moles of oxidizing gas per mole of titanium halide are introduced and reacted with a gas containing titanium halide and an oxidizing gas, respectively, into the reactor. The temperature in the reactor is 800 ° C. or higher and lower than 1,100 ° C., and the gas containing titanium halide and the oxidizing gas have a residence time of 0 ° C. or higher and lower than 1,100 ° C. in the reactor. A method for producing titanium oxide, characterized by being 1 second or less.
( 2 ) The method for producing titanium oxide according to ( 1 ) above, wherein the gas containing titanium halide and the oxidizing gas are preheated to 600 ° C. or higher and lower than 1,100 ° C. and introduced into the reactor.
( 3 ) The method for producing titanium oxide as described in ( 1) or (2 ) above, wherein the oxidizing gas is an oxygen gas containing water vapor.
( 4 ) The method for producing titanium oxide according to the above ( 3 ), wherein the oxidizing gas contains 0.1 mol or more of water vapor with respect to 1 mol of oxygen gas.
( 5 ) The method for producing titanium oxide according to any one of ( 1 ) to ( 4 ), wherein the titanium halide is titanium tetrachloride.
( 6 ) A method for producing titanium oxide, characterized in that halogen is removed from the titanium oxide produced by the production method according to any one of ( 1 ) to ( 5 ) in a dry manner.
( 7 ) The method for producing titanium oxide as described in ( 6 ) above, wherein the method of removing halogen by a dry method is a method of heating titanium oxide to 200 to 500 ° C.
( 8 ) The method for producing titanium oxide according to the above ( 6 ), wherein the method of removing halogen by a dry method is a method in which a gas containing water vapor is heated to 200 to 1000 ° C. and brought into contact with titanium oxide.
( 9 ) The method for producing titanium oxide according to ( 8 ), wherein the gas containing water vapor is air containing 0.1% by volume or more of water vapor.
( 10 ) The method for producing titanium oxide according to ( 8 ), wherein the water vapor is 0.01 or more in terms of mass ratio with respect to titanium oxide.
( 11 ) The titanium oxide produced by the production method according to any one of ( 1 ) to ( 5 ) above is subjected to wet-type halogen removal to obtain a slurry containing titanium oxide. Production method.
( 12 ) The method for producing titanium oxide according to ( 11 ) above, wherein the method of removing halogen in a wet manner is a method of suspending titanium oxide in water and separating the halogen transferred to the liquid phase out of the system.
( 13 ) The method for producing titanium oxide according to the above ( 11 ) or ( 12 ), wherein the method of removing halogen in a wet manner is a method of separating halogen with an ultrafiltration membrane.
( 14 ) The method for producing titanium oxide according to the above ( 11 ) or ( 12 ), wherein the method of removing halogen in a wet manner is a method of separating halogen with a reverse osmosis membrane.
( 15 ) The method for producing titanium oxide according to the above ( 11 ) or ( 12 ), wherein the method of removing halogen in a wet process is a method of separating halogen with a filter press .
[0020]
DETAILED DESCRIPTION OF THE INVENTION
As the titanium halide which is a raw material of the titanium oxide of the present invention, titanium chloride which is easily available industrially, particularly titanium tetrachloride is preferable. Therefore, hereinafter, the present invention will be described by way of a representative example where the halogen is chlorine, but the present invention can also be applied to the case where the halogen is bromine or iodine.
Although the low rutile ultrafine titanium oxide of the present invention is produced using titanium tetrachloride by a vapor phase method, there is almost no chlorine inside the particles. Chlorine remaining inside the particles may diffuse from the inside of the particles to the surface over time and corrode and alter the base material, but is difficult to remove by simple dechlorination treatment such as washing with water or drying. Therefore, it is desirable that chlorine is not present inside the titanium oxide particles.
Regarding the chlorine content in the particle in the total chlorine content on the particle surface and inside the particle, chlorine extracted from pure titanium with pure water (referred to as water-extracted chlorine) and total chlorine contained in the titanium oxide particles ( The ratio of total chlorine) is used as an index, and the following formula (1)
R = WCL / TCL × 100 (1)
(In the formula, R represents the surface chlorine ratio (%), WCL represents the content (mass%) of water-extracted chlorine contained in titanium oxide, and TCL represents the total chlorine content (mass%) contained in titanium oxide. )
The higher the value of R represented by is, the lower the chlorine content in the titanium oxide particles is. In the titanium oxide in the present invention, R is preferably 80% or more, and more preferably 90% or more.
[0021]
The ultrafine particle titanium oxide obtained by the vapor phase method using titanium tetrachloride of the present invention as a raw material has a rutile content [the rutile content is abbreviated as a peak height (Hr) corresponding to a rutile crystal in X-ray diffraction. ), A ratio (= 100 × Hr / (Hr + Ha + Hb)) calculated from a peak height (abbreviated as Hb) corresponding to a brookite type crystal and a peak height (abbreviated as Ha) corresponding to an anatase type crystal. ] Is 5% or less of ultrafine titanium oxide (hereinafter sometimes referred to as low rutile ultrafine titanium oxide), and not only after the dechlorination step but also in some cases, the dechlorination step. Even before, the following general formula (2):
C ≦ 650 × e 0.02B (2)
The total chlorine content represented by In formula, C shows total chlorine content (mass%). C, for example, a solution obtained by adding a hydrofluoric acid aqueous solution to titanium oxide and heating and dissolving with microwaves is measured by potentiometric titration with silver nitrate to obtain the mass of chlorine in titanium oxide. It is obtained by dividing by mass. B represents a BET specific surface area (m 2 / g), and the range thereof is 10 to 200 m 2 / g. It has the characteristic represented by this.
[0022]
That is, the low rutile ultrafine particle titanium oxide of the present invention is a titanium oxide having a low total chlorine content that satisfies the condition of the general formula (2) in FIG. 1, and the R of the formula (1) is large. Titanium oxide particles with a small chlorine content inside the particles. Even if the conventional ultrafine particle titanium oxide by a vapor phase method using titanium tetrachloride as a raw material is a low rutile type titanium oxide, C = 650 × shown in FIG. 1 in relation to the BET specific surface area and the total chlorine content. e Titanium oxide particles having the characteristics of the region plotted at the top of the curve represented by 0.02B , and also having a high chlorine content inside the particles. In particular, titanium oxide having a large specific surface area is less likely to be dechlorinated and the chlorine content tends to increase exponentially.
[0023]
The low rutile titanium oxide of the present invention is a superfine particle in which the relationship between the chlorine content and the BET specific surface area satisfies the characteristics of the general formula (2), and the range of the BET specific surface area is usually 10 to 200 m 2. / g, preferably those 40 to 200 m 2 / g, more preferably having a range of 45~120m 2 / g.
[0024]
Further, the low rutile ultrafine titanium oxide of the present invention has Fe, Al, Si, and S contents of 100 ppm by mass or less, preferably 0.1 to 100 ppm by mass, more preferably 0.1 to 0.1 ppm by mass. -50 mass ppm, more preferably 0.1-10 mass ppm.
In order to make these impurity concentrations less than 0.1 ppm, it is necessary to make the raw material for producing titanium oxide highly pure and to use equipment materials with higher corrosion resistance. In applications in which the titanium oxide of the present invention is usually used, it is economically advantageous not to make each impurity less than 0.1 ppm by mass.
[0025]
The low rutile type titanium oxide of the present invention is characterized by high dispersibility. In the present invention, the particle size distribution was measured by adopting a laser diffraction particle size distribution measuring method as an index of dispersibility. Dispersibility measurement methods include the “ultrafine particle handbook” supervised by Shinroku Saito, Fuji Techno System, p93, (1990), such as sedimentation, microscopy, light scattering, and direct counting. Among them, the sedimentation method and the direct counting method have a measurable particle size of several hundred nm or more and are not suitable for measuring the dispersibility of ultrafine particles. In addition, the microscopic method is not a preferable measuring method because the measured value may vary depending on the sampling of the target sample or the pretreatment of the sample. On the other hand, the light scattering method can measure the particle diameter in the range of several nm to several μm and is suitable for the measurement of ultrafine particles. The measurement procedure of the particle size distribution will be described below.
[0026]
A slurry obtained by adding 50 ml of pure water and 100 μl of 10% sodium hexametaphosphate aqueous solution to 0.05 g of titanium oxide is subjected to ultrasonic irradiation (46 KHz, 65 W) for 3 minutes. The slurry is subjected to a laser diffraction particle size distribution analyzer (SALD-2000J, manufactured by Shimadzu Corporation) to measure the particle size distribution. If the value of the 90% cumulative mass particle size distribution diameter (hereinafter sometimes abbreviated as D90) in the particle size distribution measured in this way is small, it is judged that the polymer exhibits good dispersibility in the hydrophilic solvent. Is done. Although it is possible to use the 50% cumulative mass particle size distribution diameter as an index of dispersibility, it is difficult to detect agglomerated particles having poor dispersibility. The ultrafine titanium oxide of the present invention preferably has a D90 of 2.5 μm or less.
[0027]
The ultrafine titanium oxide of the present invention is included as a raw material of various compositions, a pigment or a particle component utilizing the photocatalytic effect, and includes various materials such as cosmetics, ultraviolet shielding materials, dielectrics or silicone rubbers, solar cells, etc. It can be used as a raw material and additive for products.
[0028]
Next, a manufacturing method will be described.
A general method for producing titanium oxide by a vapor phase method is known. When titanium tetrachloride is oxidized using an oxidizing gas such as oxygen or steam under a reaction condition of about 1,000 ° C., fine titanium oxide is obtained. can get.
[0029]
In order to obtain ultrafine titanium oxide in the vapor phase method, the growth time (growth zone) of the particles must be shortened. That is, grain growth due to sintering or the like can be suppressed by cooling and diluting immediately after the reaction and shortening the high temperature residence time as much as possible. Shortening the high temperature residence time also leads to suppression of thermal rearrangement from anatase to rutile, and particles having a high anatase content can be obtained.
[0030]
Generally, 0.1 to 2% by mass of chlorine remains in titanium oxide obtained by a vapor phase method using titanium tetrachloride as a raw material. On the anatase type titanium oxide surface, there are 13 points / nm 2 that can bind chlorine and the like (manufactured by Manabu Kiyono, “Titanium oxide”). The remaining chlorine content is theoretically expressed by the following formula (3).
Y = 0.077 × A (3)
(In the formula, Y represents the chlorine content (% by mass) remaining on the surface of the titanium oxide particles, and A represents the specific surface area (m 2 / g).)
For example, the chlorine content remaining on the surface of the titanium oxide particles having a specific surface area of 100 m 2 / g is about 8% by mass according to the formula (3).
[0031]
Actually, the chlorine content of titanium oxide can be obtained by the above formula (3) by replacing chlorine and oxidizing gas in the reaction and by the equilibrium transfer of chlorine due to the chlorine concentration difference between the titanium oxide particle surface and the gas phase. Although it may be slightly lower than the value, shortening the high-temperature residence time in the reaction will not complete the oxidation reaction of titanium tetrachloride, but will increase the titanium oxide that is partially chlorinated Conceivable. In addition, if the residual chlorine is left inside the titanium oxide particles, the amount of chlorine inside the particles is also increased, so that the heat treatment required for removing chlorine is increased in temperature and time, and the specific surface area is reduced. Therefore, conventionally, ultrafine particles obtained by the vapor phase method have a high anatase content but a high chlorine content, or a low chlorine content but a low anatase content.
[0032]
In the present invention, in a gas phase method for producing titanium oxide by reacting a gas containing titanium tetrachloride and an oxidizing gas (high-temperature oxidation), titanium tetrachloride heated to 600 ° C. or more and less than 1,100 ° C. is contained. Gas and an oxidizing gas heated to 600 ° C. or higher and lower than 1,100 ° C. are respectively supplied to the reaction tube, and titanium oxide obtained by the reaction is 0.1 ° C. in a high temperature condition of 800 ° C. or higher and lower than 1,100 ° C. By staying in the reaction tube for a time of less than a second, a low rutile ultrafine particle titanium oxide having a low total chlorine content, particularly a low chlorine content inside the particle in relation to the BET specific surface area and the chlorine content, is obtained. It has been found that low rutile type ultrafine particle titanium oxide having a lower total chlorine content and a lower chlorine content inside the particles can be obtained by dechlorinating.
Here, dechlorination includes a dry method and a wet method. The dry dechlorination method includes, for example, a method of removing chlorine by heating titanium oxide using a heating device such as a cylindrical rotary heating furnace, a hot air circulation heating furnace, a fluidized drying furnace, a stirring drying furnace or the like. The present invention is not necessarily limited to these heating devices. In addition, the wet dechlorination method includes, for example, a method in which titanium oxide is suspended in pure water and chlorine transferred to the liquid phase is separated from the system. After separating chlorine out of the system, the obtained titanium oxide may be dried.
[0033]
The temperature in the reaction tube into which the titanium tetrachloride-containing gas or oxidizing gas is introduced is preferably 800 ° C. or higher and lower than 1,100 ° C., more preferably 900 ° C. or higher and lower than 1,000 ° C. By increasing the temperature in the reaction tube, the reaction is completed simultaneously with mixing, so that uniform nucleation is promoted and the reaction (CVD) zone can be reduced. When the temperature in the reaction tube is lower than 800 ° C., titanium oxide having a high anatase content is easily obtained, but the reaction is insufficient and chlorine remains inside the titanium oxide particles. When the temperature in the reaction tube is 1,100 ° C. or higher, rutile transition and particle growth proceed, and low rutile type and ultrafine particles cannot be obtained.
[0034]
On the other hand, when the raw material gas is introduced into the reaction tube and the reaction proceeds, this reaction is an exothermic reaction, so that there is a reaction zone where the reaction temperature exceeds 1,100 ° C. Although there is some heat dissipation from the device, the titanium oxide particles grow more and more and the crystal form is transferred to rutile unless rapid cooling is performed. Therefore, in the present invention, the high temperature residence time of 800 ° C. or more and less than 1,100 ° C. is 0.1 seconds or less, preferably 0.005 to 0.1 seconds, particularly preferably 0.01 to 0.05 seconds. To do. If the high temperature residence time exceeds 0.1 seconds, the transition to rutile and particle sintering proceed, which is not preferable. When the high-temperature residence time is less than 0.005 seconds, the oxidation reaction time of titanium tetrachloride is also shortened. Therefore, it is necessary to carry out under conditions that facilitate oxidation, such as using a sufficiently excessive amount of oxygen compared to titanium tetrachloride. Insufficient oxidation leads to an increase in the amount of residual chlorine inside the particles.
[0035]
As the rapid cooling means, for example, a method of introducing a large amount of cooling air or nitrogen gas into the reaction mixture, a method of spraying water, or the like is employed.
[0036]
By controlling the temperature in the reaction tube to be 800 ° C. or more and less than 1,100 ° C., ultrafine particles having a low chlorine content inside the particles can be obtained, and the high temperature residence time is controlled to 0.1 seconds or less. Can suppress rutile transition and grain growth.
[0037]
In order to set the temperature in the reaction tube to 800 ° C. or higher and lower than 1,100 ° C., the heating temperature of the raw material gas is preferably adjusted to 600 ° C. or higher and 1,100 ° C. or lower. The heated source gas reacts and generates heat in the reaction tube, but if the source gas temperature is less than 600 ° C., the temperature in the reaction tube is unlikely to be 800 ° C. or higher. On the other hand, if the raw material gas temperature is 1,100 ° C. or higher, the temperature in the reaction tube tends to exceed 1,100 ° C. although there is heat dissipation from the apparatus.
[0038]
The raw material gas composition containing titanium tetrachloride is preferably 0.1 to 20 moles of inert gas, more preferably 4 to 20 moles per mole of titanium tetrachloride gas. When the inert gas is less than the above range, the titanium oxide particle density in the reaction zone increases, and it becomes easy to aggregate and sinter, so it is difficult to obtain ultrafine titanium oxide. When there are more inert gases than the said range, the reactivity will fall and the recovery rate as a titanium oxide will fall.
[0039]
The amount of oxygen gas to be reacted with the raw material gas containing titanium tetrachloride is preferably 1 to 30 mol per 1 mol of titanium tetrachloride. More preferably, it is 5-30 mol. Increasing the amount of oxygen gas increases the number of nuclei generated and makes it easier to obtain ultrafine particles. However, even if the amount exceeds 30 mol, there is almost no effect of increasing the number of nuclei generated. Even if the amount of oxygen gas exceeds 30 moles, there is no influence on the characteristics of titanium oxide, but the upper limit is set from an economical point of view. On the other hand, when the amount of oxygen gas is insufficient with respect to titanium tetrachloride, titanium oxide with many oxygen defects is formed and colored. The oxidizing gas may contain water vapor in addition to oxygen.
As the oxidizing gas, for example, oxygen, oxygen including water vapor, air, or a gas obtained by mixing an inert gas (nitrogen, argon, etc.) with these oxidizing gases can be used, but the reaction temperature is easily controlled. Oxygen containing water vapor is preferred.
[0040]
Dechlorination by heating of titanium oxide is performed while bringing steam into contact with titanium oxide powder so that the mass ratio of water to titanium oxide (= mass of water vapor / mass of titanium oxide, the same applies hereinafter) is 0.01 or more. It is preferable to carry out at a temperature of 200 ° C. or higher and 500 ° C. or lower. More preferably, the mass ratio of water and titanium oxide is 0.04 or more, and the heating temperature is 250 ° C. or more and 450 ° C. or less. When the heating temperature exceeds 500 ° C., sintering of the titanium oxide particles proceeds and grain growth occurs. When the heating temperature is lower than 200 ° C., the efficiency of dechlorination is extremely reduced. Dechlorination proceeds by the substitution reaction of chlorine on the surface of titanium oxide with water near the particles or surface hydroxyl groups of adjacent particles. When chlorine on the surface of titanium oxide particles is replaced with water, it is dechlorinated without growing grains, but when it is replaced with hydroxyl groups on the adjacent particles, grains grow simultaneously with dechlorination. . In particular, the larger the specific surface area of titanium oxide, the higher the probability of substitution reaction with the adjacent particle surface hydroxyl groups, and thus the easier the grain growth. That is, the mass ratio of water and titanium oxide is also important for dechlorination while suppressing grain growth. If the mass ratio of water and titanium oxide is 0.01 or more, the effect of suppressing grain growth is achieved. Is recognized.
[0041]
The water vapor to be brought into contact with the titanium oxide is preferably used by mixing with a gas having a role of efficiently transferring chlorine separated from the titanium oxide out of the system. An example of such a gas is air. When air is used, water vapor is preferably contained in the air in an amount of 0.1% by volume or more, more preferably 5% by volume or more, and particularly preferably 10% by volume or more. The air containing water vapor is preferably heated to 200 ° C. or higher and 1,000 ° C. or lower.
[0042]
Since the low rutile ultrafine particle titanium oxide according to the present invention has almost no chlorine inside the particles, it can be reduced in the wet state. Examples of the wet dechlorination method include a method in which titanium oxide is suspended in pure water, and chlorine transferred to the liquid phase is separated from the system by an ultrafiltration membrane, a reverse osmosis membrane, a filter press, or the like.
The low rutile ultrafine titanium oxide having a low total halogen content and a low halogen content inside the grain in the relationship between the BET specific surface area and the halogen content of the present invention thus produced is preferably a halogen on the grain surface. By completely dehalogenating, a low rutile ultrafine titanium oxide having a very low total halogen content in relation to the BET specific surface area can be obtained.
Therefore, the low rutile ultrafine titanium oxide of the present invention has a rutile content of 5% or less, a specific surface area measured by the BET single point method of 10 to 200 m 2 / g, as described above, and measured by a laser diffraction particle size analyzer. The 90% cumulative mass particle size distribution diameter is 2.5 μm or less of titanium oxide particles and the specific surface area of titanium oxide measured by the BET single point method is B (m 2 / g), and the halogen content inside the titanium oxide particles When the amount is C i (ppm by mass), the amount of halogen contained in the particle is 0 ≦ C i ≦ 650 ke 0.02B (k is 0.20), preferably 0 <C i ≦ 650 ke 0.02B (k is 0 20), more preferably 10 <C i ≦ 650 ke 0.02B (k is 0.15).
[0043]
【Example】
Hereinafter, although an Example and a comparative example demonstrate concretely, this invention is not limited to these at all.
[0044]
Example 1:
A titanium tetrachloride dilution gas obtained by diluting 11.8 Nm 3 / hr (N means standard state; the same shall apply hereinafter) gaseous titanium tetrachloride with 8 Nm 3 / hr of nitrogen gas is preheated to 900 ° C., and 8 Nm 3 An oxidizing gas in which / hr oxygen and 32 Nm 3 / hr water vapor were mixed was preheated to 800 ° C., and these raw material gases were introduced into a quartz glass reactor. Cooling air was introduced into the reaction tube so that the high-temperature residence time of 800 ° C. or more and less than 1,100 ° C. was 0.1 second, and then ultrafine titanium oxide powder was collected with a polytetrafluoroethylene bag filter.
[0045]
The obtained titanium oxide was passed through a cylindrical rotary heating furnace and dechlorinated at a mass ratio of water to titanium oxide of 0.02 and a heating temperature of 450 ° C. Thereafter, the obtained titanium oxide had a BET specific surface area of 22 m 2 / g, a rutile content ratio (also referred to as a rutile content) of 1%, a water extraction chlorine content of 900 mass ppm, and a total chlorine content of 1, It was 000 mass ppm. However, the BET specific surface area is measured with a specific surface area measuring device manufactured by Shimadzu Corporation (model is Flowsorb II, 2300), and the rutile content ratio is a peak height corresponding to a rutile crystal in X-ray diffraction (abbreviated as Hr). The ratio (= 100 × Hr / (Hr + Ha + Hb)) calculated from the peak height (abbreviated as Hb) corresponding to the brookite type crystal and the peak height (abbreviated as Ha) corresponding to the anatase type crystal. . The surface chlorine ratio calculated by substituting the water extraction chlorine content 900 mass ppm and the total chlorine content 1,000 mass ppm into the formula (1) is higher than 80%, and the total chlorine content is calculated by the formula (2) The numerical value smaller than the value calculated by substituting 22 m 2 / g for the specific surface area is shown.
[0046]
Moreover, about the particle size distribution of the titanium oxide powder obtained here, it was 1.1 micrometers as a result of measuring 90% cumulative mass particle size distribution diameter D90 by the laser diffraction type particle size distribution measuring method. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
[0047]
Example 2:
A titanium tetrachloride dilution gas obtained by diluting 5.9 Nm 3 / hr of gaseous titanium tetrachloride with 30 Nm 3 / hr of nitrogen gas is preheated to 1,000 ° C., and 4 Nm 3 / hr of oxygen and 16 Nm 3 / hr of water vapor The premixed oxidizing gas was preheated to 1,000 ° C., and these raw material gases were introduced into a quartz glass reactor. Cooling air was introduced into the reaction tube so that the high-temperature residence time of 800 ° C. or more and less than 1,100 ° C. was 0.03 seconds, and then the ultrafine titanium oxide powder was collected with a polytetrafluoroethylene bag filter.
[0048]
The obtained titanium oxide was put into a hot air circulating heating furnace and dechlorinated at a water / titanium oxide mass ratio of 0.04 and a heating temperature of 450 ° C. The titanium oxide thus obtained had a BET specific surface area of 65 m 2 / g, a rutile content of 3%, a water extraction chlorine content of 900 mass ppm, and a total chlorine content of 1,100 mass ppm. The surface chlorine ratio calculated by substituting the water extraction chlorine content 900 mass ppm and the total chlorine content 1,100 mass ppm into the formula (1) is higher than 80%, and the total chlorine content is calculated by the formula (2) A numerical value smaller than the value calculated by substituting for the specific surface area of 65 m 2 / g was shown. The 90% cumulative mass particle size distribution diameter D90 in the particle size distribution measured by the laser diffraction particle size distribution measurement method of this powder was 1.9 μm. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
[0049]
Example 3:
A titanium tetrachloride dilution gas obtained by diluting 4.7 Nm 3 / hr of gaseous titanium tetrachloride with 36 Nm 3 / hr of nitrogen gas is preheated to 1,000 ° C., and then 36 Nm 3 / hr of air and 25 Nm 3 / hr of water vapor The premixed oxidizing gas was preheated to 1,000 ° C., and these raw material gases were introduced into a quartz glass reactor. Cooling air was introduced into the reaction tube so that the high temperature residence time of 800 ° C. or higher and lower than 1,100 ° C. was 0.02 seconds, and then the ultrafine titanium oxide powder was collected with a polytetrafluoroethylene bag filter.
[0050]
The obtained titanium oxide was put into a hot air circulating heating furnace and dechlorinated at a water / titanium oxide mass ratio of 0.06 and a heating temperature of 350 ° C. The titanium oxide thus obtained had a BET specific surface area of 97 m 2 / g, a rutile content of 1%, a water extraction chlorine content of 1,800 mass ppm, and a total chlorine content of 2,000 mass ppm. The surface chlorine ratio calculated by substituting the water extraction chlorine content of 1,800 mass ppm into the formula (1) and the total chlorine content of 2,000 mass ppm is higher than 80%. A numerical value smaller than the value calculated by substituting the specific surface area of 97 m 2 / g into 2) was shown. The 90% cumulative mass particle size distribution diameter D90 in the particle size distribution measured by the laser diffraction particle size distribution measurement method of this powder was 2.2 μm. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
[0051]
Comparative Example 1:
11.8 nm 3 / hr of gaseous forty-four titanium chloride diluent gas diluted titanium tetrachloride with nitrogen gas 8 Nm 3 / hr and was preheated to 900 ° C., and mixed with oxygen and 32 Nm 3 / hr of water vapor 8 Nm 3 / hr The oxidizing gas was preheated to 800 ° C., and these raw material gases were introduced into a quartz glass reactor. Cooling air was introduced into the reaction tube so that the high-temperature residence time of 800 ° C. or more and less than 1,100 ° C. was 0.2 seconds, and then ultrafine particulate titanium oxide powder was collected with a polytetrafluoroethylene bag filter. .
[0052]
The obtained titanium oxide was passed through a cylindrical rotary heating furnace and dechlorinated at a water / titanium oxide mass ratio of 0.02 and a heating temperature of 450 ° C. The titanium oxide thus obtained had a BET specific surface area of 19 m 2 / g, a rutile content ratio of 11%, a water extraction chlorine content of 300 mass ppm, and a total chlorine content of 300 mass ppm. The surface chlorine ratio calculated by substituting the water extraction chlorine content of 300 mass ppm and the total chlorine content of 300 mass ppm into the formula (1) is higher than 80%, and the total chlorine content is compared with the formula (2). A numerical value smaller than the value calculated by substituting the surface area of 19 m 2 / g was shown. The 90% cumulative mass particle size distribution diameter D90 in the particle size distribution measured by the laser diffraction particle size distribution measurement method of this powder was 0.8 μm. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
[0053]
Comparative Example 2:
Preheated 4.7 nm 3 / hr of gaseous forty-four titanium chloride diluent gas diluted titanium tetrachloride with nitrogen gas 36 Nm 3 / hr to 800 ° C., mixing air and 25 Nm 3 / hr of steam 36 Nm 3 / hr The oxidized gas was preheated to 800 ° C., and these raw material gases were introduced into a quartz glass reactor. The reaction tube temperature was controlled at 750 ° C., and cooling air was introduced into the reaction tube so that the raw material gas was retained for 0.08 seconds, and then the ultrafine titanium oxide powder was collected with a polytetrafluoroethylene bag filter. .
[0054]
The obtained titanium oxide was put into a hot air circulating heating furnace and dechlorinated at a water / titanium oxide mass ratio of 0.04 and a heating temperature of 350 ° C. The titanium oxide thus obtained had a BET specific surface area of 74 m 2 / g, a rutile content of 2%, a water extraction chlorine content of 2,800 mass ppm, and a total chlorine content of 3,900 mass ppm. The surface chlorine ratio calculated by substituting the water extraction chlorine content of 2,800 mass ppm and the total chlorine content of 3,900 mass ppm into the formula (1) is lower than 80%. A value larger than the value calculated by substituting the specific surface area of 74 m 2 / g for 2) was shown. The 90% cumulative mass particle size distribution diameter D90 in the particle size distribution measured by the laser diffraction particle size distribution measurement method of this powder was 3.6 μm. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
[0055]
Comparative Example 3:
A titanium tetrachloride dilution gas obtained by diluting 5.9 Nm 3 / hr of gaseous titanium tetrachloride with 30 Nm 3 / hr of nitrogen gas is preheated to 1,100 ° C., and 4 Nm 3 / hr of oxygen and 16 Nm 3 / hr of water vapor The premixed oxidizing gas was preheated to 1,100 ° C., and these source gases were introduced into a quartz glass reactor. The reaction tube temperature is controlled to 1,200 ° C., cooling air is introduced into the reaction tube so that the raw material gas stays for 0.04 seconds, and the ultrafine titanium oxide powder is captured by a polytetrafluoroethylene bag filter. Gathered.
[0056]
The obtained titanium oxide was put into a hot air circulating heating furnace and dechlorinated at a water / titanium oxide mass ratio of 0.06 and a heating temperature of 450 ° C. The titanium oxide thus obtained had a BET specific surface area of 44 m 2 / g, a rutile content of 12%, a water extracted chlorine content of 1,200 mass ppm, and a total chlorine content of 1,300 mass ppm. The surface chlorine ratio calculated by substituting the water extraction chlorine content of 1,200 mass ppm and the total chlorine content of 1,300 mass ppm into the formula (1) is higher than 80%. A numerical value smaller than the value calculated by substituting the specific surface area 44 m 2 / g into 2) was shown. The 90% cumulative mass particle size distribution diameter D90 in the particle size distribution measured by the laser diffraction particle size distribution measurement method of this powder was 1.2 μm. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
Comparative Example 4:
A commercially available titanyl sulfate solution (manufactured by Kanto Chemical Co., Ltd., reagent grade 1) was boiled, and the resulting precipitate was washed with pure water to obtain hydrous titanium oxide. In order to remove the residual sulfuric acid of the hydrous titanium oxide, pure water was added to form a slurry, and the aqueous solution was adjusted to pH 5 with stirring while stirring, and stirred for 12 hours. Thereafter, the hydrous titanium oxide concentration was concentrated to 20% by mass with an ultrafiltration membrane. An aqueous ammonia solution was added to the concentrate again to adjust to pH 5. After stirring for 12 hours, the solution was filtered through an ultrafiltration membrane while adding pure water to obtain a titania sol. The obtained titania sol was dried at 300 ° C. for 2 hours to obtain ultrafine titanium oxide by a liquid phase method.
The obtained titanium oxide had a BET specific surface area of 212 m 2 / g and a rutile content of 1%. Both the water-extracted chlorine content and the total chlorine content were 0 ppm by mass. The titanium oxide was crushed in a mortar and the particle size distribution was measured by a laser diffraction particle size distribution measurement method. As a result, the 90% cumulative mass particle size D90 was 26.1 μm. Table 1 shows the analysis results of rutile ratio, BET specific surface area, total chlorine content, surface chlorine ratio, D90, and Fe, Al, Si, and S.
[0057]
[Table 1]
【The invention's effect】
According to the present invention, an anatase-type ultrafine titanium oxide by a vapor phase method, which has a low halogen content inside a particle and is particularly excellent in dispersibility, compared with a conventional titanium oxide having an equivalent BET specific surface area, is obtained by dehalogenation. Titanium oxide in which the relationship between the BET specific surface area (B) and the halogen content (C) satisfies the condition of the above formula (2), D90 measured by the laser diffraction particle size distribution measurement method is 2.5 μm or less Titanium oxides and methods for their production are provided.
[0059]
The titanium oxide of the present invention is suitable for photocatalyst use, solar cell use and the like. Particularly, since it has excellent dispersibility in aqueous solvents, it can be suitably used for photocatalyst use in water, and can be crushed as a powder. A process or the like is unnecessary, or an extremely light facility is required, and it has an industrially very large practical value.
[Brief description of the drawings]
FIG. 1 shows the relationship between the halogen content and the BET specific surface area of ultrafine titanium oxide.
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| CN102471089B (en) * | 2009-08-24 | 2015-02-25 | 国立大学法人北海道大学 | Metal oxide particle production method and production device |
| JP5223828B2 (en) * | 2009-09-18 | 2013-06-26 | 堺化学工業株式会社 | Anatase type ultrafine particle titanium oxide, dispersion containing anatase type ultrafine particle titanium oxide, and method for producing the titanium oxide |
| JP5524557B2 (en) | 2009-09-28 | 2014-06-18 | 富士フイルム株式会社 | Method for producing photoelectric conversion element, photoelectric conversion element, and photoelectrochemical cell |
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