Titanium laminate, and method for producing titanium laminate

Abstract

A titanium laminate according to this invention has a sheet-like shape, and is provided with a plurality of gas-liquid-permeable layers that are made of titanium and laminated such that titanium bonding surfaces adjacent in the lamination direction are bonded to one another and each has holes through which a gas and / or a liquid can pass. At least the gas-liquid-permeable layer among the plurality of gas-liquid-permeable layers which forms one of the laminate surfaces is a porous layer having a thickness of 500 μm or less. In the one laminate surface, the average value of the area of the holes that open to said laminate surface is 4 μm2 to 17 μm2 inclusive, the standard deviation value of the area of the holes is 20 μm2 or less, and the number of holes in a rectangular region having an aspect ratio of 4:3 and an area of 22,000 μm2 is 120 or more. In the other laminate surface positioned on the rear side relative to the one laminate surface, the average value of the area of the holes that open to said laminate surface is at least three times the average value of the area of the holes in the one laminate surface.

Description

Titanium laminate and method for manufacturing titanium laminate

[0001] The present invention relates to a sheet-like titanium laminate having a porous layer and a method for manufacturing the titanium laminate.

[0002] Porous titanium bodies produced by sintering titanium powder or titanium fibers have air or liquid permeability due to the pores, electrical conductivity, and also high corrosion resistance due to the formation of a passivation film on the surface.

[0003] Porous titanium having such properties is being considered for use in porous transport layers (PTLs) in polymer electrolyte membrane (PEM)-type water electrolysis devices, which are in environments where corrosion may occur. In particular, hydrogen produced in PEM-type or other water electrolysis devices using electricity derived from renewable energy is called "green hydrogen," and great expectations are being placed on it in recent years as efforts to realize a decarbonized society accelerate.

[0004] Patent Document 1 discloses a metal fiber nonwoven sintered sheet having an overall thickness of less than 1 mm, comprising a main layer and at least one auxiliary layer laminated and integrally sintered on the main layer, wherein the main layer is made of metal fibers having a thickness of 1 to 10 μm and a porosity of 80% or more, the auxiliary layer is made of metal fibers having a thickness at least twice that of the metal fibers of the main layer, the total thickness of the auxiliary layers is less than 2.5 times that of the main layer, and the overall porosity of the main layer and auxiliary layer is 75% or more and 90% or less. Patent Document 1 also describes that the main layer and auxiliary layer are preferably made of corrosion-resistant metal materials such as stainless steel, titanium alloys, nickel alloys, and copper alloys, and are suitable for use in filtering not only conventionally used fuel oils, lubricating oils, water, dyes, inks, etc., but also high-temperature liquids, organic solvents, acids, alkalis, etc.

[0005] Patent Document 2 describes a "power supply for a fuel cell, which is constructed by integrating a porous titanium plate having through-holes with a titanium matrix portion having voids," and a "method for fabricating a power supply for a fuel cell, which includes the steps of providing a large number of through-holes in a titanium raw plate, stacking the plate and a titanium raw material for the matrix portion, applying pressure to the stacked plate and the raw material for the matrix portion, and heating the plate and the raw material for the matrix portion to which pressure has been applied." Regarding the "method for fabricating a power supply for a fuel cell," it states that "the step of stacking the plate and the raw material for the matrix portion includes a step of disposing a binder together with the raw material for the matrix portion, and further includes a step of removing the binder," and that "the binder is a mixture of a water-soluble alkoxide and boron nitride, and the step of removing the binder includes a removal step using alcohol."

[0006] Patent Document 3 states that in "a method for producing a sheet-like porous sintered body, which is characterized by producing a titanium fiber molded body having a minor axis of 10 to 100 μm and a major axis of 1 to 10 mm, and then placing a plate material on the molded body and sintering it while pressing," it states that "it is preferable that sintered body 61 of titanium fibers 3 be placed on a sintered substrate 5 that is less likely to be welded to titanium fibers or titanium alloy fibers even when it comes into contact with them."

[0007] JP 2000-129311 A JP 2004-185946 A JP 2007-70727 A

[0008] When a porous titanium body is used as a porous transport layer in a PEM-type water electrolysis device, the porous titanium body may be pressed against the electrolyte membrane when assembled. If the pores on the surface of the porous titanium body are large, the electrolyte membrane pressed against the porous titanium body may partially penetrate into the pores, causing significant deformation in areas close to the pores and potentially damaging the electrolyte membrane. Furthermore, if the porous titanium body has protrusions on its surface, they may damage the electrolyte membrane. Such protrusions are often present on the surface of porous titanium bodies, which are sintered bodies of fibrous raw materials. Porous titanium bodies manufactured using fibrous raw materials tend to have large pores on their surface, as described above.

[0009] Therefore, from the viewpoint of preventing damage to the electrolyte membrane, it is desirable that the pores of the titanium porous body that open to the surface facing the electrolyte membrane are small. Even if the pores are small, a certain degree of air or liquid permeability can be achieved as long as there are many of them.

[0010] However, if the pores in a porous titanium body are small throughout, it is impossible to obtain high air permeability or liquid permeability, even if the number of pores is large. For this reason, it has been difficult to significantly improve air permeability or liquid permeability while suppressing damage to the electrolyte membrane using a single porous titanium body.

[0011] An object of the present invention is to provide a titanium laminate that can suppress damage to an electrolyte membrane and achieve excellent air or liquid permeability, and a method for manufacturing the titanium laminate.

[0012] As a result of extensive research aimed at solving the above-mentioned problems, the inventors have devised a sheet-like titanium laminate comprising multiple gas / liquid-permeable layers. Here, one surface of the laminate is a porous gas / liquid-permeable layer with relatively small pores opening to the laminate surface, so as to minimize damage to the electrolyte membrane when pressed against the electrolyte membrane in a PEM-type water electrolysis device. However, to ensure the required air permeability or liquid permeability even on the one surface of the laminate, the gas / liquid-permeable layer has a relatively large number of pores on the one surface of the laminate. Furthermore, to improve the air permeability or liquid permeability of the titanium laminate as a whole, the porous layer with small pores on the one surface of the laminate is made thin. On the other surface of the laminate, located behind the one surface of the laminate, a gas / liquid-permeable layer with relatively large pores opening to the laminate surface is positioned.

[0013] The titanium laminate of the present invention is in the form of a sheet, and is laminated by bonding adjacent titanium bonding surfaces to each other in the lamination direction, and comprises a plurality of titanium gas / liquid permeable layers, each having pores and allowing gas and / or liquid to pass through, and at least one of the gas / liquid permeable layers forming one of the surfaces of the laminate is a porous layer having a thickness of 500 μm or less, and the average area of ​​the pores opening to the surface of the laminate on the one surface of the laminate is 4 μm. 2 More than 17 μm 2 The standard deviation of the area of ​​the hole is 20 μm or less. 2 or less, and the area is 22000 μm 2 The number of holes present within a rectangular region having an aspect ratio of 4:3 is 120 or more, and the average area of ​​the holes opening onto the surface of the other laminate located on the back side of the one laminate surface is three times or more the average area of ​​the holes on the surface of the one laminate.

[0014] In the titanium laminate, it is preferable that the gas / liquid permeable layer forming the one surface of the laminate has the smallest thickness among the plurality of gas / liquid permeable layers.

[0015] In the titanium laminate, each of the plurality of gas / liquid permeable layers is preferably a porous layer. In the titanium laminate, the titanium content is preferably 97% by mass or more. In the titanium laminate, the oxygen content is preferably 0.4% by mass or more and 2.0% by mass or less. In the titanium laminate, the thickness of the gas / liquid permeable layer forming one of the laminate surfaces is preferably 500 μm or less.

[0016] The method for producing a titanium laminate of the present invention is a method for producing a sheet-like titanium laminate, and includes a bonding step of using a plurality of titanium gas-liquid permeable materials, each having pores that allow gas and / or liquid to pass through, wherein at least one of the gas-liquid permeable materials forming the surface of the laminate is a porous material having a thickness of 500 μm or less, and bonding the titanium bonding surfaces of the plurality of gas-liquid permeable materials together by sandwiching and pressing the gas-liquid permeable materials between pressing surfaces of opposing pressing members while heating the gas-liquid permeable materials to a temperature of 810°C or more and 1100°C or less, with the pressing surfaces of the pressing members being in contact with each other, and bonding the titanium bonding surfaces of the plurality of gas-liquid permeable materials together; and in the bonding step, the pressing members used have pressing surfaces coated with boron nitride particles using a coating agent that does not contain water.

[0017] In the above manufacturing method, a coating agent in which boron nitride particles are dispersed in an organic solvent can be used for the coating on the pressing surface.

[0018] In the above manufacturing method, it is preferable that the pressing member used in the joining step is made of graphite and has the coating applied to the pressing surface.

[0019] In the manufacturing method described above, before bonding in the bonding step, the average area of ​​pores opening on the surface of the porous material of the gas-liquid permeable material forming at least one of the laminate surfaces is 5 μm 2 More than 17 μm 2 The standard deviation of the area of ​​the hole is 20 μm or less. 2 or less, and the area is 22000 μm 2It is preferable that the number of holes present in a rectangular region having an aspect ratio of 4:3 is 250 or more.

[0020] The titanium laminate of the present invention can suppress damage to the electrolyte membrane and achieve excellent air and liquid permeability. The method for manufacturing such a titanium laminate of the present invention is suitable for manufacturing such a titanium laminate.

[0021] An embodiment of the present invention will be described in detail below. A titanium laminate according to one embodiment of the present invention comprises a plurality of titanium gas / liquid-permeable layers, each having pores and allowing gas and / or liquid to pass therethrough, which are laminated by bonding adjacent titanium bonding surfaces in the stacking direction. At least one of the gas / liquid-permeable layers, which forms the surface of the laminate, is a porous layer having a thickness of 500 μm or less.

[0022] The surface of one of the laminates formed by the gas-liquid permeable layer as the porous layer of the titanium laminate has pores with an average area of ​​4 μm 2 More than 17 μm 2 The standard deviation of the hole area is 20 μm or less. 2 or less, and the area is 22000 μm 2 The number of holes present within a rectangular region having an aspect ratio of 4:3 is 120 or more. When the average value and standard deviation of the area of ​​the holes opening on one of the laminate surfaces are small, the holes opening on one of the laminate surfaces have a relatively small and uniform area, which makes it possible to suppress damage to the electrolyte membrane when one of the laminate surfaces of the titanium laminate is pressed against the electrolyte membrane in a PEM-type water electrolysis device. Furthermore, since there are a relatively large number of holes opening on one of the laminate surfaces, it is possible to ensure the required air permeability or liquid permeability on the one of the laminate surfaces.

[0023] In contrast, a predetermined gas / liquid permeable layer is positioned on the other laminate surface located behind one of the laminate surfaces of the titanium laminate so that the average area of ​​the pores opening on that laminate surface is at least three times the average area of ​​the pores on the one laminate surface. This allows gas or liquid to easily permeate through the gas / liquid permeable layer on the other laminate surface side, greatly improving the air or liquid permeability of the titanium laminate as a whole.

[0024] To manufacture the above-described titanium laminate, multiple sheets of titanium gas-liquid permeable material corresponding to the multiple gas-liquid permeable layers must be bonded and stacked. However, if the multiple sheets of titanium gas-liquid permeable material are simply sandwiched between the opposing pressing surfaces of a pressing member and pressed while heated to a predetermined temperature, the porous titanium gas-liquid permeable material, in particular, bonds to the pressing member, making it difficult to peel it off from the pressing member. Therefore, in the bonding process of this embodiment, a pressing member whose pressing surface is coated with boron nitride particles is used. The boron nitride particle coating suppresses reaction between the pressing member material and the titanium gas-liquid permeable material. Furthermore, when a pressing member made of boron nitride is used, the boron nitride tends to peel off and adhere to the titanium laminate, causing the surface of the laminate to become rough when peeled off. However, the pressing member here has a pressing surface coated with boron nitride particles, making this problem less likely to occur. This makes it possible to manufacture the above-described titanium laminate.

[0025] (Titanium Laminate) The titanium laminate is made of titanium. If it is made of titanium, it can be said that the titanium laminate has high electrical conductivity at a certain relative density. The titanium content of the titanium laminate (and further each gas / liquid permeable layer) is preferably 97% by mass or more, and more preferably 98% by mass or more. The upper limit of the titanium content is not limited to this, but may be, for example, 99.8% by mass or less, or 99% by mass or less. This titanium content refers to the purity of titanium taking into account not only metal components but also gas component impurities such as oxygen. Therefore, the titanium content can be calculated by subtracting the total content of metal components and impurity components, including gas components, from 100% by mass.

[0026] The titanium laminate (particularly the gas / liquid permeable layer of the porous layer on one surface side of the laminate) may contain Fe as an impurity, and may also contain Ni, Cr, Al, Cu, Zn, and Sn as unavoidable impurities resulting from the manufacturing process. The Fe content may be, for example, 0.25 mass% or less. It is preferable that the content of each of Ni, Cr, Al, Cu, Zn, and Sn is less than 0.10 mass%, and that the total content of these elements is less than 0.30 mass%.

[0027] The oxygen content of the titanium laminate is not particularly limited, but may be 0.4% by mass or more and 2.0% by mass or less. The oxygen content of the titanium laminate may be 1.0% by mass or more and 2.0% by mass or less. The oxygen content can be measured by inert gas fusion-infrared absorption spectroscopy.

[0028] The titanium laminate may have a purity equivalent to JIS H 4600 (2012) pure titanium grades 1 to 4, typically grades 1 to 2, excluding carbon, nitrogen, and oxygen content.

[0029] The titanium laminate is in the form of a sheet and includes multiple titanium gas-liquid permeable layers. The multiple gas-liquid permeable layers are stacked such that adjacent titanium bonding surfaces are bonded to each other in the stacking direction. When the titanium laminate is manufactured using the manufacturing method described below, the titanium bonding surfaces of the titanium gas-liquid permeable material are bonded to each other, so that the titanium bonding surfaces are bonded to each other in the titanium laminate. It is preferable that the interfaces of the multiple gas-liquid permeable layers are substantially free of metals other than titanium or compounds not containing titanium, since this allows for the required high conductivity to be achieved at low cost. This is because joining the gas-liquid permeable layers by providing a layer containing another metal, such as platinum, to suppress an increase in electrical resistance at the interface would result in increased costs. Each of the multiple gas-liquid permeable layers has pores that allow gas and / or liquid to pass through. Titanium laminates that are permeable to gas and / or liquid in the stacking direction (sheet thickness direction) or other directions, such as a direction perpendicular to the stacking direction, may be used as the porous transport layer of a PEM water electrolysis device.

[0030] One surface of the titanium laminate is formed by a gas / liquid permeable layer (also referred to as "one-side gas / liquid permeable layer") that constitutes the surface side of that one laminate, and this laminate surface corresponds to the surface of the one-side gas / liquid permeable layer. The one-side gas / liquid permeable layer is a porous layer. The porous layer is formed by bonding titanium powder particles together and has a sponge-like three-dimensional network structure in which pores are formed between the bonded titanium powder particles. By making the one-side gas / liquid permeable layer a porous layer with the above-mentioned three-dimensional network structure, the one-side laminate surface is more likely to have a large number of predetermined microscopic pores open, as described below.

[0031] The average area of ​​the holes opening on one surface of the laminate is 4 μm 2 More than 17 μm 2 If the pores on one of the laminate surfaces have a relatively small area, the laminate surface can be said to be generally smooth, and damage to the electrolyte membrane in a PEM-type water electrolysis device can be effectively suppressed. From this perspective, the average area of ​​the pores on one of the laminate surfaces is set to 4 μm or less. 2 More than 10 μm 2 It is preferable that the standard deviation of the hole area on one of the laminate surfaces is 20 μm or less. If the average value of the hole area on one of the laminate surfaces is too small, the air permeability or liquid permeability may decrease. If the average value of the hole area on one of the laminate surfaces is too large, the electrolyte membrane may partially enter the hole, causing significant deformation in the areas close to the hole, which may lead to damage to the electrolyte membrane. From the same viewpoint, it is preferable that the standard deviation of the hole area on the laminate surface is 20 μm or less. 2 Further, 3 μm 2 ~20μm 2 , especially 5 μm 2 ~17μm 2 A small standard deviation value means that most of the pores present on one surface of the laminate are of the required small size.

[0032] In addition, on one surface of the laminate, the area is 22000 μm 2The number of pores present in a rectangular region having an aspect ratio of length:width = 4:3 is 120 or more, preferably 140 or more, and more preferably 150 or more. The presence of many fine pores as described above on one of the laminate surfaces makes it possible to achieve smoothness while ensuring the required air permeability or liquid permeability. The number of pores in the rectangular region on one of the laminate surfaces is not limited to this, but may be, for example, 400 or less, or 300 or less.

[0033] The other laminate surface of the titanium laminate means the surface located on the back or opposite side of one laminate surface, and is formed by the gas-liquid permeable layer that constitutes the portion on the surface side of the other laminate (also referred to as the "gas-liquid permeable layer on the other side"). In other words, the other laminate surface corresponds to the surface of the gas-liquid permeable layer on the other side.

[0034] In order to improve the air permeability or liquid permeability of the titanium laminate, the average area of ​​the holes opening on the other laminate surface is preferably at least three times, more preferably at least five times, or even at least seven times the average area of ​​the holes on the one laminate surface. By forming the other laminate surface side with a gas / liquid permeable layer having large pores in this manner, gas and liquid can easily flow through the titanium laminate. The upper limit of the average area of ​​the holes opening on the other laminate surface is not particularly limited, provided that the titanium laminate has the required strength for use in, for example, a PEM water electrolysis device. To cite an example, the upper limit is 200,000 times or less, 10,000 times or less, 1,000 times or less, 500 times or less, or 100 times or less, of the average area of ​​the holes on the one laminate surface. Because expanded metal, mesh, punched metal, etc., described below, sometimes have pores large enough to be visible to the naked eye, the upper limit of the average area of ​​the holes opening on the other laminate surface may be as large as 200,000 times or less.

[0035] The gas / liquid-permeable layer on the other side is not limited to a porous layer with a three-dimensional network structure, as long as the average pore area on the surface of the other laminate is a predetermined value. For example, it may be an expanded metal layer, mesh layer, or punched metal layer with regularly-formed pores of a certain size penetrating through the thickness direction. From the perspective of gradually increasing the pore size within the titanium laminate to control the flow of gas and liquid to some extent, it is preferable for the gas / liquid-permeable layer on the other side to also be a porous layer. However, even in this case, in manufacturing the titanium laminate, porous materials with different properties or obtained by different manufacturing methods can be used for the gas / liquid-permeable layers on one side and the other side, so that the average pore area on the surface of the other laminate is at least three times the average pore area on the surface of the one laminate. The porous layer on the other side may be formed not only by titanium powder particles bonded to each other, but also by a nonwoven three-dimensional network structure or mesh structure formed by titanium fibers bonded to each other. A porous material with a three-dimensional network structure produced by sintering a fibrous raw material is characterized by a nonwoven fabric-like structure with protrusions on its surface, but also by a certain degree of strength and large pores. Therefore, when a sintered body of a fibrous raw material is used as a gas / liquid permeable material in a position that is not in contact with the electrolyte membrane, it is easy to ensure excellent air or liquid permeability while obtaining the desired strength.

[0036] The average value and standard deviation of the area of ​​the holes opening on the surface of the laminate, as well as the number of holes in a predetermined rectangular area, are measured using a scanning electron microscope (Keyence Ultra-Deep Multi-Angle Lens VHX-D510). More specifically, for one side of the laminate surface, the area on the laminate surface is 22,000 μm. 2An SEM image is acquired at 2000x magnification for a rectangular region with an aspect ratio of 4:3. For the other laminate surface, the aspect ratio is the same as above, 4:3, and the observation magnification and surface area are set according to the size of the pores on the other laminate surface. Specifically, the magnification and surface area are set so that the number of pores observed on the other laminate surface is within the range of 100 to 1000. In particular, if the other side is a porous layer, the small particle removal process and hole filling process described below are performed to identify the pores. Therefore, by capturing an image within the above-mentioned number of pores, the average pore area values ​​on the one and other laminate surfaces can be more accurately compared. If the other side is a porous layer, a 900x observation magnification may be preferable. The SEM image is then analyzed using a scanning electron microscope. A threshold value is set to half the maximum brightness detected for the SEM image, and a closed region with a brightness between 0 and the threshold is considered to be a single pore. At this time, the SEM image may be subjected to binarization processing, if necessary. After the binarization process, a small particle removal process (processing to black pixels after binarization) is performed on closed areas of 50 pixels or less, and then a hole filling process (processing to white pixels after binarization) is performed on closed areas of 50 pixels or less. This is used to calculate the number and area of ​​each hole, and the standard deviation value is determined as the square root of the variance. This SEM image analysis is performed on five rectangular areas on the laminate surface, at least some of which are offset from each other, and the average values ​​of the area and number of holes in these rectangular areas are used as the average area and standard deviation of the hole areas on the laminate surface and the number of holes in the rectangular areas, respectively. In the case of a laminate surface that is a square or rectangular in plan view, the five rectangular areas are the five rectangular areas at the center and four corners.

[0037] The thickness of the sheet-like titanium laminate (total thickness including all gas / liquid permeable layers) may be 40 μm or more and 1000 μm or less. For example, a titanium laminate of such a certain thickness may be required for the porous transport layer of a PEM water electrolysis device. On the other hand, if the thickness is too large, the PEM water electrolysis device may become large. The thickness of the titanium laminate may be, for example, 700 μm or less, 400 μm or less, or 350 μm or less, or may be 40 μm or more, or 80 μm or more.

[0038] The thickness of the titanium laminate is measured at five points, four points on the periphery and one point in the center, of the titanium porous body using a digital thickness gauge with a flat probe having a diameter of 10 mm and a measurement accuracy of 0.01 mm, such as a Mitutoyo digital thickness gauge (model number 547-321), and the average of these measurements is used. When the sheet-like titanium porous body is rectangular in plan view, the four peripheral points are the four corner points.

[0039] The thickness of the gas / liquid permeable layer on one side is 500 μm or less, preferably 40 μm to 400 μm, 40 μm to 300 μm, or 40 μm to 200 μm. Because the gas / liquid permeable layer on one side is a porous layer with small pores, if its thickness is too large, the overall breathability or liquid permeability of the titanium laminate decreases. On the other hand, by increasing the thickness of the gas / liquid permeable layer on one side to a certain extent, the required strength is ensured after sintering during the production of the corresponding porous material, making the gas / liquid permeable layer less likely to crack when pressed against the electrolyte membrane together with other gas / liquid permeable layers. The gas / liquid permeable layer on one side preferably has the thinnest thickness among the multiple gas / liquid permeable layers. By making the thickness of the gas / liquid permeable layer on one side, which has small pores and is less likely to permeate gases or liquids, the breathability or liquid permeability of the titanium laminate can be significantly improved.

[0040] The thickness of the gas-liquid permeable layer on the other side is preferably 100 μm to 960 μm. By making the thickness of the gas-liquid permeable layer on the other side thicker to a certain extent, it is possible to further improve the air permeability or liquid permeability, and by not making the thickness too thick, it is possible to reduce the size of the water electrolysis device and improve the electrolysis efficiency per area.

[0041] The thickness of each gas / liquid permeable layer is measured by observing the thickness at five points on a cross section of a titanium laminate that has been embedded in resin and polished using an SEM, and the average value is used. Since different functions are required of each gas / liquid permeable layer in a titanium laminate, a portion where the pore size differs in the stacking direction is identified, and the thickness of each gas / liquid permeable layer is determined by SEM observation of that portion.

[0042] The surface area of ​​the sheet-like titanium laminate in plan view is not particularly limited and can be determined appropriately depending on various conditions. For example, it is 70 mm 2 More than 600,000 mm 2 Below, 10,000 mm 2 ~600,000mm 2 The above-mentioned "sheet-like" refers to a plate-like or foil-like shape having a small thickness relative to the dimensions in a plan view, and the shape in a plan view is not particularly limited.

[0043] The titanium laminate can be constructed of two gas-liquid-permeable layers, with one gas-liquid-permeable layer and the other gas-liquid-permeable layer directly bonded at their titanium bonding surfaces, but it can also have one or more intermediate gas-liquid-permeable layers between the two gas-liquid-permeable layers. One or more of the intermediate gas-liquid-permeable layers can be porous, or they can be expanded metal layers, mesh layers, punched metal layers, or the like. When each of the multiple gas-liquid-permeable layers is porous, the pores within the titanium laminate can be gradually enlarged, allowing for some control of the flow of gas or liquid.

[0044] (Manufacturing Method) To manufacture the above-described titanium laminate, first, a plurality of gas-liquid permeable materials corresponding to the plurality of gas-liquid permeable layers of the titanium laminate are prepared. Of these, at least the gas-liquid permeable material forming one laminate surface of the titanium laminate (the gas-liquid permeable material for the gas-liquid permeable layer on one side) is a porous material having a thickness of 500 μm or less. At least one of the other gas-liquid permeable materials may be an expanded metal material, a mesh material, a punched metal material, or the like, but is preferably a porous material.

[0045] Expanded metal, mesh, or punched metal materials that can also be used as gas-liquid permeable materials are commercially available. Commercially available porous materials may be used, but they can also be prepared as described below.

[0046] In one example of a method for producing a porous material, the steps of paste preparation, drying, debinding, and sintering are performed in this order, and this method may be referred to as a paste method.

[0047] In the paste preparation step, a pulverized powder such as titanium hydride-dehydrogenated powder or titanium hydride powder, or a spherical powder such as atomized powder, or other titanium powder, an organic binder, and an organic solvent are mixed using a mixer with a stirrer, a rotary mixer, a triple roll mill, etc. At this time, the mixture may be pulverized using a vibration mill, a bead mill, or other pulverizing mixer, etc.

[0048] The average particle size of the titanium powder contained in the paste can be, for example, 25 μm or less, preferably 18 μm or less. By using titanium powder with such a small particle size and further using a predetermined dispersant as described below, a porous material with a smooth surface can be obtained. The average particle size of the titanium powder can be 5 μm or more, or even 10 μm or more. The average particle size refers to the particle size at which the cumulative volume distribution in the particle size distribution obtained by the laser diffraction scattering method is 50%.

[0049] Various organic binders can be appropriately selected and used for the paste, including, for example, methyl cellulose, polyvinyl alcohol, ethyl cellulose, acrylic, and polyvinyl butyral. Hydrophobic organic binders are preferred. However, they are not limited to the ones listed here. The organic solvent may be, for example, alcohol (ethanol, isopropanol, terpineol, butyl carbitol, etc.). For example, the organic binder may be polyvinyl butyral and the organic solvent may be isopropyl alcohol. The paste may further contain a plasticizer (glycerin, ethylene glycol, etc.) or a surfactant (alkylbenzene sulfonate, etc.).

[0050] When manufacturing a porous material for one of the gas / liquid permeable layers, the paste should not contain water as a solvent. It is preferable that the paste also does not contain a foaming agent. It is acceptable for the paste to contain water as a solvent, but it may contain water that may be unintentionally mixed into the paste due to moisture absorption or the like. If a porous material is manufactured using a paste containing water and / or a foaming agent, large pores will be formed during the manufacturing process, making it impossible to achieve the desired pore size.

[0051] Regardless of whether or not a porous material for one of the gas / liquid permeable layers is being produced, the paste is applied relatively thinly to a substrate and then dried, for example, at a temperature of 90°C or higher and 165°C or lower for 5 minutes to 300 minutes in a drying process. This is followed by a binder removal process, in which the substrate is heated, for example, at a temperature of 300°C or higher and 450°C or lower for 3 hours to 12 hours inclusive, to volatilize and remove the organic binder.

[0052] Thereafter, a sintering step is carried out, and the sintering temperature is, for example, 1.0×10 -2 The titanium powder is sintered by heating at a temperature of 700°C or higher and 1000°C or lower for 1 hour or higher and 4 hours or lower in a vacuum of 100 Pa or lower or in an inert atmosphere of Ar or He, thereby obtaining a porous material.

[0053] Another example of a method for producing a porous material, although not described in detail here, is a method (dry method) in which titanium powder or titanium fibers are dropped and deposited in a gas such as air or in a vacuum, and then heated in a reduced pressure atmosphere such as a vacuum to sinter it.

[0054] When the porous material for one of the gas-liquid permeable layers is manufactured by the above-mentioned paste method, the average area of ​​the pores opening on the surface of the obtained porous material is 5 μm 2 More than 17 μm 2 The standard deviation of the hole area is 20 μm or less. 2 or less, and the area is 22000 μm 2The number of pores present in a rectangular region having an aspect ratio of 4:3 may be 250 or more. In addition, the standard deviation of the area of ​​the pores opening to the surface of the porous material may be 3 μm or less. 2 ~20μm 2 , especially 10 μm 2 ~20μm 2 When such a porous material is used as the gas / liquid permeable material that forms one of the laminate surfaces and the bonding step described below is carried out, the shape of the pores changes, and in the gas / liquid permeable layer on one side of the titanium laminate, the average area and number of pores that open to one of the laminate surfaces may become the values ​​described above.

[0055] After preparing the multiple gas / liquid permeable materials, a bonding step is performed in which the multiple gas / liquid permeable materials are bonded and stacked. More specifically, in the bonding step, the titanium bonding surfaces of the multiple gas / liquid permeable materials are brought into contact with each other. If necessary, the multiple gas / liquid permeable materials may be partially fixed to each other by welding or the like. However, since fixing by welding or the like may partially narrow or eliminate the pores of the gas / liquid permeable material or reduce its thickness, it is preferable to simply overlap and contact the multiple gas / liquid permeable materials without fixing them.

[0056] Then, in this state, the gas / liquid permeable materials are sandwiched and pressed from both sides between the opposing flat pressing surfaces of the pressing members, and heated to a temperature of 810°C or higher and 1100°C or lower, preferably 850°C or higher and 1000°C or lower. As a result, the multiple gas / liquid permeable materials are bonded and stacked at their titanium bonding surfaces by solid-phase diffusion, forming a titanium laminate. Note that the above temperature is the maximum temperature reached by heating.

[0057] In the bonding process, it is essential to use a pressing member, such as a setter, whose pressing surface is coated with boron nitride particles. Pressing members made of graphite or other materials without a coating on their pressing surface react with titanium during the bonding process, potentially forming impurities such as TiC on the surface of the titanium laminate, particularly on the smoother, larger-contact surface. On the other hand, using a boron nitride pressing member can cause the self-lubricating boron nitride to peel off and adhere to the laminate surface, potentially causing the laminate surface to become rough when peeled off. In contrast, a pressing member whose pressing surface is coated with boron nitride particles can suppress the formation of impurities on the laminate surface, and even if boron nitride particles adhere to the laminate surface, they can be easily removed by rinsing with water, for example. Furthermore, using a pressing member whose pressing surface is coated with boron nitride particles also makes it easy to separate the titanium laminate from the pressing member after the bonding process.

[0058] To coat the pressing surface of the pressing member with boron nitride particles prior to the bonding step, a coating agent in which boron nitride particles are dispersed in an organic solvent can be applied to the pressing surface by, for example, spraying and then drying. The particle size of the boron nitride particles used for coating is preferably 9 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. The particle size of the boron nitride particles refers to the diameter of a circle having the average area of ​​each particle calculated on a photographed image. From the viewpoint of suppressing aggregation of the boron nitride particles attached to the pressing surface after coating, it is preferable to use an organic solvent rather than water as the coating agent. This prevents the formation of agglomerated particles, which could result in uncoated areas on the pressing surface, causing bonding between the pressing surface and the laminate surface, or the agglomerated particles penetrating from the laminate surface and affecting its breathability or liquid permeability.

[0059] Preferably, the pressing member is made of graphite and has its pressing surface coated with boron nitride particles as described above. The graphite pressing member is resistant to partial peeling even at high temperatures during the bonding process. In addition, the boron nitride particles are easily adsorbed to the pressing surface of the graphite pressing member.

[0060] The pressing and heating time in the bonding step may be, for example, 30 minutes to 8 hours at a temperature of 810° C. The bonding step may be carried out in a reduced pressure atmosphere or an inert atmosphere.

[0061] Next, a prototype of the sheet-shaped titanium laminate of the present invention was produced, and the details thereof will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0062] As gas-liquid permeable materials having pores and allowing gas and / or liquid to pass through, three types of porous materials with different properties (WEBTi-K, WEBTi-T, and WEBTi-S ("WEBTi" is a registered trademark) manufactured by Toho Titanium Co., Ltd.), and an expanded metal material (Finemetal small mesh BD20 manufactured by Sanki Manufacturing Co., Ltd.) were prepared. All of these are made of titanium. WEBTi-K was produced by a paste method, WEBTi-T by a dry method using titanium powder, and WEBTi-S by a dry method using titanium fiber. WEBTi-K and WEBTi-T have a sponge-like three-dimensional mesh structure, while WEBTi-S has a nonwoven three-dimensional mesh structure.

[0063] Two types of gas-liquid permeable materials were selected from the above, and the titanium bonding surfaces were simply placed one on top of the other with the surfaces in contact with each other. They were then sandwiched between pressure members from both sides and heated while being pressed to bond the titanium bonding surfaces together, forming a laminate. The pressure was applied by placing a weight on the upper pressure member, and the pressure was 0.14 N / cm. 2 ~0.35N / cm 2 The gas-liquid permeable material was placed in a furnace together with the pressing member, and heating was performed at a temperature of 1000°C for 1 hour in Examples 1 to 4 and Comparative Examples 1 and 2, at a temperature of 1200°C for 1 hour in Comparative Example 3, and at a temperature of 775°C for 1 hour in Comparative Example 4.

[0064] Here, a graphite setter was used as the pressing member, and a predetermined coating agent was sprayed onto the pressing surface and then dried to form a coating with boron nitride particles. In Examples 1 to 4 and Comparative Examples 3 and 4, an organic solvent-based coating agent (Whitey Release N manufactured by Odec Co., Ltd.) containing 1% to 5% by mass of boron nitride particles and an organic solvent containing 65% or more by mass of dimethyl ether, but no water, was used. In Comparative Example 1, BN Release (a water-based coating agent) manufactured by Odec Co., Ltd. was used. This water-based coating agent had a water content of 50 to 60% by mass and a dimethyl ether content of 35 to 40% by mass. When using a water-based coating agent, it was heated to approximately 100°C after spraying onto the pressing surface to allow drying. In Comparative Example 2, no coating was applied to the pressing surface. Furthermore, in all Comparative Examples 1 to 4, WEBTi-K and WEBTi-T were used as the two gas-liquid permeable materials. In addition, in all of Examples 1 to 4 and Comparative Examples 1 to 4, WEBTi-K was used as the gas-liquid permeable material, which is a porous material that forms one of the laminate surfaces.

[0065] As a result, titanium laminates could be produced in Examples 1 to 4. On the other hand, in Comparative Example 1, the pressing surface of the pressing member was coated with a water-based coating agent, and agglomerated boron nitride particles entered the titanium laminate. In Comparative Example 2, the pressing surface was not coated, and therefore the pressing surface and the laminate surface bonded together, making it impossible to peel them apart. In Comparative Example 3, the pressing surface was coated, but the temperature during bonding was too high, causing the pressing surface and the laminate surface to bond together, making it impossible to peel them apart. In Comparative Example 4, the temperature during bonding was too low, resulting in weak bonding between the gas-liquid permeable materials. For this reason, titanium laminates could not be produced in Comparative Examples 1 to 4.

[0066] Furthermore, for each titanium laminate, the thickness, electrical conductivity, oxygen content, average value and standard deviation of the hole area on the laminate surface, and number of holes within a rectangular region were measured. The results are shown in Table 1. The standard deviation of the hole area will be described later. The methods for measuring the thickness, average value of the hole area, standard deviation of the hole area, and number of holes within a rectangular region were as described above. In Example 3, the holes in the gas-liquid permeable layer formed from the expanded metal material were too large compared to the holes in the WEBTi-S and other materials in Example 1, so it was not possible to measure the average value of the hole area. For this reason, in Table 1, the number of holes in the expanded metal of Example 3 is listed as "0," but this does not represent the actual number.

[0067] The electrical conductivity was measured for each laminate surface using a Mitsubishi Analytech Loresta GP MCP-T610 low resistivity meter by the four-probe method, with the laminate surface being measured positioned upward. The probe checker used was the MCP-TRPS RMH311 for the laminate surface side of expanded metal, WEBTi-T, or S, and the MCP-TP06P RMH112 for the laminate surface side of WEBTi-K. It is believed that if the titanium bonding surfaces of the gas / liquid permeable layers are sufficiently bonded together, the electrical conductivity will be high. Furthermore, if the electrical conductivity is high, it is assumed that the gas / liquid permeable layers are firmly bonded, and therefore the mechanical strength is also excellent. The electrical conductivity was measured on both sides of the manufactured titanium laminate, and both sides showed a value of 3.2 × 10 3 Before bonding the gas-liquid-permeable materials together, the conductivity of the upper gas-liquid-permeable material was measured with the two gas-liquid-permeable materials stacked together, and the results are also shown in Table 1.

[0068] In Comparative Example 4, the temperature during bonding was low, so the titanium bonding surfaces of the gas / liquid permeable layers were not bonded sufficiently, and the conductivity of the WEBTi-K side was 2.5 × 10 3 Since the resistivity was as low as 1.5 S / cm, it was determined that a titanium laminate could not be produced.

[0069]

[0070] In addition, the standard deviation of the area of ​​the holes on one surface of the titanium laminate of Examples 1 to 4 was measured by the method described above. In Example 1, the standard deviation was 11.1 μm 2 , and 10.1 μm in Example 2 2 , and 13.3 μm in Example 3 2 , and 7.6 μm in Example 4 2 The standard deviation of the area of ​​the pores on the surface of the porous material forming one of the laminate surfaces before bonding used in producing each of the titanium laminates in Examples 1 to 4 was 15.3 μm in Example 1. 2 , and 12.4 μm in Example 2 2 , and 11.9 μm in Example 3 2 , and 14.8 μm in Example 4 2 It was.

[0071] According to this invention, it is possible to suppress damage to the electrolyte membrane, and further, it has been suggested that excellent air permeability or liquid permeability can be achieved.

Claims

1. A sheet-like titanium laminate, comprising a plurality of titanium gas-liquid permeable layers laminated by bonding adjacent titanium bonding surfaces in the lamination direction, each having holes through which gas and / or liquid can pass, wherein at least one of the gas-liquid permeable layers forming one of the surfaces of the laminate is a porous layer having a thickness of 500 μm or less, and the average area of ​​the holes opening to the surface of the laminate is 4 μm. 2 More than 17 μm 2 The standard deviation of the area of ​​the hole is 20 μm or less. 2 or less, and the area is 22000 μm 2 a number of the holes present within a rectangular region having an aspect ratio of 4:3 is 120 or more, and an average value of the area of ​​the holes opening onto one of the laminate surfaces, on the other laminate surface located on the back side of the one of the laminate surfaces, is three times or more the average value of the area of ​​the holes on the one of the laminate surfaces.

2. The titanium laminate according to claim 1, wherein the gas / liquid permeable layer forming the one of the laminate surfaces has the thinnest thickness among the plurality of gas / liquid permeable layers.

3. The titanium laminate according to claim 1 or 2, wherein each of the plurality of gas / liquid permeable layers is a porous layer.

4. The titanium laminate according to claim 1 or 2, wherein the titanium content of the titanium laminate is 97 mass% or more.

5. The titanium laminate according to claim 1 or 2, wherein the oxygen content of the titanium laminate is 0.4 mass% or more and 2.0 mass% or less.

6. A titanium laminate according to claim 1 or 2, wherein the gas / liquid permeable layer forming the surface of one of the laminates has a thickness of 500 μm or less.

7. A method for producing a sheet-like titanium laminate, comprising: using a plurality of titanium gas-liquid permeable materials each having pores through which gas and / or liquid can pass, at least one of which forming a surface of the laminate is a porous material having a thickness of 500 μm or less; a bonding step of heating the gas-liquid permeable material to a temperature of 810°C or more and 1100°C or less while sandwiching and pressing the gas-liquid permeable material between pressing surfaces of opposing pressing members in a state where the respective titanium bonding surfaces of the plurality of gas-liquid permeable materials are in contact with each other, thereby bonding the plurality of gas-liquid permeable materials to each other at their titanium bonding surfaces; and wherein in the bonding step, a pressing member having a pressing surface coated with boron nitride particles using a coating agent that does not contain water is used as the pressing member.

8. The method for producing a titanium laminate according to claim 7, wherein the coating on the pressing surface is a coating agent in which boron nitride particles are dispersed in an organic solvent.

9. The method for producing a titanium laminate according to claim 7 or 8, wherein the pressing member used in the bonding step is a graphite pressing member having the coating applied to its pressing surface.

10. Before bonding in the bonding step, the average area of ​​the pores opening on the surface of the porous material of the gas-liquid permeable material forming at least one of the laminate surfaces is 5 μm 2 More than 17 μm 2 The standard deviation of the area of ​​the hole is 20 μm or less. 2 or less, and the area is 22000 μm 2 9. The method for producing a titanium laminate according to claim 7 or 8, wherein the number of the holes present within a rectangular region having an aspect ratio of 4:3 is 250 or more.

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