Titanium porous body

Abstract

To provide a titanium porous body that has an appropriate size of pores and can exhibit excellent gas or liquid permeability and required electric conducting property while suppressing the occurrence of damages to a surface of an electrolyte film and the like.SOLUTION: A titanium porous body in the present invention has a thickness of 80 μm or greater to be in a sheet form, a peak pore diameter at the highest peak in a pore-diameter distribution indicative of a relation between diameters and cubic capacities of pores of 6.5 μm or smaller, and an I value as determined by Equation (1):I=[gas permeability (μm / Pa s)×electric conductivity (kS / cm)] / [peak pore diameter (μm)]2 from a gas permeability, an electric conductivity and the peak pore diameter of 4.0 or greater.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a porous titanium body. [Background technology]

[0002] Metal porous bodies such as titanium porous bodies produced by sintering powder or fibers of a metal such as titanium are described in, for example, Patent Documents 1 to 3, and are used in electrodes, filters, and various other applications.

[0003] Patent Document 1 states that "a thickness of 0.5 mm or less and an area of ​​200 cm 2 Thus, a "titanium sintered filter characterized by a tensile strength of 150 MPa or more" is described. As a method for manufacturing this "titanium sintered filter," Patent Document 1 describes that "titanium gas atomized powder is sintered to form a porous plate material, and this porous plate material is rolled."

[0004] Patent Document 2 describes a "porous sintered metal having a thickness of 5 to 30 μm, a porosity of 25 to 70%, an average pore diameter of 0.2 to 40 μm, and a large number of pores that are isotropically interconnected through pores." Furthermore, Patent Document 3 states that "We provide a method for inexpensively producing a porous titanium thin film having a thickness of 40 μm or less and a porosity of 1 to 65%." It also proposes a method for producing a porous titanium thin film having a thickness of 40 μm or less and a porosity of 1 to 65% by a process including the following steps (a), (b), (c), and (d): (a) a green body production step in which a paste-like composition containing a titanium raw material, such as titanium hydride powder or titanium dehydrogenation powder, a binder component, and a solvent component is applied to a substrate to form a film, and then the solvent component is evaporated and the resulting film is dried to obtain a dried green body; (b) a peeling step in which the dried green body is peeled from the substrate; (c) a binder removal step in which the peeled dried green body is heated to remove the binder component; and (d) a sintering step in which the binder-removed dried green body is sintered at 700°C to 1100°C to obtain a porous titanium thin film." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-324153 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-82990 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-65968 Summary of the Invention [Problem to be solved by the invention]

[0006] Porous titanium bodies have air or liquid permeability and electrical conductivity due to their numerous pores, and also have high corrosion resistance due to the formation of a passivation film on their surfaces. For this reason, porous titanium bodies are being considered for use as porous transport layers (PTLs) in PEM-type water electrolysis devices and other devices that are exposed to environments where corrosion may occur. For such applications, porous titanium bodies with greater thicknesses than those described in Patent Documents 2 and 3 may be required.

[0007] Furthermore, when a porous titanium body is used as a porous transport layer in a PEM water electrolysis system, the porous titanium body may be pressed against the electrolyte membrane when assembled. In this case, if the pores in the porous titanium body are large, the electrolyte membrane pressed against the porous titanium body will deform, and part of the membrane's surface will penetrate into the pores of the porous titanium body, thereby damaging the surface of the electrolyte membrane. Therefore, from the perspective of suppressing damage to the electrolyte membrane, a porous titanium body with a relatively small pore size is desirable.

[0008] On the other hand, small pores in a titanium porous body not only reduce its air permeability or liquid permeability but also affect its electrical conductivity. Therefore, simply reducing the pore size of a titanium porous body does not make it suitable for certain applications, such as the porous transport layer of the PEM water electrolysis device described above.

[0009] An object of the present invention is to provide a porous titanium body that has pores of an appropriate size and that exhibits excellent air or liquid permeability and required electrical conductivity while suppressing damage to the surface of an electrolyte membrane or the like. [Means for solving the problem]

[0010] The titanium porous body of the present invention has a thickness of 80 μm or more, is sheet-shaped, and has a pore size distribution showing the relationship between pore diameter and volume, with the highest peak pore size being 6.5 μm or less. From the air permeability, electrical conductivity and the peak pore size, the following equation (1) can be used: I=[air permeability (μm / Pa s)×electrical conductivity (kS / cm)] / [peak pore size (μm)] 2 The I value calculated by is 4.0 or more.

[0011] The peak pore diameter is preferably 1.5 μm or more and 6.5 μm or less.

[0012] The thickness may be 80 μm or more and 400 μm or less.

[0013] The titanium content may be 97% by mass or more, and the oxygen content may be 0.6% by mass or more and 2.0% by mass or less. [Effects of the Invention]

[0014] The porous titanium body of the present invention has pores of an appropriate size, and can exhibit excellent air or liquid permeability and required electrical conductivity while suppressing damage to the surface of an electrolyte membrane or the like. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a graph showing an example of the pore size distribution of a titanium porous body. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described in detail. The titanium porous body according to one embodiment of the present invention is in the form of a sheet having a thickness of 80 μm or more. In this titanium porous body, the peak pore diameter of the highest peak in the pore size distribution, which shows the relationship between pore diameter and volume, is 6.5 μm or less. Furthermore, this titanium porous body can be calculated from the air permeability, electrical conductivity, and the peak pore diameter by the following equation (1): I=[air permeability (μm / Pa s)×electrical conductivity (kS / cm)] / [peak pore diameter (μm)] 2 The I value calculated by is 4.0 or more.

[0017] To produce such a porous titanium body, for example, a paste containing titanium powder, an organic binder, and an organic solvent but not containing water or a foaming agent can be applied to a substrate, followed by sequential drying, debinding, and sintering. The titanium powder has a predetermined particle size, and it is preferable to use a pulverized powder such as a hydrogenated / dehydrogenated titanium powder (HDH powder) rather than an atomized powder. It is also preferable to mix the titanium powder, the organic binder, and the organic solvent, etc., and increase the viscosity of the resulting paste to a certain degree. This makes it easier to control the peak pore size and I value within the specified ranges for a porous titanium body with a certain thickness. Inappropriate production, such as a short mixing time, can result in insufficient dissolution of the organic binder in the organic solvent, resulting in a low viscosity paste. In such cases, the peak pore size tends to be large.

[0018] (composition) The titanium porous body is made of titanium. When made of titanium, a titanium porous body having high electrical conductivity and a certain relative density can be obtained. The titanium content of the titanium porous body 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 determined by taking into account not only the metal components but also impurities such as gas components such as oxygen. In other words, the purity of titanium can be determined by subtracting the total content of impurities, including metal components and gas components, from 100% by mass.

[0019] The porous titanium body may contain Fe as an impurity, and the Fe content may be, for example, 0.25% by mass or less. The porous titanium body may also contain Ni, Cr, Al, Cu, Zn, and Sn as unavoidable impurities resulting from the manufacturing process. It is preferable that the content of each of Ni, Cr, Al, Cu, Zn, and Sn is less than 0.10% by mass, and that the total content of these elements is less than 0.30% by mass.

[0020] The oxygen content of the porous titanium body is not particularly limited, but is preferably 0.6% by mass or more and 2.0% by mass or less. If the oxygen content is 0.6% by mass or more, good breathability is likely to be maintained even when compressed for use. Furthermore, if the oxygen content is 2.0% by mass or less, the porous titanium body is prevented from becoming more brittle, making it less likely to break during handling. The oxygen content may be 0.9% by mass or more and 2.0% by mass or less. The oxygen content can be measured by inert gas fusion-infrared absorption spectroscopy.

[0021] The titanium porous body may have a purity equivalent to pure titanium grades 1 to 4, typically grades 1 to 2, of JIS H 4600 (2012), excluding the oxygen content.

[0022] (Thickness) The thickness of the sheet-shaped titanium porous body is 80 μm or more, and may be, for example, 80 μm or more and 400 μm or less. For example, a porous titanium porous body of such a certain thickness may be required for the porous transport layer of a PEM water electrolysis device. Furthermore, if the thickness is too thin, it may be difficult to control the peak pore diameter to a predetermined value, as described below. On the other hand, if the thickness is too thick, the PEM water electrolysis device may become large. The thickness of the titanium porous body may be, for example, 350 μm or less, or even 300 μm or less. The thickness of the titanium porous body may be 100 μm or more, 130 μm or more, or 160 μm or more.

[0023] The thickness 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 of 10 mm in diameter and a measurement accuracy of 0.001 to 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.

[0024] The term "sheet-like" in relation to the titanium porous body means a plate-like or foil-like body having a thickness smaller than the dimensions in a plan view, and the shape in a plan view is not particularly limited.

[0025] (peak pore diameter) A large number of pores are formed in porous titanium. The diameter and volume of each pore can be measured by mercury intrusion porosimetry, which gives a pore size distribution showing the relationship between the diameter and volume of each pore. Mercury intrusion porosimetry can be performed using an Autopore IV9500 manufactured by Micromeritec. In this case, the mercury intrusion pressure is 14 to 227 MPa, the measurement mode is the pressure increase process, and the measurement cell volume is 3.9 cm. 3 Measurements can be made on a 0.35 to 0.50 g porous titanium sample, assuming a mercury contact angle of 141.3° and a mercury surface tension of 484 dyn / cm. The measurement results can be plotted on a graph, as shown in Figure 1, with the pore diameter on the horizontal axis and the pore volume on the vertical axis.

[0026] The pore size distribution of a porous titanium body will have at least one peak. When the pore size distribution has multiple peaks, the diameter of the pore at the peak top of the highest peak will be referred to as the peak pore size.

[0027] The porous titanium body of the present invention has a peak pore diameter of 6.5 μm or less. If the peak pore diameter is greater than 6.5 μm, for example, when used as a porous transport layer in a PEM water electrolysis system, the porous titanium body may be pressed against the surface of the electrolyte membrane, resulting in potential damage. The peak pore diameter is preferably 5.5 μm or less, and more preferably 4.5 μm or less. If an appropriate paste is used during the production of the porous titanium body, the pore volume and diameter tend to be uniform throughout the porous titanium body, resulting in a small peak pore diameter. However, if the peak pore diameter is too small, the air permeability or liquid permeability of the porous titanium body decreases. For this reason, the peak pore diameter is preferably 1.5 μm or more, and more preferably 2.5 μm or more.

[0028] The porous titanium body has a three-dimensional network structure in which powder particles are bonded together and pores are formed between the powder particles. In many cases, the inside of the skeleton of the porous titanium body, which is made up of powder particles bonded together, is solid rather than hollow.

[0029] (I value) As described above, the porous titanium body of the present invention is capable of suppressing damage to the electrolyte membrane of, for example, a PEM water electrolysis device, and also has excellent breathability and required electrical conductivity.

[0030] More specifically, the porous titanium body is characterized by the following formula (1): I = [Air permeability (μm / Pa·s) × Electrical conductivity (kS / cm)] / [Peak pore diameter (μm)] 2 The I value calculated by the following equation is 4.0 or more. As mentioned above, even if a porous titanium body has a relatively small peak pore size, it can exhibit excellent air permeability and high electrical conductivity as long as the I value is 4.0 or more. Generally, porous titanium bodies with excellent air permeability also exhibit excellent performance in terms of liquid permeability.

[0031] The I value is preferably 5.0 or more, more preferably 6.0 or more, even more preferably 7.0 or more, and particularly preferably 8.0 or more. The larger the I value, the better, but there are cases where the I value is, for example, 15.0 or less.

[0032] In the above formula (1), air permeability is measured using a Gurley densometer in accordance with ISO-5636. However, the vent size used for measuring air permeability is 6 mm instead of 22 mm. Electrical conductivity is measured using the four-probe method with a Mitsubishi Analytech Loresta GP MCP-T610 low resistivity meter and its corresponding probe checker, the MCP-TRPS RMH311. For example, air permeability can range from 5 μm / Pa·s to 100 μm / Pa·s, and electrical conductivity can range from 3.0 kS / cm to 7.0 kS / cm. However, as long as the I value is 4.0 or higher, the individual values ​​of air permeability and electrical conductivity are not important.

[0033] (Application) The porous titanium body can be particularly suitably used for the porous transport layer (PTL) of a PEM water electrolysis device. A PEM water electrolysis device may include an anode, a cathode, an electrolyte membrane such as a perfluorocarbon sulfonic acid membrane disposed between the anode and the cathode and having electrode catalyst layers of a platinum group metal or the like provided on both sides, and a porous transport layer disposed between each electrode catalyst layer of the electrolyte membrane and the anode or cathode, respectively.

[0034] In the PEM water electrolysis device described above, when water is supplied to the anode and a voltage is applied, the water moves through the porous transport layer on the anode side and reaches the electrode catalyst layer, where it decomposes, producing oxygen and protons (H + The protons pass through the electrolyte membrane on the anode side and move from the anode to the cathode, where they acquire electrons at the electrode catalyst layer on the cathode side, generating hydrogen on the cathode side. Meanwhile, oxygen passes through the porous transport layer and moves to the discharge channel, where it is discharged outside the device.

[0035] In such PEM water electrolysis systems, the space where the porous transport layer is located, particularly on the anode side, is subject to strongly acidic and strongly oxidizing conditions. However, a titanium porous body with high corrosion resistance can be used successfully as a porous transport layer in such extremely harsh environments. Furthermore, as described above, the titanium porous body of the present invention has the required air permeability or liquid permeability and electrical conductivity required for a porous transport layer, and can suppress damage to the electrolyte membrane. Therefore, the titanium porous body of the present invention can be suitably used as a porous transport layer on the anode side of a PEM water electrolysis system.

[0036] In addition to the PEM-type water electrolysis device described above, the use of titanium porous bodies in organic electrolysis synthesis using a PEM-type reactor is also being considered. In such devices, electrolysis is carried out by passing protons through a proton exchange membrane. The titanium porous bodies described here may also be well suited for organic electrolysis synthesis using a PEM-type reactor. The titanium porous bodies of the embodiments described here can be used as a porous transport layer (PTL) on the anode side of an electrolysis device that uses a proton exchange membrane. [Example]

[0037] Next, a prototype of the porous titanium body of the present invention was produced and its effects were confirmed, which will be described below. However, the description here is for illustrative purposes only and is not intended to be limiting.

[0038] HDH powder was used as the titanium powder, and a titanium porous body was produced by the paste method or the pressureless deposition method, as shown in Table 1. The titanium powder had a titanium content of 99% by mass or more, a hydrogen content of 0.05% by mass or less, and an oxygen content of approximately 0.4% by mass. The titanium powder was adjusted to the particle size shown in Table 1 using a sieve before use.

[0039] In the pressureless deposition method, the raw material powder was deposited on a carbon setter without pressure, and the deposited thickness was adjusted by leveling. Then, the mixture was heated to the sintering temperature shown in Table 1 and sintered.

[0040] In the paste method, titanium powder was mixed with polyvinyl butyral as an organic binder and isopropyl alcohol as an organic solvent to prepare a paste. The paste contained 9 g of organic binder and 36 g of organic solvent per 100 g of titanium powder, and contained no water or foaming agent. No bubbles were observed in the paste obtained after mixing. In Table 1, the "high viscosity" category refers to a paste prepared by mixing the titanium powders described above, whose viscosity was measured using a rheometer at a shear rate of 1 (1 / s), resulting in a viscosity of 2600 mPa·s. On the other hand, the "low viscosity" category refers to a paste prepared using a different device, method, or conditions than the "high viscosity" category, resulting in a viscosity of 1600 mPa·s measured using a rheometer at a shear rate of 1 (1 / s). The low viscosity was thought to be due to insufficient dissolution of the organic binder in the organic solvent.

[0041] Next, the paste was applied in sheet form to a PET sheet of a release layer, and this was dried at 120°C to remove the organic solvent, obtaining a molded body, which was then peeled off from the release layer. The molded body was then heated at 360°C in an air atmosphere to remove the binder, and then heated to the sintering temperature shown in Table 1 for sintering.

[0042] For each of the sheet-shaped titanium porous bodies produced in this manner, the thickness, peak pore size, air permeability, and conductivity were measured using the methods described above, and the I value was calculated. The results are shown in Table 1. Note that the titanium porous bodies of all Examples had a titanium content of 97% by mass or more and an oxygen content of 0.9% by mass or more and 2.0% by mass or less.

[0043] [Table 1]

[0044] The titanium porous bodies of Examples 1 to 12 exhibited good values ​​for thickness, peak pore diameter, air permeability, and electrical conductivity, with an I value of 4.0 or higher. Since the titanium porous bodies of Examples 1 to 12 thus had appropriately sized peak pore diameters, it is believed that they can suppress damage to the surface of electrolyte membranes and the like. Furthermore, the titanium porous bodies of Examples 1 to 12 exhibited excellent air permeability or liquid permeability, as well as the required electrical conductivity.

[0045] On the other hand, in the titanium porous bodies of Comparative Examples 1 to 3, due to their thin thickness, the peak pore diameter was large and the I value was smaller than 4.0. In Comparative Examples 4 to 6, the particle size of the titanium powder was 10 μm to 45 μm, and some titanium powder had a large particle size, so the I value of the titanium porous bodies was 4.0 or more, but the peak pore diameter was large. In Comparative Examples 7 to 9, the viscosity of the paste was low, so the titanium porous bodies either had a large peak pore diameter or a small I value. Note that, although the peak pore diameter tends to become smaller as the sintering temperature increases, the peak pore diameter of all of the titanium porous bodies of Comparative Examples 1 to 7 became somewhat large.

[0046] The porous titanium body of Comparative Example 10 had a large peak pore diameter and a small I value. This is thought to be because the titanium powder was packed more sparsely with the pressureless deposition method than with the paste method. In Comparative Example 11, the target thickness of the porous titanium body was too thin to be produced by leveling using the pressureless deposition method, and production of the porous titanium body failed.

[0047] From the above, it has been suggested that the porous titanium body of the present invention has pores of an appropriate size, and may be able to exhibit excellent air or liquid permeability and required electrical conductivity while suppressing damage to the surface of the electrolyte membrane, etc.

Claims

1. A titanium porous body, The thickness is 80 μm or more, and the sheet is in a sheet form. In a pore size distribution showing the relationship between pore diameter and volume, the peak pore size of the highest peak is 6.5 μm or less, A porous titanium body having an I value of 4.0 or more, calculated from the air permeability, electrical conductivity and the peak pore diameter according to the following formula (1): I = [air permeability (μm / Pa·s) × electrical conductivity (kS / cm)] / [pore size (μm)] 2 (1)

2. 2. The titanium porous body according to claim 1, wherein the peak pore size is 1.5 μm or more and 6.5 μm or less.

3. 3. The titanium porous body according to claim 1, wherein the thickness is 80 μm or more and 400 μm or less.

4. 3. The titanium porous body according to claim 1, wherein the titanium content is 97% by mass or more and the oxygen content is 0.6% by mass or more and 2.0% by mass or less.

5. 5. The titanium porous body according to claim 4, having a titanium content of 98 mass % or more.

6. 5. The titanium porous body according to claim 4, wherein the oxygen content is 0.9% by mass or more and 2.0% by mass or less.

7. 3. The titanium porous body according to claim 1, which has a thickness of 100 μm or more and 350 μm or less.

8. 3. The titanium porous body according to claim 1, wherein the peak pore size is 2.5 μm or more and 5.5 μm or less.

9. A titanium porous body according to claim 1 or 2, used in a porous transport layer of a PEM-type water electrolysis device.

10. The titanium porous body according to claim 9, wherein the porous transport layer is an anode-side porous transport layer in which water is decomposed to generate oxygen and protons.

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