JP2006045647A - Method and device for forming chromium dioxide thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for forming a thin film of chromium dioxide having high safety, wherein chromium dioxide is directly formed from chromium. <P>SOLUTION: The forming device 100 for a chromium dioxide thin film comprises: a pressure resisting vessel 10 which is charged with a solution 16 of pH 1.5 to 4.0; a first electrode 12 made of a metal substrate comprising chromium on the surface which is installed in the pressure resisting vessel 10 and is dipped into the solution 16; a second electrode 14 to form a counter electrode to the first electrode which is installed in the pressure resisting vessel 10 and is dipped into the solution 16; a potential source 26 which is connected with a platinum wire 22 from the first electrode 12 and a platinum wire 24 from the second electrode 14, and controls the electrode potential of the first electrode 12 and the second electrode 14 to -4.0 to -2.0 V; and a warming apparatus (not shown in Figure) which warms the solution 16 in the pressure resisting vessel 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for forming a chromium dioxide thin film that directly forms a chromium dioxide thin film from chromium by performing a hydrothermal treatment while applying an electric potential.

Chromium dioxide (CrO ₂ ) is generally used in powder form as a magnetic recording medium. Usually, chromium dioxide has a rutile crystal structure. When CrO ₃ or Cr ₂ O ₅ is subjected to hydrothermal treatment (400 ° C.) in the presence of microcrystals of several tens of nanometers of rutile oxide, the microcrystals are used as nuclei. Chromium needle crystals grow.

Further, as starting materials, chromic anhydride (CrO ₃ ), chromyl chloride (CrO ₂ Cl ₂ ), ammonium chromate ((NH ₄ ) ₂ CrO ₄ ), ammonium dichromate ((NH ₄ ) ₂ Cr ₂ O ₇ ) A magnetic recording medium in which a deposited film of chromium dioxide is formed on a support using a compound containing a hexavalent chromium ion, such as a reaction carried out under high pressure heating, particularly a thermal decomposition reaction under high pressure heating in an oxygen atmosphere Has been proposed (for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-106835

  However, the method for producing a deposited film of chromium dioxide proposed in Patent Document 1 described above uses a compound containing hexavalent chromium ions, and the hexavalent chromium ions come into contact with the body or mucous membrane. Toxic. On the other hand, in recent years, the trend toward green chemicals has increased, and there has been a shift toward avoiding the use of toxic compounds as much as possible.

  Further, in Patent Document 1, although a chromium dioxide deposition film can be formed, a dense thin film of chromium dioxide has not been produced.

  This invention is made | formed in view of the said subject, and it aims at providing the formation method and forming apparatus of the chromium dioxide thin film which form a chromium dioxide thin film directly from chromium.

  In order to achieve the above object, the method and apparatus for forming a chromium dioxide thin film of the present invention have the following characteristics.

  (1) A metal substrate having chromium on its surface is used as one electrode, and in a solution having a pH of 1.5 or more and 4.0 or less, the electrode potential is −4.0 V or more and −2.0 V or less with respect to the other electrode. The method of forming a chromium dioxide thin film comprises forming a chromium dioxide thin film on a metal substrate having chromium on its surface by performing hydrothermal electrochemical treatment.

  According to the method for forming a chromium dioxide thin film, chromium on a metal substrate having chromium on the surface can be directly formed into chromium dioxide by hydrothermal electrochemical treatment. Therefore, it is not necessary to produce chromium dioxide through a compound containing hexavalent chromium ions having toxicity as in the prior art, and safety is further improved. Further, since the hydrothermal electrochemical treatment is used, a dense chromium dioxide thin film can be formed on the metal substrate.

  (2) In the method for forming a chromium dioxide thin film according to (1) above, the other electrode is a platinum electrode.

  Since the platinum electrode is a stable electrode without undergoing an electrochemical reaction by itself, a chromium dioxide thin film can be efficiently generated on the metal substrate of one of the electrodes.

  (3) In the method for forming a chromium dioxide thin film according to (1) or (2), the solution is a sulfuric acid solution.

  In particular, when the other electrode is a platinum electrode, if it is a sulfuric acid solution, the electrochemical reaction is stable, and a thin film of chromium dioxide can be efficiently produced on the metal substrate of one electrode.

  (4) In the method for forming a chromium dioxide thin film according to any one of (1) to (3), the hydrothermal electrochemical treatment is performed by saturation of water at a temperature of 100 ° C. to 250 ° C. and a pressure of the treatment temperature. Electrochemical treatment is performed by involving high-temperature and high-pressure water at a pressure higher than the vapor pressure.

  In particular, the production of a single-phase thin film of chromium dioxide is promoted under the conditions of the hydrothermal electrochemical treatment.

  (5) a pressure-resistant container filled with a solution having a pH of 1.5 or more and 4.0 or less, a first electrode made of a metal substrate having chromium on the surface, which is installed in the pressure-resistant container and immersed in the solution; A second electrode that is installed in the pressure-resistant container and is immersed in the solution, and a counter electrode; a potential source that adjusts the electrode potential of the first electrode and the second electrode; A chromium dioxide thin film forming apparatus having a heating device for heating the solution in the pressure vessel.

  According to the apparatus for forming a chromium dioxide thin film, chromium on a metal substrate having chromium on the surface can be directly produced in chromium dioxide by hydrothermal electrochemical treatment. Therefore, as described above, there is no need to generate chromium dioxide through a compound containing hexavalent chromium ions having toxicity as in the prior art, and safety is further improved. Further, since the hydrothermal electrochemical treatment is used, a dense chromium dioxide thin film can be formed on the metal substrate.

  (6) In the chromium dioxide thin film forming apparatus according to (5) above, the potential source adjusts the electrode potential of the first electrode and the second electrode to −4.0 V or more and −2.0 V or less. .

  By adjusting to the above electrode potential, a single-layer chromium dioxide thin film can be formed.

  (7) In the chromium dioxide thin film forming apparatus according to (5) or (6), the first electrode is a platinum electrode.

  As described above, since the platinum electrode is a stable electrode without undergoing an electrochemical reaction itself, a chromium dioxide thin film can be efficiently generated on the metal substrate of one electrode.

  (8) In the chromium dioxide thin film forming apparatus according to any one of (5) to (7), the solution is a sulfuric acid solution.

  As described above, in particular, when the other electrode is a platinum electrode, if it is a sulfuric acid solution, the electrochemical reaction is stabilized, and a thin film of chromium dioxide can be efficiently generated on the metal substrate of one electrode. .

  (9) In the chromium dioxide thin film forming apparatus according to any one of (5) and (8), the heating device heats the solution in the pressure vessel to 100 ° C. or more and 250 ° C. or less. .

  By making it the conditions of the said hydrothermal electrochemical treatment, the production | generation of the single phase thin film of especially chromium dioxide can be accelerated | stimulated.

  (10) A fuel cell separator having a chromium dioxide thin film formed by the method of forming a chromium dioxide thin film according to any one of (1) to (4) above.

  A fuel cell separator in which a dense chromium dioxide thin film is formed is obtained, and the cell efficiency of the fuel cell is also improved.

  According to the present invention, it is possible to form a dense chromium dioxide thin film with high safety, in which chromium having no toxicity is directly generated in chromium dioxide.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Production method of chromium dioxide thin film]
In the method for forming a chromium dioxide thin film according to the present embodiment, a metal substrate having chromium on the surface is used as one electrode, and in a solution having a pH of 1.5 or higher and 4.0 or lower, the other electrode is −4.0 V. This is a method of forming a chromium dioxide thin film on a metal substrate having chromium on its surface by performing hydrothermal electrochemical treatment under an electrode potential of −2.0 V or less.

  Here, the hydrothermal electrochemical treatment refers to performing an electrochemical treatment under the conditions of “hydrothermal reaction”, which is a reaction involving high-temperature and high-pressure water at 100 ° C. and 1 atm (0.1 MPa) or more. . In the above-mentioned “hydrothermal reaction”, when water becomes high temperature and high pressure, the ionic product increases and the dielectric constant and viscosity decrease.

As described above, the pH of the solution is preferably 1.5 or more and 4.0 or less, and more preferably 1.6 or more and 3.5 V or less. When the pH of the solution is less than 1.5 or exceeds 4.0, it is difficult to form a single-phase thin film of chromium dioxide (CrO ₂ ) on a metal substrate having Cr on the surface.

As the solution, for example, a sulfuric acid solution (H ₂ SO ₄ aq.), A hydrochloric acid solution, or the like can be used. However, as described later, when a platinum electrode is used as the other electrode, a sulfuric acid solution is used. Is preferred. Since the electrochemical reaction of the platinum electrode in the sulfuric acid solution is stable, a thin film of chromium dioxide can be efficiently produced on the metal substrate of one electrode.

  The electrode potential of one electrode which is a metal substrate having Cr on the surface and the other electrode which is a counter electrode is preferably −4.0V or more and −2.0V, more preferably −3.5V or more and −2.0V. It is as follows. Outside this range, it is difficult to produce a single phase thin film of chromium dioxide on a metal substrate having Cr on its surface.

  Examples of the other electrode described above include a platinum electrode, a gold electrode, and a mercury amalgam electrode. Since these are stable electrodes without undergoing an electrochemical reaction themselves, a chromium dioxide thin film can be efficiently generated on the metal substrate of one of the electrodes. Here, when a sulfuric acid solution is used as the solution, a platinum electrode is preferable for the above reason.

  The hydrothermal electrochemical treatment is preferably performed by involving high-temperature and high-pressure water having a pressure of 100 ° C. or higher and 250 ° C. or lower and a pressure equal to or higher than the saturated vapor pressure of water at the treatment temperature. Outside the above range, it is difficult to produce a single phase thin film of chromium dioxide on a metal substrate having Cr on its surface.

  Depending on the desired thickness of the chromium dioxide thin film, it is desirable to appropriately select the energization time during which the potential is applied in the hydrothermal electrochemical treatment. In addition, depending on the film thickness of the chromium dioxide single-phase thin film, It is desirable to appropriately adjust the thickness of the Cr layer on the metal substrate.

[Chromium dioxide thin film forming equipment]
Next, the chromium dioxide thin film forming apparatus 100 of the present embodiment will be described below with reference to FIG.

  As shown in FIG. 1, a chromium dioxide thin film forming apparatus 100 includes a pressure-resistant container 10 filled with a solution 16 and a metal substrate having chromium placed on the surface and installed in the pressure-resistant container 10 and immersed in the solution 16. A first electrode 12; a second electrode 14 which is placed in the pressure vessel 10 and is immersed in the solution 16; and a counter electrode; a platinum wire 22 and a second electrode from the first electrode 12; A platinum wire 24 from the electrode 14 is connected to a potential source 26 that adjusts the electrode potential of the first electrode 12 and the second electrode 14, and a gas introduction path that constitutes a pressurizing device that pressurizes the inside of the pressure vessel 10. 18, a valve 20, and a heating device (not shown) for heating the solution 16 in the pressure vessel 10.

  The pressure vessel 10 is preferably capable of withstanding pressurization up to at least 4.02 MPa (maximum temperature in hydrothermal electrochemical treatment: saturated vapor pressure of water at 250 ° C.). As the material of the pressure vessel, for example, a stainless steel material such as SUS304 or SUS316 is preferable. An autoclave may be used as the pressure vessel 10.

As described above, the pH of the solution 16 is preferably 1.5 or more and 4.0 or less, more preferably 1.6 or more and 3.5 V or less. For example, a sulfuric acid solution (H ₂ SO ₄ aq.), A hydrochloric acid solution, or the like can be used as the solution 16. However, as described below, when a platinum electrode is used as the second electrode 14, sulfuric acid solution is used. It is preferable to use a solution. Since the electrochemical reaction of the platinum electrode in the sulfuric acid solution is stable, a thin film of chromium dioxide can be efficiently generated on the metal substrate of the first electrode 12.

  The potential source 26 adjusts the electrode potential of the first electrode and the second electrode to −4.0 V to −2.0 V, preferably 3.5 V to −2.0 V. Outside this range, it is difficult to produce a single phase thin film of chromium dioxide on a metal substrate having Cr on its surface.

  It is preferable that the thickness of the Cr layer on the surface of the first electrode 12 is appropriately adjusted according to the thickness of the single phase thin film of chromium dioxide formed on the substrate of the first electrode 12. In addition, it is preferable that the metal of the metal substrate which has Cr on the surface is a metal with high acid resistance, and chromium, Ta, Nb, Ti, Cu, Mo, W, Ni, Monel, Hastelloy ), Nickel alloys such as Inconel, stainless steel (for example, SUS316L), and the like.

  Examples of the second electrode 14 include a platinum electrode, a gold electrode, and a mercury amalgam electrode as described above. Since these are stable electrodes without undergoing an electrochemical reaction themselves, a chromium dioxide thin film can be efficiently generated on the metal substrate of one of the electrodes.

  The hydrothermal electrochemical treatment is preferably performed by involving high-temperature and high-pressure water having a pressure of 100 ° C. or higher and 250 ° C. or lower and a pressure equal to or higher than the saturated vapor pressure of water at the treatment temperature. Outside the above range, it is difficult to produce a single phase thin film of chromium dioxide on a metal substrate having Cr on its surface.

  A heating device (not shown) is provided on the outer peripheral surface of the pressure vessel 10 so as to heat the solution 16 in the pressure vessel 10 to 100 ° C. or more and 250 ° C. or less. An oil bath installed on the outer periphery may be used.

  Next, the operation of the chromium dioxide thin film forming apparatus will be described.

  First, the pressure vessel 10 is filled with an acidic solution 16 adjusted to a desired pH, for example, 1.5 to 4.0. Next, the first electrode 12 made of a metal substrate having chromium on its surface and the second electrode 14 as a counter electrode are immersed in the solution 16. Next, the valve 20 is opened and nitrogen gas as an inert gas is introduced into the pressure vessel 10 through the gas introduction path 18 to raise the pressure to a desired pressure, and the inside of the pressure vessel 10 is heated using a heating device. Heating is performed to obtain a desired high-temperature and high-pressure state, for example, the above-described high-temperature and high-pressure state of 100 ° C. or higher and 250 ° C. or lower and a pressure higher than the saturated vapor pressure of water at this treatment temperature. Subsequently, a desired potential, for example, −4.0 V or more, is applied to both electrodes from the potential source 26 via the platinum wire 22 connected to the first electrode 12 and the platinum wire 24 connected to the second electrode 14. Apply a potential of -2.0V or less. And it supplies with electricity from the potential source 26 until the film thickness of a predetermined chromium dioxide single phase thin film is formed on the first electrode 12.

  Thereby, a chromium dioxide single-phase thin film having a desired thickness is formed on the first electrode 12.

[Fuel cell separator]
The separator for a fuel cell according to the present embodiment uses the above-described method for forming a chromium dioxide thin film according to the present embodiment, using a metal substrate having a Cr layer formed on the surface of a substrate used as a separator as one electrode or the first electrode. In addition, a chromium dioxide single-phase thin film can be easily formed on the separator surface using the forming apparatus.

  EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail, this invention is not limited only to these Examples.

(Examples 1-11, Comparative Examples 1-11)
Using the apparatus shown in FIG. 1, a stainless steel (SUS316) autoclave having an internal volume of 500 mL is used as the pressure vessel 10. In this autoclave, the Cr substrate is used as the first electrode 12, and the platinum electrode is used as the second electrode 14. 200 mL of a sulfuric acid solution having a pH of 1.25 to 4.5 is placed in a PTFE (polytetrafluoroethylene) beaker, and electrolytic treatment is applied to a power failure of −4.0 V to +2.0 V with respect to a platinum electrode as a reference. The test was performed at 300 ° C. for 16 hours. The results are shown in Table 1. The generation confirmation of CrO ₂ single phase was identified CrO2 from the crystalline form with an X-ray diffractometer.

As shown in part in Table 1 and FIG. 2, chromium dioxide (100 to 200 ° C.) at an electrode potential of −4.0 to −2.0 V in a solution having a pH of 1.5 to 4.0 A CrO ₂ ) single phase thin film was obtained. In FIG. 2, the Cr substrate is designated as the first electrode, the Pt electrode is designated as the second electrode, the pH is 2 with sulfuric acid solution, and the potential is −4.0 V to −1.0 Vvs. It is the result of having measured the pattern of the thin film formed on Cr board | substrate after performing 16 hours by CE using XRD (X-Ray Diffractometer: X-ray diffractometer).

Example 12
Instead of the first electrode 12 made of the Cr substrate in Example 1, a sample plate of stainless steel SUS316L having a Cr layer formed on the surface by sputtering was used as the first electrode 12, according to Example 1, When hydrothermal electrochemical treatment was performed, similarly, in a solution having a pH of 1.5 or more and 4.0 or less, chromium dioxide (100 to 200 ° C.) was applied at an electrode potential of −4.0 V or more and −2.0 V or less. A CrO ₂ ) single phase thin film was obtained.

(Comparative Example 12)
As in Example 1, the treatment was carried out with a sulfuric acid solution having a pH of 1 to 3 without applying a potential, but the peak observed at pH 1.06 or higher was only due to the Cr substrate, and no product was observed. It was. In addition, the main peaks appearing at 2θ = 29.08 ° and 42.32 ° of the product having a pH of 1.04 or less correspond to CrO ₂ , but have the same level of intensity as the CrO ₂ peak. An unknown phase peak was also observed, and a single phase of CrO ₂ was not obtained.

  The method and apparatus for forming a chromium dioxide thin film of the present invention is useful for applications such as production of a separator for a fuel cell and production of a magnetic recording medium.

It is the schematic which shows the structure of the formation apparatus of the chromium dioxide thin film of this invention. The X-ray diffraction apparatus is a diagram showing the results of identification of the CrO ₂ from the crystalline form.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Pressure-resistant container, 12 1st electrode, 14 2nd electrode, 16 Solution, 18 Gas introduction path, 20 Valve, 22, 24 Platinum wire, 26 Potential source, 100 Chromium dioxide thin film formation apparatus.

Claims (10)

  A metal substrate having chromium on its surface is used as one electrode, and in a solution having a pH of 1.5 or higher and 4.0 or lower, water is applied to the other electrode at an electrode potential of −4.0 V or higher and −2.0 V or lower. A method for forming a chromium dioxide thin film, comprising performing a thermoelectrochemical treatment to form a chromium dioxide thin film on a metal substrate having chromium on the surface. In the formation method of the chromium dioxide thin film of Claim 1,
The method of forming a chromium dioxide thin film, wherein the other electrode is a platinum electrode. In the formation method of the chromium dioxide thin film of Claim 1 or Claim 2,
The method for forming a chromium dioxide thin film, wherein the solution is a sulfuric acid solution. In the formation method of the chromium dioxide thin film of any one of Claims 1-3,
The hydrothermal electrochemical treatment is carried out by involving high temperature and high pressure water having a pressure of 100 ° C. or higher and 250 ° C. or lower and a pressure equal to or higher than the saturated vapor pressure of water at the treatment temperature. Forming method. a pressure resistant container filled with a solution having a pH of 1.5 or more and 4.0 or less,
A first electrode comprising a metal substrate having chromium on its surface, which is placed in the pressure vessel and immersed in the solution;
A second electrode that is installed in the pressure-resistant container and that is counter to the first electrode that is immersed in the solution;
A potential source for adjusting an electrode potential between the first electrode and the second electrode;
A heating device for heating the solution in the pressure vessel;
An apparatus for forming a chromium dioxide thin film, comprising: The apparatus for forming a chromium dioxide thin film according to claim 5,
The said potential source adjusts the electrode potential of a 1st electrode and a 2nd electrode to -4.0V or more and -2.0V or less, The formation apparatus of the chromium dioxide thin film characterized by the above-mentioned. In the formation apparatus of the chromium dioxide thin film of Claim 5 or Claim 6,
The apparatus for forming a chromium dioxide thin film, wherein the first electrode is a platinum electrode. In the formation apparatus of the chromium dioxide thin film of any one of Claims 5-7,
An apparatus for forming a chromium dioxide thin film, wherein the solution is a sulfuric acid solution. In the formation apparatus of the chromium dioxide thin film of any one of Claim 5 or Claim 8,
The said heating apparatus heats the solution in the said pressure-resistant container to 100 to 250 degreeC, The chromium dioxide thin film formation apparatus characterized by the above-mentioned.   The fuel cell separator which has the chromium dioxide thin film formed by the formation method of the chromium dioxide thin film of any one of Claims 1-4.

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