JP2018104806A - Titanium material, separator, cell and solid polymer fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium material excellent in conductivity, corrosion resistance and hydrogen embrittlement resistance.SOLUTION: There is provided a titanium material having a base material consisting of pure titanium or a titanium alloy and a titanium oxide coating formed on the base material and containing a main phase. The main phase is a crystal phase corresponding to a maximum peak excluding peaks corresponding to an α-Ti phase and a β-Ti phase in peaks obtained by thin film X ray diffraction analysis with an incident angle of 0.3° on a surface layer of the titanium material and one of TiOphases, wherein n is an integer of 1 to 9. Thickness of the titanium oxide coating is 30 to 500 nm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a titanium material, a separator of a polymer electrolyte fuel cell using the titanium material, a cell using the separator, and a polymer electrolyte fuel cell using the cell.

Examples of the use of the metal material having excellent conductivity include a battery current collector and a battery case. In the fuel cell application, such a metal material is used as a metal current collector separator material. The metal material used for the separator material is required to have corrosion resistance and hydrogen embrittlement resistance. A titanium material is used as a metal material excellent in corrosion resistance and hydrogen embrittlement resistance. The reason why the titanium material has corrosion resistance is that an oxide film mainly composed of TiO ₂ is formed on the surface of the titanium material to protect the base material. The titanium material has hydrogen embrittlement resistance because the entry of hydrogen is shielded by the presence of the oxide film described above, and hydrogen embrittlement can be suppressed.

An oxide film mainly composed of TiO ₂ is useful for improving corrosion resistance and hydrogen embrittlement resistance, but is poor in conductivity and is an obstacle to utilizing the original conductivity of the metal constituting the base material. It has become. As titanium materials having hydrogen embrittlement resistance, the following reports have been made.

Patent Document 1 discloses a titanium material in which the Ti phase contains Cu up to the solid solubility limit by adding Cu in an amount not less than the solid solubility limit and depositing a certain amount of Ti ₂ Cu phase. . This titanium material is said to have high hydrogen absorption resistance and improved hydrogen embrittlement resistance.

  Patent Document 2 discloses a titanium alloy to which Zr or Hf is added. It is said that the effect of suppressing hydrogen absorption can be obtained by adding Zr or Hf.

  Patent Document 3 discloses a titanium material in which a titanium hydride-containing layer is formed on a titanium surface to improve hydrogen embrittlement resistance. In this titanium material, hydride is precipitated in advance by forcibly introducing hydrogen by cathode electrolysis, and this titanium hydride-containing layer is used as a barrier against hydrogen.

  Patent Document 4 discloses a fuel cell separator including a base material made of titanium or a titanium alloy, a conductive carbon layer covering the surface, and an intermediate layer provided between the base material and the carbon layer. ing. The intermediate layer contains titanium carbide and has an oxygen content of 0.1 to 40 atomic%. This separator is said to be excellent in corrosion resistance and maintain a low contact resistance for a long period of time.

JP 2013-1973 Japanese Patent No. 2006-291263 JP 2005-36314 A JP 2014-22250 A

Toshiki Sato and one other, "Characteristics of Titanium Separator for Polymer Electrolyte Fuel Cell Coated with Graphite", Kobe Steel Technical Report, Vol. 65 No. 2 (Sep. 2015)

  In patent documents 1-3, corrosion resistance and electroconductivity are not fully examined. In patent document 4, although corrosion resistance and electroconductivity are examined, an intermediate | middle layer is granular and workability is inadequate as a material for separators.

  An object of the present invention is to provide a titanium material excellent in conductivity, corrosion resistance, and hydrogen embrittlement resistance, and a separator for a polymer electrolyte fuel cell. Another object of the present invention is to provide a polymer electrolyte fuel cell and a polymer electrolyte fuel cell capable of maintaining high power generation efficiency.

The titanium material of the embodiment of the present invention is
A base material made of pure titanium or a titanium alloy;
A titanium oxide film formed on the base material and including a main phase,
The main phase is the maximum except for the peaks corresponding to the α-Ti phase and β-Ti phase among the peaks obtained by thin film X-ray diffraction analysis at an incident angle of 0.3 ° for the surface layer of the titanium material. A crystal phase corresponding to a peak and any of Ti _n O _(2n-1) (n is an integer of 1 to 9) phase,
The titanium oxide film is a titanium material having a thickness of 30 to 500 nm.

The separator of the polymer electrolyte fuel cell according to the embodiment of the present invention includes the titanium material.
A cell of a polymer electrolyte fuel cell according to an embodiment of the present invention includes the separator.
A polymer electrolyte fuel cell according to an embodiment of the present invention includes the cell.

  The titanium material and the separator of the polymer electrolyte fuel cell are excellent in conductivity, corrosion resistance, and hydrogen embrittlement resistance. The polymer electrolyte fuel cell and the polymer electrolyte fuel cell can maintain high power generation efficiency. This titanium material can also be used as a component for electrical contacts in environments where brittle fracture due to hydrogen absorption is a problem, such as seawater desalination plants and chemical plants. Also in this case, excellent conductivity, corrosion resistance, and hydrogen embrittlement resistance can be obtained.

FIG. 1 is a diagram showing the configuration of an apparatus for measuring the contact resistance of a titanium material.

  Hereinafter, embodiments of the present invention will be described in detail. In the following description, “%” means mass% unless otherwise specified.

[Titanium material]
The titanium material includes a base material, a titanium oxide film formed on the base material, and a carbon material formed on the titanium oxide film and having conductivity.

<Base material>
The base material is made of pure titanium or a titanium alloy. Here, “pure titanium” means a metal material containing 98.8% or more of Ti and the balance being impurities. As pure titanium, for example, JIS type 1 to JIS type 4 pure titanium can be used. Among these, JIS class 1 and JIS class 2 pure titanium have the advantages of being economical and easy to process. “Titanium alloy” means a metal material containing 70% or more of Ti, with the balance being an alloy element and an impurity element. As the titanium alloy, for example, JIS11, 13, or 17 for corrosion resistance, or JIS60 for high strength can be used.

<Titanium oxide film>
The titanium oxide film includes a main phase. The main phase is specified by X-ray diffraction analysis described later. The main phase is any of Ti _n O _(2n-1) (n is an integer of 1 to 9; hereinafter the same unless otherwise specified). Specifically, the Ti _n O _(2n-1) phase includes Ti ₉ O ₁₇ (n = 9), Ti ₈ O ₁₅ (n = 8), Ti ₇ O ₁₃ (n = 7), Ti ₆ O _11. (N = 6), Ti ₅ O ₉ (n = 5), Ti ₄ O ₇ (n = 4), Ti ₃ O ₅ (n = 3), Ti ₂ O ₃ (n = 2), and TiO (n = 1). As described below, this titanium oxide film is excellent in conductivity, corrosion resistance, and hydrogen embrittlement resistance.

The Ti _n O _(2n-1) phase has higher conductivity than the TiO ₂ phase. Since the titanium oxide film includes a Ti _n O _(2n-1) phase as a main phase, it has excellent conductivity. Further, the Ti _n O _(2n-1) phase has corrosion resistance. Since the titanium oxide film contains a Ti _n O _(2n-1) phase as a main phase, it has excellent corrosion resistance. Furthermore, the Ti _n O _(2n-1) phase becomes a barrier for hydrogen permeation. Since the titanium oxide film contains a Ti _n O _(2n-1) phase as a main phase, it has excellent hydrogen embrittlement resistance.

In the Ti _n O _(2n-1) (n is an integer of 1 to 9) phase, the smaller the value of n, the higher the barrier effect against hydrogen permeation and the better the conductivity. In order to obtain a good balance of conductivity, corrosion resistance, and hydrogen embrittlement resistance, n is preferably an integer of 1 to 5, and n is more preferably 1 or 2. The titanium oxide film may contain two or more of Ti _n O _(2n-1) (n is an integer of 1 to 9) phase. In this case, _{n of} any Ti _n O _(2n-1) phase is preferably an integer of 1 to 5. Most preferably, the Ti _n O _(2n-1) phase is at _{least one} of a Ti ₂ O ₃ phase and a TiO phase.

The thickness of the titanium oxide film is 30 nm or more and 500 nm or less. When the thickness of the titanium oxide film is 30 nm or more, sufficient hydrogen embrittlement resistance can be obtained. Further, when the thickness of the titanium oxide film is 30 nm or more, sufficient corrosion resistance can be obtained even when the crystallinity of the Ti _n O _(2n-1) phase in the titanium oxide film is not high. On the other hand, the Ti _n O _(2n-1) phase, which is the main phase of the titanium oxide film, has lower conductivity than the base material. However, when the thickness of the titanium oxide film is 500 nm or less, the electrical resistance of the titanium oxide film is sufficiently low (conductivity is sufficiently high). Further, when the thickness of the titanium oxide film is 500 nm or less, the titanium oxide film is hardly cracked when the titanium material is pressed.

  The thickness of the titanium oxide film is preferably 40 nm or more, more preferably 50 nm or more. The thickness of the titanium oxide film is preferably 400 nm or less, more preferably 300 nm or less.

  The thickness of the titanium oxide film can be determined as follows. First, the O content is analyzed by XPS (X-ray Photoelectron Spectroscopy) while sputtering with Ar in the depth direction from the surface of the titanium material. The O content is calculated assuming that the concentration of Ti, a component contained in the base material by 1% or more, C, and O is 100%. The depth at which the O content is reduced to ½ of the maximum value is defined as the thickness of the titanium oxide film.

  A carbon material having conductivity may be provided on at least a part of the surface of the titanium oxide film. In this case, conductivity and corrosion resistance are improved.

<Thin film X-ray diffraction analysis>
In this titanium material, the main phase of the titanium oxide film is identified by performing a thin film X-ray diffraction analysis with an incident angle of 0.3 ° (deg) on the surface layer. The main phase is a crystal phase corresponding to the maximum peak except for the peaks corresponding to the α-Ti phase and β-Ti phase among the peaks obtained by thin film X-ray diffraction analysis. The α-Ti phase and β-Ti phase are excluded to specify the main phase because most of these phases do not constitute a titanium oxide film but are Ti contained in the base material. is there. Here, the surface layer includes at least a titanium oxide film and a portion in the vicinity of the titanium oxide film in the base material.

The identification of the crystal phase can be performed, for example, by the following procedure. First, a crystal phase candidate is determined as a crystal phase expected to be detected. The candidate for the crystal phase may be, for example, a compound containing Ti and one or more of Ti, C, and O. Specific candidates include TiO ₂ (rutile type), TiO ₂ (anatase type), Ti _n O _(2n-1) , α-Ti, β-Ti, and TiC. When the base material is a titanium alloy, a compound containing an alloy element may be a candidate. In the titanium material manufacturing process, when the treatment is performed in an atmosphere containing H, a compound containing H may be a candidate. Candidates include at least TiO ₂ (rutile type), TiO ₂ (anatase type), Ti _n O _(2n-1) , α-Ti, and β-Ti.

The conditions of the X-ray diffraction analysis can be as follows, for example.
X-ray: Co-Kα ray Excitation: 100 mA electron beam irradiation with an acceleration voltage of 30 kV Diffraction angle of measurement object: 2θ = 20-100 °
Scan: Step scan at 0.02 ° step Fixed time for each step: 10 seconds

  The peak intensity is the area above the continuous background of the X-ray diffraction curve. Here, the “area” is an integrated intensity obtained using the measured count number.

  Then, using the X-ray diffraction pattern database of the above-mentioned candidate metal titanium and titanium compound, it is determined that there is a candidate crystal phase that matches the result of thin-film X-ray diffraction analysis. The procedure is as follows, for example. First, the obtained data is smoothed with a 21-point parabolic filter. For this smoothed data, peak detection is performed by a second derivative method with a peak intensity threshold of 20 cps and a peak width threshold of 0.1 °. The peak position is the center of gravity angle. Hereinafter, the peak detected in this way is referred to as “measured diffraction line”.

Corresponds to the largest of the measured diffraction lines except the ones within the angle of 0.1 ° with the α-Ti and β-Ti diffraction lines in the database (hereinafter referred to as “DB diffraction lines”). The crystal phase to be used is the main phase. That is, the main phase is identified as one of the above candidates. Since the base material is made of pure titanium or a titanium alloy, the Ti _n O _(2n-1) phase and the TiO ₂ phase exist in the titanium oxide film. In the titanium material of the present invention, the titanium oxide film includes a Ti _n O _(2n-1) phase as a main phase.

When multiple types of crystal phases correspond to the maximum diffraction line, the main phase is the one with the highest accuracy evaluation. As the accuracy evaluation, for example, it is first attempted to determine which of the above-described plural types is the main phase based on the following criterion (i). If the determination criteria cannot be used, the determination is attempted according to the following determination criteria (ii).
(i) The number of DB diffraction lines that coincide with the actually measured diffraction lines among the DB diffraction lines up to the third in order of increasing intensity in the DB diffraction lines of the candidate crystal phase.
(ii) Similarly, the number of DB diffraction lines that coincide with the actual measurement diffraction lines among the up to eighth DB diffraction lines in descending order of intensity.

  In the determination criteria (i) and (ii) above, the greater the number of matching DB diffraction lines, the higher the accuracy. Further, when the number of the measured diffraction lines that match the DB diffraction lines is the same, the average of the difference between the diffraction angle of the DB diffraction lines and the diffraction angle of the actual diffraction lines is calculated for the corresponding DB diffraction lines and the measured diffraction lines. In comparison, it is assumed that the accuracy is higher when the average of the angular differences is smaller. Thereby, the main phase can be identified objectively. The above procedure can be implemented using, for example, software attached to the X-ray diffraction analyzer.

Since the TiO ₂ phase is poor in conductivity, the strongest peak intensity I _TiO2 of the TiO ₂ phase (rutile type or anatase type) is preferably zero. When I _TiO2 is not 0, that is, when a peak due to the TiO ₂ phase is observed, the strongest peak intensity I1 of the main phase is preferably 5 times or more that of I _TiO2 . That is, in this case, the peak intensity according to the thin film X-ray diffraction analysis of the titanium material satisfies the following formula (1).
I1 ≧ 5 × I _TiO2 (1)

Formula (1) means that the main phase having conductivity is sufficiently present in the titanium oxide film as compared with the TiO ₂ phase which is a crystalline phase having poor conductivity. Therefore, the titanium oxide film of the titanium material that satisfies the formula (1) has high conductivity.

Whether or not a peak due to the TiO ₂ phase is observed is a measured diffraction line that is not identified in the main phase after performing the above-described peak detection, and a peak (diffraction line) that can be attributed to the TiO ₂ phase exists. Judgment by whether or not.

[Production method of titanium material]
This titanium material can be manufactured by a method including a first step and a second step described below. In the first step, the surface layer of the base material is oxidized to form an oxide film mainly composed of a TiO ₂ phase (hereinafter referred to as “intermediate oxide film”). In the second step, the intermediate oxide film is reduced to form a titanium oxide film having a Ti _n O _(2n-1) phase as a main phase.

<First step>
The first step may include a heat treatment in an oxidizing atmosphere or an anodic oxidation treatment. From the viewpoint of forming a uniform oxide film on the surface of the base material, it is preferable to employ an anodic oxidation treatment. By this 1st process, the intermediate | middle oxide film | membrane of the thickness which can obtain a 30-500-nm-thick titanium oxide film by a 2nd process is produced | generated.

《Heat treatment in oxidizing atmosphere》
The oxidizing atmosphere can be an air atmosphere, for example. In order to form an intermediate oxide film on the surface of the base material in an air atmosphere, heating is performed at a temperature of 350 ° C. or higher and 700 ° C. or lower. When heating at less than 350 ° C., the thickness of the intermediate oxide film produced is thin, and the oxide film may disappear due to the reduction treatment in the second step. Moreover, when it heats at the temperature over 700 degreeC, there exists a possibility that the intermediate | middle oxide film with a large porosity may produce | generate, and the intermediate | middle oxide film itself may fall out. A more preferable temperature range is 500 ° C. or more and 700 ° C. or less where the interference color changes from blue to purple. The heating time can be, for example, 5 minutes to 90 minutes after reaching a predetermined temperature.

<Anodizing treatment>
The anodizing treatment can be performed using an aqueous solution used for general anodizing of titanium, for example, an aqueous phosphoric acid solution or an aqueous sulfuric acid solution. The anodizing voltage is 15 V or more, and the upper limit is a voltage that does not cause dielectric breakdown (about 150 V). The anodizing voltage is preferably 40V to 115V. By setting the voltage to 40 V or more, an anatase TiO ₂ phase is formed in the intermediate oxide film. When the second step is performed on such an intermediate oxide film, a titanium oxide film containing a large amount of Ti _n O _(2n-1) phase can be formed. 115 V is an upper limit voltage at which titanium can be easily anodized industrially.

Even when the intermediate oxide film is formed by any of heat treatment in an oxidizing atmosphere and anodizing treatment, Ti constituting the titanium oxide film is derived from the base material. As a result, the adhesion of the titanium oxide film to the base material is increased, and the conductive path between the titanium oxide film having a conductivity in the titanium oxide film (Ti _n O _(2n-1) phase, etc.) and the base material is improved. It becomes easy to obtain.

On the other hand, when a titanium oxide film is formed by adding Ti not derived from the base material on the base material by means such as vapor deposition, the adhesion of the titanium oxide film to the base material is insufficient. May be. In such a case, a TiO ₂ phase having poor conductivity may be formed on the surface of the base material before adding Ti. In this case, conduction between the titanium oxide having conductivity in the titanium oxide film and the base material may be hindered. The existence of such a TiO ₂ phase is obtained by obtaining an O (oxygen) content profile in the depth direction from the surface of the titanium material, and there is a portion with a high O content in the boundary region between the base material and the titanium oxide film. It can be confirmed by whether or not. For example, GD-OES (Glow Discharge Optical Emission Spectrometry) can be used as an analysis means for obtaining the O content rate profile.

<Second step>
The second step can include a reduction treatment with carbon or a reduction treatment with hydrogen.

《Reduction treatment with carbon》
This treatment can be a heat treatment using a carbon source containing carbon that contributes to reduction. In this heat treatment, for example, TiO ₂ is reduced to a lower-order oxide (in this example, Ti ₂ O ₃ ) by the reaction of the following formula (a).
2TiO ₂ + C → Ti ₂ O ₃ + CO ↑ (a)

  In this method, first, a carbon source used for reduction is supplied onto the intermediate oxide film. The carbon source can be supplied, for example, by performing skin pass rolling, that is, rolling with a rolling reduction of 5% or less on the base material having an intermediate oxide film formed on the surface. In this case, rolling oil is used as the carbon source. If the rolling reduction exceeds 5%, the intermediate oxide film may be destroyed, and the metal may be exposed on the surface. In this case, a titanium material having a predetermined titanium oxide film uniformly formed on the surface cannot be obtained.

  Alternatively, a C-containing resin film may be laminated on the intermediate oxide film, and then the film may be carbonized by heat treatment. This also provides a carbon source on the intermediate oxide film.

  The supply of the carbon source may be carried out, for example, by attaching a substance that is carbonized by heating in a substantially oxygen-free atmosphere to the intermediate oxide film. Examples of such a substance include a substance composed of C (carbon), H (hydrogen), and O (oxygen), and a substance composed of C, H, and Cl (chlorine). The substance composed of C, H and O is, for example, polyvinyl alcohol (hereinafter abbreviated as “PVA”) and carboxymethyl cellulose (hereinafter abbreviated as “CMC”). The substance composed of C, H, and Cl is, for example, polyvinylidene chloride and polyvinyl chloride.

  PVA and CMC are water soluble. Since these aqueous solutions have an appropriate viscosity, they are suitable for application to an intermediate oxide film. Any carbon source that is soluble in an organic solvent can be used after being dissolved in an organic solvent and having no water solubility.

The temperature of the heat treatment is 400 ° C. or higher and 850 ° C. or lower. If it is less than 400 degreeC, a reductive reaction does not fully advance. When the temperature exceeds 850 ° C., C diffuses from the carbon source into the base material through the intermediate oxide film or the titanium oxide film, and TiC may be formed in the base material. TiC has poor corrosion resistance and dissolves in an acid solution. For this reason, the titanium material in which TiC is formed on the base material may not be suitable for use in an environment in contact with an acid solution, for example, as a separator for a polymer electrolyte fuel cell. The heat treatment time is 10 seconds to 10 minutes after reaching a predetermined temperature. If it is less than 10 seconds, the reduction reaction does not proceed sufficiently. If it exceeds 10 minutes, a TiC phase may be formed in addition to the Ti _n O _(2n-1) phase.

  When a sufficient amount of carbon source is supplied on the intermediate oxide film before heat treatment, or when the heat treatment time is short, the conductivity derived from the carbon source is formed on the titanium oxide film after heat treatment. Of carbon remains. The remaining carbon becomes a carbon material. A titanium material having a carbon material on at least a part of the surface of the titanium oxide film has better conductivity and corrosion resistance.

  The carbon source may be supplied to the surface of the titanium oxide film by, for example, sliding a block (such as a block) conductive carbon material against the titanium oxide film. The conductive carbon material is preferably graphite. In graphite, the bond between the faces of a six-membered ring consisting of carbon atoms is weak. For this reason, when the graphite is slid against the titanium oxide film, the graphite becomes scale-like particles and is oriented substantially parallel to the surface of the titanium oxide film. Thereby, the surface of a titanium oxide film can be efficiently covered with graphite.

  If economically acceptable, C may be supplied to the surface of the titanium oxide film by vapor deposition.

<Reduction treatment with hydrogen>
This treatment can be a heat treatment in an atmosphere containing hydrogen that contributes to reduction. In this heat treatment, as an example, TiO ₂ is reduced to a lower-order oxide (in this example, Ti ₂ O ₃ ) by the reaction of the following formula (b).
2TiO ₂ + H ₂ → Ti ₂ O ₃ + H ₂ O (b)

In this method, heat treatment is performed in an atmosphere containing hydrogen. The heat treatment temperature is 400 ° C. or higher and 850 ° C. or lower. In the intermediate oxide film, the ratio of amorphous oxide with low crystallinity is high, but when the reduction treatment is performed at a temperature of 400 ° C. or higher, crystallization progresses and hydrogen embrittlement resistance is good. Become. If the temperature exceeds 850 ° C., the hydrogen diffusion rate increases, and titanium hydride may be formed and hydrogen embrittlement may occur. Although the heat treatment time depends on the treatment temperature, the holding time is usually from 10 seconds to 5 minutes after reaching a predetermined temperature. If it is less than 10 seconds, the reduction does not proceed sufficiently. When it exceeds 5 minutes, TiH is generated in addition to Ti _n O _(2n-1) . In this case, the corrosion resistance is insufficient.

[Separator for solid polymer fuel cells]
This separator includes the titanium material. Thereby, the initial contact resistance between the separator and the electrode film is low. Further, since the titanium material has corrosion resistance, this low contact resistance is maintained in the separator environment of the polymer electrolyte fuel cell. Furthermore, the separator provided with the titanium material is excellent in hydrogen embrittlement resistance.

  The separator can have a shape with grooves formed on the surface. For example, a groove for flowing fuel gas is formed on one surface of the separator. A groove for flowing an oxidizing gas is formed on the other surface of the separator. Such a separator can be obtained by press-molding a thin plate-like titanium material.

Further, after forming a plate-like base material into the shape of a separator, a titanium oxide film having a thickness of 30 to 500 nm including a Ti _n O _(2n-1) phase as a main phase on the surface of the base material May be formed. Also in this case, a separator including a titanium material having a base material and a predetermined titanium oxide film formed on the base material can be obtained.

[Cells and polymer electrolyte fuel cells]
The cell may have a known structure in which the separator, the solid polymer electrolyte membrane, the fuel electrode membrane (anode), and the oxidant electrode membrane (cathode) are laminated in a predetermined order. . The polymer electrolyte fuel cell may have a known structure in which a plurality of cells are stacked and electrically connected in series. In these cells and polymer electrolyte fuel cells, the low contact resistance between the separator and the electrode film is maintained due to the excellent conductivity and corrosion resistance of the separator. Thereby, these cells and the polymer electrolyte fuel cell can maintain high power generation efficiency. In addition, because the separator is excellent in hydrogen embrittlement resistance, even if the battery is operated for a long time, the separator is hardly broken due to embrittlement. This also maintains high power generation efficiency.

In order to confirm the effect of the present invention, various titanium materials were produced and evaluated.
1. Preparation of Base Material As a base material, a plate-shaped JIS class 1 titanium material having a thickness of 0.1 mm and a plate-shaped JIS class 17 titanium alloy material having a thickness of 1 mm were used. Table 1 shows the composition of the base material.

2. Formation of Titanium Oxide Film As a first step, an intermediate oxide film was formed on the surface of the base material. Thereafter, a titanium oxide film was formed by reducing the intermediate oxide film as a second step.

2-1. First Step: Formation of Intermediate Oxide Film The intermediate oxide film was formed by subjecting the surface of the base material to atmospheric oxidation or anodization. Atmospheric oxidation was carried out using a gas displacement muffle furnace manufactured by ASONE and introducing air into the furnace at a flow rate of 0.5 L / min from an air cylinder. Anodization was performed by applying a predetermined voltage between the base material and the counter electrode in an aqueous solution containing 1% by mass of hydrogen peroxide and 1% by mass of phosphoric acid by a direct current stabilized power source. The counter electrode was made of platinum. After the voltage application was started, the voltage was increased at a rate of 0.3 V / second to a predetermined voltage, and held for 60 seconds to complete the process.

The obtained sample, using a Rigaku Corporation X-ray diffraction apparatus RINT2500, by a thin film X-ray diffraction analysis, the type of the surface layer of TiO ₂ phase, i.e., to identify whether the anatase or rutile. At this time, Co was used as the target, and the incident angle was set to 0.3 °. TiO ₂ constitutes an intermediate oxide film.

2-2. Second Step: Reduction of Intermediate Oxide Film Reduction of the intermediate oxide film was performed by heat treatment in a hydrogen atmosphere. When supplying a carbon source on an intermediate | middle oxide film before this heat processing, it supplied with either of the following methods 1-4.

<Method 1> Application of conductive resin A polyaniline toluene solution (trade name: PANT, manufactured by Kaken Sangyo Co., Ltd.) is applied to one surface of the titanium material subjected to the first step using a bar coater, and drafted It was dried in the internal atmosphere (room temperature) for 3 hours. After visually confirming that the coating film was dried and that there was no peeling of the coating film, the other surface of the titanium material was similarly coated with resin, and further dried in the atmosphere in the draft for 24 hours.

<Method 2> Vacuum deposition of carbon Carbon was vacuum deposited on one side of the titanium material subjected to the first step by using an auto carbon coater (JEC-560) manufactured by JEOL Ltd. as a deposition apparatus. The inside of the chamber was depressurized by a vacuum pump, set to MANUAL mode, and carbon deposition was carried out with the energization condition set at 4 V for 5 seconds. After the chamber was brought to atmospheric pressure, carbon was deposited on the other surface of the titanium material under the same conditions.

<Method 3> Lamination of resin film The titanium material subjected to the first step is sandwiched between resin films (MS pouch film manufactured by Meiko Trading Co., Ltd., thickness 100 μm), and a laminator (Fusion 5100L manufactured by Ako Brands Japan Co., Ltd.) is used. Used for thermocompression bonding. The edge part which became only the resin film was cut off and removed.

<Method 4> Application of rolling oil Rolling oil as a carbon source was applied to the surface of the intermediate oxide film, and a skin pass with a rolling reduction of 1% was performed. As rolling oil, Idemitsu Kosan Daphne Roll Oil FX-60 was used.

  A base material supplied with a carbon source on an intermediate oxide film by any one of the above methods 1 to 4, or a base material that was not supplied with a carbon source, in a hydrogen atmosphere at normal pressure (containing 25 at% nitrogen) ) To reduce the intermediate oxide film.

3. Thin Film X-ray Diffraction Analysis Thin film X-ray diffraction analysis was performed on the sample surface layer portion of the titanium material under the same conditions as the identification of the TiO ₂ phase of the intermediate oxide film described above. Based on the results, the main phase was identified. In addition, peak intensities I1 and _ITiO2 were measured. Based on these intensities, for each sample, if the peak attributable to TiO ₂ phase was observed, it was determined I1 / I _TiO2.

4). Titanium oxide film thickness The thickness of the titanium oxide film was determined by the above-described method using XPS. As a measuring device, Quantum2000 manufactured by ULVAC-PHI was used. The X-ray source was Al Kα ray, and the beam diameter was 200 μm.

5. Measurement of Contact Resistance The obtained titanium material sample was measured for contact resistance according to the method described in Non-Patent Document 1. FIG. 1 is a diagram showing the configuration of an apparatus for measuring the contact resistance of a titanium material. Using this apparatus, the contact resistance of each sample was measured. Referring to FIG. 1, first, a prepared sample 11 is sandwiched between a pair of carbon papers (TGP-H-90 manufactured by Toray Industries, Inc.) 12 used as a gas diffusion layer for a fuel cell. It was sandwiched between a pair of plated electrodes 13. The area of each carbon paper 12 was 1 cm ² .

Next, a load of 10 kgf / cm ² (9.81 × 10 ⁵ Pa) was applied between the pair of gold-plated electrodes 13. In FIG. 1, the direction of the load is indicated by a white arrow. In this state, a constant current was passed between the pair of gold-plated electrodes 13, and the voltage drop between the carbon paper 12 and the sample 11 generated at this time was measured. Based on this result, the resistance value was determined. The obtained resistance value is a value obtained by adding the contact resistances of both surfaces of the sample 11, and is divided by 2 to obtain a contact resistance value per one surface of the sample 11. The contact resistance measured in this way was defined as the first contact resistance.

Next, the load applied between the pair of gold-plated electrodes 13 is repeated between ⁵ kgf / cm ² (4.90 × 10 ⁵ Pa) and 20 kgf / cm ² (19.6 × 10 ⁵ Pa). Changed 10 times. Thereafter, the pressure was set to 10 kgf / cm ² (9.81 × 10 ⁵ Pa), and the contact resistance was similarly measured. The contact resistance measured in this way was defined as the contact resistance after 10 times load.

6). Investigation of Corrosion Resistance The obtained titanium material sample (without repeated load variation) was immersed in an aqueous solution of H ₂ SO _{4 at} 90 ° C. and pH 2 for 96 hours, and then sufficiently washed with water and dried. And contact resistance was measured by the above-mentioned method. When the corrosion resistance is not good, a passive film on the surface of the titanium material grows, so that the contact resistance increases as compared to before immersion.

7). Investigation of hydrogen embrittlement resistance The stability of hydrogen in the titanium material was investigated by thermal desorption spectroscopy (TDS analysis) using an Anelva M201QA-TDM type analyzer. The temperature of the sample was raised at 0.5 ° C./second, the amount of hydrogen gas generated was measured, and the temperature at which the generated amount peaked was taken as the hydrogen desorption temperature. The hydrogen desorption temperature indicates a temperature necessary for diffusing and releasing hydrogen gas in the titanium material. From room temperature to the hydrogen desorption temperature, substantially no hydrogen intrusion occurs. Therefore, the higher the hydrogen desorption temperature, the less likely hydrogen will enter. For this reason, the hydrogen desorption temperature is an index of hydrogen embrittlement resistance.

  In addition, as an evaluation of hydrogen embrittlement resistance, the titanium material was exposed to a 100% hydrogen atmosphere of 0.15 MPa at 200 ° C. for 100 hours, and processing cracks when the exposed titanium material was pressed into a separator shape. The presence or absence was investigated.

  Table 2 shows the production conditions and evaluation results of the titanium material.

The symbols in the column of “work crack” in Table 2 indicate that the presence or absence of work cracks when the titanium material is exposed to a hydrogen atmosphere in the above conditions and then pressed into a separator shape is as follows.
○: No processing crack ×: With processing crack

In each of Invention Examples 1 to 13, the main phase was any of Ti _n O _(2n-1) phases, and the thickness of the titanium oxide film was 30 to 500 nm. In these samples, the value of contact resistance was as low as ²⁰ mΩ · cm ² or less both in the initial stage and after the corrosion resistance test. That is, it was confirmed that these samples were excellent in conductivity and corrosion resistance. In these samples, there was no work cracking during press working after exposure to a hydrogen atmosphere. That is, it was confirmed that these samples were excellent in hydrogen embrittlement resistance.

  From the results of Invention Examples 7 to 10, it was confirmed that the titanium material of the present invention can be produced by supplying carbon by any of the methods 1 to 4.

Comparative Examples 1 and 7 are base materials A and B that have not been processed, respectively. It is considered that a natural oxide film mainly composed of a TiO ₂ phase in which a Ti _n O _(2n-1) phase is not substantially formed is formed on these surface layer portions. In Comparative Examples 1 and 2, the contact resistance exceeded 100 mΩ · cm ^{2 in the} initial stage, and was significantly increased after the corrosion resistance test. Moreover, hydrogen embrittlement resistance was also poor.

In Comparative Examples 2, 4, and 5, the main phase of the titanium oxide film was a Ti _n O _(2n-1) phase, but the thickness of the titanium oxide film was less than 30 nm. In these samples, the contact resistance after loading at least 10 times after the corrosion resistance test exceeded 40 mΩ · cm ² . Moreover, hydrogen embrittlement resistance was also poor.

In Comparative Examples 3, 6, and 8, the main phase was not a Ti _n O _(2n-1) phase but a TiO ₂ phase. This is because in Comparative Example 3, step 2 (carbon reduction) was not performed. In Comparative Example 6, since the heat treatment temperature in Step 2 was as low as 350 ° C., the reduction of the oxide film did not proceed. In Comparative Example 8, since the heat treatment temperature in Step 2 was as high as 860 ° C., carbon did not function as a reducing agent for the oxide film, and TiC was formed. The contact resistance of these samples exceeded 300 mΩ · cm ² both in the initial stage and after the corrosion resistance test. It is considered that the contact resistance was increased due to the poor conductivity of the TiO ₂ phase. Moreover, hydrogen embrittlement resistance was also poor.

    11: Sample (titanium material)

Claims (5)

A base material made of pure titanium or a titanium alloy;
A titanium material formed on the base material and including a titanium oxide film including a main phase,
The main phase is the maximum except for the peaks corresponding to the α-Ti phase and β-Ti phase among the peaks obtained by thin film X-ray diffraction analysis at an incident angle of 0.3 ° for the surface layer of the titanium material. A crystal phase corresponding to a peak and any of Ti _n O _(2n-1) (n is an integer of 1 to 9) phase,
A titanium material, wherein the titanium oxide film has a thickness of 30 to 500 nm. 2. The titanium material according to claim 1, wherein when the peak due to the TiO ₂ phase is observed in the thin film X-ray diffraction analysis, the strongest peak intensity of the main phase is 5 of the strongest peak intensity of the TiO ₂ phase. Titanium material that is more than double.   A separator for a polymer electrolyte fuel cell, comprising the titanium material according to claim 1.   A polymer electrolyte fuel cell comprising the separator according to claim 3.   A polymer electrolyte fuel cell comprising the cell according to claim 4.

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