Titanium material or titanium alloy material having surface electrical conductivity and method for producing the same, and fuel cell separator and fuel cell using the same

Abstract

In a titanium material or a titanium alloy material, in an oxide film formed on a surface of a titanium or a titanium alloy, the composition ratio of TiO (I.sub.TiO/(I.sub.Ti+I.sub.TiO)100 found from the maximum intensity of the X-ray diffraction peaks of TiO (I.sub.TiO) and the maximum intensity of the X-ray diffraction peaks of metal titanium (I.sub.Ti) in X-ray diffraction measured at an incident angle to the surface of 0.3 is 0.5% or more. A titanium material or a titanium alloy material, and a fuel cell separator and a polymer electrolyte fuel cell having good contact-to-carbon electrical conductivity and good durability can be provided.

Claims

1. A titanium material or a titanium alloy material, comprising: a titanium or titanium alloy; and a titanium oxide film on a surface of the titanium or titanium alloy, wherein an outermost surface of the titanium oxide film comprises TiO.sub.2, wherein a composition ratio of TiO (I.sub.TiO/(I.sub.Ti +I.sub.TiO))100 based on a maximum intensity of X-ray diffraction peaks of TiO (I.sub.TiO) and a maximum intensity of X-ray diffraction peaks of metal titanium (I.sub.Ti) in X-ray diffraction measured at an incident angle to a surface of 0.3 is 0.5% or more, and wherein each of amounts of increase in contact resistance from before to after deterioration test 1 and deterioration test 2 below is 10 mcm.sup.2 or less: deterioration test 1: immersion for 4 days in a sulfuric acid aqueous solution at 80 C. adjusted to pH 3 and having a fluoride ion concentration of 20 ppm, deterioration test 2: application of an electric potential of 1.0 V (vs. SHE) for 24 hours in a sulfuric acid solution at 80 C. and pH 3.

2. The titanium material or the titanium alloy material according to claim 1, wherein a diffraction peak of TiO is detected in X-ray diffraction measured at the surface at an incident angle of 0.3 and the maximum intensity of the X-ray diffraction peaks of a titanium hydride is at a background level.

3. The titanium material or the titanium alloy material according to claim 1, wherein a thickness of the oxide film is 3 to 15 nm.

4. A method for producing a titanium material or a titanium alloy material, comprising: providing a titanium intermediate material or a titanium alloy intermediate material, forming a titanium hydride layer on an outer layer of the titanium intermediate material or titanium alloy intermediate material, wherein a composition ratio of the titanium hydride (I.sub.TiH/(I.sub.Ti +I.sub.T-H)) at a surface, based on a maximum intensity of metal titanium (I.sub.Ti) and a maximum intensity of the titanium hydride (I.sub.TiH) in X-ray diffraction peaks measured at an incident angle to a surface of 0.3 is 55% or more, and subjecting the titanium intermediate material or titanium alloy intermediate material, having the titanium hydride layer on an outer layer thereof, to a heating treatment at a temperature of not less than 260 C. and less than 350 C. in an oxidizing atmosphere to form an oxide film.

5. A fuel cell separator comprising a titanium material or a titanium alloy material, wherein: the titanium material or titanium alloy material comprises a titanium or titanium alloy, and a titanium oxide film on a surface of the titanium or titanium alloy; and a composition ratio of TiO (I.sub.TiO/I.sub.Ti+I.sub.TiO))100 based on a maximum intensity of X-ray diffraction peaks of TiO (I.sub.TiO), and a maximum intensity of X-ray diffraction peaks of metal titanium (I.sub.Ti) in X-ray diffraction measured at an incident angle to a surface of 0.3 is 0.5% or more.

6. A polymer electrolyte fuel cell comprising the fuel cell separator according to claim 5.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram showing X-ray diffraction profiles (XRDs) of the surface of an intermediate material (a titanium intermediate material or a titanium alloy intermediate material). (a) is an XRD of the surface of a conventional intermediate material (a surface after common pickling with nitrohydrofluoric acid), (b) is an XRD of the surface of a comparative intermediate material that has been subjected to hydrogenation treatment, and (c) is an XRD of the surface of an intermediate material of the present invention that has been subjected to hydrogenation treatment.

(2) FIG. 2 is a diagram showing the relationships between the value of [I.sub.TiH/I.sub.Ti+I.sub.TiH)]100 (Formula (1)) found from the result of X-ray diffraction measured at the surface of a titanium intermediate material or a titanium alloy intermediate material, the contact resistance with carbon paper after a deterioration test after the intermediate material is subjected to heating treatment in the air (an oxidizing atmosphere), and the amount of increase in the contact resistance from before to after the deterioration test. Both deterioration tests 1 and 2 described above are shown in the figure.

(3) FIG. 3 is a diagram showing X-ray diffraction profiles (XRDs) of the surface of a titanium material or a titanium alloy material. (a) and (b) are XRDs of the surface of the present invention material that has been subjected to heating treatment in the air, which is an oxidizing atmosphere, after hydrogenation treatment, and (c) is an XRD of the surface of the present invention intermediate material in a state where hydrogenation treatment before heating treatment has been performed.

(4) FIG. 4 is a diagram showing the results of X-ray photoelectron spectroscopy (XPS) (photoelectron spectra of Ti 2p) of the surfaces of two titanium materials or titanium alloy materials of the present invention. (a) shows the result of XPS of the surface of one titanium material or titanium alloy material, and (b) shows the result of XPS of the surface of the other titanium or titanium alloy material.

(5) FIG. 5 is a diagram showing a transmission electron microscope image of a cross section immediately below the surface of a titanium material or a titanium alloy material of the present invention.

DESCRIPTION OF EMBODIMENTS

(6) A titanium material or a titanium alloy material of the present invention has a feature in an oxide film formed on the surface of a titanium or a titanium alloy; in the oxide film, the composition ratio of TiO (I.sub.TiO/(I.sub.Ti+I.sub.TiO)) found from the maximum intensity of the X-ray diffraction peaks of TiO (I.sub.TiO) and the maximum intensity of the X-ray diffraction peaks of metal titanium (I.sub.Ti) is 0.5% or more. By using such a composition ratio, the oxide film is made a film having stable electrical conductivity.

(7) As an example of the specific method for producing the titanium material or the titanium alloy material of the present invention, a titanium or a titanium alloy material having a surface structure in which the composition ratio of a titanium hydride (I.sub.TiH/(I.sub.Ti+I.sub.T-H)) of the surface satisfies Formula (1) below is used as a titanium intermediate material or a titanium alloy intermediate material before the oxide film is formed (hereinafter, occasionally referred to as simply an intermediate material).
[I.sub.TiH/(I.sub.Ti+I.sub.TiH)]10055%(1)

(8) I.sub.TiH: the maximum intensity of the X-ray diffraction peaks of the titanium hydride (TiH, TiH.sub.1.5, TiH.sub.2, or the like)

(9) I.sub.Ti: the maximum intensity of the X-ray diffraction peaks of metal Ti

(10) I.sub.TiH/(I.sub.Ti+I.sub.TiH) is an index that indicates the composition ratio between metal titanium and the titanium hydride at the surface of the titanium intermediate material or the titanium alloy intermediate material, and a larger value of the index means a phase configuration containing a larger amount of the titanium hydride. Hence, it is limited to 55% or more in (1) above. It is preferably 60% or more. By producing the titanium material or the titanium alloy material of the present invention using the titanium intermediate material or the titanium alloy intermediate material in which the composition ratio of the hydride [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 at the surface is 60% or more, each of the amounts of increase in the contact resistance from before to after deterioration test 1 and deterioration test 2 described later is 4 mcm.sup.2 or less.

(11) Here, the X-ray diffraction is a method using oblique incidence in which the incident angle of X-ray is fixed to a low angle, for example to 0.3, with respect to the surface of the titanium intermediate material or the titanium alloy intermediate material, and is a measurement method that identifies the structure immediately below the surface.

(12) The method for forming a titanium hydride on the outer layer of the titanium intermediate material or the titanium alloy intermediate material (hereinafter occasionally referred to as hydride formation treatment) is not particularly limited; for example, (x) a method in which the titanium or the titanium alloy material is immersed in hydrochloric acid or sulfuric acid, which is a non-oxidizing acid, (y) a method in which the titanium or the titanium alloy material is cathodically electrolyzed, and (z) a method in which the titanium or the titanium alloy material is subjected to heat treatment in a hydrogen-containing atmosphere are given. A prescribed titanium hydride can be formed on the outer layer of the titanium or the titanium alloy by any of these methods.

(13) Next, in the titanium material or the titanium alloy material of the present invention (hereinafter occasionally referred to as the present invention material), it is preferable that a diffraction peak of TiO is detected in the X-ray diffraction measured at an incident angle of 0.3 of the resulting surface, and the diffraction of the titanium hydride is at a background level when the intermediate material containing a prescribed titanium hydride in its outer layer is subjected to heating treatment in an oxidizing atmosphere.

(14) By subjecting the intermediate material mentioned above to heating treatment in an oxidizing atmosphere, the titanium hydride is oxidized to form TiO (an oxide film), and the composition ratio of TiO (I.sub.TiO/(I.sub.Ti+I.sub.TiO)) at the surface satisfies Formula (2) below.
[I.sub.TiO/(I.sub.Ti+I.sub.TiO)]1000.5%(2)

(15) I.sub.TiH: the maximum intensity of the X-ray diffraction peaks of TiO

(16) I.sub.Ti: the maximum intensity of the X-ray diffraction peaks of metal Ti

(17) [I.sub.TiO/(I.sub.Ti+I.sub.TiO)] is an index that indicates the composition ratio between metal titanium and TiO at the surface of the titanium material or the titanium alloy material, and indicates that a larger value of the index means a phase configuration containing a larger amount of TiO. Hence, it is limited to 0.5% or more in Formula (2) above. It is preferably 2% or more.

(18) Here, the X-ray diffraction is performed by oblique incidence in which the incident angle of X-ray is fixed to a low angle, for example to 0.3, with respect to the surface of the titanium material or the titanium alloy material. By the oblique incidence, the structure immediately below the surface can be identified.

(19) When, in the X-ray photoelectron spectroscopy of the surface of the titanium material or the titanium alloy material, a peak is detected in a Ti 2p spectrum at the position of the binding energy of TiO.sub.2, which is a titanium oxide, i.e. approximately 459.2 eV, the formation of the titanium oxide film of the outermost surface can be confirmed. The thickness of the titanium oxide film is preferably 3 to 15 nm, and the thickness of the titanium oxide film can be measured by, for example, observing a cross section immediately below the surface with a transmission electron microscope.

(20) As an example of the method for producing the present invention material (hereinafter occasionally referred to as the present invention material production method), (i) the intermediate material containing a titanium hydride in its surface is subjected to (ii) heating treatment in an oxidizing atmosphere.

(21) The temperature of (ii) the heating treatment in an oxidizing atmosphere is preferably not less than 260 C. and less than 350 C. The air is most convenient as the oxidizing atmosphere.

(22) The intermediate material or the present invention material is produced such that, in the titanium oxide film of the outermost surface and immediately below it, the amount of carbides, nitrides, carbonitrides, and/or borides of titanium is reduced within the extent of practical usability as a separator, in view of costs as well.

(23) When at least one of C, N, and B is present as an unavoidably mixed-in element in the titanium base material, a carbide, a nitride, a carbonitride, and/or a boride of titanium may be formed during the heat treatment process. To suppress the formation of carbides, nitrides, carbonitrides, and borides of titanium to the extent possible, the total amount of C, N, and B contained in the titanium base material is preferably set to 0.1 mass % or less. It is more preferably 0.05 mass % or less.

(24) In the present invention material, it is preferable that, in the titanium oxide film, the amount of titanium compounds containing at least one of C, N, and B be reduced within the extent of practical usability, in view of costs as well. The effect of the present invention is exhibited when C is at 10 atomic % or less, N at 1 atomic % or less, and B at 1 atomic % or less as a result of an analysis of the surface using X-ray photoelectron spectroscopy (XPS) after the surface is subjected to sputtering of 5 nm with argon.

(25) Here, the depth of argon sputtering is the value converted from the sputtering rate when the sputtering is performed on SiO.sub.2. Since a peak is detected in a Ti 2p spectrum also from the surface after sputtering of about 5 nm at the position of the binding energy of TiO.sub.2, which is a titanium oxide, i.e. approximately 459.2 eV, the result is an analysis result of the interior of the titanium oxide film.

(26) For the data analysis, MutiPak V. 8.0, an analysis software application produced by Ulvac-phi, Incorporated, was used.

(27) It has been known that the contact resistance of the surface is a relatively small value in a state where oil components of cold rolling remain or in a state where a carbide, a nitride, and/or a carbonitride of titanium, which is an electrically conductive substance, is dispersed on the surface due to heating in a nitrogen gas atmosphere. However, in the state as it is, during the exposure to an acidic corrosion environment of the actual use, these titanium compounds are dissolved and re-precipitated as an oxide that inhibits the contact electrical conductivity, and reduce the contact electrical conductivity.

(28) A fuel cell separator of the present invention (hereinafter occasionally referred to as the present invention separator) is formed of the present invention material.

(29) A polymer electrolyte fuel cell of the present invention (hereinafter occasionally referred to as the present invention battery) includes the present invention separator.

(30) The present invention will now be described in more detail with reference to the drawings.

(31) The intermediate material can be obtained by forming a titanium hydride near the surface of a titanium base material by hydride formation treatment.

(32) FIG. 1 shows X-ray diffraction profiles (XRDs) of the surface of a titanium intermediate material or a titanium alloy intermediate material. FIG. 1(a) shows an XRD of the surface of a conventional intermediate material (a surface after common pickling with nitrohydrofluoric acid) is shown; FIG. 1(b) shows an XRD of the surface of a comparative intermediate material that has been subjected to hydrogenation treatment; and FIG. 1(c) shows an XRD of the surface of an intermediate material of the present invention that has been subjected to hydrogen treatment.

(33) For the X-ray diffraction peaks, in the conventional intermediate material of (a), only diffraction peaks of metal titanium (the circle marks in the drawing) are detected; on the other hand, in the comparative intermediate material of (b) and the present invention intermediate material of (c) that have been subjected to hydrogenation treatment, strong diffraction peaks of a titanium hydride (the inverted triangle marks in the drawing) are detected.

(34) When the maximum intensities of the diffraction peaks are compared, it is found that the ratio of the titanium hydride to metal titanium is larger in the present invention intermediate material of (c) than in the comparative intermediate material of (b).

(35) In the comparative intermediate material of (b), the value of [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 is 51%; on the other hand, in the present invention intermediate material of (c), the value is 79% and satisfies Formula (1) above. The intermediate material satisfying Formula (1) above may be referred to as the present invention intermediate material.

(36) The titanium hydrides of the comparative intermediate material of (b) and the present invention intermediate material of (c) are found to be TiH.sub.1.5 from the positions of the diffraction peaks. The element concentration distribution in the depth direction from the surface was measured by glow discharge optical emission spectrometry, and it has been found that hydrogen is concentrated in an outer layer portion.

(37) Here, the method of the X-ray diffraction measurement and the method for identifying the diffraction peaks are described.

(38) The X-ray diffraction profile was measured by oblique incidence in which the incident angle of X-ray was fixed to 0.3 with respect to the surface of the titanium or the titanium alloy material, and the diffraction peaks thereof were identified.

(39) Using SmartLab, an X-ray diffraction apparatus manufactured by Rigaku Corporation, Co-K (wavelength: =1.7902 ) was used for the target at an incident angle of 0.3, and a W/Si multiple-layer film mirror (on the incident side) was used for the K removal method. The X-ray source load power (tube voltage/tube current) is 9.0 kW (45 kV/200 mA).

(40) The analysis software application used is X'pert HighScore Plus produced by Spectris Co., Ltd. The measured X-ray diffraction profile may be compared to a database in which a titanium hydride such as ICDD Card No. 01-078-2216, 98-002-1097, 01-072-6452, or 98-006-9970 is used as the reference material; thereby, the diffraction peaks can be identified.

(41) The depth of X-ray entry in the measurement conditions mentioned above is approximately 0.2 m for metal titanium and approximately 0.3 m for the titanium hydride, and therefore the X-ray diffraction peaks are X-ray diffraction peaks that reflect the structure extending approximately 0.2 to 0.3 m in depth from the surface.

(42) Also in the conventional material, when the titanium oxide film is subjected to a prescribed passivation treatment and stabilization treatment, the durability to a simple acidic environment is enhanced, but there is a case where the durability cannot be maintained in a corrosion environment in which fluorine is contained or in a usage environment in which an electric potential is applied.

(43) In the conventional material, when the concentration of fluoride ions in the environment is 20 ppm or more, the contact resistance with carbon paper is increased to approximately 100 m.Math.cm.sup.2 or more and further to approximately 1000 m.Math.cm.sup.2, and the amount of increase in the contact resistance is 90 m.Math.cm.sup.2 or more. In the present invention material, the contact resistance is as low as 10 to 20 m.Math.cm.sup.2 or less even when the concentration of fluoride ions is 20 to 30 ppm, and the amount of increase in the contact resistance can be suppressed to 10 mcmm.sup.2 or less at most, in a preferred case to 4 mcm.sup.2 or less, and high resistance to fluorine is exhibited.

(44) Thus, in the present invention material, in deterioration test 1 in which immersion is performed for 4 days in a sulfuric acid aqueous solution at 80 C. adjusted to pH 3 and having a fluoride ion concentration of 20 ppm, the amount of increase in the contact resistance with carbon paper after the deterioration test is 10 mcm.sup.2 or less at a surface pressure of 10 kgf/cm.sup.2. It is preferably 4 m cm.sup.2 or less. For reference, in the present invention material, the value of the contact resistance after deterioration test 1 is 20 m.Math.cm.sup.2 or less, preferably 10 m.Math.cm.sup.2 or less. On the other hand, in the conventional material, the value of the contact resistance is approximately 100 m.Math.cm.sup.2 or more, and the amount of increase in the contact resistance is approximately 90 m.Math.cm.sup.2 or more, which values are very large.

(45) In deterioration test 2 in which an electric potential of 1.0 V (vs. SHE) is applied for 24 hours in a sulfuric acid aqueous solution at 80 C. and pH 3, the amount of increase in the contact resistance with carbon paper after the deterioration test is 10 mcm.sup.2 or less at a surface pressure of 10 kgf/cm.sup.2. It is preferably 4 mcm.sup.2 or less. For reference, in the present invention material, the value of the contact resistance after deterioration test 2 is as low as 20 m.Math.cm.sup.2 or less, preferably as low as 10 m.Math.cm.sup.2 or less, and high tolerance can be maintained even when an electric potential is applied. On the other hand, in the conventional material, the value of the contact resistance is as high as approximately 30 m.Math.cm.sup.2, and the amount of increase in the contact resistance is as high as approximately 20 m.Math.cm.sup.2.

(46) Each of deterioration tests 1 and 2 can measure the tolerance (the degree of stability) to fluorine and the applied voltage by means of the amount of increase in the contact resistance. As the test time whereby a significant difference can be identified sufficiently, 4 days and 24 hours are selected, respectively. In general, there is seen a tendency for the contact resistance to increase almost linearly with the test time, and when the value has become approximately 30 m.Math.cm.sup.2 or more, increase rapidly thereafter. The (vs. SHE) represents the value with respect to the standard hydrogen electrode (SHE).

(47) In view of the fact that the contact resistance varies depending on the carbon paper used, the contact resistance measured using TGP-H-120 produced by Toray Industries, Inc. was taken as the standard in the accelerated deterioration test of the present invention.

(48) The present inventors have thought up the idea that the contact resistance of the present invention material being stable at a lower level than existing contact resistances is caused by the titanium hydride formed on the outer layer of the intermediate material before performing heating treatment in an oxidizing atmosphere. With focus on the diffraction peaks from the titanium hydride at the surface of the intermediate material shown in FIG. 1, the present inventors made extensive studies on the correlation between the diffraction intensity of metal titanium (Ti) and the diffraction intensity from the titanium hydride (TiH).

(49) The results are shown in FIG. 2. The [I.sub.TiH/(I.sub.Ti+I.sub.T-H)]100 of the intermediate material on the horizontal axis was found from the result of identification of the diffraction peaks in the X-ray diffraction profile measured by oblique incidence in which the incident angle of X-ray was fixed to 0.3 with respect to the surface of the titanium material or the titanium alloy material.

(50) The horizontal axis represents an index of the composition ratio between metal titanium and the titanium hydride at the surface of the titanium intermediate material or the titanium alloy intermediate material (before the heating treatment in an oxidizing atmosphere), and quantitatively indicates that a larger value of the index corresponds to a phase configuration containing a larger amount of the titanium hydride. The vertical axis represents the contact resistance measured by performing a deterioration test after the intermediate material is subjected to heating treatment in the air, which is an oxidizing atmosphere, and the amount of increase in the contact resistance.

(51) The material that had been subjected to heating treatment was subjected to deterioration test 1 described above (immersion for 4 days in a sulfuric acid aqueous solution at 80 C. adjusted to pH 3 and having a fluoride ion concentration of 20 ppm) and deterioration test 2 described above (application of an electric potential of 1.0 V (vs. SHE) for 24 hours in a sulfuric acid solution at 80 C. and pH 3). As can be seen from FIG. 2, the contact resistance after each of deterioration tests 1 and 2 and the amount of increase in the contact resistance are very low when the [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 of the intermediate material is 55% or more; and it is found that, in the intermediate material, the correlation of Formula (1) exists between the X-ray diffraction intensity of metal titanium (Ti) and the X-ray diffraction intensity from the titanium hydride (TiH).

(52) Thus, in the intermediate material, [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 is set to 55% or more, preferably set to 60% or more, where the contact resistance after the deterioration test and the amount of increase in the contact resistance are stable at a low level as shown in FIG. 2. The upper limit thereof is 100% or less as a matter of course. Although embrittlement due to the titanium hydride is a concern, the contact resistance of the objective of the present invention material has been obtained also when bending-back processing was performed and then heating treatment was performed on an intermediate material with an [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 of 85% which had been subjected to hydride formation treatment with hydrochloric acid.

(53) Here, FIG. 3 shows X-ray diffraction profiles (XRDs) of the surface of a titanium material or a titanium alloy material for a fuel cell separator (the present invention material). FIGS. 3(a) and 3(b) show XRDs of the surface of the present invention material that has been subjected to heating treatment in the air, which is an oxidizing atmosphere, after hydrogenation treatment; and FIG. 3(c) shows an XRD of the surface of the present invention intermediate material in a state where hydrogenation treatment before heating treatment has been performed.

(54) When the present invention intermediate material is subjected to heating treatment in an oxidizing atmosphere, in the present invention material as shown in FIG. 3, the diffraction peaks of the titanium hydride present in the present invention intermediate material of (c) (the inverted triangle marks in the drawing) disappear, and in exchange diffraction peaks of TiO (the square marks in the drawing) appear.

(55) When the present invention intermediate material with an [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 of 55% or more is subjected to heating treatment in an oxidizing atmosphere to produce TiO, the composition ratio of TiO [I.sub.TiO/(I.sub.Ti+I.sub.TiO)]100 is 0.5% or more. When [I.sub.TiO/(I.sub.Ti+I.sub.TiO)]100 is 2% or more, a lower contact resistance is obtained, and consequently also the amount of the increase is suppressed to a lower level.

(56) On the other hand, in the case of an intermediate material with an [I.sub.TiH/(I.sub.Ti+I.sub.TiH)]100 of less than 55%, the [I.sub.TiO/(I.sub.Ti+I.sub.TiO)]100 after heating treatment is less than 0.5%; and as shown in FIG. 2, the contact resistance after the deterioration test is more than 20 m.Math.cm.sup.2, and also the amount of the increase in the contact resistance is more than 10 m.Math.cm.sup.2.

(57) In a similar manner to the X-ray diffraction of the titanium hydride described above, the X-ray diffraction profile was measured by oblique incidence in which the incident angle of X-ray was fixed to 0.3 with respect to the surface of the titanium or the titanium alloy material, and the diffraction peaks were identified. The measured X-ray diffraction profile may be compared to a database in which TiO of ICDD Card No. 01-072-4593 or 01-086-2352 is used as the reference material; thereby, the diffraction peaks can be identified.

(58) The depth of X-ray entry in the measurement conditions mentioned above is approximately 0.2 m for metal titanium and approximately 0.2 to 0.3 m for the titanium oxide, and therefore the X-ray diffraction peaks are X-ray diffraction peaks that reflect the structure extending approximately 0.2 to 0.3 m in depth from the surface.

(59) FIG. 4 is a diagram showing the results of X-ray photoelectron spectroscopy (XPS) (photoelectron spectra of Ti 2p) of the surfaces of two titanium materials or titanium alloy materials for a fuel cell separator of the present invention. FIG. 4(a) shows the result of XPS of the surface of one titanium material or titanium alloy material for a fuel cell separator; and FIG. 4(b) shows the result of XPS of the surface of the other titanium material or titanium alloy material for a fuel cell separator. FIG. 5 shows a transmission electron microscope image of a cross section immediately below the surface of the present invention material.

(60) Although as shown in FIG. 3 no diffraction peak from TiO.sub.2 (anatase or rutile) is seen in the X-ray diffraction profile of the present invention material, as shown in FIG. 4 a very strong peak is detected from the outermost surface at the position of the binding energy of TiO.sub.2, which is a titanium oxide, i.e. approximately 459.2 eV; thus, it is found that a titanium oxide film mainly made of TiO.sub.2 is formed on the outermost surface.

(61) As shown in FIG. 5, a portion 2 in a bright (whitish) film form in the upper portion of Ti 1 is a titanium oxide film. Ti and O are detected from the portion 2 by energy dispersive spectrometry (EDS), and hence a titanium oxide film is formed in the portion 2.

(62) Thus, when the intermediate material in which a titanium hydride satisfying Formula (1) above is formed on the outer layer is subjected to heating treatment in an oxidizing atmosphere, in the present invention material, a surface structure in which TiO satisfying Formula (2) above is distributed on the surface and the outermost surface is formed of a titanium oxide film is created, and large electrical conductivity and high resistance to fluorine are obtained. On the other hand, in the case where the atmosphere of the heating treatment is a vacuum atmosphere, an inert gas atmosphere, or a reducing atmosphere, which is not an oxidizing atmosphere, even when a platinum group element, Au, or Ag is added, a surface structure in which TiO is distributed and the outermost surface is formed of a titanium oxide film as in the present invention is not obtained, and the effect thereof is not exhibited either.

(63) It is presumed that, in the present invention material, a structure in which TiO with a higher electrical conductivity than TiO.sub.2 coexists in the titanium oxide film of the outermost surface is formed, and thereby a significant effect is exhibited.

(64) The titanium hydride formed on the outer layer of the intermediate material whereby the present invention material is obtained plays an important role. The action of the titanium hydride is presumed to be due to the mechanism described below.

(65) Although the titanium hydride present on the outer layer of the intermediate material is oxidized by the surrounding oxygen in the atmosphere during the heating treatment in an oxidizing atmosphere, it is presumed that the titanium hydride has the action of suppressing the progress of oxidation by means of the hydrogen that it possesses and stably forming the state of TiO before reaching TiO.sub.2, which has small electrical conductivity.

(66) Since no X-ray diffraction peak of the titanium hydride is detected after heating treatment, it is presumed that the hydrogen of the titanium hydride is finally diffused into the titanium base material or has reacted with oxygen to escape and diffuse to the outside, and consequently the hydrogen concentration of the outer layer portion is significantly reduced.

(67) In order to obtain a significant effect of the present invention material by such a mechanism, it is necessary that, as shown in FIG. 2, a prescribed amount or more of the titanium hydride be present on the outer layer of the intermediate material (before the heating treatment in an oxidizing atmosphere).

(68) In the present invention material obtained by subjecting the present invention intermediate material to heating treatment in an oxidizing atmosphere, a titanium oxide film is formed on the outermost surface as shown in FIG. 4 and FIG. 5. The thickness of the titanium oxide film is preferably 3 to 15 nm from the viewpoints of suppressing the initial contact resistance to a low level and ensuring durability to fluorine and applied voltage in the environment to which the present invention material is exposed.

(69) If the thickness of the titanium oxide film is less than 3 nm, the contact resistance after the accelerated deterioration test in which fluorine is added or a voltage is applied will be more than 20 m.Math.cm.sup.2 and the amount of increase in the contact resistance will be more than 10 m.Math.cm.sup.2, and the durability will be insufficient. On the other hand, if the thickness of the titanium oxide film is more than 15 nm, the initial contact resistance is more than 10 m.Math.cm.sup.2.

(70) The thickness of the titanium oxide film of the outermost surface can be measured by observing a cross section immediately below the surface with a transmission electron microscope. As shown in FIG. 5, the portion 2 in a bright (whitish) film form is the titanium oxide film. On the other hand, in the case where a prescribed heating treatment is not performed, although the initial contact resistance is low, the contact resistance is increased to approximately 100 m.Math.cm.sup.2 after the deterioration test.

(71) In the conventional material, a carbide, a nitride, and/or a carbonitride of titanium present in a large amount in or immediately below the titanium oxide film is dissolved out in a corrosion environment in which fluorine is contained or in a usage environment in which an electric potential is applied, and is re-precipitated as an oxide that inhibits the contact electrical conductivity.

(72) On the other hand, in the present invention material, it is preferable that cold rolling oil components containing C etc. which cause carbide formation be removed by pickling as pre-treatment after the cold rolling, or a carbide, a nitride, and/or a carbonitride of titanium produced on the surface by bright annealing be almost removed by performing pickling with nitrohydrofluoric acid or hydride formation treatment after the bright annealing.

(73) As described above, the effect of the present invention has been exhibited when C is at 10 atomic % or less, N at 1 atomic % or less, and B at 1 atomic % or less as a result of an analysis of the surface using X-ray photoelectron spectroscopy (XPS) after the surface is subjected to sputtering of about 5 nm with argon.

(74) Thus, a surface structure, in which a carbide, a nitride, and/or a carbonitride of titanium is hardly present, is formed on the surface of the present invention material; thereby, the durability in a corrosion environment in which fluorine is contained or in a usage environment in which an electric potential is applied is significantly improved.

(75) Thus, in the present invention material, the amount of increase in the contact resistance after the deterioration test is 10 m.Math.cm.sup.2 or less. It is preferably 4 m.Math.cm.sup.2 or less. For reference, the contact resistance after the deterioration test is 20 m.Math.cm.sup.2 or less, preferably 10 m.Math.cm.sup.2 or less, and more preferably 8 m.Math.cm.sup.2 or less.

(76) Next, the method for producing the present invention material is described.

(77) In producing a piece of foil serving as a titanium base material, in order to make it less likely for a carbide, a nitride, and a carbonitride of titanium to be produced on the surface, the component design described above is implemented, and the conditions of cold rolling, cleaning (including pickling), and annealing (atmosphere, temperature, time, etc.) are selected and these processes are performed. As necessary, subsequently to annealing, pickling cleaning is performed with a nitrohydrofluoric acid aqueous solution (e.g. 3.5 mass % hydrogen fluoride+4.5 mass % nitric acid).

(78) After that, the titanium base material is subjected to any one of the treatments of (x) immersion in hydrochloric acid or sulfuric acid, which is a non-oxidizing acid, (y) cathodic electrolysis, and (z) heat treatment in a hydrogen-containing atmosphere; thus, a titanium hydride (TiH, TiH.sub.1.5, or TiH.sub.2) is formed on the outer layer of the titanium or the titanium alloy material.

(79) If a large amount of the hydride is formed up to the interior of the titanium base material, the entire base material may be embrittled; thus, the method of (x) immersion in hydrochloric acid or sulfuric acid, which is a non-oxidizing acid, and the method of (y) cathodic electrolysis, in which methods hydrogen can be concentrated only relatively near the surface, are preferable.

(80) Subsequently, the outer layer on which the titanium hydride is formed is subjected to heating treatment at 260 C. or more in an oxidizing atmosphere to form TiO as described above; thus, the surface structure of the present invention material is obtained. The air is most convenient as the oxidizing atmosphere. If the heating temperature is 350 C. or more, oxidation progresses rapidly, and the control for obtaining the present invention material is difficult; hence, the heating temperature is preferably less than 350 C. On the other hand, if the atmosphere of the heating treatment is a vacuum atmosphere, an inert gas atmosphere, or a reducing atmosphere, which is not an oxidizing atmosphere, a surface structure, in which TiO is distributed and the outermost surface is formed of a titanium oxide film, as in the present invention is not obtained, and the effect thereof is not exhibited either.

(81) The heating treatment time needs to be designed so that the thickness of the titanium oxide film is controlled at the temperature of the heating treatment of not less than 260 C. and less than 350 C. While the suitable treatment time varies with the temperature and the atmosphere dew point of the heating treatment, the treatment time is preferably 1 to 15 minutes, more preferably 2 to 8 minutes, from the viewpoints of the degree of stability in the production and productivity.

(82) The present invention material has excellent electrical conductivity and excellent durability as described above, and is very useful as a base material for a separator for a fuel cell.

(83) The fuel cell separator using the present invention material as the base material effectively uses the surface of the present invention material as it is, as a matter of course. On the other hand, also a case where a noble metal-based metal such as gold, carbon, or a carbon-containing electrically conductive film is further formed on the surface of the present invention material may be possible, as a matter of course. However, in this case, in a fuel cell separator using the present invention material as the base material, even when there is a defect in the noble metal-based metal such as gold, the carbon film, or the carbon-containing film, the corrosion of the titanium base material is more suppressed than in conventional ones because the surface having excellent contact electrical conductivity and excellent corrosion resistance of the present invention material is present immediately below the film.

(84) In the fuel cell separator using the present invention material as the base material, the surface has contact electrical conductivity and durability at the same level as those of the conventional carbon separator, and furthermore is less likely to crack; thus, the quality and lifetime of the fuel cell can be ensured over a long period of time.

EXAMPLES

(85) Next, Examples of the present invention are described, but the conditions in Examples are only condition examples employed to assess the feasibility and effect of the present invention, and the present invention is not limited to these condition examples. The present invention may employ various conditions to the extent that they do not depart from the spirit of the present invention and they achieve the object of the present invention.

Example 1

(86) To confirm that the target properties are obtained by the present invention intermediate material and the present invention material, test materials were prepared while various conditions of the titanium material or the titanium alloy material (hereinafter referred to as a titanium base material), the pre-treatment, the hydride formation treatment, and the heating treatment were changed.

(87) A test piece of a prescribed size was taken from the test material, and the surface was investigated by X-ray diffraction and the contact resistance (contact electrical conductivity) after an accelerated deterioration test was measured.

(88) The X-ray diffraction was performed using the conditions described above, and examples of the measurement results are as shown in FIG. 1 (the intermediate material before heating treatment) and FIG. 3 (after heating treatment).

(89) The preparation conditions of the test material are shown below. The measurement results are shown in Tables 1 to 4 together with the various conditions.

(90) [Titanium Base Material]

(91) The titanium base material (material) is as follows.

(92) M01: a titanium (JIS H 4600 type 1 TP270C); an industrial pure titanium, type 1

(93) M02: a titanium (JIS H 4600 type 3 TP480C); an industrial pure titanium, type 2

(94) M03: a titanium alloy (JIS H 4600 type 61); Al (2.5 to 3.5 mass %)V (2 to 3 mass %)Ti

(95) M04: a titanium alloy (JIS H 4600 type 16); Ta (4 to 6 mass %)Ti

(96) M05: a titanium alloy (JIS H 4600 type 17); Pd (0.04 to 0.08 mass %)Ti

(97) M06: a titanium alloy (JIS H 4600 type 19); Pd (0.04 to 0.08 mass %)Co (0.2 to 0.8 mass %)Ti

(98) M07: a titanium alloy (JIS H 4600 type 21); Ru (0.04 to 0.06 mass %)Ni (0.4 to 0.6 mass %)Ti

(99) M08: a titanium alloy; Pd (0.02 mass %)Mm (0.002 mass %)Ti

(100) Here, Mm is mixed rare-earth elements before isolation and purification (misch metal), and the composition of the Mm used is 55 mass % Ce, 31 mass % La, 10 mass % Nd, and 4 mass % Pr.

(101) M09: a titanium alloy; Pd (0.03 mass %)Y (0.002 mass %)Ti

(102) M10: a titanium alloy (JIS H 4600 type 11); Pd (0.12 to 0.25 mass %)Ti

(103) Note: M08 and M09, which are a titanium alloy other than those in JIS standards, refer to a base material obtained by performing smelting on a laboratory scale and performing hot rolling and cold rolling.

(104) [Pre-Treatment]

(105) The pre-treatment of the titanium base material is as follows.

(106) P01: perform cold rolling up to a thickness of 0.1 mm, perform alkaline cleaning, then perform bright annealing at 800 C. for 20 seconds in an Ar atmosphere, and then clean the surface by pickling with nitrohydrofluoric acid

(107) P02: perform cold rolling up to a thickness of 0.1 mm, perform cleaning by pickling with nitrohydrofluoric acid to remove the rolling oil, and then perform bright annealing at 800 C. for 20 seconds in an Ar atmosphere

(108) P03: perform cold rolling up to a thickness of 0.1 mm, perform alkaline cleaning, and then perform bright annealing at 800 C. for 20 seconds in an Ar atmosphere

(109) In the surface cleaning with nitrohydrofluoric acid of P01 and P02, immersion was performed at 45 C. for 1 minute in an aqueous solution containing 3.5 mass % hydrogen fluoride (HF) and 4.5 mass % nitric acid (HNO.sub.3). The portion extending approximately 5 m in depth from the surface was dissolved.

(110) [Hydride Formation Treatment]

(111) (x) Pickling

(112) H01: a 30 mass % hydrochloric acid aqueous solution

(113) H02: a 30 mass % sulfuric acid aqueous solution

(114) (y) Cathodic electrolysis treatment

(115) H03: a sulfuric acid aqueous solution; pH 1; current density: 1 mA/cm.sup.2

(116) H04: an aqueous solution mainly based on sodium sulfate; pH 2; current density: 1 mA/cm.sup.2

(117) (z) Heat treatment in a hydrogen-containing atmosphere

(118) H05: an atmosphere (450 C.) of 20% hydrogen+80% Ar gas

(119) [Heating Treatment]

(120) K01: Heating treatment is performed in a heating furnace in the air atmosphere. The heating temperature was varied in the range of not less than 250 C. and less than 350 C., and the heating time was varied in the range of 1 to 8 minutes.

(121) K02: Heating treatment is performed in an Ar atmosphere.

(122) K03: Heating treatment is performed in a vacuum atmosphere (510.sup.4 Torr).

(123) [Deterioration Test]

(124) Deterioration test 1 is performed by immersion for 4 days in a sulfuric acid solution at 80 C. adjusted to pH 3 and having a fluoride ion concentration of 20 ppm.

(125) Deterioration test 2 is performed by application of an electric potential of 1.0 V (vs. SHE) for 24 hours in a sulfuric acid solution at 80 C. and pH 3.

(126) Evaluative determination: In the amount of increase in the contact resistance, A refers to 4 mcm.sup.2 or less, B to more than 4 mcm.sup.2 and not more than 10 mcm.sup.2, and C to more than 10 mcm.sup.2. The value of the contact resistance measured using the conditions described above was 10 mcm.sup.2 or less in the case of A, more than 10 and not more than 20 mcm.sup.2 in the case of B, and more than 20 mcm.sup.2 in the case of C.

(127) The results when the conditions of the titanium base material and the pre-treatment were changed are shown in Table 1.

(128) TABLE-US-00001 TABLE 1 Implementation No. 1-4 1-5 1-6 1-1 1-2 1-3 Present Present Present Comparative Comparative Comparative Invention Invention Invention Summary Example Example Example Example Example Example Material Base Material M01 M01 M01 M01 M01 M02 (Before Preparation Pre-treatment P01 P02 P03 P02 P02 P01 heating conditions Hydride formation H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 material ( C.) Treatment time (min) 15 25 15 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 0 0 0 64 76 62 of surface 100 (%) (-) (-) (-) Heating Heating treatment Heating treatment K01 K01 K01 treatment conditions Treatment temperature 300 300 300 ( C.) Treatment time (min) 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 0 0 0 5.0 5.8 5.0 surface 100 (%) (-) (-) (-) Thickness of titanium 5 6 5 7 7 7 oxide coating film (nm) Contact electrical Before accelerated 40 53 15 5 5 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 1000 1000 1000 7 7 8 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination C C C A A A Contact electrical Before accelerated 40 53 15 5 5 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 1000 1000 1000 7 7 8 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination C C C A A A Implementation No. 1-7 1-8 1-9 1-10 1-11 1-12 Present Present Present Present Present Present Invention Invention Invention Invention Invention Invention Summary Example Example Example Example Example Example Material Base Material M02 M02 M03 M04 M05 M06 (Before Preparation Pre-treatment P01 P02 P01 P01 P01 P01 heating conditions Hydride formation H01 H01 H01 H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 70 70 70 material ( C.) Treatment time (min) 25 25 25 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 80 72 71 71 74 73 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K01 K01 K01 treatment conditions Treatment temperature 300 300 300 300 300 300 ( C.) Treatment time (min) 5 5 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 6.1 5.3 5.3 5.2 5.7 5.5 surface 100 (%) Thickness of titanium 7 6 7 6 8 6 oxide coating film (nm) Contact electrical Before accelerated 6 6 6 6 6 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 8 8 8 8 7 8 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination A A A A A A Contact electrical Before accelerated 6 6 6 6 6 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 7 7 7 8 8 8 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination A A A A A A Implementation No. 1-13 1-14 1-15 1-16 Present Present Present Present 1-17 1-18 Invention Invention Invention Invention Comparative Comparative Summary Example Example Example Example Example Example Material Base Material M07 M08 M09 M10 M04 M05 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 P01 heating conditions Hydride formation H01 H01 H01 H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 70 70 70 material ( C.) Treatment time (min) 25 25 25 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 75 73 74 74 75 74 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K01 treatment conditions Treatment temperature 300 300 300 300 ( C.) Treatment time (min) 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 5.2 5.3 5.5 5.4 0 0 surface 100 (%) (-) (-) Thickness of titanium 7 7 8 8 6 6 oxide coating film (nm) Contact electrical Before accelerated 5 6 6 6 7 7 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 7 8 8 8 108 109 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination A A A A C C Contact electrical Before accelerated 5 6 6 6 7 7 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 7 7 7 7 31 30 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination A A A A C C Implementation No. 1-19 1-20 1-21 1-22 1-23 Comparative Comparative Comparative Comparative Comparative Summary Example Example Example Example Example Material Base Material M06 M07 M08 M9 M10 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 heating conditions Hydride formation H01 H01 H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 70 70 material ( C.) Treatment time (min) 25 25 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 73 75 73 74 74 of surface 100 (%) Heating Heating treatment Heating treatment treatment conditions Treatment temperature ( C.) Treatment time (min) Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 0 0 0 0 0 surface 100 (%) (-) (-) (-) (-) (-) Thickness of titanium 6 7 7 6 7 oxide coating film (nm) Contact electrical Before accelerated 6 7 6 7 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 106 110 104 102 101 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination C C C C C Contact electrical Before accelerated 6 7 6 7 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 31 33 31 30 27 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination C C C C C

(129) The results when the treatment method, the treatment time, and the treatment temperature were varied in the hydride formation treatment are shown in Table 2.

(130) TABLE-US-00002 TABLE 2 Implementation No. 2-1 2-2 2-3 2-4 2-5 2-6 Summary Compar- Compar- Compar- Compar- Present Present ative ative ative ative Invention Invention Example Example Example Example Example Example Material Base material M01 M01 M01 M01 M01 M01 (Before Preparation Pre-treatment P03 P01 P01 P01 P01 P01 heating conditions Hydride formation treatment H01 H01 H01 H01 H01 treatment) Treatment temperature ( C.) 70 70 70 70 70 Intermediate Treatment time (min) 0.5 5 10 15 20 material Titanium hydride [I.sub.TiH/(I.sub.Ti + I.sub.TH)] 100 (%) 0 0 25 51 55 63 of surface () () () () Heating Heating treatment Heating treatment K01 K01 K01 K01 K01 K01 treatment condtions Treatment temperature ( C.) 300 300 300 300 300 300 Treatment time (min) 5 5 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 100 (%) 0 0 0 3.9 4.5 4.8 surface () () () Thickness of titanium oxide coating 6 6 7 7 7 7 film (nm) Contact electrical Before accelerated deterioration test 73 205 65 6 6 6 conductivity (m .Math. cm.sup.2) Accelerated After accelerated deterioration test 1000 504 112 42 9 7 deterioration (m .Math. cm.sup.2) test conditions 1 Determination C C C C A A Contact electrical Before accelerated deterioration test 73 205 65 6 6 6 conductivity (m .Math. cm.sup.2) Accelerated After accelerated deterioration test 1000 780 136 22 8 7 deterioration (m .Math. cm.sup.2) test conditions 2 Determination C C C C A A Implementation No. 2-7 2-8 2-9 2-10 2-11 2-12 Summary Present Present Present Present Present Present Invention Invention Invention Invention Invention Invention Example Example Example Example Example Example Material Base material M01 M01 M01 M01 M01 M01 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 P01 heating conditions Hydride formation treatment H01 H01 H01 H02 H02 H03 treatment) Treatment temperature ( C.) 70 70 50 50 70 50 Intermediate Treatment time (min) 25 30 30 30 15 360 material Titanium hydride [I.sub.TiH/(I.sub.Ti + I.sub.TH)] 100 (%) 79 85 56 65 61 75 of surface Heating Heating treatment Heating treatment K01 K01 K01 K01 K01 K01 treatment conditions Treatment temperature ( C.) 300 300 300 300 300 300 Treatment time (mm) 5 5 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 100 (%) 6.0 6.6 4.2 5.0 4.5 5.8 surface Thickness of titanium oxide coating 6 6 6 7 7 6 film (nm) Contact electrical Before accelerated deterioration test 5 6 7 6 6 6 conductivity (m .Math. cm.sup.2) Accelerated After accelerated deterioration test 6 7 9 7 8 7 deterioration (m .Math. cm.sup.2) test conditions 1 Determination A A A A A A Contact electrical Before accelerated deterioration test 5 6 7 6 6 6 conductivity (m .Math. cm.sup.2) Accelerated After accelerated deterioration test 6 7 9 8 7 7 deterioration (m .Math. cm.sup.2) test conditions 2 Determination A A A A A A Implementation No. 2-13 2-14 2-15 Summary Present Invention Present Invention Present Invention Example Example Example Material Base material M01 M01 M01 (Before Preparation Pre-treatment P01 P01 P01 heating conditions Hydride formation treatment H04 H04 H05 treatment) Treatment temperature ( C.) 50 50 400 Intermediate Treatment time (mm) 10 30 60 material Titanium hydride [I.sub.TiH/(I.sub.Ti + I.sub.TH)] 100 (%) 66 76 62 of surface Heating Heating treatment Heating treatment K01 K01 K01 treatment conditons Treatment temperature ( C.) 300 300 300 Treatment time (min) 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 100 (%) 5.0 5.9 4.6 surface Thickness of titanium oxide coating 7 6 7 film (nm) Contact electrical Before accelerated deterioration test 6 6 6 conductivity (m .Math. cm.sup.2) Accelerated After accelerated deterioration test 8 7 8 deterioration (m .Math. cm.sup.2) test conditions 1 Determination A A A Contact electrical Before accelerated deterioration test 6 6 6 conductivity (m .Math. cm.sup.2) Acclerated After accelerated deterioration test 8 7 8 deterioration (m .Math. cm.sup.2) test conditions 2 Determination A A A

(131) The results when the atmosphere, the treatment time, and the treatment temperature were varied in the heating treatment are shown in Table 3.

(132) TABLE-US-00003 TABLE 3 Implementation No. 3-3 3-4 3-5 3-6 3-1 3-2 Present Present Present Present Comparative Comparative Invention Invention Invention Invention Summary Example Example Example Example Example Example Material Base Material M01 M01 M01 M01 M01 M01 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 P01 heating conditions Hydride formation H01 H01 H01 H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 70 70 70 material ( C.) Treatment time (min) 25 15 15 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 77 55 55 78 79 76 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K01 K01 treatment conditions Treatment temperature 250 260 275 300 300 ( C.) Treatment time (min) 5 5 5 1 2.5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 0 0.2 0.6 1.3 2.1 3.8 surface 100 (%) (-) (-) Thickness of titanium 5 5 7 7 7 6 oxide coating film (nm) Contact electrical Before accelerated 8 7 8 8 7 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 121 90 14 10 8 7 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination C C B A A A Contact electrical Before accelerated 8 7 8 8 7 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 33 30 13 9 8 8 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination C C B A A A Implementation No. 3-7 3-8 3-9 Present Present Present 3-10 3-11 3-12 Invention Invention Invention Comparative Comparative Comparative Summary Example Example Example Example Example Example Material Base Material M01 M01 M01 M01 M01 M01 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 P01 heating conditions Hydride formation H01 H01 H01 H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 70 70 70 material ( C.) Treatment time (min) 25 25 25 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 79 78 78 80 79 77 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K02 K03 K03 treatment conditions Treatment temperature 300 300 340 300 300 500 ( C.) Treatment time (min) 5 7.5 8 5 5 10 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 6.0 5.9 3.7 0 0 0 surface 100 (%) (-) (-) (-) Thickness of titanium 6 7 12 6 5 6 oxide coating film (nm) Contact electrical Before accelerated 5 5 8 7 8 8 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 6 7 9 120 122 120 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination A A A C C C Contact electrical Before accelerated 5 5 8 7 8 8 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 6 7 10 32 33 33 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination A A A C C C Implementation No. 3-13 3-14 3-15 3-16 3-17 Comparative Comparative Comparative Comparative Comparative Summary Example Example Example Example Example Material Base Material M05 M06 M07 M08 M09 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 heating conditions Hydride formation H01 H01 H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 70 70 material ( C.) Treatment time (min) 25 25 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 74 73 75 73 74 of surface 100 (%) Heating Heating treatment Heating treatment K02 K02 K02 K02 K02 treatment conditions Treatment temperature 500 500 500 500 300 ( C.) Treatment time (min) 10 10 10 10 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 0 0 0 0 0 surface 100 (%) (-) (-) (-) (-) (-) Thickness of titanium 8 9 7 8 9 oxide coating film (nm) Contact electrical Before accelerated 8 8 7 8 8 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 105 103 104 101 103 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination C C C C C Contact electrical Before accelerated 8 8 7 8 8 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 31 30 32 33 31 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination C C C C C Implementation No. 3-18 3-19 3-20 Comparative Comparative Comparative Summary Example Example Example Material Base Material M09 M10 M10 (Before Preparation Pre-treatment P01 P01 P01 heating conditions Hydride formation H01 H01 H01 treatment) treatment Intermediate Treatment temperature 70 70 70 material ( C.) Treatment time (min) 25 25 25 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 74 74 74 of surface 100 (%) Heating Heating treatment Heating treatment K02 K02 K02 treatment conditions Treatment temperature 500 300 500 ( C.) Treatment time (min) 10 10 10 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 0 0 0 surface 100 (%) (-) (-) (-) Thickness of titanium 8 9 8 oxide coating film (nm) Contact electrical Before accelerated 8 8 9 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 109 101 102 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination C C C Contact electrical Before accelerated 8 8 9 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 31 30 31 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination C C C

(133) The results when various conditions were changed are shown in Table 4.

(134) TABLE-US-00004 TABLE 4 Implementation No. 4-1 4-2 4-3 4-4 4-5 Present Present Present Present Present Invention Invention Invention Invention Invention Summary Example Example Example Example Example Material Base Material M01 M01 M01 M02 M03 (Before Preparation Pre-treatment P02 P02 P02 P02 P01 heating conditions Hydride formation H01 H01 H04 H04 H04 treatment) treatment Intermediate Treatment temperature 70 70 50 50 50 material ( C.) Treatment time (min) 25 25 10 10 10 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 79 78 68 67 69 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K01 K01 treatment conditions Treatment temperature 300 350 350 350 350 ( C.) Treatment time (min) 2.5 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 3.5 6.4 5.1 5.2 5.4 surface 100 (%) Thickness of titanium 7 7 7 6 7 oxide coating film (nm) Contact electrical Before accelerated 6 5 6 7 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 7 6 7 7 7 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination A A A A A Contact electrical Before accelerated 6 5 6 7 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 7 6 7 8 8 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination A A A A A Implementation No. 4-6 4-7 4-8 4-9 4-10 Present Present Present Present Present Invention Invention Invention Invention Invention Summary Example Example Example Example Example Material Base Material M04 M04 M05 M06 M07 (Before Preparation Pre-treatment P01 P01 P01 P01 P01 heating conditions Hydride formation H04 H05 H04 H04 H04 treatment) treatment Intermediate Treatment temperature 50 400 50 50 50 material ( C.) Treatment time (min) 10 60 10 10 10 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 65 65 67 69 65 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K01 K01 treatment conditions Treatment temperature 350 350 300 300 300 ( C.) Treatment time (min) 5 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 4.7 4.5 5.2 5.4 5.1 surface 100 (%) Thickness of titanium 7 7 7 6 7 oxide coating film (nm) Contact electrical Before accelerated 6 6 6 6 7 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 8 8 7 7 7 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination A A A A A Contact electrical Before accelerated 6 6 6 6 7 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 7 7 7 7 8 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination A A A A A Implementation No. 4-11 4-12 2-13 2-14 Present Present Present Present Invention Invention Invention Invention Summary Example Example Example Example Material Base Material M08 M09 M01 M01 (Before Preparation Pre-treatment P01 P01 P01 P01 heating conditions Hydride formation H04 H04 H04 H04 treatment) treatment Intermediate Treatment temperature 50 50 50 50 material ( C.) Treatment time (min) 10 10 10 30 Titanium hydride [I.sub.TiH/I.sub.Ti + I.sub.TH)] 66 68 66 76 of surface 100 (%) Heating Heating treatment Heating treatment K01 K01 K01 K01 treatment conditions Treatment temperature 300 300 300 300 ( C.) Treatment time (min) 5 5 5 5 Properties of [I.sub.TiO/(I.sub.Ti + I.sub.TiO)] 5.8 5.6 5.0 5.9 surface 100 (%) Thickness of titanium 7 7 7 6 oxide coating film (nm) Contact electrical Before accelerated 7 7 6 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 8 8 8 7 deterioration test deterioration test conditions 1 (m .Math. cm.sup.2) Determination A A A A Contact electrical Before accelerated 7 7 6 6 conductivity deterioration test (m .Math. cm.sup.2) Accelerated After accelerated 8 8 8 7 deterioration test deterioration test conditions 2 (m .Math. cm.sup.2) Determination A A A A

(135) From Tables 1 to 4, it is found that the contact electrical conductivity of the present invention examples using the present invention intermediate material, in which the composition ratio of the titanium hydride (I.sub.TiH/(I.sub.Ti+I.sub.T-H)) at the surface is 55% or more, is much better than the contact electrical conductivity of the comparative examples (conventional materials). The effect of the present invention has been exhibited regardless of whether a platinum group-based element is contained or not. On the other hand, in the comparative example of the case where the heating treatment in an oxidizing atmosphere is not performed or the case where the atmosphere of the heating treatment is a vacuum atmosphere or an inert gas atmosphere, which is not an oxidizing atmosphere, a surface structure in which TiO is distributed as in the present invention example is not obtained, and the effect thereof is not exhibited either.

INDUSTRIAL APPLICABILITY

(136) As described above, according to the present invention, it becomes possible to provide a titanium material or a titanium alloy material for a fuel cell separator having excellent contact-to-carbon electrical conductivity and excellent durability and a fuel cell separator having excellent contact-to-carbon electrical conductivity and excellent durability. When the fuel cell separator is used, the lifetime of the fuel cell can be greatly prolonged. Thus, the present invention has high applicability in battery manufacturing industries.

REFERENCE SIGNS LIST

(137) 1 Ti (titanium material or titanium alloy material) 2 portion in a bright (whitish) film form (titanium oxide film)