technical field
[One]
The present invention relates to a stainless steel having excellent surface electrical conductivity and a method for manufacturing the same, and more particularly, to a stainless steel for a fuel cell separator having excellent surface electrical conductivity and a method for manufacturing the same.
background
[2]
Stainless steel has excellent corrosion resistance and is easy to process, so it is being studied as a material for electronic components and fuel cell separators. However, conventional stainless steel has a problem in that the passivation film on the surface acts as a through-plane resistance element and does not secure sufficient electrical conductivity.
[3]
Until now, the effect of the passivation film on the surface electrical conductivity of stainless steel has not been clearly identified. In order to improve the surface electrical conductivity of the passivation film, Ni plating is performed in the case of a material for electronic parts, or a conductive material such as gold, carbon, or nitride is applied to stainless steel in order to lower the high contact resistance value of stainless steel for use as a fuel cell separator. A process for coating the surface of steel has been proposed. However, due to the additional process for coating Ni plating or other coating material, there is a problem in that the manufacturing cost and manufacturing time increase, thereby reducing productivity, and there is a problem that the fundamental penetration resistance of the passivation film cannot be lowered.
[4]
In addition, as another method for improving the surface electrical conductivity of stainless steel, a method of modifying the surface of stainless steel has been tried.
[5]
Patent Document 1 proposes a stainless steel for a separator plate having a low interfacial contact resistance and a high corrosion potential by controlling the surface modification process.
[6]
Patent Document 2 proposes a method of manufacturing stainless steel having excellent corrosion resistance and low contact resistance by immersing stainless steel containing 17 to 23 wt% of Cr in a [HF]≥[HNO 3] solution.
[7]
Patent Document 3 proposes a stainless steel having an atomic ratio of Cr and Fe of 1 or more, which is contained in a passivation film of stainless steel containing 15 to 45% by weight of Cr and 0.1 to 5% by weight of Mo.
[8]
However, Patent Documents 1 to 3 have a limitation in that the fundamental penetration resistance of the passivation film of stainless steel cannot be lowered by adjusting the ratio of Cr/Fe atom number of the passivation film within a few nm region.
[9]
(Patent Document 0001) Korean Patent Application Laid-Open No. 10-2014-0081161 (published on: July 1, 2014)
[10]
(Patent Document 0002) Korean Patent Application Laid-Open No. 10-2013-0099148 (Published date: 2013.09.05)
[11]
(Patent Document 0003) Japanese Laid-Open Patent Publication No. 2004-149920 (published date: May 27, 2004)
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[12]
In order to solve the above problems, the present invention is to provide a stainless steel for a fuel cell separator having excellent surface electrical conductivity applicable as a material for an electrical contact and a material for a fuel cell separator, and a method for manufacturing the same.
means of solving the problem
[13]
As a means for achieving the above object, the stainless steel for separator having excellent surface electrical conductivity according to an embodiment of the present invention is Al-Kα X by X-ray angle resolution photoelectron spectroscopy on the surface of stainless steel containing 15 wt% or more of Cr. - When the take-off angle of the photoelectron is measured under the condition of 12° to 85° using a source, the value of the surface oxide element ratio (1) measured below may be 0.08 or more.
[14]
(One)
[15]
The Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 . The total oxides and hydroxides include Cr oxide, the Cr hydroxide, Fe oxide, Fe hydroxide, and metal oxide (MO), and the metal oxide (MO) includes a mixed oxide, and M is in the base material except Cr and Fe. It is an alloying element or a combination thereof, and O means oxygen.
[16]
In the stainless steel for fuel cell separator having excellent surface electrical conductivity of the present invention, the surface oxide element ratio (1) may be 0.2 or more.
[17]
In the stainless steel for fuel cell separator having excellent surface electrical conductivity of the present invention, the band gap energy of the surface oxide layer of the stainless steel may be 2 eV or less.
[18]
In the stainless steel for fuel cell separator having excellent surface electrical conductivity of the present invention, the surface oxide layer of the stainless steel may form an ohmic contact with the base material.
[19]
In addition, as another means for achieving the above object, the method for manufacturing stainless steel for fuel cell separator having excellent surface surface electrical conductivity according to an embodiment of the present invention is immersed in a non-oxidizing acid solution, or electrolyzed after immersion. The surface of stainless steel containing 15 wt% or more of Cr, including primary surface treatment and secondary surface treatment by immersion in an oxidizing acid solution, was subjected to X-ray angle resolution photoelectron spectroscopy using an Al-Kα X-ray source. When the take-off angle of the photoelectron is measured under the conditions of 12° to 85°, stainless steel having the following surface oxide element ratio (1) value measured is 0.08 or more.
[20]
(One)
[21]
The Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 . The total oxides and hydroxides include Cr oxide, the Cr hydroxide, Fe oxide, Fe hydroxide, and metal oxide (MO), and the metal oxide (MO) includes a mixed oxide, and M is in the base material except Cr and Fe. It is an alloying element or a combination thereof, and O means oxygen.
[22]
In the method for producing a stainless steel for fuel cell separator having excellent surface electrical conductivity of the present invention, the primary surface treatment is immersing the stainless cold-rolled steel sheet in the non-oxidizing acid solution for 5 seconds or more, or 0.1A/cm after immersion It includes electrolytic treatment for 5 seconds or more at a current density of 2 or more, and the non-oxidizing acid solution may be a hydrochloric acid or sulfuric acid solution of 50° C. or more and 5 wt % or more.
[23]
In the method for producing a stainless steel for fuel cell separator having excellent surface electrical conductivity of the present invention, the secondary surface treatment includes immersing the stainless cold-rolled steel sheet in the oxidizing acid solution for 5 seconds or more, and the oxidizing acid solution is It may be a nitric acid solution of 50° C. or higher, and 5 wt % or higher.
Effects of the Invention
[24]
The present invention relates to a stainless steel for a fuel cell separator having excellent surface electrical conductivity applicable to a material for an electrical contact and a material for a fuel cell separator by making a surface oxide layer having semiconducting properties formed on the surface of the stainless steel into a conductor, and the same A manufacturing method can be provided.
[25]
According to the present invention, the following surface oxide element ratio measured when the surface of stainless steel is measured using an Al-Kα X-ray source by X-ray angle resolution photoelectron spectroscopy under the condition that the take-off angle of photoelectrons is 12° to 85° (1) By controlling the value to be 0.08 or more, it is possible to provide a stainless steel for a fuel cell separator having excellent surface electrical conductivity and having a band gap energy of 2 eV or less of the surface oxide layer.
[26]
(One)
[27]
The Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 . The total oxides and hydroxides include Cr oxide, the Cr hydroxide, Fe oxide, Fe hydroxide, and metal oxide (MO), and the metal oxide (MO) includes a mixed oxide, and M is in the base material except Cr and Fe. It is an alloying element or a combination thereof, and O means oxygen.
[28]
According to the present invention, the surface oxide layer of stainless steel forms an ohmic contact with the base material to provide a stainless steel for a fuel cell separator having excellent surface electrical conductivity.
Brief description of the drawing
[29]
1A and 1B are graphs showing the correlation between the surface oxide element ratio (1) and the bandgap energy with reference to the results of Table 2;
Best mode for carrying out the invention
[30]
In the stainless steel for separator having excellent surface electrical conductivity according to an example of the present invention, the take-off angle of photoelectrons using an Al-Kα X-ray source by X-ray angle decomposition photoelectron spectroscopy on the surface of stainless steel containing 15 wt% or more of Cr When measured under the conditions of 12° to 85°, the value of the measured surface oxide element ratio (1) may be 0.08 or more.
[31]
(One)
[32]
The Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 . The total oxides and hydroxides include Cr oxide, the Cr hydroxide, Fe oxide, Fe hydroxide, and metal oxide (MO), the metal oxide (MO) includes a mixed oxide, and M is in the base material except Cr and Fe. It is an alloying element or a combination thereof, and O means oxygen.
Modes for carrying out the invention
[33]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes preferred embodiments of the present invention. However, the embodiment of the present invention may be modified in various other forms, and the technical idea of ​​the present invention is not limited to the embodiment described below. In addition, the embodiments of the present invention are provided in order to more completely explain the present invention to those of ordinary skill in the art.
[34]
The terms used in this application are only used to describe specific examples. Therefore, for example, a singular expression includes a plural expression unless the context clearly requires it to be singular. In addition, terms such as "comprises" or "comprises" used in the present application are used to clearly indicate that the features, steps, functions, components, or combinations thereof described in the specification exist, and other features It should be noted that it is not intended to be used to preliminarily exclude the existence of elements, steps, functions, components, or combinations thereof.
[35]
On the other hand, unless otherwise defined, all terms used herein should be regarded as having the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Accordingly, unless explicitly defined herein, specific terms should not be construed in an unduly idealistic or formal sense. For example, a singular expression herein includes a plural expression unless the context clearly dictates otherwise.
[36]
Also, in this specification, "about", "substantially" and the like are used in or close to the numerical value when manufacturing and material tolerances inherent in the stated meaning are presented, and are used in the present invention. It is used to prevent unfair use by unconscionable infringers of the disclosure in which exact or absolute figures are mentioned to aid harm.
[37]
In addition, as used herein, the term "stainless cold rolled steel sheet" means a stainless steel cold rolled steel sheet manufactured according to the conventional stainless steel manufacturing process, hot rolling-heating-cold rolling-annealing, and a person skilled in the art will recognize that To the extent possible, it can be interpreted as a stainless cold-rolled steel sheet manufactured according to a typical manufacturing process of a stainless steel cold-rolled steel sheet.
[38]
In addition, as used herein, the term “surface oxide” refers to an oxide formed on the surface of stainless steel by spontaneously oxidizing a base metal element by external oxygen when the stainless steel is exposed to a temperature of about 200° C. or less. The surface oxide has Cr 2O 3 as its main component, and SiO 2, SiO, Si 2O 3, MnO, MnO 2, Mn 2O 3, VO, V 2O 3, V 2O 5, NbO, NbO 2, Nb 2O 5, TiO 2 , FeO, Fe 2O 3, Fe 3O 4 and the like may be included as an example. Although examples of surface oxides have been listed above, it is necessary to note that these are examples for helping understanding of the present invention and do not specifically limit the technical spirit of the present invention.
[39]
In addition, as used herein, the term "surface oxide layer" refers to a layer including the surface oxide of the present invention, and may be interpreted as a passivation film of stainless steel.
[40]
In addition, in the present specification, "Fe oxide" means all Fe oxides in oxide form within a range that can be clearly recognized by those skilled in the art, such as FeO, Fe 2O 3, Fe 3O 4, and the like. "Fe hydroxide" means all hydroxides of FeOOH, Fe(OH) 2-, Fe(OH) 3, etc. within the range that can be readily recognized by those skilled in the art in the form of hydroxides.
[41]
In addition, in the present specification, "Cr oxide" means all Cr oxides in oxide form within the range that can be clearly recognized by those skilled in the art, such as Cr 3O 4, Cr 2O 3, CrO 2, CrO 3, etc. .
[42]
It is known that the passivation film of conventional stainless steel has a high resistance due to the semiconducting properties of oxides. The inventors of the present invention, when the bandgap energy of the surface oxide layer of stainless steel is controlled to 2 eV or less, the surface oxide layer with semiconductor properties is made into a conductor, so that it can be applied to materials for electrical contact and fuel cell separators. A stainless steel for fuel cell separator with excellent conductivity was discovered.
[43]
According to an example of the present invention, the take-off angle of photoelectrons is 12° to 85° using an Al-Kα X-ray source by X-ray angle-resolved photoemission spectroscopy (ARPES). When measuring the surface of the stainless steel, the following surface oxide element ratio (SER) (1) value to be measured may be 0.08 or more.
[44]
(One)
[45]
The Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 . The total oxides and hydroxides include Cr oxide, the Cr hydroxide, Fe oxide, Fe hydroxide, and metal oxide (MO), and the metal oxide (MO) includes a mixed oxide, and M is in the base material except Cr and Fe. It is an alloying element or a combination thereof, and O means oxygen.
[46]
Metal oxide (MO) may be, for example, SiO 2, SiO, Si 2O 3, MnO, MnO 2, Mn 2O 3, VO, V 2O 3, V 2O 5, NbO, NbO 2, Nb 2O 5, TiO 2 have. Although examples of the metal oxide (MO) have been listed above, it is necessary to note that this is an example for helping understanding of the present invention, and does not specifically limit the technical idea of ​​the present invention.
[47]
Hereinafter, the reason for limiting the take-off angle range of photoelectrons in X-ray angle resolution photoelectron spectroscopy will be described, and then the reason for limiting the range of the surface oxide element ratio (1) value will be described.
[48]
In X-ray angle-resolved photoelectron spectroscopy, the lower the take-off angle of the photoelectron, the smaller the analysis depth from the outermost surface of the stainless steel to the depth direction, and the larger the take-off angle, the larger the analysis depth. In consideration of this, according to the present invention, the take-off angle of photoelectrons is 12 using an Al-Kα X-ray source by X-ray angle resolution photoelectron spectroscopy in order to analyze the composition of all oxides formed on the surface of stainless steel regardless of the thickness of the stainless steel. It is possible to measure the surface of stainless steel under conditions of ° to 85 °.
[49]
The reason why the value of the surface oxide element ratio (1) measured according to the above conditions is limited to 0.08 or more is that the passivation film is a limiting point at which semiconductor properties are converted into conductor properties. When the surface oxide element ratio (1) value is less than 0.08, the passivation film is not suitable as a stainless steel for separator due to semiconductor characteristics. In order to obtain stainless steel excellent in surface electrical conductivity, the value of the surface oxide element ratio (1) is more preferably controlled to be 0.08 to 0.6.
[50]
By controlling the surface oxide element ratio (1) value to be 0.08 or more as described above, the present invention can control the band gap energy of the surface oxide layer to be 2 eV or less. When the bandgap energy is 0eV, the surface oxide layer has conductor characteristics, and when the bandgap energy is more than 0eV and less than 2ev, the surface oxide layer has characteristics in the middle region between conductor and semiconductor characteristics. Suitable.
[51]
Further, according to the present invention, it is preferable to control the surface oxide element ratio (1) value to 0.2 or more so that the band gap energy of the surface oxide layer has 0 eV. The band gap energy of the surface oxide layer of 0 eV means that the base material of stainless steel and the surface oxide layer formed a new, previously unknown ohmic contact despite the passive film layer composed of oxide. In other words, it means that the surface oxide layer becomes a new conductive film layer that can form an ohmic contact with the base material of stainless steel.
[52]
For the stainless steel for fuel cell separator having excellent surface electrical conductivity according to the present invention, it is sufficient if the band gap energy of the surface oxide layer is 2 eV or less, and there is no particular limitation on the type of steel. According to one example, an austenitic, ferritic, or ferrite-austenitic two-phase stainless steel may be used as the stainless steel of the present invention.
[53]
In addition, the component composition of the stainless steel for fuel cell separator having excellent surface electrical conductivity according to the present invention is not particularly limited. However, the preferred component composition is as follows. However, it should be noted that the following component composition is only an example to help the understanding of the present invention, and does not limit the technical spirit of the present invention.
[54]
According to an example, the stainless steel according to the present invention is, in weight %, C: more than 0% and less than 0.3%, N: more than 0% and less than 0.3%, Si: more than 0% and not more than 0.7%, Mn: more than 0% and less than 10% or less, P: more than 0% 0.04% or less, S: more than 0% 0.02% or less, Cr: 15 to 34%, Ni: 25% or less, the remaining Fe and other unavoidable impurities may be included.
[55]
Hereinafter, the reason for limiting the alloy composition will be described in detail. Hereinafter, unless otherwise specified, the unit is weight % (wt%).
[56]
C: more than 0% and less than 0.3%, N: more than 0% and less than 0.3%
[57]
C and N combine with Cr in steel to form stable Cr carbonitride, and as a result, a region in which Cr is locally deficient is formed and corrosion resistance may be deteriorated. Therefore, a lower content of both elements is preferable. Accordingly, in the present invention, the content of C and N is limited to C: more than 0% and 0.3% or less, and N: more than 0% and 0.3% or less.
[58]
Si: greater than 0% and less than or equal to 0.7%
[59]
Si is an element effective for deoxidation. However, when added excessively, toughness and moldability are reduced, and SiO 2 oxide generated during the annealing process reduces electrical conductivity and hydrophilicity. In consideration of this, the content of Si in the present invention is limited to Si: more than 0% and not more than 0.7%.
[60]
Mn: more than 0% and less than 10%
[61]
Mn is an element effective for deoxidation. However, since MnS, which is an inclusion of Mn, reduces corrosion resistance, the content of Mn in the present invention is limited to more than 0% and 10% or less.
[62]
P: greater than 0% and less than or equal to 0.04%
[63]
Since P reduces not only corrosion resistance but also toughness, the content of P in the present invention is limited to more than 0% and 0.04% or less.
[64]
S: greater than 0% and less than or equal to 0.02%
[65]
S is combined with Mn in steel to form stable MnS, and since the formed MnS becomes a starting point of corrosion and reduces corrosion resistance, a lower S content is preferable. In consideration of this, the content of S in the present invention is limited to more than 0% and not more than 0.02%.
[66]
Cr: 15 to 34%
[67]
Cr is an element that improves corrosion resistance. Cr is actively added to ensure corrosion resistance in a fuel cell operating environment, which is a strong acid environment. However, since the excessive addition reduces toughness, the content of Cr in the present invention is limited to 15 to 34% in consideration of this.
[68]
Ni: 25% or less
[69]
Ni is an austenite phase stabilizing element and an element for improving corrosion resistance. In addition, Ni is generally contained in an amount above a certain level in austenitic, ferrite-austenitic two-phase stainless steels. However, since workability is reduced when excessively added, the Ni content in the present invention is limited to 25% or less in consideration of this.
[70]
The lower limit of the Ni content is not particularly limited, and may be appropriately contained depending on the type of steel. For example, in an austenitic stainless steel or a ferritic-austenitic two-phase stainless steel, the lower limit of the Ni content may be 2.0% or more. For example, the lower limit of the Ni content in the ferritic stainless steel may be less than 2.0%, preferably 1.0% or less, more preferably 0.01% or less.
[71]
In addition, the stainless steel according to an example In addition to the alloy composition described above, the steel is an optional alloy component as necessary in weight %, Cu: more than 0.01% and less than 1.5%, V: more than 0.01% and less than 0.6%, Mo: 0.01 to 5.0%, Ti: 0.01 to 0.5%, Nb: may contain one or more of 0.01 to 0.4%. However, it should be noted that the composition of the optional alloy component is only an example to help the understanding of the present invention, and is not intended to limit the technical spirit of the present invention.
[72]
Cu: more than 0.01% and less than 1.5%
[73]
Cu is an element that improves corrosion resistance. However, in the present invention, the content of Cu is limited to more than 0.01% and not more than 1.5% in consideration of this, since it is eluted when excessively added and deteriorates the performance of the fuel cell.
[74]
V: more than 0.01% and less than 0.6%
[75]
V is an element that improves the lifespan characteristics of the fuel cell by suppressing the elution of Fe in the fuel cell operating environment. However, since toughness is reduced when excessively added, the content of V in the present invention is limited to greater than 0.01% and less than or equal to 0.6% in consideration of this.
[76]
Mo: 0.01 to 5.0%
[77]
Mo is an element that improves corrosion resistance. However, in the present invention, the content of Mo is limited to 0.01 to 5.0% in consideration of the decrease in workability when excessively added.
[78]
Ti: 0.01 to 0.5%, Nb: 0.01 to 0.4%
[79]
Ti and Nb are elements that combine with C and N in steel to form stable carbonitrides, thereby suppressing the formation of regions in which Cr is locally deficient and improving corrosion resistance. However, in the present invention, the content of Ti and Nb is limited to 0.01 to 0.5% Ti and 0.01 to 0.4% Nb in the present invention in consideration of the decrease in toughness when excessively added.
[80]
The remaining component is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be mixed in the normal manufacturing process, this cannot be excluded. All of the impurities are not specifically mentioned in the present specification, since any person skilled in the art can know the impurities.
[81]
The method for manufacturing a stainless steel for fuel cell separator having excellent surface electrical conductivity according to the present invention is sufficient as long as the surface oxide element ratio (1) value can be controlled to 0.08 or more, and is not particularly limited.
[82]
According to an example of the present invention, a stainless steel for a fuel cell separator having excellent surface electrical conductivity according to the present invention can be manufactured by surface-treating a cold-rolled steel sheet manufactured according to a conventional stainless steel manufacturing process. The surface treatment according to an example may be performed in two steps, and the first surface treatment may include immersion in a nonoxidizing acid solution, or electrolytic treatment after immersion. The secondary surface treatment may include immersion in an oxidizing acid solution.
[83]
The primary surface treatment according to an embodiment of the present invention may include immersing the stainless steel cold-rolled steel sheet in a non-oxidizing acid solution for 5 seconds or more, or electrolytic treatment at a current density of 0.1A/cm 2 or more for 5 seconds or more after immersion. . In this case, the non-oxidizing acid solution may be a solution of 50° C. or more, 5 wt% or more of hydrochloric acid (HCl) or sulfuric acid (H 2 SO 4 ) solution.
[84]
The secondary surface treatment according to an embodiment of the present invention may include immersing the cold-rolled stainless steel sheet in an oxidizing acid solution for 5 seconds or more. In this case, the oxidizing acid solution may be a nitric acid (HNO 3) solution of 50° C. or more, and 5 wt % or more.
[85]
Hereinafter, the present invention will be described in more detail through examples. However, it is necessary to note that the following examples are only intended to illustrate the present invention in more detail and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.
[86]
{Example}
[87]
Steel grades having the composition shown in Table 1 below were manufactured as slabs through a steel-making-casting process. Thereafter, the prepared slab was hot rolled at 1200° C. to prepare a 4.5 mm thick hot-rolled steel sheet. The hot-rolled steel sheet was heated at 1050°C, and then cold-rolled and annealed at 1000°C were repeated to manufacture a cold-rolled steel sheet with a thickness of 0.15 mm.
[88]
In Table 1 below, steels 1 to 9 correspond to invention steels, steels 1 to 3 are ferritic stainless steels, steels 4 to 6 are austenitic stainless steels, and steels 7 to 9 are ferritic-austenitic dual-phase stainless steels. to be. Steels 10 and 11 are comparative steels and have a Cr content of less than 15% by weight.
[89]
[Table 1]
Steel grade alloy element (wt%)
C N Si Mn P S Cr Ni Cu V Mo Nb Ti
Strong 1 0.01 0.01 0.2 0.3 0.009 0.008 15.8 - - - - - 0.15
Strong 2 0.01 0.011 0.14 0.25 0.01 0.009 22 - - - 0.18 0.35 0.03
Strong 3 0.008 0.012 0.11 0.15 0.03 0.004 30.2 - - 0.32 - 0.18 0.11
Steel4 0.12 0.04 0.65 0.9 0.025 0.005 17 6.3 0.02 - - - 0.01
Steel 5 0.02 0.05 0.5 1.12 0.02 0.002 16.4 10 0.2 - 2 - -
Steel 6 0.04 0.08 0.5 1.4 0.015 0.001 25.6 19.8 0.4 - 0.09 - -
Strong 7 0.028 0.25 0.7 3.1 0.01 0.001 20.1 0.92 0.84 - 0.01 - -
Strong 8 0.016 0.14 0.43 1.43 0.013 0.001 23.1 4.11 0.25 - 0.29 - -
Strong 9 0.015 0.28 0.34 0.82 0.012 0.001 25.2 6.3 - - 3.78 - -
Strong 10 0.01 0.012 0.18 0.28 0.008 0.007 14.8 - - - - - 0.15
Steel 11 0.10 0.035 0.45 0.8 0.015 0.005 13 9 0.15 - - - 0.1
[90]
The cold-rolled steel sheet prepared in Table 1 was surface-treated according to the surface treatment conditions in Table 2 below. The surface treatment was performed in the first and second stages, and was treated according to the conditions A to H described in Table 2. The primary surface treatment was performed by immersing the cold-rolled steel sheet in a sulfuric acid solution, which is a non-oxidizing acid solution, or immersing it and then electrolytic treatment. The secondary surface treatment was made by immersing the stainless steel in a nitric acid solution, which is an oxidizing acid solution. As the primary surface treatment, it was immersed (A) in a sulfuric acid solution of 50° C., 8 wt% for 5 seconds, and then immersed (D) for 9 seconds in a 50° C., 10 wt% nitric acid solution as a secondary surface treatment.
[91]
The surface oxide element ratio (1) value in Table 2 is a value derived according to the following formula (1), and the surfaces of the invention examples and comparative examples are shown in Table 2 using an Al-Kα X-ray source by X-ray angle resolution photoelectron spectroscopy. It is a value derived when measured under the conditions of the take-off angle of the described photoelectrons.
[92]
(One)
[93]
The surface oxide element ratio (1) value was measured in the following way. First, the PHI Quantera II equipment was used to analyze the take-off angle conditions according to Table 2, and the analysis results were obtained using the CasaXPS software to obtain the peaks in the binding energy of metal oxide (MO), Cr oxide, Cr hydroxide, Fe oxide, and Fe hydroxide. was separated, and the atomic concentration was calculated using this.
[94]
The 'sum of the atomic concentration (at%) of Cr elements in Cr hydroxide' to obtain the surface oxide element ratio (1) value isolates the peak in the binding energy of Cr hydroxide, and then fits it on the Cr 2p spectrum to Cr The sum of the atomic concentrations (at%) of In this case, Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 .
[95]
The 'sum of atomic concentrations (at%) of metal elements in all oxides and hydroxides' in the surface oxide element ratio (1) value is the sum of the atomic concentrations (at%) of Cr in Cr hydroxide and 'Cr in Cr oxides' It was calculated by adding the 'sum of atomic concentrations of', 'sum of atomic concentrations (at%) of metal elements in metal oxide (MO)', and 'sum of atomic concentrations (at%) of Fe in Fe oxides and Fe hydroxides'.
[96]
The 'sum of the atomic concentrations of Cr in Cr oxide' isolates the peak in the binding energy of Cr oxide, and then fits it to the Cr 2p spectrum to derive the sum of the atomic concentrations (at%) of Cr. 'Sum of atomic concentrations (at%) of metal elements in metal oxide (MO)' isolates the peak in the binding energy of metal oxide (MO), and then fits it on the spectrum of each metal (M) to obtain a metal element The sum of the atomic concentrations (at%) of Here, the metal oxide (MO) includes a mixed oxide, M is an alloying element in the base material other than Cr and Fe or a combination thereof, and O means oxygen. The 'sum of the atomic concentration (at%) of Fe in Fe oxide and Fe hydroxide' separates the peaks in the binding energy of Fe oxide and Fe hydroxide, and then fits it on the Fe 2p spectrum to determine the atomic concentration (at%) of Fe. ) was derived.
[97]
The band gap energy in Table 2 means the band gap energy of the surface oxide layer. The band gap energy of the surface oxide layer was measured using a Current Sensing Atomic Force Microscope (Keysight 9500 model). Inventive Examples, Comparative Examples Prepare a specimen by cutting stainless steel 1 cm x 1 cm, and apply a 20 nN load in a nitrogen atmosphere with a relative humidity of 18% so that the surface oxide layer can be measured in an inactive state so that the applied bias is -10 V The bandgap energy was measured in the current probe mode from to 10V. The band gap energy was measured as the band gap energy by measuring the width of the region where the current detected when the applied bias was changed from -10 V to 10 V by measuring the specimen with an area of ​​50 μm x 50 μm five times. At this time, the probe was a silicon probe (Si tip), a platinum-coated probe with a thickness of 30 nm was used.
[98]
[Table 2]
Steel type Primary surface treatment Secondary surface treatment Photoelectron take-off angle condition Bandgap energy (eV)
(1) value at 12° (1) value at 44° (1) at 85° )value
Invention Example 1 Steel 1 A D 0.22 0.23 0.2 0
Invention Example 2 Steel 1 B D 0.28 0.3 0.25 0
Comparative Example 1 Steel 1 E D 0.06 0.04 0.03 2.9
Invention Example 3 Steel 2 B D 0.23 0.22 0.2 0.3
Invention Example 4 Steel 2 A D 0.22 0.21 0.21 0.5
Comparative Example 2 Steel 2 F D 0.07 0.05 0.03 3.5
Invention Example 5 Steel 3 B D 0.2 0.23 0.21 1
Inventive Example 6 Steel 3 C D 0.32 0.22 0.23 0
Comparative Example 3 Steel 3 F - 0.06 0.05 0.03 3.2
Invention Example 7 Steel 4 A D 0.3 0.31 0.3 0.2
Invention Example 8 Steel 4 C D 0.28 0.27 0.28 0.22
Comparative Example 4 Steel 4 - D 0.075 0.06 0.07 2.9
Inventive Example 9 Steel 5 B D 0.28 0.27 0.25 0.23
Invention Example 10 Steel 5 B D 0.08 0.09 0.08 1.8
Comparative Example 5 Steel 5 F H 0.05 0.04 0.04 4.5
Invention Example 11 Steel 6 A D 0.43 0.43 0.41 0
Inventive Example 12 Steel 6 B D 0.41 0.42 0.43 0
Comparative Example 6 Steel 6 G - 0.05 0.04 0.02 6.5
Invention Example 13 Steel 7 C D 0.35 0.33 0.32 0.1
Invention Example 14 Steel 7 A D 0.36 0.36 0.37 0
Comparative Example 7 Steel 7 F - 0.03 0.04 0.02 7.6
Invention Example 15 Steel 8 A D 0.53 0.55 0.6 0
Inventive Example 16 Steel 8 C D 0.6 0.75 0.75 0
Comparative Example 8 Steel 8 G H 0.03 0.02 0.04 6.6
Invention Example 17 Steel 9 A D 0.13 0.12 0.11 1.2
Inventive Example 18 Steel 9 B D 0.08 0.082 0.08 1.9
Comparative Example 9 Steel 9 - H 0.06 0.05 0.06 3.3
Comparative Example 10 Steel 10 E H 0.04 0.04 0.03 4.5
Comparative Example 11 Steel 10 E H 0.055 0.06 0.051 3.2
Comparative Example 12 Steel 11 F - 0.05 0.051 0.045 3.4
Comparative Example 13 Steel 11 A D 0.06 0.05 0.04 2.5
A: immersion in 50 ℃, 8% by weight sulfuric acid solution for 5 seconds, B: immersion in 50 ℃, 10% by weight sulfuric acid solution for 6 seconds, C: immersion in 50 ℃, 10% by weight sulfuric acid solution, then 0.2A Electrolytic treatment with /cm 2 for 10 seconds, D: 50 ° C., immersion in 10 wt% nitric acid solution for 9 seconds, E: 50 ° C., immersion in 8 wt% sulfuric acid solution for 3 seconds, F: 50 ° C., 10 wt% Immersion in sulfuric acid solution for 3 seconds, G: immersion in 50°C, 10 wt% sulfuric acid solution, then electrolytic treatment at 0.2A/cm 2 for 4 seconds, H: immersion in 50°C, 10 wt% nitric acid solution for 3 seconds
[99]
Hereinafter, each invention example and comparative example are compared and evaluated with reference to the results of Table 2. Referring to the results in Table 2, Inventive Examples 1 to 18 are the result of satisfying the surface treatment process according to the present invention, that the surface oxide element ratio (1) value is 0.08 or more when the take-off angle of photoelectrons is 12° to 85° , it can be seen that the band gap energy of the surface oxide layer is 2.0 eV or less. In addition, referring to Invention Examples 1, 2, 6, 11, 12, 14, 15, and 16, the band gap energy of the surface oxide layer becomes 0 eV, and in order for the surface oxide layer to form an ohmic contact with the base material, the surface oxide element ratio (1) It is preferable that a value is 0.2 or more.
[100]
In Comparative Examples 1 and 2, the time required for the primary surface treatment was too short as 3 seconds, and the surface oxide element ratio (1) value at the photoelectron take-off angles of 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[101]
In Comparative Example 3, the time required for the primary surface treatment was too short as 3 seconds, and the secondary surface treatment was not performed. In addition, the value of the surface oxide element ratio (1) at the take-off angles of the photoelectrons at 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[102]
Comparative Example 4 was not subjected to the primary surface treatment, and the surface oxide element ratio (1) value at the take-off angles of the photoelectrons of 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[103]
In Comparative Example 5, the time required for the primary and secondary surface treatment was too short as 3 seconds, and the surface oxide element ratio (1) value at the take-off angles of the photoelectrons of 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[104]
In Comparative Examples 6 and 7, the time required for the primary surface treatment was too short as 3 seconds, and the secondary surface treatment was not performed. In addition, the value of the surface oxide element ratio (1) at the take-off angles of the photoelectrons at 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[105]
In Comparative Example 8, the time required for the primary and secondary surface treatment was too short as 3 seconds, and the surface oxide element ratio (1) value at the take-off angles of the photoelectrons of 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[106]
In Comparative Example 9, the primary surface treatment was not performed, and the time required for the secondary surface treatment was too short as 3 seconds. In addition, the value of the surface oxide element ratio (1) at the take-off angles of the photoelectrons at 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[107]
In Comparative Examples 10 and 11, the time required for the primary and secondary surface treatment was 3 seconds, which was too short. In addition, the Cr content was less than 15% by weight, and the surface oxide element ratio (1) value at the take-off angles of the photoelectrons at 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[108]
In Comparative Example 12, the primary surface treatment was not performed, and the time required for the secondary surface treatment was too short as 3 seconds. In addition, the Cr content was less than 15% by weight, and the surface oxide element ratio (1) value at the take-off angles of the photoelectrons at 12°, 44°, and 85° was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[109]
In Comparative Example 13, the primary and secondary surface treatment times were 5 seconds or longer, but the Cr content was less than 15% by weight, and the surface oxide element ratio (1) value at the take-off angles of the photoelectrons at 12°, 44°, and 85° was was less than 0.08. As a result, the band gap energy of the surface oxide layer exceeded 2.0 eV.
[110]
1A and 1B are graphs showing the correlation between the surface oxide element ratio (1) value and the bandgap energy with reference to the results of Table 2; 1A and 1B, the take-off angles of the photoelectrons are 12° and 85°, respectively. The horizontal axis of FIGS. 1A and 1B is the surface oxide element ratio (1) value, and the vertical axis is the bandgap energy (eV).
[111]
Referring to FIGS. 1A and 1B , it can be seen that the bandgap energy is 2eV or less when the surface oxide element ratio (1) value is 0.08 or more based on 0.08 as a reference point. was found to be exceeded. Referring to this, it can be seen that when the value of the surface oxide element ratio (1) is controlled to be 0.08 or more, the bandgap energy can be controlled to be 2 eV or less. In addition, referring to FIGS. 1A and 1B , it can be seen that the surface oxide element ratio (1) is preferably controlled to be 0.08 or more in order for the bandgap energy to be 0 eV.
[112]
In addition, the dotted line region shown in FIGS. 1A and 1B is a region in which the surface oxide element ratio (1) is 0.08 or more and the bandgap energy is 2 eV or less. Referring to FIGS. 1A and 1B, when all of the invention examples are included in the dotted line region of FIGS. 1A and 1B and the surface oxide element ratio (1) value is controlled to be 0.08 or more, the band gap energy is 2 eV or less, fuel cell separation with excellent surface electrical conductivity It can be seen that stainless steel for plates can be provided.
[113]
From the results of the above examples, the present invention is a fuel cell with excellent surface electrical conductivity applicable to a material for electrical contact and a material for a fuel cell separator by making a surface oxide layer having semiconductor properties formed on the surface of stainless steel into a conductor. It can be seen that stainless steel for a separator and a manufacturing method thereof can be provided.
[114]
In addition, the following surface oxide element ratio (1) value measured when measuring the surface of stainless steel using an Al-Kα X-ray source by X-ray angle resolution photoelectron spectroscopy under the condition that the take-off angle of photoelectrons is 12° to 85° It can be seen that by controlling so that it is 0.08 or more, it is possible to provide a stainless steel for a fuel cell separator having excellent surface electrical conductivity of which the band gap energy of the surface oxide layer is 2 eV or less.
[115]
In the above description, exemplary embodiments of the present invention have been described, but the present invention is not limited thereto, and those of ordinary skill in the art will not depart from the concept and scope of the following claims. It will be appreciated that various modifications and variations are possible.
Industrial Applicability
[116]
The stainless steel excellent in surface electrical conductivity according to the present invention can be applied to a fuel cell separator and the like.
Claims
[Claim 1]
The following surface oxide source measured when the surface of stainless steel containing 15% by weight or more of Cr is measured under the conditions of 12° to 85° of take-off angle of photoelectrons using an Al-Kα X-ray source by X-ray angle resolution photoelectron spectroscopy. Consumption (1) stainless steel for fuel cell separator having excellent surface electrical conductivity of 0.08 or more: (1) the Cr hydroxide means CrOOH, Cr(OH) 2 or Cr(OH) 3 ; The total oxides and hydroxides include Cr oxide, the Cr hydroxide, Fe oxide, Fe hydroxide, and metal oxide (MO), the metal oxide (MO) includes a mixed oxide, and M is in the base material except Cr and Fe. It is an alloying element or a combination thereof, and O means oxygen.
[Claim 2]
The stainless steel for a fuel cell separator according to claim 1, wherein the surface oxide element ratio (1) has excellent surface electrical conductivity of 0.2 or more.
[Claim 3]
The stainless steel for a fuel cell separator having excellent surface electrical conductivity according to claim 1, wherein the band gap energy of the surface oxide layer of the stainless steel is 2 eV or less.
[Claim 4]
2. The stain according to claim 1, The surface oxide layer of lease steel is stainless steel for fuel cell separators with excellent surface electrical conductivity that forms an ohmic contact with the base material.
[Claim 5]
Surface electric for producing stainless steel according to claim 1, including immersing the stainless steel cold-rolled steel sheet in a non-oxidizing acid solution, or immersing and then electrolytically treating the primary surface, and immersing the stainless steel sheet in an oxidizing acid solution for secondary surface treatment A method of manufacturing stainless steel for fuel cell separators with excellent conductivity.
[Claim 6]
The method of claim 5, wherein the primary surface treatment includes immersing the stainless steel cold-rolled steel sheet in the non-oxidizing acid solution for 5 seconds or more, or electrolytic treatment at a current density of 0.1A/cm 2 or more for 5 seconds or more after immersion , The non-oxidizing acid solution is a hydrochloric acid or sulfuric acid solution of 50° C. or more and 5 wt % or more of a method of manufacturing stainless steel for a fuel cell separator having excellent surface electrical conductivity.
[Claim 7]
The surface electrical conductivity of claim 5, wherein the secondary surface treatment comprises immersing the stainless steel cold-rolled steel sheet in the oxidizing acid solution for 5 seconds or more, and the oxidizing acid solution is a nitric acid solution of 50° C. or more and 5 wt% or more. This excellent manufacturing method of stainless steel for fuel cell separator plate.