WO2020054072A1

WO2020054072A1 - Titanium foil and method for producing same

Info

Publication number: WO2020054072A1
Application number: PCT/JP2018/034274
Authority: WO
Inventors: 琢香川; 孝飯島; 徳野　清則; 一浩 ▲高▼橋; 禰宜　教之
Original assignee: 日本製鉄株式会社
Priority date: 2018-09-14
Filing date: 2018-09-14
Publication date: 2020-03-19

Abstract

This titanium foil 14 is provided with: a substrate layer 1 having a chemical composition including 0.080 mass% or less of C, 0.013 mass% or less of H, 0.40 mass% or less of O, 0.050 mass% or less of N, 0.50 mass% or less of Fe, and the balance being Ti and impurities; and a surface layer 20 which has conductivity and is formed on the surface of the substrate layer 1. The surface layer 20 is a Ti compound including a TiN compound 21 and a TiO compound 23 and not including a TiC compound. This titanium foil 14 exhibits excellent conductivity and corrosion resistance even in a harsh use environment in which a fuel cell has an increased capacity and decreased size and is exposed to higher temperatures, and is thus suitable to be used for a separator in a solid polymer fuel cell.

Description

Titanium foil and method for producing the same

The present invention relates to a titanium foil and a method for producing the same.

燃料 Fuel cells are being developed as driving power sources for vehicles and stationary power generation devices, against the background of recent energy problems and environmental problems such as global warming. In particular, a polymer electrolyte fuel cell that can operate at a low temperature of 100 ° C. or less has attracted attention, and its development and commercialization have been promoted. This polymer electrolyte fuel cell generally has a membrane electrode assembly (MEA: Membrane Electrode Assembly) in which a catalyst layer serving as an anode and a catalyst layer serving as a cathode are arranged with a proton-conductive electrolyte membrane interposed therebetween. And Further, a gas diffusion layer made of carbon is disposed outside the membrane electrode assembly, and a separator is disposed outside the gas diffusion layer. This basic structure is called a unit cell. A fuel cell is usually configured by stacking a required number of unit cells to achieve a required output.

In a polymer electrolyte fuel cell (unit cell) having such a basic structure, an oxidizing gas such as oxygen or air is supplied to a cathode side from gas flow paths of separators provided on an anode side and a cathode side, respectively. A fuel gas such as hydrogen is supplied to the anode side. The oxidizing gas and the fuel gas are supplied to the catalyst layer via the gas diffusion layer, respectively, and an energy difference (potential difference) between an electrochemical reaction occurring in the anode catalyst layer and an electrochemical reaction occurring in the cathode catalyst layer is performed. ) Is taken out as work to the outside. For example, hydrogen gas is used as fuel gas, and oxygen gas is used as oxidizing gas. In this case, the electrochemical reaction [H ₂ → 2H ⁺ + 2e ⁻ (E ₀ = 0 V)] occurring in the anode catalyst layer and the electrochemical reaction [O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ ] occurring in the cathode catalyst layer O (E ₀ = 1.23 V)] is taken out as work to the outside. At this time, the potential of the separator becomes equal to the potential of the catalyst layer, and particularly at the cathode, the potential is maintained at a high potential of about 1 V even if the overvoltage generated due to various causes is subtracted, and the operating temperature of the fuel cell becomes 60 to 90 ° C. Since the temperature is maintained, the separator is used under a strong oxidizing condition.

In recent years, in order to promote the spread of fuel cell vehicles, especially when used as a drive power source for vehicles, this polymer electrolyte fuel cell has a small stack, at the same time, has a large output, and is even more powerful than before. Development to make it cheaper is underway. For that purpose, we started to aim for operation at a high temperature exceeding 100 ° C. for the two purposes of increasing the catalyst activity and reducing the heat exchange load of the radiator. In response to such demands, separators are required to have higher corrosion resistance than before in order to cope with high-temperature operation, and to be thinner in order to reduce heat capacity.

固体 By the way, the polymer electrolyte fuel cell is operated under a strongly acidic condition having a pH of 4 or less and under an environment in which fluorine derived from the electrolyte membrane and halogen ions such as chloride ions taken in from the atmosphere coexist. In order to obtain sufficient corrosion resistance in such an environment, it is essential to form a highly corrosion-resistant coating on the metal surface of the separator, a so-called non-conductive coating. However, the non-conductive film formed on the metal surface is usually formed as an oxide of a metal component, that is, a metal oxide as a main component. Generally, metal oxides are often non-conductors, and special measures are required to develop the conductivity required for the separator. For this reason, an invention using a special stainless steel in which a conductive compound is precipitated in a steel material (Patent Document 1) and an invention using a titanium-based material in which TiB-based precipitates are dispersed in titanium (Patent Document 2) ), And many other inventions have been proposed so far.

For example, in Patent Document 3, on a titanium or titanium alloy substrate (titanium substrate layer), any of tantalum, titanium, vanadium, zirconium or chromium carbide, nitride, carbonitride and boride is used. It has an oxide film (conductive surface layer) in which a conductive material having a major axis diameter of 1 nm or more and 100 nm or less is dispersed, and is immersed in an aqueous sulfuric acid solution at pH 4 at 80 ° C. for 4 days. Each having a contact resistance (surface pressure of 1.0 MPa) of 20 mΩ · cm ² or less, and having excellent contact conductivity with carbon and excellent durability against fuel cell separator titanium or titanium alloy material (titanium foil for separator); And a method for producing the same have been proposed.

Further, in Patent Document 4, a titanium base layer and a surface layer are formed, the titanium base layer has a recrystallized structure, and the surface layer is formed of Ti in which O, C, and N are dissolved. , O, C, and N, only a compound-containing titanium layer (conductive surface layer) having a thickness of less than 1 μm in which a compound formed by Ti and Ti is mixed, or the compound-containing titanium layer; It consists of a passivation film (conductive surface layer composed of a compound-containing titanium layer and a passivation film) having a thickness of less than 5 nm formed on its surface, the passivation film is appropriately destroyed, and its regeneration is suppressed. A titanium plate material for a fuel cell separator (titanium foil for a separator) and a method for producing the same have been proposed that can reliably achieve a low contact resistance.

Further, Patent Document 5 proposes a composite metal foil for a fuel cell separator in which the surface of a titanium foil or a titanium alloy foil is coated with a predetermined conductive layer, and a method for producing the same. In Patent Document 5, a titanium substrate made of titanium or a titanium alloy is subjected to a dipping treatment in a non-oxidizing acid or a cathodic electrolytic treatment and a subsequent heat treatment, whereby X-rays are applied to the surface of the titanium substrate. A titanium foil or a titanium alloy foil (titanium for separator) on which an oxide film (conductive surface layer) in which TiO is dispersed is formed so that a predetermined TiO composition ratio [I _TiO / (I _Ti + I _TiO) ] is obtained at the diffraction peak. Foil) is disclosed.

JP 2000-328200 A JP-A-2004-273370 Republished WO No. 2014 / 021298A1 JP 2014-192039 A WO 2015/152379

The present inventors first conceived of using a fuel cell under a more severe use environment than previously assumed. In particular, regarding the temperature at the time of the test, a conventional accelerated deterioration test [for example, “Evaluation test of immersing in a sulfuric acid aqueous solution of pH 4 at 80 ° C. for 4 days (96 hours)” in Patent Document 3 and “ A new accelerated degradation test to investigate conductivity and corrosion resistance under even more severe conditions than that of "Impact test at 80 ° C for 4 days (96 hours) containing 100 ppm of fluoride ions at pH 3-sulfuric acid aqueous solution for 4 days (96 hours)" (Test for immersion in a sulfuric acid aqueous solution at a concentration of 0.005 wt% at pH 3 at 90 ° C. for 100 hours for evaluation) was set. In this new accelerated aging test, what kind of conductivity and corrosion resistance each titanium foil for a separator described in Patent Documents 3 to 5 has been examined. The results show that the target contact resistance (surface pressure: 1.0 MPa) of 5.5 mΩ · cm ² or less and the target contact resistance (surface pressure: 1.0 MPa) of 5.5 mΩ · It has been found that there is room for further improvement in conductivity and corrosion resistance, particularly corrosion resistance, in order to further increase the capacity and reduce the size of the fuel cell without satisfying cm ² or less.

The present inventors next examined in detail the causes of the titanium foils of Patent Documents 3 to 5 not exhibiting the desired conductivity and corrosion resistance in a new accelerated deterioration test. Focused on the presence of a TiC compound in each of the conductive surface layers (the oxide film of Patent Document 3, the compound-containing titanium layer of Patent Document 4, and the oxide film of Patent Document 5). The TiC compound dissolves relatively easily in the new accelerated aging test described above and is passivated in the conductive surface layer to form the non-conductive passive material TiO ₂ or by dissolution of the TiC compound. It has been found that the oxidation of pure titanium in the metal proceeds, and as a result, the conductivity of the conductive surface layer is reduced or the suppression of corrosion is impaired.

Here, in the titanium foils of Patent Documents 3 to 5, the reason why the TiC compound is mixed in the conductive surface layer is not necessarily clear, but the titanium plate material made of titanium or a titanium alloy used as a raw material is originally solid. It is considered that dissolved carbon and carbon derived from the rolling oil used during cold rolling of the titanium sheet material are considered to be carbon sources. The solid solution carbon and the carbon derived from the rolling oil in these titanium sheet materials are chemically bonded to Ti on the surface of the titanium sheet material during cold rolling and / or bright annealing treatment to form a TiC compound. It is considered something. Further, this TiC compound is inevitably generated on the surface of the titanium sheet material by bright annealing after cold rolling, and therefore, as long as the cold rolling and bright annealing are performed in the manufacturing process, the TiC compound is produced. It is considered that the generation of the TiC compound is inevitable even if the rolling oil is washed after the cold rolling of the sheet material.

Therefore, the present inventors have found that from the above examination results, TiO compound> TiN compound> TiC compound are superior in the order of corrosion resistance from the viewpoint of corrosion resistance, and TiC compound> TiN compound> TiO compound from the viewpoint of conductivity. Excellent in order. Focusing on the fact that the TiN compound has sufficient conductivity for use as a separator, further studies were conducted on developing a titanium foil for a separator having excellent performance in the above-mentioned accelerated deterioration test. As a result, they found that a titanium foil having a TiN compound and a TiO compound on the surface of a titanium base material layer and a surface layer of a Ti compound containing no TiC compound had excellent performance in a new accelerated deterioration test, Further, the present inventors have found a method for producing such a titanium foil, and have completed the present invention.

Accordingly, an object of the present invention is to provide a titanium foil having excellent conductivity and corrosion resistance. More specifically, the object of the present invention is not only excellent in conductivity, but also excellent in a severe use environment of a fuel cell such as being exposed to a higher temperature due to an increase in capacity and compactness. Another object of the present invention is to provide a titanium foil which can be used as a separator of a polymer electrolyte fuel cell exhibiting improved conductivity and corrosion resistance.
Another object of the present invention is to provide a method for producing the above-mentioned titanium foil.

The present invention is as follows.
[1] In mass%,
C: 0.080% or less,
H: 0.013% or less,
O: 0.40% or less,
N: 0.050% or less,
Fe: 0.50% or less,
A base material layer having a chemical composition that is a balance of Ti and impurities,
With a surface layer having conductivity formed on the surface of the base material layer,
The surface layer is a Ti compound including a TiN compound and a TiO compound, and not including a TiC compound.
Titanium foil.
[2] When the surface layer is measured by an X-ray diffraction method, one or both diffraction peaks of a TiN compound and a Ti ₂ N compound are observed, no diffraction peaks of other compounds are observed, and the surface layer When the XPS spectrum is measured from the side, one of the peaks of the TiO ₂ compound and the peak of one or both of the TiO _x compounds is observed, and other than these, the peak of Ti is not observed.
The titanium foil of the above [1].
[3] the surface layer has a thickness of 20 nm to 500 nm;
The titanium foil of the above [1] or [2].
[4] The surface layer provides the X-ray diffraction spectrum, the ratio between the peak _{P a2} of the peak _{P a1} and TiN compound of Ti ₂ N compound _{_(P} a1 _/ P _a2) is from 1.6 to 2.6
The titanium foil according to any one of the above [1] to [3].
[5] The conductive surface layer has a ratio (P _b1 / P _b2 ) of the peak P _b1 of the TiO ₂ compound to the peak P _b2 of the TiO _x compound in the XPS spectrum of Ti2p of 1.7 to 2.8. is there,
The titanium foil according to any one of the above [1] to [4].
[6] a titanium foil used for a separator of a polymer electrolyte fuel cell,
The titanium foil according to any one of the above [1] to [5].
[7] The method for producing a titanium foil according to any one of the above [1] to [6],
(1) performing a bright annealing treatment in a nitrogen gas atmosphere on a titanium sheet cold-rolled in the presence of a rolling oil to obtain an annealed titanium sheet having a Ti compound layer formed on the surface of the titanium sheet;
(2) performing a first acid treatment on the annealed titanium sheet to obtain a first acid-treated titanium sheet from which the TiC compound in the Ti compound layer has been removed;
(3) performing a second acid treatment on the first acid-treated titanium plate to obtain a titanium foil including a surface layer containing a TiN compound and a TiO compound and not containing a TiC compound;
A method for producing a titanium foil comprising:
[8] After the step (2) and before the step (3), a light-volume annealing treatment is performed.
The method for producing a titanium foil according to the above [7].
[9] The step (3) includes:
As an acid treatment liquid, a mixed solution of sulfuric acid and hydrogen peroxide, using nitric acid or hydrogen peroxide,
The method for producing a titanium foil according to the above [7] or [8].

According to the present invention, a titanium foil having excellent conductivity and corrosion resistance can be provided. By using the titanium foil of the present invention, not only the conductivity is excellent, but also the conductivity is excellent even under the severe use environment of the fuel cell which is exposed to a higher temperature due to the increase in capacity and compactness. In addition, a separator of a polymer electrolyte fuel cell that can exhibit corrosion resistance can be manufactured.
Further, according to the present invention, it is possible to provide a method for producing the above-mentioned titanium foil.

FIG. 1 is a schematic diagram showing a cross-sectional structure of a titanium foil according to the present invention. FIG. 13 is a transmission electron microscope (TEM: Transmission Electron Microscope) image of a partial cross section of the titanium foil of No. 13, (a) shows a TEM image, (b) shows the position of each compound in the TEM image of (a). Is shown. FIG. 3 is a schematic diagram showing a cross-sectional structure of the annealed titanium plate material. FIG. 4 is a schematic diagram showing a cross-sectional structure of the first acid-treated titanium plate material. FIG. 5 is a schematic diagram showing a cross-sectional structure of a titanium foil obtained by performing a second acid treatment on a first acid-treated titanium plate material. FIG. 6 is a schematic diagram showing a cross-sectional structure of a titanium sheet material (second annealed titanium sheet material) obtained by performing the second annealing on the first acid-treated titanium sheet material. FIG. 7 is a schematic diagram showing a cross-sectional structure of a titanium foil obtained by performing a second acid treatment on a second annealed titanium plate material.

1. Hereinafter, the titanium foil according to the present invention will be described in detail.

(1) Overall Configuration The titanium foil according to the present invention is used, for example, for a separator of a polymer electrolyte fuel cell. As shown in FIG. 1, the titanium foil according to the present invention includes a base layer 1 and a conductive surface layer 2 formed on the surface of the base layer 1. The surface layer 2 is a Ti compound containing a TiN compound 2a and a TiO compound 2b, but not containing a TiC compound. The titanium foil according to the present invention does not contain a TiC compound that is relatively easily dissolved in the above-mentioned new accelerated deterioration test, so that it can exhibit excellent conductivity and corrosion resistance even under a severe use environment of a fuel cell.

(2) Base material layer 1
The base material layer 1 is, by mass%, C: 0.080% or less, H: 0.013% or less, O: 0.40% or less, N: 0.050% or less, Fe: 0.50% or less, It has the chemical composition of the remainder Ti and impurities. As the base material layer 1, an industrial pure titanium material having a chemical composition belonging to any one of JIS1 to JIS4 can be used. JIS Class 1 to Class 4 are defined in JIS H4600: 2012.
JIS Class 1 means C: 0.08% or less, H: 0.013% or less, O: 0.15% or less, N: 0.03% or less, Fe: 0.20% or less, composition of balance Ti and impurities Having. JIS Class 2 means C: 0.08% or less, H: 0.013% or less, O: 0.20% or less, N: 0.03% or less, Fe: 0.25% or less, balance of Ti and impurities. Having a composition. JIS Class 3 means C: 0.08% or less, H: 0.014% or less, O: 0.30% or less, N: 0.05% or less, Fe: 0.30% or less, balance of Ti and impurities Having a composition. JIS Class 4 means C: 0.08% or less, H: 0.013% or less, O: 0.40% or less, N: 0.05% or less, Fe: 0.50% or less, balance of Ti and impurities. Having a composition.
The thickness of the base material layer 1 may be appropriately set according to its use, and is, for example, 0.03 mm or more and 0.1 mm or less. A preferred lower limit is 0.03 mm, and a preferred upper limit is 0.05 mm.

(3) Surface layer 2
The surface layer 2 is a conductive surface layer, and includes a Ti compound containing a TiN compound 2a and a TiO compound 2b and not containing a TiC compound.
The thickness of the surface layer 2 is preferably 20 nm or more and 500 nm or less. If it is less than 20 nm, it is difficult to secure sufficient conductivity and corrosion resistance, and if it exceeds 500 nm, the conductivity may be reduced. The preferred lower limit of the surface layer 2 is 100 nm, and the preferred upper limit is 300 nm.
As shown in FIG. 1, the surface layer 2 is composed of a layer composed of a TiN compound 2a as an inner layer close to the surface of the substrate layer 1, and a TiO compound 2b as an outer layer remote from the surface of the substrate layer 1. And a layer to be formed. When the surface layer 2 having such a configuration is used in an acid environment or a high-temperature environment, excellent corrosion resistance is exhibited by the TiO compound 2b constituting the outer layer, and the excellent conductivity of the TiN compound 2a constituting the inner layer is exhibited. Can be maintained for a long period of time.
Since it is difficult to strictly define the thickness of the inner layer composed of the TiN compound 2a and the thickness of the outer layer composed of the TiO compound 2b, the thickness is evaluated by the average value of the thickness measured by the following method. . That is, a thin slice sample processed to a thickness (for example, about 100 nm) that can be observed with a TEM by a method such as FIB is prepared, and an image obtained by TEM observation of this sample shows that a TiN compound is randomly selected at 50 locations. The thicknesses of 2a and TiO compound 2b are measured, and the average value is defined as the thickness of each layer.
The thickness of the inner layer made of the TiN compound 2a is preferably 20 nm or more and 499 nm or less. If it is less than 20 nm, it is difficult to secure sufficient conductivity, and if it exceeds 499 nm, it tends to crack during press working, and the durability may not be satisfied. A preferred lower limit is 100 nm, and a preferred upper limit is 300 nm.
The thickness of the outer layer made of the TiO compound 2b is preferably 1 nm or more and 20 nm or less. If it is less than 1 nm, it is difficult to secure sufficient corrosion resistance, and if it exceeds 20 nm, the conductivity may be reduced. A preferred lower limit is 2 nm, and a preferred upper limit is 15 nm.

(TiN compound 2a)
The fact that the Ti compound 2 contains the TiN compound 2a can be confirmed, for example, by observing a peak by an X-ray diffraction method. That is, when one or both diffraction peaks of the TiN compound and the Ti ₂ N compound are measured by the X-ray diffraction method, it can be determined that the Ti compound 2 includes the TiN compound 2a.
The measurement by the X-ray diffraction method described above was performed using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation) using an X-ray source: CoKα, an X-ray output: 40 kV and 135 mA, an incident angle (θ): 0.5 °, Scattering angle (2θ): 1.0 °, detector: scintillation counter, scan range: 5 ° to 110 °, scan speed: 2 ° / min, step: 0.02 ° to X-ray sample Was performed by a thin film X-ray diffraction method (thin film XRD method) in which the diffraction angle 2θ was measured by scanning while fixing the incident angle (θ) of the sample.
The TiN compound 2a, the X-ray diffraction spectrum, it is preferable the ratio between the peak _{P a2} of the peak _{P a1} and TiN compound of Ti ₂ N compound _{_(P} a1 _/ P _a2) is from 1.6 to 2.6 . When the ratio (P _a1 / P _a2 ) is less than 1.6, the conductivity may be reduced. On the other hand, when the ratio (P _a1 / P _a2 ) exceeds 2.6, the conductivity is high but the corrosion resistance is reduced. Might be.

(TiO compound 2b)
Whether the Ti compound 2 contains the TiO compound 2b can be confirmed by measuring an XPS spectrum from the surface side. That is, when one or both of a TiO ₂ (tetravalent ion of Ti) compound and a TiO _x (divalent ion of Ti) compound are observed when measuring the XPS spectrum from the surface side, the Ti compound 2 is replaced with the TiO compound 2a. Can be determined to be included. The determination as to whether or not a peak exists indicates that 2θ (deg) = 35 to 39 ° is regarded as the baseline, and indicates that the intensity with respect to this baseline is at least twice the deviation of the baseline. . It is considered that the TiO compound 2b does not show a peak in X-ray diffraction and has an amorphous structure.
When the XPS spectrum is measured, metal Ti (0 valence of Ti) or Ti in a trivalent ion state may be observed. Since these Tis may cause a problem of dissolution in the operating environment of the polymer electrolyte fuel cell, in the present invention, TiO ₂ (tetravalent ion of Ti) compound and TiO _x (divalent ion of Ti) are used. ) It is preferable that a peak of Ti other than the compound is not observed.
As the TiO compound 2b, the ratio of the peak P _b1 of the TiO ₂ compound to the peak P _b2 of the TiO _x compound (P _b1 / P _b2 ) in the XPS spectrum of Ti 2p is preferably 1.7 to 2.8. . When the ratio (P _b1 / P _b2 ) is less than 1.7, the conductivity is high, but the corrosion resistance may decrease. On the other hand, when the ratio (P _b1 / P _b2 ) exceeds 2.8, the conductivity decreases. Might be.

(TiC compound)
The fact that the Ti compound does not contain the TiC compound can be confirmed, for example, by observing a peak by an X-ray diffraction method. That is, when the diffraction peak of the TiC compound is not observed when measured by the X-ray diffraction method, it can be determined that the Ti compound does not include the TiC compound. When no peak is observed in the X-ray diffraction method, specifically, 2θ (deg) = 35 to 39 ° is regarded as the baseline, the average value of the intensity and the deviation Δ are calculated, and the intensity of the target compound is calculated. It can be defined as a state in which the peak intensity obtained by subtracting the baseline of the diffraction line is larger than 2Δ, and there is no peak whose half-value width of the peak is smaller than 3 °.
The measurement by the X-ray diffraction method is the same as the measurement of the TiN compound.

(Other compounds)
In a corrosive environment where the separator is exposed under a more severe operation such as a 120 ° C. operation of the polymer electrolyte fuel cell, if it is a compound that does not dissolve, it is included as a compound other than the above-mentioned TiN compound 2a and TiO compound 2b. You may. For example, silicon oxide such as silica, iridium oxide, ruthenium oxide, and the like may be included because they do not adversely affect the operation and effect of the present invention. However, it is preferable that these compounds are not included. Therefore, when the surface layer 2 is measured by the X-ray diffraction method, the diffraction peaks of the TiN compound and the Ti ₂ N compound are observed, the diffraction peaks of the other compounds are not observed, and the XPS spectrum is measured from the surface side. When the measurement is performed, the layer is preferably a layer in which the peak of the TiO ₂ compound and the peak of the TiO _x compound are observed, and other Ti peaks are not observed.

2. Next, a method for producing a titanium foil for a separator of the present invention will be described in detail.

(1) Cold Rolling The titanium foil according to the present invention has a desired thickness by cold rolling a titanium plate material of about 0.2 to 0.5 mm. Cold rolling is performed in the presence of rolling oil. As a method of cold-rolling the titanium sheet material to a predetermined thickness in the presence of the rolling oil, general cold rolling adopted when manufacturing a titanium foil from a titanium sheet material may be used. Usually, rolling oil contains carbon. After cold rolling, a washing step such as degreasing is usually performed. However, carbon derived from the rolling oil cannot be completely removed, and 0.001 to 0.1% by mass of carbon is added to titanium material. Inherent. Carbon present in the titanium material is deposited on the surface of the titanium material as a TiC compound in a subsequent annealing step.

(2) Light-volume annealing treatment (in the case where the second annealing treatment is performed, it may be referred to as "first annealing treatment").
In this step, bright annealing is performed on the cold-rolled titanium sheet in a nitrogen gas atmosphere to obtain an annealed titanium sheet having the titanium compound layer 20 formed on the surface of the titanium sheet. As shown in FIG. 3, the Ti compound 20 formed on the surface of the annealed titanium plate material 10 is composed of a TiN compound 21 and a TiC compound 22. The TiN compound 21 is mainly derived from N in the atmosphere, and the TiC compound 22 is derived from C contained in the annealed titanium plate material 10.
The annealing temperature is, for example, not less than 600 ° C. and not more than 840 ° C. If the temperature is lower than 600 ° C., sufficient TiN compound 21 cannot be formed on the surface of the titanium material, and excellent conductivity may not be obtained. On the other hand, when the temperature exceeds 840 ° C., the TiN compound 21 becomes too thick, so that the TiN compound 21 is liable to crack at the time of press working, and the durability may not be satisfied. A preferred lower limit is 650 ° C, and a preferred upper limit is 820 ° C.
The annealing time is, for example, not less than 10 seconds and not more than 360 seconds. If the time is less than 10 seconds, a sufficient TiN compound 21 cannot be formed on the surface of the titanium plate material 10, and excellent conductivity may not be obtained. On the other hand, when the time exceeds 360 seconds, the TiN compound 21 becomes too thick, so that the TiN compound 21 is easily cracked at the time of press working, and the durability may not be satisfied. A preferred lower limit is 15 seconds, and a preferred upper limit is 300 seconds. However, the annealing time and the annealing temperature are correlated with each other. If the annealing temperature is 840 ° C., a suitable annealing time is 10 seconds. If the annealing is performed at a higher temperature, the suitable treatment time becomes shorter. However, the composition and thickness of the surface layer formed on the surface of the base material are varied and become uncontrollable. Therefore, a combination of 840 ° C. and 10 seconds is set. Similarly, lowering the annealing temperature increases the annealing time, but at 600 ° C., 360 seconds is the optimum processing time. When the temperature is lower, the processing time needs to be further extended. However, when the processing time exceeds 360 seconds, the influence of impurities in the atmosphere occurs, so that 360 seconds is the upper limit and the corresponding processing temperature of 600 ° C. is the lower limit of the annealing temperature.
The annealing atmosphere is a nitrogen atmosphere. This is because the Ti compound layer 20 containing a large amount of the TiN compound is formed on the surface of the titanium plate.

(3) First Acid Treatment In this step, a first acid treatment is performed on the annealed titanium sheet material 10 to obtain a first acid-treated titanium sheet material 11 from which the TiC compound 22 in the Ti compound layer 20 has been removed. By this step, the TiC compound 22 is completely or mostly removed, and as shown in FIG. 4, the Ti compound layer 20 formed on the surface of the first acid-treated titanium plate 11 is basically made of the TiN compound 21. Be composed. When an acid such as nitric acid or citric acid is used, it is presumed that a slight amount of TiO compound is formed, but it is difficult to detect the TiO compound, and its substantial existence can be ignored.
In the first acid treatment, for example, a relatively weak acid aqueous solution such as an organic acid having a hydroxy, thiol, or enol as a characteristic group can be used. However, in order to sufficiently dissolve the TiC compound 22 in the Ti compound 20, an aqueous solution of a strong protic inorganic acid having a pKa value of 2 or less or a carboxyl group-containing organic acid having a PKa value of 5 or less is required as a treatment solution. It is preferable to use Specific examples include aqueous solutions of nitric acid, sulfuric acid, phosphoric acid, hydrochloric acid, hydrobromic acid, oxalic acid, acetic acid, citric acid, and the like. Further, it is preferable that the processing temperature is 80 ° C. or more and 95 ° C. or less. A more preferred lower limit is 85 ° C, and a more preferred upper limit is 90 ° C. The processing time is preferably set to 5 minutes or more and 20 minutes or less. A preferred lower limit is 10 minutes, and a preferred upper limit is 15 minutes. The concentration of the solution is not limited, but is preferably 1% by mass or more and 60% by mass or less. The pH of the solution is not limited, but is preferably 0.05 or more and 3.0 or less.

(4) Second Acid Treatment In this step, the first acid-treated titanium plate 11 is subjected to a second acid treatment, and the surface of the Ti compound 20 containing the TiN compound 21 and the TiO compound 23 but not containing the TiC compound 22 is produced. A titanium foil 12 comprising a layer is obtained. By this step, the TiC compound 22 remaining in the Ti compound 20 is completely removed, and as shown in FIG. 5, the Ti compound layer 20 formed on the surface of the titanium foil 12 includes the TiN compound 21 and the TiO compound. 23.
The purpose of the second acid treatment is to oxidize titanium to form a TiO compound 23. Although the reason why the TiO compound 23 is formed is not necessarily clear, some of the TiN compounds 21 relatively inferior in durability among the TiN compounds 21 formed at the time of annealing elute during the second acid treatment, It is thought that it is deposited as titanium oxide (TiO compound) 23 and covers the outermost surface.
In the second acid treatment, for example, it is preferable to use a mixed solution of sulfuric acid and hydrogen peroxide generally called piranhaic acid. For example, a mixed aqueous solution having a volume fraction of concentrated sulfuric acid (50% by mass) 3 with respect to 1% by mass of hydrogen peroxide solution 1 or concentrated sulfuric acid (50% by mass) with respect to 1% by mass of hydrogen peroxide solution 30% by mass. And the like. The feature of piranhaic acid is that it has a strong oxygen-imparting property, and can bind oxygen to the surface of the first acid-treated titanium plate material 11 to form an oxide film. As the solution for the second acid treatment, oxidizing agents such as nitric acid, a mixed solution of nitric acid and hydrogen peroxide, and dichromates and permanganates can be used in addition to piranhaic acid.
The processing temperature is preferably set to 80 ° C. or more and 95 ° C. or less. A more preferred lower limit is 85 ° C, and a more preferred upper limit is 90 ° C. The processing time is preferably set to 5 minutes or more and 20 minutes or less. A preferred lower limit is 10 minutes, and a preferred upper limit is 15 minutes. The concentration of the solution is not limited, but is preferably 1% by mass or more and 60% by mass or less. The pH of the solution is not limited, but is preferably 0.05 or more and 3.0 or less.

(5) Other Steps The titanium foil according to the present invention can be manufactured by performing at least the steps (1) to (4) described above. However, at the time of the first acid treatment, a part of the TiN compound 21 in the Ti compound 20 is dissolved. In particular, when the TiC compound 22 is sufficiently dissolved at the time of the first acid treatment, the amount of the TiN compound 21 dissolved also increases, and a gap is formed between the TiN compounds 21. In the subsequent second acid treatment, a part of the TiN compound 21 is oxidized to obtain the TiO compound 23. Therefore, a sufficient amount of the TiN compound 21 may not be secured after the second acid treatment. For this reason, after the first acid treatment, light annealing (second annealing) is performed before the second acid treatment to compensate for the TiN compound 21 reduced by the first acid treatment, as shown in FIG. It is preferable to form a layer of the compound 21 and obtain the second annealed titanium plate 13. If the second acid treatment is performed after the light acid annealing after the first acid treatment, the inner layer composed of the dense TiN compound 21 and the outer layer composed of the dense TiO compound 23 as shown in FIG. Thus, the titanium foil 14 having the surface layer 20 having the following structure can be obtained.
The temperature and time conditions of the light-volatilizing annealing (second annealing) are the same as those of the light-volatilizing annealing (first annealing) shown in the above (1). However, if the Ti compound layer 20 containing a large amount of a TiN compound is formed on the surface of the titanium plate material in the first light annealing (first annealing), the second annealing may be performed in an argon gas atmosphere.

The titanium foil manufactured as described above was subjected to the new accelerated deterioration test described above, that is, a test in which the titanium foil was immersed in a sulfuric acid aqueous solution having a pH of 3 at 90 ° C. for 100 hours to evaluate the contact resistance. pressure 1.0 MPa) is not more 5.5mΩ · cm ² or less, moreover, conductivity and corrosion resistance contact resistance after the test (surface pressure 1.0 MPa) and excellent under severe conditions of 5.5mΩ · cm ² or less Demonstrate.

The four types of JIS-standard titanium plates shown in Table 1 were cold-rolled to a thickness of 0.1 mm in the presence of rolling oil, and the obtained cold-rolled titanium plates were prepared under the conditions shown in Tables 2 to 5. The treatment was performed to obtain a titanium foil having a surface layer.

チタン The obtained titanium foil was analyzed according to the following method. Tables 6 to 9 show the results.

(Chemical composition of substrate layer)
For the obtained titanium foil, the method specified in JIS H1620 is used for the determination of oxygen, the method specified in JIS H1619 for the determination of hydrogen, the method specified in JIS H1612 for the determination of nitrogen, and the method specified in JIS H1612 for the determination of iron. The chemical composition of the base material layer was determined by the method specified in JIS H1614, and the carbon content was determined by the method specified in JIS H1617.

[X-ray diffraction method (thin film XRD method)]
Using an X-ray diffractometer (SmartLab manufactured by Rigaku Corporation), the obtained titanium foil was subjected to thin-film X-ray diffraction (thin-film XRD) using an X-ray source: CoKα, an X-ray output: 40 kV and 135 mA, and an incident angle (θ). ): 0.5 °, scattering angle (2θ): 1.0 °, detector: scintillation counter, scan range: 5 ° to 110 °, scan speed: 2 ° / min, step: 0.02 ° , The angle of incidence (θ) of the X-rays on the sample was fixed, and the diffraction angle 2θ was scanned and measured. The obtained X-ray diffraction spectrum was converted into data [ICDD No. 01-076-0198 (Ti2N), ICDD No. 00-038-1420 (TiN), ICDD No. 01-087-0710 (TiO2), ICDD No. Versus 00-031-1400 (TiC)], these Ti compound [TiC compound, TiN compounds _(Ti 2 N, TiN), and TiO compounds as well as confirming the presence of (TiO _2)], Ti ₂ N Compound It was determined the ratio of the peak _{P a2} of the peak _{P a1} and TiN compound _{_(P} a1 _/ P _a2).

[X-ray photoelectron spectroscopy (XPS)]
For the obtained titanium foil, using an XPS apparatus (Quantum 2000 manufactured by PHI), irradiated X-ray: single crystal spectroscopy AlKα, X-ray spot and size: 300 μm × 300 μm, binding energy range: 450 to 475 eV, and X Linear output: Measured under the measurement conditions of 15 KV and 25 W, confirm the presence of the TiO compound (TiO2, TiOx) from the obtained XPS spectrum of Ti2p, separate the waveform of this spectrum, and exclude the background by the Iterated Shirley method. in terms of the ratio (P between the peak _{P b2} of the TiO ₂ compound of 458.5 ± 0.2eV (Ti2p3 / 2) peak _{P b1} and 454.6 ± TiO _x compound of 0.2eV of (Ti2p3 / 2) _b1 / _Pb2 ) was determined.

[Measurement of contact resistance value]
A test piece having a size of 17 to 20 mm in length and 3 to 5 mm in width was cut out from the obtained titanium foil, and superimposed on standard carbon paper (trade name: TGP-H-120, manufactured by Toray Industries, Inc.). Is sandwiched between two gold-plated copper metal fittings and pressurized to form a connection part of gold-plated copper metal fitting / carbon paper / test piece / gold-plated copper metal fitting under a surface pressure of 1.0 MPa. A DC current (1 A / cm ² ) of 1 A per 1 cm ² of the contact area is applied, the voltage drop generated at this connection is measured, and the value of the contact resistance (unit: mΩ · cm ² ) is determined from this voltage drop. Was. In the present invention, ten points were measured for measuring the contact resistance, and the average value of eight points excluding the maximum value and the minimum value was obtained as the measured value of the test piece. The contact resistance value is based on a value of 5.5 mΩ · cm ² or less.

[Accelerated degradation test (corrosion resistance test)]
A test piece of about 30 mm × 50 mm was cut out from the obtained titanium foil, and a 0.005 wt% sulfuric acid aqueous solution adjusted to pH 3 was placed in a thermostatic water bath maintained at 90 ° C. (inner diameter: 38 mm × height). The test piece is immersed in an aqueous solution of sulfuric acid in this plastic container, kept for 100 hours, and then immersed. Thereafter, the test piece is taken out of the aqueous solution of sulfuric acid, washed with water, dried, and then tested. Test piece.
With respect to the obtained test piece after the test, the contact resistance value (unit: mΩ · cm ² ) was measured by the same method as the above-described measurement of the contact resistance value. The contact resistance value is based on a value of 5.5 mΩ · cm ² or less.

In addition, No. FIG. 2 shows an image obtained by preparing an observation sample by FIB and observing a cross section of the titanium foil No. 13 at a magnification of 100,000 using a transmission electron microscope (TEM). A scale bar is shown in the image.
In FIG. 2A, a portion that looks black is the base material layer 1, and the surface layer 2 is confirmed thereon. In FIG. 2B, the portion surrounded by the solid line is the TiN compound 2a, and the portion surrounded by the dotted line is the TiO compound 2b. As shown in FIGS. 2A and 2B, a layer of the TiN compound 2a is confirmed on the base material layer 1. Although the TiO compound 2b layer has low contrast in the TEM image of the thin section, the TiO compound layer covering TiN is partially confirmed at a thickness of about several nm. In the present invention, the presence of the TiO compound layer was quantitatively evaluated by a 2p spectrum of Ti in XPS. Then, in the titanium foil of Example 3, from the measurement results of the contact resistance before and after the accelerated deterioration test, the layer of the TiO compound 2b covers the entire surface of the layer of the TiN compound 2a. Is determined.

As shown in Tables 8 and 9, Each of 2 to 8, 12 to 14, 16 to 20, 22, 23, 25 to 27, 34, 35, 38 to 43, 48 to 51, 53, 54, 57 and 58 has a chemical composition of the base material layer. Within the range defined in the present invention, the Ti compound includes a TiN compound and a TiO compound, and does not include TiC. For this reason, the contact resistance value was 5.5 mΩ · cm ² or less before and after the accelerated deterioration test, and the film had excellent conductivity and corrosion resistance. On the other hand, No. 1, 9 to 11, 15, 21, 24, 28 to 33, 36, 37, 44 to 47, 52, 55, and 56, whether the chemical composition of the base material layer does not satisfy the range specified in the present invention, The Ti compound contains TiC. Therefore, in any of the examples, at least the contact resistance value after the accelerated deterioration test exceeded 5.5 mΩ · cm ² .

1 base material layer 2 surface layer (Ti compound)

2a TiN compound

2b TiO compound 10 Annealed titanium plate 11 First acid-treated titanium plate 11
12 titanium foil 13 second annealed titanium plate 14 titanium foil 20 Ti compound 21 TiN compound 22 TiC compound 23 TiO compound

Claims

In mass%,
C: 0.080% or less,
H: 0.013% or less,
O: 0.40% or less,
N: 0.050% or less,
Fe: 0.50% or less,
A base material layer having a chemical composition that is a balance of Ti and impurities,
With a surface layer having conductivity formed on the surface of the base material layer,
The surface layer is a Ti compound including a TiN compound and a TiO compound, and not including a TiC compound.
Titanium foil.
In the surface layer, when measured by an X-ray diffraction method, one or both diffraction peaks of a TiN compound and a Ti 2 N compound are observed, no diffraction peak of a compound other than these is observed, and XPS is observed from the surface side. When the spectrum is measured, a layer in which a peak of the TiO 2 compound and one or both peaks of the TiO x compound are observed, and a peak of Ti other than these is not observed,
The titanium foil according to claim 1.
The surface layer has a thickness of 20 nm to 500 nm;
The titanium foil according to claim 1.
The surface layer provides the X-ray diffraction spectrum, the ratio between the peak P a2 of the peak P a1 and TiN compound of Ti 2 N compound (P a1 / P a2) is from 1.6 to 2.6
The titanium foil according to claim 1.
The conductive surface layer has a ratio (P b1 / P b2 ) of the peak P b1 of the TiO 2 compound to the peak P b2 of the TiO x compound in the XPS spectrum of Ti 2p of 1.7 to 2.8.
The titanium foil according to any one of claims 1 to 4.
A titanium foil used for a polymer electrolyte fuel cell separator,
The titanium foil according to any one of claims 1 to 5.
It is a manufacturing method of the titanium foil in any one of Claim 1 to 6, Comprising:
(1) performing a bright annealing treatment in a nitrogen gas atmosphere on a titanium sheet cold-rolled in the presence of a rolling oil to obtain an annealed titanium sheet having a Ti compound layer formed on the surface of the titanium sheet;
(2) performing a first acid treatment on the annealed titanium plate to obtain a first acid-treated titanium plate from which the TiC compound in the Ti compound layer has been removed;
(3) performing a second acid treatment on the first acid-treated titanium plate to obtain a titanium foil including a surface layer containing a TiN compound and a TiO compound and not containing a TiC compound;
A method for producing a titanium foil comprising:
After the step (2) and before the step (3), a light-volatilizing annealing process is performed;
A method for producing a titanium foil according to claim 7.
The step (3) includes:
As an acid treatment liquid, a mixed solution of sulfuric acid and hydrogen peroxide, nitric acid or hydrogen peroxide is used,
The method for producing a titanium foil according to claim 7.