JP6805822B2 - Titanium material, separator, cell, and polymer electrolyte fuel cell - Google Patents

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.

Applications of metal materials with excellent conductivity include battery current collectors and battery cases. In fuel cell applications, such metal materials are used as metal current collector separators. The metal material used for this separator material is required to have corrosion resistance and hydrogen embrittlement resistance. Titanium material is used as a metal material having excellent corrosion resistance and hydrogen embrittlement resistance. Titanium material has corrosion resistance because an oxide film mainly composed of TIO ₂ is formed on its surface to protect the base material. The titanium material has hydrogen embrittlement resistance because the presence of the oxide film described above blocks the ingress of hydrogen and suppresses hydrogen embrittlement.

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

Patent Document 1 discloses a titanium material in which the Ti phase contains Cu up to the solid solution limit by adding Cu in an amount equal to or greater than the solid solution limit to Ti and precipitating a certain amount of the Ti ₂ Cu phase. .. It is said that this titanium material has high hydrogen absorption characteristics and improved hydrogen embrittlement resistance.

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

Patent Document 3 discloses a titanium material having a titanium hydride-containing layer formed on the surface of titanium to improve hydrogen embrittlement resistance. In this titanium material, hydrogen is forcibly introduced by cathode electrolysis to precipitate hydrides in advance, and the 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%. It is said that this separator has excellent corrosion resistance and can maintain low contact resistance for a long period of time.

Japanese Unexamined Patent Publication No. 2013-1973 Japanese Patent No. 2006-291263 Japanese Unexamined Patent Publication No. 2005-36314 Japanese Unexamined Patent Publication No. 2014-22250

Toshiki Sato, 1 person, "Characteristics of Titanium Separator for Solid Polymer Fuel Cell Coated with Graphite", Kobe Steel Technical Report, Vol. 65 No. 2 (Sep. 2015)

In Patent Documents 1 to 3, corrosion resistance and conductivity have not been sufficiently studied. In Patent Document 4, corrosion resistance and conductivity are studied, but the intermediate layer is granular and the processability as a material for a separator is insufficient.

An object of the present invention is to provide a titanium material having excellent 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 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
With a base material made of pure titanium or titanium alloy,
A titanium oxide film formed on the base material and containing a main phase,
The main phase is the largest of the peaks obtained by thin film X-ray diffraction analysis at an incident angle of 0.3 ° on the surface layer of the titanium material, except for the peaks corresponding to the α-Ti phase and the β-Ti phase. as well as a crystal phase corresponding to the _{peak, Ti n O (2n-1} ) (n is an integer from 1 to 9) is any one of phases,
It is a titanium material having a thickness of the titanium oxide film of 30 to 500 nm.

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

The titanium material and the separator of the polymer electrolyte fuel cell are excellent in conductivity, corrosion resistance, and hydrogen embrittlement resistance. The cell of 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 constituent material for electrical contacts in environments such as seawater desalination plants and chemical plants where brittle fracture due to hydrogen absorption is a problem. In this case as well, excellent conductivity, corrosion resistance, and hydrogen embrittlement resistance can be obtained.

FIG. 1 is a diagram showing a 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, unless otherwise specified, "%" means mass% for chemical composition.

[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 titanium alloy. Here, "pure titanium" means a metal material containing 98.8% or more of Ti and the balance being impurities. As the pure titanium, for example, JIS 1 to JIS 4 pure titanium can be used. Of these, JIS 1 and JIS 2 pure titanium have the advantages of being economical and easy to process. The "titanium alloy" means a metal material containing 70% or more of Ti and the balance being composed of an alloy element and an impurity element. As the titanium alloy, for example, JIS 11 type, 13 type, or 17 type for corrosion resistance, or JIS 60 type for high strength use can be used.

<Titanium oxide film>
The titanium oxide film contains the main phase. The main phase is identified by X-ray diffraction analysis described below. Major _{phase, Ti n O (2n-1} ) (n is an integer from 1 to 9; hereinafter, unless otherwise noted, the same) is either phase. Specifically, the Ti _n O _(2n-1) phase is 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.

Ti _n O _(2n-1) phase has a higher conductivity than TiO ₂ phases. Titanium oxide coatings because they contain Ti _n O _(2n-1) phase, having good conductivity as a main phase. _{Moreover, Ti n O (2n-1} ) phase has a corrosion resistance. Since titanium oxide coating comprises Ti _n O _(2n-1) phase as a main phase, it has excellent corrosion resistance. _{Moreover, Ti n O (2n-1} ) phase becomes a barrier to hydrogen permeation. Titanium oxide coatings because they contain Ti _n O _(2n-1) phase as a main phase, have excellent resistance to hydrogen embrittlement resistance.

_{Ti n O (2n-1)} (n is an integer from 1 to 9) phase, as the value of n is small, high barrier effect against hydrogen permeation, and conductivity is good. 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 more preferably n is 1 or 2. Titanium oxide _{coatings, Ti n O (2n-1} ) (n is an integer from 1 to 9) may contain two or more phases. In this case, _{n of} any Tin O _(2n-1) phase is preferably an integer of 1 to 5. Ti _n O _(2n-1) phase, it is, most preferably 1 or more Ti ₂ O ₃ phase and 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. If the thickness of the titanium oxide coating is 30nm or more, even if the crystallinity of the Ti _n O _(2n-1) phase of the titanium oxide coating in is not high, sufficient corrosion resistance can be obtained. On the other _{hand, Ti n O (2n-1} ) phase is the main phase of the titanium oxide film has a lower conductivity than the base material. However, since the thickness of the titanium oxide film is 500 nm or less, the electric resistance of the titanium oxide film is sufficiently low (the conductivity is sufficiently high). Further, since the thickness of the titanium oxide film is 500 nm or less, cracking of the titanium oxide film is unlikely to occur when the titanium material is press-processed.

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) in the depth direction from the surface of the titanium material while sputtering with Ar. The O content is calculated assuming that the concentrations of Ti, the components contained in the base material at 1% or more, C, and O are 100%. The depth at which the O content is reduced to 1/2 of the maximum value is defined as the thickness of the titanium oxide film.

A conductive carbon material 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 thin film X-ray diffraction analysis on the surface layer at an incident angle of 0.3 ° (deg). The main phase is a crystal phase corresponding to the largest peak among the peaks obtained by thin film X-ray diffraction analysis, excluding the peaks corresponding to the α-Ti phase and the β-Ti phase. The reason why the α-Ti phase and the β-Ti phase are excluded to identify the main phase is that most of these phases do not form 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 of the base material in the vicinity of the titanium oxide film.

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

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

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

Then, using the database of the X-ray diffraction patterns of the candidate metallic titanium and the titanium compound, it is determined that some of the candidate crystal phases are consistent with the result of the thin film X-ray diffraction analysis. The procedure is, for example, as follows. First, the obtained data is smoothed with a 21-point parabolic filter. For this smoothed data, peak detection is performed by a quadratic differential method with a peak intensity threshold value of 20 cps and a peak width threshold value of 0.1 °. The peak position is the angle of the center of gravity. Hereinafter, the peak detected in this way is referred to as an "actually measured diffraction line".

Corresponds to the largest measured diffraction lines except those at an angle within 0.1 ° with the α-Ti and β-Ti diffraction lines (hereinafter referred to as “DB diffraction lines”) in the above database. The crystalline phase is the main phase. That is, the prime minister is identified as one of the above candidates. Since the base material is made of pure titanium or a titanium _{alloy, Ti n O (2n-1} ) phase, and TiO ₂ phases are present in the titanium oxide film in. The titanium material of the present invention, the titanium oxide coating comprises Ti _n O _(2n-1) phase as main phase.

When a plurality of types of crystal phases correspond to the maximum diffraction line, the one with the highest accuracy evaluation is set as the main phase. As an accuracy evaluation, for example, it is attempted to determine which of the above-mentioned plurality of types is the main phase according to the following criteria (i). Then, if it cannot be determined by this criterion, the determination is attempted according to the criterion (ii) below.
(i) The number of DB diffraction lines that match the actually measured diffraction lines among the third DB diffraction lines in descending order of intensity among the DB diffraction lines of the candidate crystal phase.
(ii) Similarly, among the 8th DB diffraction lines in descending order of intensity, the number of DB diffraction lines that match the actually measured diffraction lines.

In the criteria of (i) and (ii) above, the greater the number of matching DB diffraction lines, the higher the accuracy. Further, when the number of actually measured diffraction lines that match the DB diffraction line is the same, the average of the difference between the diffraction angle of the DB diffraction line and the diffraction angle of the actually measured diffraction line is calculated for the matching DB diffraction line and the actually measured diffraction line. By comparison, the one with a smaller average of these angular differences is considered to have higher accuracy. This makes it possible to objectively identify the main phase. The above procedure can be performed, for example, by using the software attached to the X-ray diffraction analyzer.

Since the TiO ₂ phase has poor conductivity, the strongest peak intensity I _TiO2 of the TiO ₂ phase (rutile type or anatase type) is preferably 0. 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 obtained by the thin film X-ray diffraction analysis of the titanium material satisfies the following equation (1).
I1 ≧ 5 × I _TiO2 … (1)

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

Whether or not a peak caused by the TiO ₂ phase is observed is determined by the actual measurement diffraction line that has not been identified as the main phase after the above peak detection, and there is a peak (diffraction line) that can be caused by the TiO ₂ phase. Judge by whether or not.

[Manufacturing method of titanium material]
This titanium material can be produced by a method including the first step and the second step described below. In the first step, the surface layer of the base metal is oxidized to form an oxide film mainly composed of TiO ₂ phase (hereinafter, referred to as "intermediate oxide film"). In the second step, the middle oxide film by reduction treatment to form a titanium oxide film as a main phase of Ti _n O _(2n-1) phases.

<First step>
The first step can include heat treatment in an oxidizing atmosphere or anodizing treatment. From the viewpoint of forming a homogeneous oxide film on the surface of the base material, it is preferable to adopt anodizing treatment. By this first step, an intermediate oxide film having a thickness capable of obtaining a titanium oxide film having a thickness of 30 to 500 nm is produced in the second step.

《Heat treatment in an oxidizing atmosphere》
The oxidizing atmosphere can be, for example, an atmospheric atmosphere. In order to form an oxide film on the surface of the base metal in the air atmosphere, it is heated at a temperature of 350 ° C. or higher and 700 ° C. or lower. When heated at less than 350 ° C., the thickness of the formed intermediate oxide film is thin, and the oxide film may disappear by the reduction treatment in the second step. Further, when heated at a temperature exceeding 700 ° C., an intermediate oxide film having a large porosity may be formed, and the intermediate oxide film itself may fall off. A more preferable temperature range is 500 ° C. or higher and 700 ° C. or lower in which the interference color changes from blue to purple. The heating time can be, for example, 5 to 90 minutes after reaching a predetermined temperature.

《Anodizing treatment》
The anodizing treatment can be carried out using an aqueous solution used for general anodizing of titanium, for example, a phosphoric acid aqueous solution, a sulfuric acid aqueous solution, or the like. The voltage of anodization is 15 V or more, and the upper limit is a voltage (about 150 V) that does not cause dielectric breakdown. The voltage of anodization is preferably 40 V or more and 115 V or less. By setting the voltage to 40 V or higher, anatase-type TiO ₂ phase is formed in the intermediate oxide film. It is possible to form such a relative halfway oxide film when carrying out the second step Ti _n O titanium oxide film containing a large amount of _(2n-1) phases. 115V is the upper limit voltage at which titanium can be easily anodized industrially.

Whether the intermediate oxide film is formed by heat treatment in an oxidizing atmosphere or anodizing treatment, the Ti constituting the titanium oxide film is derived from the base material. Thus, with the adhesion of the titanium oxide film with respect to the base material becomes higher, the conductive path of the titanium oxide having a conductive titanium oxide film in the _{(Ti n O (2n-1} ) phase etc.) as a base material It will be easier to obtain.

On the other hand, when Ti not derived from the base material is added onto the base material to form a titanium oxide film by means such as thin film deposition, the adhesion of the titanium oxide film to the base material is insufficient. May become. Further, in such a case, before adding Ti, a TiO ₂ phase having poor conductivity may be formed on the surface of the base material. In this case, the conduction between the conductive titanium oxide in the titanium oxide film and the base material may be hindered. The presence of such a TIO ₂ phase obtains an O (oxygen) content profile in the depth direction from the surface of the titanium material, and a portion having a high O content is present in the boundary region between the base material and the titanium oxide film. It can be confirmed by whether or not to do so. As an analytical means for acquiring the O content profile, for example, GD-OES (Glow Discharge Optical Emission Spectrometry) can be used.

<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, as an example, TiO ₂ is reduced to a lower order oxide (Ti ₂ O _{3 in} this example) by the reaction of the following formula (a).
2TiO ₂ + C → Ti ₂ O ₃ + CO ↑ (a)

In this method, first, the carbon source used for reduction is supplied on the intermediate oxide film. The supply of the carbon source can be carried out, for example, by performing skin pass rolling, that is, rolling with a reduction ratio of 5% or less on the base metal having an oxide film formed on the surface thereof. In this case, rolling oil is used as the carbon source. If the reduction rate exceeds 5%, the oxide film may be destroyed and the metal may be exposed on the surface. In this case, it becomes impossible to obtain a titanium material in which a predetermined titanium oxide film is uniformly formed on the surface.

Further, 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 supplies a carbon source on top of the midway oxide film.

The supply of the carbon source may be carried out, for example, by adhering a substance that carbonizes 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 being applied to an intermediate oxide film. Any carbon source that is soluble in an organic solvent can be used by dissolving it in an organic solvent and applying it even if it is not water-soluble.

The temperature of the heat treatment is 400 ° C. or higher and 850 ° C. or lower. Below 400 ° C., the reduction reaction does not proceed sufficiently. At a temperature higher than 850 ° C., C may diffuse from the carbon source into the base metal via the intermediate oxide film or the titanium oxide film, and TiC may be formed in the base metal. TiC has poor corrosion resistance and dissolves in acid solutions. Therefore, 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 or more and 10 minutes or less after reaching a predetermined temperature. In less than 10 seconds, the reduction reaction does not proceed sufficiently. More than 10 minutes, in addition to the Ti _n O _(2n-1) phases, sometimes TiC phase is generated.

If a sufficient amount of carbon source is supplied on the intermediate oxide film before the heat treatment, or if the heat treatment time is short, the conductivity derived from the carbon source is placed on the titanium oxide film after the heat treatment. 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 supply of the carbon source to the surface of the titanium oxide film may be performed, for example, by sliding a massive (block-shaped or the like) conductive carbon material with respect to the titanium oxide film. The conductive carbon material is preferably graphite. In graphite, the bonds between the faces of the six-membered ring consisting of carbon atoms are weak. Therefore, when graphite is slid with respect to the titanium oxide film, the graphite becomes scaly particles and is oriented substantially parallel to the surface of the titanium oxide film. As a result, the surface of the titanium oxide film can be efficiently covered with graphite.

C may be supplied by thin film deposition to the surface of the titanium oxide film if it is economically acceptable.

<< 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 (Ti ₂ O _{3 in} this example) by the reaction of the following formula (b).
2TiO ₂ + H ₂ → Ti ₂ O ₃ + H ₂ O (b)

In this method, the 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 proportion of amorphous oxide with low crystallinity increases, but when the reduction treatment is carried out at a temperature of 400 ° C or higher, crystallization proceeds and hydrogen embrittlement resistance is good. Become. At a temperature exceeding 850 ° C., the diffusion rate of hydrogen increases, and titanium hydride may be formed to cause hydrogen embrittlement. The heat treatment time depends on the treatment temperature, but usually, after reaching a predetermined temperature, the holding time is set to 10 seconds or more and 5 minutes or less. In less than 10 seconds, the reduction does not proceed sufficiently. Beyond that time, in addition to _{Ti n O (2n-1)} , TiH is produced. In this case, the corrosion resistance becomes insufficient.

[Proton electrolyte fuel cell separator]
This separator includes the titanium material. As a result, 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. Further, the separator provided with the titanium material has excellent hydrogen embrittlement resistance.

The separator may have a shape in which a groove is 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. A separator having such a shape can be obtained by press-molding a thin plate-shaped titanium material.

Further, after forming the plate-shaped base material in the shape of the separator, the surface of the base _{material, Ti n O (2n-1} ) titanium oxide having a thickness of 30~500nm includes phase as a main phase coating May be formed. In this case as well, a separator having a base material and a titanium material having 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 laminated and electrically connected in series. In these cells and the polymer electrolyte fuel cell, the excellent conductivity and corrosion resistance of the separator maintain a low contact resistance between the separator and the electrode film. As a result, these cells and the polymer electrolyte fuel cell can maintain high power generation efficiency. Further, since the separator has excellent hydrogen embrittlement resistance, it is unlikely to be broken due to embrittlement of the separator even if the battery is operated for a long time. This also maintains high power generation efficiency.

In order to confirm the effect of the present invention, various titanium materials were prepared and evaluated.
1. 1. Preparation of base material As the 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. 2. Formation of Titanium Oxide Film As the first step, an intermediate oxide film was formed on the surface of the base metal. Then, as a second step, the titanium oxide film was formed by reducing the intermediate oxide film.

2-1. First step: Formation of intermediate oxide film The intermediate oxide film was formed by atmospheric oxidation or anodizing the surface of the base metal. Atmospheric oxidation was carried out using a gas replacement muffle furnace manufactured by AS ONE Corporation while introducing air into the furnace at a flow rate of 0.5 L / min from an air cylinder. Anodization was carried out by applying a predetermined voltage between the base metal and the counter electrode in an aqueous solution containing 1% by mass of hydrogen peroxide and 1% by mass of phosphoric acid using a regulated DC power supply. As the counter electrode, one made of platinum was used. After the start of application of the voltage, the voltage was increased at a speed of 0.3 V / sec to a predetermined voltage, and the voltage was held for 60 seconds to complete the process.

The obtained sample was identified by thin film X-ray diffraction analysis using an X-ray diffractometer RINT2500 manufactured by Rigaku Corporation to identify the type of TiO ₂ phase on the surface layer, that is, rutile type or anatase type. 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 the intermediate oxide film The reduction of the intermediate oxide film was carried out by heat treatment in a hydrogen atmosphere. When the carbon source was supplied on the intermediate oxide film before this heat treatment, it was supplied by any of the following methods 1 to 4.

<Method 1> Application of conductive resin A polyaniline-toluene solution (manufactured by Kaken Sangyo Co., Ltd., trade name: PANT) 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 air (room temperature) for 3 hours. After visually confirming that the coating film had dried and that the coating film had not peeled off, the other surface of the titanium material was similarly coated with the resin and further dried in the draft atmosphere for 24 hours.

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

<Method 3> Laminating 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 Aco Brands Japan Co., Ltd.) is inserted. It was heat-bonded using. The end portion containing only the resin film was cut and removed.

<Method 4> Application of rolling oil Rolling oil as a carbon source was applied to the surface of the oxide film in the middle, and a skin pass with a reduction ratio of 1% was performed. As the rolling oil, Daphne roll oil FX-60 manufactured by Idemitsu Kosan Co., Ltd. was used.

A base material in which a carbon source was supplied onto the mid-oxide film by any of the above methods 1 to 4 or a base material in which a carbon source was not supplied was placed in a hydrogen atmosphere at normal pressure (containing 25 at% of nitrogen). ), The intermediate oxide film was reduced.

3. 3. Thin film X-ray diffraction analysis A thin film X-ray diffraction analysis was performed on the sample surface layer 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 prime minister was identified. In addition, peak intensities I1 and I _TiO2 were measured. Based on these intensities, I1 / I _TiO2 was determined for each sample when a peak due to the TiO ₂ phase was observed.

4. Thickness of Titanium Oxide Film The thickness of the titanium oxide film was determined by the above-mentioned method using XPS. As a measuring device, Quantum 2000 manufactured by ULVAC-PHI was used. As the X-ray source, Al Kα rays were used, and the diameter of the beam was set to 200 μm.

5. Measurement of contact resistance The contact resistance of the obtained titanium sample was measured according to the method described in Non-Patent Document 1. FIG. 1 is a diagram showing a configuration of an apparatus for measuring the contact resistance of a titanium material. The contact resistance of each sample was measured using this device. With reference to FIG. 1, first, the 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, and this is gold. 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. The resistance value was calculated based on this result. Since the obtained resistance value is the sum of the contact resistances on both sides of the sample 11, this is divided by 2 to obtain the contact resistance value per one side of the sample 11. The contact resistance measured in this way was taken as the initial 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). It was changed 10 times. After that, the pressure was set to 10 kgf / cm ² (9.81 × 10 ⁵ Pa), and the contact resistance was measured in the same manner. The contact resistance measured in this way was defined as the contact resistance after being loaded 10 times.

6. Investigation of Corrosion Resistance The obtained titanium sample (without repeatedly fluctuating load) was immersed in an aqueous H ₂ SO ₄ solution at 90 ° C. and pH 2 for 96 hours, washed thoroughly with water, and dried. Then, the contact resistance was measured by the above method. When the corrosion resistance is not good, the passivation film on the surface of the titanium material grows, so that the contact resistance increases as compared with that before immersion.

7. Investigation of hydrogen embrittlement resistance The stability of hydrogen in titanium material was investigated by thermal desorption spectroscopy (TDS analysis) using an M201QA-TDM type analyzer manufactured by Anerva. The temperature of the sample was raised at 0.5 ° C./sec, the amount of hydrogen gas generated was measured, and the temperature at which the amount of hydrogen gas generated peaked was defined as the hydrogen desorption temperature. The hydrogen desorption temperature indicates the temperature required for the hydrogen gas in the titanium material to be diffused and released. From room temperature to the hydrogen desorption temperature, virtually no hydrogen intrusion occurs. Therefore, the higher the hydrogen desorption temperature, the less likely it is that hydrogen will enter. Therefore, the hydrogen desorption temperature is an index of hydrogen embrittlement resistance.

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

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

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

In the present invention Examples 1 to 13, both, the main phase is either Ti _n O _(2n-1) phase, 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 were no processing cracks during press processing after exposure to the hydrogen atmosphere. That is, it was confirmed that these samples have excellent hydrogen embrittlement resistance.

From the results of Examples 7 to 10 of the present invention, 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 which have not been treated, respectively. It is considered that a natural oxide film mainly composed of the TIO ₂ phase is formed on these surface layers, in which the T i _n O _(2n-1) phase is not substantially formed. In Comparative Examples 1 and 2, the contact resistance exceeded 100 mΩ · cm ² at the initial stage and became significantly higher after the corrosion resistance test. In addition, hydrogen embrittlement resistance was also poor.

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

In Comparative Examples 3, 6, and 8, the main phase was TiO ₂ phase rather than the Ti _n O _(2n-1) phases. This is because step 2 (carbon reduction) was not performed in Comparative Example 3. 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 initially and after the corrosion resistance test. It is probable that the contact resistance was increased due to the poor conductivity of the TiO ₂ phase. In addition, hydrogen embrittlement resistance was also poor.

11: Sample (titanium material)

Claims (4)

With a base material made of pure titanium or titanium alloy,
A titanium material formed on the base material and comprising a titanium oxide film containing a main phase.
The main phase is the largest of the peaks obtained by thin film X-ray diffraction analysis at an incident angle of 0.3 ° on the surface layer of the titanium material, except for the peaks corresponding to the α-Ti phase and the β-Ti phase. as well as a crystal phase corresponding to the _{peak, Ti n O (2n-1} ) (n is an integer from 1 to 9) is any one of phases,
In the thin film X-ray diffraction analysis, a peak caused by the TiO ₂ phase was observed, and the strongest peak intensity of the main phase was 5 times or more the strongest peak intensity of the TiO ₂ phase.
A titanium material for a separator of a polymer electrolyte fuel cell having a thickness of the titanium oxide film of 30 to 500 nm. A separator for a polymer electrolyte fuel cell, comprising the titanium material according to claim 1 . A cell of a polymer electrolyte fuel cell comprising the separator according to claim 2 . A polymer electrolyte fuel cell comprising the cell according to claim 3 .

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