JP5180932B2 - Method for forming metal-containing carbon film for fuel cell separator and method for forming corrosion-resistant film for fuel cell separator - Google Patents

Description

  The present invention relates to a method of forming a coating that coats the surface of a fuel cell separator used in a fuel cell to provide corrosion resistance.

  Unlike primary batteries such as dry batteries and secondary batteries such as lead-acid batteries, fuel cells that can continuously extract power by continuing to supply fuel such as hydrogen and oxidants such as oxygen have high power generation efficiency. It is not affected by the size of the system so much, and has little noise and vibration, so it is expected as an energy source covering various applications and scales. Specifically, the fuel cell includes a polymer electrolyte fuel cell (PEFC), an alkaline electrolyte fuel cell (AFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), and a solid oxide. It has been developed as a type fuel cell (SOFC) and biofuel cell. In particular, solid polymer fuel cells are being developed for fuel cell vehicles, home cogeneration systems, mobile phones and personal computers.

  A polymer electrolyte fuel cell (hereinafter referred to as a fuel cell) is a single cell in which a solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode, and has a groove serving as a flow path for gas (hydrogen, oxygen, etc.). A plurality of the single cells are overlapped through a formed separator (also called a bipolar plate).

  Since the separator is also a part for taking out the current generated in the fuel cell to the outside, a material having a low contact resistance (which means that a voltage drop occurs due to an interface phenomenon between the electrode and the separator surface). Applied. Furthermore, in recent years, separators are required to have high strength and workability to enable thinning of the fuel cell in order to reduce the thickness and weight of the fuel cell. In order to satisfy this requirement, instead of conventional carbon, not only low resistance, but also metal materials such as aluminum, titanium, nickel, alloys based on them, stainless steel, etc. that are excellent in workability and strength are used. Separators that have been made lighter are being studied.

  Since the inside of the fuel cell is in an acidic atmosphere having a pH of about 2 to 4, the separator is required to have high corrosion resistance in addition to the above characteristics, and further has a characteristic that a low contact resistance is maintained for a long time during use in this acidic atmosphere. Is done. When aluminum, stainless steel, or the like is used as a separator, the solid polymer electrolyte membrane and the catalyst are deteriorated due to corrosion in an acidic atmosphere and the elution of metal ions. On the other hand, a metal such as titanium having good corrosion resistance forms a passive film having low conductivity in a corrosive environment, so that the contact resistance is deteriorated (increased). Therefore, a separator has been developed in which these metal materials are used as a base material and the surface thereof is coated with a coating having corrosion resistance and conductivity.

  A separator in which a noble metal such as Au is applied to such a film is disclosed. For example, Patent Document 1 describes a separator in which a surface of a base material made of stainless steel is subjected to gold plating with a thickness of 10 to 60 nm. Further, Patent Document 2 describes a separator in which a noble metal such as Au or a noble metal alloy is adhered to a surface of a substrate with a thickness of 5 nm or more. Patent Document 3 describes a separator formed by using a metal having excellent corrosion resistance, such as titanium, as a base material so that the amount of noble metal used is reduced, so that the noble metal film is thin enough to provide only conductivity. Has been.

  On the other hand, when a noble metal is applied, the cost increases. Therefore, a separator using a film that does not contain a noble metal is disclosed. For example, Patent Document 4 describes a separator in which a diamond-like carbon layer containing hydrogen is formed on a substrate surface. Patent Document 5 describes a separator in which a layer made of a Group 4 to 6 metal element, silicon, or boron is formed on a substrate surface as a base for a carbon layer to improve adhesion.

JP-A-10-228914 JP 2001-6713 A JP 2004-158437 A JP-A-2005-93172 Japanese Patent Laid-Open No. 2004-14208

  The carbon films (layers) described in Patent Documents 4 and 5 are formed by a normal PVD method or a CVD method. For example, Patent Document 4 describes film formation by an ion beam method. The ion beam method can form a film over a large area, but the film formation speed is slow. On the other hand, although details of the method are not described in Patent Document 5, for example, when a film is formed by a sputtering method using a carbon target, the film formation speed is slow and the production cost is high. In addition, it is desirable to add a metal component to the carbon film in order to alleviate the stress of the carbon film, improve adhesion by improving the bonding force to the substrate, and reduce resistance. This is difficult by law. For example, in order to form a carbon film containing a metal component by sputtering, the carbon target and the metal target are discharged at the same time, but even if the arrangement of the base material and the two targets is adjusted, it is uniform over a certain area. It is difficult to form a film having a composition.

  The present invention has been made in view of the above problems, and provides a manufacturing method capable of forming a low-cost carbon film with high productivity for a fuel cell separator that can be used while maintaining low contact resistance for a long period of time. For the purpose.

  The inventor has invented Japanese Patent No. 3734656 as a method for producing a metal-containing hard carbon film. In the present invention, unlike the conventional arc ion plating (AIP) apparatus, as shown in FIG. 2, the surface (evaporation surface) on which the metal target (evaporation source) 2 evaporates or in front thereof (the object W side). An AIP apparatus having an arc evaporation source in which a magnetic field forming means (magnet) 3 is arranged so as to surround is used. With this arrangement, the magnetic field forming means 3 forms magnetic lines of force (broken lines in FIG. 2) that diverge forward or travel in a direction substantially perpendicular to the evaporation surface of the evaporation source 2 and are covered by the lines of magnetic force. This is a method of forming a hard carbon film that contains a metal without being excessive by accelerating the conversion of the hydrocarbon-based gas contained in the atmospheric gas into the vicinity of the treatment body (base material) W. In this manufacturing method, the deposition rate is high and the productivity is excellent, and the plasma of hydrocarbon gas is generated in front of the evaporation source, so that the evaporated metal ions or atoms fly into the plasma made of carbon or the like. Since the film adheres to the object to be processed and is contained in the film, a film having a uniform composition and film thickness can be easily formed. The hard film obtained by the method of the present invention does not consider the characteristics required for the film for the separator, but as a result of earnest research, the manufacturing method satisfies the specifications of the separator (contact resistance, corrosion resistance, etc.). The inventors have found the type of metal used as the evaporation source and the film forming conditions for forming the carbon film.

  In order to satisfy the specifications of the separator, the metal-containing carbon film for a fuel cell separator contains at least one metal element selected from Ti, Nb, Zr, Hf, and Ta at a rate of 2/3 or less of carbon. The carbon film contained in (at%). That is, the method for forming a metal-containing carbon film for a fuel cell separator according to the present invention is a method of forming the carbon film on a substrate made of titanium or a titanium alloy, and is −50 to −300 V with respect to the ground potential. Is applied to the substrate, and an atmospheric gas mainly composed of a carbon-containing gas and a rare gas is supplied in the atmospheric gas while supplying a flow rate ratio of the carbon-containing gas to the rare gas as 1/3 to 2. Arc discharge is performed, the cathode material composed of the metal element is evaporated, and at least one of ions and radicals is formed from each of the evaporated cathode material and the carbon-containing gas, and the cathode material is formed by magnetic field forming means. By forming a magnetic field line that diverges or travels substantially perpendicular to the surface to be evaporated and reaches at least the vicinity of the base material, Fine radicals and supplying on said substrate.

  By using a carbon film to which these metal elements are added at a predetermined content, a film having no adhesion due to the metal element and having good adhesion to a substrate made of titanium or a titanium alloy can be obtained. In addition, by setting the bias voltage applied to the base material within a predetermined range, the base material surface is appropriately sputtered by the rare gas ions of the atmospheric gas, and the film forming rate of the metal on the base material surface is reduced. A film based on carbon is formed, and the temperature of the substrate is suppressed from becoming high. Moreover, the atomic ratio of the metal contained in the carbon film can be controlled within the predetermined range by using the atmospheric gas having a predetermined composition. And, by the magnetic field lines extending from the cathode material toward the base material, the plasma of the atmospheric gas is promoted in the vicinity of the base material, so that the formed film contains a metal whose carbon atomic ratio is higher than the metal atomic ratio. It becomes a carbon film.

  By coating the surface with a metal-containing carbon film using the above method, good contact resistance and corrosion resistance can be imparted as a fuel cell separator. That is, in the method for forming a corrosion-resistant film for a fuel cell separator according to the present invention, a base metal film made of at least one selected from Ti, Nb, Zr, Hf, and Ta is formed on the surface of a base material made of titanium or a titanium alloy. A base metal film forming step to be formed, and a metal-containing carbon film that forms a carbon film on the surface of the base material on which the base metal film is formed by the method for forming a metal-containing carbon film for a fuel cell separator according to the present invention. It is preferable to further perform a heat treatment step after that.

  The corrosion-resistant coating for a fuel cell separator formed by such a method is formed by depositing the metal-containing carbon film on the basis of a metal film made of a predetermined metal element. In the state in which the passive film is formed, the film can be coated with good adhesion, and the passive film provides a corrosion-resistant film with further excellent corrosion resistance. Furthermore, by conducting heat treatment, the conductivity of the passive film is improved, and the contact resistance of the fuel cell separator provided with such a corrosion-resistant film can be lowered.

  Another method of forming a corrosion-resistant film for a fuel cell separator according to the present invention includes a passive film removing step of removing a passive film on the surface of a substrate made of titanium or a titanium alloy, and the fuel cell separator according to the present invention. And a metal-containing carbon film forming step of forming a carbon film by a method for forming a metal-containing carbon film.

  Since the corrosion resistant coating for a fuel cell separator formed by such a method exposes the metal Ti on the surface of the substrate to form the metal-containing carbon film, the metal-containing carbon film can be coated with good adhesion. Furthermore, since the passive film that impedes conductivity is removed, the contact resistance of the fuel cell separator having such a corrosion-resistant film can be reduced without performing heat treatment after the formation of the metal-containing carbon film. .

  According to the method for forming a metal-containing carbon film for a fuel cell separator according to the present invention, a low-cost carbon film can be formed on a substrate with good adhesion. According to the method for forming a corrosion-resistant film for a fuel cell separator according to the present invention, a fuel cell separator that can maintain a low contact resistance with the carbon film for a long time can be manufactured with high productivity.

It is the schematic of the arc ion plating (AIP) apparatus used for embodiment of this invention. It is a principal part expanded sectional view of an example of the arc type evaporation source with which implementation of this invention is provided. It is a schematic diagram explaining the measuring method of contact resistance. It is a principal part expanded sectional view of the conventional arc type evaporation source.

  The method for forming a metal-containing carbon film for a fuel cell separator according to the present invention and the method for forming a corrosion-resistant film for a fuel cell separator according to the present invention will be described in detail. First, a metal-containing carbon film for a fuel cell separator formed by a method for forming a metal-containing carbon film for a fuel cell separator according to the present invention (hereinafter referred to as a method for forming a metal-containing carbon film) and a fuel cell separator provided with the same Will be described.

[Fuel cell separator]
The fuel cell separator includes a substrate W made of titanium or a titanium alloy, and a metal-containing carbon film for a fuel cell separator (hereinafter referred to as a metal-containing carbon film) that covers the surface. The fuel cell separator may further include a base metal film on the surface of the base material W as a base in order to improve the adhesion of the metal-containing carbon film, or remove the passive film on the surface of the base material W. May be used. Hereafter, each element which comprises a fuel cell separator is demonstrated in detail.

(Base material)
The substrate W is an object to be processed in the method for forming a metal-containing carbon film according to the present invention. The substrate W is particularly suitable for reducing the weight of the fuel cell separator, and is formed of pure titanium or titanium (Ti) alloy having heat resistance for the method for forming a metal-containing carbon film according to the present invention. Specifically, for example, one to four kinds of pure Ti specified in JIS H 4600 and Ti alloys such as Ti-Al, Ti-Ta, Ti-6Al-4V, Ti-Pd can be applied, and in particular, the thickness is reduced. Particularly preferred is pure Ti. However, the pure Ti or Ti alloy that can be applied in the present invention is not limited to these, and may have a composition equivalent to the above pure Ti or Ti alloy containing other metal elements. Can be suitably used.

  Although the thickness of the base material W is not specifically limited, It is preferable to set it as 0.05-0.3 mm as a base material of a fuel cell separator. If the thickness of the base material W is within such a range, the fuel cell separator needs to be reduced in weight and thickness, and can be processed to such a thickness relatively easily. And handleability.

  As an example of the manufacturing method of the substrate W, the above-described pure Ti or Ti alloy ingot is hot-rolled by a known method, and if necessary, annealed / pickled, etc. Then, a product rolled to a desired thickness can be manufactured by forming a groove to be a gas flow path by press working or the like.

  Here, since pure Ti or Ti alloy forms a passive film, the substrate W has corrosion resistance, and the corrosion resistance of the fuel cell separator is improved. However, the base material W (Ti-rolled sheet) is rolled, and carbon derived from the rolling oil infiltrates from the surface to a depth of about 1 μm. The carbon is bonded to Ti, and the surface of the Ti is not dense. The active film may not be formed. A pinhole may exist in the metal-containing carbon film on the surface of the fuel cell separator, and the base material W is in contact with the acidic atmosphere through the pinhole, so that the passive film is not formed on the base material W. If there is, there is a possibility that the corrosion resistance is remarkably deteriorated, leading to peeling of the metal-containing carbon film (and the base metal film) and deterioration of conductivity. Therefore, the substrate W is pickled with a mixed solution of hydrofluoric acid and nitric acid before the metal-containing carbon film is formed (or before the base metal film is formed), so that the carbon on the surface layer enters. It is preferable to remove the region, and the pickling treatment can simultaneously form a passive film stably on the surface of the substrate W.

  Alternatively, the substrate W may be used after removing the passive film on the surface. By exposing the metal Ti of the substrate W to the surface, the adhesion with the metal-containing carbon film is improved. Since the passive film is rapidly formed in the atmosphere or the like, it is removed using the same arc ion plating (AIP) apparatus as the formation of the metal-containing carbon film as described later, and the metal-containing carbon film is subsequently formed. To do. Here, the substrate W also removes the area in which the carbon in the vicinity of the surface has entered, as described above. The carbon-infiltrated region of the surface layer of the substrate W can be removed continuously with the passive film using an AIP apparatus. However, since it is as thick as about 1 μm, time is required and productivity is reduced. . Therefore, it is preferable to remove the surface layer of the substrate W by pickling treatment in the same manner as in the formation of the passive film, and then remove the passive film formed in the atmosphere using an AIP apparatus. As described above, the base material W is removed from the carbon-infiltrated portion together with the passive film, so that the pinhole portion of the metal-containing carbon film has a dense Ti non-removability in the corrosive environment of the fuel cell separator. A working film is formed (regenerated) to provide corrosion resistance.

(Metal-containing carbon film)
The metal-containing carbon film is a hard film based on carbon that covers the surface of the fuel cell separator and imparts conductivity in a corrosive environment. The thickness of the metal-containing carbon film is not particularly limited, but is preferably 10 nm or more in order to impart sufficient conductivity to the fuel cell separator. Is preferably 1000 nm or less. Since the film composed only of carbon has insufficient adhesion to the substrate W made of Ti or Ti alloy, it contains one or more metal elements selected from Ti, Nb, Zr, Hf, and Ta. . By containing a metal, the film stress of the carbon film can be relaxed and adhesion can be improved. In particular, Ti, Nb, Zr, Hf, and Ta are base metal films described later formed on the surface of the substrate W, Or the adhesiveness to the metal Ti of the base material W from which the passive film was removed is good. Moreover, since these metal elements form a passive film, they are not corroded and eluted in an acidic atmosphere inside the fuel cell. In order to improve the adhesion of the metal-containing carbon film to the substrate W, the metal element is preferably contained so that the atomic ratio of carbon: metal element is at least 19: 1. However, as the content of these metal elements increases, the passive film reduces the conductivity, and when it exceeds 2/3 of the carbon content, the influence of metal and metal carbide rather than the carbon film is large. It becomes a film and the conductivity decreases. Therefore, at most, the atomic ratio of carbon: metal element is up to 6: 4, that is, the content (at%) in the metal-containing carbon film is 2/3 or less of carbon (the carbon content is 1.3 of the metal element). 5 times or more) and an atomic ratio of up to 7: 3 is preferable. The metal-containing carbon film having such a composition is preferably formed using an AIP apparatus. According to a method for forming a metal-containing carbon film described later, carbon is an atmospheric gas as a film material, and a metal element is an evaporation source (cathode substance). ) To form a film.

(Underlying metal film)
The base metal film is composed of one or more metal elements selected from Ti, Nb, Zr, Hf, and Ta, and is provided as a base for the metal-containing carbon film. Further improves the adhesion of the W surface to the passive film. The base metal film made of these metal elements has good adhesion to the passive film of the base material W and the metal-containing carbon film by bonding of metal elements, and the passive film is formed as described above. Because it forms, it does not corrode and dissolve. In order to ensure sufficient adhesion, the thickness of the underlying metal film is preferably 5 nm or more, and more preferably 10 nm or more so that the surface of the substrate W can be completely covered. On the other hand, even if it is too thick, the effect is saturated and productivity is lowered.

  The metal element constituting the base metal film may be the same element as the metal element contained in the metal-containing carbon film or may be a different element (for example, an Nb film is provided on the base of the Ti-containing carbon film). However, when forming these films on the substrate W, it is preferable to continuously form the base metal film and the metal-containing carbon film with the same film forming apparatus (AIP apparatus) as described later. At this time, if the metal elements contained in the respective films are made common, the evaporation source (target) that is a film material provided to the film forming apparatus can be reduced to one type at a minimum. Preferred in terms of simplicity.

  The underlying metal film can be formed by a known PVD method such as sputtering, vacuum deposition, or ion plating, but it is preferable to use the same AIP apparatus as the metal-containing carbon film as described above, that is, arc ion plating. The (AIP) method is preferred. The formation method of the base metal film by the AIP method will be described in detail in a method for forming a corrosion resistant film for a fuel cell separator described later.

[Method of forming metal-containing carbon film for fuel cell separator]
Next, a method for forming a metal-containing carbon film according to the present invention will be described. An arc ion plating (AIP) method is preferably applied to the method for forming a metal-containing carbon film according to the present invention, and an AIP apparatus shown in FIG. 1 is used as an embodiment.

(AIP device)
In the AIP method, an evaporation source made of a metal to be deposited is used as a cathode (cathode material) in a vacuum or a reduced pressure atmosphere of a rare gas such as Ar, and a chamber (processing chamber) or a dedicated electrode is provided as an anode. In this method, the metal is evaporated from the surface of the evaporation source by performing arc discharge to form a film on the object to be processed. As the evaporation source, when a metal film such as the base metal film is formed, an evaporation source composed of a metal element constituting the metal film to be formed can be applied. On the other hand, in the method for forming a metal-containing carbon film according to the present invention, an evaporation source composed of one or more selected from the metal elements to be contained in the metal-containing carbon film, that is, Ti, Nb, Zr, Hf, and Ta is applied. . In the present embodiment, two disk-shaped evaporation sources (cathode materials) 2 are used as shown in FIG. 1 and are attached to the electrodes of the AIP apparatus 10. Moreover, the base material W which is a to-be-processed object is mounted in a stage with each of both surfaces facing the evaporation sources 2 and 2 facing each other. By using such an AIP apparatus provided with two identical evaporation sources, the same film can be formed on both surfaces of the substrate W in one process, but the number and arrangement of the evaporation sources are not limited thereto. For example, as a specification of the fuel cell separator, when a metal-containing carbon film is formed only on one side, one evaporation source may be used, and after a metal-containing carbon film is formed on one side by one evaporation source, The substrate W may be placed upside down and a metal-containing carbon film may be formed on the other surface side.

  Then, after evacuating the inside of the chamber, a rare gas such as Ar gas is introduced as an atmospheric gas to adjust the inside of the chamber to a predetermined pressure (depressurized atmosphere). In the method for forming a metal-containing carbon film according to the present invention, a carbon-containing gas containing carbon constituting the metal-containing carbon film is introduced together with a rare gas as the atmospheric gas. Next, a predetermined power is applied to the evaporation sources 2 and 2 by an arc power source and a bias power source is applied to the substrate W to discharge the plasma, and the atmospheric gas is turned into plasma. The metal is evaporated from the surfaces of the evaporation sources 2 and 2 by the generated plasma of rare gas atoms such as Ar, and the metal is deposited on both surfaces of the substrate W, and the carbon film is formed by the plasma of the carbon-containing gas. The metal W is deposited on both surfaces of the material W, and these are combined to form a metal-containing carbon film.

Here, a part of the electrons e ⁻ generated by the arc discharge moves so as to be wound around the magnetic field lines generated from the magnetic field forming means, and the electrons collide with the atmospheric gas molecules to convert the atmospheric gas molecules into plasma. At least one of ions and radicals (hereinafter referred to as plasma) is generated. When the arc evaporation source attached to the AIP apparatus is a conventional one, as shown in FIG. 4, the magnetic field forming unit 103 is disposed behind the evaporation source 102 (the front side is the object to be processed). The line of magnetic force generated from is limited to the vicinity of the evaporation source 102. As a result, the plasma density of the atmospheric gas is considerably low in the vicinity of the substrate W. In contrast, in the method for forming a metal-containing carbon film according to the embodiment of the present invention, as shown in FIG. 1, the annular magnetic field forming means 3 is arranged so as to surround the circumferential surface of the evaporation source 2. An arc evaporation source 1 is used. With such an arrangement, as shown in FIG. 2, the lines of magnetic force generated from the magnetic field forming means 3 diverge almost perpendicularly to the evaporation surface of the evaporation source 2 (the surface facing the substrate W, hereinafter referred to as the evaporation surface). Or it can be made to advance in parallel and reach | attain to the base material W or its vicinity. Such magnetic field lines increase the plasma density even in the vicinity of the substrate W. In addition, it is assumed that the direction of the magnetic force line is within 30 ° with respect to the normal line of the evaporation surface when the magnetic force line is substantially orthogonal to the evaporation surface of the evaporation source 2. As the magnetic field forming means 3, a magnet or the like used in a known arc evaporation source can be applied. Further, when the two evaporation sources 2 and 2 are arranged opposite to each other with the base material W interposed therebetween as in the present embodiment, the magnetic field forming means 3 and 3 arranged to surround the evaporation sources 2 and 2 are used. One of the magnetic field forming means 3 and 3 is arranged with the N pole facing the base material W so that one of the magnetic field forming means 3 and 3 does not repel each other.

  Such a high plasma density has the following influence on the deposition behavior. First, since the film of the rare gas in the atmospheric gas is sputter-etched with the metal evaporated from the evaporation source 2, the metal deposition rate, that is, the film formation rate is reduced. Etching with this rare gas plasma increases as the negative bias voltage applied to the substrate W increases, so the balance between the etching rate and the metal deposition rate is adjusted by controlling the bias voltage as follows. Thus, a metal-containing carbon film having a predetermined composition is formed. Second, when the carbon-containing gas is included in the atmospheric gas, the carbon-containing gas is turned into plasma in the vicinity of the substrate W, so that a large number of precursors that generate a carbon film are generated and the film formation rate of the carbon film is increased. However, it is considerably faster than when a conventional evaporation source is used. In addition, since the plasma density is almost uniformly high in the vicinity of the substrate W, the deposition rate of the carbon film and the etching rate of the rare gas plasma are uniform, and the thickness and components of the metal-containing carbon film are uniform. Can be formed. In order to obtain these effects (influences), in the method for forming a metal-containing carbon film according to the present invention, the magnetic flux density at the position of the substrate W is preferably 5 G or more, and more preferably 10 G or more. This is because if the magnetic flux density is less than 5 G, the plasma of the carbon-containing gas is insufficient and the film is rich in metal.

  Further, at the time of discharge, since an arc spot having a diameter of several tens to several hundreds of μm runs around the surface of the evaporation source 2 at an estimated temperature of 4000 to 10000 ° C., the metal evaporates from the location where the arc spot of the evaporation source 2 exists. In addition, droplets (macro particles) having a diameter of about several hundreds of nanometers to several μm also jump out of the evaporation source 2 and adhere to the substrate W. For this reason, according to the present embodiment, a metal-containing carbon film having a rough surface, that is, a large surface roughness is formed, but such a surface shape does not hinder the effect of the metal-containing carbon film.

  The bias voltage applied to the substrate W is set to −50 to −300 V with respect to the ground potential. If the negative bias voltage is less than −50 V, the sputter etching action by the rare gas plasma is weakened, the deposition rate of the metal film is not reduced, and a metal film or a metal carbide film is formed. On the other hand, if the negative bias voltage is greater than −300 V, the energy of plasma ions that collide with the base material W becomes excessive, and the temperature of the base material W may increase, leading to deformation.

  The arc current is preferably 50 to 180 A, and is appropriately adjusted within this range. When the arc current is small, the arc discharge may not be stable or the film formation rate may be reduced. On the other hand, when the arc current is large, the deposition rate of the metal is faster than the deposition rate of carbon, resulting in a metal carbide film and further a metal film.

The atmosphere gas in forming the metal-containing carbon film is mainly composed of a rare gas and a carbon-containing gas. Specific examples of the carbon-containing gas include hydrocarbons such as methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), ethylene (C ₂ H ₄ ), and acetylene (C ₂ H ₂ ). Gas can be used. In addition to Ar, examples of rare gases include He, Ne, and Kr. The flow rate ratio between the rare gas and the carbon-containing gas is 3: 1 to 1: 2 (the flow rate of the carbon-containing gas is 1/3 to 2 times that of the rare gas). When the flow rate of the carbon-containing gas is less than 1/3 of that of the rare gas, carbon in the formed film is reduced, so that a metal carbide film and further a metal film are formed. On the other hand, when the flow rate of the carbon-containing gas exceeds twice that of the rare gas, when a hydrocarbon gas is applied as the carbon-containing gas, a carbon film containing a large amount of hydrogen is formed. Becomes higher. The atmosphere gas may further contain nitrogen (N ₂ ) for adjustment.

The pressure by the atmospheric gas in forming the metal-containing carbon film is preferably 0.5 to 10 Pa. If the pressure is less than 0.5 Pa, the absolute amount of the carbon-containing gas in the atmosphere is insufficient and the carbon deposition is reduced, so that the carbon in the formed film is reduced. It becomes. On the other hand, when the pressure exceeds 10 Pa, the density of the atmospheric gas molecules increases, and most of the electrons e ⁻ that are generated in the evaporation source 2 and fly to the base material W side while being wound around the magnetic field lines are reduced by a short flight distance. It collides with molecules and does not reach the substrate W. Accordingly, the atmospheric gas molecules in the vicinity of the substrate W are reduced to plasma, and the carbon formed in the film is reduced, so that a metal carbide film and further a metal film are formed.

  By the above method, a carbon film containing a desired metal (metal-containing carbon film) can be formed. Furthermore, according to the AIP apparatus used in the embodiment, the deposition rate and the etching rate of the metal can be controlled by changing the atmospheric gas, the bias voltage, etc., so that the film other than the carbon film such as metal or metal carbide is used. It is also possible to perform sputter etching without forming the film. Therefore, before and after the step of forming the metal-containing carbon film on the substrate by the method for forming a metal-containing carbon film according to the present invention, the step of forming a film having a different composition and the step of etching are performed continuously. Can do. Hereinafter, the formation method of the corrosion-resistant film for fuel cell separators which combined these processes according to the present invention is explained.

[Method of forming corrosion-resistant film for fuel cell separator]
The method for forming a corrosion-resistant coating for a fuel cell separator according to the first embodiment of the present invention is a base metal film forming step of forming a base metal film on the surface (at least one side) of a substrate using the AIP apparatus shown in FIG. And a metal-containing carbon film forming step of forming a metal-containing carbon film by the method for forming a metal-containing carbon film, and then performing a heat treatment step of performing a heat treatment at 300 to 600 ° C. preferable. By performing the base metal film forming process using the same AIP apparatus as the method for forming the metal-containing carbon film, the subsequent metal-containing carbon film forming process can be continuously performed, and the surface of the formed base metal film is formed. A passive film is not formed, and a metal-containing carbon film can be laminated with good adhesion.

(Underlying metal film formation process)
In forming the base metal film, the metal source constituting the base metal film to be formed, that is, the evaporation source 2 composed of one or more selected from Ti, Nb, Zr, Hf, Ta is used as the metal-containing carbon. It attaches to the electrode of AIP apparatus 10 similarly to the formation method of a film | membrane, and mounts the base material W on a stage (refer FIG. 1). As described above, it is preferable to use a substrate W in which a surface layer into which carbon has entered is removed by a pickling treatment and a stable passive film is formed on the surface. After evacuating the inside of the chamber, a rare gas such as Ar gas is introduced into the chamber and the inside of the chamber is adjusted to a predetermined pressure (depressurized atmosphere). Next, a predetermined power is applied to the evaporation sources 2 and 2 by an arc power source and a bias power source is applied to the substrate W to discharge, thereby generating a plasma of a rare gas atom such as Ar. , 2 evaporate the metal from the surface and deposit the metal on both surfaces (surfaces) of the substrate W to form a base metal film having a desired thickness. In the formation of the base metal film, the atmosphere gas does not contain a carbon-containing gas, so that the film material is supplied only by the evaporation source 2 to form the metal film.

  Similarly to the discharge in the method for forming the metal-containing carbon film, the metal evaporates from the location where the arc spot of the evaporation source 2 exists, and the macro particles also jump out of the evaporation source 2 and adhere to the surface of the substrate W. Therefore, the underlying metal film formed in this embodiment also has a large surface roughness. By using such a surface-shaped base metal film, the adhesion is further improved by an anchor effect to the metal-containing carbon film laminated thereon.

  The bias voltage applied to the substrate W in the formation of the base metal film is preferably −10 to −100 V with respect to the ground potential. Further, the arc current is preferably 50 to 200 A, and the pressure by the atmospheric gas (rare gas) is preferably 1 to 10 Pa. As explained in the method of forming the metal-containing carbon film, if the negative bias voltage is increased, the etching with the rare gas plasma becomes faster, so depending on the magnetic flux density, pressure, and arc current, the negative bias voltage When the voltage is −100 V or higher, etching is faster than metal deposition, and the metal film is not formed.

(Metal-containing carbon film formation process)
In the formation of the metal-containing carbon film, when the base metal film is formed as in the present embodiment, the base material W (hereinafter referred to as the base material W) on which the base metal film is formed is continuously placed on the stage of the AIP apparatus 10. The evaporation sources 2 and 2 used for forming the base metal film can be used continuously. Further, the chamber is not opened, and the inside is a noble gas decompression atmosphere. A carbon-containing gas is introduced into the chamber together with a rare gas, and the inside of the chamber is adjusted to a predetermined pressure (depressurized atmosphere). Then, a predetermined power is applied to the evaporation sources 2 and 2 by an arc power source and a bias power source is applied to the base material W to discharge the metal-containing carbon films on both surfaces of the base material W to a desired thickness. To form. Since the components and pressure of the atmospheric gas, the bias voltage, and the arc current are the same as described in the method for forming the metal-containing carbon film, description thereof is omitted.

  In the present embodiment, the same evaporation source 2 is applied in the base metal film forming step and the metal-containing carbon film forming step, with the metal element constituting the base metal film and the metal element included in the metal-containing carbon film being used in common. Alternatively, evaporation sources made of different metal elements may be used. For example, an AIP device having a plurality of electrodes may be used, different evaporation sources may be attached to the respective electrodes, and the electrodes may be switched between the base metal film forming step and the metal-containing carbon film forming step. Further, after the base metal film and the metal-containing carbon film are continuously formed on one surface side by one evaporation source, the base material W is turned over and placed, and the base metal film and the metal-containing carbon film are disposed on the other surface side. The film may be continuously formed again.

(Heat treatment process)
The substrate W on which the base metal film and the metal-containing carbon film are formed is preferably subjected to heat treatment at 300 to 600 ° C. in a vacuum or in a low oxygen atmosphere. By performing the heat treatment in such a temperature range, oxygen in the Ti passive film on the surface of the substrate W (interface with the underlying metal film) diffuses into the Ti base material of the substrate W and the underlying metal film. As a result, the passive film becomes thin or the passive film becomes an oxygen-deficient oxide film, whereby the conductivity of the passive film is improved and the contact resistance of the fuel cell separator can be lowered. If the heat treatment temperature is less than 300 ° C., this effect cannot be obtained sufficiently. On the other hand, when the temperature exceeds 600 ° C., the metal-containing carbon film may be peeled off due to thermal stress caused by the difference in thermal expansion coefficient between the base material W made of Ti or Ti alloy and the metal-containing carbon film.

In the heat treatment atmosphere, vacuum or nitrogen (N ₂ ) or Ar is supplied to lower the oxygen partial pressure to 1 Pa or less. When the oxygen partial pressure exceeds 1 Pa, the carbon of the metal-containing carbon film is oxidized by heat treatment and dissociated as carbon dioxide (CO ₂ ), and the film thickness of the metal-containing carbon film decreases. In addition, the metal of the metal-containing carbon film is oxidized and the contact resistance is increased. Such a heat treatment can be performed in any heat treatment furnace such as an electric furnace or a gas furnace as long as the heat treatment can be performed at a heat treatment temperature of 300 to 600 ° C. and the atmosphere can be adjusted.

  By such a method, a metal-containing carbon film can be formed on a substrate as a corrosion-resistant film for a fuel cell separator. Specifically, the corrosion resistant coating for the fuel cell separator formed in the first embodiment is formed by laminating a passive film formed on the surface of the metal Ti of the base material, a base metal film, and a metal-containing carbon film. Is. By adopting such a configuration, a corrosion-resistant film for a fuel cell separator is provided in which a metal-containing carbon film having low contact resistance and excellent corrosion resistance is provided on the surface with good adhesion.

  In the method for forming a corrosion-resistant film for a fuel cell separator according to the first embodiment, a metal-containing carbon film is formed with good adhesion by providing a base metal film on the surface of the substrate, but the passive film on the surface of the substrate is removed. Alternatively, the metal-containing carbon film may be formed directly. That is, the method for forming a corrosion-resistant film for a fuel cell separator according to the second embodiment of the present invention uses the AIP device to remove the passive film on the surface of the substrate W, similarly to the first embodiment. A film removing step and a metal-containing carbon film forming step of forming a metal-containing carbon film by the method for forming a metal-containing carbon film are performed. By exposing the metal Ti to the surface of the substrate W through the passive film removal step, the adhesion with the metal-containing carbon film can be improved without providing a base metal film. Furthermore, by removing the passive film that impedes conductivity, a heat treatment step after the metal-containing carbon film forming step becomes unnecessary.

(Passive film removal process)
As described above, in the AIP apparatus 10 shown in FIG. 1, the plasma density of the atmospheric gas (rare gas) increases in the vicinity of the substrate W, so that the metal in which the rare gas plasma is evaporated from the evaporation source 2 is the substrate. The film formed by depositing on W is sputter etched. Therefore, by increasing the negative bias voltage applied to the substrate W, the etching rate is made faster than the deposition rate of the metal so that the film formation of the metal film is substantially zero, and the passive state of the surface of the substrate W is further increased. The metal surface of the substrate W can be exposed by removing the film by etching. In addition, since the plasma density is almost uniformly high in the vicinity of the substrate W, the removal thickness can be made uniform. Furthermore, as with the formation of the metal-containing carbon film and the base metal film, macroparticles adhere to the surface of the base material W, and this portion is not etched. Adhesion is further improved by the anchor effect to the membrane.

  Although the film formation is not performed in the removal of the passive film, the metal-containing carbon film is formed in the same manner as the metal-containing carbon film forming method because the metal-containing carbon film forming process is continuously performed by the AIP apparatus 10. The evaporation source 2 made of an element is attached to the electrode of the AIP apparatus 10, and the substrate W is placed on the stage (see FIG. 1). As in the first embodiment, it is preferable to use the substrate W from which the surface layer into which carbon has entered is removed by pickling treatment. Next, similarly to the base metal film forming step of the first embodiment, the inside of the chamber is evacuated and then a rare gas such as Ar gas is introduced into the chamber to adjust the inside of the chamber to a reduced pressure atmosphere. Then, a predetermined power is applied to the evaporation sources 2 and 2 by an arc power source and a bias power source is applied to the base material W to be discharged to generate a plasma of a rare gas atom such as Ar. The surface of the film is sputter etched.

  In the removal of the passive film, it is preferable that the pressure by the atmospheric gas (rare gas) is a reduced pressure atmosphere of 1 to 10 Pa and the arc current is 50 to 200 A, as in the formation of the base metal film. However, the bias voltage applied to the substrate W is preferably adjusted in the range of −100 to −300 V with respect to the ground potential in order to make the etching with the rare gas plasma faster than the deposition rate of the metal. In the case of the pickled base material W, the arc discharge time is about 1 to several minutes, and the passive film can be removed.

(Metal-containing carbon film formation process)
In the formation of the metal-containing carbon film, the base material W from which the passive film has been removed is continuously placed on the stage of the AIP apparatus 10, and the evaporation sources 2 and 2 corresponding to the formation of the metal-containing carbon film are attached in advance. As in the first embodiment, the chamber is not opened and the metal-containing carbon film forming step is subsequently performed to form the metal-containing carbon film on both surfaces of the substrate W. A desired thickness is formed. Since the components and pressure of the atmospheric gas, the bias voltage, and the arc current are the same as described in the method for forming the metal-containing carbon film, description thereof is omitted.

  Also by such a method, a metal-containing carbon film can be formed on a substrate as a corrosion-resistant film for a fuel cell separator. Specifically, the corrosion resistant coating for a fuel cell separator formed in the second embodiment is composed only of a metal-containing carbon film, and is formed on the surface of the metal Ti of the base material. By adopting such a configuration, as in the first embodiment, a corrosion-resistant film for a fuel cell separator is provided in which a metal-containing carbon film having low contact resistance and excellent corrosion resistance is provided on the surface with good adhesion.

  As mentioned above, although the form for implementing this invention was demonstrated about the formation method of the metal containing carbon film for fuel cell separators concerning this invention, and the formation method of the corrosion-resistant film | membrane for fuel cell separators using this method, Examples in which the effects of the present invention have been confirmed will be described in comparison with comparative examples that do not satisfy the requirements of the present invention. In addition, this invention is not limited to this Example and the said form, It cannot be overemphasized that what was variously changed and modified based on these description is also contained in the meaning of this invention.

  An example using the method for forming a metal-containing carbon film according to the present invention was produced and evaluated as follows in the method for forming a corrosion-resistant film for a fuel cell separator according to the first embodiment of the present invention.

[Production of base material (common)]
The base material used as the object to be processed was pretreated as follows. First, a titanium material (width 20 mm × length 50 mm × thickness 0.2 mm) made of one kind of pure titanium KS40 (manufactured by Kobe Steel, Ltd.) defined in JIS H 4600 is ultrasonically cleaned in acetone. Then, as pickling treatment, it was immersed in a mixed aqueous solution of 0.25% hydrofluoric acid and 1.0% nitric acid at room temperature for 3 minutes, washed with pure water and dried.

  Note that the test material No. In No. 1, a thickness of about 5 μm was removed from the surface per side from the weight change of the base material before and after the pickling treatment. Furthermore, the surface of the base material after the pickling treatment was subjected to X-ray photoelectron spectroscopy (XPS) in the depth direction using a fully automatic traveling X-ray photoelectron spectrometer (Quantera SXM manufactured by Physical Electronics). As a result, a passive film of Ti having a thickness of about 10 nm was formed.

[Example (Test Material No. 1)]
(Formation of underlying metal film)
The base material was mounted on the stage of the AIP apparatus 10 shown in FIG. An evaporation source (φ100 mm × thickness 16 mm) made of Nb was attached to each of the two electrodes so as to face each of both surfaces of the base material. In addition, an Nd—Fe—B magnet was disposed around the evaporation source as a magnetic field forming means. At this time, as a result of measuring the magnetic flux density at the position on the substrate surface, it was 12 G. After evacuating the chamber of the AIP apparatus 10 to a vacuum of 1 × 10 ⁻³ Pa or less, as shown in the following conditions, atmospheric gas (Ar) is introduced into the chamber to adjust the pressure in the chamber, The evaporation source was simultaneously arc-discharged to form a film on both sides of the substrate.

(Under metal film formation conditions)
Atmosphere in chamber Gas type: Ar
Pressure: 2.66 Pa
Substrate bias voltage: -50V
Arc current: 100A
Arc discharge time: 30 seconds

(Formation of metal-containing carbon film)
Subsequently, as shown in the following conditions, atmospheric gases (Ar, CH ₄ ) are introduced into the chamber, the pressure in the chamber is adjusted, and two evaporation sources are simultaneously arc-discharged. A film was formed on top.

(Conditions for forming metal-containing carbon film)
Atmosphere in chamber Gas type: Ar, CH ₄ (Flow ratio 1: 1)
Pressure: 2.66 Pa
Substrate bias voltage: -100V
Arc current: 60A
Arc discharge time: 30 seconds

(Heat treatment)
The base material on which the base metal film and the metal-containing carbon film are formed on both sides is housed in a preliminary chamber of a vacuum heat treatment furnace, and the preliminary chamber and the furnace are evacuated to a vacuum of 1 × 10 ⁻³ Pa or less, Heated to 450 ° C. Thereafter, the valve between the preliminary chamber and the heat treatment furnace was opened, the base material was transferred into the furnace, and heat treatment was performed for 3 minutes. After the heat treatment, the base material is transported again to the preliminary chamber, the valve is closed, Ar is introduced into the preliminary chamber, and gas cooling is performed until the temperature of the base material becomes 100 ° C. or lower to obtain a test material for the fuel cell separator. .

(Measurement of film composition)
The composition analysis of the film in the depth (henceforth the surface vicinity) to 150 nm in the film thickness direction from the surface of the test material was performed by XPS. The composition of the metal (Nb) -containing carbon film was almost uniform in the film thickness direction, and an Nb-containing carbon film based on carbon was formed. Table 1 shows the composition of Nb, C, and O. Moreover, the cross section was observed with the transmission electron microscope (TEM). As a result, the test material has a structure of Nb-containing carbon film / Nb film (underlying metal film) / Ti passive film layer / Ti substrate from the surface, and the film thickness is 80 nm for the Nb-containing carbon film, Nb The film was 27 nm and the Ti passive film layer was 7 nm. Further, it is recognized that Nb particles of about several hundreds of nanometers, which are estimated to be macro particles, protrude from the surface of the Nb film, and an Nb-containing carbon film is formed along the surfaces of the Nb film and the macro particles. It was. Moreover, the Ti passive state film layer was thinned with respect to 10 nm before film formation (base material after pickling treatment) by heat treatment.

(Evaluation of conductivity)
The contact resistance of the test material was measured using a contact resistance measuring device shown in FIG.
As shown in FIG. 3, the test material was sandwiched between two carbon cloths from both sides, and the outside was pressurized to a load of 98 N (10 kgf) with a copper electrode having a contact area of 1 cm ² and 7.4 mA using a direct current power source. Was applied, and the voltage applied between the carbon cloths was measured with a voltmeter to calculate the resistance value. The obtained resistance values are shown in Table 1 as the initial contact resistance. In addition, the electrical conductivity acceptance criteria were such that the contact resistance after a corrosion resistance test described later was 15 mΩ · cm ² or less.

(Evaluation of corrosion resistance)
As a corrosion resistance test, the end face of the test material was masked, immersed in a sulfuric acid aqueous solution of pH 2 heated to 80 ° C., and a potential of 0.62 V was applied to a standard calomel electrode (SCE) for 100 hours. For the test material after the corrosion resistance test, the contact resistance was measured by the same method as that for the test material before the immersion, and is shown in Table 1. The acceptance standard for corrosion resistance was such that the contact resistance after the corrosion resistance test was 15 mΩ · cm ² or less.

  As shown in Table 1, the test material No. 1 is an example according to the method for forming a metal-containing carbon film according to the present invention, so that the conductivity was good and increased slightly by the corrosion resistance test, but the contact resistance could be kept sufficiently low and the corrosion resistance was also good. .

[Evaluation with an arc evaporation source (test material No. 2, 3)]
Test material No. 2 is the test material No. In the same AIP apparatus as 1, an underlying metal film and a metal-containing carbon film were formed using an evaporation source (φ100 mm × thickness 16 mm) made of Ti.
The magnetic flux density at the position on the substrate surface was 8G. Test material No. 1, as shown in the following conditions in the AIP device 10, the atmosphere in the chamber is adjusted, arc discharge is performed, and a base metal film (Ti film) and a metal (Ti) -containing carbon film are formed on both surfaces of the base material. Formed respectively. Next, the test material No. In the same manner as in No. 1, the fuel cell separator test material No. 2. The heat treatment conditions were 400 ° C. × 3 minutes.

(Under metal film formation conditions)
Atmosphere in chamber Gas type: Ar
Pressure: 2.66 Pa
Substrate bias voltage: -50V
Arc current: 80A
Arc discharge time: 20 seconds

(Conditions for forming metal-containing carbon film)
Atmosphere in chamber Gas type: Ar, CH ₄ (Flow ratio 1: 1)
Pressure: 2.66 Pa
Substrate bias voltage: -200V
Arc current: 60A
Arc discharge time: 30 seconds

  As a comparative example, test material No. The base metal film and the metal-containing carbon film were formed on the same base material as in No. 2 using an AIP apparatus having the arc evaporation source shown in FIG. As a result of measuring the magnetic flux density at the position on the surface of the base material, it was 0.1 G, indicating that almost no magnetic field lines reached the base material. Other conditions, that is, the atmospheric gas and pressure in the chamber, the substrate bias voltage, the arc current, and the arc discharge time are all test material Nos. Same as 2. Furthermore, test material No. In the same manner as in No. 2, heat treatment was performed at 400 ° C. for 3 minutes, and the test specimen No. It was set to 3.

  The obtained test material No. 2 and 3, the test material No. Similar to 1, the composition in the vicinity of the test material surface by XPS was subjected to composition analysis of Ti, C, O, and film thickness measurement by TEM. Moreover, contact resistance was measured as evaluation of electroconductivity and corrosion resistance. The results are shown in Table 1.

  As shown in Table 1, the test material No. 2 is the test material No. 1 is an example of the method for forming a metal-containing carbon film according to the present invention, so that a Ti-containing carbon film based on carbon with a substantially uniform composition in the film thickness direction is obtained, and the conductivity and corrosion resistance are improved. It was good. In contrast, the test material No. 1 formed using a conventional arc evaporation source. 3 is the test material No. Even with the same Ti evaporation source and atmospheric gas as in No. 2, the plasma density in the vicinity of the substrate was low because the magnetic field lines did not reach the substrate, and the metal (Ti) film formation rate was high. Therefore, the test material No. 3 is the test material No. The film thickness of the base metal film was thicker than that of No. 2, while a film mainly composed of Ti and Ti carbide was formed as the metal-containing carbon film, and the film thickness was thin. As a result, the test material No. No. 3 had a high initial contact resistance due to the Ti passive film, and a further increase in the contact resistance due to the formation of a passive film by the corrosion test.

  Next, the test material No. 1 of Example 1 was used. In the method for forming a corrosion-resistant coating for a fuel cell separator according to the first embodiment of the present invention, using the AIP device and the arc evaporation source (see FIGS. 1 and 2) used in 1 and 2, A comparison of conditions in formation was made. Also, the titanium material was used after pickling the titanium material.

[Evaluation by Base Material Bias Voltage (Test Material Nos. 4 to 8)]
Using an evaporation source (φ100 mm × thickness 16 mm) made of Zr, the test material No. Then, a base metal film (Zr film) was formed under the same conditions as in No. 2, and subsequently a metal (Zr) -containing carbon film was formed at the substrate bias voltage shown in Table 2. The other conditions for forming the metal-containing carbon film, that is, the atmospheric gas and pressure in the chamber, the arc current, and the arc discharge time were measured using the test material No. Same as 2. The heat treatment conditions were also the test material No. Same as 2 at 400 ° C. × 3 minutes.

  For the obtained test material, the test material No. As in 1-3, composition analysis of Zr, C, O by XPS and film thickness measurement by TEM were performed on the film near the surface of the test material. Note that the thickness of the base metal film (Zr film) was 16 nm. Moreover, contact resistance was measured as evaluation of electroconductivity and corrosion resistance. The results are shown in Table 2.

As shown in Table 2, as the substrate bias voltage increases (as a negative bias voltage), the sputter etching action on the Zr film by Ar plasma increases, and the Zr content of the Zr-containing carbon film decreases. became. As a result, the conductivity and corrosion resistance of the test material gradually improved. In addition, while the etching with Ar plasma was performed, the CH ₄ plasma density was increased and the carbon deposition was increased, so that the amount of decrease in the thickness of the Zr-containing carbon film was small. Test material No. Nos. 5 to 7 are examples in which the substrate bias voltage satisfies the method for forming a metal-containing carbon film according to the present invention, so that a Zr-containing carbon film based on carbon is obtained. Like 1 and 2, the conductivity and corrosion resistance were good. In contrast, test material No. In No. 4, since the substrate bias voltage was low (not applied), the sputter etching action by Ar plasma was weak, and the film formation rate of the metal film (Zr film) was not slowed. As a result, Zr contained a large amount of Zr. And a film mainly composed of Zr carbide was formed. Therefore, the initial contact resistance was already high within the acceptance criteria due to the passive film of Zr, and a passive film was further formed by the corrosion resistance test, resulting in a significant increase in contact resistance. On the other hand, test material No. In No. 8, the base material bias voltage was too large, so that the base material was thermally deformed.

[Evaluation by Atmospheric Gas (Test Material Nos. 1, 9-12)]
Test material No. The base metal film (Nb film) is formed on the base material using the same Nb evaporation source as 1 and under the same conditions. Subsequently, the atmospheric gas is changed to the flow ratio of Ar and CH ₄ shown in Table 3. A metal (Nb) -containing carbon film was formed. The other conditions in the formation of the metal-containing carbon film, that is, the pressure in the chamber, the substrate bias voltage, the arc current, and the arc discharge time were measured using the test material No. Same as 1. The heat treatment conditions were also the test material No. 1 and 450 ° C. for 3 minutes.

  For the obtained test material, the test material No. As in 1, the composition analysis of Nb, C, O by XPS of the film near the surface of the test material and the film thickness measurement by TEM were performed. Moreover, contact resistance was measured as evaluation of electroconductivity and corrosion resistance. The results are shown in Test Material No. 1 is also shown in Table 3.

As shown in Table 3, as the flow rate ratio of CH ₄ increased, the amount of carbon formed increased and the carbon content of the metal-containing carbon film increased. Test material No. 10 and 11 are test material Nos. As in Example 1, since the flow rate ratio of CH _{4 is} an example that satisfies the method for forming a metal-containing carbon film according to the present invention, an Nb-containing carbon film based on carbon is obtained, and the conductivity and corrosion resistance are good. Met. In contrast, test material No. No. 9 was insufficient in the flow rate ratio of CH ₄ , so that the amount of carbon formed was small, and a film mainly composed of Nb and Nb carbide was formed. Therefore, the initial contact resistance was high due to the passive film of Nb, and a passive film was further formed by the corrosion resistance test, resulting in a significant increase in contact resistance. In addition, test material No. Since No. 9 had a large Ar flow ratio, the sputtering effect by Ar plasma was strong, the film formation rate was reduced, and the film thickness was small even during the same discharge time. On the other hand, test material No. No. 12 has an excessive flow rate ratio of CH ₄ , and there is no problem as an atomic ratio of carbon to Nb in the Nb-containing carbon film, but it is presumed that the initial contact resistance is high and a large amount of CH ₄ hydrogen is contained. Thus, as the CH ₄ flow rate ratio increases, the metal content of the metal-containing carbon film decreases, but hydrogen is also included at the same time, so the carbon content rate increases due to the flow rate ratio of the hydrocarbon gas. However, there is a limit, and a further improvement effect of the contact resistance cannot always be obtained.

  Next, using the AIP apparatus and arc evaporation source (see FIGS. 1 and 2) used in Examples 1 and 2, the method for forming a corrosion-resistant film for a fuel cell separator according to the second embodiment of the present invention is used. The examples according to were prepared and evaluated.

[Evaluation by removing passive film (test material No. 13)]
Test material No. 13 is a test material No. The same titanium material as that of Nos. 1 to 12 was used as a base material, and was similarly pickled and placed on the stage of the AIP apparatus 10. The same evaporation source made of Ti as 2 was attached to the electrode. After evacuating the chamber of the AIP apparatus 10 to a vacuum of 1 × 10 ⁻³ Pa or less, as shown in the following conditions, atmospheric gas (Ar) is introduced into the chamber to adjust the pressure in the chamber, The evaporation source was simultaneously arced to remove the passive film on both surfaces of the substrate.

(Removal conditions for passive film)
Atmosphere in chamber Gas type: Ar
Pressure: 2.66 Pa
Substrate bias voltage: -150V
Arc current: 80A
Arc discharge time: 60 seconds

(Formation of metal-containing carbon film)
Subsequently, atmospheric gas (Ar, CH ₄ ) is introduced into the chamber, the pressure in the chamber is adjusted, two evaporation sources are simultaneously arc-discharged, and a metal-containing carbon film is formed on both surfaces of the substrate. To obtain a test material for a fuel cell separator. The formation conditions of the metal-containing carbon film, that is, the atmospheric gas and pressure in the chamber, the substrate bias voltage, the arc current, and the arc discharge time are all test materials No. Same as 2.

  The obtained test material No. About 13, the composition analysis of the film | membrane in the depth to 150 nm from the surface to a film thickness direction was performed by XPS. The composition of the metal (Ti) -containing carbon film was almost uniform in the film thickness direction, and a Ti-containing carbon film based on carbon was formed. Further, cross-sectional observation by TEM confirmed that no Ti passive film layer was observed at the interface between the Ti-containing carbon film and the Ti base material, and that the passive film was removed. Table 4 shows the composition of Ti, C, and O measured by XPS and the thickness of the Ti-containing carbon film measured by TEM. In addition, test material No. No. 13, test material No. Similar to 1-12, contact resistance was measured as an evaluation of conductivity and corrosion resistance. The results are shown in Test Material No. 1 is also shown in Table 4.

As shown in Table 4, the test material No. Since No. 13 is an example according to the method for forming a metal-containing carbon film according to the present invention, the conductivity and corrosion resistance were good. For reference, the test material No. As a result of measuring the contact resistance of No. 1 before heat treatment (without heat treatment), the conductivity decreased slightly at 17 mΩ · cm ² . As described above, as a method for forming a corrosion-resistant film for a fuel cell separator according to the second embodiment of the present invention, after removing the passive film on the substrate surface, the method for forming a metal-containing carbon film according to the present invention is used. By forming the metal-containing carbon film, good conductivity could be obtained without performing heat treatment.

10 Arc ion plating (AIP) equipment 1 Arc type evaporation source 2 Evaporation source (cathode material)
3 Magnetic field forming means W base material

Claims (4)

A carbon film containing one or more metal elements selected from Ti, Nb, Zr, Hf, and Ta at a content rate (at%) of 2/3 or less of carbon on a substrate made of titanium or a titanium alloy A method for forming a metal-containing carbon film for a fuel cell separator formed in
A bias voltage of −50 to −300 V with respect to the ground potential is applied to the substrate,
While supplying an atmospheric gas mainly composed of a carbon-containing gas and a rare gas with a flow ratio of the carbon-containing gas to the rare gas being 1/3 to 2, arc discharge is performed in the atmospheric gas, and the metal element And evaporating a cathode material composed of: forming at least one of ions and radicals from each of the evaporated cathode material and the carbon-containing gas;
The magnetic field forming means supplies the ions and radicals onto the substrate by forming magnetic lines of force that diverge or parallel to the surface on which the cathode material is evaporated and reach at least the vicinity of the substrate. A method for forming a metal-containing carbon film for a fuel cell separator. A base metal film forming step of forming a base metal film made of one or more selected from Ti, Nb, Zr, Hf, Ta on the surface of a base material made of titanium or a titanium alloy;
The fuel cell separator which performs the metal containing carbon film formation process which forms a carbon film in the formation method of the metal containing carbon film for fuel cell separators of Claim 1 on the surface of the base material in which the said base metal film was formed Of forming a corrosion-resistant coating film.   The method for forming a corrosion-resistant film for a fuel cell separator according to claim 2, wherein a heat treatment step is further performed after the metal-containing carbon film formation step. A passive film removing step for removing the passive film on the surface of the substrate made of titanium or a titanium alloy;
A method for forming a corrosion-resistant film for a fuel cell separator, comprising: forming a carbon film on the surface of the base material by a method for forming a metal-containing carbon film for a fuel cell separator according to claim 1. .

Images