JP2008159420A - Composite titanium material that can maintain low contact resistance over a long period of time - Google Patents

Abstract

A composite titanium material capable of maintaining a low contact resistance over a long period of time is provided.

SOLUTION: Au continuously adheres to a titanium substrate surface 4 in a network form by diffusion bonding, and a Ti oxide layer 3 is formed in a gap between the Au mesh 5 and the Au mesh 5 of the mesh Au adhered to the titanium substrate surface. The width of the Au network 5 of the mesh-like Au is at least in a range of 0.300 to 10,000 nm, and is formed in a gap between the Au network 5 of the mesh-like Au and the adjacent Au mesh 5. The oxidized Ti layer 3 is in a thickness range of 30 to 150 nm.
[Selection] Figure 1

Description

  The present invention is a composite titanium material in which Au is continuously spread in a network shape on the surface of a titanium substrate, and this network Au is diffusion-bonded to the titanium substrate and the contact resistance can be kept low over a long period of time. This composite titanium material is particularly used as a separator material for a polymer electrolyte fuel cell.

  In general, a polymer electrolyte fuel cell includes an air electrode made of a conductive porous body with a catalyst on one side of an electrolyte, and a fuel electrode made of a conductive porous body with the same catalyst on the other side of the electrolyte. The polymer electrolyte fuel cell having such a structure has a structure in which a plurality of layers are stacked via separators. The air electrode and the first separator are in contact with each other, the fuel electrode and the second separator are in contact with each other, and the contact resistance must be low. In general, a carbon plate or a metal plate is used as a separator, and a carbon fiber nonwoven fabric or a porous metal called carbon paper is used as a conductive porous body constituting an air electrode material and a fuel electrode material. In recent years, titanium plates have come to be used as separators using metal plates. However, since the titanium plate is usually coated with an oxide film with high electrical resistance on the surface, the contact resistance is large, and in order to improve this, a composite titanium plate coated with Au on the titanium plate surface by plating or the like is used as a solid polymer. It is about to be used as a separator for fuel cell. This composite titanium plate coated with Au is heat-treated to reduce contact resistance (see Patent Document 1).

Further, as a method of forming an Au film on the surface of the titanium plate, a method of attaching Au after removing the Ti oxide film formed on the surface of the titanium plate is known (see Patent Document 2).

However, the conventional composite titanium plate on which the Au plating layer is formed is obtained by uniformly coating the entire surface of the titanium plate with an Au plating layer, and since a large amount of expensive Au is used, this conventional Au plated composite A separator using a titanium plate is expensive. In order to solve this problem, in recent years, the surface of a titanium substrate is plated with island-shaped Au grains having a diameter of 1 to 100 nm and a thickness of 1 to 30 nm. At the same time, a composite titanium material has been proposed in which the amount of Au used is reduced to reduce the cost (see Patent Document 3).
JP 2004-134276 A JP 2001-6713 A JP 2006-97088 A

  However, in the case of a composite titanium material plated with island-like Au particles having a diameter of 1 to 100 nm and a thickness of 1 to 30 nm on the surface of the conventional titanium substrate, the initial contact resistance is certainly lowered. However, the plated island-shaped Au grains do not have sufficient bonding strength with the titanium substrate, and therefore may peel off when subjected to severe impacts or vibrations, and the conventional island-shaped Au grains are scattered and plated. When the composite titanium material is used as a separator for a polymer electrolyte fuel cell for a long period of 500 hours or more, there is a problem that the contact resistance rapidly increases.

Therefore, the present inventors have studied to improve the defects of the composite titanium material in which island-like Au particles having a diameter of 1 to 100 nm and a thickness of 1 to 30 nm are scattered on the surface of a conventional titanium substrate. I did it. as a result,
(A) The bonding between Au and the titanium substrate can be made stronger by diffusion bonding of Au and the underlying metal titanium in the titanium substrate.
(B) The Au formed on the surface of the titanium substrate is a continuous network rather than the islands that are independent of each other. As a whole, the network Au formed on the surface of the titanium substrate is in a conductive state between Au and the underlying metal titanium, and the contact resistance does not increase.
(C) If the Au network width of the network Au is too narrow, the contact resistance increases when immersed in a sulfuric acid aqueous solution for a long period of time. Therefore, the Au network width is 300 to 10,000 nm at least in one place. Must be within range,
(D) A network-like Au having a width of 300 to 10,000 nm is fixed by diffusion bonding at least at one place, and is formed in a gap between an Au network constituting the fixed network-like Au and an adjacent Au network. The thickness of the oxidized Ti layer is preferably an oxidized Ti layer that is thicker than usual in the range of 30 to 150 nm, in order to maintain a low contact resistance over a long period of time,
(E) Au is continuously adhered to the surface of the titanium base by a diffusion bonding, and a Ti oxide layer is formed in a gap between the Au net constituting the fixed network Au and the adjacent Au net. When the formed composite titanium material is applied as a separator material for a polymer electrolyte fuel cell, the contact resistance can be kept low over a long period of time.
I got the knowledge such as.

This invention was made based on these findings,
(1) Au continuously adheres to the surface of the titanium substrate in a network form by diffusion bonding, and a Ti oxide layer is formed in the gap between the Au network constituting the fixed network Au and the adjacent Au network. A composite titanium material that can maintain low contact resistance over a long period of time.
(2) The composite titanium material capable of maintaining a low contact resistance over a long period of time as described above in (1), wherein the width of the Au network of the network Au is at least one place is in the range of 300 to 10000 nm;
(3) The long-term oxide film according to (1) or (2), wherein the Ti oxide layer formed in the gap between the Au network of the network Au and the adjacent Au network has a thickness in the range of 30 to 150 nm. Composite titanium material that can maintain low contact resistance over
(4) A fuel cell separator made of a composite titanium material that can maintain a low contact resistance over a long period of time, made of the composite titanium material described in (1), (2), or (3). It is.

Next, a composite titanium material capable of maintaining a low contact resistance over a long period of time and a manufacturing method thereof will be described with reference to the drawings.
FIG. 1 is a copy of an electron microscopic structure of a reticulated Au formed on the surface of a composite titanium material that can maintain a low contact resistance over a long period of time.
FIG. 2 is an electron micrograph of a network of Au formed on the surface of a composite titanium material that can be maintained for a long period of time according to the present invention produced in Example 1 shown below.
FIG. 3 is a cross-sectional explanatory view of a composite titanium material capable of maintaining a low contact resistance over a long period of the present invention.
FIGS. 4-6 is sectional explanatory drawing for demonstrating the manufacturing method of the composite titanium material which can maintain contact resistance low over the long term of this invention shown by FIG.

FIG. 7 is a cross-sectional explanatory diagram for explaining that the contact resistance increases when immersed in a sulfuric acid aqueous solution for a long time when the width of the Au mesh of the network Au formed on the surface of the composite titanium material is small. .
FIG. 8 shows that the width of the Au network in the network Au formed on the surface of the composite titanium material that can maintain the contact resistance low over a long period of the present invention is within a range of 300 to 10,000 nm at least at one place. FIG. 4 is a cross-sectional explanatory diagram for explaining that it is preferable that a Ti oxide layer 3 having a thickness in a range of 30 to 150 nm is formed between the Au net and the adjacent Au net.

The composite titanium material capable of maintaining a low contact resistance over a long period of time according to the present invention has a mesh-like Au formed on the surface of the titanium substrate as shown in the drawing of FIG. 1 and the electron micrograph of FIG. It is one of the features. Since this Au is continuously formed in a mesh shape on the surface of the titanium substrate, even if a part of Au is separated from the metal titanium which is the base of the titanium substrate, the Au is connected in a mesh shape. If other portions are bonded to titanium metal which is the base of the titanium substrate, the contact resistance as a whole does not increase. For example, as shown in FIG. 1, a network Au is formed on the surface of a titanium substrate, and the Au network 5 of the network Au is continuous with the adjacent Au network 5. There is a narrow portion a, and even if the narrow portion a is immersed in a sulfuric acid aqueous solution for a long time and separated from the metal titanium 2, it is continuous with the wide portion b of the Au net 5 that is difficult to peel off. Even when immersed in a sulfuric acid aqueous solution for a long time, the contact resistance does not increase. The width b of the Au net 5 that is difficult to peel off may be at least one in the network Au, and the width is preferably in the range of 300 to 10,000 nm. The reason why this width is limited to 300 to 10000 nm will be described later.

Next, the manufacturing method of the composite titanium material which can maintain a contact resistance low over the long term of this invention is demonstrated based on FIGS. 4 to 6 are, for example, AA cross-sectional views in FIG. 1, and 5 indicates a cross section of the Au net formed on the surface of the titanium substrate.
First, a titanium substrate made of a normal pure titanium plate is prepared. As shown in FIG. 4, the titanium substrate 1 made of this normal titanium plate has a spontaneously generated Ti oxide film 4 having a thickness of several nanometers formed on the surface of the metal titanium 2. When a colloidal Au solution in which ultrafine Au particles are suspended is applied on the naturally-occurring oxidized Ti layer 4 formed on the surface of the titanium substrate and then dried in as short a time as possible, the spontaneously-oxidized Agglomerates of ultrafine Au powder adhere to the Ti layer 4 in a network form. At this time, the Au colloid liquid in which ultrafine Au particles are suspended adheres as an aggregate when dried after coating. The Au colloid liquid applied on the spontaneously generated oxidized Ti layer 4 formed on the titanium substrate is applied so as to be 20 to 80% of the surface area. If the coating amount is less than 20%, the Au colloid liquid is applied in a granular form without being applied in a mesh form. On the other hand, if it exceeds 80%, the adhesiveness of Au is weakened and it is easy to peel off. It is.

When the Au colloid solution is applied and dried in as short a time as possible, and then heated and held at a temperature of 300 ° C. or higher in a vacuum atmosphere, first, spontaneous oxidation is performed as shown in FIG. Oxygen in the Ti layer 4 is diffused and dissolved in the metal titanium 2 so that the surface of the titanium substrate becomes metal titanium. When further heated under the same conditions, the Au net 5 is diffused and bonded to the surface by forming the metal titanium 2 and the diffusion bonding portion 6 as shown in FIG.
When this Au net 5 is firmly fixed to the surface of the metal titanium 2 by diffusion bonding and further left in the air, the Au net 5 is further heated in an oxidizing atmosphere such as the air, so that a titanium substrate is obtained as shown in FIG. The Au net 5 forms a diffusion junction 6 on the surface of the metal titanium 2 in FIG. 1 and adheres to the surface of the metal titanium 2 where the Au net 5 does not exist. : The oxidized Ti layer 3 having a thickness of 30 to 150 nm is formed, and the thick oxidized Ti layer 3 is formed so as to wrap around the Au net 5, so that the Au net 5 is stronger than the metal titanium on the titanium substrate. A composite titanium material that can maintain a low contact resistance over a long period of time of the present invention can be produced. In FIG. 3, 5 shows a cross section of the Au net formed on the surface of the composite titanium material that can keep the contact resistance low over a long period of time.
The Ti oxide layer 3 can be formed even if it is left in an oxidizing atmosphere such as the air, but its thickness is several nm or less, and the composite titanium material on which such a thin oxidized Ti layer is formed is a solid polymer. When used as a separator for a fuel cell, the contact resistance increases in a short period of time. Therefore, in the composite titanium material of the present invention, the thickness of the oxidized Ti layer 3 is increased by heating in an oxidizing atmosphere such as the air, and the thickness of the oxidized Ti layer is set to 30 to 150 nm. The reason why the thickness of the oxidized Ti layer is 30 to 150 nm will be described later.

FIG. 7 shows the reason why the contact resistance increases in a short period of time when the composite titanium material having a network-like Au made of a narrow Au net 5 having a width of less than 300 nm on the surface is immersed in a sulfuric acid aqueous solution or the like. Description will be made based on ˜8. In FIG. 7, 5 represents one narrow Au net formed on the surface of the composite titanium material, while 5 in FIG. 8 represents a wide width formed on the surface of the composite titanium material. One Au net is shown.
When the composite titanium material in which the network Au made of the narrow Au net 5 is formed is immersed in the same sulfuric acid solution as the environment of the polymer electrolyte fuel cell, as shown in FIG. Layer 3 grows and thickness T becomes increasingly thicker. When the thickness T of the oxidized Ti layer 3 grows and becomes thicker, the oxidized Ti layer 3 grows from the periphery of the narrow Au net 5 into the narrow Au net 5 and is shown in FIG. 7B. As shown, the narrow Au net 5 is pushed up to the surface of the oxidized Ti layer 3. When this phenomenon further proceeds, as shown in FIG. 7C, the narrow Au net 5 is pushed up and separated from the underlying metal titanium 2, and the narrow Au net 5 and the underlying metal titanium 2 are separated. The Ti oxide layer 3 is interposed therebetween, and finally the diffusion junction 6 is absorbed and disappears, and the contact resistance increases.

However, as shown in FIG. 8, if the width S of the Au net 5 is large, the thickness T of the oxidized Ti layer 3 grows, and even if the Au net 5 grows by being buried under the Au net 5 from the periphery of the Au net 5. As shown in FIG. 7 (c), it takes a very long time for the Au net 5 to be separated from the metal titanium 2, and the Au net 5 is separated from the metal titanium 2 of the titanium base within a normal use period. This will not increase the contact resistance. If the width S of the Au network 5 is less than 300 nm, the contact resistance increases in a relatively short period when held in a sulfuric acid aqueous solution. Therefore, the width S of the Au network 5 is preferably 300 nm or more. When the width S of the Au net 5 exceeds 10000 nm, the force for enclosing and fixing the Au net 5 with the oxidized Ti layer 3 is weakened and the adhesion is lowered. As a result, the contact resistance decreases, which is not preferable.
Therefore, it is preferable that at least one width of the Au net 5 in the net-like Au formed on the surface of the composite titanium material of the present invention is in the range of 300 to 10,000 nm.

On the other hand, when the thickness T of the oxidized Ti layer 3 is 30 nm or more, the growth of the oxidized Ti layer 3 in the sulfuric acid aqueous solution is abruptly slowed, and the contact resistance increases even if left in the sulfuric acid aqueous solution for a long time. The growth of the thickness of the oxidized Ti layer 3 is slow, and the contact resistance does not increase even when immersed in a sulfuric acid aqueous solution for a long time. Therefore, it is indispensable to perform a heat treatment that is heated in an air atmosphere as a means for suppressing an increase in contact resistance. In this heat treatment step, the thickness of the Ti oxide layer 3 is preferably set to 30 nm or more. However, if the thickness T of the oxidized Ti layer 3 exceeds 150 nm after long-time heat treatment in the atmosphere, the initial resistance value increases, which is not preferable. Therefore, the thickness T of the oxidized Ti layer 3 formed on the surface of the titanium substrate between the Au net 5 formed on the surface of the composite titanium material of the present invention and the adjacent Au net 5 is in the range of 30 to 150 nm. It is preferable to be within.
That is, the width S of the Au net 5 formed in the composite titanium material that can keep the contact resistance low over the long term of the present invention is in the range of 300 to 10000 nm, and the thickness T of the oxidized Ti layer 3. Is more preferably in the range of 30 to 150 nm.

As described above, in order to produce a composite titanium material capable of maintaining a low contact resistance over a long period of time, it is preferable that the titanium substrate is a pure titanium plate, but the present invention is not limited to this. However, any titanium substrate having a surface having an area capable of forming a reticulated Au may be used. For example, porous titanium composed of continuous pores and a skeleton that are open on the surface having an area where mesh-like Au can be formed and are continuous with the internal pores, and fiber sintered titanium obtained by sintering titanium fibers, titanium It may be a titanium substrate having any shape and structure such as sintered titanium obtained by sintering powder.

  The composite titanium material capable of maintaining a low contact resistance over a long period of time of the present invention has an Au plating film formed on the entire surface of the titanium substrate since the Au net is fixed to the surface of the titanium substrate by diffusion bonding. Compared to the case, the amount of Au used is small, so the cost can be reduced as a separator for a polymer electrolyte fuel cell, and the Au net fixed to the surface of the titanium base is covered with a thick Ti oxide layer. Even if it is immersed in a corrosive aqueous solution such as sulfuric acid aqueous solution, it does not deform or drop out even when external pressure is applied due to vibration etc. And can greatly contribute to the improvement of the performance of a polymer electrolyte fuel cell or the like.

A commercially available pure titanium plate having a thickness of 0.3 mm was prepared, and this pure titanium plate was cut to have a length of 30 mm and a width of 30 mm to prepare a titanium substrate.
Further, an Au colloid solution was prepared and prepared by the following method. Prepare chloroauric acid as the main component of Au particles, γ-aminopropyltriethoxysilane as a protective agent precursor, and dimethylamine borane as a reducing agent. First, the Au concentration is 4.0% by mass. And dissolved in methanol. Next, a methanol solution in which chloroauric acid was first dissolved was gradually added to γ-aminopropyltriethoxysilane: 8.00 g and acetylacetone: 12.00 g, and a mixed solution was prepared. An appropriate amount of certain dimethylamine borane was added. The reduction was carried out while keeping the temperature of the mixed solution at 60 ° C. and stirring the mixed solution with a magnetic stirrer. The mixed solution after the reduction reaction is cooled to room temperature, and after cooling, the mixed solution is desalted by an ultrafiltration method, and water is added as a dispersion medium by appropriately adding water to adjust the concentration. % Concentration of Au colloidal solution was obtained.

Example 1
The Au colloid solution was applied so as to cover the surface of the titanium substrate at a ratio shown in Tables 1 and 2 by repeating application of the obtained Au colloid solution to the previously prepared titanium substrate by spraying. Reticulated Au was adhered to the surface of the titanium substrate by drying. In a state where the reticulated Au is attached to the surface of the titanium substrate, heat treatment is performed for 1 hour at a temperature shown in Tables 1 and 2 in a vacuum atmosphere, and then shown in Tables 1 and 2 in the atmosphere. The composite titanium materials 1 to 20 of the present invention and the comparative composite titanium materials 1 to 4 in which the network Au was diffusion bonded and fixed to the surface of the titanium substrate were prepared by performing a heat treatment for 10 minutes at a temperature to be maintained.
As a result of observing the surfaces of the composite titanium materials 1 to 20 of the present invention and the comparative composite titanium materials 1 to 4 with an electron microscope, reticulated Au was formed on these surfaces. An electron micrograph of the composite titanium material 5 of the present invention is shown in FIG.
Furthermore, the maximum width of the Au network of the mesh-like Au formed on the surfaces of the present composite titanium materials 1 to 20 and the comparative composite titanium materials 1 to 4 is measured, and further formed in the gap between the Au net and the adjacent Au net. The average thickness of the oxidized Ti layer was measured, and the results are shown in Tables 1-2.

Conventional Example 1
A conventional composite titanium material 1 formed so that island-shaped Au particles having a diameter of 35 to 50 nm occupy 55 area% was prepared by performing Au plating on the surface of the previously prepared titanium base under normal conditions.

The following fuel cell environmental energization test and vibration test were performed using the composite titanium materials 1 to 20 of the present invention and the comparative composite titanium materials 1 to 4 manufactured in Example 1 and the conventional composite titanium material 1 manufactured in Conventional Example 1. .

Fuel cell environmental energization test:
The composite titanium materials 1 to 20 of the present invention, the comparative composite titanium materials 1 to 4 and the conventional composite titanium material 1 produced in the conventional example 1 are immersed in an aqueous sulfuric acid solution maintained at a temperature of 50 ° C. and a pH of 2, respectively. The sample was taken out after 100 hours, 500 hours and 1000 hours while applying 800 V (vs. hydrogen), then washed thoroughly with distilled water and then dried in the atmosphere. After drying, the composite titanium materials 1 to 20 of the present invention, the comparative composite titanium materials 1 to 4 and the conventional composite titanium material 1 are sandwiched between two copper plates having dimensions of 50 mm in length, 50 mm in width, and 10 mm in thickness, and a spring is sandwiched. In this state, the composite titanium materials 1 to 20 of the present invention, the comparative composite titanium materials 1 to 4 and the conventional composite titanium material 1 and the copper plate are fixed via a spring so that the surface pressure is 1 MPa. The resistance between copper plates was measured, and the value was shown in Tables 1-2 as the contact resistance value.

Vibration test The present porous titanium 1-20, comparative porous titanium 1-4, and conventional porous titanium 1 are sandwiched between two copper plates having dimensions of 50 mm in length, 50 mm in width, and 10 mm in thickness, respectively, and a spring is sandwiched between them. Then, the spring deflection was adjusted so that the contact pressure between the porous titanium 1 to 20 of the present invention, the comparative porous titanium 1 to 4 and the conventional porous titanium 1 and the copper plate was 1 MPa. The resistance between copper plates was measured in a state where such a load was applied, and the value was shown in Tables 1 and 2 as the contact resistance before the vibration test.
Further, the present invention porous titanium 1-20, comparative porous titanium 1-4, and conventional porous titanium 1 are sandwiched between two copper plates having dimensions of 50 mm in length, 50 mm in width, and 10 mm in thickness, respectively. After fixing, the spring deflection was adjusted and the load was applied so that the surface pressure between the porous titanium 1 to 20 of the present invention, the comparative porous titanium 1 to 4 and the conventional porous titanium 1 and the copper plate was 1 MPa. The sample was placed on the vibration tester in the state, and a vibration test was performed for 2 hours at a frequency of 67 Hz and a vibration acceleration of 70 m / sec ² . After the vibration test, the resistance between the copper plates was measured with a load applied on the spot, and the value was shown in Tables 1 and 2 as the contact resistance after the vibration test.

  From the results shown in Tables 1 and 2, since the composite titanium materials 1 to 20 of the present invention have much lower contact resistance after 1000 hours of fuel cell environment energization test than the conventional composite titanium material 1, It can be seen that the materials 1 to 20 can maintain a low contact resistance even when used for a long time as compared with the conventional composite titanium material 1. However, it can be seen that the comparative composite titanium materials 1 to 4 deviating from the scope of the present invention provide unfavorable values.

It is a copy of the electron microscopic structure of the mesh-like Au formed on the surface of the composite titanium material that can keep the contact resistance low for a long period of the present invention. It is an electron microscopic structure photograph of reticulated Au formed on the surface of the composite titanium material which can maintain contact resistance low over the long term of this invention produced in an example. It is sectional explanatory drawing of the composite titanium material which can maintain a contact resistance low over the long term of this invention. FIG. 4 is a cross-sectional explanatory diagram for explaining a method of manufacturing a composite titanium material capable of maintaining a low contact resistance over a long period of time shown in FIG. FIG. 4 is a cross-sectional explanatory diagram for explaining a method of manufacturing a composite titanium material capable of maintaining a low contact resistance over a long period of time shown in FIG. FIG. 4 is a cross-sectional explanatory diagram for explaining a method of manufacturing a composite titanium material capable of maintaining a low contact resistance over a long period of time shown in FIG. It is sectional explanatory drawing for demonstrating that a contact resistance will increase when it immerses in sulfuric acid aqueous solution for a long time if the width | variety of Au net | network of mesh-like Au formed in the surface of a composite titanium material is small. The width of the Au network in the network Au formed on the surface of the composite titanium material that can keep the contact resistance low over a long period of the present invention is preferably in the range of 300 to 10,000 nm at least at one place. It is sectional explanatory drawing for demonstrating this.

Explanation of symbols

1: Titanium substrate, 2: Titanium metal, 3: Ti oxide layer, 4: Ti oxide layer, 5: Au net, 6: Diffusion joint

Claims (4)

Au is continuously fixed to the surface of the titanium substrate by diffusion bonding, and a Ti oxide layer is formed in a gap between the Au network constituting the fixed network Au and the adjacent Au network. A composite titanium material that can maintain a low contact resistance over a long period of time. 2. The composite titanium material capable of maintaining a low contact resistance over a long period of time, wherein at least one part of the network Au has a width of 300 to 10,000 nm. The long-term oxide film according to claim 1 or 2, characterized in that the Ti oxide layer formed in the gap between the Au net of the mesh Au and the adjacent Au net has a thickness in the range of 30 to 150 nm. A composite titanium material that can maintain low contact resistance. 4. A fuel cell separator comprising a composite titanium material capable of maintaining a low contact resistance over a long period of time.

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