JP2024017942A - Method for producing titanium porous body and titanium porous body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a method for producing a porous titanium body, which enables production of the titanium porous body rather easily and at a relatively low cost; and a titanium porous body.

SOLUTION: Provided is a method for producing a sheet-like titanium porous body, comprising: a molding step of pressing and heating a dry powder layer of raw material powder comprising titanium fibers and binder powder, a mass ratio of which to the titanium fibers is 0.05 to 0.30 to form a sheet-like molded body where the titanium fibers are bound to each other with the binder; a debinding step of heating the molded body to 300°C to 450°C to evaporate a component derived from the binder powder in the molded body; and a sintering step of heating the molded body after the debinding step to sinter the titanium fibers in the molded body.

SELECTED DRAWING: None

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for producing a sheet-like porous titanium body and a porous titanium body.

BACKGROUND ART Metal porous bodies such as titanium porous bodies manufactured by sintering titanium fibers and other metal fibers are used in batteries and various other uses.

Regarding this, Patent Document 1 states, ``A metal fiber nonwoven fabric made of metal fibers and an antibacterial and antiallergic component retained in the metal fiber nonwoven fabric, and the metal fiber nonwoven fabric is made of metal fibers. A sheet obtained by compression molding or a sheet obtained by paper-making a slurry containing metal fibers by a wet papermaking method is degreased and entangled by sintering at a temperature below the melting point of the metal fibers. "A multifunctional sheet characterized by being a nonwoven fabric-like sintered body obtained by diffusion bonding metal fibers that come into contact with each other."

Patent Document 2 describes, ``a slurry preparation step of mixing at least one of titanium powder and titanium hydride powder with an organic binder, a blowing agent, a plasticizer, water, and, if necessary, a surfactant to prepare a slurry; a molding step of applying the slurry onto a first support to form a molded body; a foaming step of producing a foamed molded body by heating and drying the molded body to foam it; A degreasing step of heating and degreasing the foamed molded article separated and placed on a second support; and a first sintering step of heating the degreased foamed molded article in a non-oxidizing atmosphere to make it conductive. a first sintering step for producing a body; and a second sintering step for producing a porous titanium sintered body by sintering the primary sintered body in a non-oxidizing atmosphere at a higher temperature than the first sintering step. A method for manufacturing a porous titanium sintered body characterized by comprising a sintering step.

JP 2017-6567 Publication Japanese Patent Application Publication No. 2009-102701

As described in Patent Documents 1 and 2, the method of preparing a slurry containing titanium fibers, removing the liquid from the slurry, and then sintering the titanium fibers is easy to prepare or adjust the slurry. It's hard to say. In addition, there are time constraints and it is necessary to maintain a predetermined composition and state of the slurry between the time the slurry is prepared and the subsequent processing.

An object of the present invention is to provide a method for manufacturing a porous titanium body that can be manufactured with a certain degree of simplicity and at relatively low cost, and a porous titanium body.

As a result of intensive study on a manufacturing method that does not use slurry, the inventor devised a method of pressurizing and heating a dry powder layer of raw material powder containing titanium fibers and binder powder in a predetermined mass ratio. The thickness of the sheet-like molded product thus obtained can also be adjusted by the above-mentioned pressurization. Next, by heating the molded body to a predetermined temperature, components derived from the binder powder in the molded body can be volatilized, and then, when heated to sinter the titanium fibers in the molded body, the titanium porous body is Obtainable.

The method for producing a titanium porous body of the present invention is a method for producing a sheet-like titanium porous body, the method comprising: titanium fibers; and a binder powder having a mass ratio of 0.05 to 0.30 to the titanium fibers. A molding step of pressurizing and heating a dry powder layer of raw material powder containing the powder to form a sheet-like molded body in which the titanium fibers are bonded together with the binder, and heating the molded body to 300°C to 450°C. a binder removal step in which components derived from the binder powder in the molded body are volatilized by heating; and a sintering step in which the molded body is heated and the titanium fibers in the molded body are sintered after the binder removal step. This includes:

In the molding step, the dry powder layer is preferably pressed and heated on a release layer.

The above manufacturing method includes a raw material mixing step in which titanium fibers and binder powder are mixed dry to obtain a raw material powder, and a powder deposition step in which the raw material powder obtained in the raw material mixing step is dry deposited to obtain a dry powder layer. It may further include a process.

The titanium porous body of the present invention has a carbon content of 0.10% by mass or less, an oxygen content of 1.0% by mass or less, a sheet shape with a thickness of 0.8mm or less, and has a fibrous portion. It has a three-dimensional network structure skeleton formed by sintering each other, has a porosity of 60% or more and 90% or less, and has an air permeability of 1000 μm/Pa・s or more and 20000 μm/Pa・s or less. It is.

According to the method for producing a titanium porous body of the present invention, a titanium porous body can be produced with some degree of simplicity and at relatively low cost.

Embodiments of the present invention will be described in detail below.
A method for manufacturing a titanium porous body according to one embodiment of the present invention is a method for manufacturing a sheet-like titanium porous body. This manufacturing method includes performing a molding step, a binder removal step, and a sintering step in this order.

In the forming step, a dry powder layer of raw material powder containing titanium fibers and binder powder is pressurized and heated. Here, the binder powder is contained in the raw material powder in a mass amount of 0.05 to 0.30 relative to the mass of the titanium fibers. In the molding process, the binder powder is melted and the titanium fibers are bonded together using the binder to form a sheet-like molded body. Next, in a binder removal step, the above molded body is heated to 300° C. to 450° C. to volatilize components derived from the binder powder in the molded body. After the binder removal process, a sintering process is performed, and in the sintering process, the molded body is heated to sinter the titanium fibers in the molded body.

Before the molding step, a raw material mixing step and a powder deposition step can be performed. However, in cases where a raw material powder or a dry powder layer has already been obtained, the raw material mixing step or both the raw material mixing step and the powder deposition step may be omitted.

(Raw material mixing process)
In the raw material mixing step, titanium fibers and binder powder are mixed dry, that is, not in a liquid but in a gas such as air or an inert gas, or in a vacuum, and the mixed powder is used as a raw material powder.

As the titanium fibers, those mainly containing Ti are used so that the titanium porous body has a predetermined composition. The titanium fiber is fibrous, and more specifically, it is preferable that the fiber length is 1 mm or more and the fiber thickness is 0.01 mm to 0.10 mm. Note that the upper limit of the fiber length is not particularly limited, but may be, for example, 10 mm or less.

To determine the fiber length and fiber thickness, images of 100 arbitrary titanium fibers are taken using a scanning electron microscope (SEM). Then, on the image, the straight line distance between the ends of the titanium fiber is defined as the fiber length, and the straight line distance of the width along the direction perpendicular to the fiber length at the midpoint between the ends is defined as the fiber thickness. Measure and calculate their average value. Note that for titanium fibers that are bent in the middle, the shortest distance between the ends is defined as the fiber length. For titanium fibers that are branched into two or more branches, the straight line distance between the farthest ends is defined as the fiber length.

Titanium fibers can be produced, for example, by subjecting a titanium-containing lump or plate to a coil cutting method, a chatter vibration cutting method, or the like. In this case, it is easy to obtain a fibrous powder rather than a spherical powder, which can be favorably used as a titanium fiber.

As the binder powder, various materials and particle sizes can be used as long as it can be dissolved in the molding process and bond titanium fibers together to form a molded body.

For example, the material of the binder powder may be at least one selected from the group consisting of methyl cellulose, polyvinyl alcohol, ethyl cellulose, acrylic, and polyvinyl butyral. From the viewpoint of binding titanium fibers well, it is preferable to use a binder powder having a size smaller than the thickness of the titanium fibers. For example, the average particle size D50 of the binder powder may be within the range of 1 μm to 50 μm, or within the range of 1 μm to 20 μm, or within the range of 5 μm to 10 μm. The average particle diameter D50 means a particle diameter at which the volume-based cumulative distribution is 50% in the particle size distribution obtained by laser diffraction scattering.

The method and device for mixing the titanium fibers and the binder powder are not particularly limited, but may be, for example, dry mixing in an air atmosphere without controlling the atmosphere.

The mass ratio of binder powder to titanium fibers in the raw material powder (mass of binder powder/mass of titanium fibers) is set to 0.05 to 0.30. From the viewpoint of reducing the amount of impurities derived from the binder powder, the mass ratio may be set to 0.05 to 0.25, and further may be set to 0.05 to 0.20. When this mass ratio is less than 0.05, the amount of binder powder is too small, making it difficult to form a molded body in the molding process. On the other hand, when the above mass ratio exceeds 0.30, the carbon content and oxygen content of the finally produced titanium porous body increase due to the use of an excessive amount of binder powder.

Typically, the raw material powder consists essentially of titanium fibers and binder powder, and here it is obtained by dry mixing, so it does not contain water as a liquid and may also contain no other components.

(Powder deposition process)
In the powder deposition step, the raw material powder described above is deposited in a dry manner (that is, not in a liquid but in a gas such as air or an inert gas, or in a vacuum) to obtain a dry powder layer. After depositing the raw material powder, it may be shaped as necessary to form a dry powder layer.

The dry powder layer here does not mean a wet powder layer obtained simply by depositing in a liquid such as a slurry, and it does not matter whether or not it is intentionally dried to remove moisture. . Since the dry powder layer does not substantially contain liquid such as water, it is formed by stacking the raw powder titanium fibers and binder powder under the action of gravity and contacting each other in gas or vacuum.

The raw material powder can be made into a dry powder layer by shaking it off and spreading it over the sheet while adjusting it so that it becomes a somewhat thin sheet. Alternatively, a sheet-like dry powder layer may be formed by depositing the raw material powder somewhat roughly and then adjusting the shape by using a spatula or other cutting tool.

The dry powder layer is preferably formed on the mold release layer by depositing raw material powder by dropping it onto the mold release layer. Thereby, the dry powder layer can be subjected to the next molding process together with the mold release layer. For example, a plate or sheet made of glass fiber cloth, ceramics, or boron nitride (BN) can be used for the release layer. Among these, those made of glass fiber cloth and boron nitride (BN) are preferable.

If a wet powder layer containing a liquid such as water is used instead of a dry powder layer, the water may be repelled by the release layer made of the above-mentioned material, making it impossible to form a sheet-like powder layer. Further, when a wet powder layer containing a liquid such as water is formed on a filter paper or the like instead of a release layer made of the above-mentioned material, the powder layer can sometimes be formed in the form of a sheet. However, in this case, heating and pressure during the molding process cause adhesion between the molded body and the release layer, making it difficult to peel off the molded body from the mold release layer without breaking the molded body after the molding process. In order to avoid such problems, raw material powder or wet powder layers that contain liquid must be dried to form a dry powder layer before the molding process, which not only increases the number of man-hours but also requires equipment for this purpose. is required. Therefore, it is preferable that the raw material mixing step and the powder deposition step be performed in a dry manner.

(molding process)
In the molding process, the dry powder layer is pressurized and heated. As a result, at least a portion of the binder powder in the dry powder layer is melted, and the titanium fibers are bonded to each other by the binder, so that the dry powder layer becomes a sheet-like molded body.

Here, the production and maintenance of slurry as described in Patent Documents 1 and 2 mentioned above is not required, so the production of the titanium porous body is simplified compared to the case where such a slurry is used. , and can be done at relatively low cost.

The dry powder layer can be heated in the molding process, for example, in an air atmosphere at a temperature of 100° C. or more and 200° C. or less for 0.5 to 3 hours. The atmosphere, heating temperature, and time may be changed as appropriate, taking various conditions into consideration.

Pressure of the dry powder layer in the molding process can be performed using a press machine, a rolling machine, or other various pressure devices. The pressurization time may be adjusted as appropriate depending on the pressurization method. For example, when using a press machine, the pressing time may be 0.5 to 3 hours, or 0.5 to 1.5 hours, but it is difficult to obtain a sheet-like molded product with the desired thickness. If possible, the pressurizing conditions can be changed as appropriate. For example, when using a rolling mill, the rolling reduction ratio may be specified rather than the pressing time or pressing force. For example, when using a rolling mill, the rolling reduction ratio ((thickness after rolling/thickness before rolling) x 100) may be 20% to 80%. Note that in the molding process, pressure is usually applied while heating. For example, by applying pressure while continuing heating after starting heating, the heating time may be longer than the pressurizing time. If heating is started before pressurization, the shape of the dry powder layer tends to be maintained to some extent by the heating, so there is an advantage that it becomes easier to transport the dry powder layer to equipment for subsequent pressurization.

The thickness of the molded body can be set depending on the thickness of the titanium porous body to be finally produced. By applying the above-mentioned pressure, for example, a sheet-like molded product having a thickness of 0.1 mm or more and 1.5 mm or less may be obtained.

The dry powder layer is preferably pressed and heated on the release layer. In this way, the molded body obtained after the molding process can be easily separated from the mold release layer. Further, it is even more preferable that the pressurization be performed with a release layer interposed between the upper surface of the dry powder layer and the pressing surface of the pressurizing device. In this way, both the upper and lower surfaces of the dry powder layer are covered with the release layer, making it easier to form a sheet-like molded product.

(Binder removal process)
The molded body obtained in the molding process is subjected to a binder removal process and heated to volatilize components derived from the binder powder contained therein. Although the atmosphere in the binder removal step is not particularly limited, it is preferable to use an atmospheric atmosphere because it is simple.

Here, the molded body is heated to a temperature of 300°C to 450°C. The molded body may be heated to 350°C to 450°C. If the heating temperature is less than 300°C, the volatilization or removal of components derived from the binder powder will be insufficient, the oxygen content and carbon content of the titanium porous body will increase, and the titanium porous body may not have the desired thickness. Things become difficult to control. On the other hand, when the heating temperature is higher than 450° C., oxidation of the titanium fibers in the molded body progresses in the air atmosphere, and the oxygen content of the titanium porous body increases.

The above heating temperature may be maintained for, for example, 3 to 10 hours, or for example, for 5 to 10 hours.

(Sintering process)
After the binder removal process, the molded body is heated in a sintering process, thereby sintering the titanium fibers in the molded body. As a result, a titanium porous body is obtained as the sintered body.

Heating in the sintering process can be performed in a reduced pressure atmosphere such as a vacuum or in an inert atmosphere. Thereby, oxidation or nitridation of the titanium fibers during heating can be suppressed. Specifically, heating is performed in a vacuum furnace to reach a vacuum degree of 10 ^-4 Pa to 10 ^-2 Pa or a lower value under a reduced pressure atmosphere, or in a helium atmosphere or an argon atmosphere. be able to. Note that nitrogen gas does not correspond to an inert gas here.

During heating, the molded body can be maintained at a temperature of, for example, 850° C. to 1100° C. for 0.5 to 6 hours, or for 0.5 to 3 hours. Note that the temperature may be 900°C to 1100°C or 950°C to 1050°C. When the heating temperature is within this range, in many cases, the titanium fibers are sintered well, and damage such as cracking to the titanium porous body is suppressed. However, the heating temperature and time are set depending on the strength and other properties required of the titanium porous body and various conditions, and are not limited to the above temperature range.

In the sintering step, increasing and then decreasing the temperature of the molded body by heating may be repeated multiple times, but from the viewpoint of manufacturing efficiency, it is preferable to do so only once. In manufacturing the titanium porous body, the number of sintering steps can be one.

(Titanium porous body)
The sheet-shaped titanium porous body produced as described above is considered to be particularly suitable for applications such as gas diffusion layers or electrodes of next-generation batteries.

The titanium porous body is made of titanium and substantially consists of Ti. The Ti content of the titanium porous body is, for example, 99.0% by mass or more, preferably 99.3% by mass or more. Although it is desirable that the Ti content be high, it may be 99.8% by mass or less.

The titanium porous body may contain Fe as an impurity, and the Fe content is, for example, 0.25% by mass or less. Further, the titanium porous body may contain Ni, Cr, Al, Cu, Zn, and Sn as unavoidable impurities resulting from the manufacturing process, for example. The content of each of Ni, Cr, Al, Cu, Zn, and Sn is preferably less than 0.10% by mass, and the total content thereof is preferably less than 0.30% by mass.

The oxygen content of the titanium porous body is 1.0% by mass or less, typically 0.1% by mass to 0.8% by mass, and when it is 0.1% by mass to 0.6% by mass. There is. If the oxygen content is too high, the hardness will be high and compressive deformation will be difficult to occur, and there is a risk that the skeleton will break when compressive force is applied in the above-mentioned applications. Oxygen content is measured by inert gas melting-infrared absorption method.

The carbon content of the titanium porous body is 0.10% by mass or less. If the carbon content is too high, the titanium porous body may become brittle. Carbon content is determined by combustion-infrared absorption method.

The thickness of the sheet-shaped titanium porous body is 0.8 mm or less, for example, 0.1 mm or more and 0.8 mm or less, or 0.1 mm or more and 0.5 mm or less, or 0.1 mm or more and 0.3 mm or less. It may be. Depending on the application, something as thin as this may be required. Note that the "sheet-like" with respect to the titanium porous body means a plate-like or foil-like shape whose thickness is small relative to the dimensions in a plan view, and the shape in a plan view is not particularly limited.

The above thickness is measured at 5 points in total, 4 points on the periphery and 1 point in the center of the titanium porous body, using a flat type with a measuring point of Φ10 mm, such as a Mitutoyo digital thickness gauge (model number 547-321). The thickness is measured using a digital thickness gauge with a thickness of 0.001 to 0.01 mm, and the measured values are taken as the average value. When the sheet-like titanium porous body has a rectangular shape in plan view, the four points on the periphery mentioned above are the four points on the four corners.

The titanium porous body is composed of a large number of fibrous parts sintered together, so that it has a skeleton of a nonwoven fabric-like three-dimensional network structure in which a large number of voids are formed inside. Note that porous titanium bodies manufactured using titanium powder instead of titanium fibers tend to have a skeleton with a three-dimensional network structure similar to titanium sponge.

The porosity of the titanium porous body is 60% or more and 90% or less. If the porosity is within this range, it is possible to ensure the required air permeability or liquid permeability depending on the application, exhibit high compression resistance, and suppress cracking during handling. If the porosity is less than 60%, there is a possibility that the air permeability or liquid permeability required for the above-mentioned uses may not be obtained. On the other hand, if the porosity exceeds 90%, there is a concern that compression resistance may decrease or cracks may easily occur during handling.

The porosity ε of the titanium porous body is determined by the volume determined from the width, length, and thickness of the titanium porous body, the apparent density ρ′ calculated from the mass, and the true density ρ of titanium constituting the titanium porous body ( 4.51g/cm ³ ) and the formula: ε=(1-ρ′/ρ)×100.

The air permeability of the titanium porous body is 1000 μm/Pa·s or more and 20000 μm/Pa·s or less. If the air permeability is within this range, it can be said that the material has excellent air permeability or liquid permeability. Air permeability is measured using a Gurley densometer.

When a titanium porous body is compressed by applying a pressure of 30 MPa in the thickness direction for 3 minutes and then unloaded, the amount of irreversible deformation, which is the ratio of the change in thickness before and after, is 0.2 to 0.3. It is preferable that Thereby, the titanium porous body can maintain a desired thickness or shape when compressive force is applied in the above-mentioned applications.

More specifically, the irreversible deformation amount Dc is determined by measuring the thickness T1 of the titanium porous body before applying a pressure of 30 MPa and the thickness T2 of the titanium porous body after unloading by applying the pressure, This is a value calculated from the formula: Dc=(1-T2/T1).

In addition, in order to measure the amount of irreversible deformation Dc, the thickness T1 of the titanium porous body is measured in advance. By sandwiching the titanium porous body in the thickness direction between the respective flat surfaces of two flat plates, etc., and displacing the flat surfaces in a direction closer to each other, the titanium porous body is evenly distributed on the surface of the titanium porous body. A pressure of 30 MPa is applied in the thickness direction for 3 minutes. After applying pressure, the pressure is released. Thereafter, the thickness T2 of the titanium porous body taken out from between the flat surfaces is measured. Here, various compression testing devices and other devices capable of applying pressure to the titanium porous body in this manner can be used. To measure the thicknesses T1 and T2 of the titanium porous body, five different positions in the plan view of the titanium porous body (for example, if the titanium porous body is square in plan view, the center and the surrounding The thickness is measured at a total of 5 locations (4 corners), and the average values thereof are defined as the thicknesses T1 and T2.

Next, the method for producing a titanium porous body of the present invention was carried out on a trial basis, and its effects were confirmed, which will be described below. However, the description here is for the purpose of mere illustration, and is not intended to be limiting.

In Examples 1 to 4, raw material powder obtained by dry mixing and consisting of titanium fibers and binder powder was dry deposited on a mold release layer to form a dry powder layer, and this was sandwiched between the mold release layers from above and below while being processed. A sheet-like molded product was obtained by heating while pressing. The heating time for molding was 0.5 hours. Next, the compact was heated in the air for 8 hours to volatilize the components derived from the binder powder, and then heated to the sintering temperature in a vacuum of 0.01 Pa or less for 1 hour to form a sintered compact. A titanium porous body was manufactured. Table 1 shows each condition. The titanium fibers were manufactured using metallic titanium (so-called pure titanium) as a raw material, and had a fiber length of 3 mm and a fiber thickness of 30 μm. In Example 2, polyvinyl alcohol (PVA) was used instead of polyvinyl butyral (PVB) as the material for the binder powder. The average particle diameter D50 of both the PVB and PVA binder powders was 5 μm.

In Comparative Example 1, titanium fibers were deposited on filter paper in a slurry containing polyvinyl butyral (PVB) and water in addition to titanium fibers to obtain a wet powder layer, but after heating for molding, the molded body was deposited on filter paper. The molded body was torn when it was peeled off.

In Comparative Examples 2 and 3, titanium porous bodies were produced in the same manner as in Example 1, except that the heating temperature during binder removal was changed.

In Comparative Example 4, when the mass ratio of binder powder to titanium fibers was changed, it was not possible to form a molded body by heating during molding due to the lack of binder powder. In Comparative Example 5, a porous titanium body was produced in the same manner as in Example 1, except that the mass ratio of binder powder to titanium fibers was changed.

The carbon and oxygen contents, porosity, air permeability, irreversible deformation amount, and thickness of the titanium porous body produced as described above were measured. The results are shown in Table 2.

As shown in Table 2, in Examples 1 to 4, porous titanium bodies with sufficiently low carbon and oxygen contents and desired characteristics could be produced.

In Comparative Example 2, the heating temperature during binder removal was too low, so the amount of binder remaining increased, and as a result, the oxygen content of the titanium porous body increased. In Comparative Example 3, it is thought that titanium absorbed a large amount of oxygen from the atmosphere because the heating temperature during binder removal was too high, and the oxygen content of the titanium porous body increased.

In Comparative Example 5, the carbon and oxygen contents increased due to too much binder powder.

According to the method for manufacturing a titanium porous body of the present invention, it is possible to manufacture a titanium porous body with a certain degree of simplicity and at relatively low cost.

Claims (4)

A method for manufacturing a sheet-like titanium porous body, the method comprising:
A dry powder layer of raw material powder containing titanium fibers and a binder powder whose mass ratio to the titanium fibers is 0.05 to 0.30 is pressurized and heated, and the titanium fibers are bonded to each other by the binder. a molding step of forming a sheet-like molded body;
a binder removal step in which the molded body is heated to 300° C. to 450° C. to volatilize components derived from the binder powder in the molded body;
A method for producing a titanium porous body, the method comprising, after the binder removal step, heating the molded body and sintering titanium fibers in the molded body. The method for producing a titanium porous body according to claim 1, wherein in the molding step, the dry powder layer is pressed and heated on a release layer. A raw material mixing step of dry mixing titanium fibers and binder powder to obtain raw material powder;
The method for producing a titanium porous body according to claim 1 or 2, further comprising a powder deposition step of dryly depositing the raw material powder obtained in the raw material mixing step to obtain a dry powder layer. A titanium porous body,
The carbon content is 0.10% by mass or less, the oxygen content is 1.0% by mass or less,
It is in the form of a sheet with a thickness of 0.8 mm or less,
It has a three-dimensional network structure skeleton formed by sintering fibrous parts, has a porosity of 60% or more and 90% or less, and has an air permeability of 1000 μm/Pa・s or more and 20000 μm/Pa・s or less. A porous titanium material.