JP2012043775A - Method for manufacturing titanic separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a titanic separator for a fuel cell having a carbon layer covering a base material with excellent adhesion.SOLUTION: The method for manufacturing a titanic separator for a fuel cell having a carbon layer made of carbon on a base material made of pure titanium or titanium alloy, comprises a carbon layer forming step S1 of forming the carbon layer on the base material by vapor phase film formation, and an intermediate layer forming step S2 of forming an intermediate layer made of titanium carbide between the base material and the carbon layer by applying heat treatment to the base material with the carbon layer formed thereon after the carbon layer forming step S1.

Description

  The present invention relates to a method for producing a titanium fuel cell separator used in a fuel cell.

  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 expected to be an energy source that covers a wide range of applications and scales because it is not significantly affected by the size of the system and has little noise and vibration. 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 mobile devices such as fuel cell vehicles, household fuel cells (household 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 a groove serving as a gas (hydrogen, oxygen, etc.) flow path. Is formed as a stack in which a plurality of the single cells are overlapped with each other through an electrode called a separator (also called a bipolar plate). The output of the fuel cell can be increased by increasing the number of cells per stack.

  Since the separator for a fuel cell is also a component for taking out the generated current to the outside of the fuel cell, the material has a contact resistance (a voltage drop occurs due to an interfacial phenomenon between the electrode and the separator surface). Is required to be maintained for a long time during use as a separator. Furthermore, since the inside of the fuel cell is in an acidic atmosphere, the separator is also required to have high corrosion resistance.

  In order to satisfy these requirements, various separators have been proposed which are formed by cutting a graphite powder molded body or a mixture of graphite and resin mixture. Although these have excellent corrosion resistance, they are inferior in strength and toughness, and therefore may be damaged when subjected to vibration or impact. Therefore, various separators based on metal materials have been proposed and variously proposed.

  Examples of the metal material having both corrosion resistance and conductivity include Au and Pt. Conventionally, a metal material such as an aluminum alloy, stainless steel, nickel alloy, titanium alloy, etc., which can be thinned and has excellent workability and high strength, is coated with a noble metal such as Au or Pt. A separator imparted with corrosion resistance and conductivity has been studied. However, these noble metal materials are very expensive and therefore expensive.

In order to solve such a problem, a method of manufacturing a metal separator that does not use a noble metal material has been proposed.
For example, a method of forming an intermediate layer and a conductive thin film on the surface of the oxide film of the substrate itself by a vapor deposition method (Patent Document 1), a portion made of a metalloid element, carbon, etc. There has been proposed a method (Patent Document 2) in which a surface treatment layer composed of a portion made of is formed by a vapor deposition method.

  Also, a method of forming a conductive carbon film on the surface of the substrate by chemical vapor synthesis or sputtering (Patent Document 3), or a coating layer comprising an amorphous carbon layer and a conductive portion on the surface of the substrate Has been proposed (Patent Document 4) in which a film is formed by sputtering, filterless arc ion plating, or the like.

Japanese Patent No. 4147925 Japanese Patent Laid-Open No. 2004-14208 JP 2007-207718 A JP 2008-204876 A

However, the techniques disclosed in Patent Documents 1, 2, and 3 are such that an intermediate layer, a conductive thin film, and the like are formed on the surface of the base material by a vapor deposition method. We are concerned that we are weak.
Further, in Patent Document 4, since the coating layer made of carbon is formed on the surface of the base material by a vapor deposition method, and the coating layer is directly formed on the surface of the base material, The adhesion may be very weak.
In addition, when the adhesiveness of each layer, such as an electroconductive thin film which influences electroconductivity and corrosion resistance, and a base material is weak, the said each layer cannot be stably maintained on a base material. Therefore, the low adhesion between the base material and the respective layers adversely affects the conductivity durability (durability: property of maintaining conductivity for a long time) and corrosion resistance of the separator.

  This invention is made | formed in view of the said subject, The subject is providing the manufacturing method of the fuel cell separator made from titanium in which the carbon layer has coat | covered the base-material surface in the state with high adhesiveness. is there.

  The present inventors heat-treat a base material made of pure titanium or a titanium alloy having a carbon layer formed on its surface, thereby forming an intermediate layer made of titanium carbide between the base material and the carbon layer. Thus, the present inventors have found that the adhesion between the base material and the carbon layer can be improved.

  In order to solve the above-mentioned problems, a manufacturing method of a titanium fuel cell separator according to the present invention is a manufacturing method of a titanium fuel cell separator in which a carbon layer made of carbon is formed on a substrate surface made of pure titanium or a titanium alloy. A carbon layer forming step of forming the carbon layer on the surface of the base material by vapor deposition, and heat-treating the base material on which the carbon layer is formed after the carbon layer forming step. And an intermediate layer forming step of forming an intermediate layer made of titanium carbide between the base material and the carbon layer.

  Thus, in the method for manufacturing a titanium fuel cell separator according to the present invention, an intermediate layer made of titanium carbide is formed by heat-treating the substrate on which the carbon layer is formed. Therefore, as in the case where the intermediate layer is formed by the vapor deposition method, the interface between the base material and the carbon layer and the intermediate layer is not a flat interface, but an interface with an uneven structure. A separator having greatly improved adhesion to the carbon layer can be produced.

  Moreover, the manufacturing method of the titanium fuel cell separator according to the present invention can manufacture a separator that is light in weight and improved in corrosion resistance by using a base material made of pure titanium or a titanium alloy. it can. In addition, since pure titanium or titanium alloy is excellent in strength and toughness, a separator with improved strength and toughness can be produced.

The heat treatment of the method for producing a titanium fuel cell separator according to the present invention is preferably performed at 300 to 850 ° C. in a non-oxidizing atmosphere.
Thus, by performing the heat treatment at a predetermined temperature, the titanium of the base material and the carbon of the carbon layer can be appropriately reacted. As a result, the separator which ensured the adhesiveness of a base material and a carbon layer can be manufactured by forming the intermediate | middle layer which consists of titanium carbide appropriately.
Further, by performing the heat treatment in a non-oxidizing atmosphere, it is possible to avoid a situation in which carbon in the carbon layer reacts with oxygen in the atmosphere (generation of carbon dioxide), and an intermediate layer made of titanium carbide can be appropriately formed. .

  The method for producing a titanium fuel cell separator according to the present invention may include a passive film removing step of removing a passive film on the surface of the substrate made of pure titanium or a titanium alloy before the carbon layer forming step. preferable.

  By removing the passive film on the surface of the base material in this way, the titanium of the base material and the carbon of the carbon layer are in direct contact, so that the reaction between titanium and carbon occurs more efficiently in the heat treatment in the intermediate layer forming process. . As a result, by appropriately forming an intermediate layer made of titanium carbide, it is possible to manufacture a separator in which the adhesion between the substrate and the carbon layer is further improved.

The method for producing a titanium fuel cell separator according to the present invention produces a separator in which the adhesion between the substrate and the carbon layer is greatly improved by including an intermediate layer forming step of heat-treating the substrate on which the carbon layer is formed. can do.
Moreover, the manufacturing method of the titanium fuel cell separator which concerns on this invention can manufacture the separator which ensured the adhesiveness of a base material and a carbon layer because the temperature of heat processing is 300-850 degreeC.
In addition, the method for producing a titanium fuel cell separator according to the present invention further improves the adhesion between the base material and the carbon layer by including a passive film removal step of removing the passive film on the surface of the base material. A separator can be manufactured.
And, by improving the adhesion between the base material and the carbon layer, a carbon layer having excellent conductivity and corrosion resistance can be stably maintained on the base material. For a long period of time) and a separator excellent in corrosion resistance.

It is a flowchart which shows the manufacturing process of the titanium fuel cell separator which concerns on embodiment. It is a figure which shows order for the separator in the manufacturing process of the titanium fuel cell separator according to the embodiment. It is the schematic of the contact resistance measurement apparatus used in the contact resistance measurement in an Example, and adhesive evaluation.

  Hereinafter, embodiments for carrying out a method for producing a titanium fuel cell separator according to the present invention will be described in detail with reference to the drawings as appropriate.

≪Titanium fuel cell separator≫
First, a titanium fuel cell separator 10 (hereinafter, appropriately referred to as a separator) formed by the method for manufacturing a titanium fuel cell separator according to the embodiment will be described.
As shown in FIG. 2 (the figure after the intermediate layer forming step S2), the separator 10 includes the base material 1, the carbon layer 2 formed on the surface (both sides or one side) of the base material 1, the base material 1, And an intermediate layer 3 formed at the interface with the carbon layer 2. In FIG. 2, the separator 10 in which the carbon layer 2 and the intermediate layer 3 are formed on both surfaces of the substrate 1 is shown, but the carbon layer 2 and the intermediate layer 3 are formed only on one surface of the substrate 1. May be.
Hereinafter, the base material 1, the carbon layer 2, and the intermediate layer 3 constituting the separator 10 will be described.

<Base material>
The substrate 1 of the separator 10 is made of pure titanium or a titanium alloy. Therefore, the base material 1 is lighter than the case where stainless steel or the like is used, and is excellent in corrosion resistance. Moreover, since pure titanium or a titanium alloy is excellent in strength and toughness, the strength and toughness of the substrate 1 can be secured.

  And the base material 1 is produced by a conventionally well-known method, for example, the method of melt | dissolving and casting pure titanium or a titanium alloy to make an ingot, hot rolling, and then cold rolling. The base material 1 is preferably annealed, but the finished state is not limited, and any finished state such as “annealing + pickling finish”, “vacuum heat treatment finish”, “bright annealing finish”, etc. It does not matter.

  In addition, although the base material 1 is not limited to titanium of a specific composition, O: 1500 ppm or less (more preferably) from a viewpoint of the ease of cold rolling of titanium raw material, and subsequent press moldability ensuring. 1000 ppm or less), Fe: 1500 ppm or less (more preferably 1000 ppm or less), C: 800 ppm or less, N: 300 ppm or less, H: 130 ppm or less, with the balance being Ti and inevitable impurities. As the base material 1, for example, a JIS type 1 cold-rolled plate can be used.

  The plate thickness of the substrate 1 is preferably 0.05 to 1.0 mm. This is because if the plate thickness is less than 0.05 mm, the strength required for the substrate 1 cannot be ensured, while if it exceeds 1.0 mm, the workability decreases.

<Carbon layer>
The carbon layer 2 of the separator 10 is made of carbon having conductivity and corrosion resistance and is 100% carbon, but hydrogen or the like may be inevitably mixed therein.
Since the carbon layer 2 is made of carbon, the conductivity and corrosion resistance of the separator 10 are improved, and the reaction between the titanium of the substrate 1 and the carbon of the carbon layer 2 occurs efficiently. Thus, the intermediate layer 3 can be appropriately formed.

  The carbon state of the carbon layer 2 is not particularly limited, and may be any of an amorphous carbon state, a crystalline graphite state, and a state where both are mixed. However, the carbon (carbon layer 2) preferably contains crystalline graphite.

  Further, the average thickness of the carbon layer 2 affects the conductivity and the corrosion resistance. If the average thickness of the carbon layer 2 is less than 20 nm, sufficient conductivity and corrosion resistance cannot be obtained. On the other hand, when the average thickness of the carbon layer 2 exceeds 5000 nm, the effects of the conductivity and durability are saturated, but the productivity is inferior. Therefore, the thickness of the carbon layer 2 is preferably 20 to 5000 nm.

  The average thickness of the carbon layer 2 can measure the cross section of the base material 1 and the carbon layer 2 using a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc. For example, when the thickness of the carbon layer is 100 nm or less, measurement is performed using TEM, and when the thickness of the carbon layer exceeds 100 nm, measurement is preferably performed using SEM. Here, the average thickness is, for example, the average thickness of the carbon layer 2 in a width range of 500 nm when a cross section is observed with a TEM, and in the range of 100 μm when the cross section is observed with an SEM. This is the average thickness of the carbon layer 2.

  In addition, the average thickness of the carbon layer 2 on the surface of the base material 1 can be controlled by a vapor deposition method in a carbon layer forming step S1 described later.

<Intermediate layer>
An intermediate layer 3 made of titanium carbide formed by the reaction of the substrate 1 and the carbon layer 2 is formed at the interface between the substrate 1 and the carbon layer 2. Since this titanium carbide has conductivity, the electrical resistance at the interface between the substrate 1 and the carbon layer 2 is reduced, and the conductivity of the separator 10 is improved. In addition, since titanium carbide is formed by the reaction of the base material 1 and the carbon layer 2, the adhesion between the base material 1 and the carbon layer 2 is improved.

The intermediate layer 3 is formed by a reaction between the titanium of the substrate 1 and the carbon of the carbon layer 2 by heat treatment, and the interface between the substrate 1 and the carbon layer 2 has an uneven shape. Therefore, compared with the case where the smooth intermediate layer 3 is formed by the vapor deposition method, the adhesion between the base material 1 and the carbon layer 2 becomes better.
The intermediate layer 3 is preferably formed at all interfaces between the base material 1 and the carbon layer 2, but is formed at 50% or more of the interfaces in order to ensure adhesion. Just do it.
And the formation state of this intermediate | middle layer 3 can be controlled by the heat processing conditions mentioned later.

The average thickness of the intermediate layer 3 made of titanium carbide is preferably 5 nm or more. This is because if the thickness is less than 5 nm, sufficient adhesion between the substrate 1 and the carbon layer 2 cannot be obtained. The upper limit of the average thickness of the intermediate layer 3 is not particularly limited, but may be 100 nm or less because there is no change in adhesion even if it exceeds 100 nm.
The average thickness of the intermediate layer 3 can be measured using a transmission electron microscope (TEM) or the like. The average thickness is an intermediate thickness in a range of 500 nm when a cross section is observed with a TEM. The average thickness of layer 3.

Next, a method for manufacturing the titanium fuel cell separator 10 according to the embodiment will be described.
≪Method for manufacturing titanium fuel cell separator≫
The manufacturing method of the titanium fuel cell separator 10 includes a carbon layer forming step S1 and an intermediate layer forming step S2. In addition, it is preferable to perform passive film removal process S0 before carbon layer formation process S1.
Hereinafter, the manufacturing method of the titanium fuel cell separator 10 will be described step by step.

<Carbon layer formation process>
The carbon layer forming step S1 is a step of forming the carbon layer 2 on the surface of the substrate 1 by a vapor phase film forming method. Here, the vapor deposition method is a method of forming a thin film on the surface of a substance in a gas phase, and can be roughly divided into PVD (physical vapor deposition) and CVD (chemical vapor deposition). it can. Examples of PVD include sputtering, vacuum deposition, and arc ion plating, and examples of CVD include thermal CVD, photo CVD, and plasma CVD.

  The vapor deposition method applicable to the present invention is not particularly limited, but an arc ion plating method (hereinafter, appropriately referred to as AIP method) capable of forming the carbon layer 2 having good conductivity with high productivity is preferable. .

The AIP method is to perform arc discharge in a vacuum or in a reduced pressure atmosphere of a rare gas such as Ar by using an evaporation source made of a material to be deposited as a cathode and an anode as a chamber or a dedicated electrode. In this method, the film is evaporated from the surface of the evaporation source to form a film on the object to be processed.
When the carbon layer 2 is formed on the surface of the substrate 1 by the AIP method, graphite carbon or the like may be used as an evaporation source.

  In the AIP method, the bias voltage applied to the substrate 1 is preferably −50 to −350 V with respect to the ground potential. When the bias voltage is less than −50 V, the sputter etching action by the rare gas plasma becomes weak, and when it exceeds −350 V, the energy of plasma ions colliding with the substrate 1 becomes excessive, and the temperature of the substrate 1 is increased. This is because there is a risk of rising and deformation.

  In the AIP method, the arc current is preferably 50 to 180 A, and is appropriately adjusted within this range. When the arc current is less than 50 A, arc discharge may not be stable or the film formation rate may be reduced. On the other hand, even if the arc current exceeds 180 A, the arc discharge may become unstable.

In the AIP method, the atmosphere is preferably 0.5 to 10 Pa. In addition, the atmospheric gas is preferably a rare gas such as Ar, He, Ne, or Kr.
In addition, what is necessary is just to use a conventionally well-known apparatus for the arc ion plating apparatus used when AIP method is selected as a vapor-phase film-forming method in carbon formation process S1.

<Intermediate layer forming step>
The intermediate layer forming step S2 is a process in which, after the carbon layer forming step S1, the base material 1 on which the carbon layer 2 is formed is heat-treated to cause the titanium of the base material 1 and the carbon of the carbon layer 2 to react with each other. In this step, an intermediate layer 3 made of titanium carbide is formed between the carbon layer 2 and the carbon layer 2.

  This heat treatment is preferably performed at a predetermined temperature in a vacuum or in a non-oxidizing atmosphere such as an Ar gas atmosphere. And as temperature of heat processing, it is preferable that it is 300-850 degreeC. If the temperature during the heat treatment is low, the reaction between the carbon of the carbon layer 2 and the titanium of the base material 1 hardly occurs, so that titanium carbide is not formed. On the other hand, if the temperature is high, the mechanical properties of the base material 1 are deteriorated. This is because there is a concern to do. A more preferable temperature range is 400 to 800 ° C, and further preferably 450 to 700 ° C.

  The non-oxidizing atmosphere in the heat treatment is an atmosphere having a low oxygen partial pressure, and is preferably an atmosphere having an oxygen partial pressure of 10 Pa or less (in the case of an inert gas: corresponding to an oxygen concentration of 100 ppm or less). If it exceeds 10 Pa, the carbon in the carbon layer 2 reacts with oxygen in the atmosphere to become carbon dioxide (causes a combustion reaction), and the amount of carbon forming titanium carbide decreases. It is.

  The heat treatment time is 0.5 to 60 minutes, and the time may be appropriately adjusted depending on the temperature, such as a long time treatment when the temperature is low and a short time treatment when the temperature is high.

  The heat treatment in the intermediate layer forming step S2 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 850 ° C. and the atmosphere can be adjusted. Can do.

  In addition, there is an example in which a titanium carbide layer (intermediate layer) and a carbon layer are formed on a titanium base material by a vapor deposition method. In this case, the titanium carbide layer is formed with a uniform thickness. As a result, a smooth and clear interface is formed between the titanium carbide layer and the carbon layer, and there is concern about peeling at this portion. On the other hand, the interface between the intermediate layer made of the titanium carbide of the present invention and the carbon layer 2 has an uneven shape. It is considered that the titanium carbide layer is formed by the reaction between the carbon layer 2 and the titanium of the substrate 1, and that the interface becomes an uneven structure, thereby improving the adhesion between them.

<Passive film removal process>
The passive film removal step S0 is a step of removing the passive film 1a on the surface of the substrate 1 made of pure titanium or a titanium alloy before the carbon layer forming step S1.
When the passive film 1a exists at the interface between the base material 1 and the carbon layer 2, the adhesion between the base material 1 and the carbon layer 2 when the carbon layer 2 is formed is slightly weakened. In addition, since the base material 1 and the carbon layer 2 are not in direct contact with each other, in the heat treatment in the intermediate layer forming step S2, the titanium of the base material 1 and the carbon of the carbon layer 2 do not react appropriately, and the intermediate made of titanium carbide. The layer 3 may not be formed efficiently. Therefore, it is preferable to form the carbon layer 2 after removing the passive film 1a on the surface of the substrate 1 (carbon layer forming step S1).
In addition, the passive film 1a is a film formed on the surface of the base material 1 and composed of an oxide or the like of the base material 1 itself.

In the passive film removal step S0, the base material 1 on which the passive film 1a is formed is sputter-etched.
Note that any apparatus may be used as long as sputter etching can be performed. However, by using an arc ion plating apparatus or the like, the passive film removing step S0 and the carbon layer forming step S1 can be continuously performed. Therefore, it is preferable to use an arc ion plating apparatus.

  When the passive film 1a is removed using the arc ion plating apparatus, the film is not formed. However, in order to perform the carbon layer forming process continuously in the apparatus, graphite carbon is installed in the evaporation source, and the apparatus The inside is adjusted to a reduced pressure atmosphere of 0.5 to 10 Pa, discharge is performed by applying a predetermined output from the arc power source to the evaporation source and the bias power source to the base material, and plasma of rare gas atoms such as Ar is generated. Then, the substrate surface is sputter etched. At this time, in order to make the etching with the rare gas plasma faster than the deposition of carbon, the bias power applied to the substrate 1 is set to −100 to −400 V with respect to the ground potential, and the arc current is set to 10 to 150 A. Is preferred.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the design can be appropriately changed without departing from the gist of the present invention described in the claims.

  Next, the titanium fuel cell separator manufacturing method according to the present invention will be specifically described by comparing an example satisfying the requirements of the present invention with a comparative example not satisfying the requirements of the present invention.

<Preparation of specimen>
As a base material, JIS 1 type titanium base material (annealing pickling finish) was used. The chemical composition of the titanium base material is O: 450 ppm, Fe: 250 ppm, N: 40 ppm, the balance is Ti and inevitable impurities, and the plate thickness of the titanium base material is 0.1 mm.

  The substrate was placed in an arc ion plating apparatus, and after removing the passive film, carbon layers having various thicknesses were formed under the following conditions by changing the film formation time.

Atmosphere in chamber Gas type: Ar gas
Pressure: 5.32 Pa
Substrate bias voltage: -200V
Arc current: 80A
Evaporation source: Graphite carbon target (φ100mm × 16mm)

After forming the carbon layer, heat treatment was performed at a temperature and time shown in Table 1 in a vacuum atmosphere with an oxygen partial pressure of 1.3 × 10 ⁻³ Pa or an Ar gas atmosphere with an oxygen concentration of 10 ppm. 1-3 were produced. Moreover, the test body which did not heat-process was set to No.4.

  Specimen No. The same base material used as 1 to 5 was installed in the sputtering apparatus, and after removing the passive film, the intermediate layer and the carbon layer of each film thickness were continuously changed under the following conditions under the following conditions. The test specimen No. 6-8 were produced.

Atmosphere in chamber Gas type: Ar gas
Pressure: 0.267 Pa
Deposition power: 400W
Target For intermediate layer: Titanium carbide target (φ100mm × 5mm)
For carbon layer: Graphite carbon target (φ100mm × 5mm)

  The test specimens thus produced were subjected to intermediate layer confirmation, carbon layer adhesion evaluation, contact resistance measurement, and durability evaluation by the following methods.

[Check middle layer]
After the sample surface was processed with an ion beam processing apparatus (Hitachi Focused Ion Beam Processing and Observation Apparatus FB-2100), the surface of the test specimen was processed with a transmission electron microscope (TEM: Hitachi field emission analytical electron microscope HF-2200) and 750,000. A cross-section was observed at a magnification of twice, and it was determined whether or not an intermediate layer was present at the interface between the carbon layer and the titanium substrate, the state of the intermediate layer was confirmed, and the thickness of the intermediate layer was measured. In addition, in the case where an intermediate layer is present, identification was made as to whether or not the intermediate layer is made of titanium carbide by electron beam diffraction.

[Adhesion evaluation]
Adhesion evaluation was performed using the contact resistance measuring apparatus 30 shown in FIG. A state in which both sides of the test body 31 are sandwiched between two carbon cloths 32 and 32 and the outside is sandwiched between copper electrodes 33 and 33 having a contact area of 1 cm ² and pressurized to a load of 98 N (10 kgf). The test body 31 was pulled out in the in-plane direction while holding (pull-out test).
After the pull-out test, the non-friction surface and the friction surface were observed at a magnification of 100 times with SEM / EDX, and when the acceleration voltage was 15 kV and titanium (Ti) and carbon (C) were quantitatively analyzed, When the amount of carbon (atomic%) is 100% and the amount of carbon on the friction surface is 80% or more of the amount of carbon on the non-friction surface, ○ (very good), the amount of carbon on the friction surface Is △ (good) when the amount of carbon on the non-friction surface is 50% or more and less than 80%, and × (defect) when the amount of carbon on the friction surface is less than 50% of carbon on the non-friction surface It was judged.

[Contact resistance measurement]
The contact resistance was measured using the contact resistance measurement device 30 shown in FIG. Specifically, both surfaces of the test body 31 are sandwiched between two carbon cloths 32 and 32, and the outside is sandwiched between two copper electrodes 33 and 33 having a contact area of 1 cm ² and pressurized with a load of 98 N (10 kgf). A 7.4 mA current was passed using a direct current power supply 34, and the voltage applied between the carbon cloths 32 and 32 was measured with a voltmeter 35 to determine the contact resistance.
When the contact resistance (shown as the initial contact resistance in Table 1) is 10 mΩ · cm ² or less, the conductivity is good, and when it exceeds 10 mΩ · cm ² , the conductivity is poor.

[Durability evaluation]
Durability evaluation (durability test) was performed on the test specimen prepared by the above method. That is, the test specimen was immersed in an 80 ° C. sulfuric acid aqueous solution (10 mmol / L) having a specific liquid volume of 20 ml / cm ² , and a potential of +600 mV was applied to the test specimen based on the saturated calomel electrode (SCE). After 200 hours of immersion treatment, the test specimen was taken out from the sulfuric acid aqueous solution, washed and dried, and contact resistance was measured by the same method as described above.
When the contact resistance after immersion (after the durability test) (shown as contact resistance after the durability test in Table 1) is 30 mΩ · cm ² or less, the durability is good, and when the contact resistance exceeds 30 mΩ · cm ² , the durability is poor. did.

  Tables 1 and 2 show the carbon layer thickness, heat treatment conditions, intermediate layer type, carbon layer adhesion, TiC layer thickness, and contact resistance measurement results after the initial and corrosion resistance tests of each specimen.

About the test body (No. 1, 2, 3, 5) which formed the carbon layer on the base material surface, and heat-processed, it is the intermediate | middle which consists of the titanium carbide formed by the heat processing in the interface of a carbon layer and a base material. The presence of the layer was confirmed, and the adhesion of the carbon layer was good. In addition, these specimens had good results with respect to conductivity and durability. Since test body No. 4 did not heat-treat after forming the carbon layer, an intermediate layer made of titanium carbide was not formed, the adhesion of the carbon layer was poor, and contact resistance was deteriorated after the durability test. It was.
On the other hand, for the specimens (Nos. 6, 7, and 8) in which an intermediate layer made of titanium carbide and a carbon layer were laminated on a base material by sputtering, although there were intermediate layers made of titanium carbide, As a result, the adhesion with the titanium carbide layer was poor. Moreover, since deterioration of contact resistance was observed after the durability test, it was found that the fuel cell separator is not preferable.

  From the results of Tables 1 and 2, the titanium fuel cell separator produced by forming a carbon layer on the surface of the base material by a vapor deposition method and then performing a heat treatment is shown in FIG. It was found that it was excellent in terms of conductivity and durability.

DESCRIPTION OF SYMBOLS 1 Base material 1a Passive film 2 Carbon layer 3 Intermediate layer 10 Titanium fuel cell separator (separator)
30 Contact Resistance Measuring Device 31 Specimen 32 Carbon Cloth 33 Copper Electrode 34 DC Current Power Supply 35 Voltmeter S0 Passive Film Removal Process S1 Carbon Layer Formation Process S2 Intermediate Layer Formation Process

Claims (3)

A method for producing a titanium fuel cell separator in which a carbon layer made of carbon is formed on a substrate surface made of pure titanium or a titanium alloy,
A carbon layer forming step of forming the carbon layer on the surface of the base material by a vapor deposition method;
After the carbon layer forming step, an intermediate layer forming step of forming an intermediate layer made of titanium carbide between the base material and the carbon layer by heat-treating the base material on which the carbon layer is formed. A method for producing a titanium fuel cell separator.   The method for producing a titanium fuel cell separator according to claim 1, wherein the heat treatment in the intermediate layer forming step is performed at 300 to 850 ° C in a non-oxidizing atmosphere.   The method for producing a titanium fuel cell separator according to claim 1 or 2, further comprising a passive film removing step of removing the passive film on the surface of the base material before the carbon layer forming step. .

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