JP2017016929A - Titanium material for separator for solid polymer fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a titanium material suitable for manufacturing a separator which is used for a cell of a solid polymer fuel battery and with which a surface modified layer is formed.SOLUTION: The titanium material comprises a substrate and a surface coating layer that is formed on an outermost layer on the substrate and contains Al as a main constituent. Surface roughness of the substrate is 0.12 to 4 μm in Ra value. The substrate contains Fe in 0.1 mass% or less and O in 0.11 mass% or less, and the remainder of the substrate consists of Ti and an impurity. Average thickness of the surface coating layer is 200 nm or more and 3 μm or less.SELECTED DRAWING: Figure 1B

Description

  The present invention relates to a titanium material used for producing a separator for a polymer electrolyte fuel cell used as a power source for automobiles, home use, etc., and in particular, for producing a separator having a surface-modified layer formed thereon. It relates to the titanium material used.

  A fuel cell is a cell that generates a direct current using hydrogen and oxygen, and is made into a solid electrolyte type, a molten carbonate type, a phosphoric acid type, and a solid polymer type depending on the constituent material of the electrolyte part of the fuel cell. Broadly divided.

  Among these fuel cells, phosphoric acid fuel cells operating near 200 ° C. and molten carbonate fuel cells operating near 650 ° C. have reached the commercial stage. In addition, due to recent technological development progress, polymer electrolyte fuel cells that operate near room temperature and solid electrolyte fuel cells that operate at 700 ° C. or higher are marketed as compact power sources for automobiles or home use. Has begun to be introduced.

FIG. 1A is a perspective view of the entire fuel cell, and FIG. 1B is an exploded perspective view of a fuel cell (single cell).
As shown in FIGS. 1A and 1B, the fuel cell 1 is an assembly of single cells. As shown in FIG. 1B, the unit cell has a fuel electrode membrane (anode) 3 laminated on one surface of the solid polymer electrolyte membrane 2 and an oxidant electrode membrane (cathode) 4 laminated on the other surface. The separators 5a and 5b are stacked. A typical material constituting the solid polymer electrolyte membrane 2 is a fluorine ion exchange resin membrane having a hydrogen ion (proton) exchange group.

  The fuel electrode film 3 and the oxidant electrode film 4 include a diffusion layer made of carbon paper or carbon cloth made of carbon fibers, and a catalyst layer provided on the surface of the diffusion layer. The catalyst layer includes a particulate platinum catalyst, catalyst-supporting carbon, and a fluororesin having a hydrogen ion (proton) exchange group. The fuel electrode film 3 and the oxidant electrode film 4 are bonded to the solid polymer electrolyte membrane 2 and used as an integral member (MEA; Membrane Electrode Assembly).

  A fuel gas (hydrogen or a hydrogen-containing gas) A flows through a flow path 6 a that is a groove formed in the separator 5 a, whereby the fuel gas is supplied to the fuel electrode film 3. In the fuel electrode film 3, the fuel gas permeates the diffusion layer and contacts the catalyst layer. Further, an oxidizing gas B such as air is flowed through the flow path 6b which is a groove formed in the separator 5b, whereby the oxidizing gas is supplied to the oxidant electrode film 4. In the oxidant electrode film 4, the oxidizing gas passes through the diffusion layer and contacts the catalyst layer. By supplying these gases, an electrochemical reaction occurs, and DC power is generated between the fuel electrode film 3 and the oxidant electrode film 4.

The main functions required for a separator of a polymer electrolyte fuel cell are as follows.
(1) Function as a “flow path” for uniformly supplying fuel gas or oxidizing gas into the battery surface (2) Water produced on the cathode side, together with a carrier gas such as air and oxygen after reaction, fuel Function as a “flow path” for efficiently discharging the battery out of the system (3) Contact with the electrode film (anode 3 and cathode 4) to form an electrical path, and further, electrical between two adjacent single cells Function as “connector” (4) Function as “partition wall” between the anode chamber of one cell and the cathode chamber of the adjacent cell between adjacent cells

  So far, carbon plates have been studied as separator materials at the laboratory level. However, the carbon plate material has a problem that it is easily broken, and further has a problem that the machining cost for flattening the surface and the machining cost for forming the gas flow path are very high. These problems make it difficult to commercialize solid polymer fuel cells.

Among the carbon materials, the thermally expansive graphite processed product is remarkably inexpensive, and thus has attracted the most attention as a material for a separator of a polymer electrolyte fuel cell. However, problems to be solved in the future include, for example, the following.
・ Responding to increasingly strict dimensional accuracy requirements ・ Aging deterioration of organic resin that occurs during fuel cell application ・ Carbon corrosion that progresses under the influence of battery operating environment ・ Hydrogen permeation called cross leak ・ Fuel Unexpected cracking accident during battery assembly and use

  In consideration of such graphite-based materials, attempts have been made to apply a thin metal plate to the separator for the purpose of cost reduction.

  Patent Document 1 discloses a fuel cell separator that is made of a metal member and that is directly gold-plated on a contact surface with an electrode of a unit cell. Examples of the material constituting the metal member include stainless steel, aluminum, and a Ni-iron alloy, and examples of the stainless steel include SUS304. This separator is gold plated. Therefore, the electrical contact resistance value between the separator and the electrode is low, and the conduction of electrons from the separator to the electrode is good. Thereby, in the fuel cell of patent document 1, it is supposed that an output voltage will become large.

  Patent Document 2 discloses a polymer electrolyte fuel cell including a separator made of a metal material on which a passive film is easily generated by contact with the atmosphere. Examples of the metal material include stainless steel and a titanium alloy. A passive film always exists on the surface of the metal used for the separator. For this reason, it becomes difficult for the surface of a metal to be chemically attacked, and the ratio of what is ionized among the water produced | generated by the fuel cell is reduced. Thereby, in the fuel battery cell of patent document 2, the fall of electrochemical reactivity is supposed to be suppressed. Further, Patent Document 2 also shows that the contact resistance value is lowered by removing the passive film at a portion in contact with the electrode film of the separator and forming a noble metal layer.

  Patent Document 3 discloses a stainless steel separator and a titanium separator. In general, a titanium separator has a large contact resistance with carbon paper serving as a current collector, so that the energy efficiency as a fuel cell is greatly reduced. Patent Document 3 describes that, in order to solve this problem, in a titanium separator, a noble metal having a film thickness of 5 nm to 1000 nm is added to the surface on the current collector side in contact by an ion vapor deposition method or an electrolytic plating method. ing. In this case, an oxide film of titanium is interposed between the titanium and the current collector, but the separator comes into contact with the current collector through the noble metal layer, and the contact resistance value becomes small.

  Patent Document 4 discloses a three-layer metal layer (so-called “clad material”) including an intermediate layer, an outer layer formed on the intermediate layer, and a conductive coating layer formed on the outer layer. ) Formed of a polymer electrolyte fuel cell separator. The intermediate layer is made of iron, aluminum, copper, titanium, stainless steel, alloy, or the like. The outer coating layer is made of at least one selected from carbon, conductive ceramics, and metal powder. With regard to conductive ceramics, it is assumed that the film is formed by a dry process such as ion plating or sputtering. Examples of conductive ceramic materials include tungsten carbide and titanium nitride. With such a configuration, it is said that the corrosion resistance of the metal layer can be maintained over a long period of time and an increase in the resistance of the separator can be suppressed.

  Patent Document 5 discloses a separator in which a metal film is formed on at least a portion of a surface of a base that is in contact with an electrode. The substrate is made of any one of stainless steel and a metal containing 80% by mass or more of at least one selected from aluminum and titanium. The metal film includes one or more metals selected from platinum group elements, gold, silver, copper, nickel, and tungsten, and includes conductive ceramics dispersed therein.

  Patent Document 5 discloses that the conductive ceramics are made of metal boride, carbide, silicide, or phosphide, and are made of titanium carbide, titanium boride, titanium nitride, tungsten silicide, or tantalum nitride. It is shown. The metal film is produced by a thin film forming method such as a PVD method such as an ion plating method, a CVD method, or a sputtering method. With such a configuration, this separator is said to be excellent in shape stability, easy to be molded, and stably maintained for a long period of time.

JP-A-10-228914 JP-A-8-180883 Japanese Patent No. 5047408 Japanese Patent No. 3723515 Japanese Patent No. 4010036

  For the purpose of reducing the contact resistance of the separator, the separator may be subjected to a surface modification treatment before being incorporated into the fuel cell. Examples of surface modification treatment include plasma treatment for cleaning the separator surface (for example, bombard treatment), treatment for adding a highly conductive material to the separator surface to form a surface modification layer ( For example, sputtering treatment) can be used. The thickness of the surface modification layer is not limited, but is, for example, a level of several nanometers to several tens of millimeters.

  The separator is preferably manufactured from a strip-shaped titanium material wound in a coil shape (hereinafter also simply referred to as “coil”) in mass production. Due to recent technological innovations, surface modification treatment for such strip-shaped titanium materials is becoming possible on an industrial scale. In particular, it can be expected that plasma treatment and sputtering treatment will be applicable in the future as a surface modification treatment of a separator of a polymer electrolyte fuel cell.

In the surface modification treatment, even if the inside of the treatment tank for treating the titanium material is maintained at a high vacuum of 1.0 × 10 ⁻² Torr (1.3 Pa) or less, the surface of the titanium material is often oxidized. . One cause of this phenomenon is thought to be water brought into the treatment tank by adhering or adsorbing to the surface of the titanium material. Such water is decomposed to generate oxygen when plasma treatment is performed as a surface modification treatment. Oxygen has an extremely strong affinity with titanium, and since the amount of oxygen solid solution in titanium is large, the surface of the titanium material activated by plasma is easily oxidized. If the surface of the titanium material is oxidized, the desired properties cannot be obtained by the surface modification treatment. In the titanium materials of Patent Documents 1 to 5, when water adheres or adsorbs to the surface and is brought into the treatment tank, it is difficult to suppress oxidation due to O (oxygen) generated by decomposition of the water. .

  When shipping titanium materials in the form of coils, in order to prevent the titanium materials from rubbing against each other and causing wrinkles on the surface of the titanium material, a roll paper called a “interleaf”, or a vinyl sheet (hereinafter referred to as “paper”) , “Interleaf paper etc.”) is usually performed simultaneously with the titanium material. However, since the interleaving paper or the like adsorbs moisture, air or the like, if interleaving paper or the like is used, moisture, air or the like is brought into the treatment tank during the surface modification treatment. In addition, it is necessary to continuously remove the interleaving paper or the like in the decompression chamber (vacuum tank) before performing the surface modification treatment. In a narrow decompression chamber, it is difficult to treat the removed slip sheet. Therefore, it is preferable not to use a slip sheet or the like for the coil material subjected to the surface modification treatment.

  When the titanium materials disclosed in Patent Documents 1 to 5 are wound in a coil shape and shipped, it is necessary to use a slip sheet or the like. For this reason, when surface-modifying these titanium materials, moisture, air, etc. are brought into the treatment tank due to the interleaf, and the surface of the titanium material can be oxidized by these moisture, air. . Or, when the slip sheet or the like is not used, it is necessary to allow the coil curl.

  An object of the present invention is to provide a titanium material suitable for manufacturing a separator used for a cell of a polymer electrolyte fuel cell and having a surface modified layer formed thereon.

The gist of the present invention is the following titanium material (A).
(A) A titanium material for a separator of a polymer electrolyte fuel cell,
A substrate;
A surface coating layer mainly composed of Al formed on the outermost layer on the substrate;
The surface roughness of the substrate is Ra value of 0.12 to 4 μm,
The base material is in mass%,
Fe: 0.1% or less,
O: 0.11% or less, the balance of the base material consists of Ti and impurities,
The titanium material whose average thickness of the said surface coating layer is 200 nm or more and 3 micrometers or less.

  When the surface coating layer is mainly composed of Al, O (oxygen) in the atmosphere can be preferentially bonded to Al to suppress the base material from being oxidized. The surface coating layer can be removed under reduced pressure, and subsequently a surface modification layer can be formed on the surface of the titanium material from which the surface coating layer has been removed to form a final separator. In this case, oxidation of the base material can be suppressed even when the surface modified layer is formed. Thereby, the adhesiveness of the surface modification layer with respect to a base material can be made high.

  Further, due to the presence of the surface coating layer, for example, when this titanium material is used as a coil, it is difficult for wrinkles to be generated on the surface of the base material. Can be avoided.

FIG. 1A is a perspective view of a polymer electrolyte fuel cell. FIG. 1B is an exploded perspective view showing the structure of a single cell constituting the polymer electrolyte fuel cell.

  The inventor has obtained the following knowledge regarding the application of a titanium material to the separator, and has completed the present invention.

  The passive film formed on the surface of the titanium material is made of oxyhydroxide or oxide and has a high electric resistance. For this reason, since the electrical surface contact resistance (hereinafter simply referred to as “contact resistance”) is high and unstable due to the passive film, the titanium material on which the passive film is formed is used as a fuel cell separator. It is difficult to apply.

  Even if the titanium material is covered with a passive film, the contact resistance value can be lowered by providing fine irregularities on the surface and processing to have an appropriate surface roughness. This is thought to be due to an increase in contact opportunity (number of points) and an increase in contact area due to plastic deformation of the convex portion that became the contact point. A preferable surface roughness is 0.12 to 4 μm in Ra value (according to JIS B 0601-1982). In addition, the separator having such a surface roughness has appropriate hydrophilicity and wettability with respect to the generated water generated in the cell during operation of the fuel cell to discharge the water out of the battery. . Thereby, it can suppress that the water produced | generated by battery reaction becomes a big water droplet, a flow path is obstruct | occluded, and battery performance falls from the part.

  For both stainless steel and titanium materials, the contact resistance value can be lowered by finely dispersing conductive metal precipitates in the material and exposing them on the surface or plating a noble metal on the surface. However, it is not preferable to use a precious metal, which is a limited valuable resource, without any possibility of recycling, from the viewpoint of securing resources to be used in the future.

  As a means of avoiding or stably suppressing the oxidation of the titanium material during the surface modification treatment of the titanium material, the present inventor slightly adds Al to the surface of the titanium material before the desired surface modification treatment. It was newly discovered that it is extremely effective to keep it present. Al has a stronger affinity with O (oxygen) than Ti and binds preferentially to O even in plasma, so that oxidation of the surface of the titanium material after the desired surface modification treatment and oxygen content in the substrate An increase in rate can be reliably suppressed.

  Also, if there is a slight amount of Al on the surface of the titanium material before the desired surface modification treatment, removing the Al layer immediately before the desired modification treatment will remove the dirt adhering to the titanium material surface. It can be wiped out.

However, if a large amount of Al remains on the exposed surface or as an impurity in the final surface modification layer after the final surface modification treatment of the separator, the separator in the polymer electrolyte fuel cell Corrosion resistance may decrease and contact resistance may increase. From the surface of the titanium material after the final surface modification treatment, Al must be a stable oxide of Al ₂ O ₃ type, even if it is completely removed or remains. .

  In other words, the Al layer present on the surface of the titanium material before the formation of the desired surface modification layer is formed immediately before the surface modification layer is formed, when the bombardment process or the surface modification layer is formed. It is necessary to be removed or oxidized due to the sputtering effect.

  The inventor achieves the intended role of Al by making the average thickness of the Al layer existing on the surface of the titanium material before the surface modification treatment within a range of 200 nm to 3 μm, stably, and high It has been found that a desired surface modification treatment can be performed efficiently.

  As described above, the material for the separator of the titanium solid polymer fuel cell of the present invention includes the base material and the surface coating layer mainly composed of Al formed on the outermost layer on the base material. The surface roughness of the substrate is 0.12 to 4 μm in terms of Ra value. The base material contains, by mass%, Fe: 0.1% or less and O: 0.11% or less, and the balance of the base material is made of Ti and impurities. The average thickness of the surface coating layer is 200 nm or more and 3 μm or less.

Hereinafter, embodiments of the present invention will be described in detail. In the following description, “%” for the chemical composition is “% by mass” unless otherwise specified.
The separator may be provided with a rectifying plate for directing the direction of gas flowing in the separator flow path in a desired direction. In the present specification, the separator may include such a current plate.

1. Titanium Material of the Present Invention The titanium material of the present invention includes a base material and a surface coating layer mainly composed of Al formed on the outermost layer.

  In recent years, when a separator is manufactured from a titanium material, surface modification treatment is often performed on the titanium material. The titanium material of the present invention assumes that such a surface modification treatment is performed in the process of manufacturing a separator. When the surface modification treatment is performed on the titanium material of the present invention, the surface coating layer is removed immediately before the surface modification treatment. The removal of the surface coating layer can be performed by a bombardment process as a pre-stage process in a vacuum chamber for performing a surface modification process, or during a final surface modification process by sputtering, particularly in the first half of this process.

  In this case, plasma-generated Al ions are generated by bombardment or sputtering, and the Al ions reduce the surface oxidation of the base material and suppress the oxidation of the surface modification layer. This is because Al has a stronger affinity with O (oxygen) than Ti and preferentially bonds with O even in plasma. As a result, the adhesion of the surface modified layer to the substrate can be improved and the contact resistance of the separator can be lowered.

  By providing the surface coating layer on the titanium material, even if the titanium materials rub against each other and wrinkles enter the surface coating layer, wrinkles are prevented from entering the base material. Therefore, when the form of the titanium material is a coil or a cut plate, it is possible to avoid using a slip sheet or the like. In addition, by not using interleaving paper or the like, it is possible to prevent water, air, etc. from being brought into the treatment tank due to interleaving paper or the like during the surface modification treatment, and in the decompression chamber. There is no need to remove the slip sheet.

2. Surface Roughness of Substrate The surface roughness of the substrate is 0.12 to 4 μm in Ra (center line average roughness) value. Ra value shall be measured by the measuring method prescribed | regulated by JISB0601-1982. Hereinafter, the surface roughness is assumed to be the Ra value according to this rule.

  In order to measure the surface roughness of the base material of the titanium material of the present invention, it is necessary to remove the surface coating layer so as not to affect the surface state of the base material. As a method for that purpose, only the surface coating layer is selectively corroded in an acid solution whose concentration is set so that the substrate does not corrode, or only the surface coating layer is selectively anodically dissolved by an electrochemical method. Can do. Since the base material is excellent in corrosion resistance due to being mainly composed of Ti, it is easy to selectively remove the surface coating layer mainly composed of Al.

  Generally, if the surface roughness of the titanium material is 0.12 to 4 μm, even if the passive film covers the surface of the titanium material, The contact resistance value can be set to a practical level. The surface roughness of the titanium material of the present invention is maintained within the range of 0.12 to 4 μm, reflecting the surface roughness of the base material, even after the removal of the surface coating layer and the surface modification treatment. it is conceivable that. Therefore, when the titanium coating material of the present invention is used as a separator by removing the surface coating layer and performing surface modification treatment, the contact resistance value with the electrode film can be brought to a practical level. .

Specifically, the target value of the contact resistance of the separator of the polymer electrolyte fuel cell is set to 20 mΩ · cm ² or less, and this target value is based on the surface roughness of the base material provided in the titanium material of the present invention. This is achieved by being 0.12 to 4 μm. Although it depends on the finally formed surface modification layer, the contact resistance value tends to be high even if the surface roughness of the separator is less than 0.12 μm or more than 4 μm. In any case, this is considered to be caused by a decrease in the number of contact points and a decrease in the contact area of the convex portion serving as a contact point.

  Moreover, when the surface of a separator is too rough, the sealing property between the opposing members will worsen. Specifically, referring to FIG. 1B, the sealing between the separator 5a and the fuel electrode film 3 and between the separator 5b and the oxidant electrode film 4 is deteriorated. In that case, the flow paths 6a and 6b The gas flowing through the air easily leaks outside through the gap.

  Furthermore, if the surface roughness of the separator is 0.12 to 4 μm, the effect of improving hydrophilicity and drainage with respect to water generated in the battery can be expected. When the hydrophilicity of the separator is not appropriate, water generated by the battery reaction becomes large water droplets and the channel is blocked, and the battery performance may be deteriorated from that portion. The separator having the surface roughness in the above range has moderate hydrophilicity and wettability for discharging this water out of the battery, and can prevent the flow path from being clogged with water.

3. Composition of base material The base material of the titanium material of the present invention is pure titanium which does not contain alloy elements except impurities, or is a titanium alloy to which a platinum group element such as Pd is added as required. The base material contains, as essential elements, 0.1% or less of Fe, 0.11% or less of O (oxygen), and optionally further contains a platinum group element of 0.25% or less, The remainder of Ti consists of Ti and impurities.

Fe: 0.1% or less Fe is an additive element that increases the strength of the titanium material, but reduces ductility. In order to ensure processability and to be able to form a separator having a desired shape, the upper limit of the Fe content is 0.10%.

  The lower limit of the Fe content is not particularly limited, but the separator is required to have a certain degree of strength. Therefore, although depending on the content of other impurities that have an effect of increasing the strength such as O (oxygen), Fe For example, it is preferable to contain 0.015% or more. In other words, the polymer electrolyte fuel cell is constructed by stacking several tens to several hundred cells and tightening them. Therefore, in order to increase the allowable fastening force when fastening and prevent buckling, It is preferable to increase the strength of the titanium material to some extent with Fe having a high content.

In addition, Fe is an additive element that can be used to adjust the crystal grain size by controlling the β-phase precipitation behavior in the manufacturing process of the substrate.
For example, the Fe content is preferably 0.035% or more and 0.060% or less.

O (oxygen): 0.11% or less O has an extremely strong affinity for Ti, tends to form an oxide on the surface, and easily dissolves in a large amount in Ti. O, like Fe, has the effect of increasing the strength of the titanium material. As described above, the separator is required to have a certain degree of strength, and for that purpose, the O content is preferably high to some extent. On the other hand, O is an additive element that causes a decrease in ductility. In order to ensure processability that can be formed into a desired shape, the O content is set to 0.11% or less, and more preferably 0.05% or less.

Platinum group element: 0.25% or less The base material in the titanium material of the present invention may contain a platinum group element as an optional element. For the purpose of improving corrosion resistance and the like, titanium materials intentionally added with a platinum group element are standardized and commercially available, and these titanium materials can also be used as a base material for the titanium material of the present invention. The platinum group element content is 0.25% or less, and more preferably 0.10% or less. When the base material contains a platinum group element exceeding 0.25%, the raw material cost increases. Examples of the platinum group element to be contained include Pd.

Hereinafter, impurities that can be contained in the substrate will be described.
C: 0.01% or less C may be introduced into the titanium material from cold rolling oil or the like used in the coil manufacturing process. When the C content of the titanium material is high, the ductility is lowered and the workability is deteriorated. Therefore, the lower the C content, the better. The C content is preferably 0.01% or less, and more preferably 0.007% or less.

H: 0.005% or less H is introduced into the titanium material in pickling, surface modification treatment steps, and the like. Since H causes the hydrogen embrittlement of the titanium material, the lower the H content, the better. The H content is set to 0.005% or less, and preferably 0.03% or less.

N: 0.02% or less N may be introduced into the titanium material in the coil manufacturing process. When the N content of the titanium material is high, the ductility is lowered and the workability is deteriorated. Therefore, the lower the N content, the better. The N content is 0.02% or less, and preferably 0.01% or less.

4). Surface coating layer The average thickness of the surface coating layer is 200 nm or more and 3 μm or less. The average thickness of the surface coating layer can be measured, for example, by a gravimetric method. Specifically, the weight (mass) of the titanium material on which the surface coating layer is formed is measured, and after the surface coating layer is dissolved, the weight of the titanium material is measured. Divide by the area formed and the density of the surface coating layer (Al density; literature values can be adopted) to obtain the average thickness of the surface coating layer. The measurement accuracy of the average thickness can be increased by increasing the area for forming the surface coating layer. The surface coating layer is mainly composed of Al and contains, for example, 60% or more of Al.

  If the average thickness of the surface coating layer is less than 200 nm, the surface coating layer disappears completely if, for example, the surface coating layer is removed by bombarding before the surface modification layer is formed on the titanium material. It becomes easy. In this case, it becomes difficult to obtain the effect of suppressing the oxidation of the base material. When the surface modification layer is formed on the oxidized substrate, the adhesion of the surface modification layer to the substrate is lowered.

  On the other hand, when the average thickness of the surface coating layer exceeds 3 μm, it takes a long time to remove the surface coating layer before forming the surface modified layer, or much Al remains without being removed. Become. When the amount of remaining Al increases, the Al often contaminates the surface modification layer itself with Al, thereby reducing the performance of the fuel cell.

  Considering the above factors, the thickness of the surface coating layer depends on the type and thickness of the surface modification layer to be formed, but is preferably 200 nm or more and 3 μm or less, for example, 300 nm or more and 2 μm. The following is more preferable. With such a thickness, it is possible to shorten the time required to remove the surface coating layer while ensuring the adhesion and desired performance of the surface modified layer. For example, when the surface coating layer is removed by bombardment, the time required for the removal can be set to several minutes or less. As a result, it is possible to increase the speed of the surface modification treatment, and it is possible to mass-produce while reducing the cost.

5. Hereinafter, an example of a method for producing the titanium material of the present invention will be described.
First, a substrate having the above chemical composition is prepared.

  And the surface of a base material is processed so that the surface roughness of a base material may be 0.12-4 micrometers. As an example of such a process, for example, immediately after performing a spray etching process or a dipping process using a nitric hydrofluoric acid aqueous solution, washing with water and drying can be mentioned. The temperature of the aqueous nitric hydrofluoric acid solution can be, for example, 20 to 80 ° C., the concentration of hydrofluoric acid can be, for example, 2% to 10% by mass%, and the concentration of nitric acid can be, for example, 5% by mass. It can be set to -30%.

  When the hydrofluoric acid concentration, nitric acid concentration, or the temperature of the aqueous nitric hydrofluoric acid solution is outside the above range, it is difficult to adjust the surface roughness of the substrate. Specifically, when the hydrofluoric acid concentration is less than 2%, the reactivity is low and the etching does not proceed substantially. When the concentration exceeds 10%, the ease of managing the liquid is significantly reduced. The reactivity becomes too high. When the temperature of the nitric hydrofluoric acid aqueous solution is less than 20 ° C., the reactivity is low and etching does not proceed substantially. When the temperature is higher than 80 ° C., the reactivity is too high and the nitric hydrofluoric acid aqueous solution deteriorates. Will progress in a short time. When the nitric acid concentration is 5% or less, the reaction does not proceed. On the other hand, when it exceeds 30%, it is necessary to cope with the generation of NOx and the workability is lowered.

  However, when a titanium material roughened in a nitric hydrofluoric acid aqueous solution is used as it is as a separator for a polymer electrolyte fuel cell, the contact resistance value of the separator tends to gradually increase with time. This is presumably because the fluoride remaining on the surface of the titanium material changes to oxide during power generation of the fuel cell. The contact resistance can be reduced by adding an inhibitor in an aqueous solution of nitric hydrofluoric acid under appropriate conditions, or by performing an additional acid treatment in an aqueous non-oxidizing acid solution that does not contain hydrofluoric acid after the treatment with the aqueous solution of nitric hydrofluoric acid. The rise is moderated to some extent.

  The etching rate by spraying and immersion can be controlled by the hydrofluoric acid concentration, nitric acid concentration, temperature, etc. of the aqueous nitric hydrofluoric acid solution. In addition to the above, the etching processing speed by spraying includes the discharge pressure from the nozzle of the aqueous fluoric acid solution, the discharge flow rate, the liquid flow velocity (linear flow velocity) on the substrate surface to be etched, the hit angle of the spray against the substrate surface, It can be controlled by the distance between the spray and the substrate.

  When the substrate is annealed in the manufacturing process, a high-temperature oxide film is formed on the surface of the substrate. Such a high-temperature oxide film is removed by etching using the above acid solution.

  In order to obtain the desired surface roughness for the substrate, non-oxidizing acid aqueous solution such as sulfuric acid and phosphoric acid containing hydrofluoric acid, sulfuric acid containing hydrogen peroxide and non-oxidizing such as phosphoric acid instead of nitric hydrofluoric acid aqueous solution An aqueous acid solution or the like may be used. In order to adjust the corrosivity, an acid aqueous solution to which an inhibitor or glycerin is added may be used. The type of the acid solution to be used can be selected in consideration of restrictions such as difficulty of application in the line equipment to be actually processed and waste acid treatment capacity.

  Next, the surface of the base material whose surface roughness is adjusted is bombarded, and then Al is added by sputtering to form a surface coating layer.

  A very thin (for example, several nm to several hundred nm) surface passive film formed during etching using an acid solution, washing with water, drying, and subsequent standing in the atmosphere is removed by bombardment. As a result, the Al coating formed on the surface of the titanium material, that is, the surface coating layer, can be processed uniformly and with high adhesion by subsequent Al sputtering treatment. The bombardment time can be shortened to such an extent that such an object can be achieved. Specifically, the bombardment time can be from several seconds to several minutes at the longest.

Ar can be used as a gas for generating plasma by the bombarding process, and H ₂ may be used in combination as necessary. Due to the large atomic weight of Ar, the effect of bombardment treatment using Ar gas is high, but titanium has a very strong affinity with oxygen, and even during bombardment treatment, thickening of the oxide film on the substrate surface, and Oxygen intrusion into the substrate may proceed. By introducing hydrogen into the gas for generating plasma, the progress of oxidation can be reduced. However, titanium is a metal that easily absorbs hydrogen and becomes brittle. For this reason, if hydrogen is used in combination only when the oxide film remains on the surface, the penetration of hydrogen into the substrate can be suppressed.

When Ar or Ar and H ₂ is employed as a gas for generating plasma, the pressure in the chamber during the bombardment process is preferably 1.0 × 10 ⁻² Torr (1.3 Pa) or less. . When the pressure in the chamber exceeds 1.0 × 10 ⁻² Torr, the formation of a titanium oxide film on the surface of the base material and the entry of oxygen into the base material tend to occur.

  The bombarding process may be performed on a strip-shaped base material drawn out from the coil, and after the molding is completed into the shape of the solid polymer fuel cell separator and the surface roughness is adjusted by the acid solution, the base material May be performed. When the bombarding process is continuously performed on the band-shaped substrate, the mass productivity is remarkably excellent and the processing cost can be significantly reduced.

  If bombarding is performed on the base material that has been molded as a separator, the processing becomes a sheet-like system. However, by using a holder that can fix multiple substrates at once, and fixing multiple substrates to this holder, performing sheet-like processing for each holder reduces processing effort and costs. Can do. In this case, a holder on which a plurality of substrates are fixed is inserted into the decompression chamber, and then transferred from the decompression chamber to the sputtering treatment chamber in a sheet-like manner to form a surface coating layer, and then the sputtering treatment It is possible to carry out from the chamber to the decompression chamber in a sheet-like manner, and to carry out from the decompression chamber.

  Next, the sputtering process will be described. As described above, the surface coating layer can be formed by adding Al to the substrate surface by sputtering. The means for forming the surface coating layer is not limited to sputtering, and a vacuum deposition method using an electron beam may be employed. However, it is essential that the surface coating layer is as thin as 200 nm to 3 μm, and it is preferable to employ a sputtering method in which the film thickness can be easily controlled. The surface coating layer may be formed by HIPIMS (High Power Impulse Magnetron Sputtering).

  The sputtering treatment may be performed on a strip-shaped base material drawn from the coil, or may be performed on a base material that has been formed into a separator shape and whose surface roughness has been adjusted with an acid solution. It is preferable that the Al sputtering process be performed continuously in the same or continuous vacuum apparatus immediately after the bombardment process is completed. In this case, it can suppress that the base-material surface after a bombardment process oxidizes.

  The surface coating layer can be formed, for example, by sputtering using a high-purity metal Al target material. In this case, the higher the purity of the target, the lower the contamination of the substrate, but the higher the cost. The purity of the target may be 99.98% or more. The target may contain Ca, rare earth metal, etc. having strong affinity with oxygen as impurities. The surface coating layer may contain impurities such as trace impurities derived from the sputtering target and O (oxygen).

The effect of the present invention will be specifically described with reference to examples.
Table 1 shows the chemical composition of the substrate used in the test.

  Strip-shaped titanium materials 1 to 6 having a chemical composition shown in Table 1, a thickness of 0.120 mm, and a width of 400 mm were each prepared in the form of a coil. Each coil was manufactured in a general mass production manufacturing process, and was a bright annealing (BA) specification material in which the final annealing treatment was performed in a bright annealing furnace. The mass of each coil was 125 kg. In materials 3, 4 and 6, the content of at least one of Fe and O was outside the range of the content defined for the substrate in the present invention at the stage of the coil material. Moreover, in the raw materials 4 and 6, the content rate of at least 1 sort (s) of C and N was not in the above-mentioned preferable range. The H content was the lowest in material 1, 0.0012%, the highest in material 4, and 0.0042%, both being 0.005% or less, which is the preferred range.

<First embodiment>
From each of the coils of material 1 to material 4, five cut plates each having a width of 400 mm and a length of 500 mm are collected, and an acid treatment line installed exclusively for titanium foil on these cut plates. Then, the high-temperature oxide film layer formed on the surface during the bright annealing was dissolved and removed, and the surface roughness was adjusted. However, some cut plates were not treated with an acid treatment line.

  Here, the outline | summary of the used acid treatment line is demonstrated. In this acid treatment line, the maximum width of the material that can be stably conveyed is 400 mm. By supporting the cut plate from below with a Teflon (registered trademark) backup roll, deformation of the cut plate accompanying conveyance was prevented. This acid treatment line has a spray spray zone for spraying from the upper and lower sides of the cutting plate and an immersion zone for immersing the cutting plate in the acid solution. The etching amount and surface roughness can be adjusted. In this example, the surface roughness of the substrate was adjusted by the transfer rate of the substrate in the acid treatment line.

  The acid solution used in the acid treatment line was circulated between the acid treatment line via a 5000 liter tank equipped with a filter, and the concentrations of acid and additive were adjustable. In this example, a nitric hydrofluoric acid aqueous solution containing 15% nitric acid and 3% hydrofluoric acid was used. The liquid temperature was adjusted to 40 ° C. ± 0.5 ° in the tank. The cut plate immediately after the acid treatment was washed with water by spraying and with water by immersion. The clean water used is a pumped-up groundwater.

  After washing with water in this way, the cut plate was dried. Drying was performed in a heat-resistant steel mesh belt conveyance type tunnel type dry oven furnace set to 150 ° C. ± 2 °. It was confirmed that the cut plate surface after drying was in a state in which only a passive film having a level of several nm to several hundred nm was present.

  The cut plate was transported to the sputtering processing apparatus within 6 hours after the above processing and subjected to the sputtering processing. The sputtering process was performed using a holder dedicated to the cut plate. In this holder, four rectangular cut plate samples having a side length of 180 mm × 250 mm can be simultaneously fixed. The cut plate that had been dried after the acid treatment was cut into this size and shape and fixed to the holder.

Hereinafter, the sputtering process will be described in detail. The decompression chamber, the pretreatment chamber, the first sputtering treatment chamber, the second sputtering treatment chamber, and the decompression chamber have a five-chamber configuration arranged in a straight line in this order. Each chamber is composed of a stainless steel chamber. The external dimensions of the processing apparatus were 1.6 m in width and 19 m in total length. The process chamber was depressurized by a vacuum pump with a mechanical booster, a diffusion pump, a turbo molecular pump, and a cryopump, and the pressure could be reduced to at least 2 × 10 ⁻⁵ mmHg (2.66 × 10 ⁻³ Pa). It was.

  The decompression chamber can carry 30 sets of the above-mentioned cutting plate holders at a time, a jig that can feed these holders into the apparatus in a sheet-like manner, and an uncoiler that feeds a strip-shaped substrate from the coil Is provided. The pretreatment chamber has one bombard zone, the first and second sputtering treatment chambers each have two sputtering zones, and the conditions of each zone can be set independently. The return pressure chamber is provided with a holder for the above-described cutting plate at a time, 30 jigs that can receive these holders in a sheet-like manner, and a coiler that winds a belt-like substrate. ing.

  The holder is configured to be capable of rotating so that the sputtering process is uniformly applied to the cut plate. A movable partition door is provided between adjacent ones of the decompression chamber, the pretreatment chamber, the first sputtering treatment chamber, the second sputtering treatment chamber, and the decompression chamber. By opening the partition door, the adjacent chambers communicated, and by closing the partition door, the gas flow was blocked between the adjacent chambers.

When the partition door between the decompression chamber and the pretreatment chamber is closed, the atmosphere will not flow into the pretreatment chamber even if the decompression chamber is opened to the atmosphere in order to carry in the holder. When the partition door between the return pressure chamber and the second sputtering treatment chamber is closed, the atmosphere flows into the second sputtering treatment chamber even if the return pressure chamber is opened to the atmosphere in order to carry out the holder. There is nothing. Accordingly, when the holder is carried into the decompression chamber and when the holder is carried out from the decompression chamber, the pressure in the pretreatment chamber and the first and second sputtering treatment chambers is set to, for example, 5 × 10 ⁻³ mmHg (6 .7 × 10 ⁻¹ Pa) can be controlled within a range not exceeding. Further, the pressure and atmosphere of each chamber are individually restricted, but can be controlled independently.

  If necessary, argon gas, hydrogen gas, or the like can be introduced into the sputtering apparatus under reduced pressure. The width that can be uniformly sputtered by this apparatus is up to 600 mm. The standard excitation frequency is 13.56 MHz. However, separately, this apparatus also has a sputtering capability by HIPIMS. At the time of sputtering, -100V (constant) was applied as a standard bias voltage to the substrate, but the setting can be changed as necessary.

A preheating device is installed in the pretreatment chamber. With this preheating device, the base material can be preheated from the back surface of the holder by the radiant heat of the heating element that is energized and heated. In the first and second sputtering processing chambers, the temperature of the substrate during the sputtering process can be measured on the back side of the substrate. In the pretreatment chamber and the first and second sputtering treatment chambers, as long as the pressure is reduced to 5 × 10 ⁻³ mmHg (6.7 × 10 ⁻¹ Pa), the substrate is not heated. The temperature drop of the substrate was extremely gradual.

  Next, the formation method and conditions of the surface coating layer with respect to a base material are demonstrated. The surface coating layer was formed by performing a bombarding process on the substrate surface in the pretreatment chamber and performing a sputtering process on the substrate in the first and second sputtering chambers.

Four holders were prepared, and a cutting plate made of materials 1 to 4 was manually attached to each holder, and these four holders were carried into the apparatus for processing. Close the atmosphere release door of the decompression chamber and start exhausting the decompression chamber. When the pressure in the decompression chamber and the pretreatment chamber becomes 2 × 10 ⁻⁵ Torr (2.7 × 10 ⁻³ Pa), H ₂ gas and Ar gas were simultaneously introduced into the apparatus. The pressure in the decompression chamber and the pretreatment chamber was 1.2 × 10 ⁻² Torr (1.6 Pa). As the H ₂ gas, a commercial industrial high purity H ₂ gas having a purity exceeding 99.999% by volume was used. As the Ar gas, a commercial industrial high purity Ar gas having a purity exceeding 99.999% by volume was used. The H ₂ gas and Ar gas were adjusted so that the H ₂ concentration was 6% by volume by adjusting the flow rate.

After maintaining the introduction of H ₂ gas and Ar gas for 20 minutes, the partition door between the decompression chamber and the pretreatment chamber was opened, and the transfer of the holder from the decompression chamber to the pretreatment chamber was started. The transfer speed of the holder was variable, but was 10 cm / min. In the pretreatment chamber, the substrate temperature was preheated to 230 to 250 ° C. by applying radiant heat from the preheating device.

During the bombardment process and the sputtering process, the holder was rotated.
In the pretreatment chamber, ion bombardment was performed in an atmosphere of Ar and H ₂ to completely remove moisture adsorbed on the outermost layer of the base material, and a thin hydroxide layer and oxide film layer.

  Next, with the exception of some of the base materials, film formation by sputtering treatment was performed on the base materials using Al targets in the first and second sputtering chambers. During the Al sputtering treatment, the maximum temperature reached by the target substrate was set to 400 ° C. or lower. The temperature control of the substrate by water cooling was not carried out, and the substrate temperature was adjusted under the sputtering conditions so as not to exceed 400 ° C. As a result of actually measuring the temperature of the substrate, the highest temperature reached during the Al sputtering treatment was about 320 to 360 ° C.

  The thickness of the Al layer formed on the substrate surface by the sputtering treatment was adjusted by sputtering conditions, the number of Al targets to be excited in the line, and the conveyance speed of the holder in the sputtering zone. Sputtering was performed by setting the target thickness of the Al layer after film formation, that is, the surface coating layer, to 35 nm, 100 nm, 250 nm, and 350 nm. This obtained the titanium material provided with the base material and the surface coating layer formed on the base material (outermost layer).

  The obtained titanium material was evaluated as described below. Table 2 shows the evaluation results of the titanium material.

  The cut plates of Comparative Examples 1 and 6 are not treated by the acid treatment line. For this reason, the surface roughness for Comparative Examples 1 and 6 was measured for an untreated cut plate. The surface roughness of the other titanium materials is measured on the cut plate after being treated with the acid treatment line.

  The thickness of the surface coating layer is determined by a method of obtaining from the Al adhesion amount due to the weight change before and after the treatment by the sputtering apparatus, and the height of the step between the Al layer formation region and the Al layer non-formation region. It evaluated by the method which asks from a photograph. In the base material before film formation by sputtering, a heat-resistant tape for masking made by Nitto Denko is pasted on the surface of the flat part at the end, and the film is formed in an area including this tape, and after the film formation is completed, this tape is peeled off. As a result, the above steps were obtained. Even when the unevenness of the substrate surface is large, it has been confirmed in advance that the in-plane thickness change of the Al layer is within 5%.

  The adhesion of the surface coating layer was evaluated by a tape peeling test on the surface of the flat portion at the end of the titanium material. As the tape, a commercially available 24 mm wide cello tape (registered trademark, product number: CT405AP-24) manufactured by Nichiban Co., Ltd. was used. After this cello tape (registered trademark) was affixed to and peeled off from the surface of the flat part, the presence and amount of peeled Al present on the adhesive surface of the cello tape (registered trademark) were visually evaluated and evaluated by rank. The rank was determined as “good” (◯) or “inferior” (Δ) depending on the small amount of peeling of Al. The visual evaluation was performed by pasting the cello tape (registered trademark) on black Kent paper in order to make it easier to confirm Al adhering to the adhesive surface of the cello tape (registered trademark). The adhesion of the surface coating layer with a thickness exceeding 3000 nm (3 μm) was inferior.

  The room temperature tensile property elongation (%) is a result of room temperature evaluation carried out using a JIS No. 13 B specimen taken in the longitudinal direction. A correlation between the content of Fe, O, C, and N of the material and the elongation is observed. That is, a titanium material using a material having a high content of these elements tends to have a smaller elongation. Specifically, the elongation of the titanium material using the material 3 as the base material is smaller than that of the titanium material using the material 1 and the titanium material using the material 2 as the base material.

  The separator molding evaluation is an evaluation of the formability when a titanium material is press-molded using an 80-ton single-acting press and an evaluation die produced for the press. Thirty straight channels (similar to the channels 6a and 6b shown in FIG. 1B) having a width of 1 mm, a length of 110 mm, and a height of 0.7 mm are formed on the titanium material by this evaluation die. It was. Accordingly, it was possible to conduct screening evaluation at a laboratory level to determine whether or not the solid polymer fuel cell separator has processability to withstand press molding. Those in which no cracks were observed were defined as “good” (◯), and those in which cracks were observed were defined as “poor” (×). In the titanium material in which the crack was recognized, the remarkable crack of the hook shape had arisen in the bending part.

  The results of the separator molding evaluation were all good for the titanium material using the material 1 or 2 as the base material, but were inferior in the titanium material using the material 3 as the base material. This is considered to be because the ductility of the titanium material using the material 3 as the base material was lower than that of the titanium material using the material 1 or 2 as the base material.

  As an example of the surface modification process that is performed before the separator is incorporated into the fuel cell, a surface modification mainly including Au is performed on a titanium material having a size of 150 mm × 150 mm by performing a sputtering process using an Au target. A layer was formed. For the titanium material on which the surface coating layer was formed, the surface modification layer was formed after removing most of the surface coating layer by bombarding. The thickness of the surface modification layer was 50 nm (target) in terms of an average basis weight.

  For the surface modified layer, the adhesion was evaluated by the same evaluation as the adhesion evaluation for the surface coating layer. As shown in Table 2, the titanium material which is an example of the present invention had good adhesion, and the surface-modified layer was not substantially peeled off. On the other hand, the titanium material of the comparative example that does not satisfy the requirements of the present invention did not have good adhesion, and the surface-modified layer was peeled although there was a difference in degree.

  In the titanium material of Comparative Example 16 in which the material 5 was used and the surface coating layer was not formed (see Table 3), the oxygen content of the base material after the Au sputtering treatment was 121 ppm compared to the oxygen amount of the material 5. It was a high value. On the other hand, in the titanium materials of Examples 10 to 14, the amount of increase in the oxygen content of the base material after the Au sputtering treatment was 20 ppm or less. It turns out that the oxygen content rate of the base material could be suppressed by the surface coating layer.

<Second embodiment>
Trial manufacture of the titanium material which simulated the mass production process was performed using the coil of the raw material 5 and the raw material 6 in Table 1. At the time of mass production, it is necessary to perform continuous pressing at least about 60 sheets per minute using a progressive press die.

  If the surface roughness of the base material is adjusted before pressing, the surface with the adjusted roughness will be damaged, and this surface will be stained with lubricating oil, and the coil material with a rough surface will be pressed. As a result, the wear of the mold increases. Therefore, using a coil with bright annealing specifications as it is, progressive press processing is performed by a 500-ton press, and surface roughness adjustment by acid treatment and formation of a surface coating film are performed on a separator-shaped substrate after pressing. The process of applying was adopted.

Below, the manufacturing method of a titanium material is demonstrated in detail.
The coils of the material 5 and the material 6 were in a state in which a slip sheet was inserted. One coil was set on an uncoiler, and the material was press-molded and punched into a predetermined shape while being wound at a progressive press speed by the coiler. The separator shape was a serpentine type in which three flow paths (grooves) were formed, and the cell reaction area through which the reaction gas flows was 100 cm ² . The depth of the valley in the channel portion was 0.60 mm. The width of the mountain valley was 1 mm. Whether or not cracking occurred in the raw material during the processing was evaluated as separator molding evaluation.

  Table 3 shows the evaluation results.

  As shown in Table 3, the material 5 had a large elongation value, and as a result of separator molding evaluation, it was confirmed that the material 5 could be molded without causing cracks. On the other hand, the material 6 had a small elongation value, and as a result of separator molding evaluation, it was confirmed that many cracks occurred. The crack of the raw material 6 occurred in the press molding stage. These results correspond to the requirement of the base material in the present invention, in which the material 5 satisfies the requirement but the material 6 does not.

  In the same comparative example, there was a molded product that can be judged as having no cracks by visual evaluation of the appearance. Evaluation continued.

  A very small amount of press oil was adhered to the surface of the molded product that had undergone the above steps, and a high-temperature oxide film formed when the coil was brightly annealed was present.

  Next, using the acid treatment line used in the first example, the surface of the molded article is adjusted by the method and conditions in the first example to form a surface coating layer. Got. The above-described press oil and high-temperature oxide film were removed by the treatment using this acid treatment line. With respect to this base material, the same sputtering processing apparatus as used in the first example was used to perform Al sputtering processing to obtain a titanium material on which a surface coating layer was formed. By substantially the same method and conditions as in the first embodiment, except that a holder suitable for the separator-shaped base material was used and that only Ar gas was introduced into the sputtering processing apparatus to create an atmosphere for the sputtering processing. A surface coating layer was formed. However, the surface coating layer was not formed on the base materials of Comparative Examples 16, 17, 20, and 21.

  As in the first example, the titanium material in which the surface coating layer was not formed and the titanium material in which the thickness of the surface coating layer did not satisfy the requirements of the present invention were not good in adhesion of the surface coating layer.

  A surface modified layer mainly composed of Au was formed on these titanium materials in the same manner as in the first example, and the adhesion of the surface modified layer was evaluated. In the titanium material in which the surface coating layer was not formed and the titanium material in which the thickness of the surface coating layer does not satisfy the requirements of the present invention, the adhesion of the surface modification layer was not good.

Furthermore, a solid polymer fuel cell was produced using the titanium material on which these surface modified layers were formed as a separator, and the cell voltage after 2000 hours of operation was measured. The operating conditions of the fuel cell were such that the utilization rate of hydrogen and oxygen was constant at 40%, and the current density was a constant current of 0.1 A / cm ² . This is a condition that simulates the operation evaluation environment of a home stationary fuel cell. The cell voltage under the evaluation conditions was about 0.788 V immediately after the operation, but gradually decreased. In Table 3, when the cell voltage after 2000 hours of operation exceeds 0.750 V, “good” (◯), and 0.750 V or less as “poor” (×).

  When a separator manufactured from a titanium material that does not satisfy the requirements of the present invention was used, the cell voltage of the fuel cell was lower than when a separator manufactured from a titanium material that satisfied the requirements of the present invention was used.

  As a reference example, using a SUS316L separator treated with 50 nm cyan bath Au plating as an average basis weight on the surface, a polymer electrolyte fuel cell similar to that when using the above titanium material was prepared, and the characteristics were the same under the same conditions. evaluated. Before the cyan bath plating treatment, an acid solution treatment for adjusting the surface roughness was performed on SUS316L, and the surface roughness of SUS316L was adjusted to the surface roughness defined in the present invention. The case where SUS316L is used is shown in Table 3 as Comparative Examples 29 and 30. A separator obtained by subjecting SUS316L to gold plating using a cyan bath is desirable in that the cell voltage of the fuel cell can be maintained high. Any of the titanium materials of the examples of the present invention could easily produce a separator having cell voltage characteristics equivalent to these gold-plated SUS316L separators.

    1: Fuel cell 5a, 5b: Separator

Claims (1)

A titanium material for a separator of a polymer electrolyte fuel cell,
A substrate;
A surface coating layer mainly composed of Al formed on the outermost layer on the substrate;
The surface roughness of the substrate is Ra value of 0.12 to 4 μm,
The base material is in mass%,
Fe: 0.1% or less,
O: 0.11% or less, the balance of the base material consists of Ti and impurities,
The titanium material whose average thickness of the said surface coating layer is 200 nm or more and 3 micrometers or less.

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