JP6627367B2 - Titanium base material, titanium material, and cell member for polymer electrolyte fuel cell - Google Patents

Description

  The present invention comprises a titanium substrate for forming a surface modified layer by a surface modification treatment, a titanium material including the substrate and a surface modified layer formed on the surface thereof, and the titanium material. And a cell member for a polymer electrolyte fuel cell.

  As the polymer electrolyte fuel cell, for example, there can be mentioned a cell used as a power source for a vehicle, for home use, or the like. The cell member is a separator or a current plate that is a constituent member of the polymer electrolyte fuel cell. Examples of the surface modification treatment include a treatment for forming a surface modification layer containing a highly conductive substance on the surface of the base material.

  A fuel cell is a battery that generates a direct current using hydrogen and oxygen.The fuel cell is divided 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. It is roughly divided.

  Among these fuel cells, the phosphoric acid fuel cell operating at around 200 ° C. and the molten carbonate fuel cell operating at around 650 ° C. have reached the commercial stage at present. Further, due to recent technological development, a polymer electrolyte fuel cell operating near room temperature and a solid electrolyte fuel cell operating at 700 ° C. or higher have become small power sources for automobiles or homes, or commercial power sources. It is starting to enter the market as a power source for buildings.

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 aggregate of single cells. As shown in FIG. 1B, in the single cell, a fuel electrode membrane (anode) 3 is laminated on one surface of a solid polymer electrolyte membrane 2 and an oxidant electrode membrane (cathode) 4 is laminated on the other surface. It has a structure in which separators 5a and 5b are overlapped. The separator is sometimes called a bipolar plate.

  A typical material constituting the solid polymer electrolyte membrane 2 is a fluorine-based ion exchange resin membrane having a hydrogen ion (proton) exchange group. Each of the fuel electrode film 3 and the oxidant electrode film 4 includes a diffusion layer made of carbon paper or carbon cloth made of carbon fiber, 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. In some cases, the solid polymer electrolyte membrane 2, the fuel electrode membrane 3, and the oxidant electrode membrane 4 are bonded to each other and used as an integral member (MEA: Membrane Electrode Assembly).

  The fuel gas (hydrogen or hydrogen-containing gas) A flows through the flow path 6a, which is a groove formed in the separator 5a, whereby the fuel gas is supplied to the fuel electrode film 3. In the fuel electrode film 3, the fuel gas passes through the diffusion layer and comes into contact with the catalyst layer. An oxidizing gas B such as air is supplied to 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 comes into contact with 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.

  In addition, a fuel cell may be provided with a rectifying plate (not shown) for rectifying or distributing a fuel gas or an oxidizing gas. The current plate is sometimes called a porous plate, a fin, or a mesh.

The main functions required of the separator of the polymer electrolyte fuel cell are as follows.
(1) Function as a "flow path" for uniformly supplying a fuel gas or an oxidizing gas into the cell surface. (2) Water generated on the cathode side is combined with a carrier gas such as air and oxygen after the reaction together with a fuel gas. Function as a "flow path" for efficiently discharging the battery from the outside of the system (3) A contact path with the electrode membranes (anode 3 and cathode 4) becomes a path for electricity, and furthermore, an electrical connection between two adjacent single cells. Function as “connector” (4) Between adjacent cells, function as “partition wall” between anode chamber of one cell and cathode chamber of adjacent cell

  At the laboratory level, carbon plate materials have been studied as separator materials. However, the carbon plate material has a problem that it is easily cracked, and furthermore has a problem that the machining cost for flattening the surface and the machining cost for forming the gas flow path are extremely high. These problems make commercialization of the polymer electrolyte fuel cell itself difficult.

Among carbon materials, a heat-expandable graphite product has been receiving the most attention as a material for a separator of a polymer electrolyte fuel cell because it is extremely inexpensive. However, problems to be solved in the future include, for example, the following.
・ Responding to increasingly stringent demands for dimensional accuracy ・ Aging deterioration of organic resin that occurs over time during use in fuel cells ・ Carbon corrosion that progresses under the influence of the battery operating environment ・ Cross leak Hydrogen permeation and unexpected cracking during fuel cell assembly and use

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

  Patent Literature 1 discloses a fuel cell separator which is made of a metal member and has a surface in contact with an electrode of a unit cell which is directly plated with gold. Stainless steel, Al, and a Ni—Fe alloy are mentioned as a material constituting the metal member, and SUS304 is mentioned as the stainless steel. This separator is plated with gold. Therefore, the electrical contact resistance between the separator and the electrode is low, and the conduction of electrons from the separator to the electrode is improved. Thereby, in the fuel cell of Patent Document 1, the output voltage is said to increase.

  Patent Literature 2 discloses a polymer electrolyte fuel cell including a separator made of a metal material whose surface is easily formed with a passivation film by contact with the atmosphere. Examples of the metal material include stainless steel and a Ti alloy. A passivation film always exists on the surface of the metal used for the separator. For this reason, the surface of the metal is less likely to be chemically attacked, and the proportion of ionized water in the fuel cell is reduced. Thereby, in the fuel cell of Patent Literature 2, it is said that the decrease in the electrochemical reactivity is suppressed. Patent Literature 2 also discloses that a contact resistance value is reduced by removing a passivation film of a portion of the separator that contacts an electrode film or the like and forming a noble metal layer.

  Patent Document 3 discloses a titanium material for an upper plate of a camera. This titanium material contains H: 0.002% by mass or less, N: 0.007% by mass or less, Fe: 0.02 to 0.06% by mass, and O (oxygen): 0.03 to 0.06% by mass. It contains, and the balance consists of titanium, the crystal grain size is 4 to 7, and the elongation is 45% or more.

  In order to form the camera upper plate, it is required that the formability is extremely excellent. When manufacturing the camera upper plate, processing (integral molding) including processes such as blanking, drawing a plurality of times, stamping, drilling, and edging is performed. According to Patent Document 3, if the crystal grain size of the titanium material to be processed is 4 (the crystal grain size is 40 to 45 μm), no crack is generated at the time of processing the camera upper plate. On the other hand, cracks are remarkably generated in a titanium material having a crystal grain size exceeding 7, for example, in a titanium material having a crystal grain size of 8 or 10 (crystal grain size of 25 to 30 μm), cracks are generated during forming of the upper plate. It cannot be applied as a product. However, if the crystal grain size is less than 4, it is said that roughened skin (wrinkles) has occurred in the processed portion.

  Patent Document 4 discloses a method of manufacturing a pure titanium sheet by repeating cold rolling and annealing. In this method, the final annealing is performed as continuous annealing at 600 to 800 ° C. for 2 to 6 minutes in an air atmosphere, so that the average crystal grain size of the product is adjusted to 3 to 60 μm and the surface gloss is increased. It is said that a pure titanium sheet in a suppressed state is obtained. After the final annealing, a pickling treatment is performed. According to this method, it is said that the occurrence of defects with a wavy surface during molding can be suppressed as compared with a vacuum-annealed material.

  Patent Literature 5 discloses a method of appropriately adjusting the crystal grain size of a titanium material by the contents of Fe and O and the conditions of batch annealing in accordance with required performance and quality. According to Patent Literature 5, the crystal grain size is set to 4 to 5 for a sheet material requiring overhang formability, and set to 5.5 to 6.5 when prevention of surface roughness is required in addition to overhang formability. It is disclosed that when roll formability is required in production, the value is set to 8 to 11.

  Patent Document 6 discloses that, by mass%, Fe: 0.035 to 0.100%, O: 0.010% or more and less than 0.030%, the balance consisting of titanium and impurities, and a crystal grain size of 8. Pure titanium plates between 0 and 11.5 are shown. The material of this titanium plate is obtained by electron beam melting or vacuum arc melting, and is said to be excellent in formability.

  Patent Document 7 discloses that, by mass, Fe: more than 0.1 and 0.5 or less, and O: 0.03 or more and 0.1 or less, with the balance being titanium and impurities, and having a grain size of 10 or more. Certain titanium materials are disclosed. This titanium material is said to be excellent in formability.

  Patent Document 8 discloses that, by mass, Fe: more than 0.10% and less than 0.60%, O: more than 0.005% and less than 0.20%, C: less than 0.015%, and N: A titanium material containing less than 0.015% and H: less than 0.015%, with the balance being titanium and impurities, is disclosed. In this titanium material, Fe is contained more than O, a two-phase structure of α phase and β phase is formed, and the α-phase equivalent circle average particle size is 10 μm or less.

  Patent Document 9 discloses that a titanium material containing, by mass%, Fe: 0.15% or less (excluding 0%) and O: 0.15% or less (excluding 0%) is press-formed. It is disclosed to obtain a titanium plate by processing. The average crystal grain size of the α phase of the titanium plate is said to be 10 to 200 μm.

  Patent Document 10 contains, by mass%, Fe: 0.15% or less (not including 0%) and O: 0.15% (not including 0%), with the balance being from Ti and impurities. Is disclosed. Patent Document 10 specifies the crystal orientation and crystal grain size of a titanium material, and describes that this titanium plate is excellent in press-formability with high proof stress. Regarding the crystal grain size, among the crystal grains existing in a square having a side of 1 mm on the surface of the titanium plate, the average crystal grain size of the top 100 crystal grains is 10 to 200 μm. The ratio of the proof stress in the rolling direction of the titanium plate to the proof stress in the rolling vertical direction of the titanium plate is set to be 0.75 or more.

  Patent Document 11 discloses a titanium plate containing, by mass%, 0.04 to 0.10% of Fe and 0.07 to 0.20% of O, with the balance being Ti and impurities. I have. This titanium material is said to be excellent in formability such as press working.

  In Patent Document 12, O: 0.07 to 0.20%, Fe: 0.04 to 0.10%, N: 0.001% or more and less than 0.02%, and C: A titanium plate containing less than 0.015% (including 0%) and the balance of Ti and impurities is disclosed. In this titanium material, the O content [% O] and the Fe content [% Fe] satisfy [% O] + 0.12 × [% Fe] ≧ 0.080, and have high strength and excellent moldability. It has been.

  Patent Document 13 discloses that, by mass%, O: 0.03% or more and less than 0.08%, Fe: 0.015% or more and less than 0.055%, and N: 0.001% or more and less than 0.02%. And C: less than 0.015% (including 0%), and the balance discloses a titanium plate composed of Ti and impurities. In this titanium material, the O content [% O] and the Fe content [% Fe] satisfy [% O] + 0.12 × [% Fe] <0.080, and are considered to be excellent in moldability. ing.

  Patent Literature 14 discloses a titanium plate containing 0.04 to 0.06% of Fe and 0.07 to 0.11% of O in mass%, with the balance being Ti and impurities. . This titanium material is said to have high proof stress and to be excellent in formability such as press working.

  Patent Literature 15 discloses a method of obtaining titanium or a titanium alloy by melting a raw material by an electron beam melting method. At this time, impurity elements such as O and Fe are reduced by introducing a purified gas comprising at least one of hydrogen, paraffin hydrocarbon, ammonia, halogen, and carbon monoxide into the electron beam melting chamber. .

  Patent Document 16 discloses that titanium is added to a titanium raw material containing O, which is dissolved by an electron beam, and O contained in the titanium raw material is gas-phase deoxidized as an oxide of Al. A method is described. Further, Patent Document 16 discloses that a shortage of Al is further added to a titanium raw material in which Al and O remain, and these are melted by an electron beam to convert O contained in the titanium raw material into an oxide of Al. Also disclosed is a method for deoxidizing titanium that is vapor phase deoxidized.

  In Patent Document 16, as an example, after a titanium sample having an initial O content of 10% by mass and an Al content of 10% by mass is melted for 6 minutes, substantially all of the metallic Al becomes O 2. And the O content was halved. As another example, Al was added to a titanium sample having an initial O content of 1.1% by mass and a titanium sample having an initial O content of 0.12% by mass, and the titanium sample was melted for 5 minutes. It is shown that the O content was reduced to less than 0.5% by mass and less than 0.05% by mass, respectively. At that time, the Al addition rates with respect to the total mass of the initial sample were 20% by mass and 5.5% by mass, respectively. Patent Document 16 does not disclose the Al content of the titanium material after adding Al and maintaining the molten state.

  Patent Literature 17 discloses an electrode having a MAX layer on a surface layer, and a method for manufacturing the same. Here, the MAX layer is a layer composed of a composition composed of at least one of carbide and nitride, and contains M, A and X defined below. A is at least one of Al, Si, Ga, Ge, Sn, and Pb, M is at least one of transition metals, and X is at least one of carbon and nitrogen.

Patent Literature 17 describes stainless steel and one or two of Al and Ni (including their alloys) as a material constituting a base material of an electrode. Further, as examples of compounds constituting the MAX layer, Ti ₂ AlC, Ti ₂ AlN, Ti ₂ AlN _0.5 C _0.5 , Ti ₃ AlC ₂ , Ti ₃ SiC ₂ , TiAlN _3, and Ti ₄ SiC ₄ are mentioned. . It is stated that the MAX layer may be doped with a noble metal such as Au, Pt, and In.

JP-A-10-228914 JP-A-8-180883 Japanese Patent Publication No. 7-62194 Japanese Patent Publication No. 64-1546 JP-A-10-317118 Japanese Patent No. 4388503 JP 2009-161816 A Japanese Patent No. 4605514 Japanese Patent No. 5123910 Japanese Patent No. 5385038 Japanese Patent No. 5400824 Japanese Patent No. 5427154 Japanese Patent No. 5444182 Japanese Patent No. 5654933 JP-A-9-25522 Japanese Patent No. 2651945 Japanese Patent No. 5512553

  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. As an example of the surface modification treatment, there is a sputtering treatment for forming a surface modification layer having high conductivity on the surface of the separator.

  None of the materials disclosed in Patent Documents 1 to 17 is based on the assumption that such a surface modification treatment is performed. When a surface modification treatment is performed on these materials, the surface of the materials is oxidized by oxygen in the treatment atmosphere, and oxygen is taken into the surface modification layer. As a result, the contact resistance of the material on which the surface modification layer is formed does not become sufficiently low.

The present invention has been made in view of such a problem, and a titanium substrate that can suppress oxidation of the substrate surface and introduction of oxygen into the surface modified layer during the surface modification treatment. The purpose is to provide.
Another object of the present invention is to provide a titanium material having a surface modified layer in which the introduction of oxygen is suppressed, in which oxidation of the substrate surface is suppressed, and a cell for a polymer electrolyte fuel cell comprising the titanium material. It is to provide a member.

  The gist of the present invention is a base material of the following (A), a titanium material of the following (B) and (C), and a cell member for a polymer electrolyte fuel cell of the following (D).

(A) In mass% or mass ppm,
Fe: 0.010% or more and 0.100% or less,
O: 0.005% or more and 0.110% or less, and Al: more than 1 ppm and 0.500% or less, with the balance being Ti and impurities,
The impurity is
C: 0.015% or less,
A titanium material containing N: 0.001% or more and 0.020% or less, and H: 0.015% or less.
This titanium material may contain no more than 0.25% of a noble metal instead of part of Ti.

(B) the base material of (A),
A surface-modified layer formed on the surface of the base material,
Including
The titanium material, wherein the surface-modified layer includes an Al-based oxide and includes at least one of Ti carbide and Ti carbonitride dispersed in the Al-based oxide.

(C) the base material of (A),
A surface-modified layer formed on the surface of the base material,
Including
The surface modified layer is a titanium material mainly composed of at least one of Ti carbide and Ti carbonitride.

(D) A cell member for a polymer electrolyte fuel cell, comprising the titanium material of (B) or (C).

  The base material of the present invention is mainly composed of Ti and contains Al. Therefore, when the substrate is subjected to a sputtering process as a surface modification process, a plasma containing Al ions and Ti ions is generated. Since Al ions have a higher affinity for O than Ti ions, O (O ions) in the sputtering atmosphere is bonded to Al ions preferentially over Ti ions, and becomes Al oxide vapor. Thereby, while being able to suppress that a base-material surface is oxidized, it can suppress that O is introduce | transduced into the surface modification layer formed by sputtering.

  The titanium material of the present invention has a surface modified layer in which oxidation is suppressed, and oxidation of the substrate surface is suppressed. The cell member for a polymer electrolyte fuel cell of the present invention includes the titanium material of the present invention. Therefore, the titanium material and the cell member have low contact resistance.

  When the base material of the present invention does not contain a noble metal, a titanium material having a surface-modified layer having excellent conductivity formed on the base material can be manufactured at low cost. On the other hand, when the substrate of the present invention contains a noble metal, the substrate, the titanium material, and the cell member of the present invention have high corrosion resistance.

FIG. 1A is a perspective view of the entire fuel cell. FIG. 1B is an exploded perspective view of the fuel cell unit.

  The present inventors have studied metal separators having excellent corrosion resistance. At that time, the goal was to find a metal separator material in which the amount of metal eluted from the separator surface was extremely small even when used as a separator for a polymer electrolyte fuel cell for a long time. By using such a metal separator, contamination of the MEA with metal ions hardly progresses, and a decrease in catalytic performance and a decrease in polymer membrane performance hardly occur.

  Metals studied for the separator include general-purpose SUS304 and SUS316L, their gold-plated materials, M2B or M23C6 type conductive metal precipitate-dispersed stainless steel materials, stainless steel materials coated or coated with conductive fine powder, and surfaces. It was a modified stainless steel material and a titanium material. As a result of the study, the following findings were obtained.

  Stainless steel is a material having excellent mass productivity and having both corrosion resistance and workability. In this regard, stainless steel can be a candidate as a material for a cell member of a polymer electrolyte fuel cell. However, in a fuel cell using stainless steel, the degree of elution of metal ions varies depending on the structure or the skill of controlling operation and suspension. Under conditions where metal ions are easily eluted, even if the stainless steel surface is kept in a passive state, metal ions are gradually eluted from the stainless steel, and irreparable damage is caused to the solid polymer film and the catalyst. May be given. In this case, the performance of the polymer electrolyte fuel cell is greatly reduced.

  Titanium is a very expensive material, but is one of the few highly corrosion-resistant metal materials on the market that hardly dissolves metals even in the environment inside a polymer electrolyte fuel cell. That is, in the titanium separator, the degree of elution of metal ions is not affected by the structure of the fuel cell or the control of operation and suspension. Therefore, if cost is ignored and only corrosion resistance is emphasized, titanium is an extremely suitable material as a constituent material of a cell member for a polymer electrolyte fuel cell.

  However, in terms of workability, titanium is generally inferior to stainless steel. However, it is known that the workability of titanium greatly changes depending on the type and content of trace elements in the material. In particular, Fe, O, and N, which are impurity elements mixed in the manufacturing process, greatly affect the workability of titanium. Further, a small amount of H in titanium has a great effect on cracking and embrittlement. However, lowering the content of impurities and lowering the manufacturing cost are conflicting requirements.

  A fuel cell is used in a state where many (for example, several hundred) cells are stacked and fastened. With pure titanium, if the content of Fe and O is too low, the yield strength becomes too low, and the load at the time of fastening may buckle the separator or the rectifying plate. On the other hand, in the case of pure titanium, if the content of Fe and O is too high, the yield strength becomes too high, and press formability and elongation properties are inferior.

  When the sputtering process is performed, high-temperature plasma containing ions of the introduced gas is generated. This plasma also contains O ions originating from water in the chamber where sputtering is performed. In such a plasma, the surface of the titanium material base material is subjected to sputtering (bombarding), and at the same time, the formation of the surface-modified layer by sputtering on the base material proceeds. At that time, when the Al content of the base material is as low as less than 1 ppm, the surface of the titanium material (base material) may be oxidized and the oxygen content of the surface modified layer may increase.

Depending on the Al content of the substrate and the sputtering conditions, if the content of Al ions originating from the substrate in the plasma increases, the most easily oxidized Al ions among the plasma ions become O ions. With aluminum oxide vapor such as Al ₂ O. Since the aluminum oxide vapor is evacuated to the outside of the apparatus, the surface oxidation of the substrate itself and the introduction of O into the surface modified layer are suppressed.

Al ₂ O ₃ is an insulator. However, even when the surface modified layer formed by the sputtering process is mainly composed of aluminum oxide, conductive Ti carbide (for example, TiC) and Ti carbonitride are included in the surface modified layer. When at least one of (for example, TiCN) is dispersed, the surface modified layer may have conductivity.

  Further, in the case where a surface modified layer mainly composed of at least one of Ti carbide and Ti carbonitride is formed, when O in the plasma is removed as aluminum oxide vapor by Al in the base material, the surface is deteriorated. The O content of the modified layer decreases. In this case, the conductivity of the surface-modified layer is significantly improved. This is because the ratio of titanium oxide having poor conductivity is reduced.

The present invention has been obtained based on these findings and a unique technical idea.
As described above, the base material of the present invention contains, by mass% or mass ppm, Fe: 0.010% to 0.100%, O: 0.005% to 0.110%, and Al: 1 ppm And at most 0.500%, with the balance being Ti and impurities. The impurities include C: 0.015% or less, N: 0.001% or more and 0.020% or less, and H: 0.015% or less.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. In the following description, unless otherwise specified, all “%” are mass% and “ppm” are mass ppm in chemical compositions.

[Base material of the present invention]
The essential elements in the substrate of the present invention are Ti, Fe, O, and Al. This base material may contain a noble metal as an optional element. Hereinafter, each element will be described.

Fe: 0.010% or more and 0.100% or less Fe is generally contained as an impurity in titanium, but is an additive element (adjusting element) that is effectively used in the base material of the present invention. In the base material, Fe is a β-phase stabilizing element, and partly forms a solid solution with the α-phase, but mostly forms a β-phase. It precipitates and acts to suppress crystal grain growth. By adjusting the Fe content and the O content, the yield strength can be increased while suppressing the decrease in ductility of the substrate. Further, by suppressing the growth of crystal grains, it is possible to suppress the occurrence of burrs at the time of cutting or forming a punched hole, and to expect an effect of reducing the wear of the mold.

  However, if the Fe content is higher than 0.100%, the moldability cannot be ensured even if the O content in the base material is reduced. On the other hand, if the Fe content is less than 0.010%, the yield strength becomes too low, the material becomes soft, and it becomes easy to buckle. In addition, it becomes difficult to secure a raw material capable of reducing the Fe content. Cost stable mass production becomes difficult. Therefore, in the base material of the present invention, the lower limit of the Fe content is set to 0.010%, and the upper limit is set to 0.100%. The Fe content is preferably 0.020% or more and 0.100% or less, and more preferably 0.030% or more and 0.100% or less.

O (oxygen): 0.005% or more and 0.110% or less O is generally contained as an impurity in titanium, but is an additive element that is effectively utilized in the base material of the present invention. The cell member of the polymer electrolyte fuel cell assumed as a main use of the base material of the present invention is required to have the following characteristics at the same time.
・ Excellent mass productivity ・ Inexpensive ・ Excellent corrosion resistance ・ Good moldability when processing as a cell member (for example, it is unlikely to generate warpage and burrs) ・ Gold used when processing into a cell member The durability of the mold must be sufficiently high. The material must have a material strength (proof strength) that does not easily buckle when the fuel cell is assembled by fastening cells.

  In order to satisfy such requirements, the O content needs to be 0.005% or more and 0.110% or less. That is, if the O content is less than 0.005%, the material strength is insufficient, the base material is soft, and the material tends to buckle, and the local elongation during punching is so high that burrs are remarkably generated. become. On the other hand, if the O content of the base material is reduced to less than 0.005%, the production cost becomes too high, and cannot be a material for the above-mentioned intended use in terms of mass productivity and cost. On the other hand, when the O content exceeds 0.110%, even if the content of other elements such as Fe is adjusted, the material strength and proof stress become too high, and the elongation performance becomes poor. It becomes difficult to form an overhang for forming the flow path of the fuel cell member. On the other hand, when the O content exceeds 0.110%, the life of the mold is shortened, which is not suitable for mass production. The O content is preferably 0.010% or more and 0.060% or less.

Al: more than 1 ppm and not more than 5000 ppm In the base material of the present invention, Al is an additive element that is actively utilized. The Al content is more than 1 ppm and 5000 ppm or less. As described below, when manufacturing the base material of the present invention, the O content of the base material can be adjusted by positively adding Al as a deoxidizing element during melting. By such a manufacturing method, a base material having an Al content exceeding 1 ppm can be manufactured.

  In addition, as described later, when a surface modification treatment is performed on a substrate to form a surface modification layer, Al in the substrate causes oxidation of the substrate surface and O Acts to suppress the introduction of If the Al content is less than 1 ppm, this effect cannot be obtained. The Al content preferably exceeds 3 ppm, and more preferably exceeds 5 ppm.

  If the Al content exceeds 5000 ppm, the moldability of forming the cell member by processing such as pressing and the corrosion resistance of the cell member will be low. In particular, since the surface-modified layer is not substantially formed on the end face of the plate-shaped cell member and the base material is exposed, when the Al content of the base material exceeds 5000 ppm, the corrosion resistance at this end face is secured. become unable. The Al content is preferably 1000 ppm or less, more preferably 100 ppm or less.

  The Al content of the substrate can be quantitatively analyzed by a titanium-ICP emission spectral analysis method standardized in JIS H 1632-2. The content of less than 10 ppm can be quantitatively analyzed by glow discharge mass spectrometry. Thereby, analysis can be performed with an accuracy of 0.01 ppm. As the measuring device, for example, VG9000 manufactured by FI ELEMENT can be used.

Hereinafter, the impurity elements will be described.
C: 0.015% or less (including 0%)
In the substrate of the present invention, C is an impurity. C easily adheres to the surface of the base material due to contamination from the rolling oil used in the rolling process. Due to the presence of C in the surface layer of the substrate, TiC or TiCN is generated on the surface of the substrate in the annealing step. Both TiC and TiCN are high-hardness intermetallic compounds, and may cause damage to a mold used for processing a base material earlier. For this reason, the C content is set to 0.015% or less (including 0%). More preferably, the C content is 0.010% or less.

N: 0.001% or more and 0.020% or less In the substrate of the present invention, N is an impurity. By absorbing N from the atmosphere in the annealing step, the N content of the base material tends to increase, and in this case, TiN is generated. TiN is a high-hardness intermetallic compound, which causes damage to a mold earlier. Therefore, the N content is set to 0.001% or more and 0.020% or less. The N content is preferably 0.015% or less, more preferably 0.010% or less.

H: 0.015% or less In the substrate of the present invention, H is an impurity. H is inevitably absorbed by the substrate due to pickling, annealing, and electrolytic treatment as necessary in the substrate manufacturing process. H causes hydrogen embrittlement and hydrogen cracking of the substrate. For this reason, the H content is set to 0.015% or less, and preferably 0.010% or less.

Other impurities: Ca
The substrate of the present invention may contain Ca as an impurity in several ppm. In the case where a cored wire having an Al exterior and a CaCl ₂ interior is used as an Al source to be added to the molten titanium in a production method described later, the obtained base material contains Ca as an impurity. Like Al, Ca also has a stronger bonding force with O than Ti, and Ca oxide has a high vapor pressure, so that it is easily removed from the high-temperature molten titanium. For this reason, in many cases, Ca does not remain on the substrate in excess of 10 ppm.

Noble metal: 0.25% or less Noble metal is not an essential additive element in the base material of the present invention. However, in order to improve corrosion resistance and electrical contact resistance performance, noble metal is contained instead of part of Ti. You may. Here, the noble metal is at least one of Au, Ag, Pt, Pd, and Ru. If the precious metal content exceeds 0.25%, the increase in material cost cannot be ignored. For this reason, when the substrate of the present invention contains a noble metal, its content is set to 0.25% or less.

  As a reference example, a case where a rare earth element is contained in the base material of the present invention will be considered. Since the rare earth element has a very strong bonding force with O, the inclusion of the rare earth element in the base material is effective for fixing O in the base material. When manufacturing such a base material, the rare earth element may be added to the molten titanium. In this case, the rare earth element is reacted with O remaining in the molten titanium to form a fine oxide of the rare earth element, thereby making it possible to control the crystal grain refinement of the base material. However, since the vapor pressure of the rare earth element oxide is low, it is not expected that gas phase (vapor) deoxidation will proceed. The rare earth element may be added as an Al cored wire containing the rare earth element.

[Method for producing the substrate of the present invention]
It is difficult to obtain a titanium base material by melting and scouring it in a melting furnace or crucible lined with an oxide refractory such as a steel material. This is because Ti is very easily combined with O and is melted under a vacuum or an inert gas atmosphere. In such an atmosphere, an oxide-based refractory is easily reduced by Ti and suffers erosion. It depends. For this reason, the titanium base material is usually obtained by dissolving the raw materials using a water-cooled copper mold.

  As a method of melting titanium ingot as a raw material of a base material, various special melting techniques with different heating methods have been developed. The current mainstream of the melting method is a vacuum arc melting (VAR) method, a plasma arc melting method (PAM), a vacuum induction melting (VIM) method, and an electron beam melting (EBM) method. : Electron Beam Melting) method.

  The base material of the present invention is assumed to be produced in large quantities in the future as a material for a polymer electrolyte fuel cell mounted on an automobile. From this point, it is preferable to use the EBM method which can use a large amount of titanium scrap and return waste among the above-mentioned melting methods. In particular, the molten raw material including a large amount of scrap and return debris is continuously or semi-continuously supplied to a fire point (a portion of the surface of a molten metal (molten metal) where an electron beam is incident), and continuously. The most preferred method is a dissolving method in which an ingot is formed into a billet, for example, a gutter method EBM method.

O in titanium is thermodynamically stable and it is very difficult to remove it. The temperature of the molten metal at the flash point is a high temperature exceeding 2000 ° C., and in this portion, it is generally thermodynamically difficult to concentrate O by the amount of evaporation of Ti and deoxidize O as Ti oxide vapor. It is. The present inventor has studied deoxidation of titanium from a molten metal, such as deoxidation as CO gas, deoxidation as Si oxide vapor, and deoxidation as Al oxide vapor. As a result, it was concluded that the most effective means for removing O in the molten titanium is to add Al and deoxidize it as Al ₂ O vapor.

In the case of smelting by the EBM method, for example, an Al source is introduced into the molten titanium, Al is reacted with O in the molten titanium, and O can be removed from the surface of the molten titanium as Al oxide vapor. According to the thermodynamic calculation using the value of the degree of vacuum in the chamber in which the electron beam melting is performed, the surface of the molten metal whose temperature exceeds 2000 ° C. is vaporized as an Al oxide gas (considered to be Al ₂ O). From this molten metal, the metal Ti is also vaporized, but the vapor pressure of the Al oxide gas is about two orders of magnitude higher, and most of the gas exhausted from the chamber is the Al oxide gas.

  In the vicinity of the fire point, the high-speed rotation (stirring) of the molten metal occurs due to the magnetic field of the high-current electron beam, and the renewal speed of the molten metal surface is extremely high. By reducing the pressure in the chamber due to the above factors, Al gas phase deoxidation proceeds efficiently at and around the flash point.

  Rather than increasing the Al concentration of the entire titanium melt, by increasing the Al concentration only at and around the flash point, the added Al can efficiently contribute to the evaporation of Al oxide, that is, deoxidation. Can be. For this purpose, the Al source is not charged into the melting tank at the same time as the titanium-dissolving raw material, but is directly and continuously charged into the flash point and the surrounding molten pool, so that the Al concentration is reduced to the flash point and It is preferable that the height be increased only in the vicinity thereof.

  On the other hand, at a temperature of 1500 ° C. or lower on the surface of the molten metal, which is far from the fire point, the vapor pressure of the Al oxide is low, so the evaporation rate of the Al oxide is low, and most of the added Al remains in the molten metal. As described above, the evaporation rate of the Al oxide varies depending on the temperature of the surface of the molten metal, and therefore, depending on the distance from the fire point. For this reason, the Al concentration of the molten titanium can be controlled by the addition position of the Al source. The Al concentration of the molten titanium can also be adjusted by the amount of Al added and the degree of vacuum in the melting tank.

As the Al source, for example, an aluminum shot, an aluminum wire, or a cored wire having an Al exterior / CaCl ₂ interior can be used. The Al source in the form of a wire can be directly charged into the molten metal using, for example, an automatic wire feeder.

  The substrate of the present invention can be produced by a method other than the above method. For example, Al may be added at the same time as the titanium scrap melting raw material to be additionally charged.

[Titanium material of the present invention]
As described above, the titanium material of the present invention includes the base material of the present invention and a surface modified layer formed on the surface of the titanium material.

The surface-modified layer contains an Al-based oxide and may include at least one of Ti carbide and Ti carbonitride dispersed in the Al-based oxide (hereinafter, referred to as “Ti carbide or the like”). The surface modified layer may be mainly composed of Ti carbide or the like, and in this case, the surface modified layer may include an Al-based oxide. Here, “mainly” means that the proportion of the surface modified layer is 50% by mass or more. The “Al-based oxide” refers to an oxide of Al and a composite oxide of Al and one or more other metals.

  Both Ti carbide and Ti carbonitride have excellent conductivity, but Al-based oxides have poor conductivity. Therefore, when the surface-modified layer is mainly composed of an Al-based oxide and contains Ti carbide or the like dispersed in the Al-based oxide, the conductivity of the surface-modified layer is obtained by Ti carbide or the like. When the surface-modified layer contains an Al-based oxide and Ti carbide, the larger the proportion of the Ti-based carbide and the like in the surface-modified layer, and the smaller the proportion of the Al-based oxide in the surface-modified layer The higher the conductivity of the surface modified layer, the higher the conductivity. The O content of the surface-modified layer is preferably less than 29%, more preferably less than 25%, even more preferably less than 20%.

  The surface modification layer may include amorphous C (carbon). Amorphous C in the surface-modified layer does not adversely affect the performance of the cell member containing the titanium material, but is rather preferable in that high conductivity is obtained.

A titanium material in a polymer electrolyte fuel cell environment by a surface-modified layer containing an Al-based oxide and containing Ti carbide or the like dispersed in the Al-based oxide or a surface-modified layer mainly containing Ti carbide or the like Can have high corrosion resistance.

When the surface-modified layer is formed by a sputtering process, the Al-based oxide in the surface-modified layer is formed from Al contained in the base material, and the Al-based oxide is formed in the surface-modified layer. Can also be regarded as impurities remaining in the substrate. However, the presence of the Al-based oxide in the surface-modified layer improves the stability of the titanium material provided with the surface-modified layer in a fuel cell. That is, in a state where the Al-based oxide is very little or hardly present in the surface-modified layer, TiO _x (x <2) having a non-stoichiometric composition is generated in the surface-modified layer. This TiO _x is unstable in the fuel cell, and changes to TiO ₂ having a stoichiometric composition with poor conductivity during operation of the fuel cell. As a result, the conductivity of the surface-modified layer is reduced, and the battery performance is reduced. When an Al-based oxide is formed instead of a Ti-based oxide having a non-stoichiometric composition, the battery performance is less likely to be reduced.

[Method for producing titanium material of the present invention]
Hereinafter, an example of a method for producing the titanium material of the present invention will be described, but the titanium material of the present invention is not limited to one produced by such a method.

  In performing the surface modification treatment, it is preferable to shorten the treatment time in order to increase mass productivity. The substrate of the present invention is, for example, a thin plate (foil). In this case, the final annealing at the time of mass production is performed, for example, in a bright annealing furnace whose atmosphere is adjusted for a titanium material, and a high-temperature oxide film of titanium is formed on the surface of the base material. In performing the surface modification treatment, it is necessary to completely remove the high-temperature oxide film of titanium on the surface layer of the substrate in order to ensure the adhesion of the surface modified layer to the substrate.

  It takes a long time to remove the high-temperature oxide film by bombarding with a gas ion plasma such as Ar. Therefore, removal of the high-temperature oxide film only by the bombardment treatment should be avoided from the viewpoint of production efficiency. In order to increase the production efficiency, it is preferable to continuously dissolve and remove the high-temperature oxide film in a dedicated acid solution treatment line after the bright annealing treatment. Thereby, most of the high-temperature oxide film is removed in a short time.

  As an acid solution used for removing the high-temperature oxide film, nitric hydrofluoric acid or the like can be used. During treatment with an acid solution, during washing with water, during subsequent drying in a drying oven (usually kept at 100 ° C. or lower), and when exposed to the atmosphere before the surface modification treatment starts, A film mainly composed of a hydroxide or an oxide is formed on the surface of the material. The thickness of this film is as thin as several nm to several tens nm. For this reason, this film can be removed by a bombarding process in a short time, for example, several seconds or at most a few minutes.

Ar can be used as a gas for generating plasma in the bombarding process, and H ₂ may be used in combination as needed. Due to the large atomic weight of Ar, the effect of the bombardment treatment using Ar gas is high. However, Ti has a very strong affinity for O, and during the bombardment treatment, O in the treatment atmosphere oxidizes the base material, that is, increases the thickness of the oxide film on the base material surface, and increases the oxygen content in the base material. Invasion may progress. By mixing H ₂ with a gas for generating plasma, the progress of oxidation of the substrate can be reduced. However, titanium is a metal that easily absorbs H and is easily embrittled. If H ₂ is used in combination only in the initial step of the bombardment treatment in which the oxide film remains on the surface of the substrate, it is possible to suppress the penetration of H into the substrate.

When Ar, or Ar and H ₂ are used as the gas for generating the plasma, the pressure in the chamber during the bombarding process is preferably set to 1.0 × 10 ⁻² Torr (1.3 Pa) or less. . When the pressure in the chamber exceeds 1.0 × 10 ⁻² Torr, a titanium oxide film is easily formed on the surface of the base material, and O easily enters the inside of the base material.

  The substrate to be subjected to the bombarding process may be formed in a belt shape and prepared in a state of being wound as a coil. When the band-shaped substrate is continuously subjected to the bombardment treatment, mass productivity can be remarkably increased, and the treatment cost can be significantly reduced. Further, the bombardment treatment may be performed on the base material after being formed into the shape of the cell member for a polymer electrolyte fuel cell and having the surface roughness adjusted by an acid solution.

  If a bombardment treatment is performed on the base material after being formed into the cell member, the treatment becomes a sheet-like method. However, by using a holder that can fix a plurality of base materials at once, and performing the sheet-like processing for each holder in a state where the plurality of base materials are fixed to the holder, processing time and cost can be reduced. Can be.

  Next, the sputtering process will be described. As described above, the surface modification layer contains a highly conductive substance and can be formed by sputtering. The highly conductive material can be, for example, Ti carbide (eg, TiC) or Ti carbonitride (eg, TiCN). These substances can be formed by sputtering in an atmosphere containing C or an atmosphere containing C and N.

  However, the means for forming the surface modified layer is not limited to sputtering, and for example, a vacuum deposition method using an electron beam may be employed. However, it is essential that the surface-modified layer be as thin as 200 nm to 3 μm, and it is preferable to employ a sputtering method that is thin and easy to control. The surface modification layer may be formed by HIPIMS (High Power Impulse Magnetron Sputtering).

  When performing the sputtering treatment, a sputtering target (hereinafter, also simply referred to as “target”) may or may not be used. When a target is not used, the composition is controlled only by sputtering the surface layer of the base material and redepositing the material (Ti, Al, etc.) constituting the surface layer as a metal material on the base material. To form a modified surface layer. However, a target containing a desired metal is additionally used, and a surface modification including a metal contained in the target (which may be the same kind of metal as that contained in the base material or a different kind of metal). A layer may be formed.

  For example, a high-purity metal Ti target may be used to form the surface-modified layer. In order to obtain a surface-modified layer having desired characteristics, the purity of the target is preferably as high as possible. However, the higher the purity of the target, the higher the cost. Generally, when the purity of the target is 99.98% or more, a surface-modified layer having desired characteristics can be obtained. The target may contain a metal element having a strong affinity for O, for example, Al, Ca, a rare earth metal, or the like, as an impurity. In this case, the oxidation of the surface of the substrate and the surface modified layer during the surface modification treatment can be suppressed.

When the surface of the substrate is subjected to a surface modification treatment involving sputtering of the surface of the substrate, a plasma containing Ti ions and Al ions, Ca ions, or rare-earth metal ions, which have jumped out of the substrate by sputtering, is generated. The sputtering atmosphere including the plasma also contains O ions originating from water which are inevitably brought into the chamber used for the processing. Since Al ions, Ca ions, or rare earth metal ions have a stronger affinity for O ions than Ti ions, O ions react preferentially with Al ions, Ca ions, or rare earth metal ions over Ti ions. , Al ₂ O, CaO and other metal oxides. Since the vapor pressure of each of these metal oxides is high and the inside of the chamber where the processing is performed during sputtering is kept at a reduced pressure by exhaustion, these metal oxides are exhausted out of the chamber as vapor. . This makes it possible to reduce the O concentration in the plasma and suppress oxidation of the substrate surface and an increase in the O content of the surface modified layer. As a result, a surface modified layer having high conductivity can be obtained, and the adhesion of the surface modified layer to the substrate is improved.

The surface modification layer containing Ti carbide can be formed by introducing a gas containing C as a reaction gas into a surface modification treatment chamber during the sputtering treatment. Further, the surface modified layer containing Ti carbonitride is formed by simultaneously introducing a gas containing C and a trace amount of gas containing N as a reaction gas into the chamber during the sputtering process. can do. In any case, a methane (CH ₄ ) gas, an acetylene (C ₂ H ₂ ) gas, or the like can be used as the C-containing gas. As the N-containing gas, a nitrogen (N ₂ ) gas, an ammonia (NH ₃ ) gas, or the like can be used.

  When forming a surface-modified layer mainly composed of an Al-based oxide, Al contained in the substrate of the present invention can be used as a raw material of the Al-based oxide. In this case, if necessary, further, sputtering using an Al target is performed simultaneously and in parallel with sputtering using a Ti target, or sputtering using a Ti—Al alloy target having an appropriate Al content. May be performed. Al contained in the Al target and the Ti—Al alloy target is also a raw material of the Al-based oxide.

  As described above, the surface modification treatment method and the application conditions can be appropriately selected depending on the desired surface modification layer and the surface modification treatment device to be used.

  According to the above-described production method, a surface-modified layer having a reduced O content can be formed to such an extent that it cannot be obtained when a substrate substantially not containing Al is used.

[Cell member for polymer electrolyte fuel cell of the present invention]
The cell member is a separator or a current plate. Since the cell member contains the titanium material, the contact resistance between the fuel electrode film 3 and the oxidant electrode film 4 (see FIG. 1B) in the polymer electrolyte fuel cell is low. In addition, the presence of the surface modification layer on the surface of the cell member results in high corrosion resistance in the polymer electrolyte fuel cell.

  This cell member can also be manufactured by appropriately forming a thin plate-shaped titanium material of the present invention (substrate having a surface-modified layer formed thereon) such as stretch forming or punching. . However, this cell member is subjected to forming processing such as overhanging and punching, as appropriate, on the thin plate-shaped base material of the present invention to obtain a desired shape as the cell member, and then the surface is formed on the surface thereof. It is preferable to manufacture by forming a modified layer. If the forming process is performed after the formation of the surface-modified layer, the surface-modified layer is damaged, and appropriate characteristics as the cell member, such as contact resistance and corrosion resistance, may not be able to be secured. This is because quality assurance becomes difficult.

  This cell member preferably has a surface roughness of 0.12 μm or more and 4 μm or less (preferably 3 μm or less) with a Ra value standardized by JIS B 0601-1982. If the surface roughness of the titanium material is less than 0.12 μm, the electrical contact resistance of the titanium material increases, and it is difficult to use the titanium material as a cell member of a polymer electrolyte fuel cell. By setting the surface roughness to 0.12 μm or more, the contact resistance can be reduced to some extent.

  This is because, by increasing the surface roughness of the cell member, the number of contact points and the contact area between the cell member and the MEA including the fuel electrode film and the oxidant electrode film, which are other components of the cell, or the same. It is because it increases. Even if the roughness exceeds 4 μm, the contact resistance increases. This is because the number of contact points and the contact area between the cell member and the other constituent member of the cell are reduced.

In addition, by appropriately adjusting the surface roughness of the cell member, water generated by the battery reaction can be easily discharged through the channel.
When adjusting the surface roughness of the cell member, the molded substrate is subjected to a surface treatment with an acid solution, for example, a spray etching process or an immersion process using an acid solution containing hydrofluoric acid. The surface roughness tends to increase as the time of the surface treatment increases and as the temperature or concentration of the acid solution used for the treatment increases. The treatment may be performed before the surface modification treatment.

  When an acid solution containing hydrofluoric acid is used, titanium fluoride is generated on the surface of the substrate. If the cell member with the remaining titanium fluoride is incorporated into a fuel cell, the titanium fluoride becomes an oxide during the operation of the fuel cell, causing an increase in contact resistance. For this reason, after treating the base material with an acid solution containing hydrofluoric acid, it is preferable that the base material is treated with an acid solution containing no hydrofluoric acid to adjust the final surface roughness. The formation of the surface modified layer is performed after the surface roughness is adjusted.

<First embodiment>
In order to confirm the effects of the present invention, a titanium base material was prepared and the moldability was evaluated. Table 1 shows the chemical composition of the base material used.

  Each of the substrates was obtained by processing an ingot and finally forming a coil. The ingot was obtained by dissolving the raw materials by the EBM method in a chamber of a vacuum melting apparatus. The Fe content and the O content of the base material (ingot) were adjusted by the following method. First, a first titanium sponge, a second titanium sponge, and a return scrap material were prepared as raw materials. The Fe and O contents of the first titanium sponge were known and lower than the target values for the substrate. The Fe and O contents of the second titanium sponge were known and were higher than the target values for the substrate. The Fe content and the O content of the return scrap material were also known.

  The first and second titanium sponges were produced by the Kroll method. Then, the first titanium sponge and the second titanium sponge were melted by the EBM method, and a return scrap material was added to the resulting molten metal. The Fe concentration and the O concentration of the molten metal were adjusted by the ratio of the amount of the dissolved first sponge titanium to the amount of the added second sponge titanium and the return scrap material. The Fe concentration of the molten metal corresponds to the Fe content of the base material.

  During melting, an appropriate amount of aluminum wire was put into the molten metal using a wire addition device installed in a chamber of a vacuum melting device. The aluminum wire was directly charged into the molten pool at the hot spot and in the vicinity of the hot spot exceeding 2000 ° C. Thereby, gas phase (evaporation) deoxidation with Al oxide was performed to adjust the Al concentration and the O concentration in the molten metal. The Al concentration and the O concentration correspond to the Al content and the O content of the substrate, respectively.

  After melting, a titanium ingot having a thickness of 200 mm, a width of 500 mm, and a mass of 2 tons was obtained for each of the substrates 1 to 9. This ingot has a composition corresponding to the coil as the base material, and as shown in Table 1, the Al content is 0.53 to 5530 ppm, and the O content is 0.031 to 0.098%. , Fe content was 0.051 to 0.095%.

  Next, after the surface of the ingot was machine-cut, an antioxidant was applied thereto, and formed into a slab for hot rolling having a thickness of 55 mm and a width of 560 mm by hot forging. The forged slab was subjected to shaving again on the surface to completely remove flaws. Subsequently, an antioxidant was applied to the surface of the slab, and the surface was heated and maintained at 730 ° C. in an electric furnace, and then hot-rolled so that the rolling reduction per pass was 10 to 23%. A hot-rolled coil having a thickness of 4.8 mm was obtained.

  This hot-rolled coil was subjected to an intermediate annealing treatment at 700 ° C. for 5 minutes in a continuous-passing annealing furnace, followed by a descaling treatment by a continuous pickling treatment. After performing cold rolling on this coil so that the finished plate thickness becomes 0.125 mm, the formability of each material becomes the best by a preliminary study using a bright annealing furnace dedicated to titanium. An annealing treatment was performed at a heating temperature for 90 seconds. Further, after this annealing, skin pass rolling with a rolling reduction of 1.2% was performed.

  Of the substrates 1 to 9, only the substrate 9 had cracks (ear cracks) on the coil end faces during the cold rolling, but the production itself was not at a difficult level.

<Second embodiment>
Using the cold-rolled coil (substrate) produced in the first example, it was investigated whether or not molding as a cell member for a polymer electrolyte fuel cell was possible.

  Each coil was pressed with an 80-ton press using a small press-molding die for forming the flow path shape of the cell member, and the formability was evaluated. This press-molding mold is for forming a serpentine-type flow path, the width of each of the peaks and valleys of the flow path is 0.8 mm, and the depth of the flow path is 0.4 mm And the shoulder radius was 0.15 mm.

  The evaluation results are shown in the column of “Comprehensive evaluation of moldability” in Table 1. As described above, the base material 9 was cracked at the coil end face during the cold rolling, so that the base material 9 was selectively sampled at a portion having no cracked portion and formed by pressing. However, as for the base material 9, although not the total number, the occurrence of cracks at the time of pressing could not be avoided. The base material 9 was determined to be difficult to use for mass production of cell members in terms of moldability.

<Third embodiment>
Using the cold-rolled coil manufactured in the first example, a surface modification treatment was performed, and characteristics of the titanium material after the treatment were evaluated. Before performing the surface modification treatment, the surface roughness of the cold-rolled coil was adjusted by treatment with an acid solution, and a 15-cm-square evaluation test piece was cut out from the cold-rolled coil. The target values of the surface roughness after the acid solution treatment are three levels of 0.15, 0.30, and 0.35 μm, and the conditions of the treatment with the acid solution are set so that the surface roughness of each target value is obtained. Set.

  The specimen was transported to a sputtering apparatus within 12 hours after the surface roughness was adjusted, and subjected to a surface modification treatment by sputtering. The surface modification treatment was performed with the test pieces fixed to a holder capable of setting four test pieces simultaneously.

Hereinafter, the sputtering apparatus will be described in detail. The sputtering apparatus had a five-chamber configuration in which a decompression chamber, a pretreatment chamber, a first sputtering chamber, a second sputtering chamber, and a pressure recovery chamber were linearly arranged in this order. Each chamber had a stainless steel chamber. The external dimensions of the processing apparatus were 1.6 m in width and 19 m in total length. The pressure in the processing chamber is reduced by a vacuum pump equipped with a mechanical booster, a diffusion pump, a turbo molecular pump, and a cryopump, and can be reduced to at least 2 × 10 ⁻⁵ mmHg (2.66 × 10 ⁻³ Pa). Was.

  In the decompression chamber, 30 sets of the above-described test piece holders can be carried in at one time, a jig capable of sending out these holders into the apparatus in a sheet-like manner, and an uncoiler for feeding a band-shaped base material from the coil. Was provided. The pretreatment chamber had one bombardment zone, and the first and second sputtering treatment chambers each had two sputtering zones, and each zone could be independently set for conditions. The recompression chamber is capable of accommodating 30 sets of the above-mentioned test piece holders at a time, and is provided with a jig capable of receiving these holders in a sheet-like manner, and a coiler for winding a band-shaped substrate. Was.

  The holder was configured to be able to rotate so that the test piece was uniformly subjected to the sputtering process. A movable partition door was provided between adjacent ones of the decompression chamber, the pretreatment chamber, the first sputtering chamber, the second sputtering chamber, and the pressure recovery chamber. By opening the partition door, the adjacent chambers communicated, and by closing the partition door, the gas flow between the adjacent chambers was shut off.

When the partition door between the decompression chamber and the pretreatment chamber is closed, the atmosphere does 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 partitioning door between the pressure recovery chamber and the second sputtering processing chamber is closed, the air flows into the second sputtering processing chamber even if the pressure recovery chamber is opened to the atmosphere in order to carry out the holder. do not do. Accordingly, when the holder is carried into the decompression chamber and when the holder is carried out from the pressure recovery chamber, the pressures in the pretreatment chamber and the first and second sputtering chambers are, for example, 5 × 10 ⁻³ mmHg (6). (0.7 × 10 ^-1 Pa). The pressure and atmosphere in each chamber were individually controlled, but could be controlled independently.

  Argon gas, hydrogen gas, and the like could be introduced into the sputtering apparatus under reduced pressure, if necessary. The width of an object which can be uniformly sputtered by this apparatus was up to 600 mm. The excitation frequency was 13.56 MHz as standard. However, this apparatus also had a sputtering capability by HIPIMS. At the time of sputtering, -100 V (constant) was applied as a standard bias voltage to the test piece, but the setting could be changed as necessary.

A pre-heating device was installed in the pre-treatment chamber, and the test piece could be pre-heated from the back of the holder by the radiant heat of the heating element heated by the electric current. In the first and second sputtering processing chambers, the temperature of the test piece during the sputtering process could be measured on the back side of the test piece. 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), even if no heat is applied to the test piece. The temperature drop of the test piece was extremely slow.

  Next, a method and conditions for forming the surface modified layer on the test piece will be described. A bombardment treatment was performed on the surface of the substrate in the pretreatment chamber, and a sputtering treatment was performed on the substrate in the first and second sputtering treatment chambers, thereby forming a surface-modified layer.

  A holder to which test pieces cut out from each of the substrates 1 to 9 (hereinafter, also simply referred to as “substrates”) are prepared by hand, and these are carried into the apparatus in a plurality of times and processed. went.

After carrying the holder into the decompression chamber, the air release door of the decompression chamber is closed, and the evacuation of the decompression chamber is started, and the pressure inside the decompression chamber and the pretreatment chamber becomes 2 × 10 ⁻⁵ Torr (2.7). × 10 ⁻³ Pa), a commercially available industrial high-purity H ₂ gas having a purity of 99.999% by volume or more, and a commercially available industrial high-purity Ar gas having a purity of 99.999% by volume or more. Was introduced into the apparatus at the same time. At that time, was adjusted to concentration of H ₂ is 6% by volume ratio. The pressure inside the decompression chamber after the introduction of the H ₂ gas and the Ar gas and the pressure inside the pretreatment chamber were set to 1.2 × 10 ⁻² Torr (1.6 Pa).

  After maintaining this state 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 set to 10 cm / min in this embodiment. In the pretreatment chamber, the substrate temperature was preheated to 230 to 250 ° C. by applying radiant heat from the preheating device.

The holder was rotated during the bombarding process and the sputtering process.
In the pretreatment chamber, ion bombardment treatment was performed in an atmosphere of Ar and H ₂ to completely remove the moisture adsorbed on the outermost layer of the substrate and the thin hydroxide layer and oxide film layer. The time of the bombarding process was fixed at 60 seconds based on the result of the preliminary study.

  Next, a sputtering process was performed on the substrate in the first and second sputtering processing chambers. Regarding the composition and thickness of the surface modification layer formed on the substrate surface, whether or not to use a sputtering target, the composition of the target, sputtering conditions, the number of targets in the line to be excited, and the transfer of the holder in the sputtering zone Adjusted with speed. Thus, a titanium material having a surface modified on the surface of the substrate was obtained.

  During the sputtering process, conditions were set with the target that the temperature of the substrate was 400 ° C. or lower. Although the temperature of the base material rose to about 320 to 360 ° C. as measured values, the target temperature of 400 ° C. or less could be achieved.

  About the obtained surface-modified layer, the ratio of the Ti content (% by mass) to the Al content (% by mass) in the product and stable composition region (the region in which the composition does not substantially vary in the depth direction). (Hereinafter, referred to as “Ti / Al”), thickness, O content, and adhesion to a substrate were investigated.

  The product, Ti / Al, and O content of the surface-modified layer were determined by qualitative and quantitative analysis using a Quantara SXM scanning X-ray photoelectron spectrometer manufactured by ULVAC-PHI. Al constituting the surface modified layer includes those originating from Al in the base material and those originating from the Al sputtering target.

  The method for determining the thickness of the surface modified layer from the change in mass between before and after the sputtering treatment, and the method for determining the height of the step between the formation region and the non-formation region of the surface modified layer from the SEM image Was measured by The method for obtaining from the SEM image is specifically as follows. On 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, film is formed in the area including this tape, and after the film formation is completed, this tape is peeled off As a result, the step described above was obtained. It has been previously confirmed that even when the surface of the base material has large irregularities, the in-plane thickness change of the surface-modified layer is within 5%. The SEM image was taken using the above-mentioned scanning X-ray photoelectron spectroscopy analyzer.

  The adhesion of the surface modified layer to the substrate was evaluated by a tape peel test. The tape peeling test was performed before performing a process such as bending on the titanium material (initial stage) and after performing the U-bending. The tape peeling test was performed on the flat surface of the end of the titanium material. As the tape, a commercially available cellophane tape (registered trademark, product number: CT405AP-24) having a width of 24 mm manufactured by Nichiban Co., Ltd. was used. This cellotape (registered trademark) was adhered to the surface of the flat part and peeled off, and then the presence or absence and the amount of the peeled surface modified layer present on the adhesion surface of the cellotape (registered trademark) were visually evaluated, and ranked. evaluated. The visual evaluation was performed by attaching Cellotape (registered trademark) on black Kent paper in order to easily confirm the surface-modified layer attached to the adhesive surface of Cellotape (registered trademark).

  The ranks were rated "very good", "good", "slightly poor", and "poor" due to the small amount of peeling of the surface-modified layer. In the case of "very good", no peeling was observed.

  The tape peeling test after U-bending is a test also called “flexibility evaluation test”. In the U-bending, in the present embodiment, a strip-shaped test piece (titanium material) having a width of 20 mm is the same as the thickness of the eight titanium materials (0.125 mm × 8 = 1.0 mm in the present embodiment). The plate was bent into a U-shape along the edge of the plate having the thickness. The same tape peeling test as above was performed on the outer surface of the deformed portion after U-bending. The surface-modified layer has poor ductility, and is easily cracked or peeled off from the substrate when bent. With respect to the surface-modified layer, the effect of the O content on the bending workability can be evaluated from the properties of the titanium material after being bent into a U-shape and the analysis results of the chemical composition.

Further, assuming that each titanium material was applied to a cell member of a polymer electrolyte fuel cell, the electrical surface contact resistance with the MEA was measured. The contact resistance was measured by a four-terminal method in which the titanium material was sandwiched between a pair of Toray carbon paper TGP-H-90 and sandwiched between a pair of platinum plates. This is a measurement method generally performed in evaluating a fuel cell separator material. The load applied during the measurement was 10 kgf / cm ² (9.81 × 10 ⁵ Pa). The lower the measured value of the contact resistance, the smaller the IR loss at the time of power generation of the fuel cell, that is, the smaller the energy loss due to heat generation. The Toray carbon paper TGP-H-90 was replaced every measurement.

  Table 2 shows the numbers of the substrates used (see Table 1), the surface roughness after treatment with the acid solution, the characteristics of the surface modified layer, and the contact resistance of the titanium material.

In Table 2, in the column of the product of the surface-modified layer, TiC, TiCN, and Al ₂ O ₃ are not only stoichiometric compositions but also amorphous phase, non-stoichiometric. It also includes the case where it is a composition. In the column of Ti / Al, the surface-modified layer having an Al ratio of 5 or more (Ti / Al ratio of 95/5 or less) contained Al ₂ O ₃ as an Al-based oxide. In the surface modified layer in which the ratio of Al is less than 5 (Ti / Al ratio is more than 95/5) in the column of Ti / Al, those other than Al ₂ O ₃ in the product column are the surface modified layers. And Al ₂ O ₃ was dispersed therein. In the column of this product, what is described as "C" indicates that the presence of amorphous C (carbon) not bonded to other elements was confirmed.

  In addition to the test shown in Table 2, a test for forming a thicker surface modified layer was performed. As a result, as the thickness of the surface modified layer increased, cracks were observed in the surface modified layer, and the warpage of the titanium material after the surface modification treatment increased. This is because a compressive stress is generated inside the surface modified layer. In order to prevent such cracks and warpage from occurring, the thickness of the surface-modified layer is preferably 3 μm or less, more preferably less than 2 μm. It is considered that the thickness of the surface-modified layer is preferably 50 nm or more and 500 nm or less, but the thickness of the surface-modified layer in the titanium material of the present invention is not limited to this range.

  In order to increase the ductility of the surface modified layer, the O content of the surface modified layer is preferably as low as possible. When a surface modification treatment is performed using an ordinary commercial titanium material as a base material, the O content in the surface modification layer exceeds 30%, the conductivity is low, and the ductility is poor. When a substrate containing Al is used as in the examples of the present invention, the O content in the surface-modified layer is 20% or less.

In Table 2, those having an electrical surface contact resistance value of 20 mΩ · cm ² or more are regarded as “poor”. According to this standard, the contact resistance values of the titanium materials according to the examples of the present invention are all good and low. This is considered to be because the surface modified layer has high conductivity due to a small amount of oxide in the surface modified layer. In addition, the titanium material of the example of the present invention has a good adhesion evaluation result after U-bending, and it can be said that the ductility of the surface-modified layer is high.

  With the titanium materials of Comparative Examples 5 to 7, the adhesion evaluation results after U-bending are not good. This is considered to be related to the low Ti / Al (high Al ratio). In addition, the reason why Ti / Al is low in the titanium materials of Comparative Examples 5 to 7 is that the Al content of the used base material (base material 9) was high, and thus the remaining Al supplied from the base material to the surface modified layer was low. It is considered that the amount of the oxide was large.

<Fourth embodiment>
In order to confirm the moldability of the base material with the actual separator, the cold-rolled coil (having no surface-modified layer) produced in the first embodiment was slit to a thickness of 0.1 mm. Two coils of 125 mm in width and 240 mm in width were collected. The coil was pressed using a press machine having a capacity of 250 tons and a progressive press die to produce a separator as a cell member for a polymer electrolyte fuel cell. This separator had three serpentine channels. The flow channel area contributing to the battery reaction was 100 cm ² , the width of the peaks and valleys in the flow channel portion was 1 mm, and the depth of the flow channel was 0.6 mm.

  When molding a coil into a separator, cracks occur if the formability of the material (coil) is poor. The coil using the base materials 1 to 8 could be pressed into a desired shape. On the other hand, in the case of the coil using the base material 9, as in the second embodiment, the occurrence of cracks could not be completely avoided. This is considered to be related to the fact that the Al content of the base material 9 was as high as 5530 ppm.

<Fifth embodiment>
A part of the separator prepared in the fourth example was treated with an acid solution in an acid treatment line to adjust the surface roughness, and then washed with water.

  Hereinafter, the details of the surface roughness adjustment will be described together with the outline of the acid treatment line used. The width of the material through which the acid treatment line could be stably passed was 400 mm at the maximum. When the material was passed through the acid treatment line, the material was supported from below by a Teflon (registered trademark) backup roll, thereby preventing deformation of the separator.

  In the acid treatment line, the separator was passed through a spray spray zone for spraying an acid solution from above and below the material, and an immersion zone for immersing the material in the acid solution. The amount of etching of the separator and the surface roughness were adjusted by adjusting the conditions of spraying and the conditions of immersion.

  The acid solution was circulated through a 500-liter tank equipped with a filter, and the acid concentration could be adjusted. In this example, an aqueous nitric hydrofluoric acid solution containing 15% of nitric acid and 3% of hydrofluoric acid was used as the acid solution. The temperature of the acid solution was set at 40 ° C. ± 0.5 ° in the tank temperature setting.

  Immediately after the completion of the acid treatment, the coil was washed with clean water by spraying and immersing. The clean water used was obtained from groundwater. Thereafter, the coil was dried by passing it through a tunnel type dry oven furnace of a heat-resistant steel mesh belt transfer type set at 150 ° C. ± 2 °. It was confirmed that the surface of the coil having undergone the above-described steps was in a state in which only a passive film that had inevitably grown in the air after the acid treatment was present, such as during a drying treatment. The passivation film thickness immediately after the drying treatment was about 2 nm.

  These coils were subjected to a predetermined sputtering process using the same sputtering apparatus as used in the second embodiment, to obtain a separator having a surface modified surface having conductivity on the surface. A surface-modified layer was formed by substantially the same method and conditions as in the second example, except that a holder suitable for a separator-shaped test piece was used.

Each of the separators having undergone the above steps was immersed in a sulfuric acid aqueous solution simulating an environment in a fuel cell for 500 hours to evaluate corrosion resistance. The aqueous sulfuric acid solution contained 30 ppm of F ^- ions and had a pH of 2. The metal ion concentration of the aqueous sulfuric acid solution after each separator was immersed for 500 hours was measured to serve as an index of the amount of metal ions eluted from the separator by immersion in the aqueous sulfuric acid solution. When the solid polymer membrane constituting the MEA is contaminated with metal ions, the properties of the solid polymer membrane are greatly affected, and in many cases, the performance of the solid polymer membrane deteriorates. For this reason, in this immersion test, the lower the metal ion concentration of the aqueous sulfuric acid solution, the better. The metal ions detected in the aqueous sulfuric acid solution after immersing the separator were only Al ions. Therefore, the Al ion concentration was measured as the concentration of metal ions eluted in the aqueous sulfuric acid solution.

A single cell of a polymer electrolyte fuel cell was assembled using each of the produced separators and a commercially available standard MEA, and the characteristics as a fuel cell were evaluated. The operating condition of the fuel cell was a constant current operation at a current density of 0.1 A / cm ² . This is one of the operating conditions of a stationary household fuel cell. The utilization rates of H ₂ and O ₂ were kept constant at 40%. The evaluation time was 2,000 hours for the fuel cells using any of the separators.

  For comparison, a SUS316L separator having a thickness of 0.1 mm and having a surface subjected to a cyan bath gold plating treatment with an average basis weight of 50 nm was prepared. This is one of the materials that can provide the best performance as a fuel cell in a conventional separator. The surface roughness of the separator was adjusted to an Ra value of 0.30 μm by an acid solution treatment before the cyan bath gold plating treatment. A single cell of a polymer electrolyte fuel cell was assembled using the separator in the same manner as described above, and the single cell was operated under the same conditions.

  In addition, the cell resistance value during the operation of the fuel cell was measured as an AC impedance value at a frequency of 1 KHz using a resistance meter (MODEL3565) manufactured by Tsuruga Electric Co., Ltd.

  The cell voltage after operating each fuel cell for 2000 hours was measured. In the embodiment of the present invention, the cell voltage was about 0.788 V immediately after the operation, but gradually decreased. It can be determined that the higher the cell voltage, that is, the more the voltage close to the cell voltage immediately after the operation is maintained, the better the characteristics of the fuel cell are.

  In Table 3, the base material used (the numbers described in Table 1 except for Comparative Example 8), the product of the surface-modified layer and Ti / Al, and the Al ion concentration of the sulfuric acid aqueous solution after immersing the separator (Al ion (Elution amount) and characteristics of the fuel cell.

  The cell voltage after the fuel cell operation exceeded 0.750 V after the operation for 2000 hours was judged to be good. In all of the examples of the present invention, the values exceeded 0.750 V and were good, but in Comparative Example 3, the values were lower than 0.750 V and were inferior to the examples of the present invention. The cell voltage of Comparative Example 3 was low immediately after the operation. This result is considered to be related to the fact that the contact resistance before application to the fuel cell was higher in Comparative Example 3 than in the Example of the present invention. In all of the examples of the present invention, the same or better performance was obtained than that of SUS316L plated with gold (Comparative Example 8).

1: fuel cell, 2: solid polymer electrolyte membrane, 3: fuel electrode membrane (anode),
4: oxidant electrode membrane (cathode), 5a, 5b: separator
6a, 6b: flow path

Claims (6)

Mass%, or mass ppm,
Fe: 0.010% or more and 0.100% or less,
O: 0.005% or more and 0.110% or less, and Al: more than 1 ppm and 0.500% or less, with the balance being Ti and impurities,
The impurity is
C: 0.015% or less,
A base material containing N: 0.001% or more and 0.020% or less, and H: 0.015% or less. The substrate according to claim 1,
A base material containing 0.25% or less of a noble metal instead of a part of Ti. The substrate according to claim 1 or 2,
A surface-modified layer formed on the surface of the base material,
Including
The titanium material, wherein the surface-modified layer includes an Al-based oxide and includes at least one of Ti carbide and Ti carbonitride dispersed in the Al-based oxide. The substrate according to claim 1 or 2,
A surface-modified layer formed on the surface of the base material,
Including
The surface modified layer is a titanium material mainly composed of at least one of Ti carbide and Ti carbonitride. The titanium material according to claim 3 or 4,
The titanium material, wherein the O content of the surface modified layer is less than 29% by mass.   A cell member for a polymer electrolyte fuel cell, comprising the titanium material according to claim 3.

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