Titanium porous body, and titanium porous body manufacturing method

Abstract

The titanium porous body according to this invention has a sheet shape and has pores, wherein, on at least one surface, an average value of areas of the pores opening to the surface is more than or equal to 10 µm2 and less than or equal to 17 µm2, a standard deviation of the areas of the pores is 20 µm2 or less, and a number of the pores present in a rectangular region having an area of 40,000 µm2 and an aspect ratio of 4:5 is 250 or more.

Description

[Technical Field]

[0001] This invention relates to a titanium porous body and a method for producing a titanium porous body.[Background Art]

[0002] A titanium porous body produced by sintering titanium powder or the like has gas and liquid permeability due to its pores, and electrical conductivity, as well as high corrosion resistance due to formation of a passive film on its surface.

[0003] The use of such a titanium porous body as a porous transport layer (PTL) and the like in an environment where corrosion may occur in a polymer electrolyte membrane ( PEM) type water electrolytic device, is under consideration. In particular, hydrogen produced by water electrolysis devices such as the PEM type using electricity derived from renewable energy sources is referred to as green hydrogen, which is highly anticipated in recent years where the movement toward the realization of a decarbonized society is being accelerated.

[0004] As a related art, for the purpose of "providing a titanium porous plate that can be brought into sufficient contact with other adjacent members and that allows good circulation and diffusion of fluids such as liquids and gases, as well as a water electrolysis electrode and a water electrolysis device made of that titanium porous plate", Patent Literature 1 proposes "a titanium porous plate made of a sintered body of titanium or titanium alloy, wherein the titanium porous plate has a three-dimensional network structure with communicating pores that opens on the surface of the titanium porous plate and communicate with internal pores, an opening ratio of one main surface is smaller than that of the other main surface, and a difference between the opening ratios of the one main surface and the other main surface is 10% or more". It discloses that, in a "titanium-containing slurry formation step" during the production of the "titanium porous plate", raw material powder is mixed with a water-soluble resin binder (methyl cellulose), an organic solvent (neopentane, hexane, and butane), a plasticizer (glycerin and ethylene glycol), water as a solvent, a foaming agent, and optionally a surfactant (alkylbenzene sulfonate) to produce a titanium-containing slurry.

[0005] Further, for the same purpose as described above, Patent Literature 2 discloses "a titanium porous plate made of a sintered body of titanium or titanium alloy, wherein the titanium porous plate has a three-dimensional network structure with communicating pores that open on the surface of the titanium porous plate and communicate with internal pores, the titanium porous plate has a structure in which a first layer and a second layer are laminated in a thickness direction, and an average pore diameter of the second layer is larger than that of the first layer". In Patent Literature 2, to produce such a "porous titanium plate material", a "first titanium-containing slurry" is used, in which "raw material powder is mixed with a water-soluble resin binder (methyl cellulose), an organic solvent (neopentane, hexane, and butane), a plasticizer (glycerin and ethylene glycol), water as a solvent, and optionally a surfactant (alkylbenzene sulfonate)", and a "second titanium-containing slurry" is used, in which the "raw material powder is mixed with a water-soluble resin binder (methyl cellulose), an organic solvent (neopentane, hexane, and butane), a plasticizer (glycerin and ethylene glycol), water as a solvent, and optionally a surfactant (alkylbenzene sulfonate), and which further contains a foaming agent".[Citation List][Patent Literature]

[0006] [PTL 1] WO 2022 / 210421 A1 [PTL 2] WO 2022 / 210681 A1 [Summary of Invention][Technical Problem]

[0007] When the titanium porous body is used as a porous transport layer in a PEM type water electrolysis device, the titanium porous body may be pressed against an electrolyte membrane and incorporated therein. In this case, if the pores in the titanium porous body are larger, the electrolyte membrane pressed against the titanium porous body may partially penetrate into the pores, causing significant deformation in regions close to the pores and potentially damaging the electrolyte membrane.

[0008] Therefore, to prevent damage to the electrolyte membrane, it is desirable that the titanium porous body have smaller pores that open to the surface facing the electrolyte membrane, and that a large number of such pores be present on that surface. A titanium porous body having a large number of pores is difficult to cause damage to the electrolyte membrane as described above, and can serve as a porous transport layer with good air and liquid permeability.

[0009] In the techniques described in Patent Literatures 1 and 2, it appears that the titanium powder in the paste may aggregate during the production of the titanium porous body. If the titanium powder aggregates in the paste, the resulting uneven distribution of the titanium powder may result in the formation of large pores on the surface of the titanium porous body after production.

[0010] An object of the present invention is to provide a titanium porous body having a surface on which a relatively large number of fine pores are formed, and a method for producing the titanium porous body.[Solution to Problem]

[0011] As results of extensive studies, the inventors have found that a titanium porous body having a large number of fine pores formed on the surface can be obtained using a paste that has mixed titanium powders having a relatively small particle size and does not contain water but contains an alcohol as an organic solvent, the paste including a dispersant containing coal tar naphtha, and then drying, debinding and sintering the paste. This would be because the specific dispersant effectively prevents the titanium powder from agglomerating or becoming unevenly distributed in the paste.

[0012] The titanium porous body according to this invention has a sheet shape and has pores, wherein, on at least one surface, an average value of areas of the pores opening to the surface is more than or equal to 10 µm 2< and less than or equal to 17 µm 2< , a standard deviation of the areas of the pores is 20 µm 2< or less, and a number of the pores present in a rectangular region having an area of 40,000 µm 2< and an aspect ratio of 4:5 is 250 or more.

[0013] The titanium porous body preferably has a thickness of more than or equal to 40 µm and less than or equal to 500 µm.

[0014] It is preferable that the surface of the titanium porous body has the average value of areas of the pores of more than or equal to 10 µm 2< and less than or equal to 14 µm 2< .

[0015] It is preferable that the surface of the titanium porous body has a standard deviation of the areas of the pores of 17 µm 2< or less.

[0016] The surface of the titanium porous body preferably has a number of the pores of 300 or more present in a rectangular region having an area of 40,000 µm 2< and an aspect ratio of 4:5.

[0017] The titanium porous body may have a titanium content of 97% by mass or more.

[0018] The method for producing a titanium porous body according to this invention is a method for producing a titanium porous body having a sheet shape, the titanium porous body having pores, the method comprising: a drying step of drying a paste that contains titanium powder having an average particle size of 25 µm or less, an organic binder, and an organic solvent and does not contain water as a solvent to obtain a formed body having a sheet shape; a binder removal step of heating the formed body to volatilize the organic binder; and a sintering step of heating the formed body after the binder removal step to sinter the titanium powder, wherein the organic solvent in the paste is an alcohol, and the paste comprises a dispersant containing coal tar naphtha.

[0019] In the above producing method, it is preferred that a content of the dispersant in the paste is more than or equal to 0.01% by mass and less than or equal to 0.3% by mass.

[0020] The above producing method can produce a titanium porous body having a thickness of more than or equal to 40 µm and less than or equal to 500 µm.

[0021] In the above producing method, it is preferable that the titanium powder has an average particle size of 18 µm or less.

[0022] In the above producing method, it is preferable that a drying temperature in the drying step is higher than or equal to 90°C and lower than or equal to 165°C.[Advantageous Effects of Invention]

[0023] The titanium porous body according to this invention has a surface on which a relatively large number of fine pores are formed. The method for producing a titanium porous body according to this invention is suitable for producing such a titanium porous body.[Description of Embodiments]

[0024] Embodiments of the present invention will be described in detail below.

[0025] The titanium porous body according to an embodiment of this invention has a sheet shape and has pores. When the area and number of pores opening to at least one surface of the titanium porous body are confirmed, an average value of areas of the pores is more than or equal to 10 µm 2< and less than or equal to 17 µm 2< , a standard deviation of the areas of the pores is 20 µm 2< or less, and a number of the pores present in a rectangular region having an area of 40,000 µm 2< and an aspect ratio of 4:5 is 250 or more.

[0026] If a relatively large number of relatively fine pores are thus formed on at least one surface of the titanium porous body, it is believed that when the titanium porous body is used as a porous transport layer in a PEM type water electrolysis device, damage to the electrolyte membrane pressed against the surface can be effectively suppressed. This would be because the pores opening to the surface are fine so that it is difficult for the electrolyte membrane to partially penetrate into these pores, and also because if there are a large number of pores, the titanium porous body is pressed against the electrolyte membrane, thereby dispersing the load acting on the electrolyte membrane. Therefore, it can be said that the titanium porous body can be suitably used as a porous transport layer in a PEM type water electrolysis device.

[0027] The production of the titanium porous body can employ a method that involves sequentially drying a paste containing titanium powder, an organic binder, and an organic solvent, removing the binder, and sintering the titanium powder, although not limited thereto. The organic solvent of the paste is an alcohol, and the paste does not contain water as a solvent. In such a producing method, it is particularly important to use titanium powder having a predetermined small particle size and to include a dispersant containing coal tar naphtha in the paste. It is believed that a small amount of coal tar naphtha in the dispersant adheres to the surface of the titanium powder to make it easier for the titanium powder particles to slide against each other, thereby acting to disperse the titanium powder well in the paste. This prevents the titanium powder from agglomerating or becoming unevenly dispersed in the paste, and the titanium powder particles, which have small particle sizes, can be bonded together in a relatively uniform arrangement during sintering. This results in a titanium porous body in which a large number of fine pores are formed on at least one surface. Typically, a large number of fine pores are often formed on a surface opposite to the above surface of the titanium porous body.(Composition)

[0028] The titanium porous body is made of titanium. If it is made of titanium, a titanium porous body having high electrical conductivity can be obtained with a certain relative density. 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 may be, for example, 99.8% by mass or less, or 99% by mass or less, although not particularly limited thereto. The titanium content refers to the purity of titanium, taking into account not only the metallic component but also impurities in gas components such as oxygen. Therefore, the titanium content is determined by subtracting the total content of metallic components and impurity components, including gas components, from 100% by mass.

[0029] The titanium porous body may contain Fe as an impurity, and an Fe content may be 0.25% by mass or less, for example. The titanium porous body may also contain Ni, Cr, Al, Cu, Zn, and Sn as unavoidable impurities resulting from the production process, for example. It is suitable that the content of each of Ni, Cr, Al, Cu, Zn, and Sn is less than 0.10% by mass, and the total content thereof is preferably less than 0.30% by mass.

[0030] The titanium porous body may, for example, have an oxygen content of 0.9% by mass or more and 2.0% by mass or less, although not limited thereto. The oxygen content can be measured by an inert gas fusion-infrared absorption method.

[0031] The titanium porous body may have a purity corresponding to pure titanium types 1-4 in JIS H 4600 (2012), typically type 1 or 2, except for the oxygen content.(Sheet Dimension)

[0032] The thickness of the titanium porous body having the sheet shape may be more than or equal to 40 µm and less than or equal to 500 µm. For example, the titanium porous body having such a relatively large thickness may be required for the porous transport layer of the PEM type water electrolysis device. On the other hand, if the thickness t is too large, the PEM type water electrolysis device may become larger. The thickness of the titanium porous body may be, for example, 400 µm or less, 350 µm or less, 300 µm or less, 250 µm or less, or 200 µm or less, while it may be 40 µm or more, or 80 µm or more.

[0033] The thickness is measured at five points in total: four at the periphery and one at the center of the titanium porous body, using a digital thickness gage having a flat measuring element of 10 mm in diameter and a measurement accuracy of 0.001 to 0.01 mm, such as Mitutoyo's digital thickness gage (Model No. 547-321), for example. An average of these measurements is used as an average value. If the titanium porous body in the form of the sheet is rectangular in the planner view, the above four points of the periphery should be the four points of the four corners.

[0034] The area of the surface of the titanium porous body having the sheet shape in a planner view is not particularly limited because it may be determined appropriately depending on the application, but it may be, for example, more than or equal to 70 mm 2< and less than or equal to 350,000 mm 2< , or 40,000 mm 2< to 600,000 mm 2< .

[0035] It should be noted that the term "sheet shape" for the titanium porous body means a plate shape or a foil shape having a smaller thickness with respect to planar view dimensions, and there is no particular limitation on the shape in the planar view.(Pore)

[0036] The titanium porous body is composed of titanium powders bonded together and has a three-dimensional network structure with pores formed between the titanium powders bonded together. As an example, the titanium porous body may have a sponge titanium-shaped three-dimensional network structure backbone. The titanium porous body produced with titanium fibers tends to have a non-woven three-dimensional network structure. In many cases, the interior of the framework composed of titanium powders bonded to each other in the titanium porous body is solid rather than hollow.

[0037] Among the pores formed in the titanium porous body, the average value of the areas of the large number of pores opening on at least one surface is more than or equal to 10 µm 2< and less than or equal to 17 µm 2< . The standard deviation of the areas of the pores of the surface is 20 µm 2< or less. If the majority of pores on at least one surface thus have a relatively small area, the surface can be said to be generally smooth, and damage to the electrolyte membrane in the PEM type water electrolysis device can be effectively suppressed. From this point of view, the average value of the areas of the pores on the surface is preferably more than or equal to 10 µm 2< and less than or equal to 14 µm 2< . From the same point of view, it is preferable that the standard deviation of the areas of the pores on the surface is 17 µm 2< or less. If the average value of the areas of the pores is too small, the air permeability or liquid permeability may decrease. It is acceptable for a small number of pores with a relatively large area to exist on the surface.

[0038] Further, the number of pores present in the rectangular region on the surface having an area of 40,000 µm 2< and an aspect ratio of 4:5 is 250 or more, preferably 300 or more. The presence of many fine pores as described above on the surface easily ensures the required air permeability or liquid permeability, while at the same time achieving surface smoothness. The number of the pores in the rectangular region may be, but not limited to, 500 or less.

[0039] The average value and standard deviation of the areas of the pores opening to the surface as described above, as well as the number of pores in the predetermined rectangular region, are measured using a scanning electron microscope (Keyence Ultra-Deep Multi-Angle Lens VHX-D510). More specifically, an SEM image is taken at magnifications of 1500 for the rectangular region on the surface of the titanium porous body, the region having an area of 40,000 µm 2< and an aspect ratio of 4:5. Then, the SEM image is analyzed using a scanning electron microscope, and a half value of the maximum detected brightness value for the SEM image is determined to be a threshold value, and a closed region whose brightness is in the range of 0 to the threshold value is determined to be one pore. At this time, the SEM image may be subjected to binarization processing as necessary. After the binarization processing, small pixel removal processing of 50 pixels or less (processing of black pixels after binarization processing) is performed, and hole filling processing of 50 pixels or less (processing of white pixels after binarization processing) is then performed. This is used to calculate the number and area of each pore, and to obtain the standard deviation as a square root of the variance. Such an analysis of the SEM image is carried out for five rectangular regions on the surface of the titanium porous body, at least part of which is offset from one another, and an average value of the areas of the pores, a standard deviation value, and an average of the number of pores in those rectangular regions are determined to be the average value of the areas of the pores and the standard deviation value, and the number of pores in the rectangular region, respectively, of the titanium porous body. In the case of a titanium porous body that is square or rectangular in planner view, the five rectangular regions are the five rectangular regions at the center and four corners.(Use)

[0040] The titanium porous body described above is particularly suitable for use in the porous transport layer of the PEM type water electrolysis device. The PEM type water electrolysis device may have an anode and a cathode, an electrolyte membrane such as a perfluorocarbon sulfonate membrane with electrode catalyst layers such as platinum group metals on both sides, the electrolyte membrane being placed between the anode and cathode, and a porous transport layer placed between each electrode catalyst layer of the electrolyte membrane and the anode or cathode.

[0041] When water is fed to the anode and voltage is applied to the anode in the PEM type water electrolysis device described above, the water that moves through the porous transport layer on the anode side and reaches the electrode catalyst layer is decomposed to produce oxygen and protons (H +< ). The protons move from the anode to the cathode through the electrolyte membrane on the anode side, gain electrons in the electrode catalyst layer on the cathode side and generate hydrogen on the cathode side. Oxygen, on the other hand, moves through the porous transport layer to the discharge side channel and is discharged to the outside of the device.

[0042] In such a PEM type water electrolysis device, the space where the porous transport layer is placed, especially on the anode side, is subject to strong acidic and oxidizing conditions. However, if the titanium porous body has high corrosion resistance, it can be well used as a porous transport layer in such an extremely harsh environment. Further, as described above, the titanium porous body according to this invention has a large number of fine pores formed on at least one surface, so that, when the titanium porous body is placed in the PEM type water electrolysis device while pressing its surface side against the electrolyte membrane, damage to the electrolyte membrane can be suppressed.

[0043] In addition to the PEM type water electrolysis system described above, the use of the titanium porous body is also being considered for organic electrolytic synthesis using a PEM type reactor. In such a device, electrolysis is also performed by passing protons through a proton exchange membrane. It is believed that the titanium porous body described herein has the potential to be used well for organic electrolytic synthesis using PEM type reactors and can be used as a porous transport layer (PTL) on the anode side of the electrolysis device that uses a proton exchange membrane.(Producing Method)

[0044] The titanium porous body described above can be produced, for example, by performing the following steps in this order: a paste preparation step, a paste application step, a drying step, a binder removal step, and a sintering step. However, if the paste has already been prepared and obtained, or if the paste has been applied in the form of the sheet, the paste preparation step and further the paste application step may be omitted.

[0045] First, in the paste preparation step, a paste containing titanium powder, an organic binder and an organic solvent is prepared.

[0046] Here, the average particle size of the titanium powder contained in the paste can be 25 µm or less, preferably 18 µm or less. By using such a titanium powder with a small particle size and further using a specific dispersant as described below, it is possible to achieve a smooth surface for the titanium porous body to be finally produced. If the average particle size of the titanium powder is more than 25 µm, the pores on the surface of the titanium porous body tend to become large even if the predetermined dispersant is used. In addition, from the viewpoints of preventing an increase in production cost by using relatively inexpensive titanium powder and of facilitating the handling of the titanium powder, the average particle size of the titanium powder may be 5 µm or more, or even 10 µm or more. The average particle size means the particle size at which the cumulative distribution on a volume basis is 50% in the particle size distribution obtained by the laser diffraction scattering method.

[0047] Titanium powder with high purity is suitable, and pure titanium powder can be used. The titanium powder may have a titanium content of 99% by mass or more. The titanium powder can be ground powder, spherical powder such as atomized powder, or any other powder. As titanium powder, hydrogenated titanium powder, which is obtained by hydrogenation and pulverization of titanium raw materials such as sponge titanium, can also be used, and in this case, the hydrogen content of the hydrogenated titanium powder is preferably 5% or less by mass. When the titanium hydride powder is used, a dehydrogenation process may be performed between the binder removal and sintering steps described below, in a vacuum or other reduced pressure atmosphere in a temperature range of 500°C or higher and 650°C or lower. The hydrogenated dehydrogenated titanium powder (so-called HDH powder) obtained by subjecting the titanium hydride powder to dehydrogenation can also be used.

[0048] For example, as the organic binder used for the paste, various organic binders can be selected and used as needed, and they can be, for example, methyl cellulose-based, polyvinyl alcohol-based, ethyl cellulose-based, acrylic, polyvinyl butyral-based binders, and the like. Organic binders that exhibit hydrophobicity are preferred. However, they are not limited to the above-listed substances. The organic solvent should be an alcohol (ethanol, isopropanol, terpineol, butylcarbitol, etc.). As an example, the organic binder can be polyvinyl butyral and the organic solvent can be isopropyl alcohol. The paste may further contain a plasticizer (glycerin, ethylene glycol, or the like) and a surfactant (alkylbenzene sulfonate, or the like).

[0049] The paste does not contain water as a solvent. The paste is also preferably be free of a foaming agent. This is to prevent agglomeration of titanium powder in the paste and generation of pinholes on the surface of the titanium porous body due to the difference in drying behavior between the organic solvent and water during drying, when the paste contains water. Also, when the paste does not contain a foaming agent, local large voids caused by foaming of the foaming agent will not be formed in the titanium porous body. As a result, the titanium porous body tends to have a smooth surface and is less prone to cracking during handling. Therefore, here, the foaming step that generates bubbles in the paste is not performed. It should be noted that the paste may be free of water as a solvent, and the inclusion of water that may unintentionally be mixed into the paste, such as moisture absorption, is acceptable.

[0050] The paste also contains a dispersant containing coal tar naphtha. It is believed that the use of such a dispersant will disperse the titanium powder in the paste that does not contain water to prevent its aggregation or uneven distribution, thereby suppressing the formation of large pores on the surface of the titanium porous body. Furthermore, the coal tar naphtha is a hydrocarbon mixture with a relatively low boiling point, and is thought to volatilize along with the organic solvent and organic binder during the drying and binder removal steps, so that it does not have a significant effect on the titanium porous body.

[0051] In particular, when the dispersant contains 20% by mass or more of coal tar naphtha, the dispersing effect of the titanium powder can be more effectively exhibited. The dispersant may contain components other than the coal tar naphtha, and it may typically contain amine salts of polycarboxylate. To disperse the titanium powder more effectively, the content of the dispersant in the paste is preferably more than or equal to 0.01% by mass and less than or equal to 0.3% by mass, more preferably more than or equal to 0.01% by mass and less than or equal to 0.1% by mass, and even more preferably more than or equal to 0.05% by mass and less than or equal to 0.1% by mass.

[0052] The paste can be prepared by mixing the titanium powder, the organic binder, the organic solvent, and the like as described above, using, for example, a mixer with an agitator, a rotary mixer, a triple roll mill, and the like. At this time, the mixture may be pulverized using a vibration mill, a bead mill, or other pulverizing mixers.

[0053] In the paste application step, the above paste is relatively thinly applied onto a substrate. The substrate can be provided with a release layer in advance. In this case, the paste is applied on the substrate through the release layer. If the substrate is provided with the release layer, it is easier to separate the formed body obtained by drying the paste after the drying step from the substrate.

[0054] As the substrate, resin substrates that are available with a somewhat lower cost are preferred. The resin substrate also has an advantage that it is flexible and is easily handled. Specific materials for the resin substrate include polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate), and polyvinyls such as polyethylene, polypropylene, polystyrene, and polyvinyl alcohol, among which PET is preferable in that it is inexpensive and can easily separate the formed body from the substrate after the drying step.

[0055] Providing the release layer on the substrate is optional, but when providing the release layer, a silicone coating or the like can be used as the release layer. For example, the release layer can be provided on the substrate by selecting a substrate in which a material such as CERAPEEL (registered trademark) from Toray is previously applied. The provision of the release layer on the substrate allows the resulting formed body in the form of the thin film obtained after the drying step to be easily separated from the substrate.

[0056] In the drying step, the paste is dried on the substrate, for example, in an oven, a dryer or the like. This causes the organic solvent in the paste to evaporate, and provides a formed body in a form of a sheet on the substrate.

[0057] The drying temperature can be higher than or equal to 90°C and lower than or equal to 165°C. By heating and drying the paste at the temperature in this range, the drying can be completed in a relatively short period of time while preventing boiling of the organic solvent and the like in the paste. As a result, localized surface roughness and pinhole formation caused by boiling of the organic solvent components and / or prolonged heating are suppressed, making it easier to obtain a titanium porous body with a smooth surface.

[0058] The drying time is not limited and can be determined as needed, for example, 5 minutes or more and 300 minutes or less. From the viewpoint of effectively removing the organic solvent from the paste, it is desirable to perform the drying while discharging a gas from a furnace, dryer or the like. When evacuating the interior of the furnace or dryer, the interior of the furnace or dryer can in a reduced pressure atmosphere, or can have the same pressure as the outside pressure by feeding a gas such as the air atmosphere.

[0059] At the end of the drying step, and prior to the binder removal step, the formed body obtained by drying the paste may be separated from the substrate by peeling or the like. If the formed body is separated from the substrate at this stage, it is possible to prevent the titanium porous body from being deformed into a poor sheet shape due to deformation of the substrate when the formed body is subjected to the subsequent binder removal and sintering steps together with the substrate, and it is also possible to suppress contamination of the titanium porous body due to the material of the substrate. When the resin substrate is used, the formed body can be easily released from the substrate. Metal substrates may be difficult to separate the formed body from the substrate.

[0060] Next, in the binder removal step, the formed body is heated in a furnace to volatilize and remove the organic substances such as the organic binder in the formed body. For example, in the binder removal step, the formed body may be heated at a temperature of 300°C or higher and 450°C or lower for a period time of 3 hour or longer and 12 hours or shorter.

[0061] The formed body that has been subjected to the binder removal step is then subjected to a sintering step to sinter the titanium powder in the formed body. The conditions of the sintering step are not particularly limited as long as the titanium powder in the formed body is sintered. For example, in the sintering step, the formed body may be heated at a temperature of 700°C or more and 1000°C or less for a period time of 1 hour to 4 hours. Since the titanium porous body according to this embodiment is relatively thin, the titanium powder can be appropriately sintered by heating at a relatively low temperature for a short period of time. The atmosphere during sintering may be, for example, a vacuum of 1.0 x 10 -2< Pa or less, or an inert atmosphere of an Ar gas or a He gas.

[0062] After the sintering step, the titanium porous body is obtained. As described above, this titanium porous body has a large number of fine pores formed on at least one surface.[Examples]

[0063] Next, the titanium porous body according to the present invention was experimentally produced, and its effects were confirmed as described below. However, descriptions herein are merely for illustration, and are not intended to be limited thereto.

[0064] Titanium powder (HDH powder) with an average particle size of shown in Table 1 and a titanium content of 99% by mass or more was mixed with polyvinyl butyral as an organic binder and isopropyl alcohol as an organic solvent to prepare a paste. The paste did not contain any foaming agent.

[0065] In Examples 1 to 7 and Comparative Examples 2 and 4, the paste further contained a dispersant A. The dispersant A is SN Sparce 2190 manufactured by SAN NOPCO, which contains 42% by mass of coal tar naphtha and 58% by mass of an amine salt of polycarboxylate and the like.

[0066] In Comparative Example 1, a paste containing no dispersant was used. In Comparative Example 3, a paste containing a dispersant B was used. The dispersant B is SN Sparse 70 manufactured by SAN NOPCO, which contains 63% by mass of an aliphatic amide surfactant, 26% by mass of a nonionic surfactant, and 11% by mass of diethanolamine.

[0067] In all of Examples 1 to 7 and Comparative Examples 1 to 3, the mass ratio of titanium powder: organic binder: organic solvent was 100:9:36. The content of the dispersant in each paste of Examples 1 to 7 and Comparative Examples 2 to 4 is shown in Table 1.

[0068] The pastes of Examples 1 to 7 and Comparative Examples 1 to 3 did not contain water, but in Comparative Example 4, the organic solvent was reduced by 10% by mass from the paste of Example 1, and 10% by mass of water was added instead.

[0069] For each of Examples 1 to 7 and Comparative Examples 1 to 3, the above paste was applied in the form of a sheet onto a release layer provided on a PET sheet, which was heated and dried in an air atmosphere at the temperatures shown in Table 1 to remove the organic solvent, thereby obtaining a formed body. The formed body was then peeled off from the release layer and heated at 360°C in an air atmosphere to remove the binder. The titanium powder was then sintered by heating to 775°C in a vacuum atmosphere (1.0 x 10 -3< Pa or less) to produce a sheet-shaped porous titanium body having a surface area of 240,000 mm 2< and dimensions in a planner view of about 600 mm x 400 mm. In Comparative Example 4, the titanium powder in the paste was not dispersed but agglomerated, so the steps after application onto the PET sheet were not carried out and the production of the titanium porous body was abandoned.

[0070] For each of the titanium porous bodies produced as described above, the thickness, average value and standard deviation of the areas of the pores on the surface that was in contact with the release layer of the PET sheet during production, and the number of pores in the rectangular region were measured using the methods described above. Here, the titanium porous body was cut into five pieces, and each sample was observed using a scanning electron microscope. The scanning electron microscope used was a Keyence VHX-D510 ultra-deep multi-angle lens. Table 1 shows the results. In addition, the titanium porous bodies of all Examples had a titanium content of 97% by mass or more and an oxygen content of more than or equal to 0.9% by mass and less than or equal to 2.0% by mass. [Table 1]Producing MethodSheet-Shaped Titanium Porous BodyAverage Particle SizePasteDrying TemperatureThicknessPoreType of DispersantAmount of DispersantPresence or Absence of WaterAverage Value of AreasStandard Deviation of AreasNumber(µm)(% by mass)(°C)(µm)(µm 2< )(µm 2< )(Pieces)Example 115A0.1Absent1505001217320Example 215A0.1Absent1101001315323Example 315A0.1Absent150401416345Example 415A0.1Absent1501001315332Example 515A0.1Absent1502501415338Example 615A0.01Absent1501001214345Example 725A0.1Absent1501001720313Comp. 115Absent0Absent1501001663236Comp. 230A0.1Absent1501003455205Comp. 315B0.1Absent1501005158183Comp. 415A0.1Present-----

[0071] As can be seen from Table 1, all of the porous titanium bodies of Examples 1 to 7 had surfaces on which many fine pores were formed.

[0072] In contrast, in Comparative Example 1, no dispersant was added to the paste during production, so that the standard deviation of the areas of the pores on the surface of the titanium porous body was larger and the number of pores was smaller. In Comparative Example 2, the average particle size of the titanium powder used in the production was larger, so that the average value and standard deviation of the areas of the pores on the surface of the titanium porous body were both larger, and the number of pores was smaller. In Comparative Example 3, the dispersant B contained in the paste did not contain coal tar naphtha, so that the average value and standard deviation of the areas of the pores on the surface of the titanium porous body were larger, and the number of pores was smaller.

[0073] Further, to confirm the air permeability of each titanium porous body, the air permeability of each titanium porous body was measured using a Gurley densometer in accordance with ISO-5636. However, the size of the vent hole when measuring the air permeability was set to 6 mm instead of 22 mm.

[0074] The air permeability depends on the thickness of the titanium porous body, and the titanium porous body of Example 1 having a thickness of 500 µm had an air permeability of 5 µm / Pa·S or more. The titanium porous bodies of Examples 2, 4, 6 and 7 each having a thickness of 100 µm had an air permeability of 50 µm / Pa·S or more. The titanium porous body of Example 3 having a thickness of 40 µm had an air permeability of 100 µm / Pa·S or more. The titanium porous body of Example 5 having a thickness of 250 µm had an air permeability of 10 µm / Pa·S or more. All of Examples 1 to 7 had excellent air permeability according to the thickness.

[0075] In view of the foregoing, it was found that according to this invention, a titanium porous body having a surface on which a relatively large number of fine pores were formed could be obtained.

Claims

1. A titanium porous body having a sheet shape, the titanium porous body having pores, wherein, on at least one surface, an average value of areas of the pores opening to the surface is more than or equal to 10 µm2 and less than or equal to 17 µm2, a standard deviation of the areas of the pores is 20 µm2 or less, and a number of the pores present in a rectangular region having an area of 40,000 µm2 and an aspect ratio of 4:5 is 250 or more.

2. The titanium porous body according to claim 1, wherein a thickness is more than or equal to 40 µm and less than or equal to 500 µm.

3. The titanium porous body according to claim 1 or 2, wherein the average value of the areas of the pores is more than or equal to 10 µm2 and less than or equal to 14 µm2.

4. The titanium porous body according to claim 1 or 2, wherein the standard deviation of the areas of the pores is 17 µm2 or less.

5. The titanium porous body according to claim 1 or 2, wherein the number of the pores present in the rectangular region having the area of 40,000 µm2 and the aspect ratio of 4:5 is 300 or more on the surface.

6. The titanium porous body according to claim 1 or 2, wherein a content of titanium is 97% by mass or more.

7. A method for producing a titanium porous body having a sheet shape, the titanium porous body having pores, the method comprising: a drying step of drying a paste that contains titanium powder having an average particle size of 25 µm or less, an organic binder, and an organic solvent and does not contain water as a solvent to obtain a formed body having a sheet shape; a binder removal step of heating the formed body to volatilize the organic binder; and a sintering step of heating the formed body after the binder removal step to sinter the titanium powder, wherein the organic solvent in the paste is an alcohol, and the paste comprises a dispersant containing coal tar naphtha.

8. The method for producing a titanium porous body according to claim 7, wherein a content of the dispersant in the paste is more than or equal to 0.01% by mass and less than or equal to 0.3% by mass.

9. The method for producing a titanium porous body according to claim 7 or 8, wherein the titanium porous body produced has a thickness of more than or equal to 40 µm and less than or equal to 500 µm.

10. The method for producing a titanium porous body according to claim 7 or 8, wherein the titanium powder has an average particle size of 18 µm or less.

11. The method for producing a titanium porous body according to claim 7 or 8, wherein a drying temperature in the drying step is higher than or equal to 90°C and less than or equal to 165°C.

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