JP2014141732A - Corrosion-resistant and conductive nano-carbon coating method using stainless steel as base material, and fuel cell separation plate formed thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for producing a nano-carbon coating layer having corrosion resistance and conductivity with respect to a stainless steel base material, and to provide the processed stainless steel base material.SOLUTION: A nano-carbon coating method includes steps for: etching an oxide film of a stainless steel base material; depositing a metal nitride buffer layer on the surface where the oxide film of the base material is etched; and depositing a conductive carbon layer so as to have nano-size thickness on the metal nitride buffer layer.

Description

  The present invention relates to a special surface treatment method using stainless steel as a base material and having both conductivity and corrosion resistance, and more particularly to a nanocarbon coating method. Moreover, it is related with manufacture of the electrode material etc. which were excellent in electroconductivity and corrosion resistance, the PEMFC (Polymer Electrolyte Membrane Fuel Cell) separator manufactured based on it.

  Stainless steel is a material that is used very frequently, and is a material that can be used more widely by complementing physical properties or strengthening specific physical properties. In particular, it has been attracting attention as a base material for a fuel cell separator, and can be used as an electrode material if the corrosion resistance is further enhanced. In addition, cases where physical properties need to be reinforced may be required at various utilization levels.

  A fuel cell is one of environmentally friendly renewable energy sources based on a combustion reaction in which hydrogen and oxygen react in the presence of a catalyst to produce water and energy. In particular, it is possible to generate electrical energy without pollutants, and it has the advantage of being very efficient when combined with the generated heat.

  An essential part of such a fuel cell is a fuel cell separator, and physical properties that the fuel cell separator should have include strength, corrosion resistance, gas barrier properties, conductivity, size accuracy, and the like. In consideration of the practicality of the fuel cell itself, the fuel cell separator plate is required to have a manufacturing process setting suitable for mass production.

Currently, fuel cell separators that have been developed to meet the above-mentioned conditions are competitive, centering on two base materials that have a carbon material coated with a resin and a metal material that has been surface treated. Has developed.
Patent Document 1 discloses a technique using a carbon coating containing fluorine on a stainless steel material, and Patent Document 2 coats a carbon layer after enhancing conductivity by coating a Cr intermediate layer on the stainless steel material. The technology is disclosed. Such a technique is also a relatively thick film having a carbon layer thickness of 0.5 μm to 2 μm, and is difficult to apply to actual mass production.

  When stainless steel is used as a base material, it must have excellent conductivity in addition to corrosion resistance, and it is difficult to make these two properties practically compatible. Until now, the mainstream of research has been to improve the surface by nitriding a stainless steel base material, but the results have been satisfactory enough for practical use in terms of cost and physical properties. I can't get.

  Attempts were made to apply gold coating on stainless steel, focusing on improving the physical properties with a focus on cost, but this is also difficult to put into practical use.

  FIG. 1 shows the contact resistance and corrosion current measurement results with the temperature of the carbon coating on stainless steel. Fuel cell separators, where these two physical quantities must all be low, need to select a coating temperature that optimizes protons. FIG. 2 shows the measurement results of contact resistance and corrosion current with the thickness of the carbon coating film. It can be seen that the contact resistance and the corrosion current decrease as the thickness of the film increases. However, increasing the thickness of the film lowers the productivity and causes a problem in mass production. Therefore, a method for maintaining excellent characteristics while reducing the thickness of the film is required.

  In addition, in the case of stainless steel, Cr added to improve corrosion resistance covers the surface with an oxide layer to form a natural film, so the decrease in adhesion and conductivity of the coating layer is also improved in the surface treatment. It is necessary to

  Also, in the case of carbon coating, if the desired physical properties are provided by increasing the thickness of the coating, there is a problem that the practicality is low due to the characteristics of the fuel cell separator that requires mass productivity and low production cost.

Korean Registered Patent No. 10-1000697 JP2010-287542A

Andrew, S.M. Mike, A .; Michael, K .; Ken, N .; Colin, Q .; , “Industrial Ion Sources and Theair Application for DLC Coating,” Presented at the SVC 42nd Annual Technical Conference, USA, April 17-22, 1999. Robertson, J .; , “Diamond-like amorphous carbon,“ Materials Science and Engineering R 37: 129-281, 2002.

  Therefore, although the present invention improves the characteristics by applying a carbon coating to the stainless steel base material, the coating layer is made to be a very thin nanosize while improving the adhesion of the coating layer as well as improving the corrosion resistance and conductivity. To provide a corrosion-resistant and conductive nanocarbon coating method capable of making the productivity and production cost real by using a thin film, and an article utilizing such as a fuel cell separator and a method for manufacturing the same. Is an issue.

  In order to solve the above problems, the present invention activates the surface layer by etching the oxide film formed on the surface of the stainless steel base material by plasma etching, and at the same time, prevents the problem of reduced conductivity. In addition, by covering the surface on which the oxide film is etched with a metal nitride such as CrN or TiN with a nano-sized thickness, and coating this with a carbon layer with a nano-sized thickness, both conductivity and corrosion resistance are achieved. An excellent coating layer is produced with high productivity.

  That is, a step of etching an oxide film of a stainless steel base material; a step of depositing a metal nitride buffer layer with a nano-size thickness on the surface of the base material on which the oxide film has been etched; Depositing a conductive carbon layer on the layer in a nano-sized thickness.

  Here, the etching of the oxide film of the stainless steel base material may be performed by plasma etching.

  The metal nitride buffer layer may be formed by supplying a metal target and nitrogen gas to the chamber, applying a voltage to a metal arc and applying a bias voltage to the base material. You may implement at ° C.

  The conductive carbon layer may be coated by applying a voltage to the ion gun and applying a bias voltage to the base material at a temperature of 200 to 600 ° C.

  The bias voltage may be DC, AC of 0 to −800 V, or a pulse voltage having a frequency of 0.1 kHz to 500 kHz, and the conductive carbon layer may be deposited with a thickness of 1 to 150 nm.

  Etching the oxide film; depositing a metal nitride buffer layer; and depositing a conductive carbon layer to a nano-sized thickness; are performed by configuring each process chamber; Provided is a method for producing a nanocarbon coating layer having corrosion resistance and conductivity, wherein the process chambers are arranged in-line, and the above-described steps are performed in situ.

  The step of etching the oxide film is performed by plasma etching using an ion gun, and the position of the ion gun is configured to be movable so that the distance between the ion gun and the base material surface can be reduced. You can improve the etching rate.

  Further, according to the present invention, an oxide film of a stainless steel base material is etched, and in that state, a metal nitride buffer layer is vapor-deposited, and a conductive carbon layer is vapor-deposited again with a nano-size thickness thereon. A stainless steel reinforced to provide corrosion resistance and conductivity is provided.

  Here, the metal nitride film includes CrN or TiN, and the thickness thereof may be 1 to 20 nm.

  The conductive carbon layer may be 1 to 150 nm.

  Further, the stainless steel reinforced to have corrosion resistance and conductivity may be applied to the fuel cell separator or electrode material.

  The present invention also provides a first chamber in which an oxide film of a stainless steel base material is etched with plasma by installing an ion gun; after the oxide film etching process is finished in the first chamber, the stainless steel A second chamber provided with a metal arc for coating the surface of the base metal with a metal nitride film; and a conductive carbon layer on the surface of the stainless steel base material coated with the metal nitride film in the second chamber. In order to coat with a nano-sized thickness, a third chamber equipped with an ion gun is arranged in-line, and the plasma etching process, the metal nitride film coating process, and the conductive carbon layer coating process are performed in situ. An apparatus for producing a nanocarbon coating layer having corrosion resistance and conductivity is provided.

  According to the present invention, since the oxide natural film of the stainless steel base material is etched with plasma and then coated, the conductivity improvement effect by the coating process is outstanding, and the etched surface has corrosion resistance. By coating CrN or TiN with nano-size for improvement, and coating the carbon layer with nano-size again on it, the corrosion current can be greatly reduced while maintaining low contact resistance. Since the thickness of the material is very small, nano-size, an in-line process is possible, and the productivity is also excellent. Accordingly, a fuel cell separator plate, electrode material, or reinforced special stainless steel material can be provided.

Graph showing change in contact resistance and corrosion current with coating temperature of carbon coating material Graph showing contact resistance and corrosion current change with coating thickness of carbon coating material Explanatory drawing which shows the layered cross section which shows the surface treatment and coating layer structure with respect to stainless steel base material Illustration of carbon layer coating using ion gun Explanatory drawing showing in-line composition of base metal plasma etching, metal nitride layer coating and nanocarbon layer coating A graph showing the contact resistance and corrosion current of a test piece that has undergone a coating process compared to conventional technology Explanatory drawing of the method for measuring the contact resistance of the test piece after the coating process is completed Graph showing the etching rate associated with the distance between the ion gun and the base material in the process of etching the base material oxide film by plasma etching Photograph showing the difference between before and after the etching process

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention can be appropriately designed and modified by using conventionally known techniques without departing from the spirit of the present invention.

  The present invention uses a stainless steel as a base material to form a coating layer that can further enhance corrosion resistance and conductivity, so that it can be used for a fuel cell separator or a special material that reinforces the physical properties of an electrode material or stainless steel itself. Enables production of stainless steel.

  For this reason, after removing the natural oxide film layer inherent to stainless steel by plasma etching, the metal nitride layer is thinly laminated to about 1 to 20 nm on the etched surface to further enhance the corrosion resistance of stainless steel. To do. The plasma etching process removes the oxide film that covered the surface of the stainless steel, further improving conductivity, and at the same time, it is activated by forming fine irregularities of around several nanometers over the entire surface. In the subsequent coating process, the deposition rate and adhesion rate of the film are improved.

  The activated surface is coated with a metal nitride film having excellent corrosion resistance, such as CrN or TiN, as thin as 1 to 20 nm to reinforce the corrosion resistance that may weaken as the conductivity is enhanced. Since the metal nitride film has conductivity unlike the oxide film, the corrosion resistance can be improved without impairing the conductivity.

  Next, a conductive nanocarbon coating layer (300) having a thickness of 1 to 150 nm is formed thereon, and the conductivity is further enhanced while maintaining the corrosion resistance. After the entire process is completed, a layer shape as shown in FIG. 3 is formed.

  The etching process and the carbon coating process are performed using an ion gun that generates high-energy ions to provide excellent film quality and high productivity (deposition rate) as well as plasma etching efficiency. Even a thin film having a nano-size thickness can be used to produce a dense thin film having sufficiently required physical properties.

That is, the nanocarbon coating that improves all of the corrosion resistance and conductivity of the stainless steel base material is configured by an in-line coating system including an ion gun, thereby obtaining mass productivity (see FIG. 6).
Through the inline coating system, the plasma etching step, the metal nitride coating step, and the conductive nanocarbon coating layer (300) formation step are all performed in situ. The in-line coating system can be configured because the plasma etching process and the carbon coating process of the present invention all utilize a high-efficiency ion gun, thereby making it possible to obtain sufficient physical properties with a nano-sized thickness. It is because it shows. This is because, when conductive carbon is coated using a conventional PVD process, the film quality is not dense and there is a risk of peeling, so it has to be formed with a thick film of about 500 nm to several μm for 5 hours. The present invention has improved the situation where a long time as described above is required and a mass production system such as an inline system is meaningless. In particular, when keeping the manufacturing cost of the fuel cell separator plate low is the key to commercialization of the technology, the development of a mass production process and system has great technical and economic significance.

  Unlike the conventional CVD process, the ion gun used in the present invention can obtain a high bonding force and a high deposition rate. An ion gun that can give a particle energy as high as 700 eV is used to increase the bonding force and the density of the microstructure while greatly reducing the coating thickness so that it can be economically and mass-produced. [Non-Patent Document 1]. In the case of the conventional PACVD process, when considering that the particle energy was as low as 2 to 3 eV, the high energy particle generation by the ion gun of the present invention greatly improves the efficiency of the process and the quality of the film quality (non-patent Reference 2).

  In the following, as one embodiment of the present invention, a method for manufacturing a fuel cell separator will be described in detail together with presentation of detailed conditions based on the above-described contents.

  First, stainless steel processed as a base material for the fuel cell separator is prepared and cleaned cleanly. Washing can be performed based on a known technique using chemicals such as distilled water and isopropyl alcohol.

  Next, the cleaned base material is put in a chamber, and a natural oxide film such as chromium oxide formed on the surface of stainless steel is etched by plasma etching. An ion gun is prepared for plasma etching, and an inert gas such as Ar or nitrogen (N 2) is put into the ion gun, and 0.1 to 5 kW power (possible with pulse power, AC power, or DC power). Using the plasma discharged by application, the base material surface is bombarded by ions, the oxide film naturally formed on the stainless steel surface is removed by etching, and the surface itself is activated. At this time, the etching action can be efficiently performed by applying a bias voltage to the base material side to attract ions. In order to be able to etch both sides of the base material substrate at the same time, as shown in FIG. 6, ion guns are all arranged on the top and back sides of the base material, and in the etching process, the etching rate is the surface of the base material. 9 changes according to the distance between the ion gun and the ion gun, so that the ion gun is configured to be movable so that the ion gun is moved near the base material and etched (see FIG. 6).

  That is, the etching rate y≈300 / x. x is the distance between the ion gun and the surface of the base material. In this embodiment, when the distance between the ion gun and the sample is reduced from 10 cm to 3 cm, the effect of increasing the etching rate is about four times. It was seen.

  In this example, the plasma etching process for removing the oxide layer was performed for about 5 minutes by applying 250 W DC power to the ion gun and applying a bias voltage of −100 V to the base material. FIG. 9 presents the FESEM analysis results of the base material surface before and after such an etching process, and shows that the surface after the etching has become flat. Further, when the surface illuminance was measured after the etching, it was confirmed that there was an improvement effect of about 20%.

After the plasma etching process is finished, a buffer layer is formed on the surface of the base material activated thereby to enhance the corrosion resistance. That is, the CrN or TiN-based metal nitride layer is coated with a nano size. The process can use a process generally used for forming the film, such as PVD, PECVD, etc., the process temperature is room temperature to 500 ° C., the desired temperature is 300 to 500 ° C., and the process pressure is 10 − Maintain between 2 and ^10-5 torr. In the present embodiment, a corresponding metal target and nitrogen gas are supplied to the chamber, the process proceeds by PECVD using a metal arc, and a metal nitride film such as CrN or TiN is covered with a very thin film of about 1 to 20 nm, coating Although the time may vary somewhat in relation to other process variables such as power, pressure, and temperature, it is desirable to set the time so that it does not exceed 10 to 30 seconds and a maximum of 5 minutes as much as possible.

  In this example, in order to form a metal nitride film, the voltage applied to the metal arc was a DC voltage of 10 to 30 V, the current was set to 30 to 200 A, and a bias voltage of 0 to 100 V was applied to the base material. Note that sputtering may occur when a higher bias voltage is applied under the above-described conditions. The formation of a metal nitride film improves the corrosion resistance of a stainless steel base material etched with an oxide film, and when CrN or TiN is formed, the metal nitride film itself has conductivity and is combined with a high conductivity layer to be formed thereafter. Improve overall physical properties.

Next, a hydrocarbon-based gas is supplied as a carbon source, or a conductive carbon layer is deposited by a PVD or PECVD process using a graphite target. In the case of this example, it was formed by a method using an ion gun. Apply 0.1 to 5 kW power (possible with pulse power, AC power, or DC power) to the ion gun, and use a heater to set the process temperature to 200 to 1000 ° C., preferably 300 to 600 ° C., carbonization While supplying hydrogen gas and maintaining the process pressure at 10 −2 to 10 ⁻⁵ torr, the conductive carbon layer is deposited at a thickness of 1 to 150 nm, preferably 5 to 100 nm.
The vapor deposition process of the conductive carbon layer is schematically shown in FIG. At this time, it is desirable to apply a bias voltage to the base material. As the bias voltage, a (−) voltage of 0 to −800 V can be applied at DC, AC, or a pulse frequency (0.1 kHz to 500 kHz), and the bias voltage is applied to the metal separator plate during the conductive nanocarbon coating. This prevents the electric charge accumulated in the metal and improves the bonding force between the metal separator and the graphitic carbon.

  Through this process, as can be seen from the energy and temperature conditions of the carbon itself, the carbon layer is crystallized at the same time as the deposition by the thermal energy applied from the outside and the electrical energy applied to the base material, A conductive graphitic carbon layer is formed in situ. Since the conductive nanocarbon coating layer (300) representing conductivity is formed with a very thin nano-sized thickness, the time for proceeding the process is very short, and 360 coating processes are performed per hour. In some cases, it is possible to produce a fuel cell separator at a cost of less than $ 2 per piece during mass production.

  Compared to the conventional thickness of the carbon layer of 500 nm or more, in this example, the thickness of the carbon layer including the CrN layer for corrosion resistance and the carbon layer for conductivity is 60 nm or less. In particular, it was confirmed that a thinner coating layer was formed and the productivity was improved accordingly.

Further, the contact resistance and the corrosion current are measured with respect to the fuel cell separator manufactured as described above, and compared with the present embodiment, the natural coating of the stainless steel base material is not etched and the CrN or TiN buffer is not etched. A test piece in which a direct conductive carbon layer was deposited with a thickness of 50 nm without a layer was fabricated as a comparative example, and contact resistance and corrosion current were measured.
As a result, as shown in FIG. 6, in the test piece of the left comparative example, the contact resistance is 13.2 mΩcm ² @ 10 kgf / cm ² and the corrosion current is 9.13 μA / cm ^2. In the case of the example, the contact resistance is 13.7 mΩcm ² @ 10 kgf / cm ² , the corrosion current is 0.42 μA / cm ² , and the corrosion resistance is greatly increased while maintaining the contact resistance at the same level. It is confirmed that it has been lowered. This means that the fuel cell separator according to the present invention has good conductivity and excellent corrosion resistance and can satisfy mass productivity.

FIG. 7 illustrates a method for measuring the contact resistance of the fuel cell separator manufactured in this embodiment. A current of the upper and lower current collectors was applied with a load of 10 kg per cm ^{2 of the} test piece area, the voltage at both ends was measured, and the contact resistance between the separation plate and the GDL (gas diffusion layer) was measured. Asked. The contact resistance is measured by measuring the contact resistance with the separation plate positioned between the GDLs, and then separately measuring the contact resistance of the GDL to obtain the difference between the two values.

In the present example, a corrosion-resistant electrode material and special stainless steel can be manufactured in the same manner as described for the manufacture of the fuel cell separator by applying the nanocarbon coating. Of course, it can also be applied to other articles. it can.
Have

According to the present invention, a stainless steel material having enhanced conductivity and corrosion resistance can be obtained with high mass productivity and can be used for a fuel cell separator, an electrode material, and the like, which is industrially useful.

100 Base material 200 Metal nitride layer 300 (Conductive) nanocarbon layer 400 Plasma source

Claims (12)

Etching the oxide film of the stainless steel base material;
Depositing a metal nitride buffer layer on the surface of the matrix oxide film etched;
Depositing a conductive carbon layer on the metal nitride buffer layer in a nano-sized thickness. A method for producing a nanocarbon coating layer having corrosion resistance and conductivity. The method for producing a nanocarbon coating layer having corrosion resistance and conductivity according to claim 1, wherein etching of the oxide film of the stainless steel base material is performed by plasma etching. The metal nitride buffer layer is formed at a temperature of 300 to 500 ° C by supplying a metal target and nitrogen gas to a chamber, applying a voltage to a metal arc, and applying a bias voltage to a base material. 2. A method for producing a nanocarbon coating layer having corrosion resistance and conductivity according to 2. The coating of the conductive carbon layer is performed at a temperature of 200 to 600 ° C. by applying a voltage to the ion gun and applying a bias voltage to the base material. The corrosion resistance and conductivity according to claim 1. A method for producing a provided nanocarbon coating layer. The corrosion resistance according to claim 4, wherein the bias voltage is DC, AC of 0 to −800 V, or a pulse voltage having a frequency of 0.1 kHz to 500 kHz, and the thickness of the conductive carbon layer is deposited to 1 to 150 nm. And a method of manufacturing a nanocarbon coating layer having conductivity. The step of etching the oxide film, the step of depositing the metal nitride buffer layer, and the step of depositing the conductive carbon layer with a nano-sized thickness are collectively performed in each chamber arranged in-line. The method for producing a nanocarbon coating layer having corrosion resistance and conductivity according to any one of claims 1 to 5, wherein the method is performed in situ. The step of etching the oxide film is performed by plasma etching using an ion gun, and the position of the ion gun can be moved to adjust the distance between the ion gun and the base material surface. The method for producing a nanocarbon coating layer having corrosion resistance and conductivity according to any one of claims 1 to 6, wherein the etching rate can be adjusted. A stainless steel matrix oxide film is etched, a metal nitride buffer layer is deposited on the etched surface, and a conductive carbon layer is deposited on the metal nitride buffer layer in a nano-sized thickness. Stainless steel with corrosion resistance and conductivity. The stainless steel having corrosion resistance and conductivity according to claim 8, wherein the metal nitride film contains CrN or TiN and has a thickness of 1 to 20 nm. The stainless steel having corrosion resistance and conductivity according to claim 8 or 9, wherein the conductive carbon layer has a thickness of 1 to 150 nm. The stainless steel having corrosion resistance and conductivity according to claim 10, wherein the stainless steel is a fuel cell separator or an electrode material. A first chamber having an ion gun and etching an oxide film of a stainless steel base material with plasma;
A second chamber having a metal arc for coating a metal nitride film on the surface of the stainless steel base material after the oxide film etching step;
A third chamber having an ion gun for coating a conductive carbon layer with a nano-sized thickness on the surface of the stainless steel base material coated with the metal nitride film, and arranged in-line;
The apparatus for producing a nanocarbon coating layer having corrosion resistance and conductivity, wherein the plasma etching step, the metal nitride film coating step, and the conductive carbon layer coating step are continuously performed in situ.

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