WO2012077414A1 - Synthesis method for acicular titanium oxide powder - Google Patents

Synthesis method for acicular titanium oxide powder Download PDF

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WO2012077414A1
WO2012077414A1 PCT/JP2011/074025 JP2011074025W WO2012077414A1 WO 2012077414 A1 WO2012077414 A1 WO 2012077414A1 JP 2011074025 W JP2011074025 W JP 2011074025W WO 2012077414 A1 WO2012077414 A1 WO 2012077414A1
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tio
titanium oxide
powder
oxide powder
acicular
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PCT/JP2011/074025
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French (fr)
Japanese (ja)
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健 廣田
将樹 加藤
礼承 谷口
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学校法人同志社
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/003—Titanates
    • C01G23/005—Alkali titanates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G23/00—Compounds of titanium
    • C01G23/04—Oxides; Hydroxides
    • C01G23/047—Titanium dioxide
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/10—Particle morphology extending in one dimension, e.g. needle-like
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids

Definitions

  • the present invention relates to a method for synthesizing acicular titanium oxide powder having excellent temperature stability of a crystal phase.
  • the crystal phase of titanium oxide TiO 2 in order from the low temperature phase, TiO 2 (B) of the bronze phase, anatase phase a-TiO 2, rutile phase r-TiO 2, four types of brookite phase b-TiO 2 is reported ing.
  • titanium oxide powders used for electrodes of dye-sensitized solar cells and lithium ion batteries are required to have high electron conductivity and high ion conductivity, so bronze phase TiO 2 (B) and anatase phase a -TiO 2 is adopted.
  • a-TiO 2 powder added with needle-like TiO 2 (B) and other elements moves and diffuses electrons and ions in the long axis direction to produce a battery with high power generation and high charging efficiency. It is expected.
  • titanium oxide undergoes a phase transition to stable r-TiO 2 with low electron conductivity and low ion conductivity, and it is difficult to obtain the expected characteristics.
  • Needle-like powder is mainly hydrothermal synthesis method using strong alkaline solution at a temperature of 200 ° C or less (eg 185 ° C).
  • the needle-like TiO 2 (B) powder synthesized under these conditions is fine, so the filling rate is low and the stability of the crystalline phase is low, making it easy to phase transition to r-TiO 2 There was a problem to do.
  • Non-patent Document 1 spherical TiO 2 having a particle diameter of 20 nm or less can be synthesized from Ti (SO 4 ) 2 or TiCl 4 by supercritical hydrothermal synthesis.
  • Non-patent Document 3 the orientation of the unit crystal has changed between the alkali titanate after hydrothermal treatment and the heat treatment.
  • an object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a method capable of synthesizing huge acicular titanium oxide powder with high crystal phase stability.
  • the “needle shape” includes shapes such as a column shape and a rod shape.
  • Step 1 By adding a strong alkaline aqueous solution to titanium oxide powder to prepare a mixed solution, and using the mixed solution, hydrothermal synthesis is performed in the supercritical state of water at a temperature range of 375 ° C. to 22.5 MPa or more.
  • Step 2 Substituting the alkali-shaped alkali-Ti-oxide obtained in Step 1 with hydrogen ions in weakly acidic aqueous solution. And a heat treatment in the atmosphere at 300 to 500 ° C. after that.
  • the temperature and pressure conditions during the hydrothermal synthesis are in the range of 375 ° C.-22.5375MPa to 430 ° C.-40 MPa. It is also a feature.
  • the strong alkaline aqueous solution used for the hydrothermal synthesis is a solution having an alkali concentration of 8 to 13 mol / L. It is also a feature.
  • the stability of the crystalline phase is high, it is possible to synthesize a huge acicular TiO 2 (B) powder, the acicular TiO 2 (B) powder, conventional rutile Compared with anatase TiO 2 , it has a very high electric conductivity (electric conductivity ⁇ ).
  • Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) is an XRD pattern when heated at 600 ° C for 1 hour.
  • Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) is an XRD pattern when heated at 700 ° C for 1 hour.
  • Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) is an XRD pattern when heated at 800 ° C for 1 hour.
  • Each TiO 2 (B) powder obtained by the comparative example and the conventional example (hydrothermal synthesis temperature is 315, 185 ° C.) (heat treatment 400 ° C.-5 hours), heated at 600 ° C. for 1 hour, and further at 800 ° C. 1 It is a SEM image after time heating. It is the figure which shows the method of measuring the resistance of acicular titanium oxide powder, and the SEM image which shows the measurement state of an actual sample.
  • measurement is performed using the measurement method shown in FIG. It is a graph which shows the current-voltage characteristic at the time of performing.
  • FIG. 10 is an enlarged view of each graph showing the current-voltage characteristics shown in FIG. 9, where the horizontal axis is current and the vertical axis is voltage.
  • FIG. 11 is an enlarged view of each graph showing the current-voltage characteristics shown in FIG. 10, in which the horizontal axis is current and the vertical axis is voltage.
  • step 1 of the present invention titanium oxide powder (a-TiO 2 powder) is prepared as a starting material, a strong alkaline aqueous solution is added to the powder to prepare a mixed solution, and this mixed solution is used.
  • Acicular alkali-Ti-oxide is hydrothermally synthesized at a temperature and pressure in the range of 375 °C -22.5 MPa or higher, preferably 375 °C -22.5 MPa to 430 °C -40 MPa, which is the supercritical condition of water. Is synthesized as an intermediate product.
  • a commercially available a-TiO 2 powder can be used as a starting material, and an aqueous NaOH solution, an aqueous KOH solution, an aqueous LiOH solution can be used as a strong alkaline aqueous solution to be added, and an alkali concentration is 8 to 13 mol / L. 10 mol / L is particularly preferable. At a low concentration of less than 8 mol / L, granular powder is formed. On the other hand, it is difficult to prepare a strong alkaline aqueous solution having a concentration higher than 13 mol / L, which is not suitable for the purpose of the present invention.
  • the treatment time may be about 1 to 2 hours.
  • the container suitable for the hydrothermal synthesis include a platinum container, a silver container, and a gold container. Particularly preferred.
  • the above mixed solution is poured into a platinum container, the platinum container is sealed by TIG welding, this is inserted into the high pressure container, and the gap between the platinum container and the high pressure container. It is preferable to carry out hydrothermal synthesis in a temperature and pressure region at or above the supercritical condition of water by adding an appropriate amount of water to the vessel, heating the high pressure vessel. The sample temperature is measured in a platinum container, and the pressure is measured in the high-pressure container.
  • Step 2 of the present invention the needle-like alkali-Ti-oxide of the intermediate product obtained in Step 1 above is exchanged for hydrogen ions in a weakly acidic aqueous solution (for example, aqueous hydrochloric acid solution), washed with water, After drying, acicular TiO 2 (B) powder is obtained by heat treatment in the atmosphere at 300 to 500 ° C.
  • the ion exchange is preferably carried out in a 0.1 to 0.5 mol / L hydrochloric acid aqueous solution at 10 to 80 ° C., particularly preferably in a 0.1 mol / L hydrochloric acid aqueous solution at 50 ° C.
  • the heat treatment conditions are 350 to 450 ° C., preferably 2 to 6 hours, and particularly preferably 400 ° C. to 5 hours.
  • a huge acicular TiO 2 (B) powder can be synthesized. Even if the acicular TiO 2 (B) powder is heated to 700 to 800 ° C., it has a crystalline phase. High stability.
  • the needle-like TiO 2 (B) powder synthesized in this way has a very high electric conductivity as compared with conventional rutile and anatase TiO 2 .
  • TiO 2 -anatase manufactured by Wako Pure Chemical Industries TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry
  • TiO 2 -anatase made by Wako Pure Chemicals has a specific surface area S by BET of 57.4 m 2 / g, does not contain Nb, has an average particle size P s of 0.0281 ⁇ m
  • TiO 2- made by Sakai Chemical Industry Anatase (SSP-M) had a specific surface area S by BET of 98.8 m 2 / g, an Nb content of 0.265% by mass, and an average particle size P s of 0.0163 ⁇ m.
  • Example 1 Example of synthesis of acicular titanium oxide powder of the present invention via supercritical hydrothermal synthesis method
  • TiO 2 -anatase manufactured by Wako Pure Chemical Industries, Ltd. was used as a starting material.
  • NaOH aqueous solution adjusted to 10 mol / L was stirred and mixed at a rate of 100 ml. Pour this mixed solution into a platinum container, then seal the platinum container by TIG welding, insert it into a high pressure container, and perform hydrothermal treatment in a platinum container at a temperature of 377 ° C and a pressure of 22.5 MPa for 2 hours in a supercritical state. went.
  • the obtained sample was washed with distilled water three times.
  • the sample washed with water was stirred in a 0.1 mol / L HCl aqueous solution at 50 ° C for 1 hour to perform ion exchange. Further, the sample was washed with water, dried, and then subjected to heat treatment in the atmosphere at 400 ° C for 5 hours to oxidize. A titanium powder was obtained.
  • Example 2 Example of synthesis of acicular titanium oxide powder of the present invention via supercritical hydrothermal synthesis method 10 g of TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry was used as a starting material. A titanium oxide powder was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed in a supercritical state at a temperature of 378 ° C. and a pressure of 22.6 MPa for 1 hour.
  • SSP-M TiO 2 -anatase
  • Example 3 Example of synthesis of acicular titanium oxide powder of the present invention via supercritical hydrothermal synthesis method
  • 10 g of TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry was used as a starting material.
  • a titanium oxide powder was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed in a supercritical state at a temperature of 424 ° C. and a pressure of 37.0 MPa for 1 hour.
  • Example of synthesis of titanium oxide powder by hydrothermal treatment under non-supercritical conditions 10 g of TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry was used as the starting material, and the temperature in the apparatus was 315 A titanium oxide powder was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed at 0 ° C. and a pressure of 23.5 MPa for 1 hour.
  • SSP-M TiO 2 -anatase
  • Example of synthesis of titanium oxide powder by conventional method (hydrothermal treatment at a temperature of 200 ° C or lower) Using 10 g of TiO 2 -anatase from Wako Pure Chemical as the starting material, the temperature inside the device is 185 ° C In the same manner as in Example 1 except that hydrothermal treatment was performed for 8 hours, titanium oxide powder was obtained.
  • Example 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example hydroothermal synthesis temperatures of 377, 378, 424, 315, and 185 ° C., respectively
  • FE-SEM scanning electron microscope
  • the titanium oxide powder synthesized by hydrothermal treatment under non-supercritical conditions (comparative example) and the titanium oxide powder obtained by hydrothermal treatment at 185 ° C for 8 hours (conventional) While all of the examples are fine short fibers, the titanium oxide powders synthesized by the method of the present invention (Examples 1 to 3) all have large short axis diameters and long axis diameters. It was confirmed to have an acicular shape extending in the axial direction.
  • each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example hydroothermal synthesis temperatures of 377, 378, 424, 315, and 185 ° C., respectively
  • heat treatment 400 ° C. for 5 hours an XRD pattern was measured using an X-ray diffractometer.
  • the XRD pattern of each TiO 2 (B) powder is shown in FIG. From the XRD pattern of FIG. 2, it can be seen that the diffraction peak becomes sharper as the hydrothermal treatment temperature becomes higher.
  • a sharp diffraction peak of TiO 2 (B) was observed.
  • each TiO 2 (B) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example hydroothermal synthesis temperatures are 377, 378, 424, 315, and 185 ° C., respectively.
  • Powder heat treatment in air at 400 ° C for 5 hours
  • 600 ° C for 1 hour is heated at 600 ° C for 1 hour
  • 700 ° C for 1 hour is heated at 800 ° C for 1 hour (in air, at a heating rate of 10 ° C / min.)
  • 3 is an XRD pattern when each powder is heated at 600 ° C. for 1 hour
  • FIG. 4 is an XRD pattern when each powder is heated at 700 ° C. for 1 hour
  • FIG. 6 shows each TiO 2 (B) powder (heat treatment 400 ° C.-5 hours) obtained in Example 1, Example 2, and Example 3 (hydrothermal synthesis temperatures of 377, 378, and 424 ° C., respectively)
  • FIG. 7 is an SEM image after heating at 600 ° C. for 1 hour and after heating at 800 ° C. for 1 hour
  • FIG. 7 shows each TiO 2 ( B) SEM image of powder (heat treatment 400 ° C-5 hours), heated at 600 ° C for 1 hour, and then heated at 800 ° C for 1 hour.
  • the TiO 2 (B) powders (Examples 1 to 3) obtained by the synthesis method of the present invention have high temperature stability when heated at 600 to 800 ° C. for 1 hour. Even if it exists, it was confirmed that the acicular shape extended in the major axis direction was maintained.
  • each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example and Conventional Example was heated at 600 ° C. for 1 hour, 700 ° C. for 1 hour, and 800 ° C. for 1 hour.
  • the BET specific surface area of the powder after the measurement was measured using a BET specific surface area measuring device. The results are shown in Table 1 below.
  • the TiO 2 (B) powders (Examples 1 to 3) obtained by the synthesis method of the present invention have a BET specific surface area even when heated at 600 to 800 ° C. for 1 hour.
  • the BET specific surface area greatly changed in the temperature range of 600 to 800 ° C.
  • each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example was measured.
  • the measurement sample was prepared by applying a resin on a Si substrate, sprinkling each TiO 2 (B) powder on the Si substrate, and drying the resin.
  • a commercially available micro device defect analysis system manufactured by Hitachi High-Technologies Corporation, model number: Nano-Prober (registered trademark) N-6000
  • the needle-shaped powder fixed on the Si substrate was directly measured by the four-terminal (Nano-Prober) method. At this time, as shown in FIG.
  • Example 8 a fiber having a width of about 500 nm was selected and carried out.
  • the current-voltage characteristics of the respective TiO 2 (B) powders obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example are shown in FIGS.
  • FIGS. 9 to 12 in the case of acicular titanium oxide powders (Examples 1 to 3) obtained by using the synthesis method of the present invention, current-voltage characteristics with good linearity can be obtained. I understood it.
  • acicular TiO 2 (B) powder extending longitudinally, TiO 2 having such a shape ( B)
  • the powder can be used as an electrode of a dye-sensitized solar cell or a lithium ion battery by utilizing electron conductivity or ionic conductivity in the major axis direction.

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Abstract

Provided is a synthesis method for acicular titanium oxide powder that has excellent temperature stability in the crystal phase thereof. It is possible to synthesize acicular titanium oxide powder that has excellent temperature stability in the crystal phase thereof by: synthesizing (step 1) an acicular alkali-Ti-oxide as an intermediate, by using a strong alkali aqueous solution and performing hydrothermal synthesis in a range greater than or equal to 375°C and 22.5MPa, which is in the supercritical state of water; and heat-treating (step 2) the acicular alkali-Ti-oxide, the intermediate obtained in the previous step, by exchanging the alkali ions with hydrogen ions in a mildly acidic aqueous solution, and then heat-treating at a temperature of 300-500°C in the atmosphere. It is preferable for the temperature and pressure ranges during the hydrothermal synthesis to be 375-430°C and 22.5-40MPa, and for the concentration in the strong alkali aqueous solution to be 8-13 mol/L.

Description

針状酸化チタン粉体の合成法Synthesis method of acicular titanium oxide powder
　本発明は、結晶相の温度安定性に優れた針状酸化チタン粉体を合成するための方法に関する。 The present invention relates to a method for synthesizing acicular titanium oxide powder having excellent temperature stability of a crystal phase.
　酸化チタンTiO2の結晶相には、低温相から順に、ブロンズ相のTiO2(B)、アナターゼ相a-TiO2、ルチル相r-TiO2、ブルッカイト相b-TiO2の４種類が報告されている。そのうち色素増感太陽電池やリチウムイオン電池の電極に使用される酸化チタン粉体には、高電子伝導性や高イオン伝導性が要求されるので、ブロンズ相のTiO2(B)やアナターゼ相a-TiO2が採用される。特に針状のTiO2(B)や他の元素を添加したa-TiO2粉体がその長軸方向に電子やイオンを移動拡散させることで、高発電・高充電効率の電池が作製されると期待されている。しかし、電池の作製や使用に際して、酸化チタンが低電子伝導性や低イオン伝導性の、安定なr-TiO2に相転移し、期待した特性を得るのが困難である。 The crystal phase of titanium oxide TiO 2, in order from the low temperature phase, TiO 2 (B) of the bronze phase, anatase phase a-TiO 2, rutile phase r-TiO 2, four types of brookite phase b-TiO 2 is reported ing. Among them, titanium oxide powders used for electrodes of dye-sensitized solar cells and lithium ion batteries are required to have high electron conductivity and high ion conductivity, so bronze phase TiO 2 (B) and anatase phase a -TiO 2 is adopted. In particular, a-TiO 2 powder added with needle-like TiO 2 (B) and other elements moves and diffuses electrons and ions in the long axis direction to produce a battery with high power generation and high charging efficiency. It is expected. However, in the production and use of batteries, titanium oxide undergoes a phase transition to stable r-TiO 2 with low electron conductivity and low ion conductivity, and it is difficult to obtain the expected characteristics.
　TiO2(B)を合成する方法には、固相法と水熱合成法があり、針状粉体は主として200℃以下の温度（例えば185℃）で強アルカリ溶液を用いた水熱合成法で調製されるが、この条件下で合成した針状TiO2(B)粉は微細であるため、充填率が低く、かつ、結晶相の安定性が低く、容易にr-TiO2に相転移するという問題があった。 There are two methods for synthesizing TiO 2 (B): solid-phase method and hydrothermal synthesis method. Needle-like powder is mainly hydrothermal synthesis method using strong alkaline solution at a temperature of 200 ° C or less (eg 185 ° C). The needle-like TiO 2 (B) powder synthesized under these conditions is fine, so the filling rate is low and the stability of the crystalline phase is low, making it easy to phase transition to r-TiO 2 There was a problem to do.
　ところで、最近では、超臨界水熱合成に関して、フロー装置内で超臨界水を直接混合することにより、出発原料溶液を室温から急加熱し、高結晶性のTiO2-anataseナノ粒子を1.7 秒で合成したという報告がある（非特許文献１）。又、Ti(SO4)2やTiCl4から超臨界水熱合成により20 nm以下の粒子径の球状TiO2が合成できることも知られている（非特許文献２）。
　また、水熱処理後のアルカリチタネートから熱処理を施すまでの間に単位結晶の向きが変わったという報告もある（非特許文献３）。 By the way, recently, with regard to supercritical hydrothermal synthesis, the starting material solution is rapidly heated from room temperature by directly mixing supercritical water in a flow apparatus, and highly crystalline TiO 2 -anatase nanoparticles are obtained in 1.7 seconds. There is a report of synthesis (Non-patent Document 1). It is also known that spherical TiO 2 having a particle diameter of 20 nm or less can be synthesized from Ti (SO 4 ) 2 or TiCl 4 by supercritical hydrothermal synthesis (Non-patent Document 2).
There is also a report that the orientation of the unit crystal has changed between the alkali titanate after hydrothermal treatment and the heat treatment (Non-patent Document 3).
　本発明は、従来技術における上記の問題点を解決し、結晶相の安定性が高く、巨大な針状酸化チタン粉体を合成可能な方法を提供することを課題とする。尚、この際、「針状」には、柱状、棒状などの形状も含まれる。 An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a method capable of synthesizing huge acicular titanium oxide powder with high crystal phase stability. In this case, the “needle shape” includes shapes such as a column shape and a rod shape.
　上記課題を解決可能な本発明の針状酸化チタン粉体の合成方法は、
　工程１：酸化チタン粉末に強アルカリ水溶液を添加して混合溶液を調整し、当該混合溶液を使用して、水の超臨界状態である375℃-22.5 MPa以上の範囲で水熱合成することにより針状アルカリ-Ti-酸化物を中間生成物として合成する工程、及び
　工程２：前記工程１で得られた針状アルカリ-Ti-酸化物を、弱酸性水溶液中でアルカリイオンを水素イオンに置換し、その後300～500℃で大気中にて熱処理する工程
を含むことを特徴とする。 The method for synthesizing the acicular titanium oxide powder of the present invention capable of solving the above problems is as follows.
Step 1: By adding a strong alkaline aqueous solution to titanium oxide powder to prepare a mixed solution, and using the mixed solution, hydrothermal synthesis is performed in the supercritical state of water at a temperature range of 375 ° C. to 22.5 MPa or more. Step of synthesizing acicular alkali-Ti-oxide as an intermediate product, and Step 2: Substituting the alkali-shaped alkali-Ti-oxide obtained in Step 1 with hydrogen ions in weakly acidic aqueous solution. And a heat treatment in the atmosphere at 300 to 500 ° C. after that.
　又、本発明は、上記の特徴を有した針状酸化チタン粉体の合成方法において、上記水熱合成時の温度及び圧力条件が、375℃-22.5 MPaから430℃-40 MPaの範囲であることを特徴とするものでもある。 In the method for synthesizing acicular titanium oxide powder having the above characteristics, the temperature and pressure conditions during the hydrothermal synthesis are in the range of 375 ° C.-22.5375MPa to 430 ° C.-40 MPa. It is also a feature.
　又、本発明は、上記の特徴を有した針状酸化チタン粉体の合成方法において、上記水熱合成に使用される前記強アルカリ水溶液が、アルカリ濃度8～13モル／Ｌの溶液であることを特徴とするものでもある。 Further, in the present invention, in the method for synthesizing acicular titanium oxide powder having the above characteristics, the strong alkaline aqueous solution used for the hydrothermal synthesis is a solution having an alkali concentration of 8 to 13 mol / L. It is also a feature.
　本発明の方法を用いることにより、結晶相の安定性が高い、巨大な針状TiO2(B)粉体を合成することができ、この針状TiO2(B)粉体は、従来のルチルやアナターゼTiO2と比較して、非常に高い電気伝導度（電気伝導率σ）を有している。 By using the method of the present invention, the stability of the crystalline phase is high, it is possible to synthesize a huge acicular TiO 2 (B) powder, the acicular TiO 2 (B) powder, conventional rutile Compared with anatase TiO 2 , it has a very high electric conductivity (electric conductivity σ).
実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度が377、378、424、315、185℃）で得られた各TiO2(B)粉体のSEM像である。SEM images of each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperatures of 377, 378, 424, 315, and 185 ° C.) is there. 実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度が377、378、424、315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）のXRDパターンである。Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) XRD pattern. 実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度が377、378、424、315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）を、600℃で１時間加熱した際のXRDパターンである。Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) is an XRD pattern when heated at 600 ° C for 1 hour. 実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度が377、378、424、315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）を、700℃で１時間加熱した際のXRDパターンである。Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) is an XRD pattern when heated at 700 ° C for 1 hour. 実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度が377、378、424、315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）を、800℃で１時間加熱した際のXRDパターンである。Each TiO 2 (B) powder (heat treatment 400 ° C.) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperature is 377, 378, 424, 315, 185 ° C.) -5 hours) is an XRD pattern when heated at 800 ° C for 1 hour. 実施例１、実施例２、実施例３（水熱合成温度が377、378、424℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）、600℃で１時間加熱後、更に800℃で１時間加熱後のSEM像である。Each TiO 2 (B) powder obtained in Example 1, Example 2 and Example 3 (hydrothermal synthesis temperature 377, 378, 424 ° C.) (heat treatment 400 ° C.-5 hours), 600 ° C. for 1 hour It is a SEM image after heating for 1 hour at 800 ° C after heating. 比較例、従来例（水熱合成温度が315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）、600℃で１時間加熱後、更に800℃で１時間加熱後のSEM像である。Each TiO 2 (B) powder obtained by the comparative example and the conventional example (hydrothermal synthesis temperature is 315, 185 ° C.) (heat treatment 400 ° C.-5 hours), heated at 600 ° C. for 1 hour, and further at 800 ° C. 1 It is a SEM image after time heating. 針状酸化チタン粉体の抵抗を測定する方法を示す図及び、実際の試料の測定状態を示すSEM像である。It is the figure which shows the method of measuring the resistance of acicular titanium oxide powder, and the SEM image which shows the measurement state of an actual sample. 実施例１、実施例２、実施例３（水熱合成温度が377、378、424℃）で得られた各TiO2(B)粉体を用いて、図８に示される測定方法にて測定を行った際の電流‐電圧特性を示すグラフである。Using the TiO 2 (B) powders obtained in Example 1, Example 2, and Example 3 (hydrothermal synthesis temperatures of 377, 378, and 424 ° C.), measurement is performed using the measurement method shown in FIG. It is a graph which shows the current-voltage characteristic at the time of performing. 比較例、従来例（水熱合成温度が315、185℃）で得られた各TiO2(B)粉体を用いて、図８に示される測定方法にて測定を行った際の電流‐電圧特性を示すグラフである。Current-voltage when measured by the measurement method shown in FIG. 8 using each TiO 2 (B) powder obtained in the comparative example and the conventional example (hydrothermal synthesis temperature is 315, 185 ° C.). It is a graph which shows a characteristic. 図９に示された電流‐電圧特性を示す各グラフを拡大したものであり、このグラフにおいては横軸が電流で、縦軸が電圧である。FIG. 10 is an enlarged view of each graph showing the current-voltage characteristics shown in FIG. 9, where the horizontal axis is current and the vertical axis is voltage. 図１０に示された電流‐電圧特性を示す各グラフを拡大したものであり、このグラフにおいては横軸が電流で、縦軸が電圧である。FIG. 11 is an enlarged view of each graph showing the current-voltage characteristics shown in FIG. 10, in which the horizontal axis is current and the vertical axis is voltage. 実施例１、実施例２、実施例３（水熱合成温度が377、378、424℃）で得られた各TiO2(B)粉体についての抵抗値の比較、並びに、測定試料間の抵抗値のばらつきを示すグラフである。Comparison of resistance values for each TiO 2 (B) powder obtained in Example 1, Example 2, and Example 3 (hydrothermal synthesis temperatures of 377, 378, and 424 ° C.), and resistance between measurement samples It is a graph which shows the dispersion | variation in a value. 実施例１、実施例２、実施例３（水熱合成温度が377、378、424℃）で得られた各TiO2(B)粉体と、アナターゼ、ルチルTiO2粉体についての、水熱処理温度と電気伝導度の関係を示すグラフである。Hydrothermal treatment of each TiO 2 (B) powder obtained in Example 1, Example 2, and Example 3 (hydrothermal synthesis temperatures of 377, 378, and 424 ° C.) and anatase and rutile TiO 2 powder It is a graph which shows the relationship between temperature and electrical conductivity.
　以下、本発明の方法における各工程について説明する。
　まず、本発明における工程１では、出発原料として酸化チタン粉末（a-TiO2粉末）を準備し、当該粉末に強アルカリ水溶液を添加して混合溶液を調整し、この混合溶液を使用して、温度・圧力を、水の超臨界条件である375℃-22.5 MPa以上の範囲、好ましくは375℃-22.5 MPaから430℃-40 MPaの範囲で水熱合成し、針状アルカリ-Ti-酸化物を中間生成物として合成する。この際、出発原料としては市販のa-TiO2粉末が使用でき、添加される強アルカリ水溶液としては、NaOH水溶液、KOH水溶液、LiOH水溶液が使用でき、アルカリ濃度としては8～13モル／Ｌが好ましく、特に10モル／Ｌが好ましい。8モル／Ｌ未満の低濃度では粒状粉が生成し、一方、13モル／Ｌより高濃度の強アルカリ水溶液の調整は困難であり、本発明の目的にそぐわない。
　本発明の方法における水熱合成を行う際、処理時間は1～2時間程度で良く、上記の水熱合成に適した容器としては、白金容器、銀容器、金容器が挙げられ、白金容器が特に好ましい。本発明の合成方法を実施する場合、上記の混合溶液を白金容器内に注ぎ入れ、TIG溶接にて白金容器を密閉し、これを高圧容器内に挿入し、白金容器と高圧容器の間の隙間に適当量の水を入れ、高圧容器を加熱し、水の超臨界条件以上の温度及び圧力領域にて水熱合成を行うのが好ましい。なお、試料温度は、白金容器内で測定し、圧力は高圧容器内の圧力を測定している。
　上記の水熱合成条件に限定される理由は、水の臨界点（375℃-22.5 MPa）未満の領域で水熱処理を実施した場合には、次工程（工程２）を行っても巨大な針状TiO2(B)粉体が得られないからである。 Hereinafter, each step in the method of the present invention will be described.
First, in step 1 of the present invention, titanium oxide powder (a-TiO 2 powder) is prepared as a starting material, a strong alkaline aqueous solution is added to the powder to prepare a mixed solution, and this mixed solution is used. Acicular alkali-Ti-oxide is hydrothermally synthesized at a temperature and pressure in the range of 375 ℃ -22.5 MPa or higher, preferably 375 ℃ -22.5 MPa to 430 ℃ -40 MPa, which is the supercritical condition of water. Is synthesized as an intermediate product. At this time, a commercially available a-TiO 2 powder can be used as a starting material, and an aqueous NaOH solution, an aqueous KOH solution, an aqueous LiOH solution can be used as a strong alkaline aqueous solution to be added, and an alkali concentration is 8 to 13 mol / L. 10 mol / L is particularly preferable. At a low concentration of less than 8 mol / L, granular powder is formed. On the other hand, it is difficult to prepare a strong alkaline aqueous solution having a concentration higher than 13 mol / L, which is not suitable for the purpose of the present invention.
When performing the hydrothermal synthesis in the method of the present invention, the treatment time may be about 1 to 2 hours. Examples of the container suitable for the hydrothermal synthesis include a platinum container, a silver container, and a gold container. Particularly preferred. When carrying out the synthesis method of the present invention, the above mixed solution is poured into a platinum container, the platinum container is sealed by TIG welding, this is inserted into the high pressure container, and the gap between the platinum container and the high pressure container It is preferable to carry out hydrothermal synthesis in a temperature and pressure region at or above the supercritical condition of water by adding an appropriate amount of water to the vessel, heating the high pressure vessel. The sample temperature is measured in a platinum container, and the pressure is measured in the high-pressure container.
The reason for being limited to the above hydrothermal synthesis conditions is that when hydrothermal treatment is performed in a region below the critical point of water (375 ° C-22.5 MPa), even if the next step (step 2) is performed, a huge needle This is because no TiO 2 (B) powder can be obtained.
　本発明における工程２では、上記工程１で得られた中間生成物の針状アルカリ-Ti-酸化物を、弱酸性水溶液（例えば塩酸水溶液）中でアルカリイオンを水素イオンに交換し、水洗し、乾燥後、300～500℃で大気中にて熱処理することによって針状TiO2(B)粉体を得る。上記のイオン交換は、0.1～0.5モル／Lの塩酸水溶液中10～80℃で実施することが好ましく、0.1モル／Lの塩酸水溶液中50℃で実施することが特に好ましい。上記熱処理条件としては350～450℃で、2～6時間が好ましく、400℃-5時間が特に好ましい。
　上記の本発明の方法を用いることによって、巨大な針状TiO2(B)粉体が合成でき、この針状TiO2(B)粉体は、700～800℃に加熱しても結晶相の安定性が高い。
　そして、このようにして合成された針状TiO2(B)粉体は、従来のルチルやアナターゼTiO2と比較して、非常に高い電気伝導度を有する。
　以下、本発明の実施例を示して本発明を説明するが、本発明は実施例に記載したものに限定されるものではない。 In Step 2 of the present invention, the needle-like alkali-Ti-oxide of the intermediate product obtained in Step 1 above is exchanged for hydrogen ions in a weakly acidic aqueous solution (for example, aqueous hydrochloric acid solution), washed with water, After drying, acicular TiO 2 (B) powder is obtained by heat treatment in the atmosphere at 300 to 500 ° C. The ion exchange is preferably carried out in a 0.1 to 0.5 mol / L hydrochloric acid aqueous solution at 10 to 80 ° C., particularly preferably in a 0.1 mol / L hydrochloric acid aqueous solution at 50 ° C. The heat treatment conditions are 350 to 450 ° C., preferably 2 to 6 hours, and particularly preferably 400 ° C. to 5 hours.
By using the above-described method of the present invention, a huge acicular TiO 2 (B) powder can be synthesized. Even if the acicular TiO 2 (B) powder is heated to 700 to 800 ° C., it has a crystalline phase. High stability.
The needle-like TiO 2 (B) powder synthesized in this way has a very high electric conductivity as compared with conventional rutile and anatase TiO 2 .
EXAMPLES Hereinafter, although an Example of this invention is shown and this invention is demonstrated, this invention is not limited to what was described in the Example.
　以下の実験を実施するに当たり、出発原料として、２種類の酸化チタン（和光純薬製のTiO2-anatase、堺化学工業製のTiO2-anatase(SSP-M)）を準備した。和光純薬製のTiO2-anataseは、BETによる比表面積Sが57.4 m2/gで、Nbを含有せず、0.0281μmの平均粒径Psを有し、堺化学工業製のTiO2-anatase(SSP-M)は、BETによる比表面積Sが98.8 m2/gで、Nb含有量が0.265質量%で、0.0163μmの平均粒径Psを有していた。なお，平均粒径Psの算出にはPs（μm）=　6／[SDx(TiO2-anatase)]、ただしDx(TiO2-anatase)=3.72 g/cm3を用いた。 In carrying out the following experiments, two types of titanium oxide (TiO 2 -anatase manufactured by Wako Pure Chemical Industries, TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry) were prepared as starting materials. TiO 2 -anatase made by Wako Pure Chemicals has a specific surface area S by BET of 57.4 m 2 / g, does not contain Nb, has an average particle size P s of 0.0281 μm, TiO 2- made by Sakai Chemical Industry Anatase (SSP-M) had a specific surface area S by BET of 98.8 m 2 / g, an Nb content of 0.265% by mass, and an average particle size P s of 0.0163 μm. The average particle size P s was calculated using P s (μm) = 6 / [SD x (TiO 2 -anatase)], where D x (TiO 2 -anatase) = 3.72 g / cm 3 .
実施例１：超臨界水熱合成法を経由した本発明の針状酸化チタン粉体の合成例
　出発原料として、上記の和光純薬製のTiO2-anataseを使用し、この出発原料10 gに対して、10モル／Lに調整したNaOH水溶液を100 mlの割合で攪拌し混合した。この混合溶液を白金容器内に注ぎ，ついでTIG溶接にて白金容器を密閉し、これを高圧容器内に挿入し、白金容器内温度377℃，圧力22.5 MPa，2時間超臨界中で水熱処理を行った。得られた試料は蒸留水を用いて3回水洗した。
　次に、水洗した試料を0.1モル／LのHCl水溶液中50℃で1 時間攪拌して、イオン交換を行い、更に試料を水洗し、乾燥後、大気中400℃, 5 h熱処理を行い、酸化チタン粉体を得た。 Example 1: Example of synthesis of acicular titanium oxide powder of the present invention via supercritical hydrothermal synthesis method As a starting material, TiO 2 -anatase manufactured by Wako Pure Chemical Industries, Ltd. was used as a starting material. On the other hand, NaOH aqueous solution adjusted to 10 mol / L was stirred and mixed at a rate of 100 ml. Pour this mixed solution into a platinum container, then seal the platinum container by TIG welding, insert it into a high pressure container, and perform hydrothermal treatment in a platinum container at a temperature of 377 ° C and a pressure of 22.5 MPa for 2 hours in a supercritical state. went. The obtained sample was washed with distilled water three times.
Next, the sample washed with water was stirred in a 0.1 mol / L HCl aqueous solution at 50 ° C for 1 hour to perform ion exchange. Further, the sample was washed with water, dried, and then subjected to heat treatment in the atmosphere at 400 ° C for 5 hours to oxidize. A titanium powder was obtained.
実施例２：超臨界水熱合成法を経由した本発明の針状酸化チタン粉体の合成例
　出発原料として、上記の堺化学工業製のTiO2-anatase(SSP-M) 10 gを使用し、装置内温度378℃，圧力22.6 MPa，1時間超臨界中で水熱処理を行った以外は実施例１と同様にして、酸化チタン粉体を得た。 Example 2: Example of synthesis of acicular titanium oxide powder of the present invention via supercritical hydrothermal synthesis method 10 g of TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry was used as a starting material. A titanium oxide powder was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed in a supercritical state at a temperature of 378 ° C. and a pressure of 22.6 MPa for 1 hour.
実施例３：超臨界水熱合成法を経由した本発明の針状酸化チタン粉体の合成例
　出発原料として、上記の堺化学工業製のTiO2-anatase(SSP-M) 10 gを使用し、装置内温度424℃，圧力37.0 MPa，1時間超臨界中で水熱処理を行った以外は実施例１と同様にして、酸化チタン粉体を得た。 Example 3: Example of synthesis of acicular titanium oxide powder of the present invention via supercritical hydrothermal synthesis method As a starting material, 10 g of TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry was used. A titanium oxide powder was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed in a supercritical state at a temperature of 424 ° C. and a pressure of 37.0 MPa for 1 hour.
比較例：超臨界でない条件下での水熱処理による酸化チタン粉体の合成例
　出発原料として、上記の堺化学工業製のTiO2-anatase(SSP-M) 10 gを使用し、装置内温度315℃，圧力23.5 MPa，1時間水熱処理を行った以外は実施例１と同様にして、酸化チタン粉体を得た。 Comparative example: Example of synthesis of titanium oxide powder by hydrothermal treatment under non-supercritical conditions 10 g of TiO 2 -anatase (SSP-M) manufactured by Sakai Chemical Industry was used as the starting material, and the temperature in the apparatus was 315 A titanium oxide powder was obtained in the same manner as in Example 1 except that hydrothermal treatment was performed at 0 ° C. and a pressure of 23.5 MPa for 1 hour.
従来例：従来法（200℃以下の温度での水熱処理）による酸化チタン粉体の合成例
　出発原料として、上記の和光純薬製のTiO2-anatase 10 gを使用し、装置内温度185℃で8時間水熱処理を行った以外は実施例１と同様にして、酸化チタン粉体を得た。 Conventional example: Example of synthesis of titanium oxide powder by conventional method (hydrothermal treatment at a temperature of 200 ° C or lower) Using 10 g of TiO 2 -anatase from Wako Pure Chemical as the starting material, the temperature inside the device is 185 ° C In the same manner as in Example 1 except that hydrothermal treatment was performed for 8 hours, titanium oxide powder was obtained.
　上記の実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度がそれぞれ377、378、424、315、185℃）で得られた各TiO2(B)粉体について、走査型電子顕微鏡(FE-SEM)を用いて粉体の形状を測定した。各TiO2(B)粉体のSEM像を図１に示す。
　この図１のSEM像の比較から、超臨界でない条件下での水熱処理により合成された酸化チタン粉（比較例）と、185℃で8時間水熱処理して得られた酸化チタン粉体（従来例）がいずれも微細な短繊維状であるのに対して、本発明の方法により合成された酸化チタン粉体（実施例１～３）はいずれも短軸径及び長軸径が大きく、長軸方向に伸びた針状形状を有していることが確認された。 Regarding each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperatures of 377, 378, 424, 315, and 185 ° C., respectively) Then, the shape of the powder was measured using a scanning electron microscope (FE-SEM). The SEM image of each TiO 2 (B) powder is shown in FIG.
From the comparison of the SEM images in Fig. 1, the titanium oxide powder synthesized by hydrothermal treatment under non-supercritical conditions (comparative example) and the titanium oxide powder obtained by hydrothermal treatment at 185 ° C for 8 hours (conventional) While all of the examples are fine short fibers, the titanium oxide powders synthesized by the method of the present invention (Examples 1 to 3) all have large short axis diameters and long axis diameters. It was confirmed to have an acicular shape extending in the axial direction.
　次に、実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度がそれぞれ377、378、424、315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）について、Ｘ線回折装置を用いてXRDパターンを測定した。各TiO2(B)粉体のXRDパターンを図２に示す。
　この図２のXRDパターンから、水熱処理温度が高温になるにつれて回折ピークがシャープになることがわかり、本発明の方法により合成された酸化チタン粉体（実施例１～３）の場合には、シャープなTiO2(B)の回折ピークが観察された。 Next, each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperatures of 377, 378, 424, 315, and 185 ° C., respectively) With respect to (heat treatment 400 ° C. for 5 hours), an XRD pattern was measured using an X-ray diffractometer. The XRD pattern of each TiO 2 (B) powder is shown in FIG.
From the XRD pattern of FIG. 2, it can be seen that the diffraction peak becomes sharper as the hydrothermal treatment temperature becomes higher. In the case of the titanium oxide powder synthesized by the method of the present invention (Examples 1 to 3), A sharp diffraction peak of TiO 2 (B) was observed.
　次に、上記の実施例１、実施例２、実施例３、比較例、従来例（水熱合成温度がそれぞれ377、378、424、315、185℃）で得られた各TiO2(B)粉体（熱処理大気中400℃-5時間）を、600℃で１時間、700℃で１時間、800℃で１時間加熱し（大気中、昇温速度10℃/min.）、各粉体の結晶相の安定性（温度安定性）を調べた。
　図３は、各粉体を600℃で１時間加熱した際のXRDパターンであり、図４は、各粉体を700℃で１時間加熱した際のXRDパターンであり、図５は、各粉体を800℃で１時間加熱した際のXRDパターンである。
　図３～５のXRDパターンから、比較例及び従来例のTiO2(B)粉体は、結晶相の温度安定性が低く、600～800℃で1時間加熱した場合にTiO2(B)相が消滅して、TiO2(B)からa-TiO2へ相転移するが、実施例１～３のTiO2(B)粉体は、結晶相の温度安定性が高く、600～800℃で1時間加熱した場合であってもTiO2(B)からa-TiO2への相転移が起こりにくく、TiO2(B)相が残存することが確認された。特に実施例３（水熱合成温度が424℃）の酸化チタン粉体は、結晶相の温度安定性が非常に優れていることが確認された。 Next, each TiO 2 (B) obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example (hydrothermal synthesis temperatures are 377, 378, 424, 315, and 185 ° C., respectively). Powder (heat treatment in air at 400 ° C for 5 hours) is heated at 600 ° C for 1 hour, at 700 ° C for 1 hour, and at 800 ° C for 1 hour (in air, at a heating rate of 10 ° C / min.) The crystal phase stability (temperature stability) of was examined.
3 is an XRD pattern when each powder is heated at 600 ° C. for 1 hour, FIG. 4 is an XRD pattern when each powder is heated at 700 ° C. for 1 hour, and FIG. It is an XRD pattern when a body is heated at 800 ° C. for 1 hour.
From the XRD patterns of FIGS. 3 to 5, the TiO 2 (B) powders of the comparative example and the conventional example have low temperature stability of the crystal phase, and the TiO 2 (B) phase when heated at 600 to 800 ° C. for 1 hour. Disappears and a phase transition from TiO 2 (B) to a-TiO 2 occurs. However, the TiO 2 (B) powders of Examples 1 to 3 have high crystal phase temperature stability at 600 to 800 ° C. Even when heated for 1 hour, it was confirmed that the phase transition from TiO 2 (B) to a-TiO 2 hardly occurred and the TiO 2 (B) phase remained. In particular, it was confirmed that the titanium oxide powder of Example 3 (hydrothermal synthesis temperature is 424 ° C.) has very excellent temperature stability of the crystal phase.
　図６は、実施例１、実施例２、実施例３（水熱合成温度がそれぞれ377、378、424℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）、600℃で１時間加熱後、800℃で１時間加熱後のSEM像であり、図７は、比較例、従来例（水熱合成温度がそれぞれ315、185℃）で得られた各TiO2(B)粉体（熱処理400℃-5時間）、600℃で１時間加熱後、800℃で１時間加熱後のSEM像である。
　図６のSEM像からも、本発明の合成方法により得られたTiO2(B)粉体（実施例１～３）は、温度安定性が高く、600～800℃で1時間加熱した場合であっても長軸方向に伸びた針状形状を維持することが確認された。 FIG. 6 shows each TiO 2 (B) powder (heat treatment 400 ° C.-5 hours) obtained in Example 1, Example 2, and Example 3 (hydrothermal synthesis temperatures of 377, 378, and 424 ° C., respectively) FIG. 7 is an SEM image after heating at 600 ° C. for 1 hour and after heating at 800 ° C. for 1 hour, and FIG. 7 shows each TiO 2 ( B) SEM image of powder (heat treatment 400 ° C-5 hours), heated at 600 ° C for 1 hour, and then heated at 800 ° C for 1 hour.
Also from the SEM image of FIG. 6, the TiO 2 (B) powders (Examples 1 to 3) obtained by the synthesis method of the present invention have high temperature stability when heated at 600 to 800 ° C. for 1 hour. Even if it exists, it was confirmed that the acicular shape extended in the major axis direction was maintained.
　更に、実施例１、実施例２、実施例３、比較例、従来例で得られた各TiO2(B)粉体を600℃で１時間、700℃で１時間、800℃で１時間加熱した後の粉体について、BET比表面積測定装置を用いてBET比表面積を測定した。その結果を、以下の表１に示す。 Furthermore, each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example and Conventional Example was heated at 600 ° C. for 1 hour, 700 ° C. for 1 hour, and 800 ° C. for 1 hour. The BET specific surface area of the powder after the measurement was measured using a BET specific surface area measuring device. The results are shown in Table 1 below.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　上記の表１の結果から、本発明の合成方法により得られたTiO2(B)粉体（実施例１～３）は、600～800℃で1時間加熱した場合であってもBET比表面積は大きく変化しないが、比較例及び従来例の場合は、600～800℃の温度範囲においてBET比表面積が大きく変化することが確認された。 From the results of Table 1 above, the TiO 2 (B) powders (Examples 1 to 3) obtained by the synthesis method of the present invention have a BET specific surface area even when heated at 600 to 800 ° C. for 1 hour. However, in the case of the comparative example and the conventional example, it was confirmed that the BET specific surface area greatly changed in the temperature range of 600 to 800 ° C.
　次に、上記の実施例１、実施例２、実施例３、比較例、従来例で得られた各TiO2(B)粉体についての電気伝導度を測定した。測定用試料は、Si基板上に樹脂を塗り、その上に各TiO2(B)粉体をふりかけ、樹脂を乾燥させることにより作製した。
　針状TiO2(B)粉体の電気伝導度の測定には、市販の微小デバイス欠陥解析システム（株式会社日立ハイテクノロジーズ製、型番：ナノ・プローバ（登録商標）N-6000）を使用し、Si基板上に固定された針状粉を直接四端子（Nano-Prober）法にて測定し、この際、図８に示されるようにして、幅が500 nm程度のファイバーを選択して実施した。
　前記の実施例１、実施例２、実施例３、比較例、従来例で得られた各TiO2(B)粉体についての電流‐電圧特性を、図９～図１２に示す。
　図９～図１２に示されるように、本発明の合成法を用いて得られた針状酸化チタン粉体（実施例１～３）の場合、線形性が良好な電流‐電圧特性が得られることがわかった。 Next, the electrical conductivity of each TiO 2 (B) powder obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example was measured. The measurement sample was prepared by applying a resin on a Si substrate, sprinkling each TiO 2 (B) powder on the Si substrate, and drying the resin.
To measure the electrical conductivity of acicular TiO 2 (B) powder, a commercially available micro device defect analysis system (manufactured by Hitachi High-Technologies Corporation, model number: Nano-Prober (registered trademark) N-6000) is used. The needle-shaped powder fixed on the Si substrate was directly measured by the four-terminal (Nano-Prober) method. At this time, as shown in FIG. 8, a fiber having a width of about 500 nm was selected and carried out. .
The current-voltage characteristics of the respective TiO 2 (B) powders obtained in Example 1, Example 2, Example 3, Comparative Example, and Conventional Example are shown in FIGS.
As shown in FIGS. 9 to 12, in the case of acicular titanium oxide powders (Examples 1 to 3) obtained by using the synthesis method of the present invention, current-voltage characteristics with good linearity can be obtained. I understood it.
　又、上記実施例１～実施例３で得られた各TiO2(B)粉体についての電気抵抗値の比較、並びに、測定試料間の抵抗値のばらつきを示す図１３のグラフから、実施例２のTiO2(B)粉体が抵抗値最小で、ばらつきも小さく、実施例１のTiO2(B)粉体が抵抗値最大であることがわかった。これは、出発原料である酸化チタン中に含有されるNbの影響によるものと考えられる。 Further, from the graph of FIG. 13 showing the comparison of the electric resistance values of the respective TiO 2 (B) powders obtained in Examples 1 to 3 and the resistance values among the measurement samples, the examples are shown. 2 of TiO 2 (B) powder resistance minimum, the variation is small, it was found that TiO 2 (B) powder of example 1 is the maximum resistance value. This is considered to be due to the influence of Nb contained in the starting titanium oxide.
　上記実施例１～実施例３で得られた各TiO2(B)粉体と、アナターゼ、ルチルTiO2粉体についての、水熱処理温度と電気伝導度の関係を示す図１４のグラフから、本発明の合成法を用いて得られた針状酸化チタン粉体（実施例１～３）の電気伝導度は、従来のアナターゼ、ルチルTiO2と比較して、電気伝導度が約１０10～１０11倍高いことを確認した。 From the graph of FIG. 14 showing the relationship between hydrothermal treatment temperature and electrical conductivity for each TiO 2 (B) powder obtained in Examples 1 to 3 above, anatase and rutile TiO 2 powder, The electrical conductivity of the acicular titanium oxide powders (Examples 1 to 3) obtained by using the synthesis method of the invention is about 10 10 to 10 compared with the conventional anatase and rutile TiO 2. 11 times higher.
　本発明の合成方法を用いることによって、結晶相の温度安定性に優れ、長軸方向に伸びた針状のTiO2(B)粉体を合成することができ、このような形状のTiO2(B)粉体は、長軸方向への電子伝導性やイオン伝導性を利用して、色素増感型太陽電池やリチウムイオン電池の電極として利用することが可能である。 By using the synthesis method of the present invention, excellent temperature stability of the crystal phase, can be synthesized acicular TiO 2 (B) powder extending longitudinally, TiO 2 having such a shape ( B) The powder can be used as an electrode of a dye-sensitized solar cell or a lithium ion battery by utilizing electron conductivity or ionic conductivity in the major axis direction.

Claims (3)

  1. 　針状酸化チタン粉体の合成法であって、当該方法が、
    　工程１：酸化チタン粉末に強アルカリ水溶液を添加して混合溶液を調整し、当該混合溶液を使用して、水の超臨界状態である375℃-22.5 MPa以上の範囲で水熱合成することにより針状アルカリ-Ti-酸化物を中間生成物として合成する工程、及び
    　工程２：前記工程１で得られた針状アルカリ-Ti-酸化物を、弱酸性水溶液中でアルカリイオンを水素イオンに置換し、その後300～500℃で大気中にて熱処理する工程
    を含むことを特徴とする針状酸化チタン粉体の合成法。     A method for synthesizing acicular titanium oxide powder, the method comprising:
    Step 1: By adding a strong alkaline aqueous solution to titanium oxide powder to prepare a mixed solution, and using the mixed solution, hydrothermal synthesis is performed in the supercritical state of water at a temperature range of 375 ° C. to 22.5 MPa or more. Step of synthesizing acicular alkali-Ti-oxide as an intermediate product, and Step 2: Substituting the alkali-shaped alkali-Ti-oxide obtained in Step 1 with hydrogen ions in weakly acidic aqueous solution. And thereafter, a method of synthesizing acicular titanium oxide powder, comprising a step of heat treatment in the atmosphere at 300 to 500 ° C.
  2. 　上記水熱合成時の温度及び圧力条件が、375℃-22.5 MPaから430℃-40 MPaの範囲であることを特徴とする請求項１に記載の針状酸化チタン粉体の合成法。 The method for synthesizing acicular titanium oxide powder according to claim 1, wherein the temperature and pressure conditions during the hydrothermal synthesis are in the range of 375 ° C-22.5 MPa to 430 ° C-40 MPa.
  3. 　上記水熱合成に使用される前記強アルカリ水溶液が、アルカリ濃度8～13モル／Ｌの溶液であることを特徴とする請求項１又は２に記載の針状酸化チタン粉体の合成法。 The method for synthesizing acicular titanium oxide powder according to claim 1 or 2, wherein the strong alkaline aqueous solution used for the hydrothermal synthesis is a solution having an alkali concentration of 8 to 13 mol / L.
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